Bi1^δ+-O-Ce^3+ synergistic sites on rod ceria for unprecedentedly efficient transesterification

Domain: physics
Published: 2026-01-08
Editorial outcome: major_revision

Abstract
Heterogeneous catalysts for transesterification reaction are highly desirable, but normally suffer from low activity or severe deactivation. Here we report a Bi-ceria catalyst for transesterification that exhibits catalytic activity of 2499 g g−1 h−1 and stability for 800 h, in the synthesis of 1,2-butylenecarbonates from 1,2-butanediol and dimethyl carbonate. Our study reveals that the constructed Bi1 does not serve as the conventional catalytic centre but regulates the acidity-basicity of the active sites through remote catalysis, realized by the induced delocalization of the f electron of Ce3+ and the remote propagation of electrons via the conductive lattice oxygen. The highly active sites lead to the Bi1 centred re-construction into BiOx during the reaction, which triggers tardily decline in catalytic activity. Nevertheless, the catalyst can be readily regenerated with thermal treatment by restoring the migrated oxygen. These findings open an avenue for the rational design of single-atom catalysts for transesterification reactions.

Introduction
Transesterification is the key step for a variety of important organic reaction processes, e.g., the alcoholysis in biodiesel production and the synthesis of polyesters and cyclic carbonates1–5. Herein, the transesterification with alkyl carbonates and diols was recently found to be a typical green approach to synthesize cyclic carbonates with different ring sizes and functional groups6–9. Compared to the CO2-based route that heavily relies on homogeneous catalysts (e.g., ionic liquids), the transesterification pathway offers distinct advantages10,11. The diols can be obtained from biomass or coal, and the reaction is feasible within a solvent-freely heterogeneous catalysis system12–17, in which efficient heterogeneous catalysts would be of great significance.

It was reported that the transesterification of dimethyl carbonate (DMC) and glycerol achieved a yield of glycerol carbonate for 90% (space-time yield of 33.3 g h−1 g−1), at a high temperature of 170 °C on roasted hydrotalcite/hexagonal silica (CHT-HMS), with a catalyst dosage of 15 wt.% and a DMC/glycerol molar ratio of 3/118. Mayra G. reported a glycerol carbonate yield of 93% in the transesterification using excessive diethyl carbonate over rehydrated hydrotalcite, but the space-time yield was only 0.77 g h−1 g−1 19. Current heterogeneous catalytic systems with alkyl carbonates and polyols mostly rely on high temperature and excessive dialkyl carbonates, eminent heterogeneous catalysts for the transesterification at low temperatures are still needed20.

Previous study indicates that the transesterifications generally take place with acid-base catalysis. ZnO catalysts with sufficient acid-base properties were able to promote the activation of urea carbonyls and diols21,22, where Zn served as the acidic sites for the activation of carbonyl groups, and the basic sites activated the hydroxyl groups in diols. Strong acid sites are deemed inactive and would lead to by-products formation via side reactions, e.g., oligomerization23,24. Oxygen-based sites usually serve as the basic site in the reaction, which has profound effects on catalytic transesterification and curbs the side reactions. Liu et al. prepared a series of transition metal doped hydrotalcites and demonstrated that the catalytic activity is proportional to the density of basic centres in the synthesis of glycerol carbonate, and revealed that Ni could dramatically boost the strength of all three basic sites (O-H, M-O, and O2−) in the calcined hydrotalcite25.

Despite the above endeavours, precisely modulating the distance and local environment of the acid-base sites to realize an appropriate acid-base balance remains a great challenge. Besides, a comprehensive understanding of the catalytic mechanisms, including the interfacial interactions and intermediate identification remains a key question to answer14,15.

Cerium dioxide (CeO2) serves as a versatile heterogeneous platform for heterogeneous catalysis, given its rich surface defects (oxygen vacancies Ov or Ce3+) and abundant Lewis acid-base sites (Ce3+, O2−)26–28. Element doping may offer extensive opportunities to regulate the surface acidity and basicity. In this work, we fabricated a single-atom bismuth catalyst supported on rod ceria (Bi1-CeO2-R), which demonstrated ultra-high activity in the transesterification synthesis of 1,2-butylenecarbonates (1,2-BC) reaction. The catalyst achieved a high 1,2-BC selectivity of 99% and a space-time yield of 2499 g h−1 g−1, which is the highest heterogeneous catalytic activity known to date for such a reaction, and it could maintain stability for 800 h in a one-batch test. The presence of Bi1 modified the chemical environment of the active sites, thereby benefiting the reaction. We also noticed that Bi1 experienced gradual deactivation after a long-term operation beyond 800 h, nevertheless, the catalyst could be readily regenerated with an in situ thermal treatment and maintained stability for an overall 1400 h.

Results
Catalyst structure and activity
Bi-based catalysts were prepared by a one-step hydrothermal method, and the details are described in the Supplementary Information. The Bi content in the samples was confirmed by inductively coupled plasma-optical emission spectrometry (ICP-OES) (Supplementary Table 2). X-ray diffraction (XRD) patterns of both x%Bi-CeO2-R and CeO2 rods (CeO2-R) showed a pure cubic fluorite phase structure of CeO2 (JCPDS-34-0394), and no characteristic peaks of Bi species were found, indicating that Bi species are highly dispersed in CeO2 (Fig. 1b)27,29–32. Further, the diffraction peak of CeO2 (111) shifts significantly from 28.81° to 28.55° for CeO2 (111) with increasing Bi content, suggesting that Bi species may exist in the interstitials of the CeO2 lattice (Fig. 1c)27,30–33.

Aberration-correction high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) shows that Bi species were uniformly dispersed on the CeO2, and the bright spots were identified as atomic dispersion Bi (Fig. 1d) (0.6%Bi-CeO2-R, denoted as Bi1-CeO2). Such homogeneous dispersion of Bi species has been confirmed by the EDX mapping results (Fig. 1g). Besides, our study also reveals the mesoporous structure of the catalysts (Supplementary Figs. 3–4 and Supplementary Table 3).

The catalytic activity of the x%Bi-CeO2-R catalysts for synthetic cyclic carbonates was investigated (Fig. 1f). The conversion over 0.6% Bi-CeO2-R exhibits the most extraordinary catalytic activity of 87.4% for the conversion and 99% for the selectivity of 1,2-BC. The space-time yield over 0.6% Bi-CeO2-R was 2499 g h−1 g−1, which achieves the record high among the heterogeneous catalytic activities to our knowledge (an improvement of more than 100 times) (Fig. 1e, f). The 0.6% Bi-CeO2-R shows excellent catalytic activity in a wide range of cyclic carbonate syntheses, e.g., glycerol carbonate (Supplementary Table 18). Furthermore, we extended the evaluation of 0.6% Bi-CeO2-R to the synthesis of N-substituted carbamates through amine carbonylation. The results demonstrate a marked enhancement compared to sole CeO2, underscoring the broad applicability of 0.6% Bi-CeO2-R in the analogue transesterification reactions. (Supplementary Fig. 59).

The activity of sole Bi2O3 and CeO2-R with various Bi content were also compared in Fig. 1f. When using pure CeO2 as catalyst, the conversion of 1,2-BDO was only 26.5%. After doping 0.2% Bi on CeO2, the conversion increased to 57.4%. By increasing the Bi content to 0.6%, the optimal conversion of 87.4% was achieved. However, when the Bi content continued to increase, the conversion of 1,2-BDO eventually dropped to 24.7% with 5% Bi. The activity exhibits a volcano tendency with the loading ratios of Bi, implying an intrinsic change relevant to the doping ratios. Besides, the Bi2O3 was found to be almost inactive with trace conversion of 1,2-BDO for only 2.1%.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results (Supplementary Fig. 2) show that the length of the CeO2-R was about 100 nm and the width was about 10 nm, and the addition of Bi species does not change the rod-like morphology of CeO2. Lattice spacings visible in the images of 0.19, 0.27, and 0.31 nm areascribed to the (110), (100), and (111) facets of CeO2, respectively. Compared to 0.6%Bi-CeO2-R, cubic and octahedral CeO2 (0.6%Bi-CeO2-C and 0.6%Bi-CeO2-O) mainly processed (100) and (111) facets, respectively, which showed no activity in the transesterification (Fig. 1f). It is concluded that CeO2 (110) facet is essential for its ultra-high activity, and Bi species plays a key role in the elevated catalytic activity, while Bi1 does not show the special synergy with CeO2 (100) and CeO2 (111) (Supplementary Fig. 2).

The electronic structure and coordination environment of the Bi1-CeO2 catalyst was further investigated by X-ray absorption fine structure (XAFS). The K-edge X-ray absorption near edge spectroscopy (XANES) curve of Bi for Bi1-CeO2 locates between Bi foil and Bi2O3, indicating that the general valence of Bi ranges from 0 to +3 (Supplementary Fig. 5). The k3-weighted extended X-ray absorption fine structure (EXAFS) and the corresponding wavelet transform spectra (Fig. 2a, b and Supplementary Figs. 6–10) confirms that Bi exists as isolated atoms in the catalyst34–36. Fitting curves of EXAFS for Bi1-CeO2 show that the isolated Bi site is coordinated by two O atoms (coordination number: 1.8) with an average Bi-O bond length of 2.15 Å (Supplementary Table 4). Therefore, we conclude the actual microstructure for Bi1-CeO2 should be Biδ+-Ov. Six different coordination models for Biδ+-Ov active site were proposed and simulated on CeO2 (110) to investigate their stability at 774 K, using machine learning assisted Ab-initio molecular dynamics (ML-AIMD) (Supplementary Video 1). The simulation shows that the Biδ+-Ov with one adjacent oxygen vacancy maintains stability throughout the 10 ps tests at 774 K, implying it is supposed to be the real structure for Bi1-CeO2 (Fig. 2c & Supplementary Fig. 11), which will be adopted in our following calculations.

The effect of the incorporation of Bi species on CeO2 was further revealed by visible laser Raman spectroscopy (Raman) and electron paramagnetic resonance (EPR). The vibrational mode of 1076 cm−1 is inferred to be ascribed to the Bi-O bond, and the vibrational mode F2g at 462 cm−1 is ascribed to the symmetric stretching vibration of Ce-O (Supplementary Fig. 12)33,37. The weak band at 595 cm−1 is ascribed to the defect-induced mode ID of CeO2. The integral area ratio (ID/F2g) that reflect the concentration of Ov increases from 0.0398 for CeO2 to 0.0541 for Bi1-CeO2, and then decline to 0.0472 for 1.0%Bi-CeO2 (Supplementary Table 5). The results indicate that abundant oxygen defects exist in x%Bi-CeO2. More importantly, the volcano relationship reveals that the addition of Bi may enrich Ov38, which would then affect the catalytic activity39. In line with the results from Raman spectroscopy, the 0.2%Bi-CeO2 catalyst exhibited stronger spin signals compared to pristine CeO2. Further increasing the Bi content to 0.6% gives rise to the strongest spin signal in Bi1-CeO2, approximately seven times that of pristine CeO2 (Supplementary Table 6), indicating the presence of more Ov in the Bi-doped state (Fig. 2e). However, it should be noted that when the Bi content increased to 5%Bi-CeO2, the presence of excessive oxide (not detected by XRD, Fig. 1b) may cause a significant decrease in the effective Ov concentration on CeO2 surface, leading to a corresponding reduction EPR signal and catalytic activity (Fig. 1f).

The X-ray photoelectron spectroscopy (XPS) results shows that the binding energy peaks of Bi 4f spectra were at 163.2 and 158.3 eV, which are ascribed to the Bi 4f7/2 and Bi 4f5/2 spin orbitals of Bi3+, and no Bi0+ species were observed (Fig. 2d). In addition, by comparing the sample with different loadings, a shift of the Bi 4f spectra towards higher binding energies was observed, indicating the electron loss from the Bi atom to the O atom in the Biδ+-Ov-Ce3+-OL structure. Compared to the intact CeO2, Ov concentration in Bi1-CeO2 is significantly enriched, leading to the rise of Ce3+ proportion from 22.09% to 35.89% (Supplementary Table 5). A sharp concentration rise of Ov from 22.4% (CeO2) to 31.9% (Bi1-CeO2) was observed in the O 1s spectra, confirming that Bi1 induced the increase in Ov (Supplementary Fig. 13 and Supplementary Table 4)40,41. In addition, the binding energy of OL shifts towards lower binding energies, suggesting that OL gains electrons with the addition of Bi. The effect of Ov on the charge transfer between Bi and CeO2 was quantitatively analysed by the charge density difference (CDD) (Fig. 2f–i). The results reveal that Bi with an adjacent Ov carries a positive charge of +0.62e, and Bi on the intact CeO2 shows more positive charge of +0.85e. The results confirm that electrons migrate from the Bi atom to the support via the O atom while there is more electron back-donation from the support to Bi in the presence of Ov. The addition of Bi alters the local electronic structure of adjacent lattice oxygen (OL) and may have a remarkable effect on the acid-base properties of the CeO2 matrix.

We investigated the change in acidity and basicity of the catalyst surface with the addition of Bi species by temperature programmed desorption (TPD) of CO2 and NH3, respectively. Figure 2g shows CO2 desorbed at 50-200 °C, 200-400 °C, and 400-700 °C, from weak Lewis basic sites, moderate Lewis basic sites, and strong Lewis basic sites, respectively. Supplementary Table 7 shows only a trace amount of strong Lewis basic sites were present in Bi2O3, and only abundant weak basic sites for CeO2. With the addition of Bi, rich strong basic sites were observed on CeO2, and the strong basic sites on CeO2 shift to higher temperature regions with the Bi content, implying the enhancement of the basic strength. NH3-TPD results in Fig. 2h show strong acidic sites were dominant in Bi2O3 and CeO2, and with the addition of Bi, the concentration of acid sites for CeO2 shows analogues increasing tendency as the basic sites. This is because the increasing concentration of Ov induces more Ce3+ sites as weak-mediate Lewis acid (Supplementary Table 7). The result is agreed by the pyridine IR tests that the Lewis acid concentration for Bi1-CeO2 is much higher than CeO2-R (Supplementary Fig. 14 and Supplementary Table 8). Nevertheless, the shift of weak acidic sites to lower temperatures indicate the acidity is weakened.

Bader charge analysis shows that the presence of Ov leads to less charge on Ce adjacent to the defects (+2.27e), compared to intact CeO2-nonOv (+2.32 e), and this change is further enhanced by the presence of Bi1 (Bi1-CeO2-Ov, +2.23e), in line with the weaker acidity observed in experiments (Supplementary Fig. 15). Moreover, O atoms adjacent to Ov carried negative charge of −1.15e and −1.21e for CeO2-nonOv and CeO2-Ov, respectively. In the presence of Bi, the negative charge on the O atom is increased to −1.23e, in line with the strong basicity observed in experiments.

The above results revealed the unique Biδ+-Ov-Ce3+-OL coordination structure has changed the intrinsic electronic structure of CeO2 and activated the OL for abundant Ov creation, and the Ov would give rise to rich moderate acid sites and strong basic sites on CeO2 in the presence of Bi1, which are important for efficient transesterification reaction.

Reaction mechanisms
Our study has proved that the exposed (110) facet of rod-CeO2 is rich in Ov, which potentially contains the most catalytically active sites. However, the mechanism for transesterification including the selective adsorption and the activation of -C=O and -O-H bonds during the synthesis of cyclic carbonates has rarely been clarified. In situ diffuse reflectance infrared Fourier transform (in situ DRIFT) was implemented to investigate the adsorption behaviour of DMC and 1,2-BDO on Bi2O3, CeO2, and Bi1-CeO2. Figures 3a-3b and Supplementary Fig. 16 show that 1,2-BDO adsorbed onto Bi1-CeO2 mainly in a bridged butoxy conformation on the Ov (1035 cm−1) at room temperature, in addition to the on-top butoxy (1091 cm−1) and bridged butoxy (1062 cm−1) conformations42. It was found that the top butoxy and bridged butoxy conformations would gradually shift to the bridged butoxy conformation with the temperature on the Ov of Bi1-CeO2 (Figs. 3d, e). In contrast, only on-top butoxy adsorption conformation (1086 cm−1) was observed on the Bi2O3 surface that is proven to be inactive for transesterification (Supplementary Fig. 17). The adsorption behaviour of 1,2-BDO on Bi1-CeO2-C and Bi1-CeO2-O was also compared, and on-top butoxy (~1100/1098 cm−1) and bridged butoxy (~1069/1071 cm−1) have been identified on both samples, which are inactive neither for the transesterification reaction (Supplementary Figs. 18, 19). We eventually find that Ce in adjacent to Ov is the major catalytic site for the activation of 1,2-BDO with the bridged butoxy-Ov conformation at 1035 cm−1 (Fig. 3e and Supplementary Figs. 20–22). The preferable adsorption behaviour and the catalytic activity of x%Bi-CeO2 catalysts with varying Bi contents further corroborate this conclusion (Supplementary Fig. 23 and Fig. 1f). DFT study further (Supplementary Fig. 32 & Supplementary Table 9) revealed that 1,2-BDO only had weak interaction with Bi1 (Ead = −0.19 eV), and the molecule was likely to adsorb through the primary hydroxyl groups at the Ov on CeO2 with the spontaneous dissociation of Oα-H (Ea = −1.39 eV), corresponding to the conformation of bridged butoxy-Ov. Although the adsorption with dual hydroxyl groups had higher adsorption energy of above 2.0 eV, it has been observed that such adsorption conformations as the major conformation on Bi2O3 and Bi1-CeO2-C (Supplementary Figs. 17, 18), thus we infer they are less reactive for the reaction.

Regarding the adsorption of DMC, the catalysts of Bi1-CeO2-O and Bi2O3 with low activity gave rise to the bi-dentate conformation based on the prominent vibration of C=O-Ce-Ov (Supplementary Figs. 24, 25). On the contrary, DMC on Bi1-CeO2-C, CeO2 and ultra-highly active Bi1-CeO2-R all showed the predominant adsorption conformation of cis-cis-monodentate at 1766 cm−1 (Supplementary Figs. 26–28). With the increasing temperature, the cis-trans monodentate adsorption at 1751 cm−1 was completely shifted to cis-cis-monodentate adsorption conformation (Fig. 3f, g and Supplementary Figs. 29, 30). Further comparison of DMC adsorption results on x%Bi-CeO2 catalysts reveals that Bi content influences the adsorption conformation (Supplementary Fig. 31). The cis-cis monodentate adsorption conformation exhibits a direct correlation with the catalytic activity performance (Fig. 1f). This is consistent with the DFT results, where the cis-cis-monodentate C=O-Ce-Ov binding has the highest adsorption energy of −1.04 eV (Supplementary Table 9 and Supplementary Fig. 34). The calculations show that Ov facilitates 1,2-BDO adsorption (1,2-BDO-4 and 1,2-BDO-5), while Bi1 impacts on the DMC adsorption (DMC-2 and DMC-6, Supplementary Figs. 34, 35 and Supplementary Tables 9-10).

Detailed reaction pathways of catalytic transesterification were analysed using DFT modelling. Figure 3h shows the plausible reaction mechanism for synthesizing 1,2-BC from DMC and 1,2-BDO on Bi1-CeO2, and the reactions over CeO2 were calculated for comparison (Supplementary Table 11). Over Bi1-CeO2, 1,2-BDO experienced dissociative adsorption and contributed to surface proton enrichment, and DMC adsorbed in a cis-cis-monodentate conformation further dissociated and produced one molecule methanol with the surface proton. This step experienced an energy barrier of 1.91 eV, smaller than 2.25 eV over CeO2. The left moiety (structure III-1) would further engage in the synthetic reaction with an energy barrier of 0.51 eV (TS-2 Bi1-CeO2), and it was 0.87 eV over CeO2. Cyclization was the final step that had an energy barrier of 1.54 eV over Bi1-CeO2 and 0.19 eV over CeO2 to yield the 1,2-BC precursor (structure V). 1,2-BC escaped from the surface of CeO2 with a desorption energy of 0.64 eV, while over Bi1-CeO2, we observed a spontaneous desorption process with an exothermic energy of −0.09 eV. During the modelling, a unique Bi-O structure was noticed in the cyclization reaction of the 1,2-BC formation. The modelling reveals that Bi1 is not the conventional active site with direct contact with reactants, but gives rise to remote catalysis. DMC dissociation is the potential rate-controlling step in the transesterification reaction, which is more facilitated by Bi1-CeO2, and Bi1 also benefits the spontaneous desorption of 1,2-BC.

Crystal Orbital Hamilton Population (COHP) analysis revealed the C-O and O-H bonds of DMC on the surface of Bi1-CeO2 are less activated compared to those over CeO2-R (Supplementary Fig. 36 & Supplementary Table 12, but the strongest C=O bond experiences much less unnecessary activation during the reaction on the Bi1-CeO2 surface (-COHP, 0.67), in contrast to CeO2 (-COHP, 1.07) (Supplementary Fig. 37 & Supplementary Table 13). This implies that the endothermic contribution by the C=O bond is much less on Bi1-CeO2. In addition, COHP analysis also reveals that Ce-O bonds adjacent to the Bi site underwent potential cleavage and re-bonding, resulting in an overall elevated -COHP value of 0.33. This may result in additional exothermic contribution to the reaction of DMC decomposition over Bi1-CeO2 (Supplementary Figs. 38, 39 & Supplementary Table 14). The above results indicate that the structural evolution induced by Bi1 is supposed to be a key reason for the lower energy barrier for DMC decomposition on Bi1-CeO2.

Previous studies have suggested a competing reaction pathway during the formation of cyclic carbonates from DMC and o-diols via transesterification, involving the formation of chain carbonate intermediates (e.g., hydroxy-butyl methyl carbonate, HBMC) before cyclic carbonate production18,23,43–45, and it was speculated that the cyclization of alkyl carbonates and diols might be the rate-controlling step for the transesterification23,44. In-situ IR was used to track the possible intermediates in the reaction (Supplementary Figs. 40, 41), but the presence of the intermediate HBMC was not detected. DFT calculations (Supplementary Figs. 42, 43) show that the reaction pathway existed over the pristine CeO2 surface starting from the dual-hydroxyl adsorption of 1,2-BDO but with a high reaction energy barrier of 1.20 eV, and would be interrupted in the vicinity of Bi1.

Bader charge analysis provides more insights that the Ce atom adjacent to the Ov carries less positive charge in the presence of Bi1 than that on intact CeO2. Projected density of states (P-DOS) analysis of Ce and O atoms in both CeO2 and Bi1-CeO2 (Fig. 3i, j and Supplementary Figs. 44-46) further elucidates the spatial extent and mechanistic role of the electron transfer: the incorporation of Bi1 induces non-localized f-electrons at the Fermi level of Ce atoms adjacent to Ov and a richness of electrons on lattice oxygen atoms, endowing them with unexpected conductivity (Fig. 4b, d, and e) and thereby establishing efficient electron propagation pathways within the catalyst. This modulation of the electronic structure significantly enhances the intrinsic reactivity of the material, leading to the remarkable transesterification activity (Fig. 3k), which we term remote catalysis.

Deactivation and regeneration of Bi1-CeO2
We carried out an ultra-long stability test for the Bi1-CeO2 and noticed the catalyst maintained stable for 800 h in one batch and started activity decline thereafter (Fig. 4a). The deactivation by carbonaceous deposit or by-products on the catalyst was excluded by surface cleaning. TEM characterization of the deactivated catalyst suggests that Bi1 might have transformed to BiOx whilst the reaction as facet −121 of Bi2O3 was identified (Fig. 4a). The spent catalysts with different extent of deactivation (denoted as x%D-Bi1-CeO2) were tested by XRD. It has been found that the diffraction peaks of Bi2O3 (−121) at about 28° begin to appear and enhances with further deactivation (Fig. 4c). The deactivation effect of BiOx was further verified in experiments (Supplementary Fig. 47a), where the 70%D-Bi1-CeO2 catalyst showed similarly low activity as 5%Bi-CeO2 in terms of the 1,2-BC yield, of which the main Bi species was found to present as Bi2O3 in both samples, evidence by the identification of a Bi-O-Bi scattering path in the EXAFS spectra (Supplementary Figs. 47, 55–59 and Supplementary Table 15). Furthermore, a series of catalysts were synthesized on CeO2 support via the conventional wet impregnation method followed by calcination. Notably, these catalysts exhibited the same poor activity as pristine CeO2, verifying the inert behaviour of Bi2O3 clusters over CeO2. In addition, we implemented calcination for the deactivated catalyst and surprisingly observed that the BiOx species completely disappeared in 3 h at 773 K (Fig. 4c). The above results indicates BiOx may has transformed back to Bi1 during the thermal treatment. The regenerated catalyst R-Bi1-CeO2 achieves the same 1,2-BC yield as the fresh catalyst and could remain stable for another 600 h (Fig. 4a).

DFT modelling reveals that during the formation of the 1,2-BC precursor, the OL in CeO2 was activated and migrated towards Bi1 to form Bi-O3, which contributes to the high kinetic barrier of 1.54 eV in the reaction pathway (TS-3, Supplementary Fig. 60). The desorption of 1,2-BC consists of exothermic lattice recovery (−0.93 eV) and a desorption energy of product (0.84 eV), resulting in an overall exothermic process (−0.09 eV). P-DOS for Bi1-CeO2 shows that the p-electrons of the OL adjacent to Bi1 cross the Fermi level (Fig. 4d, e), indicating the related Ce-OL bonds being activated and more abundant Ov are susceptible to generate whilst the cyclization reaction of the formation of BiOx. The acidity and basicity are therefore altered by the increasing amount of Ov, leading to the change of the activity of the catalyst.

Quantitative EPR analysis regarding the Ov in Bi1-CeO2, x%D-Bi1-CeO2, and R-Bi1-CeO2 further verified the activation and dynamic migration of the lattice O (Fig. 4f). The normalized spin density gradually increased from 7.280 e^11/mm3 with the degree of deactivation, reaching 3.575 e^12/mm3 in 80%D-Bi1-CeO2. The results confirm that the cleavage of Ce-O bonds takes place to generate Ov with the deactivation. After the thermal treatment, the BiOx species was completely recovered to Bi1-O, evidenced by the drop of spin density to 7.522 e^11/mm3 for R-Bi1-CeO2, indicating that the lattice O atoms are restored. The evolution of Bi1 and BiOx nanoparticles was further confirmed by the XAFS by a new Bi-O-Bi scattering path at 3.51 Å (Figs. 5b, d and Supplementary Figs. 48–55) and the increased coordination number of O to 2.1 (Supplementary Table 15). The Bi-O-Bi scattering path disappeared after the thermal treatment, meanwhile the Bi-O path was regained (Fig. 5c, f) with an O coordination number of 1.6, resembling that of the fresh catalyst (1.8) (Supplementary Figs. 56–59 and Supplementary Table 16). The above conclusion has also been verified by the low catalytic activity of 5%Bi-CeO2, in which the Bi species mainly existed as metal oxide (Supplementary Figs. 47, 56–59 and Supplementary Table 16). These findings collectively demonstrate that the structural evolution from BiOx to the isolated Bi1 sites, driven by a straightforward thermal treatment, represent the intrinsic change for the recovery of catalytic activity.

Methods
Catalyst preparation
Chemicals. All the chemicals are used as received from the provider without further purification. Bismuth(III) nitrate pentahydrate (Bi(NO3)3·5H2O, 99.9%) and cerium(III) nitrate hexahydrate (Ce(NO3)3·6H2O, 99.9%) obtained from Sigma Aldrich were used as the precursors of x%Bi-CeO2.

Synthesis of CeO2-Rods and x%Bi-CeO2-Rods
Atomic bismuth-cerium dioxide catalysts (Bi1-CeO2-rods) were prepared by a one-step hydrothermal method. Specifically, 0.868 g of Ce(NO3)3·6H2O [Sinopharm Chemical Reagent Co.] and 9.6 g of NaOH (SCRC) were dissolved in 5 mL and 35 mL of deionized (DI) water, respectively. Subsequently, the solutions were mixed well and stirred continuously for 0.5 h. The resulting mixture was transferred to a Teflon-lined stainless steel autoclave reactor and held in an oven at 373 K for 24 h. The obtained precipitate was centrifuged and washed until the pH reached 7.0. Further, the mixture was dried at 353 K for 12 h and calcined at 773 K for 3 h to obtain CeO2. To obtain x%Bi-CeO2 catalysts with different Bi molar contents, a similar process was used, differing in that the Ce(NO3)3·6H2O and Bi(NO3)3·5H2O (SCRC) solutions were homogeneously mixed before mixing with an alkaline solution, with Bi/Ce molar ratios of 0.002. 0.004, 0.006, 0.008, and 0.01. The final catalysts were named as 0.2% Bi-CeO2, 0.4% Bi-CeO2, 0.6% Bi-CeO2, 0.8% Bi-CeO2 and 1.0% Bi-CeO2, respectively.

Synthesis of Bi1-CeO2-cubes
Bi1-CeO2-cubes were prepared similarly to Bi1-CeO2-Rods, with the difference that the hydrothermal treatment temperature was 453 K.

Synthesis of Bi1-CeO2-octahedrons
Bi1-CeO2-octahedrons were prepared by a one-step hydrothermal method. Specifically, 3.8 g of Ce(NO3)3·6H2O [SCRC], a certain molar amount of Bi(NO3)3·5H2O [SCRC], and 3.3 g of C6H6O6 (SCRC) were dissolved in 35 mL of deionized (DI) water. Subsequently, the solutions were mixed well and stirred continuously for 0.5 h. The resulting mixture was transferred to a Teflon-lined stainless steel reactor autoclave and held at 453 K for 24 h. The obtained precipitate was centrifuged and washed with deionized water and ethanol until the pH reached 7.0. Further, the mixture was dried at 363 K for 12 h and calcined at 673 K for 2 h to obtain Bi1-CeO2-octahedrons.

Characterizations
The morphology of all catalysts was investigated by Zeiss Gemini 300 scanning electron microscope (SEM) and TF20 transmission electron microscope (TEM). Subsequent image analysis and processing were carried out using the Gatan Digital Micrograph software.
Aberration-correction high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and associated EDX elemental mapping were obtained using a Thermo Fisher Scientific Titan Themis operated at 300 kV, equipped with a CEOS DCOR probe corrector and a Super-X 4-quadrant detector for EDX.
Bi content of these as-prepared catalysts was obtained by an inductively coupled plasma-optical emission spectrometer (ICP-OES).
X-ray diffraction (XRD) patterns of catalyst by D/tex ultra 250 diffraction measurements (Cu-Ka). The XRD patterns were recorded from 5 to 90° (2θ) with a scanning step of 0.01°. The employed radiation was CuK-α with a wavelength of 0.154 nm.
X-ray photoelectron spectroscopy (XPS) was obtained by Thermo Scientific K-Alpha instrument, corrected by C 1s=284.8 eV binding energy. Raman spectroscopy was tested on the HORIBA Scientific LabRAM HR Evolution spectrometer.
Electron paramagnetic resonance (EPR) spectra were recorded at room temperature on Bruker EMX plus-6/1 device. Spectra have been recorded with a Continuous Wave (CW) Bruker EMX spectrometer operating at X-band (9.8 GHz), equipped with a cylindrical cavity at 100 kHz field modulation.
The temperature-programmed (TPD) instrument equipped with a thermal conductivity detector was used to measure the acidity and basicity of catalysts on the quartz U-tube reactor. Samples were pre-treated in He atmosphere at 473 K for about 1 h and cooled to 323 K. The CO2/NH3 gas was injected at a flow rate of 100 mL/min. After saturation of adsorption, He purge purged for 40 min. The temperature rose to 1073 K at a ramp rate of 10 K/min.
In-situ IR testing of all catalysts was performed on a Mettler-Toledo ReactIR 15m device consisting of a liquid nitrogen reactor, and a diamond probe. The wavenumber range was 4000−800 cm−1, and the acquisition time was 15 seconds.
In situ diffuse reflectance infrared Fourier transforms spectroscopy (in situ DRIFTS) was performed at wavenumbers from 4000 to 750 cm−1 by accumulating 64 scans with 4 cm−1 resolution on a Nicolet iS50 FT-IR spectrometer fitted with a Harrick DRIFTS cell and a high-sensitivity MCT detector cooled with liquid nitrogen. The sample compartment was filled with 50 mg of the catalyst. The samples were pre-treated at 673 K for 2 h and then cooled to 293, 323, 353, 373, 393, and 423 K to collect the background spectra, respectively. Subsequently, the argon gas was passed through the 1,2-BDO or DMC into the DRIFTS cell at a flow rate of 30 mL/min, respectively. After the catalyst was saturated with adsorption at room temperature, N2 was purged for 30 min to remove the physical adsorption of DMC\1,2-BDO on the surface of the catalyst, and the spectra were recorded.
The edge energy of the XANES spectrum was determined from the inflection point in the leading edge, that is, the maximum in the first derivative of the leading edge of the XANES spectra. The structural parameters were obtained by a least-squares fit in R space for the k3-weighted Fourier-transformed data using Artemis. The amplitude reduction factor in these measurements was determined by EXAFS fitting of the Bi foil, which was measured simultaneously with the sample in transmission mode during the experiments.

DFT calculations
The first-principle density functional theory plus dispersion (DFT-D) calculations were implemented in the Vienna Ab-initio Simulation Package (VASP 6.4.1) with dispersion corrections by the D3 method of Grimme. The generalized gradient corrected approximation (GGA) treated by the Perdew−Burke−Ernzerhof (PBE) exchange-correlation potential was used to calculate the exchange-correlation energy. The PAW pseudopotential was employed as the scheme in the representation of reciprocal space for all the elements. The plane-wave cut-off energy was set to 520 eV for all the calculations. The Brillouin zone was sampled using a 2 × 2 × 1 Monkhorst-Pack k-point with a smearing of 0.3 eV. Ueff = 4.5 eV was applied to Ce element in the static electron structure calculations. Independence tests of both cut-off energy and k-points were carried out, as shown in Supplementary Fig. 1. Spin polarization has been considered, and the self-consistent field (SCF) tolerance was set to 10−5 eV/atom. All the modelling was performed with a convergence threshold of 0.03 eV/Å on maximum force. No symmetry constraint was used for any modelling. The computational method is believed to give high precision results, and has been validated by experimental data. In this work, the model predicted the lattice constant of the CeO2 lattice to be a = b = c=5.43662 Å, in agreement with the experimental data of a = b = c=5.411 Å, as shown in Supplementary Table 1.

Catalytic evaluation
The transesterification reaction was carried out in a 20 mL autoclave equipped with a magnetic stirrer (Anhui Kemi Machinery Technology Co., Ltd). In a typical experimental procedure, nitrogen purges and replaces the gas in the reactor before the experiment begins. At the end of the reaction, the reaction product was separated, and the appropriate amount of supernatant was taken and added to the internal standard to prepare the standard solution. The content of each substance was quantitatively analysed by gas chromatography.
The conversion of 1,2-BDO, and the selectivity of 1,2-BC are calculated as follows:
Conv. of 1,2-BDO = (n initial (1,2-BDO) − n residual (1,2-BDO)) / n initial (1,2-BDO) × 100% (1)
Sel. of 1,2-BC = n(1,2-BC) / (n initial (1,2-BDO) × Conv. of (1,2-BDO)) × 100% (2)

Catalyst stability test
Firstly, Bi1-CeO2 was sequentially pressed and sieved and then the 40-60 mesh Bi1-CeO2 particles were filtered out using a sieve. Then, it was loaded into a stainless-steel tube with a length of 300 mm and an inner diameter of about 8 mm, and the top and bottom were filled with quartz sand. A mixed DMC/1,2-BDO solution was configured and transported to the inside of the reactor via an advection pump. The reaction solution was collected at the bottom of the reactor and sampled every 16 h interval.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript entitled \" Bi1δ+-O-Ce3+ synergistic sites on rod ceria for unprecedented efficient transesterification \" by Guo et al. provides a Bi1-ceria catalyst for transesterification, achieving an unprecedented catalytic activity of 2499 g1,2-BC g cat.-1 h-1 and stability for 800 h. This study sheds light on a novel strategy for further design of highly-efficient catalysts for organic synthesis and sustainable chemistry. The manuscript is of good quality and the originality of the research is appreciable. I would advise publishment in Nature Communications after some major changes:\nSPECIFIC COMMENTS\n(1) While the authors emphasize that \"precisely modulating the spatial and chemical architecture of acid-base sites to achieve optimal acid-base equilibrium remains a formidable challenge\" the manuscript lacks explicit discussion on strategic methodologies for controlling inter-site distances and coordination environments, nor does it systematically investigate their mechanistic impacts on transesterification reaction. Clarification of these structure-function relationships is critically needed.\n(2) While the authors propose a \"remote catalysis\" mechanism for the Bi1/CeO2 rod catalyst, the operational details of this mechanism in governing transesterification kinetics remain inadequately elucidated. Furthermore, although the characterization data demonstrate that Bi single-atom doping enhances oxygen vacancy concentration and Lewis acidity in CeO2, such effects are not unique to Bi, and many low-valent metal dopants in CeO2 lattices exhibit analogous vacancy generation and acid-strengthening behaviors. A systematic comparative analysis of these isoelectronic dopants would strengthen mechanistic validation by distinguishing whether the observed catalytic enhancement arises from generic vacancy effects or Bi-specific electronic modulation critical to the proposed remote catalysis paradigm.\n(3) The authors observe that Bi1/CeO2 catalyst deactivation after 800 h operation stems from Bi single-atom agglomeration into BiOx clusters. While they assert that thermal regeneration enables BiOx redispersion into isolated Bi atoms. Specifically, the energy landscape governing the BiOx→Bi1 transformation—including critical factors like activation energy thresholds, thermal mobility of Bi species, and CeO₂ surface reconstruction dynamics—remains fundamentally unclear. A systematic investigation correlating annealing parameters with atomic-scale redispersion efficiency is essential to validate this hypothesized regeneration mechanism.", "reviewer_2": "The paper presents the synthesis of Bi1-CeO2 catalysts for the transesterification reaction, targeting the production of 1,2- butylene carbonate (1,2-BC) from 1,2-butanediol (1,2-BDO) and dimethyl carbonate (DMC). The authors report impressive catalytic performance (2499 g1,2-BC gcat.-1 h-1) and long-term stability (over 800 hours), attributing the catalyst's efficiency to Bi₁ sites that modify the electronic structure of adjacent Ce atoms. Mechanistic studies suggest that the Bi₁ center influences the reaction through \"remote catalysis.\" The paper also includes a series of characterization techniques like XAFS, DFT calculations, and DRIFTS to provide a detailed understanding of the catalyst's properties and performance. The following present some issues and comments.\n#1 The paper discusses the synthesis of cyclic carbonates via transesterification but does not explain why this method is advantageous compared to the commonly used CO2-based synthesis route. Could you clarify the practical advantages of using transesterification for cyclic carbonate synthesis, particularly in industrial applications?\n#2 Why is the transesterification reaction limited to DMC and 1,2-BDO? Could the catalyst be tested in other transesterification reactions to demonstrate its broader applicability? Additionally, could this catalyst be explored for the synthesis of non-cyclic carbonates or other types of esters? If this catalyst only functions effectively in specific transesterification systems, it cannot be called ‘unprecedented efficient’.\n#3 This work proposes a \"remote catalysis\" mechanism wherein Bi single atoms purportedly modify the electronic structure of adjacent cerium Ce atoms without directly participating in the reaction. However, the evidence supporting this mechanism suffers from critical deficiencies: Beyond EXAFS characterization of atomic distances, there is no experimental measurement of the spatial propagation range of electronic effects to confirm remote catalytic behavior. Moreover, the DFT calculations fail to account for solvent interactions and surface defects, factors known to significantly modulate electronic interactions in heterogeneous catalysis. Crucially, no comparative studies were conducted with conventional bi-metallic clusters or nanoparticles of Bi-CeO2. Should similar catalytic performance emerge from such aggregated Bi structures, it would disprove the \"remote catalysis\" hypothesis and instead indicate that localized chemical interactions at Bi sites govern the observed activity.\n#4 In Fig. 1d and Fig. 1e appear to have swapped descriptions. In Fig. 1e, the comparison of your catalyst's efficiency with literature catalysts is noted, but the literature catalysts use different reactants. Does this comparison still hold significance, and if not, could you provide a more valid comparison to strengthen your argument?\n#5 How does the specific Lewis acidity/basicity of the Bi1-CeO2 catalyst influence its catalytic activity? The paper could benefit from a deeper analysis or discussion on the specific role of these acid-base properties in enhancing the reaction efficiency.\n#6 The paper mentions a side reaction forming HBMC, yet no intermediate was detected by in situ IR. Can you provide a more detailed explanation of why this side reaction is not occurring in your system, and what role does your catalyst play in this process?\nGiven my concerns mentioned earlier, I'm afraid the manuscript fails to establish novelty beyond existing Bi-CeO2 literature or demonstrate why the transesterification route is industrially competitive. Mechanistic claims rely on incomplete evidence, particularly for \"remote catalysis,\" while the absence of generality tests and rigorous stability validation undermines practical utility. Mandatory revisions would necessitate extensive new experimentation beyond the scope of typical revisions. The manuscript does not good enough to meet the journal's standards for impact or mechanistic rigor.", "reviewer_3": "This manuscript reports an unprecedentedly highly active (2499 g1,2-BC gcat.⁻¹ h⁻¹) and long-lived (800 h) Bi1-ceria catalyst, which exhibits significant advantages in ester exchange reactions, far exceeding the catalyst performance reported in existing literature. The \"remote catalysis\" mechanism was proposed, that is, the Bi1 single atom enhances the reaction performance by regulating the adjacent Ce³⁺-O acid-base site (rather than directly serving as the active center), providing a new idea for the design of single-atom catalysts (SACs). It was found that the Bi1 site dynamically reconstructs into BiOx and can be regenerated through simple heat treatment, providing important insights into the deactivation and regeneration mechanism of the catalyst. It is recommended to carry out a major overhaul."}, "author_response": "We are deeply grateful to the reviewers for their time and their advices, which may help us to improve the quality of our manuscript. We have carefully considered all the comments and have incorporated changes accordingly. All responses in this document are highlighted in blue text (some are in red for special emphasis), and the quotations from the original manuscript and supplementary information are highlighted in black text for easy identification.\nResponse to Comments of Reviewer 1\n(1) While the authors emphasize that \"precisely modulating the spatial and chemical architecture of acid-base sites to achieve optimal acid-base equilibrium remains a formidable challenge\" the manuscript lacks explicit discussion on strategic methodologies for controlling inter-site distances and coordination environments, nor does it systematically investigate their mechanistic impacts on transesterification reaction. Clarification of these structure-function relationships is critically needed.\nResponse: The precise regulation of the spatial and chemical configurations of acid- base sites on heterogeneous catalyst surfaces to achieve the optimal acid-base balance has long remained a significant challenge. For the Bi 1 -CeO2 catalyst in our manuscript, the presence of isolated Bi sites (Bi ) induces modifications in the electronic structure of cerium 1 atoms (as evidenced by XPS and Supplementary Fig. 15), which in turn alters the adsorption behavior of the reactants 1,2-BDO and DMC on the catalyst surface (Fig. 3, and Supplementary Fig. 16-33), and the changes of acidity/basicity also enhance the DMC activation, evidenced by the reaction pathway analysis (Fig. 3H) and the catalytic performance (Fig. 1F). Besides, the structural evolution between Bi 1 -O2 and Bi 1 -O3 induced the exothermic desorption of the product 1,2-BC (line 281-298). All the above explain the mechanism how the doping of Bi improved the catalytic performance of the transesterification reaction.\nHowever, we recognized that the manuscript may need more insights on the precise control of inter-site distance and coordination environment, for which we will carry out additional experiments to clarify the microscopic structure sensitivity induced by the Bi doping ratio, if we get an opportunity to submit a revised version.\nFig. 2 (G-H) CO -TPD and NH -TPD profiles of catalysts\n2 3\nFig. 1 (F) Catalytic performance of 1,2-BC synthesis for different catalysts.\nSupplementary Fig. 15. Bader charge analysis of Ce3+ and O2- on CeO -non O , CeO -O , 2 v 2 v and Bi -CeO -O .\n1 2 v\nFig. 3 (H) Key reaction steps of the transesterification process that are shared by the CeO 2 and Bi -CeO .\n1 2\n(2) While the authors propose a \"remote catalysis\" mechanism for the Bi /CeO rod catalyst, 1 2 the operational details of this mechanism in governing transesterification kinetics remain inadequately elucidated. Furthermore, although the characterization data demonstrate that Bi single-atom doping enhances oxygen vacancy concentration and Lewis acidity in CeO , 2 such effects are not unique to Bi, and many low-valent metal dopants in CeO lattices 2 exhibit analogous vacancy generation and acid-strengthening behaviors. A systematic comparative analysis of these isoelectronic dopants would strengthen mechanistic validation by distinguishing whether the observed catalytic enhancement arises from generic vacancy effects or Bi-specific electronic modulation critical to the proposed remote catalysis paradigm.\nResponse: The “remote catalysis” mechanism proposed in our work appears as a concept, which indicates the catalysis is induced by Bi1, but the reactants are not in intimate contact with it (Fig. R1). As suggested by the reviewer, we speculated this mechanism would possibly be observed in some other circumstances with smaller size elements doping1-5, but it was first identified in the context of the transesterification over Bi 1 -CeO2 catalyst. Indeed, we have evaluated Sb 1 -CeO 2 in an experiment, but it did not show the same performance as Bi -CeO , as compared in Fig. R2. Our study has shown 1 2 that the best activity requires intermediate acid and strong basic sites, therefore, we cannot assert at the moment that Bi was not the unique option for such remote catalysis phenomenon.\nIn response, we plan to evaluate a series of dopants including Pb, Sn, Te, and other elements with analogous electronic properties as Bi by experiments and calculations, aiming to compare their impacts on doping CeO .\nFig. R2 Catalytic performance of 1,2-BC synthesis over different catalysts\nReaction condition: 50 mmol of DMC, 50 mmol of 1,2-BDO, 25 mg of catalyst (0.5 wt.% catalyst dosage based on 1,2-BDO mass, 120 ℃, 20 min)\n(3) The authors observe that Bi /CeO catalyst deactivation after 800 h operation stems 1 2 from Bi single-atom agglomeration into BiO clusters. While they assert that thermal x regeneration enables BiO redispersion into isolated Bi atoms. Specifically, the energy x landscape governing the BiO →Bi transformation—including critical factors like activation x 1 energy thresholds, thermal mobility of Bi species, and CeO surface reconstruction 2 dynamics—remains fundamentally unclear. A systematic investigation correlating annealing parameters with atomic-scale redispersion efficiency is essential to validate this hypothesized regeneration mechanism.\nResponse: We deem that the dynamic evolution from Bi → BiO is induced by the 1 x intermediate interaction with the catalyst surface, and we have confirmed the reversely dynamic evolution from BiO → Bi during the thermal treatment without reactants by our x 1 XAFS results, which is explicitly stated in the manuscript: “The evolution of Bi and BiO 1 x nanoparticles was further confirmed by the XAFS by a new Bi-O-Bi scattering path at 3.51 Å (Fig. 5B, 5D) and the increased coordination number of O to 2.1 (Supplementary Table 15). The Bi-O-Bi scattering path disappeared after the thermal treatment, meanwhile the Bi-O path was regained (Fig. 5C, 5F) with an O coordination number of 1.6, resembling that of the fresh catalyst (1.8) (Supplementary Table 16).”\nQuantitative EPR analysis of Bi -CeO , x%D-Bi -CeO , and R-Bi -CeO further verified the 1 2 1 2 1 2 dynamic evolution of the lattice oxygen (O ) (Fig. 4F), as explicitly stated in the manuscript: L “The normalized spin density gradually increased from 7.280 e^11/mm3 with the degree of deactivation, reaching 3.575 e^12/mm3 in 80%D-Bi -CeO . The results confirm that the 1 2 cleavage of Ce-O bonds takes place to generate the oxygen vacancy (O ) with the v deactivation. After the thermal treatment, the BiO species was completely recovered to x Bi -O , evidenced by the drop of spin density to 7.522 e^11/mm3 for R-Bi -CeO , indicating 1 2 1 2 that the lattice O atoms are restored.”\nAs the in situ re-dispersion of nanoparticles remains a focus of our ongoing research, we have been carrying out further experiments and DFT computations. The structural evolution of the BiO -CeO (110) with rich O was modelled by ML-AIMD, providing visual x 2 v evidence of the re-dispersion taking place on D-Bi -CeO at 773 K (Fig. R3). The 1 2 decomposition of BiO started after 2 ps, and the dispersion from 8 ps to 15 ps can be x visualized, where the O atoms populate back into the adjacent O to regenerate the Ce-O v bond. The complete dispersion of BiO into Bi -O or Bi -O occurs within 140 ps. This x 1 2 2 2 finding explains the spin decline for the catalyst after re-dispersion, and confirms that the simultaneous dispersion of O atoms is the key to recovering the catalytic activity. More insightful investigations can be carried out regarding the relationship between the annealing parameters and the efficiency of atomic-scale redispersion in experiments.\nFig. 5 (A) Fitting curves of the FT-EXAFS for the fresh Bi -CeO . (B) FT-EXAFS fitting 1 2 curve of 70% D-Bi -CeO . (C) FT-EXAFS fitting curve of Bi -CeO -Redispersion. (D) WT- 1 2 1 2 EXAFS plots of Bi -CeO Fresh.(E) WT-EXAFS plots of 70% D-Bi -CeO . (F) WT-EXAFS 1 2 1 2 plots of Bi -CeO -Redispersion.\n1 2\nFig. 4 (F) Quantitative spin quantum number results for different deactivated and re- dispersed Bi -CeO . 1 2\nFig. R3 Re-dispersion process of BiO nanoparticles on CeO surface at 773 K. Color x 2 codes: brown (C), red (O), yellow (Ce), and purple (Bi).\nResponse to Comments of Reviewer 2\n#1 The paper discusses the synthesis of cyclic carbonates via transesterification but does not explain why this method is advantageous compared to the commonly used CO -based 2 synthesis route. Could you clarify the practical advantages of using transesterification for cyclic carbonate synthesis, particularly in industrial applications?\nResponse: For the synthesis of cyclic carbonates, utilizing carbon dioxide (CO ) as a 2 feedstock represents a common pathway. Compared to transesterification, the CO -based 2 route currently relies primarily on homogeneous catalysts, such as ionic liquids, which exhibit high catalytic activity but pose significant challenges for separation and catalyst recycling6, 7. While heterogeneous catalysts often suffer from low reactivity and insufficient stability.\nFor the transesterification route, the feedstock diols can be derived from biomass or coal- based processes8, 9, and the reaction proceeds without solvent, saving additional separation cost10-15. Considering the extraordinary catalytic performance and stability of the heterogeneous catalyst in our study, transesterification is of great potential for the cyclic carbonate synthesis in industry.\n#2 Why is the transesterification reaction limited to DMC and 1,2-BDO? Could the catalyst be tested in other transesterification reactions to demonstrate its broader applicability? Additionally, could this catalyst be explored for the synthesis of non-cyclic carbonates or other types of esters? If this catalyst only functions effectively in specific transesterification systems, it cannot be called ‘unprecedented efficient’.\nResponse: Indeed, we have extended the substrate scope to include more than ten types of diols, as summarized in Supplementary Table 18. The results demonstrate that the Bi - 1 CeO catalyst exhibits exceptionally high activity for all the tested substrates, and the 2 reaction of DMC and 1,2-BDO is a typical probe reaction for transesterification.\nSupplementary Table 18. Scope and limitations of Bi -CeO synthesis of various cyclic 1 2 carbonates\nEntry Substrate Production Conv. (%) Yield (%) Space time yield\n1 a 97.1 96.7 917.7 (g g -¹ h-¹) EC cat.\n2 a 98.7 98.6 844.0 (g g -¹ h-¹) GLC cat.\n3 a 95.9 95.5 738.1 (g g -¹ h-¹) 1,2-PC cat.\n4 a 98.4 97.0 847.8 (g g -¹ h-¹) 2,3-BC cat.\n5 b 98.2 97.1 420.7.0 (g g -¹ h-¹) PDC cat.\n6 b 98.1 96.3 391.7 (g g -¹ h-¹) 1,2-HDC cat.\n7 c 96.5 82.9 738.1 (g g -¹ h-¹) 1,3-BC cat.\n8 c 97.5 83.9 648.4 (g 1,2-PC g cat. -¹ h-¹)\na, molar ratio (DMC/diols) =3:1, catalyst dosage =0.3 wt.% (calculated by diols), reaction temperature =120 ℃, reaction time =30 min\nb, molar ratio (DMC/diols) =3:1, catalyst dosage =0.3 wt.% (calculated by diols), reaction temperature =130 ℃, reaction time =60 min\nc, molar ratio (DMC/diols) =3:1, catalyst dosage =0.3 wt.% (calculated by diols), reaction temperature =150 ℃, reaction time =30 min\nConsidering the reviewer’s suggestion, we have added additional evaluation on the performance of Bi -CeO for the carbonylation synthesis of N-substituted carbamates (Fig. 1 2 R4), which further demonstrated the exceptional activity of this catalyst in relevant reactions.\nFig. R4 Catalytic performance of different catalysts in the amidocarboxylation synthesis of N-substituted carbamates. Reaction condition: 1,3-Propanediamine : Ethyl carbamate : Ethanol = 1 : 2 : 12.5, Catalyst 1.7% (based on 1,3-Propanediamine), 180 ℃, 1.0 h.\nHowever, should the term of “unprecedented efficient” be considered too strong or insufficiently precise, we are fully agree to add a determiner in the title.\n#3 This work proposes a \"remote catalysis\" mechanism wherein Bi single atoms purportedly modify the electronic structure of adjacent cerium Ce atoms without directly participating in the reaction. However, the evidence supporting this mechanism suffers from critical deficiencies: Beyond EXAFS characterization of atomic distances, there is no experimental measurement of the spatial propagation range of electronic effects to confirm remote catalytic behavior. Moreover, the DFT calculations fail to account for solvent interactions and surface defects, factors known to significantly modulate electronic interactions in heterogeneous catalysis. Crucially, no comparative studies were conducted with conventional bi-metallic clusters or nanoparticles of Bi-CeO . Should similar catalytic performance emerge from such aggregated Bi structures, it would disprove the \"remote catalysis\" hypothesis and instead indicate that localized chemical interactions at Bi sites govern the observed activity.\nWe address the concerns point by point raised by the reviewer.\n1. This work proposes a \"remote catalysis\" mechanism wherein Bi single atoms purportedly modify the electronic structure of adjacent cerium Ce atoms without directly participating in the reaction. However, the evidence supporting this mechanism suffers from critical deficiencies: “Beyond EXAFS characterization of atomic distances, there is no experimental measurement of the spatial propagation range of electronic effects to confirm remote catalytic behavior”\nResponse: The characterizations including STEM, EPR, and EXAFS have confirmed the nature of the single-atom structure and the rich oxygen vacancies of the catalyst, yet they provided limited direct insight into the propagation range of electronic effects. Based on this, we adopted X-ray photoelectron spectroscopy (XPS), CO and NH temperature- 2 3 programmed desorption (TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ-DRIFTS) in the manuscript. The tendency reflected by the results with the doping ratio of Bi has been detailed discussed in the manuscript to probe the electronic propagation that induces the remote catalytic effect, mainly in terms of acidity/basicity alteration. The following are specific justifications based on experimental results.\nFirstly, XPS measurements have provided direct evidence of electron transfer from Bi atoms to the support via oxygen bridges. The effect of O on the charge transfer between v Bi and CeO was quantitatively validated by the charge density difference (CDD) and bader 2 charge analyses with DFT modelling (Fig. 2F, 2I), as explicitly stated in the manuscript: “The results reveal that Bi with an adjacent O carries a positive charge of +0.62 e, and Bi1 v on the intact CeO shows more positive charge of +0.85 e. The results confirm that 2 electrons migrate from the Bi atom to the support via the O atom while there is more v electron back-donation from the support to Bi in the presence of O .” The addition of Bi v 1 alters the local electronic structure of (and potentially activated) adjacent lattice oxygen (O ) by direct charge transfer, so that remarkably affects the acid-base properties of the L CeO support.\nFurthermore, a detailed investigation into the acid-base properties of the catalyst was conducted using CO and NH temperature-programmed desorption (TPD) techniques. As 2 3 shown in Fig. 2G-H, we can conclude that the catalytic performance has a strong correlation with the acid/basic strength and abundance. The best performance requires moderate acidic sites and strong basic sites, as explicitly stated in the manuscript: “Fig. 2G, 2H, and Supplementary Table 7 shows only a trace amount of strong Lewis basic sites were present in Bi O , and only abundant weak basic sites for CeO . With the addition of 2 3 2 Bi, rich strong basic sites were observed on CeO , and the strong basic sites on CeO shift 2 2 to higher temperature regions with the Bi content, implying the enhancement of the basic strength. With the addition of Bi, the concentration of acid sites for CeO shows analogues 2 increasing tendency as the basic sites (NH -TPD, Fig. 2H). This is because the increasing 3 concentration of O induces more Ce3+ sites as weak-mediate Lewis acid (Supplementary v Table 7). Nevertheless, the shift of weak acidic sites to lower temperatures indicates the acidity is weakened.” The above results confirmed that the unique Bi δ+-O-Ce3+-O coordination structure has changed the intrinsic electronic structure of CeO and activated 1 v 2 the O for abundant O creation, and the O would give rise to rich moderate acidic sites L v v and strong basic sites on CeO in the presence of Bi , which are important for efficient 2 1 transesterification reaction.\nFig. 2 (G-H) CO -TPD and NH -TPD profiles of catalysts.\n2 3\nSupplementary Table 7. TPD measurements of acid-base properties for Bi O and x%Bi- 2 3 CeO (x=0, 0.2, 0.4, 0.6, 0.8, 1.0).\nWeak Moderate Strong Total Weak Moderate Strong Total\nSamples\n(< 473 K) (473–673 K) (> 673 K) (< 473 K) (473–673 K) (> 673 K)\nBi2O3 0 0 1.99 1.99 0 0 2.34 2.34\nCeO2 11.17 0.76 3.21 15.31 1.43 0.35 9.82 11.25\n0.2%Bi-CeO2 9.01 1.09 4.20 14.30 1.91 1.74 8.38 10.29\n0.4%Bi-CeO2 7.87 0.96 7.57 16.42 1.36 1.47 10.92 13.76\n0.6%Bi-CeO2 6.91 0.29 8.64 15.84 2.24 0.96 9.31 12.51\n0.8%Bi-CeO2 5.42 1.64 6.59 13.67 1.07 1.52 10.70 13.31\n1.0%Bi-CeO2 5.46 1.92 8.67 16.06 1.32 1.43 10.81 13.56\na, According to the normalization calculation (CO -TPD).\n2\nb, According to the normalization calculation (NH -TPD).\nv\nRegarding the adsorption of DMC, the inactive catalyst of Bi O favors a bidentate 2 3 adsorption conformation (1780 cm-1). However, the catalytic evaluation and the DFT calculation both reveal that the cis-cis-monodentate configuration (1766 cm-1) is the active adsorption conformation (Supplementary Fig. 24 and Supplementary Fig. 26). The presence of Bi facilitates the dissociation of DMC at lower temperatures, thereby 1 enhancing the overall catalytic activity.\nSupplementary Fig. 16 In situ DRIFTS spectra of 1,2-BDO adsorbed on Bi -CeO .\n1 2\n20 min 1086 cm-1\n) .u .a ( e on-top butoxy c n a b r o s b A Time\n0 min\n1200 1150 1100 1050 1000 950\nWavenumber (cm-1)\nSupplementary Fig. 17 In situ DRIFTS spectra of 1,2-BDO adsorbed on Bi O .\n2 3\n20 min\n1780 cm-1\n1767 cm-1\n) . Type-II u . a Type-I ( e c n a b Time r o cis-cis-monodentate adsorption s b bidentate adsorption A\n0 min\n1900 1850 1800 1750 1700 1650\nWavenumber (cm-1)\nSupplementary Fig. 24 In situ DRIFTS spectra of DMC adsorbed on Bi O .\n2 3\n1780cm-11766cm-1\n20 min\nType-Ⅰ Type-Ⅱ\n) .u .a ( e cis-cis-monodentate adsorption c Time bidentate adsorption n a Type-Ⅲ b r o 1752cm-1 s b A\n0 min\ncis-trans-monodentate adsorption\n1850 1800 1750 1700\nWavenumber (cm-1)\nSupplementary Fig. 26 In situ DRIFTS spectra of DMC adsorbed on Bi -CeO .\n1 2\nBeyond the limitation of experimental scale, the weak interaction between the reactants and Bi has been clearly identified by the density functional theory (DFT) calculations 1 (Supplementary Fig. 15, Supplementary Fig. 30 (1,2-BDO-3) and Supplementary Fig. 31 (DMC-3)), where we found the adsorption energy is -0.19 eV and -0.2 eV respectively for 1,2-BDO and DMC over the Bi site, indicating apparent physical adsorption of both molecules. Further, we revealed the range of electronic propagation by detailed Density of State (DOS) analysis (Fig. 3I, J) and (Fig. 4D, 4E), which indicates the delocalization of the f electron of Ce atoms beside Bi and that some oxygen (highlighted in Fig. 4B) are conductive so that bridge the electron propagation tunnel. These results we believe has been clearly demonstrated in the manuscript, however, we plan to update the abstract accordingly to stress the electron propagation effect by Bi doping.\n1\nupdated abstract:\n“Heterogeneous catalysts for transesterification reaction are highly desirable, but normally suffer from low activity or severe deactivation. Here we reported a Bi -ceria catalyst for 1 transesterification that exhibited unprecedented catalytic activity of 2499 g g -1 h-1 1,2-BC cat. and stability for 800 h, in the synthesis of 1,2-butylene carbonates from 1,2-butanediol and dimethyl carbonate. Our study revealed the constructed Bi did not directly serve as the 1 catalytic centre in a conventional sense, but remarkably improved the catalytic performance by regulating the acidity-basicity of the active sites, benefiting from the delocalization of the f electron of Ce and the remote propagation of electrons induced by conductive lattice oxygen. Carbonyl transferring and product desorption during the transesterification were thus boosted via the \"remote catalysis\" mechanism over the Bi δ+- 1 O-Ce3+-O site. The highly active sites also led to the Bi centred re-construction into BiO , v 1 x which triggered a decline in catalytic activity beyond 800 h ascribed to the excessive change of the acid-basic strength. Nevertheless, further study corroborated that a simple thermal treatment could readily regenerate the catalytic activity by restoring the migrated lattice oxygens, ensuring additional stability for over 600 hours. These findings have open a new avenue for the rational design of single-atom catalysts.”\nSupplementary Fig. 15 CeO -non O , CeO -O , and Bi -CeO -O differential charge 2 v 2 v 1 2 v calculations of Ce3+ and O2-.\nSupplementary Fig. 30 Adsorption configurations of 1,2-BDO on the surface of Bi -CeO .\n1 2\nColor codes: brown (C), white (H) red (O), yellow (Ce), and purple (Bi).\nSupplementary Fig. 31 Adsorption configurations of DMC on the surface of Bi -CeO . Color 1 2 codes: brown (C), white (H) red (O), yellow (Ce), and purple (Bi).\nFig. 3(I, J) Projected partial density of states of Ce20 in CeO and Bi -CeO .\n2 1 2\nFig. 4 (D) P-DOS of O1-Bi -CeO . (E) P-DOS of O1-CeO .\n1 2 2\nFig. 4 (B) Original structural modeling of Bi -CeO .\n1 2\nBy integrating the experimental and DFT modelling evidence presented above, we are able to probe the electronic propagation that underpins the remote catalysis effect.\n2. “the DFT calculations fail to account for solvent interactions and surface defects, factors known to significantly modulate electronic interactions in heterogeneous catalysis”\nResponse: Firstly, the reviewer raised concerns regarding the neglection of solvent effects and surface defects in our DFT calculations. We would like to clarify that the transesterification reaction between 1,2-BDO and DMC to form cyclic carbonate is a solvent-free process. However, we seek further clarification if the reviewer had a particular concern in this regard.\nSecondly, regarding surface defects, our DFT model was built based on a two-O coordinated Bi model with O on CeO , and we have implemented detailed electronic v 2 structure analysis towards this catalyst model and the reaction mechanism on it. Below are some key results and discussions in our original manuscript.\nAs shown in Supplementary Fig. 15, the Bader charge were analyzed for three models: CeO without O (CeO -non-O ), CeO with O (CeO -O ), and Bi -CeO with O (Bi -CeO - 2 v 2 v 2 v 2 v 1 2 v 1 2 O ). The results indicate that oxygen atoms adjacent to an O carry increased negative v v charge, from -1.15 eV in CeO₂-non-O to -1.21 eV in CeO -O . With the introduction of Bi , v 2 v 1 the charge further increases to -1.23 eV, which aligns well with the enhanced basicity observed in CO -TPD experiments.\nFig. 3(I, J) Projected partial density of states of Ce20 in CeO and Bi -CeO .\n2 1 2\nThe effects of O on the charge on Ce atoms (Fig. 2F and 2I) were also demonstrated, as v explicitly stated in the manuscript: “Bader charge analysis shows that the presence of O v leads to less charge on Ce adjacent to the defects (+2.27 e), compared to intact CeO - 2 nonO (+2.32 e), and this change is further enhanced by the presence of Bi (Bi -CeO -O , v 1 1 2 v +2.23 e), in line with the weaker acidity observed in experiments (Supplementary Fig. 15). Moreover, O atoms adjacent to O carried negative charge of -1.15 e and -1.21 e for CeO - v 2 nonO and CeO -O , respectively.”\nv 2 v\nMoreover, to investigate the effects of Bi and O on the adsorption process of DMC 1 v and 1,2-BDO, as explicitly stated in the manuscript: “we performed detailed adsorption simulations on Bi -CeO (110)-non-O and CeO (110)-non-O surfaces (Supplementary Fig. 1 2 v 2 v 29-30, and Supplementary Tables 9-10). When O was not present, the adsorption energy v of 1,2-BDO on Bi -CeO -non-O was -2.34 eV, and it was smaller than that for 1,2-BDO 1 2 v (Bi -CeO -O , -2.88 eV), indicating the presence of O would much facilitate the bridge 1 2 v v adsorption of 1,2-BDO. In another circumstance, when Bi was absent the adsorption 1 energy of 1,2-BDO on CeO -O was -1.43 eV, which is found to be almost the same as that 2 v over Bi -CeO (110) (-1.39 eV), further implying O would be the dominant factor in the BDO 1 2 v activation. With regard to the DMC, they are all adsorbed on the Bi -CeO (110)-non-O and 1 2 v CeO (110)-O surfaces in a monodentate C=O-Ce configuration, with no bidentate C=O- 2 v Ce configuration (Supplementary Table 9). Compared with the result of -1.04 eV adsorption energy of Bi -CeO (110)-O , the adsorption energy of monodentate C=O-Ce was -1.06 eV 1 2 v on the surface of Bi -CeO (110)-non-O , and -0.91 eV on the surface of CeO -O . The 1 2 v 2 v above results indicate that the presence of O favors the adsorption of 1,2-BDO, while the v presence of Bi favors the adsorption of DMC.”\n1 2\nAdsorbate 1,2-BDO-1 1,2-BDO-2 1,2-BDO-3 1,2-BDO-4 DMC-1 DMC-2 DMC-3 DMC-4\nCatalyst Bi-CeO O Bi-CeO O Bi-CeO O Bi-CeO O Bi-CeO O Bi-CeO O Bi-CeO O Bi-CeO O\n1 2- v 1 2- v 1 2- v 1 2- v 1 2- v 1 2- v 1 2- v 1 2- v\nadsorbate\n-86.65 -86.65 -86.65 -610.07 -69.38 -69.38 -69.38 -69.38\nenergy (eV)\nslab energy\n-610.07 -610.07 -610.07 -610.07 -610.07 -610.07 -610.07 -610.07\n(eV)\nComplex\n-698.11 -698.86 -696.91 -698.60 -680.20 -680.49 -679.65 -680.27\nenergy (eV)\nAdsorption\n-1.39 -2.13 -0.19 -2.88 -0.74 -1.04 -0.20 -0.82\nenergy (eV)\nSupplementary Table 10. Calculated adsorption energies of 1,2-BDO and DMC on Bi- CeO _nonO and CeO _O .\n2 v 2 v\nAdsorbate 1,2-BDO-5 DMC-5 1,2-BDO-6 DMC-6\nCatalyst Bi-CeO2_nonOv Bi-CeO2_nonOv CeO2_Ov CeO2_Ov\nadsorbate energy (eV) -86.65 -69.38 -86.65 -69.38\nslab energy (eV) -617.07 -617.07 -606.38 -606.38\nComplex energy (eV) -706.06 -687.51 -694.47 -676.68\nAdsorption energy (eV) -2.34 -1.06 -1.43 -0.91\nSupplementary Fig. 32. Adsorption configurations of DMC and 1,2-BDO on the surface of Bi -CeO -nonO . Color codes: brown (C), white (H) red (O), yellow (Ce), and purple (Bi).\n1 2 v\nSupplementary Fig. 33. Adsorption configurations of DMC and 1,2-BDO on the surface of CeO -nonO . Color codes: brown (C), white (H) red (O), yellow (Ce), and purple (Bi).\n2 v\nTogether, the above results confirm that our computational models have adequately incorporated the specific roles of O and Bi doping in the electronic structure modulation of v the active site, agreeing well with the experimental results in DRIFTS. However, we plan to carry out additional DFT analysis to clarify the microscopic structure sensitivity induced by the Bi doping ratio in an updated manuscript.\n3. “Crucially, no comparative studies were conducted with conventional bi-metallic clusters or nanoparticles of Bi-CeO . Should similar catalytic performance emerge from such aggregated Bi structures, it would disprove the \"remote catalysis\" hypothesis and instead indicate that localized chemical interactions at Bi sites govern the observed activity”.\nResponse: If we understand correctly, the reviewer was asking for the comparison with the catalyst of the Bi cluster supported on CeO . In our study, we have synthesized the 2 mentioned catalyst but found the activity was almost the same as that for pristine CeO , 2 therefore, we concluded that Bi doping has distinct effect compared to Bi cluster loading 1 (Fig. R5). Besides, we also implemented the catalytic reaction test on Bi O , and got the 2 3 same conclusion. In addition, the characterization of the deactivated catalyst, specifically through XRD and XAFS analyses (Fig. 4C, Fig. 5B, 5E, and Supplementary Fig. 48), has provided clear evidence for the formation of BiO nanoparticles.\nx\nIn a revised version, we will consider to expand the discussion of these detailed mechanisms to highlight the curtail contrast between Bi and BiO /Bi cluster on CeO to 1 x 2 address the reviewer’s concern.\nFig. R5 Performance comparison of x% Bi (cluster)-CeO catalysts with wet impregnation 2 for the synthesis of 1,2-BC.\n.\nFig. 4 (C) XRD spectra of different deactivated and re-dispersed Bi -CeO . 1 2\nFig. 5 (B) FT-EXAFS fitting curve of 70% D-Bi -CeO . (E) WT-EXAFS plots of 70% D-Bi - 1 2 1 CeO .\nSupplementary Fig. 45. Catalytic performance of fresh 0.6%Bi -CeO -R, Bi -CeO -R 70%- 1 2 1 2 deactivation, and 5%Bi-CeO -R in the synthesis of 1,2-BC.\n2\n)k(c3k TF 0 B 5 B B i -C e O 1% B i-C i O 2 3 i fo il B 7 2e O 2 i-O 0 2 % In R a + c tiv a tio n B i-O ( ) Å α -B i 4 6\nSupplementary Fig. 48 FT-EXAFS fitting curve of 5%Bi-CeO and Bi -CeO 70% 2 1 2 deactivation.\nSupplementary Table 15. Fitting parameters extracted from the Bi K-edge EXAFS fitting. (S 2=0.80 from Bi foil) 0\nSample Shell CNa R(Å)b σ2(Å2)c ΔE0(eV)d R factor\nBi-Bi1 2* 3.03±0.01 0.0069 3.6±0.1\nBi foil 0.0061\nBi-Bi2 2* 3.52±0.01 0.0045 3.6±0.1\nBi-O 2* 2.15±0.01 0.0039 2.9±0.1\nBi2O3 0.0039\nBi-O-Bi 8* 3.56±0.01 0.0067 2.9±0.1\nBi-O 2.1±0.1 2.15±0.01 0.0035 4.6±0.1\n70%D-Bi1CeO2 0.0039\nBi-O-Bi 8.1±0.1 3.56±0.01 0.0058 4.6±0.1\nBi-O 1.7±0.1 2.22±0.01 0.0014 4.8±0.1\n5%Bi-CeO2 0.0047\nBi-O-Bi 6.2±0.1 3.57±0.01 0.0068 4.8±0.1\naCN: coordination numbers; bR: bond distance; cσ2: Debye-Waller factors; d ΔE : the inner 0 potential correction. R factor: goodness of fit.\nThe obtained XAFS data was processed in Athena (version 0.9.26) for background, pre- edge line and post-edge line calibrations. Then Fourier transformed fitting was carried out in Artemis (version 0.9.26). The k3 weighting, k-range of 2.5 ~12.5 Å-1 and R range of 1 - 2 Å were used for the fitting of Bi O ; The k3 weighting, k-range of 2.5 ~11.5 Å-1 and R 2 3 range of 1 - 2 Å were used for the fitting of Samples.16-18\n#4 In Fig. 1d and Fig. 1e appear to have swapped descriptions. In Fig. 1e, the comparison of your catalyst's efficiency with literature catalysts is noted, but the literature catalysts use different reactants. Does this comparison still hold significance, and if not, could you provide a more valid comparison to strengthen your argument?\nResponse: We sincerely thank the reviewer for identifying these issues. We noticed that the captions for Fig. 1d and 1e were incorrectly placed in the original manuscript, and we have corrected this typo.\nRegarding the comparison of catalytic performance, we used the most analogues reactions with merely different vicinal diols as shown in Formula 1and Formula 2 (Formula 3, this work), considering the limited data of this reaction in the literature. We also evaluated the catalytic performance for these vicinal diols using our catalyst, as shown in Supplementary Table 18. Therefore, we believe the comparison remains valid. However, we can consider to carry out more comparative experiments with various catalysts if a revision opportunity is granted.\nFig. 1 (E) Catalytic performance of 1,2-BC synthesis for different catalysts19-27.\nFormula 1: The transesterification reaction synthesizes Ethylene carbonates from dimethyl carbonate and Ethylene glycol.\nFormula 2: The transesterification reaction synthesizes Glycerol carbonates from dimethyl carbonate and Glycerol.\nFormula 3: The transesterification reaction synthesizes 1,2-butylene carbonates from dimethyl carbonate and 1,2-butanediol.\nSupplementary Table 18. Scope and limitations of Bi -CeO synthesis of various cyclic 1 2 carbonates\nEntry Substrate Production Conv. (%) Yield (%) Space time yield\n1 97.1 96.7 917.7 (g g -¹ h-¹) EC cat.\n2 98.7 98.6 844.0 (g g -¹ h-¹) GLC cat.\nmolar ratio (DMC/diols) =3:1, catalyst dosage =0.3 wt.% (calculated by diols), reaction temperature =120 ℃, reaction time =30 min\n#5 How does the specific Lewis acidity/basicity of the Bi1-CeO2 catalyst influence its catalytic activity? The paper could benefit from a deeper analysis or discussion on the specific role of these acid-base properties in enhancing the reaction efficiency.\nResponse: It is essential to clarify that the core principle of the catalytic mechanism in this study lies in the following: Bi induces a unique activation of lattice oxygen in its adjacent 1 regions, thereby promoting the formation of abundant O sites on the CeO surface within v 2 the bulk phase. This process subsequently alters the acid-base properties of the catalyst (Fig. R6).\nFig R6. Single-atom regulation of acid-base sites enables “remote catalysis” for the synthesis of cyclic carbonates.\nIn our manuscript, we have demonstrated in different sections that the specific effects of Lewis acid-base sites of the Bi1 -CeO2 catalyst on the catalytic performance and the detailed mechanisms, for example in line 118-121, 190-211, 251-261, and line 259-380.\nFirst of all, as shown in Fig. 2G and 2H, we can conclude that the catalytic performance has a strong correlation with the acid/basic strength and abundance.\nFig. 2 (G-H) CO -TPD and NH -TPD profiles of catalysts\n2 3\nSupplementary Table 7. TPD measurements of acid-base properties for Bi O and x%Bi- 2 3 CeO (x=0, 0.2, 0.4, 0.6, 0.8, 1.0).\nWeak Moderate Strong Total Weak Moderate Strong Total\nSamples\n(< 473 K) (473–673 K) (> 673 K) (< 473 K) (473–673 K) (> 673 K)\nBi2O3 0 0 1.99 1.99 0 0 2.34 2.34\nCeO2 11.17 0.76 3.21 15.31 1.43 0.35 9.82 11.25\n0.2%Bi-CeO2 9.01 1.09 4.20 14.30 1.91 1.74 8.38 10.29\n0.4%Bi-CeO2 7.87 0.96 7.57 16.42 1.36 1.47 10.92 13.76\n0.6%Bi-CeO2 6.91 0.29 8.64 15.84 2.24 0.96 9.31 12.51\n0.8%Bi-CeO2 5.42 1.64 6.59 13.67 1.07 1.52 10.70 13.31\n1.0%Bi-CeO2 5.46 1.92 8.67 16.06 1.32 1.43 10.81 13.56\na, According to the normalization calculation (CO -TPD).\n2\nb, According to the normalization calculation (NH -TPD).\nThe best performance requires a moderate acidic sites and strong basic sites, as explicitly stated in the manuscript: “Supplementary Table 7 shows only a trace amount of strong Lewis basic sites were present in Bi O , and only abundant weak basic sites for CeO . 2 3 2 With the addition of Bi, rich strong basic sites were observed on CeO , and the strong basic 2 sites on CeO shift to higher temperature regions with the Bi content, implying the 2 enhancement of the basic strength. With the addition of Bi, the concentration of acid sites for CeO shows analogues 2 increasing tendency as the basic sites (NH -TPD, Fig. 2H). This 3 is because the increasing concentration of O induces more Ce3+ sites as weak-mediate v Lewis acid (Supplementary Table 7). The result is agreed by the pyridine IR tests that the Lewis acid concentration for Bi -CeO is much higher than CeO -R (Supplementary Fig. 1 2 2 14 & Supplementary Table 8). Nevertheless, the shift of weak acidic sites to lower temperatures indicates the acidity is weakened. The above results revealed the unique Bi δ+-O-Ce3+-O coordination structure has changed the intrinsic electronic structure of 1 v CeO and activated the O for abundant O creation, and the O would give rise to rich 2 L v v moderate acidic sites and strong basic sites on CeO in the presence of Bi , which are 2 1 important for efficient transesterification reaction.”\nWe employed in situ DRIFTS to probe the adsorption/desorption behavior of DMC and 1,2- BDO on Bi O (which possesses limited acid-base sites) and Bi -CeO (with abundant 2 3 1 2 acid-base sites) (Fig. 3A-3B, Supplementary Fig. 16, 17, 24, and 26). The results clearly show that the different acid-base properties strongly influence the adsorption and desorption behavior of the reactants on the catalyst surface, as explicitly stated in the manuscript: “Fig. 3A-3B and Supplementary Fig. 16 show that 1,2-BDO adsorbed onto Bi - 1 CeO mainly in a bridged butoxy conformation on the O (1035 cm-1) at room temperature, 2 v in addition to the on-top butoxy (1091 cm-1) and bridged butoxy (1062 cm-1) conformations28. It was found that the top butoxy and bridged butoxy conformations would gradually shifted to the bridged butoxy conformation with the temperature on the O of Bi - 1 v CeO (Fig. 3D-3E). In contrast, only on-top butoxy adsorption conformation (1086 cm-1) 2 was observed on the Bi O surface that is proven to be inactive for transesterification 2 3 (Supplementary Fig. 17).” Further DFT calculations elaborated these mechanisms shown in Fig. 3 and the Supplementary Information, as explicitly stated in the manuscript: “DFT study (Supplementary Fig. 30 & Supplementary Table 9) revealed that 1,2-BDO only had weak interaction with Bi (E = -0.19 eV). And the molecule was likely to adsorb through 1 ad the primary hydroxyl groups with the spontaneous dissociation of O -H (E = -1.39 eV)” α a and “DFT modelling reveals that during the formation of the 1,2-BC precursor, the O in L CeO was activated and migrated towards Bi to form Bi -O , which contributes to the high 2 1 1 3 kinetic barrier of 1.54 eV in the reaction pathway (TS-3, Supplementary Fig. 58). The desorption of 1,2-BC consists of exothermic lattice recovery (-0.93 eV) and a desorption energy of product (0.84 eV), resulting in an overall exothermic process (-0.09 eV). P-DOS for Bi -CeO shows that the p-electrons of the O adjacent to Bi1 cross the Fermi level (Fig. 1 2 L 4D-E), indicating the related Ce-O bonds being activated and more abundant O are v susceptible to generate whilst the cyclization reaction of the formation of BiO . The acidity x and basicity are therefore altered by the increasing amount of O , leading to the change of v activity of the catalyst.” Regarding the adsorption of DMC, where the cis-cis-monodentate C=O-Ce-O binding has the highest adsorption energy of -1.04 eV (Supplementary Table v 9 & Supplementary Fig. 26). In the DFT modelling, we revealed that the basic site is responsible for 1,2-BDO activation, and the acid site is mainly for the adsorption and activation of the C-O bond of DMC. The reaction pathway detailed described the adsorption sites of each reactant and how the twin sites work for each elementary reaction. We believe the mechanism has been clear in the manuscript and will move some key figures from Supporting Information to the revised manuscript.\nFig. 3 (A) In situ DRIFT spectra of optimal conformation of 1,2-BDO attached to Bi -CeO . 1 2 (B) The optimal conformation of DMC attached to Bi -CeO . 1 2\n20 min\n1091 cm-1\nbridging butoxy\n) .u .a ( 1062 cm-1\non-top butoxy 1035 cm-1\nc Time\nn a b r o s b A\nbridging butoxy\n0 min\n1250 1200 1150 1100 1050 1000 950 900\nWavenumber (cm-1)\nSupplementary Fig. 16 In situ DRIFTS spectra of 1,2-BDO adsorbed on Bi -CeO .\n1 2\n).u.a( ecnabrosbA T im 2 0 m in e 0 m in 1 2 0 0 1 1 5W 0a v e 1n 1u 1 0 8 0 0 m 3 b c e m r -1 o n 1 0 5 0 ( c m -1 ) - to -1 p b 1 0 u 0 0 to x y 9 5 0\nSupplementary Fig. 17 In situ DRIFTS spectra of 1,2-BDO adsorbed on Bi O .\n2 3\n).u.a( ecnabrosbA T im 2 0 1 0 m in T b id m in 8 5 0 y p e n ta e te - Ⅰ a d so rp 1 8 0 W a v 1 7 tio n 0 e n 8 0 u c m m -1 1 7 6 6 c m -1 T y p e - Ⅱ cis-cis-m o n o d e n ta te a d so rp tio n T y p e - Ⅲ -1 1 7 5 2 c m cis-tra n s-m o n o d e n ta te a d so rp tio n 1 7 5 0 1 7 0 0 -1 b e r ( c m )\nSupplementary Fig. 26 In situ DRIFTS spectra of DMC adsorbed on Bi -CeO .\n1 2\n20 min\n1780 cm-1\n1767 cm-1\n) . Type-II u . a Type-I ( e c n a b Time r o cis-cis-monodentate adsorption s b bidentate adsorption A\n0 min\n1900 1850 1800 1750 1700 1650\nWavenumber (cm-1)\nSupplementary Fig. 24 In situ DRIFTS spectra of DMC adsorbed on Bi O .\n2 3\nFig. 3 (D) In situ DRIFT spectra of 1,2-BDO on CeO with increasing temperature. (E) In 2 situ DRIFT spectra of 1,2-BDO on Bi -CeO with increasing temperature.\n1 2\nSupplementary Fig. 32 Adsorption configurations of DMC and 1,2-BDO on the surface of Bi -CeO -nonO . Color codes: brown (C), white (H) red (O), yellow (Ce), and purple (Bi).\n1 2 v\n#6 The paper mentions a side reaction forming HBMC, yet no intermediate was detected by in situ IR. Can you provide a more detailed explanation of why this side reaction is not occurring in your system, and what role does your catalyst play in this process?\nResponse: Again, we believe this question suggest us to emphasize our proposed mechanism detailed described in Fig. 3H. In many previous studies, an inferred pathway was proposed wherein a linear carbonate intermediate (hydroxy-butyl methyl carbonate, HBMC) was regarded existed prior to the cyclization step, but normally without solid experimental evidence. In our in situ infrared spectroscopic monitoring, no such intermediate was detected in the presence of the Bi1-CeO2 catalyst.\nThe DFT calculations (Supplementary Fig. 40) indicate that while this pathway is feasible for pure CeO surfaces with a high energy barrier of 1.2 eV, a different pathway exists in 2 the presence of Bi : the two methoxy groups of DMC underwent direct cleavage separately, 1 producing two methanol molecules via a lower-energy pathway, as shown in Fig. 3H.\nThis alternative pathway explains the absence of the inferred HBMC in some other studies. Indeed, the presence of Bi₁ alters the adsorption configuration of 1,2-BDO and also leads to a structural evolution (Bi -O  Bi -O  Bi -O ) during the formation and desorption 1 2 1 3 1 2 of the 1,2-BC by the lattice oxygen activation, thereby giving rise to distinct pathway with the enhanced reaction rate.\nFig. 3 (H) Key reaction steps of the transesterification process that are shared by the CeO 2 and Bi -CeO .\n1 2\n1.0\n0.5\n0.53\n) V 0.0 e ( y g r e n−0.5 1.20 E HBMC\n−1.0\n−1.5\nSupplementary Fig. 40 Calculation of reaction pathways of the intermediate HBMC on CeO . Color codes: brown (C), white (H) red (O), and yellow (Ce).\nResponse: We cannot agree with the reviewer’s conclusion so far. Based on the illustration in above replies, we believe one can find that our study has provided substantial and solid evidence supporting both the innovative nature of the catalyst and its potential for practical application.\nFirstly, the transesterification route for 1,2-BC production is industrially competitive because it has cheap feedstock supply (especially based on coal industry) and solvent- free reaction conditions.\nSecondly, regarding the mechanism, we have demonstrated the remote catalysis through a combination of in situ DRIFTS, XAFS, XPS, DFT calculations, wherein the adsorption investigation has provided straightforward evidence. These results consistently show that the isolated Bi atoms modulate the electronic structure of adjacent Ce sites and O sites, thereby enhancing the reactant adsorption, reducing the energy barrier of the rate- determining step, and enabling a unique exothermic desorption process, without direct contact with the reactant or product.\nBesides, we have conducted experiments with over ten diol substrates (Supplementary Table 18) and a long-term stability test up to 1400 h, far longer than that in most literature. These results robustly confirm the broad applicability and exceptional durability of the Bi - 1 CeO catalyst, showing good potential for industrial application.\nThis manuscript reports an unprecedentedly highly active (2499 g g -¹ h-¹) and long- 1,2-BC cat. lived (800 h) Bi -ceria catalyst, which exhibits significant advantages in ester exchange 1 reactions, far exceeding the catalyst performance reported in existing literature. The \"remote catalysis\" mechanism was proposed, that is, the Bi1 single atom enhances the reaction performance by regulating the adjacent Ce³⁺-O acid-base site (rather than directly serving as the active center), providing a new idea for the design of single-atom catalysts (SACs). It was found that the Bi1 site dynamically reconstructs into BiOx and can be regenerated through simple heat treatment, providing important insights into the deactivation and regeneration mechanism of the catalyst. It is recommended to carry out a major overhaul.\nResponse: We thank Reviewer 3 for the positive comments and the recognition of significance to our work. However, we note that the comments did not include detailed suggestions for improvement. We kindly request the editorial office to confirm if any detailed comments from Reviewer 3 were omitted. We are fully committed to addressing any further specific feedback to further improve the quality of our manuscript.\nAfter viewing the comments from the reviewers, we recognized that some expressions need to be revised, particularly in terms of the “remote catalysis” mechanism and the modulation of acidity/basicity. We plan to undertake a comprehensive revision of the manuscript as follows to better highlight the key conclusions:\n• To improve the discussion on the novelty of the catalysis mechanism, focusing on the electronic modulation and the relevant catalytic mechanism.\n• To carry out more experiments with other catalysts for a straightforward comparison with Bi -CeO . This will involve a more comprehensive analysis of the space-time yield 1 2 and operational lifetime.\n• To stress the industrial compactivity of this catalyst by testing more relevant reactions with a broader substrate scope.\nWe are confident that the above justifications and the potential refinements will be able to effectively convey the significance of this study, academic novelty, and practical implications, and sincerely hope to have the opportunity to submit an updated manuscript for reconsideration.\nREFERENCES\n2\nReply to reviewer\nWe thank the reviewer for recognition of the “remote catalysis” concept proposed in this study and for the advice to strength our work. We have provided a detailed response and made revisions to the manuscript and supplementary information accordingly.\nReviewer's comments:\nQ1. Mechanistic clarification and remote catalysis validation\nThe authors have expanded their mechanistic discussion of the “remote catalysis” concept, integrating evidence from XPS, CO /NH -TPD, in situ DRIFTS, and DFT calculations. 2 3 These results support the idea that Bi single atoms electronically modulate adjacent Ce sites rather than directly participating in the reaction. However, as acknowledged by the authors, the quantitative range of the electronic propagation and its spatial extent remain speculative. Please supplement further studies on how variations in Bi doping concentration influence the structure and catalytic behavior would greatly strengthen this novel concept.\nR1: We thank the reviewer for their positive comment on the proposed concept of “remote catalysis”. Following the suggestion by the reviewer, we have carried out additional experiments with various Bi doping concentrations and investigated their influence on catalytic performance and the catalyst structure.\n• Catalytic performance\nWe carried out additional catalytic performance of 0.2% Bi-CeO -R, 1.0 % Bi-CeO -R and 2 2 5.0 % Bi-CeO -R (Fig. R1 & updated in Fig. 1F). When using pure CeO as catalyst, the 2 2 conversion of 1,2-BDO was only 26.5%. After doping 0.2% Bi on CeO , the conversion 2 increased to 57.4%. By increasing the Bi content to 0.6%, the optimal conversion of 87.4% was achieved. However, when the Bi content continued to increase, the conversion of 1,2- BDO eventually dropped to 24.7% with 5% Bi, indicating a proper content of Bi doping is essential for the best catalytic behavior, this is because such transesterification reaction needs moderate acidity and strong basicity, which has been evidenced by the XPS and TPD tests and detailed discussed in the manuscript (lines 181-221). These results confirm that the reaction is promoted by Bi in an indirect manner of “remote catalysis”, which altering the acid-basic sites in an appropriate extent.\nFigure R1. Performance of catalysts with varying Bi contents in the synthesis of 1,2-BC from DMC and 1,2-BDO.\n• Catalyst structure\nThe actual content in the synthesized catalysts are summarized in Table 1 (updated in SI Supplementary Table 2 and lines 342-343), which were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The X-ray diffraction (XRD) patterns of both the pristine CeO and the x%Bi-CeO series catalysts (Figure R2 & 2 2 updated in Fig. 1C and lines 119-125) mainly show the diffraction peaks of CeO (JCPDS- 2 34-0394), and peaks for Bi species were not detected, indicating the high dispersion of Bi on the CeO surface. However, we found that with the increase of Bi content up to 1%, the 2 CeO (111) diffraction peak shifted toward lower angles, suggesting the lattice expansion 2 of CeO with the incorporation of Bi species. When Bi content is excessively high to 5%, 2 partial oxide species were formed (Supplementary Figures 48-53), and the lattice expansion effect is weakened.\nTable 1. Bi content of x% Bi-CeO . (x=0.2, 0.4, 0.6, 0.8, 1.0, 5.0) 2\nSample Bi content (mol.%)\n0.2%Bi-CeO 0.17 2\n0.4%Bi-CeO 0.35 2\n0.6%Bi -CeO 0.52 1 2\n0.8%Bi-CeO 0.71 2\n1.0%Bi-CeO 0.93 2\n5.0%Bi-CeO 5.21 2\nFigure R2. XRD patterns of catalysts with different Bi contents\nElectron paramagnetic resonance (EPR) spectroscopy was employed to further elucidate the structural influence of Bi species doping on the CeO lattice (Figure R3 & 2 updated in Fig. 2E and lines 173-180). 0.2%Bi-CeO catalyst aroused stronger spin signal 2 compared to pristine CeO , which is consistent with the conclusion in the manuscript in 2 lines 171-172, “More importantly, the volcano relationship reveals that the addition of Bi may enrich O 1, which would then affect the catalytic activity2.” This indicates that the v incorporation of Bi species can promote the concentration of O . 0.6%Bi-CeO saw a v 2 notable enhancement in the EPR signal, suggesting the highest concentration of O . As v noted in the manuscript, “Bi -CeO shows a stronger spin signal at g = 2.003 (Fig. 2E), 1 2 about seven times that of pristine CeO (Supplementary Table 6), indicating more O with 2 v Bi present.” The generation of a high density of O promotes a substantial increase in Ce3⁺ 1 v content, resulting in a decrease of positive charge on Ce atoms near O and an increase v in the negative charge on the adjacent oxygen atoms. This electronic modification leads to enhanced basicity and provides abundant moderate acid active sites on the catalyst, which further evidenced by the CO /NH -TPD profiles and Bader charge analysis in manuscript 2 3 Figure 2F and Figure 2I. As elaborated in the manuscript, “Bader charge analysis shows that the presence of O leads to less charge on Ce adjacent to the defects (+2.27 e), v compared to intact CeO -nonO (+2.32 e), and this change is further enhanced by the 2 v presence of Bi (Bi -CeO -O , +2.23 e), in line with the weaker acidity observed in 1 1 2 v experiments (Supplementary Fig. 15). Moreover, O atoms adjacent to O carried negative v charge of -1.15 e and -1.21 e for CeO -nonO and CeO -O , respectively. In the presence 2 v 2 v of Bi , the negative charge on the O atom is increased to -1.23 e, in line with the strong 1 basicity observed in experiments.” However, it should be noted that when the Bi content increases to 5% (as shown by the EXAFS results in Supplementary Figures 48-53), the presence of excessive oxide (not detected by XRD, Figure R2) may cause a significant decrease in the effective O concentration on CeO surface, leading to a corresponding v 2 reduction in catalytic activity (Figure R1)3.\nFigure R3. EPR spectra of CeO and Bi -CeO with different Bi contents. 2 1 2\nThe microscopic structure of the catalyst and acid-base properties are found sensitive to the Bi content. To get more insights on this perspective, we supplemented an additional in situ DRIFTS study using the catalysts with more Bi loadings. As demonstrated in our manuscript (Figure 3) and Supplementary Information DFT calculations (Supplementary Figures 16-33, Tables 9-10), our combined in situ DRIFTS and DFT analysis has established that Ce sites adjacent to O serve as the primary active sites for 1,2-BDO v adsorption. The bridged butoxy-O conformation has been identified as the active v adsorption conformation, whereas the top-butoxy and bridged-butoxy conformations are catalytically inert, as stated in the manuscript: \"In contrast, only on-top butoxy adsorption conformation (1086 cm-1) was observed on the Bi O surface that is proven to be inactive 2 3 for transesterification (Supplementary Fig. 17). The adsorption behavior of 1,2-BDO on Bi - 1 CeO -C and Bi -CeO -O was also compared, and on-top butoxy (~1100 /1098 cm-1) and 2 1 2 bridged butoxy (~1069 /1071cm-1) have been identified on both samples, which are inactive neither for the transesterification reaction (Supplementary Fig. 18-19)\".\nAs shown in Fig. R4, the supplemented in situ DRIFTS spectra collected at room temperature revealed three distinct butoxy conformations on the highly active 0.6%Bi- CeO catalyst: top-butoxy (1091 cm-1), bridged-butoxy (1062 cm-1), and the key bridged- 2 butoxy-O conformations (1035 cm-1) (Figure R4B). With the temperature increase to 403 v K, the inert top-butoxy and bridged-butoxy conformations were progressively transformed to the bridged-butoxy-O conformation (Figure R4E). In contrast, the 0.2%Bi-CeO catalyst v 2 exhibited a tri-coordinated-butoxy conformation (1018 cm-1) at room temperature (Figure R4A). Even at 403 K, the peaks of inert top-butoxy (1091 cm-1) and tri-coordinated (1033 cm-1) species persist, rationalizing its lower activity (Figure R4D). For the excessively doped 5.0%Bi-CeO , the room-temperature spectrum was dominated by top-butoxy (1098 2 cm-1) and bridged-butoxy-O (1039 cm-1) conformations. The elevated temperature up to v 403 K not only saw the intensified top-butoxy signal but also led to the transformation of the bridged-butoxy-O species (1039 cm-1) into inactive bridged-butoxy (1051 cm-1) and tri- v coordinated-butoxy (1030 cm-1) conformations, explaining its poor performance at the reaction temperature (Figure R1). These results demonstrate that varying the Bi content dominants the 1,2-BDO adsorption conformation, in well agreement with our DFT calculation results and that the optimal doping of 0.6%Bi is most favorable for the formation of cyclic carbonates.\nThe above results and discussion have been updated to the SI in Supplementary Figure 23 (lines 962-980).\nFigure R4. In situ DRIFTS spectra of 1,2-BDO on catalysts at 298 K (A: 0.2%Bi-CeO , B: 2 0.6%Bi-CeO , C: 5.0%Bi-CeO ). In situ DRIFTS spectra of 1,2-BDO at elevated 2 2 temperatures (D: 0.2%Bi-CeO , E: 0.6%Bi-CeO , F: 5.0%Bi-CeO ). (The peaks in the red 2 2 2 box indicate the optimal active adsorption conformation)\nRegarding the DMC adsorption, a comparative analysis of DMC adsorption was carried out on catalysts including the inactive Bi -CeO -O and Bi O , and the highly active Bi - 1 2 2 3 1 CeO -R, Bi -CeO -C, and CeO . The results revealed that the cis-cis monodentate 2 1 2 2 adsorption conformation based on the C=O-Ce-O motif is the primary active species v (Supplementary Figures 23–29; lines 267–275). DFT calculations further confirm that Bi species directly influence the adsorption behavior of DMC (in manuscript lines 275–278), as noted: “This is consistent with the DFT results, where the cis-cis-monodentate C=O-Ce- O binding has the highest adsorption energy of -1.04 eV (Supplementary Table 9 & v Supplementary Fig. 32). The calculations show that O facilitates 1,2-BDO adsorption (1,2- v BDO-4 and 1,2-BDO-5), while Bi impacts on the DMC adsorption (DMC-2 and DMC-6, 1 Supplementary Fig. 32-33 & Supplementary Table 9-10)”.\nWe implemented additional in situ DRIFTS test as shown in Figure R5, to illustrate the influence of Bi content to DMC adsorption behavior. Over 0.2%Bi-CeO , the intensity of 2 the cis-cis monodentate conformation (1766 cm-1) at room temperature is slightly stronger than that of the inactive bidentate conformation (1780 cm-1), as shown in Figure R5. When the temperature rose to 403 K, the adsorption band shifted to 1772 cm-1 (Figure R5D). In contrast, the cis-cis monodentate conformation (1766 cm-1) is distinctly dominant on the 0.6%Bi-CeO surface (Figure R5B). At 403 K, the cis-trans monodentate conformation 2 (1750 cm-1) transforms to cis-cis monodentate conformation, and the cis-cis monodentate conformation remains predominant. Over 5.0%Bi-CeO , a significant amount of the cis- 2 trans monodentate conformation (1745 cm-1) was present. Upon 403 K, the inactive bidentate conformation (1779 cm-1) becomes the dominant species. These observations clearly explain the changes in catalytic activity presented in Figure R1. Together with the DFT modelling of reactants adsorption, the results verify that while Bi species do not serve as the direct active sites, they modulate the catalyst’s acidity/basicity, which in turn governs the adsorption conformation of DMC and ultimately dictates the catalytic performance.\nThe above results and discussion have been updated to the SI in Supplementary Figure 31 (lines 1103-1118).\nFigure R5. In situ DRIFTS spectra of DMC adsorbed on catalysts (298 K, A: 0.2%Bi-CeO , 2 B: 0.6%Bi-CeO , C: 5.0%Bi-CeO ). In situ DRIFTS spectra of DMC desorbed on catalysts 2 2 (D: 0.2%Bi-CeO , E: 0.6%Bi-CeO , F: 5.0%Bi-CeO ). (The peaks in the red 2 2 2 box indicate the active adsorption conformation.)\nIn summary, in the “remote catalysis” context, Bi species serves to electronically engineer the active sites of Ce and O atoms on CeO catalyst remotely, thereby refining 2 the material's acid-base properties. This coordination change facilitates the preferential formation of the active cis-cis monodentate conformation for DMC and the bridged-butoxy- O conformation for 1,2-BDO. These specific conformations of DMC and 1,2-BDO v contribute to their simultaneous activation and the unprecedented catalytic performance.\nWe believe the above supplementary experiments and illustrations would well address the concern from the reviewer in terms of “remote catalysis”. All relevant sections of the manuscript and Supplementary Information have been updated accordingly to reflect this mechanistic insight.\nReferences\n(1) Y.D. Chen, Y. Li, W. Chen, et al., Continuous dimethyl carbonate synthesis from CO 2 and methanol over Bi Ce O monoliths: Effect of bismuth doping on population of oxygen x 1-x δ vacancies, activity, and reaction pathway, Nano Res. (2022), (15) 1366-1374.\n(2) Z.V. Popovic, Z. Dohcevic-Mitrovic, M.J. Konstantinovic, et al., Raman scattering characterization of nanopowders and nanowires (rods), J. Raman Spectrosc. (2007), (38) 750-755.\n(3) J. Ayastuy, A. Iglesias-González, M. Gutiérrez-Ortiz, Synthesis and characterization of low amount tin-doped ceria (Ce Sn O ) for catalytic CO oxidation, Chem. Eng. J. X 1−X 2−δ (2014), (244) 372-381."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The aurthors have addressed my concerns, and thus I recommend its publication as is.", "reviewer_2": "I have carefully read the authors' detailed rebuttal and the revised manuscript. The authors have made substantial efforts to address the concerns raised in my initial feedback, providing additional experimental evidence, mechanistic clarification, and comparative data. Their responses are thorough, technically sound, and supported by appropriate figures and calculations. Overall, the revised version demonstrates some significant improvement in both clarity and scientific rigor.Followings are some further comments:\n1.Mechanistic clarification and remote catalysis validation\nThe authors have expanded their mechanistic discussion of the “remote catalysis” concept, integrating evidence from XPS, CO2/NH3-TPD, in situ DRIFTS, and DFT calculations. These results support the idea that Bi single atoms electronically modulate adjacent Ce sites rather than directly participating in the reaction. However, as acknowledged by the authors, the quantitative range of the electronic propagation and its spatial extent remain speculative.Please supplement further studies on how variations in Bi doping concentration influence the structure and catalytic behavior would greatly strengthen this novel concept.\n2. Scope of catalytic applicability\nThe addition of substrate-scope data (Supplementary Table 18) and the new amidocarboxylation experiment effectively demonstrate that the Bi1–CeO2 catalyst exhibits broad transesterification and carbonylation activity. These results alleviate my earlier concerns regarding the generality of the system.\n3. Theoretical modelling considerations\nThe authors’ clarification that the reaction occurs under solvent-free conditions is appreciated. The inclusion of detailed adsorption-energy analyses and Bader charge calculations has improved the credibility of the DFT component.\nThe authors have provided comprehensive responses to all major comments. The newly added experimental and computational evidence substantially enhances the manuscript’s scientific depth. Although some aspects of the proposed “remote catalysis” mechanism still require further experimental quantification, the current data and analyses current data and analyses are sufficient to meet the requirements for publication.", "reviewer_3": "all the comments are well addressed by the authors and I have no more questions"}, "author_response": ""}, {"round": 3, "reviewer_comments": {"reviewer_2": "The author has improved the manuscript and addressed all concerns. I believe the manuscript can be accepted now."}, "author_response": ""}]

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