Decoupling electronic and geometric effects in Pd catalysts via thermal surface reconstruction for selective hydrogenation

Domain: physics
Published: 2026-03-18
Editorial outcome: minor_revision

Abstract
The entangled electronic and geometric effects in heterogeneous catalysis have long obscured precise attribution of their individual roles. By employing a thermal-induced surface reconstruction strategy to progressively enhance metal-support interactions, we achieve continuous tuning of Pd’s electronic and geometric structures. Using alkyne semi-hydrogenation as a prototypical structure-sensitive probe reaction, we demonstrate that despite the linear coupling of electronic and geometric structures during Pd reconstruction, the turnover frequency scales solely with the geometric descriptor W (quantifying Pd particle flattening), while selectivity regulation bifurcates into two distinct regimes: Below a critical W, electron-deficient Pd sites offset geometric constraints, yielding a non-structure-sensitive selectivity plateau; whereas above this threshold, electron-rich surfaces establish unequivocal geometric control. Moreover, surface reconstruction drastically shrinks the electronic-geometric space of Pd sites for over-hydrogenation side reaction. These insights provide a blueprint for metal catalysts regulation in hydrogenation and may open avenues for quantifying electronic-geometric interplay in other structure-sensitive reactions.

Introduction
It is well known that the structure of a catalyst determines its performance. Due to the structural complexity of supported metal catalysts, the exploration of structure-performance relationships has long been a focal point in this field. For supported metal catalysts, reconstruction has been widely recognized as an effective means to adjust the catalytic performance1–6. Among them, researchers paid special attention to the redispersion of noble metal sites, as it can transform metal nanoparticles into sub-nanometer or even single-atom sites and regenerate sintered catalysts7–10. Regeneration methods include the redox method, oxychlorination, halogenated hydrocarbon heat treatment, etc., and are applicable to a wider range of noble metals such as Pt, Pd, Ru, Rh, and Au11–14. For example, alternating H₂/O₂ cycling treatments of Pd/FeO catalysts enabled reversible aggregation and redispersion of Pd species, driven by redox-responsive migration and anchoring at surface defect sites15. For oxychlorination, sintered Pt–Re/Al₂O₃ catalysts treated with 1,2-dichloropropane in air followed by H₂ reduction triggered significant recovery of Pt dispersion and catalytic performance14. Sintered Au/activated carbon treated with CH₃X(X=Cl, Br, I) at mild temperatures also resulted in the formation of volatile Au complexes and the redispersion of large gold particles into clusters smaller than 3 nm, thereby restoring catalytic activity in acetylene hydrochlorination16. Predominantly, the mechanism of redispersion is similar and can be explained with the ‘strain model’ in most cases, in which metal oxidation is believed to be a prerequisite factor to induce dispersion17–19. More detailed theoretical research indicated that such redispersion occurs only when the Gibbs free energy of disintegration (ΔG dis) is negative20. As a typical catalyst system, a series of interesting results for CeO -supported noble metal catalysts were reported recently, such as temperature-dependent redispersion routes, hydroxyl groups acting as the main anchoring sites to stabilize and disperse metal atoms and the entropy effect of metal redispersion21–25.

Despite decades of research into these schemes, the majority of efforts have predominantly concentrated on the redispersion of metallic active components26–29. The study on the meticulous modulation of the morphology and electronic structure of these metallic active constituents on purpose along redispersion has been very limited since. A plethora of studies have reported that the orbital energy levels of metallic nanoparticles (NPs) can undergo splitting, or even transform into discrete molecular orbitals, as a result of alterations in their geometric configurations30,31. Compounding this complexity is the non-uniform conduction of electronic effects across metallic NPs, leading to a robust coupling between electronic and geometric effects32. Consequently, there remains a dearth of systematic quantitative assessment regarding the interplay between structural and catalytic properties of surface-reconstructed catalysts during reaction processes33–37. For instance, in structure-sensitive reactions like alkyne semi-hydrogenation, although studies have reported multiple kinds of structure-performance relationships, such as over-hydrogenation on low-coordinated sites and the so-called energy linear scaling relationships, there is still no systematic study on the respective influence weights of geometric and electronic effects during the reconstruction process. Although we previously decoupled and relatively quantified the electronic and geometric effects in the dehalogenation side reaction of halogenated nitrobenzene hydrogenation by combining morphology control of Pt NPs and work function modulation of supports, it is not applicable to the Pd catalyst system32. The main reason we found is that the change of the electronic structure of Pd sites on different supports prepared using the above method is not significant. By altering operating temperatures and atmospheres, it is theoretically possible to precisely control the structural evolution of the active phase and optimize the catalytic performance. Hence, analyzing the geometric and electronic effects of Pd catalyst systems in selective hydrogenation reactions through surface reconstruction may offer a viable solution. Consequently, there is an urgent need to develop simple yet controllable methods for catalyst surface reconstruction, along with appropriate research protocols to achieve these goals.

In this work, we effectively modulated the microstructure and coordination environment of active sites on Pd/CeO catalyst through a thermal-induced surface reconstruction method. Systematic characterization and first-principles molecular dynamics simulations revealed that the surface reconstruction of the active phase resulted in the formation of uniformly dispersed, flattened Pd nanostructures with an aspect ratio significantly deviated from 1. Simultaneously, the interfacial Pdδ+ species increased, significantly boosting metal-support interactions. This thermally induced surface reconstruction of Pd/CeO was driven by both the calcination atmosphere and the lattice oxygen of CeO And the extent of surface reconstruction diminished with the increasing size of Pd NPs. Further, we correlated the thermally induced surface reconstruction with reaction performance in the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY), quantifying the structure-performance relationship. A linear scaling relationship was established between the aspect ratio (W value) of the Pd active phase and the hydrogenation activity of MBY. A two-stage influence interval on olefin selectivity was also identified for electronic and geometric effects. Using matrix transformation and grid interpolation, we created Pdδ⁺–W–Sel. contour plots to visualize the structure–activity relationship for alkyne semi-hydrogenation over Pd/CeO catalysts, establishing clear design principles for catalyst optimization. The optimal Pd/CeO -500 catalyst, prepared with Pd salt as a precursor, exhibited exceptional reactivity (7291h−1) and over 96% selectivity of 2-methyl-3-buten-2-ol (MBE) without any poisoning agents, significantly outperforming the uncalcined counterpart and the commercial Lindlar catalyst (TOF=401h−1, selectivity=93.5%)38,39. Selectivity for MBE can be further improved to over 97.5% with Pd nanocrystals as precursors. The facile thermal-induced surface reconstruction method provides new insights into the quantitative study of structure–performance relationships on supported metal catalysts and the design of efficient catalysts.

Results
Structuralevolutionofsurface-reconstructedPdnanocatalysts
SupportedPdcatalysts oncommercialCeO weresynthesizedviaa simplewetimpregnationstrategy,followedbycalcinationinstaticair at different temperatures (see Experimentalsection for details) and sequentialreductioninhydrogenat200°C.Thesampleswerelabeled as Pd/CeO -T , where T denotes the calcination temperature. Inductively coupled plasma mass spectrometry (ICP-MS) confirmed similarPdcontents(~0.5wt%,SupplementaryTable1)acrosssamples, consistentwiththenominalmetalloading.Variouscharacterizations wereusedtodisclosethestructuralevolutionofPd/CeO nanocata- lysts induced by air calcination. N adsorption-desorption isotherm analysis showed minimal changes in specific areas after Pd species deposition (Supplementary Fig. 1)40. High-resolution transmission electron microscopy (HRTEM) images ofuncalcinedPd/CeO showed relativelylargePdNPswithanaveragesizeof5.01nmandunevensize distribution (Fig. 1a). Lattice fringes of 0.224 and 0.312nm, corre- sponding to Pd (111) and CeO (111) d-spacings, respectively, were observedinthetop-viewimages(SupplementaryFig.2)41,42.PulseCO chemisorption provided quantitative measurements of the exposed metalsurfaceareaaftercalcination43.Theresultsclearlyshoweda3.2- foldincreaseinsurfacePdatomsonPd/CeO -500,withPddispersion increasing from 17.5% to 57.1%, consistent with TEM observations (SupplementaryTable1).Furtherextending the treatmenttime and increasingthecalcinationtemperatureresultedinnegligiblechanges in Pd structure, asshownin SupplementaryFig. 3.H temperature- programmed reduction (H-TPR) elucidated the distribution of Pd speciesandthemetal–supportinteractionsinPd/CeO -T catalysts (Fig. 1d). A negative peak around 90°C (blue region) is typically attributed to the decomposition of Pd hydride (β-PdH )44,45. As the calcination temperature increased, the TPR curves showed a sig- nificant reduction in the peak intensity of β-PdH , indicating an increasing Pd dispersion. For the Pd/CeO -500 sample, the β-PdH negative peak almost disappeared, consistent with the high Pd dis- persion(57.1%)observedinCOtitration46,47.Accordingly,theincreased reduction peak in the range of 250–300°C indicated that the decreased β-PdH transformed to surface Pdδ+ species. Energy- dispersiveX-rayspectroscopy(EDS)mappingfurtherconfirmedthe uniformdistributionofPdinthereconstructedcatalyst(Supplemen- taryFig.4).Thesephenomenademonstratedthatthemetal–support interactions between Pd species and CeO were significantly strengthenedafterheattreatment,furtherdemonstratingtheimpact ofhigh-temperaturecalcinationoncatalyststructureandproperties.
DuringthegradualdecreaseinPdparticlesize,wealsoobserveda synchronous evolution of their morphology (Fig. 1a–c). The aspect ratio(denotedasW)ofnanoparticleswasusedtoquantifythemor- phology of Pd species. The W value is defined as the ratio of the shortest diameter (R1) to the longest diameter (R2) of the two- dimensional projection of Pd clusters, characterizing the degree of particle deformation (Fig. 1e). In the unannealed Pd/CeO sample, directlyreducedPdNPswerequasi-sphericalwithaWvalueashighas 0.88.However,asthecalcinationtemperatureincreasedfrom200°C to500°C,Pdspeciesgraduallyevolvedfromsphericaltofish-scale-like nanostructures, with the W value significantly decreasing to 0.64 (Supplementary Figs. 5, 6). This wetting growth suggests tighter bindingbetweenPdNPsandCeO ,theincreaseoftheproportionof interfacial sites and enhanced interfacial electron transfer, which is expectedtoimprovethecatalyststability48.
Tomoreintuitivelyobservethestructuralevolutioninducedby thermaltreatment,PdNPswithanaveragediameterof3.7nmwere supportedonCeO (Pd /CeO ).Then,thedynamicmigrationand morphological changes of Pd species were monitored with in situ environmental transmission electron microscopy (ETEM) (Fig. 1g–i). Prior to the initiation of calcination, electron microscopy images revealedthatthesupportedPdNPslargelyretainedtheiroriginalsize distribution.Aftermorethan30minofairtreatmentat500°C,thePd NPsgraduallyfragmentedintoagreaternumberofsmallerparticles. ThisdynamicchangeclearlydemonstratesthatthePdspeciesundergo a process of particle fragmentation and redispersion under high- temperature oxidative conditions, leading to a more uniform dis- tributionofthePdactivephase,ratherthanthroughamechanismof vapor-phase migration of metal atoms under high calcination temperatures48,49. Furthermore, this study suggests that such ther- mally induced Pdsitereconstructionmaynotbelimitedtospecific metalprecursors.

MechanismofsurfacereconstructioninPdnanocatalysts
The previous experimental results clearly demonstrated the basic reconstructionprocessofPdspeciesonCeO support.However,fur- therresearchisnecessaryonthephysicochemicalmechanismsthat leave behind. Since surface reconstruction induced by calcination occursinanairatmosphere,thecatalystprecursorimpregnatedwith PdO:PDF#41-1107 metalsaltsmaytransformintoPdOduringthecalcinationprocess50,51. Subsequently, the PdO NPs areredispersed on supports along with processessuchasfragmentation,deformation,migration,etc.There- fore, the oxygen source may play an important role in the recon- structionofPdspeciesduringthecalcinationprocess.
To verify the above hypothesis, in situ temperature- programmed XRD was conducted to characterize the structure evolutionofthecatalystprecursorimpregnatedwithPdCl andthe reducedPd /CeO catalystwithoutaircalcination.Consideringthat thepreviousPdloadingwasrelativelylow(~0.5wt%,Supplementary Fig.7),thetheoreticalPdloadingwasdeliberatelyincreasedto10wt %inordertocapturetheevolutionsignalofPdspeciesduringthe reconstructionprocess(SupplementaryFig.8).AsshowninFig.1f, duringthecalcinationprocess,thecatalystprecursorimpregnated with PdCl firstly transformed into PdO phase, and then the peak intensityofPdOunderwentaprocessfromweaktostrongandthen disappeared. Correspondingly, the half peak width of PdO under- went a process of broadening to narrowing and then widening again52.ThisindicatedthatPdOcontinuedtofragmentintosmaller pieces on CeO after the complete conversion of PdCl to PdO. Similarly,themetallicPdparticlesintheuncalcinedreducedPd / CeO catalystwerefirstlyoxidizedtoPdOduringaircalcination,and thenPdOunderwentthesamereconstructionprocessasthecatalyst precursor (Supplementary Fig. 9). The above results clearly demonstrate that oxygenspeciesareindeedinvolvedintherecon- structionprocessofPdcatalysts.
However,twooxygensourcesexistedintheprocessofcatalyst preparation:gaseous oxygen in airand latticeoxygeninCeO 53.To furtheranalyzetherespectiveeffectsofthetwooxygensources,an inertatmospherewasappliedtosynthesizePd/CeO -500-N andPd/ CeO -500-Ar catalysts for comparison (Fig. 2a–c). High-resolution transmissionelectronmicroscopy(HRTEM)resultsshowedthattheW valuesofPdNPsweredeterminedtobe0.74and0.73,respectively. ComparedwiththeWvalueoftheuncalcinedPd/CeO catalyst(0.88), the results indicated that Pd species on CeO can still undergo reconstruction process even without the involvement of gaseous oxygen,albeittoalesserextentthaninaircalcination,highlightingthe critical role of both gas oxygen and lattice oxygen in Pd structural evolution, consistent with the proposed mechanism involving frag- mentation, deformation and migration of PdO. Ab initio molecular dynamics(AIMD)simulationsfurthersupportedthestructuralevolu- tion of Pd species at the atomic level (Supplementary Figs. 10, 11). SimulationsunderinertatmospheresshowedthatatomsonPdNPs withatypicalWulffstructuregraduallymigratedtothesurfaceofCeO tobindwithsurfacelatticeoxygenandformedflatternanostructures withsignificantlyreducedWvaluesasindicatedbyyellowcirclesin Fig.2d–fwhencalcinationtimewasincreasedfrom500to4500fs. Underoxygenatmospheres,PdOformedbytheoxidationofPdNPs flattened faster at the same temperature (Fig. 2g–i), with more Pd atomsbindingtotheCeO supportandhigherinterfacialwetting.
ItisworthnotingthatsincePdNPstendtohavemorePdatoms interacting with the support during flattening, it is reasonable to assume that the driving force for Pd nanoparticle flattening is the differencebetweenPd–supportandPd–Pdinteractions54,55.Stronger interactionsgenerallyimpliedmoreelectrontransfer.Toverifythis, wetrackedtheelectronicstructureofPdspeciesduringtheevolution of Pd/CeO -T using X-ray photoelectron spectroscopy (XPS). As shown in Fig. 2j, the peak intensity of the Pd 3d core-level spectra significantly increased with the rise of the calcination temperature, which is consistent with the above conclusion of an improved dis- persionofPdNPsonthecatalystsurface56–58.FineanalysisofthePd3d spectra of Pd/CeO -T samples showed that Pd0 species with a binding energy of 335.5eV dominated in uncalcined and low- temperature calcined samples. As the calcination temperature increased,theratioofPd0graduallydiminished.Meanwhile,thecon- centrationofelectron-deficientinterfacialPdδ+speciesat337.8eVrose sharply.ForPd/CeO -500,theratioofPdδ+evenaccountedfor97.6%, inalignmentwiththeH -TPRresultsinFig.1d,furtherconfirmingthe synchronous transformation of oxidation state and coordination environment during the structural evolution of Pd sites.Surely, the increaseininterfacialPdδ+speciesalsoindicatesenhancedelectronic interactions between the CeO support and Pd NPs after thermally induced structural changes. In addition, peak fitting of the high- resolutionO1score-levelspectraofPd/CeO -T catalystsdemon- stratedthattheratioofoxygenvacancies(BE=532.2eV)alsoincreased from 27.6% to 45.6% as the calcination temperature increased to 500°C(SupplementaryFig.12)47.Sincethereductionconditionisthe sameforallthePd/CeO -T catalysts,itisreasonabletospeculate that lattice oxygen participates in the surface reconstruction of Pd sites through forming numerous Pdδ+ interfacial structures, which finallyresultsinanelevatedconcentrationofoxygenvacancies59.
Since the oxygen activity varies among different supports, this difference is expected to affect the degree of Pd reconstruction. Therefore,thereconstructionbehaviorofPdNPswasfurtherexplored on supports with different properties. Specifically, colloidal Pd NPs withanaveragesizeofabout2.9nmandaWvalueofabout0.91were depositedonTiO,SiO ,Al O ,andMgOcarriers,followedbyNaBH / tert-butylamine treatment to remove the capping agent polyvinyl pyrrolidone(PVP)32.AseriesofPdNPs-supportednanocatalystswas thenprepared(SupplementaryFigs.13,14).Aircalcinationwasthen used to induce Pd surface reconstruction. Results showed that sig- nificantstructuralchanges,likedispersionandshape,occurredonPd species supported on reducible supports like CeO and TiO . For instance,theaveragesizeofPdNPsforPd /TiO -500decreasedfrom 2.95nmto2.52nm,alongwiththeWvaluereducingfrom0.92to0.81 (Fig.3a,SupplementaryFig.15).Incontrast,aircalcinationtreatment caused serious sintering and agglomeration of Pd NPs with no sig- nificantredispersionobservedonnon-reduciblesupports(e.g.,SiO , Al O , and MgO) (Supplementary Fig. 16)60. XPS characterization of Pd /TiO andPd /SiO catalystsbeforeandafteraircalcination further showed that the electron-rich Pd0 content in reconstructed Pd /TiO-500catalystdecreasedfrom87.2%to58.9%(Fig.3c),along with the electron-deficient Pd–O–Ti species rapidly increased from 12.8%to41.1%correspondingly61,indicatingsimilarlyenhancedinter- actionbetweenPdactivesitesandsupportasthecaseforPd/CeO .In contrast,duetothesinteringcausedbyaircalcination,thePd0content inreconstructedPd /SiO-500actuallyincreasedby4.7%(Fig.3b,d). Hence, the activity to form oxygen vacancies is critical for lattice oxygentoinducethereductionofPd.
Additionally,thereconstructionbehaviorofPdNPsofdifferent sizesonreduciblesupportsalsoshowedsignificantdifferences(Sup- plementaryFigs.17–20,Table2).HRTEManalysisofthecalcinedcat- alystsrevealedthattheaverageWvalueforsampleswithsmall-sized Pd NPs, such as Pd /CeO -500, decreased from 0.91 to 0.75 (Fig. 3e). The W change amplitude reached 17.6%, indicating a sig- nificantdeformationofPdsitesaftercalcination.However,samples with large-sized Pd NPs, such as Pd /CeO , showed only a 3.3% decrease in average W value (from 0.91 to 0.88) after calcination. Theseresultssuggestthatthethermallyinducedreconstructioneffect graduallydiminisheswiththeriseofthesizeofPdNPs(Supplementary Fig.21).Thisparticlesizesensitivityofthereconstructioneffectwas alsoconfirmedbyXPSresultsofthecatalysts.AsshowninFig.3e,the ratio of Pd0 remained at about 85–90% in the series of Pd /CeO catalystswithminimalchangeinWvalues,typicallyinvolvinganinitial sizevaryingfrom3.0nmto7.8nmforcolloidalPdNPs.Incontrast,the Pd0 content in the apparent reconstructed series significantly decreased(52.1–85.8%),typicallyinvolvinganinitialsizevaryingfrom 2.2to7.7nmforcolloidalPdNPs,indicatingmoreprevalentPd–O–Ce structures and enhanced interaction between Pd sites and CeO . Similarly,the modulation ofthe electronic structure ofPd NPs also gradually faded through thermally induced reconstruction as the averagesizeofcolloidalPdNPsincreased.
Tosummarize,bothexperimentalcharacterizationsandtheore- ticalcalculationsrevealedthatoxygenintheairandlatticeoxygenin reduciblesupportsjointlyparticipatedinpromotingthereconstruc- tion of the Pd active phase, forming flattened Pd structures and enhancedPd–supportinterfacialinteractions.

Catalyticperformanceofsurface-reconstructedpdnanocata- lystsinalkynesemi-hydrogenation
Next,theimpactofPdreconstructiononthecatalyticperformance was studied in Pd/CeO -T series catalysts, using the structure- sensitivereactionofalkynesemi-hydrogenationasanexample.
As shown in Fig. 4a, the activity positively correlated with the calcination temperaturewithinthe200–500°Crange.TheoptimalPd/ CeO -500 catalyst displayed 2.35 times higher apparent catalytic activityforMBYsemi-hydrogenationcomparedtotheuncalcinedone. SinceaircalcinationcausestheredispersionofPdsites,theincreasein apparent hydrogenation activity is expected. Surprisingly, the TOF value(7291h−1)forMBYhydrogenationontheoptimalPd/CeO -500 catalyst was 57% higher than that of the uncalcined one (4640h−1) (SupplementaryFig.22).Thisimprovementinintrinsicactivityindi- catesthattheenhancedcatalyticactivityofPd/CeO -T catalystsis notsolelyduetotheincreasednumberofPdsites.Furtherincreasing thecalcinationtemperatureto600°C,thecatalyticperformanceof Pd/CeO -600 began to decline, likely due to slight sintering of the CeO carrier (Supplementary Fig. 23), reducing the accessibility of activePdsites57.
Toquantitativelyassesstheeffectofsurfacereconstructionon thereactivityofPdsites,theWvaluesofPdNPswerecorrelatedwith theTOFvaluesofthePd/CeO -T series(Fig.4b).AsPdNPsadopted flatter configurations, the intrinsic catalytic activity for MBY semi- hydrogenationincreased,showingaclearlinearscalingrelationship (R2=0.94).TheintrinsicactivityforoptimalPd/CeO -500increasedby 1.5-fold and 18.2-fold compared to the uncalcined one and Lindlar catalyst, respectively38,39. Notably, the TOF values of the catalysts calcined in inert atmospheres for MBY semi-hydrogenation also fit withinthislinearscalingrelationship(Fig.4b,SupplementaryFig.24). Thissuggeststhatthislinearrelationshipmaybeindependentofthe concrete catalyst preparation processes or methods, displaying unexpected universality. Therefore, the W value can be used as an effective descriptor for predicting the intrinsic catalytic activity of MBYsemi-hydrogenationonreconstructedPdactivesites.
ThephysicochemicaloriginoftheW-value-dependentactivityin MBYsemi-hydrogenationoverPd/CeO₂catalystsiselucidatedthrough reactionorderanalysis38,62.AsshowninFig.4c,thenegativereaction order(n)ofMBYgraduallyincreasedwithrisingcalcinationtempera- ture.Specifically,thereactionorderofMBYonPd/CeO -500(−0.09) increasedby91%comparedtothatontheuncalcinedPd/CeO catalyst (−1.03).TheseresultsindicatethatthermallyinducedPdreconstruc- tioneffectivelyreducestheself-poisoningeffectofMBYonPdsites, therebyincreasingtheavailabilityofsurfacePdsitesforhydrogena- tion,andfinallymaybebeneficialfortheenhancedintrinsichydro- genationactivity(TOF).Asimilarphenomenonwasalsoobservedfor thehydrogenreactionorder(n H₂)asshowninSupplementaryFig.25, withaslightincreasefrom1.31to1.87accordingly.Thoughthehigher n H₂valuesuggestsmorekineticallydemandingforhydrogenactiva- tion on the calcined catalyst, the overall increased hydrogenation activitydemonstratesthatthepositiveimpactofweakenedMBYself- poisoningoutweighstheunfavorablefactorsthatcomplicatehydro- gen activation.This deduction is further testifiedbycorrelatingthe MBYreactionordersofthePd/CeO -T serieswiththecorrespond- ingWvalues(Fig.4d,SupplementaryFig.25),whichalsoshowsaclear linearscalingrelationship(R2=0.97).PdNPswithlowerWvaluesor flattershapesdisplaysmallerMBYreactionordersandexhibitweaker self-poisoningeffectofMBY.BasedontheXPSresultsofthePd/CeO - T series(Fig.2j),theriseofthenegativereactionordersmaybewell attributedtotheincreaseinPdδ+sitesafterPdreconstruction.Asthed- π* back-donation of shared electrons between electron-deficient Pd andC≡Cisexpectedtoweaken,theincreaseinelectron-deficientPdδ+ sitesultimatelywillreducetheoveralladsorptionstrengthofMBYon Pdsites63,64.Toverifythis,weconstructedPd /CeO andPd /CeO modelswiththreeandtwolayersofPdatoms,respectively,tosimulate initialandcalcinedPdactivesites(Fig.4e,SupplementaryFig.26).DFT calculationsshowedthattheadsorptionenergiesofMBYdecreased significantlyafterreconstruction,whetherontopPdsitesorinterfacial Pdδ+sites,consistentwiththepreviousdeduction.
As reflected by the TOF-W linear relationship, the aboverulesalso appeartobeindependentofthePdprecursorform.Supplementary Fig. 27 shows that the impact of thermally induced surface recon- struction on the activity of Pd /CeO catalysts for MBY semi- hydrogenation follows the same pattern as for Pd/CeO -T , albeit toalesserextent,primarilyduetothelowerflatteningofPdNPsunder thesamecalcinationconditions.ThestabilityofPd/CeO canalsobe improved by thermally induced surface reconstruction. As shown, evenafterfivecycles,thelossesincatalyticactivityandselectivityfor both Pd/CeO -500 and Pd /CeO -500 were negligible, while uncalcined Pd/CeO and Pd /CeO catalysts suffered from sig- nificant deactivation (Supplementary Figs. 28–32). HRTEM analysis suggests that this deactivation may be due to significant Pd nano- particleagglomeration.
Tofurtherclarifytheintrinsiccorrelationbetweencatalyststabi- lityandPdstructuralcharacteristics,wesummarizedtherelationships amongPdδ⁺content,Wvalue,andcyclingstabilityofPd/CeO -500,Pd/ CeO -uncalcined, Pd /CeO -500, and Pd /CeO -uncalcined catalysts as shown in Fig. 4f. The Pd morphological parameter W quantifiesthedegreeofparticledeformation,andcyclingstabilityis measuredbythedifferenceinconversionratebeforeandafterfive cycles. Catalysts with a low initial W value (0.6–0.8) demonstrate negligible activity loss and constant Pd particle W values after five cycles(Fig.4f).Thisisduetoastrongmetal-supportinteraction,where electrontransferfromPdtoCeO increasesthePdδ⁺populationand flattensthePdparticles,yieldingasmallerWvalue.Consequently,a lowerWvaluereliablypredictsbetterstability.Incontrast,uncalcined Pd /CeO and Pd/CeO catalysts, with W values approaching 1, suffer from weakinteraction and inferiorstability, as shown by the activitydeclineafterfivecyclesfrom89.6%to49.3%andfrom96.7%to 73.1%,respectively.

Decouplingelectronicandgeometriceffectsmediatedbysur- facereconstruction
Itiswidelyrecognizedthattheselectivityregulationinthestructurally sensitiveMBYsemi-hydrogenationreactionismorechallenging.The mostcriticalchallengehereisthatthecurrentcatalyststructurereg- ulation methods struggle to decouple electronic and geometric effects, resulting in uncertainty about their individual impacts on selectivity36.ThisisevidentinFig.5a,whereWvaluesandtheratioof Pdδ+changesimultaneously.Toaddressthisissue,wepreviouslyused acolloidalmethodtopreparesupportedPtNPswithuniformsizeand morphology for the selective hydrogenation of halogenated nitrobenzenes32.TheelectronicstructureofthePtactivephasewas modulated using only the work functions of different supports, avoiding interference from geometric structures. This yielded a structure–performancerelationshipcurvecontainingonlyelectronic effects of supports. Based on the orthogonality of electronic and geometriceffectsinmathematicalphysics,weestablishedaCartesian coordinate system to decouple and quantify these two effects32. However,wefoundthatPdsitesdidnotshowsignificantelectronic structurechangesondifferentsupportsafterlow-temperatureNaBH / tert-butylamine treatment, indicating that this strategy was not applicabletoPdcatalystsystems.
To systematically uncover the regulatory role of thermally induced reconstruction and redispersion of Pd NPs on reaction selectivity,weusedthePd /CeO -T catalystsystem,preparedwith colloidalPdNPsofvaryingsizesasprecursortoensurebettercontrol overinitialvariables32.Toobtainsufficientdataoncatalyststructure andreactionperformance,wealsovariedthecalcinationtemperature in the Pd /CeO -T system (where T denotes the calcination temperature). Catalysts with different initial Pd particle sizes are representedbydifferentcoloredpointsandcurves.Basedonthese results,weconstructedaPdδ⁺–W–Sel.three-dimensionalrelationship diagram,asshowninSupplementaryFig.33.IntheW–(Pdδ+)plane, resultsindicatedthattheWvaluesofPdNPsoncatalystsprepared under different conditions exhibited a clear positive linear scaling relationshipwiththeratioofPdδ+(R2=0.92)(Fig.5a).Thislinearcor- relationsuggeststhatchangesinthegeometricandelectronicstruc- turesofthePdactivephaseduringreconstructionareactuallylinearly constrained.
IntheW–Sel.plane,theyellowpointsandcurveinFig.5aillustrate theselectivityvariationpatternofPd /CeO -T withaninitialsizeof 2.9nm colloidal Pd NPs at various calcination temperatures. Below 300°C,theselectivityofthecatalystforMBEincreasedsignificantly withrisingcalcinationtemperature.Thenitremainedbetween96.5% and97.2%whenfurtherraisingthecalcinationtemperature.Asimilar trendwasobservedfortheselectivityofPd /CeO -T withother colloidalPd NPs of the same initial size, achieving the highestMBE selectivity exceeding 97.5% (Fig. 5a). Comparing the differences in selectivity among Pd /CeO -T catalysts of varying Pd sizes, it is evident that smaller Pd NPs on CeO show a more significant improvement in MBE selectivity after air calcination. The five data curves,representinginitialPdparticlesizesfrom2.9to7.8nm,forma two-dimensional contour plot that illustrates how MBE selectivity changeswiththeWvalueonPd /CeO -T catalysts.AlongtheW axis, this interval can be divided into a plateau region with high selectivity and a steep region with rapidly decreasing selectivity (Fig.5a).TakingtheyellowcurveofPd /CeO -T asanexample, theselectivitywasintheplateauregionwhentheWvaluewasbelow 0.85,butfellintotherapidlydecreasingsteepregionwhentheWvalue exceeded 0.85.As the initial Pd particle size increases, the W-value thresholdfortheplateauregionshiftsslightlytotheright.
Intheplateauregion,theWvalueshowedsignificantvariation. FollowingtheWulffconstructionprinciple,thegeometricstructureof Pd NPs experienced substantial deformation65. Concurrently, the electronicstructure of Pd NPs also underwent considerable change due to the linear relationship between geometric and electronic structure evolutionduringsurfacereconstruction.Asindicatedbythe Pd3dXPSresultsinSupplementaryFig.34,thesurfacePdsitesinthe plateau region were generally electron-deficient. Consequently, the ongoingevolutionofthe electronicand geometricstructures ofPd siteshadminimalimpactonreactionselectivity,giventhepronounced electron-deficientstate ofPd.Inessence, the highselectivityofthe catalyst for MBE in this range was primarily determined by the electron-deficient state of Pd sites, despite the C≡C bond semi- hydrogenationbeingageometricallysensitivereaction66.Accordingto WulffConstructionrules,theproportionofsuchlow-coordinatedsites asedgeandcornersitesonPdparticlesurfacesgraduallyincreases withtheriseoftheWvalue65,67.Plentyofresearchresultshaveshown thattheselow-coordinatedPdsites,whichhavestrongolefinadsorp- tion capacity, often lead to over-hydrogenation side reactions, sig- nificantly reducing olefin selectivity68. Therefore, the constant MBE selectivitywithWvalueintheplateauregioncouldberegardedasa supportforelectroniceffectsonPdsites.Inthesteepregion,electron- richPdsitessuggestedtheweakregulationoftheelectronicstructure ofPdNPsbytheCeO support.Atthisstage,thegeometricstructure evolution of Pd NPs started to significantly influence selectivity, aligningwithpriorresearchfindings.AscanbeseeninFig.5a,theMBE selectivity showed significant variation on Pd /CeO -T catalysts (T <300°C) with different particle sizes, despite their similar W values.AccordingtoWulffconstructionrules,theselectivitychangeat this stage was mainly caused by different proportions of low- coordinatedsites,likeedgeandcorneratomsonthesurfacesofPd NPswithdifferentsizesormorphologies69.
It is crucial to note that the above rules for regulating alkyne hydrogenation activity and selectivity through thermally induced activecomponentreconstructionprovedeffectivewithvariousactive componentprecursorsandreduciblesupports,showcasingadegree of universality. For instance, Pd/CeO -T catalysts prepared using PdCl astheprecursormaintainedconsistentlyhighselectivityafterair calcination pretreatment at various temperatures (Supplemen- taryFig.35).
This phenomenon can be explained bythe electronic and geo- metricstructuresofthePdsitesbeingintheplateauregion,asshown inFig.5a.Similarly,theseconclusionsalsoaccountforthehighMBE selectivityofPd/TiO-500andPd /TiO -500catalysts,aswellasthe seriousover-hydrogenationsidereactiononPd/Al O ,Pd/Al O -500, Pd/MgO,Pd/MgO-500,andPd/SiO catalysts(SupplementaryFigs.36, 37,Table3).
Furtherprocessingofthethree-dimensionaldatainSupplemen- tary Fig. 32 through matrix transformation and grid interpolation yieldsthecorrespondingcontourplots.Thesecontourplotsprovide moredetailedinsightsintothestructure-activityrelationshiptrends. For Pd /CeO -T -derived data (Fig. 5b), itis evident that the Pd/ CeO₂systemexhibitssevereover-hydrogenationonlyinasmallregion of the electronic–geometric parameter space (right portion of the plot). In other words, the Pd/CeO₂ system possesses exceptionally broad tunability in both electronic and geometric structures for achieving highly selective hydrogenation of alkynes.For small-sized supported Pd NPs, surface-reconstruction-induced flattening sig- nificantly expands the parameter space for high alkene selectivity (Fig.5c).AslongastheWvalueremainsbelow0.85,allPd/CeO₂cat- alystsexhibitdesirableMBEselectivity.Moreover,thisflatteningeffect appearsmorepronouncedforsupportedPdNPssmallerthan3nm, effectivelyaddressing the challenge of alkene selectivity control on small Pd clusters and substantially improving Pd atom utilization. Concurrently,over-hydrogenationsidereactionsonsmallsupported PdNPsareconfinedtohighlyelectron-richstates(Pdδ⁺<15%)(Fig.5d). Since small supported Pd NPs often experience significant electron transfer with reducible oxide supports, their electronic structures readilymeettherequirementsforhighalkeneselectivitywhensup- portedonstronglyinteractingreducibleoxides70.Notably,whenthe sizes of Pd NPsare <3nm,theflattening effectfrom surfacerecon- struction indicates that Pd in a relatively electron-rich state (18%<Pdδ⁺<37%) exhibits higher alkene selectivity compared to Pd sitesnearbywithotherelectronicconfigurations(Fig.5d).Itiscrucial to emphasize that these trends are consistent regardless of the Pd precursors used. Data from catalysts prepared with PdCl as a pre- cursor did not significantly change the Pdδ⁺–W–Sel. contour-plot trends(Fig.5e).Instead,theadditionaldataenhancedthereliability andaccuracyofalkeneselectivitypredictions.Forinstance,theover- estimatedselectivity(Sel.>99%)intheupper-rightregionofFig.5b wascorrectedtoamorereasonablerangeof92–96%.
Thermally induced surface reconstruction of Pd/CeO yields a high-performance, additive-free catalyst for alkyne semi-hydrogena- tion,achieving97.5%olefinselectivitywith18.2-foldhigheractivitythan Lindlarcatalysts.Mechanisticstudiesrevealthatoxidativeredistribu- tion of Pd nanoparticles into flattened, electron-deficient structures enhances metal-support interactions while suppressing over- hydrogenation. A geometric descriptor (W, flattening degree) and electronic descriptor Pdδ⁺ content) uncouple structure-activity rela- tionships:TOFdecreaseslinearlywithW,whereasselectivitytransitions atW=0.85fromelectronic-dominated(Pdδ⁺)togeometric-dominated (Pd0) regimes. In addition, surface reconstruction drastically shrinks theelectronic-geometricspaceofPdsitesfortheover-hydrogenation side reaction. This work offers a unified approach for decoupling structure-sensitive effects in supported noble metal catalysts on reducible oxides. This approach is theoretically generalizable across such systemssandmayenablequantitativeseparationofelectronicand geometriccontributionsinotherstructure-sensitivereactions.

Methods
Chemicalsandmaterials
Thesubsequentchemicalswereprocuredcommerciallyandutilizedas received, devoid of any additional treatment: palladium chloride (PdCl , 99.9%, 60.0wt.% Pd), Cerium oxide (99.95%), 2-methyl-3- butyn-2-ol (MBY, AR), 2-methyl-3-buten-2-ol (MBE, AR), all sourced fromAladdinIndustrialCorporation.

Synthesisofcatalysts
Pd/CeO -T nanocatalystsweresynthesizedusingtheconventional wetness impregnation method, with a nominal metal loading of 0.5wt.%. The commercial cerium oxide supports underwent pre- treatmentat500°Cfor4hunderpureH (heatingrate:10°C·min−1) beforeutilization.Inbrief,a252μLPdCl aqueoussolution(containing 6mg·mL−1 Pd) was dissolved in 20mL of deionized water. Subse- quently,300mgofceriumoxidewasslowlyaddedtothesolutionwith continuous magnetic stirring at 50°Cfor 10h. Following impregna- tion,thesampleswerecalcinedinstaticairattemperaturesranging from 200 to 600°C for 4h (heating rate: 5°C·min-1). The resulting yellowsolidswerethensubjectedtoreductioninpureH atmosphere at200°Cfor1h,employingaheatingrateof2°C·min-1,yieldingthePd/ CeO -T catalysts (where T denotes the calcined temperature). Similarly,5Pd/CeO wassynthesizedbyadjustingthequantityofthe metalprecursor.Pd/CeO -500-N andPd/CeO -500-Arwereprepared usingthesamesyntheticapproach,withtheexceptionofcalcination underpureN orArenvironment.
ThesyntheticapproachforgeneratingPdnanoparticles(NPs)was refined based on a previously reported method24, subsequently involvingwetnessimpregnationandaircalcinationat500°Ctofab- ricatetheseriesPd /CeO -500catalystswithvaryingparticlesizes. Theremovalofthecappingagent(polyvinylpyrrolidone,PVP)from thesurfaceofPVP-Pd /CeO catalystswasexecutedusingaNaBH / tert-butylamine (TBA) aqueous solution, following the established procedures. In a typical procedure, the as-prepared PVP-Pd /CeO catalysts were treated in 6.2mL NaBH /TBA solution (TBA: H O: NaBH =5mL:1.2mL:10mg)undercontinuousstirringfor1hinice baths,followingbyseparationthroughcentrifugation.Thecollected samples were then washed with acetone three times toremove the surfaceamines.Afterdryinginavacuumat60°Covernight,aseriesof Pd /CeO catalysts with different particle sizes was successfully obtained.

Characterizations
High-resolution transmission electron microscopy (HRTEM), high- angle annular darkfield scanning transmission electronmicroscopy (HAADF-STEM),andelementalmappingwithenergydispersiveX-ray spectroscopy(EDS)testswereconductedontheJEOLJEM-2100Fatan accelerationvoltageof200kV.Toensuretheaccuracyandreliability oftheWdescriptor(definedastheratiooftheshortestdiameter(R1) tothelongestdiameter(R2)ofthetwo-dimensionalprojectionofPd clusters,characterizingthedegreeofparticledeformation,Fig.1e),the followingmeasurementrestrictionswereimplemented:(i)SinceTEM imagesreflecttwo-dimensionalprojections,onlyPdparticlesattached totheedgeofthesupportwereselectedasstatisticalobjectstoavoid theinfluenceofsupportcontrastonPdparticlemeasurement;(ii)To reduceaccidentalerrors,thenumberofPdparticlesforstatisticswas increasedasmuchaspossible,sothatthefullwidthathalfmaximum (FWHM)oftheWparameterdistributionwaslowerthan0.20,thereby ensuring the coefficient of determination (R2) of the linear scaling relationship≥0.95.Foreachcatalystsample,theaverageWvalueofPd particles was obtained through statistical analysis of at least 60Pd particles.Forexample,theWvalueofthePd/CeO -500catalystwas obtained by statistical analysis of 112Pd particles. Environmental transmission electron microscopy analysis was carried out on the HitachiH-9500(300kV)at4.5×10-2Paunderanoxygenatmosphere. Power X-ray diffraction (XRD) was measured in a Rigaku Ultima IV operating at 40kV and 20mA with Cu Kα radiation. The data was recordedinthe20°–80°2θrange.TheN adsorption-desorptioniso- thermal analysis was performed using a Micromeritics ASAP 2020 HD88. The Brunauer-Emmett-Teller (BET) method was applied to estimatethetotalsurfacearea,S .Themetalloadingofthecatalysts BET wasdeterminedbytheinductivelycoupledplasmamassspectrometry (ICP-MS)usingaPerkinElmerNexION2000equipment.Temperature- programmedreductionwithhydrogen(H -TPR)wasconductedina FINESORB-3010 apparatus equipped with a thermal conductivity detector(TCD).TheX-rayphotoelectronspectra(XPS)wereobtained onanESCALABMARKIIsphericalanalyzerwithanaluminumanode (1486.6eV)X-raysource,calibratedbytheC1speak(284.8eV).Pulsed COchemisorptionwasconductedonaFINESORB-3010apparatusto determinethedispersionofPdinthecatalyst.Thesamples(approxi- mately100mg)wereloadedinaU-shapedquartzreactorbetweentwo plugsofquartzwool,whichwerepurgedfor1hwithHeat150°Cto remove the vapor and impurities. When the sample was cooled to room temperature, the pulse CO chemisorption test was then con- ductedwith50vol%ofCOinHe.

Catalytictest
The semi-hydrogenation of MBY was evaluated under atmospheric pressure using a 50mL three-necked round-bottom flask. For each reaction,20mgPd/CeO -T and100μLsubstratewerethoroughly dispersed in 5mL of ethanol, and the mixture was exposed to a hydrogen-filledballoon(1bar).Priortoinitiatingthereaction,theflask underwentfivecyclesofhydrogenpurgingtoeliminateanyairpre- sent. During the reaction proceeding, samples were intermittently withdrawn using a syringe and subjected to analysis using gas chromatography-flame ionization detector (GC-FID). The resulting products were further characterized through gas chromatography- massspectrometry(GC-MS).Theturnoverfrequency(TOF)wascal- culatedusingtheformula:TOF=(molofalkynes×conversion)/(mol ofsurface-exposedPdatoms×reactiontime),conversion≤10%.
For the Pdδ⁺–W–selectivity contour mapping, the commercially availablesoftwareOrigin,whichiswidelyusedintheresearchfield, wasemployedformatrixtransformationandgridinterpolation.The gridinterpolationadoptedtheRandom(Renka-Cline)method,andthe data smoothing standard reached C1 continuity (first-order differ- entiable). Other settings, such as grid density, adopted the default parameters ofOriginsoftware,whichwere consistentwith the con- ventionaloperationstandardsintherelatedresearchfield.

Cyclingstabilitytest
Thereactionblendcomprising20mgofPd/CeO -500and100μLof substrate was dispersed within 5mL of ethanol. The solution was subjectedtovigorousstirring(1000rpm)at35°Cunder1barH .The 2 reaction was halted after a predetermined duration, subsequent to which the catalysts wereseparated through centrifugation. The uti- lizedcatalystsunderwentathoroughwashingprocedurewithethanol, involvingthreesuccessivewashes,beforebeingdriedundervacuum conditionsat60°Covernight,inpreparationforthecyclingstability assessment.

Densityfunctionaltheorycalculations
Calculationswereperformedbyusingperiodic,spin-polarizedDFTas implementedintheViennaabinitioprogrampackage(VASP,version 6.1),usingtheprojectoraugmentedwave(PAW)methodproposedby BlöchlandimplementedbyKresse.Acutoffenergyof400eVforplane waveswassetthroughallthecalculations.Theexchangecorrelation energy was modeled by using the Perdew-Burke-Ernzerhof (PBE) functionalwithinthegeneralizedgradientapproximation(GGA).Pd nanoparticles with 49 atoms (Pd49) were established based on the Wulff construction. A p(6×6) supercell with six atomic layers con- taining214atomsfortheCeO modelwasconstructed,andtwoofthe 2 surfaceoxygenatomswereremovedtosimulatetheoxygenvacancies. A k-point of 2×2×1 was used for the Brillouin zone sampling for structure optimization. Theperiodiccondition wasemployed along thexandydirections,andthevacuumregionbetweentheslabswas 15Å,whichissufficientlylargetokeepspuriousinteractionsnegligible. Theupperthree-layeratomsforCeO inthesupercellswereallowedto 2 relax.Meanwhile,thebottomthree-layeratomswerefixedduringthe AIMDsimulation.Thegeometryoptimizationwasstoppedwhenthe forceresidueontheatomwassmallerthan0.02eV·Å−1,andtheenergy differencewas<10−4eV.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Authors report the synthesis of Pd/CeO2 catalyst for the semi hydrogenation of an alkyne. The role of calcination\ntemperature on the Pd nanoparticle shape is investigated in detail. This has been correlated to the catalytic activity. Authors\nreport a correlation between the calcination temperature and the shape of the nanoparticle and they have used a specific\nparameter (W) that describes the flattening of the Pd nanoparticle on the surface of CeO2. Furthermore they report a\ncorrelation between the oxidation state and the catalytic activity as well. This is an interesting article and the investigation is\nthorough and it gives an interesting correlation. I am not sure about how widely we employ this kind of correlation,\nnevertheless it is an interesting article. Hence this article can be accepted for publication. A minor revision suggestion would\nbe to check the catalytic activity of the recovered catalyst. This will give an idea about the stability of these Pd naoparticles\nand how relevant this W parameter during or after the reaction.", "reviewer_2": "This manuscript makes a highly significant and timely contribution to the field of heterogeneous catalysis by addressing a\nlong-standing challenge: the quantitative disentanglement of electronic and geometric effects during catalyst reconstruction.\nThe authors introduce a simple yet powerful thermally induced surface-reconstruction strategy that continuously tunes both\nthe morphology and electronic structure of Pd sites on reducible oxides. Through rigorous characterization, mechanistic\nanalysis, and carefully chosen structure-sensitive probe reactions, they successfully decouple these two effects and identify\na universal geometric descriptor (W) that linearly governs intrinsic activity, while revealing a clear selectivity transition\nbetween electron-dominated and geometry-dominated regimes.\nImportantly, the authors establish a Pdδ⁺-W-Selectivity map that not only rationalizes the observed reaction behavior but\nalso provides a generalizable blueprint for catalyst design across supported noble metal systems. The discovery that surface\nreconstruction dramatically constrains the electronic–geometric space responsible for over-hydrogenation represents a\nconceptually impactful advance, offering a new paradigm for suppressing undesired pathways without additives. Their\ncatalyst exhibits outstanding performance—far surpassing Lindlar catalysts—highlighting the practical relevance of this\nmechanistic insight.\nOverall, this work provides rare quantitative clarity on the electronic–geometric interplay that governs structure-sensitive\nhydrogenation reactions. The methodological framework and design principles developed here are likely to influence future\nresearch on metal–support interactions, redispersion phenomena, and rational catalyst optimization. I believe this study\nrepresents an important step forward for the field and merits publication after minor revisions.\n(1)The manuscript would benefit from a clearer explanation of how the W descriptor is extracted from TEM images—\nspecifically, how many particles were statistically analyzed for each sample and how measurement uncertainty affects the\nlinear scaling relationships.\n(2) In the Pdδ⁺-W-Selectivity contour mapping, the authors mention grid interpolation and matrix transformation. Providing\nbrief methodological details (e.g., interpolation algorithm, data smoothing criteria) in the Supporting Information would help\nensure reproducibility."}, "author_response": "We sincerely thank the reviewers for their insightful and comprehensive comments\non our manuscript (ID: NCOMMS-25-88855). We have carefully revised the\nmanuscript in response to all comments and suggestions, and each point has been\naddressed in detail. Our responses to the reviewers’ comments are provided below. We\nbelieve that these revisions have significantly improved the quality and clarity of the\nmanuscript and that it now meets the criteria for publication.\nDetailed reply to the reviewers’ comments:\nReviewer #1:\nAuthors report the synthesis of Pd/CeO catalyst for the semi hydrogenation of an\n2\nalkyne. The role of calcination temperature on the Pd nanoparticle shape is investigated\nin detail. This has been correlated to the catalytic activity. Authors report a correlation\nbetween the calcination temperature and the shape of the nanoparticle and they have\nused a specific parameter (W) that describes the flattening of the Pd nanoparticle on\nthe surface of CeO . Furthermore they report a correlation between the oxidation state\n2\nand the catalytic activity as well. This is an interesting article and the investigation is\nthorough and it gives an interesting correlation. I am not sure about how widely we\nemploy this kind of correlation, nevertheless it is an interesting article. Hence this\narticle can be accepted for publication. A minor revision suggestion would be to check\nthe catalytic activity of the recovered catalyst. This will give an idea about the stability\nof these Pd naoparticles and how relevant this W parameter during or after the reaction.\nResponse: We sincerely thank the reviewer for the constructive comments on our\nmanuscript, which is crucial for clarifying the stability of Pd nanoparticles and the\nrelevance of the W parameter during and after the reaction. We have carefully\nresponded to the reviewer's relevant comments, and the specific responses are provided\nbelow. We believe that this revision has further improved the manuscript.\nIn fact, we have already conducted systematic studies on the activity and structure of\nthe recovered catalysts in the section of the original manuscript, and the relevant results\nhave been discussed in the main text, with the corresponding figures/tables added both\nin the main text and the Supporting Information (SI).\nSpecifically, we compared the performance changes of three catalysts (Pd/CeO -500,\nNP-3.7 2 NP-3.7 2\nMeanwhile, we characterized the morphology and size of Pd nanoparticles after the\nreaction by high-resolution transmission electron microscopy (HRTEM) and X-ray\ndiffraction (XRD) (Figs. S28–S31). The results show that the calcined catalysts still\nmaintain excellent activity and structural integrity after recycling, and no obvious\nagglomeration of Pd particles is observed. This phenomenon is closely related to the\nsurface reconstruction strategy we proposed and the enhanced metal-support interaction.\nFig. S28. Cycling stability test of the selective hydrogenation of MBY over Pd/CeO -\n2\n500.\nFig. S29. Morphological and structural characterizations of Pd/CeO -500-used.\n2\ncatalyst. (d) XRD pattern of Pd/CeO -500-used catalyst.\nhydrogenation of MBY over Pd /CeO and Pd /CeO -500 catalysts.\nNP-3.7 2 NP-3.7 2\nFig. S31. HRTEM images and particle size distribution histogram of Pd /CeO -3.7-\nNP 2\nused (a) and Pd /CeO -3.7-500-used (b) catalysts after the cycling stability test.\nNP 2\nRegarding the correlation between catalyst stability and the morphological parameter\n(W) of the catalyst before and after the reaction, we have supplemented the recycling\nexperiments of the uncalcined Pd/CeO -uncalcined catalyst (Fig. S32). Further, we\n2\nhave summarized the relationship among the interaction strength between Pd sites and\nthe support (Pdδ⁺), the W value, and the recycling stability (i.e., the conversion\ndifference in before and after five recycles) for the four catalysts (Pd/CeO -500,\nAs shown, when the W value is significantly lower than 1 (0.6–0.8), the catalytic\nactivity of the catalyst does not decrease significantly after five recycles; at the same\ntime, the W value of Pd particles before and after the reaction does not change\nsignificantly. This result can be attributed to the strong metal-support interaction\nformed by the obvious electron transfer (higher Pdδ⁺ ratio) between Pd particles and\nCeO support in such catalysts. It should be noted that it is these strong interactions that\n2\nlead to the smaller W value (more flattened Pd nanoparticles). By contrast, the weak\nmetal-support interaction (W ≈ 1) in the uncalcined Pd/CeO -3.7 and Pd/CeO catalysts\n2 2\nleads to poor stability, as reflected in the significant activity drop after five recycles\nfrom 89.6% to 49.3% and from 96.7% to 73.1%, respectively.\nThe specific revisions are outlined below:\nPage 14, line 374 in the revised manuscript:\nAs shown, even after five cycles, the losses in catalytic activity and selectivity for\nboth Pd/CeO -500 and Pd /CeO -500 were negligible, while uncalcined Pd/CeO\nand Pd /CeO catalysts suffered from significant deactivation (Fig. S28–32).\nNP-3.7 2\nPage 32, line 1 in the revised Supporting Information:\nFig. S32. Comparison of cycling stability for selective hydrogenation of MBY over\nPd/CeO -500 and uncalcined Pd/CeO catalysts.\n2 2\nPage 14, line 379 in the revised manuscript:\nTo further clarify the intrinsic correlation between catalyst stability and Pd structural\ncharacteristics, we summarized the relationships among Pdδ⁺ content, W value, and\ncycling stability of Pd/CeO -500, Pd/CeO -uncalcined, Pd /CeO -500, and Pd\n2 2 NP-3.7 2 NP-\n/CeO -uncalcined catalysts as shown in Fig. 4f. The Pd morphological parameter W\n3.7 2\nquantifies the degree of particle deformation, and cycling stability is measured by the\ndifference in conversion rate before and after five cycles. Catalysts with a low initial W\nvalue (0.6–0.8) demonstrate negligible activity loss and constant Pd particle W values\nafter five cycles (Fig. 4f). This is due to a strong metal-support interaction, where\nelectron transfer from Pd to CeO increases the Pdδ⁺ population and flattens the Pd\n2\nparticles, yielding a smaller W value. Consequently, a lower W value reliably predicts\nbetter stability. In contrast, uncalcined PdNP-3.7/CeO and Pd/CeO catalysts, with W\n2 2\nvalues approaching 1, suffer from weak interaction and inferior stability, as shown by\nthe activity decline after five cycles from 89.6% to 49.3% and from 96.7% to 73.1%,\nrespectively.\nPage 33, line 1 in the revised Supporting Information:\nFigure 4f. Three-dimensional plot depicting the relationship among Pdδ⁺, W value, and\ncycling stability (conversion difference after 5 cycles) for Pd/CeO -500, Pd/CeO -\n2 2\nuncalcined, Pd /CeO -500, and Pd /CeO -uncalcined catalysts; X/Y axes are W\nNP-3.7 2 NP-3.7 2\nvalue and Pdδ⁺ content respectively, and Z axis is conversion difference.\nReviewer #2:\nThis manuscript makes a highly significant and timely contribution to the field of\nheterogeneous catalysis by addressing a long-standing challenge: the quantitative\ndisentanglement of electronic and geometric effects during catalyst reconstruction. The\nauthors introduce a simple yet powerful thermally induced surface-reconstruction\nstrategy that continuously tunes both the morphology and electronic structure of Pd\nsites on reducible oxides. Through rigorous characterization, mechanistic analysis, and\ncarefully chosen structure-sensitive probe reactions, they successfully decouple these\ntwo effects and identify a universal geometric descriptor (W) that linearly governs\nintrinsic activity, while revealing a clear selectivity transition between electron-\ndominated and geometry-dominated regimes.\nImportantly, the authors establish a Pdδ⁺–W–Selectivity map that not only\nrationalizes the observed reaction behavior but also provides a generalizable blueprint\nfor catalyst design across supported noble metal systems. The discovery that surface\nreconstruction dramatically constrains the electronic–geometric space responsible for\nover-hydrogenation represents a conceptually impactful advance, offering a new\nparadigm for suppressing undesired pathways without additives. Their catalyst exhibits\noutstanding performance—far surpassing Lindlar catalysts—highlighting the practical\nrelevance of this mechanistic insight.\nOverall, this work provides rare quantitative clarity on the electronic–geometric\ninterplay that governs structure-sensitive hydrogenation reactions. The methodological\nframework and design principles developed here are likely to influence future research\non metal–support interactions, redispersion phenomena, and rational catalyst\noptimization. I believe this study represents an important step forward for the field and\nmerits publication after minor revisions.\nResponse: We sincerely thank the reviewer for the positive, encouraging and insightful\ncomments and suggestions on our manuscript. We have carefully studied and addressed\neach of the raised points in detail, and the specific responses are provided below.\nComment 1. The manuscript would benefit from a clearer explanation of how the W\ndescriptor is extracted from TEM images—specifically, how many particles were\nstatistically analyzed for each sample and how measurement uncertainty affects the\nlinear scaling relationships.\nResponse: We thank the reviewer for this helpful suggestion. We will follow the\nreviewer’s suggestion to supplement the specific method for extracting the W descriptor\nfrom transmission electron microscopy (TEM) images, in order to further improve the\nclarity and rigor of the manuscript, particularly regarding the statistical analysis and the\nimpact of measurement uncertainty on linear scaling relationships.\nIn this work, the W value is defined as the ratio of the shortest diameter (R1) to the\nlongest diameter (R2) in the two-dimensional projection of Pd clusters, which is used\nto characterize the degree of particle deformation (see Fig. 1e). To ensure the accuracy\nand reliability of the measurement results, we implemented the following constraints\non the measurement operations:\n(i) Since TEM images represent two-dimensional projections, we only selected Pd\nparticles attached to the edge of the support as statistical objects to avoid the influence\nof support contrast on Pd particle measurement;\n(ii) To reduce accidental errors, we maximized the number of Pd particles for\nstatistics, such that the full width at half maximum (FWHM) of the W parameter\ndistribution is less than 0.20, ensuring that the coefficient of determination (R2) of the\nlinear scaling relationship is ≥ 0.95. For each catalyst sample, the average W value of\nPd particles was determined by statistical analysis of at least 60 Pd particles. For\nexample, the W value of the Pd/CeO -500 catalyst was derived from the statistics of\n2\nWe have placed the relevant supplementary explanations in the Methods section of\nthe paper to further clarify the extraction process of the W descriptor and the statistical\ncriteria, which will help readers better understand the rationality of the linear scaling\nrelationship.\nThe specific revisions are outlined below:\nPage 22, line 581 in the revised manuscript:\nTo ensure the accuracy and reliability of the W descriptor (defined as the ratio of the\nshortest diameter (R1) to the longest diameter (R2) of the two-dimensional projection\nof Pd clusters, characterizing the degree of particle deformation, Fig. 1e), the following\nmeasurement restrictions were implemented: (i) Since TEM images reflect two-\ndimensional projections, only Pd particles attached to the edge of the support were\nselected as statistical objects to avoid the influence of support contrast on Pd particle\nmeasurement; (ii) To reduce accidental errors, the number of Pd particles for statistics\nwas increased as much as possible, so that the full width at half maximum (FWHM) of\nthe W parameter distribution was lower than 0.20, thereby ensuring the coefficient of\ndetermination (R2) of the linear scaling relationship ≥ 0.95. For each catalyst sample,\nthe average W value of Pd particles was obtained through statistical analysis of at least\n2\nstatistical analysis of 112 Pd particles.\nComment 2. In the Pdδ⁺–W–Selectivity contour mapping, the authors mention grid\ninterpolation and matrix transformation. Providing brief methodological details (e.g.,\ninterpolation algorithm, data smoothing criteria) in the Supporting Information would\nhelp ensure reproducibility.\nResponse: We thank the reviewer for this valuable suggestion. We fully agree that\nsupplementary relevant methodological details are crucial for ensuring the\nreproducibility of the work, which we have addressed accordingly.\nIn the Pdδ⁺–W–selectivity contour mapping, we used the commercially available\nOrigin software (widely used in scientific research) for matrix transformation and grid\ninterpolation. The grid interpolation adopted the Random (Renka-Cline) method, and\nthe data smoothing standard reached C1 continuity (first-order differentiable). Other\nsettings, such as grid density, adopted the default parameters of the Origin software,\nwhich are consistent with common operating standards in related research fields.\nWe have placed the relevant supplementary explanations in the Methods section of\nthe paper, adding the necessary methodological details, which will facilitate other\nresearchers to reproduce the contour mapping results and verify the conclusions of this\nwork.\nThe specific revisions are outlined below:\nPage 23, line 624 in the revised manuscript:\nFor the Pdδ⁺–W–selectivity contour mapping, the commercially available software\nOrigin, which is widely used in the research field, was employed for matrix\ntransformation and grid interpolation. The grid interpolation adopted the Random\n(Renka-Cline) method, and the data smoothing standard reached C1 continuity (first-\norder differentiable). Other settings such as grid density adopted the default parameters\nof Origin software, which were consistent with the conventional operation standards in\nthe related research field."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Authors have revised the manuscript satisfactorily and have addressed all the comments. This manuscript can now be\naccepted for publication.", "reviewer_2": "All raised questions have been satisfactorily addressed by the author. The revised work demonstrates exemplary innovation\nand organization, and I therefore recommend its publication without further revision."}, "author_response": ""}]

Decision letter