# Cellulose nanocrystals-supported organocatalyst for the synthesis of cyclic carbonates via cycloaddition of carbon dioxide to epoxide

N. El Idrissi, H. Aitbella, Nicolas Merle, Frederic Cazaux, J. P. P. Ramalho, L. Belachemi, H. Kaddami, Philippe Zinck

<figure><img src="image_1.png" /></figure>

## ► To cite this version:

N. El Idrissi, H. Aitbella, Nicolas Merle, Frederic Cazaux, J. P. P. Ramalho, et al., Cellulose nanocrystals-supported organocatalyst for the synthesis of cyclic carbonates via cycloaddition of carbon dioxide to epoxide. Carbohydrate Polymers, 2025, Carbohydr. Polym., 364, 10.1016/j.carbpol.2025.123762. hal-05164794

HAL Id: hal-05164794

https://lilloa.hal.science/hal-05164794v1

Submitted on 16 Jul 2025

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

# Cellulose nanocrystals-supported organocatalyst for the synthesis of cyclic carbonates via cycloaddition of carbon dioxide to epoxide

Nouaamane El Idrissi<sup>a,b</sup>, Hicham Aitbella<sup>a,b</sup>, Nicolas Merle<sup>b,*</sup>, Frédéric Cazaux<sup>c</sup>,
João P. Prates Ramalho<sup>d</sup>, Larbi Belachemi<sup>a</sup>, Hamid Kaddami<sup>a,e</sup>, Philippe Zinck<sup>b,*</sup>

<figure><img src="image_4.png" /></figure>

## ARTICLE INFO

### Keywords:

Cellulose nanocrystals

Base catalyst

Supported catalyst

Carbon dioxide

Cycloaddition

Organocatalysis

## ABSTRACT

The synthesis of cyclic carbonates can be realized via cycloaddition of CO₂ to epoxides. Organocatalysts are of interest regarding specific applications. The reaction can be co-activated by a hydrogen bond donor such as cellulose. A fully recyclable catalytic system combining an organocatalyst and a polysaccharide hydrogen bond donor has never been reported. In this study, we have supported an organocatalyst onto cellulose nanocrystals (CNC). The grafting of 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) onto microcrystalline cellulose (MCC) and onto the surface of cellulose nanocrystals (CNC) was confirmed by ¹³C solid state NMR, FT-IR, XRD and elemental analysis. The prepared heterogeneous TBD-CNC nanocatalyst was successfully assessed on a scope of five epoxides including mono- and di-substituted. The activity was found to be higher than that of the TBD-MCC supported catalyst, and higher than the homogeneous counterpart. That latter result highlights the coactivation role of the polysaccharide. Recyclability studies showed that the catalyst is reusable for at least five cycles. Density functional theory (DFT) studies indicate that the mechanism most probably involves the formation of anionic cellulosic species. Initially, the grafted TBD deprotonates a surface hydroxy to form a cellulose alkoxide, which then performs a nucleophilic attack on CO₂ or on the activated epoxide.

## 1. Introduction

Alkyl carbonates and particularly cyclic derivatives are increasingly used in the chemical industry (Balas, Villanneau, & Launay, 2022; Vranješević et al., 2022; Weidlich & Kamenická, 2022) as green solvents in various products (Ismail et al., 2021; Pescarmona, 2021), electrolyte in lithium-ion batteries (Qian et al., 2022; Yang et al., 2021), cleaning and degreasing agents (Kamphuis, Picchioni, & Pescarmona, 2019), industrial lubricants (Büttner, Longwitz, Steinbauer, Wulf, & Werner, 2017) and fuel additives (Nasirov, Nasirli, & Ibrahimova, 2021). In addition, they are used for the production of polymers such as poly-carbonates (Lalanne-Tisné et al., 2022; Lalanne-Tisné, Favrelle-Huret, Thielemans, Prates Ramalho, & Zinck, 2022) and polyurethanes (Okada, Yamada, Yokoe, & Aoi, 2001; Tomita, Sanda, & Endo, 2000).

Cyclic carbonates can be produced through a cycloaddition reaction of CO₂ to epoxides, where the CO₂ is incorporated with 100 % atom economy without the release of by-products (Aresta, Dibenedetto, & Angelini, 2014; Artz et al., 2018). The industrial manufacture of cyclic carbonates from CO₂ and epoxides began more than 40 years ago with the use of quaternary ammonium halide (Quadrelli, Centi, Duplan, & Perathoner, 2011). Current manufacturing methods still have significant limitations, including the requirement for high pressure (50–80 Bar), high reaction temperatures (180–200 °C) and a high amount of catalyst (Sakakura, Choi, & Yasuda, 2007; You et al., 2022). Other catalysts for this reaction include notably deep eutectic solvents (He et al., 2021; Yang et al., 2021; Yang, Liu, Chen, Liu, & Zhao, 2022), ionic liquids (Jasiak, Siewniak, Kopczyńska, Chrobok, & Baj, 2016; Liu et al., 2015), N-heterocyclic carbenes (Wang, Sun, Zhou, Zhang, & Lu, 2015), Lewis

<footnote><sup>a</sup> IMED-Lab, Team of Organometallic and Macromolecular Chemistry-Composite Materials, Department of Chemical Sciences, Faculty of Science and Technology, Cadi Ayyad University, Marrakech 40000, Morocco</footnote>

<footnote><sup>b</sup> Unité de Catalyse et Chimie du Solide, UMR 8181, University Lille, CNRS, Centrale Lille, University Artois, F-59650 Villeneuve d'Ascq, France</footnote>

<footnote><sup>c</sup> Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, F-59000 Lille, France</footnote>

<footnote><sup>d</sup> Chemistry Department, LAQV-REQUIMTE and Hercules Centre, Sciences and Technology School, University of Évora, Rua Romão Ramalho 59, 7000-671 Évora, Portugal</footnote>

<footnote><sup>e</sup> Sustainable Materials Research Center (SusMat-RC), Mohammed VI Polytechnic University (UM6P), Lot 660, Hay Moulay Rachid, Ben Guerir 43150, Morocco</footnote>

<footnote>* Corresponding authors.</footnote>

<footnote>E-mail addresses: nicolas.merle@univ-lille.fr (N. Merle), philippe.zinck@univ-lille.fr (P. Zinck).</footnote>
bases (Shiels & Jones, 2007; Zhang, Zhao, Wei, & Sun, 2006), metal oxides (Yamaguchi, Ebitani, Yoshida, Yoshida, & Kaneda, 1999), metal-organic frameworks (Shaikh, Pornpraprom, & D'Elia, 2018), eventually coupled to pectin (Nasiriani, Nigjeh, Torabi, & Shaabani, 2024), transition metal porphyrin complexes (Ema, Miyazaki, Shimonishi, Maeda, & Hasegawa, 2014), chitosan porphyrin complexes (Kumar, de A. e Silva, Wani, Gil, & Sobral, 2017) bimetallic macrocycle phenolate (Chen et al., 2021), amino triphenolate (Taherimehr, Al-Amsyar, Whiteoak, Kleij, & Pescarmona, 2013), ammonium, phosphonium, imidazolium halides (Cokoja, Wilhelm, Anthofer, Herrmann, & Kühn, 2015; Siewniak, Forajter, & Szymańska, 2020) and metal-salen complexes (El Aouni et al., 2023) eventually supported onto cellulose nanocrystals (CNC) (L. Hu et al., 2021).

Metal free systems are particularly suited for pharmaceutical and fine chemical applications where contamination with traces amounts of metal catalysts is highly undesired. Organocatalysts however usually present lower activities. The optimization of catalytic systems is thus of interest to reduce the cost of chemical reactions by reducing the amount of energy required and increasing the yield of the desired products. In this regard, it has been shown that the co-activation of the epoxide ring by hydrogen bond leads to an increased reaction rate. Different hydrogen bond donors have been assessed, including lecithin (Song et al., 2012), formic acid (Tharun et al., 2013), H₂O (Jaroonwatana, D'Elia, & Crespy, 2022), amino acids (Qu, Chen, & Sun, 2022), and lignin (L. Guo et al., 2022).

Cellulose is a cheap and renewable material. It is the most abundant polysaccharide. Among cellulose derivatives, nanocrystals (CNC) are particularly interesting. They are formed from the acidic hydrolysis of cellulose. They are not only interesting as materials reinforcement, but also as catalyst support due their high surface/volume ratio. (Aziz et al., 2021) Cellulose has also been used as a hydrogen bond donor co-catalyst, with KI (Liang et al., 2011) and with the organic base DBU (1,8-Diazabicyclo [5.4.0] undec-7-ene) (Sun et al., 2014) for cycloaddition reactions of CO₂ to epoxide. In this latter case, the presence of cellulose in the reactive medium led to an increase of the conversion to propylene carbonate from 80 % to 93 % after 2 h at 120 °C and 20 bar CO₂, while chitosan led to 88 % conversion in similar conditions.

These systems are however not recyclable for practical reasons, and supported organocatalysts are of interest in this sense ((Doustrkhah, Bagban, Assadi, Luque, & Rostamnia, 2019; Panahi et al., 2019; Rostamnia & Doustrkhah, 2014). The absence of catalyst residues in the product is also an asset. In these line, the efficient synthesis of cyclic carbonates by insertion of CO₂ into epoxides has been reported using an organic base (1,5,7-triazabicyclo [4.4.0] dec-5-ene or TBD) supported on silica as a heterogeneous catalyst at 50 bar CO₂ and 140 °C. This catalyst can be recovered and reused for at least three cycles. Nevertheless, the immobilisation of the TBD drastically reduces the activity of the catalysts in comparison to its homogeneous counterpart mTBD (7-Methyl-1,5,7-triazabicyclo [4.4.0] dec-5-ene) (Barbarini et al., 2003). Alumina-supported TBD was also reported, with performances lower than silica supported TBD in similar experimental conditions (Yu, Curcic, Gabriel, Morganstewart, & Tsang, 2009). Polystyrene beads supported TBD were also reported for the cycloaddition of CO₂ to propylene oxide for 2 h at 140 °C and 20 bar CO₂ with rather modest performances (Dai et al., 2019).

Combining heterogeneous catalysis and co-activation of the process using a polysaccharide has never been reported for the cycloaddition of CO₂ to epoxide as far as we know. We hypothesized that grafting of an organic base such as TBD onto cellulose nanocrystals (CNC) surface could combine the catalytic effect of the organic base with the hydrogen bond donor co-activation of cellulose together with the recyclability of heterogeneous catalysts. CNC are rod-like shape nanoparticles (Arbelaz & Orue, 2023), with a high aspect ratio ranging from 17 to 83 (length-to-width ratio) (Panchal, Ogunsona, & Mekonnen, 2019), with a diameter typically in the range of 5–20 nm and length of hundreds of nanometers (Chen, Garces, Tang, & Ayranci, 2021). As such, we report herein the

synthesis of a CNC-supported organic base catalyst and its performances for the synthesis of cyclic carbonates via cycloaddition of CO₂ to epoxides, including recyclability and mechanistic details. The positioning of our work in the literature can be graphically seen in Fig. 1.

## 2. Materials & methods

### 2.1. Synthesis of TBD-CNC in heterogeneous medium

#### 2.1.1. CNC desulfonatation

CNC desulfonation refers to the process of removing sulfonate groups (–SO₂H) from cellulose nanocrystals (CNC). By eliminating these groups, the thermal stability of the CNC is enhanced, the surface becomes less sterically hindered and more chemically accessible, allowing for a wider range of functionalization techniques. This facilitates further surface modifications.

500 mg of cellulose nanocrystals were suspended in a NaOH aqueous solution (0.25 wt%) and the pH of the suspension was adjusted to 9. The mixture was stirred continuously at room temperature for 4 to 6 h. The reaction was monitored periodically by checking the pH and ensuring that it remains in the alkaline range.

#### 2.1.2. Neutralization

After the reaction, the mixture was neutralized by slowly adding dilute hydrochloric acid (HCl) until the pH reached about 7.

#### 2.1.3. Solvent exchange

A technique was employed to replace water with pyridine. To a water suspension of 500 mg of CNC, 10 mg of NaCl were added in order to facilitate the precipitation of the cellulose nanocrystals. Then 12.5 ml of pyridine were added, centrifugation was carried out and the solid phase was recovered, several successive cycles of centrifugation (10 min and 10,000 rpm) and substitution of the supernatant from water to pyridine were performed, until the complete replacement of water with pyridine, sonication was used to homogenize the final suspension of CNC in pyridine (Mariano et al., 2015).

#### 2.1.4. Tosylation of CNC

Tosyl-CNC were synthesized using a method described in the literature (Dadkhah Tehrani & Basiryan, 2015; Feese, Sadeghifar, Gracz, Argyropoulos, & Ghiladi, 2011; Sadeghifar, Filpponen, Clarke, Brougham, & Argyropoulos, 2011; Seyednejhad, Khalilzadeh, Zareyee, Sadeghifar, & Venditti, 2019; Tehrani & Neysi, 2013) with minor modifications. CNC (500 mg) were introduced in 12.5 ml of pyridine under inert atmosphere at 10 °C under stirring until obtaining a stable dispersion of CNC in pyridine, then 2.94 g of TsCl (5 eq, 15.42 mmol) were added to this dispersion at 25 °C and the mixture was allowed to react for 48 h. The reaction mixture was poured into 100 ml of ethanol, and centrifugation was used to collect precipitated particles, which were rinsed five times with ethanol and deionised water and then lyophilised (48 h), leaving 572 mg of tosylated CNC (Tosyl-CNC).

#### 2.1.5. Coupling of TBD to CNC

Under inert atmosphere, 500 mg of dry Tosyl-CNC were suspended in 16 ml of toluene, afterward 2 eq. per glycosidic unit (858.86 mg, 6.17 mmol) of TBD were added at room temperature, and the mixture was allowed to react for 24 h at 100 °C. Then, the reaction product was poured into 100 ml of ethanol to promote decantation of the TBD-CNC produced, followed by centrifugation, the resulting product was rinsed five times with ethanol and deionised water and then lyophilised (48 h) yielding 419 mg of TBD-CNC. The overall reaction scheme is shown in Fig. 2-b.

### 2.2. Cycloaddition reactions

In a typical experiment, a 25 ml autoclave equipped with a magnetic
<figure><img src="image_5.png" /><figcaption>Fig. 1. Cellulose / amidine and supported guanidine catalytic systems used for the cycloaddition of CO₂ to epoxide (Barbarini et al., 2003; Sun et al., 2014).</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 2. Procedure for the synthesis of (a) TBD-MCC & (b) TBD-CNC.</figcaption></figure>

stirrer was dried in an oven at 80 °C overnight, then immediately placed
in a glovebox filled with argon. Once the reactor had cooled to room
temperature, epoxide and catalyst were added to the reactor in precise
quantities. After sealing and removing the reactor from the glove box,
dry dichloromethane (DCM) was injected into the reactor under argon
(Ar) using a Schlenk line, then CO₂ was added until the desired pressure
was reached. The reactor was closed and heated to the set temperature.
At the end of the reaction, the reactor was cooled to room temperature
after the set reaction time, then the CO₂ was gradually released. In the
case of heterogeneous catalysts, TBD-CNC were separated from the re-
action mixture by simple centrifugation and washed several times with
ethanol. The reminder of the mixture was placed in the rotary evapo-
rator to remove volatile DCM and ethanol. The product obtained were
then characterised by gas chromatography (GC) and ¹H NMR spectros-
copy to determine the conversion and the selectivity of the reaction,

respectively. ¹H NMR spectrum can be found in the appendix in Fig. A2.

**3. Results and discussion**

**3.1. *Catalysts synthesis***

Cellulose, which consist in an enchainment of D-anhydroglucopyranose unit (AGU) presents three reactive hydroxy groups that can potentially be chemically modified, two secondary alcohols and a primary, most reactive, alcohol. However, even for the more reactive primary alcohol, the direct nucleophilic substitution with the TBD is not operant. Thus, hydroxy groups on the surface of cellulose have to be activated before their functionalization.

The practical synthetic method to selectively activate the OH group
connected to C6 is tosylation (Fig. 1). Sulfonates (tosylates) are known
as good leaving groups in organic chemistry. Tosylation selectively activates the primary alcohol of cellulose (Rahn, Diamantoglou, Klemm, Berghmans, & Heinze, 1996; Schmidt, Liebert, & Heinze, 2014), which allows the derivatives of p-toluenesulfonyl to undergo nucleophilic displacement (SN) reactions, so the reaction with a guanidine, such as TBD, should be feasible and generate cellulose with an amine functional group. The global reaction scheme is presented in Fig. 2.

Microcrystalline cellulose (MCC), which has smaller particle size and larger particle porosity than virgin cellulose was chosen as a starting point of this study. In fact, MCC superior solubility generally accounts for improved chemical modification (Ohwoavworhua & Adelakun, 2007; Thoorens, Krier, Leclercq, Carlin, & Evrard, 2014). On the other hand, cellulose nanocrystals (CNC) displays a high specific surface area which is interesting for catalysis.

CNC functionalization is inherently different from the MCC functionalization method, because CNC cannot be solubilized and recrystallized in their original form, which means that the chemical modification is done in a heterogeneous medium on the surface of the polymer. Modification of the primary hydroxy groups on the cellulose surface for grafting of TBD was carried out in two steps (Fig. 2). At first, (1) the tosyl group selectively attacks the primary alcohols transforming them into tosylated alcohols, improving their reactivity and making them more able to participate in various subsequent chemical reactions. Then (2) the nucleophilic substitution with excess TBD is carried out.

## 3.2. Catalysts characterization

### 3.2.1. DRIFT analysis

The presence of diagnostic S=O and C=N stretching bands allows to conveniently assess cellulose modification by infrared spectroscopy before further analysis. DRIFT spectra of MCC, Tosyl-MCC and TBD-MCC are shown in Fig. 3-a. The characteristics signals of native cellulose are observed at 3420, 2912, 1630, 1371, 1175, 1041, and 902 cm⁻¹. The bands at 3420 cm⁻¹ and 2912 cm⁻¹ arise from the stretching vibration of the O—H and C—H groups, respectively (Abdelkafi et al., 2011; Owen & Thomas, 1989; A. Pandey, Kalamdhad, & Chandra Sharma, 2023), whereas the peak at 1630 cm⁻¹ corresponds to the bending mode of absorbed water (El Idrissi, Belachemi, Merle, Zinck, & Kaddami, 2022), the band at 1371 cm⁻¹ is attributable to deformation vibrations of C—H (Adel, El-Wahab, Ibrahim, & Al-Shemy, 2010; Owen & Thomas, 1989; K. K. Pandey & Pitman, 2003). C-O-C at glycosidic linkage correlates to the band at 1175 cm⁻¹ (Oh, Yoo, Shin, & Seo, 2005). C—O of secondary alcohols vibration produces a significant peak at 1041 cm⁻¹ (G. Hu, Cateto, Pu, Samuel, & Ragauskas, 2011; Schwanninger, Rodrigues, Pereira, & Hinterstoisser, 2004). Between sugar units, β-glucosidic linkages exhibit a band at 902 cm⁻¹ (Oh et al., 2005).

Infrared studies of the tosylated MCC samples, present new bands characteristic of tosyl moiety. The C=C stretching of p-substituted benzene ring at 1598 cm⁻¹. In addition to symmetric C-O-S elongation vibration at 814 cm⁻¹, asymmetric and symmetric O=S=O stretching vibration are observed at 1365 cm⁻¹ and 1175 cm⁻¹ respectively (Heinze, Rahn, Jaspers, & Berghmans, 1996; Heinze & Rahn, 1997; Y. J. Hu et al., 2019; Rahn et al., 1996).

After reaction with TBD, the characteristic tosyl absorbance bands disappear. At the same time, the appearance of a new band at 1670 cm⁻¹ is attributed to the C=N stretching vibrations of TBD (Santos et al., 2015).

DRIFT spectra of CNC, Tosyl-CNC and TBD-CNC are presented in Fig. 3-b. Tosylated cellulose nanocrystals (Tosyl-CNC) exhibit symmetric and asymmetric sulfonyl stretching vibrations O=S=O at 1165 cm⁻¹ and 1360 cm⁻¹, respectively. C-O-S elongation vibrations are observed at 815 cm⁻¹, and the aromatic structure of the tosyl group in the sample is confirmed by the absorption bands at 1575 cm⁻¹ (Seyednejhad et al., 2019). After TBD grafting, a new absorption peak appears at 1670 cm⁻¹ (Santos et al., 2015) related to the C=N stretching vibration with

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 3. DRIFT spectra of (a) MCC, Tosyl-MCC and TBD-MCC (b) CNC, Tosyl-CNC and TBD-CNC.</figcaption></figure>
complete loss of the vibrational bands associated to tosylated precursor.

### 3.2.2. ¹³C CP MAS NMR

To further characterize the intermediate and final products of cellulose modification processes, ¹³C CPMAS NMR studies were performed (Fig. 4).

The solid state ¹³C NMR spectra of all samples show common characteristic chemical shifts of the cellulose chain carbons (Brisola et al., 2022; Van Zyl et al., 2023). C6 position of the anhydroglycose rings lead to signals between 63 and 65 ppm. C2, C3, and C5, which have identical chemical environments, appear in the range between 71 and 75 ppm (Meza-Contreras, Manriquez-Gonzalez, Gutiérrez-Ortega, & Gonzalez-Garcia, 2018). In addition, C4 and C1 have chemical shifts at 82–89 ppm and 105 ppm, respectively (Oliveira et al., 2015). Moreover, it is worth noting that the sharpest peaks of C6' and C4' at 65 ppm and 88 ppm, respectively correspond to the crystalline portions of cellulose, while the resonance for C6 and C4 domains at 63 ppm and 84 ppm are attributable to amorphous regions (Groszewicz et al., 2020; Trache, Donnot, Khimeche, Benelmir, & Brosse, 2014).

In the native MCC spectrum, only signals between 110 and 60 ppm are visible (Fig. 4-a). After the tosylation reaction the ¹³C CPMAS NMR spectrum shows additional signals that confirm the presence of tosylate substituents (Fig. 4-a). The peak at 145 ppm can be attributed to the carbon in α of the sulfur; resonances of the ortho and meta carbon atoms in the aromatic ring are observed as a broad signal centered at 129 ppm with a slight shoulder at 135 ppm attributed to the methyl ipso carbon. The signal at 21 ppm is attributed to the carbon atom of the methyl group. These spectroscopic features are consistent with the ¹³C NMR spectrum of tosylated cellulose obtained by Tarchoun et al. and Groszewicz et al. (Groszewicz et al., 2020; Tarchoun, Trache, Klapötke, & Krumm, 2020). Finally, the ¹³C CP-MAS NMR spectrum of the TBD-MCC samples reveals the clear emergence of three additional peaks at 21 ppm, 39 ppm and 49 ppm, which correspond to the carbon atoms of the TBD moiety (Batagarawa & Adam, 2016). Carbon 7 is less easily identified (please note that the introduction of nitrogen is confirmed by elemental analysis in the next paragraph). The absence of residual tosylate resonances supports the effective nucleophilic displacement of C6 tosylate groups with TBD fragments.

Besides the obvious tosyl and TBD signatures, the ¹³C CPMAS NMR spectra of functionalized cellulosic materials shows additional changes compared to the unmodified MCC. Fig. 4-a shows a slight decrease in the intensities of crystalline regions C6' and C4' at 65 ppm and 88 ppm, respectively. This decrease of the crystallinity of the modified polymer may be explained either by partial depolymerization of the crystalline parts of the cellulose or by weaker adjacent chain interaction arising from the chemical modification limiting H bonding (Da Silva Filho, Santana, Melo, Oliveira, & Airoldi, 2009; Silva Filho et al., 2013).

Overall, DRIFT and NMR spectra are consistent with the complete reaction of tosylate functions to provide TBD modified cellulose after a nucleophilic attack. Owing the relatively soft reaction conditions the tosylate functions observed are expected to arise only from the reaction of tosyl chloride with primary alcohols as reported in the literature (Dadkhah Tehrani & Basiryan, 2015; El-Sayed, El-Sakhawy, Hesemann, Brun, & Kamel, 2018; Feese et al., 2011; Groszewicz et al., 2020; Sadeghifar et al., 2011; Seyednejhad et al., 2019; Tarchoun et al., 2020; Tehrani & Neysi, 2013). According to Tarchoun et al., cellulosic materials that have been tosylated to a degree of substitution lower than 1, contain only primary tosyl and can be easily and completely eliminated by nucleophilic attack SN (Tarchoun et al., 2020). It is important to mention that amines readily attack primary tosylate functions whilst nucleophilic displacement reaction does not occur with cellulose secondary tosylates (Rahn et al., 1996; Schmidt et al., 2014).

The ¹³C CP MAS NMR spectrum of the tosylated CNC (Fig. 4-b) shows characteristic changes after chemical functionalization. At 22 ppm and 129–135 ppm, additional signals corresponding respectively to the methyl carbon and the aromatic carbons are detected (Heinze & Rahn,

1997; Salama, Saleh, Cruz-Maya, & Guarino, 2023). After grafting, signals characteristic of grafted TBD can be seen at 21 ppm, 39 ppm and 49 ppm (Batagarawa & Adam, 2016; Meimoun et al., 2020) and the disappearance of the characteristic chemical shifts of the tosyl group are observed in the ¹³C CP MAS NMR spectrum of TBD-CNC (Fig. 4-b). This information allows us to highlight the successful nucleophilic substitution of the C6 tosylate groups with the TBD moieties. The DRIFT and NMR spectra provide conclusive evidence that the synthesis of the TBD-CNC was successful.

### 3.2.3. Elemental analysis

The values of the sulfur and nitrogen contents determined by elemental analysis are provided in Table 1. They were used to calculate the degrees of substitution of the TBD samples and their tosylated precursors, using the following equations (Tarchoun et al., 2020):

$$DS(\text{Tosyl}) = (\%S*M\_AGU)/(M*S*100 - (\%S*M\_Tosyl)) \quad (1)$$

$$DS(\text{TBD}) = (\%N*M\_AGU)/(\ll 3M\rr *100 - (\%N*M\_TBD)) \quad (2)$$

where MAGU is the molar mass of anhydroglycose unit (162 g/mol), Ms and Mn are the molar masses of sulfur and nitrogen atoms, respectively. The molar masses of the tosyl and TBD groups are MTosyl and MTBD, respectively.

DRIFT and NMR data do not allow to access to a fine quantification neither of the number of tosyl nor of TBD per anhydroglucose unit. However, elemental analysis that gives access to the wt% of sulfur (S) and nitrogen (N) may lead to an accurate degree of substitution for fully dried material. After chemical modification of MCC, it was found that the S content of Tosyl-MCC and the N content of TBD-MCC were 9.37 % and 11.42 % respectively. Therefore, using the equation reported by Tarchoun et al. (Tarchoun et al., 2020) the degree of substitution was calculated to be 0.87 for Tosyl-MCC and 0.71 for TBD-MCC (Table 1). These outcomes are comparable to those found in earlier investigations where ethylenediamine were grafted onto the surface of MCC as in Heinze et al. (DS Tosyl = 0.92 and DS Amine = 0.74) (Heinze, Pfeifer, Koschella, Schaller, & Meister, 2016), and Groszewics et al. (DS Tosyl = 0.92 and DS Amine = 0.74) (Groszewicz et al., 2020).

According to the results of the elemental analysis, sulfur (S) and nitrogen (N) atoms are absent from the unmodified CNC. The elemental analysis revealed that S and N contents of Tosyl-CNC and TBD-CNC were 2.46 % and 3.24 % respectively, giving a DS value of 0.14 for both compounds. This confirms that all tosyl groups have been replaced by TBD groups. TBD was grafted onto almost all primary hydroxy groups on the CNC surface, as shown by the comparison of the DS value with the theoretical maximum value of surface primary hydroxy groups (14.5 %) (Feese et al., 2011; Sadeghifar et al., 2011).

These outcomes show that the surface primary alcohol substitutions to tosyl and TBD produced by the chemical functionalization method described in this work are comparable to those reported in previous works who have grafted azide onto the surface of CNC, such as Sadeghifar et al. (DS = 0.15) (Sadeghifar et al., 2011), and Feese et al. (DS = 0.14) (Feese et al., 2011).

### 3.2.4. XRD analysis

The degree of crystallinity of cellulose materials depends on several factors, including the source of the cellulose and the processing methods used to isolate and purify the material (Sikhosana, Gumede, Malebo, Ogundeji, & Motloung, 2023). XRD analysis was used to describe the crystal structures of the MCC before and after chemical modification. As shown in Fig. 5-a, the XRD diffraction patterns of the aminated, tosylated and unmodified samples reveal the typical diffraction peaks of the cellulose I allomorph detected at values around 15.24°, 16.32°, 22.55° and 34.63°, which are related to the (110), (1 1̄ 0), (200) and (0 0 4) crystallographic planes, respectively (Tarchoun et al., 2020). However, the relative intensities of the peaks are impacted by the surface
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /><figcaption>Fig. 4. ¹³C CP MAS NMR spectra of (a) MCC, Tosyl-MCC and TBD-MCC (b) CNC, Tosyl-CNC and TBD-CNC.</figcaption></figure>
<table><caption>**Table 1**

Elemental analysis, DS and crystallinity index of cellulosic materials.</caption><thead><tr><th>Cellulosic materials</th><th>% C</th><th>% H</th><th>% N</th><th>% S</th><th>Substitution degree (Tosyl)</th><th>Substitution degree (TBD)</th><th>Crystallinity index (%)</th></tr></thead><tbody><tr><td>MCC</td><td>41.95</td><td>6.41</td><td>0</td><td>0</td><td>-</td><td>-</td><td>79.3</td></tr><tr><td>Tosyl-MCC</td><td>46.92</td><td>5.43</td><td>0</td><td>9.37</td><td>0.87</td><td>-</td><td>64.0</td></tr><tr><td>TBD-MCC</td><td>40.2</td><td>5.15</td><td>11.42</td><td>0</td><td>-</td><td>0.71</td><td>68.3</td></tr><tr><td>CNC</td><td>40.36</td><td>6.41</td><td>0</td><td>0.75</td><td>-</td><td>-</td><td>66.6</td></tr><tr><td>CNC<sup>a</sup></td><td>41.95</td><td>6.57</td><td>0</td><td>0</td><td>-</td><td>-</td><td>65.3</td></tr><tr><td>Tosyl-CNC</td><td>42.83</td><td>6.17</td><td>0</td><td>2.46</td><td>0.14</td><td>-</td><td>64.2</td></tr><tr><td>TBD-CNC</td><td>42.28</td><td>6.72</td><td>3.24</td><td>0</td><td>-</td><td>0.14</td><td>64</td></tr><tr><td>TBD-CNC<sup>b</sup></td><td>42.41</td><td>6.77</td><td>3.22</td><td>0</td><td>-</td><td>0.14</td><td>64.5</td></tr></tbody></table>

<figure><img src="image_11.png" /><figcaption>(b)</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Fig. 5.** XRD spectra of (a) MCC, Tosyl-MCC and TBD-MCC (b) CNC, Tosyl-CNC and TBD-CNC.</figcaption></figure>

modification. Still, these results suggest that the primary crystal form of the cellulose allomorph is not totally affected by the tosylation and TBD grafting procedures used because the crystal structure of cellulose is mainly determined by the arrangement of the glucose units. XRD result as a function of the chemical treatments are similar to those described in earlier researches (Da Silva Filho et al., 2009; Tarchoun et al., 2020). Furthermore, it can be seen on Fig. 5-a that, MCC compared to the

tosylated and aminated MCC samples, the pristine samples shows better resolved 1 1 0 and 1 1 − 0 peaks as well as a better defined 2 0 0 peak. In order to quantify the variation in the crystallinity of cellulose after chemical modification, the crystallinity degree of cellulose is calculated according to Segal et al. equation (Eq. (3)) (Segal, Creely, Martin, & Conrad, 1959).

$$ \text{Cr} \cdot \text{I} (\%) = (I_{200} - I_{\text{am}})/I_{200} \quad (3) $$

I$_{002}$: maximum intensity of (002) plane at 2θ = 22.55°

I$_{am}$: the intensity of the background scatter measured at 2θ = 18°

According to the results summarized in Table 1, the crystallinity indices of the various MCC samples are respectively, 79.30 %, 64.04 % and 68.31 % for MCC, Tosyl-MCC, and TBD-MCC. This finding is consistent with the solid state NMR spectra. As discussed above, the lower crystallinity degree found when tosyl groups are added to cellulose can be explained by the fact that tosyl groups disrupt the regular arrangement of the cellulose chains in the resulting material. In other words, OH substitution interferes with the formation of hydrogen bonds between the cellulose chains, which are responsible for the ordered crystalline structure of cellulose (Kovalenko, 2010; Tarchoun et al., 2019; Trache & Tarchoun, 2019; Wohlert et al., 2022). Overall, the activation of the hydroxy functions by tosyl during the functionalization process disturbs the inter and intramolecular hydrogen bonding of the cellulose chains and consequently the degree of crystallinity of the cellulose decreases. This result is in line with what was reported by Tarchoun et al. (Tarchoun et al., 2020) and Bezerra et al. (Bezerra et al., 2017). Additionally, it was found that the amine samples exhibit higher crystallinity indices than their tosylated precursors, suggesting that the increase in crystallinity is produced by the nucleophilic displacement of the tosylate functions by the TBD functions. Probably the cause of this finding is that the unreacted hydroxy groups and amine functions of the TBD moieties contribute to intramolecular and intermolecular hydrogen bonding interactions and give rise to more ordered structural configurations that allow for higher crystallinity. Overall, DRIFT, ¹³C solid-state NMR, elemental analyses and XRD analysis are consistent with a controlled modification of the cellulose.

The crystal structures of the CNC before and after the chemical functionalization were characterised by XRD analysis. As shown in Fig. 5-b, the aminated, tosylated, and unmodified samples XRD diffraction patterns showed typical cellulose I diffraction peaks at 2θ values around 14.8°, 16.3°, 22.5°, and 34.5°, respectively, which are associated to the (1 1 0), (1 ¯ 1 0), (2 0 0), and (0 0 4) crystallographic planes (French, 2014; Gong, Li, Xu, Xiang, & Mo, 2017; SriBala, Chen-nuru, Mahapatra, & Vinu, 2016). Fig. 5-b shows that CNC retains its primary crystal structure during chemical functionalization.

The results obtained (Table 1) show that the crystallinity rates of the different cellulose I samples before and following chemical functionalization are 66.6 %, 65.3 %, 64.2 %, 64 % for CNC, CNC after treatment with NaOH, Tosyl-CNC and TBD-CNC respectively. The slightly lower crystallinity ratio after functionalization is in agreement with the presence of a grafted moieties. The overall crystallinity of CNC is preserved after the chemical modifications.

<footnote>a After treatment with NaOH.</footnote>

<footnote>b After the fifth catalytic cycle.</footnote>
### 3.3. Catalytic performance of TBD-CNC

The catalytic activity of the prepared materials was assessed in CO₂ epoxide cycloaddition reactions. Styrene oxide was used as benchmark to determine the optimal reaction conditions. The influence of temperature, CO₂ pressure and reaction time on the conversion and product selectivity were studied.

#### 3.3.1. Optimization of the reaction

TBD related organocatalysts have been reported to perform in cycloaddition from 100 to 150 °C depending on the system. Co-catalyst such as alkyl halide are efficient at 100 °C (Lim, Lim, & Jang, 2016)

whereas silica supported TBD without assistance of a co-catalyst shows moderate activity at 150 °C (Barbarini et al., 2003). The effect of reaction temperature on the cycloaddition reaction was thus studied by considering four different temperatures ranging from 90 to 150 °C. In order to evaluate the temperature effect, conversion was considered after 5 h of reaction time. The conversion increased from 17 % to 99.9 % as the temperature increased from 90 °C to 130 °C for a pressure of 20 bar, as shown in Fig. 6a. There was no remarkable difference in the percentage conversion when the temperature was increased from 130 °C to 150 °C. The selectivity towards styrene carbonate is total for all temperatures.

The CO₂ pressure is also known to play a role in the kinetic of

<figure><img src="image_13.png" /><figcaption>**Fig. 6.** Styrene oxide conversion in styrene carbonate with TBD-CNC catalyst as a function of (a) temperature & (b) CO₂ pressure, (c) conversion as a function of time with TBD-CNC, TBD-MCC and mTBD catalyst.</figcaption></figure>
cycloaddition. Typical reaction conditions are situated between 10 and 50 bar (Zhang et al., 2006). Fig. 6b shows the changes in styrene oxide conversion after 5 h of reaction time at 130 °C using various CO₂ pressures ranging from 5 bar to 50 bar. Styrene oxide conversion increased with increasing CO₂ pressure until complete conversion was reached in the reaction conditions. The CO₂ pressure does not influence the selectivity with no trace of oligomers observed. As such, in 5 h at 5 bar of CO₂ pressure around 85 % of the substrate was converted. Full conversion, in the reaction conditions, was reached when 20 bar of CO₂ was used.

In order to assess both the impact of heterogenization of the TBD and the effect of the remaining hydroxy groups of the support on the catalytic activity, methyl TBD (mTBD) was used. Kinetic experiments represented on Fig. 6-c reveal that the catalytic activity of the homogeneous mTBD catalyst is lower than that of the heterogeneous TBD-CNC & TBD-MCC catalysts under the same reaction conditions. This suggests that cellulose played an important role in the reaction, as previously reported (Liang et al., 2011; Sun et al., 2014). Reference reactions provided in the appendix as Table A1 shows that the reaction did not occur using cellulose alone, and that TBD led to a lower conversion. TBD-CNC, showed the highest catalytic activity among the catalysts used. The small difference in comparison to TBD-MCC may be due to a combination of differences in specific surface area and the availability of TBD which are all on the open surface of CNC, which facilitates their contact with the epoxide in the reaction medium while in the case of TBD-MCC, a large proportion of the TBD are immobilised on the inner cellulose chain and are therefore less accessible for reaction. In addition, TBD-CNC and TBD-MCC were easily recovered after the reaction by centrifugation filtration, and were subjected to reuse for several cycles as discussed below.

The comparison of the TBD-CNC catalysts with the silica supported TBD system reported in the literature for the cycloaddition of styrene oxide to CO₂ (Barbarini et al., 2003) is provided in Table 2. TBD-CNC leads to full conversion in 5 h at a CO₂ pressure of 20 bar under a temperature of 130 °C, which are also smoother conditions.

### 3.3.2. Recyclability of the catalyst

Taking advantage of the high catalytic activity and the ease of separation from the reaction medium, the air and moisture stable heterogeneous CNC-TBD catalyst was subjected to a recycling study. Five reaction cycles, accompanied, at each cycle, with non-destructive characterization techniques such as DRIFT and XRD were performed. After each cycle the nanocatalyst was separated by centrifugation and washed several times with ethanol followed by thorough drying. In order to evaluate the catalytic activity and the eventual deactivation of the recycled catalysts, the cycloaddition reaction was stopped after 2 h at 20 bar CO₂, which correspond to a conversion of ca. 75 % for the fresh catalyst. The nanocatalyst demonstrated high reusability, it can be recycled up to five times without any significant loss of its catalytic activity as shown in the Fig. 7a. The selectivity remains total for the cycloaddition product (see Fig. A2 in the appendix). The DRIFT spectra presented in Fig. 7b show that the nanocatalyst after the 1st, 3rd and 5th cycle did not change compared to the fresh catalyst. Notably, the C≡N stretching band of the TBD can still be observed. In addition, the liquid NMR spectra of the crude products did not show any trace of free TBD. Elemental analysis performed at the end of the fifth cycle and after washing and drying reveals a nitrogen content similar to the fresh catalyst, further demonstrating the lack of TBD release during the course of the catalysis (Table 1). In addition, XRD analyses (Fig. 7c) revealed

well-conserved structure and shape. The recycled catalysts generally presented crystallinity degrees close to those of fresh catalyst, indicating the stability of cellulose support in the reaction system (Table 1).

### 3.3.3. Extension of the scope to other epoxides

The scope was extended to other epoxides and the results are compiled in Table 3. The catalyst proved to be suitable for both mono- and di-substituted epoxides studied, providing the cyclic carbonates with a full selectivity in high yields. Epichlorydrin, bearing an electron withdrawing group led to the highest activity with 99.9 % conversion and selectivity to carbonate after 3 h reaction time, and 86 % after 2 h. This is probably to be ascribed to a more electrophilic character of the carbon in β of the chlorine atom. Due to the steric hindrance 3,3-dimethyl epoxybutane is the least reactive. Extended reaction times were required to obtain higher yield. Note that despite the low reactivity of the substrate, the high stability of the catalysts account for the overall good yield at long reaction time.

## 4. DFT study of the reaction mechanism

### 4.1. Description of the different possible mechanisms

Several mechanisms can be considered for the cycloaddition of CO₂ to epoxide catalyzed by a N-heterocyclic base / cellulose combination. As discussed previously, cellulose is thought to co-activate the reaction, mainly via H-bonds of its hydroxy groups with the epoxide oxygen (Liang et al., 2011; Sun et al., 2014).

A nucleophilic attack of TBD on the so-activated epoxide may then proceed, in a similar way to that proposed with KI (Liang et al., 2011). After this, an alkyl carbonate anion is created by the interaction of the oxygen anion of the open epoxide ring with CO₂, which is then transformed into the corresponding cyclic carbonate by the ring closure process (Fig. 8).

Heterocyclic nitrogen bases such as TBD and DBU are also known to interact with CO₂ (Villiers, Dognon, Pollet, Thuéry, & Ephritikhine, 2010). In this sense, a mechanism involving an activation of CO₂ by DBU has been proposed (Sun et al., 2014) for a DBU / cellulose system. An alternative to mechanism 1 may be inspired from that, presented as mechanism 2 in Fig. A4 in the appendix. However, in our case this co-activation seems unlikely because the grafted TBD has limited mobility. In addition, Dielmann and co-workers have shown that mTBD cannot form a stable CO₂ adduct owning to the presence of steric congestion caused by the presence of the methyl substituent (Wilm et al., 2019).

Lu et al. reported that DBU can react with cellulose in the presence of carbon dioxide, leading to the formation of a cellulose carbonate ionic compound. This occurs via deprotonation of surface hydroxy by DBU to produce Cellulose-O⁻ anions and [DBU-H]⁺ as the counter cation. The former attack carbon dioxide to produce carbonate anions (Cellulose-OCOO⁻) (Fig. 9) (Lu et al., 2021; C. G. Wang et al., 2022).

In our case, we may have a mechanism that forms cellulose carbonate as an intermediate product. The activated epoxide then undergoes nucleophilic attack by the cellulose carbonate, resulting in the formation of a new carbon-oxygen bond and the opening of the epoxide ring. This step generates an alkoxide intermediate, the alkoxide intermediate subsequently undergoes a ring closing reaction, forming a new carbonate ring (Fig. 10).

<table><caption>**Table 2**
Comparison of the catalytic performance of TBD-CNC nanocatalyst in cycloaddition reaction of styrene oxide with other reported system.</caption><thead><tr><th rowspan="2">Catalyst</th><th colspan="6">Reaction conditions</th><th rowspan="2">Ref.</th></tr><tr><th>% catalyst</th><th>Solvent</th><th>Temperature (°C)</th><th>Pression (Bar)</th><th>Reaction time (h)</th><th>Conversion (%)</th></tr></thead><tbody><tr><td>TBD-Silica</td><td>4</td><td>CH<sub>3</sub>CN</td><td>150</td><td>50</td><td>70</td><td>90</td><td>(Barbarini et al., 2003)</td></tr><tr><td>TBD-CNC</td><td>3</td><td>CH<sub>2</sub>Cl<sub>2</sub></td><td>130</td><td>20</td><td>5</td><td>99.9</td><td>This work</td></tr></tbody></table>
<figure><img src="image_14.png" /><figcaption>Fig. 7. (a) Styrene oxide conversion in styrene carbonate as a function of the number of cycles (TBD-CNC catalyst - 2 h at 20 bar CO₂) (b) FT-IR spectrum of recovered nanocatalyst after recycling (c) XRD spectrum of recovered nanocatalyst after recycling.</figcaption></figure>

Guo et al. (Guo, Liang, & Jiao, 2021) have studied the mechanisms of CO₂ cycloaddition to epichlorohydrin with salophene as an organo-catalyst. The most kinetically favorable pathway involves a bi-activation, with phenolate as a nucleophile and phenol as an H-bond donor in epoxide ring opening and CO₂ addition. In our case, the concept that TBD could deprotonate cellulose seems reasonable given that TBD is commonly used as a deprotonating agent in chemical synthesis (Qiao et al., 2020; Xia et al., 2023). The bi-activation both by hydroxy group and alkoxyde anion of the cellulose on the opening of the epoxide ring may be the origin of the higher catalytic activity of TBD-CNC. A carbon of the epoxide is nucleophilically attacked by an O⁻ of the cellulose while another OH hydroxy acts as a hydrogen bond donor for the oxygen

of the epoxide. Then, CO₂ and the oxygen anion of the opened epoxide ring interact to generate an alkyl carbonate. Finally, cyclic carbonate is formed by the process of closing the cycle and simultaneously regenerating the catalyst (Fig. 11). However, this mechanism has been proposed for acidic phenol derivative and not for a more basic primary alcohol.

## 4.2. DFT results

The 3 discussed mechanisms were studied by density functional theory (DFT) calculation. All calculations were carried out using the Gaussian 16 software package, Revision B.01 (Frisch et al., 2016). Detailed computational procedures are provided in the Supporting
<table><caption>**Table 3**

Cycloaddition of CO₂ to epoxides catalyzed by the TBD-CNC nano catalyst. Reaction conditions: epoxide (1 mL), TBD-CNC (3 %), CH₂Cl₂ (1.5 mL), 130 °C, 20 bar.</caption><thead><tr><th>Epoxide</th><th>Product</th><th>Conversion (%)</th><th>Reaction time (h)</th></tr></thead><tbody><tr><td>CH₂Cl</td><td>CH₂Cl</td><td>86<br>99.9</td><td>2<br>3</td></tr><tr><td>Ph</td><td>Ph</td><td>84</td><td>3</td></tr><tr><td>OPh</td><td>OPh</td><td>80</td><td>3</td></tr><tr><td>tBu</td><td>tBu</td><td>80<br>72</td><td>20<br>60</td></tr></tbody></table>

Information. The energy profile of MEC 1 is illustrated in Fig. 12a, while Fig. 8 describes the proposed mechanism. The reaction in the MEC1 progresses with three transition states. The first step, with a barrier of 28.2 kcal/mol corresponds to a catalyzed activated nucleophilic attack of a TBD nitrogen of one of the epoxide carbon atoms. As hypothesized, a hydroxy hydrogen of the nearby cellulose row activates the oxygen atom of the epoxide through hydrogen bonding (O···HO bond distance = 1.585 Å) promoting the nucleophilic attack of TBD on a

β-carbon atom of the epoxide ring (N—C distance = 1.951 Å in the TS1_1), leading to the ring-opening of the epoxide.

The intermediate INT1_1, which possesses a reactive O⁻, is stabilized by hydrogen bonding with the cellulose hydroxy (O⁻ - H distance 1.379 Å) slightly elongating the hydroxy bond (H—O distance 1.083 Å) and conducts a nucleophilic attack on CO₂. It is conceivable that a CO₂ molecule interacts with the cellulose ring, including hydrogen bonding with a hydroxy, thus activating the CO₂ molecule. The nucleophilic attack on CO₂ produces the alkyl carbonate compound INT1_2. This step, through TS1_2, corresponds to a faint barrier of 0.3 kcal/mol.

The intermediate INT1_2 undertakes an internal rotation releasing the hydrogen bond with the methoxy and a subsequent intramolecular ring-closure follows through TS1_3, with the formation of a cyclic carbonate (O—C distance = 2.153 Å in the TS) that is simultaneously liberated (N—C distance = 2.225 Å in the TS), and the catalyst is regenerated. This final step constitutes the limiting step for this mechanism, with a considerable barrier of 60.2 kcal/mol.

Considering the MEC 3, represented by Fig. 11, the corresponding energy profile is depicted in Fig. 12b. In this mechanism, the incorporation of an additional cellulose ring proved necessary, as its hydroxy groups play a crucial role in certain steps.

The catalyzed CO₂ capture by the cellulose occurs by the conversion of an alcohol group into a carbonate, with the transfer of the hydroxy hydrogen atom to an adjacent catalyst TBD nitrogen. A hydrogen bond between the TBD nitrogen and the hydroxy hydrogen (N—H distance = 2.108 Å, INT3_1) activates the hydroxy oxygen that captures the CO₂ molecule. The corresponding energy barrier is 21.4 kcal/mol (TS3_1).

This transferred hydrogen atom promotes a hydrogen bonding interaction between the TBD catalyst and the same oxygen (H—O distance = 1.864 Å, TS3_2) constituting the driving force for the following epoxide ring opening through TS3_2. The barrier height of 44.3 kcal/mol is the rate-limiting step of this mechanism.

The ring-opened negatively charged intermediate INT3_2 is a highly reactive species and it is stabilized by hydrogen bonding with a hydroxy group of a neighbour cellulose ring (OH distance = 1.324 Å) giving rise to a slightly elongated hydroxy bond (1.107 Å compared to 0.973 Å) and

<figure><img src="image_15.png" /><figcaption>**Fig. 8.** Mechanism 1 with epoxide activation by CNC and nucleophilic attack of grafted TBD.</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>Fig. 9. Formation of ionic cellulose carbonate.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. 10. Mechanism 3 with epoxide activation by CNC and formation of a cellulose carbonate moieties.</figcaption></figure>

is finally stabilized by attacking the carbonyl carbon, thus closing the carbonate ring through a small energy barrier of 9.3 kcal/mol relative to the adduct, with the formation of **INT3_3**. This intermediate, featuring an elongated O—C bond of 1.444 Å, readily breaks apart into its constituent products via the transition state **TS3_4**, presenting a barrier of 13.6 Kcal.mol⁻¹, ultimately yielding the reaction products and regenerating the TBD catalyst.

Finally, in MEC 4 (Fig. 12c) the reactions initiate with the epoxide ring opening by the catalyzed activated cellulose hydroxy trough **TS4_1**, producing the zwitterionic intermediate **INT4_1**. A barrier height of 47.6 kcal/mol for the initial step is the rate-limiting step of this mechanism. The intermediate formed is not thermodynamically very stable possessing an elongated hydroxy bond (1.055 Å) that shares a hydrogen bond with the TBD catalyst. In a subsequent step, the shared proton migrates to the adjacent TBD catalyst through a minimal barrier (**TS4_2**).

Again, a negatively charged intermediate **INT4_2** is formed that conducts a nucleophilic attack on the CO₂ molecule producing the intermediate **INT4_3**. Searches for a transition structure for this process

were unsuccessful. In MEC 1, for a similar CO₂ molecule capture a very small barrier was found. This suggests that the related process involves an insignificant barrier (or corresponds to a barrierless process).

In the final step, in a concerted mode (**TS4_3**), the terminal negatively charged oxygen performs a nucleophilic attack on the C6 carbon resulting in the formation of the reaction cyclic carbonate product that is liberated, while the proton migrates back to the cellulose hydroxy with the regeneration of the TBD catalyst.

In conclusion, regarding the energies associated to the rate determining steps, the more probable mechanisms are MEC 3 and MEC4. If the very small difference, with 44.3 and 47.6 kcal/mol, respectively, does not allow to clearly differentiate, a common feature is the formation of an anionic species from one of the reactants linked to the cellulose. The so formed carbonate anion or alkoxide operates a nucleophilic attack on the epoxide or CO₂, respectively, to form the cyclic carbonate.

Finally, as experimental evidences of the mechanism, we provide (i) the interaction between cellulose-OH and mTBD by FTIR (see Fig. A5) and (ii) an NMR study of a mixture of isopropyl alcohol as a model alcohol and mTBD (Fig. A6 and A7). Regarding FTIR, the C≡N
<figure><img src="image_18.png" /><figcaption>Fig. 11. Mechanism 4 with epoxide activation by synergistic effect of CNC.</figcaption></figure>

stretching band of the base shifts to 1627 cm⁻¹, and the broad O—H stretching band around 3300 cm⁻¹ in MCC shows reduced intensity in the MCC-mTBD spectrum. This shift in the imine band, coupled with the decreased intensity of the O—H band, confirms the deprotonation of cellulose hydroxy groups and the subsequent formation of the cellulose alkoxide anion. Regarding NMR model study, the disappearance of the OH signal of isopropyl alcohol in the isopropyl alcohol-mTBD mixture, combined with the broadening and shifting of the -CH(CH₃)₂ signals may be an indication of the formation of an alcoholate ion (-RO⁻). ¹³C NMR also provides some insights. The chemical shift for the carbon attached to OH of the isopropyl alcohol around 63-64 ppm is clearly visible in the mixture, as well as the shift in mTBD signals, specifically a shift in the imine carbon (151-153 ppm) and the carbon near the imine (43-44 ppm), which showed slight changes that may indicate interactions.

## 5. Conclusion

We have reported in this contribution a novel selective, stable and recyclable heterogeneous nanocatalyst based on a natural product for the cycloaddition of CO₂ to epoxides to produce cyclic carbonates without the use of metals and halogens co-catalysts. TBD-CNC is synthesized in two steps. The tosylation of CNC surface hydroxy is necessary

to allow the coupling with the TBD guanidine. The reaction carried out with the so-formed heterogeneous nanocatalyst is faster than that carried out with the homogeneous mTBD, due to a co-activation of the epoxide via H-bond with cellulose hydroxys. It is also faster than that conducted using MCC as a support. The heterogeneous CNC based organo-catalyst can be easily recovered by simple filtration, allowing recycling for at least five times without significant loss of the catalytic activity. As such, our work confirms our starting hypothesis, i.e. grafting TBD as an organic base onto CNC surface does indeed combine the catalytic effect of the organic base with the hydrogen bond donor co-activation of cellulose together with the recyclability of heterogeneous catalysts for the cycloaddition reaction. Systems where the base is introduced with the cellulose are reported in the literature, as well as systems where the base is supported on a support that does not co-activate. Compared to the literature, our system combines the co-activation of the cellulose support with the possibility to be recycled. The system requires, as for common organocatalytic systems, a substantial loading.

DFT studies showed that the mechanism most probably occurs via formation of anionic species. The first alkoxide, formed by deprotonation of the cellulose by the grafted TBD, operates a nucleophilic attack on either CO₂ or the activated epoxide. The final cyclic carbonate is formed by a nucleophilic attack of either a carbonate anion or an
<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /><figcaption>**Fig. 12.** Energy profile (in kcal/mol), optimized transition state structures and relevant intermediates for MEC1 (a), MEC3 (b) and MEC4 (c). For clarity, cellulose atoms are depicted in green.</figcaption></figure>

alkoxide on the epoxide or CO₂, respectively. We believe that the results of this work will inspire the design of similar polysaccharides based catalytic systems for various reactions where co-activation by a hydrogen bond donor is an asset. Such catalyst may also be active for the ring-opening polymerization of heterocycle such as e.g. lactide.

CRediT authorship contribution statement

**Nouaamane El Idrissi:** Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis. **Hicham Ait-bella:** Writing – review & editing, Writing – original draft, Investigation, Formal analysis. **Nicolas Merle:** Writing – review & editing, Validation,
<figure><img src="image_21.png" /><figcaption>Fig. 12. (continued).</figcaption></figure>

Supervision, Formal analysis, Data curation, Conceptualization. **Frédéric Cazaux:** Writing – review & editing, Formal analysis, Data curation. **João P. Prates Ramalho:** Writing – review & editing, Writing – original draft, Validation, Methodology, Investigation, Formal analysis, Data curation. **Larbi Belachemi:** Writing – review & editing, Supervision, Methodology, Investigation, Formal analysis. **Hamid Kaddami:** Writing – review & editing, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis. **Philippe Zinck:** Writing – review & editing, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

## Funding source

This work was supported by the Franco-Moroccan bilateral programs administered by CAMPUS FRANCE, French Ministry of Foreign Affairs and CNRST Morocco under reference PHC TOUBKAL 45915RK. Chevreul Institute (FR 2638), Ministère de l'Enseignement Supérieur, de la Recherche et de l'Innovation (MESRI) and Région Hauts de France also partially supported this work as well as FCT – Foundation for Science and Technology, I.P. – under the projects UIDB/04449/2020 (HERCULES Lab) and UIDB/50006/2020 (LAQV-REQUIMTE).

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgments

Céline Delabre is gratefully acknowledged for the elemental

analyses.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.carbpol.2025.123762.

## Data availability

Data will be made available on request.

## References

Abdelkafi, F., Ammar, H., Rousseau, B., Tessier, M., El Gharbi, R., & Fradet, A. (2011). Structural analysis of alfa grass (Stipa tenacissima L.) lignin obtained by acetic acid/formic acid delignification. *Biomacromolecules, 12*(11), 3895–3902. https://doi.org/10.1021/BM2008179/SUPPL_FILE/BM2008179_S1_001.PDF

Adel, A. M., El-Wahab, Z. H. A., Ibrahim, A. A., & Al-Shemy, M. T. (2010). Characterization of microcrystalline cellulose prepared from lignocellulosic materials. Part I. Acid catalyzed hydrolysis. *Bioresource Technology, 101*(12), 4446–4455. https://doi.org/10.1016/j.BIORTECH.2010.01.047

Arbelaiz, A., & Orue, A. (2023). Walnut shells as cellulose nanocrystal source: Isolation procedure and properties characterization. *Biomass Conversion and Biorefinery, 14*(15), 1–9. https://doi.org/10.1007/S13399-023-03996-2.

Aresta, M., Dibenedetto, A., & Angelini, A. (2014). Catalysis for the valorization of exhaust carbon: From CO2 to chemicals, materials, and fuels. Technological use of CO2. *Chemical Reviews, 114*(3), 1709–1742. https://doi.org/10.1021/CR4002758./ASSET/IMAGES/CR4002758.SOCIAL.JPEG_V03.

Artz, J., Müller, T. E., Thenert, K., Kleinekorte, J., Meys, R., Sternberg, A., ... Leitner, W. (2018). Sustainable conversion of carbon dioxide: An integrated review of catalysis and life cycle assessment. *Chemical Reviews, 118*(2), 434–504. https://doi.org/10.1021/ACS.CHEMREV.7B00435/ASSET/IMAGES/MEDIUM/CR-2017-004352_0051.GIF

Aziz, T., Ullah, A., Fan, H., Ullah, R., Haq, F., Khan, F. U., ... Wei, J. (2021). Cellulose nanocrystals applications in health, medicine and catalysis. *Journal of Polymers and the Environment, 29*(7), 2062–2071. https://doi.org/10.1007/s10924-021-02045-1
Balas, M., Villanneau, R., & Launay, F. (2022). Bibliographic survey of the strategies implemented for the one-pot synthesis of cyclic carbonates from styrene and other alkenes using CO2 and green oxidants. *Journal of CO2 Utilization*, 65(May), 102215. https://doi.org/10.1016/j.jcou.2022.102215

Barbarian, A., Maggi, M., Mazzacani, A., Mori, G., Sartori, G., & Sartorio, R. (2003). Cycloaddition of CO2 to epoxides over both homogeneous and silica-supported guanidine catalysts. *Tetrahedron Letters*, *44*(14), 2931-2934. https://doi.org/10.1016/S0040-4039(03)00424-6

Batagarawa, & Adam, F. (2016). The chemical fixation of carbon dioxide by tetramethylguanidine and triazabicyclo dec-5-ene bases. *Chemsearch Journal*, 7(1), 25-31.

Bezerra, R. D. S., Leal, R. C., Da Silva, M. S., Morais, A. I. S., Marques, T. H. C., Osajima, J. A., ... Da Silva Filho, E. C. (2017). Direct modification of microcrystalline cellulose with ethylenediamine for use as adsorbent for removal amitriptyline drug from environment. *Molecules*, 22(11), Article 2039. https://doi.org/10.3390/molecules22112039

Brisola, J., Andrade, G. J. S., De Oliveira, S. A., Viana, R. M. R., De Sousa Faria Tischer, P. C., & Tischer, C. A. (2022). Covalent immobilization of lipase on bacterial cellulose membrane and nanocellulose. *Materials Research*, 25, Article e20210350. https://doi.org/10.1590/1980-5373-MR-2021-0350

Büttner, H., Longwitz, L., Steinbauer, J., Wulf, C., & Werner, T. (2017). Recent developments in the synthesis of cyclic carbonates from epoxides and CO2. *Topics in Current Chemistry 2017* 375:3, 375(3), 1-56. https://doi.org/10.1007/S41061-017-0136-5

Chen, J., Wu, X., Ding, H., Liu, N., Liu, B., & He, L. (2021). Tolerant bimetallic macrocyclic [OSO]type zinc complexes for efficient CO₂fixation into cyclic carbonates. *ACS Sustainable Chemistry & Engineering*, 9(48), 16210-16219. https://doi.org/10.1021/ACSSUSCHEMENG.1C05469/SUPPL_FILE/SC1C05469_S1001.PDF

Chen, Y., Garces, I. T., Tang, T., & Ayranci, C. (2021). Cellulose nanocrystals reinforced shape memory polymer cardiovascular stent. *Rapid Prototyping Journal*, 27(1), 37-44. https://doi.org/10.1108/RPJ-01-2020-0019/FULL/XML

Kokaja, M., Wilhelm, M. E., Antholer, M. H., Herrmann, W. A., & Kühn, F. E. (2015). Synthesis of cyclic carbonates from epoxides and carbon dioxide by using Organocatalysts. *ChemSusChem*, 8(15), 2436-2454. https://doi.org/10.1002/CSSC.201500161

Da Silva Filho, E. C., Santana, S. A. A., Melo, J. C. P., Oliveira, F. J. V. E., & Airoldi, C. (2009). X-ray diffraction and thermogravimetric data of cellulose, chlorodeoxycellulose and aminodeoxycellulose. *Journal of Thermal Analysis and Calorimetry*, 100(1), 315-321. https://doi.org/10.1007/S10973-009-0270-6

Dadkhah Tehrani, A., & Basiryan, A. (2015). Dendronization of cellulose nanowhisker with cationic hyperbranched dendritic polyamidoamine. *Carbohydrate Polymers*, 120, 46-52. https://doi.org/10.1016/j.carbpol.2014.12.004

Dai, W., Mao, J., Liu, Y., Mao, P., Luo, X., & Zou, J. (2019). Commercial polymer microsphere grafted TBD-based ionic liquids as efficient and low-cost catalyst for the cycloaddition of CO 2 with epoxides. *Catalysis Letters*, 149(3), 699-712. https://doi.org/10.1007/S10562-018-02650-1

Doustkhah, E., Bagban, A., Assadi, M. H. N., Luque, R., & Rostamnia, S. (2019). Mesoporous SBA-15/PIDA as a dendrimer Zwitterionic amino acid-type Organocatalyst for three-component Indazolazepazine synthesis. *Catalysis Letters*, 149(2), 591-600. https://doi.org/10.1007/s10562-018-2643-6

El Aouni, N., López Redondo, C., Yeamin, M. B., Aghmiz, A., Reguero, M., & Masdeul-Bulto, M. A. (2023). Influence of structural properties of zinc complexes with N4-donor ligands on the catalyzed cycloaddition of CO2 to epoxides into cyclic carbonates. *Molecular Catalysis*, 538, Article 112992. https://doi.org/10.1016/j.mcat.2023.112992

El Idrissi, N., Belachemi, L., Merle, N., Zinck, P., & Kaddami, H. (2022). Comprehensive preparation and catalytic activities of co/TEMPO-cellulose nanocomposites: A promising green catalyst. *Carbohydrate Polymers*, 295, Article 119765. https://doi.org/10.1016/j.carbpol.2022.119765

El-Sayed, N. S., El-Sakhawy, M., Hesemann, P., Brun, N., & Kamel, S. (2018). Rational design of novel water-soluble amphoteric cellulose derivatives. *International Journal of Biological Macromolecules*, 114, 363-372. https://doi.org/10.1016/J.IBIOMAC.2018.03.147

Ema, T., Miyazaki, Y., Shimonish, J., Maeda, C., & Hasegawa, J. Y. (2014). Bifunctional porphyrin catalysts for the synthesis of cyclic carbonates from epoxides and CO 2: Structural optimization and mechanistic study. *Journal of the American Chemical Society*, 136(43), 15270-15279. https://doi.org/10.1021/JA507665A. /SUPPL_FILE/JA507665A_S1001.PDF.

Fees, E., Sadeghifar, H., Gracz, H. S., Argyropoulos, D. S., & Ghiladi, R. A. (2011). Photobactericidal porphyrin-cellulose nanocrystals: Synthesis, characterization, and antimicrobial properties. *Biomacromolecules*, 12(10), 3528-3539. https://doi.org/10.1021/BM200718S/SUPPL_FILE/BM200718S_S1001.PDF.

French, A. D. (2014). Idealized powder diffraction patterns for cellulose polymorphs. *Cellulose*, 21(2), 885-896. https://doi.org/10.1007/S10570-013-0030-4/FIGURES/5

Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A., Cheeseman, J. R., Scalmani, G., Barone, V., Petersson, G. A., Nakatsuji, H., Li, X., Caricato, M., Marenich, A. V., Bloino, J., Janesko, B. G., Gomperts, R., Mennucci, B., Hratchian, H. P., Ortiz, J. V., Izmaylov, A. F., Sonnenberg, J. L., Williams-Young, D., Ding, F., Lipparini, F., Egidii, F., Goings, J., Peng, P., Petrone, A., Henderson, T., Ranasinghe, D., Zakrzewski, V. G., Gao, J., Rega, N., Zheng, G., Liang, W., Hada, M., Ehamra, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven, T., Throssell, K., Montgomery, J. A., Jr, Peralta, J. E., Ogliaro, F., Bearpark, M. J., Heyd, J. J., Brothers, E. N., Kudin, K. N., Staroverov, V. N., Keith, T. A., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A. P., Burant, J. C., Iyengar, S. S., Tomasi, J., Cossi, M., Millam, J. M., Klene, M., Adamo, C., Cammi, R., Ochterski, J. W., Martin, R. L., Morokuma, K,

Farkas, O., Foresman, J. B., & Fox, D. J. (2016). Gaussian 16. Revision B.01. Wallingford CT: Gaussian, Inc.

Gong, J., Li, J., Xu, J., Xiang, Z., & Mo, L. (2017). Research on cellulose nanocrystals produced from cellulose sources with various polymorphs. *RSC Advances*, 7(53), 33486-33493. https://doi.org/10.1039/C7RA06222B

Groszewicz, P. B., Mendes, P., Kumari, B., Lins, J., Biesalski, M., Gutmann, T., & Buntkowski, G. (2020). N-Hydroxysuccinimide-activated esters as a functionalization agent for amino cellulose: Synthesis and solid-state NMR characterization. *Cellulose*, 27(3), 1239-1254. https://doi.org/10.1007/s10570-019-02864-5

Guo, C. H., Liang, M., & Jiao, H. (2021). Cycloaddition mechanisms of CO2and epoxide catalyzed by salophen—An organocatalyst free from metals and halides. *Catalysis Science and Technology*, 11(7), 2529-2539. https://doi.org/10.1039/d0cy02256j

Guo, L., Xiong, Y., Zhang, R., Zhan, H., Chang, D., Yi, L., Chen, J., & Wu, X. (2022). Catalytic coupling of CO2 and epoxides by lignin-based catalysts: A combined experimental and theoretical study. *Journal of CO₂ Utilization*, 56, Article 101863. https://doi.org/10.1016/j.jcou.2021.101863

He, L., Zhang, W., Yang, Y., Ma, J., Liu, F., & Liu, M. (2021). Novel biomass-derived deep eutectic solvents promoted cycloaddition of CO2 with epoxides under mild and additive-free conditions. *Journal of CO₂ Utilization*, 54, Article 101750. https://doi.org/10.1016/j.jcou.2021.101750

Heinze, T., Pfeifer, A., Koschella, A., Schaller, J., & Meister, F. (2016). Solvent-free synthesis of 6-deoxy-6-(ω-aminoalkyl)amino cellulose. *Journal of Applied Polymer Science*, 133(39), 1-7. https://doi.org/10.1002/app.43987

Heinze, T., & Rahn, K. (1997). Cellulose-p-toluenesulfonates: A valuable intermediate in cellulose chemistry. *Macromolecular Symposia*, 120(1), 103-113. https://doi.org/10.1012/MASY.19971200112

Heinze, T., Rahn, K., Jaspers, M., & Berghmans, H. (1996). P-Toluenesulfonyl esters in cellulose modifications: Acylation of remaining hydroxyl groups. *Macromolecular Chemistry and Physics*, 197(12), 4207-4224. https://doi.org/10.1002/MACP.1996.021971218

Hu, G., Casteto, C., Pu, Y., Samuel, R., & Ragauskas, A. J. (2011). Structural characterization of switchgrass lignin after ethanol Organosolv pretreatment. *Energy and Fuels*, 26(1), 740-745. https://doi.org/10.1021/EF2014477P

Hu, L., Xie, Q., Tang, J., Pan, C., Yu, G., & Tam, K. C. (2021). Co(III)-Salen immobilized cellulose nanocrystals for efficient catalytic CO2 fixation into cyclic carbonates under mild conditions. *Carbohydrate Polymers*, 256, Article 117558. https://doi.org/10.1016/j.carbpol.2020.117558

Hu, Y. J., Wang, Y., Huang, Y. H., Bian, J., Li, M. F., Peng, F., & Sun, R. C. (2019). Benzoxazine enhanced amino cellulose-based composite films: Preparation, proposed mechanism, and improved performance. *Carbohydrate Polymers*, 222, Article 115008. https://doi.org/10.1016/j.carbpol.2019.115008

Ismail, N., Essalhi, M., Rahmati, M., Cui, Z., Khayet, M., & Tavajohi, N. (2021). Experimental and theoretical studies on the formation of pure β-phase polymorphs during fabrication of polyvinylidene fluoride membranes by cyclic carbonate solvents. *Green Chemistry*, 23(5), 2130-2147. https://doi.org/10.1039/D1GC00122A

Jaroonwatana, W., D'Elia, V., & Crespy, D. (2022). Hydrophobically-enhanced "on water" cycloaddition of CO2 to long-chain terminal epoxides. *Chemical Communications*, 58(82), 11535-11538. https://doi.org/10.1039/D2CC04526E

Jasiak, K., Siewniak, A., Kopczyńska, K., Krobok, A., & Baj, S. (2016). Hydrogensulfate ionic liquids as an efficient catalyst for the synthesis of cyclic carbonates from carbon dioxide and epoxides. *Journal of Chemical Technology & Biotechnology*, 91(11), 2827-2833. https://doi.org/10.1002/JCTB.4892

Kamphuis, A. J., Picchioni, F., & Pescarmona, P. P. (2019). CO2-fixation into cyclic and polymeric carbonates: Principles and applications. *Green Chemistry*, 21(3), 406-448. https://doi.org/10.1039/C8GC03086C

Kovalenko, V. I. (2010). Crystalline cellulose: Structure and hydrogen bonds. *Russian Chemical Reviews*, 79(3), 231-241. https://doi.org/10.1070/RC2010V079N03ABEH004065. /XML

Kumar, S., de A. e Silva, J., Wani, M. Y., Gil, J. M., & Sobral, A. J. F. N. (2017). Carbon dioxide capture and conversion by an environmentally friendly chitosan based meso-tetrakis(4-sulfonatophenyl) porphyrin. *Carbohydrate Polymers*, 175, 575-583. https://doi.org/10.1016/j.carbpol.2017.08.031

Lalanne-Tisné, M., Eyley, S., De Winter, J., Favrelle-Huret, A., Thielemans, W., & Zinck, P. (2022). Cellulose nanocrystals modification by grafting from ring opening polymerization of a cyclic carbonate. *Carbohydrate Polymers*, 295, Article 119840. https://doi.org/10.1016/j.carbpol.2022.119840

Lalanne-Tisné, M., Favrelle-Huret, A., Thielemans, W., Prates Ramalho, J. P., & Zinck, P. (2022). DFT investigations on the ring-opening polymerization of trimethylene carbonate catalyzed by heterocyclic nitrogen bases. *Catalysts*, 12(10), 1280. https://doi.org/10.3390/CATAL12101280/S1

Liang, S., Liu, H., Jiang, T., Song, J., Yang, G., & Han, B. (2011). Highly efficient synthesis of cyclic carbonates from CO2 and epoxides over cellulose/KI. *Chemical Communications*, 47(7), 2131-2133. https://doi.org/10.1039/c0cc04829a

Lim, S., Lim, Y. N., & Jang, H. Y. (2016). TBD/alkyl halide-catalyzed synthesis of cyclic carbonates from CO2. *Bulletin of the Korean Chemical Society*, 37(4), 608-611. https://doi.org/10.1002/BKCS.10724

Liu, M., Liang, L., Liang, T., Lin, X., Shi, L., Wang, F., & Sun, J. (2015). Cycloaddition of CO2 and epoxides catalyzed by dicationic ionic liquids mediated metal halide: Influence of the dication on catalytic activity. *Journal of Molecular Catalysis A: Chemical*, 408, 242-249. https://doi.org/10.1016/j.molcata.2015.07.032

Lu, S., Li, J., Liu, F., Chen, M., Na, H., & Zhu, J. (2021). Impact of DBU on the synthesis of cellulose-graft-poly(L-lactide) copolymer in CO2 switchable solvent with different grafting strategies. *Polymer*, 229, 124020. https://doi.org/10.1016/j.polymer.2021.124020
Mariano, M., El Kissi, Nadia, & Dufresne, Alain (2015). Melt processing of cellulose nanocrystal reinforced polycarbonate from a masterbatch process. *European Polymer Journal*, 69, 208–223.

Meimoun, J., Favrelle-Huret, A., Bria, M., Merle, N., Stoclet, G., De Winter, J., ... Zinck, P. (2020). Epimerization and chain scission of polylactides in the presence of an organic base, TBD. *Polymer Degradation and Stability*, **181**, 109188. https://doi.org/10.1016/j.POLYMDEGRADSTAB.2020.109188

Meza-Contreras, J. C., Manriquez-Gonzalez, R., Gutiérrez-Ortega, J. A., & Gonzalez-García, Y. (2018). XRD and solid state 13C-NMR evaluation of the crystallinity enhancement of 13C-labeled bacterial cellulose biosynthesized by Komagataeibacter xylinus under different stimuli: A comparative strategy of analyses. *Carbohydrate Research*, **461**, 51–59. https://doi.org/10.1016/j.carres.2018.03.005

Nasiriani, T., Nigjeh, N. A., Torabi, S., & Shaabani, A. (2024). MIL-88-NH2(Fe) conjugated pectin through a post-modification Ugi four-component reaction: A robust bio-based catalyst for the synthesis of cyclic carbonate via CO2 fixation reaction. *Carbohydrate Polymers*, **342**, Article 122418. https://doi.org/10.1016/j.CARPOL.2024.122418

Nasirov, F., Nasirli, E., & Ibrahimova, M. (2021). Cyclic carbonates synthesis by cycloaddition reaction of CO2 with epoxides in the presence of zinc-containing and ionic liquid catalysts. *Journal of the Iranian Chemical Society* 2021 **19**, 2, 192, 353–379. https://doi.org/10.1007/S13738-021-02330-9

Oh, S. Y., Yoo, D. I., Shin, Y., & Seo, G. (2005). FTIR analysis of cellulose treated with sodium hydroxide and carbon dioxide. *Carbohydrate Research*, **340**(3), 417–428. https://doi.org/10.1016/j.CARRES.2004.11.027

Ohwoavworhua, F. O., & Adelakun, T. A. (2007). Some physical characteristics of microcrystalline cellulose obtained from raw cotton of Cochlosermum planchonii. *Tropical Journal of Pharmaceutical Research*, **4**(2). https://doi.org/10.4314/TJPR.V4L2.14626

Okada, M., Yamada, M., Yokoe, M., & Aoi, K. (2007). Syntheses and thermal properties of poly(hydroxy)urethanes by polyaddition reaction of bis(cyclic carbonate) and diamines. *Journal of Applied Polymer Science*, **81**(11), 2735–2743. https://doi.org/10.1002/app.1719

Oliveira, R. L., Vieira, J. G., Barud, H. S., Assunção, R. M. N., Filho, G. R., Ribeiro, S. J. L., & Messadeqq, Y. (2015). Synthesis and characterization of methylcellulose produced from bacterial cellulose under heterogeneous condition. *Journal of the Brazilian Chemical Society*, **26**(9), 1861–1870. https://doi.org/10.5935/0103-5053.20150163

Owen, N. L., & Thomas, D. W. (1989). Infrared studies of “hard” and “soft” woods. *Applied Spectroscopy*, **43**(3), 451–455. https://doi.org/10.1366/0003702894202760

Panahi, P., Nouruzi, N., Doustkhah, E., Mohtasham, H., Ahadi, A., Ghiasi-Moaser, A., Rostamnia, S., Mahmoudi, G., & Khataee, A. (2019). Zirconium based porous coordination polymer (PCP) bearing organocatalytic ligand: A promising dual catalytic center for ultrasonic heterocycle synthesis. *Ultrasonics Sonochemistry*, **58**, Article 104653. https://doi.org/10.1016/j.ulsonch.2019.104653

Panchal, P., Ogunsona, E., & Mekonnen, T. (2019). Trends in advanced functional material applications of nanocellulose. *Processes*, **7**(1). https://doi.org/10.3390/PR7010010

Pandey, A., Kalamdhad, A., & Chandra Sharma, Y. (2023). Recent advances of nanocellulose as biobased adsorbent for heavy metal ions removal: A sustainable approach integrating with waste management. *Environmental Nanotechnology, Monitoring & Management*, **20**, Article 100791. https://doi.org/10.1016/J.ENMM.2023.100791

Pandey, K. K., & Pitman, A. J. (2003). FTIR studies of the changes in wood chemistry following decay by brown-rot and white-rot fungi. *International Biodeterioration and Biodegradation*, **52**(3), 151–160. https://doi.org/10.1016/S0964-8305(03)00052-0

Pescarmona, P. P. (2021). Cyclic carbonates synthesised from CO2: Applications, challenges and recent research trends. *Current Opinion in Green and Sustainable Chemistry*, **29**, Article 100457. https://doi.org/10.1016/j.COOGSC.2021.100457

Qian, Y., Chu, Y., Zheng, Z., Shadike, Z., Han, B., Xiang, S., ... Deng, Y. (2022). A new cyclic carbonate enables high power/low temperature ion-ion batteries. *Energy Storage Materials*, **45**, 14–23. https://doi.org/10.1016/j.ENSM.2021.11.029

Qiao, C., Villar-Yanez, M., Sprachmann, J., Limburg, B., Bo, C., & Kleij, A. W. (2020). Organocatalytic trapping of elusive carbon dioxide based heterocycles by a kinetically controlled Cascade process. *Angewandte Chemie*, **132**(42), 18604–18609. https://doi.org/10.1002/ANGE.200207350

Qu, Y., Chen, Y., & Sun, J. (2022). Conversion of CO2 with epoxides to cyclic carbonates catalyzed by amino acid ionic liquids at room temperature. *Journal of CO₂ Utilization*, **56**, Article 101840. https://doi.org/10.1016/j.JCOU.2021.101840

Quadrelli, E. A., Centi, G., Duplan, J. L., & Perathoner, S. (2011). Carbon dioxide recycling: Emerging large-scale technologies with industrial potential. *ChemSusChem*, **4**(9), 1194–1215. https://doi.org/10.1002/CSSC.201100473

Rahn, K., Diamantoglou, M., Klemm, D., Berghmans, H., & Heinze, T. (1996). Homogeneous synthesis of cellulose p-toluenesulfonates in N,N-dimethylacetamide/ LiCl solvent system. *Angewandte Makromolekulare Chemie*, **238**(1 996), 143–163. https://doi.org/10.1002/apmc.1996.052380113

Rostamnia, S., & Doustkhah, E. (2014). Nanoporous silica-supported organocatalyst: A heterogeneous and green hybrid catalyst for organic transformations. *RSC Advances*, **4**(54), 28238–28248. https://doi.org/10.1039/C4RA03773A

Sadeghifar, H., Filpponen, I., Clarke, S. P., Brougham, D. F., & Argyropoulos, D. S. (2011). Production of cellulose nanocrystals using hydrothermal acid and click reactions on their surface. *Journal of Materials Science*, **46**(22), 7344–7355. https://doi.org/10.1007/s10853-011-5696-0

Sakakura, T., Choi, J. C., & Yasuda, H. (2007). Transformation of carbon dioxide. *Chemical Reviews*, **107**(6), 2365–2387. https://doi.org/10.1021/CR068357U/ASSET/CR068357U.FP.PNG_V03

Salama, A., Saleh, A. K., Cruz-Maya, I., & Guarino, V. (2023). Bacterial cellulose/cellulose imidazolium bio-hybrid membranes for in vitro and antimicrobial

applications. *Journal of Functional Biomaterials*, **14**(2), 60. https://doi.org/10.3390/jf1402006

Santos, E. C. S., Dos Santos, T. C., Guimarães, R. B., Ishida, L., Freitas, R. S., & Ronconi, C. M. (2015). Guanidine-functionalized Fe3O4 magnetic nanoparticles as basic recyclable catalysts for biodiesel production. *RSC Advances*, **5**(59), 48031–48038. https://doi.org/10.1039/c5ra07331f

Schmidt, T., Liebert, T., & Heinze, T. (2014). Synthesis of soluble cellulose tosylates in an eco-friendly medium. *Green Chemistry*, **16**(4), 1941–1946. https://doi.org/10.1039/c3gc41994k

Schwanninger, M., Rodrigues, J. C., Pereira, H., & Hinterstoisser, B. (2004). Effects of short-time vibratory ball milling on the shape of FT-IR spectra of wood and cellulose. *Vibrational Spectroscopy*, **36**(1), 23–40. https://doi.org/10.1016/j.VIBSPEC.2004.02.003

Segal, L., Creely, J. J., Martin, A. E., & Conrad, C. M. (1959). An empirical method for estimating the degree of crystallinity of native cellulose using the X-ray diffractometer. *Textile Research Journal*, **29**(10), 786–794. https://doi.org/10.1177/004051755902901003

Seyednejhad, S., Khalilzadeh, M. A., Zareyee, D., Sadeghifar, H., & Venditti, R. (2019). Cellulose nanocrystal supported palladium as a novel recyclable catalyst for Ullmann coupling reactions. *Cellulose*, **26**(8), 5015–5031. https://doi.org/10.1007/s10570-019-02436-7

Shaikh, R. R., Pornpromap, S., & D'Elia, V. (2018). Cyclic catalytic strategies for the cycloaddition of pure, diluted, and waste CO2 to epoxides under ambient conditions. *ACS Catalysis*, **8**(1), 419–450. https://doi.org/10.1021/ACSCATAL.7B03580/ SUPPL_FILE/C5B03580_S1.001.PDF

Shiels, R. A., & Jones, C. W. (2007). Homogeneous and heterogeneous 4-(N,N-dialkylamino)pyridines as effective single component catalysts in the synthesis of propylene carbonate. *Journal of Molecular Catalysis A: Chemical*, **261**(2), 160–166. https://doi.org/10.1016/j.MOLCATA.2006.08.002

Siewniak, A., Forajter, A., & Szymańska, K. (2020). Mesoporous silica-supported ionic liquids as catalysts for styrene carbonate synthesis from CO2. *Catalysts*, **10**(11), 1363. https://doi.org/10.3390/CATAL10111363

Sikhsana, S. T., Gumede, T. P., Malebo, N. J., Ogundeji, A. O., & Motloung, B. (2023). Medicinal plants as a cellulose source for the fabrication of poly(lactic acid) composites: A mini-review. *Polymers from Renewable Resources*, **14**(1), 44–57. https://doi.org/10.1177/20412479221146249

Silva Filho, E. C., Lima, L. C. B., Silva, F. C., Sousa, K. S., Fonseca, M. G., & Santana, S. A. A. (2013). Immobilization of ethylene sulfide in aminated cellulose for removal of the divalent cations. *Carbohydrate Polymers*, **92**(2), 1203–1210. https://doi.org/10.1016/j.CARPOL.2012.10.031

Song, J., Zhang, B., Zhang, P., Ma, J., Liu, J., Fan, H., Jiang, T., & Han, B. (2012). Highly efficient synthesis of cyclic carbonates from CO2 and epoxides catalyzed by KI/lecithin. *Catalysis Today*, **183**(1), 130–135. https://doi.org/10.1016/j.CATTOD.2011.08.042

SriBala, G., Chennuru, R., Mahapatra, S., & Vinu, R. (2016). Effect of alkaline ultrasonic pretreatment on crystalline morphology and enzymatic hydrolysis of cellulose. *Cellulose*, **23**(3), 1725–1740. https://doi.org/10.1007/S10570-016-0893-2/TABLES/2

Sun, J., Cheng, W., Yang, Z., Wang, J., Xu, T., Xin, J., & Zhang, S. (2014). Superbase/cellulose: An environmentally benign catalyst for chemical fixation of carbon dioxide into cyclic carbonates. *Green Chemistry*, **16**(6), 3071–3078. https://doi.org/10.1039/c3gc41850b

Taherimehr, M., Al-Amsyar, S. M., Whiteoak, C. J., Kleij, A. W., & Pescarmona, P. P. (2013). High activity and switchable selectivity in the synthesis of cyclic and polymeric cyclohexene carbonates with iron amino triphenolate catalysts. *Green Chemistry*, **15**(11), 3083–3090. https://doi.org/10.1039/C3GC41303A

Tarchoun, A. F., Trache, D., Klapötke, T. M., Chelouche, S., Derradiji, M., Bessa, W., & Mezroua, A. (2019). A promising energetic polymer from Posidonia oceanica Brown algae: Synthesis, characterization, and kinetic modeling. *Macromolecular Chemistry and Physics*, **220**(22), 1900358. https://doi.org/10.1002/MACP.201900358

Tarchoun, A. F., Trache, D., Klapötke, T. M., & Krumm, B. (2020). New insensitive nitrogen-rich energetic polymers based on amino-functionalized cellulose and microcrystalline cellulose: Synthesis and characterization. *Fuel*, **277**(May), 118258. https://doi.org/10.1016/j.fuel.2020.118258

Tehrani, A. D., & Neysi, E. (2013). Surface modification of cellulose nanowhisker throughout graft polymerization of 2-ethyl-2-oxazoline. *Carbohydrate Polymers*, **97**(1), 98–104. https://doi.org/10.1016/j.carbpol.2013.04.082

Tharun, J., Mathai, G., Kathalikkattil, A. C., Roshan, R., Kwak, J. Y., & Park, D. W. (2013). Microwave-assisted synthesis of cyclic carbonates by a formic acid/KI catalytic system. *Green Chemistry*, **15**(6), 1673–1677. https://doi.org/10.1039/C3GC40729B

Thoorens, G., Krier, F., Leclercq, B., Carlin, B., & Evrard, B. (2014). Microcrystalline cellulose, a direct compression binder in a quality by design environment—A review. *International Journal of Pharmaceutics*, **473**(1–2), 64–72. https://doi.org/10.1016/j.ijpharm.2014.06.055

Tomita, H., Sanda, F., & Endo, T. (2000). *Polyaddition behavior of bis (five- and six-membered cyclic carbonate ) s with diamine* (pp. 860–867).

Trache, D., Donnot, A., Khimeche, K., Benelmir, R., & Brosse, N. (2014). Physicochemical properties and thermal stability of microcrystalline cellulose isolated from alfa fibres. *Carbohydrate Polymers*, **104**(1), 223–230. https://doi.org/10.1016/j.CARPOL.2014.01.058

Trache, D., & Tarchoun, A. F. (2019). Differentiation of stabilized nitrocellulose during artificial aging: Spectroscopy methods coupled with principal component analysis. *Journal of Chemometrics*, **33**(8), Article e3163. https://doi.org/10.1002/CEM.3163

Van Zyl, E. M., Kennedy, M. A., Nason, W., Fenlon, S. J., Young, E. M., Smith, L. J., ... Coburn, J. M. (2023). Structural properties of optically clear bacterial cellulose
produced by *Komagataeibacter hansenii* using arabitol. *Biomaterials Advances*, **148**, Article 213345. https://doi.org/10.1016/j.bioadv.2023.213345

Villiers, C., Dognon, J. P., Pollet, R., Thuéry, P., & Ephritikhine, M. (2010). An isolated CO2 adduct of a Nitrogen Base: Crystal and electronic structures. *Angewandte Chemie International Edition*, **49**(20), 3465–3468. https://doi.org/10.1002/ANIE.201001035

Vranješević, F., Markovic, M. K., Matulja, D., Ambrozić, G., Sordo, J. A., Laclef, S., ... Marković, D. (2022). Recent advances in the synthesis of five-membered cyclic carbonates and carbamates from allylic or propargylic substrates and CO2. *Catalysts*, **12**(5), Article 547. https://doi.org/10.3390/catal12050547

Wang, C. G., Li, N., Wu, G., Lin, T. T., Lee, A. M. X., Yang, S. W., ... Luo, D. H. K. (2022). Carbon dioxide mediated cellulose dissolution and derivatization to cellulose carbonates in a low-pressure system. *Carbohydrate Polymer Technologies and Applications*, **3**(December 2021), Article 100186. https://doi.org/10.1016/j.carpta.2022.100186

Wang, Y. B., Sun, D. S., Zhou, H., Zhang, W. Z., & Lu, X. B. (2015). CO2, COS and CS2 adducts of N-heterocyclic olefins and their application as organocatalysts for carbon dioxide fixation. *Green Chemistry*, **17**(7), 4009–4015. https://doi.org/10.1039/C5GC00948K

Weidlich, T., & Kamenická, B. (2022). Utilization of CO2 available Organocatalysts for reactions with industrially important epoxides. *Catalysts*, **12**(3). https://doi.org/10.3390/catal12030298

Wilm, L. F. B., Eder, T., Mück-Lichtenfeld, C., Mehlmann, P., Wünsche, M., Buß, F., & Dielmann, F. (2019). Reversible CO2 fixation by N-heterocyclic imines forming water-stable zwitterionic nitrogen-base–CO2 adducts. *Green Chemistry*, **21**(3), 640–648. https://doi.org/10.1039/C8GC02952K

Wohlert, M., Benselfelt, T., Wågberg, L., Furó, I., Berglund, L. A., & Wohlert, J. (2022). Cellulose and the role of hydrogen bonds: Not in charge of everything. *Cellulose*, **29**(1), 1–23. https://doi.org/10.1007/S10570-021-04325-4/TABLES/1

Xia, Y., Zhang, C., Wang, Y., Liu, S., & Zhang, X. (2023). From oxygenated monomers to well-defined low-carbon polymers. *Chinese Chemical Letters*, **35**(1), Article 108860. https://doi.org/10.1016/J.CCLET.2023.108860

Yamaguchi, K., Ebitani, K., Yoshida, T., Yoshida, H., & Kaneda, K. (1999). Mg–Al mixed oxides as highly active acid–base catalysts for cycloaddition of carbon dioxide to epoxides. *Journal of the American Chemical Society*, **121**(18), 4526–4527. https://doi.org/10.1021/JA9902165

Yang, J., Liu, Q., Pupek, K. Z., Dzwiniel, T. L., Dietz Rago, N. L., Cao, J., ... Zhang, Z. (2021). Molecular engineering to enable high-voltage lithium-ion battery: From propylene carbonate to trifluoropropylene carbonate. *ACS Energy Letters*, **6**(2), 371–378. https://doi.org/10.1021/ACSENERGYLETT.0C02400/SUPPL_FILE/NZ0C02400_ST_001.PDF

Yang, X., Liu, Z., Chen, P., Liu, F., & Zhao, T. (2022). Effective synthesis of cyclic carbonates from CO2 and epoxides catalyzed by acetylcholine bromide-based deep eutectic solvents. *Journal of CO₂ Utilization*, **58**, Article 101936. https://doi.org/10.1016/J.JCOU.2022.101936

Yang, X., Zou, Q., Zhao, T., Chen, P., Liu, Z., Liu, F., & Lin, Q. (2021). Deep eutectic solvents as efficient catalysts for fixation of CO2to cyclic carbonates at ambient temperature and pressure through synergetic catalysis. *ACS Sustainable Chemistry & Engineering*, **9**(31), 10437–10443. https://doi.org/10.1021/ACSSUSCHEMENG.1C03187/SUPPL_FILE/SC1C03187_ST_001.PDF

You, H., Wang, E., Cao, H., Zhuo, C., Liu, S., Wang, X., & Wang, F. (2022). From impossible to possible: Atom-economic polymerization of low strain five-membered carbonates. *Angewandte Chemie International Edition*, **61**(5), Article e202113152. https://doi.org/10.1002/ANIE.202113152

Yu, K. M. K., Curcic, I., Gabriel, J., Morganstewart, H., & Tsang, S. C. (2009). Catalytic coupling of CO2 with epoxide over supported and unsupported amines†. *Journal of Physical Chemistry A*, **114**(11), 3863–3872. https://doi.org/10.1021/JP906365G

Zhang, X., Zhao, N., Wei, W., & Sun, Y. (2006). Chemical fixation of carbon dioxide to propylene carbonate over amine-functionalized silica catalysts. *Catalysis Today*, **115**(1–4), 102–106. https://doi.org/10.1016/J.CATTOD.2006.02.028