Multifunctional Pd/CCS-Cu-MOF Microcapsule Catalyst: A Biomimetic Design Inspired by Metalloenzyme Structures for Sustainable Glycerol Valorizing into Glycerol Carbonate

Multifunctional Pd/CCS-Cu-MOF Microcapsule Catalyst: A Biomimetic Design Inspired by Metalloenzyme Structures for Sustainable Glycerol Valorizing into Glycerol Carbonate | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Multifunctional Pd/CCS-Cu-MOF Microcapsule Catalyst: A Biomimetic Design Inspired by Metalloenzyme Structures for Sustainable Glycerol Valorizing into Glycerol Carbonate Shuqi Qi, Jing Xu, Nan Wang, Pingbo Zhang, Mingming Fan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6418048/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Glycerol, a key byproduct generated during biodiesel production, has accumulated in excess, hindering the industry's development. A novel palladium-loaded chitosan-copper metal-organic framework (Pd/CCS-Cu-MOF) biomimetic catalyst was developed to valorize glycerol efficiently. Mimicking metalloenzyme structures, this catalyst significantly enhances catalytic performance by controlling the chitosan crosslinking sequence and the active sites' electronic environment. The crosslinked chitosan improves copper's electronic control and forms a microcapsule structure that stabilizes active sites and optimizes reactant mass transfer. Pd/CCS-Cu-MOF achieves a yield of approximately 90% and a selectivity of 99% in the oxidative carbonylation of glycerol. ICP analysis reveals that the catalyst maintains high efficiency with a remarkably low palladium loading of only 0.49wt.%, thereby reducing precious metal use and promoting green chemistry principles. Characterization further demonstrates the microcapsule structure's advantages in enhancing thermal stability, mechanical strength, and pore distribution, providing new insights into natural polymer-metal organic framework composite catalysts. In conclusion, this study offers an efficient, green catalyst for glycerol valorization and opens new avenues for sustainable catalytic technology development, laying a foundation for future industrial applications. Biomimetic Crosslinking Sequence Microcapsule Structure Glycerol Oxidative Carbonylation Pd/CCS-Cu-MOF Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Glycerol, a key byproduct generated during biodiesel production, serves as a vital chemical feedstock. However, its excessive production has become a significant bottleneck in the biodiesel industry’s development [ 1 – 2 ]. Consequently, research on converting glycerol into high-value-added chemicals has garnered significant attention [ 1 , 3 ]. Glycerol carbonate, derived from glycerol, is a sustainable chemical with various roles, such as an additive, a softening agent, and a precursor in producing medicines and agricultural chemicals [ 4 – 6 ]. Recent investigations into glycerol oxidative carbonylation have centered on designing advanced solid catalysts to enhance reaction stability while achieving higher efficiency and precision. Palladium is broadly acknowledged as the most potent catalytic material for these carbonylation transformations. Exposed palladium nanoparticles, as highly efficient noble metal catalysts [ 7 ], can facilitate various reactions, including the hydrogenation of unsaturated olefins [ 8 – 13 ] and carbon-carbon coupling reactions such as Suzuki-Miyaura and Heck reactions [ 14 – 15 ]. However, the scarcity of palladium in nature presents a cost challenge for industrial applications. Therefore, creating more active sites to increase specific surface area while maintaining a low loading is an effective strategy to enhance the catalytic activity of palladium nanoparticles [ 16 ]. Despite these advantages, the tendency of palladium nanoparticles to aggregate poses a challenge to their catalytic performance, necessitating the selection of suitable supports to overcome this issue [ 17 – 18 ]. The incorporation of natural materials helps not only to reduce costs but also to enhance the biodegradability and biocompatibility of catalysts. For instance, abundant carbohydrate chitosan is widely used due to its low cost and non-toxicity [ 19 – 20 ]. Previously, Dabbawala et al. reported using chitosan-supported palladium for synthesizing 2-phenylethanol [ 21 ]. Recently, Zeng et al. demonstrated using chitosan microspheres loaded with palladium in Heck coupling reactions [ 22 ]. These studies highlight the potential of chitosan-based catalysts in various chemical transformations, including oxidative carbonylation reactions. Industrially, the oxidative carbonylation of glycerol is considered one of the most promising conversion pathways due to its high atom economy, low cost, and low energy consumption, aligning with the core principles of green chemistry [ 23 – 25 ]. Chitosan's unique chemical structure, featuring amino and hydroxyl functional groups, provides a theoretical basis for its effectiveness as a support material. These functional groups can coordinate with palladium, mimicking the interaction mechanisms between biomolecules and metal ions. Additionally, through polycondensation reactions, chitosan can form robust cross-linked supports (e.g., chitosan cross-linked microspheres), improving the dispersion of metal nanoparticles and enhancing their recyclability. Compared to traditional chitosan microspheres, those composited with other compounds, such as metal-organic frameworks (MOFs) [ 26 – 27 ], exhibit superior performance. MOFs, with their high specific surface area, porous structure, and diverse functional properties [ 28 – 31 ], are ideal candidates for the next generation of biomimetic catalysts. The development of biomimetic catalysts, inspired by nature, aims to replicate enzyme-like structural features and catalytic mechanisms to achieve high activity, selectivity, and enhanced stability [ 32 – 36 ]. Chitosan-MOF composite catalytic supports demonstrate notable biomimetic characteristics: chitosan, derived from natural materials, has chemical and structural properties akin to biopolymers in nature; the amino and hydroxyl functional groups on chitosan coordinate with metal catalysts like palladium, mimicking interactions between biomolecules and metal ions; its three-dimensional porous structure enhances palladium dispersion and activity, optimizing substrate binding at active centers; additionally, it's green degradability and eco-friendly features align with natural material degradation and regeneration cycles, reducing environmental impact. Leveraging the biodegradability of chitosan and the porous structure with active metal sites of Cu-MOF, this study innovatively designed a palladium-loaded composite catalyst. By controlling the sequence of chitosan cross-linking, the structural characteristics of the catalyst and their influence on catalytic performance were thoroughly investigated. The findings indicate that chitosan (Cu-MOF) cross-linked with glutaraldehyde beforehand disperses palladium nanoparticles more effectively, significantly enhancing catalytic activity and selectivity. Additionally, the catalyst's unique microcapsule structure further boosts its reaction efficiency. This research not only provides an efficient, green catalytic system for glycerol oxidative carbonylation but also offers new perspectives for the design and functional expansion of natural polymer-MOF composite catalysts, showcasing the broad potential for sustainable catalyst development. 2. Materials and Experimental Procedures 2.1. Materials All chemicals utilized in this study were of analytical purity and were used as received without any additional purification. Chitosan (CS, deacetylation degree > 90%, viscosity < 100 mPa·s), palladium acetate (Pd(OAc) 2 ), terephthalic acid, copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), palladium chloride (PdCl 2 ), ethanol, glutaraldehyde (GA), acetic acid were all purchased from Shanghai Titan Technology Co., Ltd. Sodium tripolyphosphate (STPP), N, N-dimethylacetamide (DMA), methanol, sodium borohydride (NaBH 4 ) were all purchased from China National Pharmaceutical Group. 2.2 Preparation of Composite Materials 2.2.1 Fabrication of Cu-MOF Cu-MOF was synthesized by the solvothermal method previously reported [ 37 ]. Briefly, Cu(NO 3 ) 2 ·3H 2 O (2.5 g) was dissolved in a homogeneous mixture solution containing terephthalic acid (0.60 g). Once fully dissolved, the mixture was transferred into a hydrothermal reactor and maintained at 120°C for 24 h. After the reaction cooled to room temperature, the resulting product was collected by filtration and dried at 100°C for 12 h. 2.2.2 Fabrication of CS-Cu-MOF Cu-MOF was encapsulated in CS particles to form composite particles. For this, Cu-MOF (0.1 g) was suspended in an acetic acid (2 wt%, 45 mL) solution containing CS (1 g), and stirred for 1 h. Once the solution became uniform, STPP solution (2 wt%) was slowly added to form composite beads. Finally, the beads were separated and washed with distilled water until pH = 7. 2.2.3 Crosslinking of CS-Cu-MOF Composite Microspheres: CCS-Cu-MOF To enhance the stability of the wet beads, the composite microspheres were immersed in an ethanol solution with 5 wt% glutaraldehyde (GA) and heated at 70°C for 24 h. After the reaction, the microspheres were thoroughly rinsed with ethanol and left to dry at room temperature for 12 h. 2.2.4 Fabrication of Pd/Cu-MOF Cu-MOF (0.37 g) was dissolved in methanol and mixed with a solution of PdCl₂ (0.0037 g) in ammonium hydroxide, followed by stirring for 2 hours. Next, NaBH₄ (0.062 g) was introduced into the mixture and allowed to react for 24 h. The resulting product was separated by filtration and dried at 80°C for 24 h. 2.2.5 Fabrication of Pd/CS-Cu-MOF CS-Cu-MOF (0.32 g) was introduced into methanol (30 mL) and stirred for 1 h. Next, a solution containing Pd(OAc) 2 (0.0041 g) was incorporated into the system and left under continuous agitation for 2 h. Later, NaBH 4 (0.016 g) was introduced to facilitate the reduction of Pd(II) to Pd nanoparticles. Following 3 h, the resulting solid was separated by filtration, rinsed with methanol, and subjected to drying at 60°C for 24 h. 2.2.6 Fabrication of Pd/CCS-Cu-MOF The cross-linked composite microspheres were palletized by the wet impregnation method [ 38 ]. For this, the crosslinked composite microspheres (0.35 g) were introduced into methanol (30 mL) and stirred for 1 hour. Then, Pd(OAc) 2 (0.0044 g) solution was added, and the mixture was stirred for 2 h. NaBH 4 (0.018 g) was added for reduction for 3 h. The product was filtered, washed with methanol, and dried at 60°C for 24 h. 2.2.7 Fabrication of C-(Pd/CS-Cu-MOF) Pd/CS-Cu-MOF (0.35 g) was added to an ethanol solution containing 5 wt% GA and reacted at 70°C for 24 h. The product was filtered, washed repeatedly with ethanol, and dried at 60°C for 24 h. 2.2.8 Activity test A 50 mL PTFE-lined high-pressure vessel was utilized to evaluate the catalytic performance, with the transformation route illustrated in Scheme 1. An amount of glycerol (1.44 g) was fully dissolved in 10 mL of N, N-dimethylacetamide. Subsequently, 0.0188 g of KI and 0.025 g of the catalytic material were introduced into the glycerol-containing mixture. The vessel was flushed with oxygen thrice and pressurized to 1.3 MPa O₂ and 2.7 MPa CO, achieving an overall pressure of 4 MPa. The mixture was raised to 140°C and kept under these conditions for 2.5 h. The resulting mixture underwent silylation, and its composition was determined via gas chromatography employing a reference standard method. Details of the silylation procedure, calibration curves for the reference method, and corresponding formula derivations were obtained from literature sources (Figs. S1 and S2). 3. Results and discussion 3.1 Characterization and Analysis The structure of the support and catalyst was analyzed using FT-IR. The broad peak at 3427 cm − 1 in CS (O-H/N-H vibration) [ 39 ] became significantly narrower after combining with Cu-MOF, indicating that the interaction altered the hydrogen bond distribution. Glutaraldehyde crosslinking introduced a new hydrogen-bond network, broadening the peak and confirming the success of the crosslinking reaction. Palladium loading caused shifts in the C-H bending vibration of CH 3 and the C = O stretching vibration of the amide I group in the catalyst (Fig. 1 a), primarily due to coordination between acetyl/amino groups and palladium [ 40 ]. As previously reported [ 41 ], XRD confirmed that CS is amorphous, with no Cu-MOF diffraction peaks observed in this range due to its low content and high dispersion. After cross-linking, the crystallinity of CCS-Cu-MOF did not significantly increase, indicating that the reaction primarily adjusted the chemical environment rather than the crystal properties, promoting Pd immobilization and forming a unique capsule-like structure. The XRD patterns of Pd/CS-Cu-MOF and Pd/CCS-Cu-MOF (Fig. 1 c) also exhibited amorphous structures, suggesting that palladium is highly dispersed, which enhances catalytic performance. ICP-OES analysis revealed that the palladium content was only 0.49wt.%, indicating a low palladium loading and reduced detection probability. This is the unique advantage of the biomimetic catalyst: lower active component content but higher catalytic performance. However, in the other two catalysts, three new diffraction peaks at 2θ = 40°, 47°, and 66° corresponding to the (111), (200), and (220) planes of face-centered cubic (FCC) palladium [ 42 ] were observed. This suggests the formation of larger palladium particles, resulting in a reduced surface area and limited catalytic performance enhancement. Thus, Pd/CCS-Cu-MOF is an ideal biomimetic catalyst for glycerol oxidation carbonylation. TGA-DTG analysis shows that Cu-MOF significantly improves the thermal stability of chitosan-based composites. Pure CS decomposes in three stages: 50°C to 120°C (loss of adsorbed and structural water), 250°C to 400°C (dehydration and thermal decomposition), and 400°C to 600°C (further carbonization) [ 43 ]. Cu-MOF has higher thermal stability, mainly decomposing at 250°C-400°C. Notably, the decomposition rate increases sharply at 400°C-440°C, related to organic ligand decomposition and metal oxide formation [ 44 ]. CS-Cu-MOF and CCS-Cu-MOF show similar decomposition trends to Cu-MOF, but with slower mass loss from 250°C to 400°C, improving thermal stability due to the synergistic effect between chitosan and Cu-MOF. CCS-Cu-MOF has a higher thermal decomposition temperature, indicating that crosslinking further enhances structural stability. Palladium-loaded catalysts are thermally stable at 200°C (except for 100°C water loss), ensuring stable reaction conditions (140°C). The thermal stability, preparation method, and catalytic activity of palladium-loaded catalysts are closely related. Pd/CCS-Cu-MOF shows high stability, indicating that crosslinking enhances rigidity and activity. Although Pd/CS-Cu-MOF has high thermal stability, Pd/CCS-Cu-MOF shows the best catalytic activity. C-(Pd/CS-Cu-MOF) shows decreased uniformity and performance after crosslinking. Finally, Pd/Cu-MOF decomposes rapidly at high temperatures due to the lack of chitosan binding, showing poor stability and activity. These results suggest that crosslinking significantly affects catalytic activity and thermal stability, with structural rigidity and balance being key factors in determining catalyst performance. Affinity for reactants is key in MOF biomimetic catalyst design. In heterogeneous catalysis, reactant diffusion to the catalyst surface is often the rate-limiting step, so rapid diffusion and interaction with active sites are crucial for efficiency. Products must also diffuse quickly out of the framework to drive the reaction. Therefore, high porosity, large surface area, and large pore size (especially mesoporous MOFs) enhance diffusion and mass transfer. BET characterization results confirm this [ 45 ], with all samples showing type IV isotherms and H3-type hysteresis (Fig. 3 ), indicating primarily mesoporous structures. Pd/Cu-MOF and Pd/CCS-Cu-MOF have uniform pore sizes, improving diffusion rates and active site utilization. In contrast, C-(Pd/CS-Cu-MOF) exhibits pore wall collapse due to crosslinking, resulting in a wide pore size distribution that reduces reactant capture and palladium utilization, thereby limiting its catalytic performance. Table 1 Surface area, average pore size, and pore volume of Pd/Cu-MOF, C-(Pd/CS-Cu-MOF), Pd/CS-Cu-MOF, and Pd/CCS-Cu-MOF Samples Surface area a (m 2 /g) Average pore diameter b (nm) Pore volume (cm 3 /g) Pd/Cu-MOF 132.2 8.729 0.2285 C-(Pd/CS-Cu-MOF) 56.47 11.47 0.1619 Pd/CS-Cu-MOF 72.85 12.77 0.2325 Pd/CCS-Cu-MOF 114.6 10.89 0.3119 a Measured using N 2 adsorption with the Brunauer-Emmett-Teller (BET) method. b Pore size in diameter was calculated by the desorption data using Barrett-Joyner-Halenda (BJH) method. Table 1 shows that a high specific surface area increases active sites, while a large pore volume enhances the contact efficiency between reactants and active sites. Although Pd/Cu-MOF has a large specific surface area, its low pore volume and size limit mass transfer, reducing active site exposure and palladium utilization. Pd/CS-Cu-MOF, loaded with palladium without crosslinking, has uneven pore distribution and some pore damage, weakening mass transfer, and active site utilization. C-(Pd/CS-Cu-MOF), crosslinked after palladium loading, may have pore collapse or blockage, further reducing surface area, pore volume, and catalytic efficiency. In contrast, Pd/CCS-Cu-MOF, which uses crosslinking before palladium loading, improves structural stability and pore uniformity, preventing pore wall damage during palladium loading and balancing specific surface area and pore volume, providing an ideal channel for efficient glycerol-palladium interaction and showing optimal catalytic performance. The SEM images show the microstructure and particle arrangement of the samples, displaying the distribution of the support and palladium. Cu-MOF (Fig. 4 e) has a sheet-like crystal structure with good crystallinity. Pd/Cu-MOF (Fig. 4 d) retains the porous MOF structure (Loose pine branches), but uneven palladium dispersion and weak binding lead to uneven active site distribution. CS-Cu-MOF (Fig. 4 b) shows Cu-MOF crystal distribution on the surface, while Pd/CS-Cu-MOF (Fig. 4 f) maintains a spherical structure with white particles (pearl-like), confirming successful palladium loading. This structural evolution shows that CS-Cu-MOF not only supports Cu-MOF's porous structure but also promotes uniform palladium distribution and fixation through chemical interaction between chitosan groups and palladium, providing a foundation for catalytic activity. C-(Pd/CS-Cu-MOF) (Fig. 4 e) shows pore blockage and uneven palladium distribution due to crosslinking, limiting active site exposure. Pd/CCS-Cu-MOF (Fig. 4 g) exhibits improved structural stability after crosslinking, optimizing the diffusion pathway for reactants. Pd/CCS-Cu-MOF has a more uniform palladium distribution and superior performance. Notably, chitosan crosslinking enhances palladium anchoring and optimizes the electronic environment, improving catalytic efficiency in the glycerol oxidative carbonylation reaction. Therefore, the sequence of crosslinking design is crucial for material structure regulation and performance. To further study the microstructure of the catalysts, TEM analysis was performed. The TEM images of Cu-MOF (Fig. 5 a), CS-Cu-MOF (Fig. 5 b), and CCS-Cu-MOF (Fig. 5 c) illustrate the structural evolution during modification. Pd/Cu-MOF (Fig. 5 d) shows a sheet-like layered porous structure. CS-Cu-MOF (Fig. 5 b) exhibits a “core-shell” structure consistent with SEM results. Pd/CS-Cu-MOF (Fig. 5 f) has a uniform morphology with well-dispersed palladium particles. Post-crosslinked C-(Pd/CS-Cu-MOF) (Fig. 5 e) shows aggregation, indicating the timing of crosslinking affects palladium dispersion and active site exposure. Pd/CCS-Cu-MOF (Fig. 5 g) features a microcapsule structure with uniformly distributed particles, attributed to the stable glutaraldehyde crosslinking network, which anchors palladium particles, prevents aggregation, and enhances catalytic activity. These results reveal the role of preparation strategies in regulating catalyst morphology and the structure-activity relationship. To investigate the elemental composition and chemical states on the catalyst surface, XPS analysis was performed. Figure 6 a confirms the presence of Cu, Pd, C, and O. The O 1S spectra (Fig. 6 b) show Cu-O and Pd-O bonds at 529.8 eV in all samples. Notably, Pd/Cu-MOF and Pd/CCS-Cu-MOF exhibit peaks at 530.8–531.5 eV, indicating carbonyl oxygen (O = C-O) within the MOF, with Pd/CCS-Cu-MOF showing the strongest oxygen signal, reflecting its most intact structure and superior catalytic performance. The chitosan-modified catalysts show a strong hydroxyl (-OH) peak at 532.5 eV, while unmodified catalysts show a weaker hydroxyl peak. Weak peaks at 536.8 eV in C-(Pd/CS-Cu-MOF) and Pd/CS-Cu-MOF are attributed to surface-adsorbed water or other high-binding-energy oxygen species. In Fig. 6 c, the Pd/Cu-MOF sample lacks distinct Pd peaks due to its low Pd loading (0.49wt.%). However, Pd/CS-Cu-MOF, C-(Pd/CS-Cu-MOF), and Pd/CCS-Cu-MOF show characteristic Pd 0 and Pd 2+ peaks at 336/341 eV and 337/343 eV, respectively. Notably, C-(Pd/CS-Cu-MOF) displays stronger Pd0 and Pd²⁺ peaks than Pd/CS-Cu-MOF, likely due to local Pd aggregation caused by crosslinking, negatively affecting catalytic performance. In contrast, Pd/CCS-Cu-MOF shows reduced peak intensities, indicating higher Pd dispersion. This suggests that partial electronic interactions between Pd and Cu create more effective catalytic sites. Cu, although not a direct catalytic center, promotes reactions through electronic modulation (e.g., Cu-Pd synergy), reactant adsorption regulation, and redox co-catalysis. Cu 2p XPS analysis (Fig. 6 d) shows that Cu in Pd/Cu-MOF is primarily in the Cu(II) state, while in Pd/CS-Cu-MOF, the peak at 932 eV indicates a partial reduction of Cu(II) to Cu(I)/Cu(0), reflecting the chitosan-Cu-MOF interaction modulating Cu's electronic density. In the crosslinked catalyst, the intensity of Cu(I)/Cu(0) increases, suggesting that the crosslinked chitosan network strengthens interactions with Cu, promoting its reduction. However, Pd/CCS-Cu-MOF exhibits lower Cu(II) reduction, indicating that pre-crosslinked chitosan effectively stabilizes Cu's electronic environment and prevents over-reduction of Cu(II). In the glycerol oxidative carbonylation reaction, the stability of Cu(II) plays a key role by providing the appropriate oxidative power and facilitating the reaction. Crosslinked chitosan not only stabilizes Cu's electronic environment but also prevents excessive reduction, thus maintaining catalytic stability. Additionally, the synergy between Pd and Cu, along with the modulation of the electronic environment by iodine ions in the co-catalyst, further enhances catalytic efficiency, resulting in Pd/CCS-Cu-MOF exhibiting the best catalytic performance. The XPS C 1s spectrum (Fig. 7 a) shows characteristic peaks for C-C/C-H (284.7 eV), C-O (286.4 eV), and C = O (288.5 eV) in all samples. Pd/CCS-Cu-MOF shows evenly distributed C 1s signals, suggesting an ordered carbon framework with stable C = N and C-O bonds, which result from the pre-crosslinking process. This process converts amines to C = N bonds, reducing amine-oxygen reactions, and enhancing chitosan's structural stability. This ordered structure aids palladium nanoparticle dispersion, suppresses aggregation, and increases active sites, improving catalytic activity. In contrast, C-(Pd/CS-Cu-MOF) and Pd/CS-Cu-MOF display stronger peaks at 286.4 eV and 285.7 eV, indicating higher oxygen-containing functional group content. This suggests less ordered carbon structures compared to Pd/CCS-Cu-MOF. Regarding nitrogen, Pd/Cu-MOF shows no significant nitrogen signal, lacking nitrogen-based coordination for Pd electronic state regulation, which leads to lower catalytic activity. Unreacted amine groups in C-(Pd-CS-Cu-MOF) and Pd/CS-Cu-MOF show peaks at 399.3-399.5 eV, while C = N bonds induced by glutaraldehyde in Pd/CCS-Cu-MOF exhibit stronger peaks. Peaks at 400.5-402.5 eV in all modified catalysts correspond to nitrogen coordination with Cu and Pd, increasing binding energy. Notably, Pd/CCS-Cu-MOF has the highest peak at 402.5 eV, indicating that its crosslinked structure effectively retains nitrogen-active sites. The synergy between C = N bonds and metals not only provides stable support but also enhances metal dispersion. This demonstrates that chitosan-metal synergy not only stabilizes metal loading but also modulates Pd's electronic structure through coordination, facilitating CO and glycerol activation, and enhancing catalytic efficiency. In contrast, Pd/CS-Cu-MOF shows slightly lower support stability and Pd dispersion due to insufficient C = N formation. C-(Pd/CS-Cu-MOF) may suffer from potential Pd aggregation due to preloading, hindering effective synergy with C = N. These structural features directly influence catalytic performance, explaining why Pd/CCS-Cu-MOF shows the highest catalytic activity, followed by the others in decreasing order. 3.2 Catalyst Performance Evaluation In the design of MOF-based bio-inspired catalysts, reactant diffusion, and catalyst affinity are critical for catalytic efficiency. In heterogeneous catalysis, the rate-limiting step is often the diffusion of reactants to the catalyst surface. Thus, fast substrate diffusion and interaction with active sites are key for high efficiency. Dynamic contact angle testing (Fig. 8 ) reveals that Pd/CCS-Cu-MOF shows an initial contact angle of 116.7°, much higher than other catalysts, indicating a hydrophobic surface. This reduces the inhibitory effect of water on active sites and promotes glycerol adsorption. During the reaction, the contact angle rapidly drops to 12.9°, demonstrating a hydrophilic transition. This dynamic wettability adjustment creates an optimal interfacial environment, enhancing glycerol interaction with active sites and improving conversion efficiency and selectivity. In contrast, other catalysts show smaller contact angle changes, indicating weaker wettability control and limiting reactant diffusion. These findings highlight the importance of optimizing surface wettability for efficient catalysis. The hydrophobic-to-hydrophilic transition of Pd/CCS-Cu-MOF offers an ideal environment for efficient reactions, minimizing side reactions. Further optimization could improve glycerol oxidative carbonylation and enable highly selective, efficient catalysts. The performance optimization study showed that Pd loading is the most crucial factor affecting catalytic activity. Pd/CCS-Cu-MOF exhibited the highest activity at 0.6% Pd loading. This further highlights the advantage of biomimetic catalysts in achieving high activity with low component content. Pd/Cu-MOF showed the lowest activity due to its low Pd content, while C-(Pd/CS-Cu-MOF) and Pd/CS-Cu-MOF activities decreased sequentially (Fig. 9 a). This is mainly due to the stable three-dimensional porous structure of Pd/CCS-Cu-MOF, which enhances reactant diffusion and Pd active center interaction. In contrast, C-(Pd/CS-Cu-MOF) suffers from reduced Pd accessibility due to the chitosan crosslinking layer. Pd/CCS-Cu-MOF was selected for optimization, with 6 hours as the optimal crosslinking time (Fig. 9 b). Under optimal conditions (catalyst amount: 0.025 g, 140°C, 4 MPa, 2.5 hours), the catalyst achieved 92% yield and 100% selectivity. Non-crosslinked or post-crosslinked catalysts have more reactive amino and hydroxyl groups on chitosan, which can easily coordinate with Pd to form Pd-N and Pd-O bonds. This coordination stabilizes Pd and prevents aggregation, but excessive coordination can alter Pd's electronic density, affecting its catalytic activity. Some Pd sites may also be shielded by chitosan coordination, reducing accessibility and reactivity. Moreover, Pd/Cu-MOF lacks support and modulation from chitosan and crosslinking, leading to poor Pd dispersion and low activity. In pre-crosslinked Pd/CCS-Cu-MOF, glutaraldehyde reacts with amino groups to form stable Schiff base (C = N) structures, reducing free amino groups and preventing excessive coordination, thus maintaining Pd dispersion and preventing shielding. The microcapsule structure of Pd/CCS-Cu-MOF enhances surface area and porosity, promoting reactant contact with active sites. This design suppresses Pd particle migration and aggregation, improving resistance to deactivation. After five cycles, the catalyst retains a 55% yield. Combining morphology control and crosslinking, this strategy efficiently utilizes active sites and structural stability, offering insights for developing high-performance MOF catalysts. 4. Conclusions This study developed a Pd/CCS-Cu-MOF catalyst using CS as a carrier, achieving about 90% yield and 99% selectivity in glycerol oxidative carbonylation. By coordinating Pd with CS, the catalyst ensures uniform dispersion and enhanced activity. Optimizing crosslinking improved Pd site stability and formed a capsule-like structure mimicking metalloenzymes. Despite a low Pd loading (0.49wt.%), it maintains excellent performance, reducing costs and environmental impact, embodying green chemistry. Overall, Pd/CCS-Cu-MOF excels in performance and offers a sustainable approach to efficient noble metal utilization, advancing green catalysis. This research not only highlights the potential of chitosan-based MOF materials in catalysis but also provides valuable theoretical insights and technical support for developing efficient and environmentally friendly green catalytic technologies. It lays a solid foundation for the industrial application of glycerol valorization. Declarations Acknowledgments The authors sincerely acknowledge the financial support provided by the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE & SAFEA for the 111 Project (B13025). Authors’ contributions Shuqi Qi: Formal analysis, Investigation, Methodology, Writing-Original Draft. Jing Xu: Methodology, Resources, Visualization. Nan Wang: Methodology, Resources, Visualization. Pingbo Zhang: Formal analysis, Supervision, Resources, Writing-Review & Editing. Mingming Fan: Investigation, Methodology, Supervision. Funding This research was financially supported by the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE & SAFEA for the 111 Project (B13025) . Data availability Data will be made available on request. Conflict of Interest The authors declare no competing interests. References M. Balat, H. Balat, Progress in biodiesel processing. Appl. Energy. 87 , 1815–1835 (2010). https://doi.org/10.1016/j.apenergy.2010.01.012 M. Aghbashlo, W. Peng, M. Tabatabaei, S.A. Kalogirou, S. Soltanian, H. Hosseinzadeh-Bandbafha, O. Mahian, S. Su, Machine learning technology in biodiesel research: A review. Prog. Energy Combust. 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Res. Bull. 103 , 89–95 (2018). https://doi.org/10.1016/j.materresbull.2018.03.013 S. Sadjadi, F. Koohestani, Composite of cross-linked chitosan beads and a cyclodextrin nanosponge: A metal-free catalyst for promoting ultrasonic-assisted chemical transformations in aqueous media. J. Phys. Chem. Solids. 156 , 110157 (2021). https://doi.org/10.1016/j.jpcs.2021.110157 G. Wang, K. Lv, T. Chen, Z. Chen, J. Hu, Immobilizing of palladium on melamine functionalized magnetic chitosan beads: A versatile catalyst for p-nitrophenol reduction and Suzuki reaction in aqueous medium. Int. J. Biol. Macromol. 184 , 358–368 (2021). https://doi.org/10.1016/j.ijbiomac.2021.06.055 S. Sadjadi, M.M. Heravi, S.S. Kazemi, Ionic liquid decorated chitosan hybridized with clay: A novel support for immobilizing Pd nanoparticles. Carbohydr. Polym. 200 , 183–190 (2018). https://doi.org/10.1016/j.carbpol.2018.07.093 S. Sadjadi, F. Koohestani, Palladated composite of Cu-BDC MOF and perlite as an efficient catalyst for hydrogenation of nitroarenes. J. Mol. Struct. 1250 , 131793 (2022). https://doi.org/10.1016/j.molstruc.2021.131793 Y. Chen, S. Ma, Biomimetic catalysis of metal-organic frameworks. Dalton Trans. 45 , 9744–9753 (2016). https://doi.org/10.1039/C6DT00325G Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6418048","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":452958970,"identity":"da99c70a-e162-41e8-a155-20c10cda0296","order_by":0,"name":"Shuqi Qi","email":"","orcid":"","institution":"Ministry of Education, Jiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Shuqi","middleName":"","lastName":"Qi","suffix":""},{"id":452958971,"identity":"92ca77c2-6c6f-4538-a249-8aed70e812df","order_by":1,"name":"Jing Xu","email":"","orcid":"","institution":"Ministry of Education, Jiangnan 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the catalyst, (b) the support, XRD pattern of (c) the catalyst, (d) CS-Cu-MOF and CCS-Cu-MOF, (e) Cu-MOF\u003c/p\u003e","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/82d1a97e159b2b81f892237c.png"},{"id":82452623,"identity":"fb88c57c-e989-4a18-bb12-b989e70230dd","added_by":"auto","created_at":"2025-05-11 10:16:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":218611,"visible":true,"origin":"","legend":"\u003cp\u003e(a) TGA curve of the support, (b) DTG curve of the support, (c) TGA curve of the catalyst, (d) DTG curve of the catalyst\u003c/p\u003e","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/d30c15d949d949a0c74a04f6.png"},{"id":82452428,"identity":"f80aa389-4177-41ca-a131-a4d1aa47cfb0","added_by":"auto","created_at":"2025-05-11 10:08:46","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":219709,"visible":true,"origin":"","legend":"\u003cp\u003eN\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherm and pore size distribution of (a) Pd/Cu-MOF, (b) C-(Pd/CCS-Cu-MOF), (c) Pd/CS-Cu-MOF, (d) Pd/CCS-Cu-MOF\u003c/p\u003e","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/cedc06e1a0e4f60d33193171.png"},{"id":82452625,"identity":"29193fe7-e36f-4894-8f6c-3b00b2271399","added_by":"auto","created_at":"2025-05-11 10:16:46","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":5668099,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of (a) Cu-MOF, (b) CS-Cu-MOF, (c) CCS-Cu-MOF, (d) Pd/Cu-MOF, (e) C-(Pd/CS-Cu-MOF), (f) Pd/CS-Cu-MOF, (g) Pd/CCS-Cu-MOF\u003c/p\u003e","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/8caa7cbc873657c8fb04313f.png"},{"id":82452440,"identity":"30cf888a-f6b2-4ecd-be36-9fa04a4473de","added_by":"auto","created_at":"2025-05-11 10:08:46","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":5759451,"visible":true,"origin":"","legend":"\u003cp\u003eTEM image of (a) Cu-MOF, (b) CS-Cu-MOF, (c) CCS-Cu-MOF, (d) Pd/Cu-MOF, (e) C-(Pd/CS-Cu-MOF), (f) Pd/CS-Cu-MOF, (g) Pd/CCS-Cu-MOF\u003c/p\u003e","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/c093b3ba1ef1ab37fd57944d.png"},{"id":82452438,"identity":"c776583f-2479-4583-9d22-5cd57a3bd03f","added_by":"auto","created_at":"2025-05-11 10:08:46","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":267950,"visible":true,"origin":"","legend":"\u003cp\u003eXPS analysis of Pd/Cu-MOF, C-(Pd/CS-Cu-MOF), Pd/CS-Cu-MOF, and Pd/CCS-Cu-MOF, (a) survey spectra, (b) O 1s spectra, (c) Pd 3d spectra, (d) Cu 2p spectra\u003c/p\u003e","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/72bf087aedd789b034df49cd.png"},{"id":82452442,"identity":"7dee115a-ad5d-49fa-a625-555bf6b35aec","added_by":"auto","created_at":"2025-05-11 10:08:46","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":216660,"visible":true,"origin":"","legend":"\u003cp\u003eXPS analysis of Pd/Cu-MOF, C-(Pd/CS-Cu-MOF), Pd/CS-Cu-MOF, and Pd/CCS-Cu-MOF, (a) C 1s spectra, (b) N 1s spectra\u003c/p\u003e","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/2ed8107db61153e912d4982f.png"},{"id":82452441,"identity":"a7d5c21c-7420-400a-bc89-4490caed6be7","added_by":"auto","created_at":"2025-05-11 10:08:46","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":106457,"visible":true,"origin":"","legend":"\u003cp\u003eGlycerol contact angle changes within 30 seconds for (a) Pd/Cu-MOF, (b) C-(Pd/CS-Cu-MOF), (c) Pd/CS-Cu-MOF, (d) Pd/CCS-Cu-MOF catalysts\u003c/p\u003e","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/07f6d2504e76758ac08098d2.png"},{"id":82452432,"identity":"ec605929-14ca-47ac-b31a-d4e02b9ad5b8","added_by":"auto","created_at":"2025-05-11 10:08:46","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":208807,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Yield and selectivity of the four catalysts, (b) Optimization of crosslinking time, (c) Reusability test of Pd/CCS-Cu-MOF catalyst\u003c/p\u003e","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/3d551731c195770b85728d5c.png"},{"id":85319189,"identity":"d3e4a9ba-7845-43d8-8843-27b8fcd52d4b","added_by":"auto","created_at":"2025-06-24 15:01:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":18818526,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/6cc2c20e-a14e-430f-95b4-1d2fd605f32a.pdf"},{"id":82452450,"identity":"0609555a-6410-43fc-9106-e495606eb586","added_by":"auto","created_at":"2025-05-11 10:08:47","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":17058281,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6418048/v1/e8d669b6638ea97bdee037f1.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Multifunctional Pd/CCS-Cu-MOF Microcapsule Catalyst: A Biomimetic Design Inspired by Metalloenzyme Structures for Sustainable Glycerol Valorizing into Glycerol Carbonate","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eGlycerol, a key byproduct generated during biodiesel production, serves as a vital chemical feedstock. However, its excessive production has become a significant bottleneck in the biodiesel industry\u0026rsquo;s development [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Consequently, research on converting glycerol into high-value-added chemicals has garnered significant attention [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Glycerol carbonate, derived from glycerol, is a sustainable chemical with various roles, such as an additive, a softening agent, and a precursor in producing medicines and agricultural chemicals [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Recent investigations into glycerol oxidative carbonylation have centered on designing advanced solid catalysts to enhance reaction stability while achieving higher efficiency and precision. Palladium is broadly acknowledged as the most potent catalytic material for these carbonylation transformations. Exposed palladium nanoparticles, as highly efficient noble metal catalysts [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], can facilitate various reactions, including the hydrogenation of unsaturated olefins [\u003cspan additionalcitationids=\"CR9 CR10 CR11 CR12\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and carbon-carbon coupling reactions such as Suzuki-Miyaura and Heck reactions [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, the scarcity of palladium in nature presents a cost challenge for industrial applications. Therefore, creating more active sites to increase specific surface area while maintaining a low loading is an effective strategy to enhance the catalytic activity of palladium nanoparticles [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite these advantages, the tendency of palladium nanoparticles to aggregate poses a challenge to their catalytic performance, necessitating the selection of suitable supports to overcome this issue [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The incorporation of natural materials helps not only to reduce costs but also to enhance the biodegradability and biocompatibility of catalysts. For instance, abundant carbohydrate chitosan is widely used due to its low cost and non-toxicity [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Previously, Dabbawala et al. reported using chitosan-supported palladium for synthesizing 2-phenylethanol [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Recently, Zeng et al. demonstrated using chitosan microspheres loaded with palladium in Heck coupling reactions [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. These studies highlight the potential of chitosan-based catalysts in various chemical transformations, including oxidative carbonylation reactions.\u003c/p\u003e \u003cp\u003eIndustrially, the oxidative carbonylation of glycerol is considered one of the most promising conversion pathways due to its high atom economy, low cost, and low energy consumption, aligning with the core principles of green chemistry [\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Chitosan's unique chemical structure, featuring amino and hydroxyl functional groups, provides a theoretical basis for its effectiveness as a support material. These functional groups can coordinate with palladium, mimicking the interaction mechanisms between biomolecules and metal ions. Additionally, through polycondensation reactions, chitosan can form robust cross-linked supports (e.g., chitosan cross-linked microspheres), improving the dispersion of metal nanoparticles and enhancing their recyclability. Compared to traditional chitosan microspheres, those composited with other compounds, such as metal-organic frameworks (MOFs) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], exhibit superior performance. MOFs, with their high specific surface area, porous structure, and diverse functional properties [\u003cspan additionalcitationids=\"CR29 CR30\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], are ideal candidates for the next generation of biomimetic catalysts.\u003c/p\u003e \u003cp\u003eThe development of biomimetic catalysts, inspired by nature, aims to replicate enzyme-like structural features and catalytic mechanisms to achieve high activity, selectivity, and enhanced stability [\u003cspan additionalcitationids=\"CR33 CR34 CR35\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Chitosan-MOF composite catalytic supports demonstrate notable biomimetic characteristics: chitosan, derived from natural materials, has chemical and structural properties akin to biopolymers in nature; the amino and hydroxyl functional groups on chitosan coordinate with metal catalysts like palladium, mimicking interactions between biomolecules and metal ions; its three-dimensional porous structure enhances palladium dispersion and activity, optimizing substrate binding at active centers; additionally, it's green degradability and eco-friendly features align with natural material degradation and regeneration cycles, reducing environmental impact.\u003c/p\u003e \u003cp\u003eLeveraging the biodegradability of chitosan and the porous structure with active metal sites of Cu-MOF, this study innovatively designed a palladium-loaded composite catalyst. By controlling the sequence of chitosan cross-linking, the structural characteristics of the catalyst and their influence on catalytic performance were thoroughly investigated. The findings indicate that chitosan (Cu-MOF) cross-linked with glutaraldehyde beforehand disperses palladium nanoparticles more effectively, significantly enhancing catalytic activity and selectivity. Additionally, the catalyst's unique microcapsule structure further boosts its reaction efficiency. This research not only provides an efficient, green catalytic system for glycerol oxidative carbonylation but also offers new perspectives for the design and functional expansion of natural polymer-MOF composite catalysts, showcasing the broad potential for sustainable catalyst development.\u003c/p\u003e"},{"header":"2. Materials and Experimental Procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eAll chemicals utilized in this study were of analytical purity and were used as received without any additional purification. Chitosan (CS, deacetylation degree\u0026thinsp;\u0026gt;\u0026thinsp;90%, viscosity\u0026thinsp;\u0026lt;\u0026thinsp;100 mPa\u0026middot;s), palladium acetate (Pd(OAc)\u003csub\u003e2\u003c/sub\u003e), terephthalic acid, copper nitrate (Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO), palladium chloride (PdCl\u003csub\u003e2\u003c/sub\u003e), ethanol, glutaraldehyde (GA), acetic acid were all purchased from Shanghai Titan Technology Co., Ltd. Sodium tripolyphosphate (STPP), N, N-dimethylacetamide (DMA), methanol, sodium borohydride (NaBH\u003csub\u003e4\u003c/sub\u003e) were all purchased from China National Pharmaceutical Group.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of Composite Materials\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Fabrication of Cu-MOF\u003c/h2\u003e \u003cp\u003eCu-MOF was synthesized by the solvothermal method previously reported [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Briefly, Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO (2.5 g) was dissolved in a homogeneous mixture solution containing terephthalic acid (0.60 g). Once fully dissolved, the mixture was transferred into a hydrothermal reactor and maintained at 120\u0026deg;C for 24 h. After the reaction cooled to room temperature, the resulting product was collected by filtration and dried at 100\u0026deg;C for 12 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Fabrication of CS-Cu-MOF\u003c/h2\u003e \u003cp\u003eCu-MOF was encapsulated in CS particles to form composite particles. For this, Cu-MOF (0.1 g) was suspended in an acetic acid (2 wt%, 45 mL) solution containing CS (1 g), and stirred for 1 h. Once the solution became uniform, STPP solution (2 wt%) was slowly added to form composite beads. Finally, the beads were separated and washed with distilled water until pH\u0026thinsp;=\u0026thinsp;7.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Crosslinking of CS-Cu-MOF Composite Microspheres: CCS-Cu-MOF\u003c/h2\u003e \u003cp\u003eTo enhance the stability of the wet beads, the composite microspheres were immersed in an ethanol solution with 5 wt% glutaraldehyde (GA) and heated at 70\u0026deg;C for 24 h. After the reaction, the microspheres were thoroughly rinsed with ethanol and left to dry at room temperature for 12 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4 Fabrication of Pd/Cu-MOF\u003c/h2\u003e \u003cp\u003eCu-MOF (0.37 g) was dissolved in methanol and mixed with a solution of PdCl₂ (0.0037 g) in ammonium hydroxide, followed by stirring for 2 hours. Next, NaBH₄ (0.062 g) was introduced into the mixture and allowed to react for 24 h. The resulting product was separated by filtration and dried at 80\u0026deg;C for 24 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.2.5 Fabrication of Pd/CS-Cu-MOF\u003c/h2\u003e \u003cp\u003eCS-Cu-MOF (0.32 g) was introduced into methanol (30 mL) and stirred for 1 h. Next, a solution containing Pd(OAc)\u003csub\u003e2\u003c/sub\u003e (0.0041 g) was incorporated into the system and left under continuous agitation for 2 h. Later, NaBH\u003csub\u003e4\u003c/sub\u003e (0.016 g) was introduced to facilitate the reduction of Pd(II) to Pd nanoparticles. Following 3 h, the resulting solid was separated by filtration, rinsed with methanol, and subjected to drying at 60\u0026deg;C for 24 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.2.6 Fabrication of Pd/CCS-Cu-MOF\u003c/h2\u003e \u003cp\u003eThe cross-linked composite microspheres were palletized by the wet impregnation method [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. For this, the crosslinked composite microspheres (0.35 g) were introduced into methanol (30 mL) and stirred for 1 hour. Then, Pd(OAc)\u003csub\u003e2\u003c/sub\u003e (0.0044 g) solution was added, and the mixture was stirred for 2 h. NaBH\u003csub\u003e4\u003c/sub\u003e (0.018 g) was added for reduction for 3 h. The product was filtered, washed with methanol, and dried at 60\u0026deg;C for 24 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.2.7 Fabrication of C-(Pd/CS-Cu-MOF)\u003c/h2\u003e \u003cp\u003ePd/CS-Cu-MOF (0.35 g) was added to an ethanol solution containing 5 wt% GA and reacted at 70\u0026deg;C for 24 h. The product was filtered, washed repeatedly with ethanol, and dried at 60\u0026deg;C for 24 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.2.8 Activity test\u003c/h2\u003e \u003cp\u003eA 50 mL PTFE-lined high-pressure vessel was utilized to evaluate the catalytic performance, with the transformation route illustrated in Scheme 1. An amount of glycerol (1.44 g) was fully dissolved in 10 mL of N, N-dimethylacetamide. Subsequently, 0.0188 g of KI and 0.025 g of the catalytic material were introduced into the glycerol-containing mixture. The vessel was flushed with oxygen thrice and pressurized to 1.3 MPa O₂ and 2.7 MPa CO, achieving an overall pressure of 4 MPa. The mixture was raised to 140\u0026deg;C and kept under these conditions for 2.5 h. The resulting mixture underwent silylation, and its composition was determined via gas chromatography employing a reference standard method. Details of the silylation procedure, calibration curves for the reference method, and corresponding formula derivations were obtained from literature sources (Figs. S1 and S2).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characterization and Analysis\u003c/h2\u003e \u003cp\u003eThe structure of the support and catalyst was analyzed using FT-IR. The broad peak at 3427 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in CS (O-H/N-H vibration) [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] became significantly narrower after combining with Cu-MOF, indicating that the interaction altered the hydrogen bond distribution. Glutaraldehyde crosslinking introduced a new hydrogen-bond network, broadening the peak and confirming the success of the crosslinking reaction. Palladium loading caused shifts in the C-H bending vibration of CH\u003csub\u003e3\u003c/sub\u003e and the C\u0026thinsp;=\u0026thinsp;O stretching vibration of the amide I group in the catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), primarily due to coordination between acetyl/amino groups and palladium [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. As previously reported [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e], XRD confirmed that CS is amorphous, with no Cu-MOF diffraction peaks observed in this range due to its low content and high dispersion. After cross-linking, the crystallinity of CCS-Cu-MOF did not significantly increase, indicating that the reaction primarily adjusted the chemical environment rather than the crystal properties, promoting Pd immobilization and forming a unique capsule-like structure.\u003c/p\u003e \u003cp\u003eThe XRD patterns of Pd/CS-Cu-MOF and Pd/CCS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) also exhibited amorphous structures, suggesting that palladium is highly dispersed, which enhances catalytic performance. ICP-OES analysis revealed that the palladium content was only 0.49wt.%, indicating a low palladium loading and reduced detection probability. This is the unique advantage of the biomimetic catalyst: lower active component content but higher catalytic performance. However, in the other two catalysts, three new diffraction peaks at 2θ\u0026thinsp;=\u0026thinsp;40\u0026deg;, 47\u0026deg;, and 66\u0026deg; corresponding to the (111), (200), and (220) planes of face-centered cubic (FCC) palladium [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] were observed. This suggests the formation of larger palladium particles, resulting in a reduced surface area and limited catalytic performance enhancement. Thus, Pd/CCS-Cu-MOF is an ideal biomimetic catalyst for glycerol oxidation carbonylation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTGA-DTG analysis shows that Cu-MOF significantly improves the thermal stability of chitosan-based composites. Pure CS decomposes in three stages: 50\u0026deg;C to 120\u0026deg;C (loss of adsorbed and structural water), 250\u0026deg;C to 400\u0026deg;C (dehydration and thermal decomposition), and 400\u0026deg;C to 600\u0026deg;C (further carbonization) [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Cu-MOF has higher thermal stability, mainly decomposing at 250\u0026deg;C-400\u0026deg;C. Notably, the decomposition rate increases sharply at 400\u0026deg;C-440\u0026deg;C, related to organic ligand decomposition and metal oxide formation [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. CS-Cu-MOF and CCS-Cu-MOF show similar decomposition trends to Cu-MOF, but with slower mass loss from 250\u0026deg;C to 400\u0026deg;C, improving thermal stability due to the synergistic effect between chitosan and Cu-MOF. CCS-Cu-MOF has a higher thermal decomposition temperature, indicating that crosslinking further enhances structural stability. Palladium-loaded catalysts are thermally stable at 200\u0026deg;C (except for 100\u0026deg;C water loss), ensuring stable reaction conditions (140\u0026deg;C). The thermal stability, preparation method, and catalytic activity of palladium-loaded catalysts are closely related. Pd/CCS-Cu-MOF shows high stability, indicating that crosslinking enhances rigidity and activity. Although Pd/CS-Cu-MOF has high thermal stability, Pd/CCS-Cu-MOF shows the best catalytic activity. C-(Pd/CS-Cu-MOF) shows decreased uniformity and performance after crosslinking. Finally, Pd/Cu-MOF decomposes rapidly at high temperatures due to the lack of chitosan binding, showing poor stability and activity. These results suggest that crosslinking significantly affects catalytic activity and thermal stability, with structural rigidity and balance being key factors in determining catalyst performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAffinity for reactants is key in MOF biomimetic catalyst design. In heterogeneous catalysis, reactant diffusion to the catalyst surface is often the rate-limiting step, so rapid diffusion and interaction with active sites are crucial for efficiency. Products must also diffuse quickly out of the framework to drive the reaction. Therefore, high porosity, large surface area, and large pore size (especially mesoporous MOFs) enhance diffusion and mass transfer. BET characterization results confirm this [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], with all samples showing type IV isotherms and H3-type hysteresis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), indicating primarily mesoporous structures. Pd/Cu-MOF and Pd/CCS-Cu-MOF have uniform pore sizes, improving diffusion rates and active site utilization. In contrast, C-(Pd/CS-Cu-MOF) exhibits pore wall collapse due to crosslinking, resulting in a wide pore size distribution that reduces reactant capture and palladium utilization, thereby limiting its catalytic performance.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSurface area, average pore size, and pore volume of Pd/Cu-MOF, C-(Pd/CS-Cu-MOF), Pd/CS-Cu-MOF, and Pd/CCS-Cu-MOF\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurface area\u003csup\u003ea\u003c/sup\u003e(m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage pore diameter\u003csup\u003eb\u003c/sup\u003e (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePore volume (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePd/Cu-MOF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e132.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.729\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.2285\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC-(Pd/CS-Cu-MOF)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e56.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.1619\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePd/CS-Cu-MOF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e72.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.2325\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePd/CCS-Cu-MOF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e114.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.3119\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003eMeasured using N\u003csub\u003e2\u003c/sub\u003e adsorption with the Brunauer-Emmett-Teller (BET) method.\u003c/p\u003e \u003cp\u003e \u003csup\u003eb\u003c/sup\u003ePore size in diameter was calculated by the desorption data using Barrett-Joyner-Halenda (BJH) method.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows that a high specific surface area increases active sites, while a large pore volume enhances the contact efficiency between reactants and active sites. Although Pd/Cu-MOF has a large specific surface area, its low pore volume and size limit mass transfer, reducing active site exposure and palladium utilization. Pd/CS-Cu-MOF, loaded with palladium without crosslinking, has uneven pore distribution and some pore damage, weakening mass transfer, and active site utilization. C-(Pd/CS-Cu-MOF), crosslinked after palladium loading, may have pore collapse or blockage, further reducing surface area, pore volume, and catalytic efficiency.\u003c/p\u003e \u003cp\u003eIn contrast, Pd/CCS-Cu-MOF, which uses crosslinking before palladium loading, improves structural stability and pore uniformity, preventing pore wall damage during palladium loading and balancing specific surface area and pore volume, providing an ideal channel for efficient glycerol-palladium interaction and showing optimal catalytic performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe SEM images show the microstructure and particle arrangement of the samples, displaying the distribution of the support and palladium. Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) has a sheet-like crystal structure with good crystallinity. Pd/Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) retains the porous MOF structure (Loose pine branches), but uneven palladium dispersion and weak binding lead to uneven active site distribution. CS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) shows Cu-MOF crystal distribution on the surface, while Pd/CS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef) maintains a spherical structure with white particles (pearl-like), confirming successful palladium loading. This structural evolution shows that CS-Cu-MOF not only supports Cu-MOF's porous structure but also promotes uniform palladium distribution and fixation through chemical interaction between chitosan groups and palladium, providing a foundation for catalytic activity. C-(Pd/CS-Cu-MOF) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) shows pore blockage and uneven palladium distribution due to crosslinking, limiting active site exposure. Pd/CCS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg) exhibits improved structural stability after crosslinking, optimizing the diffusion pathway for reactants. Pd/CCS-Cu-MOF has a more uniform palladium distribution and superior performance. Notably, chitosan crosslinking enhances palladium anchoring and optimizes the electronic environment, improving catalytic efficiency in the glycerol oxidative carbonylation reaction. Therefore, the sequence of crosslinking design is crucial for material structure regulation and performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further study the microstructure of the catalysts, TEM analysis was performed. The TEM images of Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), CS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), and CCS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) illustrate the structural evolution during modification. Pd/Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed) shows a sheet-like layered porous structure. CS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) exhibits a \u0026ldquo;core-shell\u0026rdquo; structure consistent with SEM results. Pd/CS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef) has a uniform morphology with well-dispersed palladium particles. Post-crosslinked C-(Pd/CS-Cu-MOF) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee) shows aggregation, indicating the timing of crosslinking affects palladium dispersion and active site exposure. Pd/CCS-Cu-MOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg) features a microcapsule structure with uniformly distributed particles, attributed to the stable glutaraldehyde crosslinking network, which anchors palladium particles, prevents aggregation, and enhances catalytic activity. These results reveal the role of preparation strategies in regulating catalyst morphology and the structure-activity relationship.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate the elemental composition and chemical states on the catalyst surface, XPS analysis was performed. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea confirms the presence of Cu, Pd, C, and O. The O 1S spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb) show Cu-O and Pd-O bonds at 529.8 eV in all samples. Notably, Pd/Cu-MOF and Pd/CCS-Cu-MOF exhibit peaks at 530.8\u0026ndash;531.5 eV, indicating carbonyl oxygen (O\u0026thinsp;=\u0026thinsp;C-O) within the MOF, with Pd/CCS-Cu-MOF showing the strongest oxygen signal, reflecting its most intact structure and superior catalytic performance. The chitosan-modified catalysts show a strong hydroxyl (-OH) peak at 532.5 eV, while unmodified catalysts show a weaker hydroxyl peak. Weak peaks at 536.8 eV in C-(Pd/CS-Cu-MOF) and Pd/CS-Cu-MOF are attributed to surface-adsorbed water or other high-binding-energy oxygen species.\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec, the Pd/Cu-MOF sample lacks distinct Pd peaks due to its low Pd loading (0.49wt.%). However, Pd/CS-Cu-MOF, C-(Pd/CS-Cu-MOF), and Pd/CCS-Cu-MOF show characteristic Pd\u003csup\u003e0\u003c/sup\u003e and Pd\u003csup\u003e2+\u003c/sup\u003e peaks at 336/341 eV and 337/343 eV, respectively. Notably, C-(Pd/CS-Cu-MOF) displays stronger Pd0 and Pd\u0026sup2;⁺ peaks than Pd/CS-Cu-MOF, likely due to local Pd aggregation caused by crosslinking, negatively affecting catalytic performance. In contrast, Pd/CCS-Cu-MOF shows reduced peak intensities, indicating higher Pd dispersion. This suggests that partial electronic interactions between Pd and Cu create more effective catalytic sites. Cu, although not a direct catalytic center, promotes reactions through electronic modulation (e.g., Cu-Pd synergy), reactant adsorption regulation, and redox co-catalysis.\u003c/p\u003e \u003cp\u003eCu 2p XPS analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed) shows that Cu in Pd/Cu-MOF is primarily in the Cu(II) state, while in Pd/CS-Cu-MOF, the peak at 932 eV indicates a partial reduction of Cu(II) to Cu(I)/Cu(0), reflecting the chitosan-Cu-MOF interaction modulating Cu's electronic density. In the crosslinked catalyst, the intensity of Cu(I)/Cu(0) increases, suggesting that the crosslinked chitosan network strengthens interactions with Cu, promoting its reduction. However, Pd/CCS-Cu-MOF exhibits lower Cu(II) reduction, indicating that pre-crosslinked chitosan effectively stabilizes Cu's electronic environment and prevents over-reduction of Cu(II). In the glycerol oxidative carbonylation reaction, the stability of Cu(II) plays a key role by providing the appropriate oxidative power and facilitating the reaction. Crosslinked chitosan not only stabilizes Cu's electronic environment but also prevents excessive reduction, thus maintaining catalytic stability. Additionally, the synergy between Pd and Cu, along with the modulation of the electronic environment by iodine ions in the co-catalyst, further enhances catalytic efficiency, resulting in Pd/CCS-Cu-MOF exhibiting the best catalytic performance.\u003c/p\u003e \u003cp\u003eThe XPS C 1s spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea) shows characteristic peaks for C-C/C-H (284.7 eV), C-O (286.4 eV), and C\u0026thinsp;=\u0026thinsp;O (288.5 eV) in all samples. Pd/CCS-Cu-MOF shows evenly distributed C 1s signals, suggesting an ordered carbon framework with stable C\u0026thinsp;=\u0026thinsp;N and C-O bonds, which result from the pre-crosslinking process. This process converts amines to C\u0026thinsp;=\u0026thinsp;N bonds, reducing amine-oxygen reactions, and enhancing chitosan's structural stability. This ordered structure aids palladium nanoparticle dispersion, suppresses aggregation, and increases active sites, improving catalytic activity. In contrast, C-(Pd/CS-Cu-MOF) and Pd/CS-Cu-MOF display stronger peaks at 286.4 eV and 285.7 eV, indicating higher oxygen-containing functional group content. This suggests less ordered carbon structures compared to Pd/CCS-Cu-MOF. Regarding nitrogen, Pd/Cu-MOF shows no significant nitrogen signal, lacking nitrogen-based coordination for Pd electronic state regulation, which leads to lower catalytic activity. Unreacted amine groups in C-(Pd-CS-Cu-MOF) and Pd/CS-Cu-MOF show peaks at 399.3-399.5 eV, while C\u0026thinsp;=\u0026thinsp;N bonds induced by glutaraldehyde in Pd/CCS-Cu-MOF exhibit stronger peaks. Peaks at 400.5-402.5 eV in all modified catalysts correspond to nitrogen coordination with Cu and Pd, increasing binding energy. Notably, Pd/CCS-Cu-MOF has the highest peak at 402.5 eV, indicating that its crosslinked structure effectively retains nitrogen-active sites. The synergy between C\u0026thinsp;=\u0026thinsp;N bonds and metals not only provides stable support but also enhances metal dispersion. This demonstrates that chitosan-metal synergy not only stabilizes metal loading but also modulates Pd's electronic structure through coordination, facilitating CO and glycerol activation, and enhancing catalytic efficiency. In contrast, Pd/CS-Cu-MOF shows slightly lower support stability and Pd dispersion due to insufficient C\u0026thinsp;=\u0026thinsp;N formation. C-(Pd/CS-Cu-MOF) may suffer from potential Pd aggregation due to preloading, hindering effective synergy with C\u0026thinsp;=\u0026thinsp;N. These structural features directly influence catalytic performance, explaining why Pd/CCS-Cu-MOF shows the highest catalytic activity, followed by the others in decreasing order.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Catalyst Performance Evaluation\u003c/h2\u003e \u003cp\u003eIn the design of MOF-based bio-inspired catalysts, reactant diffusion, and catalyst affinity are critical for catalytic efficiency. In heterogeneous catalysis, the rate-limiting step is often the diffusion of reactants to the catalyst surface. Thus, fast substrate diffusion and interaction with active sites are key for high efficiency. Dynamic contact angle testing (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) reveals that Pd/CCS-Cu-MOF shows an initial contact angle of 116.7\u0026deg;, much higher than other catalysts, indicating a hydrophobic surface. This reduces the inhibitory effect of water on active sites and promotes glycerol adsorption. During the reaction, the contact angle rapidly drops to 12.9\u0026deg;, demonstrating a hydrophilic transition. This dynamic wettability adjustment creates an optimal interfacial environment, enhancing glycerol interaction with active sites and improving conversion efficiency and selectivity. In contrast, other catalysts show smaller contact angle changes, indicating weaker wettability control and limiting reactant diffusion. These findings highlight the importance of optimizing surface wettability for efficient catalysis. The hydrophobic-to-hydrophilic transition of Pd/CCS-Cu-MOF offers an ideal environment for efficient reactions, minimizing side reactions. Further optimization could improve glycerol oxidative carbonylation and enable highly selective, efficient catalysts.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe performance optimization study showed that Pd loading is the most crucial factor affecting catalytic activity. Pd/CCS-Cu-MOF exhibited the highest activity at 0.6% Pd loading. This further highlights the advantage of biomimetic catalysts in achieving high activity with low component content. Pd/Cu-MOF showed the lowest activity due to its low Pd content, while C-(Pd/CS-Cu-MOF) and Pd/CS-Cu-MOF activities decreased sequentially (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea). This is mainly due to the stable three-dimensional porous structure of Pd/CCS-Cu-MOF, which enhances reactant diffusion and Pd active center interaction. In contrast, C-(Pd/CS-Cu-MOF) suffers from reduced Pd accessibility due to the chitosan crosslinking layer. Pd/CCS-Cu-MOF was selected for optimization, with 6 hours as the optimal crosslinking time (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb). Under optimal conditions (catalyst amount: 0.025 g, 140\u0026deg;C, 4 MPa, 2.5 hours), the catalyst achieved 92% yield and 100% selectivity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNon-crosslinked or post-crosslinked catalysts have more reactive amino and hydroxyl groups on chitosan, which can easily coordinate with Pd to form Pd-N and Pd-O bonds. This coordination stabilizes Pd and prevents aggregation, but excessive coordination can alter Pd's electronic density, affecting its catalytic activity. Some Pd sites may also be shielded by chitosan coordination, reducing accessibility and reactivity. Moreover, Pd/Cu-MOF lacks support and modulation from chitosan and crosslinking, leading to poor Pd dispersion and low activity. In pre-crosslinked Pd/CCS-Cu-MOF, glutaraldehyde reacts with amino groups to form stable Schiff base (C\u0026thinsp;=\u0026thinsp;N) structures, reducing free amino groups and preventing excessive coordination, thus maintaining Pd dispersion and preventing shielding. The microcapsule structure of Pd/CCS-Cu-MOF enhances surface area and porosity, promoting reactant contact with active sites. This design suppresses Pd particle migration and aggregation, improving resistance to deactivation. After five cycles, the catalyst retains a 55% yield. Combining morphology control and crosslinking, this strategy efficiently utilizes active sites and structural stability, offering insights for developing high-performance MOF catalysts.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study developed a Pd/CCS-Cu-MOF catalyst using CS as a carrier, achieving about 90% yield and 99% selectivity in glycerol oxidative carbonylation. By coordinating Pd with CS, the catalyst ensures uniform dispersion and enhanced activity. Optimizing crosslinking improved Pd site stability and formed a capsule-like structure mimicking metalloenzymes. Despite a low Pd loading (0.49wt.%), it maintains excellent performance, reducing costs and environmental impact, embodying green chemistry. Overall, Pd/CCS-Cu-MOF excels in performance and offers a sustainable approach to efficient noble metal utilization, advancing green catalysis. This research not only highlights the potential of chitosan-based MOF materials in catalysis but also provides valuable theoretical insights and technical support for developing efficient and environmentally friendly green catalytic technologies. It lays a solid foundation for the industrial application of glycerol valorization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors sincerely acknowledge the financial support provided by the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE \u0026amp; SAFEA for the 111 Project (B13025).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eShuqi Qi:\u003c/strong\u003e Formal analysis, Investigation, Methodology, Writing-Original Draft. \u003cstrong\u003eJing Xu:\u003c/strong\u003e Methodology, Resources, Visualization. \u003cstrong\u003eNan Wang:\u003c/strong\u003e Methodology, Resources, Visualization. \u003cstrong\u003ePingbo Zhang:\u003c/strong\u003e Formal analysis, Supervision, Resources, Writing-Review \u0026amp; Editing. \u003cstrong\u003eMingming Fan:\u003c/strong\u003e Investigation, Methodology, Supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was financially supported by the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE \u0026amp; SAFEA for the 111 Project (B13025) .\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eM. 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Dalton Trans. \u003cb\u003e45\u003c/b\u003e, 9744\u0026ndash;9753 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1039/C6DT00325G\u003c/span\u003e\u003cspan address=\"10.1039/C6DT00325G\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Biomimetic, Crosslinking Sequence, Microcapsule Structure, Glycerol Oxidative Carbonylation, Pd/CCS-Cu-MOF","lastPublishedDoi":"10.21203/rs.3.rs-6418048/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6418048/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGlycerol, a key byproduct generated during biodiesel production, has accumulated in excess, hindering the industry's development. A novel palladium-loaded chitosan-copper metal-organic framework (Pd/CCS-Cu-MOF) biomimetic catalyst was developed to valorize glycerol efficiently. Mimicking metalloenzyme structures, this catalyst significantly enhances catalytic performance by controlling the chitosan crosslinking sequence and the active sites' electronic environment. The crosslinked chitosan improves copper's electronic control and forms a microcapsule structure that stabilizes active sites and optimizes reactant mass transfer. Pd/CCS-Cu-MOF achieves a yield of approximately 90% and a selectivity of 99% in the oxidative carbonylation of glycerol. ICP analysis reveals that the catalyst maintains high efficiency with a remarkably low palladium loading of only 0.49wt.%, thereby reducing precious metal use and promoting green chemistry principles. Characterization further demonstrates the microcapsule structure's advantages in enhancing thermal stability, mechanical strength, and pore distribution, providing new insights into natural polymer-metal organic framework composite catalysts. In conclusion, this study offers an efficient, green catalyst for glycerol valorization and opens new avenues for sustainable catalytic technology development, laying a foundation for future industrial applications.\u003c/p\u003e","manuscriptTitle":"Multifunctional Pd/CCS-Cu-MOF Microcapsule Catalyst: A Biomimetic Design Inspired by Metalloenzyme Structures for Sustainable Glycerol Valorizing into Glycerol Carbonate","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-11 10:08:41","doi":"10.21203/rs.3.rs-6418048/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4a48f45c-e250-407a-ac0c-1f756831f82b","owner":[],"postedDate":"May 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-06-24T14:53:09+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-11 10:08:41","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6418048","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6418048","identity":"rs-6418048","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}