Efficient isomerization of glucose into fructose by MgO-doped lignin-derived ordered mesoporous carbon

The conversion of glucose into fructose can transform cellulose into high-value chemicals. This study introduces an innovative synthesis method for creating an MgO-based ordered mesoporous carbon (MgO@OMC) catalyst, aimed at the efficient isomerization of glucose into fructose. Throughout the synthesis process, lignin serves as the exclusive carbon precursor, while Mg2+ functions as both a crosslinking agent and a metallic active center. This enables a one-step synthesis of MgO@OMC via a solvent-induced evaporation self-assembly (EISA) method. The synthesized MgO@OMCs exhibit an impeccable 2D hexagonal ordered mesoporous structure, in addition to a substantial specific surface area (378.2 m2/g) and small MgO nanoparticles (1.52 nm). Furthermore, this catalyst was shown active, selective, and reusable in the isomerization of glucose to fructose. It yields 41 % fructose with a selectivity of up to 89.3 % at a significant glucose loading of 7 wt% in aqueous solution over MgO0.5@OMC-600. This performance closely rivals the current maximum glucose isomerization yield achieved with solid base catalysts. Additionally, the catalyst retains a fructose selectivity above 60 % even after 4 cycles, a feature attributable to its extended ordered mesoporous structure and the spatial confinement effect of the OMCs, bestowing it with high catalytic efficiency.

Multiscale QM/MM modelling of catalytic systems with ChemShell

Hybrid quantum mechanical/molecular mechanical (QM/MM) methods are a powerful computational tool for the investigation of all forms of catalysis, as they allow for an accurate description of reactions occurring at catalytic sites in the context of a complicated electrostatic environment. The scriptable computational chemistry environment ChemShell is a leading software package for QM/MM calculations, providing a flexible, high performance framework for modelling both biomolecular and materials catalysis. We present an overview of recent applications of ChemShell to problems in catalysis and review new functionality introduced into the redeveloped Python-based version of ChemShell to support catalytic modelling. These include a fully guided workflow for biomolecular QM/MM modelling, starting from an experimental structure, a periodic QM/MM embedding scheme to support modelling of metallic materials, and a comprehensive set of tutorials for biomolecular and materials modelling.

Fabrication of lignin-derived mesoporous carbon/magnesium oxide composites for microwave-assisted isomerization of glucose in water

A series of mesoporous carbon/magnesium oxide composites (LDMC@MgO-x) with different Mg doping ratios were synthesized by using alkali lignin as the carbon source, potassium chloride as the salt template and magnesium nitrate as the catalytic site precursor, respectively. The BET, FTIR, SEM, and TEM analyses indicated that the as-prepared LDMC@MgO-x possessed a unique hierarchical porous structure with high specific surface area, rich functional groups, and uniformly distributed MgO nanoparticles. Among them, LDMC@MgO-20%, as an optimized base catalyst, could realize effective isomerization of glucose with a maximum fructose yield of 34.4 % in water at 130 °C for only 5 min under microwave assistance. In addition, the activation energy of glucose isomerization catalyzed by LDMC@MgO-20% was estimated to be about 43.6 kJ·mol^-1, which was lower than that of most Lewis acid-catalyzed systems.

Catalytic isomerization of glucose to fructose over organic ligands: a DFT study

CONTEXT

Isomerization processes between glucose and fructose catalyzed by four different organic ligands are investigated with quantum chemistry methods in this study. These organic ligands are the carboxylic pendant group, sulfonic pendant group, amino pendant group, and 1H-imidazole ligand. After guessing and verifying a variety of elementary reactions, transition states and energy barriers that are relevant to the optimum pathways have been confirmed. The effective barriers under the catalysis of the carboxylic pendant group, sulfonic pendant group, amino pendant group, and 1H-imidazole ligand are 97.5 kJ mol^-1, 134.7 kJ mol^-1, 146.7 kJ mol^-1, and 167.7 kJ mol^-1, respectively. Then, based on the conclusions of the non-solvation model, the effective barriers in solvents are briefly investigated. The implicit model predicts that solvents bring little improvement or setback to catalyzed reaction models. The explicit model shows that the proton transfer with the participant of water molecules can improve the catalytic performance of Lewis bases in these reactions. The detailed reaction mechanism combing and reliable reaction templates provided in this work will be useful for catalysis designs for glucose transformation to fructose.

METHODS

This work used the computational level of ωB97M-D3BJ/def2-SVP and the software package of ORCA 4.2. For solvent effects, energies of the gas phase were corrected by the combination of C-PCM and SMD.

Mechanism of Preferential Hydrogenation of Hydroxymethyl Group to Aldehyde Group in 5-Hydroxymethylfurfural over W2 C-Based Catalyst

A W₄ C₂ cluster was used to model a W₂ C catalyst with the armchair model of activated carbon support, noted as W₄ C₂ /AC. Over W₄ C₂ /AC, the mechanism for the hydrogenation of both -H₂ OH and -CHO groups in 5-hydroxymethylfurfural (HMF) was theoretically studied in tetrahydrofuran at GGA-PBE/DNP level. 5-Methylfurfural was the major product from only hydrodehydration of the -CH₂ OH group, whereas 2,5-dihydroxymethylfuran was the minor product from the hydrogenation of both -CH₂ OH and -CHO groups. The rate-determining steps were concerned with the -C(H)₂ -H bond formation for the hydrodehydration of -CH₂ OH group, and the -(OH)(H)-H bond formation for the hydrogenation of -CHO group. Kinetically, W-sites promoted the hydrodehydration of -CH₂ OH group and inhibited the hydrogenation of -CHO group. This stemmed from the strong Lewis acidity of W-sites, which easily accepted the lone-pair electrons of the oxygen atom in the -C(OH)(H)- group, making -C(OH)(H)-H bond formation hard, and hampering the hydrogenation of the -CHO group.