Effective isomerization of glucose to fructose by Sn-MFI/MCM-41 composites as Lewis acid catalysts

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.

Conversion of Glucose to 5-Hydroxymethylfurfural Using Consortium Catalyst in a Biphasic System and Mechanistic Insights

We found an effective catalytic consortium capable of converting glucose to 5-hydroxymethylfurfural (HMF) in high yields (50%). The reaction consists of a consortium of a Lewis acid (NbCl5) and a Brønsted acid (p-sulfonic acid calix[4]arene (CX4SO3H)), in a microwave-assisted reactor and in a biphasic system. The best result for the conversion of glucose to HMF (yield of 50%) was obtained with CX4SO3H/NbCl5 (5 wt%/7.5 wt%), using water/NaCl and MIBK (1:3), at 150 °C, for 17.5 min. The consortium catalyst recycling was tested, allowing its reuse for up to seven times, while maintaining the HMF yield constant. Additionally, it proposed a catalytic cycle by converting glucose to HMF, highlighting the following two key points: the isomerization of glucose into fructose, in the presence of Lewis acid (NbCl5), and the conversion of fructose into HMF, in the presence of CX4SO3H/NbCl5. A mechanism for the conversion of glucose to HMF was proposed and validated.

Enhanced Catalytic Activity of Modified ZSM-5 Towards Glucose Isomerization to Fructose

The present study focuses on generating mesopores within H-ZSM-5 (H-Z) zeolite via desilication and dealumination to incorporate Lewis acidic metal, such as Sn, into the framework (Sn₄ ZS₁₈₀ A₁₅ ) to catalyse glucose isomerisation. Sn₄ ZS₁₈₀ A₁₅ possesses enhanced surface area (457 m²  g^-1 ), mesopore volume (0.585 cm³  g^-1 ) and a high weak-medium to strong acidic sites ratio, compared to parent H-Z (395 m²  g^-1 ; 0.174 cm³  g^-1 ). DRS-UV-Vis and XPS results corroborate Sn incorporation into the framework of Sn₄ ZS₁₈₀ A₁₅ , based on the absorbance peak around 200-220 nm and peaks appearing at 495.8 and 487.4 eV, respectively. Sn₄ ZS₁₈₀ A₁₅ exhibits higher catalytic activity towards glucose isomerisation in ethanol-water at 110 °C, yielding 44.2 % fructose with 80.0 % selectivity. Conversely, the parent H-Z afforded negligible glucose conversion with a fructose yield of <1 % under identical conditions. Moreover, Sn-incorporated on dealuminated (Sn₄ ZS₀ A₁₅ ) and desilicated (Sn₄ ZS₁₈₀ A₀ ) catalysts give a low yield of fructose (7-10 %), signifying the requirement of the desilication-dealumination process before incorporating Sn into the framework.

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.