Effects of Acid Modulators on the Microwave-Assisted Synthesis of Cr/Sn Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have attracted remarkable attention for their distinguished structural designability. Precisely controlling the particle size and improving the structural stability of MOF nanoparticles influence their catalytic activity significantly. In this study, six acids (nitric, hydrochloric, formic, acetic, succinic, and citric acids) were used as modulators to prepare bimetallic MIL-101 (Cr, Sn) (MIL stands for Materials of Institut Lavoisier) via a microwave-assisted hydrothermal method. Changes in volumetric, structural, stability, and catalytic properties, size, and shape of MIL-101 (Cr, Sn) were examined using scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and N2 adsorption–desorption measurements. All modulators altered the MOF properties. Compared with other samples, acetic acid as a modulator mildly altered the MOF morphology by narrowing their particle size distribution, enhancing the specific surface area, and significantly improving their water and thermal stabilities. The addition of acetic acid was suitable for the catalytic conversion of glucose to 5-hydroxymethylfurfural (5-HMF), achieving a 43.1% 5-HMF yield with 91.4% glucose conversion in a mixed solution of γ-valerolactone and saturated salt water at 150 °C after 30 min.

Hierarchical Porous MIL-101(Cr) Solid Acid-Catalyzed Production of Value-Added Acetals from Biomass-Derived Furfural

Considering economic and environmental impacts, catalytic biomass conversion to valuable compounds has attracted more and more attention. Of particular interest is furfural, a versatile biorefinery platform molecule used as a feedstock for the production of fuels and fine chemicals. In this study, the Cr-based metal-organic frameworks (MOFs) MIL-101 were modified by chlorosulfonic acid, and MIL-101 was changed into a hierarchical MOF structure with smaller particles and lower particle crystallinity by CTAB, which significantly improved the acidic sites of the MOFs. The original and modified MIL-101(Cr) catalysts were characterized by XRD, N₂ adsorption-desorption, SEM, TEM, and FT-IR. The effects of different catalysts, reaction temperature, catalyst amount, and alcohol type on the reaction were studied. Under the action of the MOFs catalyst, a new mild route for the condensation of furfural with various alkyl alcohols to the biofuel molecules (acetals) was proposed. The conversion route includes the conversion of furfural up to 91% yield of acetal could be obtained within 1 h solvent-free and in room-temperature reaction conditions. The sulfonic acid-functionalized MIL-101(Cr) is easy to recover and reuse, and can still maintain good catalytic activity after ten runs.

Advances in Enzyme and Ionic Liquid Immobilization for Enhanced in MOFs for Biodiesel Production

Biodiesel is a promising candidate for sustainable and renewable energy and extensive research is being conducted worldwide to optimize its production process. The employed catalyst is an important parameter in biodiesel production. Metal-organic frameworks (MOFs), which are a set of highly porous materials comprising coordinated bonds between metals and organic ligands, have recently been proposed as catalysts. MOFs exhibit high tunability, possess high crystallinity and surface area, and their order can vary from the atomic to the microscale level. However, their catalytic sites are confined inside their porous structure, limiting their accessibility for biodiesel production. Modification of MOF structure by immobilizing enzymes or ionic liquids (ILs) could be a solution to this challenge and can lead to better performance and provide catalytic systems with higher activities. This review compiles the recent advances in catalytic transesterification for biodiesel production using enzymes or ILs. The available literature clearly indicates that MOFs are the most suitable immobilization supports, leading to higher biodiesel production without affecting the catalytic activity while increasing the catalyst stability and reusability in several cycles.

Functionalized Polymeric Materials for Catalytic Upgrading of Biobased Feedstocks

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