Catalyst engineering plays a key role in bridging gaps between the structure of the Lewis acid center and its corresponding catalytic performance. In this regard, work that has been done in tuning active sites of Hf-containing zeolites, which hold promising catalytic activity for a variety of hydrogen-shift reactions, is far from complete. Herein, a Hf-B-BEA catalyst was rapidly prepared (within hours) by a hydrothermal semi-reconstruction strategy, involving partial framework etching of parent B-BEA and Hf grafting during the reassembling process. Then, an acid treatment was performed for expelling the boron atoms from the framework; more importantly, Hf migration into the silanol nests was triggered. The acid treatment worked powerfully as the driving force for transforming the semi-framework Hf into well-defined tetrahedrally coordinated framework Hf, thus endowing Lewis acidity of the obtained Hf-BEA. Consequently, this operation greatly boosted the Meerwein–Ponndorf–Verley reduction performance of Hf-BEA, which was almost inactive over the pristine Hf-B-BEA. The rational regulation of Hf sites provides new concepts in designing Hf-containing zeolites and understanding the structural–activity relationship.
Meerwein-Ponndorf-Verley (MPV) reaction has been widely acknowledged to be a mild catalytic transfer hydrogenation method for selective reduction of biomass-derived furfural to furfuryl alcohol . Herein zirconium-containing mesoporous composite catalyst was developed through the combination of sol-gel process and soft templating method, in which naturally abundant glucose and F127 triblock copolymer were used as the ligand and pore-forming agent, respectively. The hydroxyl groups in glucose molecules were demonstrated to be coordinated with zirconium ion during hydrolysis-condensation of zirconium precursor, leading to the even dispersion of zirconia nanoparticles in the composite catalyst. The composite catalyst was proven to be highly efficient for catalyzing MPV reduction of furfural with the maximum furfuryl alcohol yield of 93.4% at 180 °C within 180 min in 2-propanol, which served as both solvent and reductant . The composite also showed a good reusability . After five consecutive reaction cycles, furfuryl alcohol yield was slightly reduced from 93.4% to 77.7%, but it could be recovered to 92.8% after the reused composite was regenerated with dilute alkali solution. Batch experiments and systematic characterizations demonstrated that the excellent catalytic performance of composite catalyst was determined by multiple factors mainly including the stronger Lewis acidity, a considerable amount of basic site and the rich mesoporous structure. This study provides a facile strategy to prepare multifunctional composite catalysts using naturally abundant carbohydrates as the feedstocks for lignocellulosic biorefinery .
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