Wei Zhang,Wei Hou,Tongsuo Meng,Wenxia Zhuang,Jingyan Xie,Yu Zhou,Jun Wang
Vanadium (V)-containing all-silica beta-zeolites (VSi-Beta) were directly synthesized using a dry-gel-conversion route, in which the gel was prepared from the acid-catalysed co-hydrolysis of a silica precursor and ammonium metavanadate. Besides the framework isolated V species, VSi-Beta contained tetrahedral [V2O7]4− and (VO3)nn− species that were bonded to the framework with a high dispersion. These V species resisted the over-oxidation of fructose and efficiently catalyzed the oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF). As a result, VSi-Beta demonstrated high activity in the one-pot and one-step conversion of fructose into DFF using atmospheric oxygen (O2) in the presence of sulfuric acid, affording a high yield of 86.3% and a maximum turnover number (TON) of 270. The catalyst can be easily recovered by filtration and exhibits good reusability. Various other carbohydrates (glucose, sucrose, inulin, raffinose, maltose and starch) were also effectively converted into DFF using VSi-Beta.
There is a critical need for improving catalyst activity for formaldehyde combustion due to the importance of enhancing the quality of indoor air in daily life. However, the current catalysts are either low activity (higher than room temperature) or high loading of noble metals (higher than 1 wt.% Pt). Herein, inspired by the concept of catalyst wettability, we design a siliceous Beta zeolite with more hydrophobic feature than that of aluminosilicate Beta zeolite to support Pt catalyst at very low loading (0.2 wt.%), exhibiting extremely excellent catalytic performance in formaldehyde combustion. The formaldehyde could be completely oxidized to carbon dioxide even at -20 °C. The extraordinary catalytic properties are reasonably attributed to that more hydrophobicity of the siliceous zeolite than that of the aluminosilicate zeolite is favorable for desorption of water product, shifting the oxidation equilibrium from HCOOH (intermediate of oxidation of formaldehyde) to carbon dioxide and water. The strategy of hydrophobic zeolite-supported noble metal catalysts might offer an alternative way to develop highly efficient heterogeneous catalysts for the removal of volatile organic compounds.
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