Abstract
Mesoporous silica molecular sieves are a kind of unique catalyst support due to their large pore size and high surface area. Several methods have been developed to immobilize heteropolyacids (HPAs) inside the channels of these mesoporous silicas. The mesoporous silica-supported HPA materials have been widely used as recyclable catalysts in heterogeneous systems. They have shown high catalytic activities and shape selectivities in some reactions, compared to the parent HPAs in homogeneous systems. This review summarizes recent progress in the field of mesoporous silica-supported HPAs applied in the heterogeneous catalysis area and preparation of nanostructured metal oxides using HPAs as precursors and mesoporous silicas as hard templates.
Highlights
In the last decades, heteropolyacids (HPAs) and related polyoxometalate compounds have attracted much attention as economically and environmentally friendly catalysts [1,2,3,4,5,6,7,8]
Impregnating HPAs on these supports significantly increases the specific surface area, which is very important for heterogeneous catalysis processes
It was observed that the catalytic activity for esterification of fatty acid with methanol decreased in the order of phosphotungstic acid (PTA)-silica > silicotungstic acid (STA)-silica > phosphomolybdic acid (PMA)-silica, indicating that their activities depended on the acid strength of the HPA precursors
Summary
Heteropolyacids (HPAs) and related polyoxometalate compounds have attracted much attention as economically and environmentally friendly catalysts [1,2,3,4,5,6,7,8]. Since the report of the mesoporous silica molecular sieves, such as MCM-41 [23,24], SBA-15 [25,26], and HMS [27,28], mesoporous materials have attracted much attention for their potential applications in the fields of catalysis, functional materials, and nanodevices [29,30,31] They have uniform channels, large pore size, high specific surface area and high thermal stability. Loading of HPAs on mesoporous silica allows transfer of HPA-catalysed reactions from homogeneous to heterogeneous systems to avoid the difficulty in catalyst separation, and effectively increases the surface area of HPAs [32]. With high loading of HPAs, nanowires and even three-dimensional nano-structured metal oxide(s) can be fabricated by reverse replication of the channels of mesoporous silica. We review the applications of mesoporous silica supported HPAs in heterogeneous catalysis and the preparation of nanostructured metal oxides
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