Polyoxometalates-based heterogeneous catalysts in acid catalysis

Acid catalysis,one of the most important industrial processes,suffers from the toxicity,corrosion and recyclability problems of conventional homogeneous acid catalysts.Thus,the development of green heterogeneous acid catalysts becomes the focus of fundamental research and industrial catalysis.As a class of discrete anionic metal-oxygen clusters with tunable structure at the molecular and atomic scales,polyoxometalates(POMs)benefit from their super strong Br?nsted acidity,high proton mobility,and thermal stability.POMs-based heterogeneous catalysts have been used as the potential green alternatives to conventional homogeneous acid catalysts.In this review,we summarize recent progress on the design strategies of the POMs-based heterogeneous catalysts and their catalytic properties in acid-catalyzed reactions,where they are combined with functionalized cations,modified through covalent interactions,supported onto the non-precious metal support,and introduced into the framework of porous polymers.The design,functional strategies and catalytic performance of these POMs-based heterogeneous catalysts in specific acid-catalyzed reactions are emphasized.