Studies on generation mechanism of acid site on the surface of ceramics

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The acid properties of a series of alumina-supported metal oxides (Nb2O5/Al2O3, Ta2O5/Al2O3, MoO3/Al2O3, WO3/Al2O3) catalysts with various loadings and calcined at various temperatures were investigated by acid-catalyzed reactions, and structural characterization techniques. The relationships between acid properties, structures, and catalytic performances are evaluated. Both the catalytic activity and amount of Broensted acid sites depend on calcination temperature and metal oxide loading amount. High temperature calcination (> 1100 K) generated Broensted acid property. The activities for acid-catalyzed reactions were proportional to Broensted acidity, indicating that these reactions occurred on the Broensted acid sites. Metal oxide having distorted octahedral symmetry was loaded as two-dimensional monolayer domains and these domains covered most of the alumina surface. Broensted acid sites are generated at the boundaries between tungsten oxide monolayer domains.