Role of the solid acidity on the MoO3 loaded on SnO2 in the methanol oxidation into formaldehyde

The selective oxidation activity of the molybdena thin layer loaded on SnO2 which was calcined at 773-1173 K was studied. MoO3 spread readily on SnO2, and covered the surface of support with ca. 80% coverage at most independe nt of the calcination temperature of tin oxide. On the other hand, the rum- over frequency depended on the calcination temperature, i.e., the high TOF was kept on the catalyst with the SnO2 calcined below 973 K, but it decreas ed with the SnO2 calcined above 1073 K, Characterization of the catalysts r evealed relations between the catalytic activity and the property. i,e.. re ducibility and solid acidity. In particular, the strong dependence upon the solid acidity was observed. The acid sites were generated on the molybdenu m oxide loaded on tin oxide calcined below 973 K, and possibly identified a s the Bronsted acid sites. Methanol was adsorbed more weakly on the acid si tes than on exposed surface of SnO2, and converted into formaldehyde select ively. (C) 1999 Elsevier Science B.V. All rights reserved.