Vapor phase aldol condensation of acetaldehyde on metal oxide catalysts

Vapor phase aldol condensation of acetaldehyde on silica supported alkali metal containing solid bases, silica supported tungsten and molybdenum oxides and other unsupported oxides were studied. It was found that silica supported alkali metal containing solid base catalysts can effectively catalyze the aldol condensation of acetaldehyde to produce crotonaldehyde as well as crotyl alcohol with a good selectivity (ca. 90%) and stability and moderate conversion. MoO3/SiO2 or MoOx/SiO2 (reduced state) was found to be almost inactive for this reaction. Contrary to MoO3(MoOx)/SiO2, WO3(WOx)/SiO2 catalysts are active and more selective. Most of other unsupported oxides tested in this study are not attractive for the low activity and selectivity or poor stability. ZrO2 or pre-treated ZrO2-SO42- was initially quite active, but deactivated quickly. Go-feeding hydrogen can enhance the activity of ZrO2 or inhibit deactivation of pre-treated ZrO2-SO42-. The super acidic site associated with SO42- species has a great contribution to coking but little to aldol condensation. (C) 1997 Elsevier Science B.V.