Formation of Acrylaldehyde by Vapor-Phase Aldol Condensation II. Phosphate Catalysts

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Abstract
Vapor-phase aldol condensation of formaldehyde with acetaldehyde to form acrylaldehyde was studied with various oxide and phosphate catalysts using 35% formalin as the source of formaldehyde. Almost all of the tested oxides exhibited a certain activity as the catalysts. Acidic oxides, such as MoO3 and WO3 showed a relatively high selectivity to acrylaldehyde, though the activities were low. V2O5 and amphoteric oxides exhibited a much higher activity, but they promoted also the formation of CO2 and methanol. The catalytic performance was improved, to a certain extent, by combination of an acidic oxide with an amphoteric oxide. Further, the combination of phosphorus with V2O5 or an amphoteric oxide induced a large increase in the selectivity to acrylaldehyde. A good performance was obtained with the Ni–P, Mn–P, Fe–P, and V–P systems. The yield of acrylaldehyde reached 86 mol% on the AcH basis with a very slow formation of CO2 and methanol.