An FT-IR and flow reactor study of the selective catalytic oxy-dehydrogenation of C3 alcohols on Mn3O4

The C3 alcohols 1-propanol, 2-propanol and prop-2-en-1-ol (allyl alcohol) are catalytically oxidized in He/oxygen to the corresponding carbonyl compounds propanal, acetone and acrolein with high selectivities and yields over Mn(3)O(4). The reaction occurs in the temperature range 400-550 K and yields far over 85% are obtained in the synthesis of acrolein and acetone. The reaction rate is faster for the secondary alcohol 1-propanol, than for the primary ones. The oxidation of the unsaturated allyl alcohol is faster than for the saturated one, l-propanol. Selectivity is limited by overoxidation of the carbonyl compounds. IR studies show that the high yields obtained in carbonyl compounds production over this catalyst are mainly due to their very weak adsorption. The main factor Limiting the selectivity to acetone and, mainly, propanal is their tendency to give enolate anions that further convert into acetaldehyde in both cases. Overoxidation of aldehydes to the corresponding carboxylate species is a less efficient mechanism limiting selectivity, The selectivity/activity behavior is definitely different than that observed for stoichiometric alcohols oxidations with Mn(III) compounds and also than that observed on other catalysts. This difference is associated to the low surface acidity of the Mn(3)O(4) catalyst. (C) 1998 Elsevier Science B.V.