ACTIVITY AND SELECTIVITY IN THE REACTIONS OF SUBSTITUTED ALPHA,BETA-UNSATURATED ALDEHYDES

The effect of substitution of alpha,beta-unsaturated aldehydes on the activity and selectivity of a series of platinum catalysts was investigated for the hydrogenation of these compounds. The silica-supported platinum catalysts were promoted by a selected group of additives: compounds of Na (alkali metal), V, Ti, Fe (transition metals), Ga, Sn, and Ge (nontransition elements). For all catalysts the selectivity to unsaturated alcohol (UOL) increased with increasing substitution on the terminal olefinic carbon atom (crotonaldehyde and methyl-crotonaldehyde, respectively). This indicates that the adsorption modes are related to selectivity and the selectivity is influenced by the competition of the C=O and C=C group for the same sites on the promoter. In the hydrogenation of methacrolein, wherein the methyl substituent is located on the internal olefinic carbon atom, and in the hydrogenation of methyl vinyl ketone, very pronounced differences in the selectivity to UOL were observed. The trends in activity and selectivity indicate that the substitutional effects are mainly steric in origin. In general, the activity of a specific group decreases with substitution on that group. (C) 1995 Academic Press, Inc.