Hydrogenation of crotonaldehyde over Pt based bimetallic catalysts

Gas and liquid phase hydrogenation of crotonaldehyde was studied over silica supported promoted Pt catalysts. The influence of reaction temperature and reactant pressure on the activity and selectivity of the catalysts and the role of deactivation was investigated. Addition of Ni, Co and Fe to Pt/SiO₂ increased the activity and the selectivity in gas phase hydrogenation. This is attributed to the existence of polar sites in a bimetallic phase favoring the interaction with the carbonyl group and, thus, increasing the rate for the hydrogenation to crotylalcohol. Addition of Ga, Sn and Ge improved the selectivity to crotylalcohol, but decreased the activity of the catalysts. These promoters form catalytically inactive oxides that decorate part of the Pt surface. The electron pair donor-acceptor interaction of the oxygen of the carbonyl group with the Lewis sites present in such oxide clusters is concluded to cause the enhanced selectivity to crotylalcohol. The addition of La, Bi, Pb and Sb to Pt decreased the activity and the selectivity of the parent catalyst by blocking a part of the active surface. With respect to selectivity, catalyst behavior is independent of the reaction medium. In contrast, the highest activities in gas phase were found for catalysts forming a bimetallic phase, while these catalysts showed the lowest activity in liquid phase due to a fast deactivation.