Liquid-Phase Hydrogenation of Crotonaldehyde over Platinum- and Palladium-Based Catalysts

The selective hydrogenation of crotonaldehyde in liquid phase, at a temperature of 353 K and a H 2 pressure of 400 kPa, is studied over different palladium- and platinum-based catalysts (Pd−Pb/α-Al 2 O 3, Pd−Zn/α-Al 2 O 3, Pd/ZnO, and two Pt/ZnO samples, prepared from Pt(NH 3 ) 4 (NO 3 ) 2 and H 2 PtCl 6, respectively). The intrinsic selectivity of palladium cannot be modified by alloying or following a promotion with a second metal, and the selectivity to crotyl alcohol measured over palladium-based samples is nil or extremely low. The selectivity corresponding to the Pt/ZnO catalysts increases with the time-on-stream reaching high levels. The formation of a Pt−Zn alloy is the origin of the enhanced selectivity toward crotyl alcohol; this effect is more pronounced for the sample that has been prepared from H 2 PtCl 6 .