An emergent catalytic material: Pt/ZnO catalyst for selective hydrogenation of crotonaldehyde

By using modifiers in platinum catalysts it is possible to modulate the hydrogenation selectivity in alpha,beta-unsaturated aldehydes carbonyl bond with regard to olefinic bond hydrogenation. The challenge is to find an emergent catalytic material able to produce 100% unsaturated alcohol. In this field, 1% Pt/ZnO catalysts were tested in hydrogenation of crotonaldehyde, in gas phase, at atmospheric pressure. The catalysts were prepared by impregnation of ZnO from two different precursors, H2PtCl6 and Pt(NH3)(4)(NO3)(2), followed by calcination at 673 K and tested after reduction at different temperatures, 473-773 K. The ex-nitrate and ex-chloride catalysts showed quite different catalytic behaviors. The ex-chloride was much more active and selective; in certain conditions 90% crotyl alcohol selectivity was reached. Different techniques (TPR, XRD, TEM, XPS, FTIR) were used to characterize both types of catalysts and to correlate the structure and the reactivity. The Lewis acidity of ZnO after the reduction treatment and the formation of PtZn alloy were found to be the key factors leading to high crotyl alcohol yield. It was proposed that modification of the electronic properties of platinum both by alloying to zinc and by Lewis acidity of the support reinforced by chlorine changes the adsorption mode of crotonaldehyde by favoring the binding of the terminal oxygen of the molecule to the electronically modified platinum atom. (C) 2003 Elsevier Inc. All rights reserved.