Effect of the presence of chlorine in bimetallic PtZn/CeO2 catalysts for the vapor-phase hydrogenation of crotonaldehyde

The effect of the reduction temperature has been studied on ceria-supported bimetallic platinum-zinc catalysts prepared from H2PtCl6 and Pt(NH3)(4)(NO3)(2) as the platinum precursors and Zn(NO3)(2) as the zinc precursor. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS), and their catalytic behavior has been evaluated in the vapor-phase hydrogenation of toluene and of crotonaldehyde (2-butenal) after reduction at low (473 K) and high (773 K) temperatures. The increase in the reduction temperature produces a strong decrease in the catalytic activity for toluene hydrogenation in both systems, but an C important increase of activity for crotonaldehyde hydrogenation, which is more evident for the chlorine-free catalyst. The selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol) also increases after reduction at high temperature, being somewhat higher for the Cl-containing catalyst. The results are discussed in terms of differences in surface composition of the catalysts. (c) 2006 Elsevier B.V. All rights reserved.