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

Abstract

The effect of the reduction temperature has been studied on ceria-supported bimetallic platinum-zinc catalysts prepared from H 2 PtCl 6 and Pt(NH 3 ) 4 (NO 3 ) 2 as the platinum precursors and Zn(NO 3 ) 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 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.

Influence of the metal precursor on the catalytic behavior of Pt/Ceria catalysts in the preferential oxidation of CO in the presence of H2 (PROX)

“…Similar TPR profiles were previously reported for PtZn/CeO 2 catalysts prepared using two different Pt precursors (with and without chlorine) [22]. For the chlorine-free catalyst a broad hydrogen consumption peak was observed at low temperatures, which could be deconvoluted into two contributions.…”

“…For the chlorine-free catalyst, the hydrogen consumption peak (777.3 µmol H 2 .g -1 ) showed a main contribution at 610 K together with a shoulder at low temperatures (575 K). These two contributions include the surface reduction of ceria in close contact with the noble metal together with reduction of Pt species [22]. On the contrary, the chlorinated catalyst exhibited a single reduction peak centered at 590 K (652.6 µmol H 2 .g -1 ), which can be assigned to the reduction of surface ceria in close contact with platinum, as well as the breakdown of Pt-O-CeO 2 entities formed during the calcination treatment [22].…”

“…1. For all samples it was possible to observe the six main characteristic peaks of the cubic phase, fluorite structure, of CeO 2 , which are assigned to the (111), (200), (220), (311), (222) and (400) diffraction planes [20][21][22][23].…”

“…These two contributions include the surface reduction of ceria in close contact with the noble metal together with reduction of Pt species [22]. On the contrary, the chlorinated catalyst exhibited a single reduction peak centered at 590 K (652.6 µmol H 2 .g -1 ), which can be assigned to the reduction of surface ceria in close contact with platinum, as well as the breakdown of Pt-O-CeO 2 entities formed during the calcination treatment [22]. As shown in Table 1, the catalyst prepared with the chlorinated platinum precursor after calcination still contains a large amount of chlorine which could affect the reducibility of the support and, similarly, the oxygen mobility.…”

“…These two contributions were explained by the presence of a high degree of surface heterogeneity. Furthermore, in the case of the chlorinated catalyst, a delay in the metal reduction was observed due to the formation of CeOCl entities, which inhibited the metal-support interactions [22]. DRIFTS studies (discussed below) demonstrated that the chlorine-free catalyst exhibited a higher propensity for carbonate formation compared to the chlorinated catalyst.…”