Pt/CeO 2 catalysts: correlation between nanostructural properties and catalytic behaviour in selective hydrogenation of crotonaldehyde

Abstract

The nanostructural properties of Pt/CeO 2 catalysts, already studied for their specific catalytic behaviours in the selective hydrogenation of crotonaldehyde [Catal. Lett. 69 (2000) 139] have been examined by high resolution transmission electronic microscopy (HRTEM). Three different catalysts were prepared by impregnation of a commercial ceria support (54 m 2/g) with three different precursors, Pt(NH 3) 4(NO 3) 2, H 2PtCl 6 and Pt(NH 3) 4Cl 2, calcined at 673 K and reduced at low and high temperatures (473 and 973 K). The chlorine-free catalyst showed a nanostructural evolution when increasing the reduction temperature from 473 to 973 K with the formation of epitaxial CePt 5 particles on the support. This phenomenon did not occur when chlorine was present in the catalyst, independently of the particle size. The specific catalytic behaviours of these catalysts obtained in the selective hydrogenation of crotonaldehyde have been related to these observations. It clearly appeared that the presence of chlorine partly preserves the catalytic properties of platinum metal (hydrogenation of CC bond) while the catalyst made of CePt 5 patch units epitaxial on the CeO 2 support could provide more than 80% crotyl alcohol selectivity, stable as a function of the time-on-stream, up to 45% conversion.