Bimetallic Silica-Supported Catalysts Based on Ni-Sn, Pd-Sn, and Pt-Sn as Materials in the CO Oxidation Reaction

Abstract

Silica-supported bimetallic MSn (M = Ni, Pd, Pt) samples have been prepared by two consecutive impregnation steps with solutions of [MCl2(PPh3)2] complexes and SnCl2, respectively. After treatment in H2 at 673 K, these materials were characterized in detail by X-ray diffraction (XRD), conventional transmission electron microscopy, combined with energy-dispersive X-ray microanalysis, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). In addition, their performance in CO oxidation at temperatures ranging from 298 to 623 K was examined after activation processes under O2 and/or CO/O2 mixtures. XRD, HRTEM, electron diffraction, and XPS data of the Pt- or Pd-containing samples revealed that MSn alloys are formed upon H2 treatment but that they are inactive in CO oxidation at low temperature. However, an oxidizing pretreatment produced alloys enriched in Pt or Pd (Pt3Sn, Pd3Sn2) and SnOx phases, which gave satisfactory catalytic performance in the CO oxidation. The behavior of the NiSn system was different. Although a Ni-enriched Ni3Sn2 phase was identified in reduced samples, further O2 treatment at 673 K led to a mixture of phases including NiO and Ni-rich particles embedded in Sn-rich structures. This NiSn/SiO2 sample gave poor performance in CO oxidation, which was similar to that of the Ni-free Sn/SiO2 counterpart.