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

Silica-supported bimetallic MSn (M = Ni, Pd, Pt) samples have been prepared by two consecutive impregnation steps with solutions of [MCl 2 (PPh 3 ) 2 ] complexes and SnCl 2, respectively. After treatment in H 2 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 O 2 and/or CO/O 2 mixtures. XRD, HRTEM, electron diffraction, and XPS data of the Pt- or Pd-containing samples revealed that MSn alloys are formed upon H 2 treatment but that they are inactive in CO oxidation at low temperature. However, an oxidizing pretreatment produced alloys enriched in Pt or Pd (Pt 3 Sn, Pd 3 Sn 2 ) and SnO x phases, which gave satisfactory catalytic performance in the CO oxidation. The behavior of the NiSn system was different. Although a Ni-enriched Ni 3 Sn 2 phase was identified in reduced samples, further O 2 treatment at 673 K led to a mixture of phases including NiO and Ni-rich particles embedded in Sn-rich structures. This NiSn/SiO 2 sample gave poor performance in CO oxidation, which was similar to that of the Ni-free Sn/SiO 2 counterpart.