Effect of Indium Doping of γ-Alumina on the Stabilization of PtSn Alloyed Clusters Prepared by Surface Organostannic Chemistry

Abstract

The control of the atomic-scale properties of highly dispersed multimetallic particles represents a challenging question for the optimal use of metallic active centers in nanoscience. In particular, improving the formation of PtxSn alloyed clusters on γ-alumina of a size close to 1 nm with a high Sn0/Pt ratio represents a crucial step toward more selective heterogeneous catalysts. For that purpose, bimetallic SnPt-based and trimetallic SnPtIn-based catalysts were prepared by surface organostannic chemistry on monometallic Pt and bimetallic PtIn-based catalysts. These systems were characterized by a multitechnique approach combining CO chemisorption, temperature programmed reduction, scanning transmission electron microscopy, Mössbauer spectroscopy, and X-ray absorption spectroscopy. The nature of the PtSn phase in trimetallic SnPtIn-based catalysts is found to strongly depend on the way indium is initially introduced in the parent catalyst, by either wet impregnation or coprecipitation with aluminum precursor. The key role of In3+ species on the formation of PtSn alloyed clusters is revealed. By using density functional theory calculations, we give a rational interpretation of the experimental results and provide an atomic scale description of PtxSny/γ-Al2O3 systems, with or without In3+ on the alumina surface. The formation of In–Pt, In–Sn, and O–Sn bonds is indeed favored when In3+ is present in the support. This work proposes an original approach for stabilizing PtxSn alloyed clusters with an elevated Sn0/Pt ratio and highly dispersed on γ-alumina using indium as “third element” introduced as In3+ on the support.