Intermetallic Pt-Cr Clusters in Zeolites as Models of Bimetallic Aromatization and Reforming Catalysts: I. Characterization of Oxidation States, Dispersion, and Local Structure

A variety of both structural (EXAFS, XANES, XRD, TEM) and surface-sensitive (XPS, LEISS) techniques have been applied to study the formation, dispersion, composition, and local structure of zeolite-hosted platinum-chromium metal alloys. Both XPS and XANES indicated a two-step reduction of Cr(VI) to Cr(III) and Cr(0) states, while the analysis of EXAFS data demonstrates the formation of platinum-chromium alloy particles after reduction at 823 K. Chromium stabilises small (8-10 Å) platinum particles at lower temperatures (623 K) and when alloyed the particle size increased to 12-20 Å. The Cr/Pt ratio in the alloy is low (