Evolution of the Atomic Structure of Ceria-Supported Platinum Nanocatalysts: Formation of Single Layer Platinum Oxide and Pt-O-Ce and Pt-Ce Linkages

摘要

Depending on platinum loading and gas environment vastly different platinum structures in Pt/ceria were observed by Pt L-3-edge extended X-ray absorption (EXAFS) and X-ray absorption near-edge (XANES) spectroscopies. Calcination of highly loaded platinum (4 wt %) yielded stacked layers of alpha-PtO2. The low platinum-loaded sample (2 wt %), obtained by leaching, consisted of a single layer of alpha-PtPO2 bonded to the support by Pt-O-Ce linkages. Reduction of the platinum oxide by exposure to a carbon monoxide and hydrogen (PROX) gas mixture led to complete metal reduction at temperatures above 540 K. Under these conditions platinum-cerium bonds with a distance of 2.4 angstrom were detected and particles of 0.8 and 0.6 nm for the high-loaded and low-loaded Pt/ceria samples, respectively.