Web Release Date: March 17,
CO Dissociation at Elevated Pressures on Supported Pd Nanoclusters
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012
Received: July 29, 2003
In Final Form: December 9, 2003
Abstract:
In-situ polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) is used to study CO adsorption at elevated pressures and temperatures on Pd nanoclusters deposited on crystalline SiO2 thin films. The PM-IRAS data indicate that CO dissociates on the Pd nanoclusters at 185 mbar and at temperature >600 K. Combined STM and PM-IRAS data show that the Pd nanoclusters are three-dimensional and consist predominantly of <111> facets with an average diameter and height of 3.5 and 0.7 nm, respectively. STM data indicate no change in the morphology or sintering of the Pd nanoclusters between 300 and 650 K. For comparison, CO adsorption was investigated on a Pd(111) single-crystal surface using PM-IRAS under similar conditions (PCO = 133 mbar, T = 175-750 K). Comparison of the PM-IRAS data for CO adsorption on Pd(111) and Pd nanoclusters indicate that in contrast to the Pd nanoclusters, CO adsorbs molecularly on the Pd(111) surface in a reversible manner, i.e., no dissociation.
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