Defect Enhanced Carbon Monoxide Oxidation at Elevated Oxygen Pressures on a Pt/Al2O3 Thin Film

Published

April 1, 2004

Author(s)

D J. Burnett, A M. Gabelnick, A L. Marsh, H D. Lewis, S M. Yalisove, Daniel A. Fischer, J L. Gland

Abstract

rbon monoxide oxidation experiments were performed on a well-characterized supported platinum thin film using in-situ x-raytechniques and temperature-programmed reaction spectroscopy (TPRS) experiments over the 100 to 1000 K temperature range andhigh vacuum (UHV) to 1.3 Pa pressure range. At high oxygen pressures the reaction was enhanced by oxidation at defect sites.Temperature-programmed fluorescence yield near-edge spectroscopy (TP-FYNES) studies of preabsorbed CO heated in pressures ooxygen have been obtained for a wide range of oxygen pressures (1 x 10^-3 to 1 Pa). Unlike the Pt(111) surface, the onset temperatureoxidation of a saturated monolayer of CO decreases dramatically with increasing oxygen pressure. The oxidation temperture droppefrom 340 K when heated in 1 x IO-^-3 Pa of oxygen to 230 K in I Pa of 02. Therefore, oxidation is not limited by CO desorption for highCO coverages, and defect sites control CO oxidation at high oxygen pressures. Isothermal oxidation experiments in 0.27 Pa of oxygyield an activation energy of 2.0 kJ/mol. Low-pressure, coabsorbed CO and oxygen TPRS experiments indicated a primary oxidationchannel at 350 K from the oxidation of CO on Pt(111) terraces sites and minor oxidation channels above 400 K. The thin Pt/Al₂O₃was characterized using both chemical and structural methods. CO and oxygen temperature-programmed desorption (TPD)experiments indicate the Pt film surface is similar to Pt(111), but with a higher defect site concentration. Plan-view and cross-sectiontransmission electron microscopy (TEM) experiments confirmed a I 0.0 nm Pt film consisting of -40.0 nm, well-ordered grains with(I I 1) orientation parallel to the substrate. Local area electron diffraction patterns indicated well-ordered grains.

Citation

Journal of Physical Chemistry B

Volume

108

Issue

No. 17

Pub Type

Journals

Keywords

alumina, carbon monoxide, defects, NEXAFS, oxidation, platinum, soft x-ray, thin film

Citation

Burnett, D. , Gabelnick, A. , Marsh, A. , Lewis, H. , Yalisove, S. , Fischer, D. and Gland, J. (2004), Defect Enhanced Carbon Monoxide Oxidation at Elevated Oxygen Pressures on a Pt/Al₂O₃ Thin Film, Journal of Physical Chemistry B (Accessed December 13, 2024)