AVS 59th Annual International Symposium and Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuM

Paper SS-TuM11
Variations in Reactivity for Acetaldehyde and Acetic Acid with the Crystallographic Orientation of Cerium Oxide Thin Films

Tuesday, October 30, 2012, 11:20 am, Room 21

Session: Surface Reactivity of Oxides
Presenter: P.M. Albrecht, Oak Ridge National Laboratory
Authors: P.M. Albrecht, Oak Ridge National Laboratory
D.R. Mullins, Oak Ridge National Laboratory
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Cerium oxide is a vital component in many heterogeneous catalytic processes. The various crystallographic faces of ceria present significantly different surface structures and compositions, which may result in an orientation-dependent catalytic reactivity. The structure and composition determine the availability of adsorption sites, the spacing between those adsorption sites, and the ability of surface O to participate in a reaction. The adsorption and reaction of various oxygenated hydrocarbons on cerium oxide surfaces are of interest from the standpoint of understanding the catalytic properties of the material. Studies on the interactions of alcohols, aldehydes, ketones, and carboxylic acids on well-defined CeO2 surfaces have been motivated predominantly by the rich chemistry produced by the variation in the Ce oxidation state and the associated O vacancies. Alcohols, carbonyls, and carboxylic acids vary significantly in their strength of interaction with the surface and consequently in their reaction products. Here, we report a study of the adsorption and dissociation of acetaldehyde (CH3CHO) on CeO2(100). CeO2(100) films were grown by pulsed laser deposition on Nb-doped SrTiO3(100). In addition to the fully oxidized CeO2(100) surface, experiments were conducted on reduced surfaces containing ~60% Ce3+ (CeO1.7) prepared by methanol exposure at 660 K. Reaction products were monitored by temperature programmed desorption (TPD), and surface intermediates were determined by soft x-ray photoelectron spectroscopy (sXPS) and near-edge x-ray absorption fine structure (NEXAFS). The key result is that acetaldehyde reacts with oxidized CeO2(100), whereas it does not react with oxidized CeO2(111). The most intense products are CO, CO2, and water, with trace amounts of crotonaldehyde and acetylene. On reduced CeO1.7(100), the oxygenated products are largely eliminated and ethylene and H2 are produced. Residual C is also left on the surface. Recent results indicate that the chemistry of acetic acid (CH3COOH) is also significantly different on CeO2(100) compared to CeO2(111). Acetone is a major product on CeO2(100) whereas only a trace amount of ketonization occurs on CeO2(111). Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, US Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.