AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA9
The Interaction of Carbonyls with Oxide Surfaces: The Adsorption of Formaldehyde on CeO@sub X@(111)

Monday, October 31, 2005, 4:40 pm, Room 203

Session: Oxide Surfaces Structure and Reactivity
Presenter: D.R. Mullins, Oak Ridge National Laboratory
Authors: J. Zhou, Oak Ridge National Laboratory
D.R. Mullins, Oak Ridge National Laboratory
Correspondent: Click to Email
Formaldehyde, CH@sub 2@O, chemisorbs on both oxidized and reduced cerium oxide surfaces. Near-edge X-ray Absorption Fine Structure (NEXAFS) and synchrotron-excited Soft X-ray Photoelectron Spectroscopy (SXPS) indicate that chemisorption occurs through the formation of a dioxymethylene, CH@sub 2@O@sub 2@, intermediate. On the fully oxidized surface this intermediate is weakly bound and results in molecular formaldehyde desorption between 200 K and 300 K. On a reduced cerium oxide surface the intermediate is more strongly adsorbed and desorbs as formaldehyde near 460 K. Some of the dioxymethylene disproportionates producing formate and methoxy intermediates above 450 K. These intermediates dissociate to form H@sub 2@ and CO products above 550 K. At large formaldehyde exposures polymerization occurs on both the oxidized and reduced ceria surfaces. The polymer decomposes to produce formaldehyde between 300 K and 400 K. The adsorption of formaldehyde, which occurs through the conversion of the carbonyl to carbondioxy on the oxide surface, is contrasted with the adsorption of methanol in which the hydroxyl bond is broken and methoxy is formed on the ceria. The methoxy group is more stable than dioxymethylene on the ceria surface and leads to decomposition products above 560 K rather than the recombinative desorption of methanol. Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.