AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA5
Interactions between CO and NO on Rh Loaded Ceria Films

Monday, October 25, 1999, 3:20 pm, Room 607

Session: Reactions on Metals
Presenter: D.R. Mullins, Oak Ridge National Laboratory
Authors: D.R. Mullins, Oak Ridge National Laboratory
Lj. Kundakovic, Oak Ridge National Laboratory
S.H. Overbury, Oak Ridge National Laboratory
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CO and NO were adsorbed sequentially on model catalysts composed of submonolayer amounts of Rh deposited on highly crystalline thin films of reduced cerium oxide. The chemical state of the adsorbed species was monitored by soft x-ray photoelectron spectroscopy (SXPS). It has previously been shown that a reduced ceria substrate promotes the dissociation of CO and NO on supported Rh, with essentially full dissociation occurring by 400 K or 500 K for adsorbed NO and CO, respectively. At a constant temperature of 200 K, a saturation coverage of CO blocks subsequent adsorption of NO, and vice versa. However, the reaction of CO or NO with the dissociation products of the other molecule leads to new states in the C 1s and N 1s SXPS spectra that do not occur if either gas is adsorbed separately. If NO is dosed first and then heated to decompose it into atomic N and O, subsequent CO exposure at 200 K leads to new high binding energy states in the C1s and O 1s spectra which appear after annealing to 400 K. The binding energies of these states are consistent with formation of CO@sub 2@ on Rh. Additional features occur in the C1s and N 1s spectra indicative of the formation of other forms of N and C, as yet unassigned. If CO is dosed and dissociated first, then CO@sub 2@ is not formed upon subsequent exposure to NO. However, the features associated with the unassigned, adsorbed species do appear upon annealing. The only products observed in thermal desorption are CO and N@sub 2@ and, in particular, no CO@sub 2@ is desorbed. Additional experiments are in progress to identify the unassigned species and to determine the mechanisms of their formation. * Research was sponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. under contract number DE-AC05-96OR22464.