AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM9
Isothermal Kinetic Study of the Catalytic Reduction of Nitric Oxide over Rh(111) Surfaces

Tuesday, November 3, 1998, 11:00 am, Room 309

Session: Noble Metal Catalysis
Presenter: F. Zaera, University of California, Riverside
Authors: G. Chinnakonda, University of California, Riverside
F. Zaera, University of California, Riverside
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The kinetics of the thermal decomposition of NO and of its catalytic reduction to molecular nitrogen on Rh(111) surfaces was probed by isothermal measurements using an extension of the so-called King and Wells collimated beam method. Initial NO TPD studies corroborated previously reported results, including the development of two distinct molecular nitrogen desorption peaks at 460 and above 500 K, the first of which displays apparent first-order kinetics. In the isothermal experiments the rate of molecular nitrogen production was found to be significant above 450 K, and to be controlled by the recombination of atomic nitrogen below 600 K. In addition, the adsorption of NO was found to not be affected significantly by the presence of coadsorbed nitrogen and/or oxygen atoms at any temperature below 900 K. There is an induction period during which the surface concentrations of nitrogen and oxygen atoms build up before the recombination reaction starts. When performing the experiments with NO alone oxygen deposition on the surface eventually poisons the system and stops the reaction, but when using CO + NO mixed beams that oxygen is removed and a steady-state catalytic regime is reached. In any case, the experimental data could not be reproduced in a satisfactory manner by any empirical rate law unless the order in nitrogen coverage was set to less than unity, an observation that is interpreted here as being the result of the slow diffusion of nitrogen atoms across the surface prior to their recombination. A strong additional effect due to lateral repulsions between nitrogen and/or oxygen atoms was also observed.