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Pure Appl. Chem., 2007, Vol. 79, No. 11, pp. 1895-1903

Direct NO decomposition over stepped transition-metal surfaces

Hanne Falsig1, Thomas Bligaard2, Claus H. Christensen1 and Jens K. Nørskov2

1 Center for Sustainable and Green Chemistry, Department of Chemistry, Building 206, NanoDTU, Technical University of Denmark, DK-2800 Lyngby, Denmark
2 Center for Atomic-Scale Materials Design, Department of Physics, Building 311, NanoDTU, Technical University of Denmark, DK-2800 Lyngby, Denmark

Abstract: We establish the full potential energy diagram for the direct NO decomposition reaction over stepped transition-metal surfaces by combining a database of adsorption energies on stepped metal surfaces with known Brønsted-Evans-Polanyi (BEP) relations for the activation barriers of dissociation of diatomic molecules over stepped transition- and noble-metal surfaces. The potential energy diagram directly points to why Pd and Pt are the best direct NO decomposition catalysts among the 3d, 4d, and 5d metals. We analyze the NO decomposition reaction in terms of a Sabatier-Gibbs-type analysis, and we demonstrate that this type of analysis yields results that to within a surprisingly small margin of error are directly proportional to the measured direct NO decomposition over Ru, Rh, Pt, Pd, Ag, and Au. We suggest that Pd, which is a better catalyst than Pt under the employed reaction conditions, is a better catalyst only because it binds O slightly weaker compared to N than the other metals in the study.