(651c) Reaction Mechanistic Studies of NO Reduction By H2 on Transition Metal Surfaces

Nitric oxide (NO) is a major pollutant produced mainly during the combustion of fossil fuels. Though three-way catalysts (TWC) and selective catalytic reduction (SCR) have been widely applied to decrease NO_x emissions, the fundamental reaction mechanism is not well understood.Disadvantages associated with those methods also stimulate the development of other promising NO removal processes. In this study, we employ periodic, self-consistent density functional theory (DFT-GGA) calculations to investigate the reaction mechanism of NO reduction by H₂ on transition metal surfaces. In particular, we analyze the energetics of both direct NO dissociation and H-assisted pathways, elucidating the role of H in NO activation. Possible pathways leading to the formation of N₂, the most desirable product, and side-products N₂O and NH₃ are also proposed. Due to the strong binding of NO, we incorporate a high coverage of NO into our studies and show how NO spectator molecules affect the reaction mechanism. Comparisons among different transition metal surfaces are made to elucidate trends in catalytic activity and selectivity, as well as the structure sensitivity of NO reduction by H₂. Kinetic experiments and microkinetic modeling are used, in combination with first-principles analysis, to gain an improved understanding of the reaction network.

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