Density Functional Theory Analysis of Elementary Reactions in NOx Reduction on Rh Surfaces and Rh Clusters

5 years ago

Density Functional Theory Analysis of Elementary Reactions in NOx Reduction on Rh Surfaces and Rh Clusters

Fumiko Deushi, Hiromi Nakai, Atsushi Ishikawa

The reduction of NO_x is crucial for reducing air pollution from vehicle exhaust. In the presence of Rh-based catalysts, the dissociation of NO and the formation of N₂O and N₂ constitute the important elementary steps of NO_x reduction. The present study used density functional theory (DFT) to investigate the catalytic performances of the Rh(111) surface and Rh₅₅ and Rh₁₄₇ clusters toward these elementary reactions. The NO dissociation reaction was found to have minimum activation barriers (E_a) of 0.63, 0.68, and 1.25 eV on Rh₅₅, Rh₁₄₇, and Rh(111), respectively. Therefore, it is the fastest on small Rh clusters. In contrast, the N₂ formation reaction is relatively inefficient on small clusters, with corresponding E_a values of 2.14, 1.79, and 1.71 eV. Because of the stronger binding of N atoms to the Rh clusters than to the Rh surface, N₂ formation through the recombination of N atoms has a higher E_a value on Rh clusters. The calculated reaction rate constants confirmed that small Rh clusters are less reactive for N₂ formation than Rh(111), especially at low temperatures. Our results also suggest that N₂O formation is largely endothermic and, thus, thermodynamically unfavored.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04526

DOI: 10.1021/acs.jpcc.7b04526