NO dissociation and reduction by H2 on Pd(1 1 1): A first-principles study

• Hydrogen facilitates the dissociation of NO on Pd(1 1 1) surface.
• The formation pathways for the possible products of N2, NH3, N2O, and H2O are identified on Pd(1 1 1) surface.
• The reaction NO + N → N2 + O is the exclusive pathway for N2 formation.
• The dimeric mechanism of 2NO → (NO)2 → N2O + O is feasible for N2O formation on Pd(1 1 1) surface at low temperature.
• The microkinetic modeling calculations determine the reaction rates and product selectivities for N-containing products.

Periodic density functional theory (DFT) calculations were carried out to elucidate the reaction mechanisms of NO reduction by H2 and possible products on Pd(1 1 1). The results show that direct NO dissociation is unlikely due to high-energy barrier; alternatively, NO dimer exists on Pd(1 1 1) surface followed by the N–O bond scission to form N2O. The presence of H2 promotes the NO dissociation. The N2 formation pathway is NO + N → N2 + O rather than N + N → N2. Besides, N2 is formed preferentially than N2O from the coadsorbed state of NO + N. The NH3 formation comes from the successive hydrogenation reactions of nitrogen and the NH formation is the rate-determining step. The microkinetic analysis further confirms that N2O is major at low temperature while N2 becomes dominant as temperature increases. The selectivities toward N2 and NH3 shift to slightly lower temperature as H2/NO ratio increases.

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