Catalysis of Cu Cluster for NO Reduction by CO: Theoretical Insight into the Reaction Mechanism.

ABSTRACT: Density functional theory calculations here elucidated that Cu₃₈-catalyzed NO reduction by CO occurred not through NO dissociative adsorption but through NO dimerization. NO is adsorbed to two Cu atoms in a bridging manner. NO adsorption energy is much larger than that of CO. N-O bond cleavage of the adsorbed NO molecule needs a very large activation energy (?G°^‡). On the other hand, dimerization of two NO molecules occurs on the Cu₃₈ surface with small ?G°^‡ and very negative Gibbs reaction energy (?G°) to form ONNO species adsorbed to Cu₃₈. Then, a CO molecule is adsorbed at the neighboring position to the ONNO species and reacts with the ONNO to induce N-O bond cleavage with small ?G°^‡ and very negative ?G°, leading to the formation of N₂O adsorbed on Cu₃₈ and CO₂ molecule in the gas phase. N₂O dissociates from Cu₃₈, and then it is readsorbed to Cu₃₈ in the most stable adsorption structure. N-O bond cleavage of N₂O easily occurs with small ?G°^‡ and significantly negative ?G° to form the N₂ molecule and the O atom adsorbed on Cu₃₈. The O atom reacts with the CO molecule to afford CO₂ and regenerate Cu₃₈, which is rate-determining. N₂O species was experimentally observed in Cu/?-Al₂O₃-catalyzed NO reduction by CO, which is consistent with this reaction mechanism. This mechanism differs from that proposed for the Rh catalyst, which occurs via N-O bond cleavage of the NO molecule. Electronic processes in the NO dimerization and the CO oxidation with the O atom adsorbed to Cu₃₈ are discussed in terms of the charge-transfer interaction with Cu₃₈ and Frontier orbital energy of Cu₃₈.

SUBMITTER: Takagi N 

PROVIDER: S-EPMC6648525 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature