Takagi Nozomi, Ishimura Kazuya, Miura Hiroki, Shishido Tetsuya, Fukuda Ryoichi, Ehara Masahiro, Sakaki Shigeyoshi
Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, 1-30 Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japan.
Institute for Molecular Science, Okazaki 444-8585, Japan.
ACS Omega. 2019 Feb 4;4(2):2596-2609. doi: 10.1021/acsomega.8b02890. eCollection 2019 Feb 28.
Density functional theory calculations here elucidated that Cu-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 (Δ°). On the other hand, dimerization of two NO molecules occurs on the Cu surface with small Δ° and very negative Gibbs reaction energy (Δ°) to form ONNO species adsorbed to Cu. 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 Δ° and very negative Δ°, leading to the formation of NO adsorbed on Cu and CO molecule in the gas phase. NO dissociates from Cu, and then it is readsorbed to Cu in the most stable adsorption structure. N-O bond cleavage of NO easily occurs with small Δ° and significantly negative Δ° to form the N molecule and the O atom adsorbed on Cu. The O atom reacts with the CO molecule to afford CO and regenerate Cu, which is rate-determining. NO species was experimentally observed in Cu/γ-AlO-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 Cu are discussed in terms of the charge-transfer interaction with Cu and Frontier orbital energy of Cu.
密度泛函理论计算表明，铜催化的一氧化碳还原一氧化氮反应并非通过一氧化氮的解离吸附，而是通过一氧化氮的二聚作用发生。一氧化氮以桥连方式吸附在两个铜原子上。一氧化氮的吸附能远大于一氧化碳的吸附能。吸附的一氧化氮分子的氮-氧键断裂需要非常大的活化能（Δ°）。另一方面，两个一氧化氮分子在铜表面发生二聚作用，其活化能（Δ°）较小，吉布斯反应能（Δ°）非常负，形成吸附在铜上的ONNO物种。然后，一个一氧化碳分子吸附在与ONNO物种相邻的位置，并与ONNO反应，以较小的活化能（Δ°）和非常负的Δ°诱导氮-氧键断裂，导致气相中吸附在铜上的一氧化氮和一氧化碳分子的形成。一氧化氮从铜上解离，然后以最稳定的吸附结构重新吸附到铜上。一氧化氮的氮-氧键断裂很容易发生，活化能（Δ°）较小，Δ°显著为负，形成吸附在铜上的氮分子和氧原子。氧原子与一氧化碳分子反应生成二氧化碳并使铜再生，这是速率决定步骤。在铜/γ-氧化铝催化的一氧化碳还原一氧化氮反应中，实验观察到了一氧化氮物种，这与该反应机理一致。该机理与为铑催化剂提出的机理不同，铑催化剂的反应是通过一氧化氮分子的氮-氧键断裂发生的。从与铜的电荷转移相互作用和铜的前线轨道能量的角度讨论了一氧化氮二聚作用和吸附在铜上的氧原子氧化一氧化碳的电子过程。
