Catalytic reactions on neutral Rh oxide clusters more efficient than on neutral Rh clusters |
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Authors: | Yamada Akira Miyajima Ken Mafuné Fumitaka |
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Institution: | Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan. |
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Abstract: | Gas phase catalytic reactions involving the reduction of N(2)O and oxidation of CO were observed at the molecular level on isolated neutral rhodium clusters, Rh(n) (n = 10-28), using mass spectrometry. Sequential oxygen transfer reactions, Rh(n)O(m-1) + N(2)O → Rh(n)O(m) + N(2) (m = 1, 2, 3,…), were monitored and the rate constant for each reaction step was determined as a function of the cluster size. Oxygen extraction reactions by a CO molecule, Rh(n)O(m) + CO → Rh(n)O(m-1) + CO(2) (m = 1, 2, 3,…), were also observed when a small amount of CO was mixed with the reactant N(2)O gas. The rate constants of the oxygen extraction reactions by CO for m ≥ 4 were found to be two or three orders of magnitude higher than the rate constants for m ≤ 3, which indicates that the catalytic reaction proceeds more efficiently when the reaction cycles turn over around Rh(n)O(m) (m ≥ 4) than around bare Rh(n). Rhodium clusters operate as more efficient catalysts when they are oxidized than non- or less-oxidized rhodium clusters, which is consistent with theoretical and experimental studies on the catalytic CO oxidation reaction on a rhodium surface. |
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