title: Catalytic reactions on neutral Rh oxide clusters more efficient than on neutral Rh clusters.
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.
authors.affiliation: Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Yamada
authors.forename: Ken
authors.initials: K
authors.lastname: Miyajima
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Mafuné
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry; D002384:Catalysis; D009584:Nitrogen / Q000737:chemistry; D009609:Nitrous Oxide / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*
chemical_list: D010087:Oxides; D002245:Carbon Dioxide; D002248:Carbon Monoxide; D012238:Rhodium; D009609:Nitrous Oxide; D009584:Nitrogen