Supported platinum, rhodium, and iridium clusters: Synthesis, characterization and catalysis

This dissertation is a report of synthesis of metal carbonyl clusters on metal oxide surfaces, their characterization by a variety of spectroscopic techniques, and an investigation of the catalytic properties of decarbonylated forms of these structurally well-defined supported metal clusters.; Two Longoni-Chini clusters, (Pt{dollar}sb6{dollar}(CO){dollar}sb{lcub}12{rcub}{dollar}) {dollar}sp{lcub}2-{rcub}{dollar} and (Pt{dollar}sb9{dollar}(CO){dollar}sb{lcub}18{rcub}{dollar}) {dollar}sp{lcub}2-{rcub},{dollar} were synthesized in high yield from (Pt(acac){dollar}sb2{dollar}) on the surface of MgO by surface-mediated reactions. The latter was also synthesized inside the supercages of NaY zeolite. The syntheses on basic surfaces parallel the syntheses in basic solutions.; (PtRh{dollar}sb5{dollar}(CO){dollar}sb{lcub}15{rcub}{dollar}) {dollar}sp{lcub}-{rcub}{dollar} was synthesized on the surface of MgO at room temperature in 84% yield by treatment of Na{dollar}sb2{dollar}PtCl{dollar}sb6{dollar} and RhCl{dollar}sb3{dollar} mixed with MgO in CO. This is the first report of a surface-mediated synthesis of a bimetallic cluster.; MgO-supported tetrairidium and hexairidium clusters were used as catalysts for toluene hydrogenation and cyclohexene hydrogenation. Ir{dollar}sb4{dollar}/MgO and Ir{dollar}sb6{dollar}MgO were found to be active for toluene hydrogenation. The turnover frequency at 60{dollar}spcirc{lcub}rm C{rcub}{dollar} was 1.8 {dollar}times {lcub}rm 10{rcub}sp{lcub}-4{rcub} {lcub}rm s{rcub}sp{lcub}-1{rcub}{dollar} for Ir{dollar}sb4{dollar}/MgO, and 3.5 {dollar}times {lcub}rm 10{rcub}sp{lcub}-5{rcub}{lcub}rm s{rcub}sp{lcub}-1{rcub}{dollar} for Ir{dollar}sb6{dollar}/MgO. The order of reaction in H{dollar}sb2{dollar} partial pressure was 0.8 to 1.3; the order of reaction in toluene partial pressure was near zero. The activity was two orders of magnitude less than that of a conventional supported iridium catalyst. The used catalysts were characterized by EXAFS spectroscopy. The Ir-Ir coordination number was 3.2 for Ir{dollar}sb4{dollar}/MgO and 3.7 for Ir{dollar}sb6{dollar}MgO. The EXAFS results indicate that the structures of the metal clusters were retained during the catalytic reaction.; The cyclohexene hydrogenation reaction was catalyzed by Ir{dollar}sb4{dollar}/MgO. The turnover frequency was found to be 0.018 {dollar}pm{dollar} 0.006 s{dollar}sp{lcub}-1{rcub}{dollar} at 25{dollar}spcirc{dollar}C and 1 atm. The activity is two orders of magnitude less than that of conventional supported platinum catalysts. The used catalyst was characterized by EXAFS spectroscopy. The first-shell Ir-Ir coordination number was 3.2, being the same as that of the fresh catalyst.; The results are the first quantitative reports of the activities of structurally uniform supported metal clusters for structure-insensitive reactions. The difference in activity between the catalysts reported here and the conventional catalysts is inferred to be an indication of the role of the support.