Oxide-Bound Transition Metal Complexes for Methane Activation. Final Report September 30, 1986-August 31, 1989

摘要

The effect of hydration levels of support oxides on deposition and subsequent activation chemistries was investigated. A series of silicas prepared through different techniques was studied for hydroxyl group concentration and distribution by (1)H NMR. NMR analysis showed that deposition of tris(allyl) rhodium occured on non-hydrogen-bonded OH groups. UHV studies confirmed the nature of covalency between the oxide and the overlayer and demonstrated the participation of oxide oxygens in inter-ligand conversions in the coordination sphere of the attached transition metal. New methodology was developed for directly converting bis(allyl)rhodium or rhodium dihydride complexes to (dioxygen) or (ozone) adducts. The complexes were prepared on alumina, silica, or titania. EXAFS structural data were obtained for several of the complexes. Catalytic oxidation of a test substrate, CO, was done, and rates for oxidation were measured. A flow system for methane oxidation was prepared, and oxidation of methane was examined, either catalytically or stoichiometrically, with the rhodium(dioxygen) species. Only CO2 was obtained. No intermediate level oxidation products were observed, and independent investigations showed that both methanol and formaldehyde were highly reactive substrates toward either catalytic or stoichiometric oxidation procedures. To develop mixed metal systems for methane oxidation, sequential addition of rhodium and molybdenum allyls onto silica was studied. A series of 'HPA' complexes of rhodium was prepared involving both di(carbonyl) and dioxygen adducts. The compounds were studied as soluble models for oxide-based oxidation species.