SUPPORTED AU CATALYSTS PREPARED FROM AU PHOSPHINE COMPLEXES AND AS-PRECIPITATED METAL-HYDROXIDES - CHARACTERIZATION AND LOW-TEMPERATURE CO OXIDATION

Supported Au catalysts were prepared by attaching Au phosphine complex es, Au(PPh3)(NO3) (1) and [Au-9(PPh3)(8)](NO3)(3) (2), on as-precipita ted metal hydroxides M(OH)(x) (*, as-precipitated; M = Mn2+, Co2+, Fe 3+, Ni2+, Zn2+, Mg2+, Cu2+, Ti4+, Ce4+, and La3+), followed by tempera ture-programmed calcination in a flow of dry air. The obtained Au cata lysts showed high catalytic activities in low-temperature CO oxidation . Among the obtained Au catalysts 1/Mn(OH)(2) and 1/Co(OH)(2)* were m ost highly active even at 203 K. 1/Fe(OH)(3) and 1/Ti(OH)(4)* also ca talyzed CO oxidation at low temperatures 203-273 K, whereas 1/Fe2O3 an d 1/TiO2 prepared by supporting 1 on conventional Fe2O3 and TiO2 showe d negligible activity under the similar reaction conditions. It was es timated by TEM and XRD that the mean diameter of Au particles in 1/Fe( OH)(3) was about 2.9 nm, which was about 10 times smaller than that f or 1/Fe2O3. EXAFS for 1/Ti(OH)(4) revealed that the coordination numb er of Au-Au bond was 8-10, while that for 1/TiO2 was 11.0, which also indicates that Au particle size for 1/Ti(OH)(4) is smaller than that for 1/TiO2. The catalysts obtained by attaching the Au complexes on co mmercially available metal hydroxides also showed negligible activity for the low-temperature CO oxidation under identical conditions. These results demonstrate that supported Au catalysts with small Au particl es, tremendously active for the low-temperature CO oxidation, can be p repared by attaching the Au phosphine complexes on the as-precipitated metal hydroxides. Sodium cations exhibited positive effect on the Au catalysis, whereas chloride anions drastically decreased the CO oxidat ion activity. (C) 1997 Academic Press.