Development of advanced catalysts using fine particles of intermetallic compounds.

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Supported and unsupported intermetallic compounds (IMCs), Ni_3Ge, Pd_3Bi, Pt_3Sn, PtCu and Pt_3Co, were prepared and characterized by XRD to identify their crystal phases and obtain the size of their crystallites. Temperature programmed reduction of IMCs was measured to determine the appropriate temperature of reduction. IR spectra of adsorbed CO indicated the electron transfer from Ni to Ge in the case of Ni_3Ge and from Bi to Pd in the case of Pd_3Bi. The catalytic activity for H_2-D_2 equilibration was measured and it was revealed that only Ni_3Ge showed comparable activity to Ni and that the other IMCs showed much lower activity than Pd and Pt.Silica supported IMCs were used for the catalyst in acetylene hydrogenation with a continuous flow reaction system. Ni_3Ge/SiO_2 and Pd_3Bi/SiO_2 gave high selectivity for the partial hydrogenation into ethylene. The latter was found to have higher selectivity and stability for ethylene formation than commercial Pd-Ag/SiO_2. Both IMC catalysts were also active and selective for the selective hydrogenation of a small amount of acetylene in excess ethylene. Pt_3Sn/H-SAP0-11 showed high selectivity to isobutene in the dehydroisomerization of butane. The catalytic properties for the preferential oxidation of CO in hydrogen was studied for Pt-IMCs. PtCu/SiO_2 and Pt_3Co/SiO_2 showed much higher activity than Pt/SiO_2 at low temperatures. The addition of water in the feed accelerated the rate of oxidation on PtCu/SiO_2. It was revealed that water molecules produced through the oxidation of hydrogen accelerate the adsorption of oxygen molecules on the surface to promote the oxidation of CO. In the case of Pt_3Co/SiO_2, the dissociative adsorption of 02 takes place on Co atoms to accelerate the oxidation of CO at low temperatures.