Catalytic properties of intermetallic compounds and their application to high performance catalysts

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The catalytic properties of intermetallic compounds and their application to various reactions as specific catalysts were investigated.Intermetallic compounds with the combination of transition and typical elements and of two transition elements were prepared by an arc-melting technique. They were crushed in air and reduced by hydrogen at 600-900℃ before characterization and catalytic reactions. XRD, XPS and EDX studies revealed that they were homogeneous and single-phase intermetallic compounds in the bulk and on the surface. Ni_3Sn and Pt_3Ge gave much lower catalytic activity than Ni and Pt for H_2-D_2 equilibration but much higher selectivity for partial hydrogenation of acetylene into ethylene and 1,3-butadiene into butenes, respectively. TiPt__3 gave higher activity than Pt for H_2-D_2 equilibration and ethylene hydrogenation.Fine particles of those intermetallic compounds were prepared by chemical vapor deposition (CVD) or successive impregnation techniques. In CVD, the vapor of … More Sn(CH_3)_4, Ge(acac)_2Cl_2, Ti(C_5H_5)_2Cl_2, etc. was supplied with hydrogen onto Ni/silica, Pt/H-ZSM-5, Ru/silica, etc. to deposit the second element onto the particle of first element. XRD, XPS and XAFS studies revealed that the particles were single-phase intermetallic compounds with diameters of 4-20 nm. The fine particles showed three magnitude higher activity per weight of compounds than the unsupported bulk compounds. Moreover, the selectivity of these compounds was totally different from that of supported pure metals. Ni_3Sn/silica gave benzene in the reaction of cyclohexane, while Ni/silica gave almost exclusively methane. Pd_3Bi/silica and Pd_3Pb/silica gave benzyl acetate in the oxidative acetoxylation of toluene with much higher yields than Pd/silica. Pt_3Ge/H-ZSM-5 accelerated the formation of aromatic hydrocarbons in the aromatization of butane without preferential formation of methane through the hydrogenolysis on Pt/H-ZSM-5. RuTi/silica exhibited high yield to higher hydrocarbons in Fischer-Tropsch synthesis than Ru/silica. Less