SURFACE ORGANOMETALLIC CHEMISTRY ON METALS .3. FORMATION OF A BIMETALLIC NI-SN PHASE GENERATED BY REACTION OF A SN(N-C4H9)4 AND SILICA-SUPPORTED NICKEL-OXIDE

Reaction of Sn(n-C4H9)4 with NiO/SiO2 occurs above 423 K according to the apparent following stoichiometry: NiO + xSn(n-C4H9)4 → NiSnx + (2x + 1)C4H8 + (2x - 1)C4H10 + H2O. Various compositions of the bimetallic phase can be achieved by changing the initial Sn/Ni ratio. The obtained catalysts were very active and selective in the hydrogenation of ethyl acetate to ethanol. Characterization of the bimetallic phase has shown that the particles are bimetallic (STEM). As a result of chemisorption, IR, and magnetic measurements, it appears that the presence of tin has four effects: (i) it decreases significantly the amount of CO and H2 adsorbed; (ii) it isolates nickel atoms from their neighbors; (iii) it increases electron density on nickel; and (iv) it suppresses the magnetic properties of nickel. Redox behavior of NiSn/SiO2 toward surface OH indicates that surface hydroxyls can oxidize Sn(o), probably to Sn(II) with evolution of H2H2, the process being reversible with H2. It is suggested that during this oxidation process, tin migrates to the periphery of the bimetallic particle with formation of (≥Si<.z.sbnd;O)2Sn(II) surface species. © 1990.