Catalytically Active Interface between Noble Metal and Low-valence Transition Metal for C-O Hydrogenolysis

Abstract

Two-components catalysts Rh-ReO_x/SiO₂, Rh-MoO_x/SiO₂ and Ir-ReO_x/SiO₂ were active in the C-O hydrogenolysis of glycerol, 1,2-propanediol and tetrahydrofurfuryl alcohol. The activities were much higher than those of monometallic catalysts. The selectivities to terminal alcohols decreased in the following order: Ir-ReO_x/SiO₂ > Rh-ReO_x/SiO₂ > Rh-MoO_x/SiO₂ » Rh/SiO₂. Characterization with XRD, TEM, CO adsorption, temperature-programmed reduction (TPR), XANES and EXAFS revealed that noble-metal particles were partially covered with ReO_x or MoO_x species. The MoO_x species in Rh-MoO_x/SiO₂ formed a monomeric structure. The ReO_x species in Rh-ReO_x/SiO₂ and Ir-ReO_x/SiO₂ formed monolayer clusters and multilayer clusters, respectively. A reaction mechanism was proposed where the alkoxide species formed on ReO_x (or MoO_x) was attacked by the active hydrogen species on Rh (or Ir) atoms bonded with the Re (or Mo) atom. The difference of the size of the modifier may affect the selectivity.