Surface structure and catalysis for CO hydrogenation of the supported Ru species derived from the Ru3(CO)12 inorganic oxides

Abstract

Various kinds of supported Ru cluster have been prepared by using the surface reaction of Ru₃(CO)₁₂ with inorganic oxides such as V₂O₅, SiO₂, TiO₂, Al₂O₃, K-doped Al₂O₃, and MgO followed by H₂ reduction at 723 K. Their structures have been determined by means of EXAFS. Ru₃(CO)₁₂ supported on V₂O₅ was observed to be converted to three-atomic-layer Ru metal particles, whereas one-atomic-layer [Ru]_n clusters were produced on SiO₂(n= 12) and TiO₂(n= 6). The clusters [Ru_n(OZ)_x](Z = Al or Mg) with Ru–O (surface) bonds were formed on Al₂O₃(n= 6), K-doped Al₂O₃(n= 6) and MgO (n= 3). The difference of the Ru structures on inorganic oxides may be related to the different acidity and/or basicity of the metal oxides. The catalytic properties of these different Ru structures were examined to find the correlation between structure and catalysis in CO hydrogenation. CH₄ was predominantly formed on [Ru]₁₂ on SiO₂. The 6-Ru atom clusters with the Ru–Ru distances of 0.262–0.265 nm showed the highest selectivity for the formation of C₂–C₄ hydrocarbons. The metallic [Ru]₆ clusters on TiO₂ had a higher activity than the [Ru₆(OAl)_x] clusters bonded to the surface through oxygen atoms. The smallest surface-bound clusters on MgO produced mainly CH₄ and CO₂. These results demonstrate that CO hydrogenation is a structure-sensitive reaction, depending on the size and oxidation states of the Ru clusters.