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