C-H BOND ACTIVATION OF FORMATE ON CLEAN AND K-COVERED RU(001) - A THEORETICAL-STUDY

An extended Huckel (EH) study is performed on the clusters representing a formate adsorbed on Ru(001) and on (root 3 x root 3)R30 degrees K/Ru(001) in order to investigate the effect of potassium on the selectivity of decomposition of formate on Ru(001). The adsorption geometry and the VSIP (valence state ionization potential) values of EH parameters are determined from ab initio calculations on small clusters. The EH calculation reproduces well the site preference of formate on each surface suggested from experiments. The C-H bond of formate, which is our focus in this study, is calculated to be almost the same on the two surfaces when the molecular plane of formate is perpendicular to the surface; but when the plane is tilted from the surface normal and thus the C-H bond approaches the surface, the C-H bond is weakened to a much higher extent on clean Ru(001) than on K-covered Ru(001). This is in good agreement with the experimental result that the presence of potassium changes the reaction pathway of the decomposition of formate on Ru(001) by suppressing C-H bond cleavage.