Akademik Veri Yönetim Sistemi
JOURNAL OF CATALYSIS, cilt.178, sa.1, ss.26-33, 1998 (SCI-Expanded)
The dynamics and energetics of hydrogen chemisorption on silica-supported ruthenium and ruthenium-silver bimetallic catalysts were studied by H-1 NMR spectroscopy and microcalorimetry. It was observed that the amount of hydrogen adsorbed on Ru particles having intermediate and low heats of adsorption was significantly reduced with increasing amounts of silver. The desorption and adsorption rate constants, determined from selective excitation NMR experiments, were lower on Ru-Ag catalysts than those on Ru catalysts at the same temperature and hydrogen coverage. The apparent sticking coefficients of hydrogen on a Ru-Ag catalyst with 10 at% Ag were more than 10 times lower than those on a Ru catalyst and were comparable to sticking coefficients reported in the literature for hydrogen adsorbing on Ru single crystal. Thus silver was found to greatly affect both the dynamics and energetics of hydrogen chemisorption on Ru/SiO2. However, ensemble and electronic effects did not play any role in causing these effects. It is postulated here that the influence of silver was due to its tendency to selectively segregate to edge, corner, and other low coordination structures on the Ru particle surface. Hence, hydrogen adsorption on these surfaces was found to be structure sensitive. (C) 1998 Academic Press.