Abstract
Silica-supported RuAg and RuAu bimetallic catalysts were studied by hydrogen chemisorption and by nuclear magnetic resonance (NMR) of adsorbed hydrogen. Both techniques yielded nearly the same capacity for hydrogen chemisorption on both series of bimetallic catalysts. A small difference measured by the two techniques was attributed to hydrogen spillover from ruthenium onto the silica support. This effect of hydrogen spillover was less pronounced in RuAg/SiO 2 than in RuAu/SiO 2, as indicated by the longer spin-lattice relaxation times of the silanol proton. The results of these studies are used to infer that a stronger interaction exists between silver and ruthenium than between gold and ruthenium in the supported bimetallics. Both NMR results and volumetric chemisorption results show that residual chlorine inhibits the hydrogen chemisorption capacity of the Ru/SiO 2 catalyst and RuAu/SiO 2, bimetallic catalysts. The variation of the adsorbed hydrogen chemical shift with chlorine coverage indicates an electronic interaction that is due to chlorine adsorption. A direct comparison between clean RuCu/SiO 2 (from a previous study), RuAg/SiO 2, and Ru-Au/SiO 2, bimetallic catalysts was made to illustrate the varying degrees of interaction between ruthenium and copper, silver, or gold.
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