CHARACTERIZATION OF SILICA-SUPPORTED CU MONOMETALLIC AND RU-CU BIMETALLIC CATALYSTS BY HYDROGEN CHEMISORPTION AND NMR OF ADSORBED HYDROGEN

Monometallic Ru/SiO2 and Cu/SiO2 catalysts and a series of RuCu/SiO2 bimetallic catalysts were investigated in detail by hydrogen chemisorption and nuclear magnetic resonance (NMR) of adsorbed hydrogen. NMR indicates that adsorption of hydrogen on pure Cu/SiO2 at room temperature results in formation of a mobile, atom-like adsorbed species. Hydrogen spillover from Ru to Cu in the RuCu/SiO2 bimetallic catalysts was clearly shown by the two techniques. Two distinct adsorbed states of hydrogen were observed on surfaces of the RuCu bimetallic particles. One state is reversibly adsorbed at room temperature while the other is irreversibly adsorbed. The reversible hydrogen exhibits rapid motion at the surface; the irreversible hydrogen is less mobile. Surface compositions for all the RuCu/SiO2 bimetallic catalysts were obtained from the NMR resonance lineshifts of the reversible hydrogen. The results show a preferential segregation of Cu to surfaces of Ru particles and indicate formation of large Cu islands on ruthenium and separate pure Cu particles at very high copper loadings. © 1990.