A study of the ruthenium-alumina system

Ru/alumina catalysts (0.21-5.11 wt% Ru) were characterized using temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and H-2 and CO chemisorptions. The transformations of cyclohexene were used as test reactions. The TPR data showed, for the catalysts calcined at 500 degrees C, two peaks at similar to 190 degrees C and 223 degrees C. The high temperature peak becomes quantitatively more important as the Ru content is increased. With the aid of XPS and H-2 and CO chemisorption, the low temperature peak is associated with a well-dispersed ruthenium phase while the high temperature peak is related to the reduction of RuO2 species. As expected from the dispersion measurements, the latter decreases with increasing Ru contents, in agreement with the literature. The catalytic results are in line with the characterization studies, showing an increase in the activity for the hydrogenolysis reaction (formation of methane) over the hydrogenation-dehydrogenation reactions, as the Ru content is increased. The latter can be explained in terms of the structural requirements of the hydrogenolysis reaction reported previously. (C) 1998 Elsevier Science B.V. All rights reserved.