PREPARATION AND CHARACTERIZATION OF VANADIUM OXIDE PROMOTED RHODIUM CATALYSTS

The location of the promoter element in rhodium on alumina and silica catalysts promoted by vanadium oxide has been studied by various techniques. Our results prove that an intimate contact between the active component, rhodium, and the promoter, vanadium oxide, is present in most catalysts studied. For the silica-supported systems, temperature programmed reduction and diffuse reflectance infrared spectroscopy pointed to the formation of a mixed oxide (RhVO%) during calcination. Reduction of this oxide phase resulted in a vanadium oxide layer on top of the metal particle, as could be concluded from carbon monoxide chemisorption experiments. Rh/V,O,/SiO, catalysts, CO chemisorption was suppressed in the while transmission electron microscopy showed that the rhodium particle size was not influenced by the addition of vanadium oxide. This indicates that the suppression of CO chemisorption is not due to a decrease o