Promoting effect of rhodium on Co/ZnAl2O4 catalysts for the catalytic combustion of hydrocarbons

Zinc aluminate (ZnAl) was used as support to obtain a series of rhodium-modified Co-ZnAl catalysts for the catalytic oxidation of propane and naphthalene. The catalysts were characterized by various techniques including N2 adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), diffuse reflectance spectroscopy (DRS), FTIR and X-ray photoelectron spectroscopy (XPS), to correlate chemical and physical characteristics with catalytic properties. TPR and XPS techniques show the presence of segregated cobalt compounds, as well as cobalt species interacting with the support. Segregated cobalt species are considered responsible for the catalytic activity, due to their high reducibility. The addition of Rh promotes the reducibility of the cobalt compounds yielding to an increase in the surface content of Co2+. For propane oxidation, the best activity shown by the Rh(0.5)Co(5)-ZnAl sample could be associated with a synergic effect between rhodium and cobalt species. No specific effects were revealed due to the addition rhodium for the naphthalene oxidation.