Catalytic reactions of coke with dioxygen and steam over alkaline-earth-metal-doped cerium-zirconium mixed oxides

Abstract

A series of cerium-zirconium mixed oxides doped with alkaline earth metals was prepared by calcining a mixture of Ce0.8Zr0.2O2 and the nitrate salt of alkaline earth metals at 1173K. The results from X-ray diffraction, Raman spectroscopy and analytical electron microscopy indicated the alkaline earth compounds were dispersed on the surface of Ce0.8Zr0.2O2. The doped mixed oxides were evaluated in the catalytic reaction of solid coke under tight contact conditions with 10 vol.% O2 in He at 693K and with 100vol.% H2O at 993K using thermogravimetric analysis. For coke oxidation with O2, the weight loss was first order in coke, and the measured first order rate constant was proportional to the total surface area of catalyst at low catalyst loadings. For coke gasification with H2O, the weight loss was nearly zero order in coke, and the measured areal reaction rate was independent of the total surface area of catalyst at low catalyst loadings. The addition of alkaline earth metals inhibited coke oxidation with dioxygen but promoted coke gasification with steam.