KINETICS OF METHANE OXIDATIVE COUPLING ON ZINC-DOPED TITANIUM-OXIDE

A kinetic study of methane conversion to C2-hydrocarbons was conducted by cofeeding methane and oxygen at 1 bar total pressure over a series of zinc-doped TiO2 catalysts. The zinc dopant concentration was varied between 1 and 4 wt.-% ZnO. Electrical conductivity measurements confirmed the incorporation of Zn2+ cations into the crystal lattice of rutile TiO2. It was found that the zinc oxide concentration had a larger effect on the activation energy of C2-hydrocarbons formation (between 68 and 46 kcal mol-1 in the range 0-4 wt.-% ZnO) than of methane conversion (ca. 42 kcal mol-1) and CO(x) formation (ca. 30 kcal mol-1). The relationship between the rates of methane conversion, C2-hydrocarbons and CO(x) formation and oxygen pressure in the range 650-750-degrees-C was found to depend strongly on the ZnO dopant concentration. Temperature and oxygen pressure were found to affect strongly the relationship between the selectivity of C2-hydrocarbons formation and ZnO dopant concentration. This study indicated that there is no clear correlation between electrical conductivity, basicity/acidity and kinetic parameters of the partial oxidation of methane to C2-hydrocarbons for the present Zn2+-doped TiO2 catalysts.