Distinguished Roles with Various Vanadium Loadings Of CoCr_2–xV_xO₄ (x = 0–0.20) for Methane Combustion

A series of vanadium-doped CoCr_2–xV_xO₄ (x = 0–0.20) catalysts were prepared via the citric acid method and investigated for methane combustion. A significant improvement of the catalytic activity was observed over a CoCr_1.95V_0.05O₄ catalyst, and the catalytic activity reached 90% of methane conversion at 438 °C, which was 76 °C lower than that of the undoped catalyst. Vanadium doping caused disorder in the spinel structure and various changes in physicochemical properties. The higher concentration of suprafacial, weakly chemisorbed oxygen and the active cobalt species, especially Co³⁺, could play a major role in the oxidation reaction. Results of XRD, Raman, and XPS suggested that excess vanadium probably formed separate catalytically inactive VO_x species, which would explain the decline of catalytic activity for samples with a higher substitution degree.