Positive effects of Al³⁺ partially substituted by Co²⁺ cations on the catalytic performance of Co_1+x Al_2−x O₄ (x = 0–0.2) for methane combustion

Co_1+x Al_2−x O₄ (x = 0–0.2) catalysts were prepared by sol–gel method using citric acid as a chelating agent calcined at 1100 °C and then investigated for methane combustion. The catalytic activity of CoAl₂O₄ was significantly enhanced after Al³⁺ partially substituted by Co²⁺ cations in methane combustion. X-ray diffraction showed that all the Co_1+x Al_2−x O₄ (x = 0–0.2) samples displayed a spinel-type single phase. Raman spectroscopy deduced that Al³⁺ partially substituted by Co²⁺ cations created structural defects and lattice distortion, which was indicated to be favorable for the formation of oxygen vacancy and weakening the bond strength of Al–O. X-ray photoelectron spectroscopy revealed that the excellent catalytic activity for methane combustion may be attributed to the active octahedral coordinated Co³⁺ cations and surface oxygen vacancies, especially the active octahedral coordinated Co³⁺ cations predominantly determined for methane combustion.