Catalytic combustion of methane over LaMnO<sub>3</sub> perovskite supported on La<sub>2</sub>O<sub>3</sub> stabilized alumina. A comparative study with Mn<sub>3</sub>O<sub>4</sub>, Mn<sub>3</sub>O<sub>4</sub>-Al<sub>2</sub>O<sub>3</sub> spinel oxides