Effect of La3+ substituting Ba2+ on the structure and methane combustion activity of Ba1-xLaxMn3Al9O19-alpha catalysts

Mn-substituted hexaaluminate(Ba1-xLaxMn3Al9O19-alpha) catalysts were prepared by hydrothermal synthesis based on hydrolysis of urea. Effect of La3+ substituting Ba2+ on phase compositions, structure, thermal stability and methane combustion activity was investigated. When x >= 0.4, La, ( CO, decomposed in the range of 530-580 degrees C to be converted into La2O3 La2O3 reacted with y-Al2O3 to form LaAlO3 perovskite phase in the temperature range of 800-900 degrees C. BaAl2O4 spinel phase was suppressed due to the formation of LaA10,perovskite phase, and higher dispersing of Ba2+ in the solid phase was maintained, which is more favorable for the formation of hexaaluminate phase. When x < 0.4, the BET specific surface areas and methane combustion activities of the Ba1-xLaxMn3Al9O19-alpha catalysts decreased due to the formation of BaAl2O4 spinel phase. The hexaaluminate structure distorted to some extent when Ba2+ were substituted with La3+. The larger the distortion, the lower the thermal stability of the Ba1-xLaxMn3Al9O19-alpha catalysts. The methane combustion activity of the Ba1-xLaxMn3Al9O19-alpha catalysts varied with the change of x, and the Ba0.2La0.8Mn3Al19-alpha(x =0.8)catalyst showed the highest activity for methane combustion.