Several hexaaluminate-related materials were prepared via hydrolysis of alkoxide and powder mixing method for high temperature combustion of CH4 and C3H8, in order to investigate the effect of the concentration of the fuels, O-2 and H2O on NOx emission and combustion characteristics. Among the hexaaluminate catalysts, (Sr08La0.2MnAl11O19-alpha)-La-. prepared by the alkoxide method exhibited the highest activity for methane combustion and low NOx emission capability. NOx emission at 1500 degreesC was increased linearly with O-2 concentration, whereas water vapor addition decreased NOx emission in CH4 combustion over the Sr0.8La0.2MnAl11O19-alpha catalyst. In the catalytic combustion of C3H8 over the Sr0.8La0.2MnAl11O19-alpha catalyst, the amount of NOx emitted was raised in the temperature range between 1000 and 1500degreesC when the C3H8 concentration increased from 1 to 2 vol.%. It was found that NOx emission in this temperature range was reduced effectively by adding water vapor. (C) 2003 Elsevier B.V. All rights reserved.