Catalytic oxidation of methane over hexaaluminates and hexaaluminate-supported Pd catalysts

An aqueous (NH4)(2)CO3 coprecipitation method, based on that of Groppi et al. [Appl. Catal. A 104 (1993) 101-108] was used to synthesize Sr1-xLaxMnAl11O19-alpha hexaaluminates. These materials were first synthesized by alkoxide hydrolysis. This synthesis route requires special handling of the starting materials and is not likely to be commercially practical. The materials prepared by (NH4)(2)CO3 coprecipitation have similar surface areas as those prepared by the alkoxide hydrolysis method. Their CH4 oxidation activity, measured as the temperature needed for 10% conversion of methane, is higher than those prepared by alkoxide hydrolysis. The La-substantiated material, LaMnA(11)O(19-alpha), shows high surface area with 19.3 m(2)/g after calcination at 1400 degrees C for 2 h. It is active for CH4 oxidation with T-10% at 450 degrees C using 1% CH4 in air and 70 000 cm(3)/g space velocity. The stability and activity of LaMnAl11O19-alpha a prepared by (NH4)(2)CO3 coprecipitation method is a simple and important step forward for the application of CH4 catalytic combustion for gas turbines. (C) 1999 Elsevier Science B.V. All rights reserved.