Characterization and catalytic combustion of methane over hexaaluminates

Both Sr0.8La0.2MnAl11O19 (SLMA) and Sr0.3Ba0.5La0.2MnAl11O19 (SBLMA) hexaaluminates are prepared by the co-precipitation method. Their thermal characterizations are examined by X-ray diffraction (XRD) and BET method. The activity of methane catalytic combustion also is reported. A temperature threshold of 1200degreesC has been found for the formation of the hexaaluminate structure. The surface areas retain in the range of 20-30 m(2) g(-1) upon calcination at 1200degreesC for both SLMA and SBLMA. The surface area of SBLMA is larger than that of SLMA upon calcinations above 1200degreesC illustrating the superior thermal stability of the barium hexaalummate. Partial replacement of Sr2+ ion with Ba2+ ion improves the thermal stability of the hexaaluminate. The high surface area for SBLMA can be understood from the microstructural change of pore size. The SBLMA possesses larger pore than the SLMA to resist sintering under high temperature calcination. Upon calcinations at 1300degreesC for 20 h, the SBLMA retains a surface area of 20 m(2) g(-1) and shows a good activity in methane combustion. (C) 2004 Elsevier B.V. All rights reserved.