CATALYTIC COMBUSTION OF METHANE - SURFACE CHARACTERIZATION OF MANGANESE-SUBSTITUTED BARIUM HEXA-ALUMINATE CATALYSTS

In order to achieve a good activity with respect to methane combustion , a good route would be via catalysts incorporating transition metals. For devices operating at high temperatures, such as gas turbines, sub stituted hexaaluminates present the advantage of good thermal stabilit y when compared to impregnated Al2O3. For the purpose of this study, m anganese-substituted hexa-aluminates were prepared either by the sol-g el method or by carbonate precipitation. Surfaces were analysed by sof t x-ray emission, namely low-energy electron-induced x-ray spectroscop y (LEEIXS), and by photoelectron spectroscopy, namely x-ray photoelect ron spectroscopy, The results on samples incorporating increasing amou nts of manganese show the existence of an upper limit to the number of atoms substituted at the catalyst surface, This limit is about 2.7 ma nganese ions per unit cell, for samples prepared either by the sol-gel or by the carbonate precipitation technique and then calcinated at 12 00 degrees C, The interpretation of the Auger parameter variations sho ws that the relative amount of Mn in oxidation state III increases whe n the surface amount of Mn increases, as web as with the Mn substituti on level, This fact can be related to an increased activity for methan e conversion. (C) 1998 John Wiley & Sons, Ltd.