CATALYTIC MEMBRANE REACTOR FOR OXIDATIVE COUPLING OF METHANE .1. PREPARATION AND CHARACTERIZATION OF LAOCL MEMBRANES

The sol-gel process was investigated in order to prepare LaOCl inorganic membranes on commercial alumina tubular supports which were catalytically active for the oxidative coupling of methane. The preparation of LaOCl meso and microporous membranes is described on the basis of the fundamental phenomena occurring during the sol preparation and thermal treatment. Membranes were synthesised from LaCl3 precursor in aqueous media. Important parameters, mastering the sol formation and consequently the final material textural characteristics, were the molar ratio [acetate]/La], [NH3]/[La] and the total concentration of lanthanum in the sol. Without any acetate addition, turbid sols were obtained leading at 800 degrees C to mesoporous membranes. The effect of acetate ions is shown to be of prime importance in order to limit the polycondensation reactions in the sol and to prepare microporous materials. Under these conditions, quite dense membranes were obtained at 200 degrees C due to lanthanum acetate polymerisation. The formation of carbonates and their decomposition at 600 degrees C explain the maximum microporosity observed at this temperature. When these membranes were treated at 800 degrees C, the microporous volume decreased.