EFFECT OF REDUCTIVE AND OXIDATIVE ATMOSPHERES ON THE PROPANE AROMATIZATION ACTIVITY AND SELECTIVITY OF GA H-ZSM-5 CATALYSTS/

The aromatisation of propane was investigated at 823 K on two Ga/H-ZSM -5 catalysts differing by their aluminum content (Si/Al = 18 and 128, respectively), i.e. their Bronsted acid site concentration, and having similar gallium content (1.6 wt%) as a function of successive pretrea tments by hydrogen and oxygen. Hydrogen treatment increases activity a nd selectivity to aromatics while decreasing the formation of methane. Subsequent oxygen treatment enhances further the activity and aromati cs selectivity and has little effect on methane selectivity. These imp rovements of catalytic performance are explained by gallium migration in reducing conditions. The concentration of highly dispersed gallium species is thereby enhanced. These species, in association with Bronst ed centers, were reported previously to constitute the dual catalytic sites responsible for alkane activation. Hydrogen-oxygen pretreatment of Ga/H-ZSM-5 catalysts is thus a means to ensure rapid catalyst preac tivation and stabilisation in large scale light alkane aromatisation u nits.