Catalytic properties of Ga-containing MFI-type zeolite in cyclohexane dehydrogenation and propane aromatization

Three series of gallium-containing MFI zeolite were prepared with different gallium content by weight, by hydrothermal synthesis [Ga]-MFI (0.2–4.7 wt% Ga), ion exchange Ga/P (0.5–6.8 wt% Ga) and mechanical mixture Ga+P (0.5–10 wt% Ga). Under hydrogen at 600 °C on the aluminosilicate doped with gallium, a reducing solid ionic exchange occurs between a mobile species (Ga ₂O) and the protonic sites of the zeolite. The proportion of Ga implied in this exchange depends on both the proximity between Ga ₂O ₃ and the zeolite and the initial gallium content. The solid reductive exchange remains limited, ranging from 25% to only a few percent; therefore the gallium species content located in the zeolite micropores is only 0.2–0.4 wt%. The aluminosilicates doped with Ga are more active in both cyclohexane dehydrogenation and propane aromatization than the gallosilicates: the gallium in the framework is much less active than gallium in the exchange position.