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

摘要

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 (Ga2O) and the protonic sites of the zeolite. The proportion of Ga implied in this exchange depends on both the proximity between Ga2O3and 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.