Considerations about the bifunctionality and the gallium species role in the propane aromatization reaction over [Ga]- and [Ga,Al]-ZSM-5 catalysts

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The as-synthesized alkali-free TPA, MeNH 3 -[Ga]-ZSM-5 and TPA, MeNH 3 -[Ga,Al]-ZSM-5 zeolites were calcined and/or steamed at different steam pressures, reaction times, and temperatures. The solids obtained were characterized by XRD, FT-IR, N 2 adsorption, 27 Al and 71 Ga MAS-NMR. Acidity of the solids was characterized using n-Heptane cracking as a model reaction. Acidic or bifunctional behavior of these catalysts was determined using propane aromatization as a model reaction. A clear synergistic effect is observed between acidic sites in the solids structure and dehydrogenating species composed by extraframework gallium species (EFGS). Linear dependence of initial activity in propane aromatization per protonic acidic site (A 0 /H + ), as a function of EFGS/H + relation, shows that this aromatization reaction should be kinetically limited by initial dehydrogenation step produced on EFGS, which demonstrates bifunctionality of this reaction. Finally, inactivation of acidic sites of the structure of the solid (H + ) is produced by extraframework gallium species (EFGS), and the numeric ratio between them shows that EFGS present on galloaluminosilicates, under reaction conditions, should be species with a positive charge equal to one.