Mechanochemical approach to preparation of MFI zeolites substituted isomorphously by both Al and Fe as durable catalysts for the dimethyl ether to olefin reaction

Zeolites with an MFI-type framework topology containing both Al and Fe ([Al, Fe]-MFI) atoms were prepared via a two-step mechanochemically assisted method. In the first step, reactions between SiO₂ and either α-Fe₂O₃ or γ-AlO(OH), induced by mechanical force during planetary ball-milling, produced one of the two types of amorphous composites. A second hydrothermal treatment of a mixture of these composites yielded the [Al, Fe]-MFI zeolites. The thus-prepared [Al, Fe]MFI zeolites exhibited a longer lifetime in the catalytic conversion of dimethyl ether into light olefins, compared to zeolites prepared via the conventional one-pot hydrothermal process using homogeneous reagents. Extraframework Fe species were absent and Fe atoms were well distributed throughout the MFI zeolite prepared via the two-step process, while the conventionally prepared zeolites contained extraframework Fe species. The better homogeneity of Fe atoms in the zeolite catalyst achieved by the mechanochemically assisted method led to a longer catalyst lifetime.