Development of dual-membrane coated Fe/SiO₂ catalyst for efficient synthesis of isoparaffins directly from syngas

A novel dual-membrane coated catalyst (Fe/SiO₂-S-Z) with Fe/SiO₂ core and Silicalite-1 and H-ZSM-5 zeolite membranes was developed and employed for isoparaffins direct synthesis from syngas via Fischer-Tropsch synthesis (FTS) reaction. The Silicalite-1 zeolite membrane, as a structural membrane, was prepared under a close-to-neutral synthesis condition, which avoided the structure destruction of the core catalyst Fe/SiO₂ and favored the in-situ growth of H-ZSM-5 zeolite membrane. In H-ZSM-5 zeolite membrane, as a functional membrane, the micropores and strong acidic sites were preserved in the dual-membrane catalyst, which played important roles in the isoparaffins direct synthesis. Activity tests indicated that the dual-membrane catalyst exhibited an excellent performance for isoparaffins direct synthesis. The isoparaffins selectivity of the dual-membrane catalyst was up to 29.8%, much higher than those of individual core catalyst (12.9%) and physical mixture catalyst of H-ZSM-5 zeolite and Fe/SiO₂ catalyst (16.6%). It was found for the first time that the hydrogenation and isomerization of olefins over the dual-membrane catalyst were the main reasons for the high isoparaffins selectivity. In addition, due to the spatial confinement effect of the microporous zeolite membranes, the hydrocracking and isomerization of heavy hydrocarbons (C₁₂₊) also contributed to the high selectivity of isoparaffins.