Silicalite zeolite-supported iron catalysts for enhancing isoparaffin selectivity from CO hydrogenation

Abstract

The Fischer–Tropsch synthesis (FTS) reaction is widely used to produce clean hydrocarbon fuels or chemicals. The key challenge for FTS is the control of product distributions. Herein, iron was employed as the active species, and the supported (Fe/S1 and Fe/S2) and encapsulated (Fe@S1 and Fe@S2) catalysts with pure siliceous zeolite were successfully prepared by incipient wetness impregnation and solvent-free hydrothermal method, respectively. The iron species encapsulated in silicalite zeolite, rather than being present on the surface, enhanced the acidity of zeolite, which was effective in regulating the FTS products. The acidic site can be divided into two types: Lewis and Brønsted, where the Brønsted acid sites are much more stable than Lewis acid sites at FTS reaction temperature. Moreover, Fe@S1 and Fe@S2 with much more Brønsted acid sites displayed a higher selectivity of isoparaffins in the FTS products compared to the supported catalysts (17.6% and 18.6% for Fe@S1 and Fe@S2 vs. 4.1% and 11.8% for Fe/S1 and Fe/S2, respectively). Thus, the acidity of silicalite zeolite can be regulated by encapsulating active metal in it, which is a promising prospect for tuning production distribution in FTS reactions.