Effect of the desilication of H-ZSM-5 by alkali treatment on the catalytic performance in Fischer-Tropsch synthesis

Hierarchical HZSM-5 zeolites were prepared by post-synthesis treatment of HZSM-5 zeolite with different concentrations of NaOH. The physicochemical properties of these zeolites loaded by cobalt nanoparticles in Fischer-Tropsch (FT) synthesis were investigated. It was found that the activity and CH4 selectivity increased at first, then decreased closely related to the change of catalyst reducibility indicating that higher cobalt reducibility was a prerequisite for hierarchical zeolites to improve FT catalytic performances. The catalyst treated with 0.1 M NaOH was found to be optimal for C12-18 selectivity, which was mainly attributed to bimodal porous structure to improve diffusion behavior of products combining with moderate acid sites to mitigate second reactions. While the catalyst treated with 0.15 M NaOH showed the lowest activity and higher CH4 selectivity due to its lower reducibility even the largest mesopores were observed.