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Hierarchical zeolites were synthesized by alkali treatment and their applications in Fischer-Tropsch (FT) synthesis were studied. It was found that alkali treatment not only created hierarchical structure but also could tune cobalt-support interaction. The dissolution of Si by alkali treatment became easier with the increase of Si/Al ratio, and thus the amount of mesopority increased. An optimal Si/Al molar ratio was identified over the zeolite with Si/Al ratio of 80, which was found to be superior to other catalysts in terms of better diesel selectivity and lower CH selectivity due to its relatively narrow bimodal pore size distribution and moderate cobalt-support interaction. Meanwhile alkali treatment could enhance cobalt-support interaction via the formation of ɑ-SiO Co/MZ-120 catalyst showed the lowest FT activity and higher CH selectivity due to the increase of such new phase. [ABSTRACT FROM AUTHOR]

A series of ZSM-5/SBA-15 composite supported Co catalysts were prepared and evaluated for the Fischer–Tropsch synthesis (FTS) aimed to maximise the selectivity of C 5 –C 22 hydrocarbons in the product. The composite support was prepared by physically mixing ZSM-5 and SBA-15 of varying proportions and the finished catalysts had a constant Co loading of 15wt.%. The catalysts were tested for their performance in a high pressure fixed-bed reactor operating at T = 240 °C, P = 2.0 MPa, H 2 /CO = 2 and GHSV = 1000 h − 1 . The composite supported catalysts were shown to have much improved catalytic performance over the respective single material supported catalysts. The catalyst with 20wt.% ZSM-5 in the composite support gave the maximum CO conversion (90.6%), maximum selectivity of C 5 –C 22 hydrocarbons (70.0%) and minimum selectivity of light hydrocarbons (13.3% for CH 4 and 7.0% for C 2 –C 4 alkanes). The catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy with an energy dispersive X-ray spectrometer, temperature programmed desorption and temperature programmed reduction. It was revealed that the superior catalytic performance can be attributed to the large pore size and high dispersion of Co 3 O 4 , which afforded an optimum reducibility and acid site density. [ABSTRACT FROM AUTHOR]