A preliminary evaluation of ZSM-5/SBA-15 composite supported Co catalysts for Fischer–Tropsch synthesis

Abstract

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 C5–C22 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=2.0MPa, H2/CO=2 and GHSV=1000h−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 C5–C22 hydrocarbons (70.0%) and minimum selectivity of light hydrocarbons (13.3% for CH4 and 7.0% for C2–C4 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 Co3O4, which afforded an optimum reducibility and acid site density.