Isomorphic titanium-substituted mesoporous SBA-16 as support for cobalt Fischer–Tropsch synthesis catalysts: balance between dispersion and reduction

The delicate balance between dispersion and reduction of the Co-based Fischer–Tropsch synthesis catalyst is the golden key to enhancing catalytic performance, which highly depends on an optimized metal–support interaction. In this study, we regulate the interaction between Co and mesoporous SBA-16 by substituting skeletal Si with isomorphic Ti atoms. The catalytic activity and selectivity of Co/SBA-16 are significantly improved after using a modified supporter with moderate Ti. In comparison with Co/SBA-16, when the Si/Ti molar ratio was 11, the level of catalyst reduction decreased from 80.5% to 66.4% whereas the dispersion increased from 9.5% to 13.4%. CO conversion and C5+ selectivity increased from 29.1% to 38.0% and from 77.2% to 81.8%, respectively. When the Si/Ti molar ratio was decreased to 5.5, the level of catalyst reduction decreased to 55%; however, the dispersion increased further to 16.7%. X-Ray diffraction revealed that excess Ti would result in anatase TiO2 formation on the SBA-16 surface, which adversely affected the catalytic activity. STEM results indicated that when the Si/Ti molar ratio was 11, Co3O4 particles were localized inside the channels of SBA-16 with a size of ca. 8.5 nm. The suitable particle size of Co species may be one of the causes of the good catalytic performance of Ti(11)–SBA-16. The X-ray photoelectron spectroscopy, H2 chemisorption, and O2 titration results reveal that the catalyst with the optimized metal–support interaction presents eclectic dispersion and reduction, leading to a higher CO conversion and an excellent hydrocarbon selectivity.