Chemical and structural effects of strontium on iron-based Fischer-Tropsch synthesis catalysts

A series of Fe/SiO2 catalysts with different strontium/iron molar ratios were used to investigate the chemical and structural effects of strontium on the iron-based Fischer-Tropsch synthesis (FTS) catalysts. It was found that the chemical effect of strontium strengthened Fe-O bonds of Fe2O3 and hence suppressed the reduction of iron oxide. The chemical effect also suppressed the H-2 adsorption but improved the CO adsorption, which is responsible for the low surface H/C ratios and methane selectivity. At the same time, the promotion of strontium improved the dispersion of iron oxides. The dispersion effect facilitated the reduction and carburization of catalysts. It was also helpful for the H-2 adsorption and in turn led to high surface H/C ratios and methane selectivity. Under the combined action of the chemical and structural effects, the selectivity to methane of catalysts exhibited a parabola-like trend as a function of strontium loading and passed through a minimum at Sr/Fe molar ratio of 6/100. In contrast, the selectivity of heavy hydrocarbon demonstrated an opposite tendency.