Catalytic behaviors of bifunctional Fe-HZSM-5 catalyst in Fischer–Tropsch synthesis

Fe-HZSM-5 bifunctional catalyst activity and products selectivity in Fischer–Tropsch synthesis (FTS) were investigated. HZSM-5 zeolite and iron catalyst were become near to each other step-by-step. In first step, zeolite just affected gaseous products after FTS reaction on iron catalyst. In other conditions, zeolite was incorporated in FTS process to be included in cracking and aromatization reactions. The results revealed that role of zeolite in overall reaction were increased from completely separated condition to physically mixed condition. Addition of binder in physically mixed condition was led to cover the active sites of bifunctional iron–zeolite catalyst and decrease activity of zeolite and iron catalyst. Also, decreasing amounts of Brønsted acid sites after FT reaction was related to zeolite incorporation in overall reaction that was decreased by closing the zeolite to the iron catalyst. HZSM-5 addition to FT catalyst suppressed the formation of oxygenates, which are converted to hydrocarbons on the zeolite acid sites. Furthermore, zeolite increased CO2 selectivity slightly because of oxygenate decomposition into CO2 as a side reaction that showed by co-feeding of light alcohol (with 14C) to FTS in previous works.