Deactivation behaviors of hybrid Fischer-Tropsch catalysts in the production of middle distillate from synthesis gas in a dual-bed reactor

Production of middle distillate (C-10-C-20) from synthesis gas (CO + H-2) through hydrocracking of wax (> C21+) was carried out in a dual-bed reactor. Fischer-Tropsch catalyst (Co/TiO2) was used in the first-bed reactor to produce wax from synthesis gas, and a mesoporous Pd-alumina composite catalyst (Pd-Al2O3) was used in the second-bed reactor to produce middle distillate through hydrocracking of wax. Both Fischer-Tropsch synthesis function of Co/TiO2 catalyst and hydrocracking function of Pd-Al2O3 catalyst were deactivated during 100 h-hybrid Fischer-Tropsch synthesis reaction. It was revealed that deactivation behaviors of Co/TiO2 and Pd-Al2O3 catalysts were governed by different factors. Wax accumulation and Co sintering were responsible for deactivation of Co/TiO2 catalyst in the Fischer-Tropsch synthesis reaction. Loss of Pd dispersion and Pd surface area of Pd-Al2O3 catalyst was responsible for its decreased catalytic performance in the production of middle distillate through hydrocracking of wax.