Cobalt supported on Zr-modified SiO2 as an efficient catalyst for Fischer–Tropsch synthesis

Abstract

Amorphous silica–zirconium (SZx) has been synthesized via the sol–gel method accompanied by phase separation in the presence of propylene oxide (PO) and poly(ethylene oxide) (PEO). Herein x is the mol% of zirconium (Zr), i.e. 0, 1.5, 2.8, 5.6 and 8.9 mol%, respectively. 13% wt% cobalt-based SZx (Co/SZx) catalysts were prepared by an impregnation method. The Co/SZ catalysts were characterized by XRD, N₂ adsorption–desorption, ESEM, H₂-TPR and NH₃-TPD. The catalytic behavior of Co/SZx was investigated for the Fischer–Tropsch (FT) reaction via a fixed-bed reactor under the conditions of 1.0 MPa, H₂/CO = 2, W/F = 5.05 g h mol⁻¹ and 235 °C. The results indicated that CO conversion followed the order of Co/SZ2.8 > Co/SZ1.5 > Co/SZ0 > Co/SZ5.6% > Co/SZ8.9. The activity differences for FT synthesis are mainly ascribed to the differences in SZx such as Zr dosage, pore structure and aggregation extent, which are also the direct reasons for the various Co dispersions on SZx. The existence of Zr in the Co/SZ catalysts leads to a decrement of the selectivity to CO₂/C₅⁺, and an increase of C₂–C₄ selectivity and N-p/O value. Overall, the Co/SZ2.8 catalyst exhibited the top FT reaction activity, top yield of C₅⁺ and lowest selectivity to methane and C₂–C₄ among all the Co/SZ catalysts.