Effects of macropores on reducing internal diffusion limitations in Fischer–Tropsch synthesis using a hierarchical cobalt catalyst

Abstract

Internal diffusion limitations in Fischer–Tropsch catalysts strongly affects their catalytic activities and product selectivities. Large pellet catalysts demonstrate especially severe internal diffusion limitations in fixed bed reactors. In order to overcome this problem, macropores were introduced into cobalt catalysts, and the resulting effects on reaction activity and selectivity were studied. Meso–macroporous silica (S1) with mesoporous walls was prepared by a sol–gel process and was used to prepare the Co/S1 catalyst. A bimodal mesoporous silica (S2) support with an equivalent mesopore diameter to the S1 support was also prepared for comparison. The effects of internal diffusion limitations in the S1 and S2 supports with different pellet sizes on FT synthesis were investigated. The results showed that the macropores played an important role in reducing internal diffusion limitations, especially for large pellet catalysts.