Pore Structure Model of Bimodal Catalyst Supports

Abstract

Co/ZrO2–SiO2 bimodal catalyst has higher activity and higher selectivity for the Fischer-Tropsch synthesis than conventional catalysts. This study investigated the catalyst support pore structure in detail, especially the formation of small pores with a model analysis. The analysis considered 10 wt% ZrO2–SiO2 and 20 wt% ZrO2–SiO2 bimodal catalyst supports with various loadings of ZrO2. Higher loadings of ZrO2 from 10 to 20 wt% decreased the large pore size from 59.8 to 56.7 nm, resulting in the promotion of the formation of small ZrO2 pores inside the large SiO2 pores. Interestingly, small pore size remained unchanged at 3.9 nm, irrespective of the ZrO2 loading, indicating that the small pore size was determined by the character of the ZrO2 nanoparticles participating in the self-assembly of ZrO2 nanoparticles inside the large SiO2 pores. A theoretical model of the agglutination of ZrO2 nanoparticles was established, and used to analyze the formation of small ZrO2 pores. The model suggested that 12 ZrO2 nanoparticles formed a unit cell with diamond lattice structure. The obtained small pore size and large pore size were very close to the experimental findings, and the calculated specific surface area and pore volume were also similar to the measured values.