Development of cobalt-based catalyst prepared from natural kaolin for production of green diesel by Fischer-Tropsch...

Fischer-Tropsch (FT) synthesis is a catalytic process that converts syngas into primarily linear hydrocarbons. The roles of active metals and supports are critical in determining catalytic performance. In this study, porous silica supports were synthesized from natural kaolin via a facile acid leaching method using different HCl concentrations (2 M, 5 M, and 8 M), denoted as SiO₂-2 M, SiO₂-5 M, and SiO₂-8 M. Cobalt catalysts supported on the prepared silicas were evaluated for FT synthesis and compared with those on conventional supports (Al₂O₃, ZSM-5, and SiO₂). Among the catalysts, Co/SiO₂-5 M exhibited superior performance, achieving 83.23% CO conversion and 42.40 wt% selectivity toward diesel-range hydrocarbons (C₁₂-C₂₀) at 220 °C and 20 bar. This enhanced performance is attributed to an optimal balance between cobalt particle size and metal-support interaction, where moderate acid treatment (5 M HCl) results in favorable textural properties and improved reducibility of cobalt species without significant structural degradation. The improved catalytic behavior is associated with enhanced cobalt reducibility and moderated metal-support interaction, as confirmed by H₂-TPR analysis. Overall, the results demonstrate a strong correlation between catalyst physicochemical properties, particularly pore structure, cobalt particle size, and reducibility and FT performance. Controlled acid leaching is therefore identified as an effective strategy for optimizing catalyst structure-performance relationships for diesel-range hydrocarbon production.