Enhancing the Performance of Cobalt Catalyst in Fischer-Tropsch Synthesis Using Natural Clinoptilolite Zeolite: Experimental Study and Optimization

The Fischer–Tropsch process plays a pivotal role in converting syngas into liquid and gaseous hydrocarbons; however, the performance of cobalt-based catalysts is strongly dependent on support characteristics and operating conditions. In this study, natural Clinoptilolite zeolite was investigated as an accessible and cost-effective support for a cobalt catalyst in Fischer–Tropsch synthesis, and the simultaneous effects of temperature and pressure on catalytic performance and product distribution were evaluated in a fixed-bed reactor. The natural zeolite, obtained from the Semnan mines, was prepared via physical and chemical treatment methods, and the monometallic cobalt catalyst was subsequently synthesized using the dry impregnation technique. The effects of reaction temperature in the range of 200–275 °C and pressure in the range of 2–5 bar on carbon monoxide conversion and selectivity toward hydrocarbon products, including methane, ethylene, propylene, and heavy hydrocarbons (C₅⁺), were investigated. To determine the linear, interaction, and quadratic effects of the operating variables, response surface methodology combined with analysis of variance was employed, and optimal conditions were established through a multi‑objective optimization approach. The findings revealed that increasing temperature significantly enhances carbon monoxide conversion. Moreover, raising the pressure at 275 °C concurrently improved catalyst efficiency while increasing selectivity toward both heavy hydrocarbons (C₅⁺) and methane. Furthermore, both temperature and pressure were found to increase ethylene selectivity. The developed polynomial models successfully predicted the influence of operating conditions on the selectivity of methane, ethylene, propylene, and heavy hydrocarbon production. Multi‑objective optimization, aiming at maximizing CO conversion and ethylene selectivity while minimizing methane selectivity, determined the optimum conditions as 236 °C and 3.85 bar, under which CO conversion and ethylene selectivity were predicted to be 69% and 2.1%, respectively. The results demonstrated that natural Clinoptilolite can serve as an economical and efficient support for cobalt catalysts in the Fischer–Tropsch process. The high accuracy of the statistical models and the significance of the interaction effects between operating variables underscore the importance of simultaneous optimization of temperature and pressure in controlling CO conversion and product distribution. These findings confirm the potential of natural Clinoptilolite for developing low‑cost catalysts and Fischer–Tropsch processes with controllable performance.