Thermally stabilized cobalt-based Fischer-Tropsch catalysts by phosphorous modification of Al₂O₃: Effect of calcination temperatures on catalyst stability

A phosphorous-modified Al₂O₃ support was prepared by the impregnation method and applied for the preparation of cobalt-based Fischer-Tropsch synthesis (FTS) catalysts (Co/P-Al₂O₃), which were calcined at different temperatures. The Co/P-Al₂O₃ showed a significant increase of thermal stability with a higher catalytic performance without severe deactivation even above a calcination temperature of 600 C compared with the unmodified Co/Al₂O₃. These findings are explained by the suppressed cobalt aluminate formation and less pronounced aggregation of cobalt particles. The suppressed aggregation of cobalt particles is attributed to the localized presence of aluminum phosphate by forming a thermally stable metal-phosphorous oxo-species on Al₂O₃ surfaces thus suppressing the migration of cobalt particles to the outer pore mouths of the support. These effects significantly enhance the catalytic activity with a higher thermal stability of the catalysts.