Effect of potassium promoter on phase transformation during H2 pretreatment of a Fe2O3 Fischer Tropsch synthesis catalyst precursor

Abstract

• H 2 reduction behaviors of Fe 2 O 3 based catalysts are investigated by in situ XRD. • Potassium promoter notably inhibits the reduction from α-Fe 2 O 3 to Fe 3 O 4 . • The formation of α-Fe crystallite is accelerated or unchanged during reduction. • Potassium effect on FTS performance of the Fe 2 O 3 based catalysts is studied. Effect of potassium promoter on phase transformation during the isothermal and temperature programmed reduction of the α-Fe 2 O 3 catalyst were systematically investigated by in situ XRD. The reduction pathway of Fe 2 O 3 based catalysts follows the same sequence of α-Fe 2 O 3 → Fe 3 O 4 → α-Fe during the isothermal reduction, in contrast to that of α-Fe 2 O 3 → Fe 3 O 4 → FeO/ α-Fe→ α-Fe during the temperature programmed reduction. The potassium promoter notably inhibits the reduction from α-Fe 2 O 3 to Fe 3 O 4 due to the enhanced strength of Fe-O bonds, whereas it either accelerates or has no effect on the formation rate of α-Fe crystallites during reduction. The potassium promoter increases the CO conversion during FTS, while enhances C 5 +, olefins, CO 2 selectivity, and decreases CH 4 selectivity.