Nature of active sites in hybrid metal-zeolite catalysts for the Fischer-Tropsch synthesis

Abstract

The temperature-programmed reduction, powder X-ray diffraction, and oxygen titration were applied to study reducibility, phase composition, and structure of the active surface of the hybrid metal-zeolite catalysts Mβ@Co/Al2O3 (M = Pd, Co, and Fe). The results of physicochemical studies were compared with the data on activity and selectivity of the catalysts in the synthesis of liquid hydrocarbons from the synthesis gas. The nature of transition metal and the method of its introduction into the catalyst influence the composition of synthetic liquid hydrocarbons. A comparison of the Feβ@Co/Al2O3 catalyst prepared by the ion-exchange method that exhibits the highest activity in the synthesis of liquid hydrocarbons with a similar catalyst Fe/(Hβ@Co/Al2O3) prepared by the impregnation method indicated a distinct advantage of the ion exchange procedure. A mechanism of isomerization and cracking of primary linear alkanes on the M n δ+ clusters in the Mβ@Co/Al2O3 systems was proposed. The mechanism explains the main features governing the group and fractional composition of the obtained synthetic hydrocarbons.