PREPARATION AND FISCHER-TROPSCH REACTION OF HIGHLY-REDUCED COBALT CLUSTERS IN COBALT-EXCHANGED ZEOLITE

Abstract

Impregnation of 3-5 M NaOH solution into cobalt ion-exchanged Y zeolite using the incipient wetness method enables the preparation of highly reduced cobalt clusters entrapped inside zeolite pores after the catalyst is reduced with hydrogen gas. TEM and ferromagnetic resonance experiments reveal that the cobalt clusters are extremely small and uniform in size. Reaction measurements on these catalysts show an enhanced production of linear forms of hydrocarbons such as 1-olefins and n-paraffins. The catalysts also exhibit a bimodal distribution in the selectivity pattern in which one maximum is observed at C6 with another at C-16. The formation of high-order linear hydrocarbons above C-10 is attributed to an increased chance for the chain growth owing to a hold-up effect of reaction intermediates, especially 1-olefins, which are accumulated deep inside zeolite pores during the reaction. The accumulated amount of hydrocarbon products, ranging from C1-C18, was found to be 2.3 X 10(-3) mol/g cat (about 10 vol.% of total pore volume in zeolite crystallite when the average density is assumed to be that of C-12) after reaction for 10 h. The formation of hydrocarbon isomers is related with acidic sites on the exterior surface of the zeolite particle.