(A) study on CO hydrogenation over supported cobalt, nickel and iron catalysts

Abstract

CO hydrogenation reaction was performed on partially reduced Co/$\gamma$-$Al_2O_3$ catalysts prepared by incipient-wetness method having different cobalt loadings, and the effects of the size of cobalt particles and the extent of reduction on CO hydrogenation were investigated independently. The activity increased with increasing size of cobalt particles under constant extent of reduction, while the maxima in activity were observed with extent of reduction under constant size of cobalt particles. The increasing adsorption strength of carbon containing reaction intermediates results in the increase in the production of higher hydrocarbon and decrease in he olefin fraction with the size of cobalt particles, but the extent of reduction hardly affected the product distribution and olefin fraction. Titania- and Y zeolite-supported cobalt catalysts were also employed for the comparison of the effect of cobalt loading on CO hydrogenation activity and selectivity with alumina-supported cobalt catalyst. Co/$TiO_2$ catalysts were prepared by excess-water technique, and zeolite-supported catalysts by carboxyl-complex impregnation method. The activity of alumina-supported catalysts increased with increasing cobalt loading, while in titania and zeolite-supported catalysts the activity varied only slightly. In alumina-supported catalysts more higher hydrocarbons were produced on the catalysts having higher cobalt loading, but the catalysts with the lowest cobalt loading in titania-supported catalysts was the most favorable for the production of higher hydrocarbons. On the zeolite-supported catalysts relatively large amounts of $C_3$ and $C_4$ hydrocarbons were produced irrespective of cobalt loading. The higher reduction temperature resulted in the migration of decarbonyled cobalt cluster to have a bidispersion of metal particles in Y-zeolite. The temperature of the two main maximum TPSR (Temperature Programmed Surface Reaction) peaks (one is at around 570$^\circ$C and the o...