EFFECT OF TRANSITION-METALS ON OXYGENATES FORMATION FROM SYNGAS OVER CO/SIO2

Effects of precursors and modification on Co/SiO2 catalyst for carbon monoxide hydrogenation were studied at elevated pressures. Although Co/SiO2 derived from cobalt (II) acetate (Co(A)/SiO2) was quite inactive, it exhibited dramatically high activity especially for the formation of ethanol by modification with some transition metals such as iridium, ruthenium, rhodium, rhenium, osmium and platinum. At the same time, ethanol productivities of other Co/SiO2 catalysts derived from cobalt(II) nitrate (Co(N)/SiO2) or chloride (Co(Cl)/SiO2) were not so much improved by modification with rhenium as to Co(A)/SiO2. Chloride compounds were especially unfavorable as precursors of the component elements for the formation of oxygenated compounds. The catalytic activities and product distributions of Co(A)-Sr/SiO2 catalysts modified with these noble metals were very similar to each other. An ethanol selectivity of more than 20% was obtained using these catalysts. On the other hand, iridium and ruthenium did not have any important effect as modifiers of Co/SiO2 catalyst derived from Co-2(CO)(8) (Co(CO)/SiO2) which itself had an activity similar to that of modified Co(A)/SiO2 catalysts. Using X-ray diffraction, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure to characterize the catalyst, it is concluded that highly dispersed cobalt metal is the main active site on the Co(A)/SiO2 catalyst and that transition metals promote the reduction of Co2+ cation to a metallic state by a hydrogen spill-over mechanism.