Adsorption and Hydrogenation of Carbon Monoxide on Carbon-Supported Iron Catalysts

Abstract

Adsorption and hydrogenation of carbon monoxide on iron catalysts were investigated to determine the carrier effect of carbonaceous materials, such as graphite, carbon black and activated charcoal. Activities and product distribution were measured at 623 K and 1.0 MPa by using the synthesis gas whose composition was H₂/CO= 1. Among carbon-supported iron catalysts, a freshly reduced iron catalyst supported on carbon black was most effective in adsorbing an extremely large amount of CO at 298 K. The enhanced CO uptake was most remarkable on a carbon black-supported iron catalyst (1.1%) prepared by impregnation method. The molar ratio of adsorbed CO to Fe exceeded unity, leading to the supposition that “multiple”CO chemisorption occurred on small iron particles at 298 K. Such small iron particles exhibited lower catalytic activity than relatively large iron particles. The activities of carbonsupported iron catalysts were higher than those of alumina and silica supported iron catalysts on a per gram of iron basis, while there was no appreciable difference in the distribution of product hydrocarbons. The activities of some carbon-supported iron catalysts, especially those of activated charcoal-supported one, decayed considerably with time, and the decreased activity was unable to regenerate by H₂ flushing at 623 K and 0.5 MPa. Thus, the deactivation of carbon-supported iron catalysts may not be due to deposition of carbidic carbon on iron active site, which is the case for precipitated iron.