Promotion effect of Fe–Cu catalyst for the hydrogenation of CO 2 and application to slurry reactor

Abstract

The hydrogenation of CO 2 to hydrocarbons over precipitated iron catalysts was carried out in a stirred tank slurry reactor. Effects of potassium promotion and structural promotion using Al 2O 3 or SiO 2 on the activity and selectivity were investigated with the co-precipitated Fe–Cu–Al (or Si)–K catalytic system. Also, the reaction performance in the slurry reactor was compared with that in a fixed-bed reactor. The addition of either Al 2O 3or SiO 2 by the mixing method gave hardly any improvement in the catalytic activity or selectivity in CO 2 hydrogenation. Instead, the addition of SiO 2 by the mixing method lowered the selectivities to long-chain hydrocarbons and olefins. However, the addition of Al 2O 3 by co-precipitation increased CO 2 conversion as well as the selectivity to C 2+ hydrocarbons, but decreased the selectivity to CO. The addition of potassium promoted the CO 2 hydrogenation activity and the selectivity to hydrocarbons, shifted the product distribution to the direction of olefins and long-chain hydrocarbons. In terms of CO 2 conversion and hydrocarbon selectivity, K/Fe = 6/100 is the optimum K level at the conditions employed in the present study. The comparison of slurry and fixed-bed reactors showed that the slurry reactor was not as favorable as the fixed-bed reactor for CO 2 hydrogenation.