EFFECTS OF ADDITION OF CHROMIUM, MANGANESE, OR MOLYBDENUM TO IRON CATALYSTS FOR CARBON-DIOXIDE HYDROGENATION

The hydrogenation of carbon dioxide was carried out on iron catalysts, either unpromoted or promoted with chromium, manganese, or molybdenum. The bulk phase compositions at several stages were analysed by Mossbauer spectroscopy. The presence of chromium, manganese or molybdenum leads to lower reducibility of iron catalysts. Metallic iron catalysts are carburized as well as oxidized during the course of reaction. Unpromoted and chromium-promoted iron catalysts are more likely to be oxidized, as compared with manganese- and molybdenum-promoted catalysts. In contrast, carburization dominates on the latter two catalysts. Correlation between the phase compositions and catalytic behavior indicates that the formation of Fe3O4 phase is unfavorable for yield of hydrocarbons. However, the yield of carbon monoxide is affected to a lesser extent via the reverse water-gas shift reaction. The enhancement of carbide formation in the presence of manganese or molybdenum is responsible for the higher yield of hydrocarbons.