HYDROGENATION OF CARBON-DIOXIDE ON IRON CATALYSTS DOUBLY PROMOTED WITH MANGANESE AND POTASSIUM

The effect of addition of manganese and potassium promoters onto iron catalysts for hydrogenation of carbon dioxide was investigated. Catalyst characterizations were performed using BET surface area measurement, carbon monoxide chemisorption, temperature-programmed reduction and Mossbauer spectroscopy. It was noted that metallic iron catalysts were carburized to theta-Fe3C and chi-Fe5C2 as well as oxidized to Fe3O4 during the course of reaction. The promotional effect of manganese was reflected in stabilization of catalytic behavior owing to a higher resistance to bulk oxidation. However, the distribution of hydrocarbon products did not change significantly in the presence of manganese promoter. With further addition of potassium promoter, the bulk phase was more likely to transform to carbides, and the selectivity toward olefins and long-chain hydrocarbons was remarkably enhanced.