Abstract:

The hydrogenation of CO₂ to light olefins was investigated over non-supported Fe catalysts. It was found that the addition of alkali metal ions to the Fe catalyst led to significant increases in both the CO₂ conversion and the selectivity for olefins. Over K- or Rb-modified catalysts, about 40% CO₂ conversion and more than 50% olefin selectivity were obtained. The yield of C₂-C₄ olefins exceeded 10% over these modified catalysts. Catalyst characterization suggested that the formation of iron carbide species was accelerated by the modification of the Fe catalyst with alkali metal ions, and this enhancement may be one of the key reasons for the enhanced catalytic performance. For the K-modified Fe catalysts, K content has a major influence on the catalyst behavior. An increase in the K content from 1 to 5 wt% increased both CO₂ conversion and olefin selectivity. However, too high a K content led to a decrease in the activity, probably because of decreases in the surface area and CO₂ chemisorption capacity of the catalyst. The presence of an appropriate amount of B in the K-modified Fe catalyst was found to be beneficial to the olefin selectivity, without significantly decreasing the conversion of CO₂.

Key words: Carbon dioxide, Hydrogenation, Light olefin, Iron catalyst