Hydrogenation of carbon dioxide to light olefins over non-supported iron catalyst

Abstract

The hydrogenation of CO 2 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 CO 2 conversion and the selectivity for olefins. Over K- or Rb-modified catalysts, about 40% CO 2 conversion and more than 50% olefin selectivity were obtained. The yield of C 2 –;C 4 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 CO 2 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 CO 2 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 CO 2 . 研究了非负载型铁催化剂上CO 2 加氢制低碳烯烃反应. 结果显示, 添加碱金属可显著提高铁催化剂上的CO 2 转化率和烯烃选择性. 在经K和Rb修饰的Fe催化剂上, CO 2 转化率可达约40%, 烯烃选择性达到50%以上, 其中C 2 ∼C 4 烯烃收率超过10%. 催化剂表征结果表明, 碱金属促进了催化剂中碳化铁的生成, 这可能是催化剂性能提高的一个关键原因. 随着K含量由1 wt%增加至5 wt%, CO 2 转化率及烯烃选择性均升高. 但K含量过高时, 催化剂活性降低. 这可能是由于催化剂比表面积和CO 2 化学吸附量降低所致. 当K含量为5%∼10%时, K-Fe催化剂上烯烃收率较高; 进一步添加适量的硼可进一步提高烯烃选择性, 且CO 2 转化率下降不大. The modification of a non-supported Fe catalyst by alkali metal ions, particularly K + , in combination with a small amount of B, significantly enhanced the hydrogenation of CO 2 to light olefins.