These results indicated that the addition of Mn could slightly inhibit the chain-growth reactions and enhanced the light olefins selectivity . Hence the effect of addition amount of Mn promoters on CO2 hydrogenation reaction was also specifically studied (Fig. ). With the increase of Mn addition, the changes in CO2 conversion and CO selectivity were relatively small, while the selectivity and O/P of C2-C4 hydrocarbons first increased and then decreased, and the C5 + selectivity showed the exact opposite trend. The highest selectivity for C2-C4 olefins (52.2%) was achieved over the Fe100Mn20K10 catalyst. Considering that the alkali metal K was reported to modulate the alkalinity and electronic property of iron based catalysts, thus improving the CO2 hydrogenation reaction activity and modulate the products distribution , its addition amount was also optimally investigated (Fig. ). It can be found that the selectivity and O/P of C2-C4 hydrocarbons slightly increase and then decrease with the K content, with the optimum value of 53.2% and 7.6 obtained over the Fe100Mn20K5 catalyst, respectively. Hence Fe100Mn20K5 was chosen as the target catalyst for CO2 hydrogenation to light olefins in the subsequent work.