Mn decorated Na/Fe catalysts for CO2 hydrogenation to light olefins†
A series of Mn decorated Na/Fe catalysts is synthesized and investigated to understand their promotional effect on CO2 hydrogenation to light olefins. The addition of Mn to the Na/Fe catalysts significantly improves the selectivity of light olefins and reduces the C5+ selectivity. The catalyst exhibiting optimal catalytic performance, 5Mn–Na/Fe, shows a CO2 conversion of 38.6% with high selectivity of light olefins (30.2%), high O/P ratio (7.5), and low selectivity of methane (11.8%) and CO (11.7%). XRD and Mössbauer spectra indicate that the addition of Mn to Na/Fe catalysts facilitates the formation of active Fe5C2 species. Besides, the strong interaction between the Mn promoter and Fe species is revealed by the Mössbauer spectra, XRD and XPS, which lowers the amount and strength of CO adsorption, and consequently contributes to the weakening of the chain-growth reaction leading to the high selectivity of light olefins. This work can provide guidance for catalyst design through the modulation of the ability of the chain-growth reaction to improve the catalytic performance in CO2 hydrogenation.