Ternary Fe-Zn-Al Spinel Catalyst for CO2 Hydrogenation to Linear α-Olefins: Synergy Effects between Al and Zn

Direct conversion of CO2 into linear alpha-olefins with Fe-based catalysts is promising both technically and economically. Al as a widely employed structural additive to Fe-based CO/CO2 hydrogenation catalysts is known to exhibit a side effect of shifting the selectivity from olefins to undesirable methane. Here, we report that by doping Zn into a binary Fe-Al spinel, a ternary Fe-Zn-Al spinel catalyst could be obtained with a high space-time yield with respect to linear alpha-olefins of 150.8 mmol(C).g(Fe)(-1).h(-1) in CO2 hydrogenation reactions. Multiple in situ/ex situ characterizations combined with DFT calculations illustrate that active Fe5C2 nanoparticles are wrapped with Fe-Al spinel overlayers with the introduction of Al alone, which is responsible for facilitating hydrogenation and inhibiting C-C coupling over the Fe-Al catalysts. Extra doping of Zn allows redistribution of Al to alleviate undesirable strong interactions between Fe5C2 and spinel phases, rendering a high selectivity to higher olefins. The revelation of a subtle synergy effect between Al and Zn underscores the pivotal role of precise tuning of multiple catalyst additives in optimizing the overall catalytic performance.