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 α-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 α-olefins of 150.8 mmolC·gFe–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.