Hydroxyl Regulation Enables Metal Promoter-Free Iron Catalysts for Highly Efficient CO2 Hydrogenation to Light Olefins.

The efficient hydrogenation of CO2 to light olefins over Fe-based catalysts typically relies on the metal promoters, such as alkali or transition metals. In this study, we find that the intrinsic hydroxyl environments may be the crucial but long-overlooked factor governing the activity of Fe species. With the assistance of low-concentration guar gum, hydrogen-bond networks formed by dense hydroxyls are disrupted to generate isolated or terminal hydroxyl groups, which increase the active sites and significantly facilitate the product desorption. The resulting metal promoter-free Fe achieves a CO2 conversion of 30.1% and a light olefin selectivity of 38.1% at an ultra-high gas hourly space velocity of 300 000 mL gcat -1 h-1. Meanwhile, the space-time yield of light olefins reaches 3.3 kg kgcat -1 h-1, which outperforms all of the reported Fe-based catalysts modified by various promoters. These findings redefine hydroxyls as intrinsic promoters in Fe catalysts for CO2 hydrogenation and can potentially be extended to other heterogeneous catalytic systems and reactions.