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

Abstract

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 g_cat ^-1 h^-1. Meanwhile, the space-time yield of light olefins reaches 3.3 kg kg_cat ^-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.