Balancing CO ₂ Adsorption and H ₂ Activation on Confined ZnO <i> _x </i> Species for CO ₂ Hydrogenation

Abstract

Abstract Many oxide catalysts exhibit high selectivity but low conversion in CO 2 hydrogenation due to strong CO 2 adsorption, which often impedes H 2 dissociation and subsequent hydrogenation. Herein, we report that a ZnCr 2 O 4 @ZnO x catalyst featuring monodispersed ZnO x overlayer confined on ZnCr 2 O 4 facilitates CO 2 activation without compromising H 2 activation. This catalyst demonstrates a dual‐site mechanism in which ZnCr 2 O 4 surface and/or ZnO x /ZnCr 2 O 4 interface provide sites for CO 2 activation and monodispersed ZnO x promote homolytic H 2 dissociation and formation of stable metal─H species, enabling formate formation through hydrogen spillover to CO 2 adsorption sites for hydrogenation at 303 K. In contrast, H 2 activation on ZnO or ZnCr 2 O 4 suffers from the poisoning effect of strong CO 2 adsorption. Consequently, the ZnCr 2 O 4 @ZnO x catalyst shows 2−8 folds enhancement in CO 2 hydrogenation between 623−773 K than ZnO and maintains 33% conversion and 100% CO selectivity at 723 K over 150 h. The established structure‐performance relationship illustrates the critical role of dual‐site catalysis and hydrogen spillover in hydrogenation reaction.