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

Many oxide catalysts exhibit high selectivity but low conversion in CO₂ hydrogenation due to strong CO₂ adsorption, which often impedes H₂ dissociation and subsequent hydrogenation. Herein, we report that a ZnCr₂O₄@ZnO_x catalyst featuring monodispersed ZnO_x overlayer confined on ZnCr₂O₄ facilitates CO₂ activation without compromising H₂ activation. This catalyst demonstrates a dual-site mechanism in which ZnCr₂O₄ surface and/or ZnO_x/ZnCr₂O₄ interface provide sites for CO₂ activation and monodispersed ZnO_x promote homolytic H₂ dissociation and formation of stable metal─H species, enabling formate formation through hydrogen spillover to CO₂ adsorption sites for hydrogenation at 303 K. In contrast, H₂ activation on ZnO or ZnCr₂O₄ suffers from the poisoning effect of strong CO₂ adsorption. Consequently, the ZnCr₂O₄@ZnO_x catalyst shows 2-8 folds enhancement in CO₂ 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.