Balancing CO2 Adsorption and H2 Activation on Confined ZnOx Species for CO2 Hydrogenation

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