Decoupling competitive adsorption for syngas conversion and CO2 hydrogenation over ZnCr2O4@ZnOx catalysts

Competitive adsorption between H 2 and CO x ( x = 1, 2) on oxide catalysts represents a primary limitation in hydrogenation reactions, where mutual site blocking suppresses activity and selectivity. This constraint hampers syngas conversion and CO 2 hydrogenation, yet strategies to decouple adsorbates remain elusive. Here, we show that competitive adsorption can be overcome through a partial-site-occupation mechanism that prevents surface saturation and enables independent activation. For a model ZnCr 2 O 4 @ZnO x system, in situ infrared spectroscopy directly reveals the simultaneous adsorption of H 2 with CO or CO 2 , in contrast to the mutually exclusive adsorption observed on pristine ZnO. Kinetic measurements link this decoupling to suppressed inhibition effects and altered reaction orders, driving improved catalytic performance. Density functional theory combined with temperature-programmed analyses further demonstrates that homolytic H 2 dissociation becomes thermodynamically self-limiting, resulting in intrinsically unsaturated surface coverages. These findings indicate competitive adsorption from an inherent constraint to a tunable surface property and establish practical design strategies for cooperative activation in ZnO-based oxide-catalyzed hydrogenation reactions.