Dynamic AuZn Phase Formation Stabilizes CO₂ Hydrogenation to Syngas

Abstract

Controlling selectivity and activity in CO₂ hydrogenation remains a challenge in the synthesis of sustainable fuels. We investigated a 1 wt.% Au/ZnO catalyst by AUROlite for CO₂ hydrogenation at 20 bar, combining kinetic evaluation with temperature-programmed desorption (TPD), scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) and X-ray diffraction (XRD) characterization to link performance to structural dynamics. Au/ZnO exhibited high activity for reverse water–gas shift (RWGS). This enhanced intrinsic activity correlates well with the small Au particle size of ∼2 nm. During 24-h stability tests, CO₂ conversion and CO and CH₄ yields remained constant, concurrent with the emergence of an AuZn phase in XRD. H₂-TPD revealed pronounced changes in the catalyst surface, with the initial H₂ desorption at 155 °C disappearing after reaction, consistent with significant surface restructuring and possibly alloying. STEM-EDX indicated intimate Au–ZnO contact after reaction, a configuration consistent with the alloyed domains inferred from XRD and with the observed catalytic behavior. The results suggest that the small Au particle size together with dynamic AuZn phase formation and ZnO redeposition stabilizes active sites, reflected in the nearly constant CO₂ conversion and CO and CH₄ yields. Further mechanistic studies into the role of the AuZn phase are proposed to clarify its influence and to guide catalyst design for CO₂ valorization.