NH₃-Induced Challenges in CO₂ Hydrogenation over the Cu/ZnO/Al₂O₃ Catalyst

Gas sources rich in CO₂ derived from biomass/waste gasification, anaerobic digestion, or industrial carbon capture often contain impurities such as H₂S, H₂O, and NH₃, which can significantly hinder catalyst performance. Here, we show the role of NH₃ on the reverse water-gas shift (RWGS) reaction over a commercial Cu/ZnO/Al₂O₃ catalyst, examining its effects on both the catalytic activity and the catalyst structure. We found that NH₃ reversibly decreases CO₂ conversion immediately by suppressing carbonate hydrogenation and CO desorption. This effect intensifies with an increase in NH₃ concentration but decreases at higher temperatures. However, prolonged exposure (over 100 h) to RWGS conditions in the presence of 1.4% NH₃ leads to near-total and irreversible deactivation of the Cu/ZnO/Al₂O₃ catalyst. Under NH₃ exposure, the catalyst loses Cu⁺ sites on the surface, causing a spatial separation of Cu and ZnO. Finally, to address this challenge, we propose a novel strategy to mitigate NH₃ inhibition by decomposing NH₃ into N₂ and H₂.