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

Area of Science:

• Catalysis and Chemical Engineering
• Materials Science

Background:

• Industrial gas streams from biomass/waste gasification and carbon capture contain impurities like ammonia (NH3).
• These impurities can negatively impact catalyst performance in reactions like the reverse water-gas shift (RWGS).

Purpose of the Study:

• To investigate the effect of ammonia (NH3) on the RWGS reaction kinetics and catalyst structure.
• To understand the deactivation mechanism of Cu/ZnO/Al2O3 catalysts in the presence of NH3.
• To propose a strategy for mitigating NH3 inhibition.

Main Methods:

• Studied the RWGS reaction over a commercial Cu/ZnO/Al2O3 catalyst.
• Examined the impact of varying NH3 concentrations and temperatures.
• Analyzed catalyst structure changes after prolonged NH3 exposure.
• Proposed and evaluated an NH3 decomposition method.

Main Results:

• Ammonia (NH3) reversibly suppresses CO2 conversion by inhibiting carbonate hydrogenation and CO desorption.
• Higher NH3 concentrations and lower temperatures exacerbate inhibition.
• Prolonged exposure (100+ h) to 1.4% NH3 caused irreversible catalyst deactivation.
• NH3 exposure led to loss of Cu+ sites and spatial separation of Cu and ZnO components.
• Ammonia decomposition into N2 and H2 was proposed as a mitigation strategy.

Conclusions:

• Ammonia (NH3) poses a significant challenge for RWGS catalysis, causing both reversible activity loss and irreversible deactivation.
• Understanding the structural impact of NH3 is crucial for designing robust catalysts.
• Catalyst deactivation can be mitigated by decomposing NH3 prior to reaction.