Harnessing Ammonia as a Hydrogen Carrier for Integrated CO₂ Capture and Reverse Water-Gas Shift.

Area of Science:

• Chemical Engineering
• Catalysis
• Materials Science

Background:

• The reverse water-gas shift (rWGS) reaction is crucial for CO2 utilization.
• Conventional rWGS processes often require separate steps for CO2 capture and reaction.
• Developing integrated processes can improve efficiency and reduce energy consumption.

Purpose of the Study:

• To propose and investigate an integrated CO2 capture and reverse water-gas shift (ICCrWGS) process.
• To evaluate the use of ammonia (NH3) as a hydrogen carrier in the ICCrWGS process.
• To explore the performance of Ni/CaZr dual-function materials (DFMs) in this integrated system.

Main Methods:

• Calculation of CO2 efficiency and thermal energy consumption for conventional and integrated processes.
• Experimental investigation of ICCrWGS using H2 and NH3 over Ni/CaZr DFMs.
• Analysis of NH3 decomposition, CO2 capture, CO2 conversion, and CO selectivity at various temperatures.
• In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) to elucidate reaction mechanisms.

Main Results:

• The optimal temperature for the NH3-ICCrWGS process was determined to be 650 °C.
• Ni/CaZr DFMs demonstrated stable CO2 capture capacity and CO productivity using NH3 as a carrier.
• The process achieved efficient CO2 conversion and high CO selectivity.
• A carbonate spillover mechanism involving a bridged bidentate carbonate route at the Ni-CaO interface was proposed.

Conclusions:

• The proposed NH3-ICCrWGS process is a viable and efficient method for CO2 utilization.
• Ni/CaZr DFMs are effective catalysts for the integrated process, showing stability and high performance.
• Understanding the reaction mechanism provides insights for further catalyst design and process optimization.