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

In this paper, a concept of integrated CO₂ capture and reverse water-gas shift (ICCrWGS) process was proposed using NH₃ as the H₂ carrier. The CO₂ efficiency and total thermal energy consumption for the conventional rWGS, ICCrWGS using H₂ (H₂-ICCrWGS) and NH₃ (NH₃-ICCrWGS), were calculated. ICCrWGS using H₂ and NH₃ was conducted over the thermally stable Ni/CaZr dual-function materials (DFMs). NH₃ decomposition, CO₂ capture capacity, CO₂ conversion, and CO selectivity were addressed at different reaction temperatures, and the optimal temperature was determined to be 650 °C. The Ni/CaZr DFMs exhibited stable CO₂ capture capacity and CO productivity during ICCrWGS using the NH₃ carrier. A carbonate spillover mechanism for CO production over the Ni/CaZr DFMs in NH₃-ICCrWGS was proposed using in situ diffuse reflectance infrared Fourier transform spectroscopy. It was found that CO is produced from the bridged bidentate carbonate route in the Ni-CaO interface.