The proposed CaL methane reforming process was tested using the prepared CaO-Ni bifunctional sorbent-catalysts in a ChemBET PULSAR TPR/TPD chemisorption analyzer. Approximately 0.1 g of the sorbent-catalyst was placed in a quartz U-tube and heated to 1073 K at a rate of 25 K min−1 under a N2 flow of 8 ml min−1. Then, the temperature was held for 60 min with the introduction of H2 (2 ml min−1) to reduce the sample. After that, the temperature was decreased to 873 K, followed by the introduction of a CO2 flow of 2 ml min−1 instead of the H2 flow to carbonate the sample for 6 min (the CO2 capture step). Then, the temperature was increased to 1073 K at a rate of 40 K min−1, followed by the introduction of a CH4 flow of 2 ml min−1 instead of the CO2 flow to calcine the sample for 6 min (the CO2 conversion and CH4 reforming step). Subsequently, the temperature was decreased to 873 K, and then a new CaL CH4 reforming cycle was started by the introduction of a CO2 flow. Ten CaL CH4 reforming cycles were investigated in this study, and a blank run was performed to correct for the effects of temperature and gas flow switches. During the whole experiment, concentrations of CO2, CH4, and H2 in the outlet gas from the reaction tube were monitored every 1.2 min using a micro-gas chromatograph (GC; 490-GC, Varian), while the concentration of CO in the outlet gas was monitored every 1.2 min using another GC (7890B, Agilent). Both the Varian micro-GC and the Agilent GC were equipped with a molecular sieve 5A column and a thermal conductivity detector (TCD).

In situ XRD experiments were performed in a Bruker D8 Advance x-ray diffractometer to compare the process decarbonation kinetics of CaL reforming of methane and separate CaL. The diffractometer was equipped with an Anton Paar XRK 900 reactor chamber, which enables the XRD investigation of solid-state or solid-gas reactions under controlled temperatures and atmospheres. During the experiment, an appropriate amount of the powder sample, resting on a ceramic-sieve holder, was placed in the reactor chamber and heated to 873 K at a rate of 10 K min−1 in a N2 atmosphere. Once the reaction temperature was reached, a gas flow containing 20 volume % CO2 (balance in N2) was introduced into the reactor chamber to carbonate the sample for 30 min. After that, the temperature was increased to 1073 K, and then the atmosphere was switched to a N2 flow or a gas flow containing 20 volume % CH4 (balance in N2), with the sample held at this temperature for another 30 min, during which the time-resolved XRD data of the sample were acquired in the 2θ range of 27° to 47° at a scanning rate of 10° min−1. In addition, the decarbonation rate of the materials during both processes was determined by carrying out the in situ XRD experimental procedures mentioned above in the chemisorption analyzer, and concentrations of CO2 and CO in the outlet gas during isothermal decarbonation were monitored using the Varian 490 micro-GC and the Agilent 7890B GC, respectively.

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