Carbon dioxide capture and reduction (CCR) to CH4 using dual-functional materials (DFMs) have recently attracted significant attention as a promising strategy for carbon capture and utilization. In this study, we investigate the mechanism of CCR to CH4 over Al2 O3 -supported Ni-Ca DFMs (Ni-Ca/Al2 O3 ) under cyclic feeds of model combustion exhaust (2.5 % CO2 +0 or 10 % O2 /N2 ) and H2 at 500 °C. Various spectroscopic analyses, including time-resolved in situ X-ray diffraction and X-ray absorption spectroscopy, were conducted during CO2 capture and the subsequent H2 -reduction steps. Based on these analyses, we propose a mechanism of CCR to CH4 over Ni-Ca based DFMs. During the CO2 capture step, the Ni0 species underwent complete oxidation in the presence of O2 to yield NiO. Subsequently, CO2 was captured through the interaction between the CaO surface and CO2 , resulting in the formation of CaCO3 layers on the CaO particles. When the gas flow was switched to H2 , NiO was partially to provide Ni0 sites, which acted as active sites for H2 -reduction of the adjacent CaCO3 layers to yield CaO and gas-phase products, CH4 and H2 O.
Keywords: CO2 capture and reduction (CCR); CO2 methanation; Ni−Ca/Al2O3; dual functional materials.
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