In Situ Spectroscopic Study of CO 2 Capture and Methanation over Ni-Ca Based Dual Functional Materials.

Carbon dioxide capture and reduction (CCR) to CH 4 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 CH 4 over Al 2 O 3 -supported Ni-Ca DFMs (Ni-Ca/Al 2 O 3 ) under cyclic feeds of model combustion exhaust (2.5 % CO 2 +0 or 10 % O 2 /N 2 ) and H 2 at 500 °C. Various spectroscopic analyses, including time-resolved in situ X-ray diffraction and X-ray absorption spectroscopy, were conducted during CO 2 capture and the subsequent H 2 -reduction steps. Based on these analyses, we propose a mechanism of CCR to CH 4 over Ni-Ca based DFMs. During the CO 2 capture step, the Ni 0 species underwent complete oxidation in the presence of O 2 to yield NiO. Subsequently, CO 2 was captured through the interaction between the CaO surface and CO 2 , resulting in the formation of CaCO 3 layers on the CaO particles. When the gas flow was switched to H 2 , NiO was partially to provide Ni 0 sites, which acted as active sites for H 2 -reduction of the adjacent CaCO 3 layers to yield CaO and gas-phase products, CH 4 and H 2 O.