Investigation of DFMs for CO2 Capture and Methanation by Coupled Microreactor Experiments and FT-IR Spectroscopy

In this work, we discuss the role of different atmospheres and process conditions on the catalytic performances of Ru- and K/Ba-based dual-function materials (DFMs) for CO2 capture and methanation. By a combination of microreactor experiments and Fourier transform infrared (FT-IR) spectroscopy, we clarify the effect of temperature and H2 partial pressure during the hydrogenation step and the effect of water and oxygen during the CO2 adsorption step. In particular, we show that between 250 and 400 °C CO2 is rapidly adsorbed as bidentate carbonates on the basic sites (K or Ba) and as CO on Ru metal surfaces with decreasing storage capacity with increasing temperature. Increasing the operating temperature and the H2 partial pressure, the methanation rate of the bidentate carbonates increases. We also show that during the CO2 capture step, water not only reduces the amount of CO2 adsorbed by competitively adsorbing on basic sites but also changes the nature of the adsorbed carbonates, increasing their ionic character and hence their stability. This is observed in the case of both a K-based DFM and a Ba-based DFM, though in the case of the alkaline earth, the phenomenon is more evident. Finally, we point out that the presence of O2 during the CO2 capture step removes metallic Ru as CO adsorption site and reduces the amount of bidentate carbonates, possibly due to the additional presence of water formed upon Ru reduction in the methanation step. The information presented in this work is of interest to improve the design of DFMs to be used for flue gas, where the partial pressure of water and oxygen is relevant.