Effect of CO2 adsorbents on the Ni-based dual-function materials for CO2 capturing and in situ methanation

The present work studied the effect of different carbon dioxide (CO2) adsorbents on Ni-based dual-function materials (DFMs) for the development of carbon capture and on-site utilization in a reactor at isothermal condition. The DFMs containing Ni functioning as a methanation catalyst with various CO2 adsorbents (i.e., CaO, MgO, K2CO3, or Na2CO3) were prepared on gamma-Al2O3 through sequential impregnation. The result indicated that Ni-Na2CO3/gamma-Al2O3 had the highest methanation capacity (i.e., 0.1783 mmol/g) and efficiency (i.e., 71.09%) in the CO2 adsorption-methanation test. The CO2 uptake and the subsequent methanation capacity of the Ni-Na2CO3/gamma-Al2O3 increased to more than 24 times and more than 17 times, respectively, compared to Ni/gamma-Al2O3. The high methanation capacity was correlated to its highest amount of weak basic sites, substantial CO2 capture capacity and capture/release efficiency, and reactivity to H-2 at a lower temperature, supported by CO2-TPD, TGA analyses for adsorption or adsorption-desorption at the isothermal condition, and H-2-TPRea, respectively. A continuous cyclic CO2 adsorption-methanation was performed by using the Ni-Na2CO3/gamma-Al2O3 and Ni-CaO/gamma-Al2O3, showing that the CO2 adsorption capacity was stabilized from third cycle onward, whereas the methanation capacity was stabilized at all cycles, indicating the high stability of the DFMs for both CO2 adsorption and subsequent methanation. This work demonstrated successful synthesis of the Ni-based, low-cost, and stable DFMs with the ability to produce methane via the direct capture of CO2.