Ni loading effects on dual function materials for capture and in-situ conversion of CO2 to CH4 using CaO or Na2CO3

Anthropogenic CO2 emissions are one of the main causes of global warming. One alternative is the CO2 capture and valorization through catalytic processes to produce CH4 using dual function materials. In this work, Ni-15CaO/Al2O3 and Ni-10Na2CO3/Al2O3 catalyst have been synthesized varying the Ni loading, i.e. 5, 10 and 15 wt.%, and the impregnation methodology of the adsorbent and the metallic phase. All prepared samples have been physically and chemically characterized by adsorption-desorption of N2, XRD, TEM, H2 chemisorption, XPS, H2-TPR, CO2-TPD and TPSR with H2. The presence of CaO or Na2CO3 provides the catalyst with basic sites with different strength for the adsorption of CO2. Specifically, carbonates with lower stability are formed onto Na2CO3 in comparison to CaO. Besides, increasing Ni loadings slightly promote the decomposition of CO2 adsorbed species. The reducibility of Ni species is enhanced in the presence of the adsorbent and for increasing Ni loadings. CH4 formation during TPSR experiments is observed between 200–600 °C for CaO containing samples, whereas CH4 formation is observed in a narrower temperature range of 200–400 °C for Na2CO3 containing samples. A reaction scheme is proposed which describes the temporal evolution of reactants and products during the CO2 storage and hydrogenation cycles. The formation of CH4 increases with Ni loading. Maximum CH4 formation (142 μmol g−1) is observed for 15Ni15Ca sample at 520 °C. On the other hand, the formation of CH4 is higher (185 μmol g−1) operating at lower temperature, i.e. 400 °C, with 10Ni10Na sample containing a lower amount of nickel.