Hollow Submicrospherical Ni/Co-Promoted CaO/Ca₁₂Al₁₄O₃₃ for H₂ Production from Sorption-Enhanced Water–Gas Shift with In Situ CO₂ Conversion via CH₄ Reforming of CaCO₃

CaO sorbent/catalyst bifunctional materials are promising for CO2 capture in sorption-enhanced H2 production such as sorption-enhanced water–gas shift. For simultaneous H2 production with CO2 in situ capture and utilization, the integrated process of sorption-enhanced water–gas shift and in situ CO2 conversion by CH4 reforming of CaCO3 was proposed. This work focused on the tailored design of a CaO sorbent/catalyst bifunctional material for both efficient H2 production and in situ CO2 conversion in this integrated process. The template-assisted strategy of hydrothermal carbonization followed by self-reduction and template removal via steam gasification was first proposed to obtain the hollow submicrospherical Ni/Co-promoted CaO/Ca12Al14O33. The as-synthesized material exhibits high and stable H2 production, CO2 capture, and in situ CO2 conversion performance in the integrated process due to the unique hollow submicrospherical structure and enhanced catalytic activity. Ni–Co interaction boosts oxygen vacancy and Ni–Co alloy, which are the active catalytic sites for the water–gas shift and CH4–CaCO3 reactions. Moreover, the oxygen vacancy-mediated mechanism on CH4 reforming of CaCO3 over the hollow submicrospherical Ni/Co-promoted CaO/Ca12Al14O33 is confirmed. After 20 cycles, CO conversion from sorption-enhanced water–gas shift using the as-synthesized material retains 97.0%, accompanied by high CH4 conversion of 95.1% and the H2/CO molar ratio close to unity from CH4 reforming of CaCO3.