Ni/support-CaO bifunctional combined materials for integrated CO2 capture and reverse water-gas shift reaction: Influence of different supports

Integrated CO2 capture and utilisation (ICCU) is a promising strategy for restricting carbon emissions and achieving carbon neutrality. Bifunctional combined materials (BCMs), containing adsorbents and active catalysts, are widely applied in this process. Producing syngas via reverse water–gas shift reaction (RWGS) and integrating with Fischer-Tropsch (F-T) synthesis is an attractive and valuable CO2 utilisation route. This work investigated a series of Ni/support-CaO BCMs (supports = ZrO2, TiO2, CeO2 and Al2O3) for the integrated CO2 capture and RWGS (ICCU-RWGS) process. The Ni/support-CaO BCMs were prepared by physically mixing various metal oxide supports loaded Ni with sol–gel derived CaO. The ICCU-RWGS performance (CO2 conversion, CO yield and CO generation rate) of these BCMs followed the order during tested conditions (550–750 °C): Ni/CeO2-CaO > Ni/TiO2-CaO > Ni/ZrO2-CaO > Ni/Al2O3-CaO. A comprehensive characterisation of Ni/support materials showed that Ni/CeO2 had the characteristics of stronger basicity, optimal Ni dispersion and improved NiO reducibility, which led to the outperforming ICCU-RWGS activity over Ni/CeO2-CaO (e.g. 56.1% CO2 conversion, 2.68 mmol g−1 CO yield and ∼100% CO selectivity at 650 °C). Furthermore, the Ni/CeO2-CaO BCM showed a stable, yet, self-optimising catalytic performance during the cyclic ICCU-RWGS reaction over 20 cycles. The TEM characterisation suggested that was ascribed to the volume expansion and shrinkage of CaO in the cyclic adsorption–desorption altering the distance between the adsorbent and Ni/CeO2, resulting in an enhanced CO2 conversion during the cycle.