CO2 capture from H2O and O2 containing flue gas integrating with dry reforming methane using Ni-doping CaO dual functional materials

Abstract

Reducing carbon emissions remains a formidable challenge under present energy demands and structures. Integrated CO2 capture and utilisation (ICCU) provides a promising pathway for directly capturing and simultaneously utilising CO2 from the diluted exhaust gas. Dry reforming of methane (DRM) can be integrated into the step of catalytic conversion of the captured CO2 with the advantages of utilising two greenhouse gases to yield valuable syngas (CO + H2). The process has great challenges of materials development for efficient performance, in particular under realistic conditions such as the presence of O2 and H2O in the flue gas. This work investigated the ICCU-DRM using simulated flue gases (10 % CO2 + 6.7 % O2 + 6.0 % H2O) in the presence of Ni-CaO dual functional materials, aiming to optimise Ni loading and metal support interaction. It is found that Ni would significantly sinter and further affect the morphologies of CaO adsorbents, resulting in poorer CO2 capture performances. More notably, the Ni was firstly oxidised during CO2 capture and subsequently went through a pre-reduction period in the DRM step. Increased Ni loading decreased the difficulty of activation; however, it derived in more severe carbon deposition. To avert the direct contact of carbon deposition and flue gas, extra carbon steam gasification was introduced, and higher Ni loading contributed to selectively yielding syngas as a by-product. The Ni10-CaO DFM optimally performed <150 s pre-reduction delay, ∼85 % CO2 conversion and ∼2 H2:CO ratio in the DRM step and ∼75 % CO selectivity in the CSG step at 650 °C. The interaction between Ni and CaO poorly contributes to the performance due to the poor reducibility and accessibility, and the Ni particle size effects only play as spectators in this integrated process.