Direct capture of low-concentration CO2 and selective hydrogenation to CH4 over Al2O3-supported Ni–La dual functional materials

Abstract

CO₂ capture and reduction with H₂ (CCR) to synthesise CH₄ over dual-functional materials (DFMs) possessing CO₂ capture and hydrogenation abilities has recently attracted attention as a promising methodology for utilising low-concentration CO₂ in air or exhaust gases without pressure and/or temperature swing operations. Much effort has been devoted to the development of Ni-based DFMs for the CCR of CH₄ formation owing to their low cost and high catalytic potential for methanation. However, previous studies have been investigated under relatively high reaction temperatures (400–600 °C) and/or pressurised H₂ conditions. In addition, experiments were conducted in the absence of O₂ in the simulated CO₂ gas. The development of efficient Ni-based DFMs under milder and more realistic reaction conditions is still necessary. In this study, we developed La-modified Al₂O₃-supported Ni nanoparticles (Ni–La(X)/Al₂O₃, X denotes the La loading) for the selective formation of CH₄ from low-concentration CO₂ (1%) in a simulated gas containing O₂ (20%). The optimised Ni–La(15)/Al₂O₃ showed 99% selectivity for CH₄ formation under isothermal (350 °C) and non-pressurised conditions. The effect of the La loading amount on the CCR performance was studied using X-ray diffraction, temperature-programmed surface reactions, and steady-state CO₂ hydrogenation. Furthermore, the developed Ni–La(15)/Al₂O₃ was applied to direct capture of ultralow concentration CO₂ in air (ambient direct air capture (DAC)) and methanation.