Unraveling the CO2 methanation and capture ability of NiO@metal oxides†

Abstract

The present study reports the development of different core–shell nanoparticles using Ni/NiO as the core and other active metal oxides such as SiO₂, Co₃O₄, CeO₂ and ZrO₂ as shells for CO₂ methanation. Among all the studied core–shell materials, NiO@SiO₂ and NiO@CeO₂ showed the highest catalytic activity of >62% for CO₂ conversion and >99% selectivity towards CH₄ with a high GHSV of 47 760 h⁻¹ at 325 °C. The catalysts were thoroughly tested under lean and realistic feed conditions. XRD revealed the presence of NiO as the dominant core. All these catalysts were further subjected to characterization techniques such as SEM, TEM, XPS, N₂ adsorption–desorption, H₂-TPR, H₂ pulse, and CO₂-TPD-MS to understand their morphology, ionic nature, physical properties, reduction nature, active site dispersion, adsorption of CO₂ and desorption of surface intermediates. Investigation into the formation and consumption of various intermediates via DFT studies revealed that the CO₂ methanation reaction proceeds via a combination of the CO and formate pathways. These findings correlate with in situ FTIR studies, unveiling structure–property relations and methanation mechanisms. At 25 °C, NiO@SiO₂ exhibited a superior CO₂ capture performance of 301.96 mg of CO₂ per g at 50 bar, while NiO@Co₃O₄ adsorbed 90.40 mg of CO₂ per g at 1 bar. Interestingly, H₂ adsorption was nearly uniform across all these materials even at 50 bar and 25 °C. The core–shell materials show CO₂ capture and hydrogenation abilities towards methane formation.