Hydrogenation of CO2 to synthetic natural gas (SNG) with 100% selectivity over a Ni–ZnO–MgO catalyst†

Abstract

The CO₂ hydrogenation activity of a Ni–ZnO–MgO catalyst prepared by the co-precipitation technique is evaluated in a down-flow tubular reactor. The physicochemical properties of the catalyst were characterized by various techniques, including N₂-physisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), hydrogen chemisorption, FE-SEM, TGA, TEM, XPS, etc. Hydrogenation experiments were performed at different temperatures (200–400 °C) and mild pressure (1–15 bar) at a constant feed gas (H₂/CO₂/N₂) molar ratio of 3 : 1 : 3. The total feed flow rate was maintained at 3 × 10⁻³ mol min⁻¹. Results demonstrated that the Ni–ZnO–MgO catalyst was ∼100% selective to CH₄. ZnO helped to improve not only the catalyst stability via hydrogen spillover effect but also the nickel metal dispersion, and MgO enhanced the CO₂ adsorption. Overall, the reaction mechanism followed the formate species pathway to obtain almost 100% methane selectivity. Time-on-stream study suggested that the catalyst was stable with negligible carbon formation. The used catalyst characterization results showed that the catalyst morphology remained unchanged before and after the reaction. Therefore, the developed Ni–ZnO–MgO catalyst is very promising for the selective hydrogenation of CO₂ to synthetic natural gas (SNG).