Steady-state and controlled heating rate methanation of CO2 on Ni/MgO in a bench-scale fixed bed tubular reactor

Chemical hydrogen storage via conversion with carbon dioxide into methane is a promising technology in an energy system that relies on renewable energy resources. Robust heterogeneous catalysts are needed for this reaction to proceed at relevant levels. Ni/MgO is a promising catalyst in terms of activity and stability. Although several microscale catalyst studies exist, there is a lack of knowledge on catalyst performance and reactor control at larger scale for carbon dioxide methanation at ambient pressure and a technically relevant stoichiometric H2:CO2 (4:1) feed. Two catalysts with a loading of 11 and 17 wt.% nickel were prepared by wet impregnation, producing a Ni/MgO solid solution with a cubic lattice. Controlled increase (‘scanning experiment’) of the catalyst temperature to 500 °C for the highly exothermic CO2 methanation was compared to steady-state experiments. Scanning and steady-state experiments yield comparable results in terms of carbon dioxide conversion and methane selectivity, whereas scanning experiments lead to considerable time saving. At a moderate temperature of 325 °C and a feed flow consisting of H2:CO2:N2 = 4:1:5 at a flow rate of 250 cm3 STPmin−1, CO2 conversion and CH4 selectivity near thermodynamic equilibrium are achievable. The long-term stability of Ni/MgO (17 wt.% Ni) at 330 °C was proven during reactor operation for several days.