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 H-2: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 degrees 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 degrees C and a feed flow consisting of H-2: CO2: N-2 = 4: 1: 5 at a flow rate of 250 cm(STP)(3)min(-1), CO2 conversion and CH4 selectivity near thermodynamic equilibrium are achievable. The long-term stability of Ni/MgO (17 wt.% Ni) at 330 degrees C was proven during reactor operation for several days.