Enhanced Activity Of Co-Precipitated Nifealox In Co2 Methanation By Segregation And Oxidation Of Fe

Commercial application of the CO2 methanation reaction demands for the development of catalysts that feature an enhanced stability to increase catalyst lifetime. By time-resolved aging studies, we show that the improved deactivation resistance of co-precipitated NiFeAlOx catalysts compared to NiAlOx is obtained by a temporal increase of the intrinsic catalytic activity of NiFeAlOx, provoked by aging at elevated temperature and pressure in thermodynamic equilibrium. Detailed structural characterization of reduced and aged catalysts resolves that aging triggers the partial segregation of (gamma Fe,Ni) nanoparticles initially formed during activation, accompanied by the oxidation of Fe. Thereby, the intrinsic catalytic activity increases, which can be explained by the generation of redox-active Fe2+ sites that offer an additional reaction pathway for CO2 activation. The deactivation behavior of NiFeAlOx can be described by a superimposition of activity increase related to Fe2+ site formation and decrease due to the loss of active sites by sintering processes.