Synthesis, characterization and activity of CeO2-doped coprecipitated NiAlOx catalysts for CO2 methanation

CeO 2 -doped NiAlO x mixed oxide catalysts with molar Ce/Ni ratios of 0.05, 0.1 and 0.3 were prepared via coprecipitation and analyzed in detail regarding structure and activity in CO 2 methanation. A cerium-free NiAlO x , a CeO 2 and a NiCe-based sample served as references. Characterization revealed a two-phase composition of the doped materials consisting of a NiAlO x mixed oxide and a CeO 2 phase. The latter features highly reactive oxygen vacancies upon reduction with hydrogen, which provide additional binding sites for CO 2 . Reduction of the CeO 2 phase (and with that the formation of oxygen vacancies in the doped catalysts) was demonstrated to be only feasible in the presence of Ni which, in this context, acts as a hydrogenation catalyst providing dissociated hydrogen. The detection of completely reversible reduction-oxidation-reduction cycles of CeO 2 -doped NiAlO x by quasi in-situ XPS suggested diminutively-sized Ni particles provided by synthesis via coprecipitation. Catalytic testing of the CeO 2 -doped samples in CO 2 methanation revealed up to three times higher turnover frequencies and CH 4 weight-time yields compared to undoped NiAlO x . An optimum in catalytic activity at Ce/Ni = 0.1 indicated the prerequisite of a balance between Ni and Ce amounts in the catalyst to avoid undesired byproduct formation. • Successful CeO2 doping of NiAlOx catalysts over a broad molar Ce/Ni range of 0.05 to 0.3 by means of coprecipitation method • Improved catalytic performance in CO2 methanation reaction associated with CeO2 doping • Improved CO2 sorption associated with CeO2 doping • CeO2 oxygen vacancies as additional active sites in CeO2-doped NiAlOx catalysts • Fully reversible oxidation/reduction cycle of CeO2-doped NiAlOx