Exploring Synthesis Approaches of Co-based Catalysts for the Efficient Oxidation of CH4 and CO

Co-based catalysts were synthesized and studied as novel oxidation catalysts, exploring and optimizing the effect of synthesis method on the redox behavior, the oxygen storage ability and thus the catalytic performance of the derived Co3O4 materials in the complete CH4 and/or CO oxidation reactions. Thus, a series of Co-based catalysts were synthesized applying either the precipitation and/or the hydrothermal method, using different precipitating agents (Na2CO3, NH3, urea or NaOH), Co precursor salt (nitrate or acetate) and finally varying the Co/Na ratio. In addition, the reaction time (6 or 24 h aging) was also investigated for the hydrothermally prepared Co3O4. The best catalysts for the CH4 oxidation are the precipitated Co3O4, using cobalt acetate as precursor salt and NaOH as precipitating agent, presenting the highest surface areas and the lowest Co3O4 particle sizes. On the other side, hydrothermally prepared cobalt oxides reveal higher performance for CO oxidation, with Co3O4 prepared with cobalt acetate, NaOH and low aging time shown as the optimum materials. The best catalysts were further promoted with incorporation of Pd (0.5wt.%) and explored for both reactions. The addition of Pd enhanced the activity of Co3O4 for CH4 oxidation, while Pd did not improve any further the catalyst performance for CO oxidation, presenting thus the same activity with pure cobalt oxides.