Preparation of cerium-cobalt composite oxygen carrier and its performance in methane chemical looping combustion

A series of CeO₂/Co₃O₄ composite oxygen carriers with different CeO₂ loadings were prepared and characterized by XRD and H₂-TPR. The performance of CeO₂/Co₃O₄ as an oxygen carrier in methane chemical looping combustion was investigated in a fixed-bed reactor by temperature-programmed and isothermal reactions; the effect of CeO₂ loading on the structure, activity and selectivity of the oxygen carrier was considered in detail. The results show that the addition of CeO₂ can reduce the reaction temperature and increase the effective reaction time of the CeO₂/Co₃O₄ oxygen carriers for methane oxidation. However, loading of excessive CeO₂ may promote the partial oxidation of methane forming CO and H₂ and leads to a decrease in the selectivity to CO₂. The CeO₂/Co₃O₄ composite oxygen carrier with a CeO₂ loading of 30% (mol ratio) exhibits the highest activity and redox stability in the chemical looping combustion of methane; over it, methane can be quickly converted to CO₂ and H₂O with high selectivity (over 90%) at 650 ℃ and the reduced oxygen carrier can be fully recovered in O₂ atmosphere. Moreover, no obvious decline in the conversion of methane and selectivity to CO₂ is observed in the successive CH₄-reduction and O₂-oxidation redox process for over 20 cycles.