Design of hybrid oxygen carriers with CeO2 particles on MnCo2O4 microspheres for chemical looping combustion

Abstract

Chemical looping combustion (CLC) is a novel technology that offers effective CO2 capture and power generation, which strongly relies on the properties of oxygen carrier. Here, a new type of CeO2/MnCo2O4 oxygen carrier was prepared by dispersing CeO2 nanoparticles on MnCo2O4 microspheres for CLC of methane. The results reveal that the pure MnCo2O4 shows high activity for methane combustion (methane conversion is as high as 94% at 800 °C), but the methane conversion sharply decreases to lower than 40% after 20 redox cycles, indicating poor redox stability. The presence of CeO2 on MnCo2O4 microspheres significantly improves the redox stability, which is benefited from the partial incorporation of high valence Ce4+ cations into the MnCo2O4 lattice that results in the generation of abundant oxygen vacancies due to the charge balance. Among different xCeO2/MnCo2O4 samples, the 10% CeO2/MnCo2O4 shows the highest stability during the successive CLC testing either in the capacity for CH4 combustion or in the aspect of structure, which shows a capacity for CH4 combustion at 2.22 mmol/g and the average CH4 conversion higher than 90% on the stable state. Kinetic analysis indicates that the reduction process of recycled 10%CeO2/MnCo2O4 can be divided into two steps (the main reduction of Co and Mn oxides, respectively) based on apparently different reaction rates, and both the two steps can be mainly described by a 1D growth of nuclei model. The activation energy for step 1 and step 2 are 32.34 kJ/mol and 88.54 kJ/mol, respectively.