Experimental and theoretical studies on the reactivity and reaction mechanism of LaMnO3 with CO in chemical looping combustion

Abstract

LaMnO3 perovskite was developed as a promising oxygen carrier in chemical looping combustion due to its abundant oxygen amounts and excellent thermal stability. The reactivity and reaction mechanism of LaMnO3 with CO were systemically studied based on thermogravimetric experiments and density functional theory calculations. The results indicate that LaMnO3 is reduced to Mn3O4 and La2O3 at 707 °C, and finally to MnO. The weight loss of LaMnO3 is 8.67% during the whole reduction process. The reaction rate of LaMnO3 at low temperature can be improved with the increase of CO concentration. The maximal reaction rate of LaMnO3 with CO increases as the heating rate rises. The higher reaction temperature leads to the complete reduction of LaMnO3. Besides, SEM analysis reveals that LaMnO3 has no sintering-agglomeration phenomenon and exhibits good sintering resistance. Density functional theory calculations indicate that the Mn–O bridge sites are the most favorable for CO adsorption on the LaMnO3 surface. The adsorbed CO reacts with a bridging surface lattice O to generate CO2 precursor, revealing the key intermediate for CO oxidation. CO2 precursor will break through the energy barrier of 56.03 kJ/mol to generate free CO2 molecule.