Characterization of Zr‐Doped Ceria and Sr‐Doped La−Mn Perovskites as Redox Intermediates for Solar Chemical‐Looping Reforming of Methane

Abstract

Zr‐doped ceria and Sr‐doped lanthanum manganese perovskites are investigated as candidate redox materials for the chemical‐looping reforming of methane to produce syngas. Herein, the effect that these compositions have on syngas selectivity, partial oxidation of methane (POM) rate, and yield in the temperature range of 800−1000 °C is probed. POM reaction rates increase when using 10% Zr‐doped ceria (CZO10) compared with pure ceria at all conditions, but the yields are generally less except at 800 °C. In the case of (La0.65Sr0.35)0.95MnO3 (LSM35), POM yields are equal to or greater than ceria under all conditions investigated. For all materials, selectivity to syngas during POM is relatively high and typically above 85%. However, selectivity of CZO10 and LSM35 is lower than ceria, likely because of their lower reduction enthalpies and more accessible surface oxygen. This is validated by demonstrating improvements in POM selectivity by suppressing the oxidation extent; in this case, there is no observable H2O or CO2 formation. POM rates increase and activation energy (Ea) decreases for all materials following oxidation with O2 versus CO2. Ceria and CZO10 Ea decrease from about 225 to <50 kJ mol−1 and LSM35 from 150 to 100 kJ mol−1.