Lanthana-doped ceria as active support for oxygen carriers in chemical looping combustion

Abstract

The redox properties and oxygen buffering capacity of reducible oxides, such as ceria, make them interesting support materials for oxygen carriers in Chemical Looping Combustion (CLC), an emerging clean combustion technology. However, the effectiveness of reducible oxides for redox applications depends crucially on oxygen mobility in the oxide lattice. In the present work, we demonstrate that addition of an aliovalent dopant (La) strongly enhances oxygen mobility in ceria, resulting in multiple performance benefits. A series of La-doped ceria (LaxCe1−xO2−x/2, 0<x<0.3) were investigated as supports for low-cost Fe-based oxygen carrier materials. Combining carrier synthesis and characterization with reactive tests, we demonstrate that La doping of ceria not only results in a drastic improvements in carrier reactivity and oxygen carrying capacity, but also strongly improved carrier stability during redox cycling. This is consistent with the creation of oxygen defects, which stabilize the supported Fe particles and facilitate oxygen transport in the ceria lattice. A balance between enhancement of oxygen mobility and lowered reducibility upon formation of a lanthana phase results in a strongly nonlinear dependence of carrier reactivity on the dopant concentration and gives rise to an optimum at low dopant concentrations. Overall, the results suggest that doping of reducible supports constitutes a highly attractive, effective, and low-cost way to strongly enhance the performance of oxygen carriers in chemical looping applications.