(760b) Core-Shell Redox Catalysts for Chemical Looping Reforming of Methane

The chemical looping reforming (CLR) process represents an alternative, potentially efficient approach for methane valorization. Unlike conventional partial oxidation schemes which require cryogenic air separation, the CLR process inherently avoids air separation by replacing gaseous oxygen with regeneratable ionic oxygen (O^2-) from a redox catalyst lattice. As such, the performance of CLR is largely dependent upon the activity and selectivity of the redox catalyst.  Many perovskite-structured mixed metal oxides are known to be active for methane oxidation.  Their oxygen storage capacities; however, tend to be low.  In contrast, iron oxides can store up to 30 w.t.% of lattice oxygen but are less selective for syngas generation.  We report redox catalysts that utilize the advantages of both perovskites and iron oxide, by incorporating a mixed ionic-electronic conductive (MIEC) perovskite shell to an iron oxide based nanoparticle core.  It is proposed that the MIEC perovskite facilitates countercurrent conduction of O^2- and electrons, allowing facile O^2- transport to and from the iron oxide irrespective to the porosity of the redox catalyst particle.  In this work, reduction scheme of a Fe₂O₃@La_.8Sr_.2FeO₃ redox catalyst is investigated. Using transient pulse injection and isotope exchange approaches, a complex series of reaction regions is revealed, giving insight into a dynamic reaction mechanism that relies upon lattice oxygen transport, active surface species, and bulk oxygen availability.  Effects of core and shell compositions on redox catalyst performance are also investigated. It is shown that Fe₂O₃@La_.8Sr_.2FeO₃ and Co₃O₄@La_.8Sr_.2FeO₃ core-shell redox catalysts are highly effective for CLR.