(629d) Methane Conversion to Syngas Using Dopant Modified Metal Oxide Composites in Chemical Looping Reforming

Metal oxide composites are used as enabling materials for operation in many energy conversion systems including shale gas and coal gas reforming using chemical looping systems. When metal oxide composites are involved in redox reactions, ionic diffusion takes place which is accompanied by the creation and diffusion of defects that decide such their morphology and chemical properties. Rare earth element dopants can affect the redox reactions by providing alternative reaction sites, thus change the ionic diffusivity and reaction reactivity of metal oxides. In this study, we examine at nanoscale to delineate the characteristics of undoped and doped iron oxide that undergo methane reforming reaction. 0-2% lanthanum doped iron oxides are fabricated by modified wet chemical synthesis. XRD and SEM/EDS characterization implies that the dopant changes lattice parameters of metal oxides whose surface energy is changed. The atomistic thermodynamics methods and ab initio calculations are carried out to investigate the interaction between methane molecules and undoped/doped iron oxide. It is found that dissociation of C-H bond in the CH-La species is the key step for CH₄ partial oxidation reaction, and low-fold O atoms neighboring dopants in metal oxide composites could more readily dissociate from external surface to create oxygen vacancies. Moreover, the presence of rare earth element dopants can significantly decrease the barrier of CH₄ disociation, hence the reaction between CH₄ and oxygen carrier is promoted, which is in good agreement with our experimental results. The fundamental insight into the mechanism of cyclic redox reactions of La dopant modified metal oxide composites at nanoscale revealed in this study can be applied to other rare earth element dopant modified metal oxide systems and to guide future efforts to improve oxygen carriers for methane conversion.