Exsolved Perovskite Systems Applied for the Production of Syngas via Chemical Looping Methane Reforming

Abstract

The development of materials with tailorable properties that will lead to tuneable performance has always been key for the advancement of catalytic and energy technologies. Challenging transformations like that of methane to syngas at low temperatures introduce multiple challenges for both material and process. Due to methane’s slow activation kinetics traditional processes and materials lack efficiency. To address this, attractive alternative technologies like Chemical Looping have been designed. In this, mixing of fuel and oxidant is eliminated and oxygen exchange between the reactant streams is facilitated via an oxygen carrier material (OCM) which is cycled between them. This allows for side reaction elimination, leading to a safer process in which potentially increased conversions and higher selectivity can be achieved. However, material design for such a process remains a challenge since an OCM should tackle all problems associated with a catalytic process that also involves methane activation such as: particle agglomeration and carbon deposition, while exhibiting excellent oxygen storage and exchange ability that will allow the material to perform reliably under repeated redox cycling. An emerging concept for material design promising to address these limitations is redox exsolution. According to this, nanoparticles with tuneable characteristics can be grown on the surface of oxide supports, exhibiting high resistance to agglomeration and carbon deposition owning to their socketed and strained nature. In this study the exsolution concept is employed and evolved for the design of perovskite systems with active particles present not only on their surface but for the first time, also in their bulk. The produced materials are decorated throughout with self-strained highly active nanoparticles and exhibit enhanced oxygen transport and storage capabilities. The systems are employed for the activation of methane while their structural and compositional changes are investigated in situ and operando via synchrotron X-ray. They manage to activate methane at lower temperatures than state of the art systems, exhibiting high selectivity to syngas while minimizing agglomeration and carbon deposition. It is demonstrated that submerged, redox active nanoparticles work synergistically with their surface exsolved counterparts and can be actively involved in driving redox transformations. The system’s micro-structural and nano structural characteristics are tuned and their pivotal role on the system’s performance is investigated. The insight gained on exo- endo- systems is used to produce an even more reactive against methane system that successfully activates methane while maintaining high selectivity at even lower temperatures, proving that the techniques developed can be applied for the application-driven design of tailored materials. The produced systems are employed for long term cycling for Chemical Looping methane partial oxidation, exhibiting steady and selective performance showcasing their robustness. The insights gained in this study demonstrate the capabilities and provide insight on this new class of composite material which will enable the rational design of such systems for a plethora of catalytic and energy applications.