Exploiting the ‘chemical memory’ of non-stoichiometric materials to create new processes
Prof Ian Metcalfe (Newcastle)
Chemical looping involves a sequence of cyclic reactions and e.g. a solid carrier material to store and release a reaction intermediate. Theoretically, the carrier at the end of the cycle will remain unchanged whilst the products from the reduction and the oxidation step are separated. For example, iron oxide can be used as an oxygen carrier material (OCM) for hydrogen production from the water-gas shift reaction. However, although iron oxide shows significant usable oxygen capacity for this reaction, it loses its activity rapidly due to sintering and agglomeration. Perovskites, such as La0.7Sr0.3FeO3-δ, have been proposed as alternative oxygen carrier materials due to their high stability and stable productivity under long term redox cycles. They are also oxygen-permeating mixed ionic and electronic conductors (MIECs) allowing rapid oxygen transport throughout their structure. Being non-stoichiometric they can exhibit a ‘chemical memory’ of the conditions to which they have been exposed. We investigate this memory and its thermodynamic advantages through the in-situ operation of a chemical looping reactor with spatially and temporally resolved XRD data from ID22 of the European Synchrotron Radiation Facility.