Development of a bespoke sample environment for operando neutron diffraction studies of chemical looping materials and processes.

The MatCoRE group at Newcastle University has significant expertise in the advancement of chemical looping (CL) processes for a number of applications, including hydrogen production from the water-gas-shift (WGS) reaction. The central concept of CL is to split a target reaction into two or more separate reactions which are facilitated by an intermediate material. This ensures that reactants are never directly mixed and so products do not require separation, therefore improving the efficiency of the overall process.
The success of any CL process is highly dependent on the nature of the intermediate material used. For the WGS reaction, and other oxidation processes such as chemical looping combustion (CLC), the material used is termed an oxygen carrier material (OCM) and it allows oxygen to be indirectly transferred between the reactants leading to formation of the products. Non-stoichiometric oxides with the perovskite (ABO3-o) structure are the current focus of most development work due to their ability to undergo successive redox cycles while maintaining structural integrity.
In order to evaluate these materials for CL processes it is paramount to understand how the crystal structure changes during reduction and oxidation of the material and relate these changes to oxygen content and degree of non-stoichiometry (0). The Metcalfe group have recently achieved this using operando synchrotron X-ray diffraction (XRD).
However, neutron diffraction can offer significant advantages versus XRD for the elucidation of these structures, primarily due to a higher sensitivity to oxygen atoms. This project aims to design, construct and commission a sample environment that will allow a working CL reactor to be monitored operando by neutron diffraction. At present, there is experimental capability at ISIS and elsewhere to perform in situ neutron diffraction at high temperatures and under reducing and oxidising gas environments, therefore allowing CL conditions to be mimicked. However, there is currently no existing sample environment that would allow a working CL reactor to be probed in real-time by neutron diffraction. In particular, the ability to position discrete sections of the reactor bed into the neutron beam and obtain a structural profile during operation is not currently possible. This project aims to bridge this gap in methodology and advance our understanding of OCMs using neutron diffraction, enabling the development of superior materials for CL. It is envisaged that the sample environment will be beneficial to future groups studying flow systems and catalysis at ISIS and will therefore be designed with operational flexibility in mind.