Probing dynamic oxygen exchange for hydrogen production with operando neutron diffraction.

A chemical looping process exploiting the variable oxygen content of ABO_3-δ perovskite materials can achieve super-equilibrium conversions of societally important reactions such as the water-gas shift reaction (CO + H₂O ⇋ CO₂ + H₂). The approach relies on an evolving oxygen chemical potential gradient within a reactor bed. Here we show that the oxygen-sensitivity of operando neutron powder diffraction experiments can reveal how the reactor functions with high spatial- (≲1 cm) and time- (≲30 s) resolution. We show how this operando method enables rapid testing of new high-capacity bed materials without previous knowledge of their thermodynamic properties, and gives direct information on their long-term stability. We introduce how this memory reactor concept can also be applied to the steam methane reforming reaction (CH₄ + H₂O ⇋ CO + 3H₂), the key preprocess to the water-gas shift reaction in H₂ production.