Probing dynamic oxygen exchange for hydrogen production with operando neutron diffraction

Abstract

A chemical looping process exploiting the variable oxygen content of ABO3−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. Efficient hydrogen production is a major societal challenge. Here the authors use operando neutron diffraction to quantitatively support the operating principle of a memory reactor that allows super-equilibrium operation of the water–gas shift reaction, which can also be used for steam methane reforming.