A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic...

Gas-solid interfaces enable a multitude of industrial processes, including heterogeneous catalysis; however, there are few methods available for studying the structure of this interface under operating conditions. Here, we present a new sample environment for interrogating materials under gas-flow conditions using time-of-flight neutron scattering under both constant and pulse probe gas flow. Outlined are descriptions of the gas flow cell and a commissioning example using the adsorption of N₂ by Ca-exchanged zeolite-X (Na_78-2xCa_xAl₇₈Si₁₄₄O₃₈₄,x ≈ 38). We demonstrate sensitivities to lattice contraction and N₂ adsorption sites in the structure, with both static gas loading and gas flow. A steady-state isotope transient kinetic analysis of N₂ adsorption measured simultaneously with mass spectrometry is also demonstrated. In the experiment, the gas flow through a plugged-flow gas-solid contactor is switched between N215 and N214 isotopes at a temperature of 300 K and a constant pressure of 1 atm; the gas flow and mass spectrum are correlated with the structure factor determined from event-based neutron total scattering. Available flow conditions, sample considerations, and future applications are discussed.