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

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Review of Scientific Instruments
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Gas-solid interfaces enable myriad 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 ${N}_2$ by Ca-exchanged Zeolite-X (Na$_{78-2x}$Ca$_x$Al$_{78}$Si$_{144}$O$_{384}, x\approx 38$). We demonstrate sensitivities to lattice contraction and ${N}_2$ adsorption sites in the structure, with both static gas loading and gas flow. A steady-state isotope transient kinetic analysis (SSITKA) of ${N}_2$ 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 $^{15}\mbox{N}_2$ and $^{14}\mbox{N}_2$ 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.