Capturing the Details of N₂ Adsorption in Zeolite X Using Stroboscopic Isotope Contrasted Neutron Total Scattering

Porous materials have widespread industrial applications in adsorption and catalysis, but experimental studies providing atomistic data regarding gas–sorbent interactions under application-relevant conditions are limited. Current analytical methods give information about either the crystal structure or the macroscopic kinetics involved in these processes, but not their interplay. The development of a new combination of stroboscopic, isotope-contrasted neutron total scattering and steady-state isotopic transient kinetic analysis provides insight into both areas. An advanced data reduction procedure was developed to isolate the differential isotope signal from the stroboscopic neutron diffraction. These data, combined with measurement of adsorption isotherms and theoretical considerations from Grand Canonical Monte Carlo simulation, enabled the location of a heterogeneous distribution of nitrogen adsorption sites in calcium exchanged zeolite X under operational conditions (1 atm, 300 K). The nitrogen is found to adsorb primarily at Ca site II, drawing the associated Ca atoms further out into the cage structure. This approach has great potential for the investigation of gas sorption, separation, and catalysis processes in process-relevant conditions.