Insertion of Oxygen and Nitrogen in the Siliceous Zeolite TON at High Pressure

The
insertion of oxygen and nitrogen molecules in the one-dimensional
(1D) pore system of the zeolite TON was studied at high pressure by
vibrational spectroscopy, X-ray diffraction, and Monte Carlo (MC)
molecular modeling. Rietveld refinements and MC modeling indicate
that, on average, six diatomic molecules per unit cell enter the pores
of the zeolite. This induces changes in compressibility and distortion
related to the Cmc21-to-Pbn21 phase transition compared to the empty-pore material.
The filling behavior with N2 and O2 under pressure
is similar to that of argon, suggesting that the kinetic diameter,
which is very close in these three systems, plays a major role. The
orientation of the diatomic molecules appears to have a rather minor
effect on filling occurring at a slightly higher pressure for N2, which has a larger kinetic diameter. Both inserted molecules,
initially not showing any marked orientation, begin to exhibit a degree
of orientational order above 2 GPa.