NH as simple clathrate-hydrate catalyst: Experiment and theory.

The catalytic action of NH within the all-vapor approach for instant clathrate hydrate (CH) formation is studied using both FTIR spectroscopy and ab initio molecular dynamics simulations. A unique property of NH, namely, the rapid abundant penetration and occupation of the water network, creates defects, particularly Bjerrum D-defects, in the hydrate frame that are generally stabilized by guest NH molecules in the cages. Furthermore, insertion of NH seriously disturbs the hydrate network where the guest NH molecules also make fluxional H-bonds with the host water molecules. These defects strongly facilitate a sub-second formation of the simple NH s-II gas hydrate at 160 K. FTIR spectra of aerosols of the NH s-II CH have been measured, and the displacement of both small and large cage NH guests by CO and tetrahydrofuran is examined.