Synthesis and Characterization of sI Clathrate Hydrates Containing Hydrogen

Abstract

Previously, large cage occupancy of H 2 has only been confirmed in the structure II (sII) hydrate. Utilizing a hydrate synthesis pathway involving pressurizing preformed structure I (sI) hydrates, we now show H 2 occupancy in both the small and the large cages of sI, as evidenced by powder X-ray diffraction and Raman spectroscopic measurements. The new H 2 environments were determined to be singly and doubly occupied 5 12 6 2 cages occurring at 4125−4131 and 4143−4149 cm −1 , respectively. This work serves as proof-of-concept that, by altering the conventional hydrate synthesis procedure to incorporate preformed hydrates, it may be possible to promote the occupancy of H 2 or possibly other guests in a desired structure through a "templating" effect by simply changing the initial hydrate structure.

Theoretical study of hydrogen storage in binary hydrogen-methane clathrate hydrates

“…For the small cavities occupation varied between zero 19,21 to single or even double in a limited number of cavities. 20,22,23 Moreover, the occupation of large cavities by H 2 molecules was also achieved for the H 2 þ CH 4 binary hydrates. 22,23 In principle, the contradictory results may be explained by differences in pressure/temperature conditions, molar compositions of the feed gases, and experimental techniques.…”

“…20,22,23 Moreover, the occupation of large cavities by H 2 molecules was also achieved for the H 2 þ CH 4 binary hydrates. 22,23 In principle, the contradictory results may be explained by differences in pressure/temperature conditions, molar compositions of the feed gases, and experimental techniques. Theoretical study of the phase diagrams of the multi-component clathrate hydrates could be useful for understanding the experimental data, which is still a challenging task due to their complexity.…”

“…The single occupancy of the small cage and multiple occupancy of the large cages (up to 4 H 2 molecules in the CS-II hydrate) were also proposed at a small concentration of methane (5%) using the data obtained from analysis of Raman spectra of the CH 4 þ H 2 hydrate. 22,23 However, there are recent papers 43,44 that proposed double occupancy of small cavities in binary hydrates. The binary N 2 þ H 2 hydrate was studied and small peaks around 4153 cm À1 and 4159 cm À1 were observed and attributed to double occupancy of the S-cage in the CS-II hydrates.…”

“…The calculated results can be compared with experimental data because the binary H 2 þ CH 4 hydrate has already been synthesized. [21][22][23] …”

Influence of cationic and non-ionic surfactants on the kinetics of mixed hydrogen/tetrahydrofuran hydrates

“…However, there is a substantial reduction in the hydrogen storage capacity due to the promoter molecules occupying most of the large cages in hydrate structure limiting the hydrogen stored in hydrates. Mixed hydrogen hydrates with structures like sII, sH, semiclathrates and sI have been reported to form with different promoter molecules or compounds (Du et al, 2012;Duarte et al, 2009;Grim et al, 2012;Trueba et al, 2011). Strobel et al (2007) computed maximum theoretical hydrogen storage capacities possible in different hydrate structures like sI, sII, sH, semi-clathrates and sVI with the assumption of single hydrogen molecule occupancy in 5 12 small cages and multiple hydrogen occupancy in medium and large cages of hydrate structures (only hydrogen was assumed to occupy all hydrate cages).…”