Synthesis and Characterization of sI Clathrate Hydrates Containing Hydrogen

Previously, large cage occupancy of H₂ 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 H₂ occupancy in both the small and the large cages of sI, as evidenced by powder X-ray diffraction and Raman spectroscopic measurements. The new H₂ environments were determined to be singly and doubly occupied 5¹²6² 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 H₂ or possibly other guests in a desired structure through a “templating” effect by simply changing the initial hydrate structure

Investigating the Thermodynamic Stabilities of Hydrogen and Methane Binary Gas Hydrates

When hydrogen (H₂) is mixed with small amounts of methane (CH₄), the conditions required for clathrate hydrate formation can be significantly reduced when compared to that of simple H₂ hydrate. With growing demand for CH₄ as a commercially viable source of energy, H₂+ CH₄ binary hydrates may be more appealing than extensively studied H₂ + tetrahydrofuran (THF) hydrates from an energy density standpoint. Using Raman spectroscopic and powder X-ray diffraction measurements, we show that hydrate structure and storage capacities of H₂ + CH₄ mixed hydrates are largely dependent on the composition of the initial gas mixture, total system pressure, and formation period. In some cases, H₂ + CH₄ hydrate kinetically forms structure I first, even though the thermodynamically stable phase is structure II