The most important process to make hydrogen is based on steam reforming of natural gas according to an overall reaction CH 4 + 2H 2 O!4H 2 + CO 2 , where after reformation of the natural gas to a CO/H 2 mixture (syngas) a water-gas shift reaction results in a predominantly CO 2 /H 2 mixture. [1,2] Steam reforming potentially offers one technological path to extend the trend of decarbonization of the primary fossil fuel by taking advantage of the low 1:4 carbon-to-hydrogen ratio of methane compared to coal (~8:4) and oil (~2:4), provided that subsequent separation of the CO 2 /H 2 mixture and sequestration of CO 2 is cost-effective and feasible. We present here a guest-free hydroquinone (HQ) clathrate, prepared by gas-phase synthesis, which reveals unique selectivities towards CO 2 /CH 4 and CO 2 /H 2 mixtures. A dynamical pore-widening process allows CO 2 to be adsorbed with a selectivity of 29:1 from a CO 2 /CH 4 (50:50 v/v) mixture and with a selectivity of 60:1 reversibly stored at 7 MPa and 298 K in the presence of a CO 2 /H 2 (50:50 v/v) mixture. This first example of a flexible hydrogen-bonded organic framework (HOF) that can reversibly and selectively absorb and store CO 2 opens up a host of applications.The

Landfill gas (LFG), which is primarily composed of CH(4), CO(2), and N(2), is produced from the anaerobic digestion of organic materials. To investigate the feasibility of the storage and transportation of LFG via the formation of hydrate, we observed the phase equilibrium behavior of CO(2)-CH(4)-N(2) mixture hydrates. When the specific molar ratio of CO(2)/CH(4) was 40/55, the equilibrium dissociation pressures were gradually shifted to higher pressures and lower temperatures as the mole fraction of N(2) increased. X-ray diffraction revealed that the CO(2)-CH(4)-N(2) mixture hydrate prepared from the CO(2)/CH(4)/N(2) (40/55/5) gas mixture formed a structure I clathrate hydrate. A combination of Raman and solid-state (13)C NMR measurements provided detailed information regarding the cage occupancy of gas molecules trapped in the hydrate frameworks. The gas storage capacity of LFG hydrates was estimated from the experimental results for the hydrate formations under two-phase equilibrium conditions. We also confirmed that trace amounts of nonmethane organic compounds do not affect the cage occupancy of gas molecules or the thermodynamic stability of LFG hydrates.

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The structural transition from hydroquinone clathrates to crystalline α-form hydroquinone was observed up to the range of 3 THz frequency as a function of temperatures. We found that all three hydroquinone clathrates, CO(2)-, CH(4)-, and CO(2)/CH(4)-loaded hydroquinone clathrates, transform into the α-form hydroquinone at around 102 ± 7 °C. The resonance peak of the CO(2)-loaded hydroquinone clathrate at 2.15 THz decreases with increasing temperature, indicating that CO(2) guest molecules are readily released from the host framework prior to the structural transformation. This reveals that the hydroquinone clathrates may transform into the stable α-form hydroquinone via the metastable form of guest-free clathrate, which depends on guest molecules enclathrated in the cages of the host frameworks. A strong resonance of the α-form hydroquinone at 1.18 THz gradually shifts to the low frequency with increasing temperature and shifts back to the high frequency with decreasing temperature.

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