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As a potential candidate for hydrogen storage, Li3N can absorb more than 9 wt % hydrogen. However, because of its incomplete dehydrogenation at a temperature of 280 °C, only about 5.5 wt % reversible hydrogen capacity could be reached. Although by increasing the temperature one can enhance dehydrogenation, this paper demonstrates that dehydrogenation of hydrogenated Li3N at the high temperature of 400 °C is followed by a very low (0.4 wt %) rehydrogenation capacity. Furthermore, scanning electron microscopy, Brunauer−Emmett−Teller surface area, and X-ray powder diffraction measurements have shown that both the sintering and the lattice structure change of Li2NH, which is a product of hydrogenation, might be responsible for such a major deactivation.

Although Li3N can theoretically absorb as much as about 10 wt % hydrogen, its reversible hydrogen capacity is only about 5.5 wt % because only a fraction of the hydrogen absorbed can be desorbed at relatively low temperatures. In the present paper, it is shown that the addition of LiNH2 to Li3N constitutes an effective method to increase the reversible hydrogen capacity. It was found that the reversible hydrogen capacity of the LiNH2/Li3N mixture depends on its composition. A maximum reversible hydrogen capacity of 6.8 wt % could be achieved when the pre-added LiNH2 content in the LiNH2/Li3N mixture was between 28 and 50 mol %. Furthermore, the LiNH2/Li3N mixtures have fast hydrogenation kinetics and excellent cyclibility.

A comparison between the hydrogen storage performances of untreated and heat-treated Li3N was carried out using a volumetric method, temperature-programmed hydrogenation (TPH), and scanning electron microscopy (SEM). It was found that, during the first hydrogenation, the untreated Li3N could absorb fast (3 min), 5.5 wt % of hydrogen at 230 °C, and that 3200 min was needed to absorb an additional 2.5 wt % of H2. In contrast, the Li3N preheated at 400 °C in a vacuum for 4.5 h absorbed only 3 wt % in 3 min at 230 °C but required only 300 min to absorb an additional 6.5 wt % of H2. Furthermore, during rehydrogenation after desorption, the pretreated Li3N could quickly absorb (3 min) 5.2 wt % of hydrogen, and this performance did not change with increasing hydrogenation−dehydrogenation cycle number. TPH and SEM investigations indicated that the higher performance of the preheated Li3N was due to its relatively large particle sizes.

The refueling time and safe hydrogen storage are critical factors in the development of a hydrogen economy for transportation. The finding of a fast and high-capacity H2 storage material represents a worldwide challenge. The short-term target of the U.S. Department of Energy for a hydrogen storage material is a 4.5 wt % reversible hydrogen capacity. In this paper, we report that reversible 5 wt % H2 can be reached in only 3 min even at the relatively low temperature of 180 °C by a Li2O/Li3N solid material. Furthermore, this material has excellent stability because successive cycles of absorption−desorption did not decrease the reversible hydrogen capacity and absorption rate.

The pore size distributions of bundled single-walled carbon nanotubes were investigated by N2 adsorption and desorption. It was found that the pore sizes are in two main ranges:  <5 nm and 10−100 nm. Furthermore, their heating in an inert gas, CO2, or H2 at 800 °C did not change the pore size distribution, even though significant amounts of nanotubes were consumed during the latter two treatments. In contrast, the nitric acid treatment at 70 °C completely changed the pore size distribution, generating an active-carbon-like pore size distribution and a large increase of the total surface area.

Hydrogen storage in Li3N was investigated via temperature-programmed hydrogenation (TPH) and temperature-programmed dehydrogenation (TPD). TPH spectra indicated an initial hydrogenation temperature of Li3N of ~150 °C, independent of the H2 partial pressure even below 0.5 atm. However, the increase in H2 partial pressure accelerated the hydrogenation rate. The TPD curves exhibited three H2 peaks located at 240, 270, and above 380 °C. The maximum amount of low-temperature released H2 corresponding to the two peaks at 240 and 270 °C was 6.0 wt %. XRD indicated that most of the low-temperature released hydrogen can be attributed to the transformation of LiNH2 to Li2NH. The amount and properties of the releasable hydrogen are also dependent on the duration and temperature of the Li3N hydrogenation.

To overcome the explosions that can occur during the partial oxidation of methane, the latter exothermic reaction is coupled with an endothermic one, namely, the CO2 reforming of CH4. These combined reactions have been carried out over NiO/MgO solid solution, NiO/Al2O3, and NiO/SiO2 catalysts. About 90% conversion of CH4 and about 98% selectivities to CO and H2 were obtained at 790 °C and a GHSV(gas hourly space velocity) of 90 000 cm³ g^-1 h^-1 (O2/CO2/CH4 = 14.5/26.9/58.6), over a reduced NiO/MgO solid solution catalyst. Almost no change in activity and selectivity occurred during 50 h of reaction. Compared to the reduced NiO/MgO, the reduced NiO/SiO2 and NiO/Al2O3 catalysts provided lower activities and stabilities. The effects of the reaction temperature, space velocity, and feed gas composition for a ratio CH4/(CO2 + 2O2) = 1 were investigated. The increase in O2 in the feed gas resulted in a higher conversion of CH4, but the apparent conversion of CO2 passed through a maximum. The CH4 conversion decreased with increasing space velocity, while during the partial oxidation, because of the hot spots, it would have increased. This means that the coupling can, indeed, control the thermal behavior of the reactor.

The catalytic reduction of NO to N2 and CO2 by C over Cu/C was investigated and a relationship between the conversion of NO and Cu loading obtained. An optimum conversion of 100% was obtained at 410 °C over a Cu/C sample that contained 20 wt % Cu. For higher Cu contents the conversion decreased. The selectivities to N2 and CO2 at 360 and 410 °C were 100% over the samples that contained 5−30 wt % Cu. As the reaction time increased, the conversion of NO first decreased and later increased. An explanation is provided for this behavior. H2 titration was employed to determine the change of the exposed surface area of Cu during reaction. The change of the surface area and of the pore size distribution of Cu/C during the reaction was also investigated.

During the partial oxidation of methane over Ni-supported catalysts, oscillations of the catalyst temperature were detected over NiO/SiO2, but not over NiO/Al2O3 and NiO/MgO. Hot spots were observed for all the three Ni-based catalysts, but only for the NiO/SiO2 catalyst were they moving down and up. This movement causes the oscillation of the catalyst temperature and is probably due to the reduction and oxidation of the catalyst by the reactants.