Desorption of hydrogen

Fig. 20. Pressure concentration curves of MmNi (—) and LaNi (— ) at 45°C where open circles denote absorption and closed circles desorption of hydrogen. H/M represents the ratio in the hydride of the mole fraction of hydrogen to the mole fraction of the metal.

Indirect methods used can profit by the thermodynamic data of a particular metal-hydrogen system. The determination of the H/Me ratio after complete desorption of hydrogen from a sample, despite an apparent simplicity of the method, gives adequate results only when the bulk metal sample was entirely saturated with hydrogen, and that is a very rare case. The metal catalyst crystallites can be saturated in a nonuniform way, not through their whole thickness. The surface of this polycrystalline sample varies to such extent in its behavior toward interaction with hydrogen that hydride forms only in patches on its surface. A sample surface becomes a mosaique of /3-hydride and a-phase areas (85). 

Taking into account the studies of electric conductivity as a function of Phj as well as the studies of kinetics of electric conductivity accompanying desorption of hydrogen the authors of paper [89] established that apart from processes (2.59) - (2.61) there is a recombination... 

Zhao, X., Bo. Xiao, A.J. Fletcher, K.M. Thomas, D. Bradshaw, M.J. Rosseinsky, Hysteretic adsorption and desorption of hydrogen by nanoporous metal-organic frameworks. Science 306,1012,2004. 

The present results also suggest the following model for the ethylene/Ru(001) interaction. The interaction of ethylene with Ru(001) at 323 K is accompanied by substantial dissociation and subsequent desorption of hydrogen. The resulting adlayer consists... 

The dependence of the PL intensity and peak position on oxidation temperature for three different PS samples is shown in Fig. 7.20. Oxidation at 600°C destroys the PL, while the initial PL intensity is restored or even increased after oxidation at 900°C. This effect can be understood as a quenching of PL because of a high density of defects generated during the desorption of hydrogen from the internal surface of PS. Electron spin resonance (ESR) investigations show a defect with an isotropic resonance (g= 2.0055) in densities close to 101 cm for oxidation at 600°C [Pel, Me9]. This corresponds to one defect per crystallite, if the crystallite diameter is assumed to be about 5 nm in diameter. 

I0 lnterrupted-temperature programmed desorption of hydrogen over silica-supported platinum catalysts, Arai, M., Fukushima, M., Nishiyama, Y., Applied Surf. Sci., vol. 99, no. 2, pp. 145-150, 1996. 

Temperature-Programmed Desorption of Hydrogen from Platinum Particles on Gamma-AI203, Alexeev, O, et. al, J. Catalysis, vol. 185, no. 1, pp. 170-181, 1999. 

Thomas KM. Adsorption and desorption of hydrogen on metal-organic framework materials for storage applications comparison with other nanoporous materials, Dalton Trans 2009, 2009,1487-1505. 

J.F. Ferndndez, C.R. Sanchez, Rate determining step in the absorption and desorption of hydrogen by magnesium, J. Alloys Compd. 340 (2002) 189-198. 

Unfortunately, quite promising hydrogen desorption behavior in DSC as shown in Fig. 3.4 did not translate into desorption in a Sieverts-type apparatus as shown in Fig. 3.5. The powder milled sequentially for 270 h desorbed in a Sieverts-type apparatus at 250 and 290°C (Fig. 3.5) under primary vacuum only about 1.2 wt%Hj which is approximately a half of the hydrogen content obtained during DSC and TGA tests. No desorption of hydrogen was detected in a Sieverts-type apparatus at 250 and 290°C after 128 and 70 min, respectively, from the powder continuously milled for 270 h. The latter easily desorbed 3.13 and 2.83 wt%Hj in DSC and TGA... 

Figure5.47 (a) X-ray diffraction pattern (Cu Ka) of a commercial UBH4 sample (b) X-ray diffraction patter after the thermal desorption of hydrogen from the sample (a) (c) X-ray diffraction pattern of the sample upon reabsorption of the hydrogen.

The thermal desorption of hydrogen from lithium nitride (LiNHa) was investigated by Chen et al. [92,93]. The thermal desorption of pure lithium amide mainly evolves NH3 at elevated temperatures following the reaction (Figure 5.54)... 

Figure 5.61 Thermal desorption of hydrogen from borazane.

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