Thermal desorption of hydrogen

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.

Thermal desorption of hydrogen from platinum and Pt-Au films (146) results in a similar conclusion for these alloys. On average, hydrogen is more loosely bound to the alloys than to pure platinum. About 50% of the adsorbate is desorbed by pumping at 78 K from the alloys, while only a very small percentage is desorbed from platinum at this temperature. 

V. Philipps, E. Vietzke, M. Erdweg, K. Flaskamp, Thermal desorption of hydrogen and various hydrocarbons from graphite bombarded with thermal and energetic hydrogen, J. Nucl. Mater. 145-147 (1987) 292... 

K. Ashida, K. Ichimura, M. Matsuyama, K. Watanabe, Thermal desorption of hydrogen, deuterium and tritium from pyrolytic graphite, J. Nucl. Mater. 128-129 (1984) 792... 

Figure 2.24. Thermal desorption of hydrogen from chemisorbed ethylene on Rh( 111) due to thermal dehydrogenation starting from different coverages, ranging from 0.1 L to 10 L.

Figure 7. Thermal desorption of hydrogen from the flat stepped and kinked platinum single crystal surfaces. (Reproduced with permission from ref. 5. Copyright 1980 Elsevier Science Publishers.)...

The stability as an enthalpy difference between the complex hydride and an intermediate product in the decomposition reaction M[BH4] MH + B. AH tetrahydroborates where the MH exhibits a heat of formation between the complex hydride and its elements go through the above-mentioned intermediate product in the thermal desorption of hydrogen. 

Figure 2.17 Thermal desorption of hydrogen pre-adsorbed in atomic form on a sintered An thin film. Adapted from Lisowski et with permission from Elsevier.

Second, the target is heated so that the positrons trapped in the surface state are thermally activated to form thermal positronium in the ground state[21j. Fig. 6 shows the thermal activation of Ps from a Cu(lll) surface. The process is analogous to thermionic emission of electrons or to thermal desorption of hydrogen, and can be described by the usual statistical mechanics arguments[28]. 

Then the reduction of stored NOx with hydrogen is addressed. The bulk of data points out that the reduction of stored nitrates occurs under near isothermal conditions through a Pt-catalysed surface reaction that does not involve the thermal desorption of the stored nitrates as a preliminary step. A specific role of a Pt—Ba interaction was suggested, which plays a role in the NOx storage phase as well. 

Calculations carried out by Gottesfeld et al. [52], who borrowed from studies of thermal desorption of H2 from Cu [56, 57], indicate that H2 rather than H20 should be a product of formaldehyde oxidation at Cu at potentials up to ca. +0.4 V vs. RHE. This is provided conditions are such that the activation energy for hydrogen recombination and desorption does not exceed 10 kcal/mole. Obviously a relatively high activation energy (which appears never to be observed at Cu) favors eventual oxidation of adsorbed H atoms, before recombinative desorption can occur. Gottesfeld et al. s calculation is interesting, but perhaps not a definitive calculation since it is... 

Fig. 15. Linear ramp thermal desorption of oxidized stainless steel samples implanted with 300 eV hydrogen at room temperature (Clausing, R. E., et. al. in Ref.39), p. 573). The thermal desorption technique shows that (1) a large amount of hydrogen is adsorbed in or near the sample surface, (2) the hydrogen is easily desorbed...

Figure 6.14. (a) Temperature-programmed desorption of hydrogen from the thermal decomposition of chemisorbed ethylene on Pt(l 11) [31]. (b) Proposed surface reaction mechanisms to account for the sequential decomposition [32, 33]. Asterisk denote data taken from reference [331 daggers denote data taken from reference [32]. 

Thermal desorption of purged and trapped garlic breath was studied by GC/MS [53] in which allyl methyl sulfide, diallyl sulfide, diallyl disulfide, -cymene and D-limonene were found consistently in all subjects, however, allyl thiol was detected occasionally. Preliminary evidence suggest that stomach acid caused increased evolution of hydrogen sulfide, a potential breath odor compound, during digestion. 

Figure 16.24 DSC thermal curve of adsorption and desorption of hydrogen from a precious metal catalyst under constant pressure.

---