Desorption peak temperature

The results of a similar experiment with adsorbed hydrogen is shown in Fig. 2.3b. Only one desorption peak was observed in the temperature range studied [50], The desorption peak temperature lies at 420 K for the experiment with 0.8 L and is shifted to lower temperatures as the H2 concentration increases indicating second order desorption kinetics. Surface states with desorption temperatures at 165 K, 220 K, 280 K and 350 K were reported for the adsorption of H2 and D2 at 120 K [51]. Thermal desorption experiments after H2 adsorption at 350 K show only one desorption state at ca. 450 K [52],... 

An important question now arises what microstructural factor(s) is (are) responsible for the observed decrease of the DSC desorption peak temperature with increasing... 

The corresponding DSC curves of Mg powders milled in hydrogen atmosphere after various milling times under the HES mode are shown in Fig. 2.40. The 5 h milled sample has only one small peak at 410.5°C, but the others show double peaks (peak doublets). Desorption peak temperatures of the doublet peak first decrease as... 

The desorption peak temperature maxima for the MgH constituent in a composite are plotted in Fig. 3.31 as a function of the content of LiAlH. It is seen that the ROM for the MgH desorption temperature in the (MgH -i- LiAlH ) nanocomposite... 

As mentioned before in order to determine whether or not the free A1 formed upon decomposition of LiAlH /LijAlH in the composite could act as a catalyst, we also prepared composites with the content of A1 equivalent to the content of A1 in the Awt%LiAlH. Their DSC desorption peak temperature maxima are also plotted in Fig. 3.31. The composites with the equivalent content of A1 do not seem to follow the ROM behavior. Therefore, one can tentatively conclude that the underlying physical mechanism for the ROM behavior is not related to the catalytic effect of free Al. However, this possibility, however remote, cannot be completely ruled out of hand because the particle size of free Al formed upon decomposition might be much smaller than that obtained by ball milling of Al metal powder added to MgH powder. Nanosized free Al could aquire catalytic behavior. However, at the moment we do not have any evidence for that. 

Wt%MgH, in composite Wt%NaBH in composite Processing DSC desorption peak temperature of MgH (°C) (heating rate 10°C/min)... 

Fig. 19. The Linear relationship between desorption peak temperature and desorption energy assuming a pre-exponential factor of 1013 s 1 and a heating rate of I K s 1.

From the TPR experiments, it was concluded that the temperature for maximum rate in the H2S fonnation increase with increasing age of the catalyst. The SO2 (I) desorption peak temperature (with sulfate origin) decreased with increasing field ageing. 

The decrease in the SO2 (I) desorption peak temperature is more difficult to explain with this model. 

Table 1. Summary of experimental results for halogen adsorption on (100) surfaces of fee transition metals. The "coverage" refers to the maximum coverage obtained for the corresponding adsorbate stmcture. The initial sticking coefficient is denoted by So, the temperature programmed desorption (TPD) peak temperature Tp, and the maximum work function change by A( ). For surfaces where more than one adsorbate structure is observed, the desorption peak temperature refers to new desorption features observed when the stmcture changes. ...

Fig. 15. Thermal desorption spectra of carbon monoxide on Rh(lll) measured as a function of coverage following adsorption near 300 K. The crystal heating rate was linear at 15 K/sec. Note the desorption peak temperature shift as a function of coverage...

The idea that the promoting effect of K is due to a stabilization of N2 has been examined within the model of NH3 synthesis by Stoltze and Norskov. The stabilization of N2 in the presence of K is 12 kJ/mole for Fe(l 11) [396,625] as deduced from the changes in the temperature programmed desorption peak temperatures [231, 466]. Although it is a complication that the different basal planes exposed in the catalyst have very different catalytic activity in the absence of K, the results of the calculations strongly support the electrostatic picture of the promoting effect of K [396, 625]. 

FIGURE 14 (a) Binding energy shift in Pd 3d5/2 level for 1.0 ML Pd on several single crystal substrates relative to the surface atoms of Pd(100). (b) The TPD desorption peak temperature maxima of 1.0 ML Pd deposited on several substrates. [Reprinted with permission from Physical Review B, Vol. 46, No. 1, p. 7082, 1992 Copyright 1992, American Physical Society.]... 

---