Hydrogen adsorption activation energy

In the laminated membranes, thin palladium (or palladium alloys) layer avoids the formation of oxides on the metallic surfaces resulting in a reduction of the hydrogen adsorption activation energy and, as a consequence, in an increase of the hydrogen permeation flux [55]. 

Butanethiol addition decreases catalytic activity but not selectivity in 1,3-butadiene hydrogenation. Both activation energy and pre-exponential factor decrease with increasing S/Pd ratio. Sulfur adsorption not only reduces the number of active sites but also weakened the adsorption strength of the remaining sites. It has been demonstrated that physico-chemical information from AFM XPS combined with kinetic data enables prediction of conversion at other conditions based on the S/Pd ratio. 

Reactions (5.3) and (5.4) describe the overall dissociative adsorption of hydrogen. The activation energy for desorption of atomic hydrogen (E 5 4) is 109 kJ moP (32) having zero activation energy to dissociative adsorption (E5 3F5 4). 

On K modified Ni(100) and Ni(lll)62,63 and Pt(lll)64 the dissociative adsorption of hydrogen is almost completely inhibited for potassium coverages above 0.1. This would imply that H behaves as an electron donor. On the other hand the peaks of the hydrogen TPD spectra shift to higher temperatures with increasing alkali coverage, as shown in Fig. 2.22a for K/Ni(lll), which would imply an electron acceptor behaviour for the chemisorbed H. Furthermore, as deduced from analysis of the TPD spectra, both the pre-exponential factor and the activation energy for desorption... 

In Eq. (1.11b) the constant A depends on the equilibrium constant fC . This will vary also with the adsorption energy of C or O, but will be much less sensitive to these variations than the activation energies of CO dissociation and hydrogenation [5]. 

The comparison of experimental data on adsorption of various particles on different adsorbents indicate that absorbate reaction capacity plays a substantial role in effects of influence of adsorption on electric conductivity of oxide semiconductors. For instance, the activation energy of adsorption of molecular oxygen on ZnO is about 8 kcal/mole [83] and molecular hydrogen - 30 kcal/mole [185]. Due to such high activation energy of adsorption of molecular hydrogen at temperatures of adsorbent lower than 100 C (in contrast to O2) practically does not influence the electric conductivity of oxides. The molecular nitrogen and... 

In addition to the desirable thermodynamics (enthalpy of adsorption), a fast adsorption/ desorption kinetics is required for a fast recharging and discharging of hydrogen. Hence, the activation energies of the adsorption and desorption steps play an important role... 

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