Dissociative adsorption of hydrogen

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... 

Mills G, Jonsson H, Schenter GK. 1995. Reversible work transition state theory application to dissociative adsorption of hydrogen. Surf Sci 324 305-337. 

Thiophene is the typical model compound, which has been extensively studied for typifying gasoline HDS. Although, some results are not completely understood, a reaction network has been proposed by Van Parijs and Froment, to explain their own results, which were obtained in a comprehensive set of conditions. In this network, thiophene is hydrodesulfurized to give a mixture of -butenes, followed by further hydrogenation to butane. On the considered reaction conditions, tetrahydrothiophene and butadiene were not observed [43], The consistency between the functional forms of the rate equations for the HDS of benzothiophene and thiophene, based on the dissociative adsorption of hydrogen, were identical [43,44], suggesting equivalent mechanisms. 

Burstein (145) in an extensive study of the exchange between H2 and Da on charcoal found that this process is governed by the dissociative adsorption of hydrogen in the range of temperatures between 500°K. and... 

Hydrogen adsorption on MgO can, in principle, be either molecular or dissociative. Dissociative adsorption of hydrogen on high-surface-area MgO has already been reported, and both homolytic and heterolytic pathways have been proposed 12). Homolytic splitting is supposed to operate under UV-irradiation only (117-119) and is not discussed further here. Heterolytic splitting takes place in the dark and at 300 K on coordinatively unsaturated (cus) Mg O surface pairs following the schematic mechanism illustrated in Scheme 2. 

Results indicate that deposition is facilitated on active (copper, NijCr) compared to inert substrates. This is attributed to an easier decomposition of the precursor on copper or NijCr rather than on glass or carbon surfaces. Hydrogen can be dissociatively adsorbed on NijCr substrates enhancing the decomposition of NiCp. On copper substrates, the dissociative adsorption of hydrogen is not easy. In that case, the enhanced nucleation is certainly due to the... 

Thus, the adsorption of CO on active ZrOa catalysts led to the formation of various types of adsorption species of CO having different reactivities toward Ha, and these species were found to play a significant role in the hydrogenation of CO. Moreover, it is likely that CO is adsorbed on the active surface sites of low coordination and that an electron transfer from the other surface sites to this CO species leads to the formation of the dimeric adsorbed species (CO)a. These dimeric species react, step by step, with CO molecules from the gas phase to from a relatively stable cyclic polymer species of (CO)s and then (CO) ", Such adsorbed CO species easily react with hydrogen and are also activated through the dissociative adsorption of hydrogen on surface sites of low coordination or the coordina-tively unsaturated surface sites on the catalyst. 

In the account of this chemisorption work, hydrogen chemisorption was also described. Hydrogen chemisorption was consistently less than the CO (after correction for substrate contribution) and it is suggested that this difference is owing to the need for nickel crystallites large enough to provide adjacent sites for dissociative adsorption of hydrogen atoms, whereas the CO can adsorb as an undissociated molecule on individual surface nickel atoms. 

For the dissociative adsorption of hydrogen on the Ge surface, the equation analogous to (10-84) is... 

Hydrogen adsorpiion measurements were made on the catalysts in conventional static volumetric equipment Hydrogen uptake was obtained from the isotherm plateau. Metal surface area was calculated assuming dissociative adsorption of hydrogen with one hydrogen atom on each surface nickel atom and assuming the cross-sectional area of nickel to be 0.065 nm. ... 

Hydrogen is used as the chain length regulator in Ziegler-Natta polymerization. A proposed mechanism postulates that there exists a pre-established equilibrium of dissociative adsorption of hydrogen on TiCls catalyst surface as... 

For a dual site mechanism with dissociative adsorption of hydrogen. 

H magic angle spinning NMR evidence for dissociative adsorption of hydrogen on Ag -exchanged A- and Y-zeolites , Langmuir, 15, 7894. 

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