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Small molecule chemisorption on metals and carbon-hydrogen and hydroxy 1 bond activation by electron hold centers: Molecular orbital theory
| Title: | Small molecule chemisorption on metals and carbon-hydrogen and hydroxy 1 bond activation by electron hold centers: Molecular orbital theory |
| Author: | Awad, Mohamed Khaled Hassan |
| Description: | CO is calculated to favor adsorption at 3-fold sites on Pd (111) and at 2-fold sites on Pd (100) surfaces in agreement with experimental literature. It is shown that the different binding site preferences of CO on Pd and Pt are caused by the different metal valence band positions. The adsorption of Ru and O atoms and RuO n (n = 1-4) on the Ru (001) surface has been studied. It is found that the Ru and RuO n have about the same barrier to surface diffusion, all equal to about half of the oxygen barrier. The binding energy of RuO n decreases as n increases. These findings show how oxide molecules may provide a transport mechanism for oxide nucleation on the Ru (001) surface, which supports suggestions in the experimental literature. Calculations show that π*gets n excited p-benzoquinone abstracts an H atom from coordinated H2O to form semiquinone. In acidic solution, hydroquinone is most likely to form by a second hydrogenation of semiquinone leaving stable di-μ-oxo Mn IV dimers. It is proposed that dimers disproportionate, going through a 4 Mn intermediate, to give O2 and a stable O-bridged Mn III dimer. According to the calculations, this last step is rate limiting. It is shown that dimerization of the Mn complexes is the key to O2 evolution in the active systems, and this is controlled by the ligand structure. CH4 activation by N2- hole centers in AlN is calculated to be very similar to activation by O- hole centers in oxides such as MgO. Surface HN2- and gas phase methyl radical are formed by H abstraction. Recent experimental literature has demonstrated the photodimerization of cyclohexene by excited W10O324- to yield 3,3′-dicyclohexene. Our calculations show that the hole in the top of O 2p band of photoexicted polyoxyanion is reduced by an electron from the CH bond early in the course of H abstraction, and this is why the activation energly is low. The adsorption of ethylidyne on cluster models of Rh(100) and (111) surfaces has been studied. Higher coordination sites are favored, with the C-C bond of ethylidyne perpendicular to the surface. (Abstract shortened with permission of author. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=case1054910441
http://hdl.handle.net/2374.OX/16092 |
| Date: | 1990 |
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