Decomposition of cyclohexene on platinum (111): a BPTDS and HREELS study
| Autor: | Charles T. Campbell, F. C. Henn, A. L. Diaz, Melanie E. Domagala, Mark E. Bussell, Markus B. Hugenschmidt |
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| Rok vydání: | 1992 |
| Předmět: | |
| Zdroj: | The Journal of Physical Chemistry. 96:5965-5974 |
| ISSN: | 1541-5740 0022-3654 |
| DOI: | 10.1021/j100193a059 |
| Popis: | The interactions of cyclohexene with a Pt(111) surface have been studied using a combination of bismuth postdosing thermal desorption mass spectroscopy (BPTDS) and high-resolution electron energy loss spectroscopy (HREELS). BPTDS is a technique which utilizes vapor-deposited Bi (at a surface temperature of {approximately} 100 K) to passivate a previously prepared adlayer against intraadsorbate bond-breaking reactions. After such passivation, the surface is heated and adsorbed intermediates desorb intact for mass spectral indentification, provided they have stable gas-phase analogues. Here, the authors show that BPTDS is a useful technique for monitoring the coverages of adsorbed intermediates produced during the dehydrogenation of cyclohexene on Pt(111). At 95 K, cyclohexene adsorbs molecularly in a di-{sigma} fashion. By 200 K (E{sub a} {congruent} 13.7 kcal/mol) this species converts to another form of di-{sigma}, molecularly adsorbed cyclohexene, which itself converts to {pi}-allyl c-C{sub 6}H{sub 9,a} (plus adsorbed hydrogen) at 200-240 K (E{sub a}{congruent} 14.4 kcal/mol). At about the same temperature, part of the cyclohexene decomposes, producing small amounts of adsorbed benzene and cyclohexadiene. At about 340 K, the c-C{sub 6}H{sub 9,a} species converts to adsorbed benzene (E{sub a} = 20.8 kcal/mol) and the adsorbed hydrogen desorbs as H{sub 2}. The c-C{sub 6}H{sub 9,a} intermediate is identifiedmore » in BPTDS by its deuteration to c-C{sub 6}H{sub 9}D gas at {approximately} 190 K when coadsorbed with deuterium. No significant H-D exchange occurs between coadsorbed deuterium and molecularly adsorbed hydrocarbons when probed by BPTDS. 48 refs., 6 figs., 2 tabs.« less |
| Databáze: | OpenAIRE |
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