Decomposition of cyclohexene on Pt(111): A BPTDS and HREELS study

Journal Article · Thu Jul 09 04:00:00 EDT 1992 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/j100193a059· OSTI ID:273608

Henn, F C; Diaz, A L; Bussell, M E; Hugenschmidt, M B; Domagala, M E; Campbell, C T ^[1]

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1. Univ. of Washington, Seattle, WA (United States)

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 identified 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.

• Sponsoring Organization: USDOE
• OSTI ID: 273608
• Journal Information: Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 14 Vol. 96; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
10 SYNTHETIC FUELS
40 CHEMISTRY
CATALYTIC EFFECTS
CYCLOALKENES
DECOMPOSITION
DEHYDROGENATION
DESORPTION
DEUTERIUM
ISOTOPIC EXCHANGE
MASS SPECTROSCOPY
PLATINUM
REACTION INTERMEDIATES