Enhanced kinetic stability of {gamma}-C-H bonds in surface alkoxides: The reactions of tert-butyl alcohol on clean and oxygen-covered Rh(111)
- Harvard Univ., Cambridge, MA (United States)
The reactions of tert-butyl alcohol (t-BuOH) on clean and oxygen-covered Rh(111) have been investigated under ultrahigh vacuum conditions using temperature-programmed reaction and X-ray photoelectron spectroscopies. Surface oxygen inhibits nonselective C-H, C-C, and C-O bond breaking. t-BuOH forms tert-butyl oxide (t-BuO) on the oxygen-covered surfaces below 300 K. On Rh(111)-p(2x1)-O, {theta}{sub o} = 0.5, t-BuO remains intact up to 370 K where it decomposes to t-BuOH and butene. There is a substantial kinetic isotope effect for t-BuOH decomposition on Rh(111)-p(2x1)-0, suggesting that C-H bond breaking is the rate-limiting step. t-BuO is kinetically more stable than 2-propoxide on Rh(111)-p(2x1)-O. This enhanced stability is attributed to the fact that t-BuOH has no C-H bond at the carbon adjacent to oxygen. The C-H bond adjacent to oxygen has been shown to be more labile in alkoxide reactions on Rh(111)-bond cleavage produces H{sub 2}O and irreversibly bound hydrocarbon products below 300 K on clean Rh(111). For intermediate oxygen coverages, such as Rh(111)-p(2x2)0O which has an oxygen coverage of 0.25, no gaseous butene is evolved. This may be due to rapid dehydrogenation of butene on Rh(111)-(2x2)-O. The relatively weak C-O bond combined with the enhanced kinetic stability of t-BuOH opens pathways for C-O bond cleavage on both clean and oxygen-covered Rh(111). 30 refs., 6 figs., 1 tab.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 391019
- Journal Information:
- Langmuir, Vol. 8, Issue 4; Other Information: PBD: Apr 1992
- Country of Publication:
- United States
- Language:
- English
Similar Records
Role of coverage in determining adsorbate stability: Phenol reactivity on Rh(111)
Isotope effects in hydrogen atom transfer. VII. Benzylic hydrogen abstraction by tert-butoxy and other radicals