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Title: Enhanced kinetic stability of {gamma}-C-H bonds in surface alkoxides: The reactions of tert-butyl alcohol on clean and oxygen-covered Rh(111)

Abstract

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 onmore » both clean and oxygen-covered Rh(111). 30 refs., 6 figs., 1 tab.« less

Authors:
;  [1]
  1. Harvard Univ., Cambridge, MA (United States)
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
391019
Resource Type:
Journal Article
Journal Name:
Langmuir
Additional Journal Information:
Journal Volume: 8; Journal Issue: 4; Other Information: PBD: Apr 1992
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; RHODIUM OXIDES; CHEMICAL REACTION KINETICS; BUTANOLS; DEHYDROGENATION; ALKOXIDES; X-RAY SPECTROSCOPY; PHOTOELECTRON SPECTROSCOPY; ISOTOPE EFFECTS; CHEMICAL REACTIONS

Citation Formats

Xu, X, and Friend, C M. Enhanced kinetic stability of {gamma}-C-H bonds in surface alkoxides: The reactions of tert-butyl alcohol on clean and oxygen-covered Rh(111). United States: N. p., 1992. Web. doi:10.1021/la00040a016.
Xu, X, & Friend, C M. Enhanced kinetic stability of {gamma}-C-H bonds in surface alkoxides: The reactions of tert-butyl alcohol on clean and oxygen-covered Rh(111). United States. https://doi.org/10.1021/la00040a016
Xu, X, and Friend, C M. 1992. "Enhanced kinetic stability of {gamma}-C-H bonds in surface alkoxides: The reactions of tert-butyl alcohol on clean and oxygen-covered Rh(111)". United States. https://doi.org/10.1021/la00040a016.
@article{osti_391019,
title = {Enhanced kinetic stability of {gamma}-C-H bonds in surface alkoxides: The reactions of tert-butyl alcohol on clean and oxygen-covered Rh(111)},
author = {Xu, X and Friend, C M},
abstractNote = {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.},
doi = {10.1021/la00040a016},
url = {https://www.osti.gov/biblio/391019}, journal = {Langmuir},
number = 4,
volume = 8,
place = {United States},
year = {Wed Apr 01 00:00:00 EST 1992},
month = {Wed Apr 01 00:00:00 EST 1992}
}