Critical role of oxygen in silver-catalyzed glaser-hay coupling on Ag(100) in vacuum and in solution on Ag particles

Abstract

The essential role of oxygen in enabling heterogeneously catalyzed Glaser-Hay coupling of phenylacetylene on the Ag(100) was elucidated by STM, laboratory and synchrotron photoemission and DFT calculations. In the absence of co-adsorbed oxygen, phenylacetylene formed well-ordered dense overlayers which, with increasing temperature, desorbed without reaction. In striking contrast, even at 120 K, the presence of oxygen led to immediate and complete disruption of the organic layer due to abstraction of acetylenic hydrogen with formation of a disordered mixed layer containing immobile adsorbed phenylacetylide. At higher temperatures phenylacetylide underwent Glaser-Hay coupling to form highly ordered domains of diphenyldiacetylene that eventually desorbed without decomposition leaving the bare metal surface. DFT calculations showed that while acetylenic H abstraction was otherwise an endothermic process, oxygen adatoms triggered a reaction-initiating exothermic pathway leading to OH(a) + phenylacetylide, consistent with the experimental observations. Moreover, it was found that with a solution of phenylacetylene in nonane and in the presence of O2, Ag particles catalyzed Glaser-Hay coupling with high selectivity. Rigorous exclusion of oxygen from the reactor strongly suppressed the catalytic reaction. Interestingly, too much oxygen lowers the selectivity towards diphenyldiacetylene. Thus vacuum studies and theoretical calculations revealed the key role of oxygen in the reaction mechanism, subsequently borne out by catalytic studies with Ag particles that confirmed the presence of oxygen as a necessary and sufficient condition for the coupling reaction to occur. The direct relevance of model studies to mechanistic understanding of coupling reactions under conditions of practical catalysis was reaffirmed.

Publication DOI: https://doi.org/10.1021/acscatal.7b00431
Divisions: College of Engineering & Physical Sciences
College of Engineering & Physical Sciences > Energy and Bioproducts Research Institute (EBRI)
College of Engineering & Physical Sciences > School of Infrastructure and Sustainable Engineering > Chemical Engineering & Applied Chemistry
Additional Information: This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to http://dx.doi.org/10.1021/acscatal.7b00431
Uncontrolled Keywords: C-C bond formation,catalysis,DFT,Glaser-Hay coupling,silver surface,STM,XPS,Catalysis
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Related URLs: http://www.scop ... tnerID=8YFLogxK (Scopus URL)
PURE Output Type: Article
Published Date: 2017-05-05
Published Online Date: 2017-03-30
Accepted Date: 2017-03-22
Authors: Orozco, Noé
Kyriakou, Georgios
Beaumont, Simon K.
Fernández Sanz, Javier
Holgado, Juan P.
Taylor, Martin
Espinós, Juan Pedro
Márquez, Antonio
Watson, David J.
Gonzalez-Elipe, Agustin R.
Lambert, Richard M.

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