Efficient Epoxidation of a Terminal Alkene Containing Allylic Hydrogen Atoms: <i>trans</i>-Methylstyrene on Cu{111}

Cropley, Rachael L.; Williams, Federico J.; Urquhart, Andrew J.; Vaughan, Owain; Tikhov, Mintcho S.; Lambert, Richard M.

doi:10.1021/ja042758e

Cited by 65 publications

(52 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the present context, the ability of oxygenated silver surfaces to react with unsaturated organic adsorbates without totally disrupting them by deep oxidation-unlike the platinum group metals, which induce total combustion 14 [20][21][22][23][24] In this paper we report the first observation of the silver-catalyzed homocoupling of phenylacetylene on extended Ag(100) single crystal surfaces in vacuum and also the corresponding behavior of Ag particles in solution. STM and XPS single crystal results unambiguously established that the presence of chemisorbed oxygen was critical for efficient reaction to occur and that the crucial reaction-initiating step was abstraction of the acetylenic hydrogen atom by O(a), which caused the reaction to propagate over the entire metal surface, as opposed to being confined to island boundaries.…”

Section: Introductionmentioning

confidence: 90%

Critical Role of Oxygen in Silver-Catalyzed Glaser–Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles

et al. 2017

Self Cite

View full text Add to dashboard Cite

The essential role of oxygen in enabling heterogeneously catalyzed Glaser−Hay coupling of phenylacetylene on Ag(100) was elucidated by STM, laboratory and synchrotron photoemission, and DFT calculations. In the absence of coadsorbed 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 O 2 , 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 toward 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 a mechanistic understanding of coupling reactions under conditions of practical catalysis was reaffirmed.

show abstract

Section: Introductionmentioning

confidence: 90%

Critical Role of Oxygen in Silver-Catalyzed Glaser–Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles

et al. 2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…C K-edge data were acquired at five angles of photon incidence (θ) at both coverages and the raw data were processed following standard methodology 16,17 by first extracting the integrated π* intensities and then analyzing their angular dependence. The spectra exhibit two sharp 1s π* resonances whose dependence on photon incidence angle is markedly different: they are assigned to the C=C bond (282.5 eV) and the C=O bond (284.3 eV), 13,15 the intensity of the latter transition decreased to almost zero at normal photon incidence, at which point substantial C=C intensity remained. From the well known selection rules for 1s π* transitions of adsorbates on (111) surfaces we may draw the qualitative conclusion that C=O bond is almost parallel to the metal surface whereas the C=C is appreciably tilted.…”

Section: Nexafs Of Crotonaldehydementioning

confidence: 96%

Adsorption Geometry Determines Catalytic Selectivity in Highly Chemoselective Hydrogenation of Crotonaldehyde on Ag(111)

et al. 2012

Self Cite

View full text Add to dashboard Cite

The chemoselective hydrogenation of crotonaldehyde to crotyl alcohol was studied by temperature programmed desorption/reaction, high resolution XPS and NEXAFS. The organic molecule adsorbed without decomposition, all three possible hydrogenation products were formed and desorbed, and the clean overall reaction led to no carbon deposition. Selectivities up to 95% were found under TPR conditions.The observed behavior corresponded well with selectivity trends previously reported for Ag/SiO 2 catalysts and the present findings permit a rationalization of the catalytic performance in terms of pronounced coverage-dependent changes in adsorption geometries of the reactant and the products.Thus at low coverages the C=O bond in crotonaldehyde lay almost parallel to the metal surface whereas the C=C was appreciably tilted, favoring hydrogenation of the former and disfavoring hydrogenation of the latter. With increasing coverage of reactants, the C=C bond was forced almost parallel to the surface, rendering it vulnerable to hydrogenation, thus markedly decreasing selectivity towards formation of crotyl alcohol. Butanol formation was the result of an overall twostep process: crotonaldehyde crotyl alcohol butanol, further hydrogenation of the desired product crotyl alcohol being promoted at high hydrogen coverage due to the C=C bond in the unsaturated alcohol being driven from a tilted to a flat-lying geometry. Finally, an explanation is offered for the strikingly different behavior of Ag(111) and Cu(111) in the chemoselective hydrogenation of crotonaldehyde in terms of the different degrees of charge transfer from metal to C=O π bond, as suggested by C 1s XPS binding energies.

show abstract

“…Further characterizations with high-resolution transmission electron microscopy (HRTEM) and Auger spectroscopy indicated that highly dispersed metal Cu NPs (\5.0 nm) might be responsible for PO formation. In addition, Lambert et al [87] found that model catalyst Cu(111) catalyzed the epoxidation of alkene containing allylic hydrogen (trans-methylstyrene) under ultrahigh vacuum conditions. Theoretical calculation suggested that in propene Fig.…”

Section: Copper Catalystsmentioning

confidence: 99%

Gas-phase propene epoxidation over coinage metal catalysts

2011

View full text Add to dashboard Cite

Propene oxide (PO) is a very important bulk chemical and is produced on a scale of about 7.5 million tons per year. In industry, PO is produced via multiple reaction steps in the liquid phase, using hazardous chlorine or costly organic hydroperoxides as oxidants. Accordingly, development of a simple and green process to produce PO has been desired. This paper presents an overview of one-step propene epoxidation in the gas phase over coinage metal catalysts with a mixture of O 2 and H 2 or with molecular O 2 alone as oxidant. Silver (Ag) and gold (Au) catalysts can catalyze propene epoxidation with a mixture of O 2 and H 2 , with high selectivity, whereas copper (Cu) catalysts cannot. In this reaction Au catalysts are much more active than Ag catalysts. All the coinage metals can catalyze propene epoxidation by molecular O 2 , but with selectivity usually below 60%. The valence states of Cu species and the sizes of Ag particles and Au particles are of crucial importance in PO synthesis.

show abstract

Efficient Epoxidation of a Terminal Alkene Containing Allylic Hydrogen Atoms: trans-Methylstyrene on Cu{111}

Cited by 65 publications

References 34 publications

Critical Role of Oxygen in Silver-Catalyzed Glaser–Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles

Critical Role of Oxygen in Silver-Catalyzed Glaser–Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles

Adsorption Geometry Determines Catalytic Selectivity in Highly Chemoselective Hydrogenation of Crotonaldehyde on Ag(111)

Gas-phase propene epoxidation over coinage metal catalysts

Contact Info

Product

Resources

About