Probing Surface Reaction Mechanisms Using Chemical and Vibrational Methods:  Alkyl Oxidation and Reactivity of Alcohols on Transitions Metal Surfaces

Weldon, M. K.; Friend, Cynthia M.

doi:10.1021/cr950224d

Cited by 107 publications

(117 citation statements)

References 111 publications

(335 reference statements)

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“…To observe the DKIE for -hydrogen elimination on the Cu(111) surface, the TPR spectra shown in Figure 1 were obtained for CH 3 . These spectra were obtained by starting with saturated coverages of the ethoxy groups, as described previ-…”

Section: Resultsmentioning

confidence: 99%

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Transition State for β-Elimination of Hydrogen from Alkoxy Groups on Metal Surfaces

et al. 2000

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Experimental investigations of -hydrogen elimination from alkoxy and alkyl groups bound to a Cu(111) surface have been coupled with computational studies of gas-phase analogues to provide insight into the transition state for catalytic hydrogenation and dehydrogenation on metal surfaces. Previous studies have shown that fluorination increases the activation barrier (∆E act ) to -hydrogen elimination in ethoxy groups (RCH 2 O (ad) f RCHdO (ad) + H (ad) , where R ) CH 3 , CFH 2 , CHF 2 , CF 3 ) and propyl groups (RCH 2 CH 2,(ad) f RCHdCH 2,(ad) + H (ad) , where R ) CH 3 , CF 3 ) on the Cu(111) surface. The increase in barrier height with increasing fluorination was attributed to the inductive influence of fluorine, which energetically destabilizes a hydride-like transition state of the form [RC δ+ ‚‚‚H δ-] ‡ . In this paper, deuterium kinetic isotope effects (DKIE) show that fluorination does not alter the mechanism for -hydrogen elimination from ethoxy groups. Furthermore, the DKIE measurements confirm that the effects of fluorine on the kinetics of -hydrogen elimination do not result from the change in mass when hydrogen is substituted by fluorine. A systematic study of fluorine substitution of surface-bound isopropoxy groups reveals combined steric and electronic effects. An excellent correlation is found between the ∆E act for -hydrogen elimination in adsorbed alkoxy groups and the calculated reaction energetics (∆H rxn ) for gas-phase dehydrogenation of fluorinated alcohols in trans antiperiplanar conformations (e.g., RCH 2 OH (g) f RCHdO (g) + H 2,(g) , where the hydroxyl hydrogen is antiperiplanar to a carbon and the oxygen is antiperiplanar to a fluorine). Hammett plots for -hydrogen elimination give a reaction parameter of F ) -26. These correlations both suggest that the transition state for -hydrogen elimination develops a greater partial positive charge on the carbinol carbon than is found in the adsorbed reactant. Furthermore, the transition state is energetically late in the reaction coordinate for -hydrogen elimination.

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Section: Resultsmentioning

confidence: 99%

“…The TPR spectra showing the desorption of CH 3 CDdO and CH 3 CHdO during reaction of a saturation coverage of CH 3 CHDO (ad) are shown in Figure 2. The ratio of the yields of CH 3 CDdO and CH 3 CHdO produced by this reaction is a direct measure of the primary kinetic isotope effect. The first fact to (111) surface.…”

Section: Resultsmentioning

confidence: 99%

Transition State for β-Elimination of Hydrogen from Alkoxy Groups on Metal Surfaces

et al. 2000

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“…CH 3 OH catalytic oxidation is a complex process with long list of possible reactions involving different intermediates and final products, which also depend on the catalyst chemical state [18,19]. The first common step on both metal and oxide surfaces is H abstraction, yielding H s or OH s and methoxy, CH 3 Os, where the subscript 's' indicates that the species is bonded at the surface.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of methanol on Ru catalyst: Effect of the reagents partial pressures on the catalyst oxidation state and selectivity

et al. 2007

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In situ core level photoelectron spectroscopy and mass spectrometry have been utilized to study the methanol oxidation on a model RuO2 catalyst at pressures ranging from 10 -6 to 10 -1 mbar. The experiments were carried out varying the O 2 /CH 3 OH molecular mixing ratio from 0.25 to 3.3 and the reaction temperature from 350 to 720 K. The Ru 3d 5/2 and O 1s core level spectra were used to characterise the dynamic changes in the Ru oxidation state by exposing the oxide pre-catalyst to different reagents partial pressures and temperatures. Full oxidation to CO 2 + H 2 O or partial oxidation to CO + H 2 O + H 2 have been observed in the whole pressure range for specific reaction conditions, which preserve the oxide catalyst state or reduce the oxide to metallic Ru. The selective oxidation to formaldehyde is observed only at pressures in the 10 -1 mbar range, catalyzed by a RuOx surface oxide formed by partial reduction of the oxide pre-catalyst.

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“…A key characteristic of palladium is its ability to perform selox chemistry at temperatures between 60 and 160°C and with ambient oxygen pressure [39,142] via the wi dely accepted oxidative dehydrogenation route illustrated in Scheme 3 [39,67]. Whether O-H or C-H scission of the a-carbon is the first chemical step remains a matter of debate, since the only fundamental studies over well-defined Pd(111) surfaces to date employed temperature-programmed XPS [143] and metastable de-excitation spectroscopy (MDS) [144] with temporal resolutions on the second ?…”

Section: Surface Reaction Mechanismmentioning

confidence: 99%

“…minute timescale, over which loss of both hydrogens appears coincident. However, temperature-programmed mass spectrometric [145] and vibrational [146] studies of unsaturated C 1 -C 3 alcohols implicate O-H cleavage and attendant alkoxy formation over Pd single crystal surfaces as the first reaction step [142,147]. It is generally held that the resultant hydrogen adatoms react with dissociatively absorbed oxygen to form water, which immediately desorbs at ambient temperature thereby shifting the equilibrium to carbonyl formation [39,67].…”

Section: Surface Reaction Mechanismmentioning

confidence: 99%

Catalysing sustainable fuel and chemical synthesis

Lee

2014

Appl Petrochem Res

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Concerns over the economics of proven fossil fuel reserves, in concert with government and public acceptance of the anthropogenic origin of rising CO 2 emissions and associated climate change from such combustible carbon, are driving academic and commercial research into new sustainable routes to fuel and chemicals. The quest for such sustainable resources to meet the demands of a rapidly rising global population represents one of this century's grand challenges. Here, we discuss catalytic solutions to the clean synthesis of biodiesel, the most readily implemented and low cost, alternative source of transportation fuels, and oxygenated organic molecules for the manufacture of fine and speciality chemicals to meet future societal demands.

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Probing Surface Reaction Mechanisms Using Chemical and Vibrational Methods: Alkyl Oxidation and Reactivity of Alcohols on Transitions Metal Surfaces

Cited by 107 publications

References 111 publications

Transition State for β-Elimination of Hydrogen from Alkoxy Groups on Metal Surfaces

Transition State for β-Elimination of Hydrogen from Alkoxy Groups on Metal Surfaces

Oxidation of methanol on Ru catalyst: Effect of the reagents partial pressures on the catalyst oxidation state and selectivity

Catalysing sustainable fuel and chemical synthesis

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