Mimicking Aspects of Heterogeneous Catalysis:  Generating, Isolating, and Reacting Proposed Surface Intermediates on Single Crystals in Vacuum

Bent, Brian E.

doi:10.1021/cr940201j

Cited by 349 publications

(370 citation statements)

References 443 publications

(1,174 reference statements)

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“…These findings are in agreement with previous studies reporting on the dissociative adsorption of small alkyl or aryl halides on metal surfaces. 31 Specifically, the C-I bond in iodobenzene, which can be regarded as a subunit of CHP, has been reported to dissociate below room temperature on Cu(111), [32][33][34] Au(111), 35 and Ag(111), 36 resulting in adsorbed phenyl and iodine.…”

Section: Adsorptionmentioning

confidence: 99%

Two-Dimensional Polymer Formation on Surfaces: Insight into the Roles of Precursor Mobility and Reactivity

et al. 2010

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Abstract:We report on a combined scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) study on the surface-assisted assembly of the hexaiodosubstituted macrocycle cyclohexa-m-phenylene (CHP) toward covalently bonded polyphenylene networks on Cu(111), Au(111), and Ag(111) surfaces. STM and XPS indicate room temperature dehalogenation of CHP on either surface, leading to surface-stabilized CHP radicals (CHPRs) and coadsorbed iodine. Subsequent covalent intermolecular bond formation between CHPRs is thermally activated and is found to proceed at different temperatures on the three coinage metals. The resulting polyphenylene networks differ significantly in morphology on the three substrates: On Cu, the networks are dominated by "open" branched structures, on the Au surface a mixture of branched and small domains of compact network clusters are observed, and highly ordered and dense polyphenylene networks form on the Ag surface. Ab initio DFT calculations allow one to elucidate the diffusion and coupling mechanisms of CHPRs on the Cu(111) and Ag(111) surfaces. On Cu, the energy barrier for diffusion is significantly higher than the one for covalent intermolecular bond formation, whereas on Ag the reverse relation holds. By using a Monte Carlo simulation, we show that different balances between diffusion and intermolecular coupling determine the observed branched and compact polyphenylene networks on the Cu and Ag surface, respectively, demonstrating that the choice of the substrate plays a crucial role in the formation of two-dimensional polymers.

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Section: Adsorptionmentioning

confidence: 99%

Two-Dimensional Polymer Formation on Surfaces: Insight into the Roles of Precursor Mobility and Reactivity

et al. 2010

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“…8 On the basis of the Helmholtz equation (4Φ ) 4Πn i µ, where n i is the number of EC molecules in each of the first three layers (i ) 1, 2, 3) that orient chlorine down (n 1 , n 3 ) or ethyl down (n 2 ) and µ is the (fixed) dipole moment of an adsorbed EC molecule) one can extract the fraction of a monolayer of EC molecules that orient in either orientation. Assuming all EC molecules in the first layer orient (on average) the same way, namely chlorine down at the completion of the first monolayer, then n 2 ) 0.14n 1 and n 3 ) 0.034n 1 .…”

Section: Work Function Change Measurements (∆φ)mentioning

confidence: 99%

“…[1][2][3][4] This is partially due to their importance in the pesticide industry as well as their unique photochemistry and its damaging impact on the ozone layer. 5 The first experimental demonstration of a molecular cage in amorphous solid water (ASW) was that of N 2 6 more than a decade ago.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Ethyl Chloride with Amorphous Solid Water Thin Film on Ru(001) and O/Ru(001) Surfaces

Ayoub

Asscher

2009

J. Phys. Chem. A

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The adsorption of ethyl chloride (EC) on clean and oxygen covered Ru(001) surfaces and its interaction with coadsorbed amorphous solid water (ASW) is reported based on temperature-programmed desorption (TPD) and work function change (4Φ) measurements. Adsorption of EC is characterized by a decrease of 2.1 eV in work function at monolayer coverage. Flipped adsorption geometry on average (ethyl facing the surface) is found in the second layer with a 0.3 eV increase in the work function. On ruthenium substrates the orientation of EC molecules could be controlled chlorine down or up by varying the oxygen coverage, as indicated by work function change measurements. ∆P-TPD from clean Ru(001) surface reveals a complete dissociation of the EC molecules on the clean Ru(001) surface at coverages up to 0.1 ( 0.05 ML. At higher coverage it leads to two distinct TPD peaks: at T )175 and 120-130 K, for the monolayer and multilayer coverage, respectively. Compression of preadsorbed 0.3 ML EC molecules into small islands on the surface occurs when ASW layers at coverage in the range 0.5-6 bilayers (BL) are adsorbed on top of the EC covered surface, associated with a shift in peak desorption from 190 K down to 125 K. A Caging process of EC molecules within the layers of ASW takes place by adsorbing more than 6 BL until a fully caged system has developed above 20 ASW BL. A reversed TPD peak shift of the trapped EC molecules occurs from its compressed phase at 125 K up to 165 K, the onset for ASW transition to crystalline ice and desorption. The detachment process leads to partial flipping over the geometry of the EC at the second layer, as determined by 4Φ measurement. The distance of the lifted and caged EC molecules from the Ru surface has been determined to reside 1.0 ( 0.2 nm above the solid surface, based on the thermal dissociation and hydrogen uptake measurements of sandwiched EC molecules between a variable thickness ASW film and a fixed 10 BL layer, on top of clean Ru(001). We conclude that the caged EC molecules are trapped in a micelle-like geometry with the ethyl groups pointing inward. This conclusion is based on photodecomposition studies of the caged EC molecules at 193 nm, as a function of EC initial coverage.

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“…[1][2][3][4] The hydrogenation reactions occur either in high-pressurized hydrogen atmospheres 5 or on catalytic metal (or semiconductor) surfaces. [6][7][8] On metal surfaces, adsorbed hydrogen atoms could associate with other adsorbed species (e.g., hydrocarbon intermediates) to form various hydrogenated or saturated hydrocarbon products.…”

Section: Introductionmentioning

confidence: 99%

“…[6][7][8] On metal surfaces, adsorbed hydrogen atoms could associate with other adsorbed species (e.g., hydrocarbon intermediates) to form various hydrogenated or saturated hydrocarbon products. 1 For example, an adsorbed CH 3 and an atomic H associate to form CH 4 . 9 The reactivity of hydrogenation reaction depends on many factors such as catalytic activity of a substrate and geometry of an adsorbate.…”

Section: Introductionmentioning

confidence: 99%

Hydrogenation of Phenylacetylene to Styrene on Pre-C_xH_y- and C-Covered Cu(111) Single Crystal Catalysts

Sohn¹,

Wei²,

White³

2011

Bulletin of the Korean Chemical Society

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Thermal hydrogenation of phenylacetylene (PA, C 8 H 6 ) to styrene (C 8 H 8 ) on pre-C x H y -and C-covered Cu(111) single crystal substrates has been studied using temperature-programmed desorption (TPD) mass spectrometry. Chemisorbed PA with an acetylene group has been proved to be associated with hydrogen of pre-adsorbed C x H y to form styrene (104 amu) on Cu surface. For the parent (PA) mass (102 amu) TPD profile, the TPD peaks at 360 K and 410 K are assigned to chemisorbed vertically aligned PA and flat-lying cross-bridged PA, respectively (J. Phys. Chem. C 2007, 111, 5101). The relative I 360K /I 410K TPD ratio dramatically increases with increasing pre-adsorbed C x H y before dosing PA, while the ratio does not increase for pre-C-covered surface. For PA on pre-C x H y -covered Cu(111) surface, styrene desorption is enhanced relative to the parent PA desorption, while styrene formation is dramatically quenched on pre-C-covered (lack of adsorbed hydrogen nearby) surface. It appears that only cross-bridged PA associates with adsorbed hydrogen to form styrene that promptly desorbs at 410 K, while vertically aligned PA is less likely to participate in forming styrene.

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Mimicking Aspects of Heterogeneous Catalysis: Generating, Isolating, and Reacting Proposed Surface Intermediates on Single Crystals in Vacuum

Cited by 349 publications

References 443 publications

Two-Dimensional Polymer Formation on Surfaces: Insight into the Roles of Precursor Mobility and Reactivity

Two-Dimensional Polymer Formation on Surfaces: Insight into the Roles of Precursor Mobility and Reactivity

Interaction of Ethyl Chloride with Amorphous Solid Water Thin Film on Ru(001) and O/Ru(001) Surfaces

Hydrogenation of Phenylacetylene to Styrene on Pre-C_xH_y- and C-Covered Cu(111) Single Crystal Catalysts

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Mimicking Aspects of Heterogeneous Catalysis: Generating, Isolating, and Reacting Proposed Surface Intermediates on Single Crystals in Vacuum

Cited by 349 publications

References 443 publications

Two-Dimensional Polymer Formation on Surfaces: Insight into the Roles of Precursor Mobility and Reactivity

Two-Dimensional Polymer Formation on Surfaces: Insight into the Roles of Precursor Mobility and Reactivity

Interaction of Ethyl Chloride with Amorphous Solid Water Thin Film on Ru(001) and O/Ru(001) Surfaces

Hydrogenation of Phenylacetylene to Styrene on Pre-CxHy- and C-Covered Cu(111) Single Crystal Catalysts

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Hydrogenation of Phenylacetylene to Styrene on Pre-C_xH_y- and C-Covered Cu(111) Single Crystal Catalysts