X-ray photoelectron spectroscopy study of the interaction of alcohols with oxide surfaces

Tobin, J.; Hirschwald, W.; Cunningham, Joseph

doi:10.1016/0584-8547(85)80122-1

Cited by 11 publications

(5 citation statements)

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“…The higher binding energy at low temperature coincides with a more electronegative chemical environment requiring greater energy for the ejection of an electron, such as would occur with weak binding of methanol and methoxy species to the surface. The O 1s binding energy of 533.8 ± 0.2 eV for methoxy adsorbed on MoS 2 (Figure ) is much larger than the 530.1–530.9 eV binding energies reported for methoxy bound to copper surface, − but more in line with the 533.1 eV binding energy reported for methoxy on Cu(111) and the binding energy of 532.8 eV observed for methanol condensed on ZnO . Yet MoS 2 , even with sulfur vacancies, the molybdenum atoms are still well coordinated to sulfur and a higher binding energy is expected than for a methoxy species on a bare metal surface.…”

Section: Sulfur Vacancies and Induced Defectsmentioning

confidence: 52%

Methoxy Formation Induced Defects on MoS₂

et al. 2018

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We find that exposure of the MoS2 basal plane to methanol leads to the formation of adsorbed methoxy and coincides with sulfur vacancy generation. The conversion of methanol to methoxy on MoS2 is temperature dependent. Density functional theory simulations and experiment indicate that the methoxy moieties are bound to molybdenum, not sulfur, while some adsorbed methanol is readily desorbed near or slightly above room temperature. Our calculations also suggest that the dissociation of methanol via O–H bond scission occurs at the defect site (sulfur vacancy), followed subsequently by formation of a weakly bound H2S species that promptly desorbs from the surface with creation of new sulfur vacancy. Photoluminescence and scanning tunneling microscopy show clear evidence of the sulfur vacancy creation on the MoS2 surface, after exposure to methanol.

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Section: Sulfur Vacancies and Induced Defectsmentioning

confidence: 52%

Methoxy Formation Induced Defects on MoS₂

et al. 2018

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“…Tobin et al 26 have reported XPS observations for methanol on polycrystalline Cu 2 0 pellets, however, they observed a decrease in the C Is binding energy of 1.4 e V on the transition from multilayer to adsorbed species. Their investigation also included methanol adsorption on ZnO and CuO, but only CU 2 0 caused a large decrease in the C Is binding energy.…”

Section: Discussion a Surface Intermediatesmentioning

confidence: 97%

“…On the basis of their XPS data and the observation of CU z (OCH 3 ) and CU 3 (CH 2 ) by SIMS of adsorbed methanol, Tobin et al 26 conclude that methoxy is formed with some c-o bond breaking on polycrystalline CU 2 O. While we see no evidence for C-O bond breaking in TDS or in our XPS measurements for CuzO(lll), we note that the CIs binding energy of 284.8 eV reported by Tobin et al 26 for adsorbed methanol at 300 K is identical to the value seen on our single crystals for hydrocarbon fragments.…”

Section: Discussion a Surface Intermediatesmentioning

confidence: 99%

Methanol decomposition on single crystal Cu₂O

Cox¹,

Schulz²

1990

Journal of Vacuum Science & Technology A: Vacuum, Surfaces,

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CH 3 0D decomposition has been studied over the stoichiometric, nonpolar (111) and polar, copper-terminated (100) surfaces ofCu 2 O. Thermal desorption studies for monolayer coverages of methanol at 90 K show similar conversions, but the product distributions vary significantly, indicating a structure sensitive reaction. The (111) surface shows a maximum selectivity for complete oxidative dehydrogenation to CO, while the ( 100) surface shows a maximum selectivity for partial dehydrogenation to CH 2 O. Thermal desorption spectroscopy (TDS) and x-ray photoelectron spectroscopy (XPS) data are consistent with a decomposition pathway which proceeds through a methoxy intermediate for both surfaces. Possible origins for the structure sensitivity are discussed.

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“…Kung et al have used the single-crystal surfaces of ZnO to probe the decomposition of CH 3 OH; they showed that the ZnO(0001) surface is the dominant surface for this reaction where the main decomposition product was CO under the conditions of their experiment. The mechanism of methanol decomposition on the binary catalyst and ZnO has been extensively studied. − A formate surface species is thought to be a decomposition intermediate on both the binary catalyst and ZnO. Its relevance to the MSR relates to the CO 2 hydrogenation reaction , and its possible role in the water-gas shift reaction, where the binary catalyst is extremely effective in this reaction.…”

Section: Introductionmentioning

confidence: 99%

“…The mechanism of methanol decomposition on the binary catalyst and ZnO has been extensively studied. [35][36][37][38][39][40][41][42][43][44][45] A formate surface species is thought to be a decomposition intermediate on both the binary catalyst and ZnO. Its relevance to the MSR relates to the CO 2 hydrogenation reaction 46,47 and its possible role in the watergas shift reaction, where the binary catalyst is extremely effective in this reaction.…”

Section: Introductionmentioning

confidence: 99%

Electron Spectroscopic Studies of CH₃OH Chemisorption on Cu₂O and ZnO Single-Crystal Surfaces: Methoxide Bonding and Reactivity Related to Methanol Synthesis

et al. 1998

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Adsorption of CH 3 OH on Cu 2 O(111), ZnO(0001), and ZnO(1010) has been investigated with XPS, NEXAFS, variable-energy photoelectron spectroscopy (PES), and SCF-XR Scattered Wave (SW) molecular orbital calculations. At high coverage (g25.0L), CH 3 OH is adsorbed as molecular multilayers on all three surfaces. At low temperatures (140 K) and coverage (0-0.6L), CH 3 OH is deprotonated to form chemisorbed methoxide on all of the surfaces investigated. Under these conditions the C1s XPS peak positions are 289.5, 290.2, and 290.2 eV below the vacuum level, respectively. Annealing the CH 3 O -/Cu 2 O(111) surface complex to 523 K produces no other surface intermediate. Alternatively, at temperatures above 220 K on the ZnO-(0001) surface methoxide decomposes to produce a formate intermediate that is stable at the methanol synthesis reaction temperature (523 K). No formate surface intermediate is observed on the ZnO (1010) surface. The NEXAFS spectrum of chemisorbed methoxide on the Cu 2 O(111) surface exhibits a σ* shape resonance at 294.8 eV giving a C-O bond length of 1.41 Å, a 0.02 Å contraction from the gas-phase methanol value. Methoxide chemisorbed on the ZnO(0001) surface is found to have a NEXAFS determined C-O bond length of 1.39 Å. These bond length contractions of the chemisorbed methoxide are due to the greater polarization of the C-O bond upon deprotonation and surface bonding. Variable-energy PES of the chemisorbed methoxide on Cu 2 O(111) gives a four peak valence band spectrum, with features at 20.0 (3a′), 15.6 (3a′′, 5a′′), 14.0 (σ CO ), and 10.0 eV (π O , σ O ), below the vacuum level. SCF-XR-SW molecular orbital calculations indicate that the bonding between the Cu(I) site and the CH 3 O -is dominated by the π O , σ O , and σ CO levels, with a calculated σ charge donation from these levels into the empty Cu 4s and Cu 4p z levels of 0.4e. As a consequence of deprotonation and σ donation the carbon atom in CH 3 O -is calculated to be 0.085e more positive than gas-phase methanol. The variable-energy PES of CH 3 O -on ZnO(0001) also exhibits four methoxide peaks, at 21.0 (5a′), 16.7 (2a′′, 5a′), 13.6 (σ CO ), and 9.8 eV (π O , σ O ). However, the σ donation is calculated to be less than half that found for CH 3 O -on the Cu(I) site (0.12e) and with 0.015 greater positive charge on the carbon atom, consistent with the relative binding energies of the C1s peaks and the greater C-O bond contraction. These results show that methoxide bonding to both Cu(I) and Zn(II) surface sites is dominated by σ donation. The electronic and geometric origins of the differences in bonding and reactivity among the Cu(I) and Zn(II) sites are addressed and provide insight into the molecular mechanism of the methanol synthesis reaction.

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X-ray photoelectron spectroscopy study of the interaction of alcohols with oxide surfaces

Cited by 11 publications

References 9 publications

Methoxy Formation Induced Defects on MoS₂

Methoxy Formation Induced Defects on MoS₂

Methanol decomposition on single crystal Cu₂O

Electron Spectroscopic Studies of CH₃OH Chemisorption on Cu₂O and ZnO Single-Crystal Surfaces: Methoxide Bonding and Reactivity Related to Methanol Synthesis

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X-ray photoelectron spectroscopy study of the interaction of alcohols with oxide surfaces

Cited by 11 publications

References 9 publications

Methoxy Formation Induced Defects on MoS2

Methoxy Formation Induced Defects on MoS2

Methanol decomposition on single crystal Cu2O

Electron Spectroscopic Studies of CH3OH Chemisorption on Cu2O and ZnO Single-Crystal Surfaces: Methoxide Bonding and Reactivity Related to Methanol Synthesis

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Product

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Methoxy Formation Induced Defects on MoS₂

Methoxy Formation Induced Defects on MoS₂

Methanol decomposition on single crystal Cu₂O

Electron Spectroscopic Studies of CH₃OH Chemisorption on Cu₂O and ZnO Single-Crystal Surfaces: Methoxide Bonding and Reactivity Related to Methanol Synthesis