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Journal ArticleDOI

Complex reactions on a convertible catalyst surface: A study of the S-O-Cu system

TL;DR: In this paper, the interaction of clean and partially oxidized Cu(110) with sulphur was studied by scanning tunneling microscopy and density functional theory calculations in the low-coverage range.
About: This article is published in Surface Science.The article was published on 2018-12-01 and is currently open access. It has received 3 citations till now.

Summary (2 min read)

Introduction:

  • Copper catalyzes a number of industrially important chemical reactions.
  • It is used for instance as desulfurization catalyst [1, 2], in the low-temperature stage of the water gas shift reaction[3, 4] and in catalytic CO2 reduction [5, 6].
  • The catalytic activity of copper can in part be attributed to its electronic structure [7], but morphology, e.g. number density and type of under-coordinated sites etc. is an important descriptor as well[8].
  • The Sulfur-Cu interaction has been addressed in several previous surface science studies, both experimentally [9-20] and theoretically [21-25].
  • The authors expected this to simplify the surface reactions in comparison to SO2 or H2S exposure, since disproportionation reactions and hydroxyl or water formation should be suppressed in this case.

Experiment and Theory:

  • The experiments have been carried out in a UHV system featuring a preparation chamber and a separate cryostate chamber housing the STM.
  • In the following, the authors give the sulfur dose in atoms per cm2.
  • The calculations were performed with plane-wave density functional theory (DFT) using the Vienna ab initio simulation package (VASP) [27, 28].
  • For bulk optimization, the lattice parameters were obtained by minimizing the total energy of the unit cell using a conjugated gradient algorithm to relax the ions and considering a set of 4×4×4 Monkhorst−Pack k-points to sample the Brillouin Zone. Cu(110) surfaces were modelled with slabs of five layer thicknesses.
  • A kinetic energy cutoff of 400 eV was employed for all the calculations.

Results and Discussion:

  • Three major changes occur at the Cu(110) surface upon S dosing.
  • More importantly, the 110 chains formed between the oxide stripes after SO2 exposure have a twofold periodicity and form occasionally a local p(2×2) configuration.
  • The 110 chains observed here are also located in the troughs between the top-layer copper rows and they are also mobile to some extent (see Fig. 3C, where the 110 chain seems to change position while the image is recorded).
  • Notably, the 110 chains form only in the presence of the Cu-O-Cu chains in the Cu surface oxide and the surface oxide stripes are consumed during the formation of the chains.
  • We first followed the suggestion of Alemozafar et al. [15, 17] trying to construct the chains from Cu and SO3 building units or from SO3 alone.the authors.the authors.

Summary:

  • Even under UHV conditions and moderate temperatures the interaction of Cu(110) with S gives rise to a variety of restructuring processes.
  • Long-bridge and hollow sites are both occupied with a slight preference for the latter.
  • Sx species terminated by Cu+ atoms within –O-Cu-O- chains.
  • Each of the observed structures might result in different reaction paths in a catalytic process.
  • This work was supported by the Office of Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, of the U.S. Department of Energy (DOE) under contract no.

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Citations
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Journal ArticleDOI
TL;DR: The LPDOS reveals that all of the considered interfaces exhibit metallic character and the stability of the interface is found to be related to the type of formed interfacial boundary and bond, the interfacial bond populations, and the interf facial bond numbers.
Abstract: The interfacial stability of copper/diamond directly affects its mechanical properties and thermal conductivity. The atomic structures and electronic properties of Cu/diamond and Cu/X/diamond interfaces have been identified to investigate the effect of interfacial additive X (X = Ni or N) on the low-index interfacial adhesion of copper/diamond composites. For unmodified composites, the interfacial stability decreases in the order of Cu(001)/diamond(001) > Cu(111)/diamond(111) > Cu(011)/diamond(011). The metallic interfacial additive Ni is found to enhance the Cu(011)/diamond(011) interfacial stability and exchange the interfacial stability sequence of (011) and (111) composites. The nonmetallic element N will promote the stability of Cu(111)/diamond(111) but not alter the stability order of the composites at different interface. To explain the origin of interfacial stability, a series of analyses on atomic structures and electronic properties have been carried out, including the identification of the type of formed interfacial boundary, the measurement of interfacial bond lengths, and the calculations of density of states, bond populations, and atomic charge. The stability of the interface is found to be related to the type of formed interfacial boundary and bond, the interfacial bond populations, and the interfacial bond numbers. The LPDOS reveals that all of the considered interfaces exhibit metallic character. The interfacial Ni additive is found to be an electron donor contributing the electrons to its bonded Cu and C atoms while interfacial N atom is an electron acceptor where it mainly accepts the electrons from its bonded Cu and C.

12 citations

Journal ArticleDOI
TL;DR: To the knowledge, this is the first example of an isolated linear sulfur-metal-sulfur complex, based upon density functional theory (DFT) and its comparison with experimental observations including bias dependence and separation between complexes.
Abstract: Adsorbed sulfur has been investigated on the Ag(110) surface at two different coverages, 0.02 and 0.25 monolayers. At the lower coverage, only sulfur adatoms are present. At the higher coverage, there are additional bright features which we identify as linear, independent AgS2 complexes. This identification is based upon density functional theory (DFT) and its comparison with experimental observations including bias dependence and separation between complexes. DFT also predicts the absence of AgS2 complexes at low coverage, and the development of AgS2 complexes around a coverage of 0.25 monolayers of sulfur, as is experimentally observed. To our knowledge, this is the first example of an isolated linear sulfur-metal-sulfur complex.

4 citations

01 Jan 2019
TL;DR: In this article, the authors present the CHARACTERISTICS of SULFUR ATOMS ADSORBED ON Ag(100), Ag(110), and Ag(111) as PROBED with SCANNING TUNNELING MICROSCOPY: EXPERIMENT AND THEORY.
Abstract: .................................................................................................................................. vi CHAPTER 1. GENERAL INTRODUCTION ............................................................................... 1 1. Motivation ............................................................................................................................... 1 1.1 Coinage metals ................................................................................................................ 2 1.2 Metal-sulfur complexes ..................................................................................................... 2 2. Experimental details and methods........................................................................................... 3 2.1 Equipment .......................................................................................................................... 3 2.2 Sample materials................................................................................................................ 6 2.3 Data analysis ...................................................................................................................... 9 3. Dissertation organization....................................................................................................... 10 4. References ............................................................................................................................. 11 CHAPTER 2. CHARACTERISTICS OF SULFUR ATOMS ADSORBED ON Ag(100), Ag(110), AND Ag(111) AS PROBED WITH SCANNING TUNNELING MICROSCOPY: EXPERIMENT AND THEORY .................................................................................................. 17 1. Abstract ................................................................................................................................. 17 2. Introduction ........................................................................................................................... 18 3. Methods ................................................................................................................................. 20 3.1 Experimental details ........................................................................................................ 20 3.2 Computational methodology ........................................................................................... 21 4. Experimental results .............................................................................................................. 27 4.1 S/Ag(100): STM results ................................................................................................... 27 4.2 S/Ag(110): STM results ................................................................................................... 30 5. DFT results ............................................................................................................................ 31 5.1. S/Ag(100): DFT results .................................................................................................. 32 5.2. S/Ag(110): DFT results .................................................................................................. 37 5.3. S/Ag(111): DFT results .................................................................................................. 38 6. Discussion ............................................................................................................................. 39 7. Conclusions ........................................................................................................................... 43 8. References ............................................................................................................................. 44 9. Acknowledgements ............................................................................................................... 48 10. Appendix 1: Coverage dependence of S/Ag(100)............................................................... 49 11. Appendix 2: STM tunneling conditions .............................................................................. 57

3 citations


Cites background from "Complex reactions on a convertible ..."

  • ...and Heegemann et al.(31) Sulfur coverage (θS) was taken as the ratio of adsorbed S atoms to the number of Ag atoms in the surface plane, and was determined by counting individual S atoms in a given area....

    [...]

  • ...Specifically, it has been observed that both oxygen and sulfur can strongly accelerate coarsening on many coinage metal surfaces.(26-31) While M3S3 is a strong candidate on the (111) surfaces, MS2 and MO2 are reasonable candidates for (110) and (100) surfaces....

    [...]

  • ...The sulfur source was an in situ electrochemical evaporator following the design by Wagner,29 which has been characterized in detail by Detry et al.30 and Heegemann et al.31 Sulfur coverage (θS) was taken as the ratio of adsorbed S atoms to the number of Ag atoms in the surface plane, and was determined by counting individual S atoms in a given area....

    [...]

References
More filters
Journal ArticleDOI
TL;DR: It is found that a copper nanoparticle covered electrode shows better selectivity towards hydrocarbons compared with the two other studied surfaces, an electropolished copper electrode and an argon sputtered copper electrode.
Abstract: This communication examines the effect of the surface morphology of polycrystalline copper on electroreduction of CO2. We find that a copper nanoparticle covered electrode shows better selectivity towards hydrocarbons compared with the two other studied surfaces, an electropolished copper electrode and an argon sputtered copper electrode. Density functional theory calculations provide insight into the surface morphology effect.

551 citations


Additional excerpts

  • ...is an important descriptor as well[8]....

    [...]

Journal ArticleDOI
TL;DR: He diffraction and scanning-tunneling-microscopy investigations on the growth or the Cu{110}-(2×1)O added-row structure reveal a novel phenomenon: the long-range spatial self-organization or two-dimensional islands.
Abstract: He diffraction and scanning-tunneling-microscopy investigations on the growth of the Cu{110}-(2\ifmmode\times\else\texttimes\fi{}1)O added-row structure reveal a novel phenomenon: the long-range spatial self-organization of two-dimensional islands. In a wide coverage range the anisotropic Cu-O islands arrange themselves in a striped periodic supergrating, with the stripes running along the 〈001〉 direction. The spacing of the supergrating depends on oxygen coverage and temperature and varies between 140 and 60 \AA{}.

332 citations


"Complex reactions on a convertible ..." refers background in this paper

  • ...5 ML corresponds to a uniform O(2×1)-Cu(110) surface [32]....

    [...]

Journal ArticleDOI
TL;DR: GC-FPD results showed that the pi-complexation sorbents selectively adsorbed highly substituted thiophenes, benzothiophene, and dibenzothiophene from diesel, which is not possible by using conventional hydrodesulfurization (HDS) reactors.
Abstract: Desulfurization of a commercial diesel fuel by vapor-phase ion exchange (VPIE) copper(I) faujasite zeolites was studied in a fixed-bed adsorber operated at ambient temperature and pressure. The zeolite adsorbed approximately five thiophenic molecules per unit cell. After treating 18 cm3 of fuel, the cumulative average sulfur concentration detected was 0.032 ppmw-S. GC−FPD results showed that the π-complexation sorbents selectively adsorbed highly substituted thiophenes, benzothiophenes, and dibenzothiophenes from diesel, which is not possible by using conventional hydrodesulfurization (HDS) reactors. The high sulfur selectivity and high sulfur capacity of the VPIE Cu(II)−zeolites were due to π-complexation.

318 citations


"Complex reactions on a convertible ..." refers methods in this paper

  • ...It is used for instance as desulfurization catalyst [1, 2], in the low-temperature stage of the water gas shift reaction[3, 4] and in (electro)catalytic CO2 reduction [5, 6]....

    [...]

Journal ArticleDOI
TL;DR: It is proposed that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy, which would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
Abstract: Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.

307 citations


"Complex reactions on a convertible ..." refers methods in this paper

  • ...It is used for instance as desulfurization catalyst [1, 2], in the low-temperature stage of the water gas shift reaction[3, 4] and in (electro)catalytic CO2 reduction [5, 6]....

    [...]

Journal ArticleDOI
TL;DR: This work reveals the essential first step for activating CO2 on a Cu surface, in particular, highlighting the importance of copper suboxide and the critical role of water, and provides fresh insights into how to design improved carbon dioxide reduction catalysts.
Abstract: A national priority is to convert CO2 into high-value chemical products such as liquid fuels. Because current electrocatalysts are not adequate, we aim to discover new catalysts by obtaining a detailed understanding of the initial steps of CO2 electroreduction on copper surfaces, the best current catalysts. Using ambient pressure X-ray photoelectron spectroscopy interpreted with quantum mechanical prediction of the structures and free energies, we show that the presence of a thin suboxide structure below the copper surface is essential to bind the CO2 in the physisorbed configuration at 298 K, and we show that this suboxide is essential for converting to the chemisorbed CO2 in the presence of water as the first step toward CO2 reduction products such as formate and CO. This optimum suboxide leads to both neutral and charged Cu surface sites, providing fresh insights into how to design improved carbon dioxide reduction catalysts.

245 citations

Frequently Asked Questions (1)
Q1. What are the contributions in "Complex reactions on a convertible catalyst surface: a study of the s-o-cu system" ?

In this paper, the authors revisited the interaction of pure S onto Cu ( 110 ) by scanning tunneling microscopy ( STM ) and found an extremely complex variety of surface reactions with mobile cluster formation, long distance mass transport, and most notably formation of different minority species.