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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
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Journal ArticleDOI
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.

81,985 citations


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

  • ...The calculations were performed with plane-wave density functional theory (DFT) using the Vienna ab initio simulation package (VASP) [27, 28]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

57,691 citations


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

  • ...Potentials within the projector augmented wave method (PAW) [29] and the generalized gradient approximation (GGA) with the Perdew-Wang 91 functional were used [30]....

    [...]

  • ...augmented wave method (PAW) [29] and the generalized gradient approximation (GGA) with the Perdew-Wang 91 functional were used [30]....

    [...]

Journal ArticleDOI
TL;DR: A detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set is presented in this article. But this is not a comparison of our algorithm with the one presented in this paper.

47,666 citations


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

  • ...The calculations were performed with plane-wave density functional theory (DFT) using the Vienna ab initio simulation package (VASP) [27, 28]....

    [...]

Journal ArticleDOI
TL;DR: A way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects as well as significant interconfigurational and interterm errors remain.
Abstract: Generalized gradient approximations (GGA's) seek to improve upon the accuracy of the local-spin-density (LSD) approximation in electronic-structure calculations. Perdew and Wang have developed a GGA based on real-space cutoff of the spurious long-range components of the second-order gradient expansion for the exchange-correlation hole. We have found that this density functional performs well in numerical tests for a variety of systems: (1) Total energies of 30 atoms are highly accurate. (2) Ionization energies and electron affinities are improved in a statistical sense, although significant interconfigurational and interterm errors remain. (3) Accurate atomization energies are found for seven hydrocarbon molecules, with a rms error per bond of 0.1 eV, compared with 0.7 eV for the LSD approximation and 2.4 eV for the Hartree-Fock approximation. (4) For atoms and molecules, there is a cancellation of error between density functionals for exchange and correlation, which is most striking whenever the Hartree-Fock result is furthest from experiment. (5) The surprising LSD underestimation of the lattice constants of Li and Na by 3--4 % is corrected, and the magnetic ground state of solid Fe is restored. (6) The work function, surface energy (neglecting the long-range contribution), and curvature energy of a metallic surface are all slightly reduced in comparison with LSD. Taking account of the positive long-range contribution, we find surface and curvature energies in good agreement with experimental or exact values. Finally, a way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects.

17,848 citations

Journal ArticleDOI
TL;DR: Density functional theory calculations explain copper's unique ability to convert CO2 into hydrocarbons, which may open up (photo-)electrochemical routes to fuels as mentioned in this paper, which may lead to new energy sources.
Abstract: Density functional theory calculations explain copper's unique ability to convert CO2 into hydrocarbons, which may open up (photo-)electrochemical routes to fuels.

2,420 citations


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

  • ...The catalytic activity of copper can in part be attributed to its electronic structure [7], but morphology, e....

    [...]

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.