LEED-I(V) Structure Analysis of the (7 × √3)rect SO₄ Phase on Ag(111): Precursor to the Active Species of the Ag-Catalyzed Ethylene Epoxidation

Abstract

According to a recently proposed mechanism, the silver-catalyzed industrial synthesis of ethylene oxide (EO) involves adsorbed SO 4 . The O atoms that are added to the ethylene molecules to give EO originate from SO 4 , which may solve the long-standing question about the active oxygen species in this reaction. Here, we report a low-energy electron diffraction structure analysis of an ordered phase of SO 4 on the Ag(111) surface, forming a (7 × √3)rect structure and containing the oxygen species that before had been spectroscopically identified on the active catalyst. Using I(V) data from a low-energy electron microscope and an input model from density functional theory, the complex structure could be solved. It contains SO 4 moieties on a reconstructed Ag(111) surface in which all four O atoms bind to Ag atoms. In the proposed ethylene epoxide reaction model, the structure represents the parent phase from which the active SO 4 phase is formed by a lifting of the reconstruction.

Formation and Behavior of Carbonates on Ag(110) in the Presence of Ethylene and Oxygen

“…A number of oxygen species have been proposed as candidates for the O elec species: adsorbed atomic oxygen, subsurface oxygen, ozone, and so on. Jones and co-workers reported from detailed experimental and theoretical investigations that the O elec species are covalently bound oxygen species. , Recently, it has been evidenced that adsorbed sulfate (SO 4 ) originating from impurity sulfur is one of the O elec species. , …”

“…20,21 Recently, it has been evidenced that adsorbed sulfate (SO 4 ) originating from impurity sulfur is one of the O elec species. 26,27 Carbonate (CO 3 ) is also a covalently bound oxygen species and gives an O 1s peak at around 530 eV when it is adsorbed on Ag surfaces. 28,29 The surface carbonate has not been considered as a candidate for the O elec species.…”

Active Site of Catalytic Ethene Epoxidation: Machine-Learning Global Pathway Sampling Rules Out the Metal Sites

“…With the recent advance in near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), the Schlögl group observed various oxygen species on Ag(111) at low O 2 pressures. The electrophilic O with the O 1s XPS signal at about 530 eV was suggested to be the O species for EO production as it appears along with the EO production. − These electrophilic O species were suggested to be from the impurity SO 4 , , and also argued to be from O 3 species . Due to the very low EO conversion and selectivity under low-pressure conditions, these understandings, such as on SO 4 impurities, should not be simply transferred to industrial EO production.…”

Low-Energy Electron Diffraction With Energy Invariant Carrier Wave Wavenumber Modulated by Exchange-Correlation Interaction

“…Finally, EEAS phase shifts are calculated, the qualifications of which we successfully test by recalculating four published LEED investigations. [8][9][10][11] We initiate the EEAS theory by constructing the carrier potential. The surface unit cell of the crystal is supposed to contain N ieq inequivalent atom types i = 1, 2, .…”

“…The result is expressed in terms of atomic XC potentials (8) where r and r s share the same radial point grid. A fitness factor f XC is multiplied into the right-hand member of eq.…”