The Concept of Quasimolecular Electrophilic Oxygen in Ethylene Epoxidation over Silver
Full article
| Общее |
Language:
Английский,
Genre:
Full article,
Status:
Published,
Source type:
Translated
|
| Journal |
Kinetics and Catalysis
ISSN: 0023-1584
, E-ISSN: 1608-3210
|
| Output data |
Year: 1999,
Volume: 40,
Number: 5,
Pages: 653-672
Pages count
: 20
|
| Authors |
Boronin A.I.
,
Avdeev V.I.
,
Koshcheev S.V.
,
Murzakhmetov K.T.
,
Ruzankin S.F.
,
Zhidomirov G.M.
|
| Affiliations |
| 1 |
Boreskov Institute of Catalysis SB RAS
|
|
The ethylene-epoxidizing form of oxygen (O-ep) adsorbed on Ag(111) and Ag(110) single crystals and polycrystalline silver foil was examined by X-ray and UV photoelectron spectroscopy (XPS and UPS). It was shown that O-ep has a quasimolecular nature and exhibits high thermal stability (T > 700 K). The quantum-chemical study of associative forms of oxygen on the defects of the silver surface was carried out by the methods of density functional theory (DFT) in a cluster approximation. It was found that the associative (molecular) ozone-like species of oxygen on the surface of silver with cationic vacancies (V) is more stable than atomic oxygen (the energy difference is 44 kcal/mol). The identification of emission bands in UV photoelectron spectra performed on the basis of theoretical calculations of the ozone-like structure supported the quasimolecular nature of O-ep. The mechanisms known for ethylene epoxidation were analyzed. A new mechanism implying the participation of quasimolecular electrophilic oxygen O-ep in epoxidation was proposed. This mechanism describes the major regularities of epoxidation observed in the experiments on a regular basis.