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Chlorine and Caesium Promotion of Silver Ethylene Epoxidation Catalysts
Author(s) -
Özbek M. Oluş,
Önal Işik,
van Santen Rutger A.
Publication year - 2013
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201200690
Subject(s) - selectivity , catalysis , ethylene , chemistry , oxygen , adsorption , ethylene oxide , oxide , inorganic chemistry , caesium , photochemistry , aldehyde , organic chemistry , copolymer , polymer
Abstract The effect of co‐adsorbed Cs and Cl on the selectivity of ethylene epoxidation was studied computationally on an Ag 2 O(0 0 1) surface model. Cl blocks the oxygen vacant sites and prevents oxometallacycle (OMC) formation, which is responsible for aldehyde formation on the oxide surface. Cl also prevents unfavorable surface reconstruction induced by co‐adsorption of ethylene. It also has a positive effect on the stability of selective oxygen species when Cs co‐exists. Introduction of Cs on the Ag 2 O(0 0 1) surface results in the formation of CsO x ‐type of complexes in the absence of Cl. Whereas oxygen atom adsorption energies are increased, Cs also introduces surface oxygen vacancies that reduce catalyst selectivity. Cs and Cl co‐exist on the surface in the form of CsCl x O y complexes. Under reaction conditions, these complexes stabilize the oxide surface and reduce oxygen surface vacancy formation, which results in higher ethylene oxide (EO) selectivity.