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Towards an understanding of promoter action in heterogeneously catalyzed ethene epoxidation: Why chlorine is the best halogen

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Abstract.
A detailed theoretical study is presented focusing on the role of halogens as promoters for the silvercatalyzed partial oxidation of ethylene to the epoxide (EO) and, in particular, aiming to understand why Cl is best. The study is based on periodic density functional theory calculations carried out for the reaction between ethene and atomic oxygen on the Ag(111) surface, taken as a model catalyst, in the presence
of coadsorbed halogens. It is found that the presence of co-adsorbed halogens significantly decreases
the energy barrier from the oxametallacycle intermediate (OMME) to EO relative to that from the same
OMME intermediate to the undesired acetaldehyde (AC) product. However, co-adsorbed halogens are also
found to increase the desorption energy of the reaction products. We present compelling evidence that
the superior activity of Cl is due to the additional presence of subsurface Cl that favors EO formation
with respect to AC but at the same time facilitates EO desorption, hampering further transformations.
The results provide a signpost for the rational design of catalyst promoters.

Keywords:
Ethene epoxidation
Silver catalyst
Halogen promoters
Selectivity

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2008

Deskripsi Fisik

Journal of Catalysis 260 (2008) 380–383

Bahasa

English

ISBN/ISSN

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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