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Bimetallic PdAu–KOac/SiO2 catalysts for vinyl acetate monomer (VAM) synthesis: Insights into deactivation under industrial conditions

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Abstract.
Structural changes of a commercial supported PdAu/SiO2 catalyst for VAM production aged under
laboratory and industrial conditions were studied by XRD, TEM/EDXS, XPS, ICP-OES and FTIR spectroscopy.
The fresh catalyst contains alloy particles with a wide range of Pd/Au ratios formed by agglomerated
crystallites of different sizes. The particles do not show any noticeable sintering during deactivation up
to 6 month use but undergo serious restructuring which is connected to the migration of Pd to the
particle surface during early stages on stream followed by formation of water-soluble Pd, most probably
Pd acetate, which is leached out of the catalyst upon extended time on stream. Considering earlier
studies which identified single Pd atoms isolated from each other by surrounding Au atoms as active
sites [M. Chen, D. Kumar, C.-W. Yi, D.W. Goodman, Science 310 (2005) 291], it is concluded that the
partial enrichment of Pd on the exposed noble metal alloy surface is a major reason for loss of activity
in the present type of catalyst. Additionally it is demonstrated that simultaneous calculation of crystallite
sizes and alloy compositions from the width and position of the XRD reflections, as usually performed,
can in principal, give information on dynamic changes in the noble metal phase but it is not a meaningful
approach for calculations both of crystallite size and composition in such inhomogeneous systems.

Keywords:
Alloy
Silica supported palladium gold catalysts
Deactivation
TEM/EDXS
XRD
XPS
FTIR

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2009

Deskripsi Fisik

Journal of Catalysis 262 (2009) 314–323

Bahasa

English

ISBN/ISSN

00219517

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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