Mathastasys

Catalysis Today 51 (1999) 289±299

Invited Review

Ole®n metathesis over supported rhenium oxide catalysts
Johannes C. Mol*
Institute of Molecular Chemistry, Faculty of Chemistry, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV,
Amsterdam, The Netherlands

Abstract
Supported rhenium oxide has attracted much attention as solid catalyst for the ole®n metathesis reactionbecause of
practical applications. These catalysts are composed of rhenium oxide dispersed over a high surface-area support, such as
alumina or silica±alumina. They have a high activity and high selectivity at temperatures of 0±1008C, while they bring about
the metathesis of functionally substituted ole®ns when promoted with a suitable organometallic compound. The interaction of
rhenium oxide withthe support has been studied by a number of characterisation techniques, resulting in a detailed picture of
the structure of the supported rhenium oxide. In this paper an overview is given of the current knowledge about rhenium-based
metathesis catalysts, in particular the industrially used Re2O7/Al2O3 catalyst. # 1999 Elsevier Science B.V. All rights
reserved.
Keywords: Alumina;Silica±alumina; Metathesis catalysts; Ole®n metathesis; Rhenium oxide

1.

Introduction

Ole®n metathesis is a conversion process that can
adapt the availability of ole®ns to the demand. In
addition, it offers a unique path for producing important intermediates and end products from ole®ns, for
example in the ®eld of speciality chemicals and
polymers [1]. For normal ole®ns, this catalytic reaction canbe represented by reaction (1):
2 RÀCHˆCHÀRH „ RÀCHˆCHÀR
‡RH ÀCHˆCHÀRH

(1)

where R and RH are alkyl groups or hydrogen. A simple
example is the metathesis of propene into ethene and
but-2-ene (RˆH, RH ˆCH3). This was the ®rst indus*Tel.: +31-20-525-6490; fax: +31-20-525-6456; e-mail:
jcmol@anorg.chem.uva.nl

trial application of ole®n metathesis as a means of
converting surpluspropene into useful products (the
Phillips Triole®n Process) [2]. In fact, many ole®nic
substrates can undergo metathesis in the presence of a
suitable catalyst, resulting in a wide variety of possible
products [1].
For acyclic ole®ns the metathesis process is essentially thermoneutral, a statistical distribution of reactant and product molecules eventually results. This
means that in the caseof reaction (1), if both metathesis products remain in the reaction medium, the
equilibrium mixture consists of reactant and products
in the approximate molar ratio of 2:1:1.
The metathesis reaction is catalysed both in heterogeneous and homogeneous phases. A wide variety of
transition metal compounds will catalyse the reaction
and the most successful are based on W, Mo and Re.
Heterogeneouscatalysts generally consist of a transi-

0920-5861/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 0 - 5 8 6 1 ( 9 9 ) 0 0 0 5 1 - 6

290

J.C. Mol / Catalysis Today 51 (1999) 289±299

tion metal oxide, or an organometallic complex,
deposited on a high-surface-area support (an inorganic
oxide). Examples are Re2O7/Al2O3, MoO3/SiO2,
WO3/SiO2, and(%-C4H7)4W/SiO2. Sometimes an
organometallic compound of a non-transition metal
is used as a promoter (cocatalyst), e.g. R4Sn
(Rˆalkyl), to increase the activity of the catalyst.
At the moment there are various commercial applications of ole®n metathesis. The Triole®n Process for
the production of high-purity ethene and but-2-ene
from propene started to operate in 1966. The reaction
takesplace in a ®xed-bed reactor with a WO3/SiO2
catalyst, doped with sodium to prevent double-bond
shift reactions, at a reaction temperature of 350±
4258C. A change in the economic climate and an
increase in demand for propene led to the closure
of the plant in 1972. Nowadays it is more attractive to
use the Triole®n Process in the reverse direction as
strong global demand for propene...