L. M. Kustov et al.
art, including diverse Mo-, W- and Re-supported systems
based on different oxide carriers, with alumina being the
most abundant one [4]. Rhenium-containing heterogeneous
catalysts are typically most active among the heterogeneous
analogs. [5] The formation of active metathesis sites occurs
during the interaction of the olefinic substrate molecules
with the preactivated catalyst. It is generally supposed that
carbene Re complexes are the result of such an interaction
[5, 6]. However numerous spectroscopic studies, including
IR spectroscopy [2, 7–11], Raman spectroscopy [12–14],
ESR [15–17], Moessbauer spectroscopy [18, 19], XPS [20–
24], and XAFS [11, 25, 26] have not provided convincing
experimental support for this concept so far: the assumed
active reaction intermediates have not been detected using a
handful of the sensitive and informative methods. A few
publications are known where the authors tried to reveal the
nature and to postulate the structure of the metathesis
reactive species by analyzing the very initial products
formed at the first contact of the alkene with the catalyst [27,
28]. Nevertheless, the results obtained did not bring an
unequivocal answer either. Some authors consider 1-butene
formed during the metathesis of propene as a product of
isomerization of 2-butene [27]. However, such a migration
of the double bond is not quite agreeable with thermody-
namics of the system. The peculiar features of the conditions
and procedures used by different authors in studying the
reaction of alkene metathesis (olefin/Re ratio, addition of
certain organometallic activators, types of the reactors used
in the experiments) make the adequate comparison of the
literature data difficult.
It should be noted that a number of interesting publi-
cations appeared just recently on the subject. Analysis of
the literature data on terminal alkene metathesis [32–37]
reveals the general experimental peculiarities in the tests
aimed at establishing the composition and structure of the
products of interaction of a Cn terminal alkene with the
forming active sites:
•
At high initial olefin:Re ratios, the reaction mixture
contains, as a rule, only two main products—ethylene
and the expected C2n-2 metathesis product;
Other alkenes qualified as side products are observed at
reduced alkene:Re ratios.
•
The goal of the present study is to find new data about the
products of the primary interaction of terminal C5–C8
alkenes with the sites located at the activated surface of the
Re2O7–Al2O3 catalyst, with these products being formed at
the very initial instants of the contact of the terminal alkenes
with the active sites at different alkene:Re molar ratios.
2 Experimental
2.1 Catalysts and Materials
Re/alumina catalysts ([Re] = 3, 6, or 9 wt.%) were pre-
pared by incipient wetness impregnation of c-Al2O3
(Ryazan refinery, specific surface area 196 m2/g, size of the
particles 0.3–0.6 mm) with an aqueous solution of NH4
ReO4 (Aldrich), the impregnated samples were kept for 2 h
at 20 °C and dried 2 h at 150 °C. Before the catalytic tests,
the catalysts were calcined in a flow of dry air for 1.5 h at
520–550 °C and then cooled to room temperature in an Ar
flow. The catalytic tests were performed both in a plug-
flow reactor and in a batch reactor under stirring. The
reactor was loaded with 0.14–0.7 g of a catalyst both in the
flow and batch conditions. The reactions of 1-pentene,
1-hexene, 1-heptene, and 1-octene metathesis was studied
at room temperature using n-heptane as a diluent, except
for the case of 1-heptene metathesis when n-octane was
used as a solvent. All the hydrocarbons were preliminarily
purified by distillation in an Ar flow over metallic Na and
were kept over NaA molecular sieve calcined at 500 °C in
argon. The purity of alkenes was better than 99 %. The
molar ratio alkene:Re was varied from 0.2 to 100.
It was assumed that ethylene is not capable of activating
the catalyst in the metathesis reaction [2, 28], but other
authors reported on the formation of small amounts of
propene and 2-butene when ethylene was supplied to the
rhenium catalyst [29]. Only two metathesis reaction prod-
ucts were found upon the interaction of 1-heptene or
1-octenewith CsNO3–Re2O7–Al2O3 in a plug-flow reactor:
dodecene-6 or tetradecene-7, respectively, and ethylene
[30]. However in the case of 1-hexene, some amounts of
2-heptene and 4-nonene were detected in the metathesis
products in addition to decene-5. C5, C7, C8, C9, and C11
olefins were identified in metathesis of 1-hexene, beside the
main product, i.e. 5-decene, but the structure of these
olefins and their origin were not revealed [31]. The NH4
ReO4–Al2O3 catalyst calcined at 550 °C and c-irradiated in
a reducing atmosphere of CH4 or CO demonstrates a rather
high activity. The 1-hexene conversion is close to 60 %,
however, the authors failed to identify the presumably
active p- or Ren?=CH2 complexes. The conclusion drawn
by the authors is quite heuristic: the interaction of methane
with the surface species leads to the formation of a Re–CH3
moiety and further possible genesis of Re=CH2 by proton
transfer or elimination of a water molecule.
Deuterated hexene-1,1-D2-1-hexene was prepared using
the reaction:
LiAlD4
CH3ðCH2Þ3CH2COOCH3 À! CH3ðCH2Þ3CH2CD2OD
CH3ðCH2Þ3CH2CD2OD
þ ðCH3COÞ2O ! CH3ðCH2Þ3CH2CD2OOCCH3
123