In situ -DRIFTS study: Influence of surface acidity of rhenium-based catalysts in the metathesis of various olefins for propylene production

Article abstract of DOI:10.1039/c7ra06181a

Various olefins including 1- and 2-butene, 2-pentene, and ethylene were used as the reactants for producing propylene by self- and cross-metathesis reactions at 60 °C on supported Re-based catalysts (4 wt% Re). A similar surface structure of rhenium oxides in the form of isolated ReO₄ species was observed on Al₂O₃ and SiO₂-Al₂O₃ supported rhenium oxide catalysts. The catalysts, however, differed in terms of the types (Lewis/Bronsted) and strengths of the acidic sites, as revealed by ammonia temperature programmed desorption (NH₃-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) of NH₃ adsorption and thermodesorption results. Weak Lewis acidity, especially high ratios of Lewis acid bands at 1280 cm^-1/1622 cm^-1, led to high metathesis activity of the Re-based catalysts. The additional isomerization activity, however, required strong Bronsted acid sites. The product distribution from the various feeds depended largely on the size of the olefins, and not only on the acid properties of the catalysts. Re₂O₇/SiO₂-Al₂O₃ appeared to be a versatile catalyst for obtaining a high yield of propylene using either a single reactant (1- or 2-butene) or an ethylene mixed feed.

Full text of DOI:10.1039/c7ra06181a

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In situ-DRIFTS study: influence of surface acidity of
rhenium-based catalysts in the metathesis of
various olefins for propylene production
Cite this: RSC Adv., 2017, 7, 38659
Siriporn Vorakitkanvasin,a Weena Phongsawat,b Kongkiat Suriye,b
a
Piyasan Praserthdama and Joongjai Panpranot
*
Various olefins including 1- and 2-butene, 2-pentene, and ethylene were used as the reactants for
producing propylene by self- and cross-metathesis reactions at 60 ꢀC on supported Re-based catalysts
(4 wt% Re). A similar surface structure of rhenium oxides in the form of isolated ReO4 species was
observed on Al2O3 and SiO2–Al2O3 supported rhenium oxide catalysts. The catalysts, however, differed
in terms of the types (Lewis/Bronsted) and strengths of the acidic sites, as revealed by ammonia
temperature programmed desorption (NH3-TPD) and in situ diffuse reflectance infrared Fourier
transform spectroscopy (in situ DRIFTS) of NH3 adsorption and thermodesorption results. Weak Lewis
acidity, especially high ratios of Lewis acid bands at 1280 cmꢁ1/1622 cmꢁ1, led to high metathesis activity
of the Re-based catalysts. The additional isomerization activity, however, required strong Bronsted acid
sites. The product distribution from the various feeds depended largely on the size of the olefins, and not
only on the acid properties of the catalysts. Re2O7/SiO2–Al2O3 appeared to be a versatile catalyst for
obtaining a high yield of propylene using either a single reactant (1- or 2-butene) or an ethylene mixed feed.
Received 3rd June 2017
Accepted 26th July 2017
DOI: 10.1039/c7ra06181a
rsc.li/rsc-advances
oen been correlated to either Bronsted15 or Lewis acid sites.16
Bouchmella et al.17 used a nonhydrolytic sol–gel method
1. Introduction
(NHSG) to prepare highly active Re–Si–Al metathesis catalysts.
The most active NHSG catalyst in the cross-metathesis of
ethylene and butene to propylene was found on the catalysts
containing the highest amount of acidic sites with well
dispersed rhenium oxide species and high surface areas. A
recent study from our group11 showed that the higher acidic OH
group on the alumina support provided higher Lewis acid sites
necessary for the formation of the rhenium oxide active species
whereas the higher Bronsted acidity led to higher amount of
coke and C5+ products. In addition, the acid strength of Lewis
acid sites appeared to be another important factor determining
metathesis activity of supported Re2O7 catalysts.
Due to olens price uctuation, nowadays ethylene price is
getting higher than propylene,18 therefore, other reactants such
as butene and pentene are considered as alternative reactants
for metathesis reaction for propylene production. This work
aims to dene the catalyst properties especially the types (Lewis
or Bronsted) and the strength of the acidic sites on supported
rhenium oxide-based catalysts that could provide high yield of
propylene from different feedstocks. Production of propylene
via the metathesis of ethylene and 2-butene, ethylene and
2-pentene, pure 2-butene, pure 1-butene, and pure 2-pentene
was obtained over the low rhenium loading catalysts (4 wt% Re)
supported on silica and silica-alumina. The surface structures
of rhenium oxide species were determined by Raman micros-
copy. The types and the strength of acidity on the catalyst
Propylene is one of the major feedstocks in the petrochemical
industry used to produce various chemical intermediates and
polymers. Since propylene demand is expected to continue to
grow, on-purpose propylene production technology, such as
olen metathesis, is becoming an increasingly important reac-
tion for propylene supply.1 Metathesis of ethylene and 2-butene
to propylene is typically carried out over heterogeneous catalysts
based on tungsten oxide, molybdenum oxide, and rhenium
oxide.2–4 Rhenium oxide-based catalysts are of interest because
of their high activity and selectivity for olen metathesis at low
reaction temperatures.3 The typical supports used for prepara-
tion of highly dispersed rhenium oxide catalysts are alumina
and silica-alumina.3,5–7
Surface structures of the active isolated ReO4 species on
alumina have been identied by a number of studies based on
Raman, in situ Raman, and in situ IR spectroscopy.8–13 The
surface rhenium oxide species presented on silica-alumina
support were similar to those of alumina supported ones but
they were inactive on the Si–OH.14 Besides, the catalytic
performances of supported rhenium oxide-based catalysts have
aCenter of Excellence on Catalysis and Catalytic Reaction Engineering, Department of
Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok
10330, Thailand. E-mail: joongjai.p@chula.ac.th; Fax: +66-2218-6877; Tel: +66-
2218-6869
bSCG Chemicals Co., Ltd, 1Siam-cement Rd, Bang sue, Bangkok 10800, Thailand
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surface were identied by ammonia temperature programmed at a heating rate 10 ꢀC minꢁ1. The spectra were collected using
desorption (NH3-TPD) and in situ diffuse reectance infrared a MCT detector with a resolution of 4 cmꢁ1 and an accumula-
Fourier transform spectroscopy (in situ DRIFTS) of NH3 tion of 64 scans.
adsorption and thermodesorption.
2.3 Reaction test
The performances of supported rhenium oxide catalysts were
evaluated in the metathesis reactions using 2-pentene and
2. Experimental
2.1 Catalyst preparation
ethylene (2-C5 + C2), pure 2-pentene (2-C5), 2-butene and
Supported rhenium oxide catalysts with 4 wt% rhenium loading
ethylene (2-C4 + C2), pure 2-butene (2-C4) and pure 1-butene
were prepared by the incipient wetness impregnation method
(1-C4) as the reactants. For the cross metathesis reaction (mixed
using an aqueous solution of ammonium perrhenate
feeds), an excess of the molar ratio of ethylene : 2-pentene and
(NH4ReO4, Aldrich). The supports were impregnated several
ethylene : 2-butene was used for the reaction tests. The reac-
times to obtain the 4 wt% of rhenium loading. Between
tants were mixed with high purity nitrogen in order to have the
impregnation steps, the catalysts were held for 2 h at room
temperature and then dried at 110 ꢀC for 12 h. Aer the
composition of 6 vol% of reactants in nitrogen balance. The
reactions were carried out with a weight hourly space velocity
(WHSV) 1.7 hꢁ1 using 1.5 g catalyst in a xed-bed reactor (ID
impregnation step, the catalysts were calcined in dry air at
ꢀ
550 C for 8 h. For comparison purposes, commercial g-Al2O3
tube ¼ 15.8 mm) under atmospheric pressure. Prior to the
(Fluka) and SiO2–Al2O3 (Grade 135, Aldrich) were employed as
reaction, the catalyst was pretreated at 500 ꢀC for 1 h and then
the support for the preparation of Re2O7/g-Al2O3 and Re2O7/
cooled down to reaction temperature 60 ꢀC under nitrogen ow.
SiO2–Al2O3 catalysts. The catalysts were denoted as Re/Al and
Re/SiO2–Al2O3, respectively. The ANN support was prepared by
calcination of aluminium nitrate (Al(NO3)3$9H2O) under air at
550 ꢀC for 4 h. The rhenium catalyst on ANN was denoted as Re/
During the reaction, both reactants and products were analyzed
by an on-line Agilent 7820A gas chromatograph equipped with
a GS-Gaspro 113-4362 capillary column, 0.32 mm diameter and
60 m in length. The GC signals were processed by an EZChrom
ANN. According our previous paper, the use of alumina support
Elite integrated peak program integrator.
ꢀ
prepared from ANN calcined at 550 C led to the formation of
higher amount of the second rhenium oxide species and
improved catalytic performances in the metathesis of ethylene
and 2-pentene than the conventional Re2O7/g-Al2O3.11
3. Results and discussion
3.1 Catalyst characterization
The low loading Re oxide catalysts (4 wt% Re) in this study were
2.2 Catalyst characterization
prepared on three different supports including commercial
g-alumina (Re/Al), alumina obtained by calcination of
aluminium nitrate at 550 C (Re/ANN), and commercial silica-
alumina (Re/SiO2–Al2O3). All the catalysts exhibited similar
Raman bands at 970, 920 and 325 cmꢁ1 under ambient condi-
tions, which were assigned to ns(Re]O), nas(Re]O), and
The surface structures of rhenium oxide species were examined
by Raman microscopy under ambient conditions using a Sen-
terra Dispersive Raman microscopy equipped with the visible
laser at 532 nm and a TE-cooled CCD detector. The amount of
acidity on catalyst surface was measured by the NH3-TPD in
a quartz U-tube reactor. Firstly, approximately 0.10 g catalyst
sample was pretreated in a helium gas ow (25 mL minꢁ1) at
ꢀ
ꢀ
ꢀ
500 C for 1 h and then cooled down to 40 C. Aer that, the
sample was saturated with 15% NH3/He. The physisorbed
ammonia was desorbed in a helium gas ow for about 2 h.
Finally, the sample was heated up from 40 to 500 ꢀC at a heating
rate 10 ꢀC minꢁ1. The amount of ammonia in effluent was
recorded via TCD signal and analyzed with a Micromeritic
Chemisorb 2750 automated system (ChemiSoTPx soware).
The in situ diffuse reectance infrared Fourier transform spec-
troscopy (DRIFTS) of NH3 adsorption spectra were recorded
with a Bruker Vertex-70 FT-IR spectrometer equipped with
a Harrick Praying Mantis attachment for diffuse reectance
spectroscopy. About 20–25 mg of sample was placed in a Har-
rick cell, which were cooled by owing water. Then, the sample
ꢁ1
ꢀ
ꢀ
was dehydrated at a heating rate of 10 C min up to 500 C
and held for 1 h in a nitrogen gas ow. Aer that, the sample
ꢀ
was cooled to 60 C. Aer pretreatment procedure, the sample
was saturated with 15% NH3/He. Aer saturation, the phys-
isorbed ammonia was desorbed in a nitrogen gas ow about 2 h.
Fig. 1 The Raman spectra of: (a) Re/Al, (b) Re/ANN and (c) Re/SiO2–
Then, the sample was heated from 60 ꢀC temperature to 500 ꢀC Al2O3 under ambient condition.
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da,as(O–Re–O), respectively (Fig. 1). Such results indicate that the
surface rhenium oxide species on the prepared catalysts were
presented in the form of isolated ReO4 structure. Additional
strong Raman band at 815 cmꢁ1 of the Re/SiO2–Al2O3 was due to
the interference from the SiO2.8 A small band at around
600 cmꢁ1 was detected for the Re/ANN catalyst and was
assigned to the Al3+–oxygen symmetric stretching mode of the
[Al(OH2)6]3+ cation, which was resulted from the decomposition
of Al(NO3)3$9H2O precursor.19,20
The Re/Al, Re/ANN, and Re/SiO2–Al2O3 differed largely on the
nature of acidity (total amount, acid strength, and type of
acidity). As shown by the NH3-TPD proles in Fig. 2, the areas
under the NH3-TPD proles were in the order: Re/SiO2–Al2O3 >
Re/ANN > Re/Al. The Re/Al and the Re/ANN exhibited only weak
and medium acidity whereas the Re/SiO2–Al2O3 exhibited weak,
medium, and strong acidity. The peak area for weak acidity of
the Re/ANN was slightly higher than that of the Re/Al. The types
of surface acidity on these catalysts were elucidated by the in situ
DRIFTS of adsorbed NH3 and the results are shown in Fig. 3.
The bands at 1280 and 1622 cmꢁ1 assigned to adsorbed NH3 on
Lewis acid sites and the bands at 1470 and 1686 cmꢁ1 assigned
to NH4+ on Bronsted acid sites were detected for all the rhenium
oxide catalysts.11,21–23 Additional broad bands at 1240, 1405,
1506, 1570 cmꢁ1 were assigned to NH2 vibration.23–25 The
amounts of Bronsted and Lewis acid sites calculated from the
integrated peak areas based on the in situ DRIFTS results are
given in Table 1. The areas of Lewis acid sites at 1280 cmꢁ1 were
in the order: Re/SiO2–Al2O3 > Re/ANN > Re/Al whereas and
opposite trend was found for another Lewis acid sites at
1622 cmꢁ1. The area for the Bronsted acid sites at 1470 cmꢁ1 of
the Re/SiO2–Al2O3 catalyst was much larger than the Re/ANN
and Re/Al catalysts. Such results suggest that additional
strong acidity observed in the NH3-TPD proles for the Re/SiO2–
Al2O3 were strong Bronsted acid sites.
Fig. 3 The in situ DRIFTS substracted spectra of the chemisorbed
ammonia over the catalysts at 60 ꢀC.
Al2O3 started to decrease aer the temperature was raised to
above 250 ꢀC. In the present work, the fractions of weak and
strong Bronsted and Lewis acid sites were calculated from
subtracted peak areas of the in situ DRIFTS of NH3 thermode-
sorption results as summarized in Table 2. The peak areas in
the temperature range lower and above 250 ꢀC were assigned to
weak and strong acid sites, respectively. The fractions of weak
and strong Lewis acid sites on all the catalysts were not signif-
icantly different. The fraction of Bronsted acid sites on the Re/
ANN and Re/Al catalysts inclined to the weak acid while most
of the Bronsted acid sites on the Re/SiO2–Al2O3 catalyst was
classied as strong acid.
3.2 Reaction results
The relative strength of Bronsted and Lewis acid sites
present on the different catalysts was compared by the in situ
DRIFTS of thermodesorption of NH3 experiments (Fig. 4). It was
found that the bands corresponding to the Bronsted acid sites
on Re/ANN and Re/Al markedly decreased with increasing
temperature starting from 100 ꢀC whereas those of Re/SiO2–
The supported rhenium oxide catalysts with different acid prop-
erties were employed in the metathesis reaction using various
reactants including 2-pentene and ethylene (2-C5 + C2), pure
2-pentene (2-C5), 2-butene and ethylene (2-C4 + C2), pure 2-butene
(2-C4), and pure 1-butene (1-C4) at 60 ꢀC, 1 atm, and WHSV
1.7 hꢁ1. The yield of propylene of the catalysts with various
feedstocks aer 8 h reaction time are shown in Fig. 5. From the
results, it was found that for a given set of reactants, the SiO2–
Al2O3 supported Re2O7 catalysts gave much higher yield of
propylene than the Al2O3 supported ones. The yields of propylene
obtained from the Re/SiO2–Al2O3 were in order: 2-C4 + C2 > 2-C5 +
C2 > 1-C4 > 2-C4 > 2-C5. On the other hand, the Re/ANN and Re/Al
produced the highest propylene yield when 2-C5 and C2 were used
as the reactants under the reaction conditions used with the
Re/ANN exhibited higher propylene yield than the Re/Al. The
distribution of products obtained from various feedstocks over
the Re/SiO2–Al2O3, Re/ANN, and Re/Al are shown in Fig. 6. The
major reactions involved in the propylene production from
various feedstocks are shown below in eqn (1) to (9).
Primary metathesis reactions
Fig. 2 NH3-TPD profiles of different catalysts.
2-Butene + ethylene / 2(propylene)
(1)
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Table 1 The amounts of Bronsted and Lewis acid sites over the catalysts determined from the in situ DRIFTS of adsorbed NH3 at 60 ꢀC after
pretreatment
Bronsted acid (a.u.)
Lewis acid (a.u.)
Bronsted acid
Lewis acid (a.u.)
Lewis acid (1280
cmꢁ1)/(1622 cmꢁ1
)
Catalyst
(1682 cmꢁ1
)
(1622 cmꢁ1
)
(a.u.) (1470 cmꢁ1
)
(1280 cmꢁ1
)
Re/SiO2–Al2O3
Re/ANN
Re/Al
3.5
3.0
6.7
2.2
7.4
9.3
35.4
10.9
21.9
14.2
12.1
8.4
6.4
1.6
0.9
According to the stoichiometry of reaction, the mixed
ethylene and 2-butene provides the highest yield of propylene.
Using this feed, the Re/SiO2–Al2O3 exhibited high metathesis
activity for the cross-metathesis of ethylene and 2-butene
(eqn (1)), producing propylene as the major product with very
low amount of isomerization side reaction products. Surpris-
ingly, little propylene was produced when using the mixed
ethylene and 2-butene feedstocks on the Re/ANN and the Re/Al
catalysts. It is likely that only the self metathesis of 2-butene
occurred on the alumina-supported rhenium oxide catalysts
under the reaction conditions used.
2-Pentene + ethylene / propylene + 1-butene
2-Pentene + 2-pentene / 2-butene + 3-hexene
1-Butene + 1-butene / ethylene + 3-hexene
Isomerization reaction
(2)
(3)
(4)
1-Butene / 2-butene
(5)
(6)
2-Butene / 1-butene
Using mixed ethylene and 2-pentene as the feedstocks, the
major product selectivity obtained on the Re/SiO2–Al2O3 were
propylene and 2-butene with 1-butene, hexenes, and C7+ as the
minor products. On the contrary, on the Re/Al and the Re/ANN,
2-butene and hexenes were the main products with lower
selectivity to propylene and 1-butene. From the product distri-
bution results, it reveals that both cross metathesis of ethylene
Secondary metathesis reactions
2-Butene + 1-butene / propylene + 2-pentene
2-Pentene + 1-butene / propylene + 3-hexene
2(Hexenes) / 2-butene + C7+
(7)
(8)
(9)
Fig. 4 The in situ DRIFTS of NH3 adsorption spectra with increment of temperature: (a) Re/Al, (b) Re/ANN and (c) Re/SiO2–Al2O3.
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Table 2 The fraction of strength of the Bronsted and Lewis acid sites determined from the in situ DRIFTS of NH3 thermodesorption
BA (1682 cmꢁ1
Weak
)
LA (1622 cmꢁ1
Weak
)
BA (1470 cmꢁ1
Weak
)
LA (1280 cmꢁ1
)
Catalyst
Strong
Strong
Strong
Weak
Strong
Re/SiO2–Al2O3
Re/ANN
Re/Al
62
49
79
38
51
21
76
47
63
24
53
37
32
61
82
68
39
18
54
55
55
46
45
45
and 2-pentene (eqn (2)) and self-metathesis of 2-pentene cross metathesis of ethylene and 2-butene on the Re/SiO2–Al2O3
(eqn (3)) occurred on all the catalysts. However, as suggested by (eqn (1)). Although propylene could not be obtained using
Lwin et al.,13 the rate-determining step of metathesis reaction is 2-pentene as the single reactant, the catalysts were active
the rate of olen adsorption and the adsorption rate increases enough to catalyze 2-pentene self-metathesis reaction, yielding
¼
¼
¼
with the size of olens (i.e., C4 > C3 > C2 ). Thus, the self- 2-butene and 3-hexene (eqn (3)). And due to their much higher
metathesis of 2-pentene may occur more easily than the cross- activity, the Re/SiO2–Al2O3 exhibited additional side reactions
metathesis of ethylene and 2-pentene. In addition, due to the self-metathesis of hexene, forming C7+ products (eqn (9)).
higher isomerization activity of the Re/SiO2–Al2O3, 1-butene,
In summary, in order to produce propylene using pure
which was one of the products from the cross-metathesis of feedstocks such as 1-butene and 2-butene, the catalyst must
ethylene and 2-pentene, was isomerized to 2-butene (eqn (5)) exhibit high isomerization activity to convert 1-butene to
and further reacted with excess ethylene to produce augmen- 2-butene and 2-butene to 1-butene in addition to high metath-
tative propylene.
esis activity. Under the reaction conditions used, the isomeri-
Using 2-butene as the single feedstock, the Re/Al and Re/ zation of 1-butene to 2-butene occurred more easily than the
ANN were not active under the conditions used while the Re/ isomerization of 2-butene to 1-butene.
SiO2–Al2O3 produced propylene and 2-pentene as the main
products. It is indicated that 2-butene was isomerized to
1-butene (eqn (6)) and then reacted with 2-butene to produce
propylene and 2-pentene according to eqn (7) and (8). In the
case of using 1-butene as the single feedstock, the Re/Al and Re/
ANN were active for the self-metathesis of 1-butene, forming
ethylene and 3-hexene products (eqn (4)). Since propylene and
2-pentene were also observed, it is suggested that isomerization
of 1-butene to 2-butene (eqn (5)) occurred on these catalysts and
then further underwent the secondary metathesis reaction
between 1-butene and 2-butene (eqn (7)). It should be noted that
these catalysts were active enough to isomerization 1-butene to
2-butene but they could not isomerize 2-butene to 1-butene.
From the product distribution results, the Re/SiO2–Al2O3
appeared to be much more active than the Al2O3 supported
ones. Additional propylene production was obtained from the
3.3 Activity–acidity relationship
Due to the interference of the SiO2 bands in the Raman spectra,
it was difficult to quantitatively determine the amount of active
Re species on the Re/SiO2–Al2O3 in order to compare with the
Al2O3 supported ones. The catalyst performances in this study,
thus, were correlated to the acidity presented. Nevertheless, it
should be noted that acidity was arisen from both the rhenium
oxide species and the supports themselves. Based on the NH3-IR
results of the catalysts at 60 ꢀC aer pretreatment (Table 1),
which represented the surface species before reaction, it was
found that the Re/Al catalysts possessed signicant amount of
Bronsted acidity but they exhibited the lowest activity for both
isomerization and metathesis reactions. It is suggested that the
strength of acidity should be taken into account as well. From
the calculated fractions of weak and strong Bronsted and Lewis
acid sites based on the in situ DRIFTS of NH3 adsorption and
thermodesorption results, only the Re/SiO2–Al2O3 displayed
emphatically strong Bronsted acidity. The Re/Al contained
relatively high quantity of Bronsted acidity but most of them
was weak acid. From these results, it is suggested that the strong
Bronsted acidity was necessary for the isomerization of
2-butene to 1-butene. On the other hand, there were no differ-
ences in terms of the fractions of weak and strong Lewis acid
among the prepared catalysts. A number of studies in the
literature suggested that Lewis acidity plays signicant role in
metathesis reaction.11,21 The present work, however, revealed
various Lewis acid sites with different bond strengths on the
supported Re oxide catalysts. It was found that the higher ratios
of the weak Lewis acid bands at wavenumber 1280 cmꢁ1/1622
cmꢁ1 led to higher metathesis activity as observed in the order:
Re/SiO2–Al2O3 [ Re/ANN > Re/Al. From the reaction test
results, the Re/SiO2–Al2O3 showed high activity in all the
Fig. 5 The yield of propylene of the catalysts with various feedstocks
at 8 h reaction time.
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Fig. 6 Product distributions of various feedstocks over the catalysts: (a) pure 2-butene, (b) pure 1-butene, (c) pure 2-pentene, (d) mixed ethylene
and 2-pentene and (e) mixed ethylene and 2-butene.
reactions necessary for propylene production from various oxide catalysts has been related to the bridging of the silanol
feedstocks including isomerization of 2-butene to 1-butene groups (Si–OH) with the Al2O3 in the form of Si–OH–Al. These
and self- and cross-metathesis reactions, resulting in the bridging hydroxyl groups generate active rhenium sites while
highest yield of propylene. Therefore, to handle ethylene– silanol groups would generate inactive rhenium sites.3,5,26 The
propylene price uctuation, supported rhenium oxide-based high olens metathesis activity of SiO2–Al2O3 supported
catalysts should possess certain weak Lewis acid species rhenium oxides thus could not be generalized for any
(high ratio of weak Lewis acid bands at wavenumber SiO2–Al2O3 support since it was found to depend on many
1280 cmꢁ1/1622 cmꢁ1) and strong Bronsted acid sites. factors such as the SiO2–Al2O3 composition27 and the prepa-
Generally, the role of SiO2 in SiO2–Al2O3 supported rhenium ration method of SiO2–Al2O3.17,28
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J. Catal., 2013, 301, 233–241.
The low loading Re/SiO2–Al2O3 catalyst allows the production of
propylene from various feedstocks. Under the reaction condi-
tions used (60 ꢀC, 1 atm), the yield of propylene from different
feeds was in the order: 2-C4 + C2 > 2-C5 + C2 > 1-C4 > 2-C4 > 2-C5.
The high metathesis activity was correlated well to the presence
of high ratio of the Lewis acidity bands (1280 cmꢁ1/1622 cmꢁ1
)
in the form of weak Lewis acid. The strong Bronsted acidity,
however, was necessary for the isomerization side reactions
when using 2-butene or 1-butene as the single reactant in order
to produce propylene from the cross metathesis of 1-butene and
2-butene. The results provide easy selection of feedstocks for
propylene production when there is olens price uctuation.
Acknowledgements
The authors would like to thank the nancial supports from the
Grant for International Research Integration: Chula Research
Scholar, Ratchadaphiseksomphot Endowment Fund and the
Thailand Research Fund (BRG5780010 and IRG5780014). The
Royal Golden Jubilee Ph.D. scholarship for S. V. from the
Thailand Research Fund (TRF), SCG Chemicals, and the Office
of Higher Education Commission is also gratefully
acknowledged.
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