Enhanced metathesis activity of low loading Re2O7/Al2O3 catalysts for propylene production by using aluminum nitrate as Al2O3 precursor

Article abstract of DOI:10.1016/j.apcata.2016.01.008

A series of alumina supported Re₂O₇ catalysts (4 wt% Re loading) were prepared by using aluminium nitrate (ANN) calcined at different temperatures (400, 550, and 750 °C) as the supports and impregnated with ammonium perrhenate solution. Despite their lower pore volume and smaller average pore size, the catalyst performances in the metathesis of ethylene and 2-pentene in terms of 2-pentene conversion and propylene selectivity of all the Re₂O₇/ANN were much improved as compared to the commercial γ-Al₂O₃ supported one (Re₂O₇/Al-com) with the Re₂O₇/ANN-550 exhibited the best performances. Based on the in situ Infrared spectroscopy, the in situ Raman spectroscopy, and the in-situ IR spectroscopy of chemisorbed ammonia and thermodesorption results, the use of ANN as Al₂O₃ precursors provided higher acidic OH group and higher Lewis acid sites, which were necessary for the formation of the 2nd rhenium oxide active species especially for low Re loading. The higher Bronsted acidity on the Re₂O₇/Al-com, on the other hand, produced higher amount of coke and C₅₊ products. In addition, the acid strength of the Lewis acid sites appeared to be another important factor determining metathesis activity of the supported Re₂O₇ catalysts.

Full text of DOI:10.1016/j.apcata.2016.01.008

Accepted Manuscript
Title: Enhanced Metathesis Activity of low loading
Re O /Al O catalysts for Propylene Production by using
2
7
2
3
Aluminum Nitrate as Al O Precursor
2
3
Author: Siriporn Vorakitkanvasin Sirachaya Kunjara Na
Ayudhya Kongkiat Suriye Piyasan Praserthdam Joongjai
Panpranot
PII:
S0926-860X(16)30008-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2016.01.008
APCATA 15723
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
30-9-2015
26-11-2015
11-1-2016
Please cite this article as: Siriporn Vorakitkanvasin, Sirachaya Kunjara Na Ayudhya,
Kongkiat Suriye, Piyasan Praserthdam, Joongjai Panpranot, Enhanced Metathesis
Activity of low loading Re2O7/Al2O3 catalysts for Propylene Production by
using Aluminum Nitrate as Al2O3 Precursor, Applied Catalysis A, General
http://dx.doi.org/10.1016/j.apcata.2016.01.008
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Enhanced Metathesis Activity of low loading Re
2
O
7
/Al
2
3
O catalysts for Propylene
Production by using Aluminum Nitrate as Al
2
O
3
Precursor
a
b
b
Siriporn Vorakitkanvasin , Sirachaya Kunjara Na Ayudhya , Kongkiat Suriye , Piyasan
a
a,*
Praserthdam , and Joongjai Panpranot
aCenter of Excellence on Catalysis and Catalytic Reaction Engineering,
Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University,
Bangkok 10330, Thailand
bSCG Chemicals Co., Ltd. 1Siam-cement Rd, Bang sue, Bangkok 10800, Thailand
Date: November 26, 2015
Submitted to: Applied Catalysis A. General
*To whom all correspondence should be addressed.
Tel.: 66-2218-6869 Fax: 66-2218-6877 E-mail: joongjai.p@chula.ac.th
1

Graphical Abstract
Primary metathesis
Isomerization
1-C4=
2-C4=
Secondary metathesis
L
B
Lewis acid sites
Brönsted acid sites
=
=
C3= + 1-C4=
=
=
C3=
C + C
2-C
4
+ C
2
2
5
B
L
L
L
L
L
L
L
B
ReO -
Catalyst surface
4
1st rhenium
oxide species
2nd rhenium
oxide species
ReO -
Isomerization
4
2
-C4=
Primary metathesis
OH-
OH-
=
=
2
C3= + 1-C =
4
ReO -
OH-
C + C
5
4
OH-
neutral
OH-
OH-
OH-
Secondary metathesis
OH-
acidic
basic
Self metathesis
3
-C6= + 2-C =
4
γ-Al O
2
3
Reaction pathway
-
Aluminium nitrate
γ-Al O (high acidic OH )
2
3
O
5
50 C

Highlights
.
.
.
.
Metathesis of ethylene and 2-pentene over low loading Re
2
O
3
/Al
2
O
3
( 4 wt%).
o
Al(NO)
3
precursor calcined at 550 C provided higher acidic -OH than the Al-com.
nd
The 2 rhenium oxide active species could be formed at relatively low Re loading.
Amount and strength of the Lewis acid sites play important role in metathesis.
.
Bronsted acidity was responsible for the formation of coke and C5+ products.
2

Abstract
A series of alumina supported Re
2
O
7
catalysts (4 wt% Re loading) were prepared by
o
using aluminium nitrate (ANN) calcined at different temperatures (400, 550, and 750 C) as
the supports and impregnated with ammonium perrhenate solution. Despite their lower pore
volume and smaller average pore size, the catalyst performances in the metathesis of ethylene
and 2-pentene in terms of 2-pentene conversion and propylene selectivity of all the
Re
Re
situ Infrared spectroscopy, the in situ Raman spectroscopy, and the in-situ IR spectroscopy of
chemisorbed ammonia and thermodesorption results, the use of ANN as Al precursors
2
O
7
/ANN were much improved as compared to the commercial -Al
2
3
O supported one
(
2
O
7
/Al-com) with the Re /ANN-550 exhibited the best performances. Based on the in
2
O
7
2
O
3
provided higher acidic OH group and higher Lewis acid sites, which were necessary for the
nd
formation of the 2 rhenium oxide active species especially for low Re loading. The higher
Bronsted acidity on the Re
and C5+ products. In addition, the acid strength of the Lewis acid sites appeared to be another
important factor determining metathesis activity of the supported Re catalysts.
2
O
7
/Al-com, on the other hand, produced higher amount of coke
2
O
7
Keywords: metathesis; propylene production; rhenium; aluminium nitrate; 2-pentene; Lewis
acidity
3

1
. Introduction
Propylene is one of the most important basic chemicals in petrochemical industry,
which is used in the production of polypropylene, acrylonitrile, acrylic acid, acrolein,
propylene oxide, glycols, plasticizer oxo alcohols, cumene, isopropyl alcohol, and acetone.
The growth in propylene production is primarily driven by the industry demand for
polypropylene and is expected to be about 5.7% per year in the near future [1].
The majority of propylene is produced as a byproduct of petroleum refineries and
olefin plant steam crackers. Due to the possibility of a supply/demand imbalance, the
catalytic, on-purpose technology for propylene production such as metathesis and propane
dehydrogenation has gained more interest recently. Supported rhenium oxide-based catalyst
o
is known to be active for olefin metathesis at low temperatures (i.e., 25 C), whereas,
molybdenum oxide- or tungsten oxide-based catalysts require much higher reaction
o
temperatures (100-500 C) [2-4]. The catalytic performance of Re
2
O
7
/γ-Al
2
3
O with low
rhenium loading can be further improved by addition of the third metal oxides such as MoO
, or WO . The MoO -, V -, or WO -modified low rhenium loading catalysts were
reported to be active and highly selective for the metathesis of methyl oleate. Moreover, their
price is lower than the Re /Al -SnR catalyst for the same reaction [5]. The use of mixed
3
,
V
2
O
5
3
3
2
O
5
3
2
O
7
2
O
3
4
supports such as silica-alumina and alumina-borate also improved the performances of Re-
based catalysts in the metathesis reaction because of their high acidity and appropriate
amount of Bronsted acidity compared to alumina-supported ones [6]. The alumina-borate-
supported rhenium oxide catalysts were tested in both the metathesis of functionalized
alkenes [7] and the metathesis of propylene [8]. The Re
2
O
7
/Al
2
O
3
-B
2
O
3
catalysts showed high
activity and selectivity than the conventional Re /A1
2
O
7
2
O
3
catalyst and was attributed to the
increase in support acidity and their strong Bronsted acidity. Andreini et al. [9], treated the
catalyst based on silica-alumina with hexamethyldisilazane in order to remove surface OH
4

groups and concluded that the acid-base function of these catalysts (mainly their Bronsted
acidity) is involved in the reaction. In our recent studies, a relatively high propylene yield
(
88%) was obtained under mild reaction conditions using the unconventional feed of ethylene
and 2-pentene over SiO -Al supported Re -based catalysts [4, 10-12]. The catalyst
performances were found to be influenced by the properties of the SiO -Al supports,
which were modified by the SiO -Al compositions [11] and/or the preparation methods
12]. The treating of Al with phosphate also resulted in more acidic surface, belonging to
2
2
O
3
2
O
7
2
2
O
3
2
2
O
3
[
2
O
3
acidic phosphorus-bonded OH groups [13]. At low Re loadings, these supports have also
-
reacted with the ReO
4
ions resulting in active metathesis sites.
In the present work, the catalytic properties of Re
2
O
7
/γ-Al
2
3
O in the metathesis of
ethylene and 2-pentene were enhanced by using aluminium nitrate supports calcined at
different calcination temperatures. The catalyst performances were correlated with the
formation of well-dispersed active rhenium species. The catalyst properties were further
characterized by N physisorption, X-ray diffraction (XRD), inductively‐coupled plasma
2
optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM), in situ
Infrared spectroscopy (in situ IR), and in situ Raman spectroscopy (in situ Raman), and in
situ IR spectroscopy of chemisorbed ammonia and thermodesorption (in situ NH -IR)
3
2
. Experimental
2
.1 Catalyst preparation
The catalyst supports were prepared by calcination of Al(NO
3
)
3
·9H O under air at
2
o
4
00, 550, and 750 C for 4 h and were denoted as ANN-400, ANN-550, and ANN-750,
respectively. The supports were impregnated with an aqueous solution of ammonium
perrhenate (NH
4
ReO
4
, Aldrich) several times to obtain the 4 wt% of rhenium loading.
5

Between impregnation steps the catalyst was held for 2 h at room temperature and then dried
o
o
at 110 C for 12 h. After the impregnation step, the catalyst was calcined in dry air at 550 C
for 8 h. For comparison purposes, a commercial γ-Al (Fluka) was also used for
preparation of 4 wt% Re /γ-Al catalyst. The catalyst was denoted as Re /Al-com.
2
O
3
2
O
7
2
O
3
2
O
7
2
.2 Catalyst characterization
The specific surface area, the pore volume, and the pore size of the supports and the catalysts
o
were measured by N
2
physisorption at -196 C using a Micromeritics ASAP 2020 automated
system. The specific surface area was calculated according to Brunauer-Emmett-Teller (BET)
method and the pore volume and pore size were determined from Barret-Joyner-Halenda
(BJH) method. The XRD patterns were collected using a SIEMENS D5000 X-ray
diffractometer with Cu K
α
radiation and Ni filter. The scans were recorded in the 2 range of
o
o
2
0-80 using a step size of 0.04 . The actual metal loading for each catalyst were measured by
by ICP-OES on a Perkin Elmer Optima 2100DV instrument. The sample was performed by
o
digestion with a mixture of hydrofluoric and nitric acids at 60 C. The in situ IR spectra were
acquired with a Thermo Nicolet 8700 FT-IR spectrometer equipped with a Harrick Praying
Mantis attachment for diffuse reflectance spectroscopy. The sample was placed in a Harrick
cell, which were cooled by flowing water. Then the sample was heated from room
o
o
temperature to 500 C at a heating rate 10 C/min and holding the temperature for 1 h. After
o
that the sample was cooled to 60 C. The spectra were collected using a DTGS detector with
a resolution of 4 cm-1 and an accumulation of 72 scans. The collection of the initial IR gas
phase background was performed by placing a reflective mirror in the laser path. For in-situ
IR spectroscopy of chemisorbed ammonia and thermodesorption, after pretreatment
procedure the sample was saturated with 15% NH /He. After saturation, the physisorbed
3
ammonia was desorbed in a helium gas flow about 1 h. Then the sample was heated from 60
6

o
o
o
C temperature to 500 C at a heating rate 10 C/min. The spectra were collected every
minute. For in-situ Raman spectroscopy, the Raman spectra of catalysts were collected by a
high resolution Raman spectrometer system (Horiba-Jobin Yvon Labram-IR) equipped with
the visible laser at 532 nm. The LabSpec 5 software was used to operate the experiment and
collect the Raman spectra. The laser calibration was performed with a silica slide at 520.7
-1
cm . The sample was loaded into the same cell used for IR measurements. The same
pretreatment procedure as in the IR experiments was followed. The dehydrated Raman
o
spectra of catalysts were collected at 60 C. The TEM micrographs were obtained using a
JEOL JEM-2100 transmission electron microscope with an accelerating voltage of 120 kV.
The amount of coke was examined by the temperature programmed oxidation (TPO). The
spent catalyst was in a quartz tube under the 1% O /He flow and heated with the heat rate of
2
5 oC/min until the temperature reached 900 C, analyzed by GC-8AIT.
o
2
.3 Reaction test
The catalyst performances were tested in the gas-phase metathesis reaction between
ethylene and 2-pentene with the molar ratio of ethylene: 2-pentene 3:1, weight hourly space
-1
velocity (WHSV) 5.33 h , and 1 g catalyst in a fixed-bed reactor (ID tube = 7.5 mm) under
o
atmospheric pressure. In a typical run, the catalyst was pretreated at 500 C for 1 h and then
o
cooled down to reaction temperature at 60 C under nitrogen flow. During the reaction, the
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 Elite integrated peak program integrator.
The conversion of the limiting reactant (2-pentene), the selectivity of products, and
the yield of products were calculated by the following equations:
7

Amount of 2-pentene in feed - amount of 2-pentene remained in product
Amount of 2-pentene in feed
2
-Pentene conversion %ꢀ=
× 100
Amount of component i in products
Selectivity of component i %ꢀ=
× 100
Amount of total products
Amount of component i in products
Amount of total products
Yield of component i (%) = 2-Pentene conversion ×
3
. Results and discussion
3
.1 Catalyst characterization
The physical properties of the various Al
2
O
3
supported Re
2
7
O catalysts are shown in
2
Table 1. The surface area of the Re
Re
pore size of the Re
2
O
7
/Al-com was 136 m /g whereas those of the
2
2
O
7
/ANN catalysts were ranging between 130-170 m /g. The pore volume and the average
2
O
7
/Al-com were slightly higher than those of the Re
2
7
O /ANN catalysts.
The actual Re contents were ranged between 3.70-3.94 wt% which were closed to the
expected values (4 wt%). Figure 1 shows the XRD patterns of all the prepared catalysts. The
o
o
o
o
o
major XRD peaks at 37 , 39 , 46 , 61 and 67 were attribtued to the γ-phase alumina [14].
The characteristic peaks corresponding to Re crystals were absent on all the catalysts
2
O
7
because of the low amount of rhenium loading and the Re
2
7
O crystals could be volatile at the
o
calcination temperature above 300 C [3, 15, 16]. However, from the ICP results, the values
of actual Re loadings on all the catalysts were closed to the desired amount, suggesting that
most of the Re were well dispersed on the alumina support.
The TEM images of 4Re/Al-com, 4Re/ANN-400, 4Re/ANN-550, and 4Re/ANN-750
are shown in Fig. 2. The rhenium oxides or rhenium metal species could not be distinguished
from the alumina supports. The TEM results were consistent with the XRD results, in which
the diffraction patterns corresponding to Re
2
O
7
crystals were not detected. Such results
8

suggested that non-crystalline rhenium oxide species were well dispersed on the alumina
surface in the form of isolated active Re species [17].
According to previous studies [13, 18-21], the surface OH groups of alumina support
consists of five different types: two types with basic characteristic, one neutral type, and two
types with acidic characteristic. Normally, during the catalyst preparation, the reaction
between ions and surface OH groups of support occurs and then ReO -
ions turn into
4
rhenium oxide on the support. The properties of these rhenium oxides depend on the type of
-
OH groups that they replace. At low rhenium oxide loading, ReO
4
ions first replace the most
-
basic OH groups, resulting in inactive sites, whereas ReO
4
ions that replace more acidic OH
groups at higher loading results in active sites for metathesis reaction.
The in-situ IR spectra representing the OH stretching of the dehydrated Al
2
O
3
-1
-1
-1
supports are shown in Figure 2. The IR bands at 3775 cm , 3730 cm , and 3690 cm
corresponded to the basic, neutral, and acidic OH groups, respectively [22]. It was found that
-1
the Al-com support showed much higher peak area at 3775 cm , compared to the ANN
supports. This indicates that most ReO -
O /Al-com probably reacted with
4
ions of the Re
2
7
-1
basic OH groups and turned into inactive sites. On contrary, the IR band at 3775 cm was not
-
detected on the ANN-550 support. Therefore, the ReO
4
ions of the Re
2
7
O /ANN mostly
replaced the acidic OH groups, forming metathesis active sites.
The influence of rhenium loading on the formation of surface rhenium oxide
structures under dehydrated conditions was studied by Vuurman et al. [23]. The first species
were observed at low Re loading by the in situ Raman spectra at 1002, 970, 879 and 340 cm-
1,
The second species were observed at high Re loading at 1012, 976, 890 and 340 cm Raman
bands, which were specified to  (Re=O), as(Re=O),  (Re−O−Al), and δ(O−Re−O),
which were assigned to 
s
(Re=O), as(Re=O), 
s
(Re−O−Al), and δ(O−Re−O), respectively.
-1
s
s
respectively [23, 24]. At low rhenium loading the catalytic performace was extremely low
9

due to the presence of the first species. When Re
the second species were formed and as a consequence, the catalytic performaces increased
20].
2
7
O loading was increased to about 6 wt%,
[
The in situ Raman spectra of the different alumina supported Re
dehydrated condition at 60 °C are shown in Figure 3. The Re /Al-com showed the Raman
bands at 1001, 967, 882 and 339 cm , which were attributed to the first surface rhenium
oxide species whereas all the Re /ANN exhibited the Raman bands at 1009, 976, 890 and
2
O
7
catalysts under
2
O
7
-1
2
O
7
-1
3
38 cm , which were attribtued to the second surface rhenium oxide species.
Based on the in situ IR and the in situ Raman data under dehydrated conditions at 60
oC results, it is revealed that the rhenium oxides on the Al-com support were the first surface
rhenium oxide species,which were formed by the reaction of ReO -
ions and basic OH group,
4
-
while the rhenium oxide on ANN support was a result of the reaction of ReO
4
ions with more
acidic OH group forming the second surface rhenium oxide species. It should be noted that
the active rhenium oxide species can be formed on the ANN supports at relatively low Re
loading (4% Re metal) compared to those reported in the literature [23].
The Lewis/Bronsted nature of surface acidity of all the catalysts was further
investigated by the in situ IR spectroscopy of ammonia adsorption. The in-situ IR substracted
spectra of the chemisorbed ammonia over the catalysts are shown in Figure 4. The presence
-1
of Lewis acid sites was confirmed by the bands at 1621 and 1280 cm whereas the Bronsted
-1
acid sites were detected by the IR bands at 1682 and 1460 cm [25]. The amount of
Lewis/Bronsted acidity, which were calculated from the integrated peak areas, are given in
Table 1. It appears that Lewis acidity on the Re
2
O
7
/ANN catalysts were much higher than
/Al-com. Moreover, the Bronsted acidity of the Re /ANN catalysts was
/Al-com. The strength of Lewis/Bronsted acidity was also considered
those on the Re
2
O
7
2
O
7
lower than the Re
2
O
7
by the in-situ IR spectroscopy and ammonia thermodesorption. The in-situ IR spectra of
1
0

o
chemisorbed ammonia results over the Re
. The peaks at 1621, 1460 and 1280 cm were observed on the Re
Re /ANN-750 catalysts whereas there was no signal for the Re /ANN-550 catalyst.
Such results suggest that the Lewis and Bronsted acidity of the Re /ANN-550 catalyst was
weaker than those on the Re /ANN-400 and Re /ANN-750 catalysts.
2
7
O /ANN catalysts at 250 C are shown in Figure
-1
5
2
7
O /ANN-400 and
2
O
7
2
O
7
2
O
7
2
O
7
2
O
7
3
.2 Reaction results
The metathesis activity of the different alumina-supported Re
2
7
O catalysts was
evaluated in the gas-phase metathesis of ethylene and 2-pentene at 60 °C. Figure 6 shows the
conversion of 2-pentene as a function of time-on-stream during the 11 h reaction time. The 2-
pentene conversion of the Re
Re /ANN-550 showed the highest yield of propylene. The metathesis activity results
corresponded well with the in situ IR and the in situ Raman results that the ANN supported
Re catalysts contained higher amount of the more active second surface rhenium oxide
2
O
7
/ANN was much higher than the Re
2
O
7
/Al-com with the
2
O
7
2
O
7
species, which were formed in the presence of more acidic OH groups.
The metathesis of 2-pentene and ethylene produces propylene and 1-butene as by
products. In this study, excess ethylene in the feed was used because it has been found that 1-
butene product from the metathesis of 2-pentene and ethylene can isomerize to 2-butenes and
react with excess ethylene, resulting in more propylene formation [4]. Figure 7 shows the
product distribution at 1 and 11 h reaction time while the product distribution of the prepared
catalysts as a function of reaction time is also shown in Figure 8. It can be seen that the
propylene yield obtained over the Re
43 wt% based on the complete conversion of 2-pentene) whereas the propylene yield of the
Re /Al-com catalyst remained close to its stoichiometric values. In addition, the 1-butene
yield decreased with increasing 2-butene yield, suggesting that 1-butene isomerized to 2-
2
O
7
/ANN exceeded the theoretical stoichiometric value
(
2
O
7
1
1

butenes and reacted with excess ethylene to produce additional propylene. From the in-situ IR
of chemisorbed ammonia results, the Re /ANN catalysts contained much higher Lewis
acidity than the Re /Al-com. It is suggested that Lewis acidity plays an important role in
2
O
7
2
O
7
metathesis activity. Such results were in good agreement with Schekler-Nahama et al., in
which Lewis acidity was reported to be the key for the metathesis reaction [25]. Comparing
the streght of acidity among the Re
Re /ANN-550 seemed to be appropriate for the reaction so that it exhibited the best
catalytic performance.
2
7
O /ANN catalysts, the weaker acidity of the
2
O
7
The amount of coke deposited on the spent catalysts after the metathesis reaction of
ethylene and 2-pentene at 60 °C for 11 h was determined by TPO and the results are shown in
Figure 9. The TPO profiles of the Al-com and ANN supported rhenium catalysts after being
used in the reaction as a function of CO
under the TPO profiles were directly correlated with the amount of coke deposit. It is
demonstrated that the total amounts of coke deposit increased in the order: Re /ANN-550
Re /ANN-750 < Re /ANN-400 < Re /Al-com. From the metathesis reaction and
coke formation results, it can be further suggested that the presence of Bronsted acidity on the
Re /Al-com facilitated oligomerisation and/or polymerisation side-reactions [25]. The
yield of C5+ and coke formation over the Re /Al-com was higher than on the Re /ANN.
2
formation are displayed in Figure 10. The areas
2
O
7
<
2
O
7
2
O
7
2
O
7
2
O
7
2
O
7
2
O
7
In addition, the two main peaks of coke burning in the TPO profiles (Figure 10) can be
assigned to coke deposited on different locations. The low temperature peak was attributed to
the oxidation of coke deposited on the metal species whereas the higher temperature peak
corresponded to coke deposited on acid sites of the support, mostly Bronsted acid sites [26].
It was found that the Re
sites of the alumina support than the Re
it appears that the major of coke deposit was on the metal species, leading to blocking of the
2
O
7
/Al-com contained higher amount of coke deposited on the acid
2
O
7
/ANN catalysts. For all the Re /ANN catalysts,
2
O
7
1
2

active sites. Therefore, the Re/Al-com was found to be more stable compared to the ANN-
supported ones.
4
. Conclusions
The catalytic activity in the metathesis of ethylene and 2-pentene over Re
2
O
7
/Al
2
O
3
o
catalysts was significantly enhanced by using aluminium nitrate calcined at 550 C as the
nd
support. The catalyst performances were correlated well with the presence of the 2 surface
rhenium oxide species. As revealed by the in situ IR, the in situ Raman, and the in-situ IR
spectroscopy of chemisorbed ammonia and thermodesorption results, the use of aluminium
nitrate as the Al
Lewis acidity, compared to the commercial -Al
of active rhenium oxide species. Among the various Re
50 showed the best catalyst performances in terms of 2-pentene conversion and selectivity
2
O
3
precursor provided acidic OH group rather than basic OH and higher
, which were important for the formation
/ANN catalysts, the Re /ANN-
2
O
3
2
O
7
2
O
7
5
to propylene. On the other hand, the higher Bronsted acidity observed on the Re
2
7
O /Al-com
was responsible for higher coke formation and C5+ selectivity.
Acknowledgements
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 gratefully
acknowledged. Financial support from the Grant for International Research Integration:
Chula Research Scholar, Ratchadaphiseksomphot Endowment Fund is gratefully
acknowledged. The authors also would like to acknowledge the Operando Molecular
Spectroscopy and Catalysis Laboratory at Lehigh University for the Raman and IR
spectroscopy results and analysis.
1
3

References
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1
5

(1)
(
2)
3)
(
(4)
2
0
30
40
50
60
70
80
2
-Theta (degree)
Figure 1 XRD patterns of the prepared catalysts: (1) 4Re/Al-com, (2) 4Re/ANN-400, (3)
Re/ANN-550 and (4) 4Re/ANN-750
4
1
6

1
7

3
730
3
690
3
775
(1)
(2)
(
3)
4)
(
3
800
3700
3600
-
1
Wavenumber (cm )
Figure 2 In situ IR spectra in the OH stretching region of supports under dehydrated
condition at 60°C: (1) Al-com, (2) ANN-400, (3) ANN-550 and (4) ANN-750
1
8

s(Re=O)
1
001
as(Re=O)
67
s(Re-O-Al)

(O-Re-O)
39
9
3
8
82
4
Re/Al-com
1
009
4
Re/ANN-400
4
Re/ANN-550
Re/ANN-750
4
1
200
1000
800
600
400
200
-1
Raman shift cm
Figure 3 In situ Raman spectra of catalysts under dehydrated condition at 60 °C
1
9

Lewis
Lewis
Bronsted
Bronsted
(
4)
(
3)
2)
(
(
1)
1
800
1600
1400
1200
-1
Wavenumber (cm )
o
Figure 4 In situ IR substracted spectra of chemisorbed ammonia over the catalysts at 60 C:
(1) 4Re/Al-com, (2) 4Re/ANN-400, (3) 4Re/ANN-550 and (4) 4Re/ANN-750
2
0

Lewis
Lewis
4
Re/ANN-750
Re/ANN-550
4
4
Re/ANN-400
1
700
1600
1500
1400
1300
1200
-1
Wavenumber (cm )
o
Figure 5 In situ IR substracted spectra of chemisorbed ammonia over the catalysts at 250 C
2
1

1
00
9
8
7
6
5
0
0
0
0
0
4
4
4
4
Re/Al-com
Re/ANN-400
Re/ANN-550
Re/ANN-750
0
2
4
6
8
10
12
Time (hours)
Figure 6 The 2-pentene conversion of the prepared catalysts over the metathesis reaction as a
function of reaction time
2
2

6
5
4
3
2
1
0
0
0
0
0
0
0
60
50
40
30
20
10
0
(a)
(b)
4
4
4
4
Re/Al-com
Re/ANN-400
Re/ANN-550
Re/ANN-750
propylene 1-butene t-2-butene c-2-butene
C5+
propylene 1-butene t-2-butene c-2-butene
C5+
Figure 7 Product distributions of different catalysts at (a) 1 h and (b) 11 h reaction time
2
3

Figure 8 The product distribution of the prepared catalysts over the metathesis reaction as a
function of reaction time ◊: 4Re/Al-com, ∆: 4Re/ANN-400, □: 4Re/ANN-550, ○: 4Re/ANN-
7
50
2
4

0
0
0
0
.6
.4
.2
.0
4
Re/Al-com 4Re/ANN-400 4Re/ANN-550 4Re/ANN-750
Figure 9 The amount of coke deposit on the spent catalysts
2
5

Figure 10 Temperature programmed oxidation (TPO) patterns of the spent catalysts
2
6

Table 1 The physicochemical properties of the supported rhenium oxide catalysts
Normalized amount of
Actual Re-metal loadinga Surface Area Pore volume Avg. Pore size
Support
Brönsted acidb Lewis acidb
(wt% Re)
(m²/g)
(cm³/g)
(nm)
2
2
(µmol/m )
(µmol/m )
4
4
4
Re/Al-com
3.94
3.94
3.73
3.70
136
150
130
170
0.22
0.18
0.15
0.17
4.35
3.51
3.50
3.35
21.52
10.97
11.42
12.20
8.00
22.18
21.07
17.83
Re/ANN-400
Re/ANN-550
Re/ANN-750
4
a
Based on the ICP-OES results.
b
Based on the in-situ IR spectroscopy of chemisorbed ammonia results.
2
7