Effect of pretreatment atmosphere of WOx/SiO2 catalysts on metathesis of ethylene and 2-butene to propylene

Article abstract of DOI:10.1039/c8ra01093e

The effect of a gas pretreatment atmosphere (pure N₂, pure H₂ and mixed H₂/N₂) on the metathesis reaction between ethylene and 2-butene to propylene over calcined and non-calcined WO₃/SiO₂ catalysts was investigated. The non-calcined catalysts exhibited higher activity than the calcined catalysts under different gas pretreatment atmospheres. The non-calcined catalyst with the use of pure H₂ pretreatment showed the highest catalytic performances. As revealed by various characterization results from N₂ physisorption, XRD, XPS, TEM, SEM-EDX, UV-Vis, Raman, H₂-TPR, and NH₃-TPD techniques, the WO_2.83 phase occurring from the H₂ pretreatment of the non-calcined catalyst played an important role on the high activity of the catalyst. In addition, better tungsten dispersion, higher isolated surface tetrahedral tungsten oxide species, and W⁵⁺ species were obtained on the H₂-Treated non-calcined WO₃/SiO₂ catalyst.

Full text of DOI:10.1039/c8ra01093e

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Effect of pretreatment atmosphere of WO /SiO
x
2
catalysts on metathesis of ethylene and 2-butene
to propylene
Cite this: RSC Adv., 2018, 8, 11693
Krittidech Gayapan, Sirada Sripinun, Joongjai Panpranot,
and Suttichai Assabumrungrat
Piyasan Praserthdam
*
The effect of a gas pretreatment atmosphere (pure N
reaction between ethylene and 2-butene to propylene over calcined and non-calcined WO
catalysts was investigated. The non-calcined catalysts exhibited higher activity than the calcined catalysts
under different gas pretreatment atmospheres. The non-calcined catalyst with the use of pure H
pretreatment showed the highest catalytic performances. As revealed by various characterization results
from N physisorption, XRD, XPS, TEM, SEM-EDX, UV-Vis, Raman, H -TPR, and NH -TPD techniques, the
WO2.83 phase occurring from the H pretreatment of the non-calcined catalyst played an important role
2
, pure H
2
and mixed H
2
/N
2
) on the metathesis
3
/SiO
2
2
2
2
3
Received 4th February 2018
Accepted 19th March 2018
2
on the high activity of the catalyst. In addition, better tungsten dispersion, higher isolated surface
5+
DOI: 10.1039/c8ra01093e
2
tetrahedral tungsten oxide species, and W species were obtained on the H -treated non-calcined
rsc.li/rsc-advances
3 2
WO /SiO catalyst.
over WO
species on the WO
Light olens have played an important role in the petrochem- active sites to propylene product. Many factors affect catalytic
3
/SiO
2
catalysts involves the formation of W–carbene
1
. Introduction
3
surface, followed by metathesis on these
9
1
0
ical industry. In the past, the most important raw material in activity including the content of tungsten oxide loading,
11
the petrochemical industry was ethylene and the second one oxidation state of tungsten species, conditions of prepara-
1
12–14
8,15
was propylene. However, nowadays propylene demand has tion,
properties of support,
and pretreatment condi-
Experimental studies have reported that the
16,17
increased since it is used for production of organic chemicals tions.
such as polypropylene, acrylonitrile, propylene oxide, alcohol tetrahedral tungsten oxide species are the active sites for
2
2,18
and acrylic acid. Propylene production can be obtained from metathesis and that WO
3
crystals are not active in metathesis
3
several processes such as catalytic and thermal crackers,
methanol to olens, propane dehydrogenation and olen surface.
metathesis. At present, the metathesis of light olens has
and catalyst sites should be contained in the amorphous
4
5
19
6
In order to improve performance of supported WO /SiO
x 2
become of particular interest because it could regulate the catalysts in metathesis reaction, the effect of pretreatment has
stocks of light olens (ethylene, propylene, and butene) upon been investigated. Conventional pretreatment in most studies
7
20,21
the market demand at low energy and environmental cost.
Supported tungsten oxide catalysts (especially, WO /SiO ) are Choung and Weller showed that some intermediate non-
involves high temperature calcination and inert gas purging.
22
3
2
the most widely used catalysts because of their better resistance stoichiometric tungsten oxide (WO3ꢀx) occurring from N
2
or H
2
to poisoning, lower price, better stability and easy regenera- gas pretreatments on WO
tion. The metathesis of ethylene and 2-butene to propylene on species for propylene self-metathesis. Westhoff and Moulijn
3
/SiO
2
catalysts was the most active
8
23
WO
3
/SiO
2
catalyst has been commercialized as the olen found that the slight reduction by H
conversion technology (OCT). The reaction takes place in exhibited activity in propylene self-metathesis better than
2
over WO
3
/SiO
2
catalysts
2
a xed-bed reactor at a temperature > 553 K and pressure of 3.0– calcined sample and the sample intermediate between WO
3
and
3
.5 MPa. Since then, many studies have been carried out to WO2.95 (formed by hydrogen treatment) exhibited the maximum
24
develop WO /SiO catalysts with improved performances. The activity. Zaki et al. reported that the formation of WO
3
catalysts
mechanism of the metathesis reaction of ethylene and 2-butene intermediates in the forms of WO2.96, WO2.9, and WO2.72
oxidation states could be adjusted by controlling the H
3
2
2
17
reduction conditions. Liu et al. studied effect of gas pretreat-
Center of Excellence in Catalysis and Catalytic Reaction Engineering, Department of
Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok
ments including N , mixed H /N , H and air over the mixed
2
2
2
2
catalysts between MgO and WO /SiO catalysts on metathesis
3
2
1
2
0330, Thailand. E-mail: suttichai.a@chula.ac.th; Fax: +66-2218-6877; Tel: +66-
218-6868
reaction of 1-butene and ethylene. The results showed that H
2
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 11693–11704 | 11693

View Article Online
RSC Advances
Paper
content for pretreatment caused the catalyst transformed to the nitrogen gas. The reaction condition was kept at 623 K with
ꢀ
1
tetragonal WO and partially reduced W2.92, which were active a WHSV of 0.52 h . The operating pressure was varied at 0.1
3
phases for the reaction.
and 2.1 MPa. The catalysts were denoted as W-cal-fresh and W-
From the previous studies mentioned above, all the noncal-fresh for calcined and non-calcined fresh catalysts, but
researchers used the air-calcined catalysts for further pretreat- catalysts with different gas pretreatments were denoted as W-
ment or experimental study. To the best of our knowledge, the cal-xxx and W-noncal-xxx represented the calcined and non-
effect of pretreatment atmosphere on the non-calcined catalysts calcined catalyst where “xxx” represents the gas pretreatment
has not been reported yet. In addition, most studies reported in including N
the literatures performed the reaction tests under atmospheric pure H and mixed H
The products from the reaction tests were analyzed by using
2
, H
2
and H
2
2 2
/N for gas pretreatment with pure N ,
2
2
/N
2
, respectively.
10–14,25
pressure and high temperature around 723 K,
while study
on high pressure operation was scarce. In this research, the an online gas chromatography (Agilent 7820A), which was
calcined and non-calcined WO /SiO catalysts for metathesis of equipped with a ame ionization detector (FID). The reaction
3
2
26,27
ethylene and 2-butene to propylene were studied by using the pathways were illustrated in Scheme 1 in details.
various gas pretreatments (pure N , pure H and mixed H /N ). reaction was the metathesis of ethylene and 2-butene to
The main
2
2
2
2
The catalytic activity was performed at the temperature of 623 K produce propylene as the conventional reaction for propylene
under low and high pressure conditions at 0.1 and 2.1 MPa. The production in industrial plants and the side reactions included
properties of pretreated catalysts were characterized by the isomerization, cross-metathesis and self-metathesis reaction as
Brunauer–Emmett–Teller (BET) method of N physisorption, X- shown in this scheme. The 2-butene conversion, product
2
ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), selectivity and yields were determined by the following
transmission electron microscopy (TEM), scanning electron equations:
microscopy (SEM) together with energy dispersive X-ray (EDX)
spectroscopy, diffuse reectance ultraviolet-visible spectra (UV-
Vis DRS), Raman microscopy, temperature-programmed
2
-Butene conversion ¼ ((amount of trans- and cis-2-butene in
feed ꢀ amount of trans- and cis-2-butene in products)/amount
of trans- and cis-2-butene in feed) ꢁ 100
reduction of hydrogen (H
programmed desorption of ammonia (NH
2
-TPR) and temperature-
-TPD) to investigate
3
Product selectivity ¼ (amount of any product/amount of total
product) ꢁ 100
the relationship of activity, crystallinity, dispersion and inter-
action of tungsten on the support, and acidity of the catalysts.
Product yield ¼ (2-butene conversion ꢁ product selectivity)/100
2. Experimental
2.1 Catalyst preparation
The 9 wt% WO /SiO catalysts were prepared by wetness
3
2
2.3 Catalyst characterization
impregnation using an aqueous solution of ammonium meta-
tungstate hydrate (Aldrich, 99.9%) over silica gel (Davisil Grade
XRD patterns of the catalysts were determined by using a D8
Advance of Bruker AXS using Ni-lter Cu K radiation in the 2q
a
646, 40–60 mesh, supplied by Aldrich). The impregnated sample
ꢂ
ꢂ
range of 20 to 80 . For phase composition identication
purposes, the diffraction patterns were matched with standard
diffraction data les. The BET surface areas, pore volumes and
pore sizes were obtained using Micromeritics Chemisorbs 2750
with nitrogen adsorption studies. The surface structures of
tungsten oxide species were examined by Raman microscopy
under ambient conditions using a Senterra Dispersive Raman
Microscopy (Bruker Optics) equipped with the laser wavelength
was dried at room temperature for 2 h and subsequently in an
oven at 383 K for 24 h. The catalysts were grouped into two types
as the calcined and non-calcined catalysts before pretreatment
and reaction testing. For calcined catalysts, the samples were
calcined at temperature of 823 K in air for 8 h and then the
catalysts were packed in a xed bed reactor for further
pretreatment and reaction. For non-calcined catalysts, the
samples aer drying were packed in a xed bed reactor for
further pretreatment and reaction.
2
.2 Pretreatment atmosphere and catalytic evaluation
WO /SiO catalyst of 3 g was packed at the center of the stainless
steel tubular xed-bed reactor (internal diameter ¼ 19.05 mm).
The catalyst was heated to 773 K by a furnace under N gas at
a ow rate of 30 ml min and held at 773 K for 1 h. Aer that,
3
2
2
ꢀ
1
pretreatment gas (pure N
a total ow rate of 30 cm min was fed to the reactor for 1 h.
2
, pure H
2
or mixed 1 : 1 H
2
/N
2
) at
3
ꢀ1
The reactor was then cooled down to operating temperature of
6
23 K under N gas at the same ow rate. The reaction was
2
started by introducing a feed containing 4% 2-butene (2% cis-2-
butene and 2% trans-2-butene) and 8% ethylene balanced in Scheme 1 Reaction pathways of ethylene and 2-butene.
11694 | RSC Adv., 2018, 8, 11693–11704
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
at 532 nm and a TE-cooled CCD detector. The UV-Vis DRS was and ethylene to produce propylene with different gas pretreat-
ꢀ1
used to investigate surface structure of tungsten oxide species. ments. The reaction conditions were operated at 623 K, 0.52 h
The catalyst samples were recorded on Lambda 650 spectro- of WHSV at two pressures (0.1 and 2.1 MPa) with the reactant of
photometer in the range between 200 and 800 nm. The XPS was 2% cis-2-butene, 2% trans-2-butene and 8% ethylene in N2
carried out using an AMICUS photoelectron spectrometer balanced, and the reaction tests were terminated aer 12 h.
equipped with an Mg K
KRATOS VISION2 soware. XPS elemental spectra were non-calcined catalysts with different gas pretreatment atmo-
acquired with 0.1 eV energy step at a pass energy of 75 eV. spheres for operation of 1 h. The 2-butene conversion at
a
X-ray as a primary excitation and Table 1 shows the activity and product yields of the calcined and
The TEM images were used to investigate the particle 0.1 MPa for the calcined catalysts with different gas pretreat-
morphology and lattice spacing of the samples, which was ments was around 12–23%, while those of the non-calcined
conducted on a JEOL JEM-2010 microscope equipped with catalysts were around 22–24%. For operation at 2.1 MPa, the
a LaB electron gun in the voltage range of 200 kV. TEM samples 2-butene conversion for the calcined and non-calcined catalysts
6
were prepared by dispersing in ethanol by sonication and a few were around 24–26% and 48–69%, respectively. These results
drops of suspension onto a carbon-coated copper grid followed showed that the non-calcined catalysts exhibited the 2-butene
by solvent evaporation in air at room temperature. The tungsten conversion higher than the calcined catalysts. Considering the
distribution over the silica support were investigated by SEM effect of gas pretreatment at pressure of 0.1 MPa, the increase of
(Hitachi S3400N) equipped with EDX (EDAX Apollo-X).
2
H content in the gas pretreatment was likely to increase 2-
H -TPR was performed to investigate the reducibility of butene conversion in both calcined and non-calcined catalysts.
2
catalysts by a Micromeritics Chemisorb 2750 automated system. At pressure of 2.1 MPa, the difference in 2-butene conversion
The catalyst was loaded into a quartz U-tube reactor. Prior to H2- with increasing H2 content between the calcined and non-
TPR experiment, the sample was pretreated under N
2 2
ow at 773 calcined catalysts was more pronounced. The pure H
K for 1 h and then cooled to 313 K. Subsequently, the catalyst pretreatment of the non-calcined catalyst exhibited the highest
ꢀ
1
was reduced by using 10% H
2
/Ar with a ow rate of 25 ml min
2-butene conversion. Considering the product yields, when
ꢀ1
at a heating rate of 5 K min from 313 to 1173 K. The amount of comparing the propylene and 1-butene yields, the non-calcined
hydrogen uptake was determined by measuring the areas of the catalysts also exhibited the propylene yield higher than the
reduction proles on the thermal conductivity detector (TCD).
calcined catalysts, while the 1-butene yield for the non-calcined
NH -TPD was used to determine the acidity of catalysts by catalysts was lower than the calcined catalysts at both pressures.
3
+
a Micromeritics Chemisorb 2750 automated system. The cata- In addition, when considering isobutene and C ] yields, the
5
lyst packed in a quartz U-tube reactor was pretreated with a He non-calcined catalysts were higher than the calcined catalysts.
ꢀ
1

ow rate of 25 ml min at 773 K for 1 h and then cooled down Comparing among different gas pretreatments, the use of pure
to 313 K. Aer that, it was exposed to a 15% NH /He mixed gas for pretreatment increased the propylene yield for both 0.1
with a ow rate of 25 ml min for 30 min. Subsequently, the and 2.1 MPa pressures, while the yields of side reaction prod-
3
H
2
ꢀ
1
ꢀ1
+
sample was purged with a He gas stream (25 ml min ) for 1 h ucts such as 1-butene, isobutene, and C
5
] were slightly
and the temperature was increased linearly with a rate of 5 decreased, except for the pure N pretreatment of the calcined
2
ꢀ
1
K min to 773 K. The desorbed ammonia was detected by using catalyst that the side product yields were lower than the others.
the TCD.
The 2-butene conversion and product yields at operation of
.1 and 2.1 MPa as a function of time on stream for 12 h were
0
presented in Fig. 1 and 2, respectively. For operation at 0.1 MPa
as shown in Fig. 1, the 2-butene conversion was unchanged
among the different gas pretreatments for both calcined and
non-calcined catalysts and rather constant through 12 h time-
3
. Results and discussion
3.1 Catalytic performances of the calcined and non-calcined
catalysts
The metathesis performance was measured for the calcined and on-stream, except the case of N pretreatment of the calcined
2
non-calcined catalysts in metathesis of 2-butene (trans- and cis-)
Table 1 2-Butene conversion and product yields of the calcined and non-calcined WO
atmospheres at pressure of 0.1 and 2.1 MPa
3
/SiO
2
catalysts under different gas pretreatment
a
2-Butene conversion (%)
Yield (%) at 0.1 MPa
Yield (%) at 2.1 MPa
Catalysts
0.1 MPa
2.1 MPa
Propylene
1-Butene
Isobutene
C
5
+]
Propylene
1-Butene
Isobutene
C
5
+]
W-noncal-N
W-noncal-H
W-noncal-H
2
22.3
23.4
23.7
12.4
22.7
22.8
48.4
66.6
68.8
24.6
45.3
46.2
0.71
1.10
1.31
0.32
0.31
0.40
21.1
20.8
20.8
11.8
21.4
21.3
0.32
1.25
1.38
0.09
0.79
0.95
0.18
0.23
0.18
0.18
0.15
0.18
35.3
56.7
59.3
8.10
33.2
34.8
7.41
5.05
5.05
15.4
8.14
7.82
1.55
1.33
1.02
0.42
1.18
1.02
4.05
3.60
3.46
0.70
2.71
2.58
2
/N
2
2
W-cal-N
2
W-cal-H
W-cal-H
2
/N
2
2
a
Reaction conditions: T ¼ 623 K; WHSV ¼ 0.52 hꢀ1; time on stream ¼ 1 h.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 11693–11704 | 11695

View Article Online
RSC Advances
Paper
catalyst, it showed the lower 2-butene conversion than the other butene conversion and propylene yield and caused the lower 1-
pretreatments. However, the 2-butene conversion of the non- butene yield. Pure H pretreatment of the non-calcined catalysts
2
calcined catalysts was better than the calcined samples. The exhibited the best catalytic activity and performances for the
propylene yields (see Fig. 1b) of the catalysts followed the order: metathesis of ethylene and 2-butene.
W-noncal-H
cal-H /N > W-cal-N
indicated the opposite trend to that of the propylene yield. In catalysts
2
> W-noncal-H
2 2 2 2
/N > W-noncal-N > W-cal-H > W-
2
2
2
, while the 1-butene yield (see Fig. 1c) 3.2 Characterization of the calcined and non-calcined
+
addition, the C
5
yield (see Fig. 1d) was very low and insigni-
The study of pretreatment atmospheres of the WO /SiO cata-
3
2
cantly different for all the catalysts. Nevertheless, the propylene
yield of the non-calcined catalysts decreased initially and
became constant aer 8 h, whereas 1-butene yield of the non-
calcined catalyst was slightly constant. When operating at
pressure of 2.1 MPa as shown in Fig. 2, the differences in 2-
butene conversion and product yields of the calcined and non-
calcined catalysts were more pronounced. The non-calcined
catalysts exhibited the activity of 2-butene conversion and
propylene yield higher than the calcined samples, while the 1-
lysts on metathesis reaction of ethylene and 2-butene showed
that the non-calcined catalysts exhibited the activity and
performance higher than the calcined catalysts and the pure H
2
pretreatment of the non-calcined catalyst exhibited the highest
activity. Different gas pretreatments could lead to the changes
of the dispersion of tungsten species, the interaction of the
tungsten and support, the structure of surface tungsten
compounds, and the partial oxidation state of the catalysts,
which played an important role in activity of metathesis reac-
butene yield of the non-calcined catalysts was lower than the
tion. The calcined and non-calcined WO /SiO catalysts pre-
+
3
2
calcined catalyst and the C ] yield of the non-calcined cata-
5
treated under different gas atmospheres were characterized by
BET, XRD, XPS, TEM, SEM-EDX, UV-Vis, Raman, H -TPR and
NH -TPD techniques.
.2.1 physisorption. The BET surface areas, pore
volumes, and average pore sizes of fresh catalysts obtained from
lysts was higher than the calcined catalysts. Considering the
effect of gas pretreatment, it was found that the results of
2
3
2.1 MPa were the same trend as the operation at 0.1 MPa. The
3
N
2
increasing H content for pretreatment exhibited the high 2-
2
Fig. 1 2-Butene conversion and product yields of the calcined (continuous lines) and non-calcined (dotted lines) WO
3 2
/SiO catalysts under
+
different pressures and gas pretreatments at pressure of 0.1 MPa: (a) 2-butene conversion, (b) propylene yield, (c) 1-butene yield and (d) C
5
]
ꢀ1
yield (reaction condition: T ¼ 623 K; WHSV ¼ 0.52 h ).
11696 | RSC Adv., 2018, 8, 11693–11704
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
Fig. 2 2-Butene conversion and product yields of the calcined (continuous lines) and non-calcined (dotted lines) WO
3
/SiO
2
catalysts under
+
different pressures and gas pretreatments at pressure of 2.1 MPa: (a) 2-butene conversion, (b) propylene yield, (c) 1-butene yield and (d) C
5
]
ꢀ1
yield (reaction condition: T ¼ 623 K; WHSV ¼ 0.52 h ).
25
different gas pretreatments were analyzed and the results are better dispersed tungsten species on the surface. As shown in
shown in Table 2. It was found that the calcined and non- the activity results (Fig. 1 and 2), the N pretreatment of the non-
2
calcined catalysts showed no signicant differences in the calcined catalyst exhibited higher activity than the calcined
specic surface area, pore volume, and average pore size. In catalyst, indicating that less WO crystallinity was active in
3
19
other words, the gas pretreatment did not affect the physical metathesis. For the mixed H /N and pure H , the non-
2
2
2
properties of the calcined and non-calcined catalysts.
calcined catalysts exhibited the patterns assigned to WO2.83
3
.2.2 X-ray diffraction (XRD). The XRD diffraction patterns phase, while the calcined catalysts exhibited WO2.92 phase,
17
of catalysts with different gas pretreatments are shown in Fig. 3. occurring from the partial reduction of WO
The as-prepared non-calcined WO /SiO catalyst (W-noncal-
3
.
The published
3
2
fresh) showed no obvious peaks corresponding to crystalline
Table 2 BET surface areas, pore volumes and pore sizes of the
phase of WO , indicating that the W phase was well dispersed
3
10
calcined and non-calcined WO
pretreatment atmospheres
3 2
/SiO catalysts for different gas
on the supports forming an amorphous phase. The fresh
catalyst aer calcination (W-cal-fresh) at 823 K for 8 h exhibited
XRD patterns assigned to monoclinic WO
calcined and non-calcined) were pretreated with different gases Catalysts
including pure N (W-xxx-N ), mixed H /N (W-xxx-H /N ), and
pure H (W-xxx-H ), the diffraction peaks based on standard
data reference in JCPDS showed different patterns. Pure N
pretreatment for the calcined and non-calcined catalysts
3
. When the catalysts
BET surface area
Pore volume
Pore size
(nm)
2
ꢀ1
3
ꢀ1
(
(m g
)
(cm g
)
2
2
2
2
2
2
W-noncal-fresh
W-noncal-N
288
296
303
298
285
286
288
287
1.01
1.02
1.03
1.03
0.97
1.02
1.00
1.04
9.51
9.50
9.39
9.45
9.41
9.15
9.39
9.21
2
2
2
2
W-noncal-H
W-noncal-H
2
/N
2
2
exhibited the same XRD patterns as monoclinic WO , but the W-cal-fresh
3
W-cal-N
W-cal-H
W-cal-H
2
patterns of the non-calcined catalysts exhibited a lower crys-
tallinity than those of the calcined catalysts, indicating the
2
/N
2
2
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 11693–11704 | 11697

View Article Online
RSC Advances
Paper
Fig. 4 XPS spectra of the calcined (a) and non-calcined (b) WO
Fig. 3 XRD patterns of the calcined (colored continuous lines) and catalysts with different gas pretreatments.
non-calcined (dotted lines) WO /SiO catalysts with different gas
3 2
/SiO
3
2
pretreatments and standard data reference from JCPDS (black
continuous lines).
6
+
2
pure H pretreatment conrmed that the W was converted to
W
5
+
5+
and that the amount of the W oxidation state increased
with increasing hydrogen in the gas pretreatment. Nevertheless,
it was found that the mixed H /N and pure H pretreatment on
literatures reported that the partial reduction or intermediate of
tungsten oxide on support affected the metathesis activity.
2
2
2
5
+
the non-calcined catalysts exhibited the W peak higher than
the calcined samples (see Table 2). Such results indicated the
2
3
Westhoff et al. proposed that the intermediate between WO
and WO2.95 was the active phase for metathesis reaction and
3
6
+
5+
higher degree of W conversion to W state, which was
consistent with the XRD results that showed WO2.83 phase for
the non-calcined catalyst and WO2.92 phase for the calcined
catalyst.
22
Choung et al. showed some intermediate WO3ꢀx to be the
17
most active for propylene metathesis, while Liu et al. indicated
that the tetragonal WO and partially reduced WO were the
3
2.92
active phases for metathesis. In our results (Fig. 1 and 2), we
found that H pretreatment of the non-calcined catalyst
The surface compositions of the calcined and non-calcined
WO /SiO catalysts were determined by XPS and the results
2
3
2
exhibited higher activity than the calcined catalysts. Therefore,
it could be proposed that WO2.83 crystalline phase of the cata-
lysts played an important role on the active phase in the
metathesis reaction of ethylene and 2-butene. When comparing
between using mixed H /N and pure H pretreatment, the pure
are shown in Table 3. All the catalysts showed insignicant
changes of oxygen and carbon content on the catalyst surface
whereas silica and tungsten compounds were different on the
calcined and the non-calcined catalysts. Considering the ratios
of W/(Si + W), which indicated the surface dispersion and
2
2
2
H pretreatment exhibited the lower crystallinity than the mixed
2
31
concentration of tungsten on silica support, the non-calcined
catalysts showed higher ratios of W/(Si + W) than those of the
calcined samples. It is suggested that the W surface concen-
tration on the non-calcined catalysts was higher than the
calcined catalysts, which was consistent to the XRD results.
There was little effect of the gas pretreatment atmosphere on
H /N pretreatment. Therefore, the pure H2 pretreatment
2
2
offered the better dispersion of W species on the support and
that of the non-calcined catalyst showed the best dispersion.
3.2.3 X-ray photoelectron spectroscopy (XPS). XPS
measurements were used to determine the surface chemical
state of tungsten on the surface of the calcined and non-
calcined WO /SiO2 catalysts obtained with various gas
3
pretreatments and the results are shown in Fig. 4. The decon-
voluted peaks were based on the full width at half-maximum Table 3 Surface characterization by X-ray photoelectron spectros-
(
FWHM) of 1.4 eV, the binding energy difference between W copy (XPS) on the calcined and non-calcined WO
4f5/2 and W 4f7/2 of 2.1 eV, the peak intensity ratio of W 4f5/2
3
/SiO
2
catalysts with
different gas pretreatments
and W 4f7/2 (I(f7/2) : I(f5/2)) of 4 : 3, and the binding energy
difference between W 4f7/2 and W 4f7/2 peak about 0.9–
Elements (at%)
Si
5
+
6+
W/
(Si + W)
2
8,29
5+
6+
1
.1 eV.
The binding energies of 38.8 and 40.9 eV were Catalysts
O
C
W
W
(%)
W
(%)
6
+
6+
assigned to W 4f7/2 and W 4f5/2, while the ones of 37.8 and
9.9 eV were assigned to W 4f7/2 and W 4f5/2. The fresh and
5
+
5+
W-noncal-fresh 78.1 4.66 10.6 6.57 0.38
0.00
0.00
100.0
100.0
45.3
3
W-noncal-N
W-noncal-H
on the silica support. W-noncal-H2
2
78.5 4.57 11.1 5.83 0.35
78.5 3.48 11.5 6.53 0.36
79.0 3.91 11.2 5.89 0.35
79.1 3.62 11.7 5.56 0.32
78.6 3.24 12.1 6.01 0.33
79.2 2.46 12.1 6.23 0.34
78.5 3.55 12.0 5.89 0.33
pure N pretreatment of the calcined and non-calcined catalysts
2
2
/N
2
54.7
56.6
0.00
0.00
45.0
47.2
6
+
exhibited only W phase, indicating WO
While the mixed H /N and pure H pretreatment exhibited W
and W phases, indicating the WO3ꢀx on the silica support.
As shown in the gure, the XPS analysis for the mixed H /N and
3
43.4
5
+
W-cal-fresh
W-cal-N2
100.0
100.0
55.0
2
2
2
6
+
30
W-cal-H
W-cal-H
2
/N
2
2
2
2
52.8
11698 | RSC Adv., 2018, 8, 11693–11704
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
the dispersion of W species for both inside the pores and on the tungsten on the support. Therefore, tungsten dispersion of the
outer surface of the catalysts. non-calcined catalysts was higher than the calcined catalysts,
.2.4 Transmission electron microscopy (TEM). The consistent with the XRD, XPS, and TEM results. Under the
3
particle morphology and lattice spacing of the samples were different gas pretreatment atmospheres, pure H pretreatment
2
investigated by TEM and high resolution TEM images as shown of the non-calcined catalyst offered the best tungsten dispersion
in Fig. 5. It was found that the calcined catalysts showed more on the support.
tungsten agglomerates dispersed on the surface of silica than
3.2.6 Diffuse reectance ultraviolet-visible spectra (UV-Vis
the non-calcined catalysts, indicating poor tungsten dispersion DRS). Structure of tungsten species produced by different gas
of the calcined catalysts. Such results were consistent to the pretreatments on the calcined and non-calcined catalysts were
XRD and XPS results. Under different gas pretreatment atmo- analyzed by UV-Vis DRS as shown in Fig. 7. Two absorption
spheres, pure H2 pretreatment on the non-calcined catalyst bands at 230 and 270 nm were observed in the spectra for all the
showed the best dispersion of tungsten on the support. From catalysts, whereas the adsorption band at 400 nm was observed
the high resolution TEM images (inset gure), only one crystal obviously for the fresh calcined catalyst and N pretreatment of
2
lattice plane was observed. The lattice spacing of all the pre- both calcined and non-calcined catalysts. Nevertheless, the
treated catalysts was approximately around 0.38 nm, except the adsorption bands between 400 and 800 nm were observed for
2 2 2 2
fresh non-calcined catalyst, in which the lattice spacing was not pure N , pure H and mixed 1 : 1 H /N pretreatment for both
found due to its amorphous structure. From the XRD standard calcined and non-calcined catalysts. According to the litera-
1
0,32
data reference in JCPDS, the lattice spacing of the (020) planes ture,
the absorption bands at 230 nm could be assigned to
2
ꢀ
of monoclinic WO , (010) planes of WO and (010) planes of isolated tetrahedral [WO4]
species, while the absorption
WO2.83 were about 0.377, 0.382 and 0.379 nm, respectively. bands at 270 nm corresponded to octahedral polytungstate
Therefore, the lattice spacing obtained from the high resolution species. The band at 400 nm was assigned to WO crystal-
whereas the adsorption bands between 400 and
3
2.92
3
1
0,33
TEM images was consistent with the XRD standard data.
lites,
4
+
5+
32
3
.2.5 Scanning electron microscopy with energy dispersive 800 nm could be assigned to W and W species. The
X-ray spectroscopy (SEM-EDX). The SEM and SEM-EDX were adsorption bands at 230 and 270 nm were attributed to W
used to investigate the tungsten distribution over the surface of species.
6
+
1
0,32
As shown in Fig. 7, the intensity of adsorption band
silica (Fig. 6). The SEM results revealed that the topology of at 230 nm for all the samples was not much different, except the
catalysts was non-uniform with irregular shape. The non- fresh calcined catalyst in which the band intensity was lower
calcined catalysts with gas pretreatment showed fewer than the others. However, the pure H pretreatment of the non-
2
agglomerates compared to the calcined catalysts. In addition, calcined catalyst exhibited the highest intensity. For the
from the measurement of tungsten on the silica support by adsorption band at 270 nm, the non-calcined catalysts exhibited
SEM-EDX, the non-calcined catalysts showed higher amount of the intensities higher than the calcined catalysts and the pure
Fig. 5 TEM images and high-resolution TEM image (inset) of the calcined (top) and non-calcined (bottom) WO
pretreatments; (a) W-cal-fresh, (b) W-noncal-fresh, (c) W-cal-N , (d) W-noncal-N , (e) W-cal-H /N , (f) W-noncal-H
W-noncal-H
3
/SiO
2
catalysts with different gas
2
2
2
2
2
/N , (g) W-cal-H and (h)
2
2
2
.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 11693–11704 | 11699

View Article Online
RSC Advances
Paper
Fig. 6 SEM and SEM-EDX images of the calcined (left) and non-calcined (right) WO
3
/SiO
2
catalysts with different gas pretreatments; (a) W-cal-
2 2 2 2 2 2 2 2
fresh, (b) W-noncal-fresh, (c) W-cal-N , (d) W-noncal-N , (e) W-cal-H /N , (f) W-noncal-H /N , (g) W-cal-H and (h) W-noncal-H .
H pretreatment of the non-calcined catalyst showed the high- supported catalysts are shown in Fig. 8. The bands at 263–275,
2
ꢀ
1
est band intensity. Intensity of the band at 400 nm was obvi- 707–720 and 805–808 cm were assigned to the deformation
ously observed for the fresh calcined catalyst and mode of W–O–W, bending mode of W–O, and symmetric
pretreatment of the calcined and non-calcined catalysts. The stretching mode of W–O, respectively.
N
2
1
5,31
The Raman band at
calcined samples showed more obvious peaks than the non- 325–329 cm assigned to bending mode of O–W–O of surface
ꢀ
1
1
0
8,10
ꢀ1
calcined catalysts, indicating a poor dispersion on silica,
WO
x
.
The broad band at 970 cm
was assigned to the
which was consistent with the XRD and XPS results. When O]W]O band of isolated surface tetrahedral tungsten oxide
3
1
pretreating with H (mixed H /N and pure H ), the adsorption species. Fresh catalyst without calcination (W-noncal-fresh)
2
2
2
2
ꢀ1
band at 400 nm was converted to adsorption bands between 400 showed the clear Raman band at 970 cm and a small broad
ꢀ
1
and 800 nm. In other words, the crystalline WO
gas pretreatment, which was consistent with the XRD and XPS WO
results. Comparing the cases of mixed H /N and pure H and N
pretreatment for the calcined and non-calcined samples lysts showed the four strongest peaks (263–275, 325–329, 707–
3
was reduced by peak at 807 cm , indicating the signature bands of distorted
34
6
units. While fresh catalyst with calcination (W-cal-fresh)
pretreatment on both calcined and non-calcined cata-
2
2
2
2
ꢀ
1
8
showed that the bands between 400 and 800 nm of the non- 720 and 805–808 cm ) of crystalline WO
calcined catalysts were broader than the calcined catalysts, peaks at 970 cm . For the H
which were ascribed to ordered mesoporous structure and at 710 and 807 cm
3
and a broad small
pretreatment, the Raman bands
became broader as the H2 content
ꢀ1
2
ꢀ
1
5
+
enlarged oxygen vacancies due to higher
W
in sub- increased. It is suggested that there was a gradual degradation
of the crystallinity upon hydrogen treatment due to an
30
stoichiometric WO3ꢀx
.
3
.2.7 Raman spectroscopy. The Raman spectroscopy increasing amount of oxygen vacancies in the form of WO3ꢀx
30
results showing the structure of tungsten species present on the phase. Comparing the cases of H
2
pretreatment for the
11700 | RSC Adv., 2018, 8, 11693–11704
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
ꢀ1
Table 4 Integral of Raman band area at intensity of 807 and 970 cm
and its relative intensities (I970/I807) on the calcined and non-calcined
WO
3
/SiO
2
catalysts with different gas pretreatments
4
Peak area of intensity (ꢁ10 )
ꢀ1
ꢀ1
Catalysts
807 cm
970 cm
I970/I807 ratio
W-noncal-fresh
W-noncal-N
1.73
69.2
84.1
31.5
34.6
48.2
49.0
18.2
25.5
4.27
5.69
3.60
0.89
1.44
2.40
1.19
14.8
0.06
2
W-noncal-H
W-noncal-H
W-cal-fresh
2
/N
2
0.07
0.11
0.03
0.03
0.05
0.07
2
W-cal-N
2
W-cal-H
W-cal-H
2
/N
2
2
vacancies to WO3ꢀx than the calcined ones and the pure H
Fig. 7 UV-Vis DRS patterns of the calcined (continuous lines) and pretreatment of the non-calcined catalyst showed the highest
non-calcined (dotted lines) WO /SiO
pretreatments; (a) W-cal-fresh, (b) W-noncal-fresh, (c) W-cal-N
W-noncal-N , (e) W-cal-H /N , (f) W-noncal-H /N , (g) W-cal-H
h) W-noncal-H
2
3
2
catalysts with different gas amount of isolated surface tetrahedral tungsten oxide.
2
, (d)
and
3
.2.8 Temperature-programmed desorption of ammonia
-TPD). The NH -TPD was performed to characterize the
surface acidity of the catalysts. In Fig. 9, the ammonia desorp-
tion peaks of the non-calcined WO /SiO catalysts occurred at
higher temperature than the calcined catalysts, indicating the
2
2
2
2
2
2
(
NH
3
3
(
2
.
3
2
31
higher acid strength as stronger acidity. The amounts of NH
3
desorption decreased with changing gas pretreatment as
follows; pure N > mixed H /N > pure H . In addition, the gas
2
2
2
2
pretreatment caused the ammonia desorption peak to slightly
shi to lower temperature, indicating the lower acid strength.
This demonstrated that using the gas pretreatment could result
in a lower amount of total acid and acid strength. The surface
acidity as shown in Fig. 10 also conrmed clearly that gas
pretreatment affected to the total acid amount and strength. It
Fig. 8 Raman spectra of the calcined (continuous lines) and non-
calcined (dotted lines) WO
pretreatments.
3
/SiO
2
catalysts with different gas
calcined and non-calcined catalysts, the Raman band at
ꢀ
1
9
70 cm of non-calcined catalysts showed more obvious peaks
than those of the calcined samples, indicating more isolated
surface tetrahedral tungsten oxide species as also conrmed by
the UV-Vis results. The ratios of relative Raman intensities of
ꢀ
1
the peak at 970 to 807 cm (I970/I807) are shown in Table 4 as an
indicative of the relative amount of isolated surface tetrahedral
tungsten oxide species (active site) to WO
3
crystal (non-active
pretreatment of the non-calcined cata-
lyst exhibited the highest I970/I807 ratio among the catalysts
35,36
site).
The pure H
2
Fig. 9 NH -TPD profiles of the calcined (continuous lines) and non-
3
studied. Based on the characterization results described above, calcined (dotted lines) WO
pretreatments; (a) W-cal-fresh, (b) W-noncal-fresh, (c) W-cal-N
W-noncal-N , (e) W-cal-H /N , (f) W-noncal-H /N , (g) W-cal-H
h) W-noncal-H
3
/SiO
2
catalysts with different gas
, (d)
and
we can conclude that the H pretreatment (mixed H /N and
pure H ) of the non-calcined catalysts exhibited higher oxygen
2
2
2
2
2
2
2
2
2
2
2
(
2
.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 11693–11704 | 11701

View Article Online
RSC Advances
Paper
Fig. 11
2
H -TPR patterns of the calcined (continuous lines) and non-
Fig. 10 The total and strong acidity of the calcined and non-calcined calcined (dotted lines) WO
WO /SiO catalysts with different gas pretreatments.
pretreatments.
3
/SiO
2
catalysts with different gas
3
2
appeared that the N2 pretreatment exhibited both total acid
amount and strong acid strength higher than the mixed H /N
According to the characterization results, it was concluded
that the non-calcined catalysts had better dispersion of tung-
2
2
and pure H
catalysts. In other words, H
caused only a slight change of acid amount and strength.
.2.9 Temperature-programmed reduction of hydrogen the support exhibited high activity of the metathesis reac-
2
pretreatment for both calcined and non-calcined sten on the silica support (as conrmed by the BET, XRD, XPS,
content of gas pretreatment TEM and SEM-EDX results) than the calcined catalysts. Many
researchers mentioned that higher dispersion of tungsten on
2
3
14,25,35
(
H
2
-TPR). The interaction between W active species and silica tion.
Additionally, the UV-Vis and Raman results also
support was determined by the H -TPR technique. The H -TPR indicated the higher amount of isolated tetrahedral tungsten
2
2
results of the calcined and non-calcined WO /SiO catalysts oxide and octahedral polytungstate species which were active
3
2
32
(
1
Fig. 11) showed three peaks at 769–789, 1030–1062 and 1135– species for the metathesis reaction on the non-calcined cata-
170 K. The low temperature peak was attributed to the lysts than the calcined catalysts. The NH -TPD and H -TPR
3
2
reduction of W species in octahedral coordination, and the two results also showed the higher degrees of metal-support of the
high temperature peaks were assigned to the reduction of the non-calcined catalysts due probably to the strong acidity pre-
1
0,32
37
surface amorphous WO
calcined and non-calcined WO
3
species.
/SiO
Comparing between the sented on the non-calcined ones. For the comparison of gas
catalysts, the reduction pretreatment atmospheres, the XRD patterns of H content
3
2
2
peak at low temperature of the non-calcined catalysts appeared pretreatment atmosphere of the non-calcined catalysts revealed
at higher temperature than the calcined ones, indicating that the formation of a WO2.83 phase, while those of the calcined
interaction of W species in octahedral coordination on silica catalysts revealed the WO2.92 phase. The results showed that the
support of the non-calcined catalysts (789 K) was stronger than pure H pretreatment of the non-calcined catalyst exhibited the
2
the calcined catalysts (769 K). The two reduction peaks at high highest activity and performance in metathesis of ethylene and
temperature of the non-calcined catalysts (1052 and 1135 K) 2-butene. Therefore, it could be proposed that WO2.83 crystal-
appeared at lower temperature than the calcined catalysts (1062 line phase of the catalysts played an important role on the active
and 1170 K), indicating that reduction of WO
non-calcined catalysts was weaker than the calcined catalysts, less, the XPS results of pure H
3
crystal of the in the metathesis reaction of ethylene and 2-butene. Neverthe-
pretreatment of the non-
2
10
5+
which reected an improved reducibility of dispersed species.
calcined catalysts showed the highest amount of the W
32
(6ꢀy)+
Considering the effect of gas pretreatment, the pure H2 content. Huang et al. proposed that W
(0 < y < 1) was the
pretreatment led to a boarder low temperature peak while the highly active centers for supported tungsten catalysts. There-
high temperature peaks of each type (calcined or non-calcined) fore, the improvement of the activity for metathesis reaction of
catalysts were not different. Nevertheless, the H
pretreatment was likely to shi the low H
consumption peaks pretreatment atmosphere without the calcination with air. The
to lower temperature. Liu et al. mentioned that the strong concept of the summarized results is shown in Scheme 2. The
acidity was partly responsible for the strong interaction between catalytic performance of WO /SiO catalysts could be developed
tungsten oxides and support. Therefore, these results were without the calcination of air. The air calcination caused the
consistent with the NH -TPD results.
stronger interaction of crystalline WO phase on the support
2
2
content of gas ethylene and 2-butene could be adjusted by the H gas
2
37
3
2
3
3
11702 | RSC Adv., 2018, 8, 11693–11704
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
RSC Advances
Acknowledgements
The authors acknowledge the support from the Department of
Chemical Engineering, Faculty of Engineering, Chulalongkorn
University.
References
1
L. G. Wade, Organic Chemistry, Pearson Prentice Hall, 6th
edn, 2006.
J. C. Mol, J. Mol. Catal. A: Chem., 2004, 213, 39–45.
J. Towghi, A. Niaei, R. Karimzadeh and G. Saedi, Korean J.
Chem. Eng., 2006, 23, 8–16.
Scheme 2 The summarized results of the non-calcined and air-
calcined catalysts with H pretreatment.
2
2
3
and when reduced with H
oxygen vacancies converting crystalline WO
2
pretreatment, it exhibited the low
to WO2.92 phase,
4
5
M. St ¨o cker, Microporous Mesoporous Mater., 1999, 29, 3–48.
F. Cavani, N. Ballarini and A. Cericola, Catal. Today, 2007,
3
which was less active for metathesis reaction. Whilst on the
non-calcined catalysts with H2 pretreatment led to higher
127, 113–131.
6 X. Li, W. Zhang, S. Liu, L. Xu, X. Han and X. Bao, J. Phys.
Chem. C, 2008, 112, 5955–5960.
oxygen vacancies converting amorphous WO to WO
phase.
3
2.83
The higher oxygen vacancies could provide more active sites for
metathesis reaction.
7
8
9
D. P. Debecker, M. Stoyanova, U. Rodemerck and
E. M. Gaigneaux, J. Mol. Catal. A: Chem., 2011, 340, 65–76.
A. Spamer, T. I. Dube, D. J. Moodley, C. van Schalkwyk and
J. M. Botha, Appl. Catal., A, 2003, 255, 153–167.
P. Jean-Louis H ´e risson and Y. Chauvin, Die Makromolekulare
Chemie, 1971, 141, 161–176.
4
. Conclusions
1
1
1
1
1
0 Q. Zhao, S.-L. Chen, J. Gao and C. Xu, Transition Met. Chem.,
009, 34, 621–627.
1 A. G. Basrur, S. R. Patwardhan and S. N. Was, J. Catal., 1991,
27, 86–95.
2 S. Chaemchuen, S. Phatanasri, F. Verpoort, N. Sae-ma and
K. Suriye, Kinet. Catal., 2012, 53, 247–252.
3 H. Liu, S. Huang, L. Zhang, S. Liu, W. Xin and L. Xu, Catal.
Commun., 2009, 10, 544–548.
4 N. Poovarawan, K. Suriye, J. Panpranot, W. Limsangkass,
F. J. Santos Cadete Aires and P. Praserthdam, Catal. Lett.,
The effect of catalyst pretreatment atmosphere of the calcined
and non-calcined WO /SiO catalysts for metathesis reaction of
2
3
2
ethylene and 2-butene to produce propylene was investigated.
The gas pretreatment atmosphere consisted of pure N , pure H
1
2
2
and mixed 1 : 1 H /N . The catalytic activity tests were carried
2
2
out at 2 pressure levels (0.1 and 2.1 MPa). At low pressure of
.1 MPa, the gas pretreatment atmosphere for the calcined and
0
non-calcined catalysts was not much different, while at high
pressure of 2.1 MPa, the effect of pretreatment atmosphere of
the non-calcined catalyst became more pronounced. The results
showed that the non-calcined catalysts exhibited higher activity
than the calcined catalysts. The NH -TPD and H -TPR results
2015, 145, 1868–1875.
1
1
1
5 Y. Wang, Q. Chen, W. Yang, Z. Xie, W. Xu and D. Huang,
Appl. Catal., A, 2003, 250, 25–37.
6 S. K. Gangwal, J. Fathi-kalajahi and G. B. Wills, Prod. R&D,
3
2
showed a stronger interaction of the catalysts and the support
for the non-calcined catalysts than the calcined catalysts.
1977, 16, 237–241.
Among different gas pretreatment atmospheres, pure H
pretreatment of the non-calcined catalyst exhibited the highest
activity and performances. The pure H pretreatment atmo-
2
7 H. Liu, K. Tao, H. Yu, C. Zhou, Z. Ma, D. Mao and S. Zhou, C.
R. Chim., 2015, 18, 644–653.
8 A. J. Van Roosmalen and J. C. Mol, J. Catal., 1982, 78, 17–23.
9 S. Huang, F. Chen, S. Liu, Q. Zhu, X. Zhu, W. Xin, Z. Feng,
C. Li, Q. Wang and L. Xu, J. Mol. Catal. A: Chem., 2007,
2
1
1
sphere of the non-calcined catalyst led to the phase change of
tungsten species from WO to WO2.83, while that of the calcined
3
catalyst converted the WO to WO
phase, as supported by the
2.92
3
267, 224–233.
XPS, UV-Vis and Raman results. In addition, the XPS, UV-Vis
and Raman results showed that the pure H pretreatment
atmosphere of the non-calcined catalyst exhibited the high
2
0 K. Ding, A. Gulec, A. M. Johnson, T. L. Drake, W. Wu, Y. Lin,
E. Weitz, L. D. Marks and P. C. Stair, ACS Catal., 2016, 6,
5740–5746.
1 S. Lwin and I. E. Wachs, ACS Catal., 2014, 4, 2505–2520.
2 S. J. Choung and S. W. Weller, Ind. Eng. Chem. Process Des.
Dev., 1983, 22, 662–665.
3 R. Westhoff and J. A. Moulijn, J. Catal., 1977, 46, 414–416.
4 M. I. Zaki, N. E. Fouad, S. A. A. Mansour and A. I. Muah,
Thermochim. Acta, 2011, 523, 90–96.
2
5
+
isolated surface tetrahedral tungsten oxide species and W
species. The WO2.83 phase of the catalysts played an important
2
2
role on the high activity of the WO
reaction.
x 2
/SiO catalyst in metathesis
2
2
2
5 S. Maksasithorn, P. Praserthdam, K. Suriye and
D. P. Debecker, Microporous Mesoporous Mater., 2015, 213,
125–133.
Conflicts of interest
There are no conicts to declare.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 11693–11704 | 11703

View Article Online
RSC Advances
Paper
2
2
2
2
6 N. Kasempremchit, P. Praserthdam and S. Assabumrungrat, 32 S. Huang, S. Liu, W. Xin, J. Bai, S. Xie, Q. Wang and L. Xu, J.
Korean J. Chem. Eng., 2016, 33, 2842–2848. Mol. Catal. A: Chem., 2005, 226, 61–68.
7 H. Liu, L. Zhang, X. Li, S. Huang, S. Liu, W. Xin, S. Xie and 33 X.-L. Yang, R. Gao, W.-L. Dai and K. Fan, J. Phys. Chem. C,
L. Xu, J. Nat. Gas Chem., 2009, 18, 331–336. 2008, 112, 3819–3826.
8 J.-S. Lee, I.-H. Jang and N.-G. Park, J. Phys. Chem. C, 2012, 34 C. Yue, X. Zhu, M. Rigutto and E. Hensen, Appl. Catal., B,
16, 13480–13487. 2015, 163, 370–381.
9 A. P. Shpak, A. M. Korduban, M. M. Medvedskij and 35 S. Huang, S. Liu, Q. Zhu, X. Zhu, W. Xin, H. Liu, Z. Feng,
1
V. O. Kandyba, J. Electron Spectrosc. Relat. Phenom., 2007,
56, 172–175.
C. Li, S. Xie, Q. Wang and L. Xu, Appl. Catal., A, 2007, 323,
94–103.
1
3
3
0 L. Wang, Y. Wang, Y. Cheng, Z. Liu, Q. Guo, M. N. Ha and 36 W. Limsangkass, P. Praserthdam, S. Phatanasri,
Z. Zhao, J. Mater. Chem. A, 2016, 4, 5314–5322.
J. Panpranot, N. Poovarawan, W. Jareewatchara, S. Kunjara
1 S. Maksasithorn, D. P. Debecker, P. Praserthdam,
Na Ayudhya and K. Suriye, Catal. Lett., 2014, 144, 1524–1529.
J. Panpranot, K. Suriye and S. K. N. Ayudhya, Chin. J. 37 N. Liu, S. Ding, Y. Cui, N. Xue, L. Peng, X. Guo and W. Ding,
Catal., 2014, 35, 232–241. Chem. Eng. Res. Des., 2013, 91, 573–580.
11704 | RSC Adv., 2018, 8, 11693–11704
This journal is © The Royal Society of Chemistry 2018