A novel strategy for constructing mesoporous solid superbase catalysts: Bimetallic Al-La oxides supported on SBA-15 modified with KF

Article abstract of DOI:10.1039/c6cy02334g

Bimetallic Al-La oxides were conjointly precoated on SBA-15 prior to the introduction of potassium fluoride to achieve solid superbases at low temperature by a modified wetness impregnation method. This breaks the tradition of decomposition of KNO₃ at high temperature and gives rise to a new approach to generating superbasic sites on SBA-15. The physico-chemical characteristics of the prepared KF/Al-La@SBA-15 materials were investigated using FT-IR, XRD, TG-DTG, N₂ adsorption-desorption, TEM, SEM-EDS, acid-base titration, Hammett indicators and CO₂-TPD measurements. The results demonstrated that the addition of Al species promoted the dispersion behavior of La species inside the channels, and the bimetallic species could synergistically protect the mesoporous structures of SBA-15 against KF corrosion. With increasing Al content, KF/Al-La@SBA-15 exhibited a long-range ordering of the pores with relatively narrow pore size distribution as well as high specific surface area. The research results showed that the KF/Al-La@SBA-15 (0.4) catalyst possessed a total basicity up to 0.79 mmol g^-1 and superbasicity with a strength of 26.5. The catalytic activity of the prepared materials was evaluated in the ring-opening reaction of propylene oxide with methanol. Compared with the SBA-15 supported monometallic oxide (Al or La) catalysts, KF/Al-La@SBA-15 (0.4) exhibited the highest catalytic activity for the ring-opening reaction of propylene oxide with methanol. This is associated with the synergistic effects between Al and La species and the high dispersion of active components on the SBA-15 support.

Full text of DOI:10.1039/c6cy02334g

View Article Online
View Journal
Catalysis
Sc ience &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: N. Liu, Z. M. Wu,
M. Li, S. Li, Y. Li, R. Yu, L. Pan and Y. Liu, Catal. Sci. Technol., 2017, DOI: 10.1039/C6CY02334G.
Volume 6 Number 1 7 January 2016 Pages 1–308
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
www.rsc.org/catalysis
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2044-4753
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
rsc.li/catalysis

Please do not adjust margins
Catalysis Science & Technology
Page 1 of 9
View Article Online
DOI: 10.1039/C6CY02334G
Catalysis Science & Technology
Paper
A novel strategy for constructing mesoporous solid superbase
catalysts: bimetallic Al-La oxides supported on SBA-15 modified
Received 6th November 2016,
Accepted 00th November 2016
with KF
†
a
ab
a
a
ac
a
ab
DOI: 10.1039/x0xx00000x
Ning Liu, Zhimin Wu,* Meng Li, Shanshan Li, Yongfei Li,* Rongdong Yu, Langsheng Pan,
*ab
Yuejin Liu,
www.rsc.org/
The bimetallic Al-La oxides were conjointly precoated on the SBA-15 prior to the conduction of potassium fluoride to
achieve solid superbases at low temperature by a modified wetness impregnation method. It breaks the tradition of
decomposition of KNO
The physico-chemical characteristics of the prepared KF/Al-La@SBA-15 materials were investigated by FT-IR, XRD, TG-DTG,
adsorption-desorption, TEM, SEM-EDS, acid-base titration, Hammett indicator and CO -TPD measurements. The results
3
at high temperature and realizes a new approach to generating superbasic sites on the SBA-15.
N
2
2
demonstrated that the addition of Al species promoted the dispersion behavior of La species inside the channels, and the
bimetallic species could synergistically protect the mesoporous structures of SBA-15 against KF corrosion. With increasing
Al contents, the KF/Al-La@SBA-15 exhibited a long-range ordering of the pores with relatively narrow pore size
distribution as well as high specific surface area. The research results showed that the KF/Al-La@SBA-15 (0.4) catalyst
possessed total basicity up to 0.79 mmol/g and superbasicity with a strength of 26.5. The catalytic activity of the prepared
materials was evaluated in the ring-opening reaction of propylene oxide with methanol. Compared with the SBA-15
supported monometallic oxide (Al or La) catalysts, the KF/Al-La@SBA-15 (0.4) exhibited the most highly catalytic activity
for the ring-opening reaction of propylene oxide with methanol. This is associated with the synergistic effects between Al
and La species and the high dispersion of active components on the SBA-15 supporter.
1
. Introduction
In recent years, solid superbase catalysts have received much Many attempts have been made to fabricate strong basic sites
attention due to their advantages of easy separation, negligible by introducing inorganic species with excellent heat-resistance
corrosion, high catalytic activities, etc. These properties make into the channels of silica-based mesoporous SBA-15 due to its
1
-3
them widely used in various organic reactions. The metal well-defined structure, tunable pore diameter, narrow pore-size
oxides modified by alkali metals and/or alkali-metal oxides, distribution, thicker framework walls, excellent thermal and
1
3,14
such as MgO, Al
2
O
3
, ZrO
2
, La
2
O
3
and CeO
2
, were frequently hydrothermal stability.
Nevertheless, the poor alkali-
4
-8
used as solid superbase catalysts. Generally, some alkaline resistance of mesoporous SBA-15 would lead to a relatively
metal oxides could exhibit high basic strength and good low surface area and collapsed mesostructure when some metal
catalytic activity. However, these alkaline metal oxides oxides with strong basicity were directly introduced. Recently,
catalysts have several drawbacks such as low specific surface a method has been developed to generate strong basicity on
9
-12
area, low basicity, and wide distribution of basic strength.
mesoporous silica SBA-15 by pre-coating a metal oxide layer
Therefore, a great deal of effort has been devoted to the prior to modification by base precursor of alkali metal nitrates
o
12,15
development of solid superbase catalysts immobilized on (e.g. KNO
3
) which decomposed in N
In this case, SBA-15 precoated with MgO or Al
both ordered mesostructure and strong basicity, while SBA-15
2
flow at above 600 C.
supports with high surface area.
2 3
O
possessed
modified with ZrO
1
collapsed structure.
2
4,16-18
and CeO
2
exhibited weak basicity and
This is related to the electronegativity
of cations in introduced metal oxides, which can influence the
dispersion of metal oxides on the silica-based supporters.
Furthermore, the moderate interaction between metal oxides
and SBA-15 would improve degree of dispersion and form
compact interlayer to enhance the alkali-resistance of the
1
6-18
siliceous supporters.
In order to reduce the decomposition
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 9
View Article Online
DOI: 10.1039/C6CY02334G
ARTICLE
Journal Name
temperature of the precursor, the redox strategy was performed
at relative low temperatures. The carbon interlayer precoated
firstly on the mesoporous silica endowed the host with
reducibility, which would facilitate the conversion of the
subsequently introduced alkali metal nitrates such as KNO
LiNO
reaction, leading to the generation of strong basic sites.
3
and
3
at a low temperature via the precursor-host redox
1
9,20
By
3
utilizing the redox strategy between the base precursor (KNO )
and the reducing agent (methanol), the strong basic sites can
also be produced on the surface of mesoporous silica at much
2
1
lower temperature. Besides the above-mentioned strategy for
low-temperature formation of strong basicity on mesoporous
silica, the isolated lithium sites can also be anchored on the
surface of pure SBA-15 by a molecular precursor approach at
room temperature. It could realize molecular-level dispersion of
Scheme 1. The superbasic sites generation on mesoporous
SBA-15 by a modified wetness impregnation method.
2
2
active sites. Despite the efforts, the development of an
effective method to create superbasic sites on mesoporous silica
at lower temperatures remains a great challenge.
Rare-earth oxides such as La O with acid-basic properties
2
3
2. Experimental section
have been used as supporters for producing superbasic sites
or/and catalytic promoters, which is essentially attributed to the
2
.1 Chemicals
low polarizing power of the cations with large size and Poly(ethyleneoxide)-block-poly-(propyleneoxide)-block-poly
5
,7,8,23
relatively low charge.
However, La O modified with (ethyleneeoxide)-block (P123, EO PO EO , average
2 3
20 70 20
some common alkaline species such as KF exhibited superbasic molecular weight of 5800, Sigma-Aldrich), Tetraethylortho-
9,24
1
sites but low specific surface.
Although the SBA-15 silicate (TEOS, 98%, Aladdin corp., China), Hydrochloric acid
modified with La O showed high specific surface by the (HCl, 37%, Sigma-Aldrich), Ethyl alcohol (EtOH, 99%,
2
3
conventional method, the La O on the SBA-15 tend to Aladdin corp., China), Aluminium nitrate (Al(NO ) ·9H O,
2
3
3 3
2
aggregate and block the mesopores of the siliceous supporter 99%, Aladdin corp., China), lanthanum nitrate (La(NO ) ·6H O,
2
3
3
during the high-temperature calcination of the corresponding 99%, Aladdin corp., China), Potassium fluoride (KF, Aladdin
precursor. Furthermore, the siliceous framework of the corp., China), Methanol (99.5%, Guanghua Corp., China),
supporter would probably be corroded when the strong base Propylene oxide (99.5%, SCR Corp., China).
species were introduced to enhance the basicity. It was also
reported that KF supported on Al O exhibited mediate strong
2
3
2
.2 Catalyst preparation
basicity, although the compact layer of Al O could be formed
2
3
2
5,26
on the SBA-15.
Mesoporous silica SBA-15 was synthesized according to the
2
7
As mentioned above, monometallic protective layer of Al O3 reported method
2
as follows: Typically, 2.0 g of triblock
or La O was not very beneficial to the formation of generated copolymer P123 was first dissolved in 75 g of 1.6 M HCl
2
3
by KF on the mesoporous SBA-15 at low temperature. It was aqueous solution with stirring at 40 °C, and then 4.25 g of
difficult to achieve both superbasic sites and non-destroyed TEOS was added to the homogeneous solution and stirred for
mesoporous structure of SBA-15 supporter. Herein, a novel 24 h at 40 °C. Finally, the temperature was increased to 100 °C
strategy was proposed to fabricate superbasic sites on SBA-15 and held at this temperature for another 24 h under a static
supporter without collapse of the mesoporous structure of SBA- condition. The as-prepared sample was recovered by filtration,
1
5. The bimetallic Al-La species were conjointly precoated on washed with water, and air-dried at room temperature. The
the SBA-15 supporter prior to the introduction of KF by a removal of the template was performed at 550 °C in still air for
−
1
modified wetness impregnation method. The introduction of Al 5 h with a heating ramp of 2 °C·min . The calcined SBA-15
species could contribute to avoiding the agglomeration of was preserved in small transfusion bottle at room temperature.
La
2
O
3
during the calcination process, and the formation of Al-
2 3 2 3
Mixture of Al O and La O were introduced in SBA-15 by
La protective interlayer in the channels of SBA-15 could be incipient wetness impregnation method. Typically, 3.0 mmol of
achieved. The KF promoter could be introduced in the SBA-15 mixture of Al(NO ) ·9H O and La(NO ) ·6H O with different
3
3
2
3 3
2
supported bimetallic Al-La oxides to improve the basicity of molar ratios was dissolved in EtOH, followed by addition 1.0 g
bimetallic oxides at low temperature, which breaks the tradition of SBA-15. After being stirred at 40 °C for 24 h, the resulting
of thermally induced decomposition of KNO
3
at high mixture was heated at 60 °C under stirring to remove the
temperature. The catalytic activity of the prepared KF/Al- solvent and subsequently dried at 60 °C overnight. The
La@SBA-15 was evaluated in the ring-opening reaction of obtained solid was calcined under an air atmosphere at 550 °C
propylene oxide with methanol.
for 4 h to convert the nitrate to oxides. The resulting samples of
bimetallic Al-La oxides supported on SBA-15 were denoted as
Al-La@SBA-15(x), x represents Al/La molar ratio.
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
Cat Pa ll ey as si es dS oc ni eo nt ca ed j &u s Tt me ca hr gn i on ls ogy
View Article Online
DOI: 10.1039/C6CY02334G
Journal Name
ARTICLE
o
The introduction of potassium fluoride to Al-La@SBA-15(x) ratio 5:1. After running at 125 C for 5 h with magnetic stirring,
was performed by wet impregnation method. The 7.5wt% of the reactor was cooled down to room temperature. The products
potassium fluoride (the mass percentage of potassium fluoride were analyzed by gas chromatograph with a flame ionization
to Al-La@SBA-15) was dissolved in absolute methanol in detector.
polytetrafluoroethylene beaker, followed by addition of the
obtained Al-La@SBA-15(x). After stirring for 4 h at room
3
. Results and discussion
temperature, the mixture was evaporated at 55 °C with stirring
and subsequently dried for 24 h under vacuum at 60 °C. The
Low-angle XRD patterns of the samples are shown in Fig.1
obtained power was calcined at 350 °C for 4 h to activate (A). The pure SBA-15 and the modified SBA-15 samples
potassium fluoride, leading to the formation of KF/Al- exhibit three diffraction peaks in the 2θ range 0.9-2.2°
La@SBA-15(x). The monometallic KF/Al@SBA-15 and corresponding to the (100), (110) and (200) reflections
KF/La@SBA-15 materials were obtained by the similar method associated with p6mm hexagonal symmetry. It suggested the
described above. The KF@SBA-15 was achieved by directly hexagonally ordered structure remained almost unchanged after
2
8
introducing KF on SBA-15 supporter following the similar the modification. With increasing Al contents, the intensity of
method, and the mass ratio of KF to SBA-15 is 7.5. the (100) reflection significantly increased, which is probably
K
2
O/La@SBA-15 was prepared according to the previously ascribed to the increasing scatter contrast between pore walls
reported method except for the mass ratio 0.12 of KNO
1
precursor to La@SBA-15.
3
and the metallic species loaded on the inner surface of SBA-15,
8
(
100)
2.3 Materials characterization
(A)
(
200)
X-ray diffraction (XRD) patterns of the prepared samples were
recorded using a Bruker D8 Advance diffractometer with
monochromatic Cu Kα radiation in the 2θ ranges from 0.7° to 5°
and 10° to 80°, respectively. The pore structures of catalysts
were determined by transmission electron microscopy (TEM)
on a JEOL JEM-2010 UHR transmission electron microscope
with an accelerating voltage of 200 kV. The morphology of the
materials were characterized using a Zeiss Ultra 55 scanning
electron Microscope (SEM) equipped with an Oxford X-Max
(
110)
(a)
(b)
(c)
(
d)
e)
(
(f)
2
type energy dispersive spectroscopy (EDS). N adsorption-
desorption experiments were carried out using a Belsorp II
o
system at -196 C. The temperature of the degasification was
(g)
o
50 C and the degasification time was 3 h. The multipoint
1
1
2
3
4
5
Brunauer-Emmet-Teller (BET) surface areas were calculated
over the relative pressure range from 0 to 1.0. Fourier transform
infrared (IR) measurements were carried out on a Nicolet
2θ (degree)
(B)
−
1
Nexus 470 spectrometer with a spectra resolution of 2 cm
using transparent KBr pellets. The base strength ( ) of the
H
−
(a)
catalyst was detected using a series of Hammett indicators, and
the total surface basicity of the catalysts was studied by acid-
basic titration. The basicity and the basic strength distribution
of the catalyst was studied by Temperature-programmed
(b)
c)
(d)
e)
(
desorption of CO
apparatus. The samples were activated at 300 C for 1 h prior to
the adsorption of CO at room temperature. After the physical
adsorbed CO was purged by a He flow at room temperature,
the samples were heated to 800 C at the rate of 10 C·min ,
and the CO liberated was detected by an Omni Star mass
spectrometer.
2 2
(CO -TPD) on a BELSORP BEL-CAT-A
o
(
2
2
(f)
o
o
−1
(g)
2
1
0
20
30
40
50
60
70
80
2
.4 Evaluation of catalytic performance
2
θ (degree)
The obtained basic materials were applied to catalyze the
synthesis of 1-methoxy-2-propanol via the addition reaction of Fig. 1 Low-angle and wide-angle XRD patterns for the SBA-15
propylene oxide with methanol. The typical process was carried (a) and KF/Al-La@SBA-15 samples with Al molar content of
out in a 50ml autoclave with methanol/propylene oxide mole (b)0, (c) 0.1, (d) 0.2, (e) 0.3, (f) 0.4 and (g) 1.0.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 9
View Article Online
DOI: 10.1039/C6CY02334G
ARTICLE
Journal Name
suggesting
a
9
high degree of hexagonal mesoscopic with the stretching vibraions of Si-O-Al and Si-O-La during the
39,40
For the KF/Al-La@SBA-15, the vibrational
2
organization. As shown in Figure S1, the intensity of the (100) calcination.
-1
reflection of Al-La@SBA-15 sample is obviously stronger than band at 3442 cm could be ascribed to the stretching vibration
4
that of La@SBA-15, suggesting that monometallic La tends to of Al-O-K and La-O-K groups.
1
+
K ions could replace the
agglomerate into tiny particles blocking the mesopores of SBA- protons of isolated hydroxyl groups attached to Al-La to form
3
0
1
5. Furthermore, when the trimetallic species were introduced Al-O-K and La-O-K groups in the activation process.
to the pores, the (100) reflection peak slightly shift to the higher The TG-DTA curves of the as-prepared Al-La@SBA-15 (0.4)
-thea values in comparison with the parent SBA-15, implying before and after calcination were shown in Fig 3. In the case of
the network shrinkage possibly due to a higher degree of un-calcined Al-La@SBA-15 (0.4), the first weight loss below
silicate condensation after the trimetallic species 200 °C with an endothermic peak maximum at 88 °C is
modification. It suggested that the K, Al and La species have attributed to the removal of water molecules and solvent
been loaded on the silica supporter. methanol. The second weight loss occurred ranging from 330 to
2
3
1
As shown in Fig.1(B), the modified SBA-15 samples have no 600 °C, which is associated with the transformation of the
sharp diffraction peaks associated with the supported metal precursors to the corresponding oxides, as well as the formation
crystallites and exhibit a slight broad diffraction peak with low of different La species intermediates. For the calcined Al-
intensity at about 2θ = 27.5°. It suggested that the introduced La@SBA-15 (0.4), there is only one weight loss at around
metallic species are well dispersed on the SBA-15 supporter as 100 °C which is attributed to the removal of water molecules.
3
2-34
amorphous phases or nanocrystals.
As seen from the above- As the temperature increased above 200 °C, no significant
mentioned discussion, the introduction of Al species can reduce weight loss could be observed, which maybe suggested Al and
agglomeration and improve dispersion of the La species on the La nitrates supported on SBA-15 supports decomposed to the
channels of supporters during the calcination.
corresponding oxides after calcination at 550 °C in still air.
The N adsorption-desorption isotherms and pore size
The FT-IR spectra of pure SBA-15 and KF/Al-La@SBA-15
2
with different Al contents were shown in Fig 2. The two IR distribution of the KF/Al-La@SBA-15 and the pure SBA-15
absorption bands related to the molecular sieves framework samples are presented in Fig.4. All the modified SBA-15
were the asymmetric and symmetric stretching of Si-O-Si at samples exhibited type IV adsorption isotherm with an H1
−
1
−1
−1
1
087 cm and 820 cm , and the absorption peak at 465 cm
3
adsorption-desorption hysteresis loop caused by capillary
condensation in mesopores, which is characteristic of
5,36
could be ascribed to the Si-O bending stretching vibration.
-1
-1
Besides, the peaks at 3441 cm and 1627 cm are ascribed to mesoporous silica, confirming the preservation of the porous
4
the stretching vibration of O-H associated with physisorbed structure after the modification. However, in the case of the
2
3
7,38
water and surface silanol groups of SBA-15.
As the Al, La KF/Al-La@SBA-15(0), the desorption branch almost overlaps
-1
and K species were introduced, the peak at 960cm assigned to the adsorption one, which means a relative small capillary
the stretching vibration of the silanols (Si-OH) on the surface of condensation. It suggested the agglomerated La species would
SBA-15 disappeared, and the relatively broad vibrational band make the surfaces of silica-based supporters exposed, which
-1
around 1076 cm was formed. This is probably because the maybe result in the corrosive destruction of mesoporous
asymmetric stretching vibration of Si-O-Si bond overlapped structure by KF. With the addition of Al species, KF/Al-La@
0
0
0
0
.6
（
（
a）
b）
100 (b1)
.5
.4
.3
90
（
（
c）
d）
80
（
e）
70
60
50
40
（
（
f）
0.2
(
a1)
g）
(
b2)
(a2) 0.1
0
.0
1
00 200 300 400 500 600 700 800
o
3
600 320018001600140012001000 800 600 400
-
Temperature ( C)
1
Wavenumber (cm
)
Fig. 2 FT-IR spectra of the (a) SBA-15 and KF/Al-La@SBA-15
samples with Al molar contents of (b) 0, (c) 0.1, (d) 0.2, (e) 0.3,
Fig. 3 TG and DTG curves for the Al-La@SBA-15 (0.4) before
(a1 and a2) and after (b1 and b2) calcination.
(f) 0.4 and (g) 1.0.
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 5 of 9
View Article Online
DOI: 10.1039/C6CY02334G
Catalysis Science & Technology
Paper
SBA-15 exhibited a narrow hysteresis loop with parallel Nevertheless, when the content of Al species exceed 30%, the
adsorption and desorption branches at a relative pressure of 0.6- peaks became narrowed, which was probably ascribed to the
0
.8 as shown in Fig.4(A). It suggested uniform mesopores with synergistic protection of silica-based supporter against the
a narrow pore size distribution, and the result occurred in the destruction from the corrosive KF.
corresponding pore size distribution curves with an average
It could be seen from Table 1 that the BET surface area, pore
mesopore size around 6.0 nm in Fig.4(B) obtained from the volume and average pore diameter decreased obviously after
desorption branch of hysteresis loop of the isotherm. the introduction of mono- or bi-metallic species and KF. With
（
A
）
3
5cm /g
(B)
3
00 cm /g
2
(
a)
(a)
(b)
(b)
(
c)
d)
(
c)
(
(
d)
(
e)
(e)
(f)
(
f)
(g)
(g)
0
.0
0.2
0.4
0.6
0.8
1.0
5
10
15
20
25
30
Relative pressure (P/P )
o
Pore diameter (nm)
2
Fig.4 N adsorption-desorption isotherms and pore size distributions calculated by the BJH method of SBA-15 (a) and KF/Al-
La@SBA-15 samples with Al molar content of (b)0, (c) 0.1, (d) 0.2, (e) 0.3, (f) 0.4 and (g) 1.0.
Table 1 Physicochemical properties and amount of basic sites of different samples
a
b
c
d
e
S
BET
V
p
D
p
Basic strength
Amount of basic sites
(mmol/g)
Samples
2
m /g)
3
(cm /g)
(
(nm)
-
(H )
SBA-15
729.6
217.7
246.2
252.7
263.8
270.1
355.3
0.83
0.40
0.42
0.45
0.47
0.48
0.57
5.7
6.3
5.9
5.9
6.0
6.1
5.9
＜
9.3
0
KF/Al-La@SBA-15 (0)
KF/Al-La@SBA-15 (0.1)
KF/Al-La@SBA-15 (0.2)
KF/Al-La@SBA-15 (0.3)
KF/Al-La@SBA-15 (0.4)
KF/Al-La@SBA-15 (1.0)
18.4
27.0
27.0
27.0
27.0
27.0
0.18
0.21
0.37
0.71
0.79
0.83
a
b
S
BET was the total specific surface area obtained by the BET equation;
c
p
V was the total pore volume measured by the
d
p
desorption; D is the average pore diameter measured by the desorption branch; Base strength was determined by Hammett
e
indicators; the amount of base was measured by acid-base titration.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 6 of 9
View Article Online
DOI: 10.1039/C6CY02334G
Catalysis Science & Technology
Paper
increasing the Al/La ratio, the specific surface area and pore
volume increased slightly, whereas the average pore diameter
did not change obviously. It suggested that adding appropriate
amount of Al species will contribute to the uniformly
dispersion of La species on the internal pore surface of the
supports, and the formative compact metal oxides layer can
effectively protect the silica-based host from corrosion by KF
promoter.
The TEM micrographs of the KF/Al-La@SBA-15 samples
with different Al-La ratios were presented in Fig.5. These
materials possessed an ordered mesostructure with the
hexagonal ordered array of one dimensional mesoporous
channel, which is in agreement with the typical SBA-15
4
3
morphology. However, some spots appeared on the surface of
KF/Al-La@SBA-15 (0) and the ordered silica channels became
indistinct, which suggests that there are some agglomerations of
La on the supporter or/and the corrosion of silica supports by
Fig.5 TEM images of the KF/Al-La@SBA-15 samples with Al molar
KF maybe occurred (Fig. 5a). With increasing the Al/La ratios, content of (a) 0, (b) 0.2, (c) 0.4 and (d) 1.0.
these spots would disappear. It means no agglomerations of Al
or/and La existed on the surfaces of KF/Al-La@SBA-15 (0.4 or
1
.0), suggesting that the Al and La species well dispersed on
the supporter (Fig. 5c and 5d). Therefore, it seemed that the
aggregations of La species can be avoided by adding
appropriate amounts of Al.
T
he microscopic SEM images and the corresponding SEM-
EDS mappings of KF/Al-La@SBA-15 samples are shown in
Fig.6 and Fig S5. It can be seen that the KF/Al-La@SBA-15
samples exhibited regular rod-shaped morphology with about
1
-2
ꢀm length, which is in agreement with the typical SBA-15
4
4,45
morphology,
suggesting the structure remained almost
unchanged after modification. Elemental analysis of the
introduced species over the surface of SBA-15 was performed
using EDS spectra derived from SEM-EDS analysis. The
selected three areas of about 500 × 500 ꢀm and corresponding
EDS spectrum on the KF/Al-La@SBA-15 samples were
presented in Fig. S6 (a) and (b), and the relative compositions
were given in Table S1 (a) and (b). The elements of Si, Al, La,
K, F and O were detected, while both ratio of the atomic
percent and weight percent of Al/La, Al/Si, La/Si and K/Si
were closely matched those of the theoretical values by the post
synthesis method under the given conditions. These indicated
that Al-La bimetallic species and KF well dispersed in the desorption of the CO
Fig.6 SEM images of the KF/Al-La@SBA-15 samples with Al
molar content of (a) 0, (b) 0.2, (c) 0.4 and (d) 1.0.
2
adsorbed by isolated O anions located
-
2
4
6-48
channels of SBA-15, which is in good agreement with the in a particular position of the Al-O surface,
and the
o
otheroverlapping peak at 690 C was related to the desorption
results from TEM and low-angle XRD.
TPD profiles of CO adsorbed on the Al-La@SBA-15 (0.4), of nucleophilic lattice oxygen anions from La species,
2
KF/Al@SBA-15, KF/La@SBA-15, and KF/Al-La@SBA-15 suggesting the existence of a relatively small amount of strong
4
0.4) catalysts are shown in Fig. 7. It can be seen that the profile basic sites. When the KF was loaded on the SBA-15
9
(
of Al-La@SBA-15 catalyst showed two broad desorption peaks. supported single metal oxide, the peaks shifted toward high
o
The overlapping peak at around 180 C was attributed to
temperature followed by two desorption broad peaks at 440 °C
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 6
Please do not adjust margins

Page 7 of 9
Cat Pa ll ey as si es dS oc ni eo nt ca ed j &u s Tt me ca hr gn i on ls ogy
View Article Online
DOI: 10.1039/C6CY02334G
Journal Name
ARTICLE
(
d)
(
c)
b)
(
(a)
Fig. 8 Possible distribution of Al-La bimetallic oxides on SBA-15
1
00 200 300 400 500 600 700 800
o
Temperature ( C)
electronegativity of Al ions (χAl = 1.61) in oxide lies between
that of La and Si ions ( Si = 1.90), the combining forces of Al-O
Fig.7 CO
2
-TPD profiles of samples of (a) Al-La@SBA-15 (0.4),
b)KF/Al@SBA-15, (c) KF/La@SBA-15, (d) KF/Al-La@SBA-15
0.4)
χ
(
(
bonds with Si-OH is weaker than that of the La-O with Si-OH.
Then, during the calcination, the La-O species would attach Al-
O species to react with the supporters. In addition, due to the
ionic radius of La cation far larger than that of Al cation, the
mixed metal oxides could synergistically form a compact layer
and 792°C, respectively, in comparison with the profile of Al-
-
La@SBA-15 catalyst. Because the F ion has a higher electro-
2
negativity than the O ion resulting to the negative charge of
5
6
on the internal surface of the supporters (Fig. 8). Hence, the
addition of Al species can prevent the agglomeration of La
species, and the combination of the two oxides is beneficial to
form a protective layer on the internal surfaces of SBA-15
against the corrosion of basic promoter. The superficial
bimetallic layers consisting of Al-La oxides would combine
with KF to generate strong basic and superbasic sites, which
-
-
50
lattice oxygen would be drawn toward F ion. Thus, the KF-
promoted single metal oxide (Al or La ) supported on
SBA-15 possesses more strong basic sites, compared with the
2
O
3
2 3
O
5
1,52
corresponding pure metal oxide.
This might be a proof of
the reaction between the superficial metal species and KF. The
two peaks of KF/Al-La@SBA-15 catalyst were observed in
2
can be evidenced by the results obtained from CO -TPD.
o
high-temperature region 400 C - 800 C, and the corresponding
o
3
.2. Catalytic performance
strong basic sites and urtra-basic sites may mainly originate
2 3 2 3
from the oxygen anions of Al O and La O jointly interacting The catalytic activity of the prepared materials was evaluated in
with the highly dispersed KF species, respectively, which result the ring-opening reaction of propylene oxide with methanol,
-
in the generation of F anions showing Lewis base sites. and the results were shown in Table 2. Compared with the
Meanwhile,
a significant tailing peak observed on the bimetallic KF/Al-La@SBA-15 catalysts, the monometallic
desorption peaks at the high temperature may be ascribed to oxide modified SBA-15 exhibited poor catalytic activities
existence of Lewis base site derived from KF combined with (entry 1 and 2). Only 32.1% of PO conversion could be
2 3 2
isolated existent La O . The CO -TPD results were in good achieved over the La@SBA-15 catalyst. When the bimetallic
agreement with the results of the acid-base titration and Al-La oxides supported on SBA-15 were promoted by KF, their
Hammett-indicator method summarized in Table 1, providing catalytic activities could be greatly improved, by which the
additional evidence for the basicity of the KF/Al-La@SBA-15 high PO conversion, high PM yield as well as high PPM
catalyst. It is clearly observed that the basicity was significantly selectivity could be obtained (entry 4-8). This could be related
increased by introduction of Al. This is because the Al- to the increases of basic sites caused by the KF loading. The
promoted dispersion of La species may increase the contact catalytic activities of the catalysts could be gradually improved
area between the KF promoter and bimetallic oxides.
with increasing mole ratio of Al/La from 0.1 to 0.4 (entry 4-7).
The electronegative metal element in oxide has a great When the molar ratio Al to La was increased to 0.4, the PM
influence on the strengths of metal-oxygen bond. Generally, the yield and PPM selectivity reached to 95.1% and 94.9%,
strengths of metal-oxygen bonds decrease with reducing respectively. It may be ascribed to the enhancement of strong
5
3,54
electronegativity of metal ions in oxide.
electronegative La element ( La = 1.10) would make the contact basic sites and/or the strength of strong bases have obvious
of La-O weak, leading to the relatively strong interaction of the effects on the catalytic activity.
The lower basic strength. Consequently, it can be seen that the amount of
χ
5
5
La-O with the supporters. Take into consideration the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 8 of 9
View Article Online
DOI: 10.1039/C6CY02334G
Catalysis Science & Technology
Paper
Table 2 Catalytic performance over different catalysts
Entry
Catalysts
PO conversion (%)
PM yield (%)
PPM selectivity (%)
1
2
3
4
5
6
7
8
La@SBA-15
32.1
43.9
89.5
92.6
93.2
96.0
96.3
82.3
67.6
40.6
86.3
89.4
92.9
95.5
95.1
78.5
67.6
52.3
92.4
91.6
91.7
94.3
94.9
86.2
Al@SBA-15
KF/Al-La@SBA-15 (0)
KF/Al-La@SBA-15 (0.1)
KF/Al-La@SBA-15 (0.2)
KF/Al-La@SBA-15 (0.3)
KF/Al-La@SBA-15 (0.4)
KF/Al-La@SBA-15 (1.0)
PO: propylene oxide, PPM: 1-methoxy-2-propanol；PM (propylene glycol monomethyl ether): 1-methoxy-2-propanol and 2-
o
；Reaction temperature: 125 C, Reaction time 4 h, MeOH:PO=20mmol:4.0mmol, Catalyst:0.80g
Methoxy-1-propanol
Conclusions
The bimetallic Al-La species were conjointly precoated on the the China Postdoctoral Science Foundation (No.2014M552143)
SBA-15 supporter prior to the introduction of KF by a modified and the Research Foundation of Education Bureau of Hunan
wetness impregnation method, which was a novel strategy for Province (No.13C912).
constructing mesoporous solid superbase catalysts. The
introduction of Al species could contribute to avoiding the
Notes and references
agglomeration of La during the calcination process, and the
formation of Al-La protective interlayer in the channels of
SBA-15 could be achieved. The KF promoter could be
introduced in the SBA-15 supported bimetallic Al-La oxides to
improve the basicity of bimetallic oxides at low temperature.
The ratio of Al/La has a significant effect on the chemical and
textural properties of KF-modified bimetallic Al-La species
supported on SBA-15. The KF/Al-La@SBA-15 (0.4) catalyst
possessed total basicity up to 0.79 mmol/g and superbasicity
with a strength of 26.5. Compared with the SBA-15 supported
monometallic oxide (Al or La) catalysts, KF/Al-La@SBA-15
1
2
3
4
5
6
7
8
9
1
1
1
Z. Wang, G. Z. Lu, Y Guo, Y. L. Guo and X. Q. Gong, ACS
Sustain. Chem. Eng., 2016, , 1591.
M. Iꢁık, M. Y. Unver and C. Tanyeli, J. Org. Chem., 2015,
, 828.
Liu, X. Y. Liu, L. B. Sun, X. D. Liu, X. D. Liu, A.G. Li, F.
Lu and X. Q. Liu, ACS Appl. Mater. Inter., 2013, , 9823.
H. Tian, X. Y. Li, L. Zeng and J. L. Gong, ACS Catal.
2015, , 4959.
H. V. Lee, J. C. Juan and Y. H. Taufiq-Yap, Renew. Energ.
015, 74, 124.
S. G. Liu, X. L Zhang, J. P. Li and N. Zhao, Wei, W.; Sun,
Y. H. Catal. Commun., 2008, , 1527.
R. L. Song, D. M. Tong, J. Q. Tang and C. W. Hu, Energ.
Fuel., 2011, 25, 2679.
Y. D. Wei, S. G. Zhang, S. F. Yin, C. Zhao, S. L. Luo and
C. T. Au, Catal. Commun., 2011, 12, 1333.
N. Pasupulety, K. Gunda, Y. Q. Liu, G. L. Rempel and F. T.
T. Ng, Appl. Catal., A, 2013, 452, 189.
4
8
0
5
,
,
5
2
9
(0.4) exhibited the most highly catalytic activity for the ring-
opening reaction of propylene oxide with methanol.
Acknowledgements
0
1
2
P. Unnikrishnan and D. Srinivas, Ind. Eng. Chem. Res.
012, 51, 6356.
,
We gratefully acknowledge the support to this research by the
National Natural Science Foundation of China (No.21676229,
2
R. L. Song, D. M. Tong, J. Q. Tang and C. W. Hu, Energ.
Fuel., 2011, 25, 2679.
L. Chen, J. Zhao, S. F. Yin and C. T. Au, RSC Adv., 2013,
2
1276217), Graduate Innovation Fund of Hunan province (No.
CX20132013B276), the Innovation Platform Open Funds of the
Hunan Provincial Education Department (No.15K215,16K086),
3, 3799.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 8
Please do not adjust margins

Page 9 of 9
Cat Pa ll ey as si es dS oc ni eo nt ca ed j &u s Tt me ca hr gn i on ls ogy
View Article Online
DOI: 10.1039/C6CY02334G
Journal Name
ARTICLE
13
14
15
L. Zhao and W. Xie, Energy. Convers. Manage., 2014, 79, 35 A. A. Romero, M. D. Alba, W. Z. Zhou and J. Klinowski, J.
4. Phys. Chem. B, 1997, 101, 5294.
L. B. Sun, X. Q. Liu and H. C. Zhou, Chem. Soc. Rev. 36 W. C. Zhan, Y. L. Guo, Y. Q. Wang, X. H. Liu, Y. Guo, Y.
015, 44, 5092. S. Wang, Z. G. Zhang and G. Z. Lu, J. Phys. Chem. B
M. Kumar, F. Aberuagba, J. K. Gupta, K. S. Rawat, L. D. 2007, 111, 12103.
Sharma and G. M. Dhar, J. Mol. Catal. A: Chem., 2004, 37 D. Halamová, M. Badaničová, V. Zeleňák and T. Gondová,
13, 217. Appl. Surf. Sci., 2010, 256, 6489.
L. B. Sun, Y. H. Sun, X. D. Liu, L. Zhu and X. Q. Liu, Curr. 38 X. G. Wang, K. S. K. Lin J. C. C. Chan and S. Cheng, J.
3
,
2
,
2
16
17
18
19
20
21
22
23
24
25
26
Org. Chem., 2014, 18, 1296.
X. Y. Liu, L. B. Sun, F. Lu and T. T. Li, J. Mater. Chem. A
013, 1, 1623.
Y. H. Sun, L. B. Sun, T. T. Li, X. Q. Liu, J. Phys. Chem. C
010, 114, 18988
X. Y. Liu, L. B. Sun, F. Lu, X. D. Liu and X. Q. Liu, Chem. 41 W. L. Xie and H. T. Li, J. Mol. Catal. A: Chem., 2006, 255,
Commun., 2013, 49, 8087. 1.
L. B. Sun, X. Y. Liu, A. G. Li, X. D. Liu and X. Q. 42 S. Viswanathan, B. Narayanan, Z. Yaakob, P. Periyat and S.
Liu, Chem. Commun., 2014, 50, 11192. Padikkaparambil, J. Porous Mater., 2014, 21, 251.
L. Zhu, F. Lu, X. D. Liu, X. Q. Liu and L. B. Sun, Chem. 43 W. Xie, X. Yang and M. Fan, Renew. Energ., 2015, 80,
Commun., 2015, 51, 10058. 230.
T. T. Li, L. B. Sun, X. Y. Liu, Y. H. Sun, X. L. Song and X. 44 S. F. He, C. Y. Han, H. Wang, W. J. Zhu, S. Y. He, D. D.
Q. Liu, Chem. Commun., 2012, 48, 6423. He and Y. M. Luo, J. Chem. Eng. Data., 2015, 60, 1300.
L. G. Wang, Y. B. Ma, Y. Wang, S. M. Liu and Y. Q. Deng, 45 W. Xie and M. Fan, Chem. Eng. J., 2014, 239, 60.
Phys. Chem. B, 2005, 109, 1763.
39 Y. Qian, P. Wei, P. K. Jiang, Z. Li, Y. G. Yang and K. Ji, J.
Compos. Sci. Technol., 2013, 82, 1.
40 H. Yu, and Q. Z. Zhai, J. Solid State Chem., 2008, 181,
2424.
,
,
2
2
Catal. Commun., 2011, 12, 1458.
46 C. K. S. Choong, Z. Y. Zhong, L. Huang, Z. Wang, T. P.
Ang, A. Borgna, J. Y. Lin and L. Hong, Appl. Catal., A
2011, 407, 155.
47 H. M. Liu and D. H. He, Int. J. Hydrogen Energ. 2011, 36,
14447.
Z. Y. Wu, Q. J. Yi, Y. M. Wang, H. J. Wang, L. B. Sun, L. 48 A. Siahvashi, D. Chesterfield and A. A. Adesina, Chem.
R. Santório, C. de Oliveira Veloso and C. A. Henriques, J.
Mol. Catal. A: Chem., 2015, 422, 234.
,
S. Sandesh, G. V. Shanbhag and A. B. Halgeri, Catal. Lett.
013, 143, 1226.
,
2
Y. Shi, J. H. Xu. Y. W. Wang, Y. Chun and J. H. Zhu,
Chem. Mater., 2006, 18, 4600.
D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H.
Fredrickson, B. F. Chmelka and G. D. Stucky, Sci., 1998,
Eng. Sci. 2013, 93, 313.
49 Q. H. Liu, L. Wang, C. X. Wang, W. Qu, Z. J. Tian, H. J.
Ma, B. C. Wang and Z. S. Xu, Appl. Catal., B, 2013, 136,
210.
2
7
8
279, 548.
D. Wang, Y. J. Zhu, C. G. Tian, L. Wang, W. Zhou, Y. L.
50 W. Jiang, X. Y. Niu, F. L. Yuan, Y. J. Zhu and H. G. Fu,
Catal. Sci. Technol., 2014, 4, 2957.
2
Dong, Q. Han, Y. F. Liu, F. L. Yuan and H. G. Fu, Catal, 51 A. Islam, Y. H. Taufiq-Yap, C. M. Chu, P. Ravindra and E.
Sci. Technol., 2016, 6, 2403. S. Chan, Renew. Energy. 2013, 59, 23.
N. Osakoo, R. Henkel, S. Loiha, F. Roessner and J. 52 Siahvashi, D. Chesterfield, A. A. Adesina, Chem. Eng. Sci.
Wittayakun, Catal. Commun., 2015, 66, 7. 2013, 93, 313.
L. Mo, K. K. M. Leong and S. Kawi. Catal. Sci. Technol.
014, 4, 2107.
X. Wang, T. Sun, J. Yang, Chem. Eng. J., 2008, 142, 48.
C. M. Yang, P. H. Liu, Y. F. Ho, C.Y. Chiu and K. J. Chao, 54 M. Iwamoto, H. Furukawa, K. Matsukami, T. Toshihisa and
Chem. Mater., 2003, 15, 275. S. Kagawa, J. Am. Chem. Soc., 1983, 105, 3719.
J. A. Calles, A. Carrero and A. J. Vizcaíno, Micropor. 55 S. S. Fang, X. S Xiao, L. Xia, W. H. Li and Y. D. Dong, J.
Mesopor. Mat., 2009, 119, 200. Non-Cryst. Solids., 2003, 321, 120.
F. Subhan, B. S.Liu, Y. Zhang and X. G. Li, Fuel process. 56 L. B. Sun, X. Q. Liu and H. C. Zhou, Chem. Soc. Rev., 2015,
2
9
0
,
3
,
53 M. Kumar, F. Aberuagba, J. K. Gupta, K.S. Rawat, L. D.
Sharma and G. M. Dhar, J. Mol. Catal. A: Chem., 2004,
213, 217.
2
3
3
1
2
3
3
4
3
technol., 2012, 97, 71.
44, 5092.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins