The carbonylation of dimethyl ether catalyzed by supported heteropoly acids: The role of Br?nsted acid properties

Article abstract of DOI:10.1016/j.cattod.2018.04.001

The carbonylation of dimethyl ether (DME) to methyl acetate (MA) is a vital step in a direct route of ethanol production from syngas. Heteropoly acids (HPAs) as a kind of solid acid catalysts can facilitate the reaction. To improve the accessibility of Br?nsted acid sites, we prepared a series of supported HPAs catalysts by wetness impregnation on SBA-15. The impact of the HPAs loading and composition on the textural structure and acidic properties was investigated by comparing with the bulk HPAs. Taking acidity analysis (Pyridine-IR and TPD) and catalytic measurement results, we explored the effect of the amount and strength of Br?nsted acid site on this reaction. The observations demonstrated that more and stronger acid sites are prone to MA formation.

Full text of DOI:10.1016/j.cattod.2018.04.001

Accepted Manuscript
Title: The carbonylation of dimethyl ether catalyzed by
supported heteropoly acids: The role of Brønsted acid
properties
Authors: Hongbao Shen, Ying Li, Shouying Huang, Kai Cai,
Zaizhe Cheng, Jing Lv, Xinbin Ma
PII:
S0920-5861(18)30374-2
DOI:
Reference:
https://doi.org/10.1016/j.cattod.2018.04.001
CATTOD 11357
To appear in:
Catalysis Today
Received date:
Revised date:
Accepted date:
31-1-2018
27-3-2018
1-4-2018
Please cite this article as: Shen H, Li Y, Huang S, Cai K, Cheng Z,
Lv J, Ma X, The carbonylation of dimethyl ether catalyzed by supported
heteropoly acids: The role of Brønsted acid properties, Catalysis Today (2010),
https://doi.org/10.1016/j.cattod.2018.04.001
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

The carbonylation of dimethyl ether catalyzed by
supported heteropoly acids: the role of Brønsted acid
properties
Hongbao Shen, Ying Li, Shouying Huang*, Kai Cai, Zaizhe Cheng, Jing Lv and
Xinbin Ma
Key Laboratory for Green Chemical Technology of Ministry of Education;
Collaborative Innovation Center of Chemical Science and Engineering, School of
Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
Corresponding author
* Shouying Huang: huangsy@tju.edu.cn
Graphical abstract
1

Highlight
 Supporting heteropoly acids on SBA-15 modifies their accessibility to reactants.
 Supported catalysts improve the efficiency of heteropoly acids in DME
carbonylation.
 More and stronger Brønsted acid sites facilitate the formation of methyl acetate.
Abstract
The carbonylation of dimethyl ether (DME) to methyl acetate (MA) is a vital
step in a direct route of ethanol production from syngas. Heteropoly acids (HPAs) as a
kind of solid acid catalysts can facilitate the reaction. To improve the accessibility of
Brønsted acid sites, we prepared a series of supported HPAs catalysts by wetness
impregnation on SBA-15. The impact of the HPA loading and composition on the
textural structure and acidic properties was investigated by comparing with the bulk
HPAs. Taking acidity analysis (Pyridine-IR and TPD) and catalytic measurement
results, we explored the effect of the amount and strength of Brønsted acid site on this
reaction. The observations demonstrated that more and stronger acid sites are prone to
MA formation.
Key words: Carbonylation; Dimethyl ether; Heteropoly acids; Brønsted acidity;
SBA-15
2

1 Introduction
Ethanol is an important raw material in the synthesis of various chemicals, such
as acetaldehyde, ether, ethylamine and so on. It is also a good solvent for both
organics and inorganics. More important, ethanol is considered as a promising
substitute for fossil fuels, benefiting from its negligible negative impacts on
environment. In addition to the biomass fermentation [1] and ethylene hydration [2], a
new path for ethanol production from syngas has drawn much attention recently, for
the syngas can be obtained from coal, biomass as well as the nature gas [3, 4]. In the
whole process, the carbonylation of DME to MA and the hydrogenation of MA to
ethanol are indispensable intermediate steps [5, 6]. As the former in this route, the
carbonylation of DME to MA is usually catalyzed by solid acid catalysts.
Heteropoly acids (HPAs) especially Keggin types HPAs are a kind of solid acid
catalysts which possess strong Brønsted acid strength [7]. The Keggin unit consists of
central atom and heteroatom, satisfying this formula Hn(XM12O40)n-, where X is PV or
SiIV within the cage and M is WV or MoVI, typically. In heterogeneous catalytic
reactions, HPAs are excellent catalysts for many acid-catalyzed reactions [7-11], due
to their solid state structures, strong Brønsted acidities, and interesting chemical
characteristics. However, bulk HPAs have low surface area (<10 m2/g) and poor
porosity, many Brønsted acid sites are not accessible for reactants, which hinders their
performance as a heterogeneous catalyst.
As the carbonylation of DME is mainly a “surface-type” reaction catalyzed by
heteropoly acids [12], the activity of the catalyst is also limited by the accessibility of
3

HPAs. Many efforts have been made to improve the activity of DME carbonylation on
HPAs. The addition of precious metals such as Rh [13, 14], Pt and Ag [15] can
accelerate the reaction by promoting the insertion of CO, but available Brønsted acid
sites are still not improved. The iodine agent such as methyl iodide facilitate the
reaction by changing the pathway [16], whereas the corrosion is inevitable. The
substitute of H+ ions with Cs+ can enlarge the surface area due to the larger ion radius
of Cs+ with the consumption of acidic protons [17].
Actually, supported HPAs on some carriers with high surface area can increase
the active sites accessibility significantly. A great variety of supports, such as metal
oxides [18-20], clays [21], silica gel [22], mesoporous Si-MCM-41 and Al-MCM-41
[23], hexagonal silica (HMS) [24] or neutral salt Cs3PW12O40 [20], have already been
used for supporting HPAs. Numerous studies have shown that the nature of supports
and the surface coverage affect the textural and catalytic properties of the catalysts
[25-27]. Mesoporous silicon molecular sieves exhibit excellent performance in
comparison to metal oxides and fumed silica, owing to abundant porosity and lack of
basicity and Lewis acidity [28, 29].
In this work, we support HPAs on SBA-15 for the carbonylation of DME to
improve the availability of Brønsted acid sites. Firstly, we prepare a series of
HPW/SBA-15 samples with different loadings. The influence of loading on the
textural structure and acid strength was investigated in reference to the bulk HPW.
Subsequently, we support three kinds of heteropoly acids (HPW, HSiW and HPMo)
on SBA-15 to study the role of acid strength. By analyzing the relation between the
4

acid property and the reactivity, we put forward the positive impact of Brønsted acid
strength on the carbonylation of DME.
2 Experiment
2.1 Catalyst preparation
Phosphotungstic acid (H3PW12O40, Tianjin Kemiou Chemical Reagent Co., Ltd)
was dispersed on SBA-15 (Nanjing XFNANO Materials Tech Co., Ltd) using wet
impregnation method. Wet impregnation was performed by dissolving the required
amount of H3PW12O40 in 40 mL deionized water, followed by the addition of a certain
amount of support SBA-15. The mixture was stirred for 48 h at room temperature to
ensure uniform distribution of clusters in SBA-15 channels and subsequently dried by
solvent evaporation under vacuum. Then, the samples were treated at 110 oC
overnight and stored for catalytic test and characterization. Bulk phosphotungstic acid
was dried at 110 oC in air and taken as a reference. Silicotungstic acid (H4SiW12O40,
Tianjin Guangfu Fine Chemical Research Institute) and phospomolybdic acid
(H3PMo12O40, Tianjin Guangfu Fine Chemical Research Institute) were supported on
SBA-15 by the same method. The samples were denoted as χ wt. % HPAs/SBA-15 (i.
e. HPW/SBA-15, HSiW/SBA-15, HPMo/SBA-15), with χ representing the amount of
heteropoly acids (wt. %) in the catalysts.
2.2 Catalyst characterization
The surface area and the porosity of the catalysts were analyzed by N2
physisorption on a Micromeritics ASAP-2020 instrument at -196 oC. The samples
were degassed at 300 oC for 3 h prior to analysis. Specific surface area was obtained
5

by the Brunauer-Emmett-Teller (BET) equation. The total pore volume and pore size
distribution of samples were determined by the BJH method, according to the
adsorption of isotherm.
The actual content of heteropoly acids (HPW, HSiW, HPMo) was calculated by
the elemental analysis of W or Mo in the samples on inductively coupled plasma
optical emission spectroscopy (ICP-OES) (VISTA-MPX, Varian).
Powder X-ray diffraction (XRD) patterns of the catalysts were recorded by a
Rigaku D/max-2500 diffractometer equipped with Cu Kα (λ = 0.154 nm) radiation
over the 2θ range of 5 o-80 o, at the rate of 8 o/min.
Fourier transform infrared (FTIR) spectra of catalysts were taken on a Nicolet
6700 using powdered catalysts diluted with KBr (1 mg catalysts diluted into 100 mg
KBr). The fingerprint spectra of Keggin units were recorded at room temperature. The
IR spectra of adsorbed pyridine were recorded on the same instrument equipped with
an in-situ cell connected to a vacuum system. The samples (~18 mg) were pressed
into a 13 mm self-supporting wafer and placed in the cell with CaF2 windows. Prior to
pyridine adsorption, the samples were pre-treated at 200 oC for 2 h under high
vacuum, approximating 10-5 Pa. Thereafter the wafer was cooled down and
maintained at 150 oC to record the background spectrum. Then the sample was
exposed to pyridine vapor until it was saturated, followed by pumping out the
physically adsorbed pyridine for 30 min. Finally, the spectra were collected in the
range of 650-4000 cm-1 by averaging 32 scans at a resolution of 4 cm-1. The amount
of Brønsted acid sites was estimated by integrating the surface area of the band at
6

1540 cm-1, according to the Ref. [30].
Temperature-programmed desorption of pyridine was implemented to investigate
the strength of Brønsted acid sites for the catalysts. Prior to analysis, the catalysts
were pretreated at 200 oC for 2 h, then cooled down to 150 oC and maintained at this
temperature to achieve saturated adsorption of pyridine. Subsequently, the excess
pyridine was flushed with He flow for more than 1 h until the baseline was stable. The
desorption of pyridine was carried out in He flow with a ramp of 10 oC /min in the
range of 150 oC-800 oC for χ wt.% HPW/SBA-15 and 25 wt.% HSiW/SBA-15. As the
decomposition of HPMo has been proved above 650 oC by TG analysis (not shown
here), we performed the pyridine desorption on 25 wt.% HPMo/SBA-15 in the range
of 150 oC-600 oC. The desorbed pyridine was detected using a thermal conductivity
detector (TCD).
Transmission electron microscopy (TEM) images were obtained on a Philips
Tecnai G2F20 system. The sample powder was dispersed in methanol with the
assistance of ultrasonic. Then, the suspension was dropped on the ultra-thin carbon
film. According to the TEM images, we make statistics of particle distribution and
calculate the average diameter based on above 200 particles.
2.3 Catalyst testing
The reaction of DME with CO to produce MA was carried out in a fixed-bed
down-flow reactor (8 mm inner diameter). In a typical run, 1 g of catalyst (40-60
mesh) was loaded in the reactor. The reactor pressure was kept at 1.5 MPa throughout
the process. Prior to the reaction, the catalyst was pre-treated in N2 atmosphere
7

(99.99%, Tianjin Zhenhao Gas Co., Ltd) at 200 oC for 2 h. The reactant mixture
(DME/CO = 1/49, mol/mol) was introduced into the reactor at a total flow rate of 30
mL/min. The product stream was analyzed by an online gas chromatograph (Agilent
7890B GC). The facility was equipped with both flame ionization detector (FID) for
detecting DME, MA, and other organic by-products and TCD for detecting the
permanent gases (CO, CO2 and N2). Methanol, methyl formate and acetic acid were
detected as by-products. The selectivity and space time yield (STY) of MA were
calculated by Eq. (1) and Eq. (2), respectively.
SMA = MA / (CH3OH/2 + HCOOCH3/2 + MA + CH3COOH)
STYMA = XDME × SMA
(1)
(2)
3 Results and discussion
3.1 Textural and morphological properties of the catalysts
The textural and morphological properties of catalysts and support are shown in
Figure 1. All the catalysts show typical IV isotherms, demonstrating that all supported
samples maintained the mesoporous structure of the support SBA-15 with similar
pore diameter distribution in the vicinity of 7 nm. The calculated specific surface area
and pore volume are listed in Table 1. The support SBA-15 possesses largest surface
area and pore volume, up to 702 m2/g and 0.99 cm3/g, respectively. After loading
HPAs, there is an apparent decrease in the surface area and pore volume. This trend is
even more pronounced with the increase of loading for χ wt.% HPW/SBA-15 (χ from
15 to 75). The decrease can be attributed to the location of Keggin units in
mesoporous channels of SBA-15 at low loading [29, 31]. When the loading is above
8

35 wt.%, some agglomerate Keggin units block the channel ports, leading to the sharp
decrease of surface area and pore volume. In spite of this, the surface area had a
significant improvement in comparison to the bulk HPW. In addition, the samples of
25 wt.% heteropoly acids loadings, show similar textural properties with surface area,
pore volume and pore diameter distribution.
Elemental analysis (Table 1) and XRD (Figure 2) demonstrate that HPAs are
successfully supported on SBA-15. All the samples show a broad diffraction peak
from 13 o to 35 o except 75 wt.% HPW/SBA-15, corresponding to the characteristic of
SBA-15. At low HPW loading (< 25 wt.%), HPW/SBA-15 samples only exhibit the
parent support diffraction peak, suggesting HPW is well-dispersed on the SBA-15.
When the loading is above 25 wt.%, peaks at 2θ about 10, 20, 27 and 35 o referring to
HPW Keggin unit [32] begin to appear. The reflections of supported samples are
consistent with the bulk HPW, attributed to the hexahydrated structures
(H3PW12O40·6H2O) [33]. The emergence of reflections characteristic is presumably
due to the aggregate of individual Keggin units, whose peak-intensities increase and
peak-widths decrease with the rising of HPW loading. For the other two kinds of
heteropoly acids supported samples, there are no characteristic diffraction peaks of
HSiW or HPMo, illustrating fine dispersion is also obtained for 25 wt.% HSiW/SBA-
15 and 25 wt.% HPMo/SBA-15.
FTIR was employed to detect the Keggin structure of HPAs on SBA-15. The
spectra of SBA-15 and different bulk HPAs are displayed as references in Figure 3.
Keggin anions (PW12O403-) of HPW show typical IR bands at 1080 cm-1 (P-Oi-W,
9

central oxygen atom), 976-995 cm-1 (W-Ot, terminal oxygen atom), 890-900 cm-1 (W-
Oc-W, bridge-corner oxygen atom), 805-810 cm-1 (W-Oe-W, bridge-edge oxygen
atom) [34, 35]. For the supported samples, even though some of the IR bands are
over-lapped by those of SBA-15, the bands at 983 and 890 cm-1 are well-defined,
which is indicative of Keggin anions. This suggests the existence of HPW on silica
surface and the preservation of the structure of Keggin units [34, 36]. The intensity of
these two bands are strengthened with the increase of HPW loading and when the load
is up to 35 wt.% and even higher, the band at 1080 cm-1 is observed. Combined with
the XRD results (Figure 2), we deduce the formation of large HPW crystallites in the
channel and on the external surface of SBA-15, which behave like the bulk HPW and
cover Brønsted acid sites, reducing the utilization efficiency of HPW. For HSiW and
HPMo supported samples, Keggin anions of HSiW show IR bands at 1020 cm-1, 982
cm-1, 926 cm-1, 884 cm-1, 778 cm-1 [37] and HPMo show IR bands at 1064 cm-1, 962
cm-1, 869 cm-1, 787 cm-1 [38], respectively. By contrasting the IR bands of the
supported samples with bulk HSiW and HPMo, we also confirmed the existence of
defined-Keggin units. Furthermore, the structure of Keggin units keeps intact at
reaction temperature, demonstrated by FTIR (not shown here).
Supported HPW samples nanostructures were observed by TEM at 25 wt.%
HPW/SBA-15 and 75 wt.% HPW/SBA-15, shown in Figure 4. It is apparent that the
dispersed and isolated HPW clusters (~1.5 nm) are obtained on 25 wt.% HPW/SBA-
15, corresponding to the absence of diffraction peaks in XRD. Conversely, high
loading affords large HPW agglomerates with the mean particle sizes of 21.7 nm on
10

SBA-15, in line with the low surface area, poor porosity in nitrogen adsorption and
strong diffraction peaks in XRD.
3.2 Acidity characterization of the catalysts
As the carbonylation of DME can be catalyzed by Brønsted acid sites, the
number and strength of acid sites are of great importance for the catalytic properties.
The IR in the range of 1400-1700 cm-1 are recorded to determine the nature of the acid
sites by using pyridine as probe molecule (Figure 5a, 5b) [39, 40]. The support SBA-
15 shows no obvious bands in the range, indicating it has negligible acid sites. The
weak band at 1450 cm-1 might result from the adsorbed pyridine on weak Lewis acid
sites or weakly hydrogen-bonded pyridine, as reported in literature [31]. In
comparison, supporting HPAs gives rise to several bands, in which 1540 and 1630 cm-
1 are associated with the pyridinium ions adsorbed on Brønsted acid sites, and 1450
and 1610 cm-1 are attributed to the interaction between pyridine and Lewis acid sites.
Furthermore, the co-contribution of Brønsted and Lewis acid sites is responsible for
the appearance of the band at 1490 cm-1. It is apparent that the band at 1540 cm-1
gradually becomes more pronounced with increasing HPW loading, indicating the
increment of Brønsted acid sites per unit mass of catalyst. Comparing with HPW
supported on SBA-15, the 25 wt.% HSiW/SBA-15 exhibits the bands with similar
intensity in Figure 5b, while the 25 wt.% HPMo/SBA-15 has a prominent band at
1450 cm-1, indicative of abundant Lewis acid sites. It possibly results from the partial
decomposition of HPMo into oxides during preparation and characterization, due to
its poor thermal stability [33]. We calculated the amount of accessible Brønsted and
11

Lewis acid sites for all samples based on pyridine-adsorption IR and the results are
summarized in Table 1. On the other hand, theoretical concentration of Brønsted acid
sites are also estimated according to actual HPAs loadings, which are determined by
ICP-OES. We plotted theoretical Brønsted acid amount versus the actual value
determined by pyridine-adsorption IR. As shown in Figure 5c and 5d, the amount of
accessible Brønsted acid sites shows a nearly proportional dependence on HPW
loadings increasing from 0 to 35 wt.%. Further increasing HPW loading, the
detectable Brønsted acid sites are less than the calculated value based on actual
loading, and the deviation between them becomes much larger on 75 wt.%
HPW/SBA-15. It is due to the agglomeration of HPW within SBA-15 mesopores,
which blocks the channels of SBA-15 and covers Brønsted acid sites. Consequently,
the Brønsted acid sites are poorly accessible to pyridine molecule. On the other hand,
it is noted that the theoretical and actual number of Brønsted acid sites are
approximate for 25 wt.% HPW/SBA-15 and 25 wt.% HSiW/SBA-15. However, the
deviation is remarkable for HPMo/SBA-15 with same designed loading, resulting
from the decomposition of HPMo as we mentioned above.
For acid catalyzed reaction, the strength of acid sites always plays an important
role in activity and selectivity. We synthesized HPAs/SBA-15 catalysts with similar
loading but different kinds of HPAs, aiming at controllable acid strength. On the other
hand, the acid strength of supported HPAs samples shows a dependence on dispersion
of HPAs [41]. Therefore, pyridine-TPD measurements were conducted to explore the
effect of acid strength on carbonylation of DME, as shown in Figure 6. As Brønsted
12

acid sites are exclusively formed on χ wt.% HPW/SBA-15 samples (seen from
pyridine-adsorbed IR), the peak can be ascribed to the removal of pyridine molecules
adsorbed on Brønsted acid sites. It is obvious that the centre of desorption peak shifts
towards higher temperature with increasing HPW loading, indicating the enhanced
acid strength at higher coverage of HPW on SBA-15 surface. A similar phenomenon
has been reported for HPW supported on metal oxides and metal organic framework
[42]. Generally, dispersed HPAs on support will lose some of their acidic character in
comparison with the bulk ones, owing to the interaction between HPAs and support.
Taking HPW supported on silica as an example, one proton of H3PW12O40 reacts with
the OH of silanol to form (≡SiOH2)+(H2PW12O40)- species, resulting in weakened
acidity [22, 43, 44]. With increasing HPW loading, the agglomeration of the
crystalline HPW becomes severer. As a result, the strength of acid sites is recovered.
For the three 25 wt.% HPAs/SBA-15 samples, the main desorption peaks locate at
remarkably different temperatures, decreasing according to the order: 25 wt.%
HPW/SBA-15 (425 oC) > 25 wt.% HSiW/SBA-15 (413 oC) > 25 wt.% HPMo/SBA-
15 (310 oC), which maintains the original acidic strength order of bulk heteropoly
acids. Particularly, 25 wt.% HPMo/SBA-15 sample exhibits a much lower desorption
temperature than the others. It is due to the existence of a large amount of weak Lewis
acid sites, resulted from the decomposition of HPMo on SBA-15.
3.3. Catalytic performance for DME carbonylation
Considering the decrease of catalytic activity with time, the reaction data at 1.5 h
are chosen as the initial catalytic performance to be discussed in this work. Figure 7
13

illustrates the space time yield (STY) and selectivity of MA in the carbonylation of
DME reaction. For χ wt.% HPW/SBA-15 catalysts, the STYcat is improved as the
amount of Brønsted acid sites increases, but the growth becomes much lower when
the loading is above 25 wt.% (Figure 7a). This means the efficiency of active HPW
species declines gradually. We also plotted the STY based on HPW mass versus HPW
loading. It is found that the STYHPW of MA decreases monotonically with the increase
of HPW loading (Figure 7b). That is to say, the larger loading of HPW, the lower
reactivity of Keggin units. The sharp reduction in the surface area and pore volume,
together with the poor dispersion of Keggin units results in the decline of activity. The
products distribution at 1.5 h was shown in Figure 8a. The selectivity of MA
improved with the increase of HPW loading, while the selectivity of by-products (i.e.
methanol, methyl formate and acetic acid) decreased gradually. Considering acidity
characterization, we conclude that strong Brønsted acid sites are prone to catalyze MA
production, while weak acidity and Lewis acid sites lead to the formation of by-
products.
On the other hand, the type of HPAs plays an important role in activity. The
reactivity of Keggin units declines in this order: HPW > HSiW > HPMo, which is
consistent with their acid strength (Figure 7c). Furthermore, more methyl formate was
produced for 25 wt.% HPMo/SBA-15 sample, which might be induced by the metal
oxide from the decomposition of HPMo (Figure 8b).
14

4 Conclusion
In this work, we employed SBA-15 to disperse heteropoly acids for DME
carbonylation. In the impregnation process, Keggin units enter the channels of SBA-
15 with changes in porosity. XRD and IR suggest that the Keggin structure of HPAs is
finely preserved after being supported on SBA-15. Both loading and type of HPAs
influence the catalytic activity. For HPW, higher utilization efficiency of HPW can be
achieved at low loading because of better dispersion. However, the strength of
Brønsted acid sites is weakened, resulting in the formation of by-products. Increasing
HPW loading, severe aggregation of HPW Keggin units can be observed, leading to
the reduction of the surface area and pore volume. As a result, the reactivity of the
HPW decreases gradually. Investigations on different HPAs show that strong acid
sites accelerate the formation of MA. HPMo is prone to decompose on SBA-15,
leading to the formation of Lewis acid sites with a significant decrease of Brønsted
acidity.
Acknowledgements
Financial support from the National Natural Science Foundation of China
(21325626, 21406120), Postdoctoral Science Foundation of China (2015T80214) and
the Program of Introducing Talents of Discipline to Universities (B06006) is
gratefully acknowledged.
15

References
[1] M. Balat, H. Balat, C. ꢀz, Prog. Energy Combust. Sci. 34 (2008) 551-573.
[2] W. Chu, T. Echizen, Y. Kamiya, T. Okuhara, Appl. Catal. A Gen. 259 (2004)
199-205.
[3] V. Subramani, S.K. Gangwal, Energy Fuel 22 (2008) 814-839.
[4] X. San, Y. Zhang, W. Shen, N. Tsubaki, Energy Fuel 23 (2009) 2843-2844.
[5] Y. Liu, K. Murata, M. Inaba, I. Takahara, Fuel Process. Technol. 110 (2013)
206-213.
[6] G. Yang, X. San, N. Jiang, Y. Tanaka, X. Li, Q. Jin, K. Tao, F. Meng, N.
Tsubaki, Catal. Today 164 (2011) 425-428.
[7] I.V. Kozhevnikov, Chem. Rev. 98 (1998) 171-198.
[8] C.L. Hill, J. Mol. Catal. A Chem. 262 (2007) 2-6.
[9] M.N. Timofeeva, Appl. Catal. A Gen. 256 (2003) 19-35.
[10]T. Okuhara, N. Mizuno, M. Misono, Appl. Catal. A Gen. 222 (2001) 63-67.
[11]D.L. Long, E. Burkholder, L. Cronin, Chem. Soc. Rev. 36 (2007) 105-121.
[12]G.G. Volkova, L.M. Plyasova, A.N. Salanov, G.N. Kustova, T.M. Yurieva, V.A.
Likholobov, Catal. Lett. 80 (2002) 3-4.
[13]M.V. Luzgin, M.S. Kazantsev, W. Wang, A.G. Stepanov, J. Phys. Chem. C 113
(2009) 19639-19644.
[14]M.S. Kazantsev, M.V. Luzgin, A.G. Stepanov, J. Phys. Chem. C 117 (2013)
11168-11175.
[15]M.V. Luzgin, M.S. Kazantsev, G.G. Volkova, A.G. Stepanov, J. Catal. 308
16

(2013) 250-257.
[16]M.S. Kazantsev, M.V. Luzgin, G.G. Volkova, A.G. Stepanov, J. Catal. 291
(2012) 9-16.
[17]M.V. Luzgin, M.S. Kazantsev, G.G. Volkova, W. Wang, A.G. Stepanov, J. Catal.
277 (2011) 72-79.
[18]A.M. Alsalme, P.V. Wiper, Y.Z. Khimyak, E.F. Kozhevnikova, I.V.
Kozhevnikov, J. Catal. 276 (2010) 181-189.
[19]E. Rafiee, H. Mahdavi, S. Eavani, M. Joshaghani, F. Shiri, Appl. Catal. A Gen.
352 (2009) 202-207.
[20]W. Alharbi, E. Brown, E.F. Kozhevnikova, I.V. Kozhevnikov, J. Catal. 319
(2014) 174-181.
[21]M.S. Tiwari, G.D. Yadav, RSC Adv. 6 (2016) 49091-49100.
[22]J.A. Dias, E. Caliman, S.C.L. Dias, M. Paulo, A.T.C.P.d. Souza, Catal. Today 85
(2003) 39-48.
[23]B.R. Jermy, A. Pandurangan, Appl. Catal. A Gen. 295 (2005) 185-192.
[24]C. Trolliet, G. Coudurier, J.C. Védrine, Top. Catal. 15 (2001) 73-81.
[25]H. Liu, E. Iglesia, J. Catal. 223 (2004) 161-169.
[26]C. Trolliet, G. Coudurier, J.C. Védrine, Top. Catal. 15 (2001).
[27]A. Popa, V. Sasca, I. Holclajtner-Antunović, Microporous Mesoporous Mater.
156 (2012) 127-137.
[28]K.W. La, J.C. Jung, H. Kim, S.H. Baeck, I.K. Song, J. Mol. Catal. A Chem. 269
(2007) 41-45.
17

[29]L. Frattini, M.A. Isaacs, C.M.A. Parlett, K. Wilson, G. Kyriakou, A.F. Lee,
Appl. Catal. B Environ. 200 (2017) 10-18.
[30]C.A. Emeis, J. Catal. 141 (1993) 347-354.
[31]A.E.R.S. Khder, H.M.A. Hassan, M.S. El-Shall, Appl. Catal. A Gen. 411-412
(2012) 77-86.
[32]G. Nie, J.J. Zou, R. Feng, X. Zhang, L. Wang, Catal. Today 234 (2014) 271-277.
[33]V.L. Sushkevich, V.V. Ordomsky, I.I. Ivanova, Catal. Sci. Technol. 6 (2016)
6354-6364.
[34]R. Thouvenot, M. Fournier, R. Franck, C. Rocchiccioli-Deltcheff, Inorg. Chem.
23 (1984) 598-605.
[35]N. Essayem, A. Holmqvist, P.Y. Gayraud, J.C. Vedrine, Y. Ben Taarit, J. Catal.
197 (2001) 273-280.
[36]L. Zhang, H.Q. He, R.K. S/O Abdul Rasheed, W.J. Zhou, Y.H. Xue, O.L. Ding,
S.H. Chan, J. Power Sources 221 (2013) 318-327.
[37]L.R. Pizzio, M.N. Blanco, Microporous Mesoporous Mater. 103 (2007) 40-47.
[38]L.R. Pizzio, P.G. Vázquez, C.V. Cáceres, M.N. Blanco, Appl. Catal. A Gen. 256
(2003) 125-139.
[39]H. Zhan, S. Huang, Y. Li, J. Lv, S. Wang, X. Ma, Catal. Sci. Technol. 5 (2015)
4378-4389.
[40]M. Wang, S. Huang, J. Lv, Z. Cheng, Y. Li, S. Wang, X. Ma, Chinese J. Catal.
37 (2016) 1530-1537.
[41]A.D. Newman, D.R. Brown, P. Siril, A.F. Leea, K. Wilson, Phys. Chem. Chem.
18

Phys. 8 (2006) 2893-2902.
[42]K. Sabyrov, J. Jiang, O.M. Yaghi, G.A. Somorjai, J. Am. Chem. Soc. 139 (2017)
12382-12385.
[43]W. Kuang, A. Rives, M. Fournier, R. Hubaut, Appl. Catal. A Gen. 250 (2003)
221-229.
[44]F. Lefebvre, J. Chem. Soc., Chem. Commun. 10 (1992) 756-757.
19

Figure captions
Fig. 1. Nitrogen adsorption isotherms and pore distribution curves of the SBA-15, χ wt.%
HPW/SBA-15 (a, b) and 25 wt.% HPAs/SBA-15 (c, d).
Fig. 2. XRD patterns of the bulk HPW, χ wt.% HPW/SBA-15 (a) and 25 wt.% HPAs/SBA-15 (b).
20

Fig. 3. FTIR spectra of χ wt.% HPW/SBA-15 (a), 25 wt.% HPAs/SBA-15 (b) with the reference of
SBA-15 and various HPAs.
Fig. 4. TEM images of the 25 wt.% HPW/SBA-15 (a) and 75 wt.% HPW/SBA-15 (b).
21

Fig. 5. FTIR spectra of adsorbed pyridine on the SBA-15, χ wt.% HPW/SBA-15 (a) and 25 wt.%
HPAs/SBA-15 (b) and the amount of Brønsted acid versus HPAs loading and type: χ wt.%
HPW/SBA-15 (c), 25 wt.% HPAs/SBA-15 (d).
Fig. 6. Pyridine-TPD profiles of the SBA-15, χ wt.% HPW/SBA-15 (a), and 25 wt.% HPAs/SBA-
15 (b) .
22

Fig. 7. Space time yield and selectivity for MA over χ wt.% HPAs/SBA-15. Reaction conditions:
catalyst weight = 1 g, reactant gas DME/CO (1:49), temperature = 200 oC, pressure = 1.5 MPa,
total flow rate = 30 mL/min, reaction time = 1.5 h.
Fig. 8 Selectivity of MA and by-products (methanol: MeOH; methyl formate: MF; acetic acid:
AcOH) on χ wt.% HPW/SBA-15 (a) and 25 wt.% HPAs/SBA-15 (b). Reaction conditions: catalyst
weight = 1 g, reactant gas DME/CO (1:49), temperature = 200 oC, pressure = 1.5 MPa, total flow
rate = 30 mL/min, reaction time = 1.5 h.
23

Table 1 Composition, textural properties and amount of acid sites in χ wt.% HPAs/SBA-15
samples.
HPA
Amount of B Amount of L
Surface area Pore volume
Sample
contenta
(wt.%)
acid siteb
acid siteb
(m2/g)
(cm3/g)
(μmol/g)
(μmol/g)
SBA-15
0
702.0
588.2
485.5
461.5
344.5
117.9
429.0
456.0
0.99
0.70
0.59
0.56
0.40
0.06
0.64
0.66
nd
nd
15 wt.% HPW/SBA-15
25 wt.% HPW/SBA-15
35 wt.% HPW/SBA-15
50 wt.% HPW/SBA-15
75 wt.% HPW/SBA-15
25 wt.% HSiW/SBA-15
25 wt.% HPMo/SBA-15
12.2
19.5
24.2
38.3
63.2
20.9
23.1
127.7
215.0
259.1
372.5
394.7
269.2
245.2
23.8
21.7
23.5
10.9
2.9
24.2
169.9
a calculated based on ICP measurement.
b calculated based on the area of band at 1540 cm-1 (B) and 1450 cm-1 (L) in pyridine adsorbed IR.
24