Framework-Substituted Sn-MOR Zeolite Prepared by Multiple pH-Adjusting Сo-Hydrolysis As Efficient Catalyst for tert-Butylation of Toluene

Article abstract of DOI:10.1134/S0036024418130095

Abstract: A series of Sn-MOR samples with different tin species loadings were prepared via a mutiple pH?adjusting co-hydrolysis method. Their properties were characterized by XRD, XRF, UV–Vis, FT-IR, Py-IR, N₂ sorption and SEM techniques. The catalytic performance was evaluated in liquid-phase toluene alkylation with tert-butyl alcohol. The characterization results shows that compared to framework destruction of mordenite for the Sn/MOR sample with floccule prepared by ion exchange method, higher relative crystallinity and larger surface area and pore volume for Sn-MOR samples with walnut morphology can be obtained. The doping with tin species can increase the Lewis acidity and decrease the pore size resulting in both higher toluene conversion and p-tert-butyltoluene (PTBT) selectivity. The Sn-MOR(0.010) sample shows the highest catalytic performance with toluene conversion of 48.0% and PTBT selectivity of 85.6%. It?shows high stability: toluene conversion of 45.3% and PTBT selectivity of 87.2% can be obtained even after 5 consecutive runs.

Full text of DOI:10.1134/S0036024418130095

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2018, Vol. 92, No. 13, pp. 2640–2646. © Pleiades Publishing, Ltd., 2018.
CHEMICAL KINETICS
AND CATALYSIS
Framework-Substituted Sn-MOR Zeolite Prepared
by Multiple pH-Adjusting Сo-Hydrolysis As Efficient Catalyst
1
for tert-Butylation of Toluene
a
a,
b
a
a
a,
Fuling Cheng , Zhiwei Zhou *, Juan Qin , Dong Li , Jianzong Wang , and Wenliang Wu **
a
College of Chemical Engineering, Nanjing Tech University, Nanjing, 210009 P. R. China
b
Technology and Finance Service Center of Jiangsu Province, Productivity Center of Jiangsu Province,
Nanjing, 210042 P. R. China
*e-mail: zhiweizhou@njtech.edu.cn
*
*e-mail: wwl@njtech.edu.cn
Received December 12, 2017
Abstract—A series of Sn-MOR samples with different tin species loadings were prepared via a mutiple
pH-adjusting co-hydrolysis method. Their properties were characterized by XRD, XRF, UV–Vis, FT-IR,
Py-IR, N sorption and SEM techniques. The catalytic performance was evaluated in liquid-phase toluene
2
alkylation with tert-butyl alcohol. The characterization results shows that compared to framework destruction
of mordenite for the Sn/MOR sample with floccule prepared by ion exchange method, higher relative crys-
tallinity and larger surface area and pore volume for Sn-MOR samples with walnut morphology can be
obtained. The doping with tin species can increase the Lewis acidity and decrease the pore size resulting in
both higher toluene conversion and p-tert-butyltoluene (PTBT) selectivity. The Sn-MOR(0.010) sample
shows the highest catalytic performance with toluene conversion of 48.0% and PTBT selectivity of 85.6%.
It shows high stability: toluene conversion of 45.3% and PTBT selectivity of 87.2% can be obtained even after
5
consecutive runs.
Keywords: Sn-MOR, multiple adjusting, co-hydrolysis, toluene, p-tert-butyltoluene
DOI: 10.1134/S0036024418130095
INTRODUCTION
molecular dehydration of tert-butyl alcohol [2–8].
The PTBT selectivity over mordenite is higher than
over other zeolites owing to the close dimensions of
zeolite pores and molecular diameter of PTBT
p-tert-Butyltoluene (PTBT), one of three isomers
of tert-butyltoluene, is an important chemical inter-
mediates. It can be oxidized to p-tert-butylbenzalde-
hyde and p-tert-butylbenzoic acid, which are used in
production of fragrances, resins, polyesters or phar-
maceuticals. Up to now, PTBT is often prepared by
Friedel-Crafts alkylation of toluene with various
reagents including isobutylene, tert-butyl chloride and
tert-butyl alcohol using liquid acid catalysts, such as
BF , AlCl , H SO , HF, or H PO , etc. [1], which
(
0.58 nm) [9]. However, its catalytic activity is rather
limited because of the low acidity, especially Lewis
acidity, which has been proved to be beneficial to the
toluene conversion. Therefore, the mordenite based
catalysts modified for increasing their Lewis acidity
would show good catalytic performance in liquid-
phase toluene alkylation with tert-butyl alcohol.
3
3
2
4
3
4
Among the modification methods, the introduc-
tion of the active components with high Lewis acidity
into the framework with good catalytic stability would
be a promising strategy, and some heteroatom mor-
denite catalysts have been prepared by replacing tetra-
hedrally coordinated sites of parent Si or Al atom
under controlled conditions [10–16]. For example,
would suffer from some drawbacks regarding both dif-
ficult catalyst recovery resulting in environment pollu-
tion and severe equipment corrosion. In order to avoid
these problems, many solid acid catalysts, such as zeo-
lites, heteroatom mesoporous materials and hetero-
polyacid supported catalysts have been explored.
In the liquid-phase alkylation of toluene with tert- Sn-beta zeolite prepared by incorporation of tetrava-
butyl alcohol, zeolites-based materials with high lent tin into the framework has been proved to be a
hydrothermal stability and shape selectivity would be solid Lewis acid catalyst with high activity in the glu-
promising catalysts because water is formed by intra- cose epimerization, Bayer–Villiger oxidation and
glycerol acetalization [17–20]. In addition, since the
atomic diameter of tin is larger than that of Si or Al, its
1
The article is published in the original.
2640

FRAMEWORK-SUBSTITUTED Sn-MOR ZEOLITE PREPARED
2641
successful incorporation would effectively reduce the added resulting in mixture pH of 5.0–6.0 with contin-
pore size of mordenite, which would probably be uously stirring for 12 h. Finally, the aqueous NaOH
favorable for the PTBT selectivity [21]. However, the solution (50 wt %) was dropwise added for adjusting
heteroatom Sn-MOR zeolite in situ synthesis has not the pH of the slurry to 11.9. The resulting gels were
been widely reported so far, which may be owing to the transferred into a sealed Teflon-lined autoclave and
layered structure of mordenite itself and to the longer heated under static conditions at 413 K for 5 days. The
Si–O–Sn bonds or higher bond angles strain resulting final solid product was filtered, dried at 383 K for 24 h,
in the structural distortion [22].
and then calcined at 823 K for 5 h in air stream. The
obtained samples are designated as Sn-MOR(n),
where n stands for the molar ratio of tin species to sil-
icon species. For comparison, the MOR zeolite was
synthesized in the absence of tin chloride under the
above preparation conditions, and the Sn/MOR zeo-
lite was also prepared by ion exchange method with
The synthesis of heteroatomic zeolites is affected
by a variety of factors, such as synthesis routes, reac-
tion conditions, and the nature of heteroatoms [23]. It
is well known that basic conditions (pH 9–13) are
essential for the preparation of heteroatom zeolite by
the conventional procedure, when the metal oxide is
usually formed resulting in the difficulty of incorpora-
tion into the zeolite framework for the metal atom. On
the contrary, the hydrolysis rate of silica source would
be slower under acidic conditions, which can provide
more chance to isolate and disperse the metal ion and
would be beneficial to the formation of the bond
between metal ion and silanol groups followed by crys-
tallization under the basic condition. Thus, the Sn-
0.1 mol/L aqueous tin chloride solution (1 g : 10 mL).
Characterizations of Catalysts
The crystalline structures of the prepared samples
were characterized by X-ray diffraction analysis
(
XRD) using a SmartLab diffractometer from Rigaku
equipped with a 9 kW rotating anode Cu source at
−1
doped zeolite can be successfully obtained using the 40 kV and 40 mA with a scan rate of 0.2 deg s in the
above multiple pH-adjusting co-hydrolysis method 2θ range from 5° to 50°. Nitrogen sorption was mea-
[
22]. The template type would affect severely the sured at 77 K using a BEL SORP-MAX instrument.
structure of the final product. Ionic liquids (ILs) with The surface area was calculated by BET method, and
weak structural orientation ability exhibit an extended the average pore size was determined by BJH method.
hydrogen bond network in the liquid state and a con- The chemical compositions of samples were obtained
tinuous three dimensional network of ionic channels, using ADVANT’XP X-ray fluorescence (XRF) spec-
which can coexist with nonpolar domains created by trometer (ZSX Primus II). FT-IR spectra were
the grouping of lipophilic alkyl chains. When pH value recorded on a Nicolet 360 instrument. The sample was
−2
of sol is less than 7 [24–28], IL can be an effective pretreated in 10 Pa vacuum at 573 K for 3 h and then
template for the preparation of mordenite. Therefore, cooled down to room temperature for adsorbing pyri-
the successful preparation of Sn-MOR zeolite would dine for 2 h. After that, the temperature was raised to
be possible using ILs as template in a multiple pH- 473 K for 1 h to remove the physisorbed pyridine, and
adjusting co-hydrolysis method, which was not the Py-IR spectra were measured at room tempera-
reported so far.
ture. Diffuse reflectance UV–Vis spectra were mea-
sured on PE Lambda 950 UV–Vis spectrophotometer.
The wavelength range was from 200 to 800 nm and
In this work, a series of Sn-MOR zeolites were pre-
pared using a multiple pH-adjusting co-hydrolysis
method, and their physical chemical properties were
characterized by different techniques. Furthermore,
their catalytic performance was also investigated in the
liquid-phase alkylation of toluene with tert-butyl alco-
hol.
BaSO was used as a reference compound. Particle
4
morphology of the samples was observed by SEM
using a Hitachi S-4800 field-emission scanning elec-
tron microscope (FESEM).
Catalytic Tests
EXPERIMENTAL
The catalytic alkylation of toluene with tert-butyl
alcohol was carried out in a 0.1 L stainless steel auto-
clave with a magnetically driven impeller. The catalyst
Preparation of Catalysts
The Sn-MOR zeolites with different tin species sample (0.2 g) was added into a mixture of 9.35 g of
loadings were synthesized by a multiple pH-adjusting n-hexane with 2.0 g toluene and 3.22 g tert-butyl alco-
co-hydrolysis method described in [24]. In a typical hol. The above mixture was sealed in the reactor and
procedure, 8.0 g silicic acid was dissolved in 12.0 g flushed for multiple times with nitrogen to replace air.
water, and a certain amount of hydrochloric acid Then the mixture was heated to the preset reaction
(
98 wt %) was slowly added with vigorous stirring until temperature of 453 K with the initial pressure of
pH 0.8–1.0, followed by addition of a preset amount 1.0 MPa. After 5 h, the mixture was cooled down to
of tin chloride at 298 K for another 24 h. After that, room temperature, and the catalyst was removed by
0
.3 g of NaAlO and 4.4 g of 1-butyl-3-methylimidaz- filtration. The reaction mixture was analyzed on a
2
olium bromide ([BMIm]Br) were simultaneously SP-6890 gas chromatograph equipped with a SE-30
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 92 No. 13 2018

2642
FULING CHENG et al.
H O, hydrochloric acid
2
siticic acid, Sn source,
Al source, [BMIm]Br,
NaOH
CH3
CH
C C CH
OH
3
Sn-MOR
+
H3
3
Hydrothermal
crystallization
pH = 1.0
→
→
5−6
12.5
CH3
CH3
Al
O
Gel preparation
+
CH
3
C
H C
Si
Si
CH3
O
H3C
C
CH
CH3
3
O
Sn
3
Fig. 1. Schematic diagram of the synthesis procedure of framework-substituted Sn-MOR zeolite for toluene alkylation with tert-
butyl alcohol.
column (0.25 μm × 50 m) and a flame ionization the bigger atom radius of tin than that of aluminum.
detector (FID). To estimate the catalyst stability, the The surface area would slightly increase with increas-
catalyst after previous run was collected by filtration ing tin species load, further indicating that the tin spe-
and reused without any further treatment. Schematic cies incorporated into the framework. For
diagram of the synthesis procedure of framework-sub- Sn/MOR(0.010) sample, the surface area is only
2
–1
stituted Sn-MOR zeolite is shown in Fig. 1.
253.1 m g , which can be attributed to the destruc-
tion of the framework resulting in the average pore size
3
–1
of 0.81 nm and pore volume of 0.11 cm g . At the
same time, the molar ratio of SiO to Al O for
RESULTS AND DISCUSSION
2
2
3
Catalyst Characterization
Sn/MOR(0.010) sample slightly increased from 18.1
to 19.0, indicating that the dealumination would hap-
pen in the ion exchange method, which may be owing
to the weak acidity of aqueous tin chloride solution
resulting in partical formation of substitution of alumi-
num species by tin species.
XRD patterns for different Sn-MOR samples are
shown in Fig. 2. The Sn-MOR(0) sample shows the
identical characteristic peaks with the simulated sam-
ples, suggesting the successful preparation of mor-
denite [24, 29]. Although the intensity of these peaks
was slightly decreased with the tin species loading
Figure 3 shows the UV–Vis DRS spectra for differ-
increasing [30], the characteristic peaks can be clearly ent Sn-MOR samples. For the Sn-MOR(0) sample,
observed for all the Sn-MOR samples, which indi- no obvious absorption band in the region of 200–
cated that the incorporation of tin species would not 800 nm can be observed. However, a new absorption
severely affect the framework. However, when the band centered at about 210 nm corresponding to the
molar ratio of Sn/Si reaches 0.020, some other peaks tetrahedrally coordinated tin species for Sn-
corresponding to other impurities appeared, which
may be probably unfavorable to its catalytic perfor-
mance. In addition, no obvious peaks corresponding
f
to tin species can be observed owing to either their
highly dispersion or small particles size undetected by
e
XRD patterns. However, the intensities of these char-
acteristic peaks for Sn/MOR(0.010) sample prepared
by ion exchange were very low, suggesting its break-
down of the mordenite framework, suggesting that the
ion exchange process destroys the structure and crys-
tallinity of MOR. In addition, the weak characteristic
peaks centered at 2θ = 26.6°, 33.9°, and 37.9°
d
c
appeared, indicating that the SnO particles would be
b
a
2
formed by ion exchange method.
Table 1 was the textural parameters for different
samples. For the pure Sn-MOR(0) sample, the surface
2
–1
3
–1
area of 441.5 m g , pore volume of 0.23 cm g and
average pore size of 0.76 nm can be obtained. The
molar ratio of SiO to Al O would be promoted by the
10
20
30
40
50
θ, deg
2
2
2
3
incorporation of tin species suggesting that the alumi-
num into the framework of pure MOR zeolite would
be substituted by the tin species resulting in the smaller
pore volume and average pore size, which is owing to
Fig. 2. XRD patterns for different Sn-MOR samples;
(
a) Sn-MOR(0); (b) Sn-MOR(0.0025); (c) Sn-
MOR(0.005); (d) Sn-MOR(0.010); (e) Sn-MOR(0.020);
(f) Sn/MOR(0.010).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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FRAMEWORK-SUBSTITUTED Sn-MOR ZEOLITE PREPARED
Table 1. Textural parameters for different Sn-MOR samples
2643
2
–1 a
3
–1 b
D (nm)c Sn/Si(molar ratio)d SiO /Al O (molar ratio)
d
Samples
SBET (m g )
V (cm g )
2 2 3
Sn-MOR(0)
441.5
476.3
478.0
482.9
497.1
0.23
0.23
0.22
0.21
0.19
0.11
0.76
0.71
0.69
0.63
0.52
0.81
0
18.1
Sn-MOR(0.0025)
Sn-MOR(0.005)
Sn-MOR(0.010)
Sn-MOR(0.020)
0.0022
0.0042
0.0055
0.0070
0.0053
18.7
19.1
20.5
24.2
19.0
Sn/MOR(0.010)
253.1
a
b
c
d
BET surface areas, P/P = 0.99, average pore size, XRF.
0
MOR(0.0025) sample emerged. No obvious absorp- particles were formed [34], which is consistent with
tion band centered at 250 nm corresponding to tin the XRD results. Therefore, the difference for the tin
dioxide can be observed, suggesting its total incorpo- species between the two samples with the same con-
ration [31–33]. With increasing tin species loading, tent would strongly affect the catalytic performance in
the tert-butylation of toluene.
the band intensity became stronger, indicating that
more tin species were successfully tetrahedrally incor-
porated, but some new absorption band centered
between 230 and 300 nm emerged, suggesting some
hexahedrally coordinated tin species or tin dioxide
were formed, which were either highly dispersed or too
small to be detected by XRD resulting in the decreas-
ing relative crystallinity of mordenite. At the same
time, it was found that no obvious bands centered at
FT-IR spectra for different Sn-MOR samples are
shown in Fig. 4. Compared to the Sn-MOR(0) sample,
a weak absorption band centered about at 960 cm for
–1
Sn-MOR(0.0025) sample corresponding to the
Si‒O–Sn vibrations [35–37] based on the results of
UV–Vis DRS spectra was observed, although it can be
assigned to the Si–OH [38]. In addition, the peak
would become weaker and gradually disappear with
increasing tin species loading, which is consistent with
3
00–450 nm corresponding to the bulky SnO parti-
2
cles even for Sn-MOR(0.020) sample were present. literature [39]. At the same time, the bands centered
–1
Compared to the Sn-MOR(0.010) sample, the weaker 461, 814, and 1102 cm for Sn-MOR(0) sample,
absroption band centered at about 210 nm for the which is owing to the Si–O–Si bending mode, sym-
Sn/MOR(0.010) sample can also appear even though metric stretching vibration of Si–O–Si and Si–O–Si
the tin species were the same, which is owing to the vibrational stretching [40], respectively, would be
dealumination by aqueous tin chloride resulted in the somewhat red-shifted to lower wavenumber because of
partial substitution of aluminum hole by tin species. the larger atomic weight of Sn and the longer Sn–O
However, a broad band centered at 300–450 nm can band [22], which further indicated that the interaction
between tin and silicon [41] resulting in the successful
incorporation of tin species into the framework of
mordenite.
also be observed, suggesting that some bulky SnO
2
Figure 5 shows Py-IR spectra of different Sn-MOR
samples after pyridine adsorption. The bands at 1445
f
–1
and 1545 cm are attributed to the interactions
between Lewis and Brønsted acid sites and pyridine,
respectively [42–44]. It can be seen from Fig. 5 that
the pure mordenite Sn-MOR(0) sample has mainly
Lewis acidity. However, the Lewis acidity increased
remarkably after incorporation of tin species, which
increases with increasing tin species load resulting in
promoting catalytic performance. For Sn/MOR(0.010)
sample, the Lewis acidity slightly increased, which
may be owing to the substitution of aluminium species
by tin species with stronger acidity.
e
d
c
b
a
The morphology of these samples was studied by
2
00
300
400
500
600
700
800 SEM, and the results are shown in Fig. 6. A plate mor-
λ, nm
phology with rectangle for Sn-MOR(0) sample was
observed. After incorporation of tin species into the
framework of mordenite, the morphology gradually
changed into spherical, and more and more spherical
Fig. 3. UV–Vis DRS spectra for different Sn-MOR sam-
ples; (a–f) see Fig. 2.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 92 No. 13 2018

2644
FULING CHENG et al.
f
f
e
804
d
c
457
e
1088
b
a
d
c
b
a
814
461
1102
1400
1200
1000
800
600
400
1
1400
1440
1480
1520
1560
ν, cm−
−1
ν, cm
Fig. 4. FT-IR spectra for different Sn-MOR samples; (a–
f) see Fig. 2.
Fig. 5. FT-IR spectra of pyridine-adsorbed for different
Sn-MOR samples; (a–f) see Fig. 2.
2
0 ꢀm
0 ꢀm
20 ꢀm
20 ꢀm
20 ꢀm
(
а)
d)
(b)
(e)
(c)
(f)
(g)
3
ꢀm
2
20 ꢀm
(
Fig. 6. SEM images for different Sn-MOR samples; (a–f) see Fig. 2.
particles with a diameter of ~5 μm would be observed identified as PTBT and meta-tert-butyltoluene
with the tin species loading increase. Figure 6g shows (MTBT). However, ortho-tert-butyltoluene (OTBT)
the high resolution image for Sn-MOR(0.020) sam- cannot be found in the products, which is attributed to
ple. The walnut morphology was a result of the aggre- the steric hindrance between methyl and voluminous
gation with small-sized flake-like crystal, which may tert-butyl group. DTBT is 3,5-di-tert-butyltoluene,
be owing to the acceleration the nucleation and growth whose tert-butyl groups are both in the meta positions.
by the introduction of tin species into the Al-rich sys- It can be seen from Table 2 that toluene conversion of
tem resulting in its specific surface areas increase [45]. 19.3% and PTBT selectivity of 71.9% for Sn-MOR(0)
The floccule can be obtained for Sn/MOR(0.010) sample can be obtained. With increasing tin species
sample shown in Fig. 6f owing to the partical collapse loading, the conversion of toluene increased, and then
of mordenite framework by the ion exchange method. decreased at higher tin loadings. The Sn-MOR(0.010)
sample gives a toluene conversion of 48.0%, which is
2
.5 times than that over pure Sn-MOR(0) sample and
Catalytic Performance
much higher than with other samples owing to its
The catalytic performances of different samples in appropriate surface area, pore volume and Lewis acid-
the alkylation of toluene with tert-butyl alcohol are ity. Toluene conversion of 34.3% was obtained for the
listed in Table 2. In all cases, the main products are Sn-MOR(0.020) sample with highest acid amount,
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FRAMEWORK-SUBSTITUTED Sn-MOR ZEOLITE PREPARED
2645
Table 2. Catalytic performances of different samples in the alkylation of toluene with tert-butyl alcohol
Distribution of products, mol %
Toluene
conversion, %
Catalysts
SPTBT, %*
OTBT
MTBT
PTBT
DTBT
Sn-MOR(0)
19.3
27.1
39.5
48.0
34.3
8.9
–
–
–
–
–
–
27.1
23.8
18.4
14.0
22.5
39.6
69.5
74.4
78.6
83.2
71.3
56.3
3.4
1.8
3.0
2.8
6.2
4.1
71.9
75.8
81.0
85.6
76.0
58.7
Sn-MOR(0.0025)
Sn-MOR(0.005)
Sn-MOR(0.010)
Sn-MOR(0.020)
Sn/MOR(0.010)
Reaction conditions: w(toluene)/w(catalyst) = 10; calcination temperature of catalyst 823 K; n(toluene) : n(tert-butyl alcohol) : n(n-hex-
ane) = 1 : 2 : 5; reaction temperature 453 K; initial pressure 1.0 MPa; reaction time 5 h.
*
SPTBT: the molar ratio of PTBT to mono-TBT.
which may be owing to the smaller pore size (0.52 nm) carbonization. The above results indicated that the
than PTBT molecular diameter (0.58 nm) resulting in Sn-MOR(0.010) catalyst shows high catalytic stability,
the reaction only on the outer surface. The selectivity which would provide a good application prospect in
to PTBT increases with increasing tin species loading. the industrial process.
Selectivity value of 85.6% can be obtained for the Sn-
MOR(0.010) sample, and it would be dropped with
CONCLUSION
the tin species further increasing. However, a toluene
conversion of only 8.9% and PTBT selectivity of
In this paper, Sn-doped mordenite with different
tin species loadings were successfully via a multiple
pH-adjusting co-hydrolysis method. Tin species can
be incorporated into tetrahedral positions of the mor-
denite framework by substitution of aluminum result-
ing in promoting its Lewis acidity. Compared to
Sn/MOR sample with floccule morphology prepared
by ion exchange method, the Sn-MOR samples with
walnut morphology can be obtained. The catalytic
performances in the toluene alkylation with tert-butyl
alcohol for Sn-MOR catalysts are much higher than
that of pure mordenite. The catalyst activity remains
high even after 5 consecutive runs. The described
method can be valuable for industrial applications
requiring solid acid catalysts.
5
8.7% for Sn/MOR(0.010) sample were observed
because of the destruction of framework by ion
exchange of tin species although the tin species are
almost the same as for the Sn-MOR(0.010) sample.
Figure 7 shows the catalytic stability of Sn-
MOR(0.010) catalyst in the alkylation of toluene with
tert-butyl alcohol. It can be seen from Fig. 7 that tolu-
ene conversion decreased slightly and it can also reach
up to 45.3% even after 5 consecutive runs. On the con-
trary, PTBT selectivity would be slightly promoted
owing to the blocking of the pores probably of coke
formed by oligomerization of isobutene followed by
100
Toluene conversion
PTBT selectivity
ACKNOWLEDGMENTS
8
0
0
0
0
This work was supported by Jiangsu Planned Proj-
ects for Postdoctoral Research Funds (1302121C);
Open Project of Beijing Key Laboratory for Enze Bio-
mass and Fine Chemicals; Project Funded by the Pri-
ority Academic Program Development of Jiangsu
Higher Education Institutions.
6
4
2
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RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 92
No. 13
2018