Hybrid Catalysts Based on Sulfated Zirconium Dioxide and H-beta Zeolite for Alkylation of Isobutane with Isobutylene

Article abstract of DOI:10.1134/S1070427217100081

Physicochemical properties of new hybrid catalysts based on sulfated zirconium oxide supported by zeolite of the Beta structural type were investigated. The acid-base characteristics of the catalysts were determined by the amount of the supported component, the maximum concentration of Br?nsted acid centers (277 Μmol/g) was achieved upon deposition of 1.7 wt.% sulfated zirconium oxide. The texture characteristics of the final catalyst were determined by the starting support. Tests of the catalysts in the reaction of isobutane alkylation with isobutylene demonstrated their advantage in selectivity and stability over the classical bulk sulfated zirconium oxide. The variation of the surface acidity is correlated with the amount of the deposited sulfated zirconium dioxide and has an extremum point at around 4 wt.%. Hybrid catalysts based on H-Beta zeolite with supported sulfated zirconium dioxide are more stable and exhibited a higher selectivity with respect to C8 hydrocarbons and trimethylpentanes, compared with bulk sulfated zirconium dioxide.

Full text of DOI:10.1134/S1070427217100081

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2017, Vol. 90, No. 10, pp. 1605−1613.© Pleiades Publishing, Ltd., 2017.
Original Russian Text © E.A. Yuferova, S.Yu. Devyatkov, S.P. Fedorov, K.V. Semikin, D.A. Sladkovskii, N.V. Kuzichkin, 2017, published in Zhurnal Prikladnoi
Khimii, 2017, Vol. 90, No. 10, pp. 1323−1331.
VARIOUS TECHNOLOGICAL
PROCESSES
Hybrid Catalysts Based on Sulfated Zirconium Dioxide
and H-beta Zeolite for Alkylation
of Isobutane with Isobutylene
E. A. Yuferova*, S. Yu. Devyatkov, S. P. Fedorov, K. V. Semikin,
D. A. Sladkovskii, and N. V. Kuzichkin
St. Petersburg State Technological Institute (Technical University), Moskovskii pr. 26, St. Petersburg, 190013 Russia
*e-mail: Y_katryn@mail.ru
Received October 31, 2017
Abstract—Physicochemical properties of new hybrid catalysts based on sulfated zirconium oxide supported by
zeolite of the Beta structural type were studied. The acid-base characteristics of the catalysts are determined by
the amount of the supported component, the maximum concentration of Brønsted acid centers (277 μmol g–1) is
reached upon deposition of 1.7 wt % sulfated zirconium oxide. The texture characteristics of the final catalyst are
determined by the starting support. Tests of the catalysts in the reaction of isobutane alkylation with isobutylene
demonstrated their advantage in selectivity and stability over the classical bulk sulfated zirconium oxide.
DOI: 10.1134/S1070427217100081
New international and domestic gasoline regulations
(Euro-4, 5; MSAT II) contain severe saturated vapor
pressure constraints and strongly restrict the content of
benzene, aromatic hydrocarbons, olefin hydrocarbons,
and sulfur, which requires that high-octane nonaromatic
components should be added to gasoline.
One of ways to produce components of this kind is
by alkylation of isobutane with butylenes. The alkylate
(target product of this process) has a low saturated vapor
pressure and contains no sulfur, oxygen, nitrogen, and
aromatic compounds.
At present isobutane is alkylated with olefins, with the
role of catalysts played by sulfuric and hydrofluoric acids
and also by mixtures of these with addition of other acids.
Both processes have good parameters as regards the
yield, selectivity, and quality of alkylates. However,
the application of liquid-acid (homogeneous) catalysts
is, first, complicated by their high specific expenditure,
toxicity, and corrosion activity and necessary separation
of the catalyst-product mixture and the subsequent
utilization of spent acids and, second, is hazardous for
the health of the operating personnel.
liquid acids to solid catalysts, which will avoid the
above-mentioned problems and gain technological and
economical advantages.
In the last decades, there have appeared a number
of publications concerned with anion-promoted metal
oxides, such as sulfated or tungstic oxides of zirconium,
titanium, and aluminum [1]. These catalysts have a
specific surface area of 50 to 180 m2 g–1 and strength
of acid centers exceeding that of 100% sulfuric acid.
Sulfated zirconium dioxide (SZ) is mostly used in
the hydroisomerization of alkanes, which occurs at a
substantially lower temperature and does so with higher
selectivity, compared with zeolites.
One of ways to modify sulfate-zirconium catalysts is
by their deposition onto large-surface-area mesostructured
materials having no acidity (e.g., SBA-15) [2]. Deposition
of sulfated zirconium dioxide onto the surface of zeolites
originally having acid centers may give rise to two types
of acid centers that can be simultaneously involved
in various catalytic cycles. Examples of such systems
were described in [3], where zirconium dioxide was
simultaneously promoted with tungsten trioxide WO3
and sulfate anions SO42–. These systems, named hybrid
catalysts in the literature [4], possess characteristics that
At present, the development of the industrial
alkylation is primarily associated with passing from
1605

1606
YUFEROVA et al.
can exhibit a certain synergism and can even exhibit new
properties that are not simply a sum of the properties of
the starting components.
dried until the optimal molding moisture content was
reached. The materials obtained were molded with a
manual extrusion device of piston type with channel
diameter of 1.5 mm and dried for 12 h at room temperature
and then for 3 h at a temperature of 110°C, with the
subsequent calcination at 700°C.
The main problem consists in that only a little progress
in the development of heterogeneous alkylation catalysts
has been made during the recent years because all
these catalysts are rapidly deactivated and show a poor
selectivity with respect to the target products.
Zeolite of the H-Beta structural type was preliminarily
calcined at 300°C for 1 h and then a calculated amount
of zirconium dioxide was deposited by the full moisture
absorption method from an aqueous solution of ZrOCl2.
The resulting samples contained 4, 8, and 16 wt %
zirconium dioxide. After the samples were dried at a
temperature of 110°C for 3 h, zirconium oxychloride
was hydrolyzed in an excess amount of distilled water.
Ammonium hydroxide was added dropwise under
thorough agitation until the pH reached a value of 11.
Then the samples were filtered and washed with an excess
of twice-distilled water until Cl– anions disappeared
(controlled by AgNO3 test), with the subsequent drying
at 110°C for 3 g. The sulfation was performed by
impregnation by the incipient wetness impregnation
method with a sulfuric acid solution (8 wt % SO3 relative
to zirconium dioxide). The samples were dried at a
temperature of 80°C and calcined at 700°C.
The goal of our study was to examine the physico-
chemical characteristics of catalysts having the form of
sulfated zirconium dioxide supported by H-Beta zeolite
and their effect on the stability and activity in the target
reaction of isobutane alkylation with isobutylene.
EXPERIMENTAL
H-Beta zeolite with Si/Al = 25 was produced by the
method described in [5]. Pseudoboehmite of Pural SB
brand was used as a binder for catalysts. Zirconium
oxychloride (Sigma Aldrich) served as the precursor
of zirconium oxide. Sulfate zirconium hydroxide was
produced by the method described in [6]: 85 g of
concentrated sulfuric acid, 277 mL of deionized water,
and 970 g of zirconium oxychloride octahydrate were
mixed, and the mixture was cooled to 10°C. Further, a
10% solution of ammonium hydroxide was added under
permanent agitation to until pH 12–13 was reached. On
being formed, the precipitate was washed until no Cl–
and SO42– ions were found in washing water. On being
washed, the precipitate was repeatedly humidified to a
moisture content of about 50 wt % and then was subjected
to a hydrothermal treatment for 5 h under an excess
pressure of approximately 1.5 atm.After the hydrothermal
treatment, the precipitate was humidified with a twofold,
relative to its mass, amount of deionized water, and
concentrated sulfuric acid was added to the resulting
suspension (8 wt % SO42– ions relative to zirconium
oxide). After the acid was added, the suspension was
agitated 30 min and then dried at 100°C until the whole
amount of moisture was removed. After the drying, an
additional treatment with sulfuric acid (to additionally
introduce 6 wt % sulfo groups) was performed by the
method of incipient wetness inpregnation.
To examine the activity, the materials synthesized,
which contained zeolite and zirconium dioxide deposited
onto the zeolite in amounts of 4, 8, and 16 wt %, were
shaped together with Pural SB (Sasol) pseudoboehmite
as a binder into extrudates (25 wt % binder in the calcined
base). The extrudates were dried at 80°C and calcined at
700°C for 4 h. Prior to the catalytic tests, the catalysts
were ground, sieved to obtain a 0.5–1-mm fraction and
again calcined at 350°C for 1 h. All the samples are
described in Table 1.
The acid centers were quantitatively determined by
IR spectroscopy of adsorbed pyridine with a Shimadzu
IR Tracer-100 FT-IR spectrometer having an attached
vacuum gas cell [7]. Pyridine was desorbed at temperatures
of 150, 250, and 350°C. The molar extinction coefficients
for Lewis and Brønsted acid centers were taken from the
literature [8].
The phase compositions were examined by X-ray
diffraction (XRD) analysis on a Shimadzu XRD-7000
instrument with monochromatic CuKα radiation (λ =
0.154051 nm).
The molding compound was produced by mixing of
a twice sulfated zirconium hydroxide with a calculated
amount of pseudoboehmite in a 75 : 25 ratio (calculated
for calcined materials) in an excess amount of deionized
water. The suspensions were agitated for 1 h and then
The texture characteristics were determined with
a Quantachrome Autosorb-6 ISA specific surface
area analyzer. Nitrogen gas served as adsorbate, the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

HYBRID CATALYSTS BASED ON SULFATED ZIRCONIUM DIOXIDE
1607
Table 1. Description of the catalysts synthesized
Sample
Description
SZ
Sulfated zirconium hydroxide calcined at 700°C
Starting H-Beta zeolite calcined at 700°C
H-Beta
B4, B8, B16
Samples containing 4, 8, and 16 wt % zirconium dioxide, supported by H-Beta zeolite and calcined at
700°C
B4S, B8S, B16S
Samples containing 4, 8, and 16 wt % zirconium dioxide, supported by H-Beta zeolite, sulfated, and
calcined at 700°C
adsorption was performed at a temperature of 77.3 K.
Adsorption-desorption isotherms were recorded at 27
points; for the adsorption isotherm, the specific surface
area was calculated by multiple-point Brunauer–Emmett–
Teller (BET) equation. The volume of mesopores was
determined by the Barrett-Joyner–Halenda (BJH) method
from the desorption branch of the isotherm, the volume
of micropores was determined by the Dubinin method.
The catalytic activity was determined in a reactor
a with fixed catalyst bed (Fig. 1). A catalyst (15 cm3)
was placed in the reactor, the pressure in the system
was maintained at 13 bar with nitrogen, and the bed
temperature was maintained at 80°C with thermostated
circulated water. As the starting substance served a 20 :
1 mixture of isobutane with isobutylene, the raw material
was delivered at a mass rate of 0.35 h–1 (in terms of
olefin). After 30 min from the beginning of the reaction,
the collected alkylate was analyzed with a Shimadzu GC-
2010-plus gas chromatograph equipped with a Petrocol
DH column 100 × 0.25 capillary column.
An elemental no-reference semi-quantitative analysis
of the catalyst samples was made by the method of energy-
dispersive X-ray fluorescence spectroscopy (EDX) on a
Shimadzu-8000 instrument. The analysis was performed
in air, the spectrometer was equipped with a rhodium
anode with 50 kV and 137 μA, the concentrations were
calculated by the no-reference method of fundamental
parameters.
XRD and EDX analyses. The diffraction patterns of
the samples are shown in Fig. 2. For each XRD pattern,
the signal associated with the presence of the amorphous
phase was separated from the initial spectrum.
Fig. 1. Schematic of the reactor installation.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

1608
YUFEROVA et al.
Table 2. Degree of crystallinity of catalyst samples
with increasing content of zirconium dioxide, which is
accounted for by the screening of X-rays and distortion
of their diffraction pattern, caused by the presence of the
supported zirconium dioxide.
Sample
Crystallinity, %
H-Beta
B4
71
59
60
49
60
56
49
It should be noted that the structure of the zeolites
may change under alkaline (in deposition of zirconium
dioxide) and acid conditions (in sulfation of the supported
zirconium hydroxide) due to the partial dissolution of
silicon dioxide or aluminum oxide forming the lattice
of the zeolite. Based on published data, we can assume
that the crystal structure of the starting zeolite was
preserved after all the treatments, as, e.g., it was noted
in [10] according to XRD data, where a decrease in the
intensity of reflections in diffraction patterns of a coked
catalyst based on H-Beta zeolite was observed, with its
structure preserved.
B8
B16
B4S
B8S
B16S
The degree of crystallinity was calculated by
Atotal – Ahalo
Cryst = –––––––––– × 100%,
Atotal
Elemental analysis shows that all the supported
samples contain S and Zr elements (Table 3). The
presence of sulfur in calcined samples indicates that an
active component is formed as sulfo groups bound to the
surface of zirconium dioxide, which are preserved after
the thermal treatments of the samples.
(1)
where Atotal is the area under the curve in the spectrum,
and Ahalo is the area under the curve corresponding to the
amorphous phase of a sample.
Specific surface area and porosity. The isotherms
of low-temperature adsorption-desorption of nitrogen are
shown in Fig. 3 for catalysts based on H-Beta (the range of
relative adsorbate pressures of 0.3–1 is distinguished). The
specific surface area and the mesopore volume, calculated
by BET and BJH methods, and the micropore volume
found by the Dubinin method are presented in Table 4.
The results of this determination are listed in Table 2.
Tetragonal or monoclinic modifications of zirconium
dioxide were expected to be observed for supported
sulfated and sulfate-free catalyst samples. However,
according to XRD data, no reflections characteristic
of these modifications at angles 2θ = 27–33° were
observed [9]. Instead, the peak intensities became lower
(b)
(a)
I, rel. units
2θ, deg
2θ, deg
Fig. 2. XRD patterns of samples calcined at 700°C: sulfated zirconium dioxide, zirconium dioxide supported by H-Beta zeolite, and
sulfated zirconium dioxide supported by H-Beta zeolite. (I) Intensity and (2θ) Bragg angle The designations T and M correspond to the
positions of the reflections associated with the tetragonal and monoclinic crystalline modifications of zirconium dioxide.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

HYBRID CATALYSTS BASED ON SULFATED ZIRCONIUM DIOXIDE
1609
Table 3. EDX data for samples of sulfated zirconium dioxide supported by H-Beta zeolite
Concentration of elements in terms of the indicated oxides, wt %
Sample
SiO2
Al2O3
ZrO2
SO3
B4S
B8S
B16S
92.2
90.1
89.1
3.7
3.4
3.4
1.7
2.7
3.3
2.4
3.8
4.3
Table 4. Texture properties of catalysts
Mesopore volume
Micropore volume
Sample
Specific surface area by BET, m2 g–1
cm3 g–1
H-Beta
600
577
569
539
568
568
504
190
0.24
0.18
0.19
0.31
0.19
0.18
0.27
0.29
0.29
0.28
0.28
0.31
0.28
0.28
0.29
0
B4
B8
B16
B4S
B8S
B16S
SZ
The starting H-Beta zeolite has the adsorption- particles forming narrow pores [12]. After zirconium
desorption isotherm belonging to type-IIb, with an H3 dioxide is deposited onto the starting zeolite, the
hysteresis loop [11], which is characteristic of materials hysteresis loop becomes wider, which indicates that
constituted by aggregates (weakly bound) of lamellar the number of mesopores in the samples increases. It is
Vads, cm3 g–1
(a)
(b)
Vads, cm3 g–1
Prel
Prel
Fig. 3. Isotherms of low-temperature adsorption of nitrogen for supported catalyst samples. (Vads) Adsorbed volume and (Prel) relative
pressure. The isotherms are shifted along the vertical axis for perception convenience.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

1610
YUFEROVA et al.
Table 5. Results of IR spectroscopic analysis of the catalysts
Brønsted centers, μmol g–1
Lewis centers, μmol g–1
Sample
Bstrong/ΣL
medium-
strength
weak
strong
total
weak
medium
strong
total
H-Beta
B4S
31
46
49
39
9
13
33
22
27
14
138
199
119
71
182
278
190
137
141
246
187
144
115
19
99
66
43
29
12
52
26
20
9
397
280
208
153
36
0.35
0.71
0.57
0.46
3.0
B8S
B16S
SZ
108
5
example, the adsorbate present in a partly blocked pore
can leave it only if the relative pressure of the adsorbate
is lowered. In the present study, the adsorption and
desorption branches of isotherms converge at the same
possible to determine whether or not zirconium dioxide
blocks pores of the starting zeolite from the change in the
relative pressure of the adsorbate, at which the adsorption
and desorption branches of an isotherm converge. For
I, rel. units
I, rel. units
I, rel. units
I, rel. units
ν, cm–1
ν, cm–1
Fig. 4. IR spectra of chemisorbed pyridine on the surface of H-Beta, B4S, B8S, and B16S catalysts after the desorption of pyridine at
150, 250, and 350°C. (I) Intensity and (ν) wave number.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

HYBRID CATALYSTS BASED ON SULFATED ZIRCONIUM DIOXIDE
1611
S, K, wt %
relative pressure; thus, the porous structure of the starting
zeolite is not distorted.
The specific surface area of the samples based on
H-Beta zeolite tends to decrease with increasing amount
of zirconium oxide, with the volume of micropores
remaining unchanged. This indicates that zirconium
dioxide particles are localized in the intercrystallite space
of the zeolite and they form the intrinsic porosity [13].
Acidity. Measurements of the acidity of the catalyst
samples demonstrated that Lewis (L) and Brønsted
(B) acid centers are present in the samples under
study. Detailed information about their concentration
is presented in Table 5. Figure 4 shows IR spectra of
pyridine adsorbed on the surface of catalyst samples based
on zeolite at desorption temperatures of 150, 250, 350°C.
The starting sample of H-Beta zeolite shows that Lewis
acid centers are predominant in number over Brønsted
centers. The concentration of Brønsted acid centers (both
the total concentration and that of strong acid centers) in
supported catalyst samples passes through a minimum
in the dependence on the content of sulfated zirconium
dioxide, whereas the concentration of Lewis acid centers
gradually decreases. The maximum B/L concentration
ratio is observed for sample B4S. Acidity measurements
demonstrated that sulfated zirconium dioxide (sample
SZ) is characterized by the predominance of Brønsted
acid centers over Lewis centers. Thus, the increase in
the concentration of Brønsted acid centers in sample B4S
suggests that the supported phase exhibits the highest
activity in the given catalyst sample as compared with
the rest of the supported samples.
Catalyst
Fig. 5. Results obtained when determining the selectivity S after
210 min of the reaction (1) with respect to C8 hydrocarbons;
(3) with respect to trimethylpentanes; (4) with respect to C9+
hydrocarbons; (5) with respect to C5–C7 hydrocarbons; and
(2) conversion K of isobutylene.
amount of the supported phase may be due both to the
inhomogeneous distribution of sulfuric acid throughout
the supported catalyst sample in the sulfation stage
(different degrees of sulfation due to the falling of a part
of sulfuric acid onto the zeolite substrate) and also to the
possible differences in crystallization and distribution of
the supported component in the synthesis stage.
Alkylation of isobutane with isobutylene. The
activity was experimentally determined for each catalyst
sample, the reaction product (alkylate) was sampled in 30
min. The distribution of hydrocarbons in the alkylate is
It can be assumed that the nonlinear dependence of
the concentration of acid centers of both types on the
Table 6. Data on the catalyst activity after 30 min of the reaction
Group composition of the alkylate, wt %
Catalyst
Share of 2,2,4-TMP among C8 hydrocarbons,
Conversion
wt %
С5–С7
С8
С9+
H-Beta
B4S
2
11
11
0
1
80
21
1
97
9
–
23.5
24.2
–
44
62
51
47
60
69
B8S
68
99
12
23
B16S
SZ
4
84
60
10.4
–
SZ + H-Beta
18
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

1612
YUFEROVA et al.
presented in Table 6. Because just the strong Brønsted
acid centers are active in the alkylation reaction [14],
the selectivity with respect to the target products
grows as their fraction in the samples increases.
The maximum selectivity with respect to C8 was
reached when sample B4S was tested. Bulk sulfated
zirconium dioxide SZ demonstrated a low selectivity
with respect to C9+ hydrocarbons and a high yield
of C8 hydrocarbons. Nevertheless, the share of the
main component 2,2,4-trimethylpentane (2,2,4-TMP)
among C8 hydrocarbons indicates that predominantly
polymerization and cracking of oligomeric products
occur on the catalyst. According to the results of these
tests, the conversion of isobutylene decreases with
increasing amount of C9+ hydrocarbons in the reaction
product, which evidences that the catalysts under study
are poisoned by oligomeric by-products.
particle size of about 14 nm. Otherwise, the deactivation
mechanism includes the pore blocking by by-products
formed in the reaction. Thus, it can be concluded that the
higher activity and the longer service life of the supported
catalyst B4S, compared with the starting zeolite, are due
to the protective function of sulfated zirconium dioxide
that is deposited on the surface of zeolite crystallites and
precludes accumulation of by-products via cracking of
oligomerization products.
CONCLUSIONS
(1) It was sown that, when supported by H-Beta zeolite,
zirconium dioxide is deposited in the intercrystallite space
of the zeolite, with the structure of the starting zeolite
not disturbed after the deposition and sulfation stages.
The variation of the surface acidity is correlated with the
amount of the deposited sulfated zirconium dioxide and
has an extremum point at around 4 wt %.
A1 : 1 mechanical mixture of two active components
(designated as SZ + H-Beta), H-Beta zeolite and bulk
sulfated zirconium dioxide, was molded with a Pural SB
binder. The composition of the alkylate obtained with this
catalyst demonstrates simultaneously a high yield of C8
and C9+ hydrocarbons. No high concentration of heavy
hydrocarbons was observed, as, e.g., in the case for the
supported catalyst B4S. Thus, it can be concluded that the
supported catalyst samples possess a unique activity and
selectivity, with a certain synergism exhibited between
the active components in the formulation. These results
are promising and demonstrate the advantage of new
supported catalysts, which combine different in nature
and mutual arrangement types of acid centers in the same
hybrid material.
(2) It was confirmed experimentally that hybrid
catalysts based on H-Beta zeolite with supported
sulfated zirconium dioxide (sample with 4 wt % sulfated
zirconium oxide) are more stable and exhibit a higher,
in the course of time, selectivity with respect to C8
hydrocarbons and trimethylpentanes, compared with bulk
sulfated zirconium dioxide. Thus, the hybrid catalysts are
a promising trend in the development of the industrial
alkylation process.
ACKNOWLEDGMENTS
The study was carried out under a State contract
based on a grant from the Government of the Russian
Federation for support of research performed under
supervision of leading scientists from Russia’s higher-
school institutions, research institutes, and state research
centers of the Russian Federation of March 19, 2014,
no. 14.Z50.31.0013.
The stability of the catalysts was compared for B4S
and SZ samples (Fig. 5).Analysis of the reaction products
formed in 210 min shows that SZ sample demonstrates an
isobutylene conversion exceeding that for the supported
catalyst sample B4S. Nevertheless, the selectivity of B4S
sample with respect to the key products, C8 hydrocarbons,
including trimethylpentanes, after 210 min of the reaction
is higher, which is an advantage of the supported catalyst
over its analog.
REFERENCES
1. Vlasov, E.A., Catal. Lett., 2015, vol. 145, no. 9, pp. 1651–
It has been shown [15] that the effective removal of
carbon deposits and primary products of the alkylation
reaction from the outer surface of H-Beta zeolite and
pore mouths makes slower its deactivation rate. It was
shown in [16] that the deactivation of H-Beta zeolite as
a result of only poisoning of the acid centers occurs at its
1659.
2. Chen, A., J. Chinese Chem. Soc., 2010, no. 57, pp. 820–
828.
3. Busto, M., Fuel Process. Technol., 2012, vol. 104, pp. 128–
135.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017

HYBRID CATALYSTS BASED ON SULFATED ZIRCONIUM DIOXIDE
1613
4. Kustov, L.M., Russ. J. Phys. Chem. A, 2015, vol. 89, no. 11,
10. Adebajo, M.O., Spectrochim. Acta, Part A, 2004, vol. 60,
pp. 2006–2021.
no. 4, pp. 791–799.
5. Gizetdinova, A., J. Chem. Chem. Eng., 2014, vol. 8, no. 5,
11. Qi, X., J. Mater. Sci., 2008, vol. 43, no. 16, pp. 5626–5633.
12. Sing, K.S.W., Assessment of Mesoporosity, Elsevier, 2014.
13. Ye, F., Catal. Commun., 2009, vol. 10, pp. 2056–2059.
14. Feller,A., J. Catal., 2003, vol. 216, nos. 1–2, pp. 313–323.
pp. 453–460.
6. US Patent 7 794 687 B2 (publ. 2010).
7. Devyatkov, S.Y., Ind. Eng. Chem. Res., 2016, vol. 55,
no. 23, pp. 57–64
15. Salinas, A.L., Appl. Catal., A, 2008, vol. 336, nos. 1–2,
8. Emeis, C.A., J. Catal., 1993, vol. 14, no. 2, pp. 347–354.
pp. 313–323.
9. Gauna, M.R., Ceram. - Silik., 2015, vol. 50, no. 4, pp. 318–
325.
16. Loenders, R., J. Catal., 1998, vol. 176, pp. 545–551.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 90 No. 10 2017