Effect of the support nature on the catalytic properties of iron in benzene benzylation

Article abstract of DOI:10.1134/S0965544116080181

The effect of the support nature on the dispersion, structure, and catalytic activity of iron oxides supported on ZrO₂, TiO₂, ZnO, Al₂O₃, and silicas of different structures has been analyzed using the example o

Full text of DOI:10.1134/S0965544116080181

ISSN 0965-5441, Petroleum Chemistry, 2017, Vol. 57, No. 1, pp. 93–99. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © O.I. Vernaya, I.N. Krotova, Yu.V. Maksimov, T.N. Rostovshchikova, 2017, published in Neftekhimiya, 2017, Vol. 57, No. 1, pp. 96–102.
Effect of the Support Nature on the Catalytic Properties
of Iron in Benzene Benzylation
O. I. Vernayaa, *, I. N. Krotovaa, Yu. V. Maksimovb, and T. N. Rostovshchikovaa
aFaculty of Chemistry, Moscow State University, Moscow, Russia
bSemenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia
*e-mail: olga_vernaya@mail.ru
Received February 11, 2016
Abstract⎯The effect of the support nature on the dispersion, structure, and catalytic activity of iron oxides
supported on ZrO2, TiO2, ZnO, Al2O3, and silicas of different structures has been analyzed using the example
of benzene benzylation. The structure and electronic properties of the catalysts prepared from iron acetylac-
etonate have been studied by Mössbauer spectroscopy. It has been shown that the use of SiO2, ZrO2, and ZnO
supports characterized by weak oxide–oxide interaction leads to the formation of small iron oxide clusters of
a 2–10 nm size, which exhibit the highest activity in catalysis.
Keywords: iron oxide, alkylation, catalysis, nanoparticles, oxide supports, Mössbauer spectroscopy
DOI: 10.1134/S0965544116080181
Friedel–Crafts alkylation is an important reaction tion is a key objective. The choice of the support, pre-
of organic chemistry. The C–C bond formation pro-
cesses are used to produce high-octane fuel, antioxi-
dants, surfactants, fragrances, ethylbenzene (styrene
production feedstock), and other products (e.g.,
cumene and thymol). In the presence of homoge-
neous catalysts—AlCl3 and FeCl3 Lewis acids—the
reaction follows the ionic mechanism of electrophilic
substitution. Searching for a more environmentally
friendly and handy heterogeneous alkylation catalyst
remains a demanding problem. Active and selective
heterogeneous Friedel–Crafts alkylation catalysts are
iron compounds (oxides, iron-containing spinels,
zeolites, and molecular sieves) [1–4]. Their activity is
typically higher than that of Al3+-based catalysts; this
feature casts doubt upon the generally accepted ionic
mechanism of alkylation. The radical cation mecha-
nism of benzylation involving the intermediate forma-
tion of Fe2+ has been proposed for alumina-supported
iron chloride [5]. The important role of the simultane-
ous presence of Fe3+ and Fe2+ ions and their ratio in
providing the activity of iron-containing alkylation
catalysts has been also shown in [6]. The reducibility
of iron oxides is mostly determined by the size of its
particles and the strength of their interaction with the
support. It is this ability that, along with the acidic
properties and structure of the support, affects the cat-
alytic properties of iron-containing catalysts and
makes the catalyst activity strongly dependent on the
size and structure of the oxide phase. Therefore, in
designing metal oxide catalysts, the possibility of con-
trolling their dispersion, morphology, and composi-
treatment conditions, and iron introduction method is
responsible not only for the size and composition, but
also for the degree of imperfection of the resulting
oxides and plays an important role in solving the prob-
lem of increasing the efficiency of metal oxide cata-
lysts [7].
Catalysts based on γ-Fe2O3 nanoparticles depos-
ited on silicas of different structures from an iron
acetylacetonate solution in toluene proved to be effec-
tive catalysts for some chloroolefin conversion reac-
tions, in particular, the isomerization of allylic chlo-
roolefins and the alkylation of benzene with allyl chlo-
ride or benzyl chloride (BC) [8–10]. In all cases, the
activity and stability of these catalysts are higher than
those of α-Fe2O3-based catalysts prepared from iron
nitrate, which is a more common precursor. The high-
est activity in benzylation was exhibited by samples on
an activated silica gel matrix (AGM) with a high iron
loading (18%), which simultaneously contain γ-Fe2O3
and Fe3O4 nanoparticles of a 2–3 nm size [10].
To analyze the effect of the nature and pretreat-
ment of the support on the dispersion, structure, and
catalytic activity of supported iron oxides, this study
summarizes data on benzene benzylated over iron cat-
alysts prepared from iron acetylacetonate with an iron
content of 5%. Silicas of different structures and ZrO2,
TiO2, ZnO, and Al2O3 oxides were used as supports.
93

94
VERNAYA et al.
Mössbauer radiation source was 57Co(Rh) with an
EXPERIMENTAL
activity of 1.1 GBq. Isomer shifts were calculated from
the center of the magnetic hyperfine structure (HFS)
of metallic iron. The Mössbauer spectra were pro-
cessed using standard least-square method programs
(LOREN (Semenov Institute of Chemical Physics,
Russian Academy of Sciences) and NORMOS (Ger-
many)) assuming a Lorentzian line shape.
Specific surface area was determined by thermal
desorption of argon using a setup based on a Chrom-5
chromatograph.
The following supports were used: layered silica
(activated silica matrix (ASM)) prepared by two-
step acid etching of natural mineral vermiculite [10];
KSK-2 silica gel of a globular structure without pre-
treatment (SiO2) and after preactivation (AGM) by a
single-step treatment with hydrochloric acid and sub-
sequent washing; and oxides of zirconium (ZrO2),
titanium (TiO2), zinc (ZnO), and aluminum (Al2O3)
without acidic pretreatment.
The catalysts (Fe/support) were prepared by incip-
ient wetness impregnation and subsequent drying in
air and heating at 673 K for 4 h. The precursor salt was
iron acetylacetonate Fe(acac)3 in toluene. The use of
Fe(acac)3 leads to the formation of γ-Fe2O3, which is
more active in C–C bond activation, on the support
surface [8–10]. This feature distinguishes this method
from most other known techniques used for support-
ing iron oxides, where α-Fe2O3 is generally formed
on the support surface; this modification is inferior to
γ-Fe2O3 in catalytic properties in this class of reactions
involving chlorohydrocarbons [8]. The metal loading
on the support was determined by atomic absorption
spectroscopy on a Thermo iCE 3000 AA spectrometer
after dissolving iron in concentrated hydrochloric
acid. According to atomic absorption spectroscopy
data, the iron loading on the catalysts—5 wt %—cor-
responded to the calculated value.
Benzene alkylation with BC was conducted in air-
sealed glass tubes in the temperature range of 353 K
with stirring. A reaction mixture in an amount of
0.2 mL was placed into the tube; the mixture was com-
posed of benzene (8.9 mol/L) and BC (1.75 mol/L)
taken in a ratio of 4 : 1 and a catalyst weighed portion
of 0.005 g (CFe = 0.0022 mol/L). Special experiments
conducted under similar conditions in the absence of
oxygen showed that the rate of the process does not
depend on the presence of oxygen.
In all cases, the reaction between benzene and BC
mostly leads to the formation of diphenylmethane
(DPM). Only at high degrees of conversion of BC
(98–100%), up to 0.4% of polyalkylation products
were observed in the reaction products.
The activities of the different samples were com-
pared according to specific catalytic activity (turnover
frequency (TOF)) calculated from the maximum pro-
cess rate as follows: TOF = mol DPM/(mol Fe h).
Chromatographic analysis of the precursors and
the reaction solutions was conducted by GLC on a
Kristallyuks-4000 chromatograph (analysis condi-
tions: chromatographic column, SE-30; l, 3 m; col-
umn temperature, 343 K; and detector, FID).
57Fe Mössbauer spectra were recorded on a Wissel tively large nonstoichiometric magnetite clusters
electrodynamic spectrometer (Germany) in the (about 8–10 nm). It can be assumed that, unlike other
temperature range of 16–300 0.1 K using a Janis supports, the formation of these clusters can be
CCS-850 helium cryostat equipped with a Lake Shore affected by the presence of interfaces between two
Cryotronics temperature controller (model 332). The crystalline modifications—monoclinic and tetrago-
RESULTS AND DISCUSSION
Structure and Electronic Properties
of Iron-Containing Catalysts
The Mössbauer spectra and magnetic properties of
Fe/ASM and Fe/AGM samples containing similar
amounts of iron were described previously [9, 10].
According to [9, 10], Fe/AGM mostly contains super-
paramagnetic γ-Fe2O3 particles with a size of 2–4 nm
and, additionally, ~10% nonstoichiometric magnetite.
The replacement of the support by layered silica
(ASM) leads to a change in the composition of the
active phase of the catalyst. The Fe/ASM sample
comprises, along with γ-Fe2O3 clusters of a 2–4 nm
size, larger γ-Fe2O3 particles with a size of 8–10 nm; in
this case, Fe(III) does not undergo reduction to Fe(II)
during the sample synthesis. This finding is attributed
to the higher strength of interaction between iron(III)
oxide and the layered matrix. In this study, Mössbauer
spectroscopy was also used to analyze differences in
the composition, structure, and electronic properties
between catalysts prepared on supports of different
types.
Figure 1 shows the Mössbauer spectra of the test
samples recorded at T = 300 K; Table 1 summarizes
the spectral parameters. All the spectra of the original
catalysts exhibit a doublet of the “paramagnetic”
iron(III) ion in a high-spin state. The parameters of
the doublets in Fig. 1 are characteristic of both small
superparamagnetic iron oxide clusters and the insu-
lated iron(III) ion localized on the support. The pres-
ence of superparamagnetic γ-iron oxide clusters with a
size of about 2–4 nm in the Fe/SiO2 sample confirms
the occurrence of characteristic HFS lines in the spec-
trum at 16 K (Fig. 2). The same particles were previ-
ously detected in the case of AGMs and ASMs used as
a support; the presence of the particles was addition-
ally confirmed by analysis of the magnetic properties
of the samples [9, 10].
Even at 300 K, the spectrum of Fe/ZrO2 exhibits
magnetic HFS lines of magnetically ordered and rela-
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EFFECT OF THE SUPPORT NATURE
95
I, arb. units
I, arb. units
1.00
1.00
0.98
0.96
0.94
0.99
T = 300 K
Fe/TiO2
Fe/ZnO
0.98
0.97
0.96
1.000
0.996
0.992
1.00
1.00
0.98
0.96
0.94
0.92
0.99
T = 78 K
0.98
0.97
0.96
Fe/SiO2
1.00
0.98
0.96
1.00
Fe/Al2O3
T = 16 K
0.99
1.00
0.99
0.98
0.98
Fe/ZrO2
0.97
–10
–5
0
5
10
V, mm/s
–10
–5
0
5
10
V, mm/s
Fig. 2. Mössbauer spectra of the 5%Fe/SiO sample at T =
2
Fig. 1. Mössbauer spectra at T = 300 K for the Fe species
in the Fe/TiO , Fe/ZnO, Fe/SiO , Fe/Al O , and
100, 78, and 16 K.
2
2
2 3
Fe/ZrO samples.
2
law [12]. Most likely, Fe/TiO2 contains the “paramag-
netic” Fe(III) ions that dope the surface or near-sur-
face layers of the support and form dimers or trimers,
rather than individual superparamagnetic iron oxide
clusters.
Temperature measurements for the Fe/Al2O3 sam-
ple (Fig. 3) showed that at T = 16 K, the iron(III) ion
remains paramagnetic. This behavior can be attributed
to the formation of mixed spinel FexAl2xO3, in which
the magnetic stability of oxide is low because of the
presence of a nonmagnetic aluminum ion. In other
words, the magnetic phase transition temperature
(Curie or Neel point) in the Fe/Al2O3 sample is sig-
nificantly lower than that, for example, in the Fe/SiO2
sample (Fig. 2). Thus, for cubic FeAl2O4, the Neel
point is TN = 8 K [11].
nally distorted—in the structure of ZrO2. With respect
to the magnitude of quadrupole splitting of the para-
magnetic component of the spectrum (Fig. 1,
Table 1), this form is close in parameters to the Fe(III)
ion on the surface of tetragonal ZrO2 [12].
The spectra of the Fe/ZnO sample (Fig. 1) differ
from the spectra of other samples by the abnormally
low magnitude of the Mössbauer effect. This feature is
most probably due to the dynamic effect [13], which
consists in that paramagnetic Fe(III) ions weakly
interact with the support. Having a large vibration
amplitude, they exhibit almost an order of magnitude
lower value of the Mössbauer effect than that of the
other test systems and a low intensity of lines in the
spectra. Weak interaction with the support suggests
that these ions correspond to extremely small clusters
on the iron oxide surface.
According to XRD data, the iron-containing phase
in all the test samples was X-ray amorphous, as in the
previously studied samples [8–10], thereby indicating
a high dispersion (d < 5 nm) of iron oxide nanoparti-
cles on the surface in agreement with the Mössbauer
According to magnetic measurements in the range
of 77–300 K, tetragonal Fe/TiO2 crystallites exhibit a
paramagnetic behavior that obeys the Curie–Weiss data.
PETROLEUM CHEMISTRY Vol. 57 No. 1 2017

96
VERNAYA et al.
Table 1. Mössbauer spectrum parameters* recorded at 300 K for iron species supported on different inorganic oxides
Hin
δ
Δ
А
Sample
Fe/TiO2
Fe species
Source
0.03 mm/s
0.5 T
0.05
Fe3+ paramagnetic
Fe3+ paramagnetic
Fe3+ paramagnetic
Fe3+ paramagnetic
0.38
0.34
0.33
0.31
0.34
0.30
0.71
0.33
0.33
0.34
0.30
0.70
0.70
0.87
–
–
1.00
1.00
1.00
1.00
0.47
0.34
0.19
0.66
0.34
0.89
0.06
0.06
Fe/ZnO
Fe/SiO2
Fe/Al2O3
0.96
–
This study
0.95
–
Fe3+ paramagnetic
0.93
–
Fe/ZrO2
Fe/АSM
Fe/АGM
Fe3O4+δ (A)**
0.08
48.2
45.2
–
Fe3O4+ δ (B)**
–0.10
1.05
Fe3+ paramagnetic
γ-Fe2O3
–0.06
0.87
49.6
–
Catalysis Today 152
(2010) 48–53
Fe3+paramagnetic
Fe3O4+ δ (A)**
Fe3O4+ δ (B)**
–0.06
0.00
46.8
44.7
57
* δ is the isomer shift with respect to α-Fe; ∆, the quadrupole splitting or quadrupole shift; H , the internal field at the Fe nucleus;
in
and A, the relative abundance of the respective species.
** A and B are the tetrahedral and octahedral positions of nonstoichiometric magnetite.
The specific surface areas of the supports and the
catalysts are shown in Table 2. The use of supports
with a specific surface area of ≥50 m2/g (SiO2, AGM,
ASM, TiO2) leads to a slight decrease in their specific
surface area after the introduction of iron. A slight
increase in specific surface area is observed in the case
of depositing small γ-Fe2O3 clusters on ZrO2 and ZnO
supports, which have the least developed surface (less
than 50 m2/g). In the case of Al2O3, the highest loss of
Benzene Alkylation with Benzyl Chloride
The reaction between benzene and BC occurs in
the presence of any of the test catalysts at temperatures
above 50°C to give diphenylmethane and hydrogen
chloride. As noted in Experimental, the presence of
oxygen does not have an effect on the rate of the pro-
cess, unlike the case of previously studied reactions
involving allylic chloroolefins [8, 9]. The effect of the
silica structure (acid-treated silica gel (AGM) and ver-
miculite-based layered silica (ASM)) on the structure
the surface area is observed (30%); according to Möss- of supported catalysts based on γ-Fe2O3 and their
acidic properties and catalytic activity in benzylation
was studied in [10]. It was shown that the formation of
DPM over the two studied silicas occurs quantitatively
after a long induction period. The activity of Fe/AGM
after the induction period was higher than the activity
of Fe/ASM, as calculated from the data corresponding
to the maximum rate. The higher activity is primarily
associated with the structural features of the catalysts
and, probably, with a slight difference in their acidic
properties (Brønsted acidity of ASM is slightly higher
than that of AGM [10]).
bauer data, it can be assumed that this loss is due to a
change in the Al2O3 surface structure by the formation
of mixed spinel FexAl2xO.
Table 2. Specific surface area of supports and benzene ben-
zylation catalysts
Specific surface area
Specific surface area
Support
of support S, m2/g of 5%Fe/support S, m2/g
ZrO2
ZnO
SiO2
28
37
440
145
350
51
40
47
380
140
290
42
In this study, iron catalysts were prepared using a
number of supports with a wide range of acid–base
properties [14]. The features of the process over all the
test catalysts turned out to be similar. In all cases, the
quantitative formation of DPM was also preceded by
an induction period (Fig. 4). Figure 5 shows data on
the duration of the induction period and TOF values
of the iron-containing samples on different supports,
АGM
АSM
TiO2
Al2O3
220
160
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EFFECT OF THE SUPPORT NATURE
97
which were calculated as described in [10] for the
range of the maximum reaction rate. It is evident
(Figs. 4, 5) that the induction period varies from
20 min to a few hours depending on the nature of the
support.
I, arb. units
1.00
T = 300 K
0.98
0.96
The data obtained in this study suggest that the cat-
alytic activity of iron oxides supported on inorganic
oxides is determined by a number of factors. First of
all, the highest TOF of 248 mol DPM/(mol Fe h) and
the shortest induction period of 20 min were observed
for the Fe/SiO2 catalyst with the most developed sur-
face and intermediate acidity. In addition, the acid
treatment of silica gel (Fe/AGM) leads to a slight
decrease in the TOF of the catalyst to 220 mol
DPM/(mol Fe h). This feature differs benzylation
from the previously studied isomerization of 3,4-
dichlorobutenes and benzene alkylation with allyl
chloride, where the acid treatment of the silica gel led
to an increase in the catalysis efficiency [10]. Short
induction periods (about 20 min) are also characteris-
tic of the Fe/ZrO2 and Fe/ZnO samples; the TOF values
of these samples—241 and 220 mol DPM/(mol Fe h)—
are close to that of Fe/SiO2.
1.00
0.99
0.98
0.97
T = 78 K
1.00
0.99
0.98
0.97
0.96
T = 16 K
In accordance with the literature [14] and our data
[10], the supports used in this study can be arranged in
the following order of increasing acidity: ZrO2 <
ZnO < SiO2 < АGM < АSM < TiO2 < Al2O3. In accor-
dance with the results of this study and previous re-
search [10], the efficiency of the catalysts on different
–10
–5
0
5
10
V, mm/s
supports increases in the order: Al2O
TiO < АSM
3 ꢀ
< АGM < ZnO < ZrO2 < SiO2. It is evident2that this
order is almost opposite to the order of increasing acid
properties of the support. Thus, higher acidity of
ASM, TiO2, and Al2O3 apparently do not play a signif-
icant role in providing the catalytic ability, as might be
Fig. 3. Mössbauer spectra of the 5%Fe/Al O sample at
T = 100, 78, and 16 K.
2
3
5% Fe/ZnO
5% Fe/ZrO2
1.6
1.4
1.2
1.0
5% Fe/AGM
5% Fe/TiO2
5% Fe/SiO2
5% Fe/ASM
0.8
0.6
0.4
0.2
5% Fe/Al2O3
0
0.2
0.4
0.6
0.8
1.0
t, h
1.2
1.4 2.5 3.5 4.5 5.5
Fig. 4. Diphenylmethane buildup rate curves in the presence of iron catalysts (С
= 1.75 mol/L, C = 0.0022 mol/L).
Fe
maхDPM
PETROLEUM CHEMISTRY Vol. 57 No. 1 2017

98
VERNAYA et al.
250
200
150
100
50
mol DPM/(mol Fe h)
Induction period, min
0
5% Fe 5% Fe 5% Fe 5% Fe 5% Fe 5% Fe 5% Fe
ZrO2 ZnO SiO2 AGM ASM TiO2 Al2O3
Fig. 5. Effect of the support nature on the duration of the induction period and TOF of iron-containing benzene benzylation cat-
alysts.
expected for the ionic mechanism of alkylation. At the the iron oxides. Thus, the reducibility of Fe(III) to
same time, the use of ZrO2 and ZnO oxides exhibiting Fe(II) determines both the efficiency and stability of
the catalysts and depends on the size and structure of
the supported oxide and the pattern of interaction
between the oxide and the support. The reduction of
more than 50% Fe(III) leads to almost complete deac-
tivation of the catalyst.
relatively low acidity and even basic properties [15] as
supports leads to the formation of active Fe/ZrO2 and
Fe/ZnO catalysts. The highest efficiency of Fe/SiO2
in catalysis can also be partly due to a high specific sur-
face area of the silica gel (Table 2).
It can be assumed that the simultaneous presence
of Fe(III) and Fe(II), for example, γ-Fe2O3 nanopar-
ticles and nonstoichiometric magnetite, in the catalyst
composition in the case of Fe/ZrO2 and Fe/АGM is
favorable for the catalysis of benzene alkylation. Activ-
ity in benzene benzylation was also exhibited by the
Fe/ZnO, Fe/АSM, and Fe/SiO2 samples comprising
γ-Fe2O3 nanoparticles that can be partially reduced
during synthesis under the action of chlorohydrocar-
bons. The activity is facilitated by the following fac-
tors: similar inverse spinel structures of γ-Fe2O3 and
magnetite and weak interaction between Fe(III) and
the support, which promotes the formation of iron
oxide clusters on the support surface, rather than the
incorporation of iron ions into the surface or near-sur-
face layers of the oxide support.
In addition, the enhanced catalytic activity of iron
oxide supported on ZrO2 can be due to a higher degree
of imperfection of these samples, which is associated
with the presence of different types of defects on the
support surface attributed to the presence of a small
amount of tetragonal ZrO2 in addition to the mono-
clinic modification [16]. The fact that the Mössbauer
parameters of the samples are close to the values char-
acteristic of the Fe(III) ion on the surface of tetragonal
ZrO2 [12] suggests that the formation of iron oxide in
this case occurs at the interface between the two
phases, thereby increasing the imperfection of the par-
ticles and enhancing the catalysis.
Thus, summarizing the structural and kinetic data,
it can be concluded that short induction periods and
high TOF values are exhibited by samples character-
ized by the presence of particular clusters of iron
oxides with an inverse spinel structure and the forma-
tion of iron oxide–support oxide interfaces. The same
is true of the 5%Fe/ZnO sample, in which the pres-
ence of an abnormally low Mössbauer effect suggests
that the iron ions weakly interact with the support.
Most probably, these ions can also be classified as
extremely small iron oxide clusters.
The lower catalytic activity of the samples sup-
ported on ASM and TiO2 and almost complete
absence of activity in Fe/Al2O3 can be associated with
strong interaction and the incorporation of iron ions
into the structure of the support. The Mössbauer spec-
troscopy data suggest that a strong interaction between
supported Fe2O3 and Al2O3 leads to the formation of a
FexAl2 – xO3 mixed spinel structure. In addition, iron
ions are incorporated into the surface or near-surface
layers of the support in the case of TiO2 and, most
likely, superparamagnetic iron oxide clusters are not
formed on the support surface.
The role of small clusters of nonstoichiometric iron
oxides with γ-Fe2O3 inverse spinel and magnetite
structures in reactions involving chlorohydrocarbons
was discussed in [9, 10]. It was shown that under reac-
tion conditions, iron(III) oxides on the catalyst sur-
face are converted to iron(II) chloride exhibiting low
activity. However, the partial reduction of Fe(III) ions
The fact that the catalytic activity of iron
to Fe(II) contributes to an increase in the activity of oxides in alkylation with chlorohydrocarbons
PETROLEUM CHEMISTRY
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EFFECT OF THE SUPPORT NATURE
99
correlates with the simultaneous presence of with benzyl chloride through the intermediate
Fe(III) and Fe(II) in the catalyst composition formation of the radical cation according to the
suggests that the redox mechanism alkylation following scheme:
Cl
–
Fe2+
Fe3+
Fe2+
Fe2+
Fe3+
Fe2+
,
O
O
O
R Cl
CH+2
R Cl
R
where R+
CH+2
+
H
CH2
+H+
.
7. O. G. Ellert, M. V. Tsodikov, and V. M. Novotortsev,
The use of SiO2, ZrO2, ZnO, and AGM supports,
which do not exhibit pronounced acid properties and
are characterized by weak oxide–oxide interaction
with supported oxides, contributes to the formation of
small clusters of iron oxides with an inverse spinel
structure involving simultaneously both Fe(III) and
Fe(II) ions during the synthesis of catalysts from iron
acetylacetonate or under the action of reactants. These
catalysts exhibit the highest activity in the benzene
alkylation with benzyl chloride.
Usp. Khim. 79, 758 (2010).
8. M. V. Tsodikov, T. N. Rostovshikova, V. V. Smirnov,
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kovskaya, Handbook of Physical Quantities (Energoat-
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