The Continuous Synthesis of 2-(2'-Hydroxy-5'-Methylphenyl)Benzotriazole over Cu/γ-Al2O3

Article abstract of DOI:10.1134/S0023158419050124

Abstract: The samples of 20% Cu/γ-Al₂O₃, 20% Co/γ-Al₂O₃ and 20% Ni/γ-Al₂O₃ were prepared as hydrogenation catalysts for continuous synthesis of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole. The best yield (86.62%) was afforded by the 20% Cu/γ-Al₂O₃ catalyst. The characterizations results obtained for the 20% Cu/γ-Al₂O₃ sample confirmed that Cu particles are evenly distributed over the surface of γ-Al₂O₃. A reduction of acid sites in the catalyst favored the selectivity to 2-(2'-hydroxy-5'-methylphenyl)benzotriazole. Furthermore, the effect of Cu content, reaction temperature, hydrogen pressure and liquid hourly space velocity was studied. Finally, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole in 86.62% yield was attained under the optimized conditions.

Full text of DOI:10.1134/S0023158419050124

ISSN 0023-1584, Kinetics and Catalysis, 2019, Vol. 60, No. 5, pp. 635–641. © Pleiades Publishing, Ltd., 2019.
The Continuous Synthesis of 2-(2'-Hydroxy-5'-
Methylphenyl)Benzotriazole over Cu/γ-Al2O3
L. Yana, L. Sib, Q. Taoa, L. Liua, B. Wanga, c, d, *, and Y. Lia, c, d, **
aSchool of Chemical Engineering and Technology, Tianjin University, Tianjin, 300350 P.R. China
bDisha Pharmaceutical Group Co. Ltd., Tianjin, P.R. China
cCollaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin, 300072 P.R. China
dTianjin Engineering Research Center of Functional Fine Chemicals, Tianjin, P.R. China
*e-mail: bwwang@tju.edu.cn
**e-mail: liyang777@tju.edu.cn
Received January 27, 2019; revised April 8, 2019; accepted May 13, 2019
Abstract—The samples of 20% Cu/γ-Al2O3, 20% Co/γ-Al2O3 and 20% Ni/γ-Al2O3 were prepared as hydro-
genation catalysts for continuous synthesis of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole. The best yield
(86.62%) was afforded by the 20% Cu/γ-Al2O3 catalyst. The characterizations results obtained for the 20%
Cu/γ-Al2O3 sample confirmed that Cu particles are evenly distributed over the surface of γ-Al2O3. A reduc-
tion of acid sites in the catalyst favored the selectivity to 2-(2'-hydroxy-5'-methylphenyl)benzotriazole. Fur-
thermore, the effect of Cu content, reaction temperature, hydrogen pressure and liquid hourly space velocity
was studied. Finally, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole in 86.62% yield was attained under the
optimized conditions.
Keywords: catalytic hydrogenation, benzotriazole, transition metal catalysts
DOI: 10.1134/S0023158419050124
INTRODUCTION
From earlier patents describing catalytic hydroge-
nation the information on attractive yields of benzotri-
azoles can be derived [21–23]. However, no detailed
explanation of the experimental results could be found
in patent reports. Besides, in these experiments the
catalytic hydrogenation was carried out in a flask or
autoclave and the results could be hardly scaled to the
industrial production of benzotriazoles. Thus, there is
a need for an efficient and economically feasible
method of synthesis of benzotriazoles. In a number of
studies, hydrogenation of 2-nitro-2'-hydroxy-5'-
methylazobenzene (NAB) was described [24–26]. In
our previous works [27], the continuous catalytic
hydrogenation of NAB to 2-(2′-hydroxy-5′-methyl-
phenyl)benzotriazole (BTA) was investigated by using
Pd/γ-Al2O3 as a catalyst. It was found that Pd-based
catalyst exhibited an excellent performance. But the
Benzotriazole ultraviolet absorbers, as a class of the
light stabilizers, are used to prevent degradation of
polymer materials [1, 2]. Accordingly, the synthesis of
benzotriazoles has also attracted worldwide attention
[3–6]. Generally, a two-step preparation of benzotri-
azoles conventionally involves synthesis and reductive
cyclization of azo dyes intermediate. Synthesis of azo
dyes is quite mature, including microwave irradiation,
solid phase and solution reaction methods [7–9].
However, the reductive cyclization of azo dyes, as the
key step in the preparation of benzotriazoles, is diffi-
cult to control because it is accompanied by side reac-
tions [10–14]. At present, the reductive cyclization is
mainly conducted by using zinc powder, hydrazine
hydrate, SmI2, or sulfides [15–18]. However, using
these reagents has certain disadvantages. For instance, additional base was required in this reaction to restrain
while zinc powder reduction method is widely applied the generation of amino by-products [10, 28]. To over-
come this obstacle, solid base-hydrogenation bifunc-
tional catalysts were employed and the effect of differ-
ent alkali metals over Pd/γ-Al2O3 was studied [29, 30].
Although the satisfactory results were obtained, it was
desirable to find a catalytic system as an alternative to
in the industry with a satisfactory yield of benzotri-
azoles, it is associated with serious environmental
problems [16, 18, 19]. Considering the cost and envi-
ronmental consequences, the catalytic hydrogenation
appears as an ideal alternative because it can be
expected that the catalytic hydrogenation generates noble metal catalyst used in this reaction and optimize
water as the only by-product [20]. the reaction conditions. Less expensive transition
635

636
YAN et al.
metal systems were developed as catalysts for the con- excellent catalytic performance with 86.62% yield of
tinuous catalytic hydrogenation, but results obtained
were far from ideal [27]. Therefore, the exploration of
high-performance transition metal catalysts remains
an important challenge.
In the present work, we focused on the preparation
of a series of transition metal systems including Cu/γ-
Al2O3, Co/γ-Al2O3 and Ni/γ-Al2O3 as catalysts for the
continuous catalytic hydrogenation of NAB to BTA
(Scheme 1) [30]. Among these, Cu/γ-Al2O3 showed
BTA. The catalysts were characterized by X-ray dif-
fraction (XRD), transmission electron microscopy
(TEM), Brunauer–Emmer–Teller (BET) surface area
measurements and temperature programmed desorp-
tion of ammonia (NH3-TPD) to discuss the structure-
activity relationship. Moreover, reaction parameters
were optimized in terms of Cu content, reaction tem-
perature, hydrogen pressure and liquid hourly space
velocity (LHSV).
OH
NH2
NH2
NH2
+
HO
H2/catalyst
N
N
AC
HO
HO
NO2
HO
N
N
N
N
N
N
N
H2/catalyst
H2/catalyst
N
N
NAB
O
NO
THB
BTA
Scheme 1. Catalytic hydrogenation of NAB.
EXPERIMENTAL
between 7–8 as monitored during the dropping pro-
cess. Then, the solution was stirred for 1 h and aged for
another 1 h. The mixture was filtered, washed and
dried at 120°C for 6 h. Adding 76.8 g of pseudo-boeh-
mite and a moderate amount of water pulverized the
solid. Then, the mixture was kneaded adequately and
then extruded by an extrusion machine. After drying at
120°C for 6 h, the bars were calcined at 550°C for 4 h
in a muffle and then the obtained precursor was acti-
vated at 240°C at a hydrogen pressure of 1.0 MPa for
4 h. Other catalysts were prepared by a similar process
applying the activation temperatures of 400 and 360°C
for Co/γ-Al2O3 and Ni/γ-Al2O3, respectively.
Materials
Nitrate hydrates Cu(NO3)2 · 3H2O (analytical
reagent (AR)), Co(NO3)2 · 6H2O (AR) and Ni(NO3)2 ·
6H2O (AR) were provided by Tianjin Ruijinte Chemi-
cal Co., Ltd. (China). Toluene (AR), triethylamine
(AR) and anhydrous sodium carbonate (AR) were
purchased from Tianjin Jiangtian Chemical Co., Ltd.
(China). Pseudo-boehmite was obtained from Jiang-
yan Chemical Auxiliary Factory (China). 2-Nitroani-
line (AR) and p-Cresol (AR) were respectively gained
from Tianjin Yuanli Chemical Co., Ltd. and Tianjin
Guangfu Technology Development Co., Ltd. (China).
Commercially available reagents were used without fur-
ther purification. 2-Nitro-2′-hydroxy-5′-methylazoben-
zene (≥ 90%, as determined by high performance liquid
chromatography (HPLC) was produced by diazotization
and coupling reaction.
Catalyst Characterization
The XRD patterns were measured with a Rigaku
D/max 2500 (Rigaku Corporation, Japan) using CuKα
X-ray radiation (40 kV, 100 mA). TEM micrographs
were performed on a Tecnai G2 F20 high-resolution
analytical electron microscope (FEI, Netherlands)
Catalyst Preparation
The transition metal catalysts were prepared by the operating at an electron beam voltage of 200 kV. The
co-precipitation-kneading method [27, 31–33]. To specific surface areas were determined by BET
prepare the 20% Cu/γ-Al2O3 (20 wt. % Cu in the cat- method with N2 adsorption-desorption measurements
alyst) 48.32 g of Cu(NO3)2 · 3H2O and 23.32 g of at 77.4 K using a NOVA 2000e analyzer (Quanta-
chrome Instruments, USA). NH3-TPD was carried
out on a TP-5000 instrument (XQ, China) equipped
with a thermal conductivity detector. The samples
were treated under argon at 800°C for 2 h, cooled
down to 25°C in flowing argon, and then treated with
flowing NH3 for 10 min at 30°C. Finally, the sample
Na2CO3 were separately dissolved into 500 mL deion-
ized water to form the solutions A and solution B. Both
of the solution A and B were simultaneously dropped
slowly into a big beaker with 500 mL deionized water
under mechanical stirring at room temperature. The
pH value of the reaction mixture was maintained
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THE CONTINUOUS SYNTHESIS
637
Table 1. The catalytic hydrogenation of NAB over transition metal catalysts
Selectivity, %
BTA
Catalysts
Conversion of NAB, %
AC
NO
THB
others
20% Cu/γ-Al2O3
20% Co/γ-Al2O3
20% Ni/γ-Al2O3
99.52
98.85
0.45
58.34
10.20
1.44
25.70
5.84
87.04
2.47
1.31
0.76
−
9.76
12.73
12.13
100.00
71.83
Reaction conditions: solvent—toluene, base—triethylamine (molar ratio of NAB : triethylamine = 1 : 2), catalyst—40 mL, reaction tem-
–1
perature—120°C, hydrogen pressure—2.5 MPa, and LHSV—0.23 h
.
was heated to 700°C with a ramping temperature of catalysts were characterized by XRD, TEM, BET and
15°C/min. NH3-TPD techniques.
Catalytic Reactions
Catalyst Characterization
The catalytic hydrogenation of NAB was accom-
plished under the requisite temperature, hydrogen
pressure and LHSV in a fixed bed reactor with an inner
diameter of 15 mm and a length of 650 mm. The reac-
tion was carried out using 40 mL catalyst with a parti-
cle size of 3 mm. A 5 wt. % solution of NAB in toluene
was fed into the reactor by a tranquil flow pump. A
proportion integration differentiation cascade con-
troller regulated the temperature inside the catalyst
layer. Gas valves controlled the hydrogen pressure.
The analysis of sample was collected continuously and
the sampling frequency was set to one acquisition per
hour. The components of reaction mixture were ana-
lyzed using HPLC with a column of Extend C18 (250 ×
4.6 mm, 10 μm, Agilent technologies, USA).
The XRD analysis. The XRD patterns of 20%
Cu/γ-Al2O3, 20% Co/γ-Al2O3 and 20% Ni/γ-Al2O3
catalysts are shown in Fig. 1. The three peaks at 37°,
46° and 67° corresponding to (111), (400) and (440)
planes of γ-Al2O3 respectively that are present in each
sample are consistent with the formation of the
γ-Al2O3 phase [27, 29, 34]. Furthermore, for 20%
Cu/γ-Al2O3, the sharp diffraction maxima at 43°, 50°
and 74° were observed assignable to the diffraction
peaks of metal Cu (111), (200) and (220) planes,
respectively (Fig. 1a) [35, 36]. The signal at 90° can
also be attributed to metal Cu (111) crystal face
(JCPDS 04-0836). XRD pattern of the 20% Co/γ-
Al2O3 catalyst showed characteristic peaks at 48°, 76°
and 93° corresponding respectively to (101), (110) and
(112) planes of metal Co crystallites (JCPDS 29-0021
and JCPDS 05-0727) (Fig. 1b). Meanwhile, the dif-
fraction peak at 45° is assigned to the (110) crystal face
of Al–Co phase (JCPDS 29-0021). A diffraction peak
attributable to Al2O structure is also found at 52°
(JCPDS 75-0277). XRD profile of the 20% Ni/γ-
Al2O3 catalyst clearly showed four peaks at 45°, 52°,
76° and 93° belong to (111), (200), (220) and (311)
RESULTS AND DISCUSSION
Catalyst Selection
Initially, 20% Cu/γ-Al2O3, 20% Co/γ-Al2O3 and
20% Ni/γ-Al2O3 were employed for the catalytic
hydrogenation of NAB. The results are presented in
Table 1. These catalysts displayed excellent activities in
the catalytic hydrogenation with conversions of NAB planes of Ni0 respectively (JCPDS 04-0850 and
exceeding 98%. However, three catalysts showed con- JCPDS 03-1051) (Fig. 1c). Therefore it emerges that
siderable variations in the BTA selectivity. Selectivity metal Cu, Co and Ni were successfully supported on
for BTA over 20% Cu/γ-Al2O3 was as high as 87.04%. the surface of γ-Al2O3 and the presence of zero-
When 20% Ni/γ-Al2O3 was applied for the hydrogena- charged metals can be recognized in all samples sug-
gesting the existence of active sites for the catalytic
hydrogenation.
tion, the selectivity for BTA was 71.83%. In the presence
of 20% Co/γ-Al2O3 the main products were 2-amino-p-
cresol, o-phenylenediamine (AC, amino compounds)
TEM analysis. Fig. 2 presents the images illus-
trating the morphological features of 20% Cu/γ-
Al2O3, 20% Co/γ-Al2O3 and 20% Ni/γ-Al2O3 cata-
lysts. The average diameter of Cu particles was found
to be 3.29 nm (Fig. 2a). However, the size of Co parti-
cles is about 79.66 nm and it appears that the initial
crystals are formed into polycrystalline aggregates
shown in Fig. 2b. Partial agglomeration of Ni particles
and
2-(2′-hydroxy-5′-methylphenyl)benzotriazole
N-oxide (NO). The level of selectivity for AC (58.34%)
indicates that the azo bond was broken [10]. From the
above results it can be inferred that the 20% Cu/γ-Al2O3
catalyst showed the best catalytic performance. To fur-
ther explore the structure-activity relationship of 20%
Cu/γ-Al2O3, 20% Co/γ-Al2O3 and 20% Ni/γ-Al2O3, the
KINETICS AND CATALYSIS Vol. 60 No. 5 2019

638
YAN et al.
catalysts seem to be similar. The lowest BET surface
Intensity
area (186 m2/g) was found for the 20% Cu/γ-Al2O3
sample, whereas the highest value (212 m2/g) was
recorded for the 20% Co/γ-Al2O3 catalyst. The infor-
mation outline above indicates that the structural
properties are not the main factors that govern the cat-
alytic performance.
NH3-TPD analysis. NH3-TPD was carried out to
study the acidity of the three catalysts. As can be read-
ily recognized in Fig. 3, all catalysts exhibit two
ammonia desorption peaks. It appears that the
amount of acid sites in the 20% Cu/γ-Al2O3 sample is
lower than that in other two catalysts. According to the
reports [10], the reductive cyclization of NAB pro-
ceeded readily in alkaline environment. The acid sites
of the catalyst may cause the cleavage of the N=N
bond, which is not favorable for the progress of the
reaction. The results are consistent with the fact that a
high selectivity for BTA was observed in the presence
of 20% Cu/γ-Al2O3 (Table 1).
According to the results derived from XRD, TEM,
BET and NH3-TPD measurements, Cu particles were
uniformly dispersed in the 20% Cu/γ-Al2O3 catalyst
and the amount of acid sites was less than in other two
catalysts. A high fraction of copper exposed and a
moderate acidity can be the main factors responsible
for a good performance of the 20% Cu/γ-Al2O3 cata-
lyst. It can also be deduced from the foregoing that
BET surface area of catalysts has little effect on the
catalytic hydrogenation.
*
*
*
3
2
1
20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
2θ, deg
Fig. 1. The XRD patterns: (1) 20% Cu/γ-Al O , (2) 20%
2
2 3
3
Co/γ-Al O , and (3) 20% Ni/γ-Al O . Symbols:
2
3
* γ-Al O , s Cu, n Al-Co phase, r Co, × Al O, d Ni.
2
3
2
can account for an average diameter of 21.02 nm cal-
culated for polycrystalline spheroids in the 20% Ni/γ-
Al2O3 catalyst (Fig. 2c). The phenomenon of particle
aggregation may be related to a high reduction tem-
perature [37]. The differences in the dispersion degree
may also significantly affect the catalytic performance
[38, 39]. The presence of metal nanoparticles loaded
on the surface of γ-Al2O3 agrees with the XRD results.
Catalytic Hydrogenation of NAB to BTA
BET analysis. The BET surface area, total pore vol-
ume and average pore diameter were characterized by
N2 adsorption–desorption measurements. Table 2
shows that the BET surface area and total pore volume
of γ-Al2O3 are 252 m2/g and 0.70 cm3/g, respectively.
The BET surface area and the pore volume calculated
for Cu, Co and Ni catalysts supported on γ-Al2O3
show a small reduction caused by occlusion of metals
In order to further improve the conversion of NAB
and selectivity for BTA a series of reaction parameters
including Cu content, reaction temperature, hydrogen
pressure and LHSV were optimized with the results
shown in Fig. 4.
At the first step, the effect of copper loading on the
continuous catalytic hydrogenation of NAB was
in pore voids. The structural properties of the three explored. Based on the data shown in Fig. 4a, increas-
10 nm
0.2 μm
100 nm
(a)
(b)
(c)
Fig. 2. TEM images of (a) 20% Cu/γ-Al O , (b) 20% Co/γ-Al O , and (c) 20% Ni/γ-Al O .
2
3
2
3
2 3
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THE CONTINUOUS SYNTHESIS
Table 2. The structure properties of support and different catalysts
639
SBET, m2/g*
Vtotal, cm3/g**
Daverage, nm***
Catalysts
20% Cu/γ-Al2O3
186
212
202
252
0.46
0.56
0.60
0.70
4.94
5.32
5.91
5.59
20% Co/γ-Al2O3
20% Ni/γ-Al2O3
γ-Al2O3
* BET surface area.
** Total pore volume.
*** Average pore diameter.
ing the Cu content from 10 to 20% leads to an
The influence of hydrogen pressure on the hydroge-
improvement both in conversion of NAB and selectiv- nation reduction of NAB was also explored (Fig. 4c). As
ity for BTA was observed. This effect is probably due to reaction pressure was raised from 2.0 to 3.0 MPa, the
an increase in the population of active sites. However conversion of NAB increased from 95.14 to 99.52%
and then remained nearly constant. Meanwhile, the
selectivity of BTA was found to parallel the conversion
trend reaching a value of 87.63%. Considering the pro-
duction cost, 2.5 MPa hydrogen pressure was chosen as
the optimal reaction pressure with 86.62% BTA yield.
when the Cu content was further increased to 25% the
conversion for NAB decreased to a value of 87.73%
with a concomitant reduction of the BTA selectivity. It
can be speculated that the deterioration of the catalytic
performance can be accounted for by the particle
agglomeration that is caused by the presence of excessive
amounts of Cu [40]. Obviously, 20% Cu/γ-Al2O3 is the
optimal catalyst, which afforded 86.62% yield of BTA.
Finally, the influence of LHSV was also investi-
gated (Fig. 4d). Normally, the LHSV directly affects
the residence time of raw material on the catalyst bed.
The smaller LHSV lead to longer residence times,
which may result in the increase of by-products selec-
tivity. However, excessively large LHSV can cause a
decline in the conversion of NAB. As shown in
Fig. 4d, when the LHSV was increased from 0.15 to
0.30 h–1, the conversion of NAB gradually decreased
to 90.01% whereas the selectivity of BTA first increased
from 73.56 to 87.04% and then decreased to 84.23%. As
a result, a value of LHSV 0.23 h–1 that afforded 86.62%
BTA yield was considered as the best choice.
On the basis of the foregoing discussion the opti-
mal reaction conditions were chosen: catalyst − 20%
Cu/γ-Al2O3, solvent—toluene, base—triethylamine
(molar ratio of NAB : triethylamine = 1 : 2). The reac-
tor operates at a temperature of 120°C, a hydrogen
pressure of 2.5 MPa, and a LHSV of 0.23 h–1. Under
the above conditions, the continuous catalytic hydro-
genation of NAB proceeded effectively to yield 87.04%
of BTA at 99.52% NAB conversion.
At the next step, the effect of the reaction tempera-
ture was studied (Fig. 4b). As the reaction was raised
from 80 to 120°C, the conversion of NAB increased
from 56.21 to 99.52% whereas the selectivity for BTA
increased from 18.09 to 87.04%. Between the reaction
temperatures of 120 and 130°C, the conversion of
NAB remained at a level near 99%, however, the selec-
tivity for BTA declined to 74.11%. A possible explana-
tion is that the selectivity for by-products also
increases with increasing temperature. Thus, a reac-
tion temperature of 120°C was found to be optimal and
was further used in the present work.
Intensity
2
3
1
CONCLUSIONS
The samples of 20% Cu/γ-Al2O3, 20% Co/γ-Al2O3
and 20% Ni/γ-Al2O3 were prepared as hydrogenation
catalysts for continuous synthesis of 2-(2'-hydroxy-5'-
methylphenyl)benzotriazole in a fixed bed reactor.
These catalysts were characterized by XRD, TEM,
BET and NH3-TPD to explain the structure-activity
relationship. As evidenced by TEM images of the 20%
Cu/γ-Al2O3 sample Cu particles are evenly distributed
over the surface of γ-Al2O3. The other two catalysts
show signs of particle agglomeration. The particle
agglomeration may be related to the reduction tem-
200
300
400
500
600
Temperature, °C
Fig. 3. NH -TPD profiles: (1) 20% Cu/γ-Al O , (2) 20%
3
3
2 3
Co/γ-Al O and (3) 20% Ni/γ-Al O .
2
2 3
KINETICS AND CATALYSIS Vol. 60 No. 5 2019

640
YAN et al.
(a)
Conversion/selectivity, %
(b)
Conversion/selectivity, %
100
100
1
2
1
2
75
80
50
60
25
40
10
15
20
25
70
80
90
100 110 120 130
Cu content, %
Reaction temperature, °C
(c)
(d)
Conversion/selectivity, %
100
Conversion/selectivity, %
100
1
90
80
70
90
80
70
1
2
2
2.0
2.5
3.0
0.15
0.20
0.25
0.30
Hydrogen pressure, MPa
LHSV, h–1
Fig. 4. The conversion of NAB (1) and selectivity of BTA (2) as functions of (a) Cu content, (b) reaction temperature, (c) hydro-
–1
gen pressure, and (d) LHSV. Reaction conditions: (a) temperature 120°C, hydrogen pressure 2.5 MPa, and LHSV 0.23 h
;
–1
(b) catalyst 20% Cu/γ-Al O , hydrogen pressure 2.5 MPa, and LHSV 0.23 h ; (c) catalyst 20% Cu/γ-Al O , temperature 120°C,
and LHSV 0.23 h ; (d) catalyst 20% Cu/γ-Al O , temperature 120°C, and hydrogen pressure 2.5 MPa. Other conditions: sol-
2
3
2 3
–1
2
3
vent—toluene, base—triethylamine (molar ratio of NAB : triethylamine = 1 : 2).
perature and can affect catalytic performance. The ceeded effectively to yield 87.04% of BTA at 99.52%
amount of acid sites in the 20% Cu/γ-Al2O3 sample is
lower than in other two catalysts, a reduction of acid
sites in the catalyst favored the selectivity to BTA. To
achieve the optimal reaction performance the activity
and selectivity were investigated as functions of the Cu
content, reaction temperature, hydrogen pressure and
LHSV. The following optimal parameters were cho-
sen: catalyst—20% Cu/γ-Al2O3, solvent—toluene,
base—triethylamine (molar ratio of NAB : triethyl-
amine = 1 : 2). The reactor operates at a temperature
of 120°C, a hydrogen pressure of 2.5 MPa, and a
LHSV of 0.23 h–1. Under the above conditions, the
continuous catalytic hydrogenation of NAB pro-
NAB conversion.
ABBREVIATIONS AND NOTATION
AC
AR
amino compounds
analytical reagent
BET
Brunauer–Emmer–Teller surface area mea-
surements
BTA
HPLC
LHSV
2-(2′-hydroxy-5′-methylphenyl)benzotriazole
high performance liquid chromatography
liquid hourly space velocity
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THE CONTINUOUS SYNTHESIS
641
19. US Patent 3018269, 1962.
20. CA Patent 1154779, 1983.
21. EP Patent 380839, 1990.
22. FRG Patent 2620970, 1976.
23. FRG Patent 2455155, 1975.
NAB
2-nitro-2'-hydroxy-5'-methylazobenzene
NH3-TPD temperature programmed desorption of
ammonia
NO
2-(2′-hydroxy-5′-methylphenyl)benzotriazole
N-oxide
transmission electron microscopy
X-ray diffraction
TEM
XRD
24. Lefedova, O.V., Gostikin, V.P., and Ulitin, M.V., Russ.
J. Phys. Chem., 2001, vol. 75, p. 1433.
FUNDING
25. Lefedova, O.V., Gostikin, V.P., and Nemtseva, M.P.,
Russ. J. Phys. Chem., 2001, vol. 75, p. 62.
This work was supported by the National Natural Sci-
ence Foundation of China (grant no. 21808161).
26. Nemtseva, M.P. and Lefedova, O.V., Kinet. Catal.,
1994, vol. 35, p. 547.
27. Wang, B.W., Fang, W.W., Si, L.L., Li, Y., Yan, X.L.,
Chen, L.G., and Wang, S.T., ACS Sustainable Chem.
Eng., 2015, vol. 3, p. 1890.
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