Copper-modified TS-1 catalyzed hydroxylation of phenol with hydrogen peroxide as the oxidant

Article abstract of DOI:10.1039/c6ra20980g

Herein, TS-1, Cu incorporated TS-1 (Cu-TS-1) and TS-1 supported with different Cu contents (Cu/TS-1-x) are synthesized. The resultant catalyst samples are characterized via X-ray powder diffraction (XRD), nitrogen physical adsorption (N₂-adsorption), inductive coupling plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance (UV-vis) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FT-IR), and studied in the hydroxylation of phenol using H₂O₂ as the oxidant. The results reveal that the framework Ti content and particle diameter of the Cu/TS-1-x samples are almost the same as the untreated TS-1 sample, and that active Cu²⁺ species exist on the catalyst surface. However, the framework Ti of the Cu-TS-1 sample is lost and its particle size increases. This feature may be attributed to the fact that a small amount of Cu species is introduced into the TS-1 framework, which inhibits the formation of framework Ti. Furthermore, the Cu/TS-1-2 catalyst exhibits the best catalytic activity due to the existence of framework Ti and Cu²⁺ species which can promote the conversion of phenol. Furthermore, the phenol conversion of 49.77% and diphenol selectivity of 99.28% are obtained when phenol hydroxylation is carried out at 353 K for 3 h over this catalyst.

Full text of DOI:10.1039/c6ra20980g

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PAPER
Copper-modified TS-1 catalyzed hydroxylation of
phenol with hydrogen peroxide as the oxidant
Cite this: RSC Adv., 2016, 6, 101071
a
a
b
a
a
Guoqiang Wu,* Jianhui Xiao, Lei Zhang, Wenjun Wang, Yanping Hong,
c
a
a
a
Huajun Huang, Yan Jiang, Liang Li and Chunrong Wang
Herein, TS-1, Cu incorporated TS-1 (Cu–TS-1) and TS-1 supported with different Cu contents (Cu/TS-1-x)
are synthesized. The resultant catalyst samples are characterized via X-ray powder diffraction (XRD),
nitrogen physical adsorption (N
ICP-OES), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance (UV-vis)
spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and
Fourier-transform infrared spectroscopy (FT-IR), and studied in the hydroxylation of phenol using H
as the oxidant. The results reveal that the framework Ti content and particle diameter of the Cu/TS-1-x
2
-adsorption), inductive coupling plasma optical emission spectrometry
(
2 2
O
2+
samples are almost the same as the untreated TS-1 sample, and that active Cu species exist on the
catalyst surface. However, the framework Ti of the Cu–TS-1 sample is lost and its particle size increases.
This feature may be attributed to the fact that a small amount of Cu species is introduced into the TS-1
framework, which inhibits the formation of framework Ti. Furthermore, the Cu/TS-1-2 catalyst exhibits
Received 20th August 2016
Accepted 8th October 2016
2+
the best catalytic activity due to the existence of framework Ti and Cu species which can promote the
conversion of phenol. Furthermore, the phenol conversion of 49.77% and diphenol selectivity of 99.28%
are obtained when phenol hydroxylation is carried out at 353 K for 3 h over this catalyst.
DOI: 10.1039/c6ra20980g
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application. Therefore, it is necessary that high catalytic activity
and stability for the TS-1 catalyst be developed for phenol
1
. Introduction
Catechol (CAT) and hydroquinone (HQ) are important high hydroxylation.
value phenolic chemicals, which are widely used in pharma-
It is well known that various metals incorporation and sup-
ceuticals, compound drugs, perfumes, dyes, photographic and ported porous materials have been widely investigated, such as
1
–4
6
16
17
18
agrochemical materials, polymerization inhibitors and so on.
The conventional production of diphenols is mainly via the carbon, Fe
Cu–SBA-15, Sn–S-1,
Zn–TS-1,
Fe/ZSM-5,
Fe/activated
19
20
21
22
2
O
3
/MCM-41, V/MCM-41, CuO/MCM-48, and
23
homogeneous catalytic hydroxylation of phenol with mineral Cu–MOF. The loading of metal species in novel materials has
acids, simple metal ions, and their complexes as catalysts. At been used as an important technique to adjust the catalytic
present, heterogeneous catalysts, such as metal oxides, hetero- active sites, surface properties, chemical composition and also
5,6
1,7–9
polyacids, nanoparticles and zeolites,
important role in the hydroxylation reaction due to their envi- tion.
have played a very the catalytic activity and selectivity of materials in a reac-
5,24,25
The main reason for the change in catalyst properties
ronmental friendliness and catalyst recoverability. Following is that the metal species are heterogeneously distributed both
this, various solid catalysts, such as titanium silicalite zeolite inside and outside the pore channels surface of zeolites.
1
0
11
12
13
series, Ti-b, Ti–ZSM-48, and Cu–AlPO
4
-5, have also been
In the last two decades, copper-modied molecular sieves,
5,26
27
28
29
investigated for the hydroxylation reaction. Particularly, tita- such as Cu/MCM-41,
CuAPO-11, Cu/Y, Cu–HMS, and
nium silicalite-1 (TS-1) has been industrially used as a hetero- Cu–ZSM-5, have exhibited excellent catalytic activity for the
geneous catalyst for the production of diphenol from hydroxylation of phenol with hydrogen peroxide (H ).
However, the drawbacks of low catalytic activity and However, there are only a few reports where phenol hydroxyl-
easy deactivation of the catalyst have limited its wide ation on a Cu-modied TS-1 catalyst is systematically examined
30
2 2
O
1
4,15
phenol.
2
+
and the interrelation between Cu and the catalyst activity is
studied deeply, which are very important to develop a catalyst of
high activity and stability for the hydroxylation of phenol.
In the present study, TS-1, Cu incorporated TS-1 (Cu–TS-1)
a
School of Food Science and Engineering, Jiangxi Agricultural University, Nanchang,
Jiangxi 330045, P. R. China. E-mail: wgoing-651@163.com; Fax: +86-791-83813655;
Tel: +86-791-83813655
b
Tianjin Key Laboratory of Applied Catalysis Science and Technology, School of and TS-1 supported Cu series catalysts (Cu/TS-1-x) are
Chemical Engineering, Tianjin University, Tianjin 300072, P. R. China
prepared and used for phenol hydroxylation. All the catalyst
samples are characterized via XRD, N -physical adsorption, ICP,
c
School of Land Resources and Environment, Jiangxi Agricultural University,
2
Nanchang, Jiangxi 330045, P. R. China
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XPS, UV-vis, SEM, TEM and FT-IR to investigate the correlation temperature of liquid nitrogen (77 K). The chemical composi-
between catalyst and activity. In addition, the effects of reaction tions of the catalyst samples were determined on a Perkin-
time, different catalysts, catalyst amount, Cu content, solvent, Elmer Optima 2000 DV ICP optical emission spectrometer
reaction temperature and catalyst reusability on phenol (ICP-OES). XPS was performed on an AXIS ULTRA DLD X-ray
hydroxylation are studied.
photoelectron spectrometer instrument using an Al Ka radia-
tion source. Specic surface area and pore volume were calcu-
lated according to the BET and BJH methods, respectively. SEM
images were recorded on a SUPRA55 apparatus. TEM images
were obtained on a JEM-2100F microscope. FT-IR spectra of the
2. Experimental
2.1 Materials
Tetrabutyl titanate (TBOT, AR), tetraethyl orthosilicate (TEOS, catalyst samples were recorded on a Thermo Nicolet iS5 FT-IR
AR), isopropyl alcohol (AR), acetone (AR), phenol (AR), and spectrometer (KBr pressed ake). UV-vis spectra in the range
3
0 wt% hydrogen peroxide (AR) were purchased from Tianjin from 190 to 500 nm were obtained on a Shimadzu UV-3600
Guang Fu Fine Chemical Research Institute Co., Ltd, China. spectrometer using pure BaSO as the reference.
wt% tetrapropyl-ammonium hydroxide (TPAOH) was
purchased from Sinopharm Chemical Reagent Co., Ltd, China.
4
25
2.4 Hydroxylation of phenol
The hydroxylation of phenol with H
2 2
O was carried out in
2.2 Synthesis of TS-1, Cu–TS-1 and Cu/TS-1
a 25 mL glass ask equipped with a magnetic stirrer, and the
reaction temperature was controlled by a thermostatic circu-
lating water bath. In a standard reaction, the reaction mixture
contained 1.50 g phenol, 1.00 g acetone and 0.10 g catalyst in
the reactor. When the system temperature reached 353 K, it was
maintained at this temperature for the entire duration of the
test under stirring. Then, 1.80 g hydrogen peroxide (H O , 30
TS-1 was synthesised according to the literature with modi-
31
cations. In brief, a solution of 1.29 g TBOT, 7.9 g dried iso-
propanol and 31.5 g TEOS were added dropwise to a 49.8 g
solution of 15 wt% TPAOH in water over 40 min with vigorous
stirring under an N
2
atmosphere. The composition of the nal
solution was SiO : 0.025TiO : 0.24TPAOH : 26.30H O (molar
2
2
2
2
2
ratio). Aer further stirring for 2 h, the mixture was heated to
53 K and kept at this temperature for 1.5 h to remove alcohol.
wt%) was added to the reaction mixture (phenol : H
2
O
2
¼ 1 : 1
3
(molar ratio), catalyst : phenol ¼ 1 : 15 (mass ratio), stirring rate
During this time, deionized water was added to compensate for
any weight loss. Then, the mixture was transferred to a 100 mL
PTFE lined stainless steel autoclave and crystallized at 448 K for
¼
300 rpm). Aer the reaction, the liquid mixture was separated
by centrifugation, and the products were analyzed on a gas
chromatograph (GC 7890A) equipped with a FID detector and
HP-5 capillary column with nitrogen as the carrier gas. The
72 h under static conditions. Aer cooling to room temperature,
the crystalline product was obtained by ltration, and washed
with deionized water to pH ¼ 7, dried for 6 h at 393 K, and
concentration of unreacted H
titration.
2 2
O was determined by iodometric

nally calcined for 5 h at 823 K in air. This unmodied TS-1
CAT and HQ were the main target products and benzoqui-
none (BQ) was the main by product. Xphenol denotes the
conversion of phenol, and XH2O2 and UH2O2 denote the conver-
sion and utilization of H O , respectively. SCAT, SHQ and SBQ
sample was designated as TS-1-Null.
Cu–TS-1 was prepared by the hydrothermal method
following the procedure reported in ref. 32. Moreover, the
preparation details were similar to that for TS-1 except that in
this case, aer the addition of the mixture of TBOT, TEOS and
2
2
denote the selectivity to CAT, HQ and BQ, respectively, which
were calculated according to the following six equations.
ꢀ1
3 2
isopropanol dropwise, 15.0 mL of 0.01 mol L Cu(CH COO)
0
phenol
n
ꢀ nphenol
phenol
aqueous solution was added dropwise in the solution. The Cu
incorporated TS-1 sample was obtained and designated as
Cu–TS-1.
Cu/TS-1 was prepared by the ion-exchange method following
the procedure reported in ref. 33. In brief, 4 g TS-1 was
X
phenol
¼
ꢁ 100%
(1)
0
n
n
CAT
SCAT ¼ n
ꢁ 100%
ꢁ 100%
ꢁ 100%
(2)
(3)
(4)
CAT þ nHQ þ nBQ
3 2
immersed in 350 mL of the desired concentration of Cu(NO )
n
HQ
SHQ ¼ n
solution for 24 h with continuous stirring at room temperature.
The obtained mixture was washed twice with deionized water,
dried at 393 K for 6 h and calcined in air at 823 K for 5 h. A series
CAT þ nHQ þ nBQ
n
BQ
S
BQ ¼ n
2
+
of Cu/TS-1-x samples with different Cu concentrations were
CAT þ nHQ þ nBQ
prepared, with the concentrations of 0.005, 0.01, 0.015 and
ꢀ
1
0
H O
n
ꢀ nH O
0
.03 mol L . The corresponding samples are designated as
2
2
2
2
XH2O2
¼
ꢁ 100%
(5)
(6)
0
Cu/TS-1-x, where x is 1, 2, 3 and 4, respectively.
n
H2O2
n
CAT þ nHQ þ nBQ
2
.3 Catalyst characterization
XRD patterns were obtained with a RIGAKU UltimalV diffrac-
tometer using Cu Ka radiation. N
obtained on a Micromeritics ASAP 2020M apparatus at the content of phenol, respectively. nH O is the initial mole content
UH2O2
¼
ꢁ 100%
0
n
ꢁ XH O
H2O2
2
2
0
2
sorption isotherms were where nphenol and nphenol denote the initial and nal molar
0
2
2
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and nH O the nal mole content of H
2
O
2
. nCAT, nHQ and nBQ TS-1-Null sample as 100%, showed differences. The results in
2
2
represent the molar content of CAT, HQ and BQ, respectively. In Table 1 indicate that the Cu-modied TS-1 samples have slightly
all the experiments, because the amounts of the other by higher crystallinity than the TS-1-Null sample, which is attrib-
products are too low to be measured, they were not taken into uted to the fact that the impurities in the channel of the zeolite
account in the calculations of selectivity to products.
may be removed during the modication process of TS-1. Based
on the experimental data, it can be assumed that the amount of
Cu species introduced by the ion-exchanging, impregnation
and hydrothermal methods promotes slightly the crystallization
of zeolite structure. The Si/Ti molar ratios and Cu contents of
the TS-1-Null, Cu–TS-1 and Cu/TS-1-x samples were determined
3. Results and discussion
3.1 Characterization results of the TS-1-Null, Cu–TS-1 and
Cu/TS-1-x samples
Fig. 1 shows the XRD patterns of TS-1-Null, Cu–TS-1 and a series by ICP-OES (see Table 1). It can be seen that the Si/Ti molar
of Cu/TS-1 with different Cu loadings. The ve diffraction peaks ratios have no evident differences between the TS-1-Null and
ꢂ
ꢂ
4,35
ꢂ
ꢂ
ꢂ
that appear at 2q ¼ 7.9 , 8.8 , 23.1 , 23.9 and 24.4 demonstrate Cu/TS-1-x samples. However, the Cu content of the Cu/TS-1-x
3
the typical MFI structure.
It can be seen that the framework samples increases with an increase in Cu(NO ) concentration.
3 2
structures of all the samples have no differences, which indi- The textural parameters of all the samples are also listed in
2
+
cates that the post-treatment of the TS-1 zeolite with Cu does Table 1. Compared with the TS-1-Null sample, the BET specic
not destroy the MFI framework structure. On the Cu-modied surface areas and pore volumes of the Cu/TS-1-x samples do not
TS-1 samples, no other crystalline phases are detected, which change, whereas that of the Cu–TS-1 sample decreases slightly.
implies that Cu species are highly dispersed on these zeolite It is likely that some pores are blocked when atomic Cu is doped
samples. The relative crystallinity (RC), which is calculated by into the molecular sieve framework in the synthesis of Cu–TS-1.
comparing the total intensity of the ve characteristic peaks
The FT-IR spectra of the samples are shown in Fig. 2. The
with that of each sample and choosing the total intensity of the main absorption bands are observed at 450, 550, 800, 960, 1100
Fig. 1 XRD diffraction patterns of the TS-1-Null, Cu–TS-1 and Cu/TS- Fig. 2 FT-IR spectra of the TS-1-Null, Cu–TS-1 and Cu/TS-1-x
1
-x samples.
samples.
Table 1 The chemical compositions, relative crystallinity, specific surface areas and pore volumes of all samples
Si/Ti molar
ratio
2
ꢀ1
3
ꢀ1
3
ꢀ1
Sample
Si/wt%
Ti/wt%
Cu content/wt%
RC/%
S
BET/m g
V
Mesopore/cm g
V
Micropore/cm g
TS-1-Null
Cu–TS-1
30.31
25.12
28.84
29.19
28.67
29.93
29.23
1.349
1.223
1.325
1.381
1.332
1.372
1.357
0
38.29
35.02
37.09
36.02
36.67
37.17
36.71
100
103
104
101
105
102
415
386
424
415
428
422
409
0.27
0.23
0.22
0.20
0.20
0.23
0.20
0.10
0.11
0.12
0.11
0.12
0.12
0.12
3.13
0.29
0.38
0.45
0.55
0.37
Cu/TS-1-1
Cu/TS-1-2
Cu/TS-1-3
Cu/TS-1-4
Reused Cu/TS-1-2
a
ND
a
Not detected.
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ꢀ1
and 1230 cm in the IR spectra of all the samples, which agree all the Cu-modied TS-1 samples, and this conclusion agrees
3
6
with the typical FT-IR spectra of TS-1 reported in the literature.
with the XRD results.
ꢀ
1
The characteristic bands at around 550 and 1230 cm in the
FT-IR spectra are attributed to the MFI structure. The signals TS-1-Null and Cu/TS-1-x samples exhibit uniform ellipsoids
The SEM images of all the samples are shown in Fig. 4. The
37
ꢀ
1
at 450, 800 and 1100 cm are attributed to the bend stretch, particles with sizes of 200–220 nm. This means that the crystal
symmetry stretch and asymmetry stretch of Si–O in the SiO morphology and particle size are impregnable aer the TS-1
Moreover, the band at 960 cm indicates sample is supported with different Cu contents. Although the
4
38,39
ꢀ1
tetrahedral unit.
the presence of the Si–O–Ti structure within the silicalite Cu–TS-1 sample shows the same morphology of ellipsoids, its
framework, and its intensity is related to the content of titanium particle size becomes bigger and reaches about 300 nm. The
36
in the framework. Compared with the TS-1-Null sample, the representative TEM images of the TS-1-Null, Cu–TS-1 and
intensity of this band almost does not change with an increase Cu/TS-1-2 samples are shown in Fig. 5. It is clear that the Cu
in the Cu loading content in Cu/TS-1-x samples. However, an particles are dispersed on the Cu-modied TS-1 (the white
appreciable decrease in intensity is found in the Cu–TS-1 arrows point to the black spots, Fig. 5b and c). However, it is
sample, which indicates the loss of the framework Ti species. worth noting that the size of the copper particles of the Cu–TS-1
It is possible that a number of Cu atoms are introduced into the sample is larger, which may be due to the fact that several Cu
MFI framework structure of TS-1, which hinders the formation particles are accumulated under the high Cu content condition.
of framework Ti. UV-vis spectroscopy is a very effective way to Fig. 6 reveals the XPS spectra of all the samples. The Ti 2p region
40
characterize the Ti coordination state in the TS-1 zeolite. As of all the samples is exhibited in Fig. 6a. Two major peaks are
shown in Fig. 3, the two major peaks of all the samples are found at 460.3 eV and 458.8 eV, which are assigned to frame-
44,45
found at 210 nm and 240 nm, which are assigned to tetrahe- work Ti and anatase TiO (extra-framework Ti), respectively.
2
drally coordinated titanium in the zeolite framework and The weak peak at 462.0 eV is due to isolated [TiO
a charge transfer process in isolated [TiO ] or [HOTiO
] units which corresponds to the band at ꢃ240 nm in the UV-vis spectra
extra-framework Ti), respectively. In the Cu/TS-1-x samples, (see Fig. 3). Compared with the untreated TS-1 sample (TS-1-
4 3
] or [HOTiO ],
4
3
41
46
(
the peak shapes of the two strong absorption bands are similar Null), the relative intensity of the peak at 460.3 eV does not
to that of the TS-1-Null sample. However, compared with the change with an increase in Cu content in the Cu/TS-1-x samples.
TS-1-Null sample, the peak intensity of the Cu–TS-1 sample This result can be illustrated by the fact that a loss of framework
2
+
appreciably decreases at the 210 nm band but increases at Ti does not occurred when the TS-1 zeolite is treated with Cu
2
40 nm. This may be because the Ti species cannot enter the by the ion-exchange method. In the Cu–TS-1 sample, Cu species
2
+
framework during the synthetic process due to the effect of Cu
are introduced into the MFI framework, which replace the
in the gel, thus resulting in the formation of relatively more framework Ti species and results in the formation of more
extra-framework Ti, which is in agreement with the results ob- anatase TiO and loss of framework Ti, and therefore the peak at
2
46
tained by FT-IR (see Fig. 2). In addition, in the Cu–TS-1 and 460.3 eV shis to a lower binding energy (458.8 eV). Fig. 6b
Cu/TS-1-x samples, no characteristic band at around 440 nm is displays the Cu 2p signals of the samples, in which the Cu 2p
42,43
observed, which is assigned to dimeric Cu species (Cu O ).
2
2
This result suggests that the Cu species are highly dispersed in
Fig. 4 SEM images of the catalyst samples: (a) TS-1-Null, (b) Cu–TS-1,
c) Cu/TS-1-1, (d) Cu/TS-1-2, (e) Cu/TS-1-3 and (f) Cu/TS-1-4.
(
Fig. 3 UV-vis spectra of the TS-1-Null, Cu–TS-1 and Cu/TS-1-x Fig. 5 TEM images of the (a) TS-1-Null, (b) Cu–TS-1 and (c) Cu/TS-1-2
samples. samples.
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phenol conversion and selectivity to products are almost
unchanged when the reaction reaches chemical reaction equi-
librium aer 3.0 h. These results are in good agreement with the
3
reference reported.
3.2.2 Inuence of the different catalysts. The effect of the
TS-1-Null, Cu–TS-1 and Cu/TS-1-2 samples on the hydroxylation
of phenol are given in Fig. 7. A high selectivity to diphenols
(above 92%) is obtained for all the samples, whereas the
selectivity of BQ is less than 7% and could be neglected.
Furthermore, it is clearly observed that the highest phenol
Fig. 6 XPS spectra of the TS-1-Null, Cu–TS-1 and Cu/TS-1-x samples: conversion (49.77%) is obtained on phenol hydroxylation over
(
a) Ti 2p and (b) Cu 2p.
the Cu/TS-1-2 catalyst. In contrast, Xphenol is the lowest (7.78%)
over the Cu–TS-1 catalyst. This is probably because the Cu
species on the surface of the Cu/TS-1-2 sample promote the
signals do not appear in the TS-1-Null sample because it does catalytic conversion of phenol and the number of framework Ti
not contain copper. In the Cu/TS-1-x samples, a peak at 933.9 eV species remains unchanged. For the Cu–TS-1 sample, a small
2
+
related to Cu is observed. It is shown that the Cu species amount of Cu species may be introduced into the zeolite
2
+
47
mainly exist as Cu at the surface of these catalysts. In addi- framework, which leads to a decrease in framework Ti, and this
2
+
tion, the relative intensity of the peak for Cu increases with an result agrees with the FT-IR and UV-vis data. Moreover, less
increase in the Cu content of the Cu/TS-1-x sample. The Cu
2
+
active sites of catalyst are provided as a result of the larger
peak of the Cu–TS-1 sample shis from 933.9 to 935.2 eV, which catalyst particle and Cu particles (see Fig. 4b and 5b), which
is attributed to the fact that the chemical environment of the could reduce the activity of the catalyst. In addition, Table 1
2
+
32,48
Cu species is affected in the synthetic process.
shows that the BET specic surface areas and pore volumes of
the Cu–TS-1 sample are smaller than that of the TS-1-Null
sample. Therefore, compared with TS-1-Null, the Cu–TS-1
catalyst shows a lower phenol conversion.
3
.2 Catalytic activity for phenol hydroxylation
3
.2.1 Inuence of reaction time. The effect of reaction time
3.2.3 Inuence of Cu content of Cu/TS-1-x catalysts. Table
on phenol hydroxylation on TS-1-Null was studied in the range
of 0–6 h. Table 2 shows that the conversion of phenol and
diphenols selectivity increases with an increase in reaction time
within 3.0 h, but the selectivity of BQ and CAT/HQ ratio
decreases. However, the phenol conversion, diphenols selec-
tivity and CAT/HQ ratio do not change appreciably aer the
reaction time is increased from 3.0 to 6.0 h, and the selectivity to
diphenols remains greater than 92%. The effective conversion
of H O also follows the same trend as phenol conversion. This
3
lists the changes in catalytic properties for phenol hydroxyl-
ation with an increase in Cu content of the Cu/TS-1-x catalysts.
It can be seen that Xphenol and UH O increase with Cu content
2
2
from 0 to 0.38 wt%, but decreases evidently when the Cu
content exceeds 0.38 wt%. This is probably because the number
of catalytic activity sites increase with the increase of Cu content
in the low Cu content samples (Cu/TS-1-1 and Cu/TS-1-2).
However, a decline in the dispersion of Cu particles could
2
2
may be because phenol and H O are diffused, and contact
2
2
insufficiently with the catalytic active centres at the beginning
of the reaction. In addition, more BQ is formed compared to HQ
when the reaction time is increased, which suggests that there
3
is a balance between HQ and BQ. Therefore, more phenol and
HQ and less BQ is detected in the reaction mixture solution. The
Table 2 Effect of reaction time on the hydroxylation of phenol over
a
the TS-1-Null catalyst
Selectivity/%
Reaction
time/h
CAT/HQ
ratio
Xphenol/%
CAT
HQ
BQ
UH O2/%
2
0
1
2
3
4
6
.5
.0
.0
.0
.0
.0
18.19
24.73
29.82
35.77
35.93
35.82
55.91
50.16
50.94
51.94
51.34
52.18
19.03
27.72
33.99
40.90
41.59
40.78
25.06
22.12
15.07
7.16
7.07
7.04
2.94
1.81
1.50
1.24
1.23
1.28
22.18
27.18
31.39
36.13
36.31
35.89
Fig. 7 Effect of TS-1-Null, Cu–TS-1 and Cu/TS-1-2 on the hydroxyl-
a
ation of phenol. Reaction conditions: phenol 1.50 g, acetone 1.00 g,
Reaction conditions: phenol 1.50 g, acetone 1.00 g, H
.80 g, TS-1-Null catalyst 0.10 g, 353 K, and stirring rate 300 rpm.
2
O
2
(30 wt%)
1
2
H O
2
(30 wt%) 1.80 g, catalyst 0.10 g, 353 K, stirring rate 300 rpm, and
reaction time 3 h.
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a
Table 3 Effect of the Cu content of the Cu/TS-1-x samples on the hydroxylation of phenol
Selectivity/%
CAT/HQ
ratio
Catalyst
Cu content/wt%
X
phenol/%
CAT
HQ
BQ
UH O2/%
2
TS-1-Null
Cu/TS-1-1
Cu/TS-1-2
Cu/TS-1-3
Cu/TS-1-4
0
35.77
48.85
49.77
39.62
36.98
51.94
48.18
48.23
51.83
47.59
40.90
51.80
51.05
47.62
52.20
7.16
0.02
0.72
0.55
0.21
1.24
0.93
0.94
1.09
0.91
36.13
49.36
50.47
41.27
38.06
0.29
0.38
0.45
0.55
a
2 2
Reaction conditions: phenol 1.50 g, acetone 1.00 g, H O (30 wt%) 1.80 g, catalyst 0.10 g, 353 K, stirring rate 300 rpm, and reaction time 3 h.
occur when the Cu content is above 0.38 wt%. In the Cu/TS-1-x catalytic activities of Cu/TS-1-2 strongly depended on the
samples, the selectivity of the main products CAT and HQ solvents. It is clear that the phenol conversion decreases in the
almost remains unchanged with the increase in Cu content, and order of acetone > isopropanol > water > methanol. Moreover,
the BQ selectivity is less than 1% and thus can be neglected.
Therefore, Cu/TS-1-2 is the best catalyst for the hydroxylation of 13.34% in methanol. Lu et al. reported that a ve-ring inter-
phenol. mediate is formed in protic solvents, such as methanol or H O,
.2.4 Inuence of the amount of catalyst. Prior to the when the hydroxylation of phenol with H is catalyzed by the
Xphenol is the highest at 49.77% in acetone, but the lowest at
49
2
3
2 2
O
comparison of the catalytic performance of the Cu/TS-1-x TS-1 catalyst. However, the titanium-peroxo exists in aprotic
samples with different Cu contents (see Table 3), the Cu/TS-1-2 solvents, such as acetone. Since the interaction between TS-1
sample was selected as a representative catalyst to examine the and aprotic solvents is weak, the adsorption of phenol on
50,51
effect of the amount of catalyst. As shown in Table 4, it is clearly zeolites is mainly physical adsorption.
observed that as the catalyst content increases from 0.01 to 0.1 g chemisorption of H on the TS-1 catalyst is much stronger,
and Xphenol and Sdiphenols increase remarkably from 4.27% and which can promote the conversion of phenol.
2.43% to 49.77% and 99.28%, respectively. However, as the 3.2.6 Inuence of reaction temperature. It is well known
Therefore, the
2 2
O
7
catalyst content increases to 0.15 g, the phenol conversion that reaction temperature is one of the important factors that
increases slightly and the selectivity to diphenols remains inuence catalytic activity. The effect of reaction temperature
almost unchanged. In addition, the utilization of H O
(333, 343, 353 and 358 K) on phenol conversion, H O utiliza-
2 2
2
2
increases with the increase of catalyst content. However, the tion and selectivity to products is given in Table 6. With the
CAT/HQ ratio and selectivity of BQ appreciably decrease with increase of temperature from 333 to 353 K, the phenol conver-
the increase in catalyst content. This may be because more sion and selectivity to diphenols generally increase as expected,
catalytic active sites are provided with the increase in catalyst however the conversion of phenol decreases slightly at
content. Therefore, more phenol is converted into the main a temperature above 353 K. The lower conversion at 358 K than
2 2
products in the reaction process. Considering the phenol that at 353 K may be due to the enhancement of H O self-
conversion, catalyst content and economic cost, 0.1 g catalyst is decomposition at higher temperatures. In addition, the H O2
2
the most reasonable catalyst dosage under this experimental utilization decreases with the increase in temperature, since
condition.
.2.5 Inuence of solvent. In liquid–solid catalytic reac-
more H O decomposition occurs at a higher temperature.
2 2
3
3.2.7 Reusability of the Cu/TS-1-2 catalyst. The reusability
tions, the solvent oen plays an important role and participates of the Cu/TS-1-2 catalyst in the phenol hydroxylation reaction
in the cycle of the catalytic reaction. As shown in Table 5, the was examined and the results are displayed in Table 7. At the
end of the reaction, each catalyst was separated by ltration and
subsequently washed with solvent several times, and then dried
Table 4 Effect of the amount of Cu/TS-1-2 catalyst on the hydrox-
ylation of phenol
a
a
Table 5 Effect of solvent on the hydroxylation of phenol
Selectivity/%
CAT/HQ
ratio
Selectivity/%
HQ
Catalyst content/g
X
phenol/% CAT HQ
BQ
U
H O2/%
CAT/HQ
ratio
2
Solvent
X
phenol/% CAT
BQ
UH O2/%
2
0
0
0
0
0
.01
.025
.05
.10
.15
4.27
9.57
23.44
49.77
52.12
61.21 12.22 26.57 5.01
61.03 20.60 18.37 2.96
58.99 29.00 12.01 2.03
48.23 51.05 0.72 0.94
47.86 51.93 0.61 0.93
8.21
13.48
26.04
50.47
53.85
Water
Methanol
Isopropanol 41.31
Acetone
37.37
13.34
46.78 49.26 3.96 0.95
57.97 39.22 2.81 1.48
49.12 50.57 0.31 0.97
48.23 51.05 0.72 0.94
44.05
21.67
46.59
50.47
49.77
a
a
Reaction conditions: phenol 1.50 g, acetone 1.00 g, H
2
O
2
(30 wt%)
Reaction conditions: phenol 1.50 g, solvent 1.00 g, H
2
O
2
(30 wt%)
1
.80 g, Cu/TS-1-2 catalyst, 353 K, stirring rate 300 rpm, and reaction 1.80 g, Cu/TS-1-2 catalyst 0.1 g, 353 K, stirring rate 300 rpm, and
reaction time 3 h.
time 3 h.
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Table 6 Effect of reaction temperature on the hydroxylation of a decrease in catalytic activity. The synthesis of TS-1 supported
a
phenol
Cu in this work will be important to develop excellent perfor-
mance catalysts for the hydroxylation of phenol in the future.
Selectivity/%
CAT/HQ
Solvent
Xphenol/%
CAT
HQ
BQ
ratio
UH O2/%
2
Acknowledgements
3
3
3
3
33
43
53
58
27.05
35.26
49.77
48.68
47.21
47.65
48.23
52.36
48.87
50.44
51.05
47.32
3.92
1.91
0.72
0.32
0.97
0.95
0.94
1.11
74.15
66.85
50.47
48.86
This work is supported by the Ph. D Starting Foundation of
Jiangxi Agricultural University (09004712) and Jiangxi Provincial
Department of Education Fund (GJJ150432).
a
Reaction conditions: phenol 1.50 g, acetone 1.00 g, H
2
O
2
(30 wt%)
1
.80 g, Cu/TS-1-2 catalyst 0.1 g, stirring rate 300 rpm, and reaction
Notes and references
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Run 1
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49.77
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a
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