The preparation and properties of Cu doped TS-1 zeolite

Article abstract of DOI:10.1039/c3ra44127j

A modified hydrothermal method was used to synthesize Cu doped TS-1 zeolite (Cu-TS-1) from TEOS, TBOT and Cu(CH₃COO)₂ with TPAOH as the template. The impregnation of TS-1 with aqueous solution of Cu(NO ₃)₂ was also carried out to introduce Cu species onto TS-1 to obtain Cu/TS-1 catalyst. The TS-1, Cu/TS-1 and Cu-TS-1 samples were characterized by XRD, XPS, SEM, UV-VIS, FT-IR, Raman and NH₃-TPD-MS to reveal the effect of the preparation procedure and Cu contents on the properties of Cu-TS-1 zeolite samples. Cu species doped via the modified hydrothermal method made the crystal shape of the samples change from round to polygon, however, the crystal shape was almost unchanged when Cu species was doped via wet impregnation. A proper amount of Cu species in the Cu-TS-1 zeolite could promote the crystallization of MFI structure and limit the formation of extra-framework TiO₂. The Cu-TS-1 zeolite was employed as a catalyst in the nitration of benzene with ammonium acetate as the nitrating agent and hydrogen peroxide as the oxidizing agent under mild conditions. The synergetic effect of doped Cu and TS-1 zeolite with MFI structure restrained the hydroxylation reaction, and increased the yield and selectivity to nitrobenzene. 47.8 μmol (about 0.4%) yield and 57.0% selectivity to nitrobenzene with a ^ITOF = 9.6 h^-1 and a ^IITOF = 38.3 h ^-1 were obtained on Cu-TS-1 (1.76 wt% Cu content) catalyst under optimized reaction conditions. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra44127j

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PAPER
The preparation and properties of Cu doped TS-1 zeolite
*
*
Qian Zhang, Tianhua Yu, Sheng Xia, Guiying Li and Changwei Hu
Cite this: RSC Adv., 2013, 3, 21628
A modified hydrothermal method was used to synthesize Cu doped TS-1 zeolite (Cu-TS-1) from TEOS, TBOT
and Cu(CH3COO)2 with TPAOH as the template. The impregnation of TS-1 with aqueous solution of Cu(NO3)2
was also carried out to introduce Cu species onto TS-1 to obtain Cu/TS-1 catalyst. The TS-1, Cu/TS-1 and Cu-TS-
1 samples were characterized by XRD, XPS, SEM, UV-VIS, FT-IR, Raman and NH3-TPD-MS to reveal the effect of
the preparation procedure and Cu contents on the properties of Cu-TS-1 zeolite samples. Cu species doped via
the modified hydrothermal method made the crystal shape of the samples change from round to polygon,
however, the crystal shape was almost unchanged when Cu species was doped via wet impregnation. A
proper amount of Cu species in the Cu-TS-1 zeolite could promote the crystallization of MFI structure and
limit the formation of extra-framework TiO2. The Cu-TS-1 zeolite was employed as a catalyst in the
nitration of benzene with ammonium acetate as the nitrating agent and hydrogen peroxide as the
oxidizing agent under mild conditions. The synergetic effect of doped Cu and TS-1 zeolite with MFI
structure restrained the hydroxylation reaction, and increased the yield and selectivity to nitrobenzene.
Received 3rd August 2013
Accepted 2nd September 2013
DOI: 10.1039/c3ra44127j
47.8 mmol (about 0.4%) yield and 57.0% selectivity to nitrobenzene with a TOF ¼ 9.6 hꢀ1 and a IITOF ¼
I
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38.3 hꢀ1 were obtained on Cu-TS-1 (1.76 wt% Cu content) catalyst under optimized reaction conditions.
indicated that doping different metals and doping metal via
different methods could both lead to change in the property of
1 Introduction
Since a group at Enichem rst reported the synthesis of TS-1
zeolite in 1983,1 many researchers have tried to understand the
properties of this microporous catalyst.2–5 TS-1 zeolite is a redox
molecular sieve with a MFI structure which is usually used in
the selective oxidation of various organic compounds with
hydrogen peroxide as oxidant under mild conditions, such as
the epoxidation of olens,6–9 the hydroxylation of aromatic
compounds,10–13 the ammoximation of ketones,14,15 and the
oxidation of alkanes, alcohols and sulfur-containing
compounds.16–21 It is indicated that TS-1 is capable of catalyzing
the hydroxylation reaction of aromatics in the presence of
hydrogen peroxide. In our previous work,22 TS-1 and Cu/TS-1
catalysts were employed to catalyze the amination of benzene to
aniline with hydrogen peroxide under mild conditions. It is
revealed that TS-1 and Cu/TS-1 catalysts could simultaneously
activate the N–H bond of ammonia and the C–H bond of
benzene. Actually, the selective activation of C–H bonds is still
TS-1 zeolite. For example, the introduction of Au via the DP
method promoted the gas phase epoxidation of propylene with
hydrogen, oxygen and nitrogen;33,34 and the introduction of Pt
and Pd via the WI method promoted the epoxidation of olens
with hydrogen peroxide;35 while the introduction of Cu via the WI
method promoted the amination of benzene with aqueous
ammonia and the oxidative desulfurization of thiophene with
hydrogen peroxide.22,36 To modify the property of TS-1 zeolite, we
doped Cu species in TS-1 zeolite via a modied hydrothermal
(MH) method comparatively with the WI method. This Cu doped
TS-1 (Cu-TS-1) zeolite was employed as catalyst in the nitration of
benzene with ammonium acetate (NH4Ac) as the nitrating agent.
2 Experimental
2.1 Preparation of TS-1 zeolite sample
A MH method was used to prepare the TS-1 zeolite.22,37,38 In a
typical preparation procedure, 80.0 g of tetrapropylammonium
hydroxide (TPAOH) (20.0 wt%) was added slowly to a beaker
containing 41.7 g of tetraethyl orthosilicate (TEOS). The mixture
was stirred for 20 minutes before 5.1 g of tetrabutyl titanate
(TBOT) in 40.0 g of isopropanol was added dropwise with stir-
ring. Then 30.0 g of water was added dropwise. Aer stirred for
10 minutes at room temperature, the obtained sol was heated to
358 K and stirred for another 6 hours. Proper amount of water
was added to compensate for the evaporation loss during the
heating process. Aer cooling the sol to 313 K, 13.0 mL of
aqueous solution of ammonium carbonate (22.5 wt%) was
an important and attractive work.23–29 Among
a lot of
reports,22,30–32 the introduction of a N-containing group into
C–H bond to form C–N bond is challenging and attractive.
A lot of authors introduced metals onto the TS-1 zeolite
surface via wet impregnation (WI) method or deposition precip-
itation (DP) method to adjust the property of TS-1 zeolite. It is
Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of
Chemistry, Sichuan University, Chengdu, Sichuan, 610064, China. E-mail: gchem@
scu.edu.cn; chwehu@mail.sc.cninfo.net; changweihu@scu.edu.cn; Fax: +86-28-
85411105; Tel: +86-28-85411105
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dropped with stirring. The obtained gel was crystallized at 448 K
under 1 MPa of N2 in a PTFE-lined autoclave for 120 h. The
crystalline solid was separated from the mother liquor by
vacuum ltration, washed with distilled water until neutrality,
dried at 383 K overnight, and calcined at 823 K in air for 8 h.
2.5 Characterization of the zeolite samples
The X-ray diffraction (XRD) patterns of different zeolite samples
were obtained with a DX-1000 CSC diffraction instrument using
˚
Cu Ka (l ¼ 1.54056 A) radiation. The apparatus was operated at
25 mA and 40 kV. In the 2-theta range of 5–80ꢂ, the data were
collected with a step of 0.0544ꢂ, using continuous scanning
mode.
2.2 Preparation of Cu-TS-1 zeolite samples
X-ray photoelectron spectroscopy (XPS) of different zeolite
The Cu-TS-1 zeolite was also prepared by MH method, and the
preparation details were similar to that for TS-1 zeolite (Section
2.1). Merely in this case, aer dropping the mixture of TBOT and
isopropanol, 30.0 mL of aqueous solution with desired
concentration of the Cu(CH3COO)2 replaced the water be added
dropwise in the sol. The Cu-TS-1 zeolite samples with various
controlled copper contents were prepared and named as Cu-TS-
1-1 (1.18 wt%), Cu-TS-1-2 (1.76 wt%), Cu-TS-1-3 (2.33 wt%),
Cu-TS-1-4 (2.90 wt%) and Cu-TS-1-5 (3.45 wt%) according to the
controlled content of Cu.
samples were taken with
spectrometer.
a AXIS Ultra DLD (KRATOS)
The surface morphology of different zeolite samples was
characterized by scanning electron microscopy (SEM) (JSM-
7500F, JEOL, Tokyo, Japan). The apparatus was operated at 5 kV.
Gold was employed to coat the samples with a vacuum sputter-
coater to improve the conductivity of the samples and the
quality of the SEM images.
The ultraviolet visible diffuse reectance (UV-VIS) spectra of
different zeolite samples were taken with a Hitachi U-4100
spectrophotometer equipped with photomultiplier (UV-VIS
region) and cooled PBs (NIR region) detectors. BaSO4 was used
as the reference material. Before characterization, the samples
were dried at 373 K overnight.
2.3 Preparation of Cu/TS-1 zeolite sample
The Cu/TS-1 (1.76 wt%) zeolite sample was prepared by WI
method. Cu species was introduced onto the TS-1 zeolite with
Cu soluble salt Cu(CH3COO)2. The TS-1 zeolite was impregnated
in the isopycnic aqueous solution of the Cu salt for 24 h. The
obtained mixture was dried with stirring at 363 K for 2 h and
calcined in air at 773 K for 8 h.
Fourier transform infrared (FT-IR) spectra of different zeolite
samples were taken with a Nicolet Nexus 670 FT-IR instrument
(KBr pressed ake).
The Raman spectra of different zeolite samples were per-
formed with a LabRAM HR (HORIBA Jobin Yvon) instrument
using a Nd:Yag laser as an illumination source (532 nm).
All the zeolite samples were characterized by ammonia
temperature programmed desorption (NH3-TPD). 0.10 g of
sample was put in a stainless steel U-tube. N2 gas ow with a
rate of 15 mL minꢀ1 was used to ush the sample at 573 K for 60
minutes. Aer cooling to 303 K, N2 ow was switched to pure
NH3 gas with a rate of 30 mL minꢀ1 for 25 minutes. Then, He
gas with a rate of 30 mL minꢀ1 was introduced to ush the
sample at 303 K. Finally, the sample was heated at a ramp rate of
10 K minꢀ1 from 303 K to 923 K. A multichannel mass spec-
trometry (TPD-MS, HP R-20QIC) was employed to analyze on-
line the released gas. The possible molecules (such as N2O, NO
and NH3) from the desorption or reactive desorption of NH3
were detected by recording the signals at m/z ¼ 44, 30 and 17.
2.4 Nitration reaction
The nitration reaction was carried out in a one-necked round ask
at atmosphere pressure in open air. Under the optimal reaction
conditions, 0.30 g of catalyst, 11.25 mmol of NH4Ac, 11.25 mmol
(1.00 mL) of benzene and 3.00 mL of water were added in the ask
and heated to 343 K with continuous stirring under reux. When
the temperature reached 343 K, 2.40 mL of H2O2 (23.28 mmol)
(30.0 wt%) was added in six parts in a 15 minute-interval and the
reaction proceeded for 1.5 h. Aer cooling the resultant mixture to
room temperature, 40.0 mL of acetonitrile was added in the
mixture to avoid stratifying. The liquid phase was separated from
the catalyst by ltration. We used GC-MS (coupled gas chroma-
tography and mass spectroscopy, Agilent, 5973 Network 6890N) to
identify and HPLC (high performance liquid chromatography,
Agilent, 1200, equipped with a C18 column and a UV-visible
detector) to quantify the main products (nitrobenzene, phenol and
3 Results and discussion
diphenol) in the resultant liquid. The selectivity to nitrobenzene, 3.1 XRD characterization
yield of products and TOF were calculated by the following:
All the zeolite samples were characterized by XRD technique,
and the patterns were shown in Fig. 1. The diffraction peaks at
2qꢂ of 7.9ꢂ, 8.8ꢂ, 23.1ꢂ, 23.9ꢂ and 24.4ꢂ corresponded to
the characteristic of MFI structure.5,39 All samples exhibited the
characteristic XRD patterns of highly crystalline zeolites. On the
Cu/TS-1 and Cu-TS-1 zeolite samples, no characteristic crystal-
line phase related to Cu species was observed, implying that Cu
species was highly dispersed on these zeolite samples. The
relative crystallinity (RC) of the zeolite samples was determined
Yield (mmol) ¼ mole amount of product (nitrobenzene, etc.) ꢁ 106
Selectivity to nitrobenzene (%) ¼ mole amount of nitrobenzene
ꢁ (summation of mole amount of products)ꢀ1 ꢁ 100
ITOF (hꢀ1) ¼ mole amount of nitrobenzene ꢁ (mole amount of
titanium contained)ꢀ1 ꢁ (reaction time)ꢀ1 ꢁ 100
IITOF (hꢀ1) ¼ mole amount of nitrobenzene ꢁ (mole amount of using the ratio of the total intensity of the diffraction peaks. The
copper contained)ꢀ1 ꢁ (reaction time)ꢀ1 ꢁ 100.
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Cu-TS-1-2 was chosen as standard and its RC was set as 100%. It
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Fig. 1 The XRD spectra of different zeolite samples.
could be clearly seen that the RC of 1.76 wt% Cu/TS-1 zeolite
was similar to that of TS-1 zeolite. However, when Cu species
was doped via the MH method, the RC of the Cu-TS-1-1 and Cu-
TS-1-2 samples increased, indicating that the crystalline struc-
ture of the two Cu-TS-1 samples was superior to that of TS-1 and
Cu/TS-1 samples. With further increase of Cu content, the RC of
the zeolite samples (Cu-TS-1-3 to Cu-TS-1-5) decreased contin-
uously. Based on the above discussion, it was assumed that a
certain amount of Cu species introduced by the MH method
promoted the crystallization of MFI structure and the Cu-TS-1-2
zeolite sample (among the TS-1, Cu/TS-1 and all Cu-TS-1 zeolite
samples) had the optimal crystalline structure.
Fig. 2 The XPS results of (A) Ti2p and (B) Cu2p in different zeolite samples.
3.2 XPS characterization
Cu-TS-1 samples (Cu-TS-1-1 and Cu-TS-1-2), only Cu2+ peak
(934.4 eV) was observed, but on the excess Cu content (more
than 1.76 wt%) samples (Cu-TS-1-3 to Cu-TS-1-5), a new peak
related to Cu2O was observed at 932.4 eV,42 revealing that the
excess Cu species (more than 1.76 wt%) would lead to the
formation of Cu2O.
All the zeolite samples were characterized by XPS technique,
and the spectra were shown in Fig. 2. The Ti2p3/2 region (Fig. 2A)
of all zeolite samples exhibited two peaks. One peak at 460.0 eV
was assigned to the tetrahedral Ti(IV) (framework Ti species),
and the other one at 458.4 eV related to the anatase TiO2 (extra-
framework Ti species).10,40 The relative intensity of the peak at
458.4 eV (RI458.4) was determined using the area ratio of the
458.4 eV peak/460.0 eV peak. It could be clearly seen that the
RI458.4 of the Cu-TS-1 samples decreased with increasing Cu
3.3 SEM characterization
content from 1.18 wt% (Cu-TS-1-1) to 1.76 wt% (Cu-TS-1-2), and The SEM images of all zeolite samples were shown in Fig. 3. All
increased with further increase of Cu content to 3.45 wt% (Cu- samples exhibited typical crystalline particles with a size of 0.3–
TS-1-5). Based on the above results, it was assumed that a proper 0.5 mm. It could be clearly seen that TS-1 zeolite sample (Fig. 3a)
amount of Cu species doped via the MH method limited the was a round-shaped crystal. The Cu-TS-1 zeolite samples with
formation of the extra-framework Ti species. The Cu2p3/2 signals low Cu content (Fig. 3b and c) were polygon-shaped crystals.
of Cu/TS-1 and Cu-TS-1 samples were displayed in Fig. 2B. On Then the polygon crystal shape of the Cu-TS-1 zeolite samples
the Cu/TS-1 sample (prepared by WI method), a symmetric (Fig. 3d to f) turned to be more and more unclear with further
main peak at 933.8 eV related to Cu2+ was observed, though the increase of Cu content. However, when Cu was introduced by
shake-up satellite peak is very weak because of the low Cu WI method, the 1.76 wt% Cu/TS-1 zeolite sample (Fig. 3g)
content. It is revealed that Cu species mainly existed as Cu2+ on showed round-shaped crystal similar to that of TS-1 zeolite
the sample surface.41 On the Cu-TS-1 samples, when Cu was sample. Such a big difference in the crystal shape among the TS-
doped via the MH method, the Cu2+ peak shied from 933.8 to 1 (Fig. 3a), 1.76 wt% Cu/TS-1 (Fig. 3g) and 1.76 wt% Cu-TS-1
934.4 eV, indicating that the preparation process affected the (Fig. 3c) zeolite samples indicated that the Cu species in the Cu-
chemical environment of Cu2+ species. On the low Cu content TS-1 zeolite samples probably promoted the formation of
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Fig. 3 SEM micrographs of (a) TS-1, (b) Cu-TS-1-1, (c) Cu-TS-1-2, (d) Cu-TS-1-3, (e) Cu-TS-1-4, (f) Cu-TS-1-5, (g) Cu/TS-1; the scale is 100 nm.
polygon crystal shape and the preparation procedure affected
the crystallization of the zeolite samples; while the presence of
excess amount of Cu (Cu2O) altered the formation of polygon
crystal shape. Combining with the results of XRD, it was infer-
red that the crystallinity of MFI structure inuenced the
formation of polygon crystal shape.
3.4 UV-VIS characterization
Fig. 4 compared the UV-VIS spectra of the TS-1, Cu/TS-1 and Cu-
TS-1 zeolite samples. On the Cu/TS-1 and Cu-TS-1 zeolite
samples, no characteristic bond around 440 nm, 22 700 cmꢀ1
related to dimeric Cu species (Cu2O2)43,44 was observed. The XRD
results showed that Cu species was highly dispersed on all Cu
doped TS-1 zeolite samples, implying that there was not aggre-
gated Cu species on these samples. On the 1.76 wt% Cu/TS-1
zeolite sample, the weak bond around 690 nm (14 500 cmꢀ1
)
44
was assigned to the d–d transitions of isolated Cu2+ ions.
The TS-1 sample exhibited two strong absorption bonds, of
which the one around 210 nm corresponded to the O2ꢀ 2p /
Ti4+ 3d charge transfer transition of tetrahedrally coordinated Ti
Fig. 4 The UV-VIS spectra of different zeolite samples.
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in the silicalite framework.45–47 It indicated the formation of
framework Ti species. The other between 240 and 390 nm was
assigned to the extra-framework Ti species, such as anatase
phase and nano-phase TiO2.48 On the 1.76 wt% Cu/TS-1 sample
(prepared by WI method), the peak shape of the two strong
absorption bonds was similar to that of TS-1 zeolite sample. On
the Cu-TS-1 zeolite samples (prepared by MH method), the peak
shape of the bond between 240 and 390 nm was changed
possibly due to the contribution of O / Cu(II) charge transfer
transitions.43,44,49
3.5 FT-IR characterization
Fig. 5 compared the FT-IR spectra of the TS-1, Cu/TS-1 and CuTS-
1 zeolite samples. All samples exhibited the absorption bands at
445, 545, 796, 962, 1100 and 1220 cmꢀ1. The characteristic bands
at 545 and 1220 cmꢀ1 were attributed to the MFI structure.40 The
signals at 445, 796 and 1100 cmꢀ1 were the characteristic of
internal linkages in SiO4 tetrahedral.50 The peak at 962 cmꢀ1 was
assigned to the vibration of Si–O–Ti bond in framework.51 All
above data indicated the formation of TS-1 zeolite structure in
these samples. Obviously, the maximum peak intensity at 545,
1220 and 962 cmꢀ1 was obtained on Cu-TS-1-2 zeolite sample,
indicating that this zeolite sample (among the TS-1, Cu/TS-1 and
all Cu-TS-1 zeolite samples) had the optimal MFI structure, in
agreement with the results of XRD.
Fig. 6 The Raman spectra of different zeolite samples.
and 1.76 wt%) Cu-TS-1 (Cu-TS-1-1 and Cu-TS-1-2) zeolite
samples. With further increase of Cu content to 3.45 wt%
(Cu-TS-1-5), the peak at 639 cmꢀ1 gradually shied to 619 cmꢀ1
and the relative intensity of the peak at 513 cmꢀ1 among the
three peaks was attenuated. These phenomena appeared
possibly due to the effect of the existence of Cu2O species.
3.7 NH3-TPD-MS characterization
3.6 Raman characterization
The TS-1, Cu/TS-1 and Cu-TS-1 zeolite samples were character-
ized by NH3-TPD and the evolved gases were detected by TPD-MS.
As shown in Fig. 7, the NH3-desorption happened mostly below
920 K. On all zeolite samples, the main evolved gases were NH3,
NO and N2O. Obviously, a small part of the chemisorbed NH3 was
oxidized to NO and N2O during the adsorption–desorption
process by the zeolite samples. Notably, the desorption temper-
ature range of NH3 gas (Fig. 7b) was almost the same as that of
NO gas (Fig. 7a). Three desorption peaks were obtained on the TS-
1 zeolite sample, indicating that there were three kinds of
interaction between the TS-1 zeolite and NH3. One (NH3 peak) of
the three desorption peaks between 400 and 500 K was assigned
to the weak interaction which made the NH3 be adsorbed–des-
orbed without being broken. The second one (NO peak) over the
same temperature range as that of NH3 peak was assigned to the
interaction which made the NH3 be oxidized to NO. While the last
one (N2O peak) between 800 and 900 K related to the relatively
stronger interaction which made the NH3 be oxidized to N2O.
Aer the incorporation of Cu, the desorption temperature of NO
and NH3 peaks remained almost unchanged, while that of N2O
peak became different. On the Cu/TS-1 zeolite sample, the
desorption temperature of N2O peak decreased to 460–550 K.
While on the Cu-TS-1 zeolite samples (Cu-TS-1-1 to Cu-TS-1-5),
two new N2O peaks were obtained over the relatively lower
desorption temperature ranges of 460–550 K and 670–790 K while
the one in the range of 800–900 K disappeared. The above fact
suggested that the Cu species doped via different method would
result in different change in the active site of the zeolite samples
and lead to different interaction between the zeolite samples and
The Raman spectra of all zeolite samples were shown in Fig. 6.
On the Cu/TS-1 and Cu-TS-1 zeolite samples, no characteristic
peaks around 290, 340 and 630 cmꢀ1 related to bulk CuO were
observed,52 implying that Cu species was highly dispersed on
these zeolite samples, in agreement with the results of XRD.
Three peaks at 393, 513 and 639 cmꢀ1 related to anatase TiO2
were obtained on the TS-1 zeolite sample.50,53 It indicated the
formation of extra-framework Ti species. Aer the incorpora-
tion of Cu, the position of the three peaks were almost
unchanged on the 1.76 wt% Cu/TS-1 and low Cu content (1.18
Fig. 5 The FT-IR spectra of different zeolite sample.
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The above results showed that a proper amount of Cu species
(doped via the MH method) perfected the MFI structure of the
zeolite samples. This structure with a polygon crystal shape
provided specic chemisorption sites to make NH3 be selec-
tively oxidized to N2O at relatively lower temperature in the TPD
process. It was indicated that this Cu doped zeolite possessed
the ability to activate the N–H bond of NH3.
3.8 Catalytic activity tests
The results of benzene nitration to nitrobenzene on TS-1, Cu/
TS-1 and Cu-TS-1 zeolite samples were shown in Table 1.
On TS-1 zeolite, benzene was converted to nitrobenzene,
phenol and diphenol with a higher selectivity to hydroxylation
than to nitration (Table 1, entry 1). It was conrmed that TS-1
zeolite could simultaneously activate the C–H bond of benzene
and the N–H bond of NH4Ac, and promote the formation of
nitrobenzene. In a control experiment using phenol as the
reactant under the same conditions, diphenol was obtained
while nitrobenzene was not detected, indicating that diphenol
was produced by the deep oxidation of phenol and phenol was
not the possible intermediate for the formation of nitroben-
zene. In another control experiment using nitrobenzene as the
reactant under the same conditions, phenol was not obtained.
The above data suggested that hydroxylation and nitration
reactions were competitive in this system.
The nitrobenzene yield and ITOF was signicantly increased
on the 1.76 wt% Cu-TS-1 (Table 1, entry 3) and slightly increased
on the 1.76 wt% Cu/TS-1 (Table 1, entry 7), revealing that the
catalytic nitration activity of the two zeolite samples was higher
than that of TS-1 zeolite. In another word, Cu species in the TS-1
zeolite promoted the nitration reaction and restrained the
hydroxylation reaction. The above data also indicated that the
Cu-TS-1 zeolite was the most efficient catalyst (among the TS-1,
Cu-TS-1 and Cu/TS-1 zeolite samples) for the nitration with
restrained activity for the formations of phenol and diphenol in
this system. From the above discussion, it could be concluded
that the preparation procedure affected the catalytic nitration
property of these zeolite samples. To investigate the possible
active Cu species for the nitration reaction, CuO, Cu/SiO2,
Cu(NO)3 and the mixtures of (1) CuO and TS-1 (1.76 wt% Cu)
and (2) Cu/SiO2 and TS-1 (1/1, wt/wt) were employed respectively
Fig. 7 The NH3-TPD-MS pictures of different zeolite samples.
NH3. On the Cu-TS-1 zeolite samples, the area of N2O peak
increased with increasing Cu content from 1.18 wt% (Cu-TS-1-1)
to 1.76 wt% (Cu-TS-1-2), and decreased with further increase of
Cu content to 3.45 wt% (Cu-TS-1-5), indicating that a proper
amount of Cu species (1.76 wt%) introduced by the MH method
could increase the amount of NH3 being oxidized to N2O, but the
excess amount of Cu species (more than 1.76 wt%) would restrain
the interaction and lead to the decrease of the desorbed N2O.
Table 1 Catalytic performance of different zeolite samples for the nitration of benzenea
Entry
Catalysts
Ydiphenol/mmol
Yphenol/mmol
Ynitrobenzene/mmol
ITOF/hꢀ1
IITOF/hꢀ1
Snitrobenzene/%
1
2
3
4
5
6
7
8b
TS-1
9.0
23.3
11.8
11.8
13.1
11.6
10.2
14.5
41.4
62.8
25.2
29.8
20.3
37.8
19.3
21.6
14.3
28.7
33.4
27.1
25.0
24.9
16.9
47.8
3.2
6.4
7.5
6.2
5.7
5.7
3.8
9.6
—
22.1
25.0
47.5
39.5
42.8
33.5
36.4
57.0
Cu-TS-1-1
Cu-TS-1-2
Cu-TS-1-3
Cu-TS-1-4
Cu-TS-1-5
Cu/TS-1
38.5
30.1
18.5
13.7
11.4
15.2
38.3
Cu-TS-1-2
a
Reaction conditions: 0.20 g of catalyst, 11.25 mmol of ammonium acetate, 11.25 mmol of benzene, 4.00 mL of water, 19.40 mmol of H2O2 (3.88
b
mmol/24 min), 343 K, 2 h. (Optimal reaction conditions): 0.30 g of catalyst, 11.25 mmol of ammonium acetate, 11.25 mmol of benzene, 3.00
mL of water, 23.28 mmol of H2O2 (3.88 mmol/15 min), 343 K, 1.5 h.
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as catalysts under the same reaction conditions. Only 12.8 and
9.4 mmol nitrobenzene was obtained on the mixtures (1) and (2).
On the CuO, Cu/SiO2 and Cu(NO)3, no nitrobenzene was
observed, indicating that the catalytic contribution of the Cu-
TS-1 zeolite was originated from the synergetic effect of doped
Cu species and TS-1 zeolite.
Notes and references
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