Synthesis of bimetal Fe and Cu altered TUD-1: A mesoporous catalyst for phenol hydroxylation reaction

Article abstract of DOI:10.1166/jnn.2018.14270

Fe and Cu ions incorporated (Si/Cu = 50, Si/Fe = 50 and Si/Cu+ Fe = 50) amorphous, wormhole structured mesoporous catalysts (CuTUD-1, FeTUD-1 and FeCuTUD-1) (TUD-1-Technische Universiteit Delft) have been synthesized hydrothermally using low cost, non-surfactant template triethanolamine (TEA). Physicochemical properties of the catalysts were made using X-ray diffraction (XRD), Nitrogen sorption, FT-IR, DRS UV Visible, FT Raman, SEM, TEM and TG-DTG techniques. The results showed that the materials possess mesoporous, foam type morphology, surface area 485-634 m2/g, pore size 4.8-6.8 nm, pore volume 0.67-0.83 cm3/g and metal ions (Cu2+ and Fe³⁺coordinative environment. The highly dispersed Cu2+ and Fe³⁺ active sites are observed in FeCuTUD-1 catalyst. Also, the synthesized catalysts are tested in the oxidation of phenol with hydrogen peroxide (H2O₂oxidant. Further, reaction parameters such as time, temperature, and catalyst were also investigated.

Full text of DOI:10.1166/jnn.2018.14270

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 2498–2503, 2018
Copyright © 2018 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Synthesis of Bimetal Fe and Cu Altered TUD-1:
A Mesoporous Catalyst for Phenol Hydroxylation Reaction
∗
Muthusamy Poomalai Pachamuthu and Pushparaju Subhapriya
Department of Chemistry, Bannari Amman Institute of Technology, Sathyamangalam, Erode 638401, Tamil Nadu, India
Fe and Cu ions incorporated (Si/Cu = 50, Si/Fe = 50 and Si/Cu + Fe = 50) amorphous, worm-
hole structured mesoporous catalysts (CuTUD-1, FeTUD-1 and FeCuTUD-1) (TUD-1—Technische
Universiteit Delft) have been synthesized hydrothermally using low cost, non-surfactant template tri-
ethanolamine (TEA). Physicochemical properties of the catalysts were made using X-ray diffraction
(
XRD), Nitrogen sorption, FT-IR, DRS UV Visible, FT Raman, SEM, TEM and TG-DTG techniques.
The results showed that the materials possess mesoporous, foam type morphology, surface area
2
3
2+
4
85–634 m /g, pore size 4.8–6.8 nm, pore volume 0.67–0.83 cm /g and metal ions (Cu and
3
+
2+
3+
Fe ꢀ coordinative environment. The highly dispersed Cu and Fe active sites are observed
in FeCuTUD-1 catalyst. Also, the synthesized catalysts are tested in the oxidation of phenol with
hydrogen peroxide (H O ꢀ oxidant. Further, reaction parameters such as time, temperature, and
2
2
catalyst were also investigated.
Keywords: Copper, Iron, TUD-1, Bimetal, Mesoporous, Phenol Hydroxylation.
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2
+
3+
and Fe isolated ions incorpo-
1
. INTRODUCTION
Remarkably, Cu
Mesoporous materials have been synthesized and modi-
rated TUD-1, shown its excellent oxidation and alkylation
type reactivity.
1
4–18
1
–5
Besides, Al–Zr-TUD-1, Fe–Al-TUD-
fied with different procedural methods. TUD-1 type sil-
ica materials, with their three dimensional, interconnected
mesoporous structure, tunable pore size, non-surfactant
synthesis route and thermal stability are of particular inter-
1
, Co–Cr-TUD-1 and Fe–Ti-TUD-1 type bimetal cata-
lyst were also prepared and revealed remarkable activities
for the cyclisation, multicomponent, decomposition and
hydroxylation type reactions respectively.
1
9–22
6
ꢀ7
x+
At the same
est as catalyst supports.
Different metal ions (M ꢁ,
0
time, bimetals like Cu–Fe, Al–Fe, Fe–Ga, V–Fe, Zn–Ti,
Zr–Ti and Zr–Mn based catalysts were perform differently
from the mono metal counter species, due to its syner-
metal oxides (M O ꢁ and nanoparticles (M ꢁ have been
x
y
introduced into the TUD-1 to achieve suitable catalytic
8
–13
activities.
M
In general, there is need to prepare isolated
sites uniformly distributed on silica surface, which is
essential for high catalytic activity. Notably, various metal
ions (M of Al, Fe, Co, Cu, Mn, Ti, B, Sn, Ga, W, Nb
2
3–29
x+
gistic properties.
Though, the simultaneous inclusion
of bimetals into the TUD-1 is interesting, only very few
2
+
results are reported so far. In the present work, Cu and
x+
3
+
Fe ions are attempted to incorporate simultaneously into
the TUD-1 and studied by using different characterization
techniques. Also, the catalytic performance is evaluated by
hydroxylation of phenol with H O .
x+
etc.,) which include bigger size M ions have been suc-
cessfully modified over TUD-1 amorphous silica frame-
x+
works. Since the mechanism of M ion incorporation is
x+
2
2
followed a silatrane/M-atrane routes, more number of M
ions could be introduced into the TUD-1 than other meso-
porous materials. Also, the interconnected porous system
9
2. MATERIALS AND METHODS
highly facilitates the diffusion of the reactants and prod-
ucts towards the catalytic active sites. Hence this TUD-1
material reveals its excellent catalytic activities for various
transformations.
2.1. FeCuTUD-1 Catalyst Synthesis
The synthesis of FeCuTUD-1 (Si/(Fe + Cu) = 50) has
been carried out by following the method. A clear syn-
thesis mixture with a molar ratio composition of 1
SiO :0.01 CuO:0.01 FeO:0.5 TEAOH:1 TEA:10 H O was
2
2
prepared by adding a solution of corresponding metal
∗
Author to whom correspondence should be addressed.
salts (Fe(NO ꢁ .9H O and Cu(NO ꢁ · 3H O) in 3 mL
3
3
2
3
2
2
2498
J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 4
1533-4880/2018/18/2498/006
doi:10.1166/jnn.2018.14270

Pachamuthu and Subhapriya
Synthesis of Bimetal Fe and Cu Altered TUD-1
of deionized water to 21.2 mL of tetraethyl orthosilicate
was added slowly, after that the reaction mixture heated
to the reaction temperature. At different time intervals the
samples were collected from the flask. After the set reac-
tion time, the dark brown reaction mixture was filtered.
The obtained samples were analyzed by HPLC (Shimadzu)
using UV detector (220 nm and 254 nm) in C18 column.
Here 0.01 M Na HPO +ortho phosphoric acid: methanol
(
TEOS, +98%, Aldrich) and stirring for 30 min. Con-
sequently, a mixture of 13 mL triethanolamine (TEA,
7%, Aldrich) with 3 mL of deionized water was added
9
dropwise, and stirred it for 30 min. Finally, 20.3 mL of
tetraethylammonium hydroxide (TEAOH, 35% Aldrich)
was added. The obtained gel was aged at room tem-
2
4
ꢀ
perature for 24 h, dried at 100 C for 24 h and kept
(80:20) used as a mobile phase at the flow rate of 1 ml/min.
The conversion of phenol (P) was determined using the
equation given below.
ꢀ
hydrothermal treatment at 180 C for 6 h. The final
ꢀ
treated gel was calcined at 550 C for 10 h at a rate
ꢀ
of 1 C/min in the presence of air. The final mild green
Conversion %=ꢆꢇInitial CP−Final CPꢁ/Initial CPꢈ×100
CP—molar concentration of phenol.
solid (∼4 g) mentioned as FeCuTUD-1. Similarly, syn-
thesis of CuTUD-1 and FeTUD-1 with a Si/M = 50 has
been carried out as per above said procedure. A clear
synthesis mixture with a molar ratio composition of 1
1
4ꢀ17
3. RESULTS AND DISCUSSION
SiO :0.02 CuO/0.02 FeO:0.5 TEAOH:1 TEA:11 H O.
2
2
The obtained grey and pale yellow samples depicted as
CuTUD-1 and FeTUD-1 respectively.
3.1. Catalyst Characterizations
The low and high angle XRD pattern of CuTUD-1,
FeTUD-1 and FeCuTUD-1 materials are shown in
2
.2. Catalyst Characterization
ꢀ
ꢀ
The X-ray diffractograms 2ꢂ = 0ꢃ5–5 and 10–60 were
recorded on Brucker D8 and Rigaku Miniflex instrument
respectively with diffractometer using Cu-Kꢄ (ꢅ = 1ꢃ54 Å)
radiation. Nitrogen adsorption and desorption isotherms
were obtained at 77 K using Quantachrome porosime-
ter (QuadrasorbSI). Prior to the analysis, the sample was
degassed under vacuum at 200 C for 5 h. The spe-
cific surface area and pore size distribution of the sam-
ple were calculated using BET method and BJH method
ꢀ
IP: 95.160.13.208 On: Tue, 19 Jun 2018 23:48:25
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(
desorption branches) respectively. The Fourier transform
infrared (FTIR) spectrum of the sample was measured
on a Bruker (TENSOR) spectrometer in KBr pellets with
−1
a resolution of 4 cm . The morphology was examined
using SEM-EDAX imaging F E I Quanta FEG 200-High
Resolution Scanning Electron Microscope. Similarly, the
Transmission electron microscopy (TEM) was performed
on FEI Tecnai G2 fitted with a CCD camera. The chem-
ical compositions of the samples were determined by
ICP-OES (Perkin Elmer OES Optima 5300 DV spectrom-
eter) and EDAX method. The diffuse reflectance UV-Vis
spectra (DRUV Visible) were recorded in the range of
2
00–800 nm by Thermo scientific (Evolution 600) equip-
ment with a diffuse reflectance attachment, using BaSO4
as the reference. Thermal analysis of the synthesized mate-
rial was performed on a TGA SDT Q600 (TA Instruments,
Inc.) thermal analyzer. The measurements were carried out
ꢀ
in 100 mL/min. N flow with a heating rate of 10 C/min.
2
2
.3. Phenol Hydroxylation Over FeCuTUD-1
The hydroxylation reaction was carried out in a liquid
phase as follows: 100 mg of FeCuTUD-1 catalyst, 10 mL of
solvent (water) and 500 mg (5 mmol) of phenol were added
successively into a temperature controlled, two-neck-round
bottom flask having water reflux condenser. To precede the
reaction, aqueous 0.6 ml (5 mmol) of 30% H O solution
Figure 1. XRD of CuTUD-1, FeTUD-1 and FeCuTUD-1 low angle (a)
and high angle (b).
2
2
J. Nanosci. Nanotechnol. 18, 2498–2503, 2018
2499

Synthesis of Bimetal Fe and Cu Altered TUD-1
Pachamuthu and Subhapriya
Figure 3. DR UV Vis spectra CuTUD-1, FeTUD-1 and FeCuTUD-1.
Figure 2. Nitrogen sorption isotherms of CuTUD-1, FeTUD-1 and
FeCuTUD-1.
Figure 3 compares the DR UV Vis spectra of CuTUD-1,
FeTUD-1 and FeCuTUD-1. The spectrum of FeTUD-1
and CuTUD-1 exhibits a strong absorption bands at
Figures 1(a) and (b). The materials displayed a low intense
2
60 nm and 240 nm respectively. These bands have been
ꢀ
and broad peak centered at 1.2 2ꢂ, which clearly confirms
assigned to the ligand-to-metal charge transfer (LMCT)
9
ꢀ15–18ꢀ30
the meso-structured and disordered porous nature.
2
+
3+
transition of isolated Cu and Fe ions in tetrahedral
coordinated sites.
In addition, the samples showed a broad peak between 2ꢂ
1
4–18ꢀ31
In addition to this, for CuTUD-1
ꢀ
values of 10 and 30 in the high angle XRD (Fig. 1(b)) due
sample, a broad peak at above 400–800 nm was observed
which assigned to the pseudo-octohedral ligand oxygen
9
ꢀ10ꢀ14ꢀ20
to the amorphous nature of the mesoporous silica.
The CuTUD-1 sample showed aI Pp :e a9 k5 . a1 t6 30 5. 1. 53 . a2 n0 d8 3O8 n. 6: Tue, 19 Jun 2018 23:48:25
ꢀ
1
4ꢀ18
environment of copper.
The absorption of FeCuTUD-1
Copyright: American Scientific Publishers
due to the presence of CuO (∼2 nm). However, absence
resides at these two FeTUD-1 and CuTUD-1 samples
absorption regions. Besides, the higher wavelength absorp-
tion bands were absent due to the higher incorpora-
tion/grafting of metal ions. Therefore, the DR UV Vis and
XRD results indicated that FeCuTUD-1 mainly contains
Delivered by Ingenta
of CuO and Fe O crystalline peaks at 2ꢂ 35.5 and
2
3
ꢀ
3
8.6 in the FeCuTUD-1 catalyst suggesting the incorpo-
rated/grafted Cu and Fe ions existence in the TUD-1
silica.
2
+
3+
N2 adsorption desorption isotherms of CuTUD-1,
FeTUD-1 and FeCuTUD-1 samples (Fig. 2) displayed a
sharp step increase in nitrogen uptake at relative pressure
of P/P = 0ꢃ4–0.8, a Type IV isotherm with H type hys-
3+
2+
highly dispersed Fe and Cu species.
Figure 4 shows the FT IR spectra of CuTUD-1,
FeTUD-1 and FeCuTUD-1 samples. The IR peaks
0
2
8
ꢀ10ꢀ14ꢀ22ꢀ30
teresis loop, typical of TUD-1 type materials.
This also confirmed the disordered and interconnected
mesoporous nature of TUD-1 materials. The physicochem-
ical characteristics of the materials, including BET sur-
face area, BJH pore size and pore volume, are tabulated
in Table I. All the materials possessed a surface area
2
in the range of 485–634 m /g with a pore diameter of
4
.8–6.8 nm.
Table I. Physicochemical characterization of CuTUD-1, FeTUD-1 and
FeCuTUD-1 samples.
c
e
Si/M
ratio
S
V
BET
pꢀ BJH
a
b
2
d
3
Catalyst
M (wt%)
(m /g)
d
(nm)
(cm /g)
Pꢀ BJH
FeCuTUD-1
CuTUD-1
FeTUD-1
1.0, 1.2
2.1
1.9
60
54
49
634
485
612
4.8
5.7
6.8
0.67
0.76
0.83
Notes: aEDAX analysis; bICP-OES analysis; cSBET = Specific surface area;
d
dPꢀ BJH = Pore diameter; eVPꢀ BJH = Pore volume.
Figure 4. FT IR spectra CuTUD-1, FeTUD-1 and FeCuTUD-1.
J. Nanosci. Nanotechnol. 18, 2498–2503, 2018
2500

Pachamuthu and Subhapriya
Synthesis of Bimetal Fe and Cu Altered TUD-1
Figure 6. FT Raman spectra of CuTUD-1, FeTUD-1 and FeCuTUD-1.
reveals (Fig. 7) that one major weight loss takes place
ꢀ
during the heating FeCuTUD-1 up to 600 C. About 20%
of the physisorbed water, un-desorbed organic species and
ꢀ
some surface O–H groups are removed below at 100 C.
3
.2. Phenol Hydroxylation Reaction
The catalytic activity of FeCuTUD-1 in the hydroxylation
IP: 95.160.13.208 On: Tue ,o f1 9p hJ eu nno l2 0w 1i 8t h2 H3 : 4O 8:2i 5s showed in the Scheme 1. The
2
2
Copyright: American Scientific Publishers
observed major products of phenol hydroxylation reaction
Figure 5. SEM EDAX (a) and TEM micrographs (b) of FeC Du Te Ul i Dv e- 1r.ed by Ingenta
are catechol (CC), hydroquinone (HQ) and benzoquinone
BQ). The water has been employed as a preferred sol-
vent for the phenol hydroxylation reactions, due to its
(
−
1
−1
observed at 1230, 1086 cm and 806 cm are due to Si–
O–Si symmetric and asymmetric vibrations of framework
Also, the bending vibration of silanol
groups (Si–O–H) observed at 1636 cm . Further, the peak
around 966 cm is observed in the samples are usually
assigned to the stretching vibrations of Si–O–H or Si–O–
dielectric constant value (80) and based on the previous
TUD-1.1
5ꢀ17ꢀ30ꢀ31
14ꢀ22ꢀ27ꢀ32
literatures.
Table II shows the influence of reac-
−1
tion time on conversion and selectivity of products over
FeCuTUD-1 catalyst. Here, the conversion of phenol is
increased with increasing the time up to 2 h. However, a
further increase in reaction time, the selectivity was found
−1
2
0ꢀ30
M.
The SEM micrograph of FeCuTUD-1 sample showed
micrometer sized (50–100 ꢉm) irregular and agglomerated
stone-like particles (Fig. 5(a)). Also, SEM EDAX depicted
(
Fig. 5 insert) the presence of Si, O, Cu and Fe. The aver-
age weight percentage of Fe + Cu atoms present in the
TUD-1 were estimated to be about 2.2 wt.% from EDAX.
Similarly, Si/(Fe + Cu) ratio of 60 was obtained from the
ICP-OES results (Table I). Furthermore, disordered worm-
hole type/foam type morphology of TUD-1 was also evi-
denced from TEM micrograph (Fig. 5(b)). The FT Raman
spectra of CuTUD-1, FeTUD-1 and FeCuTUD-1 samples
are shown in Figure 6. The CuTUD-1 sample exhibit peaks
−
1
−1
at 295 cm and 342 cm which has assigned to the A
g
1
4
and B Raman active modes of CuO. The FeCuTUD-1
g
catalyst spectrum also showed these peak, suggesting the
Cu which is not incorporated into the lattice may forms the
nanosized oligonuclear CuO clusters. This observation is
consistent with the XRD and DR UV Vis studies. TG-DTG
Figure 7. TG-DTG of calcined FeCuTUD-1.
J. Nanosci. Nanotechnol. 18, 2498–2503, 2018
2501

Synthesis of Bimetal Fe and Cu Altered TUD-1
Pachamuthu and Subhapriya
Scheme 1. The phenol hydroxylation reaction over FeCuTUD-1
catalyst.
varied. Many reports stated the significance of reaction
1
4ꢀ22ꢀ32
time for the hydroxylation reactions.
Further, the catalyst activity for phenol hydroxylation
at different temperatures is given in the Figure 8(a). It is
observed that as increasing the reaction temperature from
ꢀ ꢀ
3
0 C to 80 C, the phenol conversion is improved up
to 72%, while the product selectivity are varied. In gen-
eral, the H O decomposition is mainly influenced by the
2
2
1
4ꢀ22
ꢀ
Here for the temperatures 30 C,
reaction temperature.
ꢀ
ꢀ
ꢀ
4
0 C, 60 C and 80 C respective H O decompositions
2
2
are 20%, 30%, 70% and 100%. Though a linear increase in
H O conversion was observed, no significant increase in
2
2
conversion and selectivity were noticed. Besides, tar like
ꢀ
product (∼4%) is also noticed at 80 C, due to over oxi-
3
2
dation of the main products. Hence, the conversion and
ꢀ
IP: 95.160.13.208 On: Tue, 19 Jun 2018 23:48:25
selectivity are nominal at 60 C. This result is consistent
Copyright: Americ14an Scientific Publishers
with CuTUD-1 catalyzed phenol hydroxylation reaction.
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Catalytic activities of CuTUD-1, FeTUD-1 and
FeCuTUD-1 samples for phenol hydroxylation were deter-
mined in the presence of H O at 60 C. Figure 8(b) shows
ꢀ
2
2
Figure 8. Effects of temperature and catalyst comparison on the phenol
hydroxylation reaction.
the conversion of phenol and selectivity of CC, HQ and
BQ for the three catalysts. Under the same reaction condi-
tions, in the absence of the catalyst or H O , the reaction
showed only 5% of conversion (not shown). It can be seen
that the FeCuTUD-1 catalyst revealed 72% phenol conver-
sion and CC 84%, HQ 10% and BQ 6% of selectivity. It
is interesting to note that the FeCuTUD-1 showed varia-
tion in product selectivity. Here, FeTUD-1 and CuTUD-1
and Fe3 sites, which is evident from the XRD, DRUV
+
2
2
2
+
Visible and FT Raman studies. The two active sites (Cu
3
+
and Fe ꢁ present in the FeCuTUD-1 generate hydroxyl
o
o
2
33
(OH ꢁ and hydroperoxyl (HO ꢁ radicals from H O .
These results indicated that the incorporated/grafted M
(Cu and Fe ꢁ and dispersed metal oxides (CuO, Fe O ꢁ
2
2
x+
2
+
3+
2
3
2
+
3+
samples containing isolated (Cu and Fe ꢁ sites as well
as metal oxide (CuO and Fe O ꢁ species. However, the
FeCuTUD-1 samples exhibited maximum of isolated Cu
are mainly influencing the reactions.
2
3
2
+
4
. CONCLUSION
In summary, three dimensional Fe–Cu-containing TUD-
catalysts had been successfully prepared via non-
Table II. Effect of time on phenol hydroxylation reaction over
1
FeCuTUD-1 catalyst.
surfactant synthesis route. XRD, N sorption and TEM
2
Selectivity (%)
characterizations confirmed that the material is of typi-
cal disordered mesopores with regular pore size arrange-
ments. FT-IR specified the presence of Si–O–Si skeletal
bonds and Si–O–M vibrations. The isolated metal ions
Time (h)
Conversion (%)
CC
HQ
BQ
0
1
2
4
.5
46
50
70
76
62
76
84
77
32
19
10
16
6
5
6
7
3
+
2+
(
Fe and Cu ꢁ incorporations and metal oxide (CuO
and Fe ꢁ were confirmed from the DRUV Visible tech-
O
3
2
nique and FT Raman studies. The synthesized FeCuTUD-1
sample revealed good thermal stability (<600 C). Also,
the bimetallic catalyst was exhibited 72% conversion of
Notes: Reaction condition: Phenol—5 mmol, H O —5 mmol, H O—10 ml,
Time—(0.5–4 h), Temperature—60 C, FeCuTUD-1—100 mg. CC—Catechol,
HQ—Hydroquinone, BQ—Benzoquinone.
2
2
2
ꢀ
ꢀ
2502
J. Nanosci. Nanotechnol. 18, 2498–2503, 2018

Pachamuthu and Subhapriya
Synthesis of Bimetal Fe and Cu Altered TUD-1
phenol with the optimum reaction condition. Thus, the
formed isolated metal ion sites in the FeCuTUD-1 led the
better catalytic activity. The catalytic activities were pre-
sumably varied if the combinations of metals are varied
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Received: 29 November 2016. Accepted: 29 December 2016.
J. Nanosci. Nanotechnol. 18, 2498–2503, 2018
2503