Evolution of iron species for promoting the catalytic performance of FeZSM-5 in phenol oxidation

Article abstract of DOI:10.1039/c6ra03552c

Facile modification of FeZSM-5 utilizing an organic directing agent (ODA) for iron species evolution toward better Fenton activity was developed. Pristine FeZSM-5, prepared hydrothermally using tetrapropylammonium bromide as the ODA, was thermally treated in nitrogen or air atmosphere for comparison. The as-prepared FeZSM-5 were evaluated by XRD, SEM, TGA, Ar physical adsorption, H₂-TPR, UV-Vis, XPS and M?ssbauer spectra, which confirmed well-dispersed iron species and partial transformation of framework iron to non-framework iron and Fe(iii) to Fe(ii) during thermal treatment in N₂. The phenol oxidation reaction was applied as a probe reaction and phenol conversion can be improved from 44% to 90% within 60 minutes. By thermal treatment in N₂ atmosphere, the ODA plays an important role in modifying non-framework iron species from Fe(iii) to Fe(ii) ions which is desirable for improving catalytic activity in Fenton-like systems. The strategy utilizing the thermal reduction effect of the ODA on iron species is a reliable method for preparing well-dispersed and valence tunable iron oxide nanoparticles encapsulated in ZSM-5.

Full text of DOI:10.1039/c6ra03552c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Evolution of iron species for promoting the
catalytic performance of FeZSM-5 in phenol
Cite this: RSC Adv., 2016, 6, 32789
oxidation†
a
a
a
b
ac
Lei Luo, Chengyi Dai, Anfeng Zhang, Junhu Wang, Chunshan Song*
a
and Xinwen Guo*
Facile modification of FeZSM-5 utilizing an organic directing agent (ODA) for iron species evolution toward
better Fenton activity was developed. Pristine FeZSM-5, prepared hydrothermally using
tetrapropylammonium bromide as the ODA, was thermally treated in nitrogen or air atmosphere for
2
comparison. The as-prepared FeZSM-5 were evaluated by XRD, SEM, TGA, Ar physical adsorption, H -
TPR, UV-Vis, XPS and M o¨ ssbauer spectra, which confirmed well-dispersed iron species and partial
transformation of framework iron to non-framework iron and Fe(III) to Fe(II) during thermal treatment in
2
N . The phenol oxidation reaction was applied as a probe reaction and phenol conversion can be
improved from 44% to 90% within 60 minutes. By thermal treatment in N atmosphere, the ODA plays
2
Received 7th February 2016
Accepted 23rd March 2016
an important role in modifying non-framework iron species from Fe(III) to Fe(II) ions which is desirable for
improving catalytic activity in Fenton-like systems. The strategy utilizing the thermal reduction effect of
the ODA on iron species is a reliable method for preparing well-dispersed and valence tunable iron oxide
nanoparticles encapsulated in ZSM-5.
DOI: 10.1039/c6ra03552c
www.rsc.org/advances
Up to now, many kinds of heterogeneous catalysts have been
1
Introduction
3,4,16
investigated in the effluent treatment.
Metals and metal
Advanced oxidation processes (AOPs), using hydroxyl radicals oxides are the most direct and simplest multiphase catalysts,
1
4
(
$OH), are one of the most effective methods for the destruction but they suffer from poor metal dispersion and catalyst
17
of organic pollutants in wastewater, and so have drawn much recovery problem.
Host–guest materials, like yolk–shell
1
–3
18–20
11,21–23
attention in an extensive range of studies. Compared with the materials,
iron-supported catalyst,
etc., have their special advantages in developing
activity and stability of heterogeneous catalysts under near the synergetic effect between host and guest. However, iron-
iron-exchanged
1
3,24
conventional homogeneous Fenton oxidation system, the catalyst,
4
–7
neutral conditions are problems that need to be solved.
supported catalyst, prepared from impregnation, suffers from
Regeneration of Fe(II) species is the rate-limiting step in cata- metal oxide agglomeration on ZSM-5 external surface or from
lytic cycling and strategies which introduce oxidation–reduc- the lower synergetic effect of ordered mesoporous materials
14
4,8
25
9–11
tion pairs to lower the energy barrier have been proposed.
because of its lower adjustable acidity and hydrothermal
Though various zeolites have been used due to their acidity and stability. In the case of iron-exchanged catalyst, the amount of
1
2,13
hydrothermal stability,
species in zeolite-based catalysts without affecting its disper- iron content is oen obtained. Fortunately, FeZSM-5 obtained
tuning the chemical state of iron iron loading greatly depends on the Si/Al ratio of zeolite and low
14,15
sion is still a problem for their application.
nding a way to optimize the physicochemical state of iron for dispersion of iron species but also maintain appropriate iron
Therefore, from hydrothermal synthesis can not only ensure the great

preventing agglomeration is of great importance.
content. However, both framework iron and non-framework
iron species of conventional FeZSM-5 have no satisfactory
activity because higher Fe(III) species and lower Fe(II) species
exist, which is not desirable for Fenton-like system.
Therefore, the direction for modication of FeZSM-5 is improve
a
State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research,
8,20,26
School of Chemical Engineering, Dalian University of Technology, Dalian 116024, P.
R. China
b
Mossbauer Effect Data Center, Dalian Institute of Chemical Physics, Chinese Academy the content of Fe(II) species.
of Sciences, Dalian, 116023, China
Reduction of Fe(III) using the thermal reduction effect of
organics is a signicant method to improve Fe(II) content. By H2
c
EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department of
Energy & Mineral Engineering, Pennsylvania State University, University Park,
Pennsylvania 16802, USA
temperature programmed reduction, Fe O can be prepared
3
4
from Fe O , but those Fe O nanoparticles are easy to be
2
3
3 4
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c6ra03552c
oxidized in air. In contrast, organics such as ethylene glycol,
1
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32789–32797 | 32789

View Article Online
RSC Advances
Paper
polyethylene glycol, and polyvinyl pyrrole, play a very important a typical procedure, 20 mg catalyst, 50 ml phenol solution (1 g
3
+
ꢀ1
role in reducing Fe which is similar to H in preparing Fe O
L ), and 10.76 ml H O solution (0.69 M) were added together
2 2
2
3
4
27
ꢁ
nanoparticles from Fe(III) salt. More importantly, those into the ask followed by maintaining at 50 C for the appro-
organics can also stabilize the Fe O from oxidation. Accord- priate time. The products were analyzed by liquid chromatog-
ing to this idea, our previous work focused on introducing raphy. The molar ratio of H O /phenol was 14. Phenol oxidation
2 2
27
3
4
15
polyethyleneimine (PEI) to optimize the physicochemical reaction was chosen to evaluate the catalytic activity of the as-
properties of iron oxides. While in order to simplify the prepa- prepared catalyst. In a typical evaluation, 50 mg of the as-
ration process, a more facile strategy was developed in the prepared catalyst, 10.76 ml of H O solution (0.77 M), and 50
2 2
ꢀ
1
present work.
ml of phenol solution (1 g L ) were added together into a 100
ꢁ
Herein, a facile strategy to preparing FeZSM-5 with improved ml round-bottom ask and stirred at 65 C water bath. The
Fenton activity has been developed which involves the use of product was sampled every other 15 minutes and analyzed by
organic direction agents (ODAs) to reduce non-framework iron liquid chromatography (Agent 1200 series) for calculating the
species. Phenol oxidation reaction is applied to evaluate the phenol conversion.
catalytic activity and stability. The structure–activity relation-
ship was also delineated based on the analytical
characterization.
2.3 Characterization
The crystalline structures of the as-prepared catalyst were
determined by a Rigaku Smartlab diffractometer with a nickel-
2
2
Experimental
ꢁ

ltered Cu Ka X-ray source. The scattering angel was between 5
.1 Chemicals and materials
The chemicals used include silica sol (30 wt%), ethylamine (EA, were obtained on a Hitachi 5-5500 instrument. Prior to the
5 wt%), tetrapropylammonium bromide (TPABr), tetraethy- measurement, the samples were sputtered with a thin lm of
lorthosilicate (TEOS), tetrapropylammonium hydroxide gold. The textual properties including the surface area, pore
TPAOH), ferric chloride (FeCl $6H O), H O , and phenol. All volume and pore size distribution were measured using
ꢁ
ꢁ
and 80 at a scanning rate of 0.02 . Morphological properties
6
(
3
2
2 2
above materials were purchased in reagent grade and used a Quantachrome autosorb-iQ2 gas adsorption analyzer with
without further treatment.
argon at 87 K. Prior to the measurement, the calcined samples
Preparation of microporous ZSM-5. FeZSM-5 was synthe- were degassed in vacuum at 573 K for 8 h. The total surface area
sized hydrothermally with the assistance of active seeds from (SBET) was measured by the Brunauer–Emmett–Teller (BET)
a gel with a molar ratio of 1 SiO
The active seeding gel was prepared from a gel with a molar the t-plot method. H
ratio of 1 TEOS : 0.36 TPAOH : 19 H
O by a conventional using ChemBET Pulsar TPR/TPD equipment (Quantachrome,
2
: 0.15 TPABr : 1 EA : 17 H
2
O. method. Microporosity and mesoporosity was determined by
-TPR measurements were carried out
2
2
1
1
hydrothermal synthesis route. Typically, a mixture which USA). The iron content of the as-prepared samples was
consists of 50 g of TEOS, 70 g of TPAOH (25 wt%), and 30 g measured by ICP-OES aer digestion with the mixture of HCl,
distilled water was stirred at 308 K and maintain for 5 h which HNO
followed by increasing temperature to 353 K and crystallize for Vis) spectra were acquired on a Jasco UV-550 spectrometer,
another 72 h. Aer cooling down, the obtained seeding gel was and pure BaSO was used as reference. Deconvolution of the UV-
directly used for the synthesis of FeZSM-5 zeolites without any Vis spectra into individual iron species' bands was conducted
3 4
, HF, HClO . Ultraviolet-visible diffuse reectance (UV-
4
28
treatment. The synthesis of FeZSM-5 was conducted by using according to the procedure detailed in literature. Thermal
the following procedure: rst, 13.34 g of TPABr was dissolved gravimetric analysis (TGA) was performed on a SDT Q600 (TA
ꢁ
ꢀ1
with 66.67 g of silica solution and aerwards with a solution of Instruments, U.S.A.) with a heating rate of 10 C min in air or
2.26 g of EA (65 wt%). The mixture was aged at room
atmosphere. X-ray photoelectron spectra (XPS) were ob-
temperature for 30 min under mechanical stirring followed by tained with a Thermo VG ESCALAB250 instrument using Al Ka
2
N
2
5
7
3 2 2
addition of a solution of FeCl $6H O and 45 g of H
O. 0.21 g as- radiation. The Fe Mossbauer spectra were recorded using
prepared active seeding gel was then added into the above a Topologic 500 A spectrometer at room temperature with
FeZSM-5 precursor and then introduced to the stainless steel a proportional counter.
autoclave (200 ml, lled volume 150 ml) with hydrothermal
treatment at 443 K for 72 h. The resulting solid was ltered,
washed, and dried overnight at 373 K. The as-synthesized 3 Results and discussion
zeolite was calcined in nitrogen or air atmosphere at 873 K for
3
.1 Material synthesis and characterization
4
h. The resulting sample was denoted as NX or AX, where N and
The XRD patterns of FeZSM-5 series with different Si/Fe ratio
and different thermal treatment atmosphere are shown in
Fig. 1. Five characteristic diffraction peaks at 7.8 , 8.8 , 23.0 ,
A represent that the calcination atmosphere is nitrogen and air,
respectively; X represents the Si/Fe molar ratio of FeZSM-5.
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
23.9 and 24.4 clearly exhibit pure MFI topology of FeZSM-5.
2.2 Catalytic testing
No diffraction peaks associated with iron phase were detec-
All catalyst evaluations were conducted in a 100 ml round- ted, indicating the high dispersion of iron species. Fig. 2 shows
bottom ask equipped with a magnetic stirring bar. In the SEM images of the six catalysts with the inset showing their
32790 | RSC Adv., 2016, 6, 32789–32797
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Fig. 3 Ar adsorption and desorption isotherms at 87 K (a) N40, (b) A40,
Fig. 1 XRD patterns of (a) N40, (b) A40, (c) N80, (d) A80, (e) N200, (f) (c) N80, (d) A80, (e) N200, (f) A200. The isotherms of each sample are
3
ꢀ1
A200.
displaced vertically by 100 cm g .
Fig. 4. The adsorption branch of the six samples shows typical
type-I adsorption line which indicates their microporosity.
Typically, pore distribution at around 0.54 nm represents the
oval-shaped and Z-shaped channel, and pore distribution at
29
around 0.9 nm represents the channel intersection. The three
samples calcined in N atmosphere all present a relatively lower
2
pore distribution compared with samples calcined in air which
denitely indicate the existence of something blocking their
channel intersection. At the same time, total pore volume (Vpore
)
(shown in Table 1) present the same principle and a relatively
smaller pore volume exists in samples calcined in N . The
2
substance which exists in the intersection is either coke-like
30
species or iron species. According to TG curves of sample
ꢁ
N40 and A40 (shown in Fig. S1†), weight loss above 600 C is
Fig. 2 SEM images of (a) N40, (b) A40, (c) N80, (d) A80, (e) N200, (f)
A200.
particle size distribution. All six catalysts have a uniform
particle size distribution around 700 nm.
Fig. 3 shows the Ar adsorption–desorption isotherms of
FeZSM-5 at 87 K with the pore size distribution presented in each sample are displaced vertically by 0.5 cm g
Fig. 4 Pore size distributions of (a) N40, (b) A40, (c) N80, (d) A80, (e)
N200, (f) A200. The pore size distributions were determined by non-
local density functional theory (NLDFT). The pore size distributions of
3
ꢀ1
.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32789–32797 | 32791

View Article Online
RSC Advances
Paper
Table 1 Textural properties of (a) N40, (b) A40, (c) N80, (d) A80, (e) N200, (f) A200
a
2
ꢀ1
a
2
ꢀ1
b
2
ꢀ1
c
3
ꢀ1
d
3
ꢀ1
Sample code
S
micro [m g
]
S
meso [m g
]
S
BET [m g
]
V
micro [cm g
]
V
pore [cm g ]
N40
A40
N80
A80
N200
A200
313
319
307
318
311
341
61
98
104
104
112
107
374
417
411
422
423
448
0.182
0.197
0.193
0.199
0.199
0.213
0.28
0.32
0.29
0.31
0.28
0.31
a
b
c
d
t-Plot method. BET method. NLDFT method. p/p
0
¼ 0.99.
approximately 0.5 wt% indicating that the organic directing
agents of those samples have almost been removed meaning
and merely have residual of coke-like species, from which we
infer the existence of iron species in channel intersection for
three samples calcined in N2.
Fig. 5 shows the TGA and DTG curves of the uncalcined
ꢁ
samples in N and air atmosphere. Weight loss below 300 C
2
can be attributed to adsorbed water and crystal water, and above
ꢁ
+
3
00 C attributed to the decomposition of TPA . It can be seen
that samples with the same Si/Fe ratio do have a difference
when hydrothermal treatment was conducted in different
+
atmosphere. The temperature for decomposition of TPA for
samples calcined in air is slightly lower than those in N which
2
is corresponding with the ref. 31. Owing to the existence of O
under air atmosphere, the oxidation of TPA would release
2
+
Fig. 6 UV-Vis spectra of (a) N40, (b) A40, (c) N80, (d) A80, (e) N200, (f)
A200.
2
energy. On the contrary, without the help of O , the decompo-
+
30,31
sition of TPA in N
2
is merely a pyrolysis process.
UV-Vis spectra between 190–800 nm were conducted to
2
8
investigate the nature of Fe(III) species of FeZSM-5, and
importantly that Fe(II) species do not contribute to the UV-Vis
spectra absorbance because the absorbance of Fe(II) species
32
transitions are expected. Bands at 215 nm and 241 nm can be
33
attributed to framework iron species, and a band at 278 nm is
attributed Fe species in octahedral sites. Octahedral Fe ions
in small oligo nuclear clusters give rise to broad bands between
3
+
3+
32
falls in the near infrared range around 1000 nm. Fig. 6 shows
3
+
the UV-Vis spectra of the as-prepared catalysts. For Fe sites,
two charge-transfer (CT) bands associated to t / t and t / e
3
00 and 450 nm and bands above 450 nm are characteristic for
28,33
1
1
1
large Fe
O
3
particle.
All six samples contain both framework
2
and non-framework iron species but with different contents.
According to the ICP-OES analysis (Table 3), samples with lower
Si/Fe ratio showed higher iron contents, so it is reasonable that
samples with lower Si/Fe ratio show higher intensity in UV-Vis
spectra. Importantly, in the case of samples with the same
iron contents, for N40 and A40 instance, compared with A40
which was treated under air atmosphere, sample N40 shows
weaker absorbance which can be attributed to that sample N40
contained some of Fe(II) ions. Therefore, it can be concluded
+
that the decomposition of TPA under N result in the genera-
2
tion of Fe(II) species in sample N40. On the other hand, from the
deconvolution of N40 and A40 (shown in Table 2), there is very
limited change in composition of Fe(III). So there exists such
a transformation of iron species to maintain the Fe(III) compo-
sition unchanged: framework iron / non-framework iron /
Fe(II). And the content of non-framework iron is much higher
for samples calcined in N than in air.
2
To investigate the reducibility of the materials, H -TPR
2
experiments were conducted, as shown in Fig. 7. For all six
Fig. 5 TG curves of uncalcined FeZSM-5 with different Si/Fe ratio. (a)
Si/Fe ¼ 40, (b) Si/Fe ¼ 80, (c) Si/Fe ¼ 200. Measure condition: air or N
samples, the three H
2
1 2 3
consumption peaks (a , a , a ) are
2
ꢁ
ꢀ1
3+
(3ꢀd)+
atmosphere, 10 C min
.
attributed to Fe and Fe
O
3
to Fe
1
(a ), with intermediate
2
32792 | RSC Adv., 2016, 6, 32789–32797
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
1 2
Table 2 Percentage of the area of the bands (I at l < 280 nm, I at 280
<
l < 400 nm, and I
3
at l > 400 nm) derived from deconvolution of the
UV-Vis spectra in Fig. 5. The values do not take into account the
2+
contribution of eventual Fe species present in the as-prepared
samples
a
b
c
Sample
I
1
(%)
I
2
(%)
3
I (%)
N40
A40
N80
A80
N200
A200
62
59
58
56
58
85
26
27
25
27
24
15
12
14
17
17
18
0
a
b
Isolated Fe ions in tetrahedral and octahedral coordination. Oligo-
c
x y
nuclear Fe O clusters (x $ 2). Bulk Fe nanoparticles.
Table
3 The composition of the synthesis gel and the real
composition
Amount of metal in
synthetic gel (wt%)
Amount of metal in
samples
a
Sample
Fe
Si/Fe
Fe
Si/Fe
N40
A40
N80
A80
N200
A200
2.26
2.26
1.15
1.15
0.46
0.46
40
40
80
80
200
200
3.01
3.09
1.72
1.85
0.65
0.66
29.6
28.9
52.9
49.1
143.1
139.8
a
Measured by ICP analysis.
Fig. 7
2
H -TPR of (a) N40, (b) A40, (c) N80, (d) A80, (e) N200, (f) A200.
2
+
valence as that in Fe
3 4 2
O , and then further reduction to Fe (a ).
At higher temperature, the peaks represent partial reduction of
2
+
0
Fe to Fe (a
5
3
). All the above-mentioned iron species in FeZSM-
is the non-framework iron
that could be reduced by H
2
species, and higher temperature leads to more framework iron's
transformation to non-framework species. According to the H2-
TPR proles of the catalysts, H2 consumption of samples
treated in N is apparently higher than samples treated in air
2
indicating higher amount of non-framework iron species, in
accordance with the UV-Vis analysis. On the other hand, the
reduction temperature of sample N40 slightly shis to lower
temperature which shows that iron species in sample N40 are
easier to be reduced. This indicates that non-framework iron
species in samples treated in N2 atmosphere have a better
dispersion.
Fig. 8 shows the Fe 2p XPS spectra of N40 and A40. From the
deconvolution of the XPS spectra for Fe 2p3/2, the peak centered
at 709.8 eV is attributed to Fe . For the peak centered at 714.0
eV, it is attributed to the framework iron with the Fe–O–Fe
bonds that make the peaks shiing to higher binding energy. In
2
+
34
Fig. 8 XPS spectra of (a) N40, (b) A40.
the case of sample A40, as some framework iron species were Fig. 9 shows the M ¨o ssbauer spectra of N40 and A40 at room
converted to non-framework species aer thermal treatment, temperature, with the hyperne interaction parameters
the binding energy correspondingly shis to the higher value summarized in Table 4. In general, the nanoparticle size of iron
centered at 712.4 eV.
To further investigate the nature of iron species, Fe and sextet.
M ¨o ssbauer spectroscopic characterization was conducted. present super-paramagnetic phenomenon therefore the peaks
species can be discussed by the peak shape including doublet
5
7
35,36
Nanoparticles with high dispersion would
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32789–32797 | 32793

View Article Online
RSC Advances
Paper
Fig. 10 Phenol conversion in the presence of (a) N40, (b) A40, (c) N80,
(d) A80, (e) N200, (f) A200.
57
Fig. 9
Fe M o¨ ssbauer spectra of (a) N40, (b) A40 samples at room
temperature.
57
Table 4
Fe M o¨ ssbauer parameters of N40 and A40 samples
Oxidation
state
Sub-
spectrum
IS
(mm s
QS
(mm s
RI
(%)
ꢀ1
ꢀ1
Sample
N40
)
)
Fe(III)
Fe(II)
Fe(III)
Fe(III)
Doublet
Doublet
Doublet
Doublet
0.38
0.92
0.32
0.34
0.92
2.51
0.76
1.18
77.3
22.7
23.8
76.2
A40
Fig. 11
2 2
H O conversion in the presence of (a) N40, (b) A40, (c) N80,
(
d) A80, (e) N200, (f) A200.
would be doublet. From Fig. 9, doublets are observed both N40
and A40 which imply well-dispersion of iron species. Both of the
M ¨o ssbauer spectra of samples N40 and A40 could be tted well
by two doublets. In the case of N40, the doublet with IS ¼ 0.38
2 2
products for phenol oxidation is mainly CO and H O, and the
intermediate products including catechol, hydroquinone, o-
benzoquinone, p-benzoquinone, oxalic acid, acetic acid.
ꢀ1
ꢀ1
mm s and QS ¼ 0.92 mm s could be attributed to Fe(III)
ꢀ
1
species, and doublet with IS ¼ 0.92 mm s and QS ¼ 2.51 mm
ꢀ
1
37–39
s
could attributed to Fe(II) species.
In contrast, according
to the 57Fe M ¨o ssbauer parameters, both of the doublets of A40 3.3 Discussion
only could be attributed to Fe(III) species which is consistent
with UV-Vis and XPS analysis.
2 2
Hydroxyl radical ($OH), produced from H O in chain reaction
2+
initiated by Fe (Table 5), is widely accepted as a strong oxidant
for its high redox potential in Fenton system. Higher amount of
2
+
Fe as well as higher dispersion is benecial for improving
3.2 Catalytic performance
4,8
catalytic activity of iron-based catalyst, and many efforts have
As Fenton-like system is very sensitive to the iron chemical been made by using Fe
3
O
4
as the active phase in the previous
26,41,42
state, phenol oxidation reaction is applied as a probe reaction to work.
evaluate the as-prepared FeZSM-5. Fig. 10 and 11 show the
FeZSM-5, obtained from hydrothermal synthesis, is with the
2 2
phenol and H O conversion, respectively, in the presence of ODAs in its channel system and with good iron dispersion. The
+
series of FeZSM-5 samples. According to the initial conversion decomposition process of TPA used as ODAs in this work is
+
of phenol and H O , the samples with higher iron contents shown in Fig. 12. The decomposition of TPA involves two
2
2
exhibit higher activity, and, importantly, samples calcined in N
exhibit higher catalytic activity than that in air. The obtained tripropylamine (Pr
2
gradual template decomposition steps. At a low temperature,
N) and propene obtained from a Hofmann
3
32794 | RSC Adv., 2016, 6, 32789–32797
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
2
+
40
Table 5 Chain reaction initiated by Fe
.
obtained from oligomerization of ODAs play an important role
in tuning the iron species to metastable state which is good for
phenol oxidation. The catalytic activity of samples calcined in
Rate constant at
ꢀ1 ꢀ1
Reaction
pH ¼ 3 (mol
s )
N is totally higher than that in air and the phenol conversion
2
2
+
3+
ꢀ
1
2
3
4
5
6
Fe + H
2
O
2
/ Fe + cOH + OH
63
can improve from 44% to 90% within 60 min. The strategy
involving using the organic directing agents as a reductant to
tune the iron species and using the connement effect of
microporous structure to get higher dispersion is a reliable
method to prepare well dispersed zeolite-encapsulated iron
oxide for phenol oxidation.
3+
2+
ꢀ
+
ꢀ3
7
H
2
O
2
+ Fe / Fe + HO
2
c/O
+ H
2
c
+ H
2.0 ꢂ 10
ꢀ
2+
cOH + H
2
O
2
/ HO
2
c/O
2
c
2
O
+ H
3.3 ꢂ 10
3
+
ꢀ
+
5
Fe + HO
2
c/O
2
c
/ Fe + O
2
7.8 ꢂ 10
2+
3+
ꢀ
8
Fe + cOH / Fe + OH
3.2 ꢂ 10
ꢀ
ꢀ
6
HO
2
c/O
+ H
cOH + HO
cOH + cOH / H
2
c
+ HO
2
c/O
2
c
/
2.3 ꢂ 10
H
2
O
2
2
O
ꢀ
9
7
8
2
c/O
2
c
/ H
2
O + O
2
7.1 ꢂ 10
9
2
O
2
5.2 ꢂ 10
Acknowledgements
This work was supported by the State Key Program of National
Natural Science Foundation of China (grant no. 21236008).
Notes and references
1
F. C. Moreira, S. Garcia-Segura, R. A. R. Boaventura, E. Brillas
and V. J. P. Vilar, Degradation of the antibiotic trimethoprim
by electrochemical advanced oxidation processes using
a carbon-PTFE air-diffusion cathode and a boron-doped
diamond or platinum anode, Appl. Catal., B, 2014, 160–161,
4
92–505.
A. D. Bokare and W. Choi, Review of iron-free Fenton-like
systems for activating in advanced oxidation
processes, J. Hazard. Mater., 2014, 275, 121–135.
M. A. Oturan and J.-J. Aaron, Advanced Oxidation Processes
2
3
2 2
H O
+
Fig. 12 Evolution process of TPA during detemplation of ZSM-5.
in
Applications. A Review, Crit. Rev. Environ. Sci. Technol.,
014, 44, 2577–2641.
P. V. Nidheesh, Heterogeneous Fenton catalysts for the
abatement of organic pollutants from aqueous solution:
a review, RSC Adv., 2015, 5, 40552–40577.
Water/Wastewater
Treatment:
Principles
and
+
elimination of TPA . In a second step, Pr
3
N was further
2
degraded into lower amines and consequently into propene.
Finally, the unsaturated products like propene undergo oligo-
4
5
30
merization, cyclization and aromatization. The oligomeriza-
tion of the template derivatives nally lead to the coke-like
species which have relatively strong interaction with ZSM-5
framework. When FeZSM-5 was calcined in air, the coke-like
species would likely convert easily to gaseous products with
W. R. P. Barros, J. R. Steter, M. R. V. Lanza and A. C. Tavares,
Catalytic activity of Fe3-xCu
O
x 4
nanoparticles for the
degradation of Amaranth food dye by heterogeneous
electro-Fenton process, Appl. Catal., B, 2016, 180, 434–441.
M. B. Kasiri, H. Aleboyeh and A. Aleboyeh, Degradation of
Acid Blue 74 using Fe-ZSM5 zeolite as a heterogeneous
photo-Fenton catalyst, Appl. Catal., B, 2008, 84, 9–15.
Y. Lei, C. S. Chen, Y. J. Tu, Y. H. Huang and H. Zhang,
Heterogeneous Degradation of Organic Pollutants by
3 4
Persulfate Activated by CuO-Fe O : Mechanism, Stability,
and Effects of pH and Bicarbonate Ions, Environ. Sci.
Technol., 2015, 49, 6838–6845.
X. Hu, B. Liu, Y. Deng, H. Chen, S. Luo, C. Sun, P. Yang and
S. Yang, Adsorption and heterogeneous Fenton degradation
the help of O
2
and iron species are seldom inuenced. In
atmosphere, the temperature for
6
7
contrast, when calcined in N
2
those carbon species to break up is much higher. Higher
temperature leads to the conversion of iron species from
framework to non-framework. At the same time, the coke-like
species can play a role in reducing the non-framework iron
species.
The strategy involving the organic structure directing agents
as a reductant to tune the iron species is also reliable in other
zeolites.
8
9
3 4
of 17a-methyltestosterone on nano Fe O /MWCNTs in
aqueous solution, Appl. Catal., B, 2011, 107, 274–283.
Y. Wang, H. Zhao and G. Zhao, Iron-copper bimetallic
nanoparticles embedded within ordered mesoporous
carbon as effective and stable heterogeneous Fenton
catalyst for the degradation of organic contaminants, Appl.
Catal., B, 2015, 164, 396–406.
4
Conclusions
A superior FeZSM-5 catalyst with excellent dispersion and
valence tunable iron species was obtained from hydrothermal
synthesis utilizing tetrapropylammonium bromide as the ODA
in its channel system. Through simple thermal treatment in
nonoxidative atmosphere, some framework iron converts to 10 X. Li, X. Liu, L. Xu, Y. Wen, J. Ma and Z. Wu, Highly dispersed
non-framework species. At the same time, the coke-like species
Pd/PdO/Fe
2
O
3
nanoparticles in SBA-15 for Fenton-like
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32789–32797 | 32795

View Article Online
RSC Advances
Paper
processes: connement and synergistic effects, Appl. Catal., 25 M. Xia, M. Long, Y. Yang, C. Chen, W. Cai and B. Zhou, A
B, 2015, 165, 79–86.
1 L. Luo, C. Dai, A. Zhang, J. Wang, M. Liu, C. Song and X. Guo,
A facile strategy for enhancing FeCu bimetallic promotion
highly active bimetallic oxides catalyst supported on Al-
containing MCM-41 for Fenton oxidation of phenol
solution, Appl. Catal., B, 2011, 110, 118–125.
1
1
1
1
1
1
for catalytic phenol oxidation, Catal. Sci. Technol., 2015, 5, 26 L. Xu and J. Wang, Fenton-like degradation of 2,4-
159–3165. dichlorophenol using Fe magnetic nanoparticles, Appl.
2 C. Dai, A. Zhang, L. Li, K. Hou, F. Ding, J. Li, D. Mu, C. Song, Catal., B, 2012, 123–124, 117–126.
M. Liu and X. Guo, Synthesis of Hollow Nanocubes and 27 A. H. Lu, E. L. Salabas and F. Schuth, Magnetic
3
3 4
O
Macroporous Monoliths of Silicalite-1 by Alkaline
nanoparticles: synthesis, protection, functionalization, and
Treatment, Chem. Mater., 2013, 25, 4197–4205.
application, Angew. Chem., 2007, 46, 1222–1244.
3 A. Cihano ˘g lu, G. G u¨ nd u¨ z and M. D u¨ kkancı, Degradation of 28 J. Perez-Ramirez, M. S. Kumar and A. Bruckner, Reduction of
acetic acid by heterogeneous Fenton-like oxidation over
N O with CO over FeMFI zeolites: inuence of the
2
iron-containing ZSM-5 zeolites, Appl. Catal., B, 2015, 165,
preparation method on the iron species and catalytic
687–699.
behavior, J. Catal., 2004, 223, 13–27.
4 C. H. Christensen, I. Schmidt, A. Carlsson, K. Johannsen and 29 A. Janda and A. T. Bell, Effects of Si/Al ratio on the
K. herbst, Crystals in crystals-nanocrystals within
mesoporous zeolite single crystals, J. Am. Chem. Soc., 2005,
distribution of framework Al and on the rates of alkane
monomolecular cracking and dehydrogenation in H-MFI, J.
Am. Chem. Soc., 2013, 135, 19193–19207.
127, 8098–8102.
5 L. Luo, C. Dai, A. Zhang, J. Wang, M. Liu, C. Song and X. Guo, 30 L. Karwacki and B. M. Weckhuysen, New insight in the
Facile synthesis of zeolite-encapsulated iron oxide
nanoparticles as superior catalysts for phenol oxidation,
RSC Adv., 2015, 5, 29509–29512.
template decomposition process of large zeolite ZSM-5
crystals: an in situ UV-Vis/uorescence micro-spectroscopy
study, Phys. Chem. Chem. Phys., 2011, 13, 3681–3685.
6 Y. Wei, T. E. Parmentier, K. P. de Jong and J. Zecevic, 31 O. Prokopova, B. Bernauer, M. Frycova, P. Hrabanek,
Tailoring and visualizing the pore architecture of
hierarchical zeolites, Chem. Soc. Rev., 2015, 44, 7234–7261.
7 J. Shi, On the synergetic catalytic effect in heterogeneous
nanocomposite catalysts, Chem. Rev., 2013, 113, 2139–2181.
A. Zikanova and M. Kocirik, Principal Features of
Tetrapropylammonium Hydroxide Removal Kinetics from
Silicalite-1 in Quasi-isothermal Heating Regimes, J. Phys.
Chem. C, 2013, 117, 1468–1476.
1
1
8 C. Dai, A. Zhang, J. Li, K. Hou, M. Liu, C. Song and X. Guo, 32 L. E. Iton, R. B. Beal and D. T. Hodul, A new approach to the
Synthesis of yolk-shell HPW@Hollow silicalite-1 for
esterication reaction, Chem. Commun., 2014, 50, 4846–
generation of metal-bearing, medium-pore, shape-selective
zeolites for scher-tropsch catalysis: spectroscopic studies
of zeolites, J. Mol. Catal., 1983, 21, 151–171.
4848.
1
2
2
2
2
2
9 C. Li, R. Younesi, Y. Cai, Y. Zhu, M. Ma and J. Zhu, 33 S. Bordiga, R. Buzzoni, F. Geobaldo, C. Lamberti,
Photocatalytic and antibacterial properties of Au-decorated
A. Zecchina, G. Leofanti, G. Petrini, G. Tozzola and
G. Vlaic, Structure and Reactivity of Framework and
Extraframework Iron in Fe-Silicalite as Investigated by
Spectroscopic and Physicochemical Methods, J. Catal.,
1996, 158, 485–501.
Fe O @mTiO core–shell microspheres, Appl. Catal., B,
3
4
2
2
014, 156–157, 314–322.
0 Y. Wang, H. Sun, X. Duan, H. M. Ang, M. O. Tad ´e and
S. Wang, new magnetic nano zero-valent iron
A
2
+
encapsulated in carbon spheres for oxidative degradation 34 T. Yamashita and P. Hayes, Analysis of XPS spectra of Fe
of phenol, Appl. Catal., B, 2015, 172–173, 73–81.
1 Y. Gao, Y. Wang and H. Zhang, Removal of Rhodamine B
3
+
and Fe ions in oxide materials, Appl. Surf. Sci., 2008, 254,
2441–2449.
with Fe-supported bentonite as heterogeneous photo- 35 Z. Xiao, S. Jin, X. Wang, W. Li, J. Wang and C. Liang,
Fenton catalyst under visible irradiation, Appl. Catal., B,
015, 178, 29–36.
2 B. Dutta, S. Jana, A. Bhattacharjee, P. G u¨ tlich, S. Iijima and
2 3
S. Koner, g-Fe O nanoparticle in NaY-zeolite matrix: 36 G. F. Goya and H. R. Rechenberg, Superparamagnetic
Preparation, structure and catalytic properties of
magnetically separable Cu–Fe catalysts for glycerol
hydrogenolysis, J. Mater. Chem., 2012, 22, 16598.
2
Preparation, characterization, and heterogeneous catalytic
2 4
transition and local disorder in CuFe O nanoparticles,
epoxidation of olens, Inorg. Chim. Acta, 2010, 363, 696–704.
Nanostruct. Mater., 1998, 10, 1001–1011.
3 Z. Ai, Z. Gao, L. Zhang, W. He and J. Yin, Core–Shell 37 G. Moretti, G. Fierro, G. Ferraris, G. B. Andreozzi and
Structure Dependent Reactivity of Fe@Fe Nanowires on V. Naticchioni, N O decomposition over [Fe]-MFI catalysts:
Inuence of the Fe O nuclearity and the presence of
2
O
3
2
Aerobic Degradation of 4-Chlorophenol, Environ. Sci.
Technol., 2013, 47, 5344–5352.
4 M. D u¨ kkancı, G. G u¨ nd u¨ z, S. Yılmaz, Y. C. Yaman,
x
y
framework aluminum on the catalytic activity, J. Catal.,
2014, 318, 1–13.
R. V. Prikhod'ko and I. V. Stolyarova, Characterization and 38 S. M. Maier, A. Jentys, E. Metwalli, P. M u€ ller-Buschbaum and
catalytic activity of CuFeZSM-5 catalysts for oxidative
degradation of Rhodamine 6G in aqueous solutions, Appl.
Catal., B, 2010, 95, 270–278.
J. A. Lercher, Determination of the Redox Processes in FeBEA
Catalysts in NH
-SCR Reaction by M o€ ssbauer and X-ray
Absorption Spectroscopy, J. Phys. Chem. Lett., 2011, 2, 950–
55.
3
9
32796 | RSC Adv., 2016, 6, 32789–32797
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
3
9 J. Taboada, A. Overweg, P. Kooyman, I. Arends and G. Mul,
Following the evolution of iron from framework to extra-
framework positions in isomorphously substituted [Fe,Al]
sonophotochemical magnetite-catalyzed Fenton-like (US/
UV/Fe O /oxalate) system, Appl. Catal., B, 2014, 160–161,
3
4
325–334.
MFI with Fe Mossbauer spectroscopy, J. Catal., 2005, 231, 42 H. Zhao, Y. Wang, Y. Wang, T. Cao and G. Zhao, Electro-
2 3
6–66. Fenton oxidation of pesticides with a novel Fe @Fe O /
5
3
O
4
4
4
0 M. Hartmann, S. Kullmann and H. Keller, Wastewater
treatment with heterogeneous Fenton-type catalysts based
on porous materials, J. Mater. Chem., 2010, 20, 9002.
1 T. Zhou, X. Wu, J. Mao, Y. Zhang and T.-T. Lim, Rapid
degradation of sulfonamides in a novel heterogeneous
activated carbon aerogel cathode: High activity, wide pH
range and catalytic mechanism, Appl. Catal., B, 2012, 125,
120–127.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 32789–32797 | 32797