Mesoporous chitosan-immobilized iron tetrakis(4-carboxyphenyl)porphyrin as a model of cytochrome P-450 enzyme for oxidation of ethylbenzene

Article abstract of DOI:10.1002/aoc.4140

Mesoporous chitosan-grafted iron tetra (4-carboxyphenyl) porphyrin catalyst (Fe TCPP/mesp-CTS) was prepared and investigated as a practical model for the nano-cavity and coordinate regulation-catalysis(CRC) function in cytochrome P-450 enzyme. Fe TCPP/mesp-CTS was characterized by X-ray Diffraction(XRD), Thermogravimetry(TG), Ultraviolet–visible spectroscopy(UV-Vis), Ultraviolet–visible–Diffuse reflectance spectroscopy(UV-DRS), Scanning electron microscope (SEM), Fourier transform infrared spectroscopy(FT-IR), and X-ray photoelectron spectroscopy(XPS) techniques. The catalytic activity of Fe TCPP/mesp-CTS for ethylbenzene oxidation was investigated and it was proved to be a better catalyst than Fe TCPP/macp-CTS based on the ethylbenzene conversion, turnover numbers(TON), and the reusability. These results are attributed to the mesocavity and CRC of amino group in Fe TCPP/mesp-CTS. The highest ethylbenzene conversion and yields of ketone and alcohol were 24.4% and 18.2%, respectively.

Full text of DOI:10.1002/aoc.4140

Received: 27 July 2017
DOI: 10.1002/aoc.4140
Revised: 20 September 2017
Accepted: 23 September 2017
F U L L P A P E R
Mesoporous chitosan‐immobilized iron tetrakis(4‐
carboxyphenyl)porphyrin as a model of cytochrome P‐450
enzyme for oxidation of ethylbenzene
Guan Huang
| Tong‐ming Su | Kai Zeng | Yong‐an Guo | Shu‐kai Zhao | Su‐juan Wei
College of Chemistry and Chemical
Engineering, Guangxi University,
Nanning 530004, China
Mesoporous chitosan‐grafted iron tetra (4‐carboxyphenyl) porphyrin catalyst (Fe
TCPP/mesp‐CTS) was prepared and investigated as a practical model for the
nano‐cavity and coordinate regulation‐catalysis(CRC) function in cytochrome
P‐450enzyme. FeTCPP/mesp‐CTS was characterized by X‐ray Diffraction(XRD),
Thermogravimetry(TG), Ultraviolet–visible spectroscopy(UV‐Vis), Ultraviolet–
visible–Diffuse reflectance spectroscopy(UV‐DRS), Scanning electron micro-
scope (SEM), Fourier transform infrared spectroscopy(FT‐IR), and X‐ray
photoelectron spectroscopy(XPS) techniques. The catalytic activity of Fe TCPP/
mesp‐CTS for ethylbenzene oxidation was investigated and it was proved to be
a better catalyst than Fe TCPP/macp‐CTS based on the ethylbenzene conversion,
turnover numbers(TON), and the reusability. These results are attributed to the
mesocavity and CRC of amino group in Fe TCPP/mesp‐CTS. The highest
ethylbenzene conversion and yields of ketone and alcohol were 24.4% and
Correspondence
Guan Huang, College of Chemistry and
Chemical Engineering, Guangxi
University, Nanning 530004, China
Email: huangg66@126.com
Funding information
Natural Science Foundation of Guangxi
Province, Grant/Award Number:
2014GXNSFDA118009; Experimental
Innovation Project Foundation of Guangxi
University, PR China, Grant/Award
Number: 201510593308; Scientific and
Technological Project of Guangxi
Province, Grant/Award Number:
18.2%, respectively.
12118008‐12‐3; National Natural Science
Foundation of China, Grant/Award Num-
ber: 51363001
KEYWORDS
catalysis, ethylbenzene oxidation, iron porphyrin, mesoporous chitosan, oxygen
1
| INTRODUCTION
of supports have been used to improve the catalytic
[6]
activity of metalloporphyrin, such as zinc oxide,
[
7]
[8]
The selective oxidation of ethylbenzene to valuable
products is an important reaction for chemical indus-
try.
multi‐wall carbon nanotubes, boehmite, merrifield
[
9]
[10]
resin, cyclodextrin polymers,
and so on.
[1,2]
Many types of metalloporphyrins have been
Natural organic polymers such as chitosan (CTS) are
promising supports for catalytic application due to the high
widely used as cytochrome P‐450 enzyme models for
catalytic oxidation of various hydrocarbons into
surface area, low cost, biodegradability, biocompatibility,
[3,4]
[11,12]
oxygenic compounds.
However, homogeneous
nontoxicity and renewability.
Chitosan has been
[
13]
metalloporphyrin catalysts are not practical in large‐scale
used as the support for Fe O
chiral bifunctional
3
4,
[
12]
[14]
[15]
process owing to the drawbacks of deactivation and low
thioureas,
imidazole Schiff,
and peroxotungstate
[5]
reusability. Immobilization of metalloporphyrin onto
various supports has been found to be an effective way
to increase the stability of metalloporphyrin and the
substrates conversion. The supported metalloporphyrin
catalyst is easier to be recovered. Therefore, many kinds
in many studies. It has been found that chitosan was also
a great support for Co(II) TPP, M TPPs, Mn TPP,
III
III
[16–23]
(TPPFe ) O, [Fe (TPP)]Cl, and M TCPP.
The N
2
atoms in the amino groups of CTS coordinate to the metal
ions of metalloporphyrins, resulting in the enhanced
Appl Organometal Chem. 2017;e4140.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.4140

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HUANG ET AL.
catalytic activity of the CTS supported metalloporphyrin.
However, the traditional CTS has very small surface area,
and the metalloporphyrins could not be well dispersed on
it for efficient catalysis of hydrocarbons oxidation reac-
tion. Therefore, new methods need to be employed to
modify the CTS to make it being a better support for
metalloporphyrins. Mesoporous materials with the advan-
tages of large surface area, well‐defined pore size, high
mechanical and thermal stability, have been used as sup-
port in many studies, and these materials present good
of 4‐carboxybenzaldehyde, the solution was heated to
180 °C. 3.0 mL of pyrrole was slowly dropped into the
solution, and then refluxed for another 2 h. The solution
was cooled to room temperature and kept overnight.
The reaction mixture was then filtered, and the resulted
filter cake was vacuum dried at 120 °C for 6 h after
washing with deionized water. The purified TCPP was
obtained by recrystallization.
0.53 g of TCPP was add into 120 ml of N,N‐dimethyl
formamide with stirring at a speed of 100 rpm. Upon com-
plete dissolution of TCPP, the solution was heated to
151 °C, and 1.54 g of FeCl ·4H O was added to the mix-
[24–27]
catalytic performance and stability.
Based on these
facts, the porous chitosan was used as the support for
metalloporphyrins and the resulted M TCPP/p‐CTS
showed great catalytic activity for aerobic oxidation of
cyclohexane due to the porosity and specific surface area
2
2
ture and refluxed for 1 h. 100 ml of deionized water was
added to the solution after the reaction mixture cooled
down to room temperature and the resulted mixture was
kept at room temperature overnight. The mixture was
filtered and the obtained cake was washed with deionized
water, and Fe TCPP was obtained by vacuum drying at
65 °C for 4 h.
[23]
of chitosan.
Even more promisingly, mesoporous
chitosan, with larger specific surface area, more mesopo-
rous cavity and coordination function, would be a more
hopeful mimic of the nano‐cavity and coordinate
regulation‐catalysis(CRC) function in cytochrome P‐450
enzyme. With these knowledge, mesoporous CTS will be
used as a promising support for metalloporphyrin to
achieve higher catalytic activity.
2
CTS
.3 | Preparation of mesp‐CTS and macp‐
In the present study, the Fe TCPP/mesoporous‐CTS
−
1
(
(
Fe TCPP/mesp‐CTS) and Fe TCPP/macroporous CTS
Fe TCPP/macp‐CTS) were prepared via an acylation
18.75 g of CTS was dissolved in 1000 ml of 0.7 mol·L
diluted acetic acid with stirring at ambient temperature
for 20 min. The resulting colloidal solution was added
reaction of Fe TCPP with mesp‐CTS. XRD, TG,
UV–Vis, UV‐DRS, FT‐IR, SEM and XPS techniques were
used to characterize the inner structure, morphology,
thermal and photo electronic properties of the prepared
catalysts. The catalytic activity for catalytic oxidation of
ethylbenzene to ketone and alcohol was investigated. In
addition, the effects of oxygen pressure, reaction temper-
ature, amount of Fe TCPP, reaction time as well as the
reuse of catalysts for ethylbenzene oxidation were
revealed.
−
1
dropwise to a 5 mol·L NaOH solution, forming micro-
particles of CTS. The microparticles were obtained by
filtering and washing with deionized water until the fil-
trate became neutral. The microparticles were added to
2.5% (m/m) of glutaraldehyde solution in a ratio of 1 g
CTS particles to 1.5 ml glutaraldehyde, and immerged
for 24 h. Hereafter, the resulting microparticles were
washed with deionized water until no glutaraldehyde
remained. A part of microparticles was dried in a freeze
dryer, then mesoporous microparticles(mesp‐CTS) were
obtained. Besides, the other part of microparticles was
dried via vacuum drying at 55 °C to obtain macroporous
microparticles (macp‐CTS).
2
2
| EXPERIMENTAL
.1 | Materials
The chemical reagents used were of analytical grade and
2.4 | Preparation of Fe TCPP/mesp‐CTS
and Fe TCPP/macp‐CTS
were employed without further purification. Chitosan
4
(
Mw ~3.9 × 10 Da, degree of deacetylation was 93%)
In order to mimic the nano‐cavity and CRC function in
cytochrome P‐450 enzyme, mesp‐CTS and macp‐CTS
grafted Fe TCPP were prepared. 0.025 g of Fe TCPP
dissolved in 130 ml of dichloromethane and 2 ml of N,
N‐dimethyl formamide (DMF) were mixed under nitro-
gen atmosphere, and 1 ml of thionyl chloride was added
dropwise into the mixture, and then it was refluxed at
53 °C for 3 h. 25 g of mesp‐CTS and 120 ml of
was purchased from Zhejiang Jinke Biochemistry Co.,
Ltd., Nanning, China.
2.2 | Preparation of Fe TCPP catalysts
6
.25 g of 4‐carboxybenzaldehyde and 180 ml of propionic
acid were mixed with stirring. Upon complete dissolution

HUANG ET AL.
3 of 11
dichloromethane were added and continuously refluxed
for another 1 h. The mixture was cooled down to room
temperature and filtered, the resulting filter‐cake was
washed with dichloromethane. The mesp‐CTS grafted Fe
TCPP (Fe TCPP/mesp‐CTS) was obtained via vacuum
drying at 55 °C for 2 h. The macp‐CTS grafted Fe TCPP
mixture of 200 ml of ethylbenzene, and certain amount
of catalyst was stirred and heated at 135–165 °C. Air was
then continuously pumped into the reaction system, and
the air pressure was maintained at 0.6–0.9 MPa. The flow
rate of air was measured with a rotameter. Samples of the
oxidation mixture were quantified on a GC‐7900 chro-
matograph, using p‐dichlorobenzene as the internal stan-
dard. After the oxidation was stopped, the grafted catalyst
was recovered by simple filtration from reaction mixture.
It was washed with ethanol and was dried in air before
use in subsequent ethylbenzene oxidation reaction.
(Fe TCPP/macp‐CTS) was obtained in the same way.
The amount of Fe TCPP grafted on per gram of mesp‐
CTS and macp‐CTS was 1.00 mg and 0.87 mg, respec-
[
28]
tively, as determined by UV–Vis spectrophotometry
and also by ICP‐AES.
[23]
2
.5 | Characterization of supported
3
| RESULTS AND DISCUSSION
catalyst materials
XRD patterns of mesp‐CTS and Fe TCPP/mesp‐CTS were
obtained using a D/MAX‐2600/PC X‐ray powder diffrac-
tion instrument, equipped with a Cu Ka radiation source.
Thermo analytical TG for the catalyst materials was
recorded on a STA 409 PC/PG Luxx thermoanalyser, the
measurements were carried out using 5 mg samples in
air over the temperature range of 0–550 °C, with a heating
3.1 | Characterization for grafted catalyst
materials
XRD analysis was applied to the cross‐linked mesoporous
chitosan and Fe TCPP/mesp‐CTS. As shown in Figure 1
(
left), after cross‐linking of glutaraldehyde with partial
amino of chitosan, there was one characteristic peak of
o
[29]
the cross‐linked chitosan at about 2θ = 20
. The
−
1
rate of 10 °C min . UV–vis spectra of the immobilized
catalyst in DMF suspension and the unsupported catalyst
in DMF solutions were recorded using a TU‐1810SPC
spectrometer. UV–vis diffuse reflectance spectra (UV‐
DRS) were recorded on a Perkin‐Elmer L–17 spectrome-
ter. Amounts of metalloporphyrins‐grafted on mesp‐ and
macp‐CTS were measured via inductively coupled plasma
atomic emission spectroscopy (ICP‐AES, Spectroflame
model FVMØ3). FT‐IR spectra were recorded on a
Nexus470 IR spectrophotometer in the range of 4000–
XRD patterns of Fe TCPP/mesp‐CTS showed one broad
peak at about 2θ = 20 , which was similar to that of
o
chitosan, indicating that the amorphous structure of
chitosan was unchanged after grafting with Fe TCPP.
However, the characteristic peak of Fe TCPP/mesp‐CTS
was more intense and wider than that of chitosan. This
is probably due to the carboxyl groups of Fe TCPP reacted
with thionyl chloride(SOCl ) to form acyl chloride, which
2
further acylated amino group(NH –) of chitosan, and
2
reduced the amount of amino group(NH –) on chitosan.
−
1
−1
2
4
00 cm at a resolution of 2 cm , using KBr pellets.
This reaction could increase the crystallinity of chitosan.
These results also indicated that Fe TCPP was grafted on
mesp‐CTS.
Figure 1(right) displays TG and DTA curves of Fe
TCPP/mesp‐CTS. It showed that, Fe TCPP/mesp‐CTS lost
SEM images were recorded in a S‐3400 scanning electron
microscope. The specific Brunauer–Emmet–Teller surface
areas (SBET), N2 adsorption/desorption isotherms and
Barrett–Joyner–Halenda (BJH) pore‐size distribution
curves at 77 K by using ultra‐high‐purity grade N2
about 1.9% of its moisture, H O, which was hydrogen‐
2
(99.999%) for the grafted metalloporphyrin materials were
bonded with amino and hydroxyl groups in mesp‐CTS,
from 60 °C to 200 °C, and lost about 4.1% of inter water
in mesp‐CTS after 200 °C, further carbonizing. The above
results demonstrated that Fe TCPP/mesp‐CTS was stable
at 200 °C, which was quite fit to our oxidation conditions
between 130 °C and 165 °C.
measured in liquid nitrogen bath with a TriStar II 3020
instrument. X‐ray photoelectron spectroscopy (XPS) was
performed with an XPS spectrometer(Kratos Ultra Axis
DLD), which was equipped with an Al Karadia‐tion
source at 150 W with pass energy of 40 eV.
Figure 2 (left) is UV–vis spectra of Fe TCPP and Fe
TCPP/mesp‐CTS (Fe TCPP/macp‐CTS). A large Soret
peak of Fe TCPP was observed at 418 nm. After Fe TCPP
was grafted on CTS, two obvious peaks appeared at
413 nm and 429 nm. The saddle‐shaped Soret peak
may be explained by the coordination between iron por-
phyrin complex and amino group in CTS, and the acyla-
tion reaction between Fe TCPP and CTS. The intensity of
2
.6 | Oxidation of ethylbenzene over the
grafted catalyst materials
Fe TCPP/mesp‐CTS, Fe TCPP/macp‐CTS and Fe TCPP
were tested as catalysts for ethylbenzene oxidation reac-
tion. The oxidation reactions were carried out in a WDF‐
0
5 autoclave reactor equipped with a magnetic stirrer. A

4
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HUANG ET AL.
FIGURE 1 XRD patterns of mesp‐CTS (left) and Fe TCPP/mesp‐
CTS, and TG and DTA curves of FeTCPP/mesp‐CTS (right)
FIGURE 2 UV–vis spectra at room temperature: (a) solution of
Fe TCPP, (b) DMF suspension of Fe TCPP/mesp‐CTS (Fe TCPP/
macp‐CTS) (left). UV‐DRS spectra for Fe TCPP/mesp‐CTS and
mesp‐CTS (right)
Soret peaks of Fe TCPP/CTS was much lower than that
of Fe TCPP, which can be ascribed to the small amount
of Fe TCPP grafted on CTS. The results indicated that
Fe TCPP was immobilized on mesp‐ and macp‐CTS via
coordination and acylation. The UV‐DRS spectra for Fe
TCPP/mesp‐ and macp‐CTS were different from those
of Fe TCPP and mesp‐ and macp‐CTS (Figure 2 right),
indicating that Fe TCPP was grafted onto mesp‐ and
macp‐CTS. This is caused by the reaction of the carboxyl
groups in Fe TCPP and the amino groups in mesp‐ and
macp‐CTS.
[
30]
−1
−1
respectively.
Bands at 2870 cm and 2928 cm were
assigned to the stretching vibrations of CH and CH
groups, and bands at 1321 cm was due to the N‐acetyl
2
−
1
[
31]
groups.
After forming the cross‐linked CTS, the origi-
−
1
nal broad band at 3370 cm changed to relatively narrow
−
1
band at 3445 cm , which was due to the decrease of
amount of amino groups and the relative increase of
amount of hydroxyl groups. The bands at about
1654 cm and 1596 cm disappeared and a new band
appeared at 1606 cm due to cross‐linking of chitosan
Figure 3 shows the IR spectra of CTS, cross‐linked
CTS(CL‐CTS), Fe TCPP, and Fe TCPP/mesp‐CTS (Fe
−
1
−1
−
1
−1
TCPP/macp‐CTS). The bands at about 3370 cm and
−
1
−1
3
445 cm in the IR spectra of CTS were assigned to the
with glutaraldehyde. The bands at about 3445 cm and
1698 cm in the IR spectra of Fe TCPP were attributed
[16]
−1
amino groups and hydroxyl groups of CTS.
about 1654 cm and 1596 cm were assigned to the
Bands at
−
1
−1
to hydroxyl and carbonyl groups in the carboxyl groups
of Fe TCPP, respectively. And the band at about
O = C and NH of the O = C‐NH‐ and amino groups,
2

HUANG ET AL.
5 of 11
[
23]
iron ions of Fe TCPP.
These results confirmed that Fe
TCPP was immobilized on mesp‐CTS.
The morphology of mesp‐CTS, macp‐CTS and corre-
sponding grafted Fe TCPP were investigated as shown in
Figure 4. The SEM images of chitosan‐grafted catalyst
material showed that Fe TCPP/mesp‐CTS provided a
mesocavity for mimicking the nano‐cavity in cytochrome
P‐450 enzyme: mesp‐CTS and Fe TCPP/mesp‐CTS
(
Figure 4a and b) exhibited mesoporous structure, with a
pore diameter (BJH adsorption average pore diameter)
of about 47 nm (Figure 4e), and the type of pore were
mostly present in the grafted catalyst. The specific surface
area of Fe TCPP/mesp‐CTS and mesp‐CTS, were found to
2
be about 58 m /g for both of them. However, macp‐CTS
and Fe TCPP/macp‐CTS showed macroporous structure,
the BJH adsorption average pore diameter was about
55.0 nm, and the type of pore were mostly present in the
grafted catalyst (Figure 4f). The specific surface area of
Fe TCPP/macp‐CTS and macp‐CTS, both were found to
2
be about 1.4 m /g. Therefore, Fe TCPP/mesp‐CTS present
the characteristics of mesostructured catalyst material,
which would bettering the catalytic activity of Fe TCPP.
The acylation and coordination of Fe TCPP on mesp‐
CTS(or macp‐CTS) changed electron cloud density of all
elements, especially the Fe and elements(Cl, N) around
it in Fe TCPP. These changes were seen and assigned in
[
33–35]
Figure 5 and in Table 1.
When the amino groups
of mesp‐CTS were acylated by Fe TCPP, and the coordina-
tion of amino groups in mesp‐CTS to Fe TCPP occured,
these reactions could cause the following Binding
Energy(BE) changes: First, the BEs of nitrogen element
3
in the NH1 or 2–Csp unit of CTS increased about 1.6 eV.
This was because the nitrogen atom of amino group
donated its electron lone pair to the iron ion in Fe TCPP,
and on another hand, the carbonyl group of Fe TCPP
attracted the electron lone pair, resulting the increased
1.5 eV of the BEs for the carbon element in the C–C–
NH1 or 2 unit. Second, the coordination of the electron
lone pair of N in amino group of CTS to the iron ion in
Fe TCPP, not only decreased the BEs of Fe ion in the
Fe–N unit about 13.7 (5.9) eV, but also caused the
decrement of 0.9(0.5) eV for the BEs of chlorine element
in the Cl–Fe unit. Third, the BEs of nitrogen elements in
the N–Fe unit have increased about 2.3 eV, which
indicated that the four‐nitrogen‐atom‐combined iron in
Fe TCPP was more stable after immobilization. The
immobilzation also resulted the other changes of BEs for
other elements shown in Table 1. The coordination of
amino groups in mesp‐CTS to Fe TCPP will improve the
catalytic activity and stability of Fe TCPP, and the acyla-
tion of Fe TCPP to mesp‐CTS would benefit to the
coordination and graft‐immobilization of Fe TCPP on
mesp‐CTS.
FIGURE 3 FT‐IR spectra of CTS, cross‐linked‐CTS (CL‐CTS), Fe
TCPP and Fe TCPP/mesp‐CTS (Fe TCPP/macp‐CTS) in the range of
−
1
4
000~400 cm
−
1
9
99 cm was believed to be the characteristic peak of
[32]
Fe–N bond in Fe TCPP.
When Fe TCPP was grafted
on mesp‐CTS to form Fe TCPP/mesp‐CTS, the original
−
1
band at 1606 cm for the amino groups of mesp‐CTS,
−
1
and band at 1698 cm for the carbonyl groups of Fe TCPP,
−
1
both disappeared. Instead, a peak at about 1635 cm for
the carbonyl groups (O = C–NH–) in Fe TCPP/mesp‐CTS
appeared, indicating the acylation of CTS by Fe TCPP.
−
1
Besides, another new peak at 560 cm for Fe TCPP/
mesp‐CTS was observed, which may be caused by the
coordination of N atoms in amino groups of CTS to the

6
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HUANG ET AL.
FIGURE 4 SEM images and pore
diameter distribution of mesp‐CTS (a and
e), Fe TCPP/mesp‐CTS (b and e), Fe
TCPP/macp‐CTS (c and f) and macp‐
CTS(d and f)
3
.2 | Catalysis of Fe TCPP/mesp‐CTS for
slowly increased with increasing pressure from 0.7 MPa
to 0.9 MPa, and the biggest ethylbenzene conversion and
TON were 24.9% and 3.12 × 10 at 0.9 MPa, respectively.
ethylbenzene oxidation with O2
5
The effect of reaction temperature on ethylbenzene oxida-
tion reaction was shown on Figure 6a. When the temper-
ature was below 150 °C, the selectivity of ketone and
alcohol increased with increasing temperature. However,
when the temperature was higher than 150 °C, the selec-
tivity of ketone and alcohol decreased from 72.2% to
However, the selectivity of ketone and alcohol (69.2%)
and yields (16.7%) were the highest at 0.8 MPa. Higher
oxygen pressure means higher initial oxygen concentra-
tion in the oxidation reaction mixture, which accounts
for the increasing ethylbenzene conversion with the
increasing of pressure. However, after a certain oxygen
concentration was reached (0.8 MPa), the ethylbenzene
conversion only increased 0.6% with further increasing
oxygen pressure to 0.9 MPa. The decrease of selectivity
(ketone and alcohol) at 0.9 MPa was because high oxygen
concentration overly oxidized ketone and alcohol into by‐
products. Furthermore, the high oxygen concentration
destroyed a small amount of the metalloporphyrin on
the catalyst surface, resulting in its catalysis decrease.
Based on the above results, the optimal oxygen pressure
for the oxidation was 0.8 MPa.
Figure 6c shows the effect of amount of Fe TCPP used
in Fe TCPP/mesp‐CTS form on its catalytic activity. As
the Fe TCPP amount was 0.75 mg, the selectivity to
ketone and alcohol (74.3%), and yields (18.2%) were the
6
8.3%. The selectivity of ketone and alcohol at 145 °C
was lower than that at 150 °C, but the ethylbenzene con-
5
version (24.2%), TON (3.02 × 10 ), and yields of ketone
and alcohol (16.8%) were the highest than those at other
temperatures. The decrease in ethylbenzene conversion
at 155 °C could be due to the destruction of the part cata-
lyst at higher temperatures, and the reduction in selectiv-
ity at higher temperatures may be attributed to further
[37]
[
36]
oxidation of the ketone and alcohol into by‐products.
Therefore, the optimal reaction temperature was 145 °C.
Pressure has an effect on the catalytic activity of Fe
TCPP/mesp‐CTS, the reaction pressure from 0.7 MPa to
0
.9 MPa was investigated at 145 °C, and the results were
shown in Figure 6b. Ethylbenzene conversion and TON

HUANG ET AL.
7 of 11
FIGURE 5 X‐ray photoelectron spectra and main spectral bands based on the binding energy (BE) of the key elements (Fe, cl, N and C) for
Fe TCPP/mesp‐CTS, mesp‐CTS and Fe TCPP
TABLE 1 Binding energy of key elements in Fe TCPP/mesp‐CTS, Fe TCPP and mesp‐CTS
Binding energy/eV
XPS
spectra
Existential form of
the key elements
Fe TCPP/mesp‐CTS
Fe TCPP
mesp‐CTS
dBE /eV
Fe 2p
Fe–N
710.8
724.5
711.4
––––
––––
−13.7
−5.9
705.5
Cl 2p
N 1 s
Cl–Fe
199.1
200.0
––––
––––
−0.9
N–C = [N = C]
197.9
198.4
398.7
397.2
––––
−0.5
0.9
2.3
1.6
1.0
399.6
N–Fe
NH1 or 2–Csp
N = Csp
399.5
399.3
401.9
––––
397.7
400.9
3
2
––––
C 1 s
C = C
C–C–NH1 or 2
C = O, C–O
285.2
285.1
286.6
284.9
––––
288.9
0.3
1.5
1.7,4.0
283.6
284.9
highest. The ethylbenzene conversion, TON, selectivity
ketone + alcohol), and yields subsequently respectively
decreased, as the Fe TCPP amount continued to increase
from 0.75 to 1.5 mg. The decrease in yields at high amount
of Fe TCPP can be ascribed to that excessive addition of
Fe TCPP may improve interactions between activated
(

8
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HUANG ET AL.
FIGURE 7 Comparison of the catalytic activity of Fe TCPP/
mesp‐CTS with that of Fe TCPP/macp‐CTS for oxidation of
ethylbenzene. Reaction conditions: Ethylbenzene, 200 ml;
temperature, 145 °C; Fe TCPP, 0.75 mg; pressure, 0.8 MPa; air flow,
3
0
.030 m /h; reaction time, 4.0 h (left); situation of Fe TCPP/mesp‐
CTS recovered (right)
intermediates and suppress the formation of ketone and
[
38]
alcohol.
Figure 6d illustrates changes in the ethylbenzene con-
version, TON, selectivity and yields of ketone and alcohol
with reaction time, for the ethylbenzene oxidation over Fe
TCPP/mesp‐CTS under an optimal temperature of 145 °C
and pressure of 0.8 MPa. From 0 to 4 h, the yields
increased with increasing reaction time. From 3.5 to 4 h,
ethylbenzene conversion slightly increased from 21.1%
to 24.2%, and the selectivity (ketone + alcohol) showed
FIGURE 6 Effect of reaction temperature (a), reaction pressure
b), amount of Fe TCPP/mesp‐CTS, and reaction time (d) on
ethylbenzene oxidation catalyzed by Fe TCPP/mesp‐CTS. Reaction
(
69.1% at 4 h. According to the previous study, CTS could
be destroyed with the increasing of reaction time at a high
temperature, and Fe TCPP would be not protected by CTS
conditions: (a) ethylbenzene, 200 ml; pressure, 0.8 MPa; Fe TCPP,
3
0
2
.75 mg; air flow, 0.03 m /h; rxn time, 4.0 h. (b) Ethylbenzene,
[
15,18]
3
00 ml; temperature, 145 °C; Fe TCPP, 0.75 mg; air flow, 0.03 m /h;
and was easily destroyed by oxidant.
This would
rxn time, 4.0 h. (c) Ethylbenzene, 200 ml; temperature, 145 °C;
reduce the reuse times of Fe TCPP/mesp‐CTS and
decrease the catalysis for the ethylbenzene oxidation. So,
the 4‐h reaction time was chosen as the best time for eth-
ylbenzene oxidation reaction.
3
pressure, 0.8 MPa; air flow, 0.03 m /h; rxn time, 4.0 h. (d)
Ethylbenzene, 200 ml; temperature, 145 °C;pressure, 0.8 MPa; Fe
3
TCPP, 0.75 mg; air flow, 0.03 m /h

HUANG ET AL.
9 of 11
3
.3 | Comparison of the catalytic activity
improve the catalytic activity of Fe TCPP for hydrocarbon
oxidation.
of Fe TCPP/mesp‐CTS with Fe TCPP/macp‐
CTS etc.
ST
According to Table 2, the 1 ‐run‐obtained conversion
and the average conversion (22.8%) and yields of ketone‐
alcohol (15.5%) were still higher than those values
(21.5% and 15.0%) of Fe TCPP/macp‐CTS after 5 cycles.
Secondly, when mesp‐CTS was used as catalyst or no cat-
alyst was used, the conversion of ethylbenzene and the
yields (ketone + alcohol) were lower than 4.1% and
3.5%, respectively, and these results were attributed to
the auto‐oxidation of ethylbenzene. Under the same reac-
tion conditions, using the Fe TCPP/mesp‐CTS as catalyst
for the first run (Table 2), the catalytic power for Fe
TCPP/mesp‐CTS was almost the same as that of Fe TCPP.
This result indicated that the catalytic activity of Fe TCPP
was maintained. However, when Fe TCPP was ligated on
the mesp‐CTS, the CRC would work. During the catalytic
oxidation process, the surface of Fe TCPP/mesp‐CTS was
scorched. Therefore, a very small part of Fe TCPP was lost
in the recovered process, resulting in the decrease of
recovered amount of iron porphyrin (Figure 7 right).
However, the TON had increased more than 5 times when
To compare the catalysis of Fe TCPP/mesp‐CTS with Fe
TCPP/macp‐CTS for the oxidation of ethylbenzene,
the changes in ethylbenzene conversion and yields
(ketone + alcohol) with reaction time were shown in
Figure 7 (left). The increasing rate of ethylbenzene con-
version and yields (ketone + alcohol) obtained from Fe
TCPP/mesp‐CTS were 6.1%/h and 4.6%/h, respectively,
which were higher than those from Fe TCPP/macp‐CTS.
These differences were partly due to considerable differ-
ences in the specific surface area between Fe TCPP/
mesp‐CTS and Fe TCPP/macp‐CTS. The catalytic activity
of Fe TCPP/mesp‐CTS could increase with the increment
of surface area. The larger the surface area, the more there
were the sites for activating molecular oxygen, thus more
ethylbenzene could be oxidized. Except for the
mesocavity, there still was the especial CRC function in
mesp‐CTS‐grafted iron porphyrin, which was similar to
that in cytochrome P‐450 enzyme. The function could
TABLE 2 Catalytic activity of reused Fe TCPP/mesp‐CTS, Fe TCPP/macp‐CTS and Fe TCPP
5
Catalysts
Run
Conversion/%
Selectivity/%
Ton/(×10 )
Yields/%
Fe TCPP/mesp‐CTS
1
2
3
4
5
24.4
21.5
24.1
22.1
21.7
22.8
74.3
66.1
69.4
65.2
64.6
67.9
4.0
4.6
7.3
10.1
22.7
9.7
18.2
14.2
16.7
14.4
14.0
15.5
Av.
CTS or no catalyst
Fe TCPP
1
1
1
<4.1
24.0
21.5
<84.8
73.8
‐
<3.5
18.4
15.0
3.1
Fe TCPP/macp‐CTS
69.6
2.8
3
Reaction conditions: ethylbenzene, 200 ml; temperature, 145 °C; Fe TCPP, 0.75 mg; pressure, 0.8 MPa; air flow, 0.030 m /h; reaction time, 4.0 h.
SCHEME 1 Plausible mechanism of
ethylbenzene oxidation over Fe TCPP/
mesp‐CTS

10 of 11
HUANG ET AL.
st
th
the grafted catalyst was reused from 1 to 5 run. The
mimic the nano‐cavity and coordinate regulation‐catalysis
function of cytochrome P‐450 enzyme.
5
average values of TON (22.7 × 10 ) was more than 3 times
5
5
of those (3.1 × 10 and 2.8 × 10 ) for the Fe TCPP and Fe
TCPP/macp‐CTS catalysts. The results are attributed to
the above coordination and mesocavity, which resulted
in the above stability and activation of Fe TCPP, which
has some reason as following.
ACKNOWLEDGEMENTS
This research was supported by the National Natural
Science Foundation of China (No: 51363001), the Guangxi
Natural Science Foundation (2014GXNSFDA118009), the
Guangxi Scientific and Technological Project (12118008‐
12‐3) and the Experimental Innovation Project Founda-
tion of Guangxi University, PR China(201510593308).
Lyons proposed a hypothetical catalytic mechanism of
hydrocarbon oxidation over iron porphyrin, which was
[
39]
similar to that of the P‐450 enzyme.
previous studies,
According to the
[
23,40,41]
it is believed that the catalytic
mechanism for hydrocarbon oxidation over the supported
M TCPP are similar to that of M TCPP:
ORCID
With the negative dBEs of Fe and Cl ion, the repulsive
Coulomb force between elements of like charge between
Guan Huang http://orcid.org/0000-0002-3746-0110
III
the Fe ion and the chloride ion of ClFe TCPP/mesp‐
III
CTS was bigger than that of ClFe TCPP. Therefore, chlo-
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