Metalloporphyrins immobilized on core-shell CeO2@SiO2 nanoparticles prepared by a double-coating method for oxidation of diphenyl methane

Article abstract of DOI:10.1016/j.apcata.2011.10.040

Metalloporphyrins immobilized on CeO₂@SiO₂ core-shell nanoparticles were synthesized by a double-coating method and used for catalytic oxidation of diphenyl methane. A variety of characterization techniques including FT-IR, UV-vis, SEM, TEM, XRD, N₂ adsorption-desorption and TGA were employed. The results show that the catalyst consists of regular nanoparticles (around 400 nm) with core-shell structure and metalloporphyrins were immobilized on CeO₂@SiO₂ core-shell nanoparticles via amide bonds. Moreover, these new developed catalysts for solvent-free selective oxidation of diphenyl methane exhibited an excellent catalytic activity, selectivity and stability. Furthermore, these catalysts could be reused 6 times without significant loss of their catalytic activity and the used catalysts maintained nearly the same physicochemical properties as the fresh.

Full text of DOI:10.1016/j.apcata.2011.10.040

Applied Catalysis A: General 413–414 (2012) 30–35
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Metalloporphyrins immobilized on core–shell CeO @SiO nanoparticles prepared
2
2
by a double-coating method for oxidation of diphenyl methane
∗
Xiang Guo, Yuan-Yuan Li, Dan-Hua Shen, Jie Gan, Mi Tian, Zhi-Gang Liu
School of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Metalloporphyrins immobilized on CeO @SiO core–shell nanoparticles were synthesized by a double-
2
2
Received 4 September 2011
Received in revised form 21 October 2011
Accepted 26 October 2011
Available online 3 November 2011
coating method and used for catalytic oxidation of diphenyl methane. A variety of characterization
techniques including FT-IR, UV–vis, SEM, TEM, XRD, N2 adsorption–desorption and TGA were employed.
The results show that the catalyst consists of regular nanoparticles (around 400 nm) with core–shell struc-
ture and metalloporphyrins were immobilized on CeO2@SiO2 core–shell nanoparticles via amide bonds.
Moreover, these new developed catalysts for solvent-free selective oxidation of diphenyl methane exhib-
ited an excellent catalytic activity, selectivity and stability. Furthermore, these catalysts could be reused
Keywords:
Metalloporphyrin
Silica
Ceria
Core–shell
Immobilization
6
times without significant loss of their catalytic activity and the used catalysts maintained nearly the
same physicochemical properties as the fresh.
© 2011 Elsevier B.V. All rights reserved.
1
. Introduction
electrostatic repulsion occurred between the surface of the CeO2
precursor and SiO , and agglomeration of SiO2 and CeO2 particles
2
Metalloporphyrins have attracted much interest because of
observed would be ascribed to that repulsion. The surface modi-
fiers such as oxalic acid and hexamethylenetetramine were used to
adjust the electronic properties of the surface in CeO2 in order to
solve this problem [16,17]. Because of the electrostatic affinity, the
CeO precursor nanoparticle was coated with SiO , and SiO -coated
CeO2 nanoparticles were obtained.
As illustrated in Scheme 1, we make use of the CeO2 sol
modified by sodium citrate and the double-coating method to
their recognized catalytic activity employed in the oxidation of
hydrocarbons [1–3]. However, unsupported metalloporphyrins are
easily degraded and difficult to reuse, which limits their practi-
cal application in actual industrial processes. Much attention has
been paid to solid supported metalloporphyrins not only because
of their increased stability and selectivity but also their ability to
be recovered from reaction media and reused [4–7].
2
2
2
Generally, inorganic supports are preferred versus organic sup-
ports because they are more robust and more efficient in preventing
catalyst deactivation caused by dimerization, e.g. formation of ␮-
achieve CeO @SiO2 core–shell nanoparticles. Metalloporphyrins
2
were immobilized, via amide bonds, on CeO @SiO2 core–shell
2
nanoparticles. The oxidation of diphenyl methane to diphenyl
ketone was used as the probing reaction. Variety of character-
ization techniques including FT-IR, UV–vis, SEM, TEM, XRD, N2
adsorption–desorption and TGA were applied. As expected, the
mixing of ceria has a beneficial influence on the catalytic perfor-
mance, which has been generally attributed to the cooperative
effect among metalloporphyrins, silica and ceria. The results show
the superior ability to immobilize the metalloporphyrins onto
oxo dimmers [8,9]. The CeO @SiO2 has been found to be very
2
suitable inorganic support for metalloporphyrins because CeO2 is
well known to store and release oxygen via forming surface and
bulk vacancies [10,11]. In addition, CeO can be used as a promoter
2
in combination with other elements to give mixed-oxide forma-
tion. On the other hand, SiO2 allows for ease of modification and
immobilization of the metalloporphyrins onto its surface [12–15].
However, the charge between the precursor of CeO2 and silica
are contrast, which cause the bulk precipitation of CeO2 or silica
CeO @SiO2 core–shell nanoparticles.
2
during the coating procedure [16]. For example, when NH OH was
used as the particle-forming agent, the surface charge of the CeO2
precursor nanoparticle was negative [17]. It was considered that
4
2. Experimental
2.1. Materials
5
-(4-Carboxyphenyl)-10,15,20-triphenyl porphyrin (TMCPP)
∗ Corresponding author. Tel.: +86 731 88821314; fax: +86 731 88821667.
E-mail addresses: liuzhigang@hnu.edu.cn, cerialiu@gmail.com (Z.-G. Liu).
was synthesized and purified in our laboratory. The metal oxides
used in this work were prepared by coprecipitation method from
0
926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.10.040

X. Guo et al. / Applied Catalysis A: General 413–414 (2012) 30–35
31
Scheme 1. Preparation of CoTMCPP grafted on CeO2@SiO2 nanoparticles.
corresponding metal nitrates. Water used in all the experiments
was deionized and doubly distilled. 4-Carboxy benzaldehyde,
benzaldehyde and pyrrole were redistilled before use. All other
reagents were obtained commercially and used without further
purification.
well dispersed in a mixture of ethanol (120 mL), deionized water
(160 mL) and concentrated ammonia aqueous solution (2.0 mL,
28 wt.%) in a three-neck flask, with stirring for 0.5 h. Then tetraethyl
orthosilicate (TEOS, 1.0 mL) and 3-aminopropyltriethoxysilane
(APTES, 0.2 mL) were added into the mixture. After stirring for
6
h at room temperature, the product was filtered, washed with
2.2. Synthesis of catalysts
ethanol and water and dried. With the soxhlet extraction device
extracting the product for 48 h, CeO @SiO2 nanoparticles with
2
2
5
.2.1. Synthesis of cobalt (II)
-(4-carboxyphenyl)-10,15,20-triphenyl porphyrin (CoTMCPP)
CoTMCPP was synthesized according to literature [18]. 200 mL
core–shell structures were gained, which were briefly named S1
with the specific surface area 498.6 m /g. Likely, we synthesized
SiO2 nanoparticles and denoted as S2.
2
of propanoic acid, 1.51 g of benzaldehyde and 2.08 g of 4-carboxy
benzaldehyde were added into a three-neck flask and refluxed
under stirring, and then 1.36 g of pyrrole was dropped through a
funnel. The mixture was kept refluxing for 30 min under stirring.
The product was cooled overnight, filtered, washed with water, and
then purified. 5-(4-Carboxyphenyl)-10,15,20-triphenyl porphyrin
was obtained. 0.50 g of the obtained porphyrin was dissolved in
2
.5. Synthesis of CoTMCPP immobilized on CeO @SiO catalysts
2 2
0
.05 g of CoTMCPP, 3.50 g of CeO @SiO2 nanoparticles (S ) and
2 1
1
00 mL of N,N-dimethylformamide (DMF) were loaded into a three-
neck flask, then heated to reflux for 12 h. 70 mL of DMF was distilled,
and then the product was washed with 70 mL of deionized water
and filtered, finally extracted with dichloromethane as solvent in
a soxhlet extractor till no color in the extracted solution. After
dried at 90 C overnight, the CoTMCPP supported on CeO @SiO
catalyst was obtained. The product was denoted as S –IM–Co. The
1
00 mL of N,N-dimethylformamide (DMF), and after the addition
2
.54 g of CoCl ·6H O, the mixture was heated to reflux under stir-
2
2
ring until the porphyrin was exhausted. After cooling overnight, the
solution was filtered and washed repeatedly with hot water, and
the product was achieved.
◦
2
2
1
2
specific surface area of S –IM–Co was 236.7 m /g and CoTMCPP
1
loading in S –IM–Co is 11.4 mg/g-cat. According to the similar pro-
1
2.3. Preparation of modified CeO2 nanoparticles
cess, FeTMCPP and MnTMCPP were immobilized on CeO @SiO2
2
nanoparticles (S ), and the products was denoted as S –IM–Fe
1
1
Surface modified CeO was synthesized, according to literatures
2
and S –IM–Mn with metalloporphyrin loadings of 11.7 mg/g-cat
1
[
19,20]. 5.996 g of Ce(NO ) ·6H O was added into a flask and dis-
3
3
2
and 12.3 mg/g-cat, respectively. Furthermore, CoTMCPP supported
on SiO2 nanoparticles was achieved with the similar method, and
solved in 250 ml of deionized water. Under stirring, NaOH solution
was slowly dropped into Ce(NO3)3 solutions until the pH value
of the precipitation almost reached 13. After stirring for 30 min,
the precipitate was filtered and washed with deionized water for 2
times and then dispersed in 200 ml 0.3 mol/L of sodium citrate solu-
designated as S –IM–Co with corresponding CoTMCPP loading of
2
1
0.1 mg/g-cat.
◦
tion. After stirring at 90 C for 6 h, the product was filtered, washed
2.6. Catalysts characterization
with ethanol and water respectively and dried. The modified CeO2
was achieved.
UV–vis patterns were recorded on
a Shimadzu UV-2450
spectrophotometer using BaSO4 as reference with a range of
200–800 nm and a scan step of 0.5 nm. FT-IR spectra were mea-
sured on an Agilent Perkin-Elmer 783 infrared spectrometer in KBr
disc. The specific surface areas of samples were determined by ana-
2
.4. Synthesis of core–shell CeO @SiO2 nanoparticles
2
0.30 g of CeO2 was well dispersed in the mixture of ethanol
◦
(
160 mL), deionized water (40 mL) and concentrated ammonia
lyzing the results of N2 adsorption at −196 C in a Micromeritics
aqueous solution (5.0 mL, 28 wt.%), under stirring for 0.5 h at ambi-
ent temperature. Then tetraethyl orthosilicate (TEOS, 0.5 mL) was
added into the mixture. After stirring for 6 h at room temperature,
the product was filtered, washed with ethanol and water, and then
dried. The single coated CeO @SiO2 core–shell nanoparticles were
obtained. 0.2 g of the single coated CeO @SiO core–shell nanopar-
ASAP2020 apparatus and applying the Brunaumer–Emmett–Teller
(BET) method to the experimental values. All samples were dehy-
◦
drated at 150 C for 24 h prior to N2 adsorption. SEM (JSM 6700F)
was used to observe the particle size and shape of samples. Prior to
the measurements, the samples were mounted on a carrier made
from glassy carbon and coated with a film of gold. TEM (Hitachi 800,
operated at 175 kV) images were obtained by dispersing samples
2
2
2
ticles and 0.6 g of hexadecyl trimethyl ammonium bromide were

3
2
X. Guo et al. / Applied Catalysis A: General 413–414 (2012) 30–35
4
28nm
S -IM-Co
1
S -IM-Fe
1
5
41nm
4
08nm
S -IM-Mn
1
1
660 1530
476nm
1
071
4000
3500
3000
2500
2000
1500
1000
500
300
400
500
600
700
-
1
Wavenumber(cm )
Wavelength (nm)
Fig. 1. FT-IR spectra patterns of S1–IM–Co, S1–IM–Fe and S1–IM–Mn.
Fig. 2. UV–vis spectra of catalysts.
3
.2. UV–vis
in ethanol using an ultrasonication bath and then depositing a drop
of liquid containing the particles into a copper grid. TGA patterns
were gained by NETZSCH STA-449C-Thermo Gravimetric Analyzer
in air.
The characteristic UV–vis spectra provided consistent evidence
for the presence of grafted metalloporphyrin complexes in the
catalysts. The solid UV–vis spectra of S –IM–Co, S –IM–Fe and
1
1
S1–IM–Mn, shown in Fig. 2, exhibited Soret band at 428 nm, 409 nm
and 469 nm, respectively [23,24]. This is similar to those of the start-
ing Co(II) porphyrin, Fe(II) porphyrin and Mn(III) porphyrin, which
2.7. Catalytic activity measurements
indicates the existence of metalloporphyrins in the CeO @SiO2
2
The catalytic activity was measured in a 100 ml four-neck flask
nanospheres and that the porphyrin rings were not significantly
affected by anchoring it to the support. A slight blueshift in the Soret
bands was observed for the solid metalloporphyrin nanospheres
compared to the metalloporphyrins in the solution. This can be
for solvent-free oxidation of diphenyl methane with a magnetic
stirrer. In a typical oxidation reaction, 30 mL of diphenyl methane
and 100 mg catalysts were loaded into the glass reactor. The reactor
was sealed and bubbled with O2 at a rate of 200 mL/min. The reac-
tor was then heated to desired reaction temperature under stirring.
Each time, 0.5 mL of sample was taken out with a syringe and ana-
lyzed by gas chromatography with internal standard method using
chlorobenzene as reference substance. After each experiment, the
reaction mixture was cooled to room temperature and the catalyst
was separated from it by simple filtration, washed with methanol
explained by the interactions of the porphyrin with CeO @SiO2
2
nanospheres [18]. When the TMCPP was functionalized onto the
CeO @SiO2 nanosphere surface, interactions of the TMCPP with
2
their chemical environment changed the symmetry of the por-
phyrin [15,18]. Evidence of this appeared as the shifts of the
adsorption bands toward higher energy.
◦
and dried at 80 C for 12 h. The recovered catalysts were used to
determine the reusability and stability of the catalyst.
3.3. SEM and TEM
The surface morphology of CeO @SiO2 and S –IM–Co was
2
1
3
. Results and discussion
obtained by SEM and shown in Fig. 3(a) and (b). The SEM images
of the CeO @SiO2 nanospheres show uniformity and spherical
2
3.1. FT-IR
morphology with an average diameter of catalyst 400 nm. Com-
pared with CeO @SiO , the nanoparticle size of S –IM–Co has been
2
2
1
In order to obtain information about the chemical environ-
changed little during the immobilization of CoTMCPP.
ment of metalloporphyrins, FT-IR spectra patterns of S –IM–Co,
Fig. 3(c) and (d) display the TEM micrographs of CeO2@SiO2
and S1–IM–Co, respectively. The core–shell structure of CeO2@SiO2
nanoparticles is clearly exhibited and it can be found the coating
of CeO2 by the spherical silica shell. There are two factors to deter-
mine the formation of core–shell structure: one is the affinity of
both surface charge of CeO2 and that of SiO2 [16,17]; second is
the loading of CeO2 should be lower than a critical value of 25%
[16,17]. In this study, the concentration of CeO2 in the CeO2@SiO2
core–shell nanoparticles is 30%, a little higher than 25%. In addition,
as for the preparation of CeO2@SiO2, CeO2 was coated first using a
small amount of SiO2, and then the obtained product, which might
not have been coated to form the core–shell structure, was coated
once again using SiO2 by the double-coating method. Obviously, the
double-coating method is beneficial to increase the ratio of CeO2 in
CeO2@SiO2.
1
S –IM–Fe and S –IM–Mn are depicted in Fig. 1. The broad
1
1
−
1
resonances observed in the range of 3000–3500 cm
and
−
1
9
00–1300 cm are characteristic of the silica [21,6]. The absorp-
−1
tion peak observed at 1071 cm is ascribed to stretching vibrations
of Si–O–Si in silica [21,6]. When metalloporphyrins were anchored
on CeO @SiO , a new absorption peak appears at 1660 cm due
−
1
2
2
to the C O group in amide (N–C O) [22]. In addition, a weak reso-
−1
nance peak is observed at 1530 cm which corresponds to the N–H
group in the surface of silica [22]. It demonstrates that a covalent
linkage between the support and TMCPP is present. This verifies
that metalloporphyrins have been immobilized in CeO @SiO2 via
2
an amide bond. From Fig. 1, it can also be found that the spectra
are nearly the same even though the coordinated metal ions are
different.

X. Guo et al. / Applied Catalysis A: General 413–414 (2012) 30–35
33
Fig. 3. SEM of (a) CeO2@SiO2; (b) S1–IM–Co and TEM of (c) CeO2@SiO2 and (d) S1–IM–Co.
3.4. XRD
3.5. TGA
In Fig. 4, for S –IM–Co the distinct diffraction peaks of CeO2 are
observed at 28.5, 33.0 and 47.4, respectively [25]. This result indi-
Thermal stabilities of the nanospheres have been determined by
using thermo gravimetric analysis (TGA). Seen from Fig. 5, the TGA
curve presents us the information that supported and unsupported
CoTMCPP were heat-treated in air at the temperature range from
1
cates that the CeO2 in CeO @SiO2 composite particles is in cubic
2
fluorite structure. No SiO2 peak is observed in the pattern of the
CeO @SiO composite particles, which is likely due to the amor-
◦
◦
room temperature to 520 C with a heating rate of 10 C/min.
In Fig. 5, the decomposition of CoTMCPP was observed at about
2
2
phous nature of the SiO particles [17]. No new phases are detected,
2
◦
◦
which demonstrate that CeO2 and SiO2 are independent phases in
the composite particles. Low-angle X-ray diffraction profiles of the
materials are also present. There is a peak at 3.4, which indicates
non-existence of silica mesopores. Herein, there must be microp-
ores in the silica shell of CeO @SiO .
180 C. As the temperature reached 380 C, the decomposition of
◦
CoTMCPP become rapid. At about 475 C, CoTMCPP was burned
absolutely under air atmosphere. Weight losses at 180–380 C
and 360–475 C for CoTMCPP were assigned to loss of carbonyl
◦
◦
and phenyl groups from porphyrin, respectively [26]. However,
2
2
100
S -IM-Co
1
8
6
4
2
0
0
0
0
0
CoTMCPP
100
200
300
400
500
1
0
20
30
40
50
Temperature (°C)
2
θ (degree)
Fig. 5. Thermal analysis (TGA) curves of S1–IM–Co and CoTMCPP in air with heating
◦
Fig. 4. XRD patterns of CeO2 and S1–IM–Co.
rate of 10 C/min.

3
4
X. Guo et al. / Applied Catalysis A: General 413–414 (2012) 30–35
7
6
5
4
3
0
0
0
0
0
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
Blank
S1-IM-Co
S1-IM-Fe
S1-IM-Mn
CoTMCPP
S -IM-Co
1
20
10
0
0
5
10
15
20
25
0
5
10
15
20
25
Time (h)
Time (h)
Fig. 6. Influence of different reaction systems on the oxidation of diphenylmethane.
Fig. 7. Influence of coordinated metals in TMCPP on the catalytic performance of cat-
Reaction conditions: catalyst 100 mg, diphenylmethane 30 ml, flow rate of O2
alysts for the oxidation of diphenyl methane. Reaction conditions: catalyst 100 mg,
◦
2
00 ml/min, temperature 130 C and pressure 1 atm.
◦
diphenylmethane 30 ml, flow rate of O2 200 ml/min, temperature 130 C and pres-
sure 1 atm.
S1–IM–Co shows somewhat different decomposition behavior due
to covalent interactions between TMCPP and CeO @SiO . It is found
Fig.
7 presents a similar trend for the conversion of
2
2
diphenyl methane over the catalysts at the temperature of
that the decomposition temperature of S –IM–Co begins at about
1
◦
1
30 C, despite the difference of the coordinated metals. More-
◦
4
00 C slowly, which is far lower than the decomposition tem-
over, the activities of these catalysts decrease as following:
S –IM–Co < S –IM–Fe < S –IM–Mn. All these indicate that the met-
als coordinated to TMCPP plays a small role in the catalytic
performance of the immobilized catalysts.
perature of CoTMCPP. This indicates that these nanospheres are
◦
1
1
1
thermally stable up to nearly 400 C, exhibiting relatively high
thermo stability.
Fig. 8 shows the conversions of diphenyl methane over CeO2,
3.6. Catalytic performance
S , S –IM–Co and S –IM–Co, respectively. It can be seen that the
1
1
2
immobilization of metalloporphyrins enhances the activity of the
catalysts. Both S –IM–Co and S –IM–Co have a higher conver-
A lot of research has been devoted to understanding the
1
2
metalloporphyrin–support interaction in order to tailor the inter-
action for optimum catalysis [27]. By using nanochemistry
techniques, metalloporphyrin can be anchored onto the surface of
CeO @SiO [8,9]. The anchored metalloporphyrins are expected to
sion of diphenyl methane than those of CeO2 and S . Moreover,
1
S1–IM–Co, the core–shell catalyst, possesses a higher activity than
that of S –IM–Co. Because of the addition of CeO , the catalytic
2
2
2
2
activity is improved. Herein, according to the above, we deduce
that there must be the cooperative effect between CeO2 and met-
alloporphyrins, even including the silica shell. But the coordinated
metals may have a small influence on the catalytic performance of
S1–IM–Co for oxidation of diphenyl methane.
Generally, an efficient catalyst requires key features such as
protection against oxidative deactivation due to the rapid self-
oxidation and easy recyclability of the catalyst [28]. Immobilization
of metalloporphyrins onto a suitable support has been suggested
interact with CeO @SiO to create a unique microenvironment giv-
2
2
ing high activity and excellent selectivity for the diphenyl methane
oxidation reaction.
The catalytic performance of CoTMCPP, S –IM–Co and blank for
1
◦
oxidation of diphenyl methane is shown in Fig. 6. At 130 C, bub-
bling with 200 mL/min O , the conversion of diphenyl methane
2
over S –IM–Co is a little higher than those of both CoTMCPP and
1
blank (i.e. autocatalysis system) at the reaction time of 24 h, namely,
the conversions over S –IM–Co, CoTMCPP and blank are 65%, 45%
1
and 13%, respectively. And as shown in Table 1, the selectivity to
7
6
5
4
3
2
0
0
0
0
0
0
diphenyl ketone over S –IM–Co is as high as about 96%. This can
1
CeO2
be explained that as for S –IM–Co, the support provides a special
1
S1
microenvironment to achieve a higher activity and excellent selec-
tivity to diphenyl ketone, compared with CoTMCPP and blank (i.e.
the autocatalysis system without catalysts).
S -IM-Co
2
S -IM-Co
1
Table 1
selecetivity for oxidation of diphenylmethane over different catalysts.a
Reaction time (h)
SCoTMCPP (%)
SS1–IM–Co (%)
Sblank (%)
0
1
2
4
6
8
0
2
4
.5
93.6
94.13
95.46
95.78
95.56
96.12
96.45
95.3
96.31
96.87
97.45
98.24
97.22
96.98
97.17
98.12
97.69
93.75
96.48
95.87
96.17
97.23
96.35
95.42
96.58
10
0
0
5
10
15
20
1
2
2
Time (h)
95.64
96.17
Fig. 8. Comparison of the catalytic performance of different catalysts for the oxida-
a
Reaction conditions: catalyst 100 mg, diphenylmethane 30 ml, flow rate of O2
tion of diphenyl methane. Reaction conditions: catalyst 100 mg, diphenyl methane
◦
◦
2
00 ml/min, temperature 130 C and pressure 1 atm.
30 ml, flow of O2 200 ml/min, temperature 130 C and pressure 1 atm.

X. Guo et al. / Applied Catalysis A: General 413–414 (2012) 30–35
35
1
9
9
9
9
9
00
8
effectively and effortlessly recovered, can retain their high catalytic
activities after being recycled six times.
3
3
3
3
3
6.4
5.0
3.6
2.2
0.8
Acknowledgments
6
The authors gratefully acknowledge the financial support from
Hunan Province Natural Science Foundation of China (No. 10JJ4008)
and the Fundamental Research Funds for the Central Universities.
4
Conversion of diphenylmethane
Selectivity to diphenyl ketone
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[
[
tigated the reusability of S –IM–Co for the oxidation of diphenyl
1
◦
methane at the reaction temperature of 130 C and the reaction
time of 8 h. From Fig. 9, it can be clearly observed that S –IM–Co,
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1
which was reused up to six times, still shows high catalytic activity
and selectivity. The conversion of diphenyl methane and selectivity
[
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6
◦
to diphenyl ketone stayed at 33.6% and 96% at 130 C, respectively.
[
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In addition, the UV–vis pattern of the reused catalyst does not show
any change compared to the fresh (shown as Fig. 2), indicating lit-
tle leaching or destruction of the metalloporphyrins grafted on the
support during reaction.
[
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4
. Conclusion
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In summary, the core–shell CeO @SiO2 has formed by a
2
[
double-coating method. Metalloporphyrins are immobilized on the
CeO @SiO via amide bonds. S –IM–Co has a beneficial influence
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2
2
1
(
1999) 7890–7901.
on the improvement of the catalytic performance, which has been
generally attributed to the cooperative effect among active centers,
[
[
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ceria and the microenvironment provided by silica shell. The con-
◦
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version of diphenylmethane over S –IM–Co is about 80% at 150 C
1
with the selectivity to diphenyl ketone of about 93% when the reac-
tion is running for 24 h. Moreover, these catalysts, which can be
[
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