Synthesis and catalytic behavior of tetrakis(4-carboxyphenyl) porphyrin-periodic mesoporous organosilica

Article abstract of DOI:10.1039/c0jm02591g

The periodic mesoporous organosilica having the tetrakis(4-carboxyphenyl) porphyrin (TCPP) unit was successfully synthesized by the direct co-condensation method using microwave with the corresponding tetra-silane. The tetra-silane precursor, TCPP-silsesquioxane was prepared through the reaction of TCPP with the APTES(3-Aminopropyltrietoxysilane). And TCPP-PMOs were synthesized with sodium metasilicate as a silica source and P123 (EO20PO70EO20) as a supramolecular template at 100 °C. The TCPP-PMO-n (n = 2.5 and 5.0, n refers to the molar percentage of TCPP precursor per silica) materials had >400 m² g^-1 of specific surface areas with ～8.7 nm of pore diameter. TCPP-PMOs were illustrated to give superiority in the organocatalytic hydrogen transfer reactions of various ketones such as acetophenone, cyclohexanone and pinacolone as well as good activity in the photocatalytic degradation of methylene blue (MB) without metal incorporation. Fe-TCPP-PMO prepared by ion-exchange method gave also good activity and selectivity in the oxidation of cyclohexene. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0jm02591g

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Synthesis and catalytic behavior of tetrakis(4-carboxyphenyl)
porphyrin-periodic mesoporous organosilica
Eun-Young Jeong, Abhishek Burri, Seung-Yeop Lee and Sang-Eon Park*
Received 9th August 2010, Accepted 8th September 2010
DOI: 10.1039/c0jm02591g
The periodic mesoporous organosilica having the tetrakis(4-carboxyphenyl)porphyrin (TCPP) unit was
successfully synthesized by the direct co-condensation method using microwave with the corresponding
tetra-silane. The tetra-silane precursor, TCPP-silsesquioxane was prepared through the reaction of
TCPP with the APTES(3-Aminopropyltrietoxysilane). And TCPP-PMOs were synthesized with
sodium metasilicate as a silica source and P123 (EO20PO70EO20) as a supramolecular template at 100
ꢀ
C. The TCPP-PMO-n (n ¼ 2.5 and 5.0, n refers to the molar percentage of TCPP precursor per silica)
2
ꢁ1
materials had >400 m g of specific surface areas with ꢂ8.7 nm of pore diameter. TCPP-PMOs were
illustrated to give superiority in the organocatalytic hydrogen transfer reactions of various ketones such
as acetophenone, cyclohexanone and pinacolone as well as good activity in the photocatalytic
degradation of methylene blue (MB) without metal incorporation. Fe-TCPP-PMO prepared by ion-
exchange method gave also good activity and selectivity in the oxidation of cyclohexene.
10–13
1
. Introduction
totally by using bridged organosilanes alone.
Some of PMOs
have random or partial organo groups on the wall, which are
usually synthesized using both bridged organo silanes together
14
Organic–inorganic hybrid materials with periodic mesoporosity
have attracted much attention in recent years, owing to their
symbiotic properties, which make it quite possible to use them in
applications such as separation, photonics, nanoelectronics, drug
with silica sources (PMO-II) (Scheme 1).
As the bridging organic moieties, short aliphatic chain-like
7
methane, ethane, and ethylene, aromatic groups of phenylene,
1–4
delivery, and heterogeneous catalysis. Mesoporous organic–
inorganic hybrid materials can be synthesized by incorporating
organo functionalities using three different methods. The first is
called grafting or the post synthetic method, which is formed by
the subsequent anchoring of organic silanes onto a silica matrix.
The other co-condensation method involves the self-assembly of
inorganic silica precursors and organosilanes in one-pot. And the
third is the unique attachment of organic functions to the sili-
ceous wall by using organic bridged alkoxysilane precursors
entirely or partially with silica source, which are named as peri-
odic mesoporous organosilicas (PMOs).
biphenylene, and xylene have been used mostly in the form of
disilanes. However, organosilane precursors in the form of tri-
15,16
silanes and tetrasilanes were rarely used.
An ethane-isocyanurate bridged PMO was synthesized simply
by using tris[3-(trimethoxysilyl)propyl]isocyanurate and 1,2-
bis(triethoxysilyl)ethane in the presence of a triblock copolymer
11
by Jaroniec and his coworkers. Park et al. prepared melamine-
bridged PMOs with high reproducibility by co-condensation
2
using N ,N ,N -tris(3-(triethoxysilyl) propyl)-1,3,5-triazine-
4
6
2,4,6-triamine (TBTS) and sodium metasilicate in the presence of
17
P123 (P123, EO20PO70EO20) at a highly acidic concentration.
Periodic mesoporous organosilicas (PMOs) are a special type
of ordered mesoporous silica in which organic moieties are
integrated onto the silica framework entirely or randomly to
form hybrid organic–inorganic materials. The most important
feature of PMOs are that they can incorporate various organo
functionalities into inorganic frameworks to form organic–
inorganic hybrid materials of which diverse organo-
functionalities offer broad application.
Corriu et al. prepared PMOs with tetraazacyclotetradecane
The organic moieties of PMOs mainly rely on various silses-
quioxanes of such as disilanes, trisilanes, and tetrasilanes with
different organic bridging groups. Their syntheses were started at
the end of the twentieth century with three independent groups.
Soon after, many trials were conducted for the integration of
5–10
organic moieties into silica frameworks.
They can be classified
into two types of PMOs. Generally, PMO-I is composed entirely
of organo groups on the walls with regular form. This is prepared
Laboratory of Nano-Green Catalysis and Nano Center for Fine Chemical
Fusion Technology, Department of Chemistry, Inha University, Incheon,
402- 751, Korea. E-mail: separk@inha.ac.kr; Fax: +82 32 872 8670
Scheme 1 Two types of PMO-I and PMO-II.
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moieties using TEOS in the presence of Pluronic 123(P123) and
oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock
copolymer under acidic conditions (Scheme 2). And the synthe-
sized TCPP-PMO(II) were applied to the hydrogen transfer
reaction, cyclohexene oxidation and methylene blue degradation
under visible light were investigated.
15
NaF with high yield, and a narrow pore size distribution.
Recently, Ozin et al. synthesized C60 –PMO by assembling C60
14
and TEOS with P123.
Porphyrin has been utilized in various applications, for
18
example, catalysis, photosynthesis, photodynamic therapy, and
19
sensors. But it has a planar structure with a macrocycle of four
pyrrole rings connected by methine bridges. Consequently, it is
difficult to assemble porphyrin-tetrasilane owing to its entirely
flat structure. To resolve this issue, we tried to synthesize type II
PMO by using porphyrin-tetrasilane with sodium metasilicate as
a silica source. The use of this silica source is expected to lower
the concentration of the organic group in the periodic meso-
porous silica. But the silica source promote the self-assembly of
organosilanes.
2
. Experimental
2.1. Materials
The surfactant Pluronic P123 (EO PO EO ; MW5800 BASF)
2
0
70
20
was used as the template. Sodium metasilicate (Na SiO $9H O;
3
2
2
Sigma Aldrich) was used as silica source. Amino propyl triethoxy
silane (Aldrich) was used for preparing tetra-silane with tetra-
kis(4-carboxyphenyl)porphyrin. Hydrochloride acid was
purchased from Daejung Chemical Company, Korea. Other
chemicals used for catalytic application were purchased either
from Aldrich or TCI Tokyo Kasei with high purity. All the
chemicals were used as received without any further purification.
However, there are no reports on porphyrin in PMO materials
up to now. Herein, we report on PMOs containing tetra-
kis(carboxyphenyl)porphyrin (TCPP). TCPP-PMO(II) is
notable as the first report in the field of periodic mesoporous
organosilica.
2
.2. Synthesis of tetrakis(4-carboxyphenyl)porphyrin(TCPP)
Also, microwave digestion was adopted for the synthesis of
PMOs in order to facilitate the assembly of organosilane.
Smeulders et al. synthesized a benzene-PMO under microwave
Pyrrole (2.33 mmol) and 4-carboxybenzaldehyde (2.33 mmol)
were dissolved in 100 ml propionic acid and stirred for 4 h at 120
20
irradiation. Benzene bridged PMOs is prepared by use of
microwave heating which can achieve a reduction in a synthesis
time of several hours up to several days. In addition, the benzene
bridged PMOs synthesized by microwave irradiation exhibit
better porosity characteristics while maintaining their molecular
ꢀ
C. Then the product solution was cooled to room temperature,
and methanol was added and continued to be chilled in an ice
bath with stirring. The deep-purple crystals were precipitated,
filltered and washed using methanol and hot water. The resulting
solid was dissolved in chloroform containing 2% acetone and
purified by column chromatography over silica gel using chlo-
roform as an eluent.
20
and mesoporous ordering. Besides those, generally microwave
synthesis offers several advantages such as rapid and homoge-
neous heating of the entire sample, improved reaction rates, ease
21
in formation of uniform nucleation centers and rapid crystal-
22
2.3. Synthesis of TCPP-silsesquioxane
lization, and environment friendly due to energy saving.
Microwave synthesis also simplifies the process for obtaining,
well-ordered mesoporous structures with enhanced hydro-
thermal stability.
In a round bottom flask, 3-aminopropyltriethoxysilane (4 mmol)
and dicyclohexyl carbodiimide (4 mmol) were suspended in 50 ml
of tetrahydrofuran (THF). The TCPP (1 mmol) was dissolved in
Here, we report the synthesis of periodic mesoporous orga-
nosilicas with TCPP-silsesquioxane as a tetra silane. All the
catalysts described herein were synthesized by the direct
co-condensation method using microwaves as a heating source.
The TCPP-tetrasilane linked in periodic mesoporous oragnosil-
ica, denoted as TCPP-PMO(II), was synthesized by self-assembly
of TCPP-tetrasilane (prepared in our laboratory) together with
sodium metasilicate as a surplus silica source and poly(ethylene
5
ml of THF and added drop-wisely. The flask was evacuated
and flushed with nitrogen gas. The mixture was refluxed over-
night under nitrogen atmosphere. After cooling down to room
temperature, the product was washed with petroleum ether.
2
.4. Preparation of TCPP-silsesquioxane bridged mesoporous
organosilica
TCPP-bridged PMOs were prepared by TCPP- silsesquioxane
and sodium metasilicate with Pluronic P123 (EO20PO70EO20
,
Aldrich) and c-HCl. In a typical synthesis, 166 ml of triblock
copolymer P123 in deionized water (DW) and 126 ml of sodium
metasilicate solution was mixed to form a clear solution with
stirring. Then organosilane precursor and hydrochloric acid
(
37.6%) was quickly added to the clear solution. The mixture was
ꢀ
ꢀ
aged at 40 C for 1 h with stirring and heated at 100 C for 2 h
under microwave irradiation (300 W, 100%, CEM Mars 5). The
solid product was filtered and washed with copious amount of
water and ethanol. And further removal of the surfactant was
performed by soxhlet extraction using ethanol and hydrochloric
acid (v : v ¼ 97 : 3) for 4 h. The resulted products were repre-
sented as TCPP-PMO-n (n refers to the molar percentage of
TCPP–Silsesquioxane). The composition of final mixture was
Scheme 2 The illustration of Tetrakis(4-CarboxyPhenyl)Porphyrin
(TCPP)-Silsesquioxane bridged PMO.
1
0870 | J. Mater. Chem., 2010, 20, 10869–10875
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ꢀ
ꢀ
ꢁ1
(
(
1 ꢁ x) SiO : x TCPP- tetrasilane: 0.018P123 : 1HCl : 117.1H O
conditions over the 2q region of 0.7– 5 at the rate of 0.1 min
2
2
x ¼ TCPP-tetrasilane/(TCPP-tetrasilane + SiO ) ¼ 0.025 and
(20 kV, 10 mA). Elemental ratio (C/N) was measured using
EA1112. The scanning electron microscope (SEM) images were
observed using a JEOL 630-F microscope. Before the measure-
ment, the samples were dispersed onto a steal plate surface and
coated with Pt metal. Transmission electron microscope (TEM)
images were observed using a JEM-3011 instrument (JEOL)
equipped with a slow-scan CCD camera operating at 300 keV.
Solid-state NMR spectra were collected through a DSX Bruker
2
0
.05).
2
.5. Preparation of Fe-TCPP-silsesquioxane bridged
mesoporous organosilica
TCPP-PMO-5 (1.0 g) was suspended in 25 ml of DMF in
a bottom round flask followed by addition of FeCl
ꢀ
2
$4H
2.0 mmol). The system was heated at 120 C during 4 h with
2
O
(
2
NMR 600 MHz. The N adsorption–desorption isotherms and
mechanical stirring and under nitrogen atmosphere. The crude
product was exhaustively washed in a Soxhlet extractor with
pore characterization were obtained by using a Micromeritics
ASAP 2020 apparatus at liquid N temperature. Thermogravi-
2
DMF, methanol and CH Cl . The Fe-(TCPP)-PMO was washed
2
2
metric analysis (Bruker 2010 SA) were carried out to detect the
decomposition temperature of the organic moieties grafted on
the mesoporous silica. The tetrakis(4-carboxyphenyl)porphyrin
was analyzed by UV-Vis-NIR spectroscopy (SolidSpec-3700).
with deionized water. The solid was washed again in the Soxhlet
ꢀ
extractor with methanol and Fe(TCPP)-PMO was dried at 80 C
per 24 h.
2
.6. The photocatalytic degradation of methylene blue
3. Results and discussion
The photocatalytic degradation of methylene blue was carried
out at room temperature. A quartz calorimetric vessel was used
as photocatalytic reaction apparatus. The vessel was filled with
3
.1. Characterization of TCPP-PMO
The low-angle powder X-ray diffraction patterns of TCPP-
PMO-2.5 and TCPP-PMO-5 are shown in Fig. 1(a). All the
samples showed three well-resolved diffraction peaks with a very
intense peak at 2q ¼ 0.9–1.18 and two peaks at 2q ¼ 1.4–1.8.
These peaks could be indexed to the (100), (110), and (200) planes
respectively, which correspond to a mesostructure of hexagonal
space group symmetry p6mm. The strong (100) peak was
ꢁ5
ꢁ3
the MB solution (1.16 ꢃ 10 mol dm ). The TCPP-PMO-2.5
was immersed in the solution. High pressure XE lamp ranging
2
30–800 nm was used with cutoff filter (UV-390) as a visible lay.
The photodegradation of methylene blue was monitored by
observing -660 nm of the characteristic peaks of methylene blue
using UV–visible spectroscopy. The reference was aqueous
solution of methylene blue with no TCPP-PMO.
2
maintained well in both TCPP-PMO (II). All the N adsorption
and desorption isotherms of the samples were type IV, with type
H1 hysteresis loops at high relative pressures (Fig. 1b). The
surface area, pore diameter and elemental analysis for TCPP-
PMO-n are shown in Table 1. The surface area is evaluated from
nitrogen adsorption isotherms by using the BET equation. Pore
size was calculated by the Barrett–Joyner–Halenda (BJH)
method using the desorption branch of the adsorption-desorp-
tion isotherms. When the TCPP tetra silane content increases
from 2.5% to 5%, the pore diameters curves shift from 8.7 nm to
2
.7. Hydrogen transfer reaction
Hydrogen transfer reaction of ketones such as acetophenone,
cyclohexanone and pinacolone were conducted in liquid phase
reaction. 20 mg catalyst (preactivated at 393 k prior to use) was
added to 3.0 mL 2-propanol. To this mixture, 0.19 mmol of KOH
ꢀ
and 1 mmol ketones was added and reacted at 80 C during 5 h.
The aliquots of the reaction mixture were withdrawn and sub-
jected to GC analysis (Agilent 6890N, DB-WAX capillary
column, FID detector).
8
.5 nm. The wall thickness increases from 3.6 nm to 3.7 nm. The
tendency of mesopore shrinkage with increasing TCPP tetra
silane loading is also exhibited by changes in the surface area and
total pore volume, which indicate worse mesostructural features
2
.8. Catalytic oxidation of cyclohexene
The oxidation of cyclohexene was performed in a conventional
glass reactor (50 ml) with a condenser and stirrer of which reactor
was loaded with 0.05 g catalyst, cyclohexene (5 mmol), 10 ml
2 2
acetonitrile and 10 mmol of 30% aqueous H O . The catalyst was
ꢀ
activated at 250 C for 4 h before loading into the glass reactor.
The reaction was monitored by analyzing the reaction samples at
different time intervals by a gas chromatograph (HP-6890)
equipped with a HP-5 capillary column and a FID detector and
ꢀ
ꢀ
oven temperature were programed from 70 C to 200 C with
ꢁ1
ꢀ
a heating rate of 10 C min . Conversion of cyclohexene and
products selectivity was calculated based on the GC analysis.
2
.9. Characterization of TCPP-PMO-n
The XRD patterns were obtained by using a Rigaku Multiflex
Fig. 1 (a) Powder XRD patterns of samples TCPP-PMO-2.5 and TCPP-
PMO-5 and (b) N2 adsorption-desorption and pore size distribution
(inset) of samples TCPP-PMO-2.5 and TCPP-PMO-5.
diffractometer with a monochromated high-intensity Cu-Ka
ꢀ
radiation (l ¼ 1.54 A). Scanning was performed under ambient
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J. Mater. Chem., 2010, 20, 10869–10875 | 10871

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Table 1 Structural, textural and compositional information of TCPP-PMO-n
Elemental
analysis
C/N ratio
BET surface
ꢁ1
Pore
diameter/nm
Total pore
volume/cm g
Wall
thickness/nm
2
area/m g
a
3
ꢁ1
b
c
Sample
d100/nm
0
a /nm
TCPP-PMO-2.5
TCPP-PMO-5.0
10.6
10.3
493
403
8.7
8.5
0.78
0.76
12.4
12.1
3.6
3.7
6.43
6.67
a
b
c
Pore diameter was calculated from desorption branch by BJH method.
a
0
¼ 2d100/root 3. Wall thickness ¼ a
0
-pore size.
with higher loading of TCPP groups. In elemental analysis data,
the expected C/N ratio of TCPP-tetrasilane was 6.51 and the
ratio observed were 6.43(TCPP-PMO-2.5) and 6.67(TCPP-
PMO-5.0) which states that maximum amount of organosilane
was introduced into the PMO.
the symmetry of the porphyrin. It was appeared as the shifts of
the absorption bands toward higher energy.
The emission spectra of TCPP-PMO-n with different loading
levels are presented in Fig. 3. TCPP-PMO-2.5 shows these two
wavelengths at 646 nm and 705 nm. The emission peak at 646 nm
coincides with the longest wavelength peak in the absorption
spectrum and thus could be assigned as the (0,0) component of
Fig. 2 shows (a, b) transmission electron microscopy (TEM)
images and (c, d) scanning electron microscopy (SEM) images of
the obtained TCPP-PMOs. The SEM images reveal shorter
channel lengths and hexagonal shape morphology. The TEM
images indicate that the lengths of the mesopore channels were in
the submicromet range and that the channel directions of the
Q . TCPP-PMO-5 exhibits two peaks at 650 nm and 706 nm. For
x
TCPP-PMO-n, the emission spectra exhibit a red shift from
646 nm to 650 nm and peak broadening was observed with
increasing of TCPP loadings. The reason is that the increase of
the concentration of TCPP-unit could increase the intermolec-
ular interactions between TCPP-unit and silica on the walls. This
might cause the formation of excimers between adjacent lumo-
2
D-hexagonal structures were parallel to the vertical direction of
the hexagonal platelet morphology. TCPP-PMO-n would be
explained to have a hexagonal space group symmetry p6mm of
high orderness in good agreement with XRD data.
24,25
phores in the walls.
TCPP unit bridged into mesoporous silica was checked by
UV-DR spectroscopy and photoluminescence spectroscopy
TCPP bridged mesoporous silica was confirmed by TG-DTA
measurements (Fig. 4). The free TCPP decomposed into several
ꢀ
(
Fig. 3). From the UV-DR spectra, the TCPP had the Soret band
steps during heating upto 800 C. An exothermic loss in weight of
ꢀ
23
at 417 nm and four Q-bands at 513, 548, 591 and 649. The
TCPP unit in the bridged mesoporous organosilica had absorp-
tion bands at 413 (Soret band) and four Q-bands at 514, 548 and
23% appeared at 345 C and additional weight loss of 70% was
ꢀ
followed at 437 C. The overlap of two steps in the TG curve
could be distinguished by the corresponding DTA curve. From
the loss in weight, we tentatively assign these steps to the
successive cleavage of TCPP unit. TCPP-PMO-n shows some-
what different decomposition behaviour due to covalent inter-
actions between TCPP unit and mesoporous silica. The TG-DTA
curve of TCPP-PMO shows less defined weight loss steps and
5
91, 647 nm. Compared with the TCPP compounds, the Soret
band of the TCPP-PMO was shifted toward shorter wavelengths.
This could be explained due to the interactions of the porphyrin
with periodic mesoporous organosilica. When the TCPP was
functionalized into the mesoporous silica walls, interactions of
the ligand of the TCPP with their chemical environment changed
ꢀ
peak maxima. A broad exothermic DTA peaks between 300 C
ꢀ
and 600 C were observed. The TCPP-PMO-2.5 decomposed
ꢀ
more rapidly than TCPP-PMO-5 and completed at ca. 500 C.
ꢀ
ꢀ
Weight losses at 200–350 C and 360–480 C for TCPP-PMO
were assigned to loss of carboxyl and phenyl groups
from porphyrin, respectively. A second weight loss in the range
Fig. 2 TEM (top) and SEM (bottom) images of TCPP-PMO-2.5 (a,c)
Fig. 3 UV-Vis spectra (a) and fluorescence spectra (b) of TCPP-PMO-
TCPP-PMO-5 (b,d).
2.5 and TCPP-PMO-5.
1
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2
3
resonances, respectively. The presence of T and T resonances
proved that the functional groups of TCPP units were func-
tionalized in the silica wall. The signals at ꢁ91, ꢁ100 and ꢁ109.8
2
3
4
ppm are due to Q , Q and Q sites, respectively. So, TCPP-PMO,
3
4
3 4
showed the presence of both Q [Si(OSi) (OH)] and Q [Si(OSi) ]
2
3
with T and T sites, which indicates the condensation reaction
between the organosilane and silica species.
3
.2. Catalytic applications of TCPP-PMO
The photocatalytic activities of pure SBA-15, TCPP-PMO-2.5
and no catalyst were evaluated by measuring the decomposition
rates of methylene blue under the visible light irradiation (>390
nm). Fig. 6 shows the changes of MB concentrations with reac-
tion time in the presence of TCPP-PMO-2.5 and without catalyst
under the visible light. The visible-light without any catalyst gave
only about 4% decomposition of MB molecules within 2 h.
TCPP-PMO-2.5 sample shows superior photocatalytic activity
with 55% degradation rate of MB within 2 h under the same
condition (Fig. 6). This could be explained by two reasons. One is
that the contribution of TCPP moiety on the surface of silica,
resulted in the production of more photoinduced electrons and
holes, and another reason is that the formed O]C–NH bond
between TCPP and tetra-silane played an important role in the
Fig. 4 TG-DTA curves of (a) free TCPP and (b) TCPP-PMO-n (n ¼ 2.5
and 5).
ꢀ
5
00–627 C was attributed to the decomposition of the porphyrin
rings. The weight losses of the bridged TCPP unit in TCPP-
ꢁ1
PMO-2.5 and TCPP-PMO-5 were 0.1 mmol g and 0.29 mmol
ꢁ
1
g , respectively.
In order to obtain information about the chemical environ-
29
ment of silicon atoms presented in the materials, Si CP MAS
n
NMR experiment was done and shown in Fig. 5. Two T and
n
three Q signals, which could be assigned to the following Si
2
species: T [C–Si(OSi)
3
2
(OH), d ¼ ꢁ58 (5.17%)]; T [C–Si (OSi)
3
,
2
d ¼ ꢁ66.01 (13.63%)]; Q [Si(OSi)
2
(OH)
2
, d ¼ ꢁ91.0 (10.64%)];
26,27
3
Q [Si(OSi)
4
electron transfer channel by accelerating electron injection.
3
(OH), d ¼ ꢁ100 (49. 2%)]; Q [Si(OSi) , d ¼ ꢁ109.8
4
Organocatalysis can be performed by organofunctionalized
mesoporous materials as green approaches. In this context,
TCPP-PMOs were applied to the catalytic hydrogen transfer
reaction, which has been important to produce key intermediates
for the synthesis of pharmaceuticals and agrochemicals. As
ketones, acetophenone and cyclohexanone and pinacolone were
chosen with isopropylalcohol as a hydrogen transfer agent. In the
case of acetophenone as a reactant, the conversion over TCPP-
PMO-2.5 and 5 reached 17% and 30%, respectively. Fig. 7 shows
that the increasing rate of conversion over TCPP-PMO-5 was
two-times higher than those over TCPP-PMO-2.5. The results
could be explained by the morphological advantage and higher
loadings of porphyrin as active sites onto TCPP-PMO. It is well
accepted that the diffusion and mass transfer of reactant
(
20.93%)]. The spectra of the samples exhibit two signals at
3
2
around ꢁ58 and ꢁ67 ppm which could be assigned to T and T
Fig. 6 Photocatalytic degradation of MB, in the presence of TCPP-
29
Fig. 5
Si solid state NMR spectra of TCPP-PMO-2.5 and – 5.
PMO-2.5 and without catalyst under the visible light.
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Fig. 7 Transfer hydrogenation of ketones over TCPP-PMO-2.5 and TCPP-PMO-5.
molecules into the pores to reach the active sites have great
cyclohexene could promote the oxidation of the double bond to
form correspondingly epoxide. It is indicated that conversion of
28
influence on liquid-phase heterogeneous catalytic reactions.
Both TCPP-PMO catalysts gave perfect selectivity toward only
one desired alcohol product. In addition to, cyclohexanone over
TCPP-PMO-5 gave better conversion (about 60%) than aceto-
phenone was used as a reactant. Also, all TCPP-PMOs gave
good catalytic activities for hydrogenation of acetophenone and
cyclohexanone with perfect selectivity. Slightly low activity was
obtained only in the case of pinacolone. As for leaching test,
TCPP-2.5 and TCPP-5 were separated after 5 h reaction and
washed. After washing, the same reaction condition was applied
repeatedly. The catalysts showed similar activities, which meant
no significant loss of the active sites were ascribed to no serious
leaching out during reaction process.
2 2
cyclohexene increased with the increase in H O /cyclohexene
mole ratio (1 to 3). Maximum cyclohexene conversion of 41.5%
ꢀ
was obtained in 3 of H O /cyclohexene mole ratio at 60 C.
2
2
However, the selectivities for cyclohexene epoxide remained the
same in all H O /cyclohexene mole ratios. The selectivity for
2
2
2-cyclohexene-1-ol was found to be maximum (35.8%) with
/cyclohexene mole ratio of 1. But the selectivities on
2
2-cyclohexene-1-ol were decreased in larger amounts of H O .
2 2
H O
2
Because higher hydrogen peroxide amounts leaded to further
oxidation to give 1, 2- cyclohexenediol during the cyclohexene
oxidation. The activities of Fe-TCPP-PMO-2.5 at different
temperatures were also tested. The activity results of Fe-TCPP-
PMO are given in Table 2. It seems that conversion of cyclo-
hexene was dependent on temperatures. The rates increased with
the increase in temperatures. The activation energy was calcu-
Finally, the oxidation of cyclohexene was investigated over
Fe-TCPP-PMO-2.5 and the results are shown in Table 2. In the
oxidation of cyclohexene using hydrogen peroxide, cyclohexene
oxide, 2-cyclo-hexen-1-one, 2-cyclo-hexen-1-ol and 1,2-cyclo-
hexanediol were formed. The Fe-TCPP-PMO catalyzed
ꢁ1
lated 24 kJ mol from the Arrhenius equation by plotting the
graph of ꢁln(rate) vs. 1/T. The oxidation of cyclohexene to
a
Table 2 Oxidation of cyclohexene with H
2
O
2
over TCPP-PMO
b
Product selectivity (%)
ꢀ
Entry
H
O
2 2
/Cyclohexene Ratio
T/ C
Cyclohexene Conv. (%)
Epoxide
Cyclo-one
Cyclo-ol
Cyclo-diol
1
2
3
4
5
1
2
3
3
3
3
3
60
60
60
60
25
40
40
20.5
36.5
41.5
10.5
6.5
19.1
17.9
16.4
12.5
34.0
25.7
—
37.0
35.4
34.5
34.6
29.6
33.0
—
35.8
34.0
34.4
33.0
28.5
31.2
—
8.0
12.6
14.1
19.7
3.5
9.7
—
d
c
d
d
6
7
30.1
0
e
a
ꢀ
b
Reaction conditions: Catalyst ¼ 50 mg, Temp. ¼ 60 C and Time ¼ 5 h. Legend: Cyclo-oxide ¼ Cyclohexene oxide; Cyclo-one ¼ 2-cycolhexene-1-
c
d
one; Cyclo-ol ¼ 2-cycolhexene-1-ol; Cyclo-diol ¼ 1, 2- cyclohexanediol. Iron-TCPP complex (homogeneous). Used for calculating of activation
e
energy. Pure SBA-15(blank catalytic test).
1
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*
provide oxygenates is endothermic in nature (enthalpy, DH ¼
9 J. Morell, G. Wolter and M. Froba, Chem. Mater., 2005, 17, 804–808.
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ꢁ1
DE – RT ¼ 6.5 kJ mol ). As shown in the Table 2, Fe-TCPP-
a
1
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PMO-2.5 gave good activity which was presumably due to high-
valent iron–oxo porphyrin as the oxidizing species. And also
higher conversions of cyclohexene showed the decreased selec-
tivities on cyclohexene epoxide due to futher oxidation which led
to the formation of other products.
304–307.
1
1
1
1
1
1
1
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2
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. Conclusion
In conclusion, TCPP bridged periodic mesoporous organosilica
was successfully synthesized and played a role as an efficient
catalyst in photodegradation of MB and especially in the
hydrogen transfer reaction by taking advantages of meso-
porosity and porphyrin functionality. Also, the Fe-TCPP-PMO
exhibited a high catalytic activity in the oxidation of cyclohexene
with hydrogen peroxide. The reaction results showed high
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