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2.2. Substituted manganese metalloporphyrins
bath. The mixture was dissolved in ethanol and the catalysts were
removed by filtration. The catalysts were washed by ethanol, dried
and then recycled in the next reaction. The cyclohexanol and cyclo-
hexanone in the product were analyzed by gas chromatography by
using chlorobenzene as the internal standard. The total acid and
ester in the product was analyzed by the chemical titration method.
All reagents and solvents used for the synthesis of porphyrin
were of analytical grade and were obtained commercially. Mn-T(p-
Br)PP, Mn-D(p-Cl)D(p-Br)PP and Mn-T(p-Cl)PP were synthesized
by modifying the reported procedures [23–25]. The Mn-TNPP
was synthesized according to the following procedures [26], The
5,10,15,20-tetrakis(4-nitrophonyl) porphyrin (1.26 mmol) was dis-
solved and refluxed in DMF (100 mL). Then, manganese acetate
(6.3 mmol) was added in four portions within 15 min. The evolu-
tion of the reaction was monitored by thin layer chromatography.
The solvent was evaporated by rotary evaporation after the reac-
tion was completed. The mixture was filtered and washed with
water. Then it was purified by column chromatography (alumina,
CH2Cl2/methanol = 10:1.5). After the solid was vacuum-dried, the
Mn-TNPP compound was obtained with the yield of about 90%.
3. Results and discussions
3.1.1. UV–vis spectra of TNPP, Mn-TNPP and Mn-TNPP/ZnO
UV–vis spectra of the TNPP, Mn-TNPP and Mn-TNPP/ZnO are
shown in Fig. 1. The spectra of TNPP exhibit one Soret band at
425 nm and four Q bands at 518 nm, 552 nm, 594 nm and 650 nm,
which indicats that the TNPP was successfully synthesized [29].
reduces to one or two with the metal entered into the porphyrin
center. When Mn-TNPP was immobilized onto the ZnO support,
the UV characteristic Soret peak was red-shifted from 480 nm to
475 nm. The red-shift phenomenon is similar to the literatures
[30,31], this means that the Mn-TNPP molecules were set on the
surface of the ZnO crystals and interacted with the oxygen atom,
Mn-TNPP/Boehmite, Mn-TNPP/Kaolin, Mn-TNPP/ZrO2 and Mn-
TNPP/Zr(OH)4 were synthesized by modifying the reported
procedures [20,27]. Mn-TNPP/ZnO was prepared by the following
procedure [28], Zinc sulfate heptahydrate (0.25 mol) was added to
500 mL of deionized water in a three-necked flask with high stirring
for 1 h. Then, NH3 aqueous (1.10 mol) was added to adjust the pH to
8.0, after filtration, the filter cake was dissolved in 250 mL ethanol
and 0.023 mmol of the Mn-TNPP ethanol solution were slowly
added into the above suspension and stirred for another 40 min,
and the mixture was heated to 65 ◦C with rapid stirring for 12 h.
After cooling to room temperature, the suspension was filtrated
and washed with distilled water, and the cake was vacuum-dried
at 170 ◦C for 24 h and then washed in a Soxhelt apparatus for 48 h
with 280 mL of CH2Cl2 to remove the weakly adsorbed metallo-
porphyrin on the surface. Finally, the solids were dried at 70 ◦C for
10 h.
3.1.2. FT-IR spectra of ZnO, Mn-TNPP and Mn-TNPP/ZnO
The FT-IR spectra of Mn-TNPP, ZnO and Mn-TNPP /ZnO are
shown in Fig. 2. From the spectra of Mn-TNPP, the sharp bands
at 1348 cm−1 and 1520 cm−1 are assigned to the symmetric and
asymmetric stretching vibration of the –NO2 group, and the band
at 825 cm−1 indicates that the nitro group is in the para position of
the nitrobenzene was introduced into the porphyrin molecules.
The sensitive metal bands appear at 1408 cm−1, 1010 cm−1 and
509 cm−1, it indicates that the metalloporphyrin was successfully
synthesized [26,32,33]. For the Mn-TNPP/ZnO (a) and ZnO (b),
the spectra are broadly similar. The ZnO vibrations bands appear
at 420 cm−1 and 602 cm−1, and the wide band at 990 cm−1 and
1108 cm−1 are assigned to the vibrations of the O–H groups from
the Zn(OH)2, which exists in the ZnO structure [34]. Compared with
the ZnO, the bands at 3320 cm−1 and 3563 cm−1 are disappeared in
Mn-TNPP/ZnO, it maybe result from the introduction of the active
components. Meanwhile, a new peak at 518 cm−1 appears in the
Mn-TNPP/ZnO, it may be assigned to the ZnO-Mn-TNPP vibration,
and it indicates the coordination of the oxygen atom of ZnO to
Mn-TNPP.
2.4. Characterization of the TNPP, Mn-TNPP and Mn-TNPP/ZnO
UV–vis spectra was obtained by UV-2550 spectrophotometry
with a scan range of 300–800 nm for TNPP, Mn-TNPP and the sup-
ported manganese metalporphyrin complexes using 1 cm quartz
cuvette.
Fourier transform infrared (FT-IR) spectra were recorded on a
Nicolet iS10 spectrometer in the range 400–4000 cm−1, the samples
were ground into fine powders, mixed with KBr, and then were
pressed into thin pellets to assay their spectra.
X-ray diffraction (XRD) patterns for powder samples of Mn-
TNPP/ZnO were collected on a Japan Rigaku D/Max 2550 VB+18 kW
X-ray diffractometer under the conditions of 40 kV, 30 mA, Cu K␣
radiation. Scans were performed from (2Â) 5 to 90 at a rate of
2 min−1
.
TG/DTG curves for Mn-TNPP/ZnO were recorded by a TGA/DCS
using air as purge gas (40 mL min−1) over a temperature range of
30–600 ◦C and with a heating rate of 10 ◦C min−1
.
Inductively coupled plasma (PS-6 ICP-AES) was used to measure
the content of manganese in the supported metalloporphyrins.
2.5. Procedures for the catalytic test
Cyclohexane oxidation was carried out in a 50 mL autoclave
reactor with a magnetic stirrer in the absence of solvent. Typi-
cally, cyclohexane (188 mmol) and catalysts were added into the
autoclave reactor. And the reactor was sealed and heated to the
setting temperature. Then it was pressurized to the setting pres-
sure with the molecular oxygen under stirring. After the reaction,
the reactor was cooled to the ambient temperature in an ice-water
Fig. 1. Ultraviolet–visible spectra: TNPP (a), Mn-TNPP (b) and Mn-TNPP/ZnO (c).