Y. Xie et al.
MolecularCatalysis452(2018)20–27
2.2.3. Preparation of meso-ZSM-5
We first synthesized microporous ZSM-5 zeolite according to the
previous report [23]. The synthesis steps were as follows: 3 g of TEAOH
as organic template was dissolved in 45 mL of deionized water, and
then NaOH was added to the mixture followed by adding a measured
amount of AIP as aluminum source. The mixed solution was stirred at
room temperature for 1 h. Then 10.4 g of TEOS was added dropwise and
the resultant solution (Si/Al = 60, molar ratio) was stirred for several
hours. Subsequently, the mixture obtained was transferred to the Te-
flon-lined autoclave and crystallized by hydrothermal treatment at
170 °C for 72 h. Then the solid product was separated via filtration and
washed with deionized water and ethanol, and dried at 80 °C for 8 h.
Finally, the collected solid was calcined at 550 °C for 6 h to obtain ZSM-
5. Meso-ZSM-5 was prepared by a simple alkaline treatment [24]. The
obtained ZSM-5 was added to a 250 mL round-baker and then refluxed
in a reflux condenser filled with a 0.5 M aqueous NaOH solution at
70 °C for 30 min. Then the solid zeolite was recovered by filtration,
washing with deionized water, drying, and calcination in air at 300 °C
for 5 h to obtain meso-ZSM-5.
Scheme 1. Oxidation of furfural to MAD catalyzed by iron-based metallopor-
phyrins.
materials mainly because they were common supports in supported
catalysts, and each had different structural characteristics. These dif-
ferences were exactly what we need in order to find the most suitable
support for immobilized iron porphyrins. The catalysts synthesized
were characterized by FT-IR, UV-vis, 1HNMR, XRD, N2-adsorption-
desorption, SEM, TEM and TGA techniques. Both unsupported and
supported porphyrin catalysts were used to catalytic the oxidation of
furfural into MAD in the presence of dioxygen (1 MPa) in aqueous phase
(Scheme 1). In addition, the effect of reaction parameters (reaction
temperature, reaction time and catalyst amount) on the catalytic ac-
tivity and the recycle tests of catalyst were also investigated in detail.
2.2.4. Preparation of different porphyrin ligands
Porphyrin ligands were synthesized by the method of Alder with
some modifications [25]. In a 100 mL of flask with three necks,
0.015 mol of corresponding benzaldehyde was dissolved in 30 mL of
propionic acid solution. The mixture was heated at reflux temperature
with vigorous stirring. Subsequently, 0.015 mol of freshly distilled
pyrrole solved in propionic acid solution (5 mL) was slowly added into
the above mixture. After a period of time of reaction, the mixture so-
lution was cooled to room temperature and placed in the refrigerator
overnight. Then the purple solid was filtered and washed with hot
water and ethanol and dried at 80 °C for 8 h. The crude product was
purified via column chromatography using neutral alumina
(100–200 mesh size) with chloroform or dichloromethane as eluent.
2. Experimental
2.1. Reagents and materials
Pyrrole, propionic acid, ferrous chloride tetrahydrate, furfural,
ammonia (28 wt%), cetyltrimethylammonium bromide (CTAB) and
tetraethyl orthosilicate (TEOS) were purchased from Sinopharm
Chemical Reagent Co. Ltd.; Maleic acid, P123, tetraethyl ammonium
hydroxide (TPAOH, wt%) and aluminum isopropoxide (AIP) were
purchased from Shanghai Aladdin Industrial Inc.; Other main reagents
used in the work were obtained from Energy Chemical Reagent Co. Ltd.
2.2.5. Preparation of iron-based porphyrins
In a typical synthetic process, 0.16 g of porphyrin ligand synthesized
above was dissolved in 30 mL of DMF. The mixed solution was heated at
reflux temperature under magnetic stirring. Then FeCl2·4H2O (four
times the molar quantities of the ligand) was added into the solution in
three batches. The reaction was carried out for 4 h and the solvent was
removed by reduced pressure distillation, then hydrochloric acid was
added slowly until the brown solid on the reactor wall was full dis-
solved. The mixture was immersed in deionized water overnight, col-
lected via filtration and washing with hydrochloric acid and deionized
water, and dried in oven at 80 °C for 8 h.
2.2. Catalyst preparation
2.2.1. Preparation of MCM-41
MCM-41 molecular sieves were prepared by the following literature
procedures [20,21]. 1.37 g of CTAB was added into 50 mL of deionized
water with gentle stirring at 40 °C. After a clear solution was formed,
TEOS (5.2 mL) was added dropwise and aqueous ammonia was added
until the pH of the mixed solution was adjusted to 10.5. With continued
stirring for 3 h, the mixture was transferred to an autoclave equipped
with a Teflon liner and heated at 105 °C for 24 h. Then the reaction was
stopped and the gel was filtered, washed with deionized water and
ethanol, dried in oven at 80 °C for 8 h. Finally, the solid was calcined at
550 °C for 6 h.
2.2.6. Preparation of supported feT(p-Br)PPCl catalysts
In a 100 mL round bottom flask, 0.5 g of support (MCM-41, SBA-15
and meso-ZSM-5) was dispersed in 15 mL of DMF. The mixture solution
was heated to 120 °C with vigorous stirring. Then 0.1 g of FeT(p-Br)
PPCl DMF solution were slowly added into the above mixture. After
24 h of reaction, the brown solid was filtered and exhaustively washed
with solvent to remove the weakly adsorbed iron porphyrins.
2.3. Catalysts characterization
2.2.2. Preparation of SBA-15
FT-IR spectra were measured with a Nicolet 360 FT-IR instrument
SBA-15 mesoporous material was synthesized according to the
method described in literature with a slight change [22]. In a typical
synthesis, 4 g of P123 as organic template was dissolved in 30 mL of
deionized water. After stirring at 42 °C for 1 h, 100 mL of HCl solution
(2 M) was added. Then 8.5 g of TEOS was added dropwise and the re-
sultant solution was stirred for 22 h, followed by hydrothermal treat-
ment at 100 °C for 24 h. The solid product was collect by filtration,
washed with deionized water and ethanol, dried in oven at 80 °C for 8 h,
and then calcined at 550 °C for 6 h.
(KBr discs) in the 4000–500 cm−1 region. UV–vis spectra were obtained
using
a TU-1901 dual-beam UV–vis spectrophotometer over the
300–700 nm range. 1H NMR spectra were recorded in CDCl3 with a
Bruker DPX 300 spectrometer. X-ray diffraction (XRD) patterns of
samples were performed on
a Bruker D8 Advance powder dif-
fractometer with a Ni-filtered Cu/Kα radiation source at 40 kV and
20 mA in the 2θ range of 0.5–50° at the rate of 0.5° min−1. The scanning
electron microscope (SEM) images were taken on a HITACHI S-4800
emission scanning microscope. Transmission electron microscope
21