Preparation, characterization and catalytic performance of bimetallic Ti-Co-MCM-41 catalysts

Article abstract of DOI:10.14233/ajchem.2015.17126

Ti-Co-MCM-41 molecular sieve catalysts were synthesized using the impregnation method. The catalysts were characterized by X-ray diffraction, UV-visible, Fourier transform infrared spectroscopy and low temperature N₂ adsorption-desorption. Their performance in 4-tert-butylbenzaldehyde synthesis was evaluated in mild conditions by oxygen oxidation 4-tert-butyltoluene. The results showed that the catalysts had large surface area and pore size and contained titanium and cobalt with four ligands, which formed the catalysts of high catalytic activity. The conversion rate of 4-tert-butyl toluene was improved by 38%, the selectivity of 4-tert-butyl benzaldehyde was improved by 85% and the yield of 4-tert-butyl benzaldehyde was up to 35%.

Full text of DOI:10.14233/ajchem.2015.17126

Asian Journal of Chemistry; Vol. 27, No. 1 (2015), 273-276
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2015.17126
Preparation, Characterization and Catalytic Performance of Bimetallic Ti-Co-MCM-41 Catalysts
1
1
2
2
2
JINFENG ZHANG1,2,*, JIYAO ZHANG , JIANSHE ZHAO , CUNSHE ZHANG , HANXI SHEN and KUI ZHOU
1College of Chemistry & Materials Science, Northwest University, Xi' an 710069, Shaanxi Province, P.R. China
2Shaanxi Provincial Research and Design Institute of Petroleum and Chemical Industry, Shaanxi Key Laboratory of Petroleum for Fine Chemicals,
Xi'an 710054, Shaanxi Province, P.R. China
*Corresponding author: Tel: +86 29 89350846, +86 13096973646; E-mail: wuqj02@163.com
Received: 27 January 2014;
Accepted: 16 May 2014;
Published online: 26 December 2014;
AJC-16554
Ti-Co-MCM-41 molecular sieve catalysts were synthesized using the impregnation method. The catalysts were characterized by X-ray
diffraction, UV-visible, Fourier transform infrared spectroscopy and low temperature N2 adsorption-desorption. Their performance in
4-tert-butylbenzaldehyde synthesis was evaluated in mild conditions by oxygen oxidation 4-tert-butyltoluene. The results showed that the
catalysts had large surface area and pore size and contained titanium and cobalt with four ligands, which formed the catalysts of high
catalytic activity. The conversion rate of 4-tert-butyl toluene was improved by 38 %, the selectivity of 4-tert-butyl benzaldehyde was
improved by 85 % and the yield of 4-tert-butyl benzaldehyde was up to 35 %.
Keywords: Ti-Co-MCM-41, Molecular sieve, Grafting, Impregnation, Catalytic activity.
MCM-41 with double active components was obtained, which
was proved to have high activity and selectivity.
INTRODUCTION
4-tert-Butyl benzaldehyde is an important intermediate
of medicines, dyes, flavors, fragrances and other fine chemical
products and its synthesis methods mainly include chemical
oxidation, O2 (air) oxidation, H2O2 oxidation, electrochemical
oxidation and so on1-4. At present, benzyl chloride hydrolysis
method is widely used in industrial production. However, this
method brings great environmental pollution and new green
synthesis techniques need to be developed in order to solve
the problem. Since 1992, the United States of America Mobil
company has invented M41S series of mesoporous molecular
sieves which show attractive prospect for shape selective cata-
lytic oxidation of organic macromolecular material and the
synthesis and application of Ti mesoporous molecular sieve
have become a hot spot5. A variety of mesoporous molecular
sieves with Ti appeared in succession, such as Ti-MCM-416,7,
Ti-HMS8,9 and Ti-SBA-1510, which exhibited good catalytic
performance in many oxidation reactions. Besides, cobalt-
based inorganic or organometallic compounds as catalysts are
EXPERIMENTAL
Preparation of Si-MCM-41: 65 g deionized water and
2 g CTAB were added to the three-necked flask of 500 mL.
The mixture was heated to 40 °C and then stirred for 0.5 h.
After CTAB was dissolved completely, 20 g aqueous ammonia
was added to the mixture under continuous stirring for 0.5 h.
Then, 8.5 g TEOS was dropped slowly into the mixture and
the mixture was strongly stirred for 2 h. The reaction mixture
was aged at ambient temperature for 24 h and then crystallized
at 110 °C for 24 h in the reaction kettle. The crystalline product
was recovered by filtration, washed with deionized water, air-
dried and calcined in air at 300 °C for 2.5 h and 650 °C for
3.5 h successively. Thus, the white powder product named Si-
MCM-41 mesoporous silica material was obtained13.
Preparation of Ti-MCM-41: Titanocene dichloride was
added to chloroform under stirring to realize complete dissolu-
tion of titanocene dichloride in the chloroform and the mixture
was marked as solution A. The prepared Si-MCM-41 powder
was added to chloroform and then triethylamine was slowly
dropped into the mixture under continuous stirring. The
obtained mixture was marked as solution B.After that, solution
A was dropped into solution B and the reaction mixture was
strongly stirred for 3 h. Then the mixture was recovered by
also widely used in catalytic oxidation reaction11,12
.
As a candidate for catalyst carrier, the mesoporous silica
MCM-41 contains rich silicon hydroxyl and has larger specific
surface area and pore size, which can play a unique role in the
catalytic reaction. In this paper, the active atoms of Ti and Co
were modified in molecular sieve carrier by virtue of grafting
method and impregnation method and the catalyst of Ti-Co-

274 Zhang et al.
Asian J. Chem.
filtration, air-dried and calcined in air at 500 °C for 2 h and
650 °C for 3.5 h. Thus, the white powder product named
Ti-MCM-41 mesoporous silica material was obtained. Samples
with different titanium contents can be obtained by changing
quality ratio of the reactants.
absorption peak intensity of the modified sample decreases
and the peak position also slightly migrates, which indicates
the metallic elements have entered into the framework of
zeolite and changed the long-range order of silicon molecular
sieve.
Preparation of Ti-Co-MCM-41: The calcined Ti-MCM-
41 was stirred in a solution of Co(OOCCH3)2·4H2O dissolved
in 30 mL glycol to steep the Ti-MCM-41 sample fully. The
obtained mixture was first vacuum-desiccated at 250 °C for
4 h and then calcined in air at 550 °C for 4 h. Samples with
different cobalt contents can be obtained by changing quantity
ratio of the reactants.
Ti-Co-MCM-41
Characterization of the catalyst: Powder X-ray diffrac-
tion (XRD) patterns were obtained on a Rigaku D/max-2500
X-ray diffraction equipped with CuKα radiation and Ni filter.
The diffraction data were collected every 0.02° at a scan speed
of 1° (2θ)/min from 1 to 8° and the experimental conditions
were as follows: voltage 40 kV, current 100 mA.
Ti-MCM-41
Co-MCM-41
MCM-41
N2 adsorption-desorption isotherms were recorded at 77 K
on a Micromeritics ASAP 2020. The samples were dried at
200 °C for 5 h before test. BET surface areas were calculated
from the linear part of the BET plot and pore size distributions
were calculated using the adsorption branches of the N2 iso-
therms and the BJH method. UV-visible diffuse reflectance
spectra were obtained on a Lambda 650S spectrometer and
the referenced BaSO4 were used for the measurements. Element
content of the products was determined using JSM-6460
scanning electron microscope (SEM) and JSM-6460 energy
spectrum analysis (ESA). Fourier-transform infrared spectro-
scopy (FT-IRS) was recorded by aVERTEX 70 infrared spectro-
meter with scanning range of 2000-500 cm-l at a resolution of
4 cm-1. X-ray photoelectron spectroscopy (XPS) was recorded
by aVG ESCALAB5 multi-function electronic energy spectro-
meter with AlKα ray under CAE mode. The spectrometer was
operated with a tube voltage of 9 KV, tube current of 18.5 mA
and overpass energy of 500 eV. C-1s scan of every level was
used as an internal reference to correct the shift in binding
energies of the present level caused by charging effect.
Catalytic testing: Catalytic reaction was performed in a
three-necked flask equipped with a condenser and thermo-
meter. The catalytic performance of each sample was tested
in the liquid phase with vigorous stirring. The oxidation of 4-
tert-butyl toluene was carried out at 70 °C for 8 h by adding
0.4 mmol TBHP and O2 to a mixture which contained 6.7 mmol
4-tert-butyl toluene, 150 mg of catalyst and 15 mL of aceto-
nitrile. After the reaction, the catalyst was filtered off, washed
with methanol and dried at 100 °C in air overnight, while the
reaction liquid was qualitatively analyzed with GC-MS and
quantitatively analyzed with GC equipped with a HP-5 capillary
column and a flame ionization detector (FID), respectively.
0
1
2
3
4
5
6
7
8
Fig. 1. XRD patterns of the samples
Pore structure and specific surface area: The nitrogen
adsorption-desorption isotherms of sample is shown in Fig. 2.
The sample exhibits typical IV isotherms as expected for
mesostructured materials, which indicates the structure of
catalyst remains intact after loading the active components in
the carrier.
350
300
250
200
150
100
50
0
0
0.1 0.2
0.3 0.4 0.5
0.6
0.7 0.8
0.9 1.0
Relative pressure (P/P0)
Fig. 2. N2 adsorption-desorption isotherm of Ti-Co-MCM-41
The textural properties of the catalyst sample are listed in
Table-1 and the figures indicate the prepared Ti-Co-MCM-41
catalyst has larger specific surface area, pore volume and pore
size, which means the catalyst has good adsorption and
catalytic performance.
TABLE-1
PORE STRUCTURE ANALYSIS OF Ti-Co-MCM-41
Pore volume
(cm3/g)
BJH pore size
(nm)
RESULTS AND DISCUSSION
Sample
SBET (m2/g)
598.0
Catalyst Structure: Fig. 1 shows XRD patterns of the
samples. It can be seen that the samples all have a strong diff-
raction peak at about 2° and two small peaks between 3° and
5.5°, which is consistent with previous reports. The samples
present six mesoporous structures of MCM-41 molecular
sieve and have better long-range order and crystallinity. The
Ti-Co-MCM-41
0.49
3.4
Infrared spectroscopy: Infrared spectroscopy provides
structure information of molecular sieves in the 1400-400 cm-1
region. Fig. 3 shows FT-IR spectra of Ti-MCM-41, Ti-Co-
MCM-41 and MCM-41 and two bands appear at the same

Vol. 27, No. 1 (2015)
Preparation, Characterization and Catalytic Performance of Bimetallic Ti-Co-MCM-41 Catalysts 275
MCM-41
Ti-MCM-41
Ti-Co-MCM-41
1800
1600
1400
1200
Wavenumber (cm–1)
Fig. 3. FT-IR spectra of the samples
1000
800
600
position of MCM-41, Ti-MCM-41 and Ti-Co-MCM-41 spectra,
of which 1085 cm-1 absorption peak is attributed to the asym-
metric stretching vibration of Si-O-Si bond and 800 cm-l
absorption peak may be caused by the symmetric stretching
vibration of Si-O-Si bond.
After introducing titanium into MCM-41, the larger
titanium atoms can make the molecular sieve asymmetry
structure increase and induce distortion and vibration of the
silicon oxygen tetrahedron, which results in the intensity
enhancement of Si-O-Si bond at 1085 cm-1. This is an indirect
evidence that titanium has entered into the molecular skeleton.
In addition, the vibration absorption peak of Ti-O-Ti bond is
not found at 652 cm-1, which indicates titanium exists in the
skeleton state. After cobalt is introduced into Ti-MCM-41, no
new absorption peaks appear in the spectrum of Ti-Co-MCM-
41, while the characteristic absorption peak of Ti-Co-MCM-
41 is enhanced obviously, which indicates cobalt also exists
in the skeleton state.
Fig. 4. SEM images of (a) MCM-41 and (b) Ti-Co-MCM-41
That is to say, cobalt atoms have also entered into the frame-
work of molecular sieve.
2.4
2.0
1.6
Scanning electron microscope: The morphology of the
catalysts was observed by SEM and the images are shown in
Fig. 4. The particle size of the two catalysts both ranges from
0.5 to 1 µm and the pore structure is distinct. Compared with
MCM-41, the morphology of Ti-Co-MCM-41 does not change
after the active components are loaded.
Ti-Co-MCM-41
1.2
0.8
0.4
Diffuse reflectance ultraviolet-visible absorption spectro-
scopy: Diffuse reflectance UV-visible absorption spectroscopy
has been widely used in analyzing silica-based mesoporous
molecular sieve which contains heteroatoms. The UV-visible
spectra of TiO2 should have three obvious peaks at 398, 517
and 638 nm according to the reported literatures. However, as
Fig. 5 shows, the three obvious peaks do not appear, which
means titanium has not formed TiO2. After titanium is intro-
duced into MCM-41, the strongest UV-visible absorption peak
of Ti-MCM-41 is at 220 nm and it is the characteristic peak of
four coordinated titanium, which indicates titanium atoms have
entered into MCM-41 framework of zeolite. After cobalt is
introduced into Ti-MCM-41, the main absorption peak of the
sample migrates to 222 nm and an acromion appears, which
should be the characteristic absorption band of cobalt element.
Ti-MCM-41
0.0
200
300
400
500
Wavelength (nm)
Fig. 5. UV-visible spectra of the samples
600
700
800
900
X-ray photoelectron spectroscopy analysis: Chemical
state information of the active components in the catalysts was
analyzed by XPS and Fig. 6 presents the XPS spectra of Ti
and Co by scanning the entire spectrum. It can be seen that Ti
photoelectron intensity is highest at 458.31 eV and Co photo-
electron intensity is highest at 782.61 eV. According to the
standard spectra, titanium exists in tetravalent ion state and
cobalt remains in trivalent ion state. The results indicate titanium

276 Zhang et al.
Asian J. Chem.
2.00×104
1.80×104
1.60×104
1.40×104
1.20×104
1.00×104
8.00×103
6.00×103
4.00×103
TABLE-2
EFFECTS OF THE CATALYSTS ON THE
OXIDATION OF 4-tert-BUTYL TOLUENE
Ti2p
ArCHO
yield (%)
1.08
ArCH3 ArCHO
conversion (%) selectivity (%)
Catalyst
Blank
2.99
31.94
38.89
32.14
9.19
36.2
83.5
86.2
84.1
80.6
91.8
76.5
74.5
76.3
75.2
3Ti-4Co-MCM-41a
4Ti-4Co-MCM-41
5Ti-4Co-MCM-41
4Co-MCM-41
26.7
33.5
27.0
7.4
5Ti-MCM-41
19.05
28.36
29.41
38.81
32.23
17.5
3Ti-3Co-MCM-41
3Ti-5Co-MCM-41
4Ti-3Co-MCM-41
4Ti-5Co-MCM-41
21.7
21.9
29.6
24.2
476 474 472 470 468 466 464 462 460 458 456 454 452 450
aNote: The 3Ti-4Co-MCM-41 in the table denotes the catalyst has a
b
titanium content of 3 % and cobalt content of 4 %; Note: Reaction
Binding energy (eV)
2.50×104
2.40×104
2.30×104
2.20×104
2.10×104
2.00×104
1.90×103
conditions were as follows: p-tert-butyl toluene 1 g, acetonitrile 15
mL, catalyst 0.15 g, oxygen 2 mL/min, accelerator 0.06 g, reaction
temperature 70 °C, reaction time 8 h
Co2p
The catalyst samples had larger specific surface area and pore
size and the content of active components could satisfy with
the requirements, which showed good adsorption capability
and catalytic activity. Catalytic experiments demonstrated that
the prepared catalyst was effective for catalytic oxidation of
4-tert-butyl toluene to 4-tert-butyl benzaldehyde and 4Ti-4Co-
MCM-41 had higher conversion rate and selectivity, with the
yield of 4-tert-butyl benzaldehyde up to 35 %.
ACKNOWLEDGEMENTS
810
800
790
780
Binding energy (eV)
The support of this research by National Science Foun-
dation grant (No. 21171139) is gratefully acknowledged. The
authors also acknowledge the partial support by the Key Project
of Technology Department of Shannxi Province of China (No.
2013k11-07).
Fig. 6. XPS spectra of (a) Ti and (b) Co for the catalyst
and cobalt have both entered into the molecular sieve frame-
work, which accords with the previous infrared spectrum
analysis.
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