Synthesis, characterization and catalytic performance in cyclohexane transformation by Bi2O3/MCM-41 nanocomposite materials

Article abstract of DOI:10.1080/24701556.2017.1357592

The nanoparticles of Bi₂O₃ supported on mesoporous MCM-41 were prepared in a simple way and were well characterized. The oxidation of cyclohexane to cyclohexanol and cyclohexanone under 1 atmospheric pressure of air in the absence of any solvent and reducing agents with Bi₂O₃/MCM-41 nanocomposites were considered. These nanoparticles of Bi₂O₃ supported on mesoporous MCM-41 were found to be the very effective catalysts for cyclohexane oxidation with air in a temperature range of 280–370 ?C. The influences of reaction temperature, the loading amount of Bi₂O₃ and space velocity on the oxidation of cyclohexane were also studied, and optimized conditions were investigated.

Full text of DOI:10.1080/24701556.2017.1357592

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt21
Synthesis, Characterization and Catalytic
Performance in Cyclohexane Transformation by
Bi2O3/MCM-41 Nanocomposite Materials
Majid Mozaffari & Amin Ebadi
To cite this article: Majid Mozaffari & Amin Ebadi (2017): Synthesis, Characterization and
Catalytic Performance in Cyclohexane Transformation by Bi2O3/MCM-41 Nanocomposite Materials,
Inorganic and Nano-Metal Chemistry, DOI: 10.1080/24701556.2017.1357592
To link to this article: http://dx.doi.org/10.1080/24701556.2017.1357592
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Date: 10 August 2017, At: 03:29

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Synthesis, Characterization and Catalytic Performance
in Cyclohexane Transformation by Bi2O3/MCM-41 Nanocomposite Materials
Majid Mozaffari 1, Amin Ebadi2,*
1Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran
2Department of Chemistry, Kazerun Branch, Islamic Azad University, Kazerun, Iran
*Corresponding author:Tel: +98 721 2230505; Fax: +98 721 2230508, E-mail address:
ebadiamin88@yahoo.com (A. Ebadi).
ABSTRACT
The nanoparticles of Bi2O3 supported on mesoporous MCM-41 were prepared in a simple way
and were well characterized. The oxidation of cyclohexane to cyclohexanol and cyclohexanone
under 1 atmospheric pressure of air in the absence of any solvent and reducing agents with
Bi2O3/MCM-41 nanocomposites were considered. These nanoparticles of Bi2O3 supported on
mesoporous MCM-41 were found to be the very effective catalysts for cyclohexane oxidation
with air in a temperature range of 280-370 ˚C. The influences of reaction temperature, the
loading amount of Bi2O3 and space velocity on the oxidation of cyclohexane were also studied,
and optimized conditions were investigated.
Keywords
Oxidation, Cyclohexane, Bi2O3/MCM-41, Cyclohexanol, Cyclohexanone
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Introduction
The aerobic oxidation of hydrocarbons is a major goal of today’s research in catalysis as
selectively oxidized hydrocarbons can be utilized as feedstock for the synthesis of appropriate
chemicals.[1-4] Among the oxidation of different alkanes, partial oxidation of cyclohexane to
cyclohexanol and cyclohexanone, the intermediates in the making of nylon-6 and nylon-6,6
polymers, have attracted commercial interest.[5] The present commercial process for cyclohexane
oxidation is carried out around 150-160°C and high pressure (1-2 MPa) under homogeneous
reaction condition that results in the conversion of less than 4% and selectivity of cyclohexanol
and cyclohexanone of around 70-85% using metal cobalt salt or metal-boric acid. Because of the
relatively harsh condition, low conversion, poor selectivity towards main products and
environmental hazards, scientists have been trying to improve aerobic conversion of cyclohexane
to favorite products since the 1960s.[6--18]
Supported oxides catalysts are frequently utilized as catalysts in partial oxidation reactions.[19--21]
In these catalysts, Al2O3, TiO2, SiO2, MCM-41 and ZrO2 are generally used as the supports. It is
well known that MCM-41 molecular sieve with ordered pore structures and large surface area
has been widely used as a carrier in many catalytic reactions.[22--24] Bismuth oxide has wide
applications as a catalyst for oxidation reactions.[25] Bulk oxides in general cannot be utilized in
oxidation reactions as they impart poor thermal stability that lead to fast degradation of the
catalyst. Furthermore, it is also known that bulk oxides leads to high combustion of
hydrocarbons to carbon oxides.[26] Yang Lou et al. [27] have studied the complete oxidation of CO
with dioxygen in the presence of Bi2O3 supported on Co3O4 as catalyst. In another report Huang
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and coworkers have employed Bi2O3 in gadolinia-doped ceria (GDC) as catalyst for direct
oxidation of methane. [28]
We reported previously synthesis and catalytic application of γ-alumina supported
metallophthalocyanines [MPcs] for cyclohexane oxidation to cyclohexanol and cyclohexanone
with air in the absence of solvents and reducing agents. [29] In the present work, we investigated
the influence of Bi2O3/MCM-41 nanocomposites on cyclohexane oxidation reaction in the gas
phase under atmospheric pressure and more optimized conditions were obtained in comparison
to the catalysts of the previous work. In addition to considering the catalytic properties, in this
work, the nanoparticles of Bi2O3 supported on mesoporous MCM-41 were also synthesized and
characterized properly with XRD and SEM. In the previous work, reaction temperature range
was of 300-410°C which was a relatively high temperature and MPc/γ-alumina catalysts
degraded in the presence of dioxygen with increasing temperature from 340 to 410°C but in the
present work, the reaction temperature decreased to 280-370°C that is a relatively mild
temperature for industrial applications and thermal stability of the catalysts was retained even up
to 370°C and no degradation observed in Bi2O3/MCM-41 catalyst. This is an advantage of the
application of Bi2O3/MCM-41 nanocomposites.
Experimental
Instrument and Reagents
The FT-IR spectra were recorded using a Perkin Elmer FT-IR spectrometer by employing KBr
pellet technique. X-ray powder diffraction (XRD) patterns of the samples were recorded using a
Bruker Advance D8 Diffractometer with Cu Kα radiation (λ = 0.154 nm). BET surface area was
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obtained from N2 adsorption isotherms at 77 K by a Strohlien. Scanning electron microscopy
(SEM) observations were performed by means of a Holland Philips XL30 microscope. TEM
images obtained on a Philips CM 200 FEG/HRTEM (high-resolution transmission electron
microscope) instrument operating at 200 Kv. The nanocomposites analysis was done by Energy
dispersive X-ray (EDAX) on a TESCAN MIRA3 FE-SEM. GC analysis of cyclohexane
oxidation products was performed on a Shimadzu 8A, using authentic samples equipped with a
TCD detector using OV-17, Propak-N, packed (2 m) columns and Helium as the carrier gas. The
products of oxidation were measured by GC--MS model of Thermoquest-Finnigan Trace,
equipped with a DB-1 fused silica column (with a length of 60 m and internal diameter of 0.25
mm and film thickness of 0.25 μm) with He as the carrier gas. All reagents used were of
commercial grade and were obtained from Merck. No impurities were found in the cyclohexane
before the oxidation reaction.
Preparation of Bi2O3 / MCM-41 Nanocomposites
Sodium silicate solution (25.5 - 28.5 wt % SiO2 and 7.5 - 8.5 wt % Na2O, MERK),
cetyltrimethylammonium bromide (CTAB, 99%, BDH), acetic acid glacial (100%, analytical
regent grade), Bi(NO3)3·5H2O (Aldrich), HNO3 (Fischer) and ammonium hydroxide solution
utilized as starting chemicals, all were of analytical grade.
Mesoporous MCM-41 silica was prepared using a gel mixture with a combination of 4SiO2:
1CTAB: 250H2O, which was described in the literature.[30] A required amount of the CTAB was
dissolved slowly in a suitable amount of deionized water and sodium silicate solution and was
stirred with an electro-magnetic stirrer for 30 min. By adding acetic acid drop wise, pH of the
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resultant mixture reached to 10 and the formed gel was transferred to a polypropylene bottle and
refluxed at 100°C for 24 h. After cooling and adjusting the pH at 10 with acetic acid, the mixture
was refluxed again for 24 h at 100°C. The pH adjustment and subsequent heating operations
were repeated several times for 5 days. After the gel was formed, it was filtered and washed by
deionized water and dried in an oven to form white MCM-41 nanopowders.
Anchoring of Bi2O3 nanoparticles on MCM-41 was carried out by a simple impregnation
method. 1.0 g mesoporous MCM-41 was mixed with n g (n = 0.11, 0.21, 0.31) Bi(NO3)3.5H2O
dissolved in 30 mL 0.53 mol/l nitric acid. Ammonium hydroxide solution was dropped into the
mixing solution under constant stirring till pH reached to 6-7. After stirring for 2 h, at room
temperature, the resulting precipitate was washed repeatedly with deionized water and dried in
an oven at 100°C overnight and calcined in flowing air at 450°C for 2 h.
Experimental Procedure
A vertical fixed-bed glass reactor with 9 cm length and internal diameter of 1.5 cm operating
under 1 atm pressure was utilized for the partial oxidation of cyclohexane with air. About 1 g of
the supported bismuth oxide sample with 50-70 mesh was placed on a sinter glass and fed with a
50 mL cyclohexane syringe by the automatic injector (Fresenius injectomats) at the desired
temperature. The reactor was placed inside a temperature controlled heating jacket and a
thermocouple, placed at the center of the catalyst bed was utilized to control the furnace
temperature. The liquid products were collected by passing the hot gasses through a water-cool
condenser. The range of reaction temperature was 280-370°C, air was injected at 30 mL/min
velocity and cyclohexane at 2 mL/h velocity at atmospheric pressure. The time of reaction of 3 h
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was selected and a dual channel (Shimadzu Model 8A) gas chromatograph (GC) was utilized
online for analyzing the products of oxidation.
Results and Discussion
Structural Characterization
Figure 1 shows low angle X-ray diffraction patterns of obtained MCM-41 and synthesized
nanocomposite samples Bi2O3/MCM-41. While the wide angle X-ray patterns for the prepared
MCM-41+10% Bi2O3 nanocomposite is shown in Figure 2. The very intense peak appeared at
low angle (2θ = 2.55) on the Figure 1 is assigned to reflections at (100) and two other additional
picks with low intensities at (110) and (200) reflections indicate to the regular pore structure of
MCM-41 and can be attributed to quasi-two-dimensional hexagonal lattice of MCM-41.[31] On
dispersing Bi2O3 over MCM-41, a reduction in the peak intensity of the characteristic (100) plan
is overcoming while, at higher bismuth oxide loadings samples, the peaks of (110) and (200)
planes tend to merge with the base line.
Decrease in the intensity can be attributed to the pores covering effects that reduce the scattering
contrast between the pores and the framework of MCM-41 sample. The wide angle X-ray
diffraction patterns, Figure 2, show the characteristic peaks appeared at 2θ = 26.94, 2θ = 27.40
and 2θ = 33.25 and confirm the presence of Bi2O3 phase in Bi2O3 / MCM-41 nanocomposites. In
our case, all diffraction peaks are assigned to Bi2O3 crystallized in monoclinic form
corresponding to JCPDS files no. 41-1449. The intensity of this peaks increases with increasing
Bi2O3 loading indicating the agglomeration of the particles at higher loadings. This indicates that
Bi2O3 nanoparticles remains mainly on the external surface since the bismuth oxide has a high
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kinetic diameter, which facilitates the coverage of the hexagonal channels of MCM-41 pores.
This interpretation is in agreement with XRD results in the low angle region that showed the
decrease in all peaks associated with MCM-41 structure. According to the Debye- Scherrer’s
equation: D = kλ / β cos θ
Where D is the average crystallite size, k is a constant equal to o.9, λ is the X-ray wavelength
equal to 0.15406 nm and β is the half-peak width, the mean crystallite size of the as-synthesized
products calculated according to this equation is about 15 nm.
Figure 3 shows the FT-IR spectra of MCM-41, Bi2O3 and MCM-41+10% Bi2O3 samples. In the
spectrum of the raw MCM-41 (Figure 3(a)), a broad band at 1075 cm1 is due to asymmetric
stretching vibrations of Si-O-Si bridges and the absorption bands observed at 467 and 812 cm1
is assigned to the asymmetric and symmetric Si-O stretching vibrations.[32,33] In the spectrum of
Bi2O3 (Figure 3(b)), the FT-IR spectra of crystalline α-Bi2O3 present absorption bands at: 510
and 540 cm1, specific to the vibrations of Bi-O bonds in BiO6 octahedral units and the
absorption bands at: 715 and 880 cm1, characteristic of the vibrations of Bi-O bonds in BiO3
pyramidal units.[34, 35] In the spectrum of MCM-41+10% Bi2O3 sample (Figure 3(c)), a broad
band at 1075 cm1 and a band at 812 cm1 were corresponding to the asymmetric and symmetric
Si-O stretching vibrations. The band at 715 cm1 due to symmetric stretching vibrations of Bi-O
bonds in BiO3 pyramidal units confirm the presence of Bi2O3 phase in Bi2O3 / MCM-41
nanocomposites.
The scanning electronic microscopy (SEM) results of the supported catalysts are presented in
Figure 4. The formation of spherical particles with the diameter varying between 50 to 90 nm
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was observed for MCM-41, which exhibited also a smooth surface and a homogeneous particle
size distribution. However, from (Figure 4b, c and d) the surface of the Bi2O3/MCM-41
nanocomposites showed rough. In addition, the impregnation of Bi2O3 nanoparticles on MCM-
41 generated an increase in the number and size of these nanocomposites but also the formation
of small like spherical aggregates with widths of approximately 0.5 µm.
Transmission electron microscopy (TEM) images of MCM-41 and 10% Bi2O3/MCM-41
nanocomposite are illustrated in Figure 5. The mesoporous framework of MCM-41 exposed
well-ordered hexagonal array of cylindrical channels and well-defined channels and walls
(Figure 5(a)). This is entirely consistent with the XRD results. The distribution of black spots
with a size between 15-20 nm can be attributed to the Bi2O3 nanoparticles, which is in agreement
with its measurements obtained by XRD (Figure 5(b)).
Figure 6 shows the energy-dispersive X-ray (EDX) spectra of Bi2O3/MCM-41 nanocomposites.
The result was analyzed on a small surface on the as-prepared catalysts. Peaks of atomic O, Si
and Bi were observed. It reveals that the Bi2O3 nanoparticles has been successfully grown on the
MCM-41 mesoporous. The EDX spectra revealed that the nanocomposites contained 4.68%,
10.87% and 15.37% Bi which is very close to the stoichiometric percent. Also, no other impurity
peak is found in EDX spectra, indicating that the products are pure.
Specific surface area measured with BET method was 1081 m2/g for MCM-41, 1019 m2/g for 5
wt.% Bi2O3/MCM-41, 881 m2/g for 10 wt.% Bi2O3/MCM-41 and 792 m2/g for 15 wt.%
Bi2O3/MCM-41.
Air Oxidation of Cyclohexane
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The cyclohexane oxidation reaction catalyzed by the nanoparticles of Bi2O3 supported on
mesoporous MCM-41 with air was as follows:
This reaction was operated at a temperature range of 280-370°C with molecular oxygen under 1
atmospheric pressure in the absence of solvents and co-catalysts. In the presence of 10 wt.%
Bi2O3/MCM-41, conversion percentage of cyclohexane was 27.56% with selectivity of 43.45%
for cyclohexanol + cyclohexanone at 310°C, a relatively mild system for industry. The products
of cyclohexane oxidation catalyzed by supported Bi2O3 were mostly cyclohexanol and
cyclohexanone. GC-MS analysis data showed that there were small amounts of cyclohexene,
cyclohexadiene, 5-hexen-1-al, CO and CO2. cyclohexene was formed by dehydrogenation of
cyclohexane. In this regard 22.10% of cyclohexene was obtained. The product distribution for 10
[36]
wt.% Bi2O3/MCM-41 is listed in Table 1. Zhou et al.
have reported that with gold
nanoparticles on MCM-41 catalyst and in autoclave a cyclohexane conversion percent of around
12.0% with 60.0% selectivity toward cyclohexanone was obtained using molecular oxygen as
[37]
oxidant. In another report Sun and coworker
have used MCM-41 encapsulated Co(III)-
porphyrin complex, in the reaction of cyclohexane oxidation. The results show that the reactivity
about 10.38% conversion of cyclohexane and 98.08% cyclohexanol selectivity with oxygen as
the oxidizing agent.
Contrastive experiment results revealed that cyclohexane aerobic oxidation with air did not
happen in the absence of the catalyst under similar reaction condition, and MCM-41
encapsulated Bi2O3 has shown better catalytic power for cyclohexane oxidation with air than the
corresponding unsupported Bi2O3.
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When the reaction was catalyzed with MCM-41 without any Bi2O3, cyclohexane conversion
and selectivity of the products reduced considerably in comparison with Bi2O3 supported on
MCM-41. This revealed that the active species which were responsible for the oxidation of
cyclohexane were loaded Bi2O3 on the support, because no reactivity and activity towards
cyclohexane oxidation were reported when we use only MCM-41 as a catalyst.
The stability of the catalyst was tested at the end of the reaction, and the result confirms that
stability of the catalyst is good, decomposition of nanocomposite was negligible and its reactivity
was preserved. The stability of the catalysts were investigated by XRD and FT-IR spectra. Trace
a in Figure 7 demonstrates FT-IR spectrum of the freshly prepared 10% of Bi2O3/MCM-41
before the reaction test. Trace b in Figure 7 is for the 10% of Bi2O3/MCM-41 after the reaction
test was performed at 370°C. FT-IR spectra shows that the absorption bands of 10%
Bi2O3/MCM-41 nanocomposite before and after catalytic procedure are completely similar and
revealed that the catalyst remained unchanged. Similar low-angle X-ray diffraction patterns were
obtained for the catalyst before and after the reaction test (Figure 8) and alone the intensities of
peaks in the used catalyst are reduced, indicating the stability of nanocomposites.
The Influences of Temperature on Cyclohexane Oxidation Reaction
In order to investigate the effect of temperature on the oxidation, we carried out the reaction
under different temperatures, such as 280, 310, 340 and 370°C. It showed that the reaction
temperature gives great influence on the oxidation. The results are concluded in Table 2. With
regard to the subject that importance of selectivity is more than the conversion percent, all three
catalysts showed their best performance in 310°C. Figures 9 and 10 shows how cyclohexane
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conversion and the selectivities of the products changed with reaction temperature in the
presence of various catalysts, respectively.
As shown in Table 2 the rise in reaction temperature from 280 to 370°C, increased the
conversion of cyclohexane and the highest value of the conversion was obtained when reaction
temperature was increased to 370°C. As for the distribution of the products, with increasing
reaction temperature from 280 to 310°C, the selectivity of cyclohexanone and cyclohexanol
increased and reached its maximum in 310°C. When reaction temperature was increased from
310°C to 370°C, selectivity of the cyclohexanone and cyclohexanol decreased considerably.
Moreover, in higher temperatures more CO and CO2 were formed that were the products of full
oxidation. The lessening of selectivity at higher temperatures may be as a result of oxidative
destruction of the products.
The Influences of the Loading Amount of Bismuth Oxide on Cyclohexane Oxidation Reaction
For investigating of the loading effect Bi2O3 on the conversion and selectivity of the products,
three catalysts were tested. In Table 2, details of the conversion and selectivity of the products
for each catalyst are shown. It is observed that maximum conversion and selectivity for desired
products occur with the catalyst of 10 wt.% Bi2O3. It is known that Bi2O3 nanoparticles can be
highly dispersed on mesoporous MCM-41 at 10 wt.% loading. The reduction of conversion of
cyclohexane and selectivity for the main products of the catalyst with higher loadings than 10
wt.% maybe due to a distortion of the long range ordering of the mesoporous structure and/or
badly built hexagonal array and more decrease of the specific surface area of the catalyst. Under
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these reaction conditions, the order of catalytic activities is as follows: 10 wt.% Bi2O3 / MCM-41
> 15 wt.% Bi2O3 / MCM-41 > 5 wt.% Bi2O3 / MCM-41.
The Influences of Space Velocity on Cyclohexane Oxidation Reaction
The effects of space velocity on the conversion of cyclohexane and selectivity of
cyclohexanol and cyclohexanone can be seen in table 3. Space velocity refers to the quotient of
the entering volumetric flow rate of substrate divided by the catalyst volume which indicates
how many reactor volumes of feed can be reacted in a unit time. Space velocity is an indicator
for contact time of substrate with the catalyst. In space velocities more than 3299 h1 (rate of
cyclohexane injection = 2.5 mL/h and rate of air flow = 30 mL/min), contact time of
cyclohexane with catalyst is short and conversion percent and selectivity of cyclohexanol and
cyclohexanone are low. Thus, in space velocities lower than 3004 h1 (rate of cyclohexane
injection = 1.5 mL/h and rate of air flow = 30 mL/min), contact time appears too much, chief
oxidation products are CO and CO2 and selectivity of cyclohexanol and cyclohexanone is
reduced. When O2 flow rate is lowered, the conversion of cyclohexane and selectivity for the
main products also reduced i.e. for space velocity 2297 h1 (rate of cyclohexane injection = 2
mL/h and rate of air flow = 20 mL/min). The best combination for high conversion percent and
good selectivity for cyclohexanol and cyclohexanone was attained at 3151 h1 space velocity
(rate of cyclohexane injection = 2 mL/h and rate of air flow = 30 mL/min). Thus, contact time of
the reactants with catalyst appears a main factor for high conversion and specificity of the
products.
Discussion
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In order to explain how the oxidation occurred, based on the literatures [38], it seems that
oxidation of cyclohexane using O2 as oxidant proceeds via a radical-chain sequence mechanism
as shown in Scheme 1.
Conclusions
This work investigates the preparation, characterization and activity of Bi2O3/MCM-41
nanocomposites for oxidation of cyclohexane with air, in the absence of any reductant, solvent
and co-catalyst. The nanoparticles of Bi2O3 supported on mesoporous MCM-41 were found to be
potentially active and selective catalysts for the partial oxidation of cyclohexane to desired
products. Bismuth oxide supported on mesoporous MCM-41 resists destructive oxidation and
can be easily separated after the reaction. Maybe, it is more suitable for industrial applications
than the equivalent unsupported catalyst. The factors that influence the oxidation were also well
investigated. It can be concluded that the optimum reaction condition of the oxidation is: catalyst
10 wt.% Bi2O3 / MCM-41, 1 atm air, space velocity 3151 h1 and temperature 310°C.
Acknowledgements
The authors are grateful to the Research Council of Shahrood and Kazerun branch, Islamic Azad
University for financial assistance.
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Table 1. Product distribution for cyclohexane partial oxidation by air at T = 310°C, P = 1 atm,
rate of cyclohexane injection = 2 mL/h, rate of air flow = 30 mL/min and catalyst 10 wt.%
Bi2O3/MCM-41
Producta
Selectivity (%)
22.10
23.14
20.31
11.25
6.77
Cyclohexene
Cyclohexanone
Cyclohexanol
CO2
Cyclohexadiene
CO
7.09
5-Hexen 1 al
6.31
Methanol
1.08
Ethanol
0.75
Phenol
0.68
Phermaldehide
0.52
a Only products with ≥0.5% selectivity are shown.
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Table 2. The effect of reaction temperature on aerobic oxidationa of cyclohexane
Catalyst
Temperature
Conversion
Selectivity productsb (%)
(°C)
280
310
340
370
280
310
340
370
280
310
340
370
280
310
340
370
(%)
A
B
C
D
E
F
5% Bi2O3/MCM-41
5% Bi2O3/MCM-41
5% Bi2O3/MCM-41
5% Bi2O3/MCM-41
10% Bi2O3/MCM-41
10% Bi2O3/MCM-41
10% Bi2O3/MCM-41
10% Bi2O3/MCM-41
15% Bi2O3/MCM-41
15% Bi2O3/MCM-41
15% Bi2O3/MCM-41
15% Bi2O3/MCM-41
Bi2O3
14.23
20.46
22.37
25.43
19.75
27.56
29.81
31.76
15.21
22.89
24.11
27.93
11.66
15.52
19.73
23.43
21.67 16.21 15.52
22.19 17.48 16.88
24.76 13.24 12.98
27.35 10.76 9.66
20.16 20.25 18.62
22.10 23.14 20.31
25.36 17.82 15.47
26.02 14.32 13.71
21.43 17.26 16.30
23.31 19.96 18.92
24.32 15.46 14.23
26.71 11.78 10.12
21.17 13.21 11.78
11.22 11.25 9.63
7.58
7.15
9.71
9.83
7.16
6.77
8.72
9.47
7.26
7.43
8.37
9.26
6.61
6.31
7.22
5.76
6.76
7.53
7.37
6.44
7.23
6.31
6.86
7.35
7.76
6.37
7.49
8.19
5.10
5.36
5.39
6.35
29.01
25.41
28.14
32.49
22.78
18.34
22.27
26.08
26.23
21.01
26.33
30.44
38.53
52.63
60.35
68.25
Bi2O3
Bi2O3
12.45
9.85
6.67
4.15
4.14
2.05
Bi2O3
a
Catalyst = X% Bi2O3/MCM-41 nanocomposites, catalyst weight = 1 g, reaction time = 3 h, P = 1 atm,
rate of cyclohexane injection = 2 mL/h and rate of air flow = 30 mL/min.
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b A = cyclohexene, B = cyclohexanone, C = cyclohexanol, D = cyclohexadiene, E = 5-hexen 1-al, F =
COx.
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Table 3. The effect of space velocity on the conversion of cyclohexane and selectivity of
cyclohexanol and cyclohexanone formationa
Space velocity (h1)
Conversion (%)
22.14
Selectivity (%)
21.36
2297
3004
3151
3299
4006
33.44
34.67
27.56
43.45
20.37
37.85
14.11
32.36
a Catalyst = 10 wt.% Bi2O3/MCM-41, T = 310°C, catalyst volume ≈ 1.5 mL, catalyst weight = 1
g, reaction time = 3 h, P = 1 atm
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Fig. 1. XRD patterns of samples MCM-41 and Bi2O3/MCM-41 nanocomposites.
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Fig. 2. XRD pattern of 10% Bi2O3/MCM-41 nanocomposite.
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Fig. 3. FT-IR spectra of: (a) MCM-41 (b)Bi2O3 (c) 10% Bi2O3/MCM-41.
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Fig. 4. SEM images of (a) MCM-41 (b) 5% Bi2O3/MCM-41 (c) 10% Bi2O3/MCM-41 (d) 15%
Bi2O3/MCM-41.
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Fig. 5. TEM images of (a) Pure MCM-41 mesoporous and (b) 10% Bi2O3/MCM-
41nanocomposite.
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Fig. 6. EDAX spectrums of (a) 5% Bi2O3/MCM-41 (b) 10% Bi2O3/MCM-41 (c) 15%
Bi2O3/MCM-41 nanocomposite.
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