MnAPO-5 as an efficient heterogeneous catalyst for selective liquid phase partial oxidation reactions

Article abstract of DOI:10.1039/c7dt03897f

Heterogeneous catalysts play a key role in addressing the economic and environmental issues of the chemical industry due to their several advantages, like ease of product separation, work-up and high recycling efficiency. Herein, we report the synthesis of a robust manganese(iv)-containing aluminophosphate material (MnAPO-5), with an AFI framework topology. This material has been characterized thoroughly by powder XRD, XPS, UHR TEM, FE SEM, ³¹P CP MAS NMR, atomic absorption spectroscopy, UV-visible spectroscopy and TGA. The Mn-containing microporous material has been employed as a heterogeneous catalyst for the oxidation of styrene and the synthesis of adipic acid from cyclohexanone in the presence of tert-butyl hydroperoxide (TBHP) as the oxidant in air and it displayed very high recycling efficiency.

Full text of DOI:10.1039/c7dt03897f

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
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MnAPO-5 as an efficient heterogeneous catalyst for selective
liquid phase partial oxidation reactions
Sauvik Chatterjee,a Piyali Bhanja,a Luna Paul,b Mahammad Ali,b and Asim Bhaumik*,a
Received 00th January 20xx,
Accepted 00th January 20xx
Heterogeneous catalysis play key role to address the economic and environmental issues of the chemical industry due to
their several advantages, like ease of separation, work-up and high recycling efficiency. Herein, we report the synthesis of
a robust manganese(IV) incorporated aluminophosphate material (MnAPO-5), with AFI framework topology. The material
has been characterized thoroughly by using the powder XRD, XPS, UHR TEM, FE SEM, 31P CP MAS NMR, atomic absorption
spectroscopy, UV-Visible spectroscopy and TGA. The Mn-incorporated microporous material has been employed as a
heterogeneous catalyst for the oxidation of styrene and synthesis of adipic acid from cyclohexanone in the presence of
tert-butyl hydroperoxide (TBHP) as oxidant in air together with high recycling efficiency.
DOI: 10.1039/x0xx00000x
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long been used as heterogeneous catalyst for liquid phase
partial oxidation reactions in the presence of dilute aqueous
H2O2 as oxidant.6 Similarly a wide range of microporous
Introduction
Selective oxidation of organics is a key step for the industrial
production of a wide range of bulk and fine chemicals.1 Several
organic reactions can undergo stoichiometrically under harsh
conditions, which lead to hazardous and toxic industrial
wastes. Further, the work-up and removal of reactants or
catalysts from the reaction mixtures require the usage of
volatile organic solvents.2 Moreover, for the removal of
organic pollutants from waste water often selective partial
oxidation routes are followed.3 An important step in achieving
higher efficiency in these organic transformations is the use of
heterogeneous catalysts, which are green, economical and
environmentally benign.4 Hence, ecological as well as
economical strategies for the chemical transformations are
very demanding.
aluminophosphates have been synthesized by using organic
amines as structure directing agent.7 For these microporous
heterogeneous catalysts catalytic sites located at the surface
of the catalyst comes in contact of the reactant during the
reaction. Thus, the successful incorporation of a transition
metal in these high surface area materials can lead to higher
catalyst efficiency.
Manganese (III) has been exploited as oxidant for oxidation
of ethyl benzene, toluene, cumene and other aromatics under
liquid phase reaction conditions.8 In this context, catalytic
oxidation of styrene have been carried out over transition
metal containing catalysts composed of a wide range of metals
like Cr, Fe, Co, Cu, Ni, Zn, Mn and several lanthanide sulphates
and chlorides as homogeneous catalyst using organic
peroxides as oxidant.9 Often the use of molecular oxygen as
oxidant found beneficial for these catalytic reactions.10 Among
the alumino-phosphate based molecular sieves AlPO4-5 is the
most widely studied material due to its open framework
structure and ease of synthesis.11 Manganese can be
incorporated in the porous nanomaterials either through
framework substitution or grafting of Mn-complexes at the
mesopore surfaces12 and due to the presence of redox active
Mn-sites these materials have great potential to be utilized in
liquid phase oxidation catalyst using peroxides as oxidant. For
these transition metal mediated organic transformations, the
oxidation can proceeds smoothly in the presence of dilute
aqueous H2O2, tert-butyl hydroperoxide (TBHP) or simply air as
oxidant. In this contest, Akolekar has reported the
incorporation of Si, Mn, Ni in the AlPO4-11 framework and
Crystalline inorganic porous materials like zeolites can
catalyze a wide range of acid catalyzed reactions.5 The pore-
size and surface area play crucial role in the catalytic efficiency
of the zeolites. CaA, ZSM-5, NaX etc. zeolites have long been
used as catalyst in the industries and framework engineering
of these inorganic porous nanostructures also make them
more versatile for a broader spectrum of chemical research.1
Transition metal incorporated microporous materials have
a.Department of Materials Science, Indian Association for the Cultivation of Science,
Jadavpur, Kolkata 700 032, India.
*Corresponding author. Email: msab@iacs.res.in
b.Department of Chemistry, Jadavpur University, Jadavpur, Kolkata – 700 032,
India.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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used the resulting materials as catalyst for several acid
catalyzed reactions.13
Here we report a very convenient and efficient synthetic
route for the incorporation of Mn(IV) in the AlPO-5 framework
and used the resulting MnAPO-5 material as a heterogeneous
catalyst for the selective oxidation of styrene. Further, adipic
acid is a very important dicarboxylic acid needed as raw
material for the synthesis of polyester nylon 6,6 and many
other condensation polymers. Conventional route for the
synthesis of adipic acid involved the use of hazardous HNO3 as
oxidant for the oxidation of cyclohexane or a mixture of Figure 1: PXRD plots of as-synthesised and calcined MnAPO-5
cyclohexanol and cyclohexanone.14 Thus, we have also (a) and indexing of the respective PXRD plot (b).
employed MnAPO-5 as an eco-friendly recyclable catalyst for
the selective oxidation of cyclohexanone to adipic acid.
Results and discussion
Powder X-Ray Diffraction (PXRD): To identify the crystalline
phase present in the Mn-loaded AlPO4 material the PXRD
analysis of the MnAPO-5 has been carried out. Powder XRD
data was taken in the range of 5-50 degrees of 2θ (Figure 1a)
and it was found to match with the pattern of standard AFI
with space group P6mm. The powder XRD patterns correspond
well with the standard AlPO-5. Peaks appear at 7.5, 12.9, 14.9,
19.8, 21.2, 22.5, 26.0, 29.1, 30.1, 33.7, 34.5, 37.0, 37.7 degrees
of 2θ, could be assigned to the 100, 110, 200, 210, 002, 211,
202, 311, 400, 222, 411, 402 and 213 planes, respectively.15
PXRD was taken both before and after calcination of the
MnAPO-5 (Figure 1b). The d100 value for MnAPO-5 was 11.77
Å, which agrees well with the metal incorporated aluminium
Figure 2: PXRD pattern for AlPO4-5 and MnAPO-5 with 1%, 3%
and 5% loading of manganese.
phosphates.16 A hump between 10 to 17 degrees of 2
θ was
observed in the as-synthesized sample and this has been
removed after calcination. We have increased the Mn-loading
from 1-3 wt%, the material has retained its 3D-hexagonal
PXRD pattern (Figure 2). For MnAPO-5 with 1% of manganese
loading the unit cell parameters were a = b = 1.363 nm c =
0.837 nm; for MnAPO-5 with 3% Manganese loading the cell
parameters are a = b = 1.366 nm c = 0.839 nm. AlPO4-5
synthesized without using Mn-precursor under indentical
conditions resulted hexagonal AFI phase. The unit cell
parameters for that AlPO4-5 material are a = b = 1.339 nm and
c = 0.836 nm. Little increase in the unit cell parameters for 1
and 3% Mn-loaded samples vis-à-vis AlPO4-5 suggested
isomorphous substitution of Al(III) by Mn (IV) in the
aluminophosphate framework (since Mn-O bond length 1.92
Å for both Mn+3 or Mn+4 is significantly larger than that of Al-O,
1.62 Å). However, further increase in Mn-loading of 5 wt%
resulted in the disappearance of AFI phase (Figure 2) and
appearance of α-manganese phosphate phase.17 This result
suggested that more than 3% loading of Mn-salt in the
synthesis gel is not favourable for the incorporation of Mn in
the AlPO4 framework.
Figure 3: 27Al and 31P MAS MNR spectrum of MnAPO-5.
Spinning sidebands are marked with asterisks (*).
framework can vary in the range of between -25 and -30
ppm.17 31P NMR of MnAPO-5 showed one resonance peak at -
26 ppm (Figure 3) and this agrees well with the related AlPO4
materials.17 Here we also observed two spinning side-bands at
0 and -49 ppm, respectively. 27Al CP MAS NMR spectrum for
the MnAPO-5 material showed an intense peak at 40 ppm,
which suggested the presence of tetraheadrally coordinated Al
atoms as observed for AlPO-5.18 Further, a broad peak with
maxima at ca. 7.0 ppm is observed, which suggested the
presence of considerable penta-coordinated aluminium
atoms.18
27Al & 31P Solid state magic angle spinning (MAS) NMR: To
understand the nature of the alumino phosphate framework
and the chemical environment of P the solid 31P CP MAS NMR
of MnAPO-5 was taken. From the literature we know that 31P
chemical shifts of P in [PO4]-3 groups of the alumina phosphate
2 | J. Name., 2012, 00, 1-3
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Thermal analysis (TG-DTA): To understand the thermal 115 m2 g-1. The pore-size distribution plot using Saito and Foley
stability of MnAPO-5 thermogravimetric analysis of calcined (SF) method is shown in the inset of Figure 5. The estimated
MnAPO-5 sample has been carried out in the temperature peak pore width found to be micropore with 0.48 nm. Further,
range of 25-800 °C (Figure 4). Initial major weight loss was the pore size distribution plot suggested the presence of larger
observed at around 100 ⁰C temperature. This could be pores with different pore diameters. Good surface area and
assigned to the absorbed water molecules inside the uniform dispersion of the incorporated Mn-centres in the
micropores of MnAPO-5. No major weight loss was observed AlPO4 framework favour higher catalytic activity of the
after this temperature. Thus, our MnAPO-5 is robust and material.
considerably stable upto 800 ⁰C.
X-ray photoelectron spectroscopic (XPS) analysis: To find out
the oxidation state and binding energy of the incorporated
manganese atoms in the AlPO4 framework the XPS analysis of
100
MnAPO-5 has been carried out. In Figure 6 the XPS survey
90
spectrum of Mn 2p3/2 is shown. The observed binding energy
80
70
60
50
40
30
for the Mn 2p3/2 was 644 eV. This binding energy suggested
the oxidation state of +4 for the manganese atoms.20 The
atomic contribution on the surface Mn(IV) was measured from
this XPS data. From the XPS data we observed the presence of
Mn(IV) on the surface to be 0.88 wt% in MnAPO-5. Further,
the short range XPS spectra for Al2p3/2, O1s, Al2s together
with full range XPS survey spectra of MnAPO-5 as shown in
Figure S1 suggested the presence of O, Al, P and Mn in Mn-
APO-5 material.
TGA
DTA
200
400
Temperature ( C)
600
800
ο
Figure 4: TG-DTA plot for MnAPO-5 under air atmosphere.
BET surface area and porosity: For an AlPO4 based material it
is crucial to find the microporosity and BET surface area after
the incorporation of the heteroelement. The N2 adsorption-
desorption isotherm of MnAPO-5 is shown in Figure 5. This
isotherm can be classified into a mixture of both type I and
type II isotherms, corresponding to the steep raise in N2
uptake at very low P/P0 region and low increase in N2 uptake
in the intermediate region of P/P0.19 This indicates
microporous nature of the material. But at higher P/P0 of N2
the reversibility of adsorption and desorption is lost slightly.
This could occur due to inter-particle porosity. The Brunauer–
Emmett–Teller (BET) surface area of the catalyst found to be
Figure 6: XPS spectrum of Mn 2p3/2.
Electron microscopic analyses: The nanostructure and
morphological feature of MnAPO-5 was analyzed through the
field-emission gun transmission electron microscopic (FEG-
TEM) and field emission scanning electron microscopic (FE-
Figure 5: N2 adsorption-desorption isotherm for MnAPO-5 at
77 K; the pore size distribution using SF method is shown in Figure 7: Electron mapping (a-d) and FE-SEM image (e) of
the inset.
MnAPO-5.
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Table 1: Catalytic activity of MnAPO-5 in oxidation of styrene under different reaction conditions using acetonitrile as solvent
Oxidant
Temp (⁰C)
Conversion Styrene oxide
(%)
Benzaldehyde
Benzoic acid
1-phenyl-1,2-ethanediol
TBHP
65
65
75
75
85
85
80.70
84.34
75.91
88.55
95.32
87.64
1.64
17.67
17.74
0.49
0.48
3.04
0.28
10.26
2.16
2.10
0.26
2.57
74.86
57.10
41.28
66.04
68.81
41.98
21.41
15.02
38.80
31.37
30.15
52.41
TBHP + Air
TBHP
TBHP + Air
TBHP + Air
TBHP
SEM) analysis of the MnAPO-5 sample. The FEG-TEM electron Catalysis:
mapping images of the constituent elements of MnAPO-5 are
shown in figure Figure 7a-d. The particle size determined from MnAPO-5 has been employed as catalyst for the liquid phase
this FE-SEM image suggested spherical particles having particle selective oxidation of styrene under different reaction
dimensions of ca. 15.0 nm (Figure 7e). The Energy-dispersive conditions. Controlled reactions have been performed to find
X-ray spectroscopy (EDXS) data showed ca. 1.0 atomic % Mn out the role of air, TBHP and catalyst. In the absence of either
loading, which agrees well with the XPS analysis. This TBHP or MnAPO-5 catalyst the reaction resulted no oxidation
elemental mapping data suggested the homogeneous product. This indicates the reaction cannot be carried out
distribution of constituent elements in MnAPO-5 material.
without catalyst. Again in the presence of catalyst and air
bubbling, but without TBHP the reaction did not proceed. This
Chemical analysis: The atomic absorption spectroscopy (AAS) is an indication that the the reaction is initiated by TBHP. With
was employed to find out the Mn loading in MnAPO-5. AAS TBHP it showed considerable yield for the oxidized products,
analysis result suggested the manganese loading of 0.97 wt% styrene oxide, benzaldehyde, benzoic acid and 1-phenyl-1,2-
in MnAPO-5 for 1% Mn loaded sample. Whereas, for the ethanediol. However, the yields of the products increase
MnAPO-5 material with input 3% Mn-salt in the synthesis gel slightly when air is bubbled into the reaction mixture during
resulted 3.06% Mn loading.
the reaction. This result suggested that MnAPO-5 has the
ability for utilizing atmospheric oxygen in this oxidation
UV-Vis Spectroscopy analysis: The UV-Visible spectra of reactions. Styrene oxidation was carried out with different
MnAPO-5 samples showed two peaks around 215 nm and 248 homogeneous catalysts containing manganese
nm and a broad band near 482 nm (Figure 8). The peak near salts/complexes. As seen from Table 1 that at elevated
482 nm could be attributed to 4A2 4T2 transition of Mn+4 temperature yield increases substantially. If we consider each
→
ions.21,22 This also confirms the oxidation state of manganese. temperature conditions separately we can observed under air
The peaks near 215 and 248 nm are two unresolved charge bubbling the yield is higher than that of without air-bubbling.
transfer bands. The intensity of the broad band at 482 nm
The selectivity of the oxidation products varied largely with the
increase in reaction temperature. At 85 ⁰C temperature the
selectivity is more for benzoic acid when the reaction takes
place under aerobic conditions but in the absence of air 1-
Table 2: Comparative table of conversion of styrene over
different catalysts under liquid phase reaction conditions
Name
of Conversion
Temp Time
Reference
catalyst
MnP
(%)
97
(
C)
(h)
24
24
24
24
6
RT
RT
RT
RT
80
80
80
RT
60
23
23
23
23
24
24
24
25
26
MnMont1
MnMont2
MnSil2
55
43
65
BW11Mn
PW11Mn
SiW11Mn
100
10
6
Figure 8: UV-Visible spectra for MnAPO-5 with different Mn
11
6
loadings.
1-Mn-Xln10A
[Mn(3-
26
18
1
3
increases when the loading is increased from 1% to 3% but
vanishes upon increasing to 5%. This result also supported the
XRD data and suggested this hydrothermal synthesis is not
feasible for higher loading of manganese in AlPO4
framework.17
MeOsalen)]@
X
MnAPO-5
95
85
8
This work
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Table 3: Selective oxidation of cyclohexanone to adipic acid over MnAPO-5 under different reaction conditions
Solvent
Oxidant
TBHP
Temperature (⁰C)
Time (h)
Yield (%)
36.2
45.4
80.6
87.0
93.2
95.6
100
TON
205
257
456
493
528
541
566
120
224
434
456
460
Acetonitrile
65
65
85
85
85
85
85
85
65
85
85
85
8
8
Acetonitrile
TBHP+ Air
TBHP
Acetonitrile
8
Acetonitrile
TBHP+ Air
TBHP+ Air
TBHP+ Air
TBHP+ Air
Air
8
Acetonitrile
12
24
72
8
Acetonitrile
Acetonitrile
Acetonitrile
21.3
39.6
76.7
80.6
81.2
Acetonitrile
TBHP
16
8
Water+ Acetic Acid
Water+ Acetic Acid
Water+ Acetic Acid
TBHP + Air
TBHP + Air
TBHP + Air
12
24
1.0 g (10.2 mmol) cyclohexanone, 1.24 g (4.1 mmol) 30% aqueous solution of TBHP 10 ml MeCN and 0.050 g (5 weight%)
MnAPO-5
phenyl-1,2-ethanediol is more favoured. This suggests that of vicinal intermediate via attack of the Mn-peroxo species,
under air at atmospheric pressure the catalyst may have which could generate in the presence of TBHP with the
oxygen binding capacity that enhanced C-C bond cleavage. MnAPO-5 catalyst. This intermediate can give epoxide or diol
Whereas, in the presence of air the epoxide yield was quite along with the C-C cleavage product benzaldehyde. The
low. A comparative study for other reported catalysts in possibility of the reaction to proceed through radical
reference of MnAPO-5 under similar reaction conditions is mechanism was checked. The reaction was started under the
given in Table 2. As seen from this table that apart from MnP optimized conditions and after 2 h of the initiation of the
and PW11Mn, most of the related Mn-catalysts showed much reaction
2,4-ditertbutylphenol
was
added.
2,4-
lower catalytic activity than MnAPO-5. A possible mechanism ditertbutylphenol is a well-known radical scavenger. The
for this liquid phase oxidation over MnAPO-5 is shown in the progress of the reaction has been monitored by a GC and after
Figure 9. Possibly the reactionproceeds through the formation
8 h and no significant change in the conversion level was
observed at the end of the reaction. This result rules out the
possibility of radical pathway for the oxidation of styrene.
Benzaldehyde obtained in the reaction was further oxidized in
the presence of excess oxidant to benzolic acid as one of the
major products.
Oxidation of cyclohexanone to adipic acid
Adipic acid (AA) is one of the most demanding dicarboxylic acid
used in chemical industry. Cyclohexanone was oxidised in the
presence of TBHP oxidant and MnAPO-5 as a catalyst for
synthesis of adipic acid. Many polyoxometalate27 and
transition metal containing microporous and mesoporous
molecular sieves are reported this conversion. But the yield of
adipic acid is often quite low. While HNO3 gives almost 100%
28
and Na2WO4 resulted 90% conversion of cyclohexanone,
these homogeneous catalysts mostly gave 50-70% selectivity
for adipic acid. Mn(acac)2 have been reported to give 67%
adipic acid29 (6h, AcOH). We have employed MnAPO-5 as
catalyst and TBHP as oxidant with different solvents and
reaction temperatures to optimize the product yield in this
reaction. As seen from Table 3 MnAPO-5 showed very good
catalytic activity and high selectivity for the synthesis of adipic
acid (ESI: Figures S2,3). In this reaction ε-caprolactone was
1
found in the intermediate as confirmed from the H NMR of
Figure 9: Probable mechanism for the partial oxidation of the crude product (ESI: Figure S4). This helps in predicting the
styrene over MnAPO-5 catalyst.
possible reaction pathway for this selective oxidation reaction.
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The presence of the peak at 4.1 ppm in the NMR of the crude cyclohexanone to adipic acid for six consecutive reaction
mixture suggests that Baeyer-Villiger oxidation takes place at cycles. An optimised reaction condition was set, where 1.0 g
first to produce ε-caprolactone and then the ring is cleaved to (10.2 mmol) cyclohexanone was taken with 1.24 g (4.1 mmol)
give adipic acid. The reaction reached optima after 8 h to give 30% aqueous solution of tert-butylhydroperoxide and 10 ml
nearly 87% yield. If the reaction is preceded further the acetonitrile for 8 h and air bubbling at 85 °C. The catalyst was
increase in yield is very slow as after 12 h of reaction at 85 ⁰C recovered after each reaction and activated at 150 °C for 2 h
the yield is 93% and after 1 day the yield is 95%. The full before the next cycle. In Table 4 we have summarized the AA
conversion to adipic acid was observed after 72 h of the start yields for 6 consecutive cycles and from these yields it is clear
of the reaction with 100% selectivity. Air-bubbling through the that the MnAPO-5 catalyst has retained its catalytic activity
reaction medium helps to increase the AA yield it suggests that consistently. The UHR-TEM image of the used catalyst after six
the aerial oxygen can bind with the Mn(IV) centres of MnAPO- reaction cycles (ESI: Figure S5) also suggested the retention of
5 and that provide necessary peroxo species for the oxidation porosity and morphological features upon reuse. To find out
reaction. When the reaction was carried out in the absence of whether any metal is leached from the catalyst during
MnAPO-5 catalyst, the observed AA yield reduced to less than
thereaction process the reaction mixture was taken at the end
of the reaction and filterer on Whatmann No.1 filter paper and
AAS was done with that. No significant presence of Mn was
detected in the reaction mixture. This result suggested almost
no leaching of manganese from MnAPO-5 under this liquid
phase catalytic reaction. This result suggested high chemical
Figure 10: Schematic representation of oxidation of stability of Mn-incorporated AlPO-5 material under liquid
cyclohexanone to adipic acid.
phase reaction conditions in the presence of peroxide
oxidants.
10%. The reaction when carried out in water and acetic acid
medium and the observed yield was 77% at 85 ⁰C after 8 h.
This reaction could reach 81% after 24 h reaction. Hence, it
seems that the reaction almost stopped after some time in
aqueous acetic acid medium. This result suggested that adipic
acid can be synthesised using water as medium but the
product yield would be much lower than the stoichiometry. On
the other hand, in acetonitrile the optimum AA yield was
observed after relatively shorter reaction time. The proposed
reaction pathway for the oxidation of cyclohexanone to AA is
shown in Figure 10. Here the reaction proceeds through
Baeyer-Villiger oxidation to ε-caprolactone, which further
undergoes oxidative cleavage of C-C to yield AA.30 These
experimental data suggested Mn-incorporated AlPO4 material
MnAPO-5 can act as an efficient oxidation catalyst for a broad
spectrum of substrates under liquid phase reaction conditions.
Experimental
Materials and methods
MnSO4.H2O was procured from Merck, India. Triethylamine,
orthophosphoric acid (85%) and cyclohexanone were
purchased from Merck, India, whereas aluminium
isopropoxide was purchased from Loba Chemicals.
The powder XRD patterns of AlPO4-5 and MnAPO-5
samples were recorded using Bruker AXS D-8 Advanced SWAX
and a PANalytical X’Pert PRO diffractometers with CuKα
(λ=0.15406 nm) radiation. For the N2 sorption measurement
Quantachrome Autosorb 1-C system was used. At first the
sample was degassed at 150 ⁰C to remove any adsorbed
moisture under vacuum. The non-local density function theory
(NLDFT) method was employed to find out the average pore
size distribution. The 31P MAS NMR spectra of the material and
1H NMR were recorded with a Bruker Advance 500 MHz NMR
spectrometer. The solid state UV/Vis spectra were recorded
Recycling efficiency of MnAPO-5: Recycling efficiency of
MnAPO-5 was checked for the selective oxidation of
Table 4: Recycling efficiency of MnAPO-5 for the selective
with
background standard sample. FE-SEM images were taken with
Jeol JEM 6700 microscope. Transmission electron
a Shimadzu UV 2401PC spectrometer BaSO4 as a
oxidation of cyclohexanone to adipic acid
a
Number of cycles
Conversion %
microscopic images were recorded on a JEOL 2010 TEM
operated at 200 kV and the sample was prepared by dropping
a sonicated ethanolic suspension of the MnAPO-5 material
1
2
3
4
5
6
87
87
86
86
86
86
onto
spectroscopy (AAS) analysis was carried out using manganese
standards on Shimadzu AA-6300 atomic absorption
a carbon-coated copper grid. Atomic absorption
a
spectrophotometer. The TG/DTA analysis was performed at a
temperature ramp of 10 °C min−1 with a TA-SDT Q-600 thermal
analyser under N2 flow. The X-ray photoluminescence
spectroscopic study has been carried out by using an Omicron
Nanotechnology GmbH XPS machine. The conversion and
selectivity of the oxidation products of styrene and
1.0 g (10.2 mmol) cyclohexanone taken with 1.24 g (4.1
mmol) of the 30% aqueous solution of tert-
butylhydroperoxide, 0.050 g (5 weight%) MnAPO-5 and 10
ml acetonitrile.
6 | J. Name., 2012, 00, 1-3
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cyclohoxanone was measured by an Agilent 7890D gas thoroughly by powder PXRD, N2 Sorption, 31P MAS NMR, FEG-
chromatography (FID detector) fitted with a capillary column.
TEM, FE-SEM and UV-Visible spectroscopic techniques. The
MnAPO-5 material displayed high catalytic activity in the
Catalyst preparation: The MnAPO-5 catalyst was synthesized selective oxidation of styrene to benzoic acid and
by using a modified hydrothermal method.13 In a typical cyclohexanone to adipic acid under mild liquid phase reaction
synthesis at first ortho-phosphoric acid (1.15 g, 0.001M) was conditions. High catalytic activity of MnAPO-5 suggested its
taken in a beaker and diluted with water (0.6 mL). To that promising future in the selective oxidation of a wide range of
aqueous solution of MnSO4.H2O (0.169 g taken in 1.3 mL organics under eco-friendly reaction conditions.
water) was added under stirring. Then aluminium isopropoxide
(2.06 g, 0.05M) was added to it in parts very slowly under
Conflicts of interest
vigorous stirring. 2.1 mL triethyl amine was added to it to
adjust its pH ca. 5.5-6.0 and stirred for 4 h under covered
conditions. Then the thick pest was transferred to a Teflon
lined autoclave and placed it in 200 ⁰C for 44 h. After the
hydrothermal treatment the autoclave was cooled to room
temperature, the resulting solid mass was filtered and the
washed repeatedly with water to remove the dissolved organic
mass. The residue was then calcined in box furnace at 873 K to
remove the triethyl amine template molecules. The final
calcined MnAPO-5 material was pink in colour. For the sample
prepared with 3% and 5% manganese loading the same
method was followed, only the concentration of MnSO4 has
been increased to 3 and 5 times respectively.
The authors declare no conflict of interest.
Acknowledgements
SC would like to thank DST, New Delhi for a INSPIRE-JRF. PB
thanks CSIR, New Delhi for a Senior Research Fellowship. AB
thanks DST, New Delhi for the Indo-Egypt joint research grant.
Notes and references
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Table of contents
MnAPO-5 as an efficient heterogeneous catalyst for selective liquid phase
partial oxidation reactions
Sauvik Chatterjee,a Piyali Bhanja,a Luna Paul,b Mahammad Ali,b and Asim Bhaumik*,a
A robust manganese(IV) incorporated aluminophosphate material (MnAPO-5) with AFI
framework has been developed which showed excellent catalytic efficiency in selective
oxidation of styrene and synthesis of adipic acid from cyclohexanone.
1