Oxidation catalyst obtained by the immobilization of layered double hydroxide/Mn(III) porphyrin on monodispersed silica spheres

Article abstract of DOI:10.1039/c7dt03656f

Several functional hybrid materials have been reported as immobilized porphyrin derivatives in various organic and inorganic host materials (polymers, mineral clays, silica, etc.), with potential applications in various fields, such as photochemistry, electrochemistry and heterogeneous catalysis. Layered double hydroxides (LDHs), commonly known as hydrotalcite-like materials, have also been analyzed for use as supports for metallocomplexes. Recently, nanocomposite materials with a core-shell structure produced by combining two kinds of nanometer-size materials have received considerable attention, since the use of these materials is a promising strategy to prevent the aggregation and self-oxidation of molecules, reducing the catalytic activity. In this study, monodispersed hierarchical layered double hydroxides on silica spheres (LDH@SiO₂) with core-shell structures were developed for metalloporphyrin immobilization and the materials were used as the oxidant catalysts of different substrates.

Full text of DOI:10.1039/c7dt03656f

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DOI: 10.1039/C7DT03656F.
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Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
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Oxidation catalyst obtained by immobilization of layered double
hydroxide/Mn(III) porphyrin on monodispersed silica spheres
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
Karen Mary Mantovani, Kátia Cristina Molgero Westrup, Renaldo Marcos da Silva Junior, Silvia
b
b*
a*
Jaerger, Fernando Wypych, Shirley Nakagaki
DOI: 10.1039/x0xx00000x
Several functional hybrid materials have been reported as immobilized porphyrin derivatives in various organic and
inorganic host materials (polymers, mineral clays, silica, etc.), with potential applications in various fields, such as
photochemistry, electrochemistry and heterogeneous catalysis. Layered double hydroxides (LDHs), commonly known as
hydrotalcite-like materials, have also been analyzed for use as supports for metalocomplexes. Recently, nanocomposite
materials with core-shell structure produced by combining two kinds of nanometer-size materials have received
considerable attention, since the use of these materials is a promising strategy to prevent aggregation and self-oxidation
of molecules, reducing the catalytic activity. In this study, monodispersed hierarchical layered double hydroxide on silica
www.rsc.org/
2
spheres (LDH@SiO ) with core-shell structures were developed for metalloporphyrin immobilization and the materials
were used as oxidant catalysts of different substrates.
In this work, monodispersed hierarchical layered double
hydroxide on silica spheres (LDH@SiO with core-shell
structures. were synthesized for use as supports for MP
immobilization. The influence of the support morphology
(sphere or platelet) on the catalytic performance of the solid in
oxidation reactions of different substrates is reported.
Introduction
2
)
Porphyrins are macrocyclic compounds with a large extended
14
conjugated
-system. They play an important role in many
1
biological systems. These compounds and their metalated
complexes exhibit unique properties, which makes them very
interesting molecules for application in various fields.
2
3
Metalloporphyrins (MPs) are present in many important
enzymes for oxidation reactions, such as cytochromes P450,
peroxidases and catalases.4 Synthetic metalloporphyrins,
especially those containing Fe(III) and Mn(III) ions, have been
extensively used as catalysts in oxidation reactions of a range
Experimental
-6
Characterization and apparatuses
For the X-ray diffraction measurements, the powdered
samples were deposited on glass sample holders. The
measurements were obtained in the reflection mode using a
Shimadzu XRD- 6000 diffractometer operating at 40 kV and 30
7-10
of organic compounds using different oxidants.
The
combination of metalloporphyrins and host materials with
appropriate structure can produce excellent functional solids
for different uses. The preparation has been reported of
several functional hybrid materials by the immobilization of
MP in various organic and inorganic host materials (polymers,
clays, silica), with potential applications in different fields, such
as photochemistry, electrochemistry and heterogeneous
catalysis.1
mA, using CuK
2
2
α
radiation (λ= 1.5418 Å) and a dwell time of
°.min , and the data were collected between 2 and 70° (in
θ).
−1
FTIR spectra were recorded with
a Biorad 3500 GX
-1
spectrophotometer in the 400-4000 cm range, using KBr
pellets. KBr was crushed with a small amount of the solid
samples, and the spectra were collected with a resolution of 4
1,12
Layered double hydroxides (LDHs), commonly known as
-1
cm and accumulation of 32 scans.
hydrotalcite-like materials, are
a
family of layered
UV-Vis spectra were recorded in the 200-800 nm range with a
Varian Cary 100 spectrophotometer, using cells with path
lengths of 1.0 cm or 0.5 cm. Qualitative spectra of the solid
samples were also recorded by diffuse reflectance.
Scanning electron microscopic images (SEM) and Energy
dispersive spectra (EDS) were obtained with a Tescan VEGA3
LMU device, using tension of 10 KV. The samples were
deposited on aluminum stubs and the EDS spectra were
nanomaterials having anionic exchange capacity (Fig. 1 left
side). Recently, nanocomposite materials with core-shell
structure produced by combining two kinds of nanomaterials
have received great attention for use as supports to prevent
the aggregation and self-oxidation of molecules, reducing the
catalytic activity.13
2
a.Laboratório de Bioinorgânica e Catálise, Departamento de Química, Universidade
collected with an SDD detected with 80 mm and in the range
Federal do Paraná, CP 19032, 81531-980, Curitiba, PR, Brazil.
Laboratório de Química de Materiais Avançados, Departamento de Química,
Universidade Federal do Paraná, CP 19032, 81531-980, Curitiba, PR, Brazil.
of 0 to 10 KeV. In sequence, the samples were gold sputtered
and the SEM images were then obtained.
b
*
Corresponding authors e-mail addresses: shirleyn@ufpr.br; wypych@ufpr.br
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Transmission electron microscopic (TEM) images were solid was separated by centrifugation and wVaieswhAirntigcle Ownilitnhe
obtained with a JEOL-JEM 1200 microscope operating at 120 ethanol/water (1:1 v/v) solution and driedDOinI:a10n.1o0v3e9/nCa7DtT60036°C56.F
kV. The samples were prepared by dispersion in ethanol at
room temperature and
a
diluted dispersion drop was Preparation of LDH@SiO
2
deposited on a carbon film supported by a 3 mm copper grid.
Nitrogen adsorption-desorption isotherms were obtained in a
Quantachrome gas sorption analyzer, model NOVA 2000e. The
samples were degassed at 110 °C under vacuum for 2 h and
the analyses were carried out in liquid nitrogen (−196 °C) and
The silica spheres (100 mg) and 20 mL of distilled water were
added to a beaker and the mixture was submitted to an
ultrasound bath until formation of a homogeneous dispersion
(
around five minutes) and 0.80 mL of aqueous ammonia
solution (28%) was then added. solution containing
Mg(NO (0.96 mmol) and Al(NO (0.48 mmol) was dripped
A
adsorption/desorption isotherms for N
2
were obtained over
3
)
2
3 3
)
the relative pressure range of 0.05-0.99. The samples’ specific
surface areas were calculated using the multi-point Brunauer-
Emmet-Teller (BET) method by the adsorption isotherm in the
range of relative pressures from 0.05-0.30. Pore diameter and
the pore volume were calculated using the desorption
isotherm or Barrett–Joyner–Halenda method (BJH), also from
the desorption isotherm.
Electron paramagnetic resonance (EPR) measurements of the
powdered materials were accomplished with a Bruker EMX
microX EPR spectrometer (frequency X, band 9.5 GHz) at room
14
onto this dispersion (20 mL) (Mg:Al molar ratio of 2:1) . After
that, the dispersion was kept in the ultrasound bath for 1 hour
and thereafter the resulting solid was centrifuged and washed
with distilled water and oven dried at 60 °C. Considering the
step of precipitation and various washing/dispersion steps,
only around 105mg of the solid was recovered as dried matter.
No leaching of the LDH layers was observed after exhaustive
2
washing of the LDH@SiO solid with distilled water.
Preparation of MnP/LDH@SiO
A methanol solution of MnP (10 mL; 4.92x10 mol
added to a methanol dispersion of the support LDH@SiO
mg/10 mL) under magnetic stirring at room temperature. After
hours under stirring, the supernatant was removed by
2
temperature and -196 °C (using liquid N
2
), and perpendicular
-5
L-1) was
(50
⋅
microwave polarization X-band.
2
All the products from the oxidation reactions were quantified
with an Agilent 6850 gas chromatograph (flame ionization
detector) equipped with a 30 m long DB-WAX capillary column
with 0.25 mm internal diameter (J&W Scientific).
3
centrifugation and collected in a volumetric flask. The solid
was washed five times with methanol and all liquids resulting
from the washing process were collected in the respective
Materials
All chemicals used in this study were purchased from Sigma- volumetric flasks mentioned above. The final volume was
Aldrich, Merck or Fluka and were of analytical grade. completed with methanol and the solution was quantitatively
Iodosylbenzene (PhIO) was synthesized according to the analyzed by UV–Vis spectroscopy in order to determine of the
literature.15 The solid was carefully dried under reduced
MnP amount that leached out from the support after the
pressure and kept at 5 °C and the purity was assessed by
reaction and the washing process. The loading value was
iodometric titration.1
6
determined indirectly by the difference between the initial
4 2
The anionic free-base porphyrin Na [H (TDFSPP)] and the
metalloporphyrin content and the leached metalloporphyrin.
The resulting pale yellow MnP/LDH@SiO
solid was dried for
4 h at 60 °C.
The purity of the MnP/LDH@SiO
dependent on the purity of the metalloporphyrin and
LDH@SiO support which had their purity proven by various
analytical techniques before carrying out this reaction. Thus,
corresponding manganese(III) porphyrin (MnP) complex
2
+
([Mn(TDFSPP)Na
4
]
= [tetrasodium-5,10,15,20-tetrakis (2,6-
2
difluoro-3-sulfonatophenyl) porphyrinate manganese(III)]) (Fig.
2
solid is intrinsically
1
right) were synthesized, purified, and characterized following
17,18
a previously described method.
2
2
the final material obtained, MnP/LDH@SiO , was considered
absent of impurities.
Catalytic oxidation reactions
2
The synthesized MnP/LDH@SiO was investigated as catalyst
for oxidation of different substrates (cis-cyclooctene and
cyclohexane) using iodosylbenzene (PhIO) as oxidant. The
following general procedure was used: in a 2.0 mL vial the
catalyst and PhIO (MnP/oxidant molar ratio 1:50) were
degassed with argon for about 10 minutes to eliminate
Fig. 1 Schematic representation of the LDH structure (left) and the structure of the
manganese(III) porphyrin (MnP) complex, [Mn(TDFSPP)Na ] (right).
4
+
Synthesis and characterization
Preparation of the SiO spheres
2
In a 50 mL Erlenmeyer flask, 50 mL of ethanol, 30 mL of water molecular oxygen. After that, the mixture of degassed solvents
and 10 mL of aqueous ammonia solution were added and (CH CN/CH Cl - 1:1 v/v) was added to a reaction flask followed
3
2
2
submitted to magnetic stirring. To the mixture, 9.2 mL of by the substrate (MnP/substrate molar ratio of 1:5000). The
tetraethyl orthosilicate (TEOS) was added, resulting in the reaction was kept under magnetic stirring and argon
formation of a white solid dispersion (silica spheres). The atmosphere at 25 °C for 1 h in a dark chamber. After an
reaction medium was stirred for 17 hours and the resulting appropriate reaction time, a saturated acetonitrile solution of
2
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sodium sulfite was added to the reaction mixture, to eliminate structure. In LDH@SiO
ARTICLE
2
, broad diffraction peaks were observed
View Article Online
DOI: 10.1039/C7DT03656F
excess PhIO and to quench the reactions. Then methanol was at around 35, 45 and 62 ° (in 2θ, indicated by ∗), typical of
added to the reaction vial to solubilize the remaining insoluble (012), (015) and (110) LDH reflections, with low stacking
1
9,20
PhIO. Next, the solid catalyst was separated from the reaction order.
solution by centrifuging and the reaction supernatant was then of 10° (in 2θ) indicated very small number of packed layers.
quantitatively transferred to a volumetric flask. The catalyst The FTIR spectra of LDH@SiO and MnP/LDH@SiO2 (data not
was washed many times with small amounts of the solvent shown) displayed the typical silica bands at 960 cm and 1100
The absence of an evident basal peak in the region
2
-1
-
1
3 2 2
mixture (CH CN/CH Cl 1:1, v/v), to extract any remaining cm , assigned respectively to the Si-OH and Si-O bond
reaction product. All extracts were combined in the same stretching and H-O-H angular deformation at 1620 cm . LDH
volumetric flask, which was analyzed in duplicate or triplicate could not be detected due to the small concentration and
by gas chromatography to quantify the reaction products, superposition of bands at 470 cm , attributed to M-O bonding
using bromobenzene as the internal standard. The reaction (M= Mg, Al, Si).21,22
-1
-
1
yields were calculated based on starting PhIO and all catalytic To confirm the presence of the MnP in LDH@SiO
reactions were also performed in duplicate or triplicate. spectra of the solid samples in the solid state were recorded
All substrates were checked prior to use by gas by diffuse reflectance (Fig. 3). Due to the white and pale yellow
chromatography, to ensure they were free of oxidation color respectively, SiO and LDH@SiO showed no spectral
products. Control reactions were carried out with signals in the analyzed region (Fig. 3a,b), while the solid
CH
CN/CH Cl mixture (1:1 v/v) using the same procedure as MnP/LDH@SiO presented a band at 564 nm, indicating the
that of the catalytic runs, but in the presence of (a) substrate + presence of immobilized MnP (Fig. 3c). The Soret band
PhIO and (b) substrate + PhIO + LDH@SiO (with no MnP). position observed at 467 nm for MnP/LDH@SiO (Fig. 3d) is
2,
UV-Vis
2
2
a
3
2
2
2
2
2
The solid catalysts recovered at the end of the oxidation slightly red shifted in comparison to the Soret band recorded
reaction were exhaustively washed, dried, and reused in for the non-immobilized MnP in aqueous solution (459 nm)
further reactions, adopting the same procedure described (Fig. 3e).
before, using cyclohexane as substrate.
This fact can be attributed to steric constraints of the inorganic
The corresponding non-immobilized MnP was also tested as support over the metalloporphyrin structure, causing
catalyst (in homogeneous medium) in an experimental
procedure similar to that used for the heterogeneous medium.
The amount of MnP used was about 2.0x10 to 3.3x10 mmol
in order to keep a MnP/PhIO/substrate molar ratio of
12,17,23-25
macrocycle ring distortions.
-4
-4
459
1
:50:5000. The washing solvents and the reaction media were
monitored by UV-Vis, to verify whether any MnP was leached
from the MnP/LDH@SiO material during either the reactions
5
53
e
d
467
2
or the catalyst washing procedures.
564
Results and discussion
Characterization of the silica, LDH@SiO
solids
c
b
a
2
and MnP/LDH@SiO
2
300
400
500
600
700
All the prepared materials were characterized by XRD, UV-Vis,
FTIR, TEM, SEM, EDS and nitrogen adsorption. Figure 2 shows
the powder X-ray diffraction pattern of the silica spheres and
the solid obtained by the preparation of LDH covering the silica
Wavelenght (nm)
Fig.
3
UV-Vis spectra of SiO
2
spheres (a), LDH@SiO
manganese(III)porphyrin (d) (pellet of MnP diluted in MgSO
MnP (e).
2
(b), MnP/LDH@SiO
) and aqueous solution of
2
(c),
4
spheres (LDH@SiO
2
) in a core shell process.
The MnP loading on the support, obtained by UV-Vis of all
-5
washing solutions, was of 2.43x10 mol of MnP per mass (g) of
the support, corresponding to immobilization yield of 72.4%.
2
Anionic MnP is expected to immobilize on LDH@SiO surface
*
thorough strong electrostatic bonding between the positive
charges of the LDH layers and the sulfonate negative charges
of the MnP structure. No leaching of MnP from the solid, even
after exhaustive washing processes, was observed, which
*
b
a
*
2
indicates a strong electrostatic MnP/LDH@SiO interaction
10
20
30
2
40
Theta (°)
50
60
70
conferring high stability to the solid.
The TEM images of the SiO
uniform radius around 240 nm and some sphere coalescence,
while the LDH@SiO solid maintained the spherical
morphology with some plate-like crystals coating the surface,
typical of LDH crystals (Fig. 4 bottom).
2
(Fig. 4) showed spheres with a
2 2
Fig. 2 X Ray diffraction patterns of the SiO spheres (a) and LDH@SiO (b).
2
SiO
2
X ray diffraction pattern present, as expected, a broad
) confirming the amorphous
halo between 15 and 35° (in 2
θ
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around 19% in wt% (considering the anhydrous Zn/Al 2:1 LDH).
View Article Online
DOI: 10.1039/C7DT03656F
Although semi-quantitative and reproducibly in both samples, this
amount will not interfere in the catalysis performance, which is
defined by the amount of porphyrin in the catalyst.
Figure 7 shows the schematic representation of the proposed
2
process of immobilization of the MnP in LDH@SiO .
2
Fig. 4 Transmission electron microscopic (TEM) images of the SiO spheres (top) and
2
LDH@SiO spheres (bottom).
2 2
Fig. 6 EDS spectra of LDH@SiO (left) and MnP/LDH@SiO (right).
The SEM images of LDH@SiO
after evaporation of the dispersions indicated raspberry-like
particles with an average diameter of 5 m (Fig. 5), which are
2 2
and MnP/LDH@SiO obtained
µ
close to 20 times bigger than the isolated silica spheres and
were clearly obtained by the silica spheres aggregations.
Plate-like particles were clearly deposited on the surface of
both samples, indicating the presence of LDH, which persisted
after the immobilization of the MnP. These images were
consistent with the TEM images (Fig. 4).
Fig. 7 Schematic representation of the MnP catalyst immobilization on the surface of
LDH@SiO and catalyst obtaining.
2
The semi-quantitative EDS results (Fig. 6) indicate that in
The specific surface areas (SBET) found for the silica spheres were
LDH@SiO
Si and Cl), while in MnP/LDH@SiO
2
only the expected elements are present (O, Mg, Al,
, sulfur was also detected,
2
-1
2
-1
3
10.2 m g , while for the neat LDH the value was of 9.0 m g .
2
When the LDH was prepared in the presence of SiO spheres, the
2
due to the presence of sulfonate groups in the MnP (Fig. 6
right).
2
-1
value SBET was reduced to 39.9 m g . This reduction of the surface
area of the core-shell compound suggests the deposition of the LDH
plated-like crystals on the surface of SiO
the silica solid and blocking the silica spheres and silica inter-
spheres pores. The solid Mn/LDH@SiO was also characterized by
EPR, and no signal was detected at -196°C (data not shown), in
2
spheres, partially covering
2
26
agreement with the presence of Mn(III) in the porphyrin core.
Catalytic investigation of Mn/LDH@SiO
cyclohexane as substrates
2
using (Z)-cyclooctene and
2
The efficiency of the MnP/LDH@SiO as catalyst in the
heterogeneous oxidation reaction process was tested using
the substrates (Z)-cyclooctene and cyclohexane, and
iodosylbenzene (PhIO) as model oxidant (Table 1).
The (Z)-cyclooctene molecule is a useful diagnostic substrate,
since it is easily oxidized in the presence of metalloporphyrins,
with (Z)-cycloocteneoxide usually being the sole reaction
27-29
product.
The catalytic activity of the MnP using (Z)-
cyclooctene as a substrate in homogeneous catalysis resulted
in about 89% yields (Table 1). After immobilization on LDH, the
yield dropped to 51%, as expected due to the change from
homogeneous to heterogeneous process and the
immobilization of the catalyst species on a solid support.30
MnP/LDH showed catalytic results comparable to their
2 2
Fig. 5 SEM images of LDH@SiO (top) and MnP/LDH@SiO (bottom). Magnifications:
left: 25k, middle: 50 k.
The amount of LDH could be estimated from the EDS Si/Mg Wt%
ratios in both samples (LDH@SiO2 24.9/3.2= 7.78 and
MnP/LDH@SiO2 = 19.8/2,5 = 7.92), which lead to percentages of
=
4
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homogeneous analogues, suggesting that the immobilization resulting solid was used as support to immobilize
did not prevent the access of the reactants to the MnP manganese(III) porphyrin (MnP) complex, in which
a
View Article Online
DOI: 10.1039/C7DT03656F
-
5
catalytic center.
immobilization loading of 2.43x10 mol of MnP per mass (g) of
the support was obtained.
a
b
Table 1 Results of the cyclooctene and cyclohexane oxidation using iodosylbenzene as The immobilized MnP on LDH and LDH@SiO
2
were
oxidant.
investigated as catalysts for oxidation of different substrates
(Z)-cyclooctene and cyclohexane) using iodosylbenzene (PhIO)
as oxidant, where high yields of products were observed.
2
Although the MnP/LDH@SiO spheres were aggregated in a
raspberry-like particles, the material presented the highest
catalytic activity, due to the monodispersed hierarchical
layered double hydroxide on silica spheres, exposing the
catalytic site of the porphyrin. Although the catalyst was only
reused in the cyclohexane oxidation, the materials showed
potential for recycling, with partial preservation of the
catalytic activity.
c
Solids
Product yield (%)
Epoxidea
89.2 ± 2.37
51.3 ± 3.20
99.6 ± 0.40
*
4.00 ± 3.80
6.7 ± 0.37
14.0 ± 1.30
Alcohol
b
Ketoneb
2.8 ± 0.13
MnP
MnP/LDH
14.3 ± 0.75
5.4 ± 0.01
9.0 ± 0.93
6.3 ± 0.95
<1
e
<1
<1
<1
<1
<1
<1
MnP/LDH@SiO
First reuse
2
d,e
LDH
e
LDH@SiO
Control
2
<1
<1
f
aEpoxide = cyclooctenoxide, balcohol = cyclohexanol and ketone = cyclohexanone.
cYields based on the amount of PhIO used in the reaction. dReaction using only LDH
(
prepared by coprecipitation under the same condition of the prepared solid
LDH@SiO ) or LDH@SiO
as catalyst. eData from reference 12. fReaction with no
catalyst using only PhIO+substrate. * Not investigated.
Conflicts of interest
2
2
The authors declare that they have no conflict of interest
.
Acknowledgements
On the other hand, MnP/LDH@SiO presented nearly 100% We are grateful to Coordenação de Aperfeiçoamento de
2
epoxide yield. The increase of the yield presented by the solid Pessoal de Nível Superior (CAPES), Conselho Nacional de
catalyst MnP/LDH@SiO in comparison to MnP/LDH suggests Desenvolvimento Científico e Tecnológico (CNPq), Fundação
2
that the dispersion of the layered compound on the Araucária, and Universidade Federal do Paraná (UFPR) for
spheres’surfaces leads to a better catalyst support for the MnP financial support. K.C.M.W. also thanks Fundação Araucária
immobilization. This is probably due to the higher surface area and Capes for the pos-doctoral scholarship (Convênio
and low number of stacked layers in the LDH structure, 396/2014 – Projeto 41060 – SIT 21045).
optimized the MnP loading and the access of the substrates to
the catalytic sites under the reaction conditions used.
References
Cyclohexane is a less reactive substrate than (Z)-cyclooctene in
oxidation reactions, and when metalloporphyrins are used as
catalysts, both cyclohexanol and cyclohexanone are obtained
1
L. R. Milgrom, The Colours of Life. An introduction to the
Chemistry of Porphyrins and Related Compounds, Oxford
University Press, Oxford, 1997.
as products, but in homogeneous catalysis, high selectivity for
2
3
K. M. Smith, Porphyrins and metalloporphyrins: A New
Edition Based on the Original Volume by J. E. Falk, Elsevier
Sci. Pub. Co., New York, 1975.
the alcohol product is frequently observed.2
7-29,31
The novel
MnP/LDH@SiO
(
(
2
solid reported here presented alcohol yield
9%) similar to that observed for the homogeneous catalysis
14%) and higher than that observed for the solid resulting
K. M. Kadish, K. M. Smith and R. Guilard. The porphyrin
handbook vol. 6, Applications: Past, Present and Future,
Academic Press, San Diego, 2000.
from the immobilization of MnP on LDH (5%). Selectivity for
alcohol was also observed, which is in agreement with
reported results of homogeneous catalysis using this MnP and
4
5
D. Mansuy, C. R. Chim., 2007, 10, 392.
Groves, J.T.; Shalyaev, K.; Lee, J. Oxometalloporphyrins in
Oxidative Catalysis. In The Porphyrin Handbook; Kadish,
K.M., Smith, K.M., Guilard, R., Eds.; Academic Press: San
Diego, CA and Burlington, MA, 1999, Vol. 4, Ch. 27, pp 17-40.
McLain, J. L.; Lee, J.; Groves, J.T. Biomimetic Oxygenations
Related to Cytochrome P450: Metal-oxo and Metal-peroxo
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other metalloporphyrins.2
7-29
and suggests that the catalytic
mechanism of the hydroxylation reaction can be similar to that
6
observed for the MnP in solution.3
2,33
MnP/LDH@SiO also showed recycling capacity since no
2
leaching of the MnP from the support solid was detected by
UV-Vis monitoring during the catalytic reaction or during the
recovery and reactivation by washing and dried step. In fact, in
the second use of the solid on the cyclohexane oxidation, a
small drop in activity was observed, but the materials were still
active.
7
8
9
J. T. Groves, T. E. Nemo and R. S. Myers. J. Am. Chem. Soc.,
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979, 101, 1032.
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10 H. M. Marques, Dalton Trans., 2007, 39, 4371.
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Monodispersed nanometric size silica spheres were obtained
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3 L. Li and J. Shi, Chem. Commun., 2008, 0, 996.
of a 2:1 Mg:Al layered double hydroxide. After observing the 14 C. Chen, P. Wang, T. Liem, L. Liu, S. Liu and R. Xu, J. Mater.
LDH plate-like crystals at the silica spheres surface, the
Chem. A., 2013, 1, 3877.
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J. Name., 2013, 00, 1-3 | 5
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