Highly selective and recyclable MoO3 nanoparticles in epoxidation catalysis

Article abstract of DOI:10.1016/j.apcata.2015.02.027

Molybdenum trioxide (MoO₃) nanoparticles with an average size below 100 nm were prepared by solvothermal synthesis of nano-crystalline molybdenum dioxide (MoO₂) and subsequent thermal oxidative annealing. The successful preparation of this type of nanoparticles was confirmed by evidence obtained from characterization by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis and Fourier transform infrared spectroscopy (FTIR). The MoO₃ nanoparticles were tested as catalytic precursor in the epoxidation of cis-cyclooctene, styrene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (tbhp) as oxygen source under different reaction conditions, namely, various solvents and temperatures. The catalytic studies show that the MoO₃ nanoparticles perform selective epoxidation of the tested substrates with very high yield, especially at high temperature and using toluene as solvent. Furthermore, the catalyst remains active across several reaction cycles with virtually no loss of activity.

Full text of DOI:10.1016/j.apcata.2015.02.027

Accepted Manuscript
Title: Highly selective and recyclable MoO3 nanoparticles in
epoxidation catalysis
Author: Cristina I. Fernandes Silvia C. Capelli Pedro D. Vaz
Carla D. Nunes
PII:
S0926-860X(15)00120-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.02.027
APCATA 15264
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
26-11-2014
14-2-2015
18-2-2015
Please cite this article as: C.I. Fernandes, S.C. Capelli, P.D. Vaz, C.D. Nunes, Highly
selective and recyclable MoO3 nanoparticles in epoxidation catalysis, Applied Catalysis
A, General (2015), http://dx.doi.org/10.1016/j.apcata.2015.02.027
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Highly selective and recyclable MoO3 nanoparticles in epoxidation catalysis
Cristina I. Fernandes[a], Silvia C. Capelli[b], Pedro D. Vaz[a,b], Carla D. Nunes[a]*
[a] Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências
da Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisboa, Portugal
[b]
ISIS Neutron & Muon Source, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire
OX11 0QX, United Kingdom
Correspondence to:
Dr. Carla D. Nunes
Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências
da Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisboa, Portugal
Tel: (+351) 217 500 876
e-mail: cmnunes@ciencias.ulisboa.pt
Abstract
Molybdenum trioxide (MoO3) nanoparticles with an average size below 100 nm were prepared by
solvothermal synthesis of nano-crystallite molybdenum dioxide (MoO2) and subsequent thermal
oxidative annealing. The successful preparation of this type of nanoparticles was confirmed by
evidenced obtained from characterization by powder X-ray diffraction (XRD), scanning electron
microscopy (SEM) and transmission electron microscopy (TEM) analysis and Fourier transform
infrared spectroscopy (FTIR). The MoO3 nanoparticles were tested as catalytic precursor in the
epoxidation of cis-cyclooctene, styrene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-
butylhydroperoxide (tbhp) as oxygen source in different reaction conditions, namely, various
solvents and temperatures. The catalytic studies show that the MoO3 nanoparticles perform
selective epoxidation of the tested substrates with very high yield, especially at high temperatures
and using toluene as solvent. Furthermore, the catalyst remains active across several reaction
cycles with virtually no loss of activity.
1
Page 1 of 36

Graphical Abstract
100 nm
MoCl5
O
R
R
Highlights
 MoO3 nanoparticles show high catalytic activity in olefin epoxidation
 Epoxide products are obtained with very high selectivity
 Styrene oxidation yields benzaldehyde in very high yields
 The catalyst is recyclable without loss of activity on a variety of substrates
Keywords
Metal oxide; Molybdenum; Nanoparticle; Oxidation catalysis; Recyclability
Introduction
Nanoscience has evolved into a major research field of Modern Society, during the 20th century,
as a result of a continuing effort to miniaturize to the nanoscale size processes that occur so far at
the microscale level. In order to achieve this objective, it is generally accepted that bottom-up
approaches should replace the classic top-down.
Metal and metal oxide-containing nanostructures with different morphologies (nanowires,
nanobelts, nanofibres etc.) are known to exhibit better adjustable properties in fields such as gas
sensors, electrodes or optoelectronics than their conventional counterparts[SCC1] [1].
In this context, MoO3 nanoparticles have attracted a great deal of attention due to their unique
physical and chemical properties that differ from those in the bulk, in particular for their high
surface-to-volume ratio, exceptionally high for nanoparticles with an approximate diameter
between 1-100 nm [2].
2
Page 2 of 36

The development of MoO3 nanoparticles have consequently increased in recent years, because
these nanoparticles can play a critical role in many industrial applications. MoO3 nanoparticles
present two structural phases: the thermodynamically stable orthorhombic α-phase and the
metastable monoclinic β-phase [3].[SCC2][SCC3] Orthorhombic α-MoO3 nanoparticles are
promising oxides with structural anisotropy and a wide n-type bandgap, which is very attractive
for technological applications such as photodegradation [4], degradation of dyes [5], gas sensor
[6], electrodes for batteries [7] and catalysis [8]. Orthorhombic α-MoO3 possesses an anisotropic
layered crystal structure that is composed of bilayers of distorted MoO6 octahedra along the (010)
direction of the Pbnm space group setting. The interlayer interaction is mainly through van der
Waals forces [9]. The -phase, although believed to be superior to the -phase in catalysis[SCC4]
[10] and electrochemical applications [11], has been quite difficult to produce in single phase [12].
Recently a microplasma method has openend the way to produce single-phase nanosheets for
applications in Li-ion batteries [13].
Various MoO3 nanostructures in the -phase, including nanowires [14], nanotubes [15], nanobelts
[16] and nanofibers [17] were fabricated by different methods, the most popular being the
hydrothermal synthesis. The hydrothermal method is simple and cost effective. It is a low
temperature process which yields various nanostructures with controlled size, stoichiometry and
shape [18].
Another important feature of molybdenum trioxide is the versatility of its catalytic properties in a
different type of reactions, such as epoxidation catalysis. To this respect the use of such metal
oxide materials in oxidation catalysis was pioneered by Volta in the late 70’s decade of the XXth
century [19,20]. These studies aimed at correlating selective oxidation processes with the
structural properties of the catalysts. For instance, in some of his works, Volta established that
MoO3 can yield products selectively, depending on the crystal face where the reaction occurs. For
instance, propene oxidation can occur at the (100) face yielding acrolein, whereas it can also yield
CO2 if the reaction occurs at the (010) face [21].
Olefin epoxidation is a major field of research in the preparation of relevant building blocks for
organic synthesis as fine chemicals as well as pharmaceuticals and agrochemicals [22-24]. Among
other metal systems, Mo-catalyzed olefin epoxidation has received interest from both academic
and industrial research laboratories [25,26]. Since the first example of a molybdenum oxo complex
catalyzing the epoxidation of alkenes with peroxides such as organic hydroperoxides and hydrogen
3
Page 3 of 36

peroxide [27], a variety of different systems has been developed [28,29]. Inclusively, in recent
times, many efficient epoxidation Mo-based catalysts are based on Mo organometallic complexes
which work as precatalysts [29].
Our group has performed intensive research on olefin epoxidation [30-32[SCC5]], and as a
continuation of those studies, we describe in the present work the preparation and subsequent
evaluation of the catalytic potential of α-MoO3 nanoparticles in the epoxidation of olefins, under
different reaction conditions.
Experimental section
General
All reagents were obtained from Aldrich and used as received. Commercial grade solvents were
dried and deoxygenated by standard procedures distilled under nitrogen, and kept over 4 Å
molecular sieves. Fourier transform infrared spectra (FTIR) were obtained as KBr pellets on a
Nicolet 6700 in the 400-4000 cm-1 range using 2 cm-1 resolution. Powder X-ray diffraction
measurements were taken on a Philips Analytical PW 3050/60 X’Pert PRO equipped with
X’Celerator detector and with automatic data acquisition in theta/2 theta mode (X’Pert Data
Collector (v2.0b) software), using Cu Kα radiation (40 kV; 30 mA). Profile fitting on the data was
performed with the FullProf suite of programs [33]. The scanning electron microscopy (SEM)
images were obtained on a FEG-SEM (Field Emission Gun Scanning Electron Microscope) from
JEOL, model JSM-7001F. The transmission electron microscopy (TEM) images were obtained on a
microscope Hitachi, model H-8100 with a LaB6 filament and using an acceleration tension of 200
kV. MoO3 Nanoparticles were prepared according to a method described in the literature [18].
In this case the MoO3 nanoparticles were prepared using 0.325 g of commercial MoCl5 that was
fully dissolved in 40 mL of distilled water and 10 mL of ethanol. After stirring for 1 h, the prepared
solution was transferred into a Teflon-line stainless autoclave and kept at 453 K overnight and
then air-cooled to room temperature. The resulting precipitate was centrifuge, washed with
distilled water and ethanol for several times, and oven-dried at 353 K. A subsequent annealing at
723 K for 1 h transformed the precipitate into MoO3 nanoparticles.
Catalytic tests
4
Page 4 of 36

The molybdenum nanoparticles were tested in the catalytic epoxidation of cis-cyclooctene,
styrene, trans-hex-2-en-1-ol and R(+)-limonene, using tert-butylhydroperoxide (tbhp) as oxidant
(5.5 M in n-decane). The catalytic tests were carried out at 353, 383 and 393 K using respectively
acetonitrile, toluene and decane as solvents. The reactions occurred under normal atmospheric
conditions in a reaction vessel equipped with a magnetic stirrer and a condenser. In a typical
experiment the vessel was loaded with the olefin or the alcohol (100%), internal standard
(dibutylether, DBE), catalyst (1%), oxidant (200%) and 3 mL of solvent (acetonitrile, toluene or
decane). The final volume of the reaction is ca. 6 mL. The addition of the oxidant determines the
beginning of the reaction. Conversion, product yields and selectivity were monitored by sampling
periodically and analyzing them using Shimadzu QP2100-Plus GC/MS system and a capillary
column (Teknokroma TRB-5MS/TRB-1MS) operating in the linear velocity mode.
Leaching and recycling tests
In general, recycling experiments were carried out as described in the previous section; after each
cycle (24 h) the catalyst was washed with dichloromethane (CH2Cl2) several times and dried prior
to reuse in a new catalytic cycle [34].These experiments were performed to assess the robustness
of the catalyst.
For the leaching experiments after 2 h reaction, the catalyst was filtered off, and the reactions
continued under the same conditions. Alternatively, similar experiments were carried out using a
centrifuging step rather than filtration for separating the catalyst. These experiments were
conducted to assess whether the catalyst was leaching into the liquid phase during catalysis.
Results and Discussion
Synthesis and characterization of nanoparticles
Molybdenum oxide nanoparticles (MoO3) were synthesized by solvothermal synthesis of nano-
crystalline MoO2, using commercial MoCl5 in the presence of a mixture of water and ethanol, and
subsequent thermal oxidative annealing as described by Kim et al. [18]. The nanoparticles were
characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR),
scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
5
Page 5 of 36

X-ray powder diffraction (XRD) patterns of the reaction products were recorded both after the
solvothermal synthesis and the oxidative annealing, in order to confirm the two-step process
having MoO2 as intermediate state of the production of MoO3 nanoparticles (Figure 1).
In Figure 1 the top diffraction pattern is from the precipitate after the solvothermal synthesis,
exhibiting the peaks characteristic of MoO2 in the monoclinic P21/c phase. Indexing and line
intensities appear compatible with both the JCPDS cards 86–0315 and 78–1073 while a LeBail
profile fitting has given refined cell parameters of: a = 5.6235(12), b = 4.8483(15), c = 5.6262(8), 
= 120.62(1), in reasonable agreement with values reported from a Rietveld refinement on neutron
powder diffraction data [35].
The bottom pattern in Figure 1 is the diffraction pattern of the precipitate after the thermal
oxidative annealing step. The diffraction peaks are those characteristic of the orthorhombic α-
MoO3 phase when compared to JCPDS card05-0508 [36]. The lattice parameters (Å) obtained by a
LeBail profile fitting in the orthorhombic space group Pbnm [37] are: a = 3.9557(6), b = 13.867(2)
and c = 3.6965(4), in agreement with a recent X-rays single-crystal determination [38,39].
[Figure 1]
The calcined MoO3 nanoparticles were further investigated by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM).
The SEM images exhibit somewhat aggregated particles with hexagonal/circular shape and with to
smooth facets (Figures 2a and 2b). TEM (Figure 2c) confirms SEM observations by displaying
nanoparticles with some aggregation. Concerning particle size, a size distribution is visually
identified in the image, and it is possible to infer that the average dimension is below 100 nm.
[Figure 2]
FTIR spectrum was performed to investigate chemical bonding states between molybdenum and
oxygen atoms. The spectrum shown in Figure 3, displays several bands that can be assigned to, the
surface adsorbed water; in particular, the O–H mode is found at 3443 cm-1 while the (H2O)
deformation mode of is detected at 1629 cm-1. The Mo–OH vibrational mode appears at 1400
cm-1, and was associated to the interaction of the Mo with some water in the surface. Bands
6
Page 6 of 36

arising from the Mo vibrations appear at 995, 865 and 615 cm-1, being assigned to the vibrations of
Mo=O, the Mo–O–Mo vibrations of MoVI and to the (Mo–O–Mo) mode. These data agree with
previous literature reported values [16], and thus confirms successful synthesis of the MoO3
nanoparticles.
[Figure 3]
Catalytic studies
The MoO3 nanoparticles were tested as catalyst precursor for the epoxidation of two sets of
substrates. The former comprises simple olefins, such as cis-cyclooctene and styrene, while the
latter includes multifunctional olefins, namely, trans-hex-2-en-1-ol and R-(+)-limonene. All
reactions were carried out using tert-butylhydroperoxide (tbhp) as oxygen donor, in different
solvents, namely, acetonitrile, toluene and decane, and at different temperatures, i.e. 353, 383
and 393 K.
[Table 1]
In the reaction with cis-cyclooctene, MoO3 nanoparticles catalyzed selectively the oxidation of
substrate to the corresponding epoxide, without formation of any by-products (Table 1, entries 1-
4). Although all the reactions converted cis-cyclooctene yielding exclusively the corresponding
epoxide (100% selectivity), the most striking result emerged when using a higher temperature
(393 K) combined with decane as solvent. In this case it was possible to totally convert the
substrate in a time as short as 1 h of reaction (Table 1, entry 4), giving an 8 fold increase in the
velocity of the reaction.
It was also important to evaluate how both solvent and temperature parameters influence catalyst
performance. Figure 4a presents the kinetics of formation of cis-cyclooctene epoxide. It is possible
to verify that at the same temperature (353 K) the choice of the solvent influences the catalyst
performance. In particular, acetonitrile (filled squares) yields better kinetics than toluene (filled
circles). It is also important to note that when toluene was used at 383 K (open squares) the
kinetics roughly matched the one obtained for acetonitrile at 353 K. For this particular system it is
clear that acetonitrile is a good choice as it is more efficient at the lowest temperature tested than
7
Page 7 of 36

toluene. On the other hand, when the temperature is further increased (393 K) and using decane
(Figure 4a, open circles) the reaction kinetics is boosted reaching 100% substrate conversion with
concomitant complete selectivity just after 1 h of reaction, which is remarkable. In this case,
however, one cannot distinguish whether such boost is a result of solvent, temperature or both
combined effects.
[Figure 4]
Styrene conversion is very efficient for all tested conditions reaching almost 100% of conversion
(Table 1, entries 5-8). Although epoxide selectivity is low in all cases (especially at 393 K, Table 1,
entry 8), the major product obtained is benzaldehyde. This product is obtained with excellent
selectivity meaning that MoO3 is most adequate to perform two-electron oxidation reactions on
this substrate. Benzaldehyde selectivity was found to increase concomitantly with temperature
(Table 1, entries 5-8).
R-(+)-limonene is a substrate with two unsaturated C=C bonds; in this way two different epoxides,
the endo- and exocyclic isomers, are feasible. In the present work, it was possible to convert the
substrate with high conversion rates across all catalytic tests (Table 1, entries 9-12) and the
endocyclic epoxide was the only isomer obtained in all the catalytic tests performed. Product
selectivity was found to range between 90% and 98% tested at both 353 and 383 K across all
conditions (Table 1, entries 9-11). The most interesting feature is that in these systems the E-
isomer was the one formed preferentially. Despite this when changing the solvent to decane and
using a higher temperature (393 K) this showed to have a detrimental effect in the performance of
the catalytic system. In this case, although limonene conversion and epoxide selectivity are still
very high, the selectivity towards the epoxide E-isomer drops (Table 1, entry 12), yielding the
epoxide Z-isomer as the by-product (34% yield). Based on this the epoxidation reaction using
decane as solvent was repeated it at 353 and 413 K. Results show that under these conditions,
epoxide Z-isomer yield changes concomitantly with temperature increase, as evidenced in Figure
4b, reaching 45% yield at the highest temperature.
In what concerns the oxidation of trans-hex-2-en-1-ol it was possible to obtain excellent results
regarding conversion of substrate (Table 1, entries 13-16). Conversions were around 100% after 4
h of reaction at 353 K in toluene (Table 1, entry 14) and after 2 h of reaction at 383 K in toluene or
8
Page 8 of 36

at 393 K in decane (Table 1, entries 15-16). Selectivity for epoxide was also quite good (between
95% and 100%) across all the tested conditions. By analyzing the kinetics of trans-hex-2-en-1-ol
epoxide yield for all the tested solvents and temperatures, Figure 4c, when toluene was used as
solvent (blue open squares) the catalyst showed a faster and higher conversion profile than for the
other tested solvents. Concerning temperature, catalyst performance was better for the
intermediate temperature (383 K) (blue line) against to what happened before for cis-cyclooctene.
Solvent effects are known to be very important but not easy to be understood as this is very much
substrate dependent [40]. In this work, strong effects were observed in the epoxidation of styrene
and R-(+)-limonene. In the case of R-(+)-limonene the solvent effect was strong when using
decane, where the ratio between diastereomers of limonene oxide changes across a temperature
range. The same effect was observed in the case of styrene, as a function of both temperature and
solvent. In this case, although benzaldehyde is always the major product, the use of apolar
solvents seems to promote this product by a great amount, being almost the sole product (Table
1, entry 8).
Reusability of the catalyst was also evaluated since robustness is a very important feature for a
catalyst allowing it to be used in several consecutive cycles using toluene at 383 K. Tests revealed
that MoO3 nanoparticles kept their catalytic activity constant and very high (around 100%) even
after four cycles in most cases (Figure 5). Although for styrene epoxidation the major product was
not the epoxide as already mentioned before. Concerning selectivity, with exception of styrene
epoxidation, all other substrates were selectively converted to the corresponding epoxides with
excellent selectivity across all cycles. Cis-cyclooctene oxide was achieved always with 100%
selectivity, while R-(+)-limonene and trans-hex-2-en-1-ol epoxides selectivity ranged between 91-
98% for the former and between 94-100% for the latter.
[Figure 5]
In order to assess the true nanometric nature of the catalyst, its stability towards leaching was also
evaluated.
Leaching experiments for the epoxidation of cis-cyclooctene catalyzed by the MoO3 nanoparticles
were carried out in toluene at 353 K. The catalyst was filtered off after 2 h reaction time (at which
substrate conversion was ca. 50%); the reaction in the remaining solution was monitored up to 24
9
Page 9 of 36

h and the final conversion was found to be near 100%. This means that the catalyst is not
heterogeneous in nature showing that the nanoparticles have a size distribution (as confirmed by
TEM images, Figure 2c) and the smaller ones are not retained by the filtration step. In a second
leaching experiment, the procedure was slightly changed. At 2 h the reaction slurry was
centrifuged to separate the solid. Then the solution was monitored again till 24 h as in the
previous leaching experiment. According to Figure 6, the centrifugation step was found to be
efficient at separating the catalyst. In this case the reaction did not proceed further as in the
previous leaching experiment.
[Figure 6]
Comparison with literature data
The catalytic performance achieved by these MoO3 nanoparticles was so impressive that a
comparison with other systems reported in the literature was inevitable[SCC6]. Table 2 collects
data from catalytic olefin epoxidation experiments tested across several materials, based on a
literature survey, for a set of olefins including cis-cyclooctene, styrene, R-(+)-limonene and trans-
hex-2-en-1-ol. The catalysts surveyed cover a wide selection, ranging from nanoparticles to
micro/mesoporous materials.
[Table 2]
As can be seen from data presented in Table 2, in general terms all catalysts show high activity and
good selectivity for epoxides in the transformations considered. Selectivity to the corresponding
epoxide products can sometimes be an issue in the systems presented. For instance, Přech
reported a Ti-pillared TS1 material that was inefficient in cyclooctene epoxidation [43]. That
material reached only 19% conversion and epoxide selectivity was as low as 80%.
By the same token the MoO3 catalyst reported in this work suffer from the same problem in the
epoxidation of styrene (Table 2, entry 12). For this substrate, the best performing catalysts were
those based on Ag nanoparticles immobilized on maghemite and Au nanoparticles immobilized on
TS1 material (Table 2, entries 8 and 14). Both systems reached high substrate conversion above
90% with epoxide selectivity of 90% in both cases.
10
Page 10 of 36

In the case of R-(+)-limonene and trans-hex-2-en-1-ol epoxidation, the best performing catalyst
was found to be the MoO3 nanoparticles reported in this work. In fact, for R-(+)-limonene, the use
of TS1 material as catalyst, reported by Wróblewska, showed to be either completely inactive or
unselective, depending on the reaction conditions (Table 2, entries 18 and 19).
Conclusions
In this work we report the successful preparation of MoO3 nanoparticles with an average size of 85
nm by solvothermal synthesis of MoO2 nano-crystalline particles and subsequent thermal
oxidative annealing. Preparation of MoO3 nanoparticles was confirmed by evidence obtained from
characterization by powder XRD, SEM/TEM analysis, as well as from data of FTIR spectroscopy.
The MoO3 nanoparticles were used as catalysts and revealed to be very active in olefin
epoxidation of a variety of olefins using tert-butylhydroperoxide (tbhp) as oxygen source. Results
of catalytic tests show that the catalyst conducts selectively to the desired epoxides, with the
exception of styrene which yields benzaldehyde. In this particular case, benzaldehyde was found
to be obtained with increasing selectivity as the temperature of the reaction increases. The best
value was achieved at 393 K with 95% selectivity for bezaldehyde.
The catalyst performance was quite good under a wide temperature range and with different
solvents, especially for higher temperatures and with acetonitrile or toluene as solvents. The
catalyst also showed to be very active over few recycling experiments without activity loss after
four cycles.
Comparison with literature data on related systems evidences that the present catalyst levels or
outperforms its counterparts across several points: excellent substrate conversion and product
selectivity and kinetic rate acceleration. In addition, this catalyst is prepared by a simple synthesis
procedure which makes it a clear advantage over others used in the same epoxidation reactions.
Based on these results, further studies are being conducted to test this catalyst under aqueous
conditions, a much greener media, which will deliver enhanced applications.
Aknowledgments
Authors thank FCT, POCI and FEDER (project Pest-OE/QUI/UI0612/2014) for financial support. CIF
thanks FCT for a research grant (SFRH/BD/81029/2011).
11
Page 11 of 36

References
[1] L. Mai, F. Yang, Y. Zhao, X. Xu, L. Xu, B. Hu, Y. Luo, H. Liu, Mater. Today 14 (2011) 346-352.
[2] E. B. Santos, F. A. Sigoli, I. O. Mazali, J. Solid State Chem. 190 (2012) 80-84.
[3] E.M. McCarron III, J. Chem. Soc., Chem. Commun., 1986, 336-338
[4] Y. Chen, C. Lu, Y. Ma, W. Hou, J.-J. Zhu, Cryst. Eng. Comm. 12 (2010) 3740–3747.
[5] J. Huang, X. Wang, S. Li, Y. Wang, Appl. Surf. Sci. 257 (2010) 116–121.
[6] W.-S. Kim, H.-C. Kim, S.-H. Hong, J. Nanopart. Res. 12 (2010) 1889-1896.
[7] T. Tao, A. M. Ghushenkov, C. Zhang, H. Zhang, D. Zhou, Z. Guo, H. K. Liu, Q. Chen, H. Hu, Y.
Chen, J. Mater. Chem. 21 (2011) 9350-9355.
[8] L. X. Song, M. Wang, S. Z. Pan, J. Yang, J. Chen, J. Yang, J. Mater. Chem. 21 (2011) 7982-7989.
[9] J. S. Chen, Y. L. Cheah, S. Madhavi, X. W. Lou, J. Phys. Chem. C. 114 (2010) 8675-8678.
[10] T. Mizushima, Y. Moriya, H.H.P. Nguyen, H. Ohkita, N. Kakuta, Catal. Commun. 13 (2011) 10-
13.
[11] I. Juárez Ramı ́nez-de la Cruz, Mater. Lett. 57 (2003) 1034–1039.
́rez, A. Martı
[12] J.B. Parise, E.M. McCarron III, R. Von Dreele, J.A. Goldstone, J. Solid State Chem. 93 (1991)
193-201.
[13] D. Mariotti, H. Lindström, A. Chandra Bose, K. Ostrikov, Nanotechnology 19 (2008) 495302.
[14] S. Wang, Q. Gao, Y. Zhang, J. Gao, X. Sun, Y. Tang, Chem. Eur. J. 17 (2011) 1465-1472.
[15] J. Huang, X. Wang, S. Li, Y. Wang, Appl. Surf. Sci. 257 (2010) 116–121.
[16] Y. Chen, C. Lu, Y. Ma, W. Hou, J.-J. Zhu, Cryst. Eng. Comm. 12 (2010) 3740–3747.
[17] M. Niederberger, F. Krumeich, H.-J. Muhr, M. Müller, R. Nesper, J. Mater. Chem. 11 (2001)
1941-1945.
[18] W.-S. Kim, H.-C. Kim, S.-H. Hong, J. Nanopart. Res. 12 (2010) 1889-1896.
[19] J.C. Volta, W. Desquesnes, B. Moraweck, G. Coudurier, React. Kin. Catal. Lett. 12 (1979) 241-
246.
[20] J.C. Védrine, G.J. Hutchings, C.J. Kiely, Catal. Today 217 (2013) 57-64.
[21] J.C. Volta, J.L. Portefaix, Applied Catal. 18 (1985) 1-32.
[22] A. Taguchi, F. Schüth, Micropor. Mesopor. Mater. 77 (2005) 1-45.
[23] M.H. Valkenberg, W.F. Hölderich, Catal. Rev. Sci. Eng. 44 (2002) 321-374.
[24] F. Hoffmann, M. Cornelius, J. Morell, M. Fröba, Angew. Chem. Int. Ed. Engl. 45(2006) 3216-
3251.
12
Page 12 of 36

[25] C.D. Nunes, P.D. Vaz, in: Andrew C. Poehler (Ed.), Homogeneous Catalysts: Types, Reactions
and Applications, Nova Science Publishers Inc., New York, 2011, pp. 43-95.
[26] P.D. Vaz, C.D. Nunes, Curr. Org. Chem. 16 (2012) 89-114.
[27] W.F. Brill, N. Indictor, J. Org. Chem. 30 (1965) 2074-2075.
[28] K.R. Jain, W.A. Herrmann, F.E. Kühn, Coord. Chem. Rev. 252 (2008) 556-568.
[29] F.E. Künh, A.M. Santos, M. Abrantes, Chem. Rev. 106 (2006) 2455-2475.
[30] M. Vasconcellos-Dias, C.D. Nunes, P.D. Vaz, P. Ferreira, P. Brandão, V. Félix, M.J. Calhorda, J.
Catal. 256 (2008) 301-311.
[31] C.I. Fernandes, N.U. Silva, P.D. Vaz, T.G. Nunes, C.D. Nunes, Appl. Catal. A Gen. 384 (2010) 84-
93.
[32] N.U. Silva, C.I. Fernandes, T.G. Nunes, M.S. Saraiva, C.D. Nunes, P.D. Vaz, Appl. Catal. A Gen.
408 (2011) 105-116.
[33] J. Rodriguez-Carvajal, Physica B 192 (1993) 55-69
[34] C.I. Fernandes, M.S. Saraiva, T.G. Nunes, P.D. Vaz, C.D. Nunes, J. Catal. 309 (2014) 21-32.
[35] A.A. Bolzan, B.J. Kennedy, C.J. Howard, Aust. J. Chem. 48 (1995) 1473-1477.
[36] A. Klinbumrung, T. Thongtem, S. Thongtem, J. Nanomat. 2012 (2012) 1-5.
[37] Pbnm is the non conventional setting of space group Pnma (n. 62 in the International Tables
of Crystallography, http://it.iucr.org/A/). It is used in this work for the description of the -MoO3
structure in order to be more easily comparable with previous work on the same material.
[38] V. V. Atuchin, T. A. Gavrilova, T. I. Grigorieva, N. V. Kuratieva, K. A. Okotrub, N. V. Pervukhina,
N. V. Surovtsev, J. Cryst. Growth, 318 (2011) 987-990
[39] A constrained Rietveld refinement using cell parameters from the profile fitting and atomic
coordinates from [33b] transformed into the Pbnm setting was performed with the Fullprof Suite
of programs [33]. The calculated diffraction pattern is not entirely describing the intensities of
peaks with high k index, suggesting the presence of preferred orientation of the crystallites in the
measured sample.
[40] W. Fan, P. Wu, T. Tatsumi, J. Catal. 256 (2008) 62–73.
[41] C.I. Fernandes, M.D. Carvalho, L.P. Ferreira, C.D. Nunes, P.D. Vaz, J. Organomet. Chem. 760
(2014) 2-10.
[42] S. Anandhakumar, M. Sasidharan, C.-W. Tsao, A.M. Raichur, ACS Appl. Mater. Interfaces 6
(2014) 3275−3281.
13
Page 13 of 36

[43] J. Přecha, P. Eliášová, D. Aldhayan, M. Kubů, Catal. Today 243 (2015) 134–140.
[44] P. Zhenyan, H. Li, Q. Yunxiang, Y. Hanmin, Z. Xiuge, F. Bo, Z. Wenwen, H. Zhenshan, Chin. J.
Catal. 32 (2011) 428–435.
[45] H. Liu, J. Bai, C. Li, W. Xu, W. Sun, T. Xu, Y. Huang, H. Li, RSC Adv., 4 (2014) 3195-3200.
[46] C. Liu, J. Huang, D. Sun, Y. Zhou, X. Jing, M. Du, H. Wang, Q. Li, Applied Catal. A: Gen. 459
(2013) 1-7.
[47] J. Huang, C. Liu, D. Sun, Y. Hong, M. Dua, T. Odoom-Wubah, W. Fang, Q. Li, Chem. Eng. J. 235
(2014) 215-223.
[48] A. Wróblewska, Molecules 19 (2014) 19907-19922.
14
Page 14 of 36

Figure and Table captions
Figure 1. XRD powder patterns of precursor MoO2 (top, space group P21/c) and annealed MoO3
nanoparticles (bottom). Peaks of MoO3 are indexed in the non-standard Pbnm setting of space
group 62, in order to be easily comparable with previous work on -MoO3.
Figure 2. TEM (a) and SEM (b and c) images of synthesized MoO3 nanoparticles.
Figure 3. FTIR spectrum of synthesized MoO3 nanoparticles.
Figure 4. a) Kinetics of cis-cyclooctene epoxide yield using MoO3 nanoparticles as catalyst for
different reaction conditions; b) Yield vs. temperature profile for Z-diasteriomer of endocyclic
epoxide in R-(+)-limonene epoxidation; c) Kinetics of trans-hex-2-en-1-ol epoxide yield using MoO3
nanoparticles as catalyst for different reaction conditions.
Figure 5. Conversion for substrates cis-cyclooctene, styrene, R-(+)–limonene and trans-hex-2-en-1-
ol at 383 K with toluene as solvent in recycling experiments after 24 hours.
Figure 6. Conversion profiles for cis-cyclooctene conversion in toluene at 353 K to screen catalyst
leaching.
Table 1. Catalytic olefin epoxidation using MoO3 nanoparticles as catalyst.
Table 2. Catalytic olefin epoxidation performance of Mo-based heterogeneous catalysts from a
recent literature survey, and comparison with MoO3 nanoparticles from this work.
15
Page 15 of 36

Figure 1
Figure 1. XRD powder patterns of precursor MoO2 (top, space group P21/c) and annealed MoO3
nanoparticles (bottom). Peaks of MoO3 are indexed in the non-standard Pbnm setting of space
group 62, in order to be easily comparable with previous work on -MoO3.
16
Page 16 of 36

Figure 2
Figure 2. TEM (a) and SEM (b and c) images of synthesized MoO3 nanoparticles.
17
Page 17 of 36

Figure 3
Figure 3. FTIR spectrum of synthesized MoO3 nanoparticles.
18
Page 18 of 36

Figure 4
Figure 4. a) Kinetics of cis-cyclooctene epoxide yield using MoO3 nanoparticles as catalyst for
different reaction conditions; b) Yield vs. temperature profile for Z-diasteriomer of endocyclic
epoxide in R-(+)-limonene epoxidation; c) Kinetics of trans-hex-2-en-1-ol epoxide yield using MoO3
nanoparticles as catalyst for different reaction conditions.
19
Page 19 of 36

Figure 5
Figure 5. Conversion for substrates cis-cyclooctene, styrene, R-(+)-limonene and trans-hex-2-en-1-
ol at 383 K with toluene as solvent in recycling experiments after 24 hours.
20
Page 20 of 36

Figure 6
Figure 6. Conversion profiles for cis-cyclooctene conversion in toluene at 353 K to screen catalyst
leaching.
21
Page 21 of 36

Table 1
Table 1. Catalytic olefin epoxidation using MoO3 nanoparticles as catalyst.
Entry Reactiona
Temp. (K)
Conv.c (%) Select.c,d (%)
TOFb (
)
Solvent
1
2
3
Acetonitrile 353
200
90
100
99
100
100
100
100e
Toluene
353
383
393
30
98
100e
4
Decane
546
O
5
6
7
Acetonitrile 353
30
85
99
99
98
23f
18f
12f
5f
Toluene
353
383
393
578
130
100
O
8
Decane
9
Acetonitrile 353
810
430
60
97
95
99
93
90g
97g
98g
67g
10
Toluene
353
383
393
O
11
12
Decane
466
13
Acetonitrile 353
450
580
109
30
97h
96h
100h
98i
95h
98g
100h
99i
14
Toluene
353
383
393
HO
15
O
HO
16
Decane
a All reactions were carried out in the presence of 200 mol% oxidant (tbhp) and 1 mol% Mo catalyst; b Turnover frequency calculated at 10 min based on
surface Mo species. c Calculated after 24 h, unless otherwise stated; d Calculated as “Yield of epoxide”/”Conversion” 100%; e After 1 h of reaction; f In
all experiments benzaldehyde formed as major product; g Values refer to E-diasteriomer of endocyclic epoxide, Z-diasteriomer formed as secondary by-
product; h After 4 h of reaction; i After 2 h of reaction.
22
Page 22 of 36

Table 2
Table 2. Catalytic olefin epoxidation performance of different heterogeneous catalysts from a
recent literature survey, and comparison with MoO3 nanoparticles from this work.
Entry Reaction
Catalyst
MNP30-Si-inic-Mo tbhp
Oxidant Temp. (K) Conv. (%) Select.a (%) Ref.
1
2
3
383
353
338
333
99
99
71
19
100
100
83
[41]
MoO3 NPs
Ag NPs
tbhp
tbhp
H2O2
this work
[42]
4
Ti-pillared TS1
80
[43]
O
5
6
7
MSh-bpy-MoVI
tbhp
328
328
338
353
353
353
353
308
333
26
93
82
90
43
46
85
53
93
14
40
80
90
33
34
23f
85
90
[34]
MNP30-Si-inic-Mo tbhp
[41]
Ag NPs
tbhp
tbhp
tbhp
tbhp
tbhp
H2O2
H2O2
[42]
O
8
[44]
Ag/-Fe2O3
Ag/Al2O3
Ag/MgO
MoO3 NPs
TS1
9
[45]
10
12
13
14
[45]
this work
[46]
Au/TS1
[47]
15
16
MSh-bpy-MoVI
tbhp
383
383
383
373
393
100
99
100
97
98
11
0
[34]
MNP30-Si-inic-Mo tbhp
[41]
O
17
MoO3 NPs
TS1
tbhp
H2O2
H2O2
99
this work
[48]
18
19
24
TS1
45
[48]
HO
20
MSh-bpy-MoVI
tbhp
328
383
383
75
86
[34]
21
MNP30-Si-inic-Mo tbhp
MoO3 NPs tbhp
91
100e
94
100e
[41]
O
HO
22
this work
a Calculated as “Yield of epoxide”/”Conversion” × 100%.
23
Page 23 of 36

Figure
Page 24 of 36

Figure
Page 25 of 36

Figure
Page 26 of 36

Figure
Page 27 of 36

Figure
Page 28 of 36

Figure
Page 29 of 36