Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of cyclohexene

Article abstract of DOI:10.1016/j.materresbull.2014.11.014

Al₂O₃ was prepared from different inorganic precursors via the Pechini method and compared with Al₂O₃ prepared by the sol-gel method. Structural characterization of these materials was carried out by FTIR, X-ray diffraction (XRD), N₂ adsorption at -196 °C and transmission electron microscopy (TEM). The solids were tested in the epoxidation of cyclohexene and a difference in their catalytic activities was observed. The characterization results indicate that the samples prepared by Pechini have a mixture of γ-alumina and boehmite, a condition favoring catalytic activity, whereas the sol-gel sample is less crystalline due to higher boehmite content. These results indicate that both the nature of the precursor and the method of synthesis strongly affect the catalytic activity of Al₂O₃.

Full text of DOI:10.1016/j.materresbull.2014.11.014

Accepted Manuscript
Title: Effect of the synthetic method on the catalytic activity of
alumina: Epoxidation of cyclohexene
˜
´
Author: N.E. Valderruten W.F. Pena A.E. Ramırez J.E.
´
´
Rodrıguez-Paez
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S0025-5408(14)00695-3
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Reference:
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Please cite this article as: N.E.Valderruten, W.F.Pena, A.E.Ramirez,
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J.E.Rodriguez-Paez, Effect of the synthetic method on the catalytic activity
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Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of
cyclohexene
Valderruten N.E.1*, Peña W.F.2, .Ramírez A.E.2, Rodríguez-Páez J.E.3
1 Departamento de Ciencias Químicas, Universidad Icesi, Cali, Colombia
2 Departamento de Química, Universidad del Cauca, Popayán, Colombia
3 Departamento de Física, Universidad del Cauca, Popayán, Colombia
* Corresponding author: Departamento de Ciencias Químicas, Universidad Icesi, Cali,
Colombia. Tel.: +572 3212077; fax: +572 3212078. E-mail address:
nevalderruten@icesi.edu.co
Keywords:
A. Oxides
B. Chemical synthesis
C. X-ray diffraction
D. Catalytic properties
Highlights
•
•
•
Aluminum oxide was synthesized using Pechini method.
The alumina obtained showed a mix of boehmite and γ-alumina phases.
We research an economically feasible method to obtain alumina for use as a
catalyst.
•
•
Alumina obtained by Pechini showed high percent conversion and/or selectivity.
The best results were 78% conversion and 78% selectivity to epoxidation
reactions.
Graphical abstractTemperature influence on percent conversion and selectivity in the
epoxidation of cyclohexene using commercial alumina as a catalyst

Abstract
Al2O3 was prepared from different inorganic precursors via the Pechini method and
compared with Al2O3 prepared by the sol-gel method. Structural characterization of these
materials was carried out by FTIR, X-ray diffraction (XRD), N2 adsorption at -196 °C
and transmission electron microscopy (TEM). The solids were tested in the epoxidation
of cyclohexene and a difference in their catalytic activities was observed. The
characterization results indicate that the samples prepared by Pechini have a mixture of γ-
alumina and boehmite, a condition favoring catalytic activity, whereas the sol-gel sample
is less crystalline due to higher boehmite content. These results indicate that both the
nature of the precursor and the method of synthesis strongly affect the catalytic activity of
Al2O3.
1. Introduction
The implementation of processes that are at the same time efficient and environmentally
friendly requires the use of non-toxic compounds that can be easily removed in the
purification process, hence the application of heterogeneous catalysts and low-cost, low
toxicity oxidizing agents and solvents. Alumina provides a useful alternative for
catalysis at the industrial level, given its minimal toxicity and low cost. Aluminum oxide
is used in the ceramic industry [1] and as an additive in the paper, rubber and polymer
industries, as well as in toothpastes, paints and coatings [1-3]. It is also commonly
employed as a drying agent and in catalytic processes [4,5]. Alumina is predominantly
used as a catalytic support for diverse chemical processes, among them the epoxidation of
olefins [6, 7]. It functions at low concentrations, under environmentally suitable

conditions, when hydrogen peroxide is the oxidizing agent and ethyl acetate the solvent
[7, 8]. Although alumina has been synthesized by various methods [9-12], Sheldon and
Sepúlveda [8, 13] showed that alumina obtained by the sol-gel method, utilizing
aluminum-sec-butoxide as a precursor, is the most highly efficient and selective catalyst
of these types of solids for the epoxidation of cyclohexene. Nevertheless, the aluminum
precursor used in this process is very expensive. Our objective is to identify a catalyst
that equals alumina synthesized by the sol-gel method in efficiency and selectivity, but
that costs less. We propose to compare alumina synthesized by the methods of sol-gel
and Pechini [12] from the same precursor (aluminum-sec-butoxide) as well as from
aluminum hydroxide and to evaluate the efficiency of both catalysts in the epoxidation of
cyclohexene.
2. Experimental
2.1. Materials and methods
Aluminum-sec-butoxide (Acros, 99%), sec-butanol (Acros, 99.5%), oxalic acid (Merck,
99%), ethylene glycol (Merck, 99.5%), ammonium hydroxide (Reagent A.C.S., 28%),
aluminum hydroxide (Merck, 95%), cyclohexene (Merck, 99%), hydrogen peroxide
(Quinm, 28%), ethyl acetate (E.M., 99.8%) and 1-octanol (Carlo Erba, 99%) were
utilized without further purification.
2.2. Synthesis of catalysts
2.2.1. Sol-gel method
Alumina (Al2O3 M1) was prepared by acid hydrolysis of aluminum-sec-butoxide (40.6
mmol) in 15 mL of sec-butanol, adding dropwise a solution of oxalic acid (5.6 mmol)

with vigorous stirring. The gel obtained was stirred for 3 h at 70 °C. The material was
then dried at 70 °C over 24 h in a WTB Binder oven and then calcined at 400 °C for 24 h
in a muffle furnace (Terrigeno model F2PGA) [8].
2.2.2. Pechini method
The aluminum-sec-butoxide (15.14 mmol) was dissolved in 11.49 mL of sec-butanol. In
a separate flask, 15.14 mmol of citric acid were diluted in 6.48 mL of ethylene glycol and
heated to 70 °C with constant stirring until a homogeneous solution was obtained. The
two solutions were then slowly mixed with constant stirring and then left to cool to room
temperature. The pH was adjusted to 8.0 with ammonium hydroxide (28%) and then the
mixture heated to 140 °C until a dark resin was obtained. The resin was precalcined at
200 °C for 2 h and then calcined at 800 °C for 4 h. The alumina obtained in this case is
referred to as Al2O3 M2.
The other alumina (Al2O3 M3) was prepared using aluminum hydroxide as a precursor.
358 mmol of ethylene glycol were mixed with 89.7 mmol of citric acid and heated to 70
°C with constant stirring until a homogeneous solution was achieved. In a separate flask,
89.7 mmol of aluminum hydroxide were dissolved in 38.37 mL of water. The two
solutions were then slowly combined with constant stirring and left to cool to room
temperature, at which time the pH was adjusted to 8.0 with ammonium hydroxide (28%).
The mixture was heated to 140 °C until a dark resin was obtained. The resin was then
precalcined at 200 °C for 2 h and calcined at 450 °C for 14 h.

2.3. Characterization of catalysts.
Fourier transform infrared spectroscopy (FTIR) spectra of catalysts in KBr discs were
recorded on a Nicolet Model IR200 spectrometer from 400 to 4000 cm-1. X-ray
diffraction analysis was performed using an XPERT_PRO diffractometer equipped with a
copper anode (λ=1.54 Å), a graphite monochromator and a scintillation detector.
Diffraction intensities were gathered by scanning from 10 to 90° (2θ). Transmission
electron microscopy was performed using a JEOL JEM-1200 EX electron microscope.
Surface area analysis was carried out using the BET method [6] and a Quantochrome
CHEMBET 3000 analyzer, determining adsorption and subsequent desorption of nitrogen
at -196 °C. Samples were degassed with sweep gases (helium / nitrogen 70/30) at 400 °C
for 3 h prior to analysis[10, 14].
2.4. Epoxidation of cyclohexene
In a 3-neck round bottom flask connected to a Dean-Stark trap, cyclohexene, hydrogen
peroxide, 1-octanol and ethyl acetate were mixed in a ratio of 10 mmol /40 mmol /10 mL
respectively. A molar ratio of cyclohexene: hydrogen peroxide of 1:4 was determined
sufficient to guarantee adequate conversion[13]. 1-octanol was used as an internal
standard. The mixture was refluxed for 1 h to ensure elimination of water, and an aliquot
was removed for use as a blank. The mixture was then transferred to a stainless steel
reactor (Bach) and 300 mg of catalyst added, with continuous stirring, to initiate
formation of the epoxide. Reactions were carried out independently at differing
temperatures (80, 90, 100, 110, and 130 °C) using commercial alumina (Carlo Erba) as a

catalyst. Evaluation of catalytic activity of the synthesized aluminas was similarly
performed, using an analogous mixture ratio and a temperature of 90 °C.
2.5. Analysis of 1,2-epoxycyclohexane
The conversion of cyclohexene into 1,2-epoxycyclohexane was confirmed by gas
chromatography using a Shimadzu GC-14A chromatographer with an FID detector and a
capillary column with a polyethyleneglycol stationary phase (SGE; 25 m x 0.32 mm).
Analysis was carried out in Split mode with a column flow of 2.22 mL/min. The injector
and detector temperatures were 250 and 230 °C respectively. The following ramp
temperature was applied to separate the mixture: 45 °C (1 min), 10 °C/min, 60 °C (1
min), 30 °C/min, 80 °C (1min), 30 °C/min, 220 °C (1 min). Calibration curves were
obtained for cyclohexane, cyclohexene, 1,2-epoxycyclohexane and 1-octanol. Aliquots
were taken at the start of the reaction and every 90 min thereafter for a total of 360 min.
The aliquot was cooled and a minimum amount of manganese dioxide added to quench
the remaining hydrogen peroxide. The solution was then dried with calcium carbonate
and filtered.
FTIR spectra were obtained using a Thermo Electronic IR200 FTIR spectrophotometer.
The samples were analyzed as KBr pellets. 1H-NMR spectra were obtained using a
Bruker BioSpin NMR (300 MHz) employing TMS as an internal standard and d6-DMSO
and d-CHCl3 as solvents[15].
3. Results and discussion

3.1. Characterization of the catalysts.
The FTIR spectra in Fig. 1 reflect the structural similarity between the prepared aluminas,
independent of the method of synthesis and precursor. The stretching frequencies of
amphoteric hydroxides fall in the region from 3690 to 2900 cm-1. Bands in the upper
limits correspond to sterically hindered hydroxyl groups that are not involved in
hydrogen bonding. Those in the lower limits show conventional values for the transitions
and soft amphoteric processes of hydroxyacids. In many cases, they are associated with
the phase transitions where all the hydroxyl groups in a compound are
crystallographically equivalent. The maximum intensity in the spectral region generally
does not exceed the number of active vibrations of O-H groups in the crystalline cell [16,
17].
The increase in the degree of covalency of the M-OH bonds is accompanied by an
increase in the frequency of liberation of hydroxyl groups and by their transformation
into the flexing of the MmOH group (m = 2 or 3). The flexing vibration frequencies of
amphoteric hydroxides depend significantly on the energy of the hydrogen bonds. As the
scientific literature indicates [15-17], the OH groups in the plane of symmetry subdivide
into two classes: in-plane flexing (δ (OH)) and out-of-plane flexing (γ (OH)). The FTIR
spectrum of polycrystalline boehmite shows in-plane flexing vibrations at 1130 cm-1 and
out-of-plane flexing vibrations at 744 cm-1, while the γ-alumina phase shows in plane
flexing vibrations at 820 cm-1 and out-of-plane flexing at 520 cm-1. The out-of-plane
flexing vibration for the hydroxyl group apparently contributes to the absorption in the
region corresponding to aluminum-oxygen bonds. This indicates that the synthesized

aluminas (Fig. 1) showed two crystalline phases: γ-alumina and to a lesser degree,
boehmite. The band at 560 cm-1 is attributed to the hydrogen bond vibration in the
spectrum of the polycrystal. The γ-alumina shows other characteristic absorptions at 840
cm-1 and 3420 cm-1 that correspond to the vibration of superoxide (O-O) and stretching of
the hydroxyl group respectively [16, 17].
The vibrations corresponding to rocking, twisting and stretching of the metal-oxygen
bond of water bonded to aluminum appear at 900, 768 and 673 cm-1, respectively. The
flexing vibration that confirms the presence of water appears at 1630 cm-1. The band
corresponding to the stretching of the O-H bond in water appears at 3420 cm-1. The
coupling between the alumina and water present on the surface of the oxide causes a
decrease in resolution [17, 18]. The wavenumbers and the shape of the external
vibrations of water in hydrated crystals depend on the metal-oxygen bond and on the
bonded hydrogens. The proton donor capacity of a water molecule increases with the
degree of covalency of the M-O bond [11], showing two characteristic absorptions at
1630 and 3420 cm-1 for the flexing and stretching of the O-H bond respectively.
The FTIR results indicate that the synthesized aluminas show absorptions characteristic
of boehmite and γ-alumina. The presence of these two crystalline phases in both
aluminas was reiterated with the XRD analysis. The coexistence of these two phases can
be attributed to a phase transition from boehmite to γ-alumina (PDF 48-0367), which
represents a reorganization of the atoms in the network [1]. Boehmite is composed of
double chains of AlOOH which form layers with sequential crystalline cubes that contain

aluminum ions organized into an octahedral structure. On the other hand, the γ-alumina
contains aluminum atoms octahedrally and tetrahedrally coordinated, allowing the
formation of a defect spinel structure where the oxygen atoms form thin cubic sheets.
Between 400 and 800 °C the γ-alumina structure is consolidated, increasing crystallinity
with increasing calcination temperature [1]. The structure becomes ordered as a result of
alignment and combination of the defects from the surface of the aluminum ions [3, 10,
17, 19].
The aluminas prepared by the Pechini method (Fig. 2) from aluminum-sec-butoxide (M2)
and aluminum hydroxide (M3) showed an intermediate degree of crystallinity and a
mixture of boehmite and γ-alumina phases. On the other hand, the alumina prepared from
aluminum-sec-butoxide by the sol-gel method (M1) was more amorphous, as is seen
from the broadening of XRD peaks, and showed a larger presence of the boehmite phase.
The crystalline phases are identified based on diffraction peaks located in the 2θ degree.
One particular point of qualitative discussion is the peak that appears at 47°, caused by a
tetragonal distortion characteristic of the spinel structure for the γ-alumina phase. The
peaks that appear at 66° and 85° also correspond to the model based on the spinel
structure and reveal a phenomenon of cell relaxation. The incipient peaks located at 33°
and 61° are exclusive to the boehmite phase, while the peak at 38° is attributed to the
change in position of the aluminum cations within the crystalline network [3, 12, 17, 20].
Fig. 3 shows that the method of synthesis of the alumina affects the size and homogeneity
of the particles. The sol-gel method favors the formation of particles with a more

homogeneous size distribution and a particle size of 1.3 µm, while the Pechini method
generates larger particles (2.3 µm). The Pechini method requires higher temperatures of
calcination, favoring the aggregation of the particles and increase in their size. Although
particle size is relatively large, on the scale of microns, the peaks in the difractograms
shown in figure 2, specifically their width at medium height (B), indicate that based on
Scherrer’s formula t = 0.9λ/BcosθB, where λ = 1.54Å and θB is the angle of diffraction,
the size of the crystallite (t) is small. Consequently, the particles shown in Figure 3 are
secondary particles (agglomerates of submicron-sized particles).
The number of active sites and the geometry are important factors in the catalytic activity
of alumina, its reactivity depending on the geometry of empty space within and between
the particles [17, 19]. Additionally, the intrinsic chemical reactivity of the particles can
increase with reduction in particle size. This is due to an increase in the superficial
concentration of edges and corner sites, which affects the superficial energy of the
particles [21]. Many studies have illustrated the effect of the ratio of edge to corner sites
on adsorption and catalytic rates [22]. Moreover, when the crystallite is small, as is the
case in our studies, the superficial energy also changes because the concentration of
anion/cation vacancies in the sample, known as Schottky defects, can be large. Table 1
shows the values corresponding to the surface area of the synthesized catalysts. Using
the sol-gel method, alumina with a larger surface area is obtained. This result is
consistent with the particle size determined by TEM for this sample. Interestingly, the
alumina synthesized from aluminum hydroxide was also shown to have a very high
surface area.

Upon consideration of the reactions involved in each synthetic method, this difference in
the values of the specific surface area becomes clear. In the sol-gel method the following
predominant reactions lead to the formation of the solid phase. Hydrolysis of
[Al(OH2)6]3+ generates [Al(OH)h(OH2)6-h](3-h)+, and condensation promotes the formation
7+
of polynuclear species including [Al2(OH)2(OH2)4]4+, [Al3(OH)4(OH2)9]5+ and the Al13
ion ([AlO4Al12(OH)24(OH2)12]7+) [23, 24]. In the Pechini method, however, esterification
reactions between ethylene glycol and citric acid [25] and polyesterification of the metal
chelate complexes formed in the system favor a polymeric resin precursor conformation
in which the Al3+ ion is uniformly distributed. Heating of this polymeric resin to 200oC
resulted in the breakdown of the polymer and the formation of an aluminum
oxycarbonate, which upon heating to 800oC for four hours, led to the formation of
aluminum oxides M2 and M3. The significantly higher temperature required for the
formation of these aluminas as opposed to that of alumina M1, which required a
temperature of only 400oC, was responsible for the reduction in the specific surface area
of M2 and M3 as indicated in Table 1. Furthermore, the loss of structurally bound water,
greater for sample M2 than for M3, led to aggregation of crystallites and consequently a
reduction in the specific surface area [26], accounting for the difference in the surface
areas of aluminum oxides M2 and M3 obtained by the Pechini method using different
aluminum precursors.
3.2. Epoxidation of cyclohexene
Good yields and selectivity have been reported for the epoxidation of cyclohexene using
alumina as a catalyst [7, 13, 27, 28, 29, 30]. However, when ethyl acetate was used as a

solvent, the maximum temperature achieved was 74 °C; thus the percent conversion of
alkene became irrelevant given that it was impossible to overcome the energetic barrier to
the formation of the epoxide (Fig. 4). For this reason, the epoxidation of cyclohexene was
performed in a Parr reactor where temperatures above 200 °C and pressures of 200 bar
could be reached. The epoxidation was carried out at 80, 90, 100, 110, and 130 °C using
commercial alumina as a catalyst.
Fig. 5 shows an increase in the percent conversion with increasing temperature, with the
best results, 78% conversion at 200 min, being observed at 130 °C. At this temperature
the alumina has the greatest interaction with the substrate given that the kinetic energy of
the particles increases in a closed system, which is isochoric but not isobaric.
The increase in conversion and selectivity of the reaction with increasing temperature
indicates a decrease in the formation of the diol. At 110 °C water exists in vapor form at
the top of the reactor, and it is unlikely that this water interacts with the epoxide.
Furthermore, at temperatures superior to 100 °C, water does not deactivate the catalyst as
it is dispersed in the organic phase. After 200 min of reaction, however, a significant loss
in selectivity is observed. This is attributed to the fact that with increasing time, the
volume of water present increases dramatically to the point where it begins to react with
the epoxide generating the diol.
The literature reports between 90 and 97% selectivity when a reflux system with
continuous extraction of water from the reaction medium is used [13, 27, 28, 29, 30].

Experiments were carried out at 90 °C, a temperature that guarantees the production of
the epoxide with the lowest expenditure of energy and permits the application of a reflux
system with a Dean-Stark trap.
The effect of the method of preparation of the catalyst on the epoxidation of cyclohexene
at 90 °C was determined by using the alumina prepared from aluminum-sec-butoxide
employing the two methods (M1 and M2). Percent conversions from 39 to 46% were
obtained, with M2 showing higher activity. The difference in the catalytic activity of γ-
Al2O3 as compared to boehmite is apparent in other reactions such as the dehydration of
methanol to generate dimethylether. The performance of these catalysts strongly depends
not only on surface area but also on their surface acidic properties [31].
The alumina obtained from aluminum hydroxide by the Pechini method (M3) shows 20%
conversion and 77% selectivity. Fig. 6 shows high selectivity with short reaction times,
but at longer times, selectivity diminishes drastically, indicating that the epoxide is being
converted into the diol. Based on these results, optimum selectivity was obtained 200
min after initiation of the reaction and M3 was the most selective catalyst. The most
effective system is determined by considering the ratio between conversion and
selectivity, measured according to the amount of product generated per unit of time.
Figure 6 shows the behavior of the three catalysts. M2 is the most active (11.7 × 10-5 mol
cyclohexene/min*g cat), followed by M1 (8.3 × 10-5 mol cyclohexene/min*g cat). M3
(5.0 × 10-5 mol cyclohexene/min*g cat) is the least active of the three. This trend in

catalytic activity is closely related to the selectivity of the catalyst throughout the course
of the reaction. In the case of the M1 and M2 catalysts, although the initial conversion
from cyclohexene to epoxide is high, a large increase in the amount of water in the
reaction mixture is also observed. This favors the formation of the diol thereby reducing
selectivity toward the synthesis of the epoxide. A combination of different factors might
account for this behavior, including the content of boehmite and γ-phases, the degree of
crystallinity and surface acidic properties.
Fig. 7 shows that the M3 catalyst promotes intermediate conversion (36%) and high
selectivity (77%), indicating that it is the most effective catalyst in generating the 1,2-
epoxycyclohexane. It is likely that the increase in the surface concentration of edges and
corners, due to the small particle size, and the mixture of phases, γ - Al2O3 and AlOOH,
could account for the increased reactivity of the M3 catalyst. Similar behavior has been
reported in other systems for example, in the deep oxidation of methane where the
stabilization of low-temperature phases of Al2O3 (γ and χ phases) accounted for the high
activity and thermal stability of the catalysts [32]. Yet another example is the oxidation
of carbon monoxide where a higher degree of dispersion of the Fe2O3 nanoparticles and
the presence of the FeOOH phase induced the disproportionation of carbon monoxide
[33].
3.3. Characterization of 1,2-epoxycyclohexane
Fig. 8 shows two bands at 2970 and 2937 cm-1 that correspond to the symmetric and
asymmetric stretching of the C-H bond of the methylene group and another at 2863 cm-1
corresponding to the symmetric stretching of the C-H bond of the methine group. The

symmetric and asymmetric flexing vibrations of the C-H bond of the methylene group
can also be seen at 1440 and 1353 cm-1 respectively. At 1260 and 1180 cm-1 the wagging
and twisting of the C-H bond of the methylene group are evident. The band at 748 cm-1
corresponds to the rocking of the C-H bond of the methylene group. The two bands at
1040 and 534 cm-1 are characteristic of the symmetric and asymmetric stretching
vibrations of the C-O-C bonds of the ether group. Two additional bands at 1088 and 837
cm-1 correspond to the symmetric and asymmetric stretching of the C-O bonds of the
oxirane ring. The absorption at 781 cm-1 represents the symmetric bending of these
bonds [15, 34].
1
Fig. 9 shows the H-NMR spectrum of the product of the epoxidation reaction. Because
1,2-epoxycyclohexane exists in a chair conformation, the interaction between axial and/or
equatorial protons generates various multiplets. The first multiplet at 0.88 ppm
corresponds to the interaction of the four axial protons. Although there are various axial
protons bonded to carbon atoms at distinct locations on the molecule, only a single
multiplet is apparent because the distribution of these protons renders them equivalent.
The equatorial position on the oxirane ring generates esoteric shifting effects and
consequent deprotection of the ecuatorial protons of 1,2-epoxycyclohexane.For this
1
reason, the H-NMR spectrum shows two multiplets associated with the ecuatorial
protons of the molecule, one at 1.27 ppm that corresponds to the protons bonded to C3,
C4, and C5 and the other at 1.55 ppm associated with the protons bonded to C2 and C5.
The final multiplet appears at 3.62 ppm and corresponds to the protons located in the

axial position and bonded to C1 and C6. The downfield shifting of these protons reflects
the deprotecting influence of the oxygen atoms of the oxirane ring[15].
4. Conclusions
In accordance with the FTIR spectra, alumina M3 and M2 are similar in structure. X-ray
diffraction shows the presence of a mixture of γ-alumina and boehmite, a condition that
favors its catalytic reactivity. M1, on the other hand, is less crystalline due to higher
boehmite content. The method utilized in the synthesis of the aluminas has a marked
influence over the size and homogeneity of the resulting particles. The sol-gel method
favors a smaller particle and more homogeneous particle size distribution. Furthermore,
the catalyst synthesized by the sol-gel method possesses a larger surface area than the
solids obtained by the Pechini method. It is, however, of interest that when aluminum
hydroxide was used as a precursor, the alumina synthesized had a considerable surface
area. The percent conversion and selectivity in the epoxidation reactions increased with
increasing temperature, the best results being obtained at 130 °C with 78% conversion
and 78% selectivity at 200 min for all the samples. The M3 catalyst shows intermediate
percent conversion and good selectivity, proving to be the most effective catalyst for the
epoxidation of cyclohexene under specific reaction conditions. Given its high specific
surface area, and the increase in the surface concentration of edges and corner sites due to
small particle size and the presence in its crystalline structure of a mixture of γ - Al2O3
and AlOOH, the catalytic behavior of M3 may be justified.
Acknowledgements
The authors thank Universidad del Cauca and Universidad ICESI for the financial
support of this project.

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Tables:
Table 1
The values of the specific surface determined by the BET method of the aluminas
synthesized by the sol-gel and Pechini processes.
Sample
Specific
area (m2/g)
317
Precursor
Method
Sol-gel
Pechini
Pechini
code
M1
M2
M3
Aluminum-sec-butoxide
Aluminum-sec-butoxide
Aluminum hydroxide
28
165

Figure captions page:
Fig. 1. FT-IR spectra of the aluminas obtained by the sol-gel method using aluminum-
sec-butoxide (M1) and by the Pechini method using aluminum-sec-butoxide (M2) and
aluminum hydroxide (M3) as precursors. Page 7.
Fig. 2. X ray diffractograms of the aluminas obtained by: (a) sol-gel method (M1) and
Pechini method using (b) aluminum-sec-butoxide (M2) and (c) aluminum hydroxide
(M3) as precursors. Page 10.
Fig. 3. Micrographs of the aluminas synthesized from aluminum-sec-butoxide: (a) by the
sol-gel method (M1) and (b) the Pechini method (M2). Page 11.
Fig. 4. Schematic representation of the epoxidation of cyclohexene using hydrogen
peroxide as an oxidizing agent and ethyl acetate as solvent. Page 12.
Fig. 5. Temperature influence on percent conversion and selectivity in the epoxidation of
cyclohexene using commercial alumina as a catalyst. Page 13.
Fig. 6. Influence of the alumina synthesis method of alumina on its catalytic activity in
the epoxidation of cyclohexene in a closed system at 90°C. Page 14.

Fig. 7. Ratio of percent conversion to selectivity in the epoxidation of cyclohexene in a
closed system using the alumina synthesized in this work as a catalyst at 90 °C. Page 15.
Fig. 8. FTIR spectrum of the product obtained from the epoxidation of cyclohexene.
Page 16.
1
Fig. 9. H-NMR spectrum of the product obtained from the epoxidation of cyclohexene.
Page 16.
Figures:

Fig. 1.

Fig. 2.

Fig. 3.
OH
Al2O3, reflux
Ethyl acetate
O
H2O2
+
+
OH
1,2-Epoxycyclohexane
Cyclohexene
Cyclohexane-1,2-diol
Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.
Fig. 8.

Fig. 9.