Effect of the CuAl2O4 and CuAlO2 Phases in Catalytic Wet Air Oxidation of ETBE and TAME using CuO/γ-Al2O3 catalysts

Article abstract of DOI:10.1002/open.201900080

This paper studies Cu/Al₂O₃ catalysts, synthesized in two ways: copper deposit in the synthesis of alumina (sol gel) and incipient impregnation stabilized at 400 °C. The materials were characterized by X-ray diffraction studies, nitrogen physisorption, temperature programmed reduction of H₂, dehydration of isopropanol, scanning electronic microscopy, transmission electronic microscopy, which were evaluated in the liquid phase oxidation reaction of ethyl tert-butyl ether and tert-amyl methyl ether. The formation of CuAl₂O₄ and CuAlO₂ in the samples synthesized by sol gel, led to a modification of the texture, thus resulting in an expansion of the specific area of the materials. CuAl₂O₄ and CuAlO₂ have been identified by DRX from a content of 10 % Copper, the first showed the highest intensity with this technique. In the same way, these species favor the presence of Lewis acid sites; this is reflected in the materials with (Di-isopropyl Ether) DIPE of 96.7 % and 91.1 % for the samples SAlCu5 and SAlCu15 respectively. The catalytic activity of the materials prepared by sol gel is in the function of the number of surface acid sites, the smaller particle size of the Cu and the surface of the contact, in the case of the ETBE meanwhile for TAME the activity was based mainly on the strength of the present acid sites. With impregnated materials, the activity is attributed to the smaller particle size of the Cu and the greater strength of the surface acid sites in the solid. The formation of spinel species inhibits the leaching phenomenon in the reaction milieu.

Full text of DOI:10.1002/open.201900080

DOI: 10.1002/open.201900080
Full Papers
1
2
3
4
5
6
7
8
9
Effect of the CuAl2O4 and CuAlO2 Phases in Catalytic Wet
Air Oxidation of ETBE and TAME using CuO/γ-Al2O3
catalysts
Cecilia Sánchez-Trinidad,[a] Gloria del Angel,[b] Gilberto Torres-Torres,*[a]
Adrián Cervantes-Uribe,[a] A. Abiu Silahua Pavón,[a] Zenaida Guerra-Que,[a, c]
Juan Carlos Arévalo-Pérez,[a] and Fancisco J. Tzompantzi-Morales[b]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
This paper studies Cu/Al2O3 catalysts, synthesized in two ways:
copper deposit in the synthesis of alumina (sol gel) and
with this technique. In the same way, these species favor the
presence of Lewis acid sites; this is reflected in the materials
with (Di-isopropyl Ether) DIPE of 96.7% and 91.1% for the
samples SAlCu5 and SAlCu15 respectively. The catalytic activity
of the materials prepared by sol gel is in the function of the
number of surface acid sites, the smaller particle size of the Cu
and the surface of the contact, in the case of the ETBE
meanwhile for TAME the activity was based mainly on the
strength of the present acid sites. With impregnated materials,
the activity is attributed to the smaller particle size of the Cu
and the greater strength of the surface acid sites in the solid.
The formation of spinel species inhibits the leaching phenom-
enon in the reaction milieu.
°
incipient impregnation stabilized at 400 C. The materials were
characterized by X-ray diffraction studies, nitrogen physisorp-
tion, temperature programmed reduction of H2, dehydration of
isopropanol, scanning electronic microscopy, transmission elec-
tronic microscopy, which were evaluated in the liquid phase
oxidation reaction of ethyl tert-butyl ether and tert-amyl methyl
ether. The formation of CuAl2O4 and CuAlO2 in the samples
synthesized by sol gel, led to a modification of the texture, thus
resulting in an expansion of the specific area of the materials.
CuAl2O4 and CuAlO2 have been identified by DRX from a
content of 10% Copper, the first showed the highest intensity
1. Introduction
interaction of the elements that constitute a catalyst, this is the
case of the workgroup Wachs[3] and Reddy,[4] to name a few.
The interaction between metal-oxide of metal or between metal
oxides exhibit a variation due to the structural complexity
resulting in the formation of interacting species, this is the case
of the copper-alumina binomial.[5] So, metal-support interac-
tions have been studied during the synthesis of copper
catalysts, mainly because they are generally strong, which limits
the load of the metal that is deposited to avoid large
agglomerates that promote sintering and nucleation.[6] Strong
copper-support interactions can cause the formation of new
crystalline phases during catalyst preparation. Although the
formation of a new phase with copper implies a loss of the
active phase, in some cases it may represent a benefit. For
example, the formation of a solid CuÀ Al2O3 solution or
aluminates. The used synthesis methods are usually conven-
tional impregnation processes, causing a heterogeneous distri-
bution of the species on the surface and, in some cases, the
reduction of the surface area,[7] which is why it is very important
to use new methodologies that allow obtaining catalysts with
high dispersion of the constituent metals, modified with
promoter species, and that are characterized by having a good
activity, selectivity and interaction between the species at
relatively low temperatures. The copper aluminate nanocompo-
sites spinel type (CuAl2O4, CuAlO2) are of interest due to their
low cost, thermal stability, non-toxic, high mechanical resist-
ance, hydrophobicity and low surface acidity,[8] characteristics
that make them attractive in various fields, for example,
photocatalysts for the degradation of organic pollutants,
The species that compose a catalyst, as well as the interactions
between them, significantly affect certain chemical reactions .[1]
For a long time, the interactions between metal and its support
have been studied in heterogeneous catalysis since 1970, when
the concept of “metal-support strong interaction” was intro-
duced for the first time.[2] To understand this phenomenon,
model reactions have been used to determine and indicate the
[a] C. Sánchez-Trinidad, G. Torres-Torres, A. Cervantes-Uribe, A. A. S. Pavón,
Z. Guerra-Que, J. C. Arévalo-Pérez
Universidad Juárez Autónoma de Tabasco, Laboratorio de Nanomateriales
Catalíticos Aplicados al Desarrollo de Fuentes de Energía y Remediación
Ambiental, Centro de Investigación de Ciencia y Tecnología Aplicada de
Tabasco (CICTAT), DACB, Km. 1 carretera Cunduacán-Jalpa de Méndez AP.
24, C.P. 86690, Cunduacán Tabasco, México
Fax: +52 19143360928
Tel: +52 19143360300
E-mail: gilberto.torres@ujat.mx
torremensajes@gmail.com
[b] G. del Angel, F. J. Tzompantzi-Morales
Universidad Autónoma Metropolitana-Unidad Iztapalapa, Departamento
de Química, Área de Catálisis, Av. San Rafael Atlixco 186, C.P. 09340; A. P.
55–534 México D.F., México
[c] Z. Guerra-Que
Instituto Tecnológico de Villahermosa, Departamento de Ing. Química-
Bioquímica-Ambiental, Km. 3.5 Carretera Villahermosa-Frontera, Cd. Indus-
trial, C.P. 86010 Villahermosa, Tabasco, México
©2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
This is an open access article under the terms of the Creative Commons
Attribution Non-Commercial NoDerivs License, which permits use and dis-
tribution in any medium, provided the original work is properly cited, the
use is non-commercial and no modifications or adaptations are made.
ChemistryOpen 2019, 8, 1143–1150
1143
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Figure 1. Adsorption-desorption isotherms a) Method of impregnation b) Method sol gel, pore distribution for the catalysts synthesized c) Impregnation d) Sol
gel.
magnetic materials, rechargeable batteries, medicine, recycling
of nuclear fuel and oxidation of organic molecules.[9–11]
presented isotherms type IVa with hysteresis type H2 and the
volume of nitrogen was increased with the 5% by weight of
copper material, however, the materials prepared by sol gel,
showed Isotherms type a, and presented two hystereses (b).
Regarding the pore diameter distribution, the impregnation
samples exhibited a range between 20 and 90 Å, only the
sample with 5% copper was bimodal (c). A similar behavior had
the samples synthesized by sol gel but with a range between
50 to 300 Å, which is higher than the impregnated samples (d).
As for the surface area, calculated by the BET equation, the
sol gel samples are 8 times larger than the samples by
impregnation, see Table 1. This event indicates that metal
Catalytic wet air oxidation (CWAO) of contaminants has
become a promising technique for solving a wide variety of
water pollution problems.[12] Several studies have been carried
out to develop suitable catalysts to be applied to this technique
in the last decades. The catalysts supported by noble metals
have proved to be the most important to oxidize a wide variety
of contaminants by CWAO[13–17] Oxidation in the liquid phase is
a treatment capable of completely oxidizing these compounds,
in besides maximizing selectivity in CO2.[18] However, copper
catalysts, usually industrial CuO/Al2O3 with 10% loading, are the
most effective in this process;[19] on the other hand, copper‘s
biggest problem is the leaching of Cu ions in water, ETBE and
TAME were selected as a model molecule due to the great
problem of the presence of gasoline oxygenates in rivers, lakes
and groundwater,[20] which is necessary to propose various
destruction techniques.
Table 1. Surface area and activity in the dehydration of isopropanol.
Catalyst BET
Surface
Propene
selectivity
(%)
DIPE
Rate
d
(nm)
selectivity (molgÀ 1 sÀ 1*10À 6
(%)
)
area
(m2/g)
IAlCu5
IAlCu10 43
IAlCu15 30
SAlCu5
SAlCu10 384
SAlCu15 370
26
46
17
39.2
3.2
49.5
8.8
53
83
60.8
96.7
50.4
91.1
5.9
1.3
15
16.9
5.7
12.4
7.1
7.3
7.4
32
35
42
2. Results and Discussion
449
Figure 1 shows the results of the nitrogen adsorption-desorp-
tion process of all materials. In part a, the impregnated samples
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1144
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Figure 2. XRD patterns of the catalysts CuO/Al2O3 a) impregnation b) sol gel method.
Figure 3. TPR a) Impregnation, b) sol gel method
interactions with active sites of alumina favor high surface
areas.[21–24] Figure 2 presents the results of the X-ray diffraction.
The structure of the alumina range in the impregnated samples
was identified, as well as slight diffraction corresponding to the
copper oxide (CuO),[25–31] see Figure 2a. Meanwhile, the samples
synthesized by sol-gel exhibited the typical diffraction of the
boehmite structure, but not those of the copper oxide, instead,
the formation of CuAlO2 was favored (Figure 2b). This crystalline
structure has been obtained using the synthesis by ball milled
or precipitation, and its subsequent thermal treatment at high-
temperature conditions.[32] This structure can also be achieved
through the orientation when depositing on a substrate of silica
oxide.[33]
impregnated materials. The consumption of hydrogen around
100 C corresponds to the CuH formation, while the consump-
tion of hydrogen around 350 C is due to the reduction of Cu
°
2+
°
À Al. interactions. On the other hand, the reduction of surface
[35]
°
copper oxide is originated at 400 C. The 10% sample is the
only one that shows a CuÀ Al2+ interaction. In Figure 3b, SAlCu5
sample presented the corresponding reduction to copper oxide
around 100 C. The reduction of Cu2+Al was performed at
°
°
350 C. The samples SAlCu15 and SAlCu10 displayed a reduction
profile different from the sample SAlCu5. A hydrogen con-
sumption was presented at 100 and 150 C. Based on the X-ray
diffraction pattern (Figure 2(b)), the compound CuAlO2 showed
a greater diffraction intensity with respect to CUAl2O4, therefore;
the abundance of CuAlO2 is greater than the one of CuAl2O4.
Taking this information into account, the reduction to 100 C
corresponds to the compound CuAlO2 and the reduction of
°
The specific synthesis and orientation under relatively mild
conditions of this structure through the sol gel method is
relevant. Even with this, the formation of copper aluminate
°
°
°
spinel (CuAl2O4, 2q:18.91 ) was also favored. This structure, as
CuAl2O4 is favored at 150 C (Figure 3a and 3b).
well as CuAlO2, has been achieved by using high-temperature
thermal treatments.[34] Figure 3a shows the reduction profiles of
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1145
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
site, whereas the formation of DIPE is almost a consequence of
the concentration of acid sites.[28] Table 1 reports activity and
selectivity for dehydration of isopropanol.
1
2
3
The SAlCu5 sample showed the best behavior, among the
materials prepared by the sol gel method, to describe a higher
concentration of acid sites in the solid (DIPE: 96.7% and
isopropanol dehydration rate: 16.9 molgÀ 1sÀ 1*10À 6). How-
ever, for materials impregnated according to the isopropanol
dehydration rate, the material with the best acidity on the
surface is the sample IAlCu15. The increasing order of surface
acidity in all the materials analyzed is mentioned below:
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
IAlCu15 > IAlCu5 > IAlCu10;
SAlCu5 > SAlCu15 > SAlCu10
Figure 4. STEM for the catalysts CuO/γ-Al2O3 a) and b) Method of impregna-
tion 10 and 15% c) and d)) Sol gel method 10 and 15%.
On the other hand, the surface acidity was higher for
samples IAlCu5 (46%) and SAlCu10% (49.5%). Although the
impregnated materials exhibited a low concentration of acid
sites, compared to those of sol gel, these sites have a higher
acid strength.
The STEM images of the impregnated samples are shown in
Figure 4a and 4b. Whereas the TEM images of the sol gel
materials are shown in Figure 4c–4d.
Here it is observed that some copper is interacting with
alumina to form copper aluminate with remnants of oxide
copper particles on the surface using sol gel method, which are
Previously our research group has reported on the presence
of acid sites in alumina, modified with other semiconductors
(CeO2) and noble metals (Rh and Sn) as active sites in catalysts,
has an important role in the reaction mechanism for Catalytic
Wet Air Oxidation (CWAO) of oxygenated organic compounds,
as proposed in this work. Since at a higher concentration of
acid sites there are fewer intermediates, such as tert-butanol, 2-
methylpropene, acetone and methanol, which allows complete
mineralization to CO2. The importance of this work lies mainly
in obtaining catalytic materials with greater acidity for the
complete oxidation of oxygenated compounds without gener-
ating reaction intermediates and replace to use of noble metals
as active sites which have a high cost.[40–42] The greater presence
of acidity in the materials modified with copper by sol gel is
possibly due to the interaction between this metal with the
alumina to form the copper aluminate spinel which conse-
quently has a significant effect on the catalytic activity.
Table 2 shows the catalytic activity of all samples tested in
the CWAO of ETBE and TAME. It is evident that the samples
prepared by the sol gel method had a better catalytic behavior,
which indicates that the activity of these materials is a function
of the number of surface acid sites, the smaller particle size of
the Cu and the surface of the contact, in the case of the ETBE,
because the SAlCu5 material was the most active. For the
larger than 20 nm and has been previously reported at temper-
[36]
°
atures below 600 C. This result coincides with the particle
size distribution (d) reported in Table 1 and shown in the
histogram of Figure 5b.
While for the impregnated samples a unimodal distribution
was obtained, in the Figure 5a for to estimate the particle size
value for Copper; resulting in an average size of 7 nm in the
three samples (Table 1).
In the decomposition of isopropanol, the main product that
is obtained is the olefin and the rate of dehydration is directly
related to the concentration of total acidity sites of the
catalyst.[37–39]
The selectivity for isopropanol dehydration provides impor-
tant information about the acidity of the catalyst. Propene and
di-isopropyl ether (DIPE), are the main products of the reaction.
The formation of propene is related to the strength of the acid
Table 2. Initial rate (ri) TOC abatement (XTOC%), ETBE and TAME Conversion
(X%) and initial rate in CWAO with CuO supported catalysts.
Catalyst
ETBE
XTOC
(%)
TAME
XTOC
(%)
X
(%)
ri (mmolgÀ 1 sÀ 1
X
(%)
ri (mmolgÀ 1 sÀ 1
IAlCu5
76
66
72
82
88
80
76
66
72
82
88
80
0.62
0.27
0.55
0.75
0.55
0.54
72
68
77
73
70
78
72
68
77
73
72
78
0.52
0.44
0.43
0.34
0.61
0.60
IAlCu10
IAlCu15
SAlCu5
SAlCu10
SAlCu15
Figure 5. Particle size distribution samples IAlCu15 (a), SAlCu15 (b).
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1146
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
TAME, the activity was based mainly on the strength of the
present acid sites and the presence of the copper aluminate
spinel, which possibly increased the strength of the acid sites,
but by increasing the amount of Cu in the materials, the acidity
diminishes, for which, we can establish that at 10% of Cu there
is the highest surface acidity strength due to the formation of
the copper aluminate spinel, as shown by the SAlCu10 material.
Among the impregnated materials, the IAlCu5 sample showed
the best catalytic activity with the two contaminating molecules
(ETBE and TAME), this is mainly attributed to the smaller particle
size of the Cu and the greater strength of the surface acid sites
in the material. According to the catalytic activity, high
sensitivity of the acid sites was observed in the degradation of
ETBE, while for TAME it was due to the presence of the species
CuAlO2 and CuAl2O4.
Previously, our research group has reported the catalytic
activity of materials prepared with alumina at different contents
of Cu (5, 10 and 15%) as an active phase, synthesized by
methods such as sol gel, impregnation and impregnation
modified with urea, used in the CWAO of ETBE and TAME. The
activity of these materials in the CWAO of ETBE, reveals that
CO2 selectivity is complete with all the materials prepared by
the impregnation method, with the sol gel method the catalysts
are completely selective only up to 10% Cu and with the
method of impregnation modified with urea no material was
totally selective to CO2.[43] Comparing the above, with the
results obtained in this investigation we observe that in this
work all the catalysts prepared have a CO2 selectivity of 100%
in the CWAO of the ETBE, which describes a greater efficiency in
the materials. In the case of TAME, the work presented above
only describes that the material prepared by the sol gel method
with 15% Cu and the material synthesized by impregnation
modified with urea with 5% Cu, are the only ones that
complete the CO2 selectivity with this pollutant model mole-
cule. However, in this investigation only the material prepared
with the sol gel method at 10% of Cu was the only one that did
not complete its CO2 selectivity, this shows that the materials
synthesized in this work show a better catalytic behavior in the
CWAO of ETBE and of the TAME.
On the other hand, alumina catalysts with a Cu content of
5%, similar to those shown here, have been used in the CWAO
of the phenol at 3 hours of reaction describing its catalytic
behavior both in the oxidized state and in the reduced state,
where better catalytic behavior occurs in the first case.
However, the incorporation of a third element such as 5% Ce in
the alumina interacting with the same Cu content improves
twice the activity in the phenol CWAO, both in the oxidized and
reduced state in the catalyst.[44] This turns out to be as relevant
as what happened in the 90’s when Striolo et al used three
different homogeneous catalysts (FeÀ CuÀ Mn) in the CWAO of
organic acids, which showed that the synergy between the
three metals considerably improves the activity in comparison
when only two or one catalysts was used in the system.[45] The
above described leaves us with important evidence so that
soon this type of catalysts can interact as shown here, with
other elements or oxides that synergistically can significantly
improve the activity in the CWAO.
Table 3. Selectivity to CO2 and leaching of Cu in CWAO of ETBE and TAME
with CuO supported catalysts.
1
2
3
4
5
6
7
8
9
Catalyst
ETBE
CO2(%)
TAME
SCO2(%)
S
Cu leaching (ppm)
Cu leaching (ppm)
IAlCu5
100
100
100
100
100
100
0.272
0.306
0.531
0
0
0
100
100
100
100
97
0.011
0.020
0.032
0
0
0
IAlCu10
IAlCu15
SAlCu5
SAlCu10
SAlCu15
100
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Table 3 shows the selectivity to CO2 formation at the end of
the reaction of ETBE and TAME. In the case of ETBE, all the
materials showed 100% of the selectivity to CO2, which can be
explained by the acid sites quantity and related by the DIPE
formation selectivity showed in Table 1. In the case of TAME,
only the sample SAICu10 showed incomplete selectivity to CO2
but the value was high too (97%). It is important to note that
this sample was the one that showed the lowest selectivity
value to the DIPE, which shows that this reaction is more
sensitive to the presence of acid sites in the catalyst than in
ETBE case. This may be due to the fact that the molecular
structure of TAME contains a methyl group more compared to
ETBE, which possibly forms intermediates of alkenes, ketones
and alcohols with a higher aliphatic chain, which require greater
acidity to later transform to CO2 and H2O.
Table 3 shows the results of the process of leaching of Cu in
the materials evaluated in the CWAO of ETBE and TAME. Here
we can observe that the materials synthesized by the sol gel
method do not present this phenomenon. These can be
attributed to the formation of copper spinel (CuAlO2 and
CuAl2O4) due to the sol-gel preparation method and observed
in the analysis of X-ray diffraction (Figure 2b) and TPR (Fig-
ure 3b) analysis. Contrary, in the case of the catalysts synthe-
sized by the impregnation method, the leaching of Cu ions with
the amount of 0.531 ppm using IACu15 catalyst in the CWAO of
ETBE which represents 3.54% of the copper in the reaction
milieu.
The materials shown in this study have better stability and
resistance to leaching, a series of catalysts similar to ours have
been reported in both composition and synthesis, varying only
the calcination temperature in the final thermal treatment and
reaction conditions (mild conditions for two hours) in the
phenol CWAO (see Table 4). From here it was observed that at
elevated temperatures the leaching is considerably reduced by
the presence of active species of Cu on the surface of the
material, but as the treatment temperature decreases from 650
°
to 450 C in the catalysts the amount of leached Cu increases in
the system,[46] this reveals that the materials analyzed, evaluated
°
and heat-treated at 400 C have a greater stability of the active
phase even after subjecting them to pressure and temperature
conditions, where the materials prepared by sol gel do not
show amount of leached Cu. The Table 4 summarizes the
catalytic behavior, reaction conditions and leaching of Cu in
materials like solids analyzed in this work. In most of the
materials compared in Table 4 they show copper leaching in
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1147
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
Table 4. Bibliographic description of the catalytic behavior of materials with Cu applied in the CWAO at different conditions.
1
2
3
4
5
6
7
8
9
Catalyst (%Cu) –
preparation method
Pollutant
Model
Molecule
Reaction Conditions
Activity
(rate, % conversion or %
oxidation)
Cu leaching (% or ppm)
Reference
°
Cu (5, 10, 15%)/Al2O3 –
ETBE/TAME
Phenol
100 C, 10 bar, 1 hour,
1000 ppm of pollutant
TOC >74%
N.M
[43]
[44]
[45]
[46]
impregnation and sol gel
Cu (5%)/Al2O3, Cu (5%)/
Al2O3À CeO2 – impregnation
Fe, Cu, Mn (Homogeneous)
°
120 C, 10 bar, 3 hours,
Rate: 341 and 809 mmol/
hgphenol
TOC >90%
N.M
1000 ppm of pollutant
98 C, H2O2, pH 3,5
°
Mixture of
organic acids
Phenol
N.M
°
Cu (5%)/Al2O3 – impregna-
40 and 70 C, 1 atm, 2 hours,
H2O2,1000 ppm of pollutant
TOC >86%
36-64%
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
°
tion (400, 650 and 900 C)
Cu (10%)/Al2O3 – impregna- Phenol
°
140 C, 0.5 Mpa, 5 hour, pH 6,
Rate: 0.4 L/hgcu to pH 7
58%-1% depending on the pH [47]
°
tion (550 C)
0.047 mol/L of pollutant
°
Cu/Al2O3À Cu/Al2O3À CeO2
Methylene
blue
Methyl or-
180 C, 1.5 Mpa, 2 hours,
COD:74.5% for Cu/Al2O3 and
84.6% for Cu/Al2O3À CeO2
COD:84.5% for CuÀ Fe/Al2O3
and 91.4% for FeÀ La/Al2O3
28.2 ppm for Cu/Al2O3 and
2.9 ppm for Cu/Al2O3À CeO2
7.5 ppm for CuÀ Fe/Al2O3 and
3.8 ppm for CuÀ FeÀ La/Al2O3
[48]
[49]
°
impregnation (450 C)
2000 ppm of pollutant
°
CuÀ Fe/Al2O3À CuÀ FeÀ La/
200 C, 2 Mpa, 2 hours,
°
Al2O3 impregnation (450 C) ange
4000 ppm of pollutant
NM: Not measured.
different quantities, which in some cases depends on the pH,
the addition of an element or the treatment temperature. In our
materials we observe that using the method of sol gel
preparation this phenomenon does not occur, which is
beneficial for the reaction conditions used here, these materials
method inhibits leaching of the copper ions in the reaction
milieu, which it’s an advantage in comparison with the classical
method of preparation by impregnation.
show good resistance and activity in the CWAO of ETBE and Experimental Section
TAME, and offer the possibility to be reused and economically
manufactured for the low cost of Cu compared to metal
elements such as Au, Ag, Pt, Pd, Ru and Rh.
Catalyst Preparation
The first series of materials were loaded with Cu by the
impregnation method to obtain 5%, 10% and 15% by weight. For
which, boehmite (Boehmite Catapal B) was placed in a solution
with a pH of 3 by nitric acid (HNO3, Baker at 66%); the temperature
3. Conclusions
°
was increased to 70 C. Subsequently, copper nitrate (Cu(NO3)2 .1/2
H2O Baker 99%) was added to the solution until the mixture was
The incorporation of copper in alumina facilitated the modifica-
tion of textural properties. By impregnation, only the presence
of the CuO and boehmite phase of the alumina was identified,
while the species CuAlO2 and CuAl2O4 by sol gel were observed.
In the impregnation materials, the CuÀ Al2+ interaction is
favoured, which possibly inhibits the activity and concentration
of acid sites of the catalyst with 10% copper for these materials.
The catalytic activity is attributed to the smaller particle size of
the Cu and the greater strength of the surface acid sites for
both polluting molecules using IAlCu5 as a catalyst. Never-
theless, the materials prepared by sol gel they act differently
depending on the contaminating molecule. SAlCu5 was the
most active in the ETBE oxidation due to the number of surface
acid sites, the smaller particle size of the Cu and the surface of
the contact. Meanwhile, SAlCu10 showed the most activity in
the CWAO of TAME by the strength of the present acid sites
and the presence of the copper aluminate spinel and the
CuAlO2 which manifest greater interaction CuÀ Al.
°
homogenized. The temperature was raised to 90 C for 4 hours. The
°
solvent was removed under vacuum and dried at 120 C. The
resulting materials were calcined at 400 C for 4 hours. The
following series of materials was prepared by the sol gel method
from the hydrolysis of titanium trisecbutoxide (Sigma Aldrich 97%)
mixed with deionized water, secbutanol (Sigma Aldrich 99.5%),
urea (JT Baker, 99%) and copper nitrate hydrate (Baker 99%) to
form a sol that was left in aging at reflux conditions at 70 C for
24 hours. Then the solid was separated from the solvents using a
rotary evaporator in vacuum at 60 C, which was dried at 120 C for
24 hours until a powder was obtained which was calcined at 400 C
°
°
°
°
°
for 4 hours.
For identification, the catalysts impregnation (I), sol-gel (S), alumina
(Al) and cupper (Cu) were labelled as IAlCuX a SAlCuX, where X (5
10 and 15 wt% of copper).
Characterization Techniques
BET Specific Surface Area
The CWAO of TAME reaction is more sensitive to the
presence of acid sites in the catalyst than ETBE. The materials
presented in this study would possibly have a similar catalytic
behavior if compared with other modified catalysts and added
with active sites of noble metals, which would present an
advantage due to the low cost of copper. Formation of the
spinel species in the copper catalysts prepared by sol-gel
The BET specific surface area was carried out in an automatic
Quantachrome Autosorb 3B analyzer. The Nitrogen adsorption
°
isotherms were conducted at À 196 C;the samples were outgassed
°
overnight at 300 C prior to the nitrogen adsorption. The specific
surface area was calculated from the adsorption isotherms by the
BET method.
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1148
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
X-Ray Diffraction (XRD)
ri ¼ ðDConvð%Þ=DtÞð60½pollutant�iÞ=mcat
(1)
1
2
3
4
5
6
7
8
9
The crystalline phase composition of the obtained materials was
determined on a Siemens D-500 instrument using CuÀ Kα radiation
(λ=1.5418 Å). The reflection intensities were measured by step
The analysis of total organic carbon (TOC) was performed by using
a 5000 TOC Shimadzu Analyzer, which was previously calibrated to
obtain concentrations in the range of 0–1000 ppm of TOC (Eq. (2));
TOCf =after 1 h of reaction and TOCi at t=0.
°
°
scanning in the 2θ range between 10–70 with a step size of 0.02
À 1
°
and a scan speed of 4 min
.
À À
�
�
i
f
i
*
XTOC
¼
½TOC� À ½TOC� =½TOC� 100
(2)
Temperature Programmed Reduction under H2 Atmosphere
(H2-TPR)
The selectivity to CO2 was calculated using the following
equation:[50]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
H2-TPR experiments were performed in a CHEMBET-3000 (QUAN-
TACHROME Co) equipment using 0.2 g of the catalyst by means of
°
the following protocol: samples were heated at 300 C under
DTOC
XðpollutantÞ
nitrogen flow (10 mLminÀ 1) during 30 min. Then, the samples were
cooled down to room temperature and mixed gas flow (5% H2/
95% N2) was passed through the cell. The TPRÀ 1profiles were
S
¼
x 100 %
CO2
(3)
°
registered using a heating program of 10 Cmin from room
temperature up to 700 C using a flow rate of the gas mixture of
°
Leaching of Cu in the Employed Catalysts in CWAO of ETBE and
TAME
10 mLminÀ 1
.
Atomic absorption analysis of the samples after the reaction was
carried out using a Perkin Elmer apparatus equipped with a
graphite fur using a lamp of copper ions to determinate the
concentration of this ion in the reaction milieu in order to study the
leaching phenomenon in the CWAO of ETBE and TAME. The
calibration curves were makes before analysis in the range of the 0
to 20 ppm of copper.
Transmission Electron Microscopy (TEM)
STEM images were obtained on a Tecnai G2 F30 instrument. The
sizes of Cu/Al2O3 nanoparticles were obtained by measuring 200
particles for each sample.
Isopropanol Dehydration
The isopropanol dehydration was carried out at atmospheric
°
°
pressure and 130 C over pre-activated catalysts (400 C 2 h, in
fluxed nitrogen). The isopropanol was fed by using a saturator
system coupled to a fixed bed glass reactor (with a volume of 3 ml
and using 20 mg of catalyst). The HGSV used for the isopropanol
dehydration was 1 hÀ 1. The activity was followed by determining
the isopropanol conversion and the selectivity was determined for
propene and di-isopropyl ether (DIPE). The analysis of products was
carried out with a gas chromatograph VARIAN CP-3800 coupled to
the catalytic activity system and equipped with a capillary Quadrex
Stationary phase, 007-FFAP with 30 m of length.
Acknowledgements
Authors thank the National Council for Science and Technology
(CONACYT) for financing the projects CB-2008 105158 and CB-
2010 132648 and thank the Universidad Juárez Autónoma de
Tabasco for the support with PFCE Project.
Conflict of Interest
Reaction Conditions
The authors declare no conflict of interest.
The catalytic wet air oxidation reaction was carried out in a batch
reactor of stainless steel high-pressure (Parr Instruments) coated
with a glass liner to prevent corrosion problems. The volume of
reaction was 150 mL of an aqueous contaminant (ETBE, TAME)
solution with a concentration of 1000 ppm and 1 g/LÀ 1 of catalyst,
then nitrogen was introduced into the reactor during 15 min to
remove the air contained and after this the reactor was heated at
Keywords: heterogeneous catalysis
scanning electronic microscopy · X-ray diffraction studies · wet
air oxidation reaction
· Cu/Al2O3 catalysts ·
°
100 C. Afterwards, an oxygen (high purity) pressure of 10 bar was
introduced into the reactor and under continuous agitation of
1000 rpm, the reaction was initiated. Previous test reactions showed
that under such conditions the reaction rate was not controlled by
the diffusion of oxygen into the liquid phase. The evolution of the
reaction was followed by performing the analysis of aliquots at
intervals of 10 min through 1 h. The aliquots were taken from the
reactor using the sampler valve equipped with a microspore glass
filter to prevent the catalyst loss and analyzed on a gas chromato-
graph (Varian 3400Cx) equipped with a flame ionization detector
(FID) on a capillary column HP-into wax. The initial rate (ri) was
calculated from the pollutant (ETBE or TAME) conversion as a
function of time curves, using the following equations:
[1] P. W. Selwood, Adv. Catal. 1951, 3, 27–106.
[2] S. J. Tauster, S. C. Fung, R. L. Garten, J. Am. Chem. Soc. 1978, 100, 170–
175.
[3] I.E. Wachs, Catal. Today 1996, 27 (3–4), 437–455.
[4] B. M. Reddy, P. M. Sreekanth, Y. Yamada, Q. Xu, T. Kobayashi, Appl. Catal.
A 2002, 228, 269–278.
[5] S. A. Hassanzadeh-Tabrizi, R. Pournajaf, A. Moradi-Faradonbeh, S.
Sadeghinejad, Ceram. Int. 2016, 42, 14121–14125.
[6] G. J. Hutchings, A. A. Mirzaei, R. W. Joyner, M. R. H. Siddiqui, S. H. Taylor,
Appl. Catal. A 1998, 166, 143–152.
[7] I. P. Chen, S. S. Lin, C. H. Wang, L. Chang, J. S. Chang, Appl. Catal. B 2004,
50, 49–58.
[8] C. G. Aguilar, C. E. Moreno, J. Mater. Sci. 2018, 53, 1646–1657.
[9] N. Yang, H. Sun, Coord. Chem. Rev. 2007, 251, 2354–2366.
[10] A. Nosal-Wiercińska, J. Electroanal. Chem. 2011, 654, 66–71.
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1149
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Full Papers
[11] N. E. Rajeevan, R. Kumar, D. K. Shukla, P. P. Pradyumnan, S. K. Arora, I. V.
Shvets, Mater. Sci. Eng. B 2009, 163, 48–56.
[12] J. A. Zazo, J. A. Casas, A. F. Mohedano, J. J. Rodríguez, Appl. Catal. B
2006, 65, 261–268.
[13] Y. Tang, K. Shih, K. Chan, Chemosphere 2010, 80, 375–380.
[14] L. Oliviero, J. Barbier, D. Duprez, A. Guerrero-Ruiz, B. Bachiller-Baeza, I.
Rodriguez-Ramos, Appl. Catal. B 2000, 25, 267–275.
[15] A. Quintanilla, J. A. Casas, A. F. Mohedano, J. J. Rodríguez, Appl. Catal. B
2006, 67, 206–216.
[16] A. Pintar, M. Besson, P. Gallezot, Appl. Catal. B 2001, 31, 275–290.
[17] L. Oliviero, J. Barbier, D. Duprez, H. Wahyu, J. W. Ponton, I. S. Metcalfe,
D. Mantzavinos, Appl. Catal. B 2001, 35, 1–12.
[35] R. N. Pease, H. S. Taylor, J. Am. Chem. Soc. 1921, 43, 2179–2188.
1
2
3
4
5
6
7
8
9
[36] S. N. Alam, N. Sharma, D. Panda, A. Kumar, D. Sampenga, A. Sairam, V.
Sarky, M. B. Krupateja, J. Alloys Compd. 2018, 753, 799–812.
[37] C. Bouzidi, H. Bouzouita, A. Timoumi, B. Rezig, Mater. Sci. Eng. B 2005,
118, 259–263.
[38] C. H. Ong, H. Gong, Thin Solid Films 2003, 445, 299–303.
[39] M. Miclau, N. Miclau, R. Banica, D. Ursu, Mater. Today 2017, 4, 6975–
6981.
[40] I. Cuauhtemoc, G. Del Angel, G. Torres, V. Bertin, Catal. Today 2008,
133–135, 588–593.
[41] A. Cervantes, G. Del Angel, G. Torres, G. Lafaye, J. Barbier Jr., J. N.
Beltramini, J. G. Cabanas-Moreno, A. E. de los Monteros, Catal. Today
2012, 212, 2–9.
[42] I. Cuauhtémoc, G. Del Angel, G. Torres, C. Angeles-Chavez, J. Navarrete,
J. M. Padilla, Catal. Today 2011, 166, 180–187.
[18] L. Oliviero, J. Barbier, D. Duprez, Appl. Catal. B 2003, 40, 163–184.
[19] Z. Lockman, L. P. Lin, C. K. Yew, S. D. Hutagalung, Sol. Energy Mater. Sol.
Cells 2009, 93, 1383–1387.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
[20] A. N. Banerjee, R. Maity, P. K. Ghosh, K. K. Chattopadhyay, Thin Solid
Films 2005, 474, 261–266.
[21] K. A. Cychosz, R. Guillet-Nicolas, J. García-Martínez, M. Thommes, Chem.
Soc. Rev. 2017, 46, 389–414.
[22] Q. J. Liu, Z. T. Liu, Vacuum 2014, 107, 90–98.
[23] Y. Lu, T. Nozue, N. Feng, K. Sagara, H. Yoshida, Y. Jin, J. Alloys Compd.
2015, 650, 558–563.
[24] A. N. Banerjee, C. K. Ghosh, K. K. Chattopadhyay, Sol. Energy Mater. Sol.
Cells 2005, 89, 75–83.
[25] M. Fang, H. He, B. Lu, W. Zhang, B. Zhao, Z. Ye, J. Huang, Appl. Surf. Sci.
2011, 257, 8330–8333.
[26] N. Wolff, D. Klimm, D. Siche, J. Solid State Chem. 2018, 258, 495–500.
[27] I. Hamada, H. Katayama-Yoshida, Phys. B 2006, 376–377, 808–811.
[28] T. Suriwong, T. Thongtem, S. Thongtem, Curr. Appl. Phys. 2014, 14,
1257–1262.
[43] Z. Guerra Que, J. G. Torres Torres, I.Cuauhtemoc Lopez, J. C. Arevalo Per-
ez, A. Cervantes Uribe, H. Perez Vidal, A. E. de los Monteros Reyna, J. G.
Pacheco Sosa, M. A. Lunagomez Rocha, C. Sanchez Trinidad, “Noncon-
ventional Wastewater Treatment for the Degradation of Fuel Oxy-
genated (MTBE, ETBE, and TAME)“ 2019, 10.5772/intechopen.84250, pp.
1–20.
[44] Z. Guerra-Que, H. Perez-Vidal, G. Torres-Torres, J. C. Arevalo-Perez, A. A.
Silahua-Pavon, A. Cervantes-Uribe, A. E. de los Monteros, M. A. Lunago-
mez-Rocha, RSC Adv. 2019, 9, 8463–8479.
[45] P. Striolo, J. N. Foussard, H. Debellefontaine, Proceedings of the 1st
International Conference on Advanced Oxidation Technologies for
Water and Air Remediation, London, Ontario, Canada, June 25–30,
1994, pp. 363–365.
[46] A. Devard, P. Brussino, F. A. Marchesini, M. A. Ulla, J. Environ. Chem. Eng.
2019, 7, 103201.
[29] C. L. Jiang, Q. J. Liu, F. S. Liu, Z. T. Liu, Curr. Appl. Phys. 2017, 17, 126–
[47] R. R. Sapico, P. Marin, F. V. Diez, S. Ordoñez, J. Environ. Chem. Eng. 2017,
129.
5, 2570–2578.
[30] K. Vojisavljević, B. Malič, M. Senna, S. Drnovšek, M. Kosec, J. Eur. Ceram.
Soc. 2013, 33, 3231–3241.
[31] C. Ruttanapun, W. Kosalwat, C. Rudradawong, P. Jindajitawat, P.
Buranasiri, D. Naenkieng, N. Boonyopakorn, A. Harnwunggmoung, W.
Thowladda, W. Neeyakorn, C. Thanachayanont, A. Charoenphakdee, A.
Wichainchai, Energy Procedia 2014, 56, 65–71.
[32] M. Senna, P. Billik, A. Y. Yermakov, M. Škrátek, M. Majerová, M.
Čaplovičová, M. Mičušík, L. Čaplovič, M. Bujdoš, M. Nosko, J. Alloys
Compd. 2017, 695, 2314–2323.
[33] K. Kamiya, T. Yoko, Y. Miyaji, K. Matusita, Int. J. High Technol. Ceram.
1987, 3, 297–307.
[48] Y. Zhang, Y. Zhou, C. Peng, J. Shi, Q. Wang, L. He, L. Shi, Appl. Surf. Sci.
2018, 436, 981–988.
[49] Y. Zhang, F. Peng, Y. Zhou, Chin. J. Chem. Eng. 2016, 24, 1171–1177.
[50] S. S. Lin, D. J. Chang, C.-H. Wang, C. C. Chen, Water Res. 2003, 37, 793–
800.
[34] R. H. Jarman, J. Bafia, T. Gebreslasse, B. J. Ingram, J. D. Carter, Mater. Res.
Bull. 2013, 48, 3916–3918.
Manuscript received: March 2, 2019
Revised manuscript received: July 20, 2019
ChemistryOpen 2019, 8, 1143–1150
www.chemistryopen.org
1150
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA