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Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
CIENCIA 26 (1,2), 28 - 41, 2018
Maracaibo, Venezuela
Effect of Sn addition in alumina- and silica-supported palladium
catalysts for n-butane dehydrogenation
(Dehydrogenation of n-butane over supported palladium catalysts)
Jonathan E. Mendez *, Douglas R. Rodríguez, Jorge L. Sánchez, Geomar J. Arteaga.
Instituto de Supercies y Catálisis, Facultad de Ingeniería, Universidad del Zulia, P. O. Box 15251,
Maracaibo 4003A, Venezuela.
Recibido: 15-01-18 Aceptado: 06-02-18
Abstract
Dehydrogenation of n-butane was studied over alumina- and silica-supported Pd and Pd-Sn catalysts with
0.5 wt. % of Pd. The reaction was carried out at 500 °C in both continuous ow and pulses systems. The catalysts
were prepared by incipient wetness impregnation. For the bimetallic catalysts, the sequential impregnation
method was used adding rst Sn and then Pd, with Sn/Pd atomic ratios of 0.1, 0.25 and 0.5. The samples
were characterized by XRF, UV-DRS, N2 adsorption, TPR, CO chemisorption and FTIR-CO techniques. On the
supported-alumina catalysts, Pd oxychloride were formed, which is highly resistant to the reduction, and it is
responsible for the high Pd dispersion. On the supported-silica catalysts, the addition of Sn modies both the
reducibility and adsorption capacity of Pd. The effects of Sn were mainly of geometric nature when supported
on alumina, and both geometric and electronic nature when supported on silica. On the supported-alumina
catalysts, the Sn addition increases the selectivity toward butenes, due to the high stabilization of Pd species;
while on the supported-silica catalysts, greater Pd-Sn interactions are evidenced, where the catalyst properties
are strongly inuenced at the lowest content of Sn added. The alumina–supported bimetallic catalysts showed
the best performance for n-butane dehydrogenation among the catalysts investigated herein.
Keywords: Palladium-tin catalysts; Sn/Pd ratio; FTIR-CO; n-butane dehydrogenation.
Efecto de la adición de estaño en catalizadores de paladio soportados sobre
alúmina y sílice para la deshidrogenación de n-butano
(Deshidrogenación de n-butano en catalizadores de paladio soportado)
Resumen
Se estudió la deshidrogenación del n-butano en catalizadores de Pd y Pd-Sn soportados sobre alúmina
y sílice, con una carga de Pd de 0,5 % p/p. La reacción se llevó a cabo a 500 ° C tanto en ujo continuo como
por pulsos. Los catalizadores fueron preparados mediante impregnación a humedad incipiente. Para los
catalizadores bimetálicos, se utilizó la impregnación secuencial, añadiendo primero Sn y luego Pd, para obtener
relaciones atómicas Sn/Pd nominales de 0,1, 0,25 y 0,5. Las muestras se caracterizaron mediante las técnicas
de XRF, UV-DRS, adsorción de N2, TPR, quimisorción de CO y FTIR-CO. En los catalizadores soportados sobre
alúmina, se formó un complejo de oxicloruro de Pd, que es altamente resistente a la reducción y es responsable
de la alta dispersión de Pd. En los catalizadores soportados sobre sílice, la adición de Sn modicó tanto la
reducibilidad como la capacidad de adsorción del Pd. Los efectos del Sn sobre el Pd fueron principalmente
del tipo geométrico en los catalizadores soportados sobre alúmina, y de naturaleza tanto geométrica como
electrónica en aquellos soportados sobre sílice. En los catalizadores soportados sobre alúmina, la adición de
Sn aumentó la selectividad, debido a la alta estabilidad de las especies de Pd; mientras que en los catalizadores
soportados sobre sílice, se evidenciaron mayores interacciones Pd-Sn, donde las propiedades de los catalizadores
se vieron fuertemente inuenciadas con el menor contenido de Sn adicionado. Los catalizadores bimetálicos
soportados sobre alúmina mostraron el mejor desempeño para la deshidrogenación de n-butano.
* Corresponding Author: Tel-fax.: +58 (261) 4128791/97. E-mail: jomendez@ng.luz.edu.ve.
Other E-mail addresses: dorodriguez@ng.luz.edu.ve, jlsanchez@ng.luz.edu.ve, garteaga@ng.luz.edu.ve
29Mendez et al.,/ Ciencia Vol. 26, Número Especial (2018) 28-41
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
Introduction
The importance of catalytic dehydrogenation of
light parafns to olens has been growing due to
the demand for these unsaturated hydrocarbons [1].
They are the starting material for some of the most
important chemical products, such as polymers,
synthetic rubbers and oxygenated compounds for
reformulated fuels. Unfortunately, light olens
are not available as a natural resource; they are
obtained in stream cracking furnaces and produced
in FCC (uid catalytic cracking) plants in reneries.
Catalytic dehydrogenation of light parafns (like
the widely available normal-butane) provides a
second way to obtain light olens, which in turn
can be transformed into more valuable chemicals,
including the methyl tertiary-butyl ether (MTBE),
ethyl tertiary-butyl ether (ETBE), and tertiary amyl
methyl ether (TAME) [1-3].
Nevertheless, the conversion of light parafns
to the corresponding olens is limited by
thermodynamics restrictions due to the strong
endothermic character of this reaction. High
temperatures (530–730 ºC) are required to reach
conversions of nearly 50% for parafns C2–C6. The
dehydrogenation temperatures are higher for light
parafns than for heavy ones [1].
Side reactions like isomerization, thermal
cracking and coking, which are thermodynamically
and kinetically favoured over dehydrogenation
reactions, can occur under operating conditions
(>530 ºC). Therefore, it is highly desirable a catalyst
with a suitable conversion and high selectivity
towards the desired olen, working at lower reaction
temperatures. Besides, the unavoidable formation
of coke on the catalyst surface that results in a
progressive reduction of catalytic activity, could be
minimized at these more benevolent conditions [2].
The use of weak acid supports in a catalytic system
is also essential to avoid side reactions, like cracking
and isomerization.
Many researchers have been devoted to study
the dehydrogenation of light parafns over Pt-based
catalysts, particularly on bimetallic Pt-Sn supported
catalyst [4-8], due to the benecial effects of tin
as a promoter: tin decreases the size of platinum
ensembles; reducing hydrogenolysis and coking
that require large ensembles of platinum, and/or
acts as electronic modier of Pt, thereby enhancing
the catalyst selectivity and stability. However, few
studies are related to the performance of these
reactions on supported Pd catalysts [1, 9-11].
Particularly, the Pd-Sn system has been studied for
nitrates removal [12, 13], methane oxidation [14, 15]
and selective hydrogenation reactions [16-18].
A catalytic system based on Pd can be an
alternative to the more expensive metals for
dehydrogenation reactions, such as Pt, Ru and Ir.
Studies carried out earlier [9] on the performance of
Pd-Sn/SiO2 catalysts for propane dehydrogenation,
revealed the effects of tin addition in low proportions
(Sn/Pd atomic ratio = 0.14-0.84), and an optimal in
both adsorption capacity of Pd and catalytic activity
was found. Rodriguez et al. [1] studied the n-butane
dehydrogenation over Pd-Ga/Al2O3 catalysts with
different atomic Ga/Pd ratios, and they found that
the effects of Ga were the same as those caused by
Sn for dehydrogenation in Pd-Sn/Al2O3 catalysts.
The aim of this work is to study the effect of Sn/
Pd ratio on the catalytic properties of supported Pd
catalysts for n-butane dehydrogenation reaction
in both continuous ow and pulses at a relatively
low temperature (500 ºC). Alumina and silica were
chosen as support due to its low acid strength, in
order to do not promote cracking reactions that
affect selectivity towards olens. Catalysts were
characterized by X-ray uorescence spectroscopy
(XRF), diffuse reectance UV-vis spectroscopy (UV-
DRS), N2 adsorption, temperature programmed
reduction (TPR), CO chemisorption and FTIR
spectroscopy of adsorbed CO (FTIR-CO).
Experimental
Catalysts preparation
Monometallic Pd and Sn samples were prepared
by incipient wetness impregnation of γ-Al2O3 (Alfa
Aesar, SBET = 210 m2/g, Vpore = 0.76 cm3/g) and
SiO2 (Cabosil M-5, Scintran, SBET = 224 m2/g),
using a rotavapor at 80 ºC, with an aqueous solution
of PdCl2 (Fisher Scientic, 99%) or SnCl4⋅5H2O
(Fisher Scientic, > 99%) in HCl, in order to obtain
Pd and Sn nominal contents of 0.5 and 0.56 wt.
%, respectively. Bimetallic Pd–Sn/Al2O3 and Pd–
Sn/SiO2 catalysts were prepared by sequential
impregnation, adding rst Sn and then Pd. Supports
were previously crushed and sieved (60/80 mesh),
and then calcined at 700 °C for 4 h. The nominal
contents of metals in bimetallic catalysts were 0.5
wt. % Pd and 0.056−0.28 wt. % Sn, (Sn/Pd atomic
ratios between 0.1 and 0.5). After impregnating, the
samples were dried at 120 °C overnight, and then
calcined at 500 °C for 2 h. Pd, Sn and Cl contents were
measured by energy dispersive X-ray uorescence
spectroscopy (XRF) using a Shimadzu EDX-700HS
spectrometer, provided with an Rh gun operated
at 50 keV. Al2O3 and SiO2 supports will be named
Al and Si, respectively. Table 1 summarizes the
notation and chemical composition of the catalysts.
Palabras Claves: Catalizadores de paladio-estaño; relación Sn/Pd; FTIR-CO; Deshidrogenación de
n-butano.
30 Effect of Sn addition in alumina- and silica-supported palladium catalysts...
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at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
Characterization techniques
BET surface areas of supports and catalysts
were determined from the N2 adsorption isotherms
at -196 ºC, using an automatic Micromeritics ASAP
2010 apparatus after the samples were outgassed at
150 ºC for 2 h. The specic surface area of selected
catalysts are also listed in Table 1.
The catalysts were studied by UV–vis diffuse
reectance spectroscopy (UV-DRS) at atmospheric
conditions, in a Perkin-Elmer spectrometer model
Lambda 2 equipped with a diffuse reectance
accessory, consisting of an integrating sphere of 50
mm coated with BaSO4 to collect the reected light.
The wavelength range varied from 190 to 700 nm.
TPR proles were measured from -50 to 700 °C
in a Vycor U-tube reactor connected to a stainless
steel apparatus provided with a thermal conductivity
detector (TCD), using a mixture of 5% H2/Ar as
reducing gas. Prior to measurements, the sample
(100 mg) was pretreated in air ow at 500 °C for 1 h,
then cooled down in owing Ar to room temperature
and, then, to -50 °C, using an isopropanol-liquid
nitrogen bath, before admitting the ow of reducing
gas. The reactor was freely heated from -50 to room
temperature (RT) by removing the cool bath, and
immediately heated up to 700 °C at 10 °C/min,
using a temperature-controlled furnace.
Dynamic CO chemisorption measurements were
carried out in the same stainless steel apparatus
used in TPR experiments, which was equipped with
a gas injection valve (Valco). Successive CO pulses
(58 µL STP) were sent to the reactor until reaching
the saturation, using He (30 mL/min) as carrier gas.
The catalysts (100 mg) were previously reduced at
400 °C in owing H2 for 1 h, and then the adsorbed
hydrogen was removed by ushing He at the same
temperature for 1 h.
Fourier transform infrared spectra of adsorbed
CO (FTIR-CO) were recorded at RT on a Shimadzu
IR Prestige 21 spectrometer, at a resolution of 2 cm-1
using around 100 scans. Self-supported samples
(20-24 mg/cm2) were put into an infrared cell
equipped with a KCl window, designed for treating
the samples in a controlled atmosphere. The samples
were submitted to the following pretreatment: (i)
drying in Ar ow at 120 °C for 1 h; (ii) reduction under
owing hydrogen at a programmed temperature
rate (10°C/min) from 120 to 400°C, plus 60 min at
400 °C; (iii) outgassing in Ar at 400°C for 30 min,
and nally cooled down in owing Ar from 400
°C to room temperature. Successive CO pulses in
a He ow were sent to the sample, registering the
IR spectrum elapsed 5 min after each injection, to
follow the formation of the absorption bands. To
obtain the IR spectrum corresponding to saturation,
a CO ow was used for 5 min, and then outgassing
in Ar for 15 min. The spectra presented here were
obtained after subtracting the gas phase and solid
contributions.
Catalytic activity test
Two different n-butane dehydrogenation tests
were carried out, one of them in a continuous
ow reactor and the other one in a system where
Table 1. Chemical composition, surface area and CO/Pd ratio
Catalysts Pd (wt. %) Sn (wt. %) Cl (wt.%) Sn/Pd atomic ratio S
BET
(m
2
/g) CO/Pd
a
Pd
0.40
Al 0.40 - 0.70 0 - 0.56
Pd
0.55
Sn
0.045
Al 0.55 0.045 0.54 0.073 210 0.53
Pd
0.52
Sn
0.091
Al 0.52 0.091 0.58 0.16 - 0.58
Pd
0.54
Sn
0.19
Al 0.54 0.19 0.66 0.32 215 0.51
Sn
0.43
Al - 0.43 0.70 ∞ - -
Pd
0.34
Si 0.34 - n.d. 0 - 0.20
Pd
0.31
Sn
0.061
Si 0.31 0.061 n.d. 0.18 218 0.08
Pd
0.36
Sn
0.12
Si 0.36 0.12 n.d. 0.30 - 0.09
Pd
0.31
Sn
0.22
Si 0.31 0.22 n.d 0.64 218 0.06
Sn
0.51
Si - 0.51 n.d ∞ - -
n.d.: not detected
a: Based on the Pd loading values obtained by XRF.
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at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
pulses of n-butane were sent to the catalyst. The
continuous ow experiment was performed at 500
°C and atmospheric pressure, in a conventional
reaction line built in stainless steel. The switching
of gases was done without mixing or access of air. A
Vycor U-tube (6 mm OD) reactor was charged with
20 mg of catalyst. Samples were pretreated in Ar ow
at 120 °C for 1 h and then reduced in H2 ow at 500
°C for 2 h. The reaction mixture contained n-C4H10
and H2, with a H2:n-C4H10 ratio of 10. A total ow
of 66 mL/min and a GHSV of 200 L·g-1·h-1 were
used. Taking into account that H2 is a by-product
of the dehydrogenation reaction, its presence as a
reagent would not be thermodynamically favorable.
However, it is very important to include H2 in the
feedstock in order to decrease the carbon formation
and hence to moderate the activity decrease along
the reaction time [19].
The pulse experiments were performed by
injecting pulses of the same hydrogen and n-butane
mixture, at the same conditions as the continuous
ow experiments. The catalytic bed was kept under
owing He (30 mL/min) between the injections
of successive pulses. The exit gases were analyzed
in a Perkin-Elmer GC, equipped with an Al2O3/
KCl 50 m x 0.25 mm capillary column and a ame
ionization detector (FID).
Specic activity (A), n-butane conversion and
selectivity were calculated on a carbon basis, using
the FID areas (Ai) and the corresponding response
factors (rfi), according to the following equations:
where Fn-c4 is the n-butane molar ow =
0.000245 mol/min; nPd= Pd moles in the sample
(based on XRF results)
Results and discussion
1. Catalysts characterization
Table 1 shows the values of Pd and Sn loadings
obtained by XRF. It is observed that catalysts
supported on alumina have a Pd loading near to the
nominal composition of 0.5 wt %, meanwhile the ones
supported on silica have lower values of Pd contents
(0.31-0.36 wt. %). This could be caused by the low
afnity of palladium precursor with silica, hindering
the anchoring of Pd anions (as PdCln(H2O)4-n2-n)
on this support [20]. According to Toebes et al. [21],
the nature of the interactions of the precursor metal
salt with a given support depends on the pH of the
solution, the zero point charge (ZPC) of the support,
and the nature of ions to be adsorbed. The ZPC
varies from 7.0 to 9.0 for γ-alumina, and 1.0 to 2.0
for silica [21]. Therefore, during the impregnation
with the Pd solution (PdCl2 in HCl 0.1 N, pH ≈ 1), the
surface of the alumina support becomes positively
charged, and tends to adsorb compensating anions
like PdCl42-, but the opposite occurs in the case of
silica, because of the pH value is in the range of its
ZPC. For the case of Sn content, the values were
slightly lower than the nominal (0.056 – 0.28 wt.
%) for all of the catalysts.
Chlorine contents were also determined by XRF.
Only the catalysts supported on alumina showed
signicant contents of Cl- ions, in the range of 0.54
- 0.70 wt. %, that increased in bimetallic catalysts, i.
e., the Cl content increased with the Sn loading, from
0.54 to 0.66%. This fact was expectable, as the Cl-
ion sources came from both the Pd and Sn solutions
in the preparation of the bimetallic catalysts.
The signicant Cl content found in the Al2O3-
supported catalysts after the calcination treatment
at 500 ºC for 2 hours, suggests that this anion was
initially well anchored to the surface of the alumina,
probably as a supercial complex of Pd and chlorine
(PdxOyClz) which has a high thermal stability [22].
Rodriguez et al. [1] concluded that this palladium
supercial complex was also formed during the
calcination of Pd-Ga/Al2O3 catalysts, considering
these species as mobile complexes that spread over
the alumina surface, which can improve the Pd
dispersion upon reduction.
The BET surface areas (SBET) of some catalysts
are also listed in Table 1. Regardless of the amount
of Pd and Sn added, the values of BET surface area of
the catalysts remain as the corresponding supports
(210 m2/g for alumina and 224 m2/g for silica).
Similar results were found for pore volumes (values
not shown). As expected, the textural properties of
the catalysts are almost the same as those of their
respective supports, due to small amounts of Pd and
Sn on the surface of the alumina and silica.
UV-DRS spectra of Pd-Sn catalysts supported
on alumina and silica are presented in Figures 1
and 2, respectively. It can be observed that samples
containing palladium (Fig. 1(a) – (d)) display similar
spectra, exhibiting bands at 214, 245, 275 and 425
nm.
32 Effect of Sn addition in alumina- and silica-supported palladium catalysts...
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
The band observed at 214 nm can be associated
to the charge transfer (Pd⋅ Cl) of PdCl2 [22],
whereas the strong band at 245 nm is assigned to
charge transfer Pd ⋅ O, and the band at 275 nm has
been attributed to PdxOyClz surface complex [22].
The band at 425 nm is related to d-d transition in
PdO species interacting strongly with the alumina
support. It is noteworthy that the unsupported
PdO phase, exhibits a signal around 490 nm, which
was not observed in the spectra shown in Fig. 1.
Furthermore, the UV spectrum of the Sn0.43Al
sample (Fig. 1e) shows a broad band in the range
225-300 nm. This broad signal is also assigned to
the charge transfer Sn ⋅ O [22]. In summary, these
results lead to the existence of a Pd and Cl phase on
the surface of the support, which can be strongly
stabilized.
Figure. 1. UV–DRS spectra for Al2O3-supported
catalysts: (a) Pd0.40Al; (b) Pd0.55Sn0.045Al;
(c) Pd0.52Sn0.091Al; (d) Pd0.54Sn0.19Al; (e)
Sn0.43Al; and (f) Al.
On the other hand, samples supported on
silica show UV-DRS spectra different from those
observed for the ones supported on alumina. UV-
DRS spectrum of Pd0.34Si (Fig. 2a) presented
a wide band in the d-d transition region around
490 nm, related to the electronic structure of PdO
crystals in supported Pd catalysts [23]. The other
signals in the charge transfer region at 250-300 nm
are contributions of the silica. In the spectra of the
bimetallic Pd0.31Sn0.061Si and Pd0.31Sn0.22Si
catalysts (Fig. 2(b) – (c)), similar bands as those in
the monometallic Pd0.34Si catalyst can be observed,
which indicates the presence of PdO phase without
any interaction with the silica support. Finally,
the signals at 200-350 nm exhibited for Sn0.51Si
sample (Fig. 2d), are ascribed to the Sn⋅O charge
transfer and silica support.
Figure. 2. UV–DRS spectra for SiO2-supported
catalysts: (a) Pd0.34Si; (b) Pd0.55Sn0.061Si; (c)
Pd0.31Sn0.22Si; (d) Sn0.51Si; and (e) Si.
The TPR proles of the catalysts supported on
alumina are shown in Figure 3. The monometallic
and bimetallic Pd-Sn catalysts show very similar
reduction proles (Figs. 3a-3d) with low intensity
signals at 19, 50-80, and 300 ° C, and a wide and
extensive signal in the temperature range of 80-260
ºC. The peaks at 19 and 50-80 ºC can be assigned
to the reduction of crystalline PdO with different
sizes, where the largest particles are reduced at
lower temperatures [1, 11, 24]. The signal with the
great broadness (80-260 ºC) has been associated
to the reduction of different species of PdxOyClz
[1, 11], while the peak at 300 ºC is attributed to the
reduction of PdO particles interacting strongly with
the support [25].
Figure3. TPR proles for Al2O3-supported
catalysts: (a) Pd0.40Al; (b) Pd0.55Sn0.045Al; (c)
Pd0.52Sn0.091Al; (d) Pd0.54Sn0.19Al and (e)
Sn0.43Al.
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For Sn0.43Al sample, a broad reduction signal
between 300 and 650 °C is observed. This signal
could be attributed to reduction of Sn4+ to Sn2+
and/or Sn0 [4, 26, 27], so that it indicates some
resistance to reduction.
TPR proles of the catalysts supported on silica
are presented in Figure 4. For bimetallic catalysts
(Figs. 4b-4d), the reduction peaks observed at
low temperatures (< 100 °C), correspond to the
reduction of large PdO particles [1, 11, 24], in
contrast to that observed in the catalysts supported
on alumina. For Pd0.34Si (Fig. 4a), the reduction
peaks observed at 21 and 38 °C, could be associated
to the reduction of PdO particles with different sizes.
In addition, the negative signal at 60 °C is ascribed to
the decomposition of β-hydride Pd phase (β-PdHx),
whose presence indicates the existence of large
palladium particles [24].
Figure 4. TPR proles for SiO2-supported
catalysts: (a) Pd0.34Si; (b) Pd0.31Sn0.061Si;
(c) Pd0.36Sn0.12Si; (d)Pd0.31Sn0.22Si and (δ)
Sn0.51Si (insert)
Some changes occurred in the reducibility of
these catalysts when increasing the Sn/Pd ratio.
For the Pd0.31Sn0.061Si catalyst, the TPR prole
shows signals at 33 and 44 °C, followed by the
decomposition of β-hydride Pd phase (PdHx) at 59
°C. For the Pd0.36Sn0.12Si and Pd0.31Sn0.22Si
catalysts (Fig. 4(c) – (d)), similar reduction signals
to those obtained in the monometallic sample are
observed, and can also be attributed to the reduction
of PdO particles and decomposition of palladium
hydride. However, in these bimetallic samples
with the highest Sn/Pd ratio, the negative signal
decreases in intensity, probably due to a geometric
effect of Sn on palladium ensembles, hindering the
β-PdHx phase, either by the formation of bimetallic
Pd-Sn particles [28] or by the dilution of Pd particles
by Sn atoms [29].
Other signals centered at 240-250 ºC observed
for Pd0.36Sn0.12Si and Pd0.31Sn0.22Si catalysts,
can be ascribed to the reduction of Sn4+ catalytically
assisted by Pd0, thus indicating a close interaction
between Pd and Sn in the bimetallic catalysts. As
can be seen in the insert in Fig. 4, the reduction of
Sn4+ occurred at higher temperatures (around 464
ºC) in the Sn0.51Si sample [27].
The values of CO/Pd ratio obtained from
chemisorption measurements are also listed in Table
1. For catalysts supported on alumina, the values of
CO/Pd ratio remained in the range of 0.51-0.58,
despite of the presence of tin. These results display
a high Pd dispersion, probably as a result of the
formation of PdxOyClz, promoted by the presence
of Cl [29]. Pd species were strongly stabilized, which
is in agreement with UV-DRS (Fig. 1) and TPR (Fig.
3) results. On the other hand, the high values of the
CO/Pd ratio corresponded with that obtained by
Daley et al. [30], who reported a high Pd dispersion
(ca. 50%) when the catalysts were subjected to
chlorination treatment, and it was ascribed to the
interactions between hydroxyl groups of the support
and anions of precursor salt.
For the catalysts supported on silica, the values
of CO/Pd ratio were signicantly lower. In this case,
they were highly dependent on the presence of Sn.
For the monometallic Pd0.34Si catalyst, a CO/
Pd ratio of 0.20 was obtained, decreasing with the
content of tin to 0.06-0.09 for the bimetallic Pd-Sn/
SiO2 catalysts.
The decrease in CO chemisorption with the
presence of tin can be attributed to a possible
blocking and/or substitution of Pd atoms by Sn
and/or the formation of alloys at high tin content
[29]. Moreover, the Sn atoms could also cause a
weakening of the strength of CO adsorption on Pd.
Changes in the stoichiometry of CO adsorption on
Pd due to the Sn addition, considering the different
forms of adsorbed CO, has been reported by Sales
et al. [29].
FTIR-CO spectra are presented in Figures 5-8.
The results were expressed as a function of CO
coverage on Pd (θCO). For the monometallic catalyst
Pd0.40Al (Fig. 5b), four bands were observed at
2155, 2125, 1990 and 1945 cm-1. The intensity of
these bands progressively increased with θCO,
and another band arose at 2085 cm-1 when the
saturation was reached (Fig. 5f). Besides, the band
at 1990 cm-1 shifted to lower frequency (1980 cm-1).
34 Effect of Sn addition in alumina- and silica-supported palladium catalysts...
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Figure 5. FTIR spectra of CO adsorbed for the
Pd0.40Al catalyst at increasing CO coverages: (a)
θ=0, (b) θ=0.20, (c) θ=0.27, (d) θ=0.31, (e) θ=0.36
y (f) θ=1.
CO adsorption on supported Pd catalysts depends
greatly on the Pd oxidation state [31], and the
location of Pd atoms in different Pd crystal planes
(111, 100, 110), with different coordination numbers
(9, 8, and 7, respectively) [29]. Hence, the band at
2155 cm-1 is attributed to the interaction of CO with
residual surface Pd2+ ions (linear carbonyls Pd2+ -
CO), which are stabilized by neighbouring chloride
ions, present in all supported alumina catalysts
after calcination (Table 1), and were not removed by
the reduction treatment (400 ºC for 60 min under
H2). The band at 2125 cm-1 was attributed to the
linear CO adsorption on Pd+ ions [31], which are
also stabilized by neighbouring chloride ions. The
weak band at 2085 cm-1 is ascribed to linear CO
species adsorbed on metallic Pd [32]. The rest of the
bands located at 1980 and 1945 cm-1 are ascribed to
CO bridged species located on different Pd crystal
planes and/or submitted to dipole–dipole coupling
of different intensities. Therefore, the CO:Pd
stoichiometry ratio can be far from 1.
In the bimetallic Pd-Sn/Al2O3 catalysts, the
spectra exhibited the same bands observed for the
monometallic one (2155, 2125, 2085, 1990 and 1945
cm-1), but slightly shifted to lower wavenumbers.
Thereby, only the infrared spectra obtained for
the bimetallic Pd0.55Sn0.045Al catalyst (Sn/Pd =
0.073) are shown (Fig. 6).
Figure 6. FTIR spectra of CO adsorbed for
the Pd0.55Sn0.045Al catalyst at increasing CO
coverages: (a) θ=0, (b) θ=0.19, (c) θ=0.25, (d)
θ=0.30, (e) θ=0.36 y (f) θ=1.
The assignments of the IR bands for the Al2O3-
supported catalysts, indicate that a fraction of Pd
species remained in oxidized state, as Pd+ and/or
Pd2+, even after reduction at 400 °C in H2 for 1 h,
while the rest of Pd is completely reduced to Pd0.
It is worth noticing in the FTIR-CO spectra in Figs.
5 and 6 that the intensity of the band in the region
35Mendez et al.,/ Ciencia Vol. 26, Número Especial (2018) 28-41
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at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
of linear carbonyls is greater than bridged ones, at
lower θCO (Figs. 5b and 6b), i. e., CO is preferentially
adsorbed on Pd sites stabilized with Cl- ions. As θCO
increased, Pd+ and Pd2+ were saturated, allowing
to increase CO adsorption on Pd0 atoms.
For the silica-supported catalysts, FTIR-CO
spectra of monometallic and bimetallic catalyst
are shown in Figures 7 and 8, respectively. For the
Pd034Si catalyst, bands are observed initially at
2087 and 1905 cm-1 (Fig. 7b). As θCO increased,
a band appeared at 1990 cm-1, and then the bands
at 1905 and 1990 cm-1 become shoulders, which
are overlapped with a new band at 1975 cm-1 when
saturation was reached. The band at 2087 cm-1 is
assigned to the linear adsorption of CO on metallic
Pd [32], while the bands located between 1990 and
1905 cm-1 are ascribed to bridged CO species, also
over metallic Pd [29, 32]. According to the spectrum
in Fig. 7f, there is a higher proportion of bridged CO
(COB) than linear CO (COL) species, resulting in a
value of COL/COB ratio of 0.30 after integration of
the signals, which indicates the largest Pd ensembles
in this sample.
Figure 7. FTIR spectra of CO adsorbed for the
Pd0.34Si catalyst at increasing CO coverages: (a)
θ=0, (b) θ=0.23, (c) θ=0.43, (d) θ=0.67, (e) θ=0.72
y (f) θ=1.
However, for the bimetallic catalysts (Fig. 8),
the COL/COB ratio increased from 0.30 to 0.68.
This is explained by a dilution of Pd by Sn on the
catalyst surface layer, and an ensemble effect should
account for the preferential suppression of bridged
CO species which requires the presence of adjacent
Pd atoms [29, 32]. Nevertheless, the presence of
tin seems to weaken the CO adsorption strength, as
linear entities are less rmly bonded than bridged
ones.
Figure 8. FTIR spectra of CO adsorbed for
the samples after saturation (θCO=1) with owing
CO: (a) Pd0.34Si; (b) Pd0.31Sn0.061Si; (c)
Pd0.36Sn0.12Si and (d) Pd0.31Sn0.22Si.
On the other hand, the maxima of the signals in
FTIR-CO spectra tend to change progressively with
the Sn/Pd atomic ratio, i.e., peaks initially located at
2087 and 1975 cm-1 for the monometallic Pd0.34Si,
shifted to 2080 and 1990 cm-1, respectively, for
the bimetallic Pd-Sn/SiO2 catalysts. Therefore,
the presence of tin can be affecting the electronic
properties of palladium in these silica-supported
catalysts [32].
2. Catalytic activity measurements.
2.1 Continuous ow reactor
The measurements were carried out at 500 ºC in
a differential ow reactor (n-butane conversion less
than 10%), and the results were expressed as moles
of n-butane converted per mole of Pd per minute,
i.e., specic activity (min-1), as a function of time
on-stream (TOS). It is known that dehydrogenation
36 Effect of Sn addition in alumina- and silica-supported palladium catalysts...
Scientic Journal from the Experimental Faculty of Sciences,
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reactions are metal-catalyzed non-demanding
reactions [33]. On the other hand, it is important
to indicate that the Sn0.43Al and Sn0.51Si catalysts
did not exhibit catalytic activity for the n-butane
dehydrogenation under the reaction conditions.
The specic activity of the Al2O3-supported
catalysts as a function of TOS is shown in Fig. 9.
The Pd0.40Al catalyst displayed an initial specic
activity of 44 min-1, suffering a fast deactivation
in the rst 15 min of TOS, and then the activity
decreased progressively along the reaction time.
Deactivation was also observed in the rest of the
catalysts, probably as a result of coke deposition on
the catalyst surface [19]. At these reaction conditions,
the formation of coke would build up on both the
metal and support sites [34, 35]. However, at the
beginning of the reaction, rst coke is deposited
on Pd atoms of high coordination number (cluster
or ensembles) and, then, coke blocks the Pd atoms
of low coordination number like corners or edges.
Therefore, low coordinated Pd palladium atoms are
more resistant to deactivation by coke [35].
Figure 9. Specic activity at 500 ºC as a
function of TOS for the Al2O3-supported catalysts.
The initial activity and deactivation rate
decreased upon Sn addition, in good agreement
with that observed by other researchers in Pt-Sn [4]
and Pd-Sn catalysts [10]. This deactivation occurred
mainly in the rst 15 minutes of TOS, and the catalyst
with the highest Sn content (Pd0.54Sn0.19Al, Sn/
Pd = 0.32) displayed the smallest activity. These
effects of the Sn addition on the catalytic behavior of
Pd supported on alumina can be explained mainly in
terms of geometric effects, as the majority of Sn in
the bimetallic catalysts blocked the Pd atoms of high
coordination number. Besides, the FTIR-CO results
(Figs. 5 and 6) show the lack of any electronic effect
of tin on palladium, probably because the electronic
properties of palladium were already modied by
the presence of chlorine.
Fig. 10 shows the specic activity for n-butane
dehydrogenation on SiO2-supported catalysts.
Specic activities of this catalysts were lower than
those obtained in alumina supported catalysts
(Fig. 9). The Pd0.34Si catalyst exhibited an initial
activity of 31 min-1, then the activity decreased
monotonically with TOS. The addition of a small
amount of Sn (Pd0.31Sn0.061Si) decreased the
initial activity, but after 15 min of TOS, this catalyst
showed the same activity as the monometallic one.
Figure 10. Specic activity at 500 ºC as a
function of TOS for the SiO2-supported catalysts.
The addition of a greater amount of Sn (Sn/Pd=
0.30 and 0.64) decreased the catalytic activity from
initial values of 23 and 16 min-1, respectively, to
nal values around 3 min-1. This decrease can be
attributed to both geometric and electronic effects of
Sn on Pd in concordance with CO chemisorption and
FTIR-CO results. Moreover, TPR results suggested
that Pd and Sn were in intimate contact on this
support, due to the possible formation of bimetallic
Pd-Sn particles after reduction. In the silica-
supported Pd catalysts, predominates the existence
of high coordination Pd atoms, indicated by the low
Pd dispersion (CO measurements). Furthermore, all
of the silica-supported Pd catalysts were deactivated
at the same extent in spite of the presence of Sn (Fig.
10).
Table 2 compiles the selectivity to all butenes
(initial: SD,0 and nal: SD,f), selectivity to
isomerization (initial: SI,0 and nal: SI,f) and the
deactivation parameter ∆R/R0, where ∆R is the
difference between the nal and initial reaction
rates (R0 and Rf, respectively).
37Mendez et al.,/ Ciencia Vol. 26, Número Especial (2018) 28-41
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at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
The addition of Sn decreased the ∆R/R0 values
only in the Al2O3-supported Pd catalysts, and this
decrease seems to be determined by the minimum
quantity of the promoter added. For the Al2O3-
supported catalysts, the deactivation parameter
values are similar to that obtained by Ballarini et
al. [19] and Bocanegra et al. [36] in monometalic
Pt(0.5%) and bimetallic Pt(0.5%)Sn(0.3%) catalysts
supported on γ-Al2O3/α-Al2O3 and MgAl2O4,
respectively. In the case of SiO2-supported catalysts,
the surface modication caused by Sn affected
structure-sensitive reactions, such as hydrogenolysis
rather than coking.
The Sn addition increased the selectivity toward
butenes in both Al2O3- and SiO2-supported
catalysts. For the Pd-Sn/Al2O3 catalysts, the
selectivity increased with the Sn content and the
time on-stream, achieving a selectivity of 94% for
the Pd0.54Sn0.19Al catalysts at 180 min of TOS;
probably Sn and coke blocked the most active
Pd sites, responsible for the reactions leading to
hydrogenolysis. Pd in the PdxClyOx phase appears
to be the most active species, because the electronic
properties of Pd were modied by means of charge
transfer Pd⋅Cl [22]. It should be pointed out that
an electronic effect of Sn on Pd was not observed for
this series of catalyst. In addition to dehydrogenation
and hydrogenolysis products, isobutene was also
observed: an isomerization selectivity between 2-4
% was registered in all Pd-Sn/Al2O3 catalysts [37].
For the silica-supported catalysts, higher
selectivity values toward butenes were observed. The
monometallic Pd0.34Si exhibited dehydrogenation
selectivity of 77 % at the beginning (1 min) and 98%
at the end (180 min of TOS) of the experiment. These
results indicate that Pd in metallic state (Pd0), as in
the silica support, exhibits high selectivity toward
dehydrogenation. In all Pd-Sn/SiO2 catalysts, the
dehydrogenation selectivity was 100 %. The SiO2-
supported catalyst with the lowest Sn loading (Sn/
Pd = 0.18) showed the best performance of these
catalysts, considering both the selectivity toward
butenes and the dehydrogenation activity. It is
worth mentioning that isobutene was not observed
as a product, probably due to the low acidity
of the support, that could not catalyse skeletal
isomerization reactions.
2.2 Pulse experiments.
In order to elucidate the catalytic behavior
for n-butane dehydrogenation over the different
mono and bimetallic supported catalysts during
the rst steps of reaction, a study of the catalytic
performance was carried out by sending pulses of
the H2/n-butane reactant mixture to the reactor.
The n-butane conversion for the indicated
Al2O3- and SiO2-supported Pd-Sn catalysts as a
function of the number of H2/n-butane pulses,
are shown in Figure 11. For the Al2O3-supported
catalysts, it can be seen that the Pd0.40Al sample
showed a conversion of 49% in the 1st pulse and
43% in the 12th pulse, while the Pd0.55Sn0.045Al
and Pd0.54Sn0.19Al catalysts showed higher
conversions of 64-68% in the 1st pulse and 46-47%
in the 12th pulse. The lower conversion obtained on
the Pd0.40Al catalyst is due to the smaller amount of
Pd atoms exposed on the surface, considering both
the lower Pd loading and the similar Pd dispersion
(Table 1). The conversion for the bimetallic catalysts
supported on alumina are in agreement to CO
chemisorption results (Table 1), where the CO/Pd
ratio was unaffected by the Sn content. Therefore,
conversion values observed in Figure 11 conrm
that Pd active sites were unaffected by Sn. Also, the
conversion decreases with pulse number, due to the
Table 2. Initial and nal selectivity for dehydrogenation (SD,0, SD,f), selectivity for isomerization (SI,0,
SI,f) and deactivation parameter (∆R/R0; ∆R: initial reaction rate [R0]−nal reaction rate [Rf]) in the
continuous ow reactor at 500 ºC.
Catalyst S
D,0
S
D,f
S
I,0
S
I,f
∆R/R
0
(%)
Pd
0.40
Al 50 89 3 4 40
Pd
0.55
Sn
0.045
Al 44 83 3 4 17
Pd
0.52
Sn
0.091
Al 63 92 3 3 25
Pd
0.54
Sn
0.19
Al 68 94 2 2 20
Pd
0.34
Si 77 98 - - 51
Pd
0.31
Sn
0.061
Si 100 100 - - 48
Pd
0.36
Sn
0.12
Si 100 100 - - 72
Pd
0.31
Sn
0.22
Si 100 100 - - 71
SD,0, SI,0: measured at 1 min of the reaction beginning. SD,f, SI,f: measured at 180 min of time of stream.
R0: measured at 15 min of the reaction beginning. Rf: measured at 180 min of time of stream.
38 Effect of Sn addition in alumina- and silica-supported palladium catalysts...
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
signicant coke deposition at this stage. This fact
was also observed by Pirngruber et al. [37] in their
studies of n-butane dehydroisomerization.
Figure 11. n-butane conversion at 500 ºC as
a function of the pulse number for the indicated
catalysts.
In the case of the catalysts supported on silica,
the Pd0.34Si sample showed a conversion of 14%
in the 1st pulse, and then gradually decreases
with subsequent pulses, until reaching about 8%
in the 12th pulse. For the Pd0.31Sn0.061Si and
Pd0.31Sn0.22Si catalysts, lower conversion values
were obtained, ranging between 3-6% along the
twelve pulses sent to the reactor. In this case, the
n-butane conversion decreased with the Sn loading
(or Sn/Pd atomic ratio). Similar to the continuous
ow experiments, the catalytic activity of the SiO2-
supported catalysts were lower than the Al2O3-
supported ones, but it should be taken in account that
both Pd loading and dispersion were lower in these
catalysts (Pd = 0.31-0.34% and CO/Pd = 0.06-0.20,
respectively). The decrease in n-butane conversion
with the amount of Sn is in agreement with CO/Pd
ratio. Nevertheless, the lower deactivation degree
in the n-butane dehydrogenation with the pulse
number indicates a lower coke deposition rate in
these catalysts.
The initial and nal selectivity for the n-butane
dehydrogenation in pulse experiments are listed
in Table 3. For the Al2O3-supported catalysts, was
observed a high selectivity for hydrogenolysis in all
of the pulses of reactant mixture sent to the reactor,
while the selectivity toward butenes were unaffected
by Sn content, ranging from 2-4% in the 1st pulse
and 5-8% in the 12th pulse, which means that, as
mentioned above, in the course of the reaction coke
deposition affected the hydrogenolysis reactions.
On the other hand, it is worth noticing that the
deactivation parameter increased in the bimetallic
catalysts, from 12 to 28-31%, but this change was
attributed to a higher amount of Pd active sites
available for the reaction (and, thus, the higher coke
formation rate) rather than the presence of Sn.
Table 3. Initial
a
and nal
b
selectivity for dehydrogenation (SD,0, SD,f), selectivity for hydrogenolysis
(SH,0, SH,f) and deactivation parameter (∆X/X0; ∆X: initial conversion [X0]−nal conversion [Xf]) in
the pulse experiments at 500 ºC.
Catalyst S
D,0
S
D,f
S
H,0
S
H,f
∆X/X
0
(%)
Pd
0.40
Al 4 8 96 92 12
Pd
0.55
Sn
0.045
Al 2 5 98 95 28
Pd
0.54
Sn
0.19
Al 2 6 98 94 31
Pd
0.34
Si 19 29 81 71 43
Pd
0.31
Sn
0.061
Si 72 90 28 10 31
Pd
0.31
Sn
0.22
Si 78 89 22 11 19
a: measured at 1st pulse of the reactant mixture.
b: measured at 12th pulse of the reactant mixture.
For the catalysts supported on silica, all of
them exhibited higher selectivity toward butenes,
especially the bimetallic ones. The monometallic
catalyst showed a selectivity to dehydrogenation
between 19-29 %, meanwhile selectivity values were
from 72% to 90% for the bimetallic catalysts. As it
was expected from previous results (Table 1, Fig. 10),
deactivation parameter decreased with Sn content
in these catalysts, from 43 to 19 %, as an evidence of
Pd-Sn interactions on the surface of the silica.
The differences in the selectivity between the
catalysts supported on alumina and those supported
on silica, point out the support´s role in Pd active
sites. From results obtained in the pulse experiments,
it can be concluded that coke deposition rate was
lower in the catalysts supported on silica, and the
39Mendez et al.,/ Ciencia Vol. 26, Número Especial (2018) 28-41
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
selectivity toward butenes increased with the Sn
addition. These results are explained by a geometric
and electronic effects of Sn on Pd, through the
dilution of Pd ensembles and the change in the Pd
nature upon Sn addition.
From results discussed above, it could be proposed
a model of the arrangement of metal particles on
the surface of the alumina and silica, in bimetallic
catalysts. On alumina, Pd atoms are highly stabilized
by chlorine species, which increased d-state
vacancies due to a charge transfer from palladium to
chlorine, as it was mentioned in the UV-DRS results
of these solids (Figure 1), which in turn hinder the
Pd-Sn interactions. The representation of these
particles on the surface of alumina is schematized in
Fig. 12, where two groups of Pd sites predominate:
“sites A” representing the Pd particles interacting
with Cl- by means of PdxOyClz surface complex, and
“sites B” representing the Pd particles interacting
with Sn. Most of the Pd is included in “site A”, which
explains why similar characterization results were
obtained (UV-DRS, TPR, CO chemisorption, FTIR-
CO). Also, these Pd species are the most active in
the n-butane dehydrogenation, and the strength
of n-butane adsorption on Pd is high enough to
favor the rupture of C-C (cracking) rather than C-H
(dehydrogenation) bonds [9]. Instead, on “sites B” Pd
particles are free of Cl, allowing the interaction with
Sn, and represent the minority of Pd. On this type
of sites, the hydrocarbon adsorption is weakened,
hindering C-C bond ruptures, and favoring the
dehydrogenation reactions toward butenes. During
the n-butane dehydrogenation in continuous ow
reactor, “sites A” were blocked by coke deposition
at the beginning (rst 15 min of TOS) and, then, the
reaction proceeded on “sites B”, where differences
in catalytic performance of the Al2O3-supported
catalysts upon Sn addition were observed. This
statement is supported by FTIR-CO results, which
indicated that CO is preferentially absorbed on Pd+/
Pd2+ species.
Figure 12. Schematic representation of the
distribution of metal particles on the surface of the
supports.
On silica, only the “sites B” predominates, as the
characterization results (XRF, UV-DRS, TPR and
FTIR-CO) showed the absence of any chlorinated
species, and the existence of large Pd ensembles,
which showed lower activity and higher selectivity
toward butenes and coking. Therefore, it is proposed
that both geometry and electronic effects of Sn on
Pd are involved in the catalysts supported on silica.
The results obtained herein showed a
commitment in the activity-selectivity relationship
for the n-butane dehydrogenation. In a continuous
ow reactor, Al2O3-supported catalysts displayed
better activity and stability for TOS higher than 15
min, with a selectivity toward butenes up to 94% for
the Pd0.54Sn0.19Al catalyst. In the case of the SiO2-
supported catalysts, all the samples displayed a high
dehydrogenation selectivity (100%), but low activity
and the worse stability on TOS.
Conclusions
The Pd species present in the Pd and Pd-Sn
supported catalysts depends on the nature of the
support. In this sense, when supported on alumina,
palladium exists primarily in two forms: (i) as
Pd oxychloride (PdxClyOx), where the electronic
properties of the metal are modied by the presence
of chlorine, by means of a charge transfer Pd⋅Cl.
This phase is highly resistant to reduction, as some of
the palladium species remained as Pd+/Pd2+ even
after reduction at 400ºC for 1 h. Besides, this Pd-
Cl interaction leads to a high metal dispersion and
high activity in the n-butane dehydrogenation, but
poor selectivity towards butenes; (ii) as Pd metallic
(Pd0), where a Pd-Sn interaction can be involved,
and a higher selectivity toward butenes can be
obtained. Over silica, only Pd0 exists after reduction,
with a very low dispersion and activity. The Al2O3-
supported bimetallic (Pd-Sn) catalysts showed a
better behavior for n-butane dehydrogenation than
the SiO2-supported ones, considering both the
activity and stability. Also, high selective toward
butenes was observed for the Pd0.54Sn0.19Al
catalysts (Sn/Pd = 0.32). These catalysts showed
the best performance for n-butane dehydrogenation
between all catalysts investigated here.
In spite of the poor performance showed by the
SiO2-supported catalysts, a better Pd-Sn interaction
was evidence in these catalysts. The performance
of the Al2O3-supported catalysts tested herein
for n-butane dehydrogenation can be compared
with the Pt-base catalysts, which encourages to
further studies of the supported Pd catalysts for this
reaction.
Acknowledgements
This research was partially supported by the
Consejo de Desarrollo Cientíco y Humanístico of
the Universidad del Zulia (CONDES), Venezuela,
40 Effect of Sn addition in alumina- and silica-supported palladium catalysts...
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
under the Projects CC-0145-08 and CC-0090-12.
The authors also thanks to Dr. Alberto Campos,
of the Laboratorio de Desarrollo de Métodos de
Análisis, of the Facultad Experimental de Ciencias
de la Universidad del Zulia, by his assistance in the
chemical analysis of the catalysts.
References
1. RODRIGUEZ, L., ROMERO, D., RODRIGUEZ,
D. SANCHEZ, J., DOMINGUEZ, F. ARTEAGA, G.
Appl. Catal. A: Gen 373:66-70.2010.
2. MIRACCA, I., PIOVESAN, L. Catal. Today 52:
259. 1999.
3. KOBAYASHI, S., KANEKO, S., OHSHIMA, M.,
KUROKAWA, H., MIURA, H. Appl.Catal. A:
Gen 417– 418:306– 312. 2012.
4. RODRÍGUEZ, D., SÁNCHEZ, J., ARTEAGA, G. J.
Mol. Catal. 228:309-317. 2005.
5. SAHEBDELFAR, S., TAKHTRAVANCHI, M.,
TAHRIRIZANGENEH, F., MEHRAZMA, S.,
RAJABI, S. Chem. Eng. Res. Des. 90:1090-
1097. 2012
6. IGLESIAS-JUEZ, A., BEALE, A., MAAIJEN, K.,
CHIENWENG, T., GLATZEL, P., WECKHUYSEN,
B. J. Catal. 276:268-279. 2010.
7. KANEKO, S., ARAKAWA, T., OHSHIMA, M.,
KUROKAWA, H., MIURA, H. Appl. Catal. A:
Gen 356:80-87. 2009.
8. PISDUANGDAW, S., PANPRANOT, J.,
METHASTIDSOOK, M., CHAISUK, C.,
FAUNGNAWAKIJ, K., PRASERTHDAM,
P., MEKASUWANDUMRONG, O. Appl.
Catal. A: Gen 370:1. 2009
9. Mendez, J., Rodriguez, D., Sanchez, J. Arteaga, G.
Ciencia 20:132-141. 2012.
10. VALECILLOS, J., RODRÍGUEZ, D., MENDEZ,
J., SOLANO, R., GONZÁLEZ, C. ACOSTA, T.,
SÁNCHEZ, J., ARTEAGA, G. Ciencia 14 (Special
Number):1.2006.
11. VIRLA, L., MEDINA, V., RODRÍGUEZ, D.,
SOLANO, R., MENDEZ, J., ARTEAGA, G.
FARAUTE Ciens. y Tec. 4(2);68-77. 2009.
12. HAMID, S., ARUN KUMAR, M., LEE, W. Appl.
Catal. B: Environ 187:37-46. 2016.
13. PIZARRO, A.H., MOLINA, C.B., RODRIGUEZ,
J.J., EPRON, F. J. Environ. Chem. Eng. 3:
2777-2785. 2015.
14. LIN, W., LIN, L., ZHU, Y.X., XIE, Y.C.,
SCHEURELL, K., KEMNITZ, E. Appl. Catal. B
57:175-181. 2004.
15. LOVÓN-QUINTANA, J.J., SANTOS, J.B.O.,
LOVÓN, A.S.P., LA-SALVIA, N., VALENÇA, G.P.
J. Mol. Catal. A: Chem. 411:117-127. 2016
16. ZHAO, J., XU, X., LI, X., WANG, J. Catal.
Commun. 43:102-106. 2014.
17. VICENTE, A., LAFAYE, G., ESPECEL, C.,
MARÉCOT, P., WILLIAMS, C.T. J. Catal.
283:133-142. 2011.
18. PATTAMAKOMSAN, K., EHRET, E., MORFIN,
F., GÉLIN, P., JUGNET, Y., PRAKASH, S.,
BERTOLINI, J. C., PANPRANOT, J., CADETE,
SANTOS AIRES, F. J. Catal. Today 164:28-33.
2011.
19. BALLARINI, A.D., ZGOLICZ, P., VILELLA, I.M.J.,
DE MIGUEl, S.R., CASTRO, A.A., SCELZA, O.A.
Appl. Catal. A: Gen 381:83-91. 2010.
20. ELDING, L.I., OLSSON, L.F. J. Phys. Chem.
82:69-74. 1978
21. TOEBES, M. L., VAN DILLEN, J. A., DE JONG, K.
P. J. Mol. Catal. A: Chem 173:75-98. 2001.
22. GASPAR, A. B., DIEGUEZ, L. C. Appl. Catal. A:
Gen 201:241-251. 2000.
23. FERRER, V., FINOL, D., RODRIGUEZ, D.,
DOMINGUEZ, F., SOLANO, R., ZÁRRAGA, J.,
SÁNCHEZ, J. Catal. Lett. 132:292-298. 2009.
24. FERRER, V., MORONTA, A., SÁNCHEZ, J.,
SOLANO, R., BERNAL, S., FINOL, D. Catal.
Today 107-108:487-492. 2005
25. FERRER, V., FINOL, D., SOLANO, R., MORONTA,
A., RAMOS. M. J. Environ Sci. 27:87–96. 2015.
26. LIESKE, H., VÖLTER. J. J. Catal. 90:96-105.
1984.
27. DAUTZENBERG, F. M., HELLE, J. N., BILOEN,
P., SACHTLER. W. M. H. J. Catal. 63:119-128.
1984
28. LEE, A.F., BADDELEY, C.J., TIKHOV, M.S.,
LAMBERT, R.M. Surf. Sci. 373:195-209. 1997.
29. SALES, E.A., JOVE, J., MENDES, M.J., BOZON-
VERDURAZ, F. J. Catal. 195:88-95. 2000.
30. DALEY, R.A., CHRISTOU, S.Y., EFSTATHIOU,
A.M., ANDERSON, J.A. Appl. Catal. B:
Environ 60:117–127. 2005.
41Mendez et al.,/ Ciencia Vol. 26, Número Especial (2018) 28-41
Scientic Journal from the Experimental Faculty of Sciences,
at the Universidad del Zulia Volume 26 Especial N° 1, 2, Enero - Junio 2018
31. VALDEN, M., KEISKI, R. L., XIANG, N., PERE,
J., AALTONEN, J., PESSA, M., MAUNULA, T.,
SAVIMÄKI, A., LAHTI, A., HÄRKÖNEN. M. J.
Catal. 161:614-625. 1996.
32. SCIRÈ, S., BURGIO, G., CRISAFULLI, C.,
MINICÒ. S. Appl. Catal. A: Gen 274:151-157.
2004.
33. MAZZIERI, V. A., GRAU, J. M., YORI, J. C., VERA,
C. R., PIECK, C. L. App. Catal. A: Gen 354:161–
168. 2009.
34. SRIHIRANPULLOP, S., PRASERTHDAM, P.
Catal. Today 93–95:723–727. 2004.
35. MARECOT, P., AKHACHANE, A., MICHEAUD,
C., BARBIER, J. Appl. Catal. A: Gen 169:189-
196. 1998.
36. BOCANEGRA, S.A., GUERRERO-RUIZ, A., DE
MIGUEL, S.R., SCELZA, O.A. Appl. Catal. A:
Gen 277:11–22. 2004.
37. PIRNGRUBER, G. D., SESHAN, K., LERCHER, J.
A. J. Catal. 186:188-200. 1999
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