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Applied Catalysis A: General 335 (2008) 103–111
Effect of pretreatment conditions on the catalytic performance
of Ni–Pt–W supported on amorphous silica–alumina catalysts
Part 1. Catalysts prepared by a sol–gel method
Yacine Rezgui *, Miloud Guemini
Laboratoire de Recherche de Chimie Appliquee et Technologie des Materiaux, Universite d’Oum El Bouaghi, B.P. 358,
Route de Constantine, Oum El Bouaghi 04000, Algeria
Received 19 September 2007; received in revised form 10 November 2007; accepted 14 November 2007
Available online 22 November 2007
Abstract
In this work, the catalytic behavior of Pt–Ni–WOx supported on amorphous silica–alumina catalysts, prepared by means of a sol–gel technique
was tested by hydroisomerization of n-hexane in a continuous fixed-bed reactor operating at atmospheric pressure. Temperature-programmed
desorption of ammonia (TPDA), temperature-programmed reduction, BET and atomic absorption spectroscopy techniques were used to
characterize the catalysts. The results revealed that both catalytic activity and surface acidity of these solids is strongly dependent on their
calcination and reduction temperatures. Besides, the collected data showed that platinum interacts with tungsten and this interaction depends on the
pretreatment conditions.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Platinum; Tungsten oxide; Nickel; Isomerization; Reduction; Acidity
1. Introduction
Environmental and public health reasons are motivating the
production of transportation fuels with increase amount of high
octane number branched alkanes [1]. These compounds are
made by alkylation and by isomerization of straight-chain
alkanes. The drawback of these two processes is that they
employ harmful and potentially polluting catalysts, such as
H2SO4, and HF [2]. Nowadays, most working isomerization
plants use Pt/Cl–Al2O3 catalysts, that have good activity and
selectivity at relatively low temperatures (Treac = 110–135 8C)
[3]. These catalysts are however candidates for replacement
because of their corrosiveness and potential for pollution.
Active, stable solid acid catalysts that might replace chlorinated
alumina are the halid-free solid acid catalysts. Among them, the
best candidate was sulfated zirconia, this latter is actually used
in industry [4], but it is said that it may undergo sulfur loss
during reaction [5] leading to structural modifications. There-
fore, the amelioration or the replacement of this solid by some
* Corresponding author.
E-mail address: yacinereference@yahoo.com (Y. Rezgui).
0926-860X/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2007.11.020
other superacid catalyst of higher stability, especially for
hydrocarbons heavier than butane, is currently desired.
Recently bulk tungsten oxide-based catalysts have attracted
considerable attention, these solids seems to be potential
catalysts for skeletal rearrangements of hydrocarbons [6–10].
The presence of noble metals (Pt or Pd) in such solids was
expected to improve their stability but also to activate the
isomerization toward saturated hydrocarbons [11–13]. How-
ever it was mentioned that, when introducing noble metals
directly to bulk tungsten oxides, the metallic function was very
sensitive to hydrocarbon poisoning, leading to catalyst
deactivation toward saturated alkanes. Thus the necessity to
stabilize the bulk oxide and metallic active phases was
mentioned and the use of a support seemed to be a potential way
[10]. Based on these facts, it would be said that tungsten
catalytic performance can be largely modified upon dispersing
on oxide supports, where variables such as calcination
temperature, nature of the supported phase and surface
acidity–basicity as well as the nature of the support used are
of paramount importance [14,15]. As mentioned by Maciej and
Zbigniew [16], catalytic behavior of supported metals in the
conversion of saturated hydrocarbons can be influenced by
components, metal and support. The relative contribution of the
Table 1
Chemical composition of the (NixPtyW/ASA)BC samples (noted (NixPty)BC)
Catalyst %Ni %Pt %W SiO2/Al2O3
Ni12Pt0 12 0.0 10 1.83
(Ni12Pt0.1)BC 12 0.1 10 1.83
(Ni12Pt0.4)BC 12 0.4 10 1.83
(Ni12Pt1)BC 12 1.0 10 1.83
Ni15Pt0 15 0.0 10 1.83
(Ni15Pt0.1)BC 15 0.1 10 1.83
(Ni15Pt0.4)BC 15 0.4 10 1.83
(Ni15Pt1)BC 15 1.0 10 1.83
Ni17Pt0 17 0.0 10 1.83
(Ni17Pt0.1)BC 17 0.1 10 1.83
(Ni17Pt0.4)BC 17 0.4 10 1.83
(Ni17Pt1)BC 17 1.0 10 1.83
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111104
support to the overall reactivity is generally attributed to its
surface acidity which could be enhanced by thermal treatments.
These thermal pretreatments are related to the catalyst
preparation method. Several methods for the preparation of
supported metal oxide catalysts have been reported in the
literature: mechanical mixing of metal compound and support,
ion exchange processes, coprecipitation of metal oxides and
support, impregnation and incipient wetness processes [17–21],
solid–solid wetting [22] and grafting of metal alkoxide
precursors onto a metal oxide support alkoxides [23–26].
A great deal of attention in the last two decades has been
given to the use of sol–gel method which is a homogeneous
process resulting in a continuous transformation of a solution
into hydrated solid precursor (hydrogel). The gelation route
(sol–gel process) has several promising advantages over the
conventional techniques. It offers better control of the texture,
composition, homogeneity and structural properties of the final
solids [27–29].
In a previous paper, we have used the latter method to
synthesize catalysts based on nickel–tungsten oxide supported
on silica–alumina [30] and we have demonstrated that these
materials can exhibit an interesting behavior in catalytic
hydroisomerization (up to 79.2% and 70% selectivity to
isomers in the case of n-hexane and n-heptane, at 24% and 29%
conversions, respectively) [30,31] and dewaxing (the selectiv-
ity to isomers, in the case of n-decane, amounts to 55% at a
conversion of 42.3%) [32] if the rate of hydrogenolysis can be
diminished. In this aim, the objective of our work was the
incorporation, by different methods, of platinum in Ni–WOx/
SiO2–Al2O3 catalysts and the attempt to study the effect of
pretreatment conditions on the activity of the prepared solids.
This issue seems important in light of common practice of using
alkanes (n-hexane) as test molecules for probing the state of
metal in supported catalysts. In this first part, we decided to
study the catalytic behavior of (NixPty)BC samples, prepared by
sol–gel method where the platinum was incorporated before
calcination.
2. Experimental
2.1. Catalyst preparation
We studied the effects of the pretreatment conditions on the
activity of Ni–Pt–WOx/SiO2–Al2O3 catalysts for n-hexane
hydroisomerization. In this order, nine catalysts were prepared
and were treated with different conditions. The prepared solids
noted (NixPty)BC (Table 1), where x and y indicate the
percentage of nickel and platinum in the catalyst, and BC
indicate that the incorporation of Pt was done before
calcination, having the same amount of tungsten (10%) and
a constant SiO2/Al2O3 ratio (1.83), were prepared using a sol–
gel method.
A sol was obtained by mixing, under vigorous stirring, an
aqueous solution of nickel nitrate (Ni(NO3)2�6H2O) prelimi-
narily acidified by nitric acid with the required amounts of
aluminum sulfate (Al2(SO4)3�18H2O), sodium tungstate
(Na2WO4) and hexachloroplatinic acid (H2PtCl6) solutions.
To the sol obtained, under vigorous stirring, an aqueous
solution of sodium silicate (Na2SiO3) was added. Next,
ammonium sulfate was used to activate the prepared gel at
60 8C (liquid to solid ratio equal to 30), under reflux conditions
in a thermostat and over a period of 48 h (this unit operation
was repeated several times). Then the solid was washed with
hot water (60 8C), dried at 120 8C for 4 h and finally calcined in
the temperature range 300–700 8C for 5 h. A heating rate of
10 8C/min was used.
For comparison purposes, Pt-free catalysts containing 12%,
15%, 17% Ni and 10% of tungsten supported on amorphous
silica–alumina were prepared as described in Ref. [31].
2.2. Catalyst characterization
The specific surface area of the catalysts was determined by
the BET method. The adsorption isotherm was measured at the
temperature of liquid nitrogen. Before the adsorption was
measured, all samples were degassed at 350 8C for 30 min, and
then reduced at 430 8C, with hydrogen, for 1 h. The tungsten,
nickel and platinum concentration was measured by inductively
coupled plasma-atomic emission spectroscopy (ICP-AES).
The surface species reducibility was determined by
temperature-programmed reduction (TPR) using an Ohkura
TP 2002 S equipped with a thermal conductivity detector. After
loading, samples were pretreated at 500 8C in an air flow for 3 h
and afterward cooled at room temperature. Next, they were
stabilized in an Ar/H2 (95/5 volumetric ratio) flow. The
temperature and detector signals were then continuously
recorded while heating at 5 8C/min to 600 8C.
The acidic properties of samples were studied by means of
temperature-programmed desorption of ammonia (TPD of
NH3). Prior to TPD experiments, the sample was pretreated, for
3 h at the desired calcination temperature, with an oxygen flow,
then purged by flowing helium at 300 8C, and then reduced, at
430 8C for 2 h, in a hydrogen flow. After reduction, the sample
was further dried in flowing He at 300 8C for 1 h and then
cooled to room temperature. When the system become steady,
ammonia was adsorbed at 100 8C for 30 min (using a 10% NH3/
He carrier gas) and then the sample was subsequently purged, at
the same temperature, by flowing He (100 ml/min) for 1 h to
remove the excess and physically adsorbed NH3. The TPD
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111 105
spectrum was obtained by heating the sample from 100 to
700 8C at a heating rate of 10 8C/min under a He flow. Evolved
NH3 was monitored with a TCD detector.
2.3. Catalytic test
The n-hexane transformation was performed in a continuous
flow fixed-bed quartz reactor, loaded with 1 g of the catalyst,
operated under isothermal conditions, and heated by a
controlled temperature electrical oven. The reaction was
carried out at atmospheric pressure, 250 8C, weight hourly
space velocity (WHSV) = 4 h�1 and a molar ratio of hydrogen/
hydrocarbon (H2/n-hexane) = 5.
The reaction products were analyzed on-line by gas
chromatography.
Fig. 1. Effect of calcination temperature on the performance of (a) (Ni12Pty)BC, (b) (
on stream (TOS) = 100 min.
3. Results and discussion
3.1. Effect of calcination temperature
The effect of calcination temperature on the catalytic
activities of the prepared solids was investigated at a reaction
temperature of 250 8C, for a time on stream of 100 min and at
various reduction temperatures (Tred). As shown in Figs. 1 and
2a and c, whatever the reduction temperature, the Ni and Pt
amounts, the catalytic activity of all the prepared samples
increased with calcination, passed through a maximum and
then decreased. Calcination at 700 8C yielded the lowest
activity. The catalyst activities depend strongly on the
calcination temperature, reduction temperature as well as on
the nickel and platinum concentrations. The calcination
Ni15Pty)BC, and (c) (Ni17Pty)BC catalysts. Tred = 260 8C, Treac = 250 8C and time
Fig. 2. Effect of calcination temperature on the performance of (a) (Ni12Pty)BC, (b) (Ni15Pty)BC, and (c) (Ni17Pty)BC catalysts. Tred = 440 8C, Treac = 250 8C and time
on stream (TOS) = 100 min.
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111106
temperatures showing the maximum activity were higher with
less nickel and platinum, which suggest that interaction of
nickel and platinum with the support surface were strong when
the active species are present in small amounts, similar trends
were reported by Hino and Arata [33] in their study on the
isomerization of n-butane over (WO3/ZrO2 + Pt/ZrO2) cata-
lysts. Besides, regardless the reduction temperature and the
nickel amount, an increase in Pt content induces a small
increase in the maximum conversion of the prepared samples.
Fig. 3a gives the dependence of the catalysts acidities on
their calcination temperatures. All samples showed virtually
identical trends with increasing calcination temperature in that
their acidities increased to reach a maximum and then they
decreased. If we combine the data collected in Fig. 2 and these
results, we can say that the catalytic performance of the
prepared materials is strongly dependent on their acid sites
density, the higher the acid sites concentration the higher the
activity showed by the catalyst. On the other hand, the collected
data showed that the BET surface areas of the prepared
catalysts were not influenced by their calcination temperatures
(Fig. 3b).
Hereafter and for labeling purposes, we specify the wt.% of
either Ni or Pt immediately after the chemical symbol as
subscripts, and the optimum calcination temperature (8C) (see
Table 2) as the label suffix. For example, the 12 wt.% Ni and
0.1 wt.% Pt catalyst that had been calcined at 500 8C was
labeled as (Ni12Pt0.1)BC-500.
3.2. Reduction behavior
Fig. 4a–c displays TPR patterns obtained for (NixPty)BC
catalysts. As it clearly can be seen, these solids exhibit an
Fig. 3. (a) Dependence of the catalysts acidities on their calcination temperatures at Tred = 430 8C. (b) Dependence of the catalysts BET surface areas on their
calcination temperatures at Tred = 430 8C.
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111 107
increase in hydrogen consumption in the temperature range
276–371 8C, followed by two peaks centered around 420, 400,
385 and 405 8C (for the first peak) and 460, 471, 477 and
465 8C (for the second peak), for Ni12Pt0, (Ni12Pt0.1)BC,
(Ni12Pt0.4)BC and (Ni12Pt1)BC catalysts, respectively. On the
other hand, the Ni15Pt0 catalyst consumes hydrogen in the
temperature range 265–375 8C and it shows a peak at about
410 8C followed by a shoulder at about 440 8C, whereas the
other (Ni15Ptx)BC (x = 0.1, 0.4 and 1) display an increase in the
base line in the temperature range 253–372 8C, followed by two
peaks centred around 380, 362 and 400 8C (for the first maxima
peaks) and 476, 495 and 464 8C (for the second maxima peaks),
for (Ni15Pt0.1)BC, (Ni15Pt0.4)BC, and (Ni15Pt1)BC catalysts,
respectively. Furthermore, the Ni17Pt0 catalyst displays a
hydrogen consumption in the temperature range 260–375 8Cand a very large peak centered at about 425 8C, whereas the
other samples with 17% Ni show almost identical profiles with
a steady increase in the base line, followed by a large low-
temperature peak and a high-temperature peak. It must be
emphased that with a rise in Pt content till 0.4%, the first peaks
maxima where shifted toward lower temperatures, while the
second ones toward higher values in all catalysts whereas the
opposite effect is observed when the Pt amount was rised from
0.4% to 1%, these phenomena were more pronounced at higher
nickel loadings (Table 2).
In a previous paper [31], we have reported that, in the case of
Pt-free catalysts (NixPt0 samples), TPR profiles appear as
composite profiles of the corresponding monometallic ones,
Table 2
TPR peak maxima and optimum calcination temperatures for the (NixPty)BC catalysts
Catalyst Optimum calcination
temperature (8C)
TPR peak maxima and increase in base line
Increase in the base line (8C) First peak or shoulder (8C) Second peak or shoulder (8C)
Ni12Pt0 525 280–370 420 460
(Ni12Pt0.1)BC 500 277–371 400 471
(Ni12Pt0.4)BC 475 276–370 385 477
(Ni12Pt1)BC 465 278–370 405 465
Ni15Pt0 500 265–375 410 440 (shoulder)
(Ni15Pt0.1)BC 450 255–355 380 476
(Ni15Pt0.4)BC 440 25–335 362 495
(Ni15Pt1)BC 436 264–372 400 464
Ni17Pt0 450 260–375 425 (large peak) –
(Ni17Pt0.1)BC 360 167–247 321 549
(Ni17Pt0.4)BC 350 167–231 300 564
(Ni17Pt1)BC 300 239–354 396 526
Fig. 4. TPR profiles for (a) (Ni12Pty)BC, (b) (Ni15Pty)BC, and (c) (Ni17Pty)BC samples.
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111108
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111 109
although somewhat modified by small shifts of the tungsten
species reduction peak toward lower temperatures and of the
nickel species reduction peak toward higher temperatures. We
have also reported that the increase in the base line was due to
the reduction of tungsten oxide species of various reducibilities,
while the low-temperature peak was ascribed to the reduction of
the nickel oxide and the high-temperature peak was assigned to
a further reduction of the tungsten oxide species. In the case of
Ni17Pt0, the large peak was the result of the superimposition of
two reduction peaks, the first of the NiO and the second of the
WOx species. Based on these observations and on the maxima
of TPR peak values given in Table 2, we can say that, in the case
of Pt-promoted catalysts ((NixPty)BC materials), increasing the
nickel loading induces a shift in the temperature corresponding
to the NiO peak toward lower values. As mentioned by Lucas
et al. [34], in the case of Pd–Pt beta agglomerated zeolite-based
catalysts, a lower reduction temperature could be associated to
the reduction of larger particles and/or particles that interact
weakly with the support, whereas a higher reduction
temperature could be associated to the reduction of nickel
that interacts strongly with the support. Larger nickel particles
were formed when the nickel loading increased. Dissociative
H2 chemisorption is easier on these large particles. Since H
atoms are better reducing agents than H2 molecules, the large
particles formed at high nickel content are reduced at lower
temperatures. The same feature was observed for platinum in
the concentration range 0.1–0.4%, the peaks representing the
reductions of nickel oxide shifted toward lower temperatures,
whereas those representing WOx species reduction shifted
toward higher values at higher platinum loading. However, it
should be emphasized that, in the case of (Ni17Pty)BC catalysts,
the introduction of Pt markedly decreased the temperature of
the nickel oxide reduction peak from 425 to 300 8C, which
suggests that the Pt effect is more pronounced at higher nickel
loadings. From the literature, it is well known that the presence
of nickel ameliorates the tungsten dispersion in solids [35],
besides and as earlier mentioned, the interaction between
platinum and tungsten is more pronounced when these species
are well dispersed, thus in the case of (Ni17Pty)BC catalysts,
where the tungsten is well dispersed, the strong interaction
between platinum and tungsten will weaken the nickel–
tungsten interaction and consequently the nickel reduction peak
will be shifted toward lower temperatures. In addition and as
above-mentioned, increasing Pt content from 0.4% to 1% result
in shifting the lower-temperature peaks (NiO peaks) toward
higher temperatures and the higher-temperature peaks (WOx
peaks) toward lower values. This effect may be interpreted by a
nickel–tungsten and platinum–tungsten interaction synergism;
at higher Pt concentrations Pt–WOx interaction is so weak that
Ni–WOx interaction effect will be more strong and more
noticeable, this latter is translated by increasing NiO peaks and
by lowering WOx species peaks
As mentioned by Wong et al. [36], Platinum reduction
usually occurs at a temperature between 100 and 200 8C, thus
we should mention here that no distinct peak due to platinum
reduction was observed in our platinum-loaded catalysts. The
same behavior was observed over Pt/ZrO2 calcined at 800 8C
[37]; it has been explained by considering that during
calcination, platinum oxide is decomposed to Pt0, detected
by XPS [37,38]. The phenomenon was previously found in
PtO2, which eliminates oxygen by heating above 350–450 8C[39]. On the other hand, in the case of Pt/SZ catalysts, Ebitani
et al. [40] and Shishido et al. [41] have demonstrated, using
XPS and EXAFS techniques, the presence of cationic Pt atoms
with poor or null properties for hydrogen chemisorption and
hydrocarbon hydrogenation–dehydrogenation [42], which
claim that Pt cannot be completely reduced to Pt0. Based on
these results, they proposed a layer of oxidized species on the
surface of a Pt0 core as a model for the Pt particle supported on
SZ. Besides, Contreras et al. [43] reported that the addition of
W6+ to 0.3% Pt/Al2O3 modifies both reducibility and
chemisorption capacity of Pt, presumably due to a strong
interaction with the oxide precursors, they stated that WOx
species produce changes in electronic and geometrical
properties of Pt particles in Pt/WO3–Al2O3 [44]. At their turn,
Yori et al. [45], mentioned that, in the case of Pt/WO3–ZrO2
catalysts, the presence of W affects Pt reducibility, the
phenomenon was explained by an WO3–Pt interaction.
Furthermore, Regabulto et al. [46] reported a decrease in CO
chemisorption upon introduction of W over Pt/SiO2. It was
argued that decoration of platinum crystallites by WOx moieties
was causing a partial physical blockage of the metallic sites.
Hoang-Van and Zegaoui [47] also found, using platinum on
WOx (for reduction temperatures in the 200–400 8C range) that
tungsten suboxides are formed at the Pt–WOx interface. These
suboxides can migrate onto platinum particles, preferentially
near the support surface. In addition, Larsen et al. [48]
considered the formation of mixed metal or metal oxide
clusters, to explain the low CO chemisorption in Pt/WOx–ZrO2
when platinum was added before calcination.
3.3. Effect of reduction temperature
The effect of the catalysts reduction temperature on their
activities was studied at 250 8C, at the optimum calcination
temperature and over a duration of 100 min. As shown in
Fig. 5a–c, regardless the Ni and Pt concentrations, the catalytic
activity increased with increasing the reduction temperature to
reach a maximum or a plateau and then decreased to remain
constant. Reduction at 600 8C yielded the lowest activity this is
believed to be due to the fact that higher reduction temperatures
induce a larger extent of undesirable tungsten (and support)
reduction [49]. Besides, increasing Pt content to 0.4% shifted
the optimum reduction temperature toward the lower values,
while the opposite trend was observed with a further rise in Pt
amount (Pt = 1%). These effects being more pronounced when
the nickel content was higher. In the case of Pt-free samples, it
was reported that the phenomenon was related to the presence
of reduced tungsten oxide species generated by hydrogen
reduction, these reduced species being more active than the
tungsten trioxide (WO3) [10,11,50,51] and to the tungsten–
nickel interaction, whereas in the case of Pt-promoted catalysts,
the phenomenon may be also interpreted by the presence of
WOx species which are more active than WO3 and by the
Fig. 5. Effect of reduction temperature on the performance of (a) (Ni12Pty)BC, (b) (Ni15Pty)BC, and (c) (Ni17Pty)BC catalysts. Reaction temperature = 250 8C,
TOS = 100 min.
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111110
synergism between Ni–WOx and Pt–WOx interaction. At lower
platinum loading the Pt–WOx interaction is very strong,
especially for solids with 17% Ni where the tungsten is well
dispersed, and it is well known that the Pt–WOx interaction
depends on the platinum and tungsten particle size, the smaller
the particle size the stronger the Pt–WOx intercation and
consequently the lower the Ni–WOx interaction. We have
previously reported that the latter effect (Ni–WOx interaction)
was translated by NiO reduction peak shift toward higher
temperatures, thus if this interaction is weakened, the NiO
reduction peak will shift toward lower temperatures and
consequently do the optimum reduction temperature. The same
result was reported by Larsen and Petkovic [49] with platinum
supported on tungstated zirconia catalysts and by Hua and
Sommer [52] with alumina-doped Pt/WOx/ZrO2 catalysts.
4. Conclusion
In the present study, we focused on the effect of the
pretreatment conditions on the catalytic performance of the Pt–
Ni–WOx/ASA catalysts prepared by a sol–gel method. The
collected data show that the catalytic activity of these solids is
strongly dependent on their calcination and reduction
temperatures. The most outstanding observations are as
follows:
� T
he catalysts activities depend strongly on their calcinationtemperature; the incorporation of Pt shifts the optimum
calcination temperature to lower values.
� T
he density of acid sites is strongly influenced by the catalystcalcination temperature, it increases to reach a maximum and
then decreases. Besides, the solids catalytic performance is
totally related to their acidities, the higher the sample acidity
the higher its activity.
� T
he reducibility of Pt–Ni–WOx/ASA (NixPty)BC samples donot exhibit the PtO reduction peak, this behavior was ascribed
to the platinum–tungsten interaction, which is dependent on
the pretreatment conditions.
References
[1] M.H. Jordao, V. Simoes, D. Cardoso, Appl. Catal. 319 (2007) 1.
Y. Rezgui, M. Guemini / Applied Catalysis A: General 335 (2008) 103–111 111
[2] S.D. Rossi, G. Ferraris, M. Valigi, D. Gazzoli, Appl. Catal. 231 (2002)
173.
[3] V.M. Benıtez, C.R. Vera, C.L. Pieck, F.G. Lacamoire, J.C. Yori, J.M. Grau,
J.M. Parera, Catal. Today 107–108 (2005) 651.
[4] S.R. Vaudagna, R.A. Comelli, N.S. Figoli, Catal. Lett. 47 (1997) 259.
[5] M.G. Falco, S.A. Canavese, R.A. Comelli, N.S. Figoli, Appl. Catal. 201
(2000) 37.
[6] A. Katrib, F. Hemming, P. Wehrer, L. Hilaire, G. Maire, J. Electron.
Spectrosc. Relat. Phenom. 76 (1995) 195.
[7] J.G. Santiesteban, D.C. Calabro, W.S. Borghard, C.D. Chang, J.C. Vartuli,
Y.P. Tsao, M.A. Natal-Sabtiago, R.D. Bastian, J. Catal. 183 (1999) 314.
[8] V. Logie, P. Wehrer, A. Katrib, G. Maire, J. Catal. 189 (2000) 438.
[9] A. Katrib, D. Mey, G. Maire, Catal. Today 65 (2001) 179.
[10] C. Bigey, L. Hilaire, G. Maire, J. Catal. 198 (2001) 208.
[11] C. Bigey, L. Hilaire, G. Maire, J. Catal. 184 (1999) 406.
[12] C. Bigey, G. Maire, J. Catal. 196 (2000) 224.
[13] S.V. Filimonova, A.V. Nosov, M. Scheithauer, H. Knozinger, J. Catal. 198
(2001) 89.
[14] C. Martin, G. Solana, P. Malet, V. Rives, Catal. Today 78 (2003) 365.
[15] K. van der Wiele, P.J. van der Berg, in: C.H. Bamford, C.F.H. Tipper
(Eds.), Comprehensive Chemical Kinetics: Complex Catalytic Processes,
Elsevier, Amsterdam, 1978.
[16] S. Maciej, K. Zbigniew, Chem. Eng. J. 90 (2002) 89.
[17] A. Scholz, B. Schnyder, A. Wokaun, J. Mol. Catal. 138 (1999) 249.
[18] C.U.I. Odebrand, A. Bahamonde, P. Avilar, J. Blanco, Appl. Catal. B 5
(1994) 117.
[19] P. Patrono, A. La Ginestra, G. Ramis, G. Busca, Appl. Catal. 107 (1994)
249.
[20] L.R. Pizzo, C.V. Caceres, M.N. Blanco, Catal. Lett. 33 (1995) 175.
[21] D. Kim, M. Ostromecki, I.E. Wachs, D. Kohler, J.G. Eckerdt, Catal. Lett.
33 (1995) 209.
[22] J. Leyrer, R. Margraf, E. Taglauer, H. Knozinger, Surf. Sci. 201 (1988)
603.
[23] J. Kijenski, A. Baiker, M. Glinski, P. Dollenmeier, A. Wokaun, J. Catal.
101 (1986) 1.
[24] M. Schraml-Marth, A. Wokaun, A. Baiker, J. Catal. 124 (1990) 86.
[25] U. Scharf, M. Schraml-Marth, A. Wokaun, A. Baiker, J. Chem. Soc.
Faraday Trans. 87 (1991) 3299.
[26] P. Iengo, M.D. Serio, V. Solinas, D. Gazzoli, G. Salvio, E. Santacesaria,
Appl. Catal. 170 (1998) 225.
[27] M. Campanati, G. Fornasari, A. Vaccari, Catal. Today 77 (2003) 299.
[28] M. Signoretto, M. Scarpa, F. Pinna, G. Strkul, P. Canton, A. Benedetti, J.
Non-Cryst. Solids 225 (1998) 178.
[29] F. Schmidt, Appl. Catal. 221 (2001) 15.
[30] M. Guemini, Y. Rezgui, A. Tighezza, A. Bouchemma, Can. J. Chem. Eng.
82 (1) (2004) 184.
[31] Y. Rezgui, M. Guemini, A. Tighezza, A. Bouchemma, Catal. Lett. 87 (1–
2) (2003) 11.
[32] Y. Rezgui, M. Guemini, Appl. Catal. 282 (2005) 45.
[33] M. Hino, K. Arata, Appl. Catal. 169 (1998) 151.
[34] A. Lucas, P. Sanchez, F. Dorado, M.J. Ramos, J.L. Valverde, Appl. Catal.
294 (2005) 215.
[35] D. Ouafi, F. Mauge, J.C. Lavalley, E. Payen, S. Kasztalan, M. Houari, J.
Grimblot, J.P. Bonnelle, Catal. Today 4 (1988) 23.
[36] S.T. Wong, T. Li, S. Cheng, J.-F. Lee, C.-Y. Mou, Appl. Catal. 296 (2005)
90.
[37] E. Ogata, Y. Kamiya, N. Otha, J. Catal. 29 (1973) 296.
[38] A. Dicko, X. Song, A. Adnot, A. Sayari, J. Catal. 150 (1994) 254.
[39] S.E. Livingstone, The Chemistry of Ru, Rh, Pd, Os, Ir and Pt, Pergamon
Text in Inorganic Chemistry, vol. 25, Pergamon Press, Oxford, 1973, p.
1334.
[40] K. Ebitani, H. Konno, T. Tanaka, H. Hattori, J. Catal. 143 (1993) 322.
[41] T. Shishido, T. Tanaka, H. Hattori, J. Catal. 172 (1997) 24.
[42] K. Ebitani, J. Tsuji, H. Hattori, H. Kita, J. Catal. 135 (1992) 609.
[43] J.L. Contreras, G. Del Toro, Y. Schifter, G.A. Fuentes, Stud. Surf. Sci.
Catal. 38 (1988) 51.
[44] J.L. Contreras, G.A. Fuentes, in: J.W. Hightower, W.N. Delgass, E. Iglesia,
A.T. Bell (Eds.), Proceedings of 11th International Congress on Catalysis,
Stud. Surf. Sci. Catal. 101 (1996) 1195.
[45] J.C. Yori, C.L. Pieck, J.M. Parera, Appl. Catal. 181 (1999) 5.
[46] J.R. Regabulto, T.H. Fleish, E.E. Wolf, J. Catal. 107 (1987) 114.
[47] C. Hoang-Van, O. Zegaoui, Appl. Catal. 164 (1997) 91.
[48] G. Larsen, E. Lotero, S. Raghavan, T.D. Parra, C.A. Querini, Appl. Catal.
139 (1996) 201.
[49] G. Larsen, L.M. Petkovic, Appl. Catal. 148 (1996) 155.
[50] A. Katrib, V. Logie, N. Saurel, P. Wehrer, L. Hilaire, G. Maire, Surf. Sci.
377–379 (1997) 754.
[51] A. Katrib, V. Logie, M. Peter, P. Wehrer, L. Hilaire, G. Maire, J. Chim.
Phys. 94 (1997) 1923.
[52] W. Hua, J. Sommer, Appl. Catal. 232 (2002) 129.
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