Support and solvent effects on the liquid-phase chemoselective hydrogenation of crotonaldehyde over Pt catalysts

Article abstract of DOI:10.1016/j.apcata.2010.07.012

A study of the selective reduction of crotonaldehyde to crotyl alcohol over Pt catalysts supported on various partially reducible solids including Fe ₂O₃, Fe₃O₄, ZrO₂, ZnO, TiO₂ and SnO₂ was conducted. The catalysts were characterized by thermal programmed reduction (TPR) and reduced at temperatures that were selected as a function of the presence of specific reduction peaks for Pt in the TPR profiles. The reduced catalysts were studied by XRD spectroscopy and TEM, and used for the liquid-phase hydrogenation of crotonaldehyde. As a rule, low reduction temperatures led to catalysts providing high yields in the unsaturated alcohol (2-butenol). Such yields were substantially increased by the addition of water in mixtures with dioxane to the medium, whether the medium was acid, neutral or basic. The highest selectivity towards crotyl alcohol was obtained with the solid Pt/ZnO reduced at 175 °C. This may have resulted from the presence of ZnO_xCl_y species forming around Pt particles, which were detected by XPS and might have acted as Lewis acid sites facilitating anchoring of crotonaldehyde via its carbonyl double bond. The optimum working conditions, which included a reaction temperature of 30 °C and an initial hydrogen pressure of 0.414 MPa, afforded a selectivity higher than 90% for crotyl alcohol at conversions in the region of 40%.

Full text of DOI:10.1016/j.apcata.2010.07.012

Applied Catalysis A: General 385 (2010) 190–200
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Support and solvent effects on the liquid-phase chemoselective
hydrogenation of crotonaldehyde over Pt catalysts
Jesús Hidalgo-Carrillo, María Angeles Aramendía, Alberto Marinas,
José María Marinas, Francisco José Urbano∗
Department of Organic Chemistry, University of Córdoba, Campus de Rabanales, Edificio C-3, Ctra Nnal IV, km 396, 14014 Córdoba, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 May 2010
Received in revised form 16 June 2010
Accepted 6 July 2010
Available online 13 July 2010
A study of the selective reduction of crotonaldehyde to crotyl alcohol over Pt catalysts supported on
various partially reducible solids including Fe2O3, Fe3O4, ZrO2, ZnO, TiO2 and SnO2 was conducted. The
catalysts were characterized by thermal programmed reduction (TPR) and reduced at temperatures that
were selected as a function of the presence of specific reduction peaks for Pt in the TPR profiles. The
reduced catalysts were studied by XRD spectroscopy and TEM, and used for the liquid-phase hydrogena-
tion of crotonaldehyde. As a rule, low reduction temperatures led to catalysts providing high yields in
the unsaturated alcohol (2-butenol). Such yields were substantially increased by the addition of water
in mixtures with dioxane to the medium, whether the medium was acid, neutral or basic. The highest
selectivity towards crotyl alcohol was obtained with the solid Pt/ZnO reduced at 175 ◦C. This may have
resulted from the presence of ZnOxCly species forming around Pt particles, which were detected by XPS
and might have acted as Lewis acid sites facilitating anchoring of crotonaldehyde via its carbonyl double
bond. The optimum working conditions, which included a reaction temperature of 30 ◦C and an initial
hydrogen pressure of 0.414 MPa, afforded a selectivity higher than 90% for crotyl alcohol at conversions
in the region of 40%.
Keywords:
Pt catalyst
Chemoselective crotonaldehyde
hydrogenation
Crotyl alcohol selectivity
Solvent effect
Catalyst reduction temperature effect
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
substantial promoting effect on its activity and alcohol selectivity
in the hydrogenation of cinnamaldehyde; the effect was ascribed
The selective hydrogenation of unsaturated aldehydes to
unsaturated alcohols over heterogeneous catalysts has aroused
considerable attention as a result of its usefulness for the flavor,
fragrance and pharmaceutical industries [1]. The most challeng-
ing class of these chemoselective hydrogenation reactions is the
reduction of ␣,␤-unsaturated aldehydes to allyl alcohols. This
chemoselective hydrogenation of carbonyl compounds over het-
erogeneous catalysts has been recently reviewed [2]. The activity
and unsaturated alcohol selectivity of unpromoted catalysts is
dependent on the particular type of metal they contain. Unpro-
moted Ir and Os catalysts are known to be highly selective, those
of Ru and Co moderately selective, and those of Pd, Rh and Ni uns-
elective towards the formation of the unsaturated alcohol [3].
The performance of unpromoted catalysts can be improved
by using an appropriate promoter. Thus, ionic metal promoters
increase alcohol selectivity by coordinating with and polarizing
the aldehyde group, thereby enhancing its activity [4]. Recently,
the addition or Zn and/or Fe to a Pt catalyst was found to have a
to electron transfer from Zn and Fe to Pt particles (reflected in
XPS analyses) and the formation of electrophilic sites for the car-
bonyl group to anchor [5]. Also, the electron density of the catalytic
metal was found to be increased by the effect of its alloying with
a more electropositive metal [6,7] or the use of an electron-rich
support [8,9]. Thus, gold supported on various oxides considerably
altered the selectivity towards hydrogenation of the conjugated
C
O bond in benzalacetone [10], which was highly correlated with
the reducibility of the support. Their correlation was ascribed to
electron transfer from the reduced support to the metal leading to
the formation of electron-enriched gold particles facilitating C
O
hydrogenation on their surface [10]. Other reducible oxides in addi-
tion to those of iron have been found to contribute to changes in
catalytic activity and selectivity in the hydrogenation of unsatu-
rated carbonyl compounds over Pt catalysts; such oxides include
TiO2 [11], SnO2 [12], Nb2O5 [13], Y2O3 [14], ZrO2 [15], ZnO [16]
and CeO2 [17].
The selective hydrogenation of crotonaldehyde over Pt sup-
ported catalysts can be used as a probe reaction sensitive to
metal–support interactions [18–20]. In other words, when the
metal is not modified by the support, the C C bond is selectively
hydrogenated; otherwise, the carbonyl bond is the selective target
∗
Corresponding author. Tel.: +34 957218638; fax: +34 957212066.
E-mail address: FJ.Urbano@uco.es (F.J. Urbano).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.07.012

J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
191
with the metal in an SMSI state. However, the origin of the specific
behavior of Pt in such a state remains a controversial subject for
some supports. Thus, the SMSI effect on the selective reduction of
the C O bond in ␣,␤-unsaturated carbonyl compounds might be
related to (a) the formation of an alloy between Pt and the reduced
metal in the support [18]; (b) an electronic effect of Pt particles due
to partial reduction of the support [21]; or (c) the decoration of Pt
particles with patches of partially reduced support [17].
In addition to the active metal, the activity and selectivity for
the reduction of the C O bond in unsaturated carbonyl compounds
is influenced by additional factors including the metal precursor
[12,16], solvent [2,22–25], metal particle size [2,26], synthetic pro-
cedure for the catalytic system [23,26], use of additives [27], various
reaction conditions such as temperature and hydrogen pressure,
and whether the process is conducted in the gas or liquid-phase
[26]. Additionally, the change in metal particle size can affect the
electronic and geometrical properties of the metal particles. The
smaller metal particles are known to be more electron deficient
than larger ones. Furthermore, the number of edges and corners,
which could have different activities and selectivities is increased
in the smaller particles [2].
The synthetic procedure was as follows: a volume of 6.57 mL
of chloroplatinic acid solution was diluted to 200 mL with Milli-
Q water and adjusted to pH 7 by adding 0.1 M NaOH (FLUKA Ref.
43617). Then, an amount of 4.75 g of support was added and the
mixture readjusted to pH 7 with NaOH for acid supports or HCl for
basic supports. The solution containing the support was refluxed at
80 ◦C under vigorous stirring for 2 h. Then, a volume of 10 mL of iso-
propanol was added, the temperature raised to 110 ◦C and refluxing
continued for 30 min, after which the mixture was vacuum filtered
and the filtrate washed with three portions of 25 mL of water each.
The resulting solid was dried in a muffle furnace at 110 ◦C for 12 h,
ground and calcined at 400 ◦C for 4 h. After calcination, the solid
was ground again, sieved through a mesh of 0.149 mm pore size and
stored in a topaz flask. The nominal proportion of Pt in the catalyst
thus obtained was 5 wt%. Finally, the catalyst was reduced under
a hydrogen stream flowing at 30 mL/min at selected temperatures
for 2 h. Reduction temperature was chosen according to significant
features observed in the temperature-programmed reduction pro-
files. The solid names used included the metal, its support and the
reduction temperature used (e.g. Pt/ZnO-175).
Singh and Vannice reviewed the solvent effects on heteroge-
neously catalysed reactions [23]. The most salient effects on the
hydrogenation of ␣,␤-unsaturated aldehydes are solvent polar-
ity, hydrogen solubility, catalyst–solvent interactions and reactant
solvation in the bulk liquid-phase. Although rationalizing solvent
effects is very difficult owing to the lack of systematic experimen-
tal data, recent trends regarding solvent polarity suggest that polar
solvents boost the hydrogenation of C O bonds and raise the selec-
tivity towards the unsaturated alcohol whereas non-polar solvents
favor hydrogenation of the non-polar C C bond [2,28,29]. Also,
the addition of water has been found to increase the selectivity
for the unsaturated alcohol in both Pd/C and Pt/C catalysts [29].
2.1.1. Characterization of catalysts
The textural properties of the solids calcined at 400 ◦C
(viz. specific surface area, pore volume and mean pore radius)
were determined from nitrogen adsorption–desorption isotherms
obtained at liquid nitrogen temperature on
a Micromerit-
ics ASAP-2010 instrument. Surface areas were calculated with
the Brunnauer–Emmett–Teller (BET) method. All samples were
degassed to 0.1 Pa at 110 ◦C prior to measurement.
Elemental analysis of Pt containing samples was performed
by the staff at the Central Service for Research Support (SCAI)
of the University of Córdoba, using inductively coupled plasma
mass spectrometry (ICP-MS). Measurements were made on a
Perkin–Elmer ELAN DRC-e instrument following dissolution of the
sample in a 1:1:1 H2SO4/HF/H2O mixture. Calibration was done
by using PE Pure Plus atomic spectroscopy standards, also from
Perkin–Elmer.
Transmission electron microscopy (TEM) images were obtained
at the SCAI of the University of Córdoba by using a Philips CM-
10 microscope for low magnification samples and a JEOL JEM
2010 microscope for high magnification samples. All samples were
mounted on 3 mm holey carbon copper grids.
EDX measurements were made with a JEOL JSM-6300 scanning
electron microscope (SEM) equipped with an energy-dispersive X-
ray (EDX) detector.
X-ray patterns for the samples were obtained with a Siemens D-
5000 diffractometer equipped with a DACO-MP automatic control
and data acquisition system. The instrument was used with CoK␣
radiation and a graphite monochromator.
Temperature-programmed reduction (TPR) measurements
were made with a Micromeritics TPD-TPR 2900 analyser. An
amount of 200 mg of catalyst was placed in the sample holder and
reduced in a 5:95 H2/Ar stream flowing at 40 mL/min. The temper-
ature was ramped from 0 to 850 ◦C at 10 ◦C min−1; by exception,
the upper limit for solids Pt/ZnO and Pt/SnO2 was 500 ◦C.
X-ray photoelectron spectroscopy (XPS) data were recorded on
4 mm × 4 mm pellets 0.5 mm thick that were obtained by gently
pressing the powdered materials following outgassing to a pressure
below about 2 × 10−8 Torr at 150 ◦C in the instrument pre-chamber
to remove chemisorbed volatile species. The main chamber of the
Leibold-Heraeus LHS10 spectrometer used, capable of operating
down to less than 2 × 10−9 Torr, was equipped with an EA-200 MCD
hemispherical electron analyser with a dual X-ray source using
AlK␣ (hv = 1486.6 eV) at 120 W, at 30 mA, with C(1s) as energy ref-
erence (284.6 eV).
Some authors have noted that the hydrophilic nature of the C
O
bond facilitates its selective hydrogenation in pure water [22] and
water/organic solvent mixtures [30].
Most of the papers published on the Pt catalysed selective hydro-
genation of crotonaldehyde deal with gas-phase reactions. In this
sense, recently, Rynkowski et al. [31] summarized the activity
and selectivity obtained for different Pt/support catalysts in selec-
tive hydrogenation of crotonaldehyde in the gas phase. However,
as far as liquid-phase selective hydrogenation of crotonaldehyde
over Pt catalysts is concerned, the published works are relatively
scarce. Bartok et al. reported the activity and selectivity for several
Pt/support catalysts in the liquid-phase providing TOF (s−1) val-
ues in the 10−1 to 10−2 range with selectivities to crotyl alcohol
between 7 and 43% [28].
In this work, we explored the liquid-phase Pt-catalysed selective
hydrogenation of crotonaldehyde as a test reaction for analysing
the effect of various reducible supports including Fe2O3, Fe3O4,
ZrO2, TiO2, ZnO and SnO2, and examining the solvent effect on
activity and selectivity towards the unsaturated alcohol.
2. Experimental
2.1. Synthesis of Pt supported catalysts
The catalysts studied were obtained from an aqueous solu-
tion containing 8% (w/w) chloroplatinic acid (Sigma–Aldrich Ref.
262587) as metal precursor and the following metal oxides as sup-
ports: tin (IV) oxide (Sigma–Aldrich Ref. 549657), zirconium (IV)
oxide (Sigma–Aldrich Ref. 544760), zinc (II) oxide (Sigma–Aldrich
Ref. 544906), iron (II,III) oxide (Sigma–Aldrich Ref. 637106), iron
(III) oxide (Sigma–Aldrich Ref. 544884) and titanium (IV) oxide
(Degussa, P-25).

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J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
Table 1
Specific surface area (SBET) and chemical composition obtained by ICP-PS and SEM-
EDX for the catalysts synthesized.
Catalyst
SBET (m2 g−1
)
%Pt, w/w
Theoretical
%Pt, w/w
ICP-MS
%Pt, w/w
EDX
Pt/Fe2O3
Pt/Fe3O4
Pt/ZrO2
Pt/ZnO
Pt/TiO2
Pt/SnO2
19
40
42
18
52
18
5
5
5
5
5
5
5.6
6.1
6.4
5.1
4.5
–
2.9
3.6
3.6
3.7
0.7
1.6
2.2. Liquid-phase hydrogenation of crotonaldehyde
The liquid-phase hydrogenation of crotonaldehyde with molec-
ular hydrogen was conducted on Parr Instruments 3911
low-pressure reactor, using a constant rate of 300 shakes min−1
a
.
The reaction vessel (500 mL in volume) was wrapped in a metal
jacket through which thermostated water was circulated. The
apparatus was equipped with a gauge that recorded the pressure
inside the reaction vessel throughout the experiment. All reactions
were performed with an overall liquid volume of 20 mL containing
0.5 M crotonaldehyde in the selected solvent, using an initial pres-
sure of 0.414 MPa and a temperature of 30 ◦C. Prior to each run, an
amount of 100 mg of calcined Pt catalyst was reduced in a hydro-
gen stream flowing at 30 mL/min at the selected temperature for
2 h and then cooled in the same stream. The standard operational
procedure used in each experiment was as follows: the reaction
vessel was loaded with 20 mL of 0.5 M crotonaldehyde, sonicated
for 15 min and 100 mg of freshly reduced catalyst were added. The
reaction vessel was then attached to the reactor and, once the tem-
perature levelled off at 30 ◦C – which took about 10 min–, the vessel
was evacuated and filled with hydrogen to a pressure of 0.414 MPa
twice. After 15 min, the pressure was readjusted, the shaking device
started and the reaction timed. Blank tests intended to ascertain
that no reaction would take place thermally in the absence of cat-
alyst were conducted with a reaction mixture consisting solely of
substrate and solvent. No signs of reaction were detected after 8 h
under these conditions.
Fig. 1. Temperature-programmed reduction (TPR) profiles obtained for the catalyst
synthesized in this work: (A) Pt/Fe3O4; (B) Pt/Fe2O3; (C) Pt/ZnO (D) Pt/ZrO2; (E)
Pt/TiO2; (F) Pt/SnO2.
to the EDX technique—which has an analysis depth capacity less
than 2 ␮m. The EDX determined Pt surface content of solid Pt/TiO2
was especially low (0.7%), even if one considers that this was the
catalyst containing the lowest total proportion of Pt (4.5%).
Reaction products were analysed on a Fisons gas chromatograph
equipped with a flame ionization detector (FID) and a Supelcowax-
10 column (30 m long × 0.25 mm ID, 0.25 ␮m film thickness). A
calibration plot for each product was constructed from com-
mercially available standards. The products of the reduction of
crotonaldehyde (designated “unsaturated aldehyde”, UAL) were
crotyl alcohol (“unsaturated alcohol”, UOL), 1-butanol (“saturated
alcohol”, SOL) and butanal (“saturated aldehyde”, SAL). Croton-
3.1.2. Temperature-programmed reduction
The TPR profiles differed markedly from one another by effect
of the marked differences in redox properties between the cata-
lysts. In some cases, the support was hardly reducible; in others, it
exhibited several reduction peaks at different temperatures. In any
case, identifying the reduction peaks for Pt and the support facili-
tated selection of the most suitable reduction temperature for each
catalyst with a view to its use in the liquid-phase hydrogenation of
crotonaldehyde.
aldehyde conversion (XUAL) was calculated as (C0 − CUAL)/C0
,
UAL
UAL
where CU0AL is the initial concentration of crotonaldehyde and CUAL
that at reaction time t. The selectivity of each reaction product was
calculated as % Seli = Ci/ꢀCi × 100.
Fig. 1 shows the TPR profiles for the solids calcined at 400 ◦C.
As can be seen, the profile for Pt/ZrO2 exhibited a reduction peak
at 181 ◦C that was assigned to the reduction of oxidized platinum
species to metallic Pt [32]. Also, it contained two weaker reduction
peaks at 317 and 477 ◦C which, based on the low reducibility of the
ZrO2 support, were assigned to the reduction of Pt species strongly
interacting with it [32] or the partial, Pt-catalysed reduction of
the support via spillover of hydrogen from the metal to the ZrO2
[32–34]. Platinum and zirconium oxide were previously found to
exhibit strong metal–support interactions, albeit in solids reduced
at temperatures above 400 ◦C [32]. Such interactions diminish the
hydrogen adsorption capacity of the reduced catalyst.
3. Results and discussion
3.1. Characterization of catalysts
3.1.1. Surface area and chemical composition
Table 1 shows the chemical composition and surface area of
the catalysts. Chemical composition data were obtained by ICP-
MS analysis and microchemical data by energy-dispersive X-ray
analysis (SEM-EDX). Based on the ICP-MS results, Pt was highly
efficiently or even virtually completely incorporated onto all sup-
ports; the EDX values, however, were roughly one-half the ICP-MS
values. This suggests that some Pt species migrate into the catalyst
particles or that, following reduction, the partially reducible sup-
ports coat or decorate Pt particles and render them less “visible”
The TPR profile for solid Pt/ZnO was finished below 500 ◦C,
where Zn sublimates under reductive conditions. In catalysts pre-
pared from chloroplatinic acid, this solid exhibits a strong reduction
peak at 250–300 ◦C [16] which has been ascribed to the reduction of
oxychloride species of the [Pt(OH)4Cl2]2− type formed by calcina-

J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
193
Table 2
tion of the platinum precursor H2PtCl6 [16,35]. The reduction takes
3 mol of H2 per mol of Pt precursor—hence the strength of the TPR
peak observed. Our TPR profile exhibited a strong reduction peak at
110 ◦C in addition to two much weaker peaks at 178 and 285 ◦C. The
reduction temperature for the first peak, 110 ◦C, was markedly low
relative to previously reported values for the reduction of oxychlo-
ride Pt species (250–300 ◦C). However, our catalysts were prepared
in such a way that the addition of 2-propanol to the catalyst mix-
ture at the end of the synthetic process may have caused the partial
reduction of chloroplatinic acid, as detected from the loss of the yel-
lowish color of its solution. This probably precludes the formation
of the above-mentioned oxychloride species after calcination [16].
A more plausible explanation in our case is that, upon calcination
of the catalyst, the platinum may be present as metal Pt or, more
probably, as Pt0 coated particles of PtO or PtO2. In this situation, the
catalyst may behave like those prepared from chloride-free precur-
sors such as Pt(NH3)4(NO3)2, calcination of which provides metal Pt
particles coated with PtO that are reduced at a lower temperature
(120–160 ◦C) [16,35]. As a result, the solid must have been reduced
at lower temperatures, as seen in our TPR profile. The small reduc-
tion peaks observed at higher temperatures can be assigned to the
reduction of ZnO to metal Zn, which may alloy with Pt [16]. The
XRD technique provided additional confirmation.
Influence of the catalyst reduction temperature on the activity (crotonaldehyde con-
version, XUAL) and selectivity to butanal (SSAL), 1-butanol (SSOL) and crotyl alcohol
(SUOL) obtained in the liquid-phase crotonaldehyde hydrogenation.
Catalyst
Reduction
temperature
(◦C)
XUAL (%)
SSAL (%)
SSOL (%)
SUOL (%)
400
317
180
50
13
37
76
83
82
23
12
14
2
6
4
Pt/ZrO2
400
175
1
1
68
25
9
0
23
75
Pt/ZnO
400
290
190
3
1
<1
89
75
46
7
0
16
4
25
38
Pt/SnO2
400
130
2
20
58
56
17
29
25
15
Pt/Fe2O3
Pt/Fe3O4
400
250
180
3
21
4
59
88
37
12
0
1
30
12
62
400
290
180
55
16
1
1
73
75
84
98
21
0
0
6
25
16
2
Pt/TiO2
2
0
The TPR profile for solid Pt/SnO2 was also stopped at 500 ◦C—like
Zn in ZnO, Sn sublimates above this temperature in a reductive
environment. Theprofileexhibitedtworeductionpeaksat lowtem-
peratures (192 and 297 ◦C) in addition to a strong, truncated peak
near 500 ◦C. The latter was assigned to the reduction of SnO2 to Sn0
[34,36] and the former two to that of PtOx species interacting to a
variable extent with the support [34].
The TPR profile for Pt/Fe2O3 exhibited three distinct regions.
The first contained a small peak at a low temperature (130 ◦C);
the second a sharp, strong peak at 223 ◦C; and the third a com-
plex, broad signal not shown in the graph which contained two
ill-defined peaks at 605 and 737 ◦C. The last region involved much
higher adsorption of hydrogen than the previous two. All this sug-
gests that the peak at 130 ◦C was due to the reduction of Pt oxidized
species to Pt0. Also, based on previously reported data for Fe2O3,
the sharp peak at 223 ◦C, and the broad signal with two maxima at
605 and 737 ◦C, can be assigned to reduction of the support [37–39].
According to Munteanu et al. [39], the reduction of Fe2O3 involves
the following three steps:
Reaction conditions: 20 mL of 0.5 M crotonaldehyde in 1,4-dioxane and 100 mg of
freshly reduced Pt catalyst. Reaction temperature: 30 ◦C; initial hydrogen pressure:
0.414 MPa; reaction time, 8 h.
However, the strong peak at 116 ◦C cannot be assigned to Pt
species since, based on the calculated hydrogen uptake, the amount
of Pt reduced was very high in relation to the nominal content of
the catalyst (5 wt%, Table 1). Therefore, it must be related to the
support and probably due to partial reduction of Fe(III) to Fe(II). Any
Pt reduction process would be concealed by the previous peak or
related to those at 184 and 271 ◦C, which must be due to Pt species
interacting to a variable extent with the support.
The temperature-programmed reduction profile for Pt/TiO2 was
quite flat and contained few reduction peaks the strongest of which
appeared at quite a low temperature (51 ◦C). There were, however,
other, weaker peaks at higher temperatures (190, 301, 471 and
694 ◦C). The peak at 51 ◦C can be assigned to the reduction of PtOx
species to Pt0, and those at 471 and 694 ◦C to the reduction of TiO2,
favored by the presence of metal Pt particles [40].
The TPR profiles for the catalysts were used to select their
respective reduction temperatures with a view to optimizing their
performance in the hydrogenation of crotonaldehyde. A temper-
ature of 400 ◦C was used for all catalysts in addition to variable
others signalling the presence of reduction peaks for Pt in the pro-
files. Table 2 shows the specific temperatures used to reduce each
catalyst.
Fe2O3 → Fe3O4 → FeO → Fe
These three steps reflect as a strong, variably sharp peak at a
low temperature (ca. 400 ◦C) and a broader, occasionally shoul-
dered peak at higher levels (500–800 ◦C) in the TPR profiles. This is
quite consistent with our profiles, the sole appreciable difference
being the temperature for the second, sharp, strong peak, which
was markedly lower than its reported values. However, the pres-
ence of a metal such as Au on a Fe2O3 support has also been found
to lower the temperature for the first reduction peak (that for the
Fe2O3 → Fe3O4 transition) through a catalytic effect of the metal
on the reduction of Fe2O3 [38,39]. Therefore, the presence of Pt
on Fe2O3 might have facilitated the reduction of Fe2O3 to Fe3O4
to an extent causing the associated peak to appear at such a low
temperature as 223 ◦C.
The profile for solid Pt/Fe3O4 was quite similar to that for
Pt/Fe2O3. It contained a strong reduction peak at a low tempera-
ture (116 ◦C) and two smaller ones at 184 and 271 ◦C in addition
to a broad band with two maxima at 596 and 736 ◦C echoing that
for Pt/Fe2O3. Based on the previous argument, such a band can be
assigned to the reduction of the oxide to metal Fe in two steps:
3.1.3. XRD diffraction
Fig. 2 shows the XRD patterns for the catalysts used in the hydro-
genation of crotonaldehyde, which were reduced at the selected
temperatures established from the TPR profiles. As can be seen,
there were some general trends in the solids. Thus, the catalysts
with a Fe-containing support (viz. Pt/Fe2O3-130 and Pt/Fe3O4-
250) exhibited a strong, relatively sharp band in the region for
Pt0 (2ꢁ = 46.7), which suggests low dispersion of platinum and its
presence as large particles relative to other catalysts. Solid Pt/TiO2-
400 exhibited a narrow, weaker band at 2ꢁ = 46.7 the width at
half height of which is also suggestive of low dispersion of Pt (i.e.
particles of an increased size). Also, its lower strength is consis-
tent with the results of the chemical elemental analysis (Table 1),
which, based on the ICP-MS results and, especially, the EDX results,
revealed that the catalyst was that containing the lowest propor-
Fe3O4 → FeO → Fe

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J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
high 2ꢁ values relative to Pt/ZnO-175, probably as a result of the
formation of a PtZn alloy [16,35].
3.1.5. X-ray photoelectron spectroscopy
The nature and oxidation state of Pt species (Pt0, Pt2+ and Pt4+
)
are usually determined with the XPS technique and, specifically,
from the Pt(4f) peak [41–44]. The binding energy of metal Pt for
4f7/2 electrons is known to be 70.7–70.9 eV and that for 4f5/2
electrons 74.0–74.2 eV. The oxidized states of platinum have much
higher binding energies (viz. 72.8–73.1 eV for 4f7/2 electrons and
76.1–76.4 eV for 4f5/2 electrons in Pt2+, and 74.0–74.9 eV for 4f7/2
electrons and 77.3–78.2 eV for 4f5/2 electrons in Pt4+).
Fig. 7 shows the XPS profiles for Pt(4f) and Zn(2p) in the calcined
solids, and in those activated at 175 and 400 ◦C. The calcined, unac-
tivated solid exhibited signals for two different Pt species, namely:
Pt2+ (maxima at 72.7 and 76.2 eV) and Pt4+ (maxima at 74.7 and
78.0 eV); the latter were due to PtO2 (74.0 eV), PtCl4 (75.1 eV) or,
more probably, to some intermediate species (e.g. Pt oxychlorinated
species) [45]. The XPS profile for the Zn solid exhibited several peaks
including one at 1021.6 eV associated to Zn2+ in ZnO and another at
1022.4 eV associated to a more unshielded Zn2+ species than that
in ZnO.
Reducing the solids at 175 ◦C altered their XPS profiles, which
now contained signals for two different Pt species. One, Pt0, gave
signals at 70.9 and 74.2 eV and another, Pt2+, which was also
detected in the XPS profile for the unreduced catalyst, appeared
at 72.1 and 75.4 eV. The profile for Zn(2p) was similar to that for
the unactivated catalyst with a signal at 1022.4 eV potentially due
to a highly electron-deficient surface species of the ZnOxCly type
around Pt particles and resembling that reported by Ammari et al. in
exchloride Pt/ZnO catalysts [35], where chloride ions would come
from the decomposition of Pt precursor species released during the
Pt4+ → Pt2+ → Pt0 reduction process.
Fig. 2. X-ray diffraction patterns obtained for the Pt catalysts reduced at selected
temperatures.
tion of Pt. Solid Pt/ZnO-175 exhibited a very broad band in the
region for Pt0 suggesting high dispersion of Pt present as small
metal particles. Pt/SnO2-290 was special in that it exhibited a band
at 2ꢁ = 48.9 previously assigned to a Pt–Sn alloy and observed in cat-
alysts reduced at temperatures as low as 170 ◦C [12]. Finally, solid
Pt/ZrO2-180 exhibited no band in the region for Pt0, possibly as a
result of a low Pt content – inconsistent with the chemical analysis
of the solid, Table 1–, or more likely a high dispersion of the metal
phase.
Finally, the dominant Pt species in the solid reduced at 400 ◦C
was Pt0 (70.9 and 74.2 eV). There were, however, additional, a weak
signal in the regions for Pt2+ (71.7 and 74.9 eV). The signal for Zn(2p)
was similar to that for the catalyst reduced at 175 ◦C; thus, the band
associated to ZnOxCly species (1022.4 eV) decreased in proportion
to the increase in the band associated to Zn2+ in ZnO (1021.6 eV);
this suggests that Zn oxychloride species gradually disappear as the
support is reduced at a high temperature.
3.2. Liquid-phase hydrogenation of crotonaldehyde
3.1.4. Transmission electron microscopy
Following reduction at their chosen temperatures, the stud-
ied catalysts were examined by transmission electron microscopy
(TEM). Fig. 3 shows their micrographs, which support the results
previously obtained from the XRD patterns. Thus, solids Pt/Fe2O3-
130, Pt/Fe3O4-250 and Pt/TiO2-400 exhibited large, round-shaped
particles of Pt consistent with their low metal dispersion. On the
other hand, Pt/ZnO-175 exhibited a highly uniform (monodisperse)
distribution of small Pt particles on the support; again, the results
are consistent with the XRD patterns for this catalyst, which exhib-
ited a very broad band in the Pt0 region. This is the most salient
feature in our catalysts and could provide crucial information about
the catalytic process.
3.2.1. Influence of the support and the catalyst reduction
temperature
The influence of the reduction temperature of the catalyst on its
activity and selectivity in the liquid-phase hydrogenation of croton-
aldehyde was studied by using various catalysts reduced at selected
temperatures. Reduction temperature was chosen according to
significant features observed in the temperature-programmed
reduction profiles (Fig. 1). In any case, all catalysts were reduced
at 400 ◦C in addition to such selected temperatures. Catalytic runs
were conducted at 30 ◦C, using 1,4-dioxane as solvent. The activity
and selectivity results thus obtained after 8 h reaction are summa-
rized in Table 2.
Solid Pt/ZnO-175 was additionally examined by HRTEM (Fig. 4),
and so was Pt/ZnO-400 by TEM (Fig. 5) and XRD (Fig. 6). Fig. 4 tes-
tifies to the highly uniform, narrow distribution (2–3 nm) of metal
particle size in Pt/ZnO-175. As can be seen from the micrographs
of Fig. 5, raising the calcination temperature from 175 to 400 ◦C
increased the size of metal particles very slightly. In fact, the mean
size of Pt particles as determined by TEM was 2.5 nm (36% disper-
sion) for Pt/ZnO-175 and 3.5 nm (26% dispersion) for Pt/ZnO-400.
However, the XRD patterns of Fig. 6 reveal a substantial change in
metal species. Thus, solid Pt/ZnO-400 exhibited a broad band at
Solid Pt/ZrO2 exhibited the highest crotonaldehyde conversion
irrespective of the reduction temperature (400, 317 and 180 ◦C). On
the other hand, its selectivity towards the unsaturated alcohol was
rather low (5–6%) at the three temperatures. In any case, it provided
acceptable activity at low reduction temperatures.
Pt/ZnO was scarcely active in the hydrogenation of crotonalde-
hyde, with conversion values in the region of 1% irrespective of its
reduction temperature. On the other hand, it exhibited a high selec-
tivity towards the unsaturated alcohol (especially when reduced at
175 ◦C, with 75% selectivity for crotyl alcohol). Raising its reduction

J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
195
Fig. 3. Transmission electron microscopy images for the catalyst reduced at selected temperatures (magnification: 250k×).
temperature considerably decreased its selectivity for the unsat-
urated alcohol (to 23%). In theory, the presence of an PtZn alloy
detected in the XRD patterns for the solid reduced at 400 ◦C resulted
in no increased selectivity towards the unsaturated alcohol rela-
tive to the solid reduced at 175 ◦C, which was found to contain no
such alloy. These results contradict others previously obtained by
Touroude et al. [16,35].
Catalyst Pt/SnO2 exhibited rather poor conversion values
whichever its reduction temperature (400, 290 or 190 ◦C). Although
conversion increased slightly with increasing temperature, the
increase was accompanied by a decrease in selectivity towards the
unsaturated alcohol, which was only 4% for the solid reduced at
400 ◦C (with 3% conversion).
Among iron oxide-supported catalysts, Pt/Fe2O3 exhibited a
dramatic loss of activity (2% conversion, 25% selectivity towards
2-butenol) in the solids reduced at high temperatures relative
to that reduced 130 ◦C, which provided 20% conversion with
15% selectivity towards the alcohol. Solid Pt/Fe3O4 provided rel-
atively poor conversion at both high (400 ◦C) and low (180 ◦C)
reduction temperatures relative to its intermediate level (250 ◦C),
which exhibited 12% selectivity towards the unsaturated alco-
hol. The Pt/Fe3O4 catalyst reduced at 180 ◦C was the most
suitable as regards selectivity for the alcohol, with 62% at 4%
conversion.
Finally, as far as Pt/TiO2 catalyst is concerned, results indicate
that high reduction temperature (400 ◦C) lead to higher conver-
sion as compared to the low temperature reduced solid, although
associated to low crotyl alcohol selectivity.
The best overall catalytic performance was that of catalyst
Pt/ZrO2-400 (XUAL = 50%), which, however, exhibited the lowest
selectivity towards crotyl alcohol (SUOL = 2%). The catalysts with
an iron oxide support reduced at medium-low temperatures (viz.
Pt/Fe2O3-130 and Pt/Fe3O4-250) had a moderate catalytic activity
(about 20%) and a selectivity for crotyl alcohol of 12–15%. Finally,
the best selectivity towards crotyl alcohol was provided by Pt/ZnO,
especially when reduced at 175 ◦C; however, its favorable selectiv-
ity was accompanied by a very low conversion to crotonaldehyde
(XUAL = 1%, SUOL = 75%). As stated before, Pt dispersion drastically
changes from one catalyst to another and, as a result, activity and
selectivity can also be affected. However, this influence cannot be

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J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
Fig. 4. High resolution transmission electron microscopy (HRTEM) images for the Pt/ZnO catalyst reduced at 175 ◦C (Pt/ZnO-175). (A) 250k×; (B) 250k×; (C) 500k×; (D)
1000k×.
quantified due to differences in catalyst supports that clearly affect
the overall behavior of the catalysts.
an electron pair is rather low (AN = 10.8) [47]. Inasmuch as this is
a non-protic solvent, it can form no hydrogen bonds by donating a
hydrogen; however, it can readily form such bonds by having their
unshared electrons accept a hydrogen atom. These properties can
be quantified via parameters ˛ (hydrogen donors) and ˇ (hydrogen
acceptors), which were introduced by Kamlet and Taft and listed in
ref [47]. 1,4-Dioxane has ˛ = 0.00 and ˇ = 0.37.
Water possesses a high dielectric constant (εr = 78.54) and a
greater dipole moment than 1,4-dioxane (ꢂ = 6.2 × 1030 C m). It is
a highly polar solvent with ETN = 1 (the upper limit of the scale for
the empirical polarity parameter). In addition, it has a donor num-
ber of 0.46, which is similar to that for 1,4-dioxane, but can accept
electron pairs more readily (i.e. it is a better electron acceptor, with
AN = 54.8) than this solvent. Finally, it has a much higher hydrogen
donor capacity that 1,4-dioxane (˛ = 1.17) in addition to a similar
proton acceptor capacity (ˇ = 0.47) [47,48].
Introducing water in the reaction medium had little effect on
crotonaldehyde conversion or selectivity towards the unsaturated
alcohol (Table 3, SENOL = 4–6%) with catalyst Pt/ZrO2-180. However,
acidifying the medium reduced the catalyst activity and completely
suppressed the selectivity towards the unsaturated alcohol. On the
other hand, the addition of KOH had the opposite effect and raised
the conversion to 47% and the selectivity towards 2-butenol to 10%.
For the Pt/ZnO-175 catalyst, the addition of water to the reac-
tion medium had a strong effect on catalytic performance of the
solid. Thus, it increased crotonaldehyde conversion to 11–13% with
a selectivity towards the unsaturated alcohol in the 92–96% range.
3.2.2. Influence of the solvent
After the initial screening of supports and reduction temper-
atures, we examined the influence of the solvent on the catalytic
activity and selectivity of the solids on the liquid-phase hydrogena-
tion of crotonaldehyde. The tests involved the supported catalysts
obtained at the particular reduction temperature leading to the best
activity and/or selectivity results. No alcohols were used as solvents
in order to avoid the potential formation of hemiacetals and acetals
from the carbonyl compounds [46]. Instead, the study was con-
ducted in mixtures of 1,4-dioxane and water in variable ratios up
to 1:1 that were supplied with moderate amounts of acetic acid or
potassium hydroxide to adjust the pH to 3.5 and 13.0, respectively.
The results thus obtained in the hydrogenation of crotonaldehyde
are shown in Table 3.
1,4-Dioxane is a non-protic polar solvent highly miscible with
water and possessing a low dielectric constant (εr = 2.21), a rela-
tively low dipole moment (ꢂ = 1.5 × 1030 C m) and a normalized
empirical parameter for solvent polarity ETN = 0.164 on a scale rang-
ing from 0 for tetramethylsilane to 1 for water [47,48]. The donor
number (DN) is a measure of the Lewis basicity (i.e. the ability to
donate an electron pair) in a solvent. 1,4-Dioxane has a DNN value
of 0.38 on a scale from 0 to 1, which suggests that it possesses donor
properties due to unshared electrons in its oxygen atoms. On the
other hand, the acceptor number (AN), that is, the ability to accept

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197
Fig. 5. Transmission electron microscopy images for the Pt/ZnO catalyst reduced at 400 ◦C (Pt/ZnO-400). (A) and (B) Pt/ZnO-175 at 250k×; (C) and (D) Pt/ZnO-400 at 250k×.
However, adding an acid or base to the medium had no appreciable
effect on the reaction, the mixture 1,4-dioxane/water providing the
best results in any case.
Dioxane–water systems provided conversions similar to those
obtained with pure dioxane with solid Pt/SnO2-270; such con-
versions never exceeded 1%. Acidifying or alkalizing the medium
resulted in zero conversion of crotonaldehyde after 8 h reaction.
With the iron oxide-based catalysts (Pt/Fe2O3-130 and
Pt/Fe3O4-250), adding water to the medium resulted in a very sub-
stantial loss of catalytic activity, which fell below 6% (against about
20% in pure dioxane). On the other hand, the presence of water
raised the selectivity towards the unsaturated alcohol to 50–80%.
The best overall performance as regards converting crotonalde-
hyde into 2-butenol (viz. 3% conversion and SENOL = 81%) was that
Table 3
Solvent effect on the activity (crotonaldehyde conversion, XUAL) and selectivity to butanal (SSAL), 1-butanol (SSOL) and crotyl alcohol (SUOL) obtained in the liquid-phase
crotonaldehyde hydrogenation.
Catalyst
Solvent
XUAL (%)
SSAL (%)
SSOL (%)
SUOL (%)
1,4-Dioxane
37
36
13
47
82
84
94
83
14
10
6
4
6
0
Pt/ZrO2-180
1,4-Dioxane/water
1,4-Dioxane/water/H+
1,4-Dioxane/water/OH−
7
10
1,4-Dioxane
1
11
12
13
25
5
8
0
0
0
0
75
96
92
95
Pt/ZnO-175
1,4-Dioxane/water
1,4-Dioxane/water/H+
1,4-Dioxane/water/OH−
5
1,4-Dioxane
1,4-Dioxane/water
1
1
75
44
0
0
25
56
Pt/SnO2-270
Pt/Fe2O3-130
1,4-Dioxane
20
3
2
56
19
44
35
29
0
2
15
81
55
65
1,4-Dioxane/water
1,4-Dioxane/water/H+
1,4-Dioxane/water/OH−
4
0
1,4-Dioxane
21
2
1
88
49
40
30
0
0
0
0
12
51
60
70
Pt/Fe3O4-250
Pt/TiO2-400
1,4-Dioxane/water
1,4-Dioxane/water/H+
1,4-Dioxane/water/OH−
6
1,4-Dioxane
16
10
69
15
73
73
88
83
21
0
5
6
27
7
1,4-Dioxane/water
1,4-Dioxane/water/H+
1,4-Dioxane/water/OH−
7
11
Reaction conditions: 20 mL of 0.5 M crotonaldehyde and 100 mg of freshly reduced Pt catalyst. Reaction temperature: 30 ◦C; initial hydrogen pressure: 0.414 MPa; reaction
time, 8 h.

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J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
Fig. 8. Product distribution profile obtained in the liquid-phase selective hydro-
genation of crotonaldehyde at the best reaction conditions: 100 mg of Pt/ZnO
catalyst reduced at 175 ◦C (Pt/ZnO-175), water–dioxane (1:1) as solvent, 0.414 MPa
of initial hydrogen pressure and a reaction temperature of 30 ◦C.
Pt/TiO2-400 while raising its selectivity towards the unsaturated
alcohol from 6 to 27%. Also, acidifying the medium caused a marked
increase in molar conversion, which amounted to 69% after 8 h
reaction—albeit, with a 2-butenol selectivity of only 7%.
In summary, the addition of water to the reaction medium
tended to increase the yield in unsaturated alcohol, with the excep-
tion of solids Pt/Fe2O3-130 and Pt/Fe3O4-250. As noted earlier,
however, the poor results for these two catalysts can be ascribed
to the water added dissolving their supports. The favorable effect
of water on the 2-butenol yield may have resulted from the water
activating the carbonyl group by hydrogen bonding; in fact, the
Kamlet–Taft parameter for water, ˛ = 1.17, is very high relative to
1,4-dioxane (˛ = 0.00).
Fig. 6. X-ray diffraction patterns obtained for the unreduced Pt/ZnO and Pt/ZnO
catalyst reduced at 175 and 400 ◦C.
obtained with Pt/Fe2O3-130 in a neutral 1,4-dioxane/water mixture
as solvent. However, the iron-based support was found to exhibit
signs of partial redissolution after 8 h reaction.
As with the previous solids, adding water to the 1,4-dioxane
solvent was found to diminish the conversion obtained with
More specifically, the addition of KOH to the reaction medium
(a dioxane/water mixture) provided the best yields in 2-butenol
Fig. 7. XPS profiles in the Pt(4f) and Zn(2p) region obtained for the unreduced Pt/ZnO and Pt/ZnO catalyst reduced at 175 and 400 ◦C.

J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
199
with solids Pt/ZrO2-180 and Pt/ZnO-175. Only Pt/TiO2-400 pro-
vided high yields with an acid medium, however. In any case, the
gains obtained by adding KOH cannot offset the environmental
hazard associated with the use of an alkaline medium.
especially if the medium was alkalized with KOH. However, the
resulting improvement cannot offset the disadvantage of requir-
ing the use of additives increasing the complexity of the reaction
medium and detracting from environmental friendliness.
The best operating conditions as regards 2-butenol yield were
used to determine the product distribution profile, using a diox-
ane/water mixture as solvent and solid Pt/ZnO-175 as catalyst.
Based on the profile, crotonaldehyde conversion increased grad-
ually with time; also, conversion was close to 40% and the catalyst
exhibited no signs of deactivation after 96 h reaction. In addition,
the selectivity towards 2-butenol was very high (91–96%) through-
out the selective reduction of crotonaldehyde. This selectivity level
is excellent and the conversion level quite acceptable and very dif-
ficult to obtain with platinum catalysts under such mild conditions
(a reaction temperature of 30 ◦C and an initial hydrogen pressure
of 0.414 MPa).
3.2.3. Product distribution profile under the optimum conditions
The best reaction conditions were taken to be those leading to
the highest yield in the unsaturated alcohol (2-butenol). Based on
the above-discussed results, Pt/ZnO-175 was the solid providing
the best yield in a medium consisting of a dioxane/water mix-
ture, whether acid, neutral or alkaline. In any case, the presence
of an alkali resulted in little improvement, so its addition to the
reaction medium was unwarranted. For this catalyst and reaction
conditions the turnover obtained (Pt/ZnO-175, TOF = 4 × 10−3 s−1
)
is lower by a factor of 10 than those described by Bartok et al. [28]
for some commercial and clay-supported Pt catalyst in the liquid-
phase crotonaldehyde hydrogenation. However the selectivity to
crotyl alcohol achieved with our catalyst (SUOL = 96% at 11% conver-
sion, 91% at 40% conversion) is largely higher than those reported in
that work (SUOL = 7–43%). This high selectivity of solid Pt/ZnO-175
may have resulted from the presence of ZnOxCly formed around
Pt particles and detected in the XPS analysis which might have
acted as Lewis acid sites facilitating anchoring of the crotonalde-
hyde molecule via its carbonyl double bond [35]. On the other
hand, the PtZn alloy detected in the solid reduced at 400 ◦C seem-
ingly had no clear-cut effect on the selectivity of the process. For
the Pt/ZnO-400 catalyst, at best reaction conditions, the turnover
was TOF = 2.5 × 10−3 s−1 similar than that achieved for the cata-
lyst reduced at 175 ◦C (TOF = 4 × 10−3 s−1). Moreover, as far as the
selectivity to crotyl alcohol is concerned, it was also in the level of
the Pt/ZnO-175 catalyst (SUOL = 95% at 5% conversion). Therefore, in
this case no structure sensitivity was apparently observed, proba-
bly due to the small change in Pt particle size, or to the additional
effect of the PtZn alloy formed at high reduction temperature.
Fig. 8 shows the product distribution profile for solid Pt/ZnO-175
in a medium consisting of 1:1 dioxane/water. As can be seen, cro-
tonaldehyde conversion increased gradually with conversion close
to 40% and no signs of catalyst deactivation after 96 h reaction. The
selectivity towards 2-butenol was very high (91–96%) throughout
the selective hydrogenation of crotonaldehyde. This is an excellent
selectivity and a more than acceptable conversion level that is very
difficult to obtain under so mild reaction conditions (at reaction
temperature of 30 ◦C and an initial hydrogen pressure of 0.414 MPa)
with a platinum catalyst.
Acknowledgements
This research was funded by Spain’s Ministry of Science and Edu-
cation (Projects CTQ2008-01330/BQU and CTQ2007-65754/PPQ),
and cofunded by FEDER and the Andalusian Regional Government
(Projects P07-FQM-02695 and P09-FQM-4781).
References
[1] B. Chen, U. Dingerdissen, J.G.E. Krauter, H.G.J. Lansink Rotgerink, K. Mobus, D.J.
Ostgard, P. Panster, T.H. Riermeier, S. Seebald, T. Tacke, H. Trauthwein, Appl.
Catal. A 280 (2005) 17–46.
[2] P. Maki-Arvela, J. Hajek, T. Salmi, D.Y. Murzin, Appl. Catal. A 292 (2005) 1–49.
[3] P. Gallezot, D. Richard, Catal. Rev. -Sci. Eng. 40 (1998) 81–126.
[4] P. Gallezot, P.J. Cerino, B. Blanc, G. Fleche, P. Fuertes, J. Catal. 146 (1994) 93–102.
[5] N. Mahata, F. Goncalves, M.F. Pereira, J.L. Figueiredo, Appl. Catal. A 339 (2008)
159–168.
[6] N.M. Bertero, A.F. Trasarti, B. Moraweck, A. Borgna, A.J. Marchi, Appl. Catal. A
358 (2009) 32–41.
[7] F. Coloma, J. Llorca, N. Homs, P. Ramirez de la Piscina, F. Rodriguez-Reinoso, A.
Sepulveda-Escribano, Phys. Chem. Chem. Phys. 2 (2000) 3063–3069.
[8] G. Szollosi, B. Torok, L. Baranyi, M. Bartok, J. Catal. 179 (1998) 619–623.
[9] Z.M. Michalska, B. Ostaszewski, J. Zientarska, J.M. Rynkowski, J. Mol. Catal. A
185 (2002) 279–283.
[10] C. Milone, R. Ingoglia, L. Schipilliti, C. Crisafulli, G. Neri, S. Galvagno, J. Catal. 236
(2005) 80–90.
[11] A. Dandekar, M.A. Vannice, J. Catal. 183 (1999) 344–354.
[12] K. Liberkova, R. Touroude, D.Y. Murzin, Chem. Eng. Sci. 57 (2002) 2519–2529.
[13] H. Yoshitake, Y. Iwasawa, J. Catal. 125 (1990) 227–242.
[14] H. Yoshitake, Y. Iwasawa, JCS, Faraday Trans. 88 (1992) 503–510.
[15] X. Han, R. Zhou, B. Yue, X. Zheng, Catal. Lett. 109 (2006) 157–161.
[16] M. Consonni, D. Jokic, D. Yu Murzin, R. Touroude, J. Catal. 188 (1999) 165–175.
[17] S. Bernal, J.J. Calvino, M.A. Cauqui, J.M. Gatica, C. Lopez Cartes, J.A. Perez Omil,
J.M. Pintado, Catal. Today 77 (2003) 385–406.
[18] M. Abid, G. Ehret, R. Touroude, Appl. Catal. A 217 (2001) 219–229.
[19] M. Abid, V. Paul-Boncour, R. Touroude, Appl. Catal. A 297 (2006) 48–59.
[20] A. Sepulveda-Escribano, F. Coloma, F. Rodriguez-Reinoso, J. Catal. 178 (1998)
649–657.
[21] P. Concepcion, A. Corma, J. Silvestre-Albero, V. Franco, J.Y. Chane-Ching, J. Am.
Chem. Soc. 126 (2004) 5523–5532.
[22] H.G. Manyar, D. Weber, H. Daly, J.M. Thompson, D.W. Rooney, L.F. Gladden, E.
Hugh Stitt, J. Jose Delgado, S. Bernal, C. Hardacre, J. Catal. 265 (2009) 80–88.
[23] U.K. Singh, M.A. Vannice, Appl. Catal. A 213 (2001) 1–24.
[24] S. Mukherjee, M.A. Vannice, J. Catal. 243 (2006) 108–130.
[25] S. Mukherjee, M.A. Vannice, J. Catal. 243 (2006) 131–148.
[26] M. Englisch, A. Jentys, J.A. Lercher, J. Catal. 166 (1997) 25–35.
[27] M.A. Aramendia, V. Borau, C. Jimenez, J.M. Marinas, A. Porras, F.J. Urbano, J.
Catal. 172 (1997) 46–54.
[28] I. Kun, G. Szollosi, M. Bartok, J. Mol. Catal. A 169 (2001) 235–246.
[29] H. Yamada, S. Goto, J. Chem. Eng. Jpn. 36 (2003) 586–589.
[30] S.I. Fujita, Y. Sano, B.M. Bhanage, M. Arai, J. Catal. 225 (2004) 95–104.
[31] E. Gebauer-Henke, J. Grams, E. Szubiakiewicz, J. Farbotko, R. Touroude, J.
Rynkowski, J. Catal. 250 (2007) 195–208.
4. Conclusions
The selective reduction of crotonaldehyde to crotyl alcohol over
Pt catalysts supported on various partially reducible solids includ-
ing Fe2O3, Fe3O4, ZrO2, ZnO, TiO2 and SnO2 was conducted. The
catalysts were characterized by thermal programmed reduction
(TPR) and reduced at temperatures that were selected as a func-
tion of the presence of specific reduction peaks for Pt in the TPR
profiles. The use of low reduction temperatures was found to pro-
vide catalysts leading to increased yields in the unsaturated alcohol
(2-butenol) in the selective hydrogenation of crotonaldehyde. The
high selectivity of solid Pt/ZnO-175 may be related to the presence
of ZnOxCly species forming around Pt particles and detected by XPS
which might act as Lewis acid sites facilitating anchoring of the
crotonaldehyde molecule via its carbonyl double bond [35]. On the
other hand, the PtZn alloy detected in the solid reduced at 400 ◦C
has no clear-cut effect on the selectivity of the process.
[32] D.L. Hoang, H. Lieske, Catal. Lett. 27 (1994) 33–42.
[33] J.M. Moreno, M.A. Aramendia, A. Marinas, J.M. Marinas, F.J. Urbano, Appl. Catal.
B 59 (2005) 275–283.
[34] T. Mitsui, K. Tsutsui, T. Matsui, R. Kikuchi, K. Eguchi, Appl. Catal. B 78 (2008)
158–165.
[35] F. Ammari, J. Lamotte, R. Touroude, J. Catal. 221 (2004) 32–42.
[36] X. Wang, Y.C. Xie, Catal. Lett. 75 (2001) 73–80.
As regards the influence of the reaction medium in general and
the addition of water to a neutral, acid or alkaline medium in partic-
ular, the latter was found to raise the yield in unsaturated alcohol,

200
J. Hidalgo-Carrillo et al. / Applied Catalysis A: General 385 (2010) 190–200
[37] N. Apostolescu, B. Geiger, K. Hizbullah, M.T. Jan, S. Kureti, D. Reichert, F. Schott,
W. Weisweiler, Appl. Catal. B 62 (2006) 104–114.
[44] S. Zafeiratos, G. Papakonstantinou, M.M. Jacksic, S.G. Neophytides, J. Catal. 232
(2005) 127–136.
[38] A. Venugopal, M.S. Scurrell, Appl. Catal. A 258 (2004) 241–249.
[39] G. Munteanu, L. Ilieva, D. Andreeva, Thermochim. Acta 291 (1997)
171–177.
[40] M.A. Aramendia, J.C. Colmenares, A. Marinas, J.M. Marinas, J.M. Moreno, J.A.
Navio, F.J. Urbano, Catal. Today 128 (2007) 235–244.
[41] T. Teranishi, M. Hosoe, T. Tanaka, M. Miyake, J. Phys. Chem. B 103 (1999)
3818–3827.
[42] Y. Nagai, H. Shinjoh, K. Yokota, Appl. Catal. B 39 (2002) 149–155.
[43] V. Romanovskaya, M. Ivanovskaya, P. Bogdanov, Sens. Actuators, Bl 56 (1999)
31–36.
[45] C.D. Wagner, W.M. Riggs, L.E. Davis, J.F. Moulder, G.E. Muilenberg, Handbook of
X-Ray Photoelectron Spectroscopy. A Reference Book of Standard Data for Use
in X-Ray Photoelectron Spectroscopy, Perkin-Elmer Corporation, Minnesota,
1979.
[46] J. Hajek, N. Kumar, P. Maki-Arvela, T. Salmi, D.Y. Murzin, I. Paseka, T. Heikkila,
E. Laine, P. Laukkanen, J. Vayrynen, Appl. Catal. A 251 (2003) 385–396.
[47] D.J. Adams, P.J. Dyson, S.T. Tavener, Chemistry in Alternative Media, John Wiley
& Sons, Chichester, 2004.
[48] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, 3rd ed.,
Wiley–VCH, Weinheim, 2003.