Selective hydrogenation of cinnamaldehyde on Pt and Pt-Fe catalysts supported on zeolite P

Article abstract of DOI:10.1007/s10562-011-0688-x

Pt- and Pt-Fe based catalysts on zeolite P (ZP) support have been prepared and widely characterized by surface area and porosity, XRD, SEM, TEM, TPR, in order to investigate their morphological and microstructural properties. The catalysts have been tested in the selective liquid-phase hydrogenation of cinnamaldehyde. Kinetic tests have shown the beneficial effect of Fe promoter on the catalysts behaviour towards the selective formation of cinnamyl alcohol (85% selectivity to 90% conversion). The ZP supported catalysts have been compared with a catalyst supported on P-zeolitized Fe containing pumice (Z-PM), confirming the role of Fe Lewis acid site in promoting the reactivity of zeolite P-based materials. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-011-0688-x

Catal Lett (2011) 141:1590–1597
DOI 10.1007/s10562-011-0688-x
Selective Hydrogenation of Cinnamaldehyde on Pt and Pt-Fe
Catalysts Supported on Zeolite P
•
•
•
•
G. Neri I. Arrigo F. Corigliano L. De Luca
A. Donato
Received: 5 July 2011 / Accepted: 14 August 2011 / Published online: 7 September 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Pt– and Pt–Fe based catalysts on zeolite P (ZP)
support have been prepared and widely characterized by
surface area and porosity, XRD, SEM, TEM, TPR, in order
to investigate their morphological and microstructural
properties. The catalysts have been tested in the selective
liquid-phase hydrogenation of cinnamaldehyde. Kinetic
tests have shown the beneficial effect of Fe promoter on the
catalysts behaviour towards the selective formation of
cinnamyl alcohol (85% selectivity to 90% conversion). The
ZP supported catalysts have been compared with a catalyst
supported on P-zeolitized Fe containing pumice (Z-PM),
confirming the role of Fe Lewis acid site in promoting the
reactivity of zeolite P-based materials.
aldehydes to corresponding unsaturated alcohols is a fun-
damental reaction [1]. Usually, most of the used catalysts
for this reaction are based on noble metals supported on
carbon or transition metal oxides [2, 3]. It is well recog-
nized that many parameters affect the selectivity of such
catalysts and among these a determinant role is played by
the support [4]. Therefore, the use of more effective sup-
ports for the dispersion of the catalytic active phases in the
selective hydrogenation reaction of carbonyl group is a key
point both in the industrial and research field.
In previous papers we reported the performance of
platinum catalysts supported on a novel P-zeolitized
pumice support (Z-PM) obtained from waste pumice [5, 6].
Pumice is a porous, natural glass formed from volcanic
activity, used as a filtering agent for water clarifying, as a
soft abrasive material in the textile industry (jeans stone-
washing) and in a number of other industrial applications
[7, 8]. Pumice powder has also been used as silica and
alumina source in the synthesis of zeolites [9–11]. The
P-zeolitized pumice material Z-PM has been synthesized
through a patented process involving a two-steps silica
extraction by an alkali aqueous solution from waste pumice
[12]. The P-zeolitized pumice material so obtained has a
surface area of about 30–40 m2/g and a high content
(around 60%) of crystalline zeolite P, making it suitable for
the development of some applications typical of zeolites,
such as cations adsorption and catalyst supporting [5, 6, 13,
14].
Keywords Cinnamaldehyde Á Selective hydrogenation Á
Pt catalysts Á Catalytic support Á Zeolite P
1 Introduction
The search for new and more effective catalysts for
selective reactions in the field of fine chemicals is of great
interest. In this regard, the hydrogenation of unsaturated
G. Neri Á I. Arrigo Á F. Corigliano
Department of Industrial Chemistry and Materials Engineering,
University of Messina, Salita Sperone 31, 98166 Messina, Italy
Pt catalysts supported on Z-PM [5, 6] exhibited high
selectivity in the hydrogenation of the carbonyl group of
campholenic aldehyde to naturanol, an unsaturated alcohol
largely used in food and perfumery industry [15]. The
results obtained in this reaction encouraged us to investi-
gate the general behaviour of Pt catalysts supported on
Z-PM in the selective hydrogenation of a,b-unsaturated
G. Neri (&)
Dipartimento di Chimica Industriale e Ingegneria dei Materiali,
`
Universita di Messina Contrada di Dio, 98166 Messina, Italy
e-mail: neri@ingegneria.unime.it
L. De Luca Á A. Donato
Department of Mechanics and Materials, University of Reggio
Calabria, Loc. Feo di Vito, 89100 Reggio Calabria, Italy
123

Selective Hydrogenation of Cinnamaldehyde
1591
aldehydes, such as cinnamaldehyde, which are versatile
raw materials for the synthesis of a,b-unsaturated alcohols
utilized as intermediates in many chemical processes of
industrial interests [16]. Cinnamaldehyde has been the
most investigated a,b-unsaturated aldehyde as a substrate
for the hydrogenation of a C=O group conjugated with the
C=C double bond [17–22].
and repeatedly washed with 200 mL of water until a pH of
12.5 was reached. The synthesized zeolite P was finally
heated at 383 K in a oven for 8 h.
2.2 Catalysts Preparation
Pt/ZP catalysts have been prepared by impregnation,
according to the incipient wetness technique, of the ZP
support with solutions of Pt acetylacetonate in acetone in
the suitable amount to have a nominal Pt content of 2 wt%.
PtFe/ZP catalysts have been prepared by a double incipient
wetness technique; two separate impregnations have been
done, first with an aqueous solution of Fe(NO3)3 and in a
second step with Pt(acac)2 in acetone. After each step a
drying treatment in air at 393 K for 12 h was carried out.
Finally the samples were reduced under H2 flowing at
623 K for 2 h. The prepared catalysts have a Fe loading
ranging from 0 up to 4 wt% (Table 1).
The high selectivity towards unsaturated alcohols
observed on the Pt/Z-PM catalyst, has been ascribed to a
promoter effect connected with the presence of iron
impurities in the Z-PM support [5, 6]. To verify this
hypothesis and elucidate the role of Fe as a promoter, a
pure zeolite P support (ZP) has been used here for the
preparation of Pt and Pt–Fe supported model catalysts. The
samples were characterized by BET surface area and
porosity, XRD, SEM, TEM and TPR with the aim to
compare these data obtained with the results of catalytic
activity in the selective hydrogenation of cinnamaldehyde
and acquire more insights about the reaction mechanism on
these novel catalysts.
2.3 Surface Area and Hydrogen Chemisorption
Surface area and porosity data were determined by adsorp-
tion–desorption of nitrogen at 77 K using a Micromeritics
ASAP 2010 instrument. The samples were evacuated at
350 °C for 3 h prior to the measurement. The mesoporous
(or external) surface area and micropore volume were
evaluated by the t-plot method.
2 Experimental
2.1 Support Preparation
The pure zeolite P to be used as support has been prepared
according to the procedure reported in Ref. [23]. In brief, a
solution ‘‘A’’ was prepared dissolving a mixture of sodium
aluminate and NaOH in water (20% Al2O3, 20% Na2O,
60% water) under stirring at 348 K. A solution ‘‘B’’ was
prepared dissolving sodium silicate in water (30% SiO2,
12% Na2O, 58% water). The solution ‘‘A’’, after a pre-
heating treatment, was poured into a reactor kept at 368 K.
When solution ‘‘B’’ was added slowly (about 5 min.) to the
aluminate solution, a silico-aluminate gel was instanta-
neously formed. The gel was maintained at 368 K under
reflux for 5 h. After this time, it was filtered on a buckner
Hydrogen chemisorption experiments were carried out
in a conventional vacuum system. The sample (approxi-
mately 0.1 g) was outgassed at 523 K for 1 h, reduced at
623 for 1 h in hydrogen and then cooled under vacuum to
room temperature at which point the chemisorption
experiments were performed. The amount of irreversible
chemisorbed hydrogen, H, was calculated from the double
adsorption isotherm method, and the number of accessible
surface platinum atoms, Pt(s), deduced from the ratio H/Pt,
assuming that one H atom adsorbed on one surface plati-
num atom.
Table 1 Main characteristics and properties of the support and catalysts
Code
Pt loading
(wt%)
Fe loading
(wt%)
Mesoporous
surface area (m2/g)
Micropore volume
(cm3(STP)/g)
H/Pt
0.18
TOF (9102)
Z-PM
–
2
–
2
2
2
2
2
–
30
7
0.0013
a
Pt/Z-PM
ZP
–
6.7
–
112
7
0.0137
a
Pt/ZP
–
0.23
0.07
0.08
0.05
0.03
3.3
20.7
28.1
48.8
80.7
a
a
a
a
PtFe0.5/ZP
PtFe1/ZP
PtFe2/ZP
PtFe4/ZP
a
0.5
1
16
11
13
24
2
4
Micropore volume below the detection limit
123

1592
G. Neri et al.
2.4 TPR
In order to check the absence of diffusional limitations,
preliminary runs have been carried out at different stirring
conditions, loading and catalyst grain size. Results
obtained indicate that measurements have been carried out
under kinetic control and are not influenced by external
and/or internal mass diffusion. Specifically, the depen-
dence of hydrogenation rate upon the stirring speed,
revealed that the rate did not depend on the stirring speed
in the range 400–1,000 rpm. The dependence of ALDC
conversion with different amounts of catalyst was linear,
confirming further the absence of external mass transfer
limitations. Experimental results with catalysts having
different support size have shown that the activity
remained nearly constant, supporting the indication that the
inner diffusion limitation was negligible.
TPR experiments were performed in a conventional TPR
apparatus. The dried samples were heated at a linear rate of
10 K/min from 298 to 900 K in a 5% H2/Ar mixture
flowing at 20 mL/min. A cold trap (maintained at 193 K)
and a tube filled with KOH were used to block water, HCl
and CO2, respectively. The signal calibration was made by
injecting, in the carrier gas, a known amount of H2.
2.5 XRD
XRD spectra were recorded on an Ital Structure mod. APD
2000 X-ray diffractometer using the CuKa radiation and
mounting powder samples on a Plexiglass holder. Dif-
fraction peaks of crystalline phases were compared with
those of standard compounds reported in the JCPDS Data
File.
3 Results and Discussion
2.6 TEM
3.1 Textural Characteristics and Hydrogen
Chemisorption
Transmission electron microscopy (TEM) studies of the
catalysts were performed on a JEOL 2010 EX instrument
operating at 200 kV and directly interfaced with a com-
puter for real-time image processing. The catalyst speci-
mens were prepared by grinding the powder samples in an
agate mortar, suspending and sonicating them in isopro-
panol, and placing a drop of the suspension on a carbon
copper grid. After evaporation of the solvent, the speci-
mens were introduced into the microscope column and
examined.
The mesoporous surface area and micropore volume,
derived by applying the t-plot method to the adsorption
isotherm registered on the support and catalysts, are reported
in Table 1. Data of the Z-PM support have been also
reported, for comparison. On both supports, the surface area
is higher compared to that of corresponding Pt-based cata-
lysts. Furthermore, the analysis of the micropore volume
reveals that it significantly decreases for the Pt-supported
catalysts with respect to supports only. This could indicate
that Pt metal particles block the access to the channels in the
support. On the ZP supported Pt catalysts loaded with Fe, a
slight increase of BET surface area was registered with Fe
loading. This can be instead attributed to the support mod-
ification, likely caused by nitric acid generated from the iron
precursor during the thermal treatment in hydrogen, as
registered by XRD analysis reported below.
2.7 Catalytic Activity
Catalytic activity tests were carried out in a 100 mL five-
necked flask, equipped with a reflux condenser. Constant
temperature (343 0.5 K) was maintained by circulation
of silicone oil in an external jacket connected with a
thermostat. The reactions were carried out as follow. The
catalyst (0.25 g) was added to 50 mL of cyclohexane
through one arm of the flask. Before introduction of the
cinnamaldehyde, the catalyst was first treated ‘‘in situ’’ at
343 K with an H2 flow (50 cc/min) for 30 min. Then,
0.1 mL of the substrate and 0.1 mL of tetradecane were
introduced (the latter was used as an internal standard for
GC analysis) in the reactor. The reaction mixture was kept
under stirring at 500 rpm with permanent magnetic cou-
pling which ensure a very efficient stirring. The hydroge-
nation reaction was carried out in H2 at atmospheric
pressure. The progress of the reaction was followed by GC,
by analyses of samples withdrawn from the reaction mix-
ture at different times.
Results obtained from chemisorption analyses for the ZP
and Z-PM supported catalysts are shown in Table 1. The
amount of irreversible H2 chemisorption was used to
determine the Pt dispersion. It can be clearly observed a
decrease in the H/Pt atomic ratio compared to the parent
monometallic catalyst. On the basis of TEM analysis (see
next paragraph), indicating no difference in the Pt particle
size with Fe loading, it can be excluded that the lower H/Pt
ratio is due to an increase of metal particle size. On the
assumption that the hydrogen uptake measured on the
bimetallic catalysts is attributed only to the noble metal, as
no hydrogen chemisorption occurs on iron, it can be sug-
gested that the decrease of the number of platinum surface
sites available for hydrogen chemisorption upon addition
123

Selective Hydrogenation of Cinnamaldehyde
1593
of the iron is due to the Fe dilution or coverage of the
surface Pt. This latter hypothesis is in agreement with TEM
results, showing a thin iron oxide layer covering the
metallic particles.
3.2 TEM
Representative TEM micrographs of ZP-supported cata-
lysts investigated in this study, are reported in Fig. 1. The
zeolite support shows a morphology characterized by
the presence of spherical aggregates with diameter in the
0.1–2 micron range, composed of smaller nanoparticles of
zeolite P. Pt particles are well distributed on the surface of
the ZP-supported catalysts. On the monometallic Pt/ZP
sample, rounded and well contrasted particles are
observed. At the addition of Fe, metallic particles on the
surface present an irregular form and seem to have a lower
contrast. This latter characteristic agree with the hypoth-
esis that these particles can be bimetallic in nature, the
lower contrast being due to the presence of an element
(Fe) having an atomic number smaller than Pt. The larger
metallic particles, having size in the range 20–40 nm, are
easily imaged on the surface of support. However, at
higher magnification the diffuse presence of metallic
particles having very small size (1–3 nm) can also be
observed, similarly to that previously reported for the
Pt/Z-PM catalyst [6]. Moreover, micrograph reveals that
Pt particles are covered by a thin iron oxide layer. How-
ever, it cannot be excluded of all the formation of a car-
bonaceous layer, due to the carbon impurities coming
from incomplete decomposition of platinum acetylaceto-
nate precursor.
200 nm
2%Pt/ZP
200 nm
3.3 XRD
The composition of the crystalline phases on the support
and active site(s) on the ZP-supported catalysts after the
reduction treatment at 623 K, was investigated by XRD
measurements. In Fig. 2, XRD pattern of the ZP support
shows the main reflections characteristic of zeolite P
(JCPDS n. 39-0219). Regarding the ZP-supported catalysts,
XRD pattern of the monometallic Pt/ZP catalyst shows the
same pattern of ZP support, confirming that the structure of
the support is not significantly changed after the thermal
reduction treatment. An intense peak at 39.86 two-theta,
attributed to metallic Pt, is also observed.
25 nm
2%Pt-4%Fe/ZP
Fig. 1 Typical TEM images of the ZP support and ZP supported
catalysts
With the increasing of iron loading, XRD patterns show
some distinctive changes. First, the peak intensity is weaker,
indicating a lower crystallinity, probably related to the
destruction of support during the thermal treatment of
the Fe-promoted catalysts. Moreover, it can be observed as
the characteristic peaks of zeolite P disappear progressively
with the increase of Fe content, indicating a transformation
of the support phase. Indeed, new peaks, related to a hydrate
sodium alumina silicate phase (JCPDS n. 24-1046), appear
in the spectra of the Fe-promoted catalysts. This is likely due
to the nitric acid generation during the reducing treatment of
the Fe-loaded catalysts by hydrogen.
123

1594
G. Neri et al.
species to metallic Pt. ZP supported catalysts promoted
with different iron loading were then characterized. An
increase of the hydrogen uptake with the Fe loading in the
region of platinum reduction can be noted, suggesting that
these reducible species are likely associated with bimetallic
Pt–Fe ensembles. The further hydrogen consumption
observed at temperature above 500 K is related to the
reduction of iron oxide species. By comparing the above
reduction temperature range with that usually reported for
impregnated iron oxide catalysts [24], it is clearly evident
as the presence of Pt leads to a marked lowering of the
reduction temperature of iron oxide species. In this regard,
it is well known the ability of metallic Pt to dissociatively
adsorb hydrogen and favour the reduction of iron species
by means of hydrogen spillover [25].
Pt Fe alloys
PtFe4/ZP
Na Al Si O x 4.3H O
zeolite P
Pt
6
6
9
30
2
*
°
°
PtFe2/ZP
PtFe0.5/ZP
Pt/ZP
°
°
Pt/Z-PM
*
*
*
*
*
ZP
*
*
10
20
30
40
50
2ϑ
3.5 Catalytic Activity
Fig. 2 XRD patterns of the reduced Pt/Z-PM, Pt/ZP and PtFe/ZP
catalysts. The XRD analysis of the ZP support is also reported for
comparison
Pt catalysts supported on zeolites have been widely
reported in many hydrogenation processes,; however, only
few studies have been reported for the hydrogenation of
unsaturated aldehydes. Generally the performances of
zeolite supported metal catalysts for selective hydrogena-
tion reactions is known to depend strongly on some specific
properties of the zeolite support such as acidity, Si/Al ratio
and the presence of extra-framework Al. The decrease of
the acidity of the support results in a greater electron
density on the small metal particles, which may cause a
suppression in the C=C hydrogenation rate by enhancing
the electrons delocalization in the adsorbed conjugated
substrate [1, 26]. On the other hand, other factors, such as
steric and electronic effects, have to be taken into account.
Gallezot et al. [27, 28] have studied platinum catalysts
supported on Y and b zeolites and concluded that an end-
on adsorption on the transition metal is imposed by the
geometric constraints in the pores causing a selective
activation of the C=O bond. Blackmond et al. [29] have
also reported geometric and electronic effects of platinum
metal supported on Y zeolite in the selective hydrogenation
of cinnamaldehyde.
By analyzing the main diffraction peak of metallic Pt, it
can also be observed a progressive base broadening and
intensity diminution with the increasing of Fe content. This
finding could be due to a decrease of platinum particle size,
but the formation of platinum-iron ensembles should also
be taken into account [5, 6].
3.4 TPR
TPR analysis of the unreduced ZP support and supported
catalysts are shown in Fig. 3. On the Pt/ZP catalyst, two
reduction peaks observed at low temperature (410 and
465 K) can be assigned to the reduction of platinum
We reported previously that Pt catalysts supported on
Z-PM [5, 6] exhibited high selectivity in the hydrogenation
of the carbonyl group of campholenic aldehyde to natura-
nol. The promising results obtained encouraged us to
extend the investigation of this catalytic system in the
hydrogenation of a,b-unsaturated aldehydes, such as cin-
namaldehyde. The hydrogenation of cinnamaldehyde, leads
to cinnamyl alcohol (see Scheme 1), as the desired product,
because it is a versatile intermediate utilized in many
chemical processes of industrial interests [16]. Different
parallel/consecutive pathways are also possible leading
to hydrocinnamaldehyde and hydro cinnamyl alcohol as
by-products.
PtFe4/ZP
PtFe2/ZP
PtFe1/ZP
Pt/ZP
Pt/Z-PM
400
600
800
1000
Temperature (K)
Fig. 3 TPR patterns of the investigated catalysts
123

Selective Hydrogenation of Cinnamaldehyde
1595
zeolitized-P supports, Pt–Fe/ZP model catalysts doped with
different amount of Fe were investigated in the hydroge-
nation of cinnamaldehyde. Figure 5 shows the typical
composition vs. reaction time curves obtained under the
experimental conditions specified in the legend. The same
experiment carried out with the Z-PM supported catalyst is
also reported, for comparison.
OH
Cinnamyl alcohol
(CALC)
OH
O
Hydrocinnamyl alcohol
(CALD)
Cinnamaldehyde
(CALD)
A summary of the results obtained, showing the activity
and selectivity to unsaturated alcohols vs. the iron content
for the Pt–Fe/ZP catalysts is presented in the Fig. 6. It can
be observed that, up to 1% of iron content, the activity
increases. Increasing further the iron content the activity
tend to remain constant. As a first hypothesis, we can
explain this behaviour considering that Fe primarily acts
inhibiting the adsorption of C=C double bond, whereas
correspondingly it enhance the C=O group adsorption,
increasing consequently the reactivity of carbonyl group.
The first effect prevails at low loading of iron, whereas the
increase of carbonyl reactivity is predominant at higher
loading. However, using the irreversible hydrogen uptakes
to determine the number of surface Pt sites, the turnover
frequency (TOF, s-1), expressed as the number of CALD
molecules converted per second and per surface Pt atom,
was calculated (see last column in Table 1), demonstrating
an increase of the platinum activity in the cinnamaldehyde
hydrogenation with the loading of Fe. This suggests instead
that the plateau observed in Fig. 6 is more likely due to Fe
dilution or coverage of the surface Pt, leading to a decrease
of the number of platinum surface sites available, balanced
by the corresponding increase of the specific activity.
Although differences exists regarding the experimental
conditions adopted, TOFs calculated for the unpromoted
catalysts are of the same order of magnitude as those
reported in literature; for instance, Lashdaf et al. reported
TOF value in the range 2–4 9 10-2 s-1 for a series of
Pt/zeolite b catalysts at 33 K, under 10 atmosphere of
hydrogen and in 2-propanol as solvent [30]. The higher
TOF observed on the Pt/Z-PM catalyst compared to Pt/ZP
one is related to the presence of Fe in this latter catalyst.
Regarding the selectivity to cinnamyl alcohol, it increa-
ses strongly with the addition of iron, reaching a maximum
value (about 85%) at 90% of conversion, on the catalyst
having a Fe loading of about 1 wt%. At higher promoter
content the selectivity decreases, mainly as a results of an
increase of the full saturated products. This indicates that the
selectivity to cinnamyl alcohol is mainly determined by Fe
loading and Pt/Fe ratio, as expected. It suggests, on the
contrary, a little influence of the support structure. The
above selectivity value (85% at 90 percent of conversion) is
only slightly lower than those reported in literature for
supported doped-platinum catalysts on zeolite. For exam-
ples, Li et al. have reported a selectivity higher than 90% to
cinnamyl alcohol for Pt/Sn catalysts on zeolite L [31].
O
Hydrocinnamaldehyde
(HALD)
Scheme 1 Cinnamaldehyde hydrogenation pathway on Pt/ZP
catalysts
1,0x10-5
100
Activity
8,0x10-6
Selectivity
80
6,0x10-6
60
4,0x10-6
40
2,0x10-6
20
0
Pt/ZP
Pt/Z-PM
Pt/SiO2
Fig. 4 Comparison of the hydrogenation activity and selectivity to
cinnamyl alcohol between Pt/SiO2, Pt/ZP and Pt/Z-PM catalysts in
the hydrogenation of cinnamaldehyde
Figure 4 compares the catalytic properties in the
hydrogenation of cinnamaldehyde of monometallic Pt
catalysts on different supports. It can be noted as the
Pt/Z-PM sample shows a high selectivity towards the
desired product, CALC. Data registered from the Pt/SiO2
catalyst used as reference, indicate that its activity is about
one order of magnitude higher than that measured on the
zeolitized-P supported catalysts, but the selectivity to
the desired unsaturated alcohol is practically negligible. On
the Pt/ZP catalyst, a slow reaction rate is monitored with no
formation of cinnamyl alcohol.
These results confirm previous data reported in the
hydrogenation of the isolated carbonyl group [5, 6] and
also indicate that the Z-PM support promote effectively the
catalytic properties of platinum for the hydrogenation of
conjugated carbonyl group. Moreover, it appears clear that
the presence of iron impurities in the amorphous phase of
the Z-PM support [8], plays a key role for this reaction.
Therefore, in order to prove this and have a better under-
standing of the properties of catalytic systems based on
123

1596
G. Neri et al.
5,0x10-6
100
80
60
40
20
0
100
80
60
40
20
0
PtFe4/ZP
4,0x10-6
3,0x10-6
2,0x10-6
1,0x10-6
CALD
CALC
HALD
HALC
Selectivity
Activity
0
200 400 600 800 1000 1200 1400
Time (min.)
100
80
60
40
20
0
0
1
2
3
4
5
PtFe1/ZP
Fe loading (wt%)
Fig. 6 Hydrogenation activity and selectivity to cinnamyl alcohol as
a function of the Fe loading over the Pt–Fe/ZP samples
CALD
CALC
HALD
HALC
Catalytic data above presented, clearly demonstrate that
increasing the iron loading on the ZP-supported catalysts,
the catalytic behaviour become similar to that of Pt/Z-PM
catalyst. According to the well established action mecha-
nism of promoters such as Fe, Sn, etc. in this reaction [1, 2,
32–35], these findings confirm the hypothesis previously
made on the role of Fe impurities present in the Z-PM
support. Iron species likely acts as Lewis acid sites
enhancing the polarization of the carbonyl group, which
would favourably react with the hydrogen dissociated on
the Pt atoms. In order to produce this effect, Fe species
must be placed in the vicinity of the Pt atoms, leading to
the formation of bi-metallic Pt–Fe ensembles or alloys, as
here suggested by TEM, XRD and TPR characterization
data reported.
0
300
600
900
1200 1500 1800
Time (min.)
100
80
60
40
20
0
Pt/ZP
CALD
CALC
HALD
HALC
0
300
600
900
1200
1500
Time (min.)
References
100
80
60
40
20
0
Pt/Z-PM
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CALD
CALC
HALD
HALC
0
300
600
900
1200 1500 1800
Time (min.)
Fig. 5 Composition of the reaction mixture vs reaction time in the
hydrogenation of cinnamaldehyde over the Pt–Fe/ZP samples.
[Cinnamaldehyde] = 1.23 9 10-2 mol/L; solvent = cyclohexane;
temp. = 343 K. cat. weight. = 0.25 g
123

Selective Hydrogenation of Cinnamaldehyde
1597
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