Chemoselective hydrogenation of aromatic ketones with Pt-based heterogeneous catalysts. Substituent effects

Article abstract of DOI:10.1016/j.apcata.2014.11.010

Catalytic reduction of aromatic ketones is an interesting reaction that leads to the obtaining of alcohols. Some of these alcohols are employed as intermediaries to produce chemical fine compounds. The bimetallic catalysts are widely used in the chemoselective hydrogenation. The Surface Organometallic Chemistry on Metals (SOMC/M) is a methodology employed to obtain bimetallic systems. In the present work the hydrogenation of ketones derived from acetophenone has been studied. The aim was observe the effect on activity and selectivity to aromatic alcohols by the presence of substituents in the ring. The chemical characteristics of substituents groups could influence the way aromatic ketones are absorbed on the metallic surface. This fact can be explained by a combination of geometric and electronic effects.

Full text of DOI:10.1016/j.apcata.2014.11.010

Accepted Manuscript
Title: Chemoselective hydrogenation of aromatic ketones with
Pt-based heterogeneous catalysts. Substituent effects
´
Author: Virginia Vetere Andrea B. Merlo Monica L. Casella
PII:
S0926-860X(14)00705-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2014.11.010
APCATA 15103
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Applied Catalysis A: General
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16-7-2014
5-11-2014
8-11-2014
Please cite this article as: V. Vetere, A.B. Merlo, M.L. Casella,
Chemoselective hydrogenation of aromatic ketones with Pt-based heterogeneous
catalysts. Substituent effects, Applied Catalysis A, General (2014),
http://dx.doi.org/10.1016/j.apcata.2014.11.010
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Chemoselective hydrogenation of aromatic ketones with Pt-based heterogeneous
catalysts. Substituent effects.
Virginia Veterea, Andrea B. Merloa,*, Mónica L. Casellaa.
aCentro de Investigación y Desarrollo en Ciencias Aplicadas “Dr. Jorge J. Ronco”
(CINDECA-CCT La Plata-CONICET-UNLP) Calle 47 Nº 257, La Plata, 1900
(Argentina). (54) 221 4254277 int. 146.
*Corresponding author: andreamerlo@quimica.unlp.edu.ar.
Keywords: aromatic ketones, bimetallic catalysts, PtSn, Surface Organometallic
Chemistry of Metals.
Highlights
PtSn catalysts were obtained by a surface reaction between Pt and SnBu4.
PtSn systems have been active in the hydrogenation of aromatic ketones.
The substituents groups could influence in the adsorption mode of aromatic ketones.
PtSn catalysts lead to an increase in the selectivity to unsatured alcohol.
Sn presence favors the interaction through C=O, hindering the adsorption of ring.
ABSTRACT
Page 1 of 33

Catalytic reduction of aromatic ketones is an interesting reaction that leads to the
obtaining of alcohols. Some of these alcohols are employed as intermediaries to produce
chemical fine compounds. The bimetallic catalysts are widely used in the
chemoselective hydrogenation. The Surface Organometallic Chemistry on Metals
(SOMC/M) is a methodology employed to obtain bimetallic systems.
In the present work the hydrogenation of ketones derived from acetophenone has
been studied. The aim was observe the effect on activity and selectivity to aromatic
alcohols by the presence of substituents in the ring. The chemical characteristics of
substituents groups could influence the way aromatic ketones are absorbed on the
metallic surface. This fact can be explained by a combination of geometric and
electronic effects.
1. INTRODUCTION
The catalytic reduction of aromatic ketones is a reaction of considerable interest,
since it leads to the production of alcohols used as intermediates in organic synthesis, in
the manufacture of pharmaceuticals, flavors, and others. The hydrogenation of 1-
phenyl-ethanone (acetophenone) to its corresponding alcohol (1-phenyl ethanol)
obtained by reduction of carbonyl group is a classic example of these reactions [1, 2].
However, the selective hydrogenation of aromatic ketones is not easy due to the variety
of products that can be obtained, both for the hydrogenation of C=O group and/or the
aromatic ring as well as for the hydrogenolysis of alcohols generated in the first reaction
step.
In general, reduction of unsaturated carbonyl compounds is usually carried out using
supported metal catalysts. Monometallic systems including Pd, Pt, Rh, Ag, Ni and Ru
have been employed in acetophenone hydrogenation [3, 4]. Rh-based catalysts,
supported over C, allowed to obtain a selectivity to unsaturated alcohol in about 70 %,
using moderate pressure [5]. Acetophenone hydrogenation over Ni/SiO2 and Ni/Y
catalysts resulted in high selectivity to phenylethanol (about 70 %). However, in some
of them the conversion was less to 10 % [1].
Pt is one of the most employed metals in the hydrogenation of carbonyl and phenyl
groups. Thereby, Chen et al. have been used Pt/SiO2 catalyst like a model to study
acetophenone hydrogenation. These authors have been studied the adsorbed species on
Pt reduced by IR spectroscopy [4]. As will be discussed later, competitive
Page 2 of 33

hydrogenation between the carbonyl and phenyl groups, and therefore the reaction
selectivity, depends of adsorption mode of acetophenone molecule on metallic surface.
It is well known that the use of bimetallic systems may be advantageous to achieve
higher activity, stability and/or selectivity to the desired product [3, 6]. Bimetallic
catalysts such as Ru-Cr, Rh-Sn and Ni-Pt have been employed in the hydrogenation of
acetophenone in liquid fase [3]. In the last case, bimetallic system produced an increase
in the stability; however the selectivity to unsaturated alcohol is lower than achieved
with monometallic catalyst [7].
There are different strategies for obtaining bimetallic systems [8]. One of the
methodologies derived from Organometallic Surface Chemistry on Metals (SOMC/M).
These techniques allow to prepare controlled catalytic phases, by reaction of a
supported transition metal with an organometallic compound as M'Rn (M' = Sn, Pb, Ge,
Sb; R = Me, Et, Bu, etc.; n = 3, 4). These interactions lead to catalytic systems with
good properties which have better activity and selectivity than the catalysts prepared by
conventional methods [9].
In our research group, we have vast experience in the preparation of bimetallic
catalysts based on Pt, Rh and Ni modified SnBu4 using n-heptane or n-decane as a
solvent. These systems proved to be active and selective in a wide range of
hydrogenation reactions of interest in fine chemistry [10-12].
The hydrogenation of ketones derived from acetophenone has been much less
studied. It has been reported in the literature the hydrogenation of p-
hydroxyacetophenone, o-methylacetophenone and 2-methylpropyl-acetophenone on Ni-
based catalysts, however very low conversions have been achieved [1]. There are a few
works about the influence of substituents of aromatic ring on activity and selectivity,
but they study primarily enantioselective hydrogenations [13].
In this paper, we propose to study the hydrogenation of 1-(phenyl) ethanone (AP), 1-
(4-metoxyphenyl) ethanone (4-MeOAP), 1-(4-chlorophenyl) ethanone (4-ClAP) and 1-
(2-metylphenyl) ethanone (2-MeAP) using PtSn and Pt catalysts supported on silica.
The objective is to analyze the influence of the chemical nature of the substituents
groups on the aromatic ketones ring, as has been reported in literature that these groups
can influence the selectivity and/or catalytic activity [14].
2. EXPERIMENTAL
Page 3 of 33

2.1 Preparation of the catalysts
The Pt/SiO2 monometallic catalyst was prepared by ionic exchange. The SiO2
(Evonik, 180 m2/g) used as support was previously functionalized by treating it with an
ammonia solution of pH 10.6, under continuous stirring for 30 minutes at room
temperature. The resulting solid was contacted with an aqueous solution of the
precursor, Pt(NH3)4Cl2 (Aldrich), which has the appropriate concentration to obtain
1wt.% of Pt in the final catalyst. After 24 h of exchange, the solid was separated by
filtration, dried in an oven at 105 °C, calcined in air at 500 °C and subsequently reduced
in H2 at 500 °C for 2 h. The catalyst so obtained was designated Pt.
For obtaining the bimetallic PtSn systems, techniques derived from Surface
Organometallic Chemistry of Metals (SOMC/M) were used. These techniques consist of
a controlled surface reaction between a reduced monometallic catalyst (Pt) and a
solution of an organometallic compound (SnBu4) in a paraffinic solvent. In this work,
bimetallic systems with Sn/Pt atomic ratios 0.2 and 0.8 were prepared; those systems
have been designated PtSn0.2 and PtSn0.8, respectively. The reaction between the
monometallic catalyst and the organotin compound solution was carried out under a H2
atmosphere for 4 h. The temperature used for the reaction was 90 and 120 °C for the
preparation of the PtSn0.2 and PtSn0.8 systems, respectively. In the first case, n-heptane
was used as solvent while for the catalyst with the highest tin content, n-decane was
employed. The bimetallic systems obtained were then washed with n-heptane in flowing
N2, dried in an oven at 105 °C and finally reduced at 500 °C in H2 flow for 2 h.
2.2 Catalysts characterization
The Pt content of the catalysts was determined by atomic absorption spectrometry
(Varian Spectra AA55). The amount of Sn present in the catalysts was measured by gas
chromatography analysis of the solution containing the organometallic compound, as a
function of reaction time, using a Varian CP-3800 gas chromatograph, equipped with a
FID detector and a Factor Four (VF-1 ms, 15mx0.25mm ID DF = 0.25) capillary
column.
Temperature-programmed reduction (TPR) tests were performed on an instrument
built in the laboratory, equipped with a thermal conductivity detector, using a mixture
Page 4 of 33

having a composition of 5% H2 in N2 at a flow of 25 mL/min. The tests were conducted
from 20 to 850 °C with a heating rate of 10 °C/min. For the measurement of H2
adsorption the method of the static volumetric chemisorption at room temperature was
used, employing an instrument from Advanced Scientific Designs Inc., USA.
The particle size distribution of the solids was determined by transmission electron
microscopy (TEM) in a JEOL 100 CX microscope with a resolution of 6 Å and an
accelerating voltage of 100 kV. The samples were prepared by its suspension in
bidistilled water and subsequent dispersion in an ultrasonic bath.
Analysis by X-ray photoelectron spectroscopy (XPS) was performed on a multi-
technical system (SPECS) equipped with a dual Mg/Al X-ray source and a PHOIBOS
150 hemispherical analyzer operating in FAT (fixed analyzer transmission) mode.
Spectra were obtained with an energy flow of 30 eV, an Al-K X-ray source operating
at 100 W and 10 kV and at a pressure of the analysis chamber lower than 5x10-7 Pa.
Data processing was performed with the XPS Casa program (Casa Software Ltd., UK).
C1s signal that appears at 284.6 eV was used as reference.
2.3 Hydrogenation of aromatic ketones
The ketones chosen for the present study were 1-(phenyl) ethanone (AP), 1-(4-
metoxyphenyl) ethanone (4-MeOAP), 1-(4-chlorophenyl) ethanone (4-ClAP) and 1-(2-
metylphenyl) ethanone (2-MeAP). Hydrogenation reactions of the aromatic ketones
were conducted in a batch reactor at 80 °C and a H2 pressure of 1 MPa. In each catalytic
test, 0.25 g of catalyst, a substrate concentration of 0.07 M and 2-propanol as solvent
were used. The progress of the reaction was followed by gas chromatography on a
Varian CP-3800 gas chromatograph equipped with a CP wax 52 CB (30 m, 0.53 mm
ID) capillary column and a FID detector. The products were identified by GC/MS on a
Shimadzu QP5050 instrument with a SUPELCO SPBTM-5 (30 m, 0.25 mm ID)
capillary column.
3. RESULTS AND DISCUSSION
3.1 Results of catalysts characterization.
Page 5 of 33

The catalysts Pt and PtSn/SiO2 were characterized by atomic absorption, CO and H2
chemisorption, temperature-programmed reduction and transmission electron
microscopy. The results are shown in Table 1.
For monometallic catalysts preparation, the impregnation method by cation exchange
was selected. This method allow to obtain reproducible systems with high dispersions
(H/Pt = 0.65, CO/Pt = 0.55). This last feature is very important for obtaining bimetallic
catalysts from controlled surface reactions.
The TPR assays results obtained for Pt catalyst system evidenced the presence of two
peaks: one at about 250 ºC and another at 450 ºC. According to the literature, the low
temperature peak can be assigned to the presence of Pt(IV) species, originated during
the calcination pretreatment. The high temperature peak could be assigned to species of
n-y
the type Pt-(O-Si≡)y (n = 2+ or 4+), formed through the interaction of metallic
precursor and the support [15].
The systems PtSn were prepared by a controlled surface reaction between the
monometallic catalyst, previously reduced, and a solution of SnBu4 in a paraffinic
solvent. The reaction occurs in two stages. In the first, a system with organotin moieties
anchored to the surface is obtained. In the second stage, at highest temperature, the
organic fragments are eliminated and a bimetallic system is formed. The following
equations represent the above-mentioned processes:
Pt/SiO2 + ySnBu4 + xy/2H2 → Pt(SnBu4-x)y/SiO2 + xyBuH
(1)
Pt(SnBu4-x)/SiO2 + (4-x)y/2H2 → PtSny/SiO2 + (4-x)yBuH
(2)
In the present work, catalysts with atomic ratios Sn/Pt of 0.2 and 0.8 were
prepared. Regarding the first atomic ratio, n-heptane was used as solvent and the
reaction proceeded at 90 ºC. As regards the catalyst with higher tin content, n-decane
was used as solvent and 120 ºC as reaction temperature. The stoichiometry of the
bimetallic catalyst was determined by chromatographic analysis, from the difference
between the initial concentration of the organometallic solution and the concentration
after four reactions hours [16].
Blank tests performed on the support demonstrated the specificity of the
reactions which take place during the preparation of bimetallic catalysts through
SOMC/M techniques, concluding that amounts of organotin modifier on SiO2 were not
detected.
Page 6 of 33

TEM results for the three catalysts prepared are shown in Table 1. As can be
seen, in all cases the mean particle size is about 2 nm. This value remains almost
constant for the bimetallic catalysts, indicating that the addition of tin does not
practically affect the particle size distribution with respect to the monometallic system.
These results, consistent with other preliminary work, show the high specificity of the
preparation method of bimetallic catalysts (SOMC/M). In the same way, tin addition
decreases the value of chemisorbed H2 (Table 1).
In Table 2 it is reported the binding energies (BE) of the Pt 4f7/2 and Sn 3d5/2
levels for Pt/SiO2, PtSn0.2 and PtSn0.8 catalysts. For all the catalysts, the region
corresponding to Pt 4f7/2 showed a single peak, which is characteristic of platinum in the
metallic state [17]. It can also be seen that the BE undergoes a shift from 71.6 eV for the
monometallic catalyst to 71.1 and 70.8 eV for PtSn0.2 and PtSn0.8 systems,
respectively. The increase in the electronic density of platinum leads to the formation of
polarized states of Ptδ− and Snδ+, which would be important in the chemisorption of
reagents containing double C=O. This fact is indicative of the existence of an electronic
effect of tin over platinum, in agreement with previous results obtained in studies
performed with PtSn catalysts supported, prepared by SOMC/M techniques [18, 19].
The Sn 3d5/2 spectra for the bimetallics PtSn0.2 and PtSn0.8 present two bands, one
centered at ca. 484 eV which can be ascribed to reduced tin, and another one at higher
BE (486.3 and 487.3 eV for PtSn0.2 and PtSn0.8, respectively), which is attributed to
oxidized tin (Sn(II) and Sn(IV)) [17, 20]. On the other hand, both bimetallic samples
have similar Sn(0)/Sntotal ratio (Table 2); the Sn(0)/Pt ratio increases when the amount
of tin increases [16]. The presence of metallic tin in bimetallic catalysts is indicative of
the existence of bimetallic PtSn phases (even alloys); as it has been readily assessed by
EXAFS analysis performed on analogous systems as the ones here employed [18]. Tin
oxidized species may be covering the metal particles in the metal-support interface.
3.2 Hydrogenation reaction
Figure 1 shows the main products from the hydrogenation of 1-(phenyl)
ethanone (AP) and its derivatives. As can be seen, the hydrogenation of the C=O leads
to the production of the corresponding aromatic alcohols, which are usually the desired
product. Furthermore, if the aromatic ring is reduced, saturated ketones are produced.
Finally, the saturated alcohols are obtained by the hydrogenation of either of the
Page 7 of 33

products above. Other possible reaction products are ethyl benzene and ethyl
cyclohexane, and their substituted derivatives.
The objective of this paper is to analyze the influence of the presence of
substituents on the aromatic ring on the activity and selectivity achieved. For this
reason, AP derivatives with substituents in different ring positions and/or electronic
properties have been selected. Both effects would have influence at the adsorption mode
on the metal surface. In this way, the results obtained can be explained from a balance
between steric and electronic effects, result of presence of substituent on the aromatic
ring.
The ketones selected for this work are AP, 2-MeAP, 4-MeOAP and 4-ClAP. As
can be seen, the substituents of two of the ketones are in para- position and therefore far
from the C=O group, whereas in the 2-MeAP the substituent is located very close to this
group. As for the electrical characteristics, –CH3 (-Me) and –OCH3 (-OMe) groups are
electron donors, while the –Cl group is an electron acceptor. Both effects would have
influence at the adsorption mode on the catalyst surface.
It is important to emphasize that, in all the cases mentioned in this work, the
reaction is initiated by the hydrogenation of the C=O group. The change of the reaction
mixture composition as a function of time for the hydrogenation of AP, 2-MeAP, 4-
MeOAP and 4-ClAP is shown in Figure 2, 3, 4 and 5, respectively. As can be seen, both
the monometallic catalyst systems as well as PtSn initially formed 1-(phenyl) ethanol
and its corresponding derivatives. As will be discussed further below, the figures show
that the presence of tin produces changes in the activity and selectivity obtained.
In Table 3, the initial reaction rate and selectivity to the desired products (to 50%
conversion), for the aromatic ketones and the catalysts studied, are reported. The
different ways that the ketone molecules can approach the metal surface could explain
the results. According to reported by Chen et al, there are two preferential modes of
adsorption of AP molecule on Pt surface [4]. One of them considers that the molecule of
1-(phenyl) ethanone approaches to the metal surface through the oxygen of the C=O
group (Figure 6a) and the aromatic ring, which is parallel to it, is susceptible to attack
dissociated hydrogen on metal. The other mode of adsorption contemplates that the
carbonyl group interacts with Pt via π electrons and the aromatic ring is tilted with
respect to the metal surface (Figure 7a).
In accordance with what was stated in the previous paragraph, for the
monometallic catalyst, it is expected that the presence of electron donor groups (-CH3
Page 8 of 33

and -OCH3) (Figure 6b and 6c) increase the electronic repulsion between the ring and
the metal surface and both favor the hydrogenation of the carbonyl group, compared
with the AP. The selectivity results reported in Table 3 for the catalyst based on Pt
shows one consequences of this. For 2-MeAP y 4-MeOAP the aromatic alcohol
selectivity is superior to that achieved for the same AP conversion (74, 75 and 63%,
respectively, at 50% conversion). On the other hand, it is expected that the electronic
effect of substituents electron donors causes an increase in the initial reaction rate to
AP, considering that we have observed that the hydrogenation starts by the attack to the
C=O. In this way, in Table 3 can also be seen that the initial rate of hydrogenation for 4-
MeOAP is higher than for AP. However, it is observed for the 2-MeAP a decrease in
the initial activity respect to unsubstituted ketone. In Figure 7b it can be seen that the
methyl group in ortho- position exerts a steric impediment, which could be responsible
for the decrease in the observed rate for this substrate. This geometric impediment
would have less significance in the case of the substituents in the para- position, furthest
from C=O (Figure 7c and 7d).
For the 4-ClAP, the molecule has an electron attractor group (-Cl) to favor the
adsorption by the aromatic ring (Figure 6d). In Table 3 can be seen that this fact affects
both the activity and selectivity to the desired product. Thus, the initial reaction rate is
less than half that achieved for AP (69 and 156 μmoles.gPtsup-1.s-1, respectively).
Regarding to target product selectivity, the observed value was lower than the
corresponding unsubstituted ketone (55 and 63%, respectively, 50% conversion).
As is known, the addition of a more electropositive metal on the Pt leads to
geometric and electronic modifications that affect the activity and selectivity of the
catalyst system. On the one hand, the blocking of active sites for hydrogenation can lead
to decrease the reaction rate. Furthermore, the presence of electrophilic tin favor
polarization of C=O group and hence the reduction [3]. Moreover, in our case, the
geometric effect could difficult the ring adsorption of the aromatic ketones and modify
the selectivity and the initial rate of hydrogenation.
As seen in Table 3, selectivity to corresponding unsaturated alcohols increases
with the presence of tin for all tested ketones. Moreover it should be noted that the
selectivity is higher for the catalyst with higher atomic ratio Sn/Pt (PtSn0.8). This could
be attributed to the combination of the mentioned effects above: the C=O polarization
by electronic effects and/or impediment of adsorption through the ring, by blocking
active sites. It is also important to highlight that the most pronounced effect is evident
Page 9 of 33

for the hydrogenation of 4-ClAP. In this case, the presence of -Cl (electron-acceptor
group) promotes the ring adsorption on the monometallic catalyst surface. Blocking of
active sites by the presence of Sn prevents this adsorption mode, leading to a marked
increase in selectivity respect to monometallic system.
In Table 3, the initial rates for the catalysts PtSn are also reported. As can be
seen in this Table, for AP, 2-MeAP and 4-MeOAP, the rate decreases as the Sn content
increases, due to the blocking of active sites for hydrogenation. However, as shown in
the Table, for 4-ClAP is observed a marked increase in the initial reduction rate. To
explain this result we must remember that initially (less than 10 % of conversion) the
only product formed comes from the hydrogenation of C=O. As has already been
mentioned, the initial reaction rate for 4-ClAP is about half of the AP, on the
monometallic catalyst. This fact can be attributed to the better attraction of the
substituted aromatic ring on the metal surface. As some sites are blocked by the Sn, it
would be harder to approach to the ring, favouring the hydrogenation of the carbonyl
group and, therefore, increasing the initial speed (Figure 7d).
As a summary, in Table 4 can be seen the relationship between initial rate of
hydrogenation of 1-(phenyl) ethanone and initial rates of substituted ketones. It can be
observed, that in the presence of Sn the rate ratios for different ketones keep the
tendency observed for Pt, but the relative rates approach each other with the Sn content
increase. As noted above, these results might be due to a combination of steric and
electronic effects, as a result of ring substituents.
4. CONCLUSIONS
The main conclusions that can be derived from this study are summarized
below:
In the hydrogenation of 2-MeAP and 4-MeOAP, employing Pt/SiO2 system, it
was observed an increment in the selectivity to aromatic alcohol in relation to the one
obtained for AP (74, 75 and 63%, respectively, at 50% of conversion). The initial rate
for the hydrogenation of 4-MeOAP was higher than the one achieved for AP, whereas
for 2-MeAP it was observed a decrease in the initial activity with respect to the non-
substituted ketone.
The activity and selectivity to desired product in the hydrogenation of 4-ClAP
were lower than those obtained for AP.
Page 10 of 33

When Pt-based catalysts modified with SnBu4 were employed for the
hydrogenation of aromatic ketones, it was observed an increase in the selectivity to
unsatured alcohol. This fact can be explained from geometric an electronic effects due
to the presence of Sn. These effects encourage the interaction through C=O, hindering
the adsorption of aromatic ring.
Finally, it was observed that the rate decreases with the Sn content for the
hydrogenation of AP, 2-MeAP y 4-MeOAP. This can be understood through blockage
of the active sites for the hydrogenation. For 4-ClAP it was seen a marked increase of
the initial reduction rate. In this case, the Sn presence could hinder the ring adsorption,
encouraging the carbonyl group hydrogenation and therefore increasing the initial rate.
5. ACKNOWLEDGEMENTS
This work was supported by Consejo Nacional de Investigaciones Científicas y
Técnicas (CONICET) (PIP 0185) and Universidad Nacional de La Plata (Project X633).
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Figure Captions
Figure 1. Main products from the hydrogenation of acetophenone and its derivatives.
Figure 2. Concentration profiles (mol%) as a function of time for the hydrogenation of
AP (a) Pt; (b) PtSn0.2 and (c) PtSn0.8. (■) 1-(phenyl) ethanone, (♦)1-(cyclohexyl)
ethanone, (▲)1-(cyclohexyl) ethanol, (●) 1-(phenyl) ethanol, () 1-(ethyl) benzene, ()
1-(ethyl) cyclohexane
Figure 3. Concentration profiles (mol%) as a function of time for the hydrogenation of
2-MeAP (a) Pt; (b) PtSn0.2 and (c) PtSn0.8. (■) 1-(2-methylphenyl) ethanone, (♦) 1-(2-
methylcyclohexyl) ethanone, (▲) 1-(2-methylcyclohexyl) ethanol, (●) 1-(2-
methylphenyl) ethanol.
Figure 4. Concentration profiles (mol%) as a function of time for the hydrogenation of
4-MeOAP (a) Pt; (b) PtSn0.2 and (c) PtSn0.8. (■) 1-(4-methoxyphenyl) ethanone, (♦) 1-
(4-methoxycyclohexyl) ethanone, (▲) 1-(4-methoxycyclohexyl) ethanol, (●) 1-(4-
methoxyphenyl) ethanol, () 1-(4-methoxy)-ethyl benzene, () 4-ethenylcyclohexyl
methyl ether.
Figure 5. Concentration profiles (mol%) as a function of time for the hydrogenation of
4-ClAP (a) Pt; (b) PtSn0.2 and (c) PtSn0.8. (■) 1-(4-chlorophenyl) ethanone, (▲)1-(4-
chlorocyclohexyl) ethanol, (♦) 1-(4-chlorocyclohexyl) ethanone, (●)1-(4-chlorophenyl)
ethanol.
Figure 6. Adsorption mode of aromatic ketones through the oxygen of the C=O group.
(a) AP; (b) 2-MeAP; (c) 4-MeOAP; (d) 4-ClAP.
Figure 7. Mode of adsorption contemplates with C=O interacts with Pt via π electrons.
(a) AP; (b) 2-MeAP; (c) 4-MeOAP; (d) 4-ClAP.
Page 13 of 33

Table 1. Catalysts characterization.
Catalyst
Pt
Sn/Pt
-
H/Pt
0.65
0.25
0.20
Pt/CO
0.55
dTEM (nm)
2.2
2.2
2.1
PtSn0.2
0.2
0.8
n.d.
PtSn0.8
0.25
n.d. not determined
Page 14 of 33

Table 2. XPS testing result for Pt and PtSn catalysts.
Catalyst
Binding Energy (eV)
Sntotal/Pt Sn(0)/Sntotal%
Pt 4f7/2
71.6
Sn0 3d5/2
Snn+ 3d5/2
Pt
-
-
-
-
PtSn0.2
PtSn0.8
71.1
484.1
484.2
486.3
487.3
0.20
0.79
55
59
70.8
Page 15 of 33

Table 3. Hydrogenation of the aromatic ketones results at 80 °C, a H2 pressure of 1
MPa and 50% of conversion.
Entry
a
Sustrate
Product
Catalyst Selectivity %
ri*
156
162
125
102
92
O
OH
Pt
63
71
84
74
86
96
75
84
90
55
96
98
1
PtSn0.2
PtSn0.8
Pt
b
c
a
O
OH
PtSn0.2
PtSn0.8
Pt
2
3
4
b
c
86
O
OH
215
187
143
69
90
94
a
b
c
a
b
c
PtSn0.2
PtSn0.8
Pt
MeO
MeO
O
OH
PtSn0.2
PtSn0.8
Cl
Cl
*ri: initial rate (mol g-1
s )
-1
Ptsup
Page 16 of 33

Table 4. The initial relative rates riAP/riX of the substituted ketones for the study
catalytic systems.
Catalyst
Pt
ri AP/ri 2-MeAP
1.53
ri AP/ri 4-MeOAP
0.72
ri AP/ri 4-ClAP

2.26
PtSn0.2
PtSn0.8
1.76
0.87
1.80
1.45
0.87
1.33
Page 17 of 33

Adsorption modes of aromatic ketones on Pt surface.
Page 18 of 33

Figure 1
Page 19 of 33

Figure 2 a
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Figure 2 b
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Figure 2 c
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Figure 3 a
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Figure 3 b
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Figure 3 c
Page 25 of 33

Figure 4 a
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Figure 4 b
Page 27 of 33

Figure 4 c
Page 28 of 33

Figure 5 a
Page 29 of 33