Effect of solvent on the hydrogenation of 4-phenyl-2-butanone over Pt based catalysts

Article abstract of DOI:10.1016/j.jcat.2015.06.008

The hydrogenation of 4-phenyl-2-butanone over Pt/TiO₂ and Pt/SiO₂ catalysts has been performed in a range of solvents and it has been observed that the solvent impacted on the selectivity of ketone and aromatic ring hydrogenation as well as the overall TOF of the titania catalyst with no solvent effect on selectivity observed using the silica supported catalyst where ring hydrogenation was favored. For the titania catalyst, alkanes were found to favor ring hydrogenation whereas aromatics and alcohols led to carbonyl hydrogenation. A two-site catalyst model is proposed whereby the aromatic ring hydrogenation occurs over the metal sites while carbonyl hydrogenation is thought to occur predominantly at interfacial sites, with oxygen vacancies in the titania support activating the carbonyl. The effect of the solvent on the hydrogenation reaction over the titania catalyst was related to competition for the active sites between solvent and 4-phenyl-2-butanone.

Full text of DOI:10.1016/j.jcat.2015.06.008

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Journal of Catalysis 330 (2015) 344–353
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Effect of solvent on the hydrogenation of 4-phenyl-2-butanone over Pt
based catalysts
a
a
b,c,
b
I. McManus a, H. Daly a, J.M. Thompson a, , E. Connor , C. Hardacre , S.K. Wilkinson
, N. Sedaie Bonab ,
⇑
⇑
J. ten Dam c, M.J.H. Simmons b, , E.H. Stitt c, C. D’Agostino d, J. McGregor d,1, L.F. Gladden d, , J.J. Delgado e
⇑
⇑
a School of Chemistry and Chemical Engineering, Queen’s University, Belfast BT9 5AG, UK
b School of Chemical Engineering, University of Birmingham, Birmingham B15 2TT, UK
c Johnson Matthey Technology Centre, P.O. Box 1, Belasis Avenue, Billingham TS23 1LB, UK
d Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, UK
e Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, E-11510 Puerto Real (Cádiz), Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The hydrogenation of 4-phenyl-2-butanone over Pt/TiO2 and Pt/SiO2 catalysts has been performed in a
range of solvents and it has been observed that the solvent impacted on the selectivity of ketone and aro-
matic ring hydrogenation as well as the overall TOF of the titania catalyst with no solvent effect on selec-
tivity observed using the silica supported catalyst where ring hydrogenation was favored. For the titania
catalyst, alkanes were found to favor ring hydrogenation whereas aromatics and alcohols led to carbonyl
hydrogenation. A two-site catalyst model is proposed whereby the aromatic ring hydrogenation occurs
over the metal sites while carbonyl hydrogenation is thought to occur predominantly at interfacial sites,
with oxygen vacancies in the titania support activating the carbonyl. The effect of the solvent on the
hydrogenation reaction over the titania catalyst was related to competition for the active sites between
solvent and 4-phenyl-2-butanone.
Received 20 April 2015
Revised 2 June 2015
Accepted 3 June 2015
Keywords:
Selective hydrogenation
Solvent effect
Aromatic ketone
Pt
Ó 2015 Elsevier Inc. All rights reserved.
Titania
1. Introduction
The effect of the solvent on the rate and selectivity of molecules
containing various functional groups such as amides, aromatic
Hydrogenation reactions are commonly used in the pharmaceu-
tical, fine chemicals and agrochemicals industries for the prepara-
tion of a wide range of organic molecules [1]. It is recognised that
several different factors can affect the rate and selectivity of a hydro-
genation reaction, such as the catalyst used (metal and support) [2],
the addition of promoters [3], the choice of metal precursor [4] as
well as the solvent used. Even with the number of studies investigat-
ing the role of solvents in liquid phase hydrogenations, their
effect on the rate and importantly the selectivity of a reaction are
at present, difficult to predict for varied reagent/catalyst systems.
rings and carboxylic acids [5–8], have been reported; however,
the most widely investigated compounds are , b unsaturated car-
bonyls [2,9–13] with formation of unsaturated alcohols desired for
use in the manufacture of drugs and fragrances. The hydrogenation
of unsaturated and aromatic ketones are not as widely studied as
a
that of
a, b unsaturated aldehydes with studies predominantly
on conjugated systems such as cyclohexenone [14], ketoisophor-
one [15], benzalacetone [16–22], benzalacetophenone [23,24],
benzophenone [23,25,26] with the most widely studied being, ace-
tophenone [23,27–32].
For the hydrogenation of acetophenone, there have been studies
using a number of different metals including Pt, Pd, Rh and Ni with
the focus on the rate of hydrogenation of the carbonyl group rela-
tive to ring hydrogenation [33]. In cases where the selectivity was
investigated it was found that hydrogenation of the ketone to phe-
nylethanol tended to be more favored than ring hydrogenation,
both in the gas phase [34–36] and liquid phase [37]. However, with
the use of supports such as TiO2 [36], and promoters such as Cr [34]
the selectivity to phenylethanol could be increased to as high as
95% [35]. It is proposed that the increased hydrogenation of the
carbonyl bond over titania catalysts is from reaction occurring at
⇑
Corresponding authors at: School of Chemistry and Chemical Engineering,
Queen’s University, Belfast BT9 5AG, UK (J.M. Thompson), Johnson Matthey
Technology Centre, P.O. Box 1, Belasis Avenue, Billingham TS23 1LB, UK (S.K.
Wilkinson), School of Chemical Engineering, University of Birmingham, Birming-
ham B15 2TT, UK (M.J.H. Simmons), Department of Chemical Engineering and
Biotechnology, University of Cambridge, Cambridge CB2 3RA, UK (L.F. Gladden).
E-mail
sam.wilkinson@matthey.com
(M.J.H. Simmons), lfg1@cam.ac.uk (L.F. Gladden).
addresses:
jillian.thompson@qub.ac.uk
(J.M.
Thompson),
(S.K. Wilkinson),
m.j.simmons@bham.ac.uk
1
Present address: Department of Chemical and Biological Engineering, The
University of Sheffield, Sheffield S1 3JD, UK.
http://dx.doi.org/10.1016/j.jcat.2015.06.008
0021-9517/Ó 2015 Elsevier Inc. All rights reserved.

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I. McManus et al. / Journal of Catalysis 330 (2015) 344–353
345
the metal support interface where the oxygen in the carbonyl
interacts with oxygen vacancies in the support to weaken the
C@O bond thereby increasing the rate of reaction [38,39].
going from methanol to tert-butanol. No clear trend in selectivity
with the property of the solvents was observed in this study.
Hydrogenation of phenylacetone was also carried out in
tert-butanol over Pt, Ru, Ir, Os, Rh and Pd supported on carbon
[41]. Low reaction rates were observed over the Pd catalyst with
the fastest rates observed over the Rh catalyst with initial high
selectivity for cyclohexylacetone with C@O hydrogenation and
hydrogenolysis to minor products phenylpropane and cyclohexyl-
propane also observed. Over Pt, Ru, Os and Ir, hydrogenation of the
C@O group resulted in the major product. Some ring hydrogena-
tion was observed over Pt (selectivity of 15% ring hydrogenation
to 85% C@O hydrogenation at 15% conversion) and Ru while only
phenylisopropanol was observed over Os and Ir with no further
hydrogenation found to occur.
In this study, for the first time, the effect of solvent
on the liquid phase hydrogenation of aromatic ketone
4-phenyl-2-butanone, (PBN), over Pt/TiO2 and Pt/SiO2 catalysts,
to 4-phenyl-2-butanol, (PBL), 4-cyclohexyl-2-butanone, (CBN),
and 4-cyclohexyl-2-butanol, (CBL), Scheme 1 is investigated. The
role of the solvent on the rate of hydrogenation of this molecule
containing both a ketone functionality and an aromatic ring is
reported. In addition, a switch in the selectivity between hydro-
genation of the aromatic ring and the carbonyl with class of solvent
has been found for platinum supported on titania catalyst.
Interestingly, a complete switch in selectivity with solvent has
been reported for the hydrogenation of acetophenone over Pd car-
bon nanofibre catalysts for reactions performed in water and cyclo-
hexane [29]. In water, over the Pd catalyst, ring hydrogenation
products cyclohexylethanone and cyclohexylethanol were the
major products with carbonyl group hydrogenation to phenyletha-
nol and further hydrogenolysis of the alcohol to ethylbenzene
being the other products identified. High selectivity to aromatic
ring hydrogenation products was also observed over the Rh cata-
lyst for reaction in water (95.4% compared with 65% for Pd).
However, when the hydrogenation of acetophenone was carried
out in cyclohexane under the same reaction conditions, 100% selec-
tivity to C@O hydrogenation (and hydrogenolysis products) was
reported over Pd/CNF. High selectivity to ring hydrogenation in
water was attributed to favorable orientation of the aromatic ring
on the metal surface brought about by solvation of the polar func-
tional group and orientation of the ring due to the local structure of
water in the proximity of the surface [29].
An effect of solvent on selectivity has also been reported for the
hydrogenation of ketoisophorone, investigated by von Arx et al.,
where only the rate of reaction over Pt/Al2O3 was found to be influ-
enced by solvent while for Pd/Al2O3 the solvent also affected the
selectivity [15]. Reactions were carried out in n-hexane, tetrahy-
drofuran, methanol, acetic acid and methanol/acetic acid mixtures.
For the Pd/Al2O3 catalyst, the polarity of the solvent was found to
have a dramatic influence on the reaction rate with reactions in
n-hexane and tetrahydrofuran giving the lowest rates as well as
lower selectivity to the unsaturated alcohol while the highest rates
and selectivities (90% to the unsaturated alcohol) were observed in
mixtures of methanol and acetic acid. The increased rate of car-
bonyl hydrogenation was reported to be due to protonation of
the carbonyl group by the acid, promoting its hydrogenation
over that of the alkene functionality [15]. The Pt/Al2O3 catalyst,
however, showed little change in selectivity with solvent polarity
with C@C and C@O hydrogenation to levodione and
2. Experimental
2.1. Materials
Hydrogen was supplied by BOC and was of research grade.
4-Phenyl-2-butanone (98%) and 4-phenyl-2-butanol (97%) were
acquired from Sigma–Aldrich. Unless otherwise stated, all the sol-
vents used were obtained from Sigma–Aldrich and were of HPLC
grade. The exceptions were: 2-propanol (Fluka 6 99.9%), trifluo-
roethanol (Fluorochem 99%), dichloroethane (Riedel De Haën
99%) and p-xylene (Fluka P 98%). When required, toluene, n-hex-
ane and all alcohol solvents were dried over calcium hydride over-
night and distilled. The water content of the solvents was
measured using Karl-Fischer analysis with a Cou-Lo aqua-max
moisture analyser.
4-hydroxyisophorone respectively occurring in
a 1:1 ratio.
Ketoisophorone is a cyclic ketone; however, application of the
same conditions to linear ketones, such as 5-hexane-2-one, found
that only saturated ketones were obtained.
The reaction intermediates 4-cyclohexyl-2-butanol and 4-
cyclohexyl-2-butanone were prepared in house. 4-Cyclohexyl-
2-butanol was synthesized by the hydrogenation of
For compounds where the C@O and the aromatic ring are not
adjacent to each other, the selectivity could be expected to differ
significantly from that of conjugated compounds. Conjugation
can influence the strength and mode of adsorption of a reactant,
activating functionalities for hydrogenation. Whether the C@O, ali-
phatic ketone part of the molecule or the aromatic ring is preferen-
tially adsorbed will depend on factors such as the strength of
adsorption of both functionalities relative to that of the products
and the interaction of these parts of the molecule with the solvent.
The choice of catalyst (metal and support) as well as the solvent
used for reaction will also have a strong influence on the adsorp-
tion strength and geometry making the choice of solvent/catalyst
for a particular selective transformation difficult to predict. There
are fewer studies reporting the hydrogenation of molecules where
the aromatic and carbonyl functionalities are separated/distal
within the molecule such as phenylacetone [40,41] and a range
of aromatic ketones including 4-phenyl-2-butanone [42].
The role of solvent was probed in the hydrogenation of pheny-
lacetone by Rylander et al. over Rh/C and Rh/Al2O3 catalysts [41].
Reactions were carried out in methanol, ethanol, 2-propanol,
tert-butanol, dioxane, acetone, ethyl acetate, dimethylformamide,
dimethylsulfoxide and cyclohexane and while ring hydrogenation
was always the major product, for the alcohols, the extent of ring
hydrogenation increased while C@O hydrogenation decreased on
4-phenyl-2-butanol in
(pre-reduced at 60 °C for 1 h, 1 bar H2) at 5 bar H2, 70 °C with
1400 rpm stirrer speed in n-hexane for 12 h.
a
Parr reactor using 4% Pt/TiO2
4-Cyclohexyl-2-butanone was prepared by oxidation (6 bar air in
a Parr reactor) of the 4-cyclohexyl-2-butanol using 4% Pt/TiO2 at
100 °C for 28 h. In each case, at the end of the reaction, the reaction
mixture was filtered and the solvent removed under vacuum giv-
ing the desired product at 99% purity determined by 1H NMR and
GC. The intermediates were used without any further purification.
2.2. Catalyst preparation
The 4% Pt/TiO2 catalyst was supplied by Johnson Matthey and
was prepared by incipient wetness from Pt(NO3)4 as the precursor
with titania as the support (P25, Degussa). The catalyst was dried
for 12 h at 120 °C and then calcined at 500 °C for 6 h. The catalyst
was ground using a mortar and pestle and sieved to 645 lm for all
reactions with the exception of the mass transfer studies where the
catalyst was sieved into various fractions (300–212, 212–150, 150–
106 and <45
Matthey. This catalyst was also ground using a mortar and pestle
and sieved to 645 m for all reactions.
lm). The 5% Pt/SiO2 catalyst was supplied by Johnson
l

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346
I. McManus et al. / Journal of Catalysis 330 (2015) 344–353
ratio. The samples were analyzed using a Perkin–Elmer Clarus
500 GC equipped with a FID with an Agilent HP-5 column.
The composition of the reaction mixture was determined by
comparison of the GC peak areas with those of known concentra-
tion and the percent of each component quoted relative to the total
molar concentration.
The rates were calculated by fitting a polynomial function
to the concentration change with time and taking the differential
of the curve at t = 0. Unless otherwise stated, the selectivities
are associated with the selectivity to 4-cyclohexyl-2-butanone
at 15% conversion. In all cases, the selectivities were
determined by:
Scheme 1. Hydrogenation pathway of 4-phenyl-2-butanone (PBN) to 4-phenyl-2-
butanol (PBL), 4-cyclohexyl-2-butanone (CBN) and 4-cyclohexyl-2-butanol (CBL).
Solid arrows indicate aromatic ring hydrogenation and dashed arrows indicate C@O
group hydrogenation.
moles of product A
sum of moles of all products
%S ¼
ꢀ 100
3. Results
2.3. Catalyst characterization
3.1. Catalyst characterisation
X-ray diffraction measurements were performed using Cu K
a
radiation (1.5405 Å) on a PANalytical X’PERT PRO MPD diffrac-
tometer in reflection geometry using a NaI scintillation counter, a
curved graphite crystal monochromator and a nickel filter. The
scattered intensities were collected from 5° to 80° (2h) by scanning
at 0.017° (2h) steps with a counting time of 0.5 s at each step.
The surface area, pore volume and average pore diameter were
measured by N2 adsorption–desorption isotherms at 77 K using
Micromeritics ASAP 2010. The pore size was calculated in the
adsorption branch of the isotherms using Barrett–Joyner–Helend
a (BJH) method and the surface area was calculated using the Bru
nauer–Emmett–Teller (BET) method.
Scanning Transmission Electron Microscopy (STEM) images
were recorded on a 200 kV JEOL JEM-2010F instrument using a
high-angle annular dark-field (HAADF) detector and an electron
beam probe of 0.5 nm. The particle size distribution was obtained
by counting up to 1000 particles and considering a cubooctaedal
morphology.
The BET surface area of the 4% Pt/TiO2 (P25) catalyst was
56 m2 gꢁ1 compared with 58 m2 gꢁ1 for the support with pore sizes
of 2.2 and 2.5 nm, respectively. XRD analysis of the support shows
an anatase to rutile ratio of 3:1, which remains constant after cat-
alyst preparation. Pt peaks could not be observed in the XRD pat-
tern obtained (Fig. S1), which suggests that the Pt particles are
very small. TEM analysis showed a metal particle size of 2.2 nm
and a dispersion of 33% (Fig. S2).
The BET surface area of the Pt/SiO2 catalyst was 294 m2 gꢁ1 and
XRD analysis (Fig. S3) of the Pt peaks by the Scherrer equation gave
a particle size of 6.9 nm while particle diameter of 3.0 nm obtained
from the TEM with a dispersion of 26% (Fig. S4).
3.2. Mass transfer
To ensure that the rates of reaction obtained were comparable,
and under kinetic control rather than limited by transport of a
reagent, a mass transfer study of 4-phenyl-2-butanone hydrogena-
tion was performed in n-hexane, chosen because of its high rate of
reaction.
2.4. Typical reaction procedure
All of the reactions were performed in a Hazard Evaluation
Laboratory (HEL) autoclave pressure reactor with a gas inducing
impeller and baffles. The reactor was heated by an internal heating
coil and the temperature was monitored by a thermocouple in the
solution. Hydrogen was added by a mass flow controller through-
out the reaction, to maintain a constant pressure.
The stirrer speed was varied between 300 and 1400 rpm
(Fig. S5) and, although, the initial rate increased up to 800 rpm,
thereafter, no further increase was observed showing that at
1400 rpm, the stirrer speed used herein, the rate is not limited
by transport of gas into the liquid phase. A linear variation in the
initial rate of reaction with mass of catalyst (proportional to the
external surface area of the catalyst) over the range 20–140 mg,
was observed (Fig. S6) showing that external liquid to solid mass
transfer of neither the gas nor liquid phase reagent is a limiting fac-
tor. An Arrhenius plot was constructed between 5 °C and 80 °C
(Fig. S7) from which was calculated an apparent activation energy
of 40.4 kJ molꢁ, 1 which although near the boundary of possible diffu-
sional limitation, when considered along with the small particle size
used it is concluded that the reaction is not under diffusion control
and the observed rate is dominated by kinetic control. All experi-
Typically, the reactions were undertaken using the following
procedure. The catalyst (0.1 g) and solvent (30 ml) were added to
the HEL reactor. The reactor was then sealed and purged with
hydrogen before heating to 60 °C while stirring the mixture at
800 rpm. Upon reaching 60 °C the reactor was held at this temper-
ature and the mixture was stirred at 1000 rpm for 1 h to reduce the
catalyst. Following the reduction of the catalyst, a solution of
4-phenyl-2-butanone (13.5 mmoles) in fresh solvent (20 ml) was
added to the reactor containing the slurry of the pre-reduced cat-
alyst. The HEL reactor was sealed and purged with hydrogen and
the reactor was then heated to the reaction temperature, during
which the mixture was stirred at 800 rpm. When the required tem-
perature was reached (typically 70 °C) the stirring was stopped and
the reactor was pressurised. The reaction started immediately
upon reaching the required pressure (typically 5 bar) by starting
the stirrer at 1400 rpm. The reactions were typically performed
for 2 h, during which time regular reaction samples of about 2 ml
were taken for analysis by GC.
ments were carried out with a particle size fraction of <45 lm, to
maximise the external surface area of the catalyst and minimise
the diffusion path of the reagents in the catalyst particle. As the par-
ticles break up under stirring, the effect of particle size could not be
tested. Analysis of the catalyst particle size after stirring at
1400 rpm, showed a size of <45 lm, irrespective of the initial
particle size. Furthermore, no reaction was observed in the absence
of H2 (Fig. S8) and the reaction was found to be apparent first
order in hydrogen (Fig. S9) and apparent zero order in
4-phenyl-2-butanone under the concentrations used (Fig. S10).
The samples for GC were passed through a syringe filter to
remove the catalyst before being diluted with solvent in a 1:10

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347
3.3. Kinetic data
type depending on their chemical structure, alkanes and
chloroalkanes, aromatics, primary and secondary alcohols and
ethers.
Fig. 1 shows the rate of conversion of 4-phenyl-2-butanone for a
selection of the solvents tested with rates of reaction ranging from
0.0026 mol dmꢁ3 minꢁ1 for n-hexane (and 0.0027 mol dmꢁ3 minꢁ1
for 2-propanol) to 0.0007 mol dmꢁ3 minꢁ1 in toluene. The similar-
ity of the rates of reaction in n-hexane and 2-propanol clearly show
that the polarity of the solvent alone does not control the outcome
of the reaction. As shown in Fig. 1, the alkane solvent gave a similar
rate to that observed in the secondary alcohol studied. In contrast,
the reaction in the primary alcohol was found to be slower than
that in the secondary alcohol and lower rates still were found on
using the aromatic solvent with the exception of tert-butyl toluene
with the ether giving the lowest rate of those shown here.
3.3.1. Alkanes
A range of alkanes of different chain length both linear and cyc-
lic were tested including n-hexane, cyclohexane, n-decane and
1,2-dichloroethane and the initial rates and selectivities are sum-
marised in Figs. 3 and 4, respectively.
The reactions in all the standard alkanes studied led to similar
initial rates of reaction, ranging from 0.0024 mol dmꢁ3 minꢁ1 in
cyclohexane to 0.0028 mol dmꢁ3 minꢁ1 in decane. In comparison,
dichloroethane was found to give a much slower reaction, at
0.0018 mol dmꢁ3 minꢁ1, than found for the non-halogenated alka-
nes. 4-Cyclohexyl-2-butanone was the major product formed in all
the alkanes studied; however, the exact proportions of each of the
products did vary between solvents, with selectivity to this pro-
duct found to be 67% in n-hexane which increased to 81% in
n-decane. The reaction carried out in dichloroethane resulted in
the greatest amount of the fully hydrogenation product
4-cyclohexyl-2-butanol but 4-cyclohexyl-2-butanone was still
the major product in this solvent.
In the case of the alkane solvents, the high selectivity to
4-cyclohexyl-2-butanone is thought to be the result of the strong
adsorption of the aromatic ring in the molecule on the platinum
compared with the weaker adsorption of the alkane solvent. It
should be noted that hydrogenation of the aromatic ring was also
the preferred reaction pathway over a Pt/SiO2 catalyst which did
not show significant solvent variation in terms of selectivity.
Furthermore, a comparison of the hydrogenation of the reaction
intermediates 4-phenyl-2-butanol and 4-cyclohexyl-2-butanone
in n-hexane showed that aromatic ring hydrogenation routes are
faster than carbonyl hydrogenation in agreement with the pro-
posal that the aromatic ring adsorption is favored in alkanes
(Fig. 5).
Similarly to the work reported by Bertero et al. [27,28] the rate
of reaction was not found to be controlled by combinations of
physical properties of the solvents, the Kamlet–Taft parameters
(hydrogen bonding donation (a) and accepting ability (b) or polar-
isability (p⁄)) or Catalan parameters (SA-H, SA-B, SPP) Figs. S11 and
S12 [43–60]. Importantly, H2 solubility, viscosity and density also
did not show any significant correlation with the rates observed,
Fig. S13, [61–63] nor did the dielectric constant (e) or polarisability
(ET(30), ENT ), Fig. S14. As with the initial rates of reaction, the selec-
tivity to 4-cyclohexyl-2-butanone was not found to be dependent
on the physical parameters of the solvents.
In all solvents tested, 4-phenyl-2-butanol, 4-cyclohexyl-
2-butanone and 4-cyclohexyl-2-butanol were formed in differing
amounts. Fig. 2 shows reaction profiles for reactions at 5 bar in
n-hexane and 2-propanol where comparable rates but different
selectivities were observed. In n-hexane, 4-cyclohexyl-
2-butanone was the main product formed whereas in 2-propanol
4-phenyl-2-butanol was predominantly observed. At higher pres-
sures (12 bar), the reaction proceeded to completion with the fully
hydrogenated product 4-cyclohexyl-2-butanol formed in both sol-
vents. This variation in selectivity, as well as rate, with solvent was
not observed for reactions over a 4% Pt/SiO2 catalyst where the
major product in all solvents tested (except toluene) was found
to be 4-cyclohexyl-2-butanone (Fig. S15 showing initial rate and
Fig. S16 showing selectivity for Pt/SiO2 reactions in a range of sol-
vents). In the case of toluene, a very slow reaction was observed
reaching only 3% conversion after 2 h of reaction with 70% selectiv-
ity to 4-phenyl-2-butanol.
3.3.2. Aromatics
In aromatic solvents, the rate of reaction and selectivity to
4-cyclohexyl-2-butanone were found to vary significantly, Figs. 6
and 7 respectively. A high reaction rate was observed in tert-butyl
toluene which was comparable to the rate observed in alkanes,
0.0024 mol dmꢁ3 minꢁ1 compared with 0.0026 mol dmꢁ3 minꢁ1
in n-hexane. Again, as found for the alkane solvents the selectivity
to 4-cyclohexyl-2-butanone was high in tert-butyl toluene.
In contrast, however, the rate of reaction and selectivity to
4-cyclohexyl-2-butanone in toluene and p-xylene were both low
The kinetic profiles for each of the solvents tested are presented
in the supplementary information, Figs. S17–S36 for Pt/TiO2 (P25),
and this information is summarized, hereafter, to provide compar-
isons of the initial rate and selectivity as a function of the solvent
Fig. 1. Initial rate of hydrogenation of 4-phenyl-2-butanone to products over Pt/TiO2 in n-hexane, toluene, tert-butyl toluene, 1-propanol, 2-propanol and dibutyl ether. Using
0.1 g 4% Pt/TiO2, 13.5 mmoles 4-phenyl-2-butanone, 5 bar H2, 70 °C and 50 ml of the respective solvent.