Liquid phase selective hydrogenation of phenol to cyclohexanone over Ru/Al2O3 nanocatalyst under mild conditions

Article abstract of DOI:10.1134/S0023158416010110

Highly monodispersed ruthenium nanoparticles were prepared via wet impregnation technique using RuCl₃ · nH₂O as a precursor. Ru nanoparticles were supported on Al₂O₃ to synthesize Ru nanocatalyst. The nanocataly

Full text of DOI:10.1134/S0023158416010110

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2016, Vol. 57, No. 1, pp. 39–46. © Pleiades Publishing, Ltd., 2016.
Liquid Phase Selective Hydrogenation of Phenol to Cyclohexanone
over Ru/Al2O3 Nanocatalyst under Mild Conditions1
,
b
,
A. N. Rauta, S. U. Nandanwara, Y. R. Suryawanshia , M. Chakrabortya *,
S. Jauharib, S. Mukhopadhyayc, K. T. Shenoyc, and H. C. Bajajd
a Chemical Engineering Department, S.V. National Institute of Technology, Surat, Gujarat, India
b Applied Chemistry Department, S.V. National Institute of Technology, Surat, Gujarat, India
c Chemical Engineering Division Bhabha Atomic Research Centre (BARC), Mumba, Maharashtra, India
d Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute (CSMCRIꢀCSIR),
Bhavnagar, Gujarat, India
*eꢀmail: mch@ched.svnit.ac.in
Received January 11, 2015
Abstract—Highly monodispersed ruthenium nanoparticles were prepared via wet impregnation technique
using RuCl3 nH2O as a precursor. Ru nanoparticles were supported on Al2O3 to synthesize Ru nanocatalyst.
⋅
The nanocatalyst was characterized by various techniques like XRD, SEM, TEM and BET analysis. The catꢀ
alyst was used for hydrogenation of phenol under mild condition. The activity of the catalyst was checked by
varying different parameters such as reaction temperature, time, H2 partial pressure, metal loading and catꢀ
alyst amount. The catalyst was recovered from product and reused up to four times without significant loss in
its catalytic activity. After a reaction time of 1 h, Ru/Al2O3 nanocatalyst showed high reactivity (82% converꢀ
sion) and selectivity to cyclohexanone (67%) at 80 C and 20 bar hydrogen pressure.
°
Keywords: ruthenium catalysts, Ru/Al2O3 nanocatalyst, hydrogenation, phenol
DOI: 10.1134/S0023158416010110
1
Hydrogenation of phenol can proceed in stepwise perature, gives significant economic advantages. Conꢀ
ventionally, hydrogenation of phenol occurs under
drastic reaction conditions over metal supported hetꢀ
erogeneous catalyst. Palladium catalyst is among the
most widely used system for phenol hydrogenation.
However, the selectivity to cyclohexanone often
decreases with the increase in phenol conversion. It is,
therefore, difficult to maintain high selectivity to
cyclohexanone at high phenol conversion with a satisꢀ
factory rate [4]. Previous studies showed that the activꢀ
ity for phenol hydrogenation is, as expected, depenꢀ
dent on the size of metal and its dispersion onto the
support. According to the literature, attempts had
been made to use a broad range of metal catalyst such
as Pt [5, 6], Ni [7, 8], Rh [9], Pd [10] and Ru [11].
Some researchers tried to improve Pd catalyst by alterꢀ
ing the nature of the support making use of Al2O3 [12, 13],
SiO2 [14], MgO [15], TiO2 [16], and C [17]. Pdꢀconꢀ
taining hyper cross linked polystyrene [18] were tested
in vapour phase phenol hydrogenation, whereas AC
[19], Carbon Nitride [20], hybrid (TiO2ꢀC) [21],
MHSS [22] and AlꢀMCMꢀ41 [23] were tested in liqꢀ
uid phase phenol hydrogenation.
fashion with cyclohexanone as a partially hydrogeꢀ
nated and cyclohexanol as a fully hydrogenated prodꢀ
uct. The selective hydrogenation of phenol to cycloꢀ
hexanone is one of the most frequently encountered
reactions and is of commercial significance as a viable
synthetic route to a key raw material in the production
of caprolactum and adipic acid which are key intermeꢀ
diate for the production of nylonꢀ6 and nylonꢀ66 [1–3].
The process is performed either in liquid phase or
vapour phase with the use of different catalysts. The
liquid phase process has some advantages over the gas
phase process such as increasing catalyst life and the
quality of reaction products. Thus, much interest has
been focused on the liquid phase phenol hydrogenaꢀ
tion rather than on the vapour phase hydrogenation.
In general, cyclohexanone can be obtained from pheꢀ
nol by either oneꢀstep or twoꢀstep processes. In a twoꢀ
step process phenol is first hydrogenated to cyclohexꢀ
anol and then again dehydrogenated to cyclohexꢀ
anone. However in a oneꢀstep process phenol is selecꢀ
tively hydrogenated to cyclohexanone and the endotꢀ
hermic step of dehydrogenation can be avoided [4].
The suppression of dehydrogenation step, that
involves expensive equipment for achieving high temꢀ
However, to the best of our knowledge Ru nanocatꢀ
alyst has not been extensively studied in phenol hydroꢀ
genation so far. We report herein the synthesis and
characterization of ruthenium nanocatalyst supported
1
The article is published in the original.
39

40
RAUT et al.
on Al2O3 for hydrogenation of phenol to cyclohexꢀ ments, United Kingdom). Analyses were carried out at
anone. The Ru based catalysts exhibited a moderate an accelerating voltage of 18 kV and probe current of
catalytic activity for hydrogenation of phenol under 102 AMP.
mild reaction conditions; they can be easily recovered
from product and effectively recycled.
Transmission electron microscope (TEM) images
were obtained with a Tecnaiꢀ20 microscope (Philips,
Holland) with acceleration voltage of 200 kV, which
provided 0.27 nm point resolution using carbon
coated 200 mesh copper grids. The samples were ultraꢀ
sonically dispersed in ethanol for 10 min and deposꢀ
ited onto carbon film using capillary and dried in air
for 30 min.
EXPERIMENTAL
Materials
Active acidicꢀalumina powder, Al2O3 of 98% purity
was purchased from S. D. Fine Chemicals Ltd.
(India). Ruthenium trichloride (RuCl3
content 37%) was purchased from SigmaꢀAldrich
· nH2O, Ru
≥
Catalytic Hydrogenation Reaction
Chemicals (United States). Phenol was purchased
from Finar Chemicals Pvt. Ltd. (India). Organic comꢀ
pounds, cyclohexane, methanol and acetone were
purchased from Fisher Scientific Pvt. Ltd. (India).
Hydrogen and nitrogen gases (99.9%) used were from
Hydro Gas India Pvt. Ltd. (India). All the chemicals
were used as such without further purification.
Catalyst activity in liquid phase hydrogenation of
phenol was evaluated in 100 mL stainless steel batch
reactor (EZEꢀSeal Reactor, Autoclave Engineers,
United States) equipped with a controlling unit. In a
typical hydrogenation experiment, 50 mg of catalyst,
500 mg substrate (phenol) and 30 mL solvent (cycloꢀ
hexane) were loaded into a stainless steel autoclave
reactor. The reactor was fitted air tight and flushed with
hydrogen three times at room temperature. Then, reacꢀ
Synthesis of Catalyst
tor was brought to desired temperature (80°C) and
The catalysts were prepared by the wet impregnaꢀ
pressurized with hydrogen (20 bar). From this moment
the reaction time was calculated. Hydrogenation reacꢀ
tion was initiated by stirring (500 rpm) the entire reacꢀ
tion mass. After a stipulated period, the stirring was
stopped and the reactor was abruptly cooled down to
room temperature with the help of iceꢀwater mixture,
depressurized, opened and decanted the reaction mixꢀ
ture from the catalyst to collect sample for a GC analysis.
The samples were analyzed with Bruker 450ꢀGC
gas chromatograph (GC) using flame ionization detecꢀ
tor (FID) having 5% diphenylꢀ and 95% dimethyl
siloxane capillary column (length 60 m, i. d. 0.25 mm).
GC oven temperature was programmed from 45 to
tion method using RuCl3 · nH2O as a ruthenium preꢀ
cursor and acidicꢀalumina powder as a support mateꢀ
rial [24, 25]. The support material was outgassed at
373 K for 2 h at atmospheric pressure in order to free
all the pores from adsorbed water and air. Then the
ruthenium salt was dissolved in methanol, solvent was
admixed with the support and the mixture was stirred
for 4 h at room temperature. The samples were dried at
353 K overnight. Finally, the catalyst precursor was
reduced by H2 at 423 K under 50 bar hydrogen pressure
for 6 h and then calcined at 573 K for 3 h in an oven
under inert (N2) atmosphere. The amount of Ru was
increased from 0.5 to 2 wt % by varying RuCl3 · nH2O
amount. The catalyst was used further for characterꢀ
ization.
220
and then raised to 55
raised to 220 at 10°
°C
. Column temperature was initially kept at 45
at C/min. Further, it was
C/min. Nitrogen was used as a
°C,
°
C
2°
°C
carrier gas. The retention time of different compounds
were determined by injecting the pure compound
under the identical conditions. The conversion of pheꢀ
Catalyst Characterization
Powder Xꢀray diffraction (PꢀXRD) data were colꢀ
lected using a model XꢀPertꢀMPD diffractometer
(Philips Analytical, Holland) employing Niꢀfiltered
nol (
X) and the selectivity to cyclohexanone (S) was
calculated according to following equations:
Cu
K
(
λ
= 1.54056 Å) radiation with 40 kV and 30 mA
θ ≥ 80° range.
X
S
= (Ct
=
/
C0
)
×
100,
100,
over αthe 10
° ≤ 2
Cc/
C
×
Σ
Surface area measurements were carried out using
a ASAP 2010 instrument (Micromeritics, United
where Ct is moles of phenol reacted, C0 is moles of pheꢀ
nol initially added, Cc is moles of cyclohexane formed,
States). The samples were activated at 100
°C for 4 h
C
is moles of all products formed.
under vacuum (
5
×
10–2 Torr) prior to N2 adsorption
Σ
measurements. The specific surface area, pore diameꢀ
ter, and pore volume of the samples were calculated
from nitrogen adsorption isotherms measured at 77 K
using the BET method.
RESULTS AND DISCUSSION
Characterization of Catalysts
Scanning electron microscopy (SEM) images of
The alumina supported Ru catalysts were characꢀ
support and catalyst were measured on a LeoꢀVP1430 terized by various instrumental techniques. A PꢀXRD
microscope (Carl Zeiss, Germany) having silicon pattern of 1 wt % Ru /Al2O3 catalysts is shown in Fig. 1.
detector equipped with EDS facility (Oxford instruꢀ The characteristic peaks corresponding to Ru metal
KINETICS AND CATALYSIS Vol. 57
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2016

LIQUID PHASE SELECTIVE HYDROGENATION OF PHENOL TO CYCLOHEXANONE
Intensity, counts/s
41
400
350
300
250
200
150
100
50
0
10
20
30
40
50
60
70
2
80
, deg
50 nm
θ
Fig. 1. PꢀXRD pattern of 1 wt % Ru/Al O nanocatalyst:
Fig. 2. TEM image of 1 wt % Ru/Al O catalyst.
2 3
2
3
᭝
—Ru,
᭹—
RuO , *—Al O
.
2
2
3
Distribution, %
18
15
12
9
6
3
0
10
20
30
40 50
Diameter, nm
1 μm
Fig. 3. Particles size distribution of 1 wt % Ru/Al O catalyst.
Fig. 4. SEM image of 1 wt % Ru/Al O fresh catalyst.
2 3
2
3
particles at
2θ around 42.3° and 44.7° were observed. alyst caused a better dispersion of ruthenium on the
surface of support.
The major diffraction peaks indicated the presence of
The surface morphology and particle size of the
Ru/Al2O3 (1 wt % Ru) catalyst were studied by TEM.
Figure 2 shows that Ru nanoparticles visible as black
dark dots were uniformly dispersed on the Al2O3 supꢀ
port, with their size ranging from 10 to 50 nm as shown
in Fig. 3.
Al2O3 (JCPDS file no. 10ꢀ0425) predominant in these
catalysts with peaks at
2 = 36.5°, 46°, and 67°. A specꢀ
θ
tral characteristic of RuO2 phase was also observed
(JCPDS file no. 40ꢀ1290). A quantitative estimation of
the RuO2 /Ru total ratio by using XRD technique is difꢀ
ficult. A limitation of the XRD method is the lack of
sensitivity in detecting low amounts of a given phase
(in our case RuO2) in a heterogeneous catalyst [26].
SEM images of Ru/Al2O3 catalyst clearly showed
that the majority of the Ru crystals of the catalyst were
dispersed and larger agglomerates of the metal were
These results indicated that a low content of Ru in catꢀ formed (Fig. 4). SEM images also confirmed that
KINETICS AND CATALYSIS Vol. 57
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42
Volume adsorbed, cm3/g
RAUT et al.
phenol. Cyclohexanone and cyclohexanol were the
only reaction products observed in the phenol hydroꢀ
genation reaction under the studied experimental
conditions.
180
160
140
120
100
80
Effect of Metal Loading and Catalyst Amount
The hydrogenation of phenol was first carried out
using 1 wt % Ru/Al2O3 at 80°C and 20 bar hydrogen
pressure. Interestingly, the 1 wt % Ru/Al2O3 catalyst
effectively hydrogenates phenol (82.12% conversion)
with 67.90% selectivity to cyclohexanone under conꢀ
ditions applied. In order to clarify the influence of Ru
loading and the role of Ru present in the catalysts, Ru
content was varied using Al2O3 as a support. The of
phenol increased with increasing Ru content (Table 2,
entries 2–4) but the initial increase in selectivity to
cyclohexanone (Table 2, entries 1, 2) was followed by
a decrease as the Ru content was further increased
(Table 2, entries 2–4) and as cyclohexanone formed
was further hydrogenated to cyclohexanol. With
increasing metal loading a decrease in the number of
small particles is evident bringing about a lower selecꢀ
tivity of cyclohexanone. Larger loading also led to
more intensive agglomeration and larger average parꢀ
ticle size [27].
60
40
20
0
0.2
0.4
0.6 0.8
Relative pressure,
1.0
P0
P
/
Fig. 5. Nitrogen adsorptionꢀdesorption isotherm for 1 wt %
Ru/Al O catalyst.
2
3
metal impregnation did not alter the surface morpholꢀ
ogy of the support.
The BET surface area of the catalyst was found to
be ~144.58 m2/g with 9.70 nm average pore diameter.
Figure 5 shows the curve of the nitrogen adsorptionꢀ
desorption isotherm analysis of the Ru/Al2O3 (1 wt %
loading Ru). The desorption run is started from a point
The effect of catalyst amount was also studied at
80°C and 20 bar H2 pressure by varying catalyst (1 wt %
Ru/Al2O3) amount from 25 to 100 mg. A higher conꢀ
version of phenol corresponds to an enhanced amount
of catalyst, the conversion decreased with decreasing
catalyst amount (Table 3). At a lower amount of cataꢀ
lyst (25 mg), the phenol conversion was 58%. The
conversion of phenol increased from 58 to 97% when
the catalyst loading was increased from 25 to 100 mg
under the same reaction conditions. From Table 3, it
can be seen that the selectivity to cyclohexanone
decreased with an increase in the catalyst amount.
Table 3 suggests that highest selectivity (72.5%) to
cyclohexanone can be obtained with a catalyst loading
of 25 mg but phenol conversion (58%) is very low with
this amount of catalyst. Above results clearly confirm
the role of Ru in catalyst and also indicate that the Ru
present in the Ru/Al2O3 catalysts is the only source of
active metal centers (or active sites) for phenol hydroꢀ
genation. For further hydrogenation experiments,
optimum amount (50 mg 1 wt % Ru/Al2O3) of catalyst
was used.
corresponding to a relative pressure (P/P0) of 0.4.
Table 1 shows that the specific surface areas (BET) of
catalysts decreased with increasing ruthenium loading.
But the decrease in pore volume after the insertion of
ruthenium nanoparticles into the support is not drastic.
It indicates that metal atoms were deposited on the surꢀ
face of the alumina, not in the pore of the support and
all atoms would be accessible to the reaction.
Catalytic Activity
The Ru/Al2O3 nanocatalysts were evaluated for the
hydrogenation of phenol. The effect of metal loading,
catalyst amount, reaction temperature, hydrogen parꢀ
tial pressure, reaction time, and reusability of catalyst
were studied systematically for the hydrogenation of
Table 1. Properties of the Ru/Al2O3 nanocatalyst
Effect of Reaction Temperature
SBET
,
Pore volume, Average pore
Ru content,
wt %
m2/g
cm3/g
diameter, nm
The reaction temperature was varied from 30 to
100°C at a constant hydrogen pressure (20 bar). The
conversion of phenol increased with increasing reacꢀ
tion temperature but the selectivity to cyclohexanone
decreased with an increased in the reaction temperaꢀ
ture. At 30°C, the phenol conversion was 31% and
selectivity to cyclohexanone was 75% (Table 4, entry 1).
The conversion reached the highest value near 95% at
0 (Acidic Al2O3) 173
0.28
9.27
9.80
9.70
9.36
8.94
0.5
1.0
1.5
2.0
150.73
0.27
144.58
138.36
116.83
0.268
0.265
0.261
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LIQUID PHASE SELECTIVE HYDROGENATION OF PHENOL TO CYCLOHEXANONE
43
Table 2. Effect of ruthenium loading in phenol hydrogenation to cyclohexanone
Yield, %
Selectivity, %
Entry
Catalyst loading, % Conversion, %
C=O
C–O(l)
C=O
C–O(l)
1
2
3
4
0.5
1.0
1.5
2.0
63.78
82.12
83.96
93.46
41.97
55.76
50.61
42.16
21.81
26.36
33.35
51.30
65.80
67.90
60.28
45.11
34.20
32.09
39.72
54.89
Reaction conditions: phenol 500 mg, catalyst amount 50 mg, temperature 80
30 mL.
°C, hydrogen pressure 20 bar, reaction time 1 h, cyclohexane
Table 3. Effect of amount of catalyst for hydrogenation of phenol
Catalyst
to substrate
ratio, wt %
Yield, %
C–O(1)
Selectivity, %
Catalyst
amount, mg
Conversion,
%
Entry
C=O
C=O
C–O(1)
1
2
3
4
25
50
75
5
10
15
20
58
82
90
97
42.0
55.5
48.5
46.0
16.0
26.5
41.5
51.0
72.5
68.0
53.7
47.0
27.5
32.0
46.3
53.0
100
Reaction conditions: phenol 500 mg, 1 wt % Ru/Al O , temperature 80°C, hydrogen pressure 20 bar, reaction time 1 h, cyclohexane
2
3
30 mL.
Table 4. Effect of temperature on hydrogenation of phenol to cyclohexanone
Yield, %
Selectivity, %
Entry
Temperature,
°C
Conversion, %
C=O
C–O(l)
C=O
C–O(l)
1
2
3
4
5
6
30
50
70
80
90
32
56
66
82
87
95
23.74
38.28
45.67
55.76
50.14
45.52
7.84
17.18
20.60
26.36
36.80
49.16
75.17
69.02
68.92
67.90
57.67
48.08
24.83
30.98
31.08
32.09
42.33
51.92
100
Reaction conditions: phenol 500 mg, catalyst amount 50 mg, 1 wt % Ru/Al O , hydrogen pressure 20 bar, reaction time 1 h, cyclohexane
2
3
30 mL.
100
°
C
but the selectivity to cyclohexanone shows a perature (80
°C). Table 5 showed that, the conversion
decrease at temperatures above 80
°C
(Table 4, entries 4–6).
of phenol increased with an increase in hydrogen presꢀ
sure, ensued slowly at low hydrogen pressure. At 10 bar
hydrogen pressure, conversion was at 57% and selecꢀ
tivity to cyclohexanone was 75% (Table 5, entry 1).
Increasing H2 partial pressure from 10 to 30 bar, the
complete conversion of phenol was achieved with
drastic decrease in selectivity above 20 bar hydrogen
pressure (Table 5). At 20 bar hydrogen pressure, conꢀ
version was 82% and highest selectivity (68%) to
cyclohexanone (Table 5, entry 3) was obtained. The
higher hydrogen pressure enhances the oxidative addiꢀ
tion of hydrogen on the metal (Ru) sites of the catalyst
and increases the concentration of hydrogen available
for phenol hydrogenation, which results in a higher
conversion of phenol. An increase in hydrogen presꢀ
The results show that rise in temperature will increase
the chance of the interaction between the phenol and
catalyst surface and in this way enhancing the converꢀ
sion of phenol [20]. However, a further increase in the
reaction temperature intensifies the processes associꢀ
ated with adsorption and desorption resulting in
reduced contact time when aromatic ring of phenol is
adsorbed on the catalyst surface. Accordingly, reducꢀ
tion in the reaction selectivity to cyclohexanone can
be expected.
Effect of Hydrogen Partial Pressure
Experiments were carried out by varying the hydroꢀ
gen partial pressure from 10 to 30 bar at constant temꢀ sure yields more cyclohexanol, as formed cyclohexꢀ
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44
RAUT et al.
Table 5. Effect of hydrogen pressure in hydrogenation of phenol to cyclohexanone
Yield, %
Selectivity, %
Entry
Pressure, bar Conversion, %
C=O
C–O(1)
C=O
C–O(1)
1
2
3
4
5
10
15
20
25
30
57
68
82
86
100
43.26
49.16
55.76
51.37
43.28
14.30
19.12
26.36
34.71
56.72
75.16
72.05
68.0
59.68
43.28
24.84
28.04
32.0
40.32
56.72
Reaction conditions: phenol 500 mg, catalyst amount 50 mg, 1 wt % Ru/Al O , temperature 80°C, reaction time 1 h, cyclohexane
2
3
30 mL.
Table 6. Effect of reaction time on phenol hydrogenation to cyclohexanone
Yield, %
Selectivity, %
Entry
Time, min
Conversion, %
C=O
C–O(1)
C=O
C–O(1)
1
2
3
4
5
6
7
0
30
0
0
0
0
0
20.5
40.5
82.0
86.0
90.0
97.0
16.71
30.20
55.76
38.09
36.82
37.95
3.84
81.314
74.458
67.901
44.127
40.911
33.948
18.686
25.542
32.099
55.873
59.089
66.052
45
10.36
26.36
48.23
53.18
64.11
60
90
120
150
Reaction condition: phenol 500 mg, catalyst amount 50 mg, 1 wt % Ru/Al O loading, temperature 80°C, hydrogen pressure 20 bar, cyꢀ
2
3
clohexane 30 mL.
anone further hydrogenates to cyclohexanol [4],
which is to be expected due to the presence of a large
excess of hydrogen.
Effect of Reaction Time and Reusability of Catalyst
To study the reaction kinetics, the reaction was carꢀ
ried out at different time keeping temperature (80°C)
and pressure (20 bar) constant. Experimental results
describing the effect of the reaction time on phenol
hydrogenation are presented in Table 6. The selectivity
towards cyclohexanone decreased slightly up to 1 h
and then the selectivity curve shows a fall. The initial
phenol conversion was high until the reaction time did
not exceed 1 h (82% conversion and selectivity to
cyclohexanone 68%). At longer reaction times the rate
of phenol conversion decreased due to increasing conꢀ
tribution of hydrogenation of cyclohexanone to cycloꢀ
hexanol. Thus, the selectivity to cyclohexanone
decreased with time whereas the selectivity to cycloꢀ
hexanol and phenol conversion increased [28].
Phenol concentration
1.6
×
10–2, mmol/L
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Concentration
Poly. (concentration)
R2 = 0.926
Figure 6 showed the phenol concentration as a
function of time for liquid phase phenol hydrogenaꢀ
tion in the presence of hydrogen. The reaction could
be considered as the first order process with respect to
phenol.
–30
0
30
60
90
120 150 180
Time, min
kt
CA
=
C
A, 0 e–
.
Fig. 6.Concentration versus time for hydrogenation of
phenol over 1 wt % Ru/Al O . Reaction conditions: phenol
500 mg, temperature 80°C, hydrogen pressure 20 bar,
The rate constant for the first order reaction can be
calculated from the following equation:
ln(CA/CA,0) = –kt,
2
3
cyclohexane 30 mL.
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LIQUID PHASE SELECTIVE HYDROGENATION OF PHENOL TO CYCLOHEXANONE
45
and desquamation of metal on Al2O3 support. It was
observed that the conversion of phenol decreased in
each run whereas the selectivity of cyclohexanone
(~67%) remains nearly constant (Fig. 8). Therefore
catalyst can be recycled without much significant loss
in activity under employed reaction condition.
Time, min
120 150
0
30
60
90
y
= –0.021
x
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
R2 = 0.929
CONCLUSIONS
Ru/Al2O3 nanocatalyst was found to be an effective
heterogeneous catalyst for the phenol hydrogenation
under mild conditions. The observation that Ru/Al2O3
catalyst efficiently catalyzes hydrogenation of phenol
is of interest because phenol is difficult to reduce with
high selectivity to cyclohexanone under mild condiꢀ
tion. The catalyst was easily recovered from product by
simple filtration and catalystꢀrecycling experiments
showed that both the catalytic activity and selectivity
to cyclohexanone was less affected in four consecutive
runs. This preliminary result can indicate a possible
use of Ru nanocatalyst in hydrogenation of phenol.
–4.0
ln(CA/CA, 0)
Fig. 7. Rate constant versus reaction time for hydrogenaꢀ
tion of phenol.
–
SC–O(I)
– SC=O – Conversion
ACKNOWLEDGMENTS
Conversion and selectivity, %
100
Authors are thankful to the director of CSMCRI,
CSIR, Bhavnagar for giving opportunity to work in
high pressure laboratory and financial support.
80
60
40
20
0
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