Catalytic hydrogenation of acetophenone over ruthenium catalysts

Article abstract of DOI:10.1135/cccc19960764

Catalytic hydrogenation of acetophenone in ethanol was studied by using 5 wt.% Ru supported on active carbon, alumina, and titania. Parameters of kinetic equations (reaction rate constants and adsorption coefficients) were evaluated and the influence of t

Full text of DOI:10.1135/cccc19960764

764
Cerveny, Dobrovolna, Belohlav, Kluson:
CATALYTIC HYDROGENATION OF ACETOPHENONE
OVER RUTHENIUM CATALYSTS
1
2
3
4
Libor CERVENY , Zuzana DOBROVOLNA , Zdenek BELOHLAV and Petr KLUSON
Department of Organic Technology, Prague Institute of Chemical Technology, 166 28 Prague 6,
Czech Republic; e-mail: 1 libor.cerveny@vscht.cz, 2 zd@env.cz, 3 zdenek.belohlav@vscht.cz,
4 petr.kluson@vscht.cz
Received October 4, 1995
Accepted December 7, 1995
Catalytic hydrogenation of acetophenone in ethanol was studied by using 5 wt.% Ru supported on
active carbon, alumina, and titania. Parameters of kinetic equations (reaction rate constants and ad-
sorption coefficients) were evaluated and the influence of the support on the reaction course was dis-
cussed. An enhanced selectivity of Ru/TiO2 towards carbonyl group hydrogenation with respect to the
hydrogenation of the aromatic ring was confirmed.
Key words: Ruthenium catalysts; TiO2 supported catalysts; Hydrogenation of acetophenone.
Ruthenium catalysts are attractive due to their high activity in hydrogenation of aro-
matic compounds. Some of them, specifically modified, exhibit outstanding selectivity
for formation of cycloalkenes1–5. Ruthenium supported on TiO2 is especially suitable
for selective hydrogenation of a carbonyl group in the presence of an aromatic system
or a double bond6–11. In the present work, the course of acetophenone hydrogenation
over Ru catalysts prepared in our laboratory was compared with that over commercial
catalysts.
EXPERIMENTAL
Chemicals
Ethanol (Kolin Distillery, Czech Republic) of analytical grade (azeotropic 4 vol.% H2O) was used as
a solvent. Acetophenone (Aroma Decin, Czech Republic) was used as a substrate. Hydrogen (grade 3.0)
was supplied by Linde-Technoplyn Prague, Czech Republic. The substrate was purified by distilla-
tion before use and was chromatographically pure. The commercial hydrogenation catalysts were
from Engelhard Co.: 5% Ru/C No. 1797 type Escat 40 (SBET = 850 m2/g) and 5% Ru/Al2O3 No. LA 9359
Escat 44 (SBET = 125 m2/g). Titania supported catalysts were prepared as described below. Ruthenium(III)
chloride (Fluka AG, Germany) was utilized as the active component precursor, and the supports were
titanium(IV) oxide No. 7702 (anatase, SBET = 40 m2/g) and No. 7701 (rutile, SBET = 21 m2/g), both
from Degussa (Germany).
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Catalysts Prepared and Kinetic Measurements
The 5 wt.% Ru/TiO2 catalysts were prepared by impregnation of the titania supports with an ethanol
solution of RuCl3 having the appropriate metal concentration. Then, the solvent was slowly distilled
off during intensive mixing of the mixture until a thick slurry was formed. The paste was dried in a
nitrogen atmosphere in a furnace at 373 K. After 1 h drying, nitrogen was replaced by hydrogen, and
the precursor was partly reduced for two hours. The final reduction was performed in hydrogen in a
furnace heated up to 673 K for 12.5 h.
All the catalysts were fully activated in a furnace in a hydrogen atmosphere before their use at 363 K
for 3.5 h, or at 453 K in the case of the carbon-supported catalyst. After activation, the catalysts were
covered by ethanol, avoiding a contact with air, and transferred into the reactor where the final acti-
vation step took place (10 min, H2).
Kinetic measurements were carried out in a semi-batch, stirred, isothermal reactor connected to
gasometric burettes. All the experiments were performed at atmospheric pressure and 303 K. Typi-
cally, experimental batch was 15 ml of ethanol, 0.2 ml of a substrate, and the catalyst weight ranged
from 0.3 to 1.0 g. The measurements were carried out in a kinetic regime excluding mass transfer
effects. Samples, withdrawn at suitable time intervals, were analyzed chromatographically. A detailed
description of a typical experiment was published elsewhere12
.
Time dependences of the concentrations of the reaction mixture components were treated by the
least square fitting with random search and gradient optimization (Random Walk method terminated
by the Gauss–Newton method).
Analytical Method
A gas chromatograph Hewlett–Packard, 5890 Series II Plus, equipped with FID and a capillary column
HP-20 M (25 m × 0.2 mm × 0.35 µm) was used to analyse the samples. The analyses were carried
out with a temperature program (373 K to 463 K) and a split ratio 1 : 25.
RESULTS AND DISCUSSION
Acetophenone hydrogenation13 can proceed through two reaction pathways (Fig. 1).
Besides the compounds given in the scheme, also benzene, cyclohexene, cyclohexane,
and ethylbenzene were found in the reaction mixture. Because only small amounts of
CH CH3
r1
r3
OH
CH CH3
OH
2
CO CH3
r2
r4
CO CH3
1
4
3
FIG. 1
The reaction scheme of acetophenone hydrogenation. 1 Acetophenone, 2 1-phenylethanol, 3 methyl
cyclohexyl ketone, 4 1-cyclohexylethanol
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

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Cerveny, Dobrovolna, Belohlav, Kluson:
these side products were detected, their formation was not included into the reaction
scheme (Fig. 2).
The experimental data were described by using the simplified form of Langmuir–
Hinshelwood equations14:
V dcA/W dt = (−k1KAcA − k2KAcA − k5KAcA)/φ
V dcB/W dt = (k1KAcA − k3KBcB)/φ
V dcC/W dt = (k2KAcA − k4KCcC)/φ
V dcD/W dt = (k3KBcB + k4KCcC)/φ
V dcE/W dt = (k5KAcA)/φ
φ = KAcA + KBcB + KCcC + KDcD + KEcE
,
with initial conditions t = 0, cA = cA0 = 1.0, cB0 = cC0 = cD0 = cE0 = 0. Symbols cX and
KX denote concentration and adsorption coefficient of individual reaction mixture com-
ponents, respectively, k denotes a rate constant, t refers to time, V denotes a reaction
volume, and W denotes weight of a catalyst. The real initial concentration of acetophe-
none was c′A0 = 0.1140 mol/l. A typical course of the acetophenone hydrogenation is
given in Fig. 3.
The kinetic data obtained are collected in Tables I and II. The confidential interval of
the evaluated parameters is somewhat limited with respect to the big standard deviation
and a large number of kinetic parameters in the proposed mathematical model. For
adsorption coefficients, only the relative values are significant because arbitrarily
multiplied absolute values of the adsorption coefficients also fit the proposed mathe-
matical model14. During the course of the reactions, the activity of the catalysts usually
B
r1
r3
A
E
D
r2
r4
r5
C
FIG. 2
The generic scheme of parallel-consecutive reactions. A Acetophenone, B 1-phenylethanol, C methyl
cyclohexyl ketone, D 1-cyclohexylethanol, E minor substances, r1 to r5 particular reaction rates
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

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767
decreased. Since the rate of the catalyst deactivation was not incorporated into the
kinetic model, the activity decrease was reflected in high values of the adsorption coef-
ficients of the hydrogenation products (predominantly of 1-cyclohexylethanol).
TABLE I
Acetophenone hydrogenation (k’s in mmol/gcat min)
Rate constants
Catalyst
k1
k2
k3
k4
k5
Ru/TiO2 (rutile)
Ru/TiO2 (anatase)
Ru/Al2O3
150.0
49.2
19.8
14.6
28.7
10.4
13.5
77.7
61.7
28.2
110.3
301.8
105.3
59.1
43.4
60.2
11.0
10.8
65.5
Ru/C
102.2
TABLE II
Adsorption coefficients K, selectivities S and maximum concentrations cmax in acetophenone hydroge-
nation
Catalyst
KA
KB
KC
SR(B)
SR(C)
cmax(B)
cmax
Ru/TiO2 (rutile)
Ru/TiO2 (anatase)
Ru/Al2O3
96.1
281.1
597.7
146.4
42.4
68.4
117.1
176.6
35.4
0.665
0.326
0.254
0.389
0.057
0.056
0.207
0.027
0.62
0.21
0.49
0.69
0.05
0.05
0.23
0.09
186.2
78.2
Ru/C
37.5
100
1
c, %
2
4
50
FIG. 3
Time course of acetophenone hydrogenation over
Ru/C catalyst. c Concentration (%), t time (min). 1
Acetophenone, 2 1-phenylethanol, 3 methyl cy-
clohexyl ketone, 4 1-cyclohexylethanol, 5 minor
substances
5
3
0
0
100
200
t, min
Collect. Czech. Chem. Commun. (Vol. 61) (1996)