Influence of residual chloride ions in alumina-supported cobalt catalysts on catalytic activity in ketone and aldehyde hydrogenation

Article abstract of DOI:10.1246/bcsj.81.653

The influence of residual chloride ions on the catalytic activity of C0/AI₂O₃ was investigated for liquid-phase hydrogenation of ketones and aldehydes using CI^--free and Cl^--containing catalysts. The Cl^--free catalyst showed high activity for hydrogenation of both, whereas the Cl^--contain-ing catalysts showed very low activity for ketone hydrogenation.

Full text of DOI:10.1246/bcsj.81.653

Short Articles
Bull. Chem. Soc. Jpn. Vol. 81, No. 5, 653–655 (2008)
653
In this work, we investigate the influence of residual chlo-
ride ions on catalytic activity in ketone and aldehyde hydroge-
nation; in addition, we report the results of hydrogenation
reactions of various ketones over alumina-supported cobalt
catalysts.
Influence of Residual Chloride
Ions in Alumina-Supported
Cobalt Catalysts on Catalytic
Activity in Ketone and
Experimental
Chloride ion-free catalyst, Co/Al2O3 (NO3-I), was prepared by
a conventional impregnation method using Al2O3 (AEROXIDEꢀ
Aldehyde Hydrogenation
Alu-C, surface area: 110 m2 gꢁ1) and Co(NO3)2 6H2O aqueous
ꢂ
solution. The resultant sample was dried at 400 K overnight and
then calcined at 673 K for 5 h in air to prepare a catalyst precursor.
The precursor was reduced at 773 K for 3 h in H2 flow before
being used in the hydrogenation reaction. The catalyst prepared
in the presence of chloride ions, Co/Al2O3 (Cl-P), was formed
by a precipitation method using Al2O3, an aqueous solution of
Akinori Otomo, Yasuyuki Tukagoshi,
Masa-aki Ohshima, Hideki Kurokawa,
ꢀ
and Hiroshi Miura
Graduate School of Science and Engineering,
Saitama University, Saitama 338-8570
CoCl2 6H2O, and KOH as a precipitant, according to the method
ꢂ
described in a previous paper.6 After the reduction, the character-
istic peaks derived from metallic cobalt were observed in the XRD
profiles of both catalysts.
Received September 25, 2007; E-mail: hmiura@apc.saitama-u.
ac.jp
The amounts of cobalt metal supported on the catalysts were
determined quantitatively using an inductively coupled plasma/
atomic emission spectrometer (Leeman Labs, JICP-PS1000UV).
The metal loadings of Co/Al2O3 (NO3-I) and Co/Al2O3 (Cl-P)
were 42.1 and 41.2 wt %, respectively. An XRF spectrometer
(Philips, PW2400) was used for quantitative analysis of potassium
and chloride ions in the catalysts. The data obtained were compen-
sated using calibration factors determined by measurement of
standard samples.
The influence of residual chloride ions on the catalytic
activity of Co/Al2O3 was investigated for liquid-phase
hydrogenation of ketones and aldehydes using Clꢁ-free and
Clꢁ-containing catalysts. The Clꢁ-free catalyst showed high
activity for hydrogenation of both, whereas the Clꢁ-contain-
ing catalysts showed very low activity for ketone hydrogena-
tion.
Seven ketones were selected as reactants: 2-butanone, 3-meth-
yl-2-butanone, 3,3-dimethyl-2-butanone, acetophenone, benzo-
phenone, cyclohexanone, and cyclopentanone. To compare the re-
activities of ketones and aldehydes, butanal and 2-methylpropanal
were also used for hydrogenation. Liquid-phase hydrogenation
over Co/Al2O3 was performed in a stainless-steel autoclave
(100 mL) equipped with a mechanical stirrer, a pressure gauge,
an inlet valve and a thermocouple. Reactant (3.0 mL), ethanol
(solvent, 50 mL), and the reduced catalyst (1.0 g for Tables 1
and 3, and 0.4 g for Figure 1) were placed into the autoclave
through the inlet valve under a H2 atmosphere. Hydrogenation
was carried out at 1.0 MPa (gauge) and 323 K for 1 h (Tables 1
and 3) or 2 h (Figure 1) without further addition of H2. Products
were analyzed by GC (GL Science, TC-WAX capillary column,
diameter ¼ 0:25 mm, length ¼ 30 m).
Catalytic hydrogenation of aldehydes and ketones to form
alcohols, using molecular hydrogen and heterogeneous cata-
lysts, is a key reaction in the production of fine chemicals.
Supported metal catalysts have been widely studied for this
reaction;1,2 in particular, supported Pt catalysts have been the
subject of extensive study in spite of the high relative cost
of the metal. In addition, cobalt catalysts have been investigat-
ed for hydrogenation because when these catalysts are used,
carbonyl groups are hydrogenated preferentially over car-
bon–carbon double bonds. In particular, the hydrogenation re-
action of (E)-2-butenal (crotonaldehyde) using supported co-
balt catalysts has been the subject of a number of investiga-
tions,3–17 because it is difficult to obtain the unsaturated alco-
hol in high yield when metal catalysts are used. We recently
found that alumina-supported cobalt catalyst prepared by a
precipitation method using dichlorocobalt hexahydrate and
potassium hydroxide as a precipitant shows high activity for
selective hydrogenation of ꢀ,ꢁ-unsaturated aldehydes to the
corresponding unsaturated alcohols,6 and that addition of chlo-
ride ions to the reaction media results in a significant increase
in the rate of carbonyl-group hydrogenation compared to that
obtained for Clꢁ-free Co/Al2O3 catalyst.15
Results and Discussion
Table 1 shows the results of ketone and aldehyde hydroge-
nation over Co/Al2O3 (NO3-I) and Co/Al2O3 (Cl-P) catalysts.
During the reaction, acetal or ketal were formed by condensa-
tion of aldehyde or ketone, respectively, with ethanol (solvent)
over the acid sites of the support. Especially, acetals and
ketals were remarkably formed over Co/Al2O3 (Cl-P) pre-
pared from CoCl2 6H2O as a raw material. Other products
were not observed in all experiments.
ꢂ
Co/Al2O3 (NO3-I) catalyst showed high activity for hydro-
genation of all aldehydes and ketones to the corresponding
alcohols. The yield of 2-butanol (41.1%) was higher than that
of 1-butanol (22.2%) under the same reaction conditions, indi-
cating that hydrogenation of ketones is faster than that of alde-
hydes. Santori et al. studied gas-phase hydrogenation of 2-bu-
tanone and butanal over supported Pt catalysts,26 and reported
Compared with aldehyde hydrogenation over supported co-
balt catalysts, the study of ketone hydrogenation has been quite
limited; reports include hydrogenation of acetone over CoB,18
Co/ZnO,19 Co/Al2O3,20,21 Co/TiO2,20 and Co/SiO2,22 and hy-
drogenation of cyclohexanone derivatives,23 substituted aceto-
phenones,24 and enones25 over Raney Co catalysts.
Published on the web May 14, 2008; doi:10.1246/bcsj.81.653

654 Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
ꢁ 2008 The Chemical Society of Japan
Table 1. Hydrogenation of Aldehydes and Ketones Using
Cl-Free (Cl-P) or Cl-Containig (NO3-I) Co/Al2O3 Cata-
lysts
Cl−P
Yield of products %a)
Cl−P−w1
Cl−P−w2
Cl−P−w3
Cl-P
NO3-I
Reactant
Product
catalyst
catalyst
40.4
(3.2)
22.2
(0.5)
O
OH
34.6
(4.9)
24.5
(0.2)
O
0
0.04
0.08
0.12
0.16
OH
Rate of hydrogenation /mmol g–cat −1min −1
O
0.8
(3.8)
41.1
(0.1)
O
O
O
OH
OH
Figure 1. Hydrogenation of butylaldehyde and 2-butanone
using NH3 aq-washed Co/Al2O3 (Cl-P).
0.5
(1.2)
33.5
(0)
Table 2. Chemical Composition of Original and Washed
Co/Al2O3 Catalysts
0.1
(0)
1.5
(0)
cÞ
Catalyst
Content/wt %
ClbÞ
COad
/mmol g-catꢁ1
O
O
OH
OH
CoaÞ
KbÞ
0.3
(0.9)
28.4
(0)
Cl-P
41.2
40.5
40.2
40.3
0.76
0.13
0.04
0.04
<0:01
<0:01
<0:01
<0:01
28
104
114
115
Cl-P-w1
Cl-P-w2
Cl-P-w3
0.1
(0)
26.7
(0)
a) Determined by ICP-AES measurement. b) Determined by
XRF measurement. c) The amount of CO chemisorption
(amount of surface Co metal).
O
OH
OH
OH
O
O
15.1
(38.6)
56.8
(0.4)
I) catalyst, and cyclohexanone showed the highest reactivity
among the reactants used. Compared with aliphatic ketone hy-
drogenation, hydrogenation of acetophenone and benzophe-
none, which contain bulky phenyl groups on the carbonyl
group, gave relatively high yields of the corresponding alco-
hols. It was found that the reactivity of aromatic ketones did
not depend on the number of bulky phenyl groups, clearly in-
dicating that electrical effects, rather than steric hindrance,
play the largest role in determining reactivity.
The activity of Co/Al2O3 (Cl-P) catalyst for aldehyde hy-
drogenation was much higher than that of Co/Al2O3 (NO3-
I), whereas no significant activity was observed for ketone hy-
drogenation over Co/Al2O3 (Cl-P), except in the case of hy-
drogenation of cyclohexanone (Table 1). We previously re-
ported that in the hydrogenation of various ꢀ,ꢁ-unsaturated al-
dehydes to ꢀ,ꢁ-unsaturated alcohols, Co/Al2O3 (Cl-P) acts as
an effective catalyst,6 and that the addition of chloride ions to
the reaction media dramatically promotes the formation of
alcohols over chloride ion-free Co/Al2O3 (NO3-I).15 These
results strongly suggest that chloride ions have a significant
effect on catalytic activity in the hydrogenation of carbonyl
groups. To investigate this, we carried out 2-butanone and
butanal hydrogenation using washed catalysts Co/Al2O3 (Cl-
P-w1–w3) prepared by washing the precursor (Co3O4/Al2O3)
of the Co/Al2O3 (Cl-P) catalyst with NH3 aqueous solution
(0.01 mol Lꢁ1) before reduction. The amounts of supported
Co metal, residual Clꢁ and Kþ ions contained in the catalysts
are summarized in Table 2.
1.9
(9.9)
39.8
(0.6)
a) The values in the parenthesis represent the yield of acetal
or ketal.
that compared with butanal, 2-butanone was more easily hy-
drogenated to the corresponding alcohol; they explained that
the difference in reactivity was attributable to the nature of
the adsorbed species.
3,3-Dimethyl-2-butanone, in which hydrogen atoms are
substituted by methyl groups at the ꢀ-position of the carbonyl
group, underwent little hydrogenation under the conditions
employed, which indicates that steric hindrance around the
C=O group strongly affects the rate of hydrogenation. The re-
activity order of butanones in the hydrogenation reaction over
Co/Al2O3 (NO3-I) catalyst was 2-butanone > 3-methyl-2-
27
´
butanone > 3,3-dimethyl-2-butanone. Simonikova et al. in-
vestigated the effects of steric hindrance on hydrogenation rate
in gas-phase hydrogenation of the above-mentioned butanones
over Cu, Rh, and Pt catalyst supported on kieselguhr, and con-
cluded that the equilibrium constant for substrate adsorption on
active sites is strongly affected by steric hindrance. The reac-
tivity order obtained in that study is the same as ours.
Aliphatic cyclic ketones cyclohexanone and cyclopentanone
also underwent effective hydrogenation over Co/Al2O3 (NO3-

A. Otomo et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
655
Table 3. Competitive Hydrogenation of Butanal and 2-
Butanone over Co/Al2O3 CatalystsaÞ
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