Catalytic ketonisation of acetic acid over modified zirconia: 1. Effect of alkali-metal cations as promoter

Article abstract of DOI:10.1016/S1381-1169(98)00184-8

The catalytic ketonisation of acetic acid was studied over fifteen different metal-doped zirconia samples. Among all, the catalytic aspects of alkali-metal cation-promoted zirconia were extensively studied and found most effective for ketonisation of acetic acid. The reactions were performed in a fixed-bed reactor by varying the temperatures, flow rates of reactant and mole percent of alkali on the catalyst. Except Li, all the alkali-metal ions were capable of enhancing the catalytic activity. Complete conversion with high selectivity for acetone was observed in the temperature range of 623- 698 K. Among all the alkali-metal-modified zirconia, sodium was the most effective promoter for ketonisation reaction. The observed activity order followed Na > K > Cs > Li.

Full text of DOI:10.1016/S1381-1169(98)00184-8

Ž
.
Journal of Molecular Catalysis A: Chemical 139 1999 73–80
Catalytic ketonisation of acetic acid over modified zirconia
1. Effect of alkali-metal cations as promoter
)
Kulamani Parida , Himangshu Kumar Mishra
Regional Research Laboratory, Bhubaneswar 751 013, Orissa, India
Received 17 January 1998; accepted 6 May 1998
Abstract
The catalytic ketonisation of acetic acid was studied over fifteen different metal-doped zirconia samples. Among all, the
catalytic aspects of alkali-metal cation-promoted zirconia were extensively studied and found most effective for ketonisation
of acetic acid. The reactions were performed in a fixed-bed reactor by varying the temperatures, flow rates of reactant and
mole percent of alkali on the catalyst. Except Li, all the alkali-metal ions were capable of enhancing the catalytic activity.
Complete conversion with high selectivity for acetone was observed in the temperature range of 623–698 K. Among all the
alkali-metal-modified zirconia, sodium was the most effective promoter for ketonisation reaction. The observed activity
order followed Na)K)Cs)Li. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: Zirconia; Ketonisation; Promoter; Acetic acid; Yield and selectivity
w
x w x
10,11 , zirconium 12–14 , rare earth metals
1. Introduction
w
x
w x
15–17 as well as alkaline earth metals 18 and
Long since it has been the practice to obtain
ketones by the pyrolytic decomposition of metal
carboxylates, mostly salts of calcium and tho-
metal oxides supported on pumica, alumina,
silica or titania are found to be active catalyst
for this reaction. Zirconia is also found active in
w
x
w
x
rium 1,2 . Later on attempts are being made to
synthesize ketones, directly by the vapor phase
ketonisation of carboxylic acids over different
the ketonisation of aldehydes and esters 19,20 .
No systematic work has so far been carried
out on the ketonisation of monocarboxylic acid
using metal oxide promoted zirconia. The pre-
sent work deals with the systematic study on the
catalytic behavior of alkali-metal-doped zirconia
for the vapor phase conversion of acetic acid to
acetone which proceeds according to the general
equation:
w
x
solid catalysts 3–5 . As this direct synthesis
method is simple, economical and versatile, ef-
forts are being made for further improvements.
w
x
w x
Oxides of thorium 6–8 , cerium 9 , manganese
)
Corresponding author. Tel.: q91-674-581636; Fax: q91-
2RCOOHsRCORqH2OqCO2
1
Ž .
674-581637; E-mail: root@csrrlbhu.ren.nic.in
1381-1169r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S1381-1169 98 00184-8

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)
74
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
2. Experimental
3.2. Determination of textural properties
2.1. Materials and method
The specific surface area of the catalysts
were determined by adsorbing N2 at liquid ni-
trogen temperature according to the BET method
Zirconium hydroxide gel was prepared by
adding required volumes of 0.4 M ZrOCl2 P
8H2O and 6.7 M NH4OH solutions simultane-
ously to an ammoniacal solution at pHs10.2,
under stirring condition. The precipitate ob-
tained was aged for 24 h, filtered, washed with
distilled water till free from chloride ion and
dried in an oven at 383 K for 12 h. The solid
crystalline mass thus obtained was crushed into
Ž
.
using a Quantasorb Quantachrome USA . Prior
to adsorption–desorption studies all the samples
were degassed at 423 K and 10y Torr for 5 h.
4
3.3. FTIR study
The FTIR spectra of pure and alkali-metal-
modified zirconia samples were recorded at
room temperature on KBr phase using a JASCO
FTIR 5300 spectrophotometer in the range 4000
to 400 cmy1. Before making palettes, all the
samples were heated at 473 K for 2 h.
Ž
.
powders, below 140-mesh y105 m size.
2.2. Precursor for the dopants
The chemicals used as precursors for doping,
Ž
.
LiOH, NaOH, KOH, CsNO3, Mg NO3 2 P
Ž
.
Ž
.
Ž
.
Ba NO3 ,
2
6H 2O, Ca NO3
,
Sr NO3
,
2
2
3.4. Surface basicity
Ž
.
Ž
.
Ž
.
Fe NO3 3 P9H2O, Co NO3 2 P6H2O, Ni NO3 2
Ž
.
Ž
.
P6H 2O, Cu NO 3 P 3H 2O, Ce NO 3 ,
3
2
Surface basicity of the catalysts were deter-
mined on the basis of irreversible adsorption of
Ž
.
Ž
.
Sm NO3 3, and Y NO3 3, unless otherwise
stated are of analytical grade.
Ž
.
some organic acids, such as Phenol pKa s9.9 ,
Ž
.
acrylic acid pKa s4.2 . In each experiment, 10
ml of freshly prepared solution of phenol–
acrylic acid in cyclohexane was pipetted into
adsorption bottle containing 0.1 g catalyst. The
bottles were shaken for 2 h at constant tempera-
2.3. Doped catalysts
The catalysts modified with different metals
were prepared by incipient wetness technique in
which required volume of 0.1 M aqueous solu-
tion of different metal ion was added to the
zirconium hydroxide powder. The pasty mass
thus obtained was evaporated to dryness on a
Ž
.
ture 298 K and the concentration of the sub-
strate in solution in equilibrium with the ad-
sorbed substrate was determined spectrophoto-
metrically.
hot plate, calcined at 723 K for 6 h in a muffled
Sorption experiments were developed at the
furnace at a heating rate of 5 K miny
.
1
Ž
.
wavelength of maximum adsorption lmax, nm
and in the concentration range of the adsorbate
where the Beer–Lambert law was followed. In
each experiment, time needed to achieve equi-
librium condition at constant temperature was
checked and never found more than 1.5 h. The
chemical interaction, adsorbate–catalyst surface
was consistent with the Langmuir adsorption
isotherm equation,
3. Characterization
3.1. Powder X-ray diffraction
Powder XRD patterns of pure and alkali-
metal-doped zirconia were recorded on a Philips
powder diffractometer, equipped with a mono-
chromator and mounted on a Philips PW 1710
c
1
c
Ž
X-ray generator with Cu Ka radiation a1s
s
q
2
Ž .
1
X
bXm
Xm
˚
.
1.54056 A .

(
)
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
75
where c is the concentration of the substrate in
solution, in equilibrium with the adsorbed sub-
strate; b is a constant; X is the amount of the
adsorbed substrate per gram of the solid and Xm
is the monolayer coverage which correspond to
the theoretical amount of solute adsorbed by 1 g
of solid if all sites are covered.
This method provides both the total concen-
tration of the basic sites and their relative
strength by the use of organic acids with differ-
ent pKa. All the samples were heated at 473 K
for 2 h before carrying the experiment. Similar
with 0.5 mol% Na leads to predominantly te-
tragonal phase, whereas samples doped with Li,
K, and Cs show little variation in phase trans-
formation from monoclinic to tetragonal. Ab-
sence of peak due to alkali-metal oxide, indi-
cates migration of metals from the surface to the
zirconia lattice. This type of phenomenon was
w
x
also observed in case of other matrices 22 . The
peaks due to monoclinic phase gradually disap-
pears with increase in sodium content and with
5 mol% Na only tetragonal phase is found in the
sample. The increase in sharpness of the peaks
with increasing Na content shows better crystal-
lization of the solid.
w
x
method was adopted else where 21 .
3.5. Ketonisation of acetic acid
The BET surface area of all the samples
calcined at 723 K are presented in Table 1. The
effect of alkali metals on the surface area have
been studied over a wide range of solids and are
found responsible for the decrease in the spe-
Catalytic ketonisation reaction was carried
out in a fixed-bed quartz reactor 10 mm, i.d.
on line with gas chromatograph. The reactor
Ž
.
w
x
was placed inside a programmable tubular fur-
cific surface area of catalyst 23,24 . Samples
doped with 0.5 mol% of Na, K, and Cs exhibit
almost the same surface area as that of pure
zirconia, whereas sample doped with 0.5 mol%
of Li causes a decrease in specific surface area
to nearly half of pure zirconia. This decrease in
specific surface area may be attributed to the
rearrangement in the original zirconia network
thus reducing the porosity of the solid.
Ž
.
nace Stanton Red croft, UK containing 0.5 g
of the catalyst. A nitrogen flow, saturated with
acetic acid vapor at room temperature was led
through the catalyst. Prior to the catalytic test,
each of the samples was pretreated under nitro-
gen flow at 473 K for 2 h. The products were
Ž
analyzed by on line Gas Chromatograph, CIC,
.
India operated on FID mode and using a Pora-
pack Q column. The authenticity of the products
were verified by comparing the retention time
with the standard sample. At the steady state,
percentage yield and selectivity of ketone were
calculated from quantitative conversion of the
acid.
Fig. 2 represents the FTIR spectra of the
alkali-metal-doped and undoped zirconia. The
1
1
band at 3418 cmy and 1633 cmy are due to
the OH stretching and bending vibrations, re-
spectively. The characteristic peaks for pure
1
zirconia, in the range 400–900 cmy are at-
tributed to monoclinic phase. This also supports
w
x
the earlier report 25 . A broad band possessed
by 5 mol% sodium doped zirconia in this range
indicates a phase transformation from mono-
clinic to tetragonal. Similar type of change is
4. Results and discussion
The X-ray powder diffraction pattern of the
samples calcined at 723 K are shown in Fig.
w
x
also observed by Kitajima 26 . This phe-
nomenon is also supported by XRD. IR spectro-
scopic study of alkali-metal carbonates shows
that the intense bands observed in the range
Ž .
Ž .
1 a and b . The patterns reveal the high crys-
tallinity nature of all the doped and undoped
catalysts. Zirconium hydroxide gel prepared with
ammonium hydroxide at pHs10.2, on calcina-
tion at 723 K shows predominantly monoclinic
phase. However, the same sample when doped
1300–1500 cmy are due to metal carbonates
1
w
x
27 . IR bands for sample b, f, and g in the same
range are not prominent and the haziness in the

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)
76
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
Fig. 1. XRD patterns of pure and alkali-metal-doped zirconia calcined at 723 K.
spectra may probably be due to the adsorbed
carbon dioxide. The vibrational features ob-
every case the absorption of organic acid is in
consistent with the Langmuir adsorption
1
served in the range 1340–1456 cmy for sam-
isotherm Eq. 2 . From the plot of crX vs. c,
we calculated the values of Xm, i.e., saturation
coverage of the solute for a particular adsorbate.
Since the absorption depends upon the pKa
values of the organic acids, thus by definition
Xm values for phenol absorption measure strong
basic sites, whereas the Xm values for acrylic
acid measure the total basicity of the catalyst.
For a particular solid, the weak basic sites are
measured from the difference of Xm of acrylic
acid and phenol absorption. The basicity thus
Ž
Ž ..
ples d and e may be due to carbonate of the
metals formed by the chemical interaction of
carbon dioxide with the hydroxyl groups or
absorbed water over the solid surface. From the
spectra of c, d, and e, it is clear that increase in
sodium contain increases the prominence of the
1
peaks in the range 1340–1456 cmy and with
Ž
.
ZrO2–Na 5.0 mol% a sharp peak at 1456
1
cmy is observed.
Ž
.
The surface basicity values Xm of the rep-
Ž
resentative catalysts are given in Table 1. In
measured with different organic acids phenol,

(
)
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
77
Table 1
metal cation promoted zirconia. However,
sodium promoted sample responds to an appre-
ciable variation in the basic strength which may
be due to the carbonate groups formed on the
surface. The carbonate groups may block the
basic sites and hinder the interaction of incom-
ing acid molecules with the sites nearer to the
carbonate groups.
Ketonisation of acetic acid over alkali-metal
cation promoted zirconia and pure zirconia are
manifested in Fig. 3. From the reaction profile it
is evident that unpromoted and 0.5 mol%
alkali-metal cation promoted zirconia exhibits
negligible activity below 573 K. Beyond this
temperature Li and Na followed a sigmoidal
path, whereas the observed conversion profiles
are linear for unpromoted, K and Cs promoted
zirconia regardless of the gas hourly space ve-
locity.
Physico-chemical properties of alkali-metal-ion-doped zirconia
calcined at 723 K
Active
phase
Alkali-metal Phase SBET Basic sites
Ž
.
mol%
Phenol
Acrylic acid
y1
Ž
y1 . Ž
.
mmol g
mmol g
ZrO2
0.0
MqT 56
MqT 25
TqM 45
39
9
–
14
–
78
80
–
51
–
82
77
ZrO2 –Li 0.5
ZrO2 –Na 0.25
ZrO2 –Na 0.5
ZrO2 –Na 5.0
ZrO2 –K 0.5
ZrO2 –Cs 0.5
T
T
58
52
MqT 59
MqT 56
36
34
TsTetragonal; MsMonoclinic.
.
acrylic acid shows that the catalysts are moder-
ately basic. Except for Na, there is little differ-
ence between the Xm values of pure and alkali-
Catalytic conversion of unpromoted and dif-
ferent mol% of sodium promoted catalyst are
highlighted in Fig. 4. This shows that the activ-
Fig. 3. Influence of active phase upon catalytic activity of alkali-
metal-doped zirconia in ketonisation of acetic acid; GHSVs160
Fig. 2. FTIR spectra of pure and alkali-metal-doped zirconia.
ml gy1 miny1
.

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)
78
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
With alkali-metal cation promoted zirconia,
most frequently observed products in the ketoni-
sation of acetic acid are acetone, carbon dioxide
Ž
Ž ..
and water Eq. 1 . Zirconium dioxide, being
moderately basic showed an appreciable activity
w
x
towards ketonisation. Yekerson 18 and Yeker-
w
x
son et al. 28 investigated some oxidic system
in detail and proposed two different path through
which acetic acid interact with the solid to give
Ž .
acetone. These were: i the formation of bulk
acetates and their decomposition to acetone, and
Ž .
ii surface interaction. The former path is gen-
erally followed by oxides of low lattice energy,
whereas the later preferentially occurs with
solids of high lattice energy. Zirconia, being an
oxide of high lattice energy thus might be al-
lowing surface interaction. Modification of zir-
conia with alkali-metal cations except Li im-
proves its catalytic activity and selectivity. This
decrease in the activity in case of Li doped
sample may be due to the drastic decrease in
surface area of the catalyst. Among the other
samples, sodium promoted zirconia was most
active and selective. The conversion over 5.0
mol% of sodium doped zirconia was almost
99% at 623 K with selectivity greater than 94%.
The above observations may be explained on
the basis of formation of surface carbonate
groups which also supports the earlier report
Fig. 4. Influence of sodium contain on zirconia in ketonisation of
acetic acid; GHSVs160 ml gy1 miny1
.
ity increases with increasing sodium content
from 0.25 to 5.0 mol% in the samples. Contrary
to the 0.5 mol% sodium promoted zirconia, a
linear conversion profile is seen for ZrO2–Na
Ž
.
5.0 mol% sample regardless of reactant space
velocity. In the case of 20 wt.% CeO2–SiO2,
similar type of observation was also observed
w x
4 .
w x
29 . However, the activity of the samples con-
Table 2
Catalytic activity of different metal ion doped zirconia for ketonisation of acetic acid
Ž .
Yield of acetone %
Active phase
548 K
573 K
598 K
623 K
648 K
673 K
698 K
ZrO2
2
3
–
–
–
5
7
5
5
3
4
7
12
13
5
3
5
15
23
23
19
21
21
21
33
25
22
13
20
39
60
55
51
38
51
48
63
51
53
39
49
74
93
90
87
52
90
60
99
78
82
76
85
99
99
99
99
80
99
72
–
–
–
–
–
–
–
–
–
–
–
–
99
Ž
Ž
.
.
ZrO2–Mg 0.5 mol%
ZrO2–Ca 0.5 mol%
ZrO2–Sr 0.5 mol%
ZrO2–Ba 0.5 mol%
ZrO2–Fe 0.5 mol%
ZrO2–Co 0.5 mol%
ZrO2–Ni 0.5 mol%
ZrO2–Cu 0.5 mol%
93
99
99
99
–
–
–
–
99
–
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
Ž
Ž
.
.
.
ZrO2–Ce 0.5 mol%
ZrO2–Sm 0.5 mol%
ZrO2–Y 0.5 mol%
Ž
.
88

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)
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
79
taining K and Cs are higher than pure zirconia
but less than the sodium promoted samples.
This reveals that not only carbonate but also the
alkali-metal cation played certain roles in modi-
fying the surface of the catalyst and thus in-
creasing the catalytic activity of zirconia. The
observed activity order is as follows: Na)K)
C)ZrO2 )Li.
Doping with alkaline earth metals rather de-
Ž
activate the catalyst towards ketonisation cf.
.
Table 2 . Only about 80% conversion is ob-
served in those cases at 698 K. Blackening of
the samples at the end of the reaction confirms
cock formation. This indicates that acetone for-
mation might be taking place by some other
route which favoured cocking. Transition metals
are observed as good promoters for zirconia, but
rapid deactivation makes them less useful for
ketonisation. A remarkable increase in the activ-
ity is observed with Sm doped zirconia, whereas
cerium and yttrium doping reduces the effi-
ciency of the catalyst.
Fig. 6. Yield of ketone in time-on-stream experiment over ZrO2 –
y1
Na 5.0 mol% at 623 K, GHSVs160 ml g
miny1
.
Ž
.
With the linear increase in gas hourly space
Ž
.
velocity GHSV , significant drop in acetone
yield is observed in the temperature range 548–
648 K and also shifts the temperature of maxi-
Ž
.
mum conversion to higher values cf. Fig. 5 .
This effect may be attributed to the variation in
proportion of active sites to reactant concentra-
tion.
Ž
Time on stream reactivity of ZrO2–Na 5.0
.
mol% is depicted in Fig. 6. A slight decrease in
activity is observed during the first 4 h of
reaction at 623 K; thereafter, it remains nearly
constant.
5. Conclusions
For ketonisation of acetic acid, alkali-metals
promoted zirconia are found most active as
compared to other metal ions doped zirconia
samples studied. Acetone is the main product
over pure as well as alkali-metal-modified zir-
conia. Zirconium dioxide, being a high lattice
energy solid, prefers surface interaction with the
Ž
.
Fig. 5. Catalytic activity of ZrO2 –Na 5.0 mol% on ketonisation
of acetic cid at various GHSV.
A

(
)
80
K. Parida, H.K. MishrarJournal of Molecular Catalysis A: Chemical 139 1999 73–80
w x
Ž
.
8
W. Kleine-Homann, Ger. Offen. DE 3709765 6 Oct., 1988 ;
CA 110; p. 5991 7x.
acid for ketonisation. Sodium stabilizes tetrago-
nal phase of zirconia and improves its catalytic
activity and selectivity. Alkali metals, specifi-
cally sodium probably favours the formation of
surface carbonate groups and also modifies the
bulk of the zirconia. Both the modifications are
responsible for acetonisation of acetic acid. The
observed activity order follows: Na)K)Cs)
ZrO2 )Li.
w x
9
Ž
.
R. Novotny, S. Pauls, Ger. Patent 1158050 28 Nov. 1963 ;
CA60; P9156a.
w
w
w
x
Ž
.
10 G.P. Hussmann, US 4 754 074 28 June 1988 ; CA 109;
P192582e.
x
11 V.I. Yekerson, A.M. Rubinshtein, L.A. Gorskaya, Br. Patent
Ž
.
1208802; CA74 14 0ct. 1970 ; 41920w.
x
12 H. Frochlich, M. Schneider, W. Himmele, M. Stromeyer, G.
Ž
.
Sandrak, K. Baer, Ger. Offen. 2758113 5 July 1979 ; CA
91; p. 140346w.
w
w
w
w
w
w
x
13 T. Yokoyama, T. Setoyama, T. Maki; Jpn. Tokyo Koho JP03
Ž
.
261739 21 Nov. 1991 ; CA 116; p. 173566f.
x
14 I.E. Sosnina, E.P. Denisova, M.B. Turova-Polyak, Vestn.
. Ž
Ž
.
Mosk. Univ. Ser 11 22 1967 94, CA 67; 81767p.
Acknowledgements
x
15 M.B. Turova-Polyak, N.T. Thuan, I.E. Sosnina, Zh. Fiz.
Ž
.
Khim. 42 1968 1372, CA 69; 86282c.
The authors sincerely thank Prof. H.S. Ray,
Director, Regional Research Laboratory,
Bhubaneswar, for giving permission to publish
this paper and Dr. S.B. Rao for his valuable
suggestion and constant encouragement. The fi-
nancial assistance from BRNS is highly ac-
knowledged.
x
16 I.E. Sosnina, M.B. Turova-Polyak, Vestn. Mosk. Univ. Ser.
. Ž
Ž
.
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.
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.
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.
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w
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.
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