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Chemistry Letters 2001
Selective Formation of Acetic Acid from Syngas in the Presence of H O
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over Zirconium Hydroxide
Ken-ichi Maruya,* Koichiro Okumura, and Teruaki Komiya
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503
(Received October 2, 2000; CL-000895)
Acetic acid was selectively synthesized from syngas using
zirconium hydroxide catalysts without precious metals.
The direct synthesis of acetic acid from syngas has been
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investigated using precious metals such as rhodium.
In this
letter, the selective formation of acetic acid from syngas in the
presence of H O over zirconium hydroxide catalysts without
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precious metals is described.
Catalysts were prepared by precipitating metal hydroxide
from the addition of an aqueous solution of 5% ammonia to an
aqueous solution of metal nitrate, washing with distilled water,
and drying the hydroxide at 403 K for overnight. The zirconi-
um hydroxides with different activity were prepared by control-
ling pH in the hydrolysis solution. The filtration follwed by
washing was repeated three times. The CO hydrogenation was
carried out in a conventional flow system with 2.0 g of catalyst
at 573 K and an atmospheric pressure with a flow rate of 100
mL min–1 (CO/H /N = 2/2/1). The products were collected in
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ethanol trap cooled at Dry Ice temperature of 233 K and deter-
mined by GC equipped with Adsorb P-1 column.
As we have already reported, the precipitation of zirconium
hydroxide at lower pH, followed by calcination at 723 K,
results in the lower activity for CO hydrogenation reaction to
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form isobutene as a main product at 673 K. However, the
reaction at 573 K with zirconium hydroxide before calcination
gave the perfectly different results. Table 1 shows the results
for CO hydrogenation over some zirconium hydroxides along
with some metal oxide catalysts. Zr(3) is most effective for the
formation of acetone and methyl acetate. Zr(4) is most effec-
tive for the formation of acetic acid. The preparation at the
higher pH leads to the less active catalyst. Yittrium hydroxide
is most active among the hydroxides of La, Ce, and Y, yielding
large amount of methyl acetate along with methanol, acetic
acid, and ketones. The activity for the formation of these com-
pounds disappears within the initial few-hour reaction, although
decrease of the organic products. It is clear that the presence of
H O leads to much longer catalyst life, indicating that the sup-
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ply of H O is indispensable to the catalytic formation of acetic
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acid. The other effect of H O is the retardation of formation of
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methanol, acetaldehyde, and ketones, leading to the higher
selectivity to acetic acid. The stable catalyst life is shown in no
color change of the catalyst after 48 h-reaction. The selectivity
(about 90%) to acetic acid is much higher and the yield of
acetic acid is lower in almost 10 times than reported best results
(about 65%) carried out at 1 MPa and 523 K with Ph/Na Y-A
the formation of CO is observed.
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On the other hand, the fact that the calcination of Zr(4) at
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23 K causes the disappearance of the catalytic activity as
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shown in Table 1 suggests that the deactivation by the long
reaction is due to the consumption of hydroxy species or water
catalyst.
XRD analysis of catalysts showed only broad spectra. It is
due to no calcination of the catalysts. The avoidance of deacti-
on the surface and, therefore, the continuous feeding of H O
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leads to the steady catalytic reaction. Figure 1 shows the time-
on-stream of CO hydrogenation in the presence over Zr(4) cata-
lyst. The products were collected for every 8 h, i.e., 0–8,
vation by the presence of H O would suggest that the catalyst
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activity is dependent on the water or hydroxy content on the
catalyst. TG measurement showed that there are three tempera-
ture ranges of weight loss from 300 to 773 K, 300–400,
450–600, and above 700 K. The weight loss between 300 and
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0–18, 20–28, 30–38, and 40–48 h, and the reaction time plot-
ted in Figure 1 is the average in the collected time. H O was
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fed by bubbling the reaction gas into water trap cooled with ice.
400 K is due to the desorption of physically adsorbed H O.
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The content of H O was about 0.5%. The increase of the con-
Since the calcination at 723 K resulted in the deactivation of
Zr(4), the weight loss above 700 K should be excluded. Thus,
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tent to 1.0% resulted in the increase of CO and the remarkable
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Copyright © 2001 The Chemical Society of Japan
Maruya, Ken-Ichi
