Purification of ammonia-containing water by catalytic selective decomposition with novel Pd-supported zirconia

Article abstract of DOI:10.1246/cl.2001.112

Pd-Supported ZrO₂ prepared through a hydrothermal treatment was found to be pronouncedly effective for purification of waste water containing ammonia; NH₃ (1000 ppm) was exclusively converted to N₂ at 433 K in the presence of O₂ and undesirable NO₂^- and NO₃^- were not detected. It was further demonstrated that the Pd/ZrO₂ was insoluble during the reaction and was reusable without any treatment.

Full text of DOI:10.1246/cl.2001.112

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Chemistry Letters 2001
Purification of Ammonia-Containing Water by Catalytic Selective Decomposition
with Novel Pd-Supported Zirconia
Junji Taguchi, Yusuke Yoshinaga, and Toshio Okuhara*
Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810
(Received October 26, 2000; CL-000980)
Pd-Supported ZrO prepared through a hydrothermal treat-
ment was found to be pronouncedly effective for purification of
aqueous solution (25 wt%) was added dropwise to the solution
to form precipitates (pH = 10). The suspension was hydrother-
mally treated at 363 K for 90 h, and then the precipitate separat-
ed was washed with distilled water until no chloride ion was
2
waste water containing ammonia; NH (1000 ppm) was exclu-
3
sively converted to N at 433 K in the presence of O and unde-
2
2
sirable NO2– and NO3 were not detected. It was further
–
detected. The obtained ZrO after the calcination at 723 K for 2
2
2
–1
demonstrated that the Pd/ZrO was insoluble during the reac-
h is denoted to ZrO (H) (surface area = 283 m ·g , amorphous
from XRD). Besides ZrO , TiO (P-25, 46 m ·g ), SiO
2 2 2
Aerosil 300, 300 m ·g ), mesoporous SiO (FSM-16, 970
m ·g , supplied from Dr. S. Inagaki, Toyota Central R&D
Lab.), Active Carbon (AC, 1155 m ·g , Wako Pure Chem.) and
γ-Al O (JRC-ALO-4, 166 m ·g ) were used. All Pd-support-
2
2
2
–1
tion and was reusable without any treatment.
2
–1
(
2
2
–1
2
–1
Removal of NH in waste water is becoming more impor-
3
2
–1
tant, since NH is a serious pollutant because of eutrophication
3
2 3
1
of river, lake, etc. The selective oxidative conversion of NH3
ed catalysts, containing 1.0 wt% Pd, were prepared by incipient
wetness impregnations with an aqueous solution (0.115
to N using solid catalysts has recently attracted much attention
2
–
3
as an alternative to the current NH removal methods such as
mol·dm ) of PdCl (Wako Pure Chem.). After drying at 373 K
3
2
biological treatment, absorption and thermal incineration,
because this catalytic process has the possibility of a single
operation with a relatively small expense. Kurita Kogyo Co.
for 6 h, they were calcined in air at 723 K for 2 h and reduced
in a flow of H at 673 K for 2 h.
2
The oxidation of NH was performed in a glass autoclave
3
3
has recently commercialized a new process, in which NH in
(Taiatsu Techno TEM-V200, 250 cm ) at 433 K as described in
the literature. After an aqueous solution (150 cm ) of NH Cl
3
–
2
6
3
waste water reacts with NO2 to form N over Pt/TiO .
2
2
4
A most desirable method is recognized to be selective
oxidative decomposition of NH with O (or air) to N (eq. (1)).
(containing 1000 ppm of NH ) and a catalyst (1 g) were put into
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3
the reactor, O (about 100 cm ) was introduced into the reactor
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2
2
2
at 5 atm at room temperature (8 atm at 433 K). The gas and liq-
6
,9
4
NH + 3O → 2N + 6H O (1)
uid phases were analyzed with GC and FIA, respectively.
3
2
2
2
–
–
For NO3 and NO , the lower limit of detection was 0.01 ppm
2
There are some reports about the wet air oxidation (WAO)
in the FIA. After the reaction, the concentrations of Pd and Zr
dissolved in the solution were analyzed with ICP (SPS3000
Seiko Instrument Inc.).
3
4
of NH along this line. Imamura et al. and Chakchouk et al.
3
examined WAO of NH (1000 ppm) over Mn–Ce oxides at 536
3
K and 40 atm of air. When pH of the solution was adjusted to
Table 1 shows the results of NH oxidation over 1wt%Pd
3
–
1
2, a large part of NH was converted, while undesirable NO
supported catalysts. Among these catalysts, Pd/ZrO (H) and
3
2
2
–
and NO3 were detected at the concentration of about 50 ppm.
Pd/FSM-16 gave the higher conversions (close to 95%) of NH3.
5
Qin and Aika claimed that RuO /Al O exhibited the highest
In addition, the yields of N reached 92–94% over both the cat-
2
2
3
2
activity for WAO of NH at pH = 12 among various supported
3
catalysts. Recently, we reported that Pt/TiO catalyzed WAO
2
at a moderate temperature, 433 K, without alkalization of the
solution.6 However, there are still issues to be solved, that is,
–
–
the formation of the undesirable NO3 and NO2 and dissolution
of the active components into the solution during the reaction.
Here we wish to report that Pd supported on a high surface
area ZrO prepared through the hydrothermal treatment cat-
2
alyzed very efficiently WAO to N without the formation of
2
NO3– and NO .
–
2
As ZrO supports, two kinds of ZrO were prepared. The
2
2
first one was obtained conventionally from ZrOCl (Wako Pure
2
Chem.) and an aqueous solution of NH (25 wt%) at pH = 10.
3
The ZrO obtained after calcination at 723 K (surface area = 55
2
2
–1
m ·g ) is denoted to ZrO (C). XRD of ZrO (C) showed a
2
2
monoclinic phase of ZrO . The second was prepared with mod-
2
7
,8
ifications of the method in the literature. ZrOCl (7.7 g) was
dissolved in distilled water (600 cm ) and 50 cm of ammonium
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Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
113
alysts. It should be noted that NO2– and NO3– were not detect-
ed over Pd/ZrO (H), while Pd/FSM-16 produced small amounts
2
of NO2– and NO . Pd/ZrO (C), Pd/Al O and Pd/TiO were
–
3
2
2
3
2
less active than Pd/ZrO (H) and Pd/FSM-16 (Table 1). On the
2
other hand, Pd/AC and Pd/SiO were rather active, but pro-
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–
–
duced large amounts of NO and NO . As reported previous-
ly, NO3 species was present on supported Pd catalysts in only
a few % of the amount of initial NH3.
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9
–
Then we examined the reusability of Pd/ZrO (H) as a
2
indispensable function of environmental catalyst. Figure 1 pro-
vides the changes in the conversion of NH by repeating the
3
reaction, where the reaction was carried out using the catalyst
separated by filtration without any pretreatment. It was found
that the conversion of NH on Pd/ZrO (H) was almost
3
2
unchanged when the reaction was repeated at least three times.
On the other hand, the conversions of NH on both Pd/FSM-16
3
and Pd/AC were greatly declined by repeating the reaction.
2
). Pd/TiO was also unfavorable for use because of the slight
2
–
–
NO2 and NO3 were not detected at the second and third runs
over Pd/ZrO (H). These results clearly indicate that
releasing of Pd. While ZrO (C) has the surface area similar to
TiO , the amount of Pd dissolved from the Pd/ZrO (C) was
much smaller than that from Pd/TiO , indicating that the sur-
face of ZrO can stabilize the Pd particles against the dissolu-
2
2
2
2
Pd/ZrO (H) is reusable, keeping the high catalytic performance
2
2
for the purification of NH -containing water.
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2
tion. This is a reason for the insolubility of Pd on the high sur-
face area ZrO (H). XRD measurement of Pd/ZrO (H) showed
2
2
that no Pd crystallite was present, suggesting the high disper-
sion of Pd on Pd/ZrO (H).
2
7
,8,10–13
There are some reports
as for preparation of high
surface area ZrO . A sol–gel method using the alkoxide gave
2
2
–1
ZrO with relatively high surface areas; 120 m ·g by Ward et
2
0
1
2
–1
11
al., and 380 m ·g by Chuah et al. after the calcination at
7
73 K. In addition, surfactant-aided synthesis was recently
1
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reported.
The obtained ZrO by this method had about 300
2
2
–1
m ·g of the surface area after the calcination at 723 K.
Considering the above reports, the hydrothermal treatment
method used in the present study is a promising method for the
preparation of ZrO with the high surface area from the view-
2
points of convenience.
This work was partly supported by Steel Industry
Foundation for the Advancement of Environmental Protection
Technology.
References
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5
6
7
Insolubility of catalyst components during the reaction is
also important for the environmental catalyst. Table 2 shows
the amount of Pd dissolved from the solid catalyst into the
aqueous solution during the reaction (433 K and 6 h). After the
solid catalyst was separated by centrifugation, the solution was
analyzed by ICP. It was clearly revealed that the amounts of Pd
8
P. Afanasiev, A. Thiollier, M. Breysse, and J. L. Dubois,
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Mesopor. Mater., 39, 381 (2000).
9
1
1
0
1
dissolved from Pd/ZrO (H) were zero within the experimental
2
error (the lower limit is 0.03%) in all the runs. Furthermore,
through were not shown in this table, the amounts of Zr dis-
solved in the solution were confirmed to be also negligible for
1
2
J. A. Knowles and M. J. Hudson, J. Chem. Soc., Chem.
Commun., 1995, 2083.
Pd/ZrO (H). On the other hand, large amounts of Pd were dis-
13 G. Pacheco, E. Zhao, A. Garcia, A. Sklyarov, and J. J. Fripiat,
2
solved in the cases of Pd/AC, Pd/FSM-16, and Pd/SiO (Table
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2