Process for preparing catalysts for removal of nitrogen oxides

A catalyst for removal of nitrogen oxides which shows extremely good catalytic activity and is excellent in durability and is low in the activity of oxidizing SO.sub.2 into SO.sub.3 be prepared at a low cost by impregnating a titanium oxide carrier with a vanadium sulfate, a vanadyl sulfate or a mixture thereof and then reacting a mixed gas consisting of 0.05 to 100% by mole of ammonia and 99.95 to 0% by mole of an inert gas which is inert to both ammonia and vanadium and vanadyl sulfates with the impregnated carrier while the reaction mixture is maintained at a temperature of 300.degree. to 520.degree. C., and preferably 370.degree. to 450.degree. C., or by shaping a mixture of titanium oxide and a vanadium sulfate, a vanadyl sulfate or a mixture thereof into a desired shape and then reacting a mixed gas consisting of 0.05 to 100% by mole of ammonia and 99.95 to 0% by mole of an inert gas which is inert to both ammonia and vanadium and vanadyl sulfates with the shaped mixture while the reaction mixture is maintained at a temperature of 300.degree. to 520.degree. C., and preferably 370.degree. to 450.degree. C.

The present invention relates to a process for preparing catalysts for 
removal of nitrogen oxides. More particularly, the invention pertains to a 
process for preparing catalysts for removal of nitrogen oxides which 
comprises reacting a mixed gas consisting of ammonia and an inert gas 
which is inert to both ammonia and vanadium and vanadyl sulfates 
(hereinafter referred to as "ammonia-containing gas") with a titanium 
oxide carrier impregnated with a vanadium sulfate, a vanadyl sulfate or a 
mixture thereof or reacting said ammonia-containing gas with a mixture of 
titanium oxide and a vanadium sulfate, a vanadyl sulfate or a mixture 
thereof shaped into a desired shape. 
Metal oxide-containing catalysts have heretofore been used in various 
catalytic reactions. Recently, these removing nitrogen oxides (hereinafter 
referred to as "NO.sub.x ") contained in various waste gases. A process 
which comprises contacting NO.sub.x contained in a waste gas with a metal 
oxide catalyst in the presence of ammonia gas to reduce NO.sub.x into 
harmless nitrogen and water is commercially advantageous and has been used 
exclusively as a process for removal of NO.sub.x. 
As a catalyst used in such a case, various catalysts have been proposed. As 
described in Japanese Patent Kokai (Laid-Open) No. 122,473/74 or Japanese 
Patent Kokai (Laid-Open) No. 128,680/75, catalysts comprising titanium 
oxide and a vanadium oxide show comparatively high catalytic activity and 
is excellent in durability in waste gases among such catalysts. These 
catalysts are prepared by mixing a solution of ammonium metavanadate in a 
solvent with titanium tetrachloride, impregnating activated alumina with 
the resulting mixture, and then drying the alumina thus impregnated. The 
catalysts obtained by said processes give substantially satisfactory 
results in durability and catalytic activity, but the catalysts can not be 
satisfactory. The vanadium-containing catalysts are expensive. Also, 
industrial waste gases often contain SO.sub.2 and O.sub.2. The SO.sub.2 is 
oxidized into SO.sub.3 by the activity of said catalysts for removal of 
NO.sub.x. As the SO.sub.3 concentration in the waste gases increases, 
therefore, the active centers of the catalysts are lost and the activity 
of the catalysts decreases. Further, the increase in the SO.sub.3 
concentration causes corrosion of equipments such as heat exchangers. On 
the other hand, ammonium sulfate and ammonium bisulfate are produced by a 
reaction of said SO.sub.3 with unreacted ammonia. The ammonium bisulfate 
are accumulated in the apparatus, resulting in the blockage of the paths 
in the apparatus which prevents smooth operation. 
As an industrially excellent catalyst for removal of NO.sub.x, therefore, 
the advent of an inexpensive catalyst having high catalytic activity, 
excellent durability and low activity of oxidizing SO.sub.2 into SO.sub.3 
has been desired. 
Therefore, an object of the present invention is to provide a process for 
preparing catalysts for removal of NO.sub.x in which the above-mentioned 
defects of prior art catalysts for removal of NO.sub.x have been obviated. 
Another object of the invention is to provide a process for preparing 
catalysts for removal of NO.sub.x having high catalytic activity and 
excellent durability at a low cost with less operational trouble. 
The other objects and advantages of the present invention will be apparent 
from the following description and claims, taken in conjunction with the 
accompanying drawing which shows a relationship between NO.sub.x removal % 
and time. 
In order to obviate the above-mentioned defects of prior art catalysts for 
removal of NO.sub.x, the present inventors made an extensive study on the 
preparation of a catalyst for reduction of NO.sub.x, and particularly NO 
and NO.sub.2, to search for a catalyst having higher catalytic activity 
and excellent durability as compared with prior art catalysts and which 
does not increase the conentration of SO.sub.3 produced by oxidation of 
SO.sub.2. As a result, processes for preparing catalyst which gives 
satisfactory results only under the specific conditions as described below 
have now been found. 
According to the present invention, there are provided a process for 
preparing a catalyst for removal of nitrogen oxides which comprises 
impregnating a titanium oxide carrier with at least one vanadium compound 
selected from the group consisting of vanadium sulfates, vanadyl sulfates 
and a mixture thereof and then reacting a mixed gas consisting of 0.05 to 
100% by mole of ammonia and 99.95 to 0% by mole of an inert gas which is 
substantially inert to both ammonia and vanadium and vanadyl sulfates with 
the impregnated carrier while the reaction mixture is maintained at a 
temperature of 300 .degree. to 520.degree. C., and a process for preparing 
a catalyst for removal of nitrogen oxides which comprises shaping a 
mixture of titanium oxide and at least one vanadium compound selected from 
the group consisting of vanadium sulfates, vanadyl sulfates and a mixture 
thereof into a desired shape and then reacting a mixed gas consisting of 
0.05 to 100% by mole of ammonia and 99.95 to 0% by mole of an inert gas 
which is substantially inert to both ammonia and vanadium and vanadyl 
sulfates with the shaped mixture while the reaction mixture is maintained 
at a temperature of 300.degree. to 520.degree. C. 
The catalysts obtained according to the process of the present invention 
show very good catalytic activity, are excellent in durability, and are 
less in the amount of SO.sub.2 oxidized into SO.sub.3. Thus, the defects 
fo prior art catalysts have been completely obviated. Further, the amount 
of vanadium supported as an active ingredient of a catalyst can be small. 
Therefore, it is a great advantage of the process of the present invention 
that catalysts for removal of NO.sub.x can be prepared at a lower cost as 
compared with prior art vanadium catalysts. 
Titanium oxide as a catalyst carrier may be one obtained by shaping powdery 
titanium oxide according to a usual method. Titanium oxide of any shape 
such as honeycomb-form, pellet-form, ring-form, etc. may be used. Also, it 
is possible to mix titanium oxide powder itself with a vanadium sulfate, a 
vanadyl sulfate or a mixture thereof and then shape the resulting mixture. 
As a vanadium compound to be supported by or mixed with titanium oxide, any 
one of V or VO compounds in the form of sulfate may be used. For example, 
vanadium (II) sulfate (VSO.sub.4), vanadium (III) sulfate [V.sub.2 
(SO.sub.4).sub.3 ], vanadyl sulfates (VOSO.sub.4), [(VO).sub.2 (SO.sub.4) 
], and [V.sub.2 O.sub.2)(SO.sub.4).sub.2 ], etc. and a mixture thereof may 
be used. The amount thereof supported is 0.1 to 5% by weight, and 
preferably 0.35 to 1.35% by weight, as vanadium atom based on the weight 
of the carrier. If the amount is less than 0.1% by weight, the NO.sub.x 
removal % obtained is low. Also if the amount is more than 5% by weight, 
no additional effect can be obtained, but, according to experimental 
results on a relationship between vanadium content and NO.sub.x removal %, 
the temperature at which the same NO.sub.x removal % can be obtained 
rather increases. It is a large difference between the catalysts of the 
present invention and previously known vanadium catalysts that the use of 
a large amount of expensive vanadium is thus not required in the catalysts 
of the present invention. It is a large advantage that the amount of 
vanadium in the cataysts of the present invention can be rather small. 
The impregnation of a carrier of shaped titanium oxide with a vanadium 
sulfate, a vanadyl sulfate or a mixture thereof may be carried out 
according to a usual method. For example, an appointed amount of a 
vanadium sulfate, a vanadyl sulfate or a mixture thereof is dissolved in 
water to form a uniform solution. A carrier of shaped titanium oxide is 
dipped in the solution, and the solution is then boiled by heating. Thus, 
the carrier can be impregnated uniformly with the solution in a short 
period of time. Also, a mixture of powdery titanium oxide and a vanadium 
sulfate, a vanadyl sulfate or a mixture thereof is moderately moistened, 
and if necessary, added with a binder such as polyvinyl alcohol, and then 
shaped by a conventional catalyst shaping machine into a desired shape 
such as a globular form, a cylindrical form, a ring-form, etc. 
Thus, the carrier is saturated with a solution, and the carrier is then 
recovered from the solution. Moisture contained in pores is evaporated to 
dry the carrier. The carrier is maintained at an appointed temperature and 
the treated with said ammonia-containing gas. The ammonia-containing gas 
used herein consists of 0.05 to 100% by mole of ammonia and 99.95 to 0% by 
mole of an inert gas which is substantially inert to both ammonia and 
vanadium and vanadyl sulfates. Thus, the catalysts of the present 
invention can be obtained. 
Also, when a mixture of powdery titanium oxide and a vanadium sulfate, a 
vanadyl sulfate or a mixture thereof is shaped into a desired shape, 
maintained at an appointed temperature and then treated with said 
ammonia-containing gas, a similar result an be obtained. The 
ammonia-containing gas used in the treatment of the shaped product 
contains 0.05 to 100% by mole of ammonia and if necessary, is diluted with 
gases substantially inert to both ammonia and vanadium and vanadyl 
sulfates such as nitrogen, helium, argon, stream, carbon dioxide, etc. Of 
course, it is possible to use ammonia gas containing no inert gas as the 
case may be. It is usually commercially advantageous to use nitrogen or 
steam as a diluent gas. If the ammonia concentration is lower than 0.05% 
by mole, a long period of time is required for the preparation of 
catalysts. Also, if the ammonia concentration is high and simultaneously 
the charging rate of ammonia is high, the reaction proceeds suddenly and 
thereby cracks are produced in the shaped product owing to thermal stress 
caused by heat of reaction. 
The preparation of catalysts in the present invention is carried out by 
charging a shaped product containing a vanadium sulfate, a vanadyl sulfate 
or a mixture thereof into an ammonia treating apparatus and then 
circulating an ammonia-containing gas through the apparatus. 
Here, the treatment temperature is 300.degree. to 520.degree. C., and 
preferably 370.degree. to 450.degree. C. If the treatment temperature is 
too low, the reaction rate is lowered and the catalyst preparation 
reaction comes to substantially not proceed. Also, if the treatment 
temperature is too high, the reaction rate remarkably increases. As a 
result, not only cracks become easy to be produced in the shaped product 
as described above, but also the temperature approaches to the 
decomposition temperature of ammonia and there is the possibility that 
part of ammonia is decomposed and consumed. Further, it is not preferable 
in that thermal degradation may be caused by sintering of the carrier due 
to the high temperature. On the preparation of catalysts, the ammonia 
concentration decreases gradually since the ammonia circulated is consumed 
by reaction with the vanadium sulfate, vanadyl sulfate or a mixture 
thereof. Therefore, it is desirable to supplement the ammonia-containing 
gas suitably to maintain the ammonia concentration in said reactor at at 
least 0.05% by mole. 
The catalysts produced according to the process of the present invention 
have a pore volume of 0.30 to 0.45 ml/g and a specific surface are of 20 
to 50 m.sup.2 /g. 
It is considered that, for example, vanadyl sulfate (VOSO.sub.4) or 
vanadium (II) sulfate (VSO.sub.4) which has permeated onto the surface of 
pores in a catalyst is subjected to addition reaction with titanium oxide 
as a carrier to form (TiO.sub.2).sub.n .multidot.VOSO.sub.4 or 
(TiO.sub.2).sub.n .multidot.VSO.sub.4, which are then reacted with ammonia 
to form (TiO.sub.2).sub.n .multidot.VO.sub.2 or TiO.sub.2).sub.n 
.multidot.VO as shown by the following reaction formulae: 
EQU 3(TiO.sub.2).sub.n .multidot.VOSO.sub.4 +2NH.sub.3.fwdarw. 
3(TiO.sub.2).sub.n .multidot.VO.sub.2 +N.sub.2 +3H.sub.2 O+3SO.sub.2 
EQU 3(tiO.sub.2).sub.n .multidot.VSO.sub.4 +2NH.sub.3 .fwdarw. 
3(TiO.sub.2).sub.n .multidot.VO+N.sub.2 +3H.sub.2 O+3SO.sub.2 
the catalysts thus prepared show outstanding characteristics in a catalytic 
reaction of removal of NO.sub.x. The catalysts are characterized in that 
less active centers are lost owing to a very low extent of oxidation of 
SO.sub.2 into SO.sub.3 and a reducing gas is selectively reacted with 
NO.sub.x for a long period of time. 
Reductive removal of NO.sub.x with the catalysts of the present invention 
is applicable to all reducing gases such as hydrogen, hydrocarbons, carbon 
monoxide, ammonia, etc. In the treatment of flue waste gas, a remarkable 
effect is produced when ammonia is used as a reducing agent. 
Previously known catalysts containing platinum or copper as an active 
ingredient show strong oxidation activity toward ammonia, and contrariwise 
ammonia is converted into NO.sub.x at high temperatures. As a result, not 
only an NO.sub.x removal percentage reduces suddenly, but also the 
catalysts are poisoned by SO.sub.2 and SO.sub.3 contained in the waste gas 
and their catalytic activity reduces with the lapse of time. Therefore, 
the temperature and SO.sub.x concentration of the waste gas are limited 
and a field of practical use of the catalysts is limited. 
On the other hand, the catalysts of the present invention show a 
selectively reducing activity toward NO.sub.x. Therefore, the catalysts 
are applicable to a wide range of the temperature and SO.sub.x 
concentration of a waste gas. 
When NO.sub.x in a waste gas is removed by reducing it with the catalysts 
of the present invention, NO.sub.x in the waste gas can be decomposed and 
removed at a removal percentage of nearly 100% by treating at a 
temperature of 200.degree. to 500.degree. C, and at a temperature of 
250.degree. 350.degree. C. as the case may be, since the catalytic 
activity of the catalysts at lower temperatures is higher as compared with 
prior art catalysts. The unreacted ammonia in the exit gas can be 
minimized. It is advantageous from viewpoints of apparatus, safety and 
economy that such an operation at low temperatures can be carried out. 
Even if the catalysts are used at an SO.sub.2 concentration of a waste gas 
as high as 2000 ppm, the SO.sub.3 concentration of the waste gas does not 
increase since the catalysts have a very low activity of oxidizing 
SO.sub.2 into SO.sub.3. Also, the catalysts can maintain a stable 
catalytic activity for a long period of time since ammonium sulfate and 
ammonium bisulfate are substantially not deposited in the pores of the 
catalysts. 
When NO.sub.x in a waste gas is removed by reductive decomposition with 
ammonia at a temperature of lower than the decomposition temperature of 
ammonium bisulfate, for example, at a temperature of 250 to 350.degree. C. 
in the presence of prior art catalysts, ammonium sulfate and ammonium 
bisulfate are produced in the pores of the catalysts from SO.sub.3 
produced by oxidation of SO.sub.2, ammonia as a reducing agent and water 
vapor with the lapse of time, and the catalytic activity of the catalysts 
is remarkably reduced. Therefore, a means for recovering the catalytic 
activity of the catalysts had to be taken by increasing the temperature to 
a temperature of higher than the decomposition temperature of ammonium 
bisulfate intermittently to decompose the accumulated ammonium bisulfate. 
On the other hand, in the case of the catalysts of the present invention, 
the amount of ammonium sulfate and ammonium bisulfate accumulated is very 
small and the system reaches its equilibrium state when a certain small 
amount of the sulfates have been accumulated and the amount of the 
sulfates accumulated does no more increase. Therefore, the catalytic 
activity of the catalysts does not change in a worse direction with the 
lapse of time. Although the reasons therefor are not enough clear, it is 
presumed that ammonium sulfate or ammonium bisulfate formed in the 
catalysts are very unstable and are decomposed into N.sub.2, SO.sub.3 and 
H.sub.2 O by reaction with NO.sub.x in the waste gas. 
When SO.sub.3 exists in the waste gas, an equilibrium value for the amount 
of ammonium sulfate and ammonium bisulfate accumulated in the catalysts 
increases in proportion to the SO.sub.3 concentration. At an SO.sub.3 
concentration of about 100 ppm or less which is encountered with usual 
waste gases, however, an NO.sub.x removal percentage merely slightly 
decreases in the early stages and does no more decrease even if time 
proceeds. This is one of the characteristics of the present invention.

The following examples and comparative examples illustrate the present 
invention in more detail. 
EXAMPLE 1 
In a solution of 16.6 g of vanadyl sulfate (VOSO.sub.4 .multidot.3H.sub.2 
O) in 185 g of water was dipped 300g of a titanium oxide (TiO.sub.2) 
carrier in the form of tablet of 5- 6 mm in diameter (trademark CS-246 
manufactured by Sakai Kagaku Co, Ltd., specific surface area 30 m.sup.2 
/g, pore volume 0.32 ml/g), and the solution was boiled for 5 minutes and 
then cooled. 
When the carrier was recovered from the aqueous solution, the carrier had a 
weight of 411.4 g. When the carrier was then dried at 300.degree. C. for 3 
hours, its weight became 307 g. 
The vanadium sulfate carried on titanium oxide carrier as thus prepared was 
packed into a quartz reaction tube of 25 mm in diameter, and was then 
treated for 3 hours by flowing nitrogen gas containing 20% by mole of 
ammonia through the reaction tube while the reaction tube was heated to 
400.degree. C. by an electric furnace. Thus, the weight of the carrier 
became 30.5 g. 
The catalyst thus obtained contained 0.72 g of vanadium atom per 100 g of a 
titanium oxide carrier and had a specific surface area of 29.8 m.sup.3 /g. 
The following NO.sub.x removal reaction was carried out by the use of this 
catalyst: 
Into a quartz reaction tube of 25 mm in diameter was packed 39 ml of the 
catalyst at a packed length of 80 mm. The reaction tube was heated to 
400.degree. C. by an electric furnace. A gas having the composition as 
described below was passed through this catalyst zone at a space velocity 
(NTP basis, based on the volume of the empty reactor, hereinafter referred 
to as "SV") of 10,000 hr.sup.-1. The NO.sub.x removal % (1 -(NO.sub.x 
remained/NO.sub.x charged.times. 100) values obtained by varying the 
reaction temperature successively are shown in Table 1. 
The amount of NO.sub.x was measured by an NO.sub.x measuring apparatus 
manufactured by Denki Kagaku Keiki Co., Ltd. 
Table 
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Gas composition 
Compo- 
nent NO NH.sub.3 
SO.sub.2 
O.sub.2 
CO.sub.2 
H.sub.2 O 
N.sub.2 
______________________________________ 
Content 
400 480 300 5% 12% 10% Balance 
ppm ppm ppm 
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EXAMPLE 2 
NO.sub.x removal reaction was carried out under the same conditions as in 
Example 1 by the use of a catalyst prepared in the same manner as in 
Example 1 except that 20.9 g of vanadium (II) sulfate (VSO.sub.4 
.multidot.7H.sub.2 O) was used in place of 16.6 g of vanadyl sulfate. The 
results obtained are shown in Table 1. 
EXAMPLE 3 
In 500 ml of an aqueous vanadyl sulfate solution prepared in the same 
manner as in Example 1 was suspended 100 g of powdery titanium oxide 
(trademark TCA-888, manufactured by Tohoku Kagaku Kogyo Co., Ltd.) and the 
suspended titanium oxide was then filtered by suction until the amount of 
the aqueous solution became 37% by weight based on the weight of titanium 
oxide. Thereafter, 20 ml of an 8% aqueous solution of polyvinyl alcohol as 
a binder was added, and the mixture was dried at 50.degree. to 70.degree. 
C. with stirring. The resulting powder was granulated, and the granules 
were sieved to adjust their size to from 32 to 42 mesh and then shaped 
into tablets having a diameter of 6 mm and a height of 26 mm by a tablet 
machine. The shaped product was burned at 450.degree. C. for 2 hours, and 
was then treated by heating it for 3 hours while nitrogen gas containing 
40% by mole of ammonia was passed. By the use of the thus obtain 
catalysts, NO.sub.x removal reaction was carried out under the same 
conditions as in Example 1. The results obtained are shown in Table 1. 
EXAMPLE 4 
NO.sub.x removal reaction was carried out under the same conditions as in 
Example 1 by the use of a catalyst prepared in the same manner as in 
Example 3 except that an aqueous vanadium sulfate solution prepared in the 
same manner as in Example 2 was used and that nitrogen gas containing 60% 
by mole of ammonia was used. The results obtained are shown in Table 1. 
COMATIVE EXAMPLE 1 
NO.sub.x removal reaction was carried out under the same conditions as in 
Exmaple 1 by the use of a catalyst prepared in the same manner as in 
Example 3 except that a solution obtained by dissolving 21.6 g of ammonium 
metavanadate in 478 g of water with heating was used as a vanadium raw 
material. The results obtained are shown in Table 1. 
EXAMPLE 5 
In an aqueous solution of 9 kg of vanadyl sulfate (VOSO.sub.4 
.multidot.3H.sub.2 O) in 91 liters of water was dipped 25 kg of a 
ring-form shaped product of titanium oxide having an inside diameter of 15 
mm, an outside diameter of 35 mm and height of 15 mm (manufactured by 
Sakai Kagaku Co., Ltd., a specific surface area 26 m.sup.2 /g, a pore 
volume 0.35 ml/g). The solution was then boiled for 10 minutes and cooled. 
After 10 hours, the shaped product was recovered from the aqueous solution 
and dried at room temperature for 3 days. The dried shaped product was 
packed in an ammonia treating apparatus having an inside diameter of 300 
mm, a height of 500 mm, an inlet for charging ammonia and an outlet for 
removing the gas produced. The inside of the apparatus was replaced by 
nitrogen, and the shaped product was treated for 3 hours by introducing 
ammonia gas at a rate of 1 l/min. at a temperature of 400.degree. to 
420.degree. C. while the apparatus was heated by an electric furnace and 1 
m.sup.3 /min of nitrogen gas was recycled by a blower. 
After the treatment, the resulting catalyst contained 0.68 of vanadium atom 
per 100 g of titanium oxide. 
The catalyst was packed into a mild steel NO.sub.x removal reaction column 
having an inside diameter of 300 mm and a height of 4 m. The waste gas 
from a boiler using bunker A oil was passed through the column and 
NO.sub.x removal reaction was carried out under various conditions. The 
results obtained are shown in Table 2. Also, a relationship between 
NO.sub.x removal (%) and time is shown in the accompanying drawing. 
EXAMPLES 6- 9 
Ring-form catalysts obtained by treating in the same manner as in Example 5 
except that the concentration of vanadyl sulfate in the aqueous solution 
was varied and the catalyst as prepared in Example 5 were pulverized to a 
size of 10 to 20 mesh, and NO.sub.x removal reaction was carried out by 
the use of the catalysts under the same conditions as in Example 1. The 
results obtained are shown in Table 3. It is seen from Table 3 that the 
catalysts of the present invention show excellent catalytic activity at 
low temperatures even if their vanadium content is low. 
COMATIVE EXAMPLE 2 
By the use of a ring-form catalyst prepared in the same manner as in 
Example 5 except that titanium oxide was not impregnated with vanadyl 
sulfate, NO.sub.x removal reaction was carried out the same manner as in 
Examples 6- 9. The results obtained are shown in Table 3. 
Table 1 
______________________________________ 
NO.sub.x removal (%) 
Temp. 
Example 200.degree. C. 
250.degree. C. 
300.degree. C. 
350.degree. C. 
400.degree. C. 
450.degree. C. 
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1 85.6 96.6 99.5 99.8 100 100 
2 82.3 94.5 98.0 99.3 99.8 100 
3 84.2 95.1 98.5 99.6 100 100 
4 81.5 92.5 97.5 99.2 99.7 100 
Comparative 
3.0 9.2 30.2 75.0 85.2 82.0 
Example 1 
______________________________________ 
Table 2 
__________________________________________________________________________ 
Waste gas composition Reaction 
(Balance N.sub.2) NH.sub.3 tempera- 
NO.sub.x 
NH.sub.3 in 
NO NO.sub.2 
SO.sub.2 
O.sub.2 
CO.sub.2 
H.sub.2 O 
Dust 
charged 
SV ture removal 
exit gas 
Ex. 
ppm 
ppm 
ppm 
% % % mg/m.sup.3 
ppm (hr.sup.-1) 
(.degree. C.) 
% (ppm) 
__________________________________________________________________________ 
5 150 
12 300 
4 12 10 20 180 3000 
200 82.5 46 
" " " " " " " " " 250 95.0 18 
" " " " " " " " " 300 99.0 5 
" " " " " " " " " 350 99.5 -- 
" " " " " " " " 7000 
350 89.0 20 
" " " " " " " 130 5000 
350 80.0 2 
__________________________________________________________________________ 
Table 3 
______________________________________ 
Example 
Reac- Comp. 
tion V/TiO.sub.2 
Ex. 2 6 5 7 8 9 
temp. content NO.sub.x removal (%) 
(.degree. C.) 
(wt. %) 0 0.30 0.68 1.4 3.4 5.0 
______________________________________ 
200 -- 85.2 90.3 85.0 81.0 75.2 
250 4.2 93.1 97.2 93.0 90.5 87.1 
300 8.0 97.7 100 97.5 96.0 95.0 
350 16.9 100 100 100 99.3 99.0 
400 23.5 100 100 100 100 100 
______________________________________