Removal of nitrogen oxides

Nitrogen oxides contained in waste gases can be effectively removed from waste gases by a novel process which comprises contacting the waste gases with activated carbon in the presence of gaseous ammonia at a temperature between about 110.degree. C. and about 350.degree. C. to convert the nitrogen oxides to nitrogen. When waste gases containing sulfur oxides together with nitrogen oxides are subjected to this process, both the nitrogen oxides and the sulfur oxides can be simultaneously removed from the waste gases with a high efficiency. The effects of this process can be enhanced by employing a specific element-supporting activated carbon or an oxidized activated carbon.

DESCRIPTION OF THE PRIOR ART 
The present invention relates to a process for treating a nitrogen 
oxide-containing waste gas. 
In recent years atmospheric pollutions due to the nitrogen oxides (e.g. NO 
and NO.sub.2) contained in waste gases from such industrial installations 
as steam power plants, chemical plants, metal refineries and metal washing 
plants have become a major social concern and a strong demand exists for 
the development and reduction to practice of a process capable of removing 
nitrogen oxides from such waste gases with a high efficiency. Furthermore, 
since the nitrogen oxides are usually contained together with sulfur 
oxides (e.g. SO.sub.2 and SO.sub.3) in the waste gases, a strong demand 
exists for the development and commercial adpatation of a process capable 
of removing nitrogen oxides and sulfur oxides in a single operation. 
The processes hitherto known for the removal of nitrogen oxides are divided 
into four groups, i.e. (1) an absorption process which involves the use of 
water or an aqueous alkali solution, (2) a catalytic decomposition process 
which depends upon, for example, a copper catalyst, (3) a catalytic 
decomposition-reduction process which involves the use of, for example, a 
platinum catalyst, and (4) an adsorption process which employs an 
adsorbent such as silica gel, zeolite or activated carbon. 
However, the above-mentioned absorption process (1) has substantially no 
effect upon NO, besides presenting problems in connection with the 
treatment of waste liquors after the absorption treatment, for instance. 
The catalytic decomposition process (2) entails a marked increase in 
activity of the catalyst due to the concomitant presence of O.sub.2 and 
SO.sub.2, and obligates one to employ a high reaction temperature of not 
lower than about 500.degree. C. The catalytic reduction process (3) in 
which the nitrogen oxide is reduced to nitrogen with a reducing gas such 
as hydrogen, carbon monoxide or a hydrocarbon has the disadvantage that 
O.sub.2, if present, reacts with such reducing gas in the first place to 
consume the latter and the resultant heat of reaction tends to cause a 
sharp increase in the gas temperature which, in turn, reduces the activity 
of the catalyst due, for example, to the sintering thereof. Moreover, when 
sulfur oxides are contained together with nitrogen oxides in the waste 
gas, the catalyst is significantly poisoned by the sulfur oxides. The 
adsorption process (4) is accompanied by such drawbacks that the 
adsorptive capacity of the adsorbent for nitrogen oxide is not 
sufficiently high and especially in the case of silica gel or zeolite, its 
adsorptive capacity is considerably reduced by water vapor which may be 
contained in the gas. To regenerate the adsorbent, the nitrogen oxide 
adsorbed must be desorbed and the gas or liquid containing the nitrogen 
oxide thus removed presents treatment problems. Furthermore, as the 
adsorption-desorption cycle is repeated, the adsorptive capacity of the 
adsorbent for nitrogen oxide is significantly lowered with time. 
On the other hand, there has been known the process involving the use of 
activated carbon for removal of sulfur oxide from waste gases, but when 
nitrogen oxide occurs as well in the waste gases, the speed at which the 
activated carbon eliminates the sulfur oxide is markedly reduced. 
SUMMARY OF THE PRESENT INVENTION 
Under the circumstances the present inventors conducted extensive research 
and have unexpectedly found that when gaseous ammonia is introduced into a 
nitrogen oxide-containing waste gas and the resultant mixture is contacted 
with activated carbon at about 110.degree. C. to about 350.degree. C., the 
nitrogen oxide is successfully reduced to nitrogen which is harmless, and 
that, in this operation, the presence of oxygen in the waste gas results 
in an increased reductive activity for the conversion of nitrogen oxide 
into nitrogen. It has been also found that while activated carbon, as 
such, is sufficiently catalytically active for the reduction of nitrogen 
oxide to nitrogen in the above-mentioned operation, the catalytic activity 
of activated carbon is significantly increased when it supports one or 
more of the specific elements of Ti, Cr, Mn, Fe, Co, Ni, Cu, V, Mo and W, 
and/or it has been previously oxidized. Furthermore, it has been also 
found that when a waste gas containing sulfur oxide together with nitrogen 
oxide is subjected to the above-mentioned operation, sulfur oxide is 
converted into and adsorbed as sulfuric acid and/or ammonium sulfate on 
the activated carbon simultaneously with the reduction of nitrogen oxide 
to nitrogen, thereby, both the nitrogen oxide and sulfur oxide can be 
removed from the waste gases in a single operation. 
The present invention has been accomplished on the basis of said findings, 
and its principal object is to provide a novel and industrially feasible 
process for removing nitrogen oxide with a high efficiency from a nitrogen 
oxide-containing waste gas. Another object is to provide a novel and 
excellent process for removing both nitrogen oxide and sulfur oxide from 
waste gases containing them in a single and simple operation. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the process of the present invention, nitrogen oxide can be removed from 
a nitrogen oxide-containing waste gas by contacting the nitrogen 
oxide-containing waste gas with activated carbon in the presence of 
gaseous ammonia to reduce the nitrogen oxide to nitrogen. The nitrogen 
oxide-containing waste gas may be any of those containing NO, NO.sub.2, 
N.sub.2 O, N.sub.2 O.sub.5 and mixtures thereof. More particularly, the 
waste gas to be treated according to the present invention may be any of 
the waste gases containing such nitrogen oxide, such as the boiler flue 
gases from steam power plants and other plants and the various waste gases 
from such industrial installations as chemical plants, metal refining 
plants and metal washing plants. These waste gases may also contain sulfur 
oxide such as sulfur dioxide, sulfur trioxide and mixtures thereof 
together with nitrogen oxide. 
Such a nitrogen oxide-containing waste gas is contacted with activated 
carbon in the presence of gaseous ammonia. The specific treating 
procedures are optional, and the specific procedure which is advantageous 
comprises previously admixing gaseous ammonia into the waste gas and then 
contacting the resultant gaseous mixture with activated carbon, while use 
may also be made of other procedures, one which comprises permitting the 
waste gas and gaseous ammonia simultaneously to flow in contact with 
activated carbon. The advantageous proportion of gaseous ammonia is not 
less than about 2/3 mole and, for still better results, about 1 to about 
50 moles, per mole of nitrogen oxide (in terms of NO) contained in the 
waste gas. The gaseous ammonia may be admixed into the waste gas after 
being diluted with a gaseous diluent such as air, nitrogen or carbon 
dioxide gas before it is admixed into the waste gas. Particularly when the 
waste gas is free from oxygen, it is desirable to dilute gaseous ammonia 
with air so as to give oxygen of not less than about 0.5 mole per mole, in 
terms of NO, of the nitrogen oxide in the gas to be contacted with 
activated carbon. 
The activated carbon to be employed in the process of the present invention 
may be any of the activated carbons which are based on such known 
materials as charcoal, coal, coke and coconut shell and have been 
activated by conventional activation procedures. It is advantageous to 
employ those activated carbons having the surface area of between about 
200 m.sup.2 /g. and 2,000 m.sup.2 /g., especially of between about 600 
m.sup.2 /g. and about 1,200 m.sup.2 /g. These activated carbons may be 
employed in an optional shape such as granular, crushed or powdery form. 
While the process of the present invention can give rise to excellent 
results with the use of these conventional activated carbons, 
significantly improved results can be attained with the employment of the 
activated carbon which supports thereon one or more of the particular 
elements, i.e. Ti, Cr, Mn, Fe, Co, Ni, Cu, V, Mo and W, and/or has been 
previously oxidized. 
One or a mixture of the above-mentioned optional elements may be supported 
predominantly in the form of the metal as such or in the form of the 
corresponding metal oxide on the activated carbon. The activated carbon 
supporting such an element or elements may be prepared by a per se 
established manner, for example (1) the process comprising compounding a 
material carbon with a compound of the corresponding metal such as a 
water- or solvent-soluble salt, e.g. nitrate or ammonium salt, of the 
metal or a solvent-insoluble oxide or salt of the metal and then, 
carbonizing the compounded material and activating the same in a per se 
established manner, or (2) the process which comprises dissolving said 
metal compound in water or an organic solvent, impregnating or spraying 
activated carbon with the resultant solution and drying the same under 
heating at a temperature between about 60.degree. C. and about 200.degree. 
C. If desired, thus-treated carbon may be further calcined at a 
temperature between about 110.degree. C. and 850.degree. C. in a suitable 
atmospheric gas such as an inert gas (e.g. nitrogen, carbon dioxide etc.), 
an oxidizing gas (e.g. air, steam etc.) or the like. The amount of such 
element supported on the activated carbon is usually not less than about 
0.0001 and, preferably about 0.001 to about 0.2 part by weight in terms of 
the corresponding metal or metals per part by weight of the activated 
carbon. From the practical viewpoints, most advantageous amount of such 
element falls within a range from about 0.001 to about 0.01 part by weight 
in terms of the corresponding metal or metals per part by weight of the 
activated carbon. The activated carbon may further comprise an optional 
additional ingredient such as boric acid, phosphoric acid or their salts. 
The activated carbon which has been oxidized, i.e. the oxidized activated 
carbon, may be obtained by oxidizing activated carbon with an oxidizing 
agent which may take any suitable form such as an oxidizing solution or an 
oxidizing gas. The oxidizing solution mentioned above may, for example, be 
an aqueous solution of H.sub.2 O.sub.2, HNO.sub.3, K.sub.2 MnO.sub.4 or 
NaClO.sub.3. While the concentration of the oxidizing agent in said 
oxidizing solution and the temperature of oxidation treatment vary with 
such factors as the type of oxidizing agent, the concentration of the 
oxidizing agent is usually about 1 to 20 weight percent and the 
temperature is usually about 10.degree. C. to about 80.degree. C. Specific 
treating procedures are optional and include, for example, the procedure 
of immersing the activated carbon in said solution and, then, drying the 
same or the procedure of spraying the activated carbon with said solution 
and, then, drying it. The crucial requirement is that the activated carbon 
and solution are brought into uniform contact with each other. The 
oxidizing gas may, for example, be O.sub.2, O.sub. 3, SO.sub.3, SO.sub.2, 
N.sub.2 O, NO or NO.sub.2. The oxidizing conditions are usually such that 
the concentration of oxidizing gas is 0.01 volume percent to 25 volume 
percent and the temperature is about 20.degree. C. to about 500.degree. C. 
This oxidation treatment may be preferably carried out in the concomitant 
presence of air, water vapor or equivalent. The specific procedure may be 
any of the conventional means heretofore used for solid-gas contact, such 
as the procedure of introducing the gas over activated carbon under 
agitation. 
In obtaining an oxidized activated carbon which supports the 
above-mentioned specific element, the process for allowing the element to 
be deposited and the oxidation process may be performed simultaneously or 
carried out one after another. Thus, the above-mentioned element 
deposition treatment can be carried out on a previously oxidized activated 
carbon, and when use is made of an oxidizing solution, for instance, the 
element deposition treatment and oxidation treatment can be performed 
simultaneously. Alternatively, when an oxidizing gas is employed, the 
oxidation treatment can be performed after the element has been supported 
on the activated carbon. 
In accordance with the present invention, the contact of the waste gas with 
such an activated carbon in the presence of gaseous ammonia should be 
conducted at a temperature between about 110.degree. C. and about 
350.degree. C. At temperatures lower than about 110.degree. C., there will 
be formed microfine particles of ammonium nitrate and/or ammonium nitrate, 
and to trap these particles, complicated operations and equipment will be 
required, whereas the catalytic activity of the activated carbon will be 
rapidly lowered at temperatures higher than about 350.degree. C. The 
advantageous contact temperatures may range between about 150.degree. C. 
and about 250.degree. C. Particularly in case of a waste gas containing 
sulfur oxide together with nitrogen oxide, the contact at a temperature 
between about 180.degree. C. and about 230.degree. C. may give rise to the 
best results. The optimal space velocity (volume of the treated gas per 
volume of the activated carbon per hour) in this contact treatment varies 
with such factors as the kind of the gases, the temperature and the type 
of activated carbon, and generally may be chosen in a range between about 
100 hr.sup.-1 and about 100,000 hr.sup.-1. The most advantageous space 
velocity lies in a range between about 500 hr.sup.-1 and about 4,000 
hr.sup.-1. The contact of the gas with the activated carbon may be 
conducted in any mode of the gas-solid contact such as moving bed, 
fluidized bed or fixed bed system. In case of the moving bed system, the 
gas may flow in a parallel current, a countercurrent or cross current 
relative to the activated carbon. 
By the above-mentioned contacting operation of the nitrogen 
oxide-containing gas with the activated carbon in the presence of gaseous 
ammonia, nitrogen oxide contained in the waste gas is substantially 
reduced to nitrogen which is harmless. This reduction reaction can be 
shown by the following reaction schemes: 
EQU 6NO+4NH.sub.3 .fwdarw.5N.sub.2 +6H.sub.2 O (1) 
EQU 6NO.sub.2 +8NH.sub.3 .fwdarw.7N.sub.2 +12H.sub.2 O (2) 
As mentioned above, the presence of oxygen in the gas to be treated results 
in a marked enhancement upon the reduction of nitrogen oxide to nitrogen, 
and this is surprising to those skilled in the art. 
When the nitrogen oxide-containing waste gas also contains sulfur oxide, 
the latter is converted into and adsorbed as sulfuric acid and/or ammonium 
sulfate on the activated carbon, simultaneously with the reduction of 
nitrogen oxide to nitrogen. This reaction can be shown by, for example, 
the following reaction scheme: 
EQU SO.sub.2 +1/2O.sub.2 +nH.sub.2 O.fwdarw.H.sub.2 SO.sub.4.(n-1)H.sub.2 O* 
(3) 
FNT (The asterisk * denotes the form in which it is adsorbed on the activated 
carbon) 
In this invention, gaseous ammonia is consumed by the reactions thereof 
with nitrogen oxides (1) and (2), but when an excess of gaseous ammonia is 
employed, the excess ammonia reacts with a portion of the sulfuric acid on 
the activated carbon which has been formed as the result of the reaction 
(3) to give ammonium sulfate as shown by the following reaction scheme: 
EQU H.sub.2 SO.sub.4.(n-1)H.sub.2 O*+2NH.sub.3 .fwdarw.(NH.sub.4).sub.2 
SO.sub.4 (n-1)H.sub.2 O* (4) 
This means that the treated gas contains no gaseous ammonia and, therefore, 
there is no fear of secondary nuisance. This is another advantage of this 
invention. 
In case of a waste gas containing nitrogen oxide but not containing sulfur 
oxide, the contact treatment can be continued with a high removal ratio of 
the nitrogen oxide in an exhaustible period without any regeneration 
operation of the activated carbon. 
When the waste gas contains sulfur oxide together with nitrogen oxide, the 
catalytic capacity of the activated carbon is slowly lowered, as sulfuric 
acid and/or ammonium sulfate are adsorbed on the activated carbon through 
the contact treatment of a long period. But, the activated carbon whose 
efficiencies to remove sulfur oxide and nitrogen oxide have been reduced 
can regain the original efficiencies if regenerated by either washing with 
water or heating, and accordingly, can be used a second time for the 
removal of nitrogen oxide and sulfur oxide. 
In conducting the regeneration of the activated carbon by aqueous washing, 
the water temperature may be from about 20.degree. C. to about 90.degree. 
C. and, preferably, about 40.degree. C. to about 80.degree. C., and the 
amount of water may be not less than twice and, preferably, 5 to 10 times 
the weight of the activated carbon. When an alkaline substance such as an 
alkali metal or alkaline earth metal is added to the recovered mixed 
solution of sulfuric acid and ammonium sulfate, gaseous ammonia is 
recovered and the sulfate, which is stable, is additionally obtained. It 
is also one of the features of this invention that the gaseous ammonia 
thus recovered can be reused as part of the ammonia source for the 
simultaneous treatment of nitrogen oxide and sulfur oxide which has 
hereinbefore been described. By way of illustration, if calcium oxide or 
calcium hydroxide is added to the mixed solution containing sulfuric acid 
and ammonium sulfate, there will be recovered gaseous ammonia and calcium 
sulfate. 
In conducting the regeneration of the activated carbon by heating, the 
regeneration temperature is usually higher than about 250.degree. C. and, 
preferably, about 350.degree. C. to about 800.degree. C. The regeneration 
time is generally not less than about 10 minutes and, preferably, 0.5 to 3 
hours. The thermal regeneration may be conducted in an inert gas (e.g. 
nitrogen, combustion gas, etc.), water vapor or a reducing gas (e.g. 
carbon monoxide, hydrogen, etc.) or the like. 
When an inert gas or water vapor is used as a carrier gas in the thermal 
regeneration process, portions of the ammonium sulfate and sulfuric acid 
on the activated carbon are first decomposed into sulfur trioxide, ammonia 
and water vapor and, ultimately, converted to sulfur dioxide, water vapor 
and nitrogen as shown by the following reaction scheme: 
EQU SO.sub.3 +2/3NH.sub.3 .fwdarw.SO.sub.2 +H.sub.2 O+1/3N.sub.2 ( 5) 
This reaction is promoted when the activated carbon suports any of Ti, Cr, 
Mn, Fe, Co, Ni, Cu, V, Mo and W. The other portions of ammonium sulfate 
and sulfuric acid on the activated carbon are first decomposed into sulfur 
trioxide, ammonia and water vapor, and ultimately, the reaction of sulfur 
trioxide with activated carbon gives rise to sulfur dioxide and carbon 
dioxide gas. 
These phenomena may be expressed by means of the following reaction 
schemes: 
EQU (NH.sub.4).sub.2 SO.sub.4 +1/2C.fwdarw.2NH.sub.3 +SO.sub.2 +1/2CO.sub.2 
+H.sub.2 O (6) 
EQU H.sub.2 SO.sub.4 +1/2C.fwdarw.SO.sub.2 +1/2CO.sub.2 +H.sub.2 O (7) 
A portion of ammonia in the reaction (6) is brought into contact with 
activated carbon at an elevated temperature and, accordingly, there is 
formed a basic compound on the surface of the activated carbon, which 
serves to improve the efficiencies to remove the sulfur oxide. 
Furthermore, in addition to the reactions (6) and (7), there takes place 
reaction (5) which suppresses the chemical exhaustion of the activated 
carbon. 
When carbon monoxide is used as the regenerating gas, there take place, in 
addition to the reactions (5), (6) and (7), the reactions (8) and (9) so 
that the chemical exhaustion of the activated carbon can be further 
suppressed. 
EQU (NH.sub.4).sub.2 SO.sub.4 +CO.fwdarw.2NH.sub.3 +SO.sub.2 +CO.sub.2 +H.sub.2 
O (8) 
EQU H.sub.2 SO.sub.4 +CO.fwdarw.SO.sub.2 +CO.sub.2 +H.sub.2 O (9) 
Throughout the present specification as well as claims the abbreviations 
"mg.", "g.", "ml.", "cm.", "m.", "m.sup.2.", ".degree.C", "sec.", "min.", 
"hr.", "wt." and "vol." respectively refer to "milligram(s)", "gram(s)", 
"milliliter(s)", "centimeter(s)", "meter(s)", "square meter(s)", 
"degree(s) centigrade", "second(s)", "minute(s)", "hour(s)", "weight(s)" 
and "volume(s)" and "surface area" is that measured by Brunauer, Emett & 
Teller (B.E.T.) method described in e.g., "Journal of the American 
Chemical Society", 60, 309(1938).

The following examples are further illustrative of this invention. 
EXAMPLE 1 
Catalysts B through K supporting 1 wt. % (in terms of the corresponding 
metal) of the element listed in Table 1 on activated carbon, the carbon 
having a surface area of 660 m.sup.2 /g. and being hereinafter referred to 
as catalyst A, were respectively prepared by adding to said carbon one of 
the aqueous solutions of the nitrates of Ti, Cr, Mn, Fe, Co, Ni and Cu or 
one of the aqueous solutions of the ammonium salts of V, Mo and W and 
calcining the resulting carbon samples in nitrogen gas stream at 
400.degree. C. for 1 hour. 
Twenty ml. each of Catalysts A through K were respectively packed into 
quartz glass columns, 1.4 cm in diameter, and at the temperature of 
110.degree. C., 150.degree. C. and 250.degree. C., respectively, a mixed 
gas composed of 0.2 vol. % of NO, 0.3 vol. % of NH.sub.3, 1.0 vol. % of 
H.sub.2 O, 5.0 vol. % of O.sub.2 and 93.5 vol. % of He was passed at the 
space velocity of 3,000 hr.sup.-1 (atmospheric temperature equivalent) for 
10 hours. The gas samples at the inlet and outlet of each column were 
analyzed by the Saltzman method described in, e.g., "Analytical 
Chemistry", 28, 1810(1956) as well as by gas chromatography. In the 
Saltzman method, the total concentration of nitrogen oxides (NO+NO.sub.2) 
in the gas was determined, and in gas chromatographic analysis (carrier 
gas:He-50 ml./min.; temperature--50.degree. C.; packing--molecular sieve 5 
A; column--4.0 mm. dia..times.2000 mm. long) the concentrations of oxygen, 
nitrogen and nitrogen oxides were determined. 
The concentrations of nitrogen oxide as determined by the two methods were 
in agreement. From the concentrations of nitrogen and nitrogen oxide as 
determined by gas chromatography, it was confirmed that under the 
experimental conditions of this example, the following reaction took 
place. 
EQU 6NO+4NH.sub.3 .fwdarw.5N.sub.2 +6H.sub.2 O 
The results of this experment on Catalysts A through K are summarized in 
Table 1. A control experiment was performed on alumina (Neobead D-4, 
manufactured by Mizusawa Chemical Industries, Ltd., Japan) and Zeolite 
(Molecular Sieve 5 A, manufactured by Linde Company, U.S.A.) The results 
are also set forth in Table 1. 
Table 1 
______________________________________ 
Percent removal of 
nitrogen oxide (%) 
Reaction Reaction 
Reaction 
Tempera- tempera- 
tempera- 
Element ture ture ture 
Catalyst 
supported 110.degree. C. 
150.degree. C. 
250.degree. C. 
______________________________________ 
A None 38 44 78 
B Ti -- 65 -- 
C Cr 55 70 95 
D Mn 50 67 88 
E Fe 52 67 90 
F Co 63 75 98 
G Ni -- 67 -- 
H Cu 91 99 100 
I V 80 88 100 
J Mo -- 70 -- 
K W -- 65 -- 
Alumina (Control) 
0 0 5 
Zeolite (Control) 
0 0 7 
______________________________________ 
Note: The symbol "--" means "not tested". This applies to all the Tables 
appearing hereinafter. 
EXAMPLE 2 
Activated carbon having a surface area of 580 m.sup.2./g. which is 
hereinafter referred to as Catalyst L and another activated carbon having 
a surface area of 840 m.sup.2./g. which is hereinafter referred to as 
Catalyst P were respectively impregnated with an aqueous solution of 
copper sulfate, ammonium vanadate or ammonium molybdate and, after 
evaporation to dryness, were calcined in nitrogen gas stream at 
300.degree. C. for 1 hour to obtain Catalysts M through O and Catalysts Q 
through S supporting 1 wt. % (in terms of the corresponding metal) of the 
element listed in Table 2 on Catalyst L or Catalyst P, respectively. 
Twenty ml. each of Catalysts L through O and Catalysts P through S were 
respectively packed into columns of quartz glass, 1.4 cm. in diameter, and 
at the reaction temperature of 150.degree. C., a mixed gas composed of 0.2 
vol. % of NO, 0.3 vol. % of NH.sub.3, 1.0 vol. % of H.sub.2 O, 5.0 vol. % 
of O.sub.2 and 93.5 vol. % of N.sub.2 was introduced at the space velocity 
of 3,000 hr.sup.-1 (atmospheric temperature equivalent). Samples of the 
gas were analyzed by the Saltzman method as set forth in Example 1 and, 
for each catalyst, the change with time in the percent removal of nitrogen 
oxide was investigated. 
The results are summarized in Table 2. It will be seen that the activity of 
the catalyst did not drop and no change in activity was encountered, 
either, when 0.1 vol. % of SO.sub.2 had been admixed into the gas 
introduced. With any of the catalysts, the SO.sub.2 admixed was completely 
removed. 
Table 2 
______________________________________ 
Unit: -Percent removal of 
nitrogen oxide (%) 
Catalyst 
Element L M N O P Q R S 
Supported None Cu V Mo None Cu V Mo 
______________________________________ 
1 40 95 80 75 35 98 75 75 
5 40 88 82 75 36 98 75 75 
10 45 90 85 75 36 95 80 78 
Reaction 
15 50 89 87 77 37 93 80 80 
time* 20 50 89 87 80 35 92 83 81 
(hours)* 
25 47 90 85 77 35 90 80 80 
30 47 90 88 81 36 88 80 -- 
65 51 90 86 80 -- 90 80 -- 
80 50 89 86 80 -- 90 81 -- 
* 95 50 88 85 80 -- 88 80 -- 
* 100 50 88 87 80 -- 88 79 -- 
______________________________________ 
*(Note) 
During 5 hours of each of the reaction times of 20 to 25 hours and 95 to 
100 hours, 0.1 vol. % of SO.sub.2 was admixed into the gas introduced. 
EXAMPLE 3 
Activated carbon having a surface area of 600 m.sup.2 /g. which is 
hereinafter referred to as Catalyst T sprayed with an aqueous solution 
containing a varying concentration of copper sulfate or ammonium vanadate 
and, then, calcined in nitrogen gas stream at 400.degree. C. to obtain 
Catalysts U through Z supporting various amounts of the copper or vanadium 
component as shown in Table 3. Twenty ml. each of Catalysts T through Z 
were respectively packed into columns of quartz glass, 1.4 cm. in 
diameter, and at the reaction temperature of 150.degree. C., a mixed gas 
composed of 0.2 vol. % of NO, 0.3 vol. % of NH.sub.3, 1.0 vol. % of 
H.sub.2 O, 5.0 vol. % of O.sub.2 and 93.5 vol. % of He was introduced at 
the space velocity of 3,000 hr.sup.-1 (atmospheric temperature equivalent) 
for 10 hours. Gas analyses were performed by the same procedure as 
described in Example 1 to determine the percent removal of nitrogen oxide 
with regard to each catalyst. The results are summarized in Table 3. 
Table 3 
______________________________________ 
Amount of 
supported Percent removal 
Element component as 
of nitrogen 
Catalyst 
supported metal (wt.%) 
oxide (%) 
______________________________________ 
T None -- 50 
U Cu 0.1 78 
V Cu 0.5 90 
W Cu 1.0 98 
X V 0.1 75 
Y V 0.5 85 
Z V 1.0 88 
______________________________________ 
EXAMPLE 4 
To 10 kg. of finely crushed coal of 50 to 200 meshes (Tyler standard sieve) 
were added 2 kg. of pitch as a binder and one of the ingredients mentioned 
in Table 4. After admixing and compounding, the mixture was formed by 
pressing. The formed products were each carbonized at 600.degree. C. and 
activated at 850.degree. C. in the presence of water vapor for 4 hours, 
whereupon the catalysts shown in Table 4 were obtained. 
By a procedure similar to that described in Example 3, 20 ml. of each 
catalyst was tested to determine the percent removal of nitrogen oxide. 
The results are summarized in Table 4. 
Table 4 
______________________________________ 
Percent 
Metal content 
Surface area 
removal of 
Added of catalyst of catalyst nitrogen 
ingredient 
(wt. %) (m.sup.2 /g.) 
oxide(%) 
______________________________________ 
NH.sub.4 VO.sub.3 
0.75 675 85 
CuSO.sub.4 
0.70 650 97 
Cu(NO.sub.3).sub.2 
0.73 680 96 
Fe(NO.sub.3).sub.2 
0.78 650 65 
None -- 680 40 
______________________________________ 
EXAMPLE 5 
Activated carbon having a surface area of 660 m.sup.2 /g. was subjected to 
oxidation and/or metal deposition treatment as set forth in Table 5. 
Twenty ml. each of the thus-obtained catalysts were packed into a quartz 
glass column, 1.4 cm. in diameter, and the mixed gas composed of 0.03 vol. 
% of NO, 0.03 vol. % of NH.sub.3, 5.0 vol. % of O.sub.2, 3.0 vol. % of 
H.sub.2 O and 91.04 vol. % of N.sub.2 was passed through the column at 
150.degree. C. and at the space velocity of 2000 hr.sup.-1 (measured at 
150.degree. C.) for 10 hours. The gas samples at the inlet and outlet of 
the column were tested by the Saltzman method for the total concentration 
of nitrogen oxides. The results are given in Table 5. 
Table 5 
__________________________________________________________________________ 
Percent removal 
of nitrogen 
Metal Deposition 
Oxidation treatment 
Sequence of treatments 
oxide (%) 
__________________________________________________________________________ 
None None 32 
None Oxidized with 2 wt. % HNO.sub.3 
54 
(60.degree. C., 1 hr.) 
None Oxidized with 5 wt. % H.sub.2 O.sub.2 
50 
(60.degree. C., 1/2 hr.) 
None Oxidized with 0.1 vol. % SO.sub.3 
58 
(300.degree. C., 1 hr.) 
None Oxidized with 0.5 vol. % N.sub.2 O 
55 
(40.degree. C., 1/2 hr.) 
None Oxidized with air (400.degree. C., 
54 
(1/3 hr.) 
None Oxidized with 0.5 vol. % O.sub.3 
55 
(15.degree. C., 1/2 hr.) 
0.1 wt.% V 
None 67 
Same as above 
Oxidized with 2.5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, V- 
84 
(80.degree. C., 1/2 hr.) 
deposition 
Same as above 
Same as above Simultaneous oxidation 
81 
and V-deposition 
Same as above 
Oxidized with 0.05 vol. % NO 
Oxidation and, then, 
83 
(200.degree. C., 10 hrs.) 
V-deposition 
Same as above 
Same as above V-deposition and, then, 
83 
oxidation 
1.0 wt. % Ti 
None 45 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
75 
(60.degree. C., 1/2 hr.) 
Ti-deposition 
1.0 wt. % Cr 
None 43 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
78 
(60.degree. C., 1/2 Hr.) 
Cr-deposition 
1.0 wt. % Mn 
None 45 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
74 
(60.degree. C., 1/2 hr.) 
Mn-deposition 
1.0 wt. % Fe 
None 40 
Same as above 
Oxidized with 5 wt. % H.sub.2 0.sub.2 
Oxidation and, then, 
75 
(60.degree. C., 1/2 hr.) 
Fe-deposition 
1.0 wt. % Co 
None 37 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
70 
(60.degree. C., 1/2 hr.) 
Co-deposition 
1.0 wt. % Ni 
None 37 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
73 
(60 .degree. C., 1/2 hr.) 
Ni-deposition 
1.0 wt. % Cu 
None 55 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
80 
(60.degree. C., 1/2 hr.) 
Ni-deposition 
1.0 wt. % Mo 
None 45 
Same as above 
Oxidized with 5 wt. % H.sub.2 O.sub.2 
Oxidation and, then, 
78 
(60.degree. C., 1/2 hr.) 
Mo-deposition 
1.0 wt. % W 
None 40 
Same as above 
Oxidized with 5 wt.% H.sub.2 O.sub.2 
Oxidation and, then, 
76 
(60.degree. C., 1/2 hr.) 
W-deposition 
__________________________________________________________________________ 
(Notes) 
(1)In the case of oxidation with oxidizing solutions, the treatments were 
carried out in aqueous solutions and the amount of each oxidizing aqueous 
solution used was 10 times the weight of activated carbon. 
(2)In the case of oxidation with oxidizing gases, the treatments were 
carried out in air laden with 3 vol. % of moisture and the space velocity 
(atmospheric temperature equivalent) of each oxidizing gas was 1,000 
hr.sup.-1. 
EXAMPLE 6 
To activated carbon having a surface area of 760 m.sup.2 /g. which is 
hereinafter referred to as Catalyst a was added an aqueous solution of the 
nitrate of Ti, Cr, Mn, Fe, Co, Ni or Cu, an aqueous solution of the 
ammonium salt of V, W or Mo or a mixed aqueous solution of ammonium 
vanadate and either phosphoric acid or boric acid. After evaporation to 
dryness, the carbon is calcined in nitrogen gas stream at 350.degree. C. 
for 1 hour, whereby Catalysts b through m listed in Table 6 were obtained. 
The amount of deposition of each metal component on activated carbon was 
0.5 wt. % in terms of the corresponding metal. The amount of deposition of 
phosphoric acid or boric acid was 0.5 wt. % 
Twenty ml. each of the metal-supporting activated carbon Catalysts b 
through m and Catalyst a were respectively packed into columns of quartz 
glass, 1.5 cm. in diameter, and at the temperature of 200.degree. C., 
N.sub.2 gas containing 0.03 vol. % of NO, 0.03 vol. % of NH.sub.3, 0.06 
vol. % of SO.sub.2, 6.0 vol. % of O.sub.2 and 10.0 vol. % of H.sub.2 O was 
introduced at the space velocity of 1,000 hr.sup.-1 (atmospheric 
temperature equivalent). The gas samples taken at the inlet and outlet of 
the column were analyzed by the Saltzman method as set forth in Example 1 
for the total concentration of nitrogen oxides, by the iodimetry method as 
described in Japan Industrial Standard K 0103 (1971) for the concentration 
of SO.sub.2, and by the indophenol method as described in Japan Industrial 
Standard K 0099 (1969) for the concentration of NH.sub.3, respectively, 
and the percent removal of nitrogen oxide and of sulfur oxide at a timed 
interval was determined. The results are summarized in Table 6. 
Table 6 
______________________________________ 
Percent removal of nitrogen 
oxide (NO.sub.x) and sulfur oxide 
(SO.sub.2) at a varying time (%) 
Element 6 hrs. 24 hrs. 48 hrs. 
Catalyst Supported NO.sub.x 
SO.sub.2 
NO.sub.x 
SO.sub.2 
NO.sub.x 
SO.sub.2 
______________________________________ 
a None 43 70 60 70 40 62 
b Ti 70 75 73 75 60 65 
c Cr 70 70 70 68 -- -- 
d Mn 78 70 78 67 -- -- 
e Fe 80 75 83 75 75 70 
f Co 80 77 80 75 -- -- 
g Ni 70 75 70 70 65 65 
h Cu 80 80 82 75 73 73 
i V 85 80 85 75 80 70 
j Mo 73 75 75 68 63 65 
k W 75 70 78 65 60 60 
l V--H.sub.3 PO.sub.4 
89 80 90 80 78 75 
m V--H.sub.3 BO.sub.3 
87 80 89 80 78 76 
______________________________________ 
For all catalysts, the concentrations of ammonia in the gases emerging from 
the outlet of the column were not more than 1 ppm irrespective of reaction 
time. 
After the simultaneous removal of nitrogen oxide and sulfur oxide from the 
gas has been conducted for 48 hours, the reaction column was heated to 
350.degree. C. while N.sub.2 gas was passed through the column at the 
space velocity of 100 hr.sup.-1 (atmospheric temperature equivalent). 
Thus, the catalyst was regenerated at 350.degree. C. for 30 minutes. The 
gas emerging from the catalyst bed was guided into a 5 wt.% aqueous 
solution of H.sub.2 O.sub.2 so as to absorb the NH.sub.3, SO.sub.2 and 
SO.sub.3. 
Following the thermal regeneration of the catalyst, the above-mentioned 
substrate gas was introduced under precisely the same conditions as above 
and the percent removal of nitrogen oxide and of sulfur oxide at a varying 
time interval was determined. The results are set forth in Table 7. 
Comparison of Tables 6 and 7 will reveal that the thermal regeneration of 
the catalyst restores its efficiencies to remove nitrogen oxide and sulfur 
oxide and improves the performance of the catalyst. 
In connection with the removal of nitrogen oxide and sulfur oxide with the 
thermally regenerated catalysts, the concentrations of ammonia in the 
gases at column outlets were not more than 1 ppm for all catalysts. 
Table 7 
______________________________________ 
Percent removal of nitrogen oxide 
(NO.sub.x) and of sulfur oxide (SO.sub.2) 
at a varying time with thermally 
Regererated catalyst (%) 
6 hrs. 24 hrs. 48 hrs. 
Catalyst 
NO.sub.x 
SO.sub.2 
NO.sub.x 
SO.sub.2 
NO.sub.x 
SO.sub.2 
______________________________________ 
a 80 75 68 70 55 65 
b 100 90 90 90 69 85 
c 100 88 85 85 65 80 
d 100 89 85 87 75 81 
e 100 85 80 80 65 75 
f 100 88 78 80 70 78 
g 100 80 85 80 65 65 
h 100 85 88 75 78 70 
i 100 98 90 95 80 95 
j 100 90 79 75 65 78 
k 100 85 75 78 68 75 
l 100 98 93 90 85 90 
m 100 95 90 90 82 91 
______________________________________ 
EXAMPLE 7 
For the Catalysts a and i of Example 6, the same mixed gas composed of 
NO--NH.sub.3 --SO.sub.2 --O.sub.2 --H.sub.2 O--N.sub.2 was passed through 
each catalyst bed for 48 hours under precisely the same conditions as in 
Example 6. Then, each column was cooled to 80.degree. C. and a two-way 
cock was attached to the bottom of the column. The column was maintained 
at a constant temperature of 80.degree. C. Then, 15 ml. of warm water at 
80.degree. C. was run down the column to allow the water to contact with 
the catalyst for about 1 hour. The bottom cock was opened to withdraw the 
extract and the cock was closed. Then, 15 ml. of warm water at 80.degree. 
C. was passed down the column. After 1 hour of contact, the extract was 
withdrawn from the column. This operation was repeated for a total of 5 
times, after which dry air at 110.degree. C. was passed through the column 
for 3 hours to dry the catalyst. Then, in the same manner as Example 6, 
the same mixed gas composed of NO--NH.sub.3 --SO.sub.2 --O.sub.2 --H.sub.2 
O--N.sub.2 was introduced and the percent removal of nitrogen oxide and 
sulfur oxide by the aqueous-regenerated catalyst at a varying time was 
determined. The results are set forth in Table 8. The concentrations of 
ammonia in the gases at the column outlets were not more than 1 ppm in all 
cases of simultaneous removal of nitrogen oxide and sulfur oxide. 
The liquid recovered by the above aqueous washing of the catalyst was a 
mixed solution of sulfuric acid and ammonium sulfate. When a slight excess 
of an aqueous solution of NaOH was added to this solution and the 
resultant mixture was heated to 80.degree. C., the ammonia of the ammonium 
sulfate was recovered in gaseous form and Na.sub.2 SO.sub.4 was also 
formed within the solution. 
Table 8 
______________________________________ 
Percent removal of nitrogen oxide 
(NO.sub.x) and of sulfur oxide (SO.sub.x) 
at a varying time with aqueous- 
regenerated catalyst (%) 
6 hrs. 24 hrs. 48 hrs. 
Catalyst 
NO.sub.x 
SO.sub.2 
NO.sub.x 
SO.sub.2 
NO.sub.x 
SO.sub.2 
______________________________________ 
a 83 75 67 68 55 63 
1 100 96 93 93 77 93 
______________________________________