United States Patent [19]
`Maeshima et al. BEST AV .h..l..l....h..J.ot.c ~vr t
`
`[11]
`
`[45]
`
`4,046,888
`Sept. 6, 1977
`
`[54] METHODS FOR CATALYTIC REDUCTION
`OF NITROGEN OXIDES
`
`[56]
`
`[75]
`
`Inventors: Tsugio Maeshima; Eiichiroh
`Nishikawa; Mitsuko Nakamura, all of
`Ohi, Japan
`
`[73] Assignee: Toa Nenryo Kogyo Kabushiki Kaisha,
`Tokyo, Japan
`
`[21] Appl. No.: 665,946
`
`[22] Filed:
`
`Mar. 11, 1976
`
`[30]
`
`Foreign Application Priority Data
`June 12, 1975
`Japan .................................. 50-71229
`
`Int. Cl.2 .............................................. BOlD 53/34
`[51)
`[52] u.s. Cl ..................................................... 423/239
`[58] Field of Search ................................ 423/212, 239
`
`References Cited
`U.S. PATENT DOCUMENTS
`9/1972
`Petit et al. ............................ 423/239
`7/1975 Carteret al .......................... 423/239
`
`3,689,212
`3,895,094
`
`OTHER PUBLICATIONS
`Katzer, J. R. in "Catalytic Chem. of Nitrogen Oxides",
`Plenum Press, 1975-symposium on 10/7/74.
`Primary Examiner-G. 0. Peters
`[57]
`ABSTRACT
`Process for removing nitrogen oxides from gaseous
`mixtures comprising the same. Ammonia in an amount
`excessive over the stoichiometric amount necessary for
`reducing the nitrogen oxides is introduced into a reac(cid:173)
`tion zone contairiing a catalyst. Then, ammonia in a
`minimum amount necessary for reduction of the nitro(cid:173)
`gen oxides is introduced into the reaction zone.
`
`11 Oainis, 1 Drawing Figure
`
`Umicore AG & Co. KG
`Exhibit 1102
`Page 1 of 7
`
`

`

`8
`
`•
`Cl.:l
`•
`
`a. -200
`
`E a.
`
`100
`
`)(
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`0 z
`0 u
`z
`1-
`LLl
`z
`1-
`z
`LLl
`lJ..
`lJ..
`...J
`::::>
`LLl
`z
`1-
`Q.
`a.
`E
`
`100
`
`z
`0
`)(
`u
`0
`z
`LLl >
`r:r:
`C/)
`0
`z
`.._,
`0
`~
`,..._
`~
`~
`
`Umicore AG & Co. KG
`Exhibit 1102
`Page 2 of 7
`
`

`

`l
`
`4,046,888
`
`2
`DETAILED DESCRIPTION OF THE
`INVENTION
`According to the present invention, nitrogen oxides
`s are removed from a gas containing the nitrogen oxides
`and oxygen by contacting the resulting gaseous mixture
`with a catalyst in the presence of ammonia to reduce the
`nitrogen oxides selectively.
`In short, the present invention relates to a method for
`10 selectively reducing nitrogen oxides contained in ex(cid:173)
`haust gases from stationary sources, such as flue gas
`from the combustion furnace of power plants, by using
`ammonia as a reducing agent, and the most characteris-
`tic feature of the present invention resides in that the
`catalyst used is contacted with ammonia in an amount
`excessive over the stoichiometric amount necessary for
`reduction of nitrogen oxides in an exhaust gas to
`thereby activate the catalyst and then, the amount of
`ammonia is reduced to a minimum amount necessary for
`reduction of the nitrogen oxides to thereby effect the
`catalytic reduction.
`A typical instance of a nitrogen oxide-containing
`exhaust gas to which the method of the present inven(cid:173)
`tion is applied is an exhaust gas from a fixed combustion
`apparatus using coal or petroleum as a fuel, and this
`exhaust gas has, in general, the following composition:
`
`METHODS FOR CATALYTIC REDUCTION OF
`NITROGEN OXIDES
`BACKGROUND OF THE INVENTION
`This invention relates to a process for reducing the
`concentration of nitrogen oxides contained in a gaseous
`mixture. In particular, this invention relates to a process
`wherein the concentration of nitrogen oxides is reduced
`by catalytic reduction.
`Nitrogen oxides are, of course, generally present in
`significant quantities in gaseous mixtures such as flue
`gases. Different methods have been used in the treat(cid:173)
`ment of these gas mixtures. One type of treatment in(cid:173)
`volves the catalytic reduction of the nitrogen oxides. As 15
`processes for catalytic reduction, two methods are
`known in the art: (1) a non-selective reduction method
`in which carbon monoxide, hydrogen or a lower hydro(cid:173)
`carbon is used as the reducing agent, and (2) a selective
`reduction method in which ammonia is used as the 20
`reducing egent. The latter catalytic reduction method
`(using ammonia) is advantageous in that the amount of
`the reducing agent used can be reduced and nitrogen
`oxides can be removed at a ·high ratio. Accordingly,
`various modifications and improvements have ·been 25
`proposed on this method:
`These reduction methods using ammonia are roughly
`c1assified into two groups, nall1ely one in which a noble
`metal component such as platinum, palladium, rhodium,
`or iridium is used as the catalyst and another in which a 30
`base metal, particularly a non-noble transition metal
`component such as copper, iron, vanadium, chromium
`or molybdenum is used as the catalyst.
`Noble metal catalysts are defective in that they are
`drastically poisoned by sulfur oxides generally con- 35
`tained in exhaust gases, and base metal catalysts are
`defective in that severe reaction conditions such as
`elevated reaction temperatures and reduced space ve(cid:173)
`locities should be adopted in order to improve their
`activities. In view of the fact that exhaust gases dis- 40
`charged in large quantities . from boilers which have
`now a very large scale should be treated for removal of
`nitrogen oxides therefrom and temperatures of these
`exhaust gases are generally low, it is desirable to de(cid:173)
`velop a methOd in which nitrogen oxides can be re- 45
`moved effectively under such reaction conditions as a
`lower temperature and a higher space velocity. Further,
`if ammonia added as the reducing agent is discharged
`into open air in the unreacted state, there is a fear that it
`causes another environmental pollution. Accordingly, it 50
`is also desirable to develop a method in which no unre(cid:173)
`acted ammonia is discharged.
`
`SUMMARY OF THE INVENTION
`In accordance with this invention, gaseous mixtures 55
`such as flue gases are treated to reduce the nitrogen
`oxides content thereof by contacting with a catalyst an
`amount of ammonia in excess of the stoichiometric
`amount necessary to reduce the nitrogen oxides in the
`gaseous mixture. Next, the gaseous mixture is contacted 60
`with a zeolite catalyst in the presence of the minimum
`amount of ammonia necessary to reduce the nitrogen
`oxides contained therein.
`
`NOx: about 100 to about 1,000 ppm
`SOx: about 100 to about 3,000 ppm
`0 2: about 1 to about 10%
`C02: about 7 to about 13%
`steam: about 7 to about 13%
`
`As pointed out hereinabove, a flue exhaust gas gener(cid:173)
`ally contains a sulfur oxides and oxygen in addition to
`nitrogen oxides. Accordingly, it is necessary to perform
`removal of nitrogen oxides while eliminating influences
`of sulfur oxides and oxygen. The nitrogen oxide present
`in flue gas (hereinafter referred to as "NOx'') is com(cid:173)
`posed mainly of nitrogen monoxide (NO) and nitrogen
`dioxide (N02). The nitrogen oxide content in the flue
`gas depends on combustion conditions such as the nitro(cid:173)
`gen compound content in a fuel, the amount of air and
`the combustion· temperature. The sulfur oxide content
`in the flue gas varies depending on the sulfur compound
`content in the fuel.
`Ammonia is contacted with the exhaust gas main(cid:173)
`tained at about 200• to about soo• C. For example, in the
`case of an exhaust gas from a combustion furnace of a
`power plant, ammonia is added to the exhaust gas main(cid:173)
`tained. at about 200° to about soo· c., which has been
`passed through an economizer.
`In the activating treatment of the present invention,
`ammonia is contacted with the exhaust gas in an amount
`excessive over the stoichiometric amount necessary for
`reduction of nitrogen oxides contained in the exhaust
`gas.
`Reduction of nitrogen oxides to nitrogen is expressed
`by the following reaction formulae:
`
`BRIEF DESCRIPTION OF THE DRAWING
`The Figure is a graph depicting the performance of
`the method of the present invention compared to prior
`art methods.
`
`65
`
`In the catalyst activating treatment of the present
`invention, the amount of ammonia is so selected that
`unreacted ammonia is not discharged, and it is generally
`at least about 1.2 times the stoichiometric amount. It is
`
`Umicore AG & Co. KG
`Exhibit 1102
`Page 3 of 7
`
`

`

`4,046,888
`
`5
`
`3
`preferred that ammonia be introduced in an amount
`about 1.2 to about 3 times the stoichiometric amount.
`This activating treatment is characterized in that the
`above-mentioned excessive amount of ammonia is
`added at prescribed intervals while the reduction reac-
`tion of nitrogen oxides is being performed. It is also
`possible to accomplish this activating treatment by mix(cid:173)
`ing ammonia into nitrogen or air before the start of
`reduction of nitrogen oxides and contacting the catalyst
`with the resulting gaseous mixture. It is preferred that. 10
`this activating treatment be conducted under the same
`conditions. as adopted for the reduction reaction of
`nitrogen oxides.
`After completion of this activating treatment, the
`amount of ammonia introduced in the reaction zone is 15
`adjusted to a minimum amount necessary for reduction
`of nitrogen oxides, generally not larger than about 1.2
`times the stoichiometric amount, especially about 1.0 to
`about 0.7 times the stoichiometric amount.
`It is preferred that contact of the nitrogen oxide-con- 20
`taining exhaust gas with the catalyst be performed by
`passing the exhaust gas through a fixed bed of the cata(cid:173)
`lyst. As the reaction conditions, there may be adopted a
`reaction temperature of about zoo· to about 5oo· c.,
`preferably about 250° to about 40()• c., and a gas space 25
`velocity of about 2,000 to about 100,000 V /H/V, pref(cid:173)
`erably about 5,000 to about 30,000 V /H/V. Since the
`activity of the ammonia reduction of nitrogen oxides is
`lowered at higher or lower temperatures, good results
`are obtained when a mixture of the exhaust gas and 30
`ammonia is contacted with the catalyst bed at a temper(cid:173)
`ature within the above-mentioned range.
`As the catalyst that can be used for practicing the
`method of the present invention, there can be men(cid:173)
`tioned (1) a crystalline aluminosilicate, (2) a product 35
`pbtained by exchanging an alkali metal ion in a crystal(cid:173)
`line alumino-silicate with at least one metal cation hav(cid:173)
`ing an activity of reducing nitrogen oxides, and (3) a
`supported catalyst formed by supporting, by the im-·
`pregnation treatment, an active metal component capa- 40
`ble of reducing nitrogen oxides on a carrier obtained by
`removing an alkali metal ion from a crystalline alumino(cid:173)
`silicate.
`The above-mentioned crystalline aluminosilicates
`used in the present invention have a chain, laminate or 45
`three-dimensional
`reticulate
`framework
`structure
`wherein methane-type Si04 tetrahedra are combined
`with A104 tetrahedra through oxygen atoms. The Al04
`tetrahedra have a negative charge and, therefore, com(cid:173)
`bine with a corresponding cation. The water of crystal- so
`lization is thereby kept by the electrostatic force of the
`cation. The cations generally include alkali metal ions
`and alkaline earth metal ions.
`Spaces surrounded by the reticulate structures of
`Si04 tetrahedra and Al04 tetrahedra form cavities or SS
`paths comprising the cavities connected with each
`other. Water of crystallization is kept in the cavities. By
`heating, the water is removed to leave porous adsorp(cid:173)
`tion medium.
`Substances to be adsorbed are introduced in the cavi- 60
`ties or paths through pores of the reticulte structure and
`thereby adsorbed therein. The pores having a uniform
`diameter exhibit a molecular sieve effect; namely, only
`molecules having diameters smaller than pore diameter
`are adsorbed and thereby separated, leaving molecules 65
`of larger diameters.
`The crystalline aluminosilicates are classified accord(cid:173)
`ing to pore diameter and Si02/ Al20 3 molar ratio. In the
`
`4
`present invention, those having pore diameters in the
`range of about 3-15 A and Si02/ Ah03 molar ratios of
`above about 2 are preferred. As the crystalline alumino(cid:173)
`silicate, there may be used both natural and synthetic
`zeolites.
`Suitable natural zeolites are:
`
`Mordenite: (Ca, K 2, Na2) [A1Sis012] 2·7H20
`Erionite: (K2, Na2, Ca) [AlSi30s]r6H20
`Natrolite: Na2[AhShOto] · ZH20
`Chabazite: (Ca, Na2) [A}zSi4012] · 6H20
`Faujasite: Na2Ca [AhS401!) 2·16H20
`
`The natural zeolites contain alkaline earth metals,
`with alkali metals.
`As the synthetic zeolites, there may .be used synthetic
`faujasite and synthetic mordenite. The synthetic fauja(cid:173)
`sites include:
`Zeolite-A: 1.0 ± 0.2M21 .. 0 :Ah03 :1.85 ± 0.5Si0z.
`:YH20 (wherein M represents a metal, n represents
`a valence of M and Y represents a number of about
`6 or below).
`Zeolite-X: l.O ± 2Mun0 :Ah03:5 ± O.SSiOz:YH20
`(wherein M represents a metal of a valence of from
`l to 3, inclusive, n repre~nts a valence of M and Y
`represents a number of about 8 or below).
`Zeolite-Y: 0.9 ±
`0.2Na20:A120 3:WSi02:YH20
`(wherein W represents a number between 3 and 6,
`inclusive, and Y represents a number of about 9 or
`below).
`The synthetic mordenites include, for example:
`Zeolite-L: 1.0 ± O.lM2JnO :Ak0:!:0.4 ± 0.5SiO:!:YH-
`20 (wherein M represents a metal, n represents a
`valence of M, and Y represents a number from 0 to
`7, inclusive).
`Especially preferred crystalline aluminosilicates are
`those having a pore diameter in the range of about 6-13
`A and Si02/ Al20 3 molar ratio of about 2-6. For exam(cid:173)
`ple, synthetic faujasite having a pore diameter of abut
`8-9 A and Si02/ A)z03 molar ratio of about 2-3 and
`other synthetic faujasites having a pore diameter of
`about 8-9 A and Si02/ Ah03 molar ratio of about 4-6
`are preferred.
`A zeolite catalyst having incorporated therein an
`active metal ion is prepared by contacting a crystalline
`aluminosilicate with an aqueous or organic solution of
`an active metal compound according to a customary
`method. The ion exchange ratio is not particularly criti(cid:173)
`cal, but it is generally preferred that the ion exchange
`ratio be about 60 to about 100%.
`As the active metal, there is employed at least one
`member selected from copper, cobalt, nickel, vanadium,
`molybdenum, chromium, tungsten, manganese, plati(cid:173)
`num, silver and iridium.
`The catalyst suitable for the practice of the present
`invention is formed by reducing the content of alkali
`metal in a crystalline aluminosilicate below 0.6 equiva(cid:173)
`lent per gram atom of aluminum and supporting at least
`one active metal compound on the so treated alumino(cid:173)
`silicate by the impregnation treatment.
`The ion-exchange for reducing the alkali metal con(cid:173)
`tent in the aluminosilicate below 0.6 equivalent per
`gram atom of aluminum may be accomplished by any
`method, as far as it can reduce the alkali metal content
`below ·the· above-mentioned level. In general, this ion
`exchange is accomplished by contacting an aluminosili(cid:173)
`cate with an aqueous or non-aqueous (organic solvent
`or the like) solution containing a hydrogen ion, an ion
`
`Umicore AG & Co. KG
`Exhibit 1102
`Page 4 of 7
`
`

`

`4,046,888
`
`5
`capable of being converted to a hydrogen ion, an alka(cid:173)
`line earth metal ion or a rare earth metal ion. For this
`ion exchange treatment, water is the medium most pre(cid:173)
`ferred in view of the operation and apparatus. Any
`organic solvents capable of ionizing the metal com- 5
`pound used can also be employed. For example, alco(cid:173)
`hols such as methanol, ethanol, propanol and butanol,
`amides such as dimethylformamide and diacetamide,
`ethers and ketones are preferably employed.
`An ion convertible into hydrogen ion is ammonium 10
`ion from organic and inorganic ammonium compounds
`such as ammonium chloride, ammonium sulfate, ammo(cid:173)
`nium carbonate, ammonium bromide, ammonium bicar(cid:173)
`bonate, ammonium sulfide, ammonium nitrate, ammo(cid:173)
`nium formate, ammonium acetate, ammonium hydrox- 15
`ide, tetraalkyl ammoniumammonium (tetramethyl am(cid:173)
`monium) and tetramethyl ammonium hydroxide. The
`aluminosilicates ion-exchanged with ammonium ion are
`converted into hydrogen ion-containing aluminosili(cid:173)
`cates by calcination, thereby releasing ammonia.
`As rare earth metal ion sources, there may be used
`salts of metals such as cerium, lathanum and praseo(cid:173)
`dymium. Suitable salts include, for example, chlorides,
`sulfates, sulfides, nitrates, nitrites, carbonates, bicarbon(cid:173)
`ates, acetates, benzoates, formates and tartarates. Partie- 25
`ularly preferred metal salts are chlorides, nitrates and
`acetates.
`As alkaline earth metal ion sources, there may be used
`inorganic and organic salts such as chlorides, bromides,
`carbonates, sulfates, nitrates, acetates, formates, oxa- 30
`lates of calcium, magnesium and strontium.
`The ion exchange treatment for the catalyst will now
`be described.
`An alkali metal-containing aluminosilicate is im(cid:173)
`mersed once or repeatedly in a medium containing a 35
`hydrogen ion, an ion capable of being converted to a
`hydrogen ion, an alkaline earth metal ion or a rare earth
`metal ion. Alternatively, a medium containing a cation
`such as mentioned above is conveyed through a contact
`column packed with an alkali metal-containing alumi- 40
`nosilicate to bring the alumino-silicate into contact with
`such medium. The specific amount of the alkali metal is
`removed from the aluminosilicate by the ion exchange
`with the above-mentioned cation.
`Such conditions as the cation concentration in the 45
`medium, the contact time and the amount of the alumi(cid:173)
`no-silicate used for the ion exchange are chosen so that
`the the alkali metal content in the aluminosilicate is
`reduced below 0.6 equivalent, preferably 0.2 to 0.6
`equivalent per gram atom of aluminum.
`The aluminosilicate ion-exchanged with ammonia can
`be converted to a hydrogen ion-exchanged aluminosili(cid:173)
`cate by washing the aluminosilicate and calcining it at
`about 300• to about 100• C. to release the ammonium
`ion.
`An especially preferred ion-exchange method is one
`in which the alkali metal ion is exchanged with an am(cid:173)
`monium ion.
`In addition to the crystalline aluminosilicate, there
`may be employed a mixture of crystalline alumino-sili- 60
`cate and, incorporated therein, about 1 to about 30% by
`weight of a refractory substance. Examples of refrac(cid:173)
`tory substances include at least one inorganic oxide
`selected from alumina, magnesia,
`titania, zirconia,
`hafnia, silica and diatomaceous earth. Further, in pre- 65
`paring a molded article of the catalyst, it is possible to
`add a suitable amount, for example, about 2 to about
`40% by weight, of alumina sol or the like as a binder.
`
`6
`The above-mentioned active metal component having
`an activity of reducing nitrogen oxides is supported on
`the thus prepared aluminosilicate carrier by the impreg(cid:173)
`nation treatment. Most preferred metals are copper,
`iron, chromium, and vanadium, and better results are
`obtained when at least one metal selected from them is
`employed.
`The active metal component is preferably employed
`in the form of a metal, a metal oxide, a metal sulfate or
`a mixture thereof. An especially preferred form is a
`sulfate in the case of copper and iron and an oxide in the
`case of chromium and vanadium.
`The amount of the active metal component in the
`catalyst is a catalytically effective amount, for example,
`about 1 to about 20% by weight (as metal), preferably
`about 2 to about 10% by weight, based on the final
`catalyst.
`The active metal component is supported on the alu(cid:173)
`minosilicate by the impregnation treatment. This im-
`20 pregnation treatment comprises steps of immersing the
`above-mentioned aluminosilicate carrier in an impreg(cid:173)
`nation solution formed by dissolving a soluble com(cid:173)
`pound of the active metal in a suitable medium and
`separating from the solution the active metal compo(cid:173)
`nent-impregnated carrier. The concentration of the
`active metal compound in the impregnation solution,
`the amount of the solution is used for the impregnation
`treatment, the impregnation time and the impregnation
`temperature are chosen appropriately so that a desired
`amount of the active metal component is supported on
`the alumino-silicate carrier.
`The preferred impregnation time is about 5 minutes to
`about 1 hour, which is much shorter than the time re(cid:173)
`quired in the ion exchange method. It is important that
`the active metal component should be supported under
`such conditions that cations in the aluminosilicate, such
`as alkali metal, alkaline earth metal, hydrogen and rare
`earth metal ions, are not removed from the aluminosili-
`cate.
`The soluble compound of the active metal to be used
`for the impregnation treatment is a compound that can
`be decomposed at a high temperature and can be con(cid:173)
`verted to an oxide by calcination. Preferred soluble
`compounds include inorganic salts such as nitrates,
`chlorides and sulfates and organic salts such as acetates,
`tartarates and oxalates.
`As the medium of· the impregnation solution, there
`may be employed water, inorganic acids, organic acids,
`so other organic solvents and mixtures thereof. Preferred
`inorganic acids are hydrochloric acid, nitric acid and
`sulfuric acid. Preferred organic acids are mono- and
`poly-carboxylic acids such as acetic acid and citric acid.
`As other organic solvent, there are preferably em-
`55 ployed alcohols, aldehydes, amines and esters. Alcohols
`having 1 to 10 carbon atoms, especially isopropyl, alco(cid:173)
`hol, n-butyl alcohol, isobutyl alcohol, pentyl alcohol
`and isopentyl alcohol, are preferably employed. Alde-
`hydes having 1 to 10 carbon atoms, especially acetalde(cid:173)
`hyde, ethylaldehyde and propylaldehyde, are prefer(cid:173)
`ably employed. As the amine, there can be employed,
`for example, alkyl amines such as dimethyl amine and
`triethyl amine, and as the ester, there can be used, for
`example, ethyl formate, ethyl acetate, isopropyl acetate
`and butyl acetate.
`Impregnation of the active metal component will now
`be described by reference to copper as the active metal
`component.
`
`Umicore AG & Co. KG
`Exhibit 1102
`Page 5 of 7
`
`

`

`4,046,888
`
`25
`
`7
`An aluminosilicate carrier prepared according to the
`above-mentioned method is immersed in an aqueous
`solution of copper nitrate, copper chloride or copper
`sulfate. The impregnation treatment is thus carried out
`under the above-mentioned conditions, and the copper 5
`component is supported on the aluminosilicate carrier.
`After this impregnation treatment, the supported cat(cid:173)
`alyst is separated from the medium, and it is heated to a
`temperature of about so· to about 150° c. in the pres(cid:173)
`ence or absence of oxygen. Then, the supported catalyst 10
`is calcined at a temperature of about 300• to about 700°
`C. to thereby convert the metal compound to an oxide
`acting as an active metal component.
`The form of the catalyst used in the method of the
`present invention is not particularly critical, but it is 15
`generally preferred that the catalyst be molded to have
`a form having a large contact surface and facilitating
`passage of the gas, such as a cylindrical or spherical
`form or a form resembling a Raschig ring.
`In one embodiment of the present invention, the tern- 20
`perature of an exhaust gas containing nitrogen oxides,
`sulfur compounds and oxygen is adjusted to about 200°
`to about soo· c. and ammonia is incorporated in the
`exhaust gas in an amount not smaller than about 1.2
`times, preferably about 1.2 to about 3 times, the stoi(cid:173)
`chiometric amount necessary for reduction of nitrogen
`oxides contained in the exhaust gas. Then, the resulting
`gas mixture is contacted with a fixed bed of a zeolite
`catalyst, wherein the zeolite catalyst is activated. Then, 30
`the amount of ammonia is reduced to about 1.0 to about
`1.2 times the stoichiometric amount necessary for re(cid:173)
`duction of the nitrogen oxides, and reduction of the
`nitrogen oxides is carried out. This catalyst-activating
`treatment is conducted at prescribed intervals for about 35
`20 to about 90 minutes by increasing the amount fed of
`ammonia to the above-mentioned excessive amount and
`contacting the catalyst with ammonia.·
`According to another embodiment of the present·
`invention, the catalyst is contacted in advance with 40
`ammonia-containing nitrogen gas or. air, and then am(cid:173)
`monia in the above-mentioned minimum amount neces(cid:173)
`sary for reduction of nitrogen oxides in the exhaust gas
`is incorporated into the exahust gas in the same manner
`as described above and the gaseous mixture is subjected 45
`to the catalytic reduction of nitrogen oxides.
`FIG. 1 is a graph showing conversions of nitrogen
`oxides obtained in the methods of the present invention
`and a comparative method. In FIG. 1, a curve connect(cid:173)
`ing points 1 and 2 shows the conversion of nitrogen 50
`oxides obtained when ammonia is added to the exhaust
`gas in an amount equal to the stoichiometric amount
`necessary for reduction of nitrogen oxides. From this
`curve, it is seen that a stationary value is attained after
`passage of about 30 minutes. When an excessive amount 55
`of ammonia is added to the above gas mixture, the con(cid:173)
`version of nitrogen oxides is improved from the point 2
`to the point 5, and, then, the stationary state is attained
`and continued. The conversion attained when nitrogen
`oxides are reduced by adding a stoichiometric amount 60
`of ammonia to the exhaust gas after the catalyst-activat(cid:173)
`ing treatment according to the present invention is
`shown by curve A, and as is seen from the curve, the
`conversion is increased to substantially 100% by the
`addition of ammonia and, then, the stationary state is 65
`attained and continued.
`The following effects can be attained by the present
`invention.
`
`8
`First, by the activating treatment comprising contact(cid:173)
`ing a zeolite catalyst with an excessive amount of am(cid:173)
`monia, the nitrogen oxide-reducing activity of the cata(cid:173)
`lyst is highly improved. Secondarily, by using ammonia
`in a minimum amount necessary for reduction of nitro(cid:173)
`gen oxides after the activating treatment, a very high
`reducing activity can be attained. Accordingly, no am(cid:173)
`monia is present in the exhaust gas discharged in open
`air and, hence, occurrence of secondary pollution can
`be prevented.
`The present invention will now be described in detail
`by reference to the following Examples.
`
`EXAMPLE 1
`20 ml of a copper-supported zeolite catalyst (extru(cid:173)
`sion-molded to a form having a diameter of 1.5 mm and
`a length of 6 mm) prepared according to a method
`described below was filled in a quartz reaction tube
`having an inner diameter of 20 mm. A gaseous mixture
`formed by incorporating ammonia into a synthetic flue
`gas having a composition described below, so that the
`ammonia content in the gas was 250 ppm ( 1.5 times the
`stoichiometric amount ofNH3 required for reducing 250
`ppm of NO in the synthetic gas according to the reac(cid:173)
`tion expressed by the formula,
`
`was introduced into the packed test tube at a gas space
`velocity of 5,000 V /H/V and a catalyst bed tempera(cid:173)
`ture of 250° C.
`Composition of Synthetic Flue Gas:
`
`NO: 250 ppm
`C02: lO%
`02:3%
`Steam: 10%
`N2: balance
`
`After the above activating treatment, ammonia was
`added to the above synthetic flue gas in such an amount
`that the ammonia concentration in the gas was 167 ppm
`(the stoichiometric amount necessary for reduction of
`250 ppm of NO), and the gaseous mixture was intro(cid:173)
`duced into the reaction tube at a gas spaced velocity of
`5,000 V /H/V and a catalyst bed temperature of 250• C.
`Results are shown in Curve A of FIG. 1, from which it
`is seen that the conversion of NO was substantially
`100% for about 50 minutes from the start of the reac(cid:173)
`tion, and after the intermediate state, the stationary state
`was attained, where the stationary value of the nitrogen
`oxide conversion was 78%. At this point, if the amount
`of ammonia was increased to 1.2 times the stoichiomet(cid:173)
`ric amount, the nitrogen oxide conversion was elevated,
`and after the intermediate state, the stationary state was
`attained again. From this fact, it was found that the
`minimum amount necessary for activation of the cata(cid:173)
`lyst was about 1.2 times the stoichiometric amount.
`
`Catalyst Preparation
`Copper-supported zeolite catalyst was prepared as
`follows.
`100 grams of zeolite-Y (extrusion-molded, synthetic
`faujasite having a diameter of 1.5 mm and a length of 6
`mm) were immersed in 1,000 ml of 2.1 N aqueous am(cid:173)
`monium chloride solution. Ion exchange was effected
`under proper agitation at room temperature for about
`24 hours. After completion of the ion exchange, the
`
`Umicore AG & Co. KG
`Exhibit 1102
`Page 6 of 7
`
`

`

`4,046,888
`
`9
`zeolite was taken out from the solution, washed with
`water, dried and then calcined at soo· c. for 3 hours in
`air to obtain catalyst carrier containing 0.33 equivalent
`of sodium per gram-atom of aluminum in the zeolite. 50
`grams of the catalyst carrier were immersed in 100 ml of
`an aqueous solution containing 3 wt. % of Cu prepared
`from copper nitrate Cu(No3) 2·3H20 and the whole was
`allowed to stand at room temperature for 30 minutes.
`The carrier was taken out from the solution, dried and 10
`calcined at soo· c. for 16 hours to obtain zeolite catalyst
`carrying 3 wt. % copper;
`
`EXAMPLE lA
`20 ml of the same copper-supported zeolite catalyst as 15
`used in the Example was filled in a quartz test tube
`having an inner diameter of 20 mm. A gaseous mixture
`obtained by incorporating ammonia into a synthetic flue
`gas having a composition described below, so that the
`ammonia concentration was 167 ppm (the stoichiomet- 20
`ric amount necessary for reduction of250 ppm of NO in
`the synthetic flue gas), was introduced into the packed
`test tube at a gas space velocity of 5,000 V /H/V and a
`catalyst bed temperature of 2so• C. Results are shown 25
`in Curve B connecting the points 1 and 2 in FIG. 1,
`from which it is seen that the stationary value of the
`nitrogen oxide conversion was 62%.
`Composition of Synthetic Flue Gas:
`
`10
`apparent that an obvious effect can be attained by the
`activating treatment of the present invention.
`What is claimed is:
`1. A process for reducing the concentration of nitro-
`5 gen oxides in a gaseous mixture which comprises
`A. introducing ammonia in an amount between about
`1.2 and 3.0 times the stoichiometric amount neces(cid:173)
`sary for reducing the nitrogen oxides into a reaction
`zone containing a catalyst said catalyst comprising
`an active metal component and natural or synthetic
`zeolite having an Si02/ Ah03 molar ratio of at least
`about 2 and an alkali metal content within the range
`from 0.2 to 0.6 equivalents per gram atom of alu(cid:173)
`mina, the introduction of ammonia at this rate con(cid:173)
`tinuing for at least about 20 minutes and then
`B. contacting the nitrogen oxides containing gas with
`the catalyst in the presence of ammonia in an
`amount between about 0.7 and 1.0 times the stoi(cid:173)
`chiometric amount necessary for reducing the ni(cid:173)
`trogen oxides.
`C. repeating step (A) periodically.
`2. The process of claim 1 wherein the reaction tem(cid:173)
`perature is between about 200" and 500" C.
`3. The process of claim 2 wherein the temperature
`range is from about 250" to about 450• C.
`4. The process of claim 1 wherein the catalyst bas a
`pore diameter of from about 3 to about 15 A.
`5, The process of claim 1 wherein about 1 to about
`30% by weight of a refractory substance is incorporated
`30 in the catalyst.
`6. The process of claim 1 wherein the active metal
`component of the catalyst is taken from the group con(cid:173)
`sisting of copper, iron, chromium and vanadium.
`7. The process of claim 6 wherein the amount of metal
`35 component is about 1 to about 20% by weight.
`8. The process of claim 1 wherein the. catalyst is
`molded into a shape having a large contact surface area.
`9. The process of claim 1 wherein the catalyst is ar(cid:173)
`ranged in a fixed bed.
`10. The process of claim 1 wherein the nitrogen ox(cid:173)
`ides containing gas is a flue gas.
`11. The process of claim 1 wherein the catalyst activa(cid:173)
`tion is accomplished before the gaseous mixture con(cid:173)
`taining nitrogen oxides is contacted with the catalyst.
`• • * * *
`
`NO: 250 ppm
`C02: 10%
`02:3%
`Steam: 10%
`N2: balance
`
`The activation treatment was then carried out for 20
`minutes under the same conditions as