JP4078427B2 - Nitrogen oxide removal method - Google Patents
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- JP4078427B2 JP4078427B2 JP2004045160A JP2004045160A JP4078427B2 JP 4078427 B2 JP4078427 B2 JP 4078427B2 JP 2004045160 A JP2004045160 A JP 2004045160A JP 2004045160 A JP2004045160 A JP 2004045160A JP 4078427 B2 JP4078427 B2 JP 4078427B2
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- methane
- nitrogen oxide
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- palladium
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- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 title claims description 307
- 238000000034 method Methods 0.000 title claims description 25
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 76
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 70
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 62
- 239000003054 catalyst Substances 0.000 claims description 57
- 238000006722 reduction reaction Methods 0.000 claims description 46
- 238000006243 chemical reaction Methods 0.000 claims description 44
- 239000000377 silicon dioxide Substances 0.000 claims description 31
- 229910052763 palladium Inorganic materials 0.000 claims description 24
- 239000003638 chemical reducing agent Substances 0.000 claims description 22
- 239000011964 heteropoly acid Substances 0.000 claims description 21
- 239000001301 oxygen Substances 0.000 claims description 18
- 229910052760 oxygen Inorganic materials 0.000 claims description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 18
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 18
- 229910004298 SiO 2 Inorganic materials 0.000 description 15
- 238000002485 combustion reaction Methods 0.000 description 13
- 239000007789 gas Substances 0.000 description 12
- 230000000694 effects Effects 0.000 description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 7
- 239000011148 porous material Substances 0.000 description 7
- 235000019441 ethanol Nutrition 0.000 description 6
- YJVFFLUZDVXJQI-UHFFFAOYSA-L palladium(ii) acetate Chemical compound [Pd+2].CC([O-])=O.CC([O-])=O YJVFFLUZDVXJQI-UHFFFAOYSA-L 0.000 description 6
- 238000011068 loading method Methods 0.000 description 5
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 5
- 229910001928 zirconium oxide Inorganic materials 0.000 description 5
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 239000005297 pyrex Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- ODUCDPQEXGNKDN-UHFFFAOYSA-N Nitrogen oxide(NO) Natural products O=N ODUCDPQEXGNKDN-UHFFFAOYSA-N 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- AQBOUNVXZQRXNP-UHFFFAOYSA-L azane;dichloropalladium Chemical compound N.N.N.N.Cl[Pd]Cl AQBOUNVXZQRXNP-UHFFFAOYSA-L 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 239000001307 helium Substances 0.000 description 2
- 229910052734 helium Inorganic materials 0.000 description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 description 2
- -1 oxygen oxides Chemical class 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 229910001930 tungsten oxide Inorganic materials 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- JEAJXDBDUKBTKP-UHFFFAOYSA-N N.O.O.O.O.O.[W+4] Chemical compound N.O.O.O.O.O.[W+4] JEAJXDBDUKBTKP-UHFFFAOYSA-N 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 239000004202 carbamide Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 125000001495 ethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- JEGUKCSWCFPDGT-UHFFFAOYSA-N h2o hydrate Chemical compound O.O JEGUKCSWCFPDGT-UHFFFAOYSA-N 0.000 description 1
- 150000004715 keto acids Chemical class 0.000 description 1
- MEFBJEMVZONFCJ-UHFFFAOYSA-N molybdate Chemical compound [O-][Mo]([O-])(=O)=O MEFBJEMVZONFCJ-UHFFFAOYSA-N 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 1
- PIBWKRNGBLPSSY-UHFFFAOYSA-L palladium(II) chloride Chemical compound Cl[Pd]Cl PIBWKRNGBLPSSY-UHFFFAOYSA-L 0.000 description 1
- GPNDARIEYHPYAY-UHFFFAOYSA-N palladium(ii) nitrate Chemical compound [Pd+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O GPNDARIEYHPYAY-UHFFFAOYSA-N 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000011973 solid acid Substances 0.000 description 1
- 239000011949 solid catalyst Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- CMPGARWFYBADJI-UHFFFAOYSA-L tungstic acid Chemical compound O[W](O)(=O)=O CMPGARWFYBADJI-UHFFFAOYSA-L 0.000 description 1
- LSGOVYNHVSXFFJ-UHFFFAOYSA-N vanadate(3-) Chemical compound [O-][V]([O-])([O-])=O LSGOVYNHVSXFFJ-UHFFFAOYSA-N 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Description
本発明は、燃焼装置から排出される燃焼排ガス中の窒素酸化物の還元に用いられる触媒およびその窒素酸化物を除去する方法に関する。 The present invention relates to a catalyst used for reduction of nitrogen oxides in combustion exhaust gas discharged from a combustion apparatus and a method for removing the nitrogen oxides.
例えばボイラー、自動車のエンジン（燃焼器）のような燃焼装置から排出される燃焼排ガスには、光化学スモッグなどを誘発する窒素酸化物（ＮＯx）が含まれている。このような窒素酸化物、特にＮＯを除去する方法としては、固体触媒の存在下で還元剤を用いて還元する方法が知られている。この還元剤としては、アンモニア、尿素、炭化水素が知られている。炭化水素の中で天然ガスは、豊富に産出することからこの成分であるメタンを還元剤として使用することが試みられている。このため、メタンを還元剤として利用し得る高活性の触媒が求められている。特に、実用条件である酸素の共存下または酸素および水蒸気の共存下で高活性を示す触媒が求められている。
パラジウム（Ｐｄ）が担持された触媒は、この窒素酸化物の還元反応で最も高活性であることが知られている。このため、このＰｄに適した担体の研究、開発が進められている。
非特許文献１には、Ｐｄの担体として酸性固体を用いることにより高い活性を発現できることが開示されている。非特許文献２には、固体酸の中でも酸化ジルコニウム担持酸化タングステン（ＷＯ3／ＺｒＯ2）をＰｄの担体として用い、窒素酸化物が水蒸気の共存下でその活性を長時間維持することが記載されている。
しかしながら、前記ＷＯ3／ＺｒＯ2を担体とする触媒は、窒素酸化物（特に酸素の共存下または酸素および水蒸気の共存下）をメタンを還元剤とした還元反応する際に十分に高い活性を示さず、実用レベルの速度で還元反応を実現するには反応場を約４００℃以上の高い温度にする必要があった。このため、例えば自動車のエンジン始動直後に燃焼排ガス中の窒素酸化物を十分除去できない問題があった。
It is known that a catalyst supporting palladium (Pd) is most active in the reduction reaction of nitrogen oxides. For this reason, research and development of a carrier suitable for this Pd is underway.
Non-Patent Document 1 discloses that high activity can be expressed by using an acidic solid as a carrier of Pd. Non-Patent Document 2 describes that among solid acids, zirconium oxide-supported tungsten oxide (WO 3 / ZrO 2 ) is used as a Pd carrier, and nitrogen oxide maintains its activity for a long time in the presence of water vapor. ing.
However, the catalyst using WO 3 / ZrO 2 as a support exhibits a sufficiently high activity when a reduction reaction using nitrogen oxide (particularly in the presence of oxygen or oxygen and water vapor) as a reducing agent using methane. In order to realize the reduction reaction at a practical speed, it was necessary to set the reaction field to a high temperature of about 400 ° C. or higher. For this reason, there existed a problem which cannot fully remove the nitrogen oxide in combustion exhaust gas immediately after the engine start of a motor vehicle, for example.
本発明は、窒素酸化物、特に酸素が共存されるか、酸素および水蒸気が共存される窒素酸化物をメタンを還元剤として還元反応させる際に比較的低温（４００℃未満）で高活性を示す触媒を提供しようとするものである。 The present invention exhibits high activity at a relatively low temperature (less than 400 ° C.) when a nitrogen oxide, particularly nitrogen oxide in which oxygen coexists or oxygen and water vapor coexist, is subjected to a reduction reaction using methane as a reducing agent. It is intended to provide a catalyst.
本発明は、窒素酸化物、特に酸素が共存されるか、酸素および水蒸気が共存される窒素酸化物をメタンを還元剤として比較的低温（４００℃未満）で還元反応させて無害な窒素として除去することが可能な窒素酸化物の除去方法を提供しようとするものである。 The present invention removes nitrogen oxides, particularly oxygen oxides, or nitrogen oxides coexisting with oxygen and water vapor, as harmless nitrogen by reducing the reaction at a relatively low temperature (less than 400 ° C) using methane as a reducing agent. It is an object of the present invention to provide a method for removing nitrogen oxides that can be performed.
本発明によると、多孔質シリカにヘテロポリ酸を担持させた担体と、この担体に担持されたパラジウムとを含む還元用触媒の存在下、窒素酸化物を酸素の共存下にて２５０〜３５０℃でメタンを還元剤として還元反応させることを特徴とする窒素酸化物の除去方法が提供される。 According to the present invention, and a carrier having supported thereon a heteropoly acid on porous silica, the presence of a reducing catalyst comprising a supported palladium in the carrier, at 250 to 350 ° C. The nitrogen oxides in the presence of oxygen There is provided a method for removing nitrogen oxides, characterized by carrying out a reduction reaction using methane as a reducing agent.
本発明によれば、多孔質シリカにヘテロポリ酸を含有させた担体にパラジウムを担持させることによって、窒素酸化物をメタンを還元剤として還元反応させる際に比較的低温（４００℃未満）で高い活性を示す窒素酸化物の還元用触媒を提供できる。 According to the present invention, when palladium is supported on a support containing a heteropolyacid in porous silica, high activity at a relatively low temperature (less than 400 ° C.) when a nitrogen oxide is reduced using methane as a reducing agent. A catalyst for reducing nitrogen oxides can be provided.
また、本発明によれば前記特定の還元触媒の存在下で窒素酸化物をメタンを還元剤として還元反させる際に比較的低温（４００℃未満）で無害な窒素に転換して窒素酸化物を除去することが可能な窒素酸化物の除去方法を提供できる。 Further, according to the present invention, when nitrogen oxide is reduced and reacted with methane as a reducing agent in the presence of the specific reduction catalyst, the nitrogen oxide is converted into harmless nitrogen at a relatively low temperature (less than 400 ° C.). A nitrogen oxide removal method that can be removed can be provided.
以下、本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail.
本発明に係る窒素酸化物の還元用触媒は、多孔質シリカにヘテロポリ酸を含有させた担体と、この担体に担持されたパラジウムとを含む。 The nitrogen oxide reduction catalyst according to the present invention includes a support in which a heteropolyacid is contained in porous silica, and palladium supported on the support.
前記多孔質シリカは、ヘテロポリ酸を含有させ、かつパラジウムを担持させるために、例えば比表面積が１００ｍ2／ｇ以上、より好ましくは１５０ｍ2／ｇ以上であることが望ましい。この多孔質シリカは、細孔容積が０．５ｃｍ3／ｇ以上であることが好ましい。このような多孔質シリカとしては、例えば日揮化学社製のＮ−６０２Ａ（比表面積が２９０ｍ2／ｇ、細孔容積が０．８ｃｍ3／ｇ）を用いることができる。
前記担体の形状を決める多孔質シリカは、粒状、ペレット状、ハニカム状などの任意の形状のものが用いられる。
The porous silica preferably contains, for example, a specific surface area of 100 m 2 / g or more, more preferably 150 m 2 / g or more in order to contain a heteropolyacid and to support palladium. This porous silica preferably has a pore volume of 0.5 cm 3 / g or more. As such porous silica, for example, N-602A (specific surface area is 290 m 2 / g, pore volume is 0.8 cm 3 / g) manufactured by JGC Chemical Co., Ltd. can be used.
As the porous silica that determines the shape of the carrier, those having an arbitrary shape such as a granular shape, a pellet shape, and a honeycomb shape are used.
前記ヘテロポリ酸としては、バナジウム酸、モリブデン酸、タングステン酸のような無機オキソ酸を含む種々のものを用いることができるが、例えばＨ4ＳｉＷ12Ｏ40，Ｈ3ＰＭｏ12Ｏ40またはＨ3ＰＷ12Ｏ40が好ましい。これらのヘテロポリ酸の中でＨ3ＰＭｏ12Ｏ40が高活性で、Ｈ3ＰＷ12Ｏ40が最も高活性である。 Examples of the heteropoly acid, vanadate, molybdate, various ones can be used including inorganic oxo acids such as tungstic acid, for example H 4 SiW 12 O 40, H 3 PMo 12 O 40 or H 3 PW 12 O 40 is preferred. Among these heteropolyacids, H 3 PMo 12 O 40 is highly active and H 3 PW 12 O 40 is most active.
前記ヘテロポリ酸は、前記多孔質シリカに全触媒量に対して２０〜４０重量％の範囲で含有されることが好ましい。このヘテロポリ酸の含有量が前記範囲を逸脱すると、高活性の還元用触媒を得ることが困難になる。
前記パラジウムは、前記多孔質シリカに全触媒量に対して０．１〜１０重量％の範囲で担持されることが好ましい。このパラジウムの担持量を０．１重量％未満にすると、高活性の還元用触媒を得ることが困難になる。一方、このパラジウムの担持量が１０重量％を超えると、担持量の増加による活性の増大化が望めず、かえってコスト高になる虞がある。より好ましい前記多孔質シリカに対する前記パラジウムの担持量は、全触媒量に対して０．２〜２重量％である。
The heteropolyacid is preferably contained in the porous silica in a range of 20 to 40% by weight with respect to the total catalyst amount. When the content of this heteropolyacid is outside the above range, it becomes difficult to obtain a highly active reduction catalyst.
The palladium is preferably supported on the porous silica in the range of 0.1 to 10% by weight with respect to the total amount of catalyst. When the supported amount of palladium is less than 0.1% by weight, it becomes difficult to obtain a highly active reduction catalyst. On the other hand, if the supported amount of palladium exceeds 10% by weight, an increase in activity due to an increase in the supported amount cannot be expected, and the cost may be increased. More preferably, the supported amount of palladium on the porous silica is 0.2 to 2% by weight based on the total amount of catalyst.
本発明に係る還元用触媒は、例えば次のような方法により製造することができる。
まず、多孔質シリカをヘテロポリ酸のアルコール溶液に浸漬してその多孔質シリカの気孔にヘテロポリ酸のアルコール溶液を含浸させた後、加熱してアルコールを揮散させることにより多孔質シリカにヘテロポリ酸を担持させる。つづいて、このヘテロポリ酸担持多孔質シリカをパラジウム原料である酢酸パラジウムのトルエン溶液に浸漬し、その多孔質シリカの気孔に酢酸パラジウムのトルエン溶液を含浸させた後、加熱してトルエンの揮散、酢酸パラジウムの分解を行うことによりヘテロポリ酸含有多孔質シリカにパラジウムを担持させて還元用触媒を製造する。
前記パラジウム原料は、酢酸パラジウムの他に、硝酸パラジウム、塩化パラジウム、塩化テトラアミンパラジウムを用いることができる。
The reduction catalyst according to the present invention can be produced, for example, by the following method.
First, porous silica is immersed in a heteropolyacid alcohol solution, the pores of the porous silica are impregnated with the heteropolyacid alcohol solution, and then heated to volatilize the alcohol to support the heteropolyacid on the porous silica. Let Next, this heteropolyacid- supporting porous silica is immersed in a toluene solution of palladium acetate, which is a palladium raw material, and the pores of the porous silica are impregnated with the toluene solution of palladium acetate, and then heated to evaporate toluene, acetic acid. By carrying out decomposition of palladium, palladium is supported on the heteropolyacid-containing porous silica to produce a reduction catalyst.
In addition to palladium acetate, palladium nitrate, palladium chloride, and tetraamine palladium can be used as the palladium raw material.
前述した多孔質シリカにヘテロポリ酸を含有させた担体と、この担体に担持されたパラジウムとを含む還元用触媒の存在下、窒素酸化物をメタンを還元剤として還元反応させてＮＯを無害な窒素（Ｎ2）として除去する。
前記窒素酸化物は、ＮＯxとして表され、除去対象は主に一酸化窒素（ＮＯ）であるが、ＮＯ2等の他の窒素酸化物が含まれてもよい。
前記窒素酸化物（ＮＯ）とメタンとは、酸素の共存下で次式（１）のようにメタン１モル、ＮＯ２モル、酸素１モルで還元反応がなされる。
ＣＨ4＋２ＮＯ＋Ｏ2→Ｎ2＋ＣＯ2＋２Ｈ2Ｏ …（１）
前記メタンは、前記窒素酸化物の反応場にメタン（ＣＨ4）：窒素酸化物（ＮＯ）のモル比で０．５：１〜１０：１になるように供給することが好ましい。ＣＨ4とＮＯとの還元反応において理論的にはＮＯ１モルに対しＣＨ4が０．５モル存在すれば足りる。ただし、窒素酸化物の反応場でのメタンの不足に伴うＮＯの残留を回避することから、メタンをＮＯに対しモル比で０．５以上にすることが好ましい。メタンがＮＯに対しモル比で１０以上にすると、還元反応に寄与しないメタンが反応場に残留し、無駄なメタンの使用、コスト増を招く。より好ましいメタン（ＣＨ4）：窒素酸化物（ＮＯ）のモル比は、１：１〜２：１である。
In the presence of a reducing catalyst containing the above-mentioned porous silica containing a heteropolyacid and palladium supported on the porous nitrogen, NO is harmless nitrogen by reducing the nitrogen oxide with methane as a reducing agent. Remove as (N 2 ).
The nitrogen oxides are represented as NO x and the removal target is mainly nitrogen monoxide (NO), but other nitrogen oxides such as NO 2 may be included.
The nitrogen oxide (NO) and methane undergo a reduction reaction with 1 mole of methane, 2 moles of NO, and 1 mole of oxygen in the presence of oxygen as shown in the following formula (1).
CH 4 + 2NO + O 2 → N 2 + CO 2 + 2H 2 O (1)
The methane is preferably supplied to the nitrogen oxide reaction field at a molar ratio of methane (CH 4 ): nitrogen oxide (NO) of 0.5: 1 to 10: 1. Theoretically, in the reduction reaction between CH 4 and NO, 0.5 mol of CH 4 is sufficient for 1 mol of NO. However, in order to avoid the NO remaining due to the lack of methane in the nitrogen oxide reaction field, it is preferable that the molar ratio of methane to NO is 0.5 or more. If the methane has a molar ratio of 10 or more with respect to NO, methane that does not contribute to the reduction reaction remains in the reaction field, leading to useless use of methane and increased costs. A more preferred molar ratio of methane (CH 4 ): nitrogen oxide (NO) is 1: 1 to 2: 1.
前記窒素酸化物の反応場には、酸素が共存される。また、窒素酸化物の反応場には水蒸気が共存されることを許容する。通常、実用条件では窒素酸化物はボイラー、自動車のエンジン（燃焼器）のような燃焼装置から排出される燃焼排ガスに含有されることから、酸素および水蒸気が共存される。酸素は、前記式（１）に示すように還元反応に関与するものの、水蒸気は一般的に触媒毒として作用して、その活性を低下させる虞がある。ただし、本発明の多孔質シリカにヘテロポリ酸を含有させた担体は酸性を示すことから、むしろ水蒸気が５〜２０モル％共存する反応場ではより高活性を発現する。
前記特定の還元用触媒の存在下での反応場は、従来に比べて低温にできることが本発明の特徴の１つであるが、通常４００℃未満、例えば２００〜３５０℃にすればよい。
以上説明した本発明に係る窒素酸化物の還元用触媒は、多孔質シリカにヘテロポリ酸を含有させた担体にパラジウムを担持した構成を有し、高い活性を示すため、窒素酸化物（主にＮＯ）を還元反応させる際、還元能力の低いメタンを使用することができる。つまり、メタンの還元能力を増大して窒素酸化物を還元することができる。
特に、前記ヘテロポリ酸としてＨ4ＳｉＷ12Ｏ40，Ｈ3ＰＭｏ12Ｏ40またはＨ3ＰＷ12Ｏ40（より好適にはＨ3ＰＷ12Ｏ40）を用いることによって、窒素酸化物の反応場の温度４００℃未満（２００〜３５０℃）においてより高活性の還元用触媒を実現できる。
また、前記ヘテロポリ酸を前記多孔質シリカに全触媒量に対して２０〜４０重量％の範囲で含有させることによって、窒素酸化物の反応場の温度４００℃未満（２００〜３５０℃）においてより高活性の還元用触媒を実現できる。
さらに、前記パラジウムを前記多孔質シリカに全触媒量に対して０．１〜１０重量％、より好ましくは０．２〜２重量％の範囲で担持することによって、窒素酸化物の反応場の温度４００℃未満（２００〜３５０℃）においてより高活性の還元用触媒を実現できる。
本発明に係る窒素酸化物の除去方法は、前述した多孔質シリカにヘテロポリ酸を含有させた担体と、この担体に担持されたパラジウムとを含む還元用触媒の存在下、窒素酸化物（主に一酸化窒素：ＮＯ）をメタンを還元剤として還元反応させることによって、高活性の還元用触媒により従来に比べて低温（４００℃未満、例えば２００〜３５０℃の温度）にて前記式（１）に示すＮＯの還元が十分に進行し、ＮＯの転化率が増大して無害な窒素（Ｎ2）として効率よく除去することができる。
また、資源的に豊富で安価なメタンを還元剤として使用できるため、各種の化学プラントの燃焼装置から多大な量で排出される燃焼排ガス中の窒素酸化物の除去に適用した場合、ランニングコストを効果的に低減することができる。
特に、前記窒素酸化物の反応場に水蒸気を５〜２０モル％共存させることによって、前記触媒の活性を増大できるため、ＮＯの転化率がより増大させることができる。
［実施例］
以下、本発明の実施例を詳細に説明する。
Oxygen coexists in the nitrogen oxide reaction field. In addition, water vapor is allowed to coexist in the nitrogen oxide reaction field. Normally, under practical conditions, nitrogen oxide is contained in combustion exhaust gas discharged from a combustion apparatus such as a boiler or an automobile engine (combustor), so oxygen and water vapor coexist. Although oxygen is involved in the reduction reaction as shown in the formula (1), water vapor generally acts as a catalyst poison and may reduce its activity. However, since the support | carrier which made the porous silica of this invention contain heteropoly acid shows acidity, rather high activity is expressed in the reaction field where water vapor | steam coexists 5-20 mol% rather.
One of the characteristics of the present invention is that the reaction field in the presence of the specific reducing catalyst can be made at a lower temperature as compared with the conventional one, but it is usually less than 400 ° C., for example, 200 to 350 ° C.
The nitrogen oxide reduction catalyst according to the present invention described above has a configuration in which palladium is supported on a support in which a heteropolyacid is contained in porous silica, and exhibits high activity. Therefore, nitrogen oxide (mainly NO) ) Can be used for the reduction reaction, methane having a low reducing ability can be used. That is, nitrogen oxides can be reduced by increasing the reducing ability of methane.
In particular, the H 4 SiW 12 O 40, H 3 PMo 12 O 40 or H 3 PW 12 O 40 (more preferably the H 3 PW 12 O 40) as a heteropoly acid by using, nitrogen oxides reaction field A highly active reduction catalyst can be realized at a temperature of less than 400 ° C. (200 to 350 ° C.).
Further, by incorporating the heteropolyacid into the porous silica in a range of 20 to 40% by weight with respect to the total amount of catalyst, the reaction temperature of nitrogen oxide is lower at a temperature of less than 400 ° C (200 to 350 ° C). An active reduction catalyst can be realized.
Furthermore, the palladium is supported on the porous silica in an amount of 0.1 to 10% by weight, more preferably 0.2 to 2% by weight, based on the total amount of catalyst, whereby the temperature of the nitrogen oxide reaction field is increased. A highly active reduction catalyst can be realized at less than 400 ° C. (200 to 350 ° C.).
The method for removing nitrogen oxides according to the present invention comprises a nitrogen oxide (mainly a catalyst containing a heteropolyacid in porous silica described above and a reduction catalyst comprising palladium supported on the carrier. Nitrogen monoxide (NO) is reduced by using methane as a reducing agent to reduce the above formula (1) at a lower temperature (less than 400 ° C., for example, 200 to 350 ° C.) with a highly active reducing catalyst. NO reduction proceeds sufficiently, and the NO conversion rate increases and can be efficiently removed as harmless nitrogen (N 2 ).
In addition, since methane, which is abundant in resources, can be used as a reducing agent, the running cost is reduced when applied to the removal of nitrogen oxides in combustion exhaust gas discharged from combustion equipment of various chemical plants in a large amount. It can be effectively reduced.
In particular, the presence of 5 to 20 mol% of water vapor in the nitrogen oxide reaction field can increase the activity of the catalyst, and therefore the NO conversion rate can be further increased.
[Example]
Hereinafter, embodiments of the present invention will be described in detail.
（実施例１）
まず、多孔質シリカ（日揮化学社製商品名：Ｎ−６０２Ａ［比表面積が２９０ｍ2／ｇ、細孔容積が０．８ｃｍ3／ｇ］）をヘテロポリ酸であるＨ3ＰＷ12Ｏ40のエチルアルコール溶液に浸漬してその多孔質シリカの気孔にＨ3ＰＷ12Ｏ40のアルコール溶液を含浸させた後、加熱してエチルアルコールを揮散させることにより多孔質シリカにＨ3ＰＷ12Ｏ40を含有させた。つづいて、このＨ3ＰＷ12Ｏ40含有多孔質シリカ（担体）をパラジウム原料である酢酸パラジウムのトルエン溶液に浸漬し、その多孔質シリカの気孔に酢酸パラジウムのトルエン溶液を含浸させた後、１２０℃で加熱してトルエンの揮散、酢酸パラジウムの分解を行うことによりＨ3ＰＷ12Ｏ40含有多孔質シリカにパラジウムを担持させた還元用触媒（以下Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2と略す）を製造した。この還元用触媒は、平均粒径が５００〜８００μｍの粒状をなし、かつＨ3ＰＷ12Ｏ40が３０重量％含有し、パラジウムが０．２重量％担持された組成を有するものであった。
得られた還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）をパイレクッス管内にそれぞれ２．０ｇ充填した。ＮＯ，ＣＨ4，Ｏ2，Ｈ2Ｏがそれぞれモル分率１０００ｐｐｍ、１０００ｐｐｍ、１％、１０％含むヘリウムガスを前記パイレクッス管の一端開口部から１５０ｃｍ3／分の流量で供給すると共に、触媒が存在するパイレクッス管内の温度を２００〜５００℃に変化させてＮＯの還元反応を行った。パイレクッス管の他端開口部から排出されるガスを採取し、その中のＮＯおよびＣＨ4の量を測定し、ＮＯおよびＣＨ4の転化率を求めた。なお、ＮＯ量は、堀場製作所社商品名のCLA-510SSを用いて測定し、ＣＨ4量は日立製作所社商品名の１６３ガスクロマトグラフィを用いて測定した。ＮＯおよびＣＨ4の転化率は、反応前後のＮＯおよびＣＨ4の測定値に基づき、反応前のそれらガス量で反応後のそれらガス量をそれぞれ除した百分率から求めた。その結果を下記表１に示す。
（比較例１）
まず、オキシ硝酸ジルコニウムを水に溶解し、この溶液を撹拌しながら、アンモニア水をｐＨ＝１０になるまで滴下した。得られた白濁溶液を濾過し、固形物を洗浄した後、３００℃で焼成して酸化ジルコニウムとした。この酸化ジルコニウムをタングステンアンモニウム５水和物の水溶液に加え、加熱して水を蒸発させた後、空気中、６５０℃で４時間焼成して酸化タングステン含有酸化ジルコニウム（ＷＯ3／ＺｒＯ2）を作った。つづいて、この酸化タングステン含有酸化ジルコニウム（担体）を塩化テトラアミンパラジウム水溶液に入れ、撹拌した後、濾紙を用いて濾過した。この濾紙上に残った固形物を窒素気流中、５００℃で４時間焼成することによりＷＯ3／ＺｒＯ2にパラジウムを担持させた還元用触媒（以下Ｐｄ／ＷＯ3／ＺｒＯ2と略す）を製造した。この還元用触媒は、平均粒径が
５００〜８００μｍの粒状をなし、かつＷＯ3が２０重量％含有し、パラジウムが０．２重量％担持された組成を有するものであった。
得られた還元用触媒（Ｐｄ／ＷＯ3／ＺｒＯ2）を用いて実施例１と同様な条件でＮＯおよびＣＨ4の転化率を求めた。その結果を下記表１に示す。
First, porous silica (trade name: N-602A manufactured by JGC Chemical Co., Ltd. [specific surface area is 290 m 2 / g, pore volume is 0.8 cm 3 / g]) is ethyl of H 3 PW 12 O 40 which is a heteropoly acid. after thereof in pores of the porous silica impregnated with alcohol solution of H 3 PW 12 O 40 it was immersed in an alcohol solution, containing of H 3 PW 12 O 40 to the porous silica by volatilization of ethyl alcohol was heated I let you. Subsequently, the porous silica (support) containing H 3 PW 12 O 40 was immersed in a toluene solution of palladium acetate as a palladium raw material, and the pores of the porous silica were impregnated with the toluene solution of palladium acetate. A catalyst for reduction (hereinafter referred to as Pd / H 3 PW 12 O 40 / SiO 2) in which palladium is supported on H 3 PW 12 O 40 -containing porous silica by evaporating toluene and decomposing palladium acetate. Abbreviated). This reducing catalyst had a composition with an average particle diameter of 500 to 800 μm, a H 3 PW 12 O 40 content of 30% by weight, and a palladium supported of 0.2% by weight.
2.0 g of each of the obtained reduction catalysts (Pd / H 3 PW 12 O 40 / SiO 2 ) was charged into a Pyrex tube. Helium gas containing NO, CH 4 , O 2 , and H 2 O at a molar fraction of 1000 ppm, 1000 ppm, 1%, and 10%, respectively, is supplied at a flow rate of 150 cm 3 / min from one end opening of the Pyrex tube, The temperature in the existing Pyrex tube was changed to 200 to 500 ° C. to perform NO reduction reaction. The gas discharged from the opening at the other end of the Pyrex tube was collected, and the amounts of NO and CH 4 therein were measured, and the conversion rates of NO and CH 4 were determined. The NO amount was measured using CLA-510SS, a trade name of Horiba, Ltd., and the CH 4 amount was measured using 163 gas chromatography, a trade name of Hitachi, Ltd. Conversion of NO and CH 4, based on the measured value of the reaction before and after the NO and CH 4, was determined from the percentage obtained by dividing each their gas amount after reaction with their amount of gas before the reaction. The results are shown in Table 1 below.
(Comparative Example 1)
First, zirconium oxynitrate was dissolved in water, and ammonia water was added dropwise until pH = 10 while stirring the solution. The resulting cloudy solution was filtered to wash the solid, and then calcined at 300 ° C. to obtain zirconium oxide. This zirconium oxide is added to an aqueous solution of tungsten ammonium pentahydrate, heated to evaporate the water, and then calcined in air at 650 ° C. for 4 hours to produce zirconium oxide-containing zirconium oxide (WO 3 / ZrO 2 ). It was. Subsequently, the tungsten oxide-containing zirconium oxide (carrier) was put into a tetraamine palladium chloride aqueous solution, stirred, and then filtered using a filter paper. In a nitrogen gas stream remaining solids on this filter paper, producing a 4-hour calcination reducing catalyst obtained by supporting palladium in WO 3 / ZrO 2 by (hereinafter referred to as Pd / WO 3 / ZrO 2) at 500 ° C. did. This reducing catalyst had a composition with an average particle diameter of 500 to 800 μm, a composition containing 20% by weight of WO 3 and 0.2% by weight of palladium.
Using the obtained reduction catalyst (Pd / WO 3 / ZrO 2 ), the conversion rates of NO and CH 4 were determined under the same conditions as in Example 1. The results are shown in Table 1 below.
前記表１から明らかなように還元用触媒（Ｐｄ／ＷＯ3／ＺｒＯ2）を用いてＮＯをメタン（還元剤）で還元反応させる比較例１の方法では、反応温度が４００℃以上において高いＮＯ転化率を示すものの、反応温度が４００℃未満の２５０℃，３００℃，３５０℃ではそのＮＯ転化率が極端に低下することがわかる。
これに対し、還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いてＮＯをメタンを還元剤として還元反応させる実施例１の方法では、反応温度が４００℃未満の２５０℃，３００℃，３５０℃の低温域において高いＮＯ転化率を示すことがわかる。
As apparent from Table 1, in the method of Comparative Example 1 in which NO is reduced with methane (reducing agent) using a reducing catalyst (Pd / WO 3 / ZrO 2 ), the NO is high at a reaction temperature of 400 ° C. or higher. Although the conversion rate is shown, it can be seen that the NO conversion rate is extremely lowered at the reaction temperatures of 250 ° C., 300 ° C. and 350 ° C. below 400 ° C.
In contrast, in the method of Example 1 in which NO is reduced using methane as a reducing agent using a reducing catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ), the reaction temperature is less than 400 ° C., 250 ° C., It can be seen that a high NO conversion is exhibited at low temperatures of 300 ° C. and 350 ° C.
（実施例２）
Ｈ3ＰＷ12Ｏ40の含有量を２０重量％，３０重量％、４０重量％とし、Ｐｄ担持量を１．０重量％にした以外、実施例１と同様な方法により３種の還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を製造した。
得られた３種の還元用触媒を用い、反応温度を２５０℃にした以外、実施例１と同様な条件で還元反応を行い、ＮＯおよびＣＨ4の転化率を求めた。その結果を下記表２に示す。
Three reducing catalysts were prepared in the same manner as in Example 1 except that the content of H 3 PW 12 O 40 was 20 wt%, 30 wt%, and 40 wt%, and the Pd loading was 1.0 wt%. (Pd / H 3 PW 12 O 40 / SiO 2 ) was produced.
The reduction reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was set to 250 ° C. using the obtained three kinds of reduction catalysts, and the conversion rates of NO and CH 4 were determined. The results are shown in Table 2 below.
前記表２の結果からＨ3ＰＷ12Ｏ40の含有量が２０重量％〜４０重量％の還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いてＮＯをメタン（還元剤）で還元反応させる方法では、反応温度が４００℃未満である２５０℃の低温域において高いＮＯ転化率を示すことがわかる。 From the results shown in Table 2, NO is converted into methane (reducing agent) using a reducing catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) having a content of H 3 PW 12 O 40 of 20 wt% to 40 wt%. It can be seen that in the method of reducing the reaction, a high NO conversion rate is exhibited in a low temperature range of 250 ° C. where the reaction temperature is less than 400 ° C.
（実施例３）
Ｐｄ担持量を１．０重量％にした以外、実施例１と同様な方法により還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を製造した。
得られた還元用触媒を用いて、実施例１と同様な条件で還元反応を行い、ＮＯおよびＣＨ4の転化率を求めた。その結果を下記表３に示す。なお、表３にはＰｄ担持量を０．２重量％の還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いた実施例１の結果を併記する。
A reduction catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) was produced in the same manner as in Example 1 except that the amount of Pd supported was 1.0% by weight.
Using the obtained reduction catalyst, a reduction reaction was performed under the same conditions as in Example 1 to determine the conversion rates of NO and CH 4 . The results are shown in Table 3 below. Table 3 also shows the results of Example 1 using a reduction catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) with a Pd loading of 0.2% by weight.
前記表３の結果からＰｄ担持量が１．０重量％の還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いてＮＯをメタン（還元剤）で還元反応させる実施例３の方法では、Ｐｄ担持量が０．２重量％の還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いて同様に還元反応させる実施例１の方法に比べて反応温度が４００℃未満の低温域においてより高いＮＯ転化率を示すことがわかる。 From the results of Table 3 above, the reduction reaction of NO with methane (reducing agent) was carried out using the reducing catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) having a Pd loading of 1.0 wt%. In the method, the reaction temperature is 400 ° C. as compared with the method of Example 1 in which the reduction reaction is similarly performed using a reduction catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) having a Pd loading of 0.2% by weight. It can be seen that a higher NO conversion is exhibited in the low temperature range of less than.
（実施例４，５）
Ｈ3ＰＷ12Ｏ40の含有量を２０重量％にした以外、実施例１と同様な方法により還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を製造した。
得られた還元用触媒を用いて、実施例１と同様な条件、およびヘリウムガス中に水蒸気を含まない以外、実施例１と同様な条件でそれぞれ還元反応を行い、ＮＯおよびＣＨ4の転化率を求めた。これらの結果を下記表４に示す。
A reduction catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) was produced in the same manner as in Example 1 except that the content of H 3 PW 12 O 40 was 20% by weight.
Using the resulting catalyst for reduction, the same conditions as in Example 1, and except containing no water vapor helium gas performs each reduction reaction under the same conditions as in Example 1, the conversion of NO and CH 4 Asked. These results are shown in Table 4 below.
前記表４の結果から還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いてＮＯをメタン（還元剤）で還元反応させる方法において、水蒸気を含む実施例４の方法は水蒸気を含まない実施例５の方法に比べて反応温度が４００℃未満の２５０℃，３００℃，３５０℃の低温域においてより高いＮＯ転化率を示すことがわかる。 From the results shown in Table 4, in the method of reducing NO with methane (reducing agent) using a reducing catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ), the method of Example 4 including water vapor is water vapor. It can be seen that the NO conversion is higher in the low temperature regions of 250 ° C., 300 ° C., and 350 ° C., where the reaction temperature is less than 400 ° C., as compared to the method of Example 5 that does not contain.
（実施例６，７）
Ｈ3ＰＷ12Ｏ40の代わりに２０重量％のＨ3ＰＭｏ12Ｏ40またはＨ4ＳｉＷ12Ｏ40を含有させた以外、実施例１と同様な方法により２種の還元用触媒（Ｐｄ／Ｈ3ＰＭｏ12Ｏ40／ＳｉＯ2、Ｐｄ／Ｈ4ＳｉＷ12Ｏ40／ＳｉＯ2）を製造した。
得られた２種の還元用触媒を用い、反応温度を２５０℃にした以外、実施例１と同様な条件でそれぞれ還元反応を行い、ＮＯおよびＣＨ4の転化率を求めた。これらの結果を下記表５に示す。なお、表５にはＰｄ担持量を０．２重量％の還元用触媒（Ｐｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2）を用いた実施例１の結果を併記する。
H 3 PW 12 H 3 instead of 20 wt% of O 40 PMo 12 O 40 or other which contains a H 4 SiW 12 O 40, 2 kinds of reducing catalyst by the same manner as in Example 1 (Pd / H 3 PMo 12 O 40 / SiO 2 , Pd / H 4 SiW 12 O 40 / SiO 2 ).
Using the obtained two kinds of reduction catalysts, the reduction reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was 250 ° C., and the conversion rates of NO and CH 4 were determined. These results are shown in Table 5 below. Table 5 also shows the results of Example 1 using a reduction catalyst (Pd / H 3 PW 12 O 40 / SiO 2 ) with a Pd loading of 0.2% by weight.
前記表５の結果からＮＯをメタン（還元剤）で還元反応させる際、反応温度が４００℃未満である２５０℃の低温域でのＮＯ転化率は、還元用触媒として実施例１のＰｄ／Ｈ3ＰＷ12Ｏ40／ＳｉＯ2が最も高く、次に実施例６のＨ3ＰＭｏ12Ｏ40、実施例７のＨ4ＳｉＷ12Ｏ40の順になることがわかる。 From the results of Table 5 above, when NO is reduced with methane (reducing agent), the NO conversion rate at a low temperature of 250 ° C. where the reaction temperature is less than 400 ° C. is the Pd / H of Example 1 as a reduction catalyst. 3 PW 12 O 40 / SiO 2 is the highest, then H 3 PMo 12 O 40 example 6, it is found to be a sequence of H 4 SiW 12 O 40 of example 7.
本発明によれば、窒素酸化物、特に酸素が共存されるか、酸素および水蒸気が共存される窒素酸化物をメタンを還元剤として還元反応させる際に比較的低温（４００℃未満）で高活性を示し、ボイラー、自動車のエンジン（燃焼器）のような各種の燃焼装置から排出される燃焼排ガスの窒素酸化物の除去に有用な触媒を提供することができる。 According to the present invention, when a nitrogen oxide, particularly a nitrogen oxide in which oxygen coexists or a nitrogen oxide in which oxygen and water vapor coexist is subjected to a reduction reaction using methane as a reducing agent, it is highly active at a relatively low temperature (less than 400 ° C.). It is possible to provide a catalyst useful for removing nitrogen oxides from combustion exhaust gas discharged from various combustion apparatuses such as boilers and automobile engines (combustors).
本発明によれば、窒素酸化物、特に酸素が共存されるか、酸素および水蒸気が共存される窒素酸化物をメタンを還元剤として比較的低温（４００℃未満）で還元反応させて無害な窒素として除去することが可能で、ボイラー、自動車のエンジン（燃焼器）のような各種の燃焼装置から排出される燃焼排ガスの処理に適用し得る窒素酸化物の除去方法を提供することができる。 According to the present invention, nitrogen oxides, particularly nitrogen oxides coexisting with oxygen, or nitrogen oxides coexisting with oxygen and water vapor, are subjected to a reduction reaction at a relatively low temperature (less than 400 ° C.) using methane as a reducing agent. Therefore, it is possible to provide a method for removing nitrogen oxides that can be applied to the treatment of combustion exhaust gas discharged from various combustion devices such as boilers and automobile engines (combustors).
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