JP2007185574A - Catalyst for decomposing nitrous oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly active catalyst capable of certainly reducing and decomposing nitrous oxide at a temperature lower than its decomposition temperature, for example at a temperature between 300°C and 400°C, and hence at a low cost into nitrogen and oxygen. <P>SOLUTION: The catalyst 1 for decomposing nitrous oxide comprises a group VIII metal or metals of the fifth or sixth period in the Periodic Table used selectively or in combination, typically such as platinum, rhodium, and palladium, adhering to and supported by a porous support 4. By virtue of the transient electron donation of an unpaired electron of the s orbit of the outermost shell of the atomic structure of the metal or metals and the transient electron capture by one or two positive hole(s) of the d orbit of the immediate inner shell or by an equivalent similar action of the atomic structure, the bonding energy and activation energy of nitrous oxide that hinders its decomposition is decreased, so that nitrous oxide contained in exhaust gas 2 is reduced and decomposed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a decomposition catalyst for nitrous oxide N ₂ O. That is, the present invention relates to a decomposition catalyst that reduces and decomposes nitrous oxide N ₂ O into nitrogen N ₂ and oxygen O ₂ at a temperature lower than its thermal decomposition temperature, for example, at a temperature of about 300 ° C. to 400 ° C.

《Technical background》
Nitrous oxide N ₂ O has traditionally been used for anesthesia, food, and others, but recently, as a causative agent for global warming, the reduction of carbon dioxide is closely related to CO ₂ Has been.
That is, when nitrous oxide N ₂ O is released into the atmosphere, it becomes a causative agent of global warming, and is said to have a warming effect about 310 times that of carbon dioxide CO _2. Expected to increase.

<Conventional technology>
As an artificial source of nitrous oxide N ₂ O, exhaust gases from factories and automobiles are typical. For example, a factory for manufacturing adipic acid and caprolactam as raw materials for nylon, a factory for manufacturing nitric acid HNO ₃ , a factory or automobile equipped with a flue gas denitration device that reduces nitrogen oxide NO _X using ammonia NH ₃ , Furthermore, it is produced as a by-product in exhaust gas from automobiles equipped with a three-way catalyst that simultaneously oxidizes and reduces harmful substances such as carbon monoxide CO, hydrocarbon HC, and nitrogen oxide NO _X , etc. Nitrous oxide N ₂ O is contained.
And measures for reducing nitrous oxide N ₂ O in various types of exhaust gas are currently under investigation and development.
Typically, a technique of reducing and thermally decomposing nitrous oxide N ₂ O alone into nitrogen N ₂ and oxygen O ₂ by heating the exhaust gas to a high temperature of, for example, about 500 ° C. to 800 ° C. can be considered.
On the other hand, it has also been studied to apply alumina, zeolite, or zinc oxide to exhaust gas with a catalyst to reduce and decompose it into nitrogen N ₂ and oxygen O ₂ .

By the way, for measures to reduce nitrous oxide N _{2 O} of such a conventional example, the following problems have been pointed out.
<About the first problem>
First, the above-described conventional example in which reduction and thermal decomposition are performed by high-temperature heating has been pointed out as problems such as high cost.
That is, since the exhaust gas is heated to a high temperature of about 500 ° C. to 800 ° C. to thermally decompose nitrous oxide N ₂ O, there is a problem that heating equipment cost and fuel cost are increased. Furthermore, it has been pointed out that carbon dioxide CO _2, which is a cause of global warming, is discharged with the combustion of fuel.

About the second problem
Secondly, the above-mentioned conventional example using alumina, zeolite, or zinc oxide with a catalyst and reducing and decomposing it does not need to be heated at a high temperature as described above, but its performance is improved by the contained substances in the exhaust gas. It was pointed out that it would decline.
That is, the exhaust gas often contains moisture H ₂ O (water vapor or water droplets), nitrogen oxides NO _X , oxygen O ₂ , sulfur dioxide SO _{2 and the} like. Then, these containing material acts as a decomposition Bogai component, has been nitrous oxide N _{2 O} reductive decomposition does not proceed smoothly, there is a drawback. In particular, when moisture H ₂ O and nitrogen oxides NO _X were contained, this became prominent. Furthermore, it was pointed out that NO _x, which is a harmful substance, is produced as a by-product of reduction and decomposition.

<< About the present invention >>
The nitrous oxide decomposition catalyst of the present invention has been developed in order to solve the above-described problems of the conventional examples in view of such circumstances.
The present invention firstly can be reduced and decomposed at a temperature lower than the thermal decomposition temperature, and thus is excellent in various costs, and secondly, reliably reduced to nitrogen and oxygen with high catalytic activity. The object is to propose a nitrous oxide decomposition catalyst that can be decomposed.

<About Claim>
The technical means of the present invention for solving such a problem is as follows.
Claim 1 is as follows. The nitrous oxide decomposition catalyst according to claim 1 is a catalyst that reduces and decomposes nitrous oxide into nitrogen and oxygen, and uses a metal of the fifth period or the sixth period of the periodic table group 8, It is characterized by.
Claim 2 is as follows. The nitrous oxide decomposition catalyst according to claim 2, wherein, in claim 1, the metal of the decomposition catalyst is a transient electron donating action of one unpaired electron in the outermost shell s orbit of the atomic structure, and Based on the transient electron-storing action of one or two holes in the inner shell d orbital, or the similar action of the atomic structure according to these, the binding and activation energy that is the decomposition barrier of the nitrous oxide And reducing and decomposing the nitrous oxide.
Claim 3 is as follows. In the nitrous oxide decomposition catalyst according to claim 3, the nitrous oxide according to claim 2 is contained in the exhaust gas. In addition, platinum, rhodium, and palladium are used selectively or in combination as the decomposition catalyst, and the nitrous oxide is reduced and decomposed at a temperature lower than the thermal decomposition temperature.
Claim 4 is as follows. In a nitrous oxide decomposition catalyst according to a fourth aspect, the exhaust gas according to the third aspect is supplied via a denitration apparatus using ammonia as a reducing agent. The decomposition catalyst is characterized by being attached and supported on a porous carrier.
Claim 5 is as follows. In a nitrous oxide decomposition catalyst according to a fifth aspect, the exhaust gas is supplied via a three-way catalytic purification device in the third aspect. The decomposition catalyst is characterized by being attached and supported on a porous carrier.
Claim 6 is as follows. The nitrous oxide decomposition catalyst according to claim 6 is the nitrous oxide decomposition catalyst according to claim 3, wherein the exhaust gas contains moisture, and the decomposition catalyst is attached and supported on the porous carrier together with the photocatalyst.
The photocatalyst generates holes in the outermost shell of the molecular structure by the decomposition catalyst, reacts with the hydroxide ions of the water to generate OH radicals having a strong electron-trapping action, and thus the catalytic activity of the decomposition catalyst Is reinforced.

《Action etc.》
Since the present invention comprises such means, the following is achieved.
(1) As the decomposition catalyst, metals of the fifth period and the sixth period of Group 8 of the periodic table, such as platinum, rhodium, and palladium, are used.
(2) And, for example, it contains nitrous oxide from the manufacturing process of adipic acid, caprolactam, nitric acid, etc., nitrogen oxide denitration equipment using ammonia as a reducing agent, automobile three-way catalytic purification equipment, etc. Exhaust gas is supplied to the cracking catalyst.
(3) The exhaust gas is supplied at a temperature lower than the thermal decomposition temperature.
(4) In the case of platinum, rhodium, and palladium as cracking catalysts, one unpaired electron in the outermost shell s orbit of the atomic structure has a transient electron donating action, and one in its inner shell d orbital. Or two holes have a transient electron-storing action, or have a similar action due to an atomic structure according to this.
(5) Therefore, nitrous oxide in the exhaust gas is first released based on the electron-storing action of the holes of the decomposition catalyst, the binding and activation energy is lowered, and the oxidation is transiently promoted to release nitrogen. Oxygen atoms are adsorbed on the cracking catalyst.
The adsorbed oxygen atoms are reduced in binding and activation energy based on the electron donating action of the unpaired electrons of the decomposition catalyst, and the reduction is promoted transiently. And liberated from the cracking catalyst.
(6) Thus, nitrous oxide is reduced and decomposed into nitrogen and oxygen at a temperature lower than the thermal decomposition temperature due to the catalytic activity of the decomposition catalyst.
(7) Although exhaust gas often contains moisture, when a decomposition catalyst is used together with a photocatalyst, the photocatalyst generates holes in the outermost shell of the molecular structure due to the action of the decomposition catalyst, and captures the electrons. Based on the action, OH radicals having a strong electron-storing action and oxidizing power are generated from the hydroxide ions of the water, so that the catalytic activity is reinforced.

(8) Therefore, according to the decomposition catalyst of the present invention, first, nitrous oxide is reduced and decomposed into nitrogen and oxygen at a temperature lower than the heat decomposition temperature. That is, due to the catalytic activity of the cracking catalyst, the binding energy and the activation energy, which are energy barriers for nitrous oxide decomposition, are lowered, so that, for example, 300 ° C. to 800 ° C. It is reduced and decomposed at about 400 ° C.
Second, nitrous oxide is reliably reduced and decomposed into nitrogen and oxygen with high catalytic activity. That is, nitrous oxide is reduced and decomposed reliably by transiently promoting oxidation and reduction by reducing the binding and activation energy due to the electron donating action and the electron trapping action of the decomposition catalyst. Even if the exhaust gas contains moisture, nitrogen oxides, oxygen, sulfur dioxide, etc., it is reliably reduced and decomposed without interference.
Although the exhaust gas often contains moisture, when a decomposition catalyst is used together with a photocatalyst, OH radicals are generated to reinforce the catalytic activity, thereby further promoting reduction and decomposition.
(9) Now, the nitrous oxide decomposition catalyst of the present invention exhibits the following effects.

<< First effect >>
First, nitrous oxide can be reduced and decomposed into nitrogen and oxygen at a temperature below its thermal decomposition temperature.
That is, the nitrous oxide decomposition catalyst according to the present invention is a nitrous oxide contained in the exhaust gas without being heated at a high temperature of about 500 ° C. to 800 ° C., for example, as in the above-described conventional example. Reduction and decomposition can be performed at a supply temperature of about 300 ° C. to 400 ° C., for example.
Therefore, unlike the above-described conventional example, the equipment cost and fuel cost for high-temperature heating are not increased, and the cost is excellent. In addition, carbon dioxide (causative substance of global warming) is not discharged with the combustion of fuel.

<< Second effect >>
Second, nitrous oxide can be reliably reduced and decomposed into nitrogen and oxygen by high catalytic activity.
That is, the nitrous oxide decomposition catalyst of the present invention can reliably reduce and decompose nitrous oxide contained in the exhaust gas based on its high catalytic activity. As in the conventional example using alumina, zeolite, or zinc oxide with a catalyst as described above, the performance may be deteriorated due to substances contained in the exhaust gas, such as moisture, nitrogen oxide, oxygen, and sulfur dioxide. Reduction and decomposition proceed smoothly.
Although the exhaust gas often contains moisture, when used with a photocatalyst, OH radicals are generated, and reduction and decomposition proceed more smoothly. That is, in this conventional example, moisture that has been regarded as a detoxifying component for reduction and decomposition can be used as a component for promoting reduction and decomposition by using a photocatalyst.
As a result, it is possible to reliably reduce nitrous oxide, which is said to have a warming effect about 310 times that of carbon dioxide, as a causative substance of global warming, and the emission of clean exhaust gas to the atmosphere is realized. . In addition, nitrogen oxides, which are harmful substances, are not generated as a by-product of reduction and decomposition.
As described above, the effects exerted by the present invention are remarkably large, such as all the problems existing in this type of conventional example are solved.

《About drawing》
Hereinafter, the nitrous oxide decomposition catalyst of the present invention will be described in detail based on the best mode for carrying out the invention shown in the drawings. FIG. 1 is used for explaining the best mode for carrying out the present invention. (1) FIG. 1 is an explanatory front sectional view of an exhaust system. (2) FIG. is there.

"For nitrous oxide _{N 2} O"
The present invention relates to a decomposition catalyst 1 for nitrous oxide N ₂ O. Therefore, hereinafter, nitrous oxide N ₂ O, the outline of the decomposition catalyst 1, the details of the decomposition catalyst 1, the combined use and action of the photocatalyst, etc. will be described in the order of the examples.
First, nitrous oxide N ₂ O will be described. Nitrous oxide N ₂ O is also called dinitrogen monoxide, laughing gas, nitrogen oxide, etc., and its reduction is required as a causative substance of global warming. In particular, the exhaust gas 2 containing nitrous oxide N ₂ O is required to be reduced before being released into the atmosphere.
Typical examples of the anthropogenic source of nitrous oxide N ₂ O are chemical manufacturing processes and automobile exhaust gas 2.

These will be described in detail. First, in the production process of adipic acid and caprolactam as raw materials for nylon, nitrous oxide N ₂ O is produced as a by-product together with adipic acid and caprolactam, and is thus contained in the exhaust gas 2. Further, it is produced in the same way in the production process of nitric acid HNO ₃ used in the production process and is contained in the exhaust gas 2.
The reaction formula for adipic acid production is shown in the following chemical formula 1 and chemical formula 2. That is, adipic acid is produced from cyclohexanone or cyclohexanol.

Further, in the illustrated exhaust gas denitration apparatus 3 that reduces and removes nitrogen oxides NO _X that are harmful substances in the exhaust gas 2 of an engine or the like into harmless nitrogen N ₂ using ammonia NH ₃ as a reducing agent, In the catalyst area attached to the porous carrier 4, nitrous oxide N ₂ O is produced as a byproduct according to the following reaction formulas 3 and 4 and the reaction formula 5: Therefore, nitrous oxide N ₂ O is contained in the exhaust gas 2 that has passed through the flue gas denitration device 3.

Also, carbon monoxide CO and hydrocarbon HC, which are harmful substances in the exhaust gas 2 of automobile engines, are oxidized to harmless carbon dioxide CO ₂ and water H ₂ O in the vicinity of the theoretical air-fuel ratio using a so-called three-way catalyst. while, at the same time, reducing nitrogen oxides NO _X is harmful substances into harmless nitrogen N _2, for exhaust gas 2 having passed through the purifying device of the three-way catalyst system also, as is well known, nitrous oxide N ₂ O Is produced and contained.
It is known that nitrous oxide N ₂ O increases in concentration when the three-way catalyst deteriorates due to long-term use. Further, once generated nitrous oxide N ₂ O generates again nitrogen oxide NO _X which is a harmful substance based on the oxidation promotion action of the three-way catalyst, by the following reaction formulas 6 and 7. Some have pointed out.

<< Outline of decomposition catalyst 1 >>
Hereinafter, the decomposition catalyst 1 for nitrous oxide N ₂ O of the present invention will be described. First, the outline is described.
As described above, nitrous oxide N ₂ O contained in the exhaust gas ₂ is reduced and decomposed into nitrogen N ₂ and oxygen O ₂ by the decomposition catalyst 1. As the decomposition catalyst 1, a metal of the fifth period or the sixth period of the eighth group of the periodic table is used. Typically, platinum Pt, rhodium Rh, and palladium Pd are used alone or in combination.
Platinum Pt, rhodium Rh, and palladium Pd have a transient electron donating action of one unpaired electron e ⁻ in the outermost shell s orbit of the atomic structure and one or two of the inner shell d orbitals. Both holes have the same effect due to the transient electron-storing action of hole hole ⁺ or the atomic structure according to these.
Based on this, the bond and activation energy, which are the decomposition barriers of nitrous oxide N ₂ O, are lowered, and at a temperature lower than the thermal decomposition temperature, Nitrogen oxide N ₂ O is reduced and decomposed into nitrogen N ₂ and oxygen O ₂ .

The cracking catalyst 1 in the illustrated example is attached and supported on the porous carrier 6 of the reduction cracking apparatus 5. That is, the reductive decomposition apparatus 5 is connected to the exhaust pipe 7 for the exhaust gas 2, and the porous carrier 6 that is a carrier base is inserted into the outer cylinder 8. For example, as the porous carrier 6, a honeycomb core made of ferritic stainless steel, alumina, or ceramic made of an aggregate of hollow columnar cell spaces 10 partitioned by cell walls 9 is used.
The porous carrier 6 has its axis directed in the flow direction of the exhaust gas 2, and the decomposition catalyst 1 is attached and supported on the cell wall 9 by coating or the like. The exhaust gas 2 is supplied to the cell space 10. ,pass.
The outline of the cracking catalyst 1 is as described above.

<< Details of cracking catalyst 1 >>
First, platinum Pt which is a typical cracking catalyst 1 will be described. First, platinum Pt has one unpaired electron e ^{− in} the 6s orbit of the outermost shell P shell of the atomic structure. In the reaction process, the self becomes Pt ⁺ transiently, and this unpaired electron e ⁻ transiently donates the electron e ⁻ to the partner (reaction target molecule), lowering the binding energy and activation energy of the partner. , Acting as a donor electron e ⁻ , transiently promoting the reduction reaction of the partner.
This together with the platinum Pt is, the one 5d orbital of inner O shell of outermost P shell of atomic structure, eight unpaired electron e ^- and one unpaired electron e ^- is exist. Since up to 10 counter electrons e ⁻ enter the O shell 5d orbital, one hole (hole) hole ⁺ lacking the electron e ⁻ exists. And in the course of the reaction, the hole hole ^+, the electrons e ^- to fill the defects, transiently electrons e from the other ^- steal, promotes the oxidation reaction of transiently partner.
The catalytic action and decomposition action of platinum Pt depend on such an electron donating action and reduction promoting ability of the unpaired electron e ⁻ , and an electron trapping action and oxidation promoting ability of the hole hole ⁺ .

Next, rhodium Rh which is an example of the decomposition catalyst 1 will be described. In rhodium Rh, first, one unpaired electron e ⁻ exists in the 5s orbit of the outermost shell O shell of the atomic structure. Therefore, like the platinum Pt as described above, during the course of the reaction, self transiently become Rh ^+, the unpaired electrons e ^- electrons e to the other party (the reaction target molecule) ^- donate, partner of the binding energy, Decrease the activation energy to transiently promote the partner's reduction reaction.
At the same time, rhodium Rh has eight counter-electrons e ^{− in} the 4d orbit of the N shell inside the outermost shell O shell of the atomic structure. Since up to 10 counter electrons e ⁻ enter the N-shell 4d orbital, there are two hole holes ⁺ lacking the electrons e ⁻ . Then, like the platinum Pt described above, in the reaction process, these two hole holes ⁺ transiently take away the electron e ⁻ from the partner and promote the oxidation reaction of the partner. However, this oxidation promoting power is inferior to the above-described oxidation promoting power of one hole hole ⁺ of platinum Pt (due to the directionality in which electrons e ⁻ are buried).
The catalytic action and decomposition action of rhodium Rh depend on such an electron donating action and reduction promoting ability of unpaired electrons e ⁻ , and an electron trapping action and oxidation promoting ability of hole hole ⁺ .

Next, palladium Pd which is an example of the decomposition catalyst 1 will be described. Palladium Pd is filled with 10 electrons e ^{− in} the 4d orbit of the outermost shell N shell of the atomic structure, and there is no vacancy hole ⁺ lacking the electrons e ⁻ . Further, the electron e ⁻ does not exist in the outer O shell 5s orbit, but the catalytic activity is understood as follows, for example.
That is, the catalytic activity of palladium Pd is such that one unpaired electron e ⁻ is transiently transferred from the N-shell 4d orbital to the outer O-shell 5s by interaction with the partner (reaction target molecule) in the reaction process. It is assumed that one hole hole ⁺ is generated in the N-shell 4d orbit in a transitional manner.
This point can be inferred from the atomic structure of the rhodium Rh whose atomic number is adjacent, and further from the atomic structure of platinum Pt or the like. This is based on the fact that (sd) hybrid orbits are likely to be formed between the two and the electrons e ^{− of the} 4d orbit, and resonance is likely to occur.
In any case, palladium Pd has an electron donating action and a reduction accelerating power, as well as an electron-storing action and an oxidation accelerating power, and thus exhibits a catalytic action and a decomposition action.
Platinum Pt, rhodium Rh, and palladium Pd of the decomposition catalyst 1 are as described above.

<About combined use of photocatalyst>
Next, the combined use of the decomposition catalyst 1 and the photocatalyst will be described. Since this type of exhaust gas 2 often contains moisture H ₂ O, it is conceivable that the decomposition catalyst 1 is attached and supported on the porous carrier 6 together with the photocatalyst.
That is, the photocatalyst is subjected to the action of the decomposition catalyst 1 to generate hole hole ^{+ in} the outermost shell of the molecular structure, and reacts with the hydroxide ion OH ⁻ of water H ₂ O to generate an OH radical having a strong electron-sorptive action. (.OH) is generated, thereby reinforcing the catalytic activity of the decomposition catalyst 1.

The combined use of such a photocatalyst will be described in detail. First, the exhaust gas 2 supplied to the reductive decomposition apparatus 5 provided with the decomposition catalyst 1 often contains moisture H ₂ O together with nitrous oxide N ₂ O (for example, the above-described chemical conversion 1, conversion (Refer to the reaction formulas of 2, 3, 3, and 5).
Moisture H ₂ O is mostly contained in the state of water vapor in the exhaust gas 2 at about 300 ° C. to 400 ° C., but it can also be contained in the form of water droplets (water). . In this specification, moisture H ₂ O broadly encompasses both gas and liquid states.
Then, the photocatalyst 11 is attached and supported together with the decomposition catalyst 1 on the cell wall 9 of the porous carrier 6 of the reductive decomposition apparatus 5. As the photocatalyst, for example, titania, that is, titanium oxide TiO ₂ is used, and the particles are adhered in a film form by coating or sintering.
Therefore, in the photocatalyst, for example, titanium oxide TiO ₂ , the outermost electron e ⁻ of the molecular structure is excited by the following chemical formula 10 based on the action of platinum Pt (rhodium Rh, palladium Pd) of the decomposition catalyst 1. It jumps out and moves to the conductor, and hole hole ⁺ is generated in the outermost shell.

Then, the hole hole ⁺ is to fill the electron-deficient, adjacent in the exhaust gas 2, and ionization of contacting water _H 2 O (water vapor having an energy of about 300 ° C. to 400 ° C. in the exhaust gas 2) The electron e ⁻ is extracted from the hydroxide ion OH ⁻ .
Accordingly, the hydroxide ion OH ⁻ deprived of the electron e ^{− according} to the following formula 11 generates an OH radical (.OH), that is, a bidoxyl radical. The generated OH radical has a very strong electron-storing action, oxidation promotion power, that is, decomposition power.

Here, it supplements about the effect | action of the decomposition catalyst 1 in Chemical formula 10 mentioned above. First, as described above, palladium Pd easily forms a hybrid orbital between the N-shell 4d orbital and the O-shell 5s orbital due to the interaction with the partner (reaction target molecule) in the reaction process. It is considered that a hybrid orbit is easily formed even between the outer 5p orbit (electron e ⁻ is zero). The same applies to rhodium Rh.
Similarly, platinum Pt is considered to easily form a hybrid orbital among the O shell 5d orbit, P shell 6s orbit, and 6p orbit (electron e ⁻ is zero) due to the interaction with the partner in the reaction process.
Further, for palladium Pd and rhodium Rh, 10 to 8 electrons e ⁻ in the N-shell 4d orbital, and for platinum Pt, 2 to 3 electrons e ⁻ for 9 electrons e ⁻ in the O-shell 5d orbital, respectively. ^- between, is considered likely to resonance to occur.
Therefore, in the decomposition catalyst 1, based on such hybrid orbits and resonances, the charged particles of electrons e ^— especially the outer shell d electrons e ⁻ move between the orbits or move in a curved manner, so that light energy such as electromagnetic waves ( (Photon) is generated or enters or exits. Then, based on the action of such cracking catalysts 1, by the formula 10 above, the photocatalyst such as titanium oxide TiO _2, so that the hole hole ⁺ is generated.
Moreover, as an example in which the catalytic activity of the decomposition catalyst 1 is reinforced by using the decomposition catalyst 1 and the photocatalyst together in this way, for example, the description in Japanese Patent No. 2633316 can be cited.
That is, in the action column and example column of the same patent publication, vanadium pentoxide V ₂ O ₅ and tungsten trioxide WO ₃ are used as a decomposition catalyst for aromatic chlorine compounds such as dioxin PCDD in exhaust gas. A TiO ₂ carrier supported is shown. And it is disclosed that dioxin PCDD etc. are oxidatively decomposed.
In other words, as this type of cracking catalyst alone vanadium pentoxide V ₂ O ₅ and tungsten trioxide WO _3, practice, the decomposition of dioxin PCDD is not sufficient, by which a combination of titanium oxide TiO _2, they As a result of the electron trapping action, hole hole ⁺ is generated in titanium oxide TiO ₂ and reacts with moisture H ₂ O to generate OH radicals. Due to the strong decomposition power of OH radicals, benzene rings such as dioxin PCDD It is understood that is now reliably opened and decomposed.
In the present invention, platinum Pt, rhodium Rh, palladium Pd, etc. having an extremely strong electron-trapping action over such vanadium pentoxide V ₂ O ₅ and tungsten trioxide WO ₃ are used together with titanium oxide TiO ₂ . It is adopted as the decomposition catalyst 1. Accordingly, the generation of OH radicals by titanium oxide TiO ₂ is further promoted, and nitrous oxide N ₂ O is reliably decomposed.
The photocatalyst is used in this way.

<About the action>
The nitrous oxide N ₂ O decomposition catalyst 1 of the present invention is configured as described above. Therefore, it becomes as follows.
(1) The nitrous oxide N ₂ O decomposition catalyst 1 uses a metal of the fifth or sixth period of Group 8 of the periodic table. Typically, platinum Pt, rhodium Rh, and palladium Pd are used selectively or in combination. For example, the platinum Pt, rhodium Rh, and palladium Pd are attached and supported on the porous carrier 6 of the reductive decomposition apparatus 5.
As the decomposition catalyst 1, the use of platinum Pt, which has the strongest ability to promote the oxidation of hole hole ⁺ , can be said to be the most orthodox, but in terms of unit price, rhodium Rh, platinum Pt, and palladium Pd are used in this order. Pd is most cost effective, and rhodium Rh is excellent in terms of durability and life.
From these viewpoints, platinum Pt, rhodium Rh, and palladium Pd are used alone or in combination as the decomposition catalyst 1. For example, it is conceivable to employ platinum Pt and rhodium Rh at a ratio of 5: 1.

(2) The exhaust gas 2 containing nitrous oxide N ₂ O is supplied to such a cracking catalyst 1 and passes therethrough.
For example, the exhaust gas 2 is supplied from a manufacturing process of adipic acid, caprolactam, nitric acid HNO ₃ or the like (see the above reaction formulas of Chemical Formula 1 and Chemical Formula 2). For example, ammonia NH ₃ is reduced as shown in the illustrated example. Nitrogen oxide NO _X used as an agent is supplied via the flue gas denitration device 3 (see the reaction formulas of Chemical Formula 3, Chemical Formula 4, and Chemical Formula 5), for example, purification of a three-way catalyst system for automobiles Supplied via the device.

(3) The exhaust gas 2 is supplied to and passes through the cracking catalyst 1 at a temperature lower than the thermal decomposition temperature of nitrous oxide N ₂ O. For example, it is supplied and passes at a temperature of about 300 ° C. to 400 ° C.

(4) The metal such as platinum Pt, rhodium Rh, palladium Pd, etc. of the decomposition catalyst 1 has a transient electron donating action, with one unpaired electron e ^{− in} the outermost shell s orbit of the atomic structure. The one or two hole holes ⁺ in the inner shell d orbital have a transient electron-storing action, or have a similar action due to an atomic structure based on these.

(5) Therefore, nitrous oxide N ₂ O in the exhaust gas 2 is first interfered with the hole hole ⁺ of the decomposition catalyst 1. Then, based on the transient electron-storing action, the binding energy and activation energy are lowered, the oxidation reaction is transiently promoted, so that nitrogen N ₂ is liberated and oxygen O atoms are adsorbed on the decomposition catalyst 1. Is done.
That is, in nitrous oxide N ₂ O, which is a reaction target molecule, the double bond between nitrogen N and oxygen O in the structural formula is composed of a σ bond and a π bond. First, π electrons having a weak binding force are interfered with the hole hole ⁺ of the decomposition catalyst 1 and are transiently pulled to the hole hole ⁺ side, so that the π bond between nitrogen N and oxygen O is first Disconnected. Next, the remaining single bond, that is, the σ bond whose bond energy has been lowered by this amount is also interfered with by the hole hole ⁺ and cut.
In this way, the nitrous oxide N ₂ O has a double bond between the nitrogen N and the oxygen O of the structural formula, so that the nitrogen N ₂ is liberated and the oxygen O atom is decomposed on the cracking catalyst 1. (Hole ⁺ -O-hole ⁺ ). Nitrous oxide N ₂ O has its activation energy, which is a decomposition reaction barrier, lowered by the interference of the hole “hole ^+” of the decomposition catalyst 1, thereby releasing nitrogen N ₂ .
Then, the oxygen O atoms adsorbed on the cracking catalyst 1 in this way are subjected to interference of unpaired electrons e ⁻ of the cracking catalyst 1. Then, based on the transient electron donating action, the binding energy and the activation energy are lowered, and the reduction reaction is transiently promoted. Accordingly, the hole hole ⁺ and the electron e ⁻ are combined, and the oxygen O is released from the restriction by the hole hole ⁺ to be diatomicized to become an oxygen molecule O ₂ and is released from the decomposition catalyst 1.

(6) Nitrous oxide N ₂ O, which is a reaction target molecule, has its binding energy and activation energy, which are decomposition barriers, lowered due to the catalytic activity of the decomposition catalyst 1 in this way, and thus is less than its thermal decomposition temperature. Under temperature, for example, at a temperature of about 300 ° C. to 400 ° C., it is reduced and decomposed into nitrogen N ₂ and oxygen O ₂ (see the reaction formulas of Chemical Formulas 8 and 9 above).
That is, nitrous oxide N ₂ O is lowered by the action of unpaired electrons e ⁻ and hole hole ⁺ of the decomposition catalyst 1 in the energy barrier that has been a reaction barrier in the reaction path of the reaction formula. That is, the activation energy required for the reaction is lowered.
Therefore, the reduction and decomposition reaction is established at a temperature of 300 ° C. to 400 ° C. or less, for example, a temperature of about 300 ° C. to 400 ° C., regardless of the thermal decomposition reaction of about 500 ° C. to 800 ° C.

(7) The exhaust gas 2 often contains moisture H ₂ O (see, for example, the reaction formulas of Chemical Formula 1, Chemical Formula 2, Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, etc.) When the decomposition catalyst 1 is attached to and supported on the porous carrier 6 together with the photocatalyst as shown in the example, the following occurs.
That photocatalyst, based on the action of the cracking catalyst 1, (see equation of the above-mentioned formula 10) hole hole ⁺ is generated in the outermost shell of the molecular structure, based on the electronic exploitation action of the hole hole ^+, adjacent OH radicals (.OH) are generated from the hydroxide ions OH ⁻ of the water H ₂ O (see the above formula 11).
And since the OH radical produced | generated in this way has a strong electron-storing effect | action, ie, an oxidation promotion power, the catalytic activity of the decomposition catalyst 1 mentioned above is reinforced.

(8) Therefore, according to the nitrous oxide N ₂ O decomposition catalyst 1 of the present invention, it is as follows.
First, nitrous oxide N ₂ O is reduced and decomposed into nitrogen N ₂ and oxygen O ₂ at a temperature lower than the thermal decomposition temperature.
That is, when this decomposition catalyst 1 is used, the energy barrier that is a barrier to the decomposition reaction of nitrous oxide N ₂ O is lowered by the catalytic activity. Transient electron donating action of one unpaired electron e ⁻ in the outermost shell s orbit of the decomposition catalyst 1, and transient electron trapping action of one or two hole holes ⁺ in its inner shell d orbital Based on this, the binding energy and activation energy of nitrous oxide N ₂ O are greatly reduced.
Therefore, nitrous oxide N ₂ O is reduced at a temperature of 300 ° C. or lower to 400 ° C. or lower, for example, a relatively low temperature of 300 ° C. to 400 ° C., for example, without requiring high temperature heating of 500 ° C. to 800 ° C. , Will be disassembled.

Second, nitrous oxide N ₂ O is reliably reduced and decomposed into nitrogen N ₂ and oxygen O _{2 due} to its high catalytic activity.
That is, in the decomposition catalyst 1, the unpaired electron e ⁻ in the outermost shell s orbital has a transient electron donating action and a strong decomposition force, and the hole hole ^{+ in the} inner shell d orbital has a transient electron trapping. It has an action and a strong resolution.
Therefore, due to the high catalytic activity based on this, nitrous oxide N ₂ O that is a reaction target molecule has its binding energy and activation energy lowered, and the transient oxidation reaction and reduction reaction are promoted, so that nitrogen N ₂ and oxygen O ₂ are reduced and decomposed.
The exhaust gas 2 often contains moisture H ₂ O, nitrogen oxide N ₂ O, oxygen O ₂ , sulfur dioxide SO ₂ , and other substances, but the cracking catalyst 1 has high catalytic activity. It promotes the reduction and decomposition of nitrous oxide N ₂ O without being disturbed by these substances.
Further, the exhaust gas 2 often contains water H ₂ O. However, when the decomposition catalyst 1 is used together with a photocatalyst, OH radicals having a strong electron-storing action, that is, an oxidation promoting ability are generated. The catalytic activity is reinforced, and the reduction and decomposition of nitrous oxide N ₂ O are further promoted. Conventionally, moisture H ₂ O, which has been regarded as a component for preventing reduction and decomposition, is used as a component for promoting reduction and decomposition.

According to the illustrated embodiment, the exhaust gas 2 that has passed through the flue gas denitration device 3 is supplied to the reductive decomposition device 5 as follows.
First, the components contained in the exhaust gas 2 are 1,000 ppm of nitrous oxide N ₂ O, 10 ppm or less of excess ammonia NH _{3 in} the exhaust gas denitration device 3, and nitrogen oxide NO that is a residue of the exhaust gas denitration device 3. _X was 100 ppm or less, oxygen O ₂ was 3%, moisture H ₂ O was 4%, and the remainder was nitrogen N ₂ . Then, platinum Pt was used as the decomposition catalyst 1 and adhered and supported on the porous carrier 6 together with titania TiO _{2 as a} photocatalyst.
Then, when the exhaust gas 2 having a temperature of 300 ° C. to 400 ° C. was supplied to the reductive decomposition apparatus 5 and tested, the nitrous oxide N ₂ O contained in the exhaust gas 2 was almost nitrogen N ₂ and oxygen O _2. It was reduced and decomposed.

The nitrous oxide decomposition catalyst according to the present invention is used to explain the best mode for carrying out the invention. (1) FIG. 1 is an explanatory front sectional view of an exhaust system, (2) FIG. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Decomposition catalyst 2 Exhaust gas 3 Flue gas denitration apparatus 4 Porous support 5 Reductive decomposition apparatus 6 Porous support 7 Exhaust pipe 8 Outer cylinder 9 Cell wall 10 Cell space

Claims (6)

  A decomposition catalyst for reducing and decomposing nitrous oxide into nitrogen and oxygen, wherein a metal of the fifth period or the sixth period of Group 8 of the periodic table is used. . 2. The nitrous oxide decomposition catalyst according to claim 1, wherein the metal of the decomposition catalyst includes a transient electron donating action of one unpaired electron in the outermost shell s orbit of the atomic structure and an inner shell d thereof. Based on the transient electron-storing action of one or two holes in the orbit, or similar actions of atomic structures based on these,
A catalyst for decomposing nitrous oxide, comprising reducing the bond and activation energy, which are decomposition barriers of the nitrous oxide, to reduce and decompose the nitrous oxide.   The nitrous oxide decomposition catalyst according to claim 2, wherein the nitrous oxide is contained in exhaust gas, and platinum, rhodium, palladium is used selectively or in combination as the decomposition catalyst. A nitrous oxide decomposition catalyst, characterized in that the nitrous oxide is reduced and decomposed at a temperature lower than its thermal decomposition temperature.   The nitrous oxide decomposition catalyst according to claim 3, wherein the exhaust gas is supplied via a denitration apparatus using ammonia as a reducing agent, and the decomposition catalyst is attached and supported on a porous carrier. A nitrous oxide decomposition catalyst characterized by the above.   The nitrous oxide decomposition catalyst according to claim 3, wherein the exhaust gas is supplied via a three-way catalytic purification device, and the decomposition catalyst is attached and supported on a porous carrier. Nitrous oxide decomposition catalyst. The nitrous oxide decomposition catalyst according to claim 3, wherein the exhaust gas contains moisture, and the decomposition catalyst is attached and supported on a porous carrier together with a photocatalyst,
In the photocatalyst, holes are generated in the outermost shell of the molecular structure by the decomposition catalyst, and react with the hydroxide ions of the water to generate OH radicals having a strong electron-storing action, so that the catalytic activity of the decomposition catalyst is increased. A nitrous oxide decomposition catalyst characterized by being reinforced.

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