CN1668373A

CN1668373A - Chemical reaction system of electrochemical cell type, method for activation thereof and method for reaction

Info

Publication number: CN1668373A
Application number: CNA038171007A
Authority: CN
Inventors: 淡野正信; 藤代芳伸; 黄海镇; 神崎修三; 瑟盖·布拉迪赫因; 片山真吾; 平松拓也; 盐野修
Original assignee: National Institute of Advanced Industrial Science and Technology AIST
Current assignee: National Institute of Advanced Industrial Science and Technology AIST
Priority date: 2002-07-31
Filing date: 2003-07-31
Publication date: 2005-09-14
Anticipated expiration: 2023-07-31
Also published as: US20060118409A1; DE10392987T5; AU2003252442A1; WO2004011135A1; CN100337739C

Abstract

The present invention relates to a chemical reaction system for efficiently excluding nitrogen oxides with low power consumption when excess oxygen is present in exhaust gas, to a method of use therefor, to an activation method therefor, and to a reaction method for oxidizing or reducing by the use of an oxidation-reduction reactor with high selectivity without the need to supply or exchange a reducing agent or oxidizing agent.

Description

Electrochemical cell type chemical reaction system, activation method and reaction method thereof

Technical Field

The present invention relates to an electrochemical cell-type chemical reaction system, and more particularly, to a chemical reaction apparatus for efficiently removing nitrogen oxides from oxygen-containing combustion exhaust gas, for example. The present invention provides a novel and useful chemical reactor which can efficiently treat a substance to be treated with a small amount of electric power consumption by introducing a micro reaction zone for causing a redox reaction of the substance to be treated into a part of a chemical reaction site of the chemical reaction apparatus and separating and adsorbing oxygen and nitrogen oxides in an exhaust gas by a specific structure of the micro reaction zone.

The present invention also relates to anenergy-saving electrochemical reaction apparatus and an activation method thereof, and more particularly, to a chemical reaction apparatus for efficiently removing nitrogen oxides from oxygen-containing combustion exhaust gas, a method of using the same, and an activation method thereof. For example, in the case of removing nitrogen oxides from exhaust gas by an electrochemical reaction apparatus, in order to solve the problem of reduced reactivity due to adsorption of oxygen molecules on the surface, the present invention provides a novel chemical reaction apparatus, which is useful in that the chemical reaction apparatus is reactivated with a small amount of electric power consumption, and the chemical reaction of a substance to be treated can be efficiently performed, a method for using the same, and a method for activating the same.

The present invention also relates to a method of reacting with a redox reactor, and more particularly, to a chemical method of oxidizing organic substances, organic chlorine compounds, hydrogen gas, carbon monoxide, nitrogen oxides, ammonia, etc., or reducing organic substances, oxygen gas, water, nitrogen oxides, etc., using a redox reactor comprising a solid electrolyte of an oxygen ion conductor and an electrode comprising at least an electron conductor. The present invention provides a useful method for removing nitrogen oxides from exhaust gas, such as a combustor, using the above-described redox reactor.

Background

For removing nitrogen oxides generated by gasoline engines, a three-way catalyst method is becoming the mainstream. However, in the case of a lean burn engine and an internal combustion engine, which may have an increased specific consumption by combustion, the presence of an excessive amount of oxygen in the combustion exhaust gas causes a drastic decrease in the catalyst activity due to the adsorption of oxygen on the surface of the three-way catalyst, and nitrogen oxides cannot be removed.

On the one hand, the oxygen in the exhaust gas can also be removed without adsorbing on the catalyst surface by energizing it with a solid electrolyte having oxygen ion conductivity. It is known that nitrogen oxides are decomposed into oxygen and nitrogen while removing surface oxygen by applying a voltage to a solid electrolyte sandwiched between two electrodes as a catalyst reactor.

However, in the above method, when there is excess oxygen in the combustion exhaust gas, the active sites of the adsorption decomposition reaction of the oxygen and nitrogen oxides coexisting are the same oxygen deficient region, and the adsorption probability of nitrogen oxides is remarkably lowered in terms of molecular selectivity and coexisting molecular ratio with respect to oxygen molecules, so that a large amount of current is required for decomposing nitrogen oxides, resulting in an increase in power consumption.

Under such circumstances, the present inventors have found that by forming a network distribution structure in which an electron conductor and an ion conductor are bonded at a distance of from nanometer to micrometer by surrounding the inner structure of a cathode of a chemical reactor with nanometer-sized through-holes in the upper part of the same layer, the substance to be treated can be treated efficiently with a small amount of electric power consumption by reducing the excess oxygen which is a disturbing factor in the chemical reaction of the substance to be treated (Japanese patent application No. 2001-225034). However, in this method, oxygen molecules remaining in the gas to be treated passing through the upper part of the same layer are adsorbed and decomposed at the reactive sites in preference to nitrogen oxides, and thus the reduction of power consumption is insufficient.

Further, in this method, continuous power supply is required for removing coexisting oxygen molecules, and there arises a problem that the reduction of power consumption is insufficient.

In one aspect, a variety of catalysts are used in chemical reactions, particularly redox reactions, typically either homogeneous catalysts or heterogeneous catalysts. An advantage when using heterogeneous catalysts, such as noble metals and solid catalysts like zeolites, is that the reactants are easily separated from the catalyst compared to homogeneous catalysts. However, in the case of a heterogeneous catalyst, the catalyst is easily separated, and since the raw material and the product are in the same place, it is necessary to separate and purify the product from the unreacted raw material and the by-product. As a method not requiring such separation and purification, a method using a reaction separation membrane has been studied (chemical general: No.41, "design of high-order function catalyst", Japanese chemical society, eds (1999) p.131).

So-called method using a reaction separation membrane, for example, in which oxygen is permeated through an oxygen permeation membrane in accordance with the oxygen content of methaneSynthesis of ethane (by oxidative compounding) ) In case of (1), according to CH₄Catalyst/oxygen permeable Membrane/O₂Is in the form of an arrangement of CH₄And O₂By separation on an oxygen-permeable membrane, CH₄Placing proper catalyst on the side permeation membrane wall to make O₂The selective synthesis of ethane is carried out by activation on this catalyst through an oxygen permeable membrane. Where the same reaction is carried out with a hydrogen-permeable membrane, it is referred to as CH₄catalyst/Hydrogen permeable Membrane/O₂Is still necessaryin CH₄And O₂A hydrogen permeable membrane is arranged between the two, and methane is arranged on the wall of the hydrogen permeable membrane for dehydrogenationAn active catalyst. Membranes used for reaction separation are roughly classified into porous membranes, metal membranes, ion conductor membranes, mixed conductor membranes, and the like according to the permeation mechanism of a permeating substance. In the porous membrane, a membrane having a nano-pore such as zeolite, through which molecules can selectively permeate, is known, but a method for synthesizing a dense zeolite membrane having no pin-hole is not established.

Among the metal membranes being used as the reaction separation membrane are a Pd membrane, a Pd — Au membrane, both of which are used as a reaction separation membrane for hydrogen (hydrogen permeation membrane). As a driving force of the hydrogen permeable membrane, a concentration difference (hydrogen partial pressure difference) between both surfaces of the membrane is used. As the ion conductor membrane (electrolyte membrane), mainly a hydrogen ion conductor and an oxygen ion conductor. When an ion conductor is used as a reaction separation membrane, electrodes are provided on both sides of the membrane and the two electrodes are connected by a lead wire, because the driving force for transporting ions is an electric field gradient. Ions pass through the membrane and, due to the simultaneous neutralization of the charges, there is a movement of electrons through the wire. In the case of a mixed conductor film, since ions and electrons (or holes) can be simultaneously transported in the film layer, wires and electrodes for transporting electrons are not required. However, the driving force of the ions is due to the difference in concentration between the two surfaces of the membrane.

In particular, in a reaction separation membrane using an ion conductor membrane, an electric field gradient is used as a driving force to advance the reaction, regardless of a concentration difference. However, electrodes are still necessary. The electrode is made of a stable material that is electronically conductive and inert to oxidation and reduction reactions. For example, noble metals such as Pt and Pd, carbon, and electron-conductive oxides such as lanthanoid cobaltite, lanthanoid ferrite, lanthanoid manganite, and lanthanoid chromite in an oxidizing atmosphere are used. An example of a reaction separation membrane using a hydrogen ion-conducting membrane is a selective hydrogenation method for removing a trace amount of acetylene from ethylene. Form a C₂H₄、C₂H₂Cu electrode/Hydrogen ion conductor film/Pt Black electrode/H₂In the reactor, a current is applied between electrodes to selectively hydrogenate (reduce) acetylene, thereby removing acetylene impurity from ethylene to ethylene. This reaction occurs due to the strong affinity of acetylene to the Cu electrode and the generation of hydrogen atoms from the hydrogen ion conductor film.

An example of a reaction separation membrane using a solid electrolyte membrane having oxygen ion conductivity is a reduction method for removing nitrogen oxides from exhaust gas. As a suggested reactor, a device for decomposing nitrogen oxides into oxygen and nitrogen while removing surface oxygen by applying a voltage to a solid electrolyte sandwiched between two electrodes is being developed. Here, in the related art document, it is proposed to form platinum electrodes on both surfaces of stabilized zirconia (containing scandia) and decompose nitrogen oxide into oxygen by applying a voltage (J, Electrochemical Soc, 122, 869 (1975)). Further, it has been proposed in the prior art document that a palladium electrode is formed on both sides of a stabilized zirconia (containing yttria) and decomposed into nitrogen and oxygen in a mixed gas of nitrogen oxide,hydrocarbon and oxygen by an applied voltage (J, chem. soc, faraday trans, 91, 1995 (1995)). In this way, when an electrode is applied to the ion conductive membrane and a voltage is applied between the electrodes to form a reaction separation membrane using an electric field gradient as a driving force, various ions from the ion conductive membrane can be activated on the electrode without depending on the concentration difference between the reactant and the product, and molecules are easily decomposed at the interface between the ion conductor and the electrode, thereby facilitating the redox reaction.

However, in the reaction separation membrane reaction method in which an electrode is applied to an ion conductive membrane and a voltage is applied between the electrodes to use an electric field gradient as a driving force, the oxidation-reduction energy is high and the reaction selectivity is poor. For example, when nitrogen oxides are reductively removed by a reactor in which an electrode is added to the oxygen ion conductor, oxygen molecules and coexisting oxygen molecules are decomposed into oxygen ions, and the efficiency of reductive removal of nitrogen oxides for the purpose of exhaust gas purification is lowered. Further, a method of performing a single oxidation-reduction reaction by using a reducing agent and an oxidizing agent with appropriate selectivity is also considered, but when the reducing agent and the oxidizing agent are consumed, the reaction does not proceed any more, and therefore, it is necessary to supply and replace the reducing agent and the oxidizing agent.

Disclosure of Invention

In view of the above-described conventional techniques, the present inventors have made extensive studies to solve the above-described problems, and as a result, have found that it is possible to form a pair of reaction fields that occur simultaneously with the reduction reaction at a chemical reaction site (for example, a working electrode layer located above a cathode), and to improve the reaction efficiency by utilizing the selective adsorption ability of oxygen molecules and nitrogen oxides, which are possessed by each of the reaction fields, thereby obtaining the result of the present invention.

Accordingly, an object of the present invention is to solve the above problems of the prior art in the 1 st aspect of the present invention, and to provide a chemical reactor capable of efficiently removing nitrogen oxides with a small amount of power consumption, which forms a pair of oxygen molecules and a selective adsorbent of nitrogen oxides when excess oxygen exists in combustion exhaust gas, and which is capable of reducing the amount of current required for decomposition of nitrogen oxides by facilitating adsorption of nitrogen oxides.

In view of the above-described conventional techniques, the present inventors have made extensive studies to solve the above-described problems, and as a result, have found that a reaction field can be formed by simultaneously performing a reduction reaction of oxygen adsorption and nitrogen oxide adsorption on a working electrode layer having a chemical reaction site located above a cathode to improve reaction efficiency, and that a certain amount of oxygen molecules are adsorbed, and then the chemical reaction apparatus is energized to ionize and desorb the oxygen molecules, thereby reactivating the apparatus, thereby obtaining the result of the present invention.

Accordingly, an object of the 2 nd aspect of the present invention is to solve the above problems of the prior art and to provide a chemical reactor capable of efficiently removing nitrogen oxides with a small amount of power consumption, which is formed as a selective adsorbent for oxygen molecules and nitrogen oxides when excess oxygen exists in combustion exhaust gas, and which is capable of reactivating a chemical reactor adsorbing a certain amount of oxygen by supplying power thereto while reducing the amount of current required for decomposition of nitrogen oxides by facilitating adsorption of nitrogen oxides.

Further, the 3 rd aspect of the present invention is to provide a novel reaction method which is developed in view of solving the above problems of the prior art and aiming to establish a novel reaction method for a redox reactor, and which can perform oxidation or reduction with high selectivity without supplying or replacing a reducing agent and an oxidizing agent.

Mode 1 of the present invention will be described in further detail below.

The present invention relates to a chemical reaction system for chemically reacting a substance to be treated, the chemical reaction system comprising: the chemical reaction site for causing the substance to be treated to react with the chemical reaction preferably further includes a barrier layer for preventing ionization of oxygen.

At the chemical reaction site where the substance to be treated chemically reacts, it is preferable to provide: the reducing phase, which accepts electrons from the elements in the material to be treated to become ions, the ion conducting phase, which transports ions from the reducing phase to the oxidizing phase, and the oxidizing phase, which donates electrons to the ions from the ion conducting phase.

In the present invention, it is preferable that the substance to be treated is nitrogen oxide in the combustion exhaust gas, and the nitrogen oxide is reduced in the reduction phase to generate oxygen ions, and the oxygen ions are transported in the ion conduction phase. However, the substance to be treated in the present invention is not limited to nitrogen oxides. By means of the chemical reactor of the invention, carbon dioxide can be reduced to carbon monoxide, a mixture of hydrogen and carbon monoxide can be produced from methane, or hydrogen can be produced from water.

The chemical reaction means may be in the form of, for example, a tube, a plate, a honeycomb, in particular, a tube, a honeycomb, having one or more through-holes with a pair of openings, preferably with a chemical reaction site in each through-hole.

The reducing phase is preferably porous at the chemical reaction site and can selectively adsorb a substance to be reacted. The reducing phase is preferably made of a conductive material that donates electrons to an element contained in the material to be treated to form ions and transfers the formed ions to the ion conducting phase. And, to facilitate the transport of electrons and ions. Preferably, the conductive material is a mixed conductive material having both electron conductivity and ion conductivity, or a mixture of an electron conductive material and an ion conductive material. The reducing phase may be a structure in which at least two or more phases of these substances are laminated.

The conductive material and the ion conductive material used as the reduced phase are not particularly limited. As the conductive material, for example, noble metals such as platinum and palladium, or metal oxides such as nickel oxide, cobalt oxide, copper oxide, lanthanum manganite, lanthanum cobaltite, and lanthanum chromite can be used. Barium-containing oxides, zeolites, and the like that selectively adsorb the substance to be treated may also be used as the reducing phase. Mixtures of at least 1 or more of the above substances and at least 1 or more of the ion-conducting substances may also be used. As the ion conductive material, for example, stabilized zirconia (containing yttria or scandia), stabilized ceria (containing gadolinia or samaria), lanthanum gallate, and thelike can be used. The reduced phase is preferably constituted by a structure in which at least two or more phases of the above-mentioned substance are laminated. More preferably, the reducing phase has a structure in which a noble metal conductive material phase such as platinum is laminated on a mixture phase of a stabilized zirconia (containing nickel oxide and yttrium oxide or scandium oxide).

The ion-conducting phase is composed of a solid electrolyte having ion conductivity, and preferably, is composed of a solid electrolyte having oxygen ion conductivity. Examples of the solid electrolyte having oxygen ion conductivity include: the stabilized zirconia (containing yttria or scandia), the stabilized ceria (containing gadolinia or samaria), and the lanthanum gallate are not particularly limited. Preferably, stabilized zirconia (containing yttria or scandia) having high conductivity and high strength and excellent long-term stability can be used.

The oxidation phase contains conductive material to allow electrons to be released from the ions of the ion-conducting phase. In order to promote the transport of electrons and ions, it is preferable to use a mixed conductive material having both electron conductivity and ion conductivity, or a mixture of an electron conductive material and an ion conductive material. The conductive material and the ion conductive material that can be used as the oxidized phase are not particularly limited. As the conductive material, for example, noble metals such as platinum and palladium, or metal oxides such as nickel oxide, cobalt oxide, copper oxide, lanthanum manganite, lanthanum cobaltite, and lanthanum chromite can be used. As the ion conductive substance, for example, stabilized zirconia (containing yttria or yttria), stabilized ceria (containing gadolinium oxide or samarium oxide), lanthanum gallate, and the like can be used.

To prevent oxygen molecules from accepting electrons from the reducing phase to form oxygen ions during surface adsorption, a material and structure that prevents the electrons from reaching the surface, which is a barrier layer, is required. The barrier is preferably an ionic conductor or a mixed conductor or an insulator. In the case of a hybrid conductor, in order to reduce the effect of suppressing excessive electron conductivity and electron conduction, it is desirable that the ratio of electron conductivity be as small as possible.

The chemical reaction site of the present invention is formed by conducting a current, an electric field, or a heat treatment in a reducing atmosphere or a reduced pressure to a contact point of an electron conducting phase and an ion conducting phase, which are formed by an arbitrary combination of an ion conductor, an electron conductor, and a mixed conductor, thereby introducing a minute reaction region for causing an oxidation-reduction reaction of a material to be treated, into a part of the chemical reaction site. In the present invention, there may be mentioned as the following: forming an interface, which is a contact between the electron-conducting phase and the ion-conducting phase, on the minute reaction region, the interface being composed of a metal phase portion of the electron-conducting phase, an oxygen-deficient portion of the ion-conducting phase, and a small gap portion (cavity) around the contact; the introduction of a minute reaction region on the cathode for the above-mentioned redox reaction; the upper part of the cathode controls the formation of a working electrode layer for oxidation-reduction reaction; and introducing a nano-to micro-sized minute reaction region in which the redox reaction occurs.

The working electrode layer located on the upper part of the cathode of the chemical reaction site comprises the initially found substance to be treated with high adsorptive decomposition (Japanese patent application No. 2001-225034), and is a structure having a function of allowing adsorption of oxygen molecules and adsorption of the substance to be treated to occur simultaneously by means of separate substances suitable for the respective reactions. Specifically, as shown in FIG. 2, the oxygen deficiency portion of the ion conducting phase existing in the vicinity thereof is brought into contact with the metal phase (preferably, ultrafine particles having a particle diameter of about 10 to 100nm to obtain high reactivity) formed by reducing the oxide, and oxygen molecules in the gas to be treated are selectively adsorbed and decomposed in the oxygen deficiency portion and the metal phase portion of the object to be treated by the small gap portions of several nm to several tens of nm or less in the vicinity of the contact, whereby the power consumption is remarkably reduced. When the size of the gap around the contact is more than tens of nanometers, the separation and adsorption effect is gradually reduced because the gap is larger than the mean free path of gas molecules, or when the size of the gap around the contact is larger than 100 nanometers, the selective separation and purification performance of the gas to be treated is obviously reduced because the gap is far larger than a Debye unit and the diffusion length of oxygen deficiency.

The metal phase and the oxygen deficient portion usually form a contact due to the mechanism of formation thereof, and do not necessarily need to be in contact in order to produce the above-described selective separation function. That is, even if the oxygen deficient portion formed as a result of the movement of oxygen by electrons from the metal phase (oxide phase before reaction) in the ion conductive phase by the passage of current and the metal phase lose contact due to the action of thermal contraction or the like after the formation, the function of selectively separating the gas to be treated which acts on the present invention is not seriously impaired.

Such a structure is formed by energizing a chemical reaction apparatus or performing a heat treatment in a reducing atmosphere or under reduced pressure, including a heat treatment step (heat treatment in an atmosphere of 1400 to 1450 ℃ C.) originally found to be necessary for forming the structure. That is, the above structure employs an oxide which is relatively easily reduced, and is energized at a high temperature of several hundred degrees celsius or more, or is heat-treated in a reducing atmosphere such as a hydrogen atmosphere or under reduced pressure to form a reduced phase.

In this step, the volume change of the crystal phase by the redox reaction is suitable for the formation of nano-to micro-sized holes introduced by the processing gas, the ultrafine particle formation by the recrystallization of the reduced phase, the formation of oxygen deficiency of the ion-conducting phase by the redox reaction, and the like, and the microstructure suitable for the efficient reaction is simultaneously formed, and particularly, the case of the electrical conduction treatment is satisfactory.

As the substance constituting such a structure, a combination of an ion-conducting phase and an electron-conducting phase, a combination of mixed conducting phases, or a combination thereof with an ion-conducting phase and an electron-conducting phase is possible. When the object to be treated is a nitrogen oxide, the reduction phase is more preferably a metal phase such as nickel, which exhibits high selective adsorption.

In the present invention, the substances constituting the whole or a part of the micro reaction regions exert oxidation and reduction effects on the substance to be treated. The metal phase is composed of ultrafine particles of a metal phase generated by oxidation-reduction reaction, which are generated in part or all ofan electron conductor or a mixed conductor, for example, by conducting an electric current to the chemical reaction apparatus or by performing a heat treatment in a reducing atmosphere. The oxygen-deficient portion is formed by applying current to the chemical reaction apparatus or by heat treatment in a reducing atmosphere, and is formed by bringing the ion conductor and the electron conductor into direct contact with each other at least 1 point of the micro reaction region comprising an oxygen-deficient layer formed by an oxidation-reduction reaction in which part or all of the ion conductor or the mixed conductor is generated, or by bringing the ion conductor and the electron conductor into contact with each other in the production process.

In the method for manufacturing the chemical reaction apparatus of the present invention, the contact of the ion conductive phase and the electron conductive phase, which is formed by arbitrarily combining the ion conductor, the electron conductor, and the mixed conductor of the chemical reaction site, is subjected to an electrical conduction treatment or a heat treatment in a reducing atmosphere or under reduced pressure, and a single-stage micro reaction region for performing an oxidation-reduction reaction on the material to be treated is introduced into the chemical reaction site. When the substance contact interface is formed, it is preferable that either one or both of them be in a reduced state.

In the chemical reaction of the present invention, it is preferable that the substance to be treated is a nitrogen oxide, the chemical reaction is a reductive decomposition of the nitrogen oxide, and the chemical reaction has a general formula:

；

(M: metal, O: oxygen atom, e: electron)

Next, embodiment 2 of the present invention will be described in further detail.

The present invention relates to a chemical reaction apparatus for chemically reacting a substance to be treated, the chemical reaction apparatus comprising: the chemical reaction site for causing the substance to be treated to react with the chemical reaction preferably further includes a barrier layer for preventing ionization of oxygen.

The chemical reaction site for chemically reacting the substance to be treated is preferably provided with: the oxidation and/or reduction catalyst having the same function, that is, the oxidation catalyst, the reduction catalyst, or the oxidation-reduction catalyst is preferably configured as a basic unit. In this case, the constituent components are not particularly limited.

In the present invention, it is preferable that the substance to be treated is nitrogen oxide in the combustion exhaust gas, the nitrogen oxide is reduced in the reduction phase to generate oxygen ions, and the oxygen ions are transported in the ion conductive phase. However, the substance to be treated in the present invention is not limited to nitrogen oxides. The chemical reactor of the present invention is suitable for the following cases: carbon dioxide is reduced to produce carbon monoxide, methane is used to produce a mixture of hydrogen and carbon monoxide, or water is used to produce hydrogen.

The chemical reaction means may be in the form of, for example, a tube, a plate, a honeycomb, etc., and particularly like a tube, a honeycomb, has one or more through-holes with a pair of openings, and the chemical reaction site is preferably located in each through-hole.

The reducing phase is preferably porous at the chemical reaction site and can selectively adsorb a substance to be reacted. The ion conductive phase for imparting electrons to the element contained in the material to be treated in the reduced phase to form ions and transporting the ions in the reduced phase is preferably made of a conductive material. In order to promote the transport of electrons and ions, it is preferable that the reduced phase is formed of a mixed conductive material having both electron conductivity and ion conductivity, or a mixture of an electron conductive material and an ion conductive material. The reducing phase may be a structure in which at least two or more phases of these substances are laminated.

The conductive material and the ion conductive material used as the reduced phase are not particularly limited. As the conductive material, for example, noble metals such as platinum and palladium, or metal oxides such as nickel oxide, cobalt oxide, copper oxide, lanthanum manganite, lanthanum cobaltite, and lanthanum chromite can be used. Barium-containing oxides, zeolites, and the like that selectively adsorb the substance to be treated may also be used as the reducing phase. Mixtures of at least 1 or more of the above substances and at least 1 or more of the ion-conducting substances may also be used. As the ion conductive material, for example, stabilized zirconia (containing yttria or scandia), stabilized ceria (containing gadolinia or samaria), lanthanum gallate, and the like can be used. The reduced phase is preferably constituted by a structure in which at least two or more phases of the above-mentioned substance are laminated. More preferably, the reducing phase has a structure in which a noble metal conductive material phase such as platinum is laminated on a mixture phase of a stabilized zirconia (containing nickel oxide and yttrium oxide or scandium oxide).

The oxidation phase contains conductive material to donate electrons from the ions of the ion conducting phase. In order to promote the transport of electrons and ions, it is preferable to use a mixed conductive material having both electron conductivity and ion conductivity, or a mixture of an electron conductive material and an ion conductive material. The conductive material and the ion conductive material that can be used as the oxidized phase are not particularly limited. As the conductive material, for example, noble metals such as platinum and palladium, or metal oxides such as nickel oxide, cobalt oxide, copper oxide, lanthanum manganite, lanthanum cobaltite, and lanthanum chromite can be used. Examples of the ion conductive material include stabilized zirconia (containing yttria or scandia), stabilized ceria (containing gadolinium oxide or samarium oxide), lanthanum gallate, and the like.

To prevent oxygen molecules from accepting electrons from the reducing phase to form oxygen ions during surface adsorption, a material and structure that prevents the electrons from reaching the surface, which is a barrier layer, is required. Or in the chemical reaction site to prevent reoxidation of the oxygen ions by providing a reduced metal of an electrically conductive oxide, such as metallic nickel, the barrier layer preferably being an ionic conductor or a mixed conductor or insulator. In the case of a hybrid conductor, in order to reduce the effect of suppressing excessive electron conductivity and electron conduction, it is desirable that the ratio of electron conductivity be as small as possible.

The present invention is characterized in that in a chemical reaction apparatus comprising an oxygen ion conductor (ion conductive phase), a cathode (reduction phase) and an anode (oxidation phase) which sandwich the ion conductor from two opposite directions, and a chemical reaction site comprising an oxidation and/or reduction catalyst as a basic unit, for causing a chemical reaction of a substance to be treated, oxygen which inhibits an adsorption reaction is ionized at the chemical reaction site by, for example, applying an electric current or an external electric field or a reduction or reduced pressure heat treatment between the cathode and the anode at the chemical reaction site, thereby activating a desorption capability. Suitable examples are: in the present invention, as the chemical reaction site, a minute reaction region for causing a redox reaction of a substance to be treated is introduced into a part of the chemical reaction site by conducting a heat treatment by passing a current, applying an electric field, or in a reducing atmosphere or under reduced pressure on a contact point of an electron conducting phase and an ion conducting phase, which are formed by an arbitrary combination of an ion conductor, an electron conductor, and a mixed conductor; and, as the above-mentioned chemical reaction site, there are selective reducing phase to oxygen and treated material separately, and the pore under the micron necessary for supplying the treated material to the reducing phase processing effectively; in addition, as the micro reaction region, an interface including a metal phase portion of the electron-conducting phase, an oxygen-deficient portion of the ion-conducting phase, and a small gap portion (cavity) around the contact is formed on the contact between the electron-conducting phase and the ion-conducting phase; as the chemical reaction part, a minute reaction region in which the oxidation-reduction reaction is initiated is introduced into the cathode; further, as the chemical reaction section, a working electrode layer for controlling an oxidation-reduction reaction is provided on the upper part of the cathode, and a nano-to micro-sized minute reaction region in which the oxidation-reduction reaction is initiated is introduced into the working electrode layer.

The working electrode layer located on the upper part of the cathode of the chemical reaction site comprises a substance to be treated which is highly efficiently decomposed by adsorption originally discovered by the present inventor (Japanese patent application No. 2001-225034), and is a structure having a function of allowing adsorption of oxygen molecules and adsorption of the substance to be treated to occur simultaneously by means of separate substances suitable for the respective reactions. Specifically, the oxygen deficiency portion (estimated value in Debye unit is about 5 nm) of the ion conductive phase existing in the vicinity thereof is brought into contact with the metal phase (preferably, ultrafine particles having a particle diameter of 10 to 100nm for high reactivity) generated by reducing the oxide, and the oxygen molecules in the gas to be treated are selectively adsorbed and decomposed in the metal phase portion by the small gap portions of about several nanometers to several hundred nanometers located in the vicinity of the contact, whereby the power consumption is remarkably reduced.

Such a structure is formed by energizing a chemical reaction apparatus or performing a heat treatment in a reducing atmosphere or the like, including a heat treatment step (heat treatment in an atmosphere of 1400 to 1450 ℃ C.) originally found necessary for forming the structure. That is, an oxide which is relatively easily reduced is used to form a reduced phase by applying a current at a high temperature of several hundred degrees celsius or more. In this step, a microstructure suitable forefficient reaction is simultaneously formed by volume change of a crystal phase by redox reaction, formation of nano-to micro-sized voids suitable for introduction of a processing gas, ultrafine particle formation by recrystallization of a reduced phase, formation of an oxygen deficiency portion of an ion-conducting phase by redox reaction, and the like. Fig. 4 shows an example of a preferred partial structure as an internal structure of the working electrode layer formed by the above-described method.

As a combination of the substance constituting such a fine structure, the ion-conductive phase and the electron-conductive phase, a combination of the mixed conductive phases or the ion-conductive phase and the electron-conductive phase is possible. When the object to be treated is a nitrogen oxide, the reduction phase is more preferably a metal phase such as nickel, which exhibits high selective adsorption.

In order to reactivate the Chemical reaction apparatus, in addition to the conventional method of introducing the reducing agent, a method of forming carbon or the like into an integrated structure with the Chemical reaction apparatus in advance and reducing the oxidized metal phase by oxidation of carbon in the Chemical reaction has been proposed (k. mira et al, Chemical Engineering Science 56, 1623 (2001)). However, this method requires a reducing agent, and since reactivation cannot be achieved without a reducing agent, it is suitable for a long-term use or a continuous use apparatus as a reactivation method by energization.

In the present invention, when the performance of the chemical reaction apparatus is deteriorated, the oxygen molecules adsorbed by the oxygen deficient portion in the chemical reaction site can be ionized by, for example, energization and removed by suction. And, the rejuvenation can be performed simultaneously with the reduction phase. Accordingly, in the presentinvention, the amount of electricity can be significantly reduced as compared to the amount of electricity required to pump oxygen from the electrochemical cell system.

The reactivation by oxygen pumping is realized by electrifying or applying voltage to the chemical reaction device or performing heat treatment in a reducing atmosphere under the condition that the chemical reaction device is at 400-700 ℃. In the present invention, it is preferable that the temperature of the chemical reaction apparatus is maintained at 400 to 700 ℃ or the temperature is raised or lowered in the same temperature range, and the cathode and the anode are electrified for 1 minute to 3 hours or subjected to an external electric field treatment. In this case, it is preferable that the electrochemical reaction is caused by applying an electric current of 5mA to 1A or an applied voltage of 0.5V to 2.5V, and the electric field treatment or the energization is performed at an oxygen partial pressure of 0% to 21% (in the atmosphere). The treatment temperature varies depending on the material and structure of the apparatus, and for example, it is preferably about 560 ℃ when a stabilized zirconia (containing yttria) is used as the solid electrolyte, and about 450 ℃ when a ceria-based electrolyte is used. Further, the present invention provides a method for activating a chemical reaction apparatus, characterized in that the temperature of the chemical reaction apparatus is maintained at 500 ℃ or higher, or the temperature is raised or lowered in the same temperature range, and heat treatment is performed in a reducing atmosphere or under reduced pressure.

The conditions for providing the treatment temperature and the constituent materials, such as the amount of electricity applied, the applied voltage, the time of application, and the partial pressure of oxygen or the total pressure in the atmosphere, are variable. For example, when stabilized zirconia (containing yttria) as a solid electrolyte, nickel oxide or zirconia as a working electrode material was used, the same nitrogen oxide decomposition performance as before the treatment was recovered by the energization treatment of 100mA and 2V for 1 hour (10% oxygen). The deterioration degree of oxygen adsorption was about 20% after 100 hours of continuous operation (no energization), and the performance was restored again by the energization treatment.

Mode 3 of the present invention will be described in further detail below.

In the present invention, as the solid electrolyte of the oxygen ion conductor, a solid electrolyte having a conductivity of 10 Ω at the use temperature can be used^-6Ω^-1·Cm^-1The above materials. 10^-6Ω^-1·Cm^-1Conductivity at less than fullToo low to perform an electrochemical redox reaction at a sufficient rate to oxidize the reduced form (R) or the reduced form (RO)_X) The original state is recovered, and the energy loss of the internal resistance is too large to be practically used. Examples of the solid electrolyte of such an oxygen ion conductor include: ZrO (ZrO)₂System, CeO₂System, Bi₂O₃、LaGaO₃Is an oxide. If it is ZrO₂Oxides, which may be stabilized with Y, Sc, etc.; if it is CeO₂The oxide may be stabilized with Gd, Sm, or the like. Furthermore, a plurality of oxygen ion conductors may be used in combination or in a laminate. Especially from a stability point of view. For removing nitrogen oxides, preference is given to ZrO₂Is an oxide.

In the present invention, the electrode material comprising the electron conductor has a conductivity of 10 at the use temperature^-6Ω^-1cm^-1The above. 10^-6Ω^-1cm^-1If the conductivity is not low, the conductivity is too low to perform an electrochemical oxidation-reduction reaction at a sufficient rate to oxidize the reduced product (R) or the reduced product (RO)_X) And (5) recovering the original state. Further, the internal resistance energy loss is too large to be practically used. Examples of the electrode material made of an electron conductor include: metal, stainless steel, alloy, and electronicConductive oxides, graphite, and carbon materials such as glassy carbon. Specific examples thereof include noble metals such as platinum and palladium, and metal oxides such as nickel oxide, cobalt oxide, copper oxide, lanthanum manganite, lanthanum cobaltite, and lanthanum chromite. A plurality of electronic conductors may be combined or laminated. Further, the oxygen ion conductive material may be compounded with a solid electrolyte of an oxygen ion conductive material, or may be formed into a mixed conductive material of oxygen ion conductivity and electron conductivity. Further, the electrode material may be compounded with a reducing agent or an oxidizing agent. Especially from the viewpoint of stability, An, Pt, Ag, Pd, Ni oxide, Cu oxide, Fe oxide, Mn oxide, or a combination thereof is preferable for removing the nitrogen oxide.

The reducing agent (R) used in the present invention is composed of a metal or a Suboxide (Suboxide) provided that the desired oxide AO is present_XThe reducing ability (x is 1/2 representing the oxidation number of A) is not particularly limited, and suitable examples include: alkaline earth metals such as Mg and Ca, transition metals such as Ti, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag and Zn, metals such as Al, Ga, In and Sn, and suboxides such as Ti (III), V (IV, III and II), Cr (III and II), Mo (IV, III and II), W (V, IV, III and II), Mn (III), Fe (II) and Cu (I). Particularly, from the viewpoint of selective reactivity, it is preferable that the nitrogen oxide be removed by a metal or a suboxide (containing at least one element selectedfrom the group consisting of Ni, Cu and Fe)The amount is 50% or more).

Oxide AO that can be reduced by the reaction method of the redox reactor of the present invention_X(x is 1/2 of the oxidation number of A) are, for example, oxygen-containing organic substances, oxygen, water, nitrogen oxides and the like which can be reduced to the reduction product AO in the redox reactor_X-Y(y is more than 0 and less than or equal to x). Oxide AO_XThe reduction of (a) can be achieved by controlling the reaction conditions such as the reaction time and the applied voltage to achieve a completely reduced a (y ═ x), or to achieve a "partial reduction" AO in the middle of the reduction_X-Y(0＜y＜x)。

Oxidized body (RO) used in the present invention_X) The compound is not particularly limited as long as it is composed of an oxide and has an ability to oxidize the target compound A. Suitable examples are: transition metal oxides such as Ti, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag, Zn, Pd, Pt, Rh, Au, Ir, etc., and metal oxides such as Al, Ga, In, Sn, etc. In particular, from the viewpoint of selective reactivity, it is preferable that the oxidation reaction of the hydrocarbon or the organic chlorine compound is an oxide (the content is 50% or more) of at least one element selected from the group consisting of Ni, Cu, Ag and Pt.

The compound A which can be oxidized by the reaction method in the redox reactor of the present invention is, for example, an organic substance, an organic chlorine compound, hydrogen, carbon monoxide, nitrogen oxide, ammonia, or the like. They can be oxidized in the redox reactor to the oxidation product AO_y. In particular, hydrocarbons such as methane, ethane, propane, butane, etc. can be partially oxidized into alcohols and carboxylic acids, and dioxins, organochlorine compounds, etc. can be oxidatively decomposed. The oxidation of the compound A can be achieved by controlling the reaction conditions such as the reaction time and the applied voltage to completely oxidize the AO_y(y ═ x), or a partial oxidation AO up to the middle thereof_X-Y(0＜y＜x)。

The redox reactors used in the present invention, when used as reduction reactors, are arranged in the form of reduction agent (R)/electrode/oxygen ion conductor/electrode; when used as an oxidation reactor, the catalyst is selected from the group consisting of electrode/oxygen ion conductor/electrode/oxidant (RO)_X) Are arranged in a pattern. Further, the reducing agent (R) and the electrode, the electrode and the oxidizing agent (RO)_X) Each of the two parties may be a mixed phase. In particular, for removing nitrogen oxides, it is preferable that the particle size of the nitrogen oxide reducing agent is in the range of 10nm to 1 μm, and if the particle size is less than 10nm, the activity is too high, and other oxides are also reduced, so that it is difficult to achieve selective reduction of nitrogen oxides. When the particle size exceeds 1 μm, the effective surface area of the nitrogen oxide reducing agent becomes small, and it is difficult to achieve efficient reduction. And, in order to effectively accelerate the oxidation-reduction reaction, a reduced body (R) layer or an oxidized body (RO)_x) The layer may also be a porous with fine poresAnd (3) a body.

The nitrogen oxide reducing agent used in the present invention is an oxide-based electron conductor selected from at least one of nickel oxide, copper oxide, iron oxide and manganese oxide, and is capable of dissociating oxygenThe solid electrolyte of the electron conductor is brought into contact with the solid electrolyte, and a part of the oxide-based electron conductor is reduced by applying a cathodic current to the electron conductor, whereby the solid electrolyte of theelectron conductor is deposited in combination with the redox reactor. In the redox reactor used in the present invention, the oxide AO is used_xReduction of RO oxidized by reducing body R_yRegenerating to original reduced body R, and energizing the electrodes to turn RO_yElectrochemically reduced to R, or, to oxidize Compound A, to oxidize the oxide R' O_xBy reduction of R' O_x-yRegeneration into the original oxide R' O_xThe electrode is electrified to turn R' O_x-yElectrochemical oxidation to R' O_x. Reduced or oxidized R' O by electrical conduction between electrodes_xThe regeneration can be realized in oxidation-reduction reaction, or can be electrified and regenerated at certain time intervals.

In the reaction method of the redox reactor of the present invention, the operating temperature of 300 ℃ to 1000 ℃ is sufficient to obtain the conductivity of the solid electrolyte of the oxygen ion conductor, and the redox reaction can be carried out at a low temperature such as room temperature, for example, only for the reduced R or the oxidized R' O_xThe electrochemical regeneration can also be carried out by heating to the above temperature. The reducing agent (R) or the oxidizing agent (RO) used in the present invention_X) Since a material suitable for its oxidation or reduction potential is selected according to a specific reaction in the redox reactor, a highly selective reaction can be carried out under conditions suitable for the reaction.

Drawings

FIG. 1 is a schematic diagram showing a chemical reaction apparatus according to an embodiment of the present invention

FIG. 2 shows an example of a preferable partial structure of the internal structure of the working electrode layer

FIG. 3 is a graph showing the performance of a chemical reaction apparatus according to the present invention, as compared with the performance of a conventional reactor, which has been already filed by the present inventors, based on the relationship between the nitrogen oxide removal performance and the amount of current applied to the chemical reaction apparatus

FIG. 4 is a partial structure example of the internal structure of the working electrode layer

FIG. 5 is a graph showing the time dependence of the decomposition rate of the nitrogen oxide removal performance in the recovery state by the energization

Description of the symbols

1 Barrier layer 5 Anode (oxide phase)

2 working electrode layer 6 chemical reaction site

3 cathode (reduction phase) 7 chemical reaction device

4 ion-conducting phase

Detailed Description

Next, an embodiment of the invention 1 will be described with reference to the drawings. FIG. 1 is a schematic diagram of a chemical reaction apparatus according to an embodiment of the present invention. The chemical reaction site 6 constituting the chemical reaction apparatus 7 facing the gas flow of the object to be treated includes a working electrode layer 2, a cathode (reduction phase) 3, an ion conductive phase 4, and an anode (oxidation phase) 5, which are disposed in order from the upstream side, respectively, and a barrier layer 1 is disposed at a position on the upstream side of the chemical reaction site 6. That is, the gas to be processed passes through the gas processing apparatus from 1 to 5 in sequence.

FIG. 2 shows an example of a preferable internal partial structure of a minute reaction region of the working electrode layer 2 of the present invention. Hereinafter, the case where nitrogen oxide is used as the substance to be treated will be specifically described.

Example 1

Stabilized zirconia (containing yttria) was used as the ion-conducting phase 4, and was formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The reducing phase 3 is a mixed layer of platinum and zirconia, and the working electrode layer 2 is a film made of a mixture of nickel oxide and stabilized zirconia (containing yttrium oxide). The platinum film is screen printed on one side of the ion-conducting phase 4 by about 1.8cm²And then formed by heat treatment at 1200 ℃. A mixed film of nickel oxide and stabilized zirconia (containing yttria) was formed by screen printing on a platinum film to the same area, and then heat treating at 1450 ℃. Mixing ratio of nickel oxide and stabilized zirconia (containing yttrium oxide)(molar ratio) is 6: 4. Screen-printed about 1.8cm on the other side of the ionically conductive phase 4 forming the reduced phase²The platinum film was then subjected to a heat treatment at 1200 ℃ to form an oxide phase 5. The barrier layer 1 is made of stabilized zirconia (containing yttria). Formed on the upper portion of the working electrode layer 2 by screen printing and heat treatment at 1400 c, and the film thickness was about 3 μm. Further, the temperature was raised to 650 ℃ while applying a current of 1.2V to 25mA between the cathode 3 and the anode 5, and the temperature was maintained for 1 hour, and then the current application was stopped to gradually cool the cathode.

The method for treating nitrogen oxides by means of the chemical reactor according to the invention of these compositions is described below. The chemical reaction apparatus 7 is disposed in the gas to be treated, fixed to the reduction phase 3 and the oxidation phase 5 by using a platinum wire as a lead wire, connected to a DC power supply, and energized by applying a DC voltage. The apparatus was evaluated at a reaction temperature in the range of 500 ℃ to 600 ℃. A sample combustion exhaust gas (as a treatment target gas) containing 1000ppm of NO, 2% of oxygen and the balance of helium was passed at a flow rate of 50 ml/min. The concentration of nitrogen oxides in the gas to be treated before and after flowing into the chemical reactor was measured by a chemiluminescence NOx meter; the concentrations of nitrogen and oxygen were determined by gas chromatography. After the removal rate of nitrogen oxides was determined from the reduction in nitrogen oxides, the current density and the power consumption were measured at a removal rate of 50%.

Heating the chemical reactor to a reaction temperature of 600 ℃, electrifying the chemical reaction part, and increasing the removal rate of the nitrogen oxide with the increase of the current amount, wherein the current density is 31mA/cm²61mW/cm power consumption²The nitrogen oxides are reduced to about 50%. Figure 3 shows the performance of the chemical reactor of the invention compared to the applied reactor and the results of the prior art. It is apparent from this figure that the performance of the chemical reactor according to the invention is outstanding compared to the results of the prior art.

Example 2

In the final energization heating treatment in the preparation process of the chemical reaction apparatus carried out in the same manner as in example 1, the temperature was raised to 650 ℃ by passing a current of 1.2V to 25mA between the cathode 3 and the anode 5, and after keeping the temperature for 1 hour, energization was stopped, and cooling was gradually carried out, and this on-off cyclewas repeated four times to adjust the temperatureThe relationship between the treatment frequency and the nitrogen oxide treatment capacity was examined. At this time, the current density at the time of 2-cycle treatment was 25mA/cm²The power consumption is 49mW/cm²The removal rate of nitrogen oxide is 50%, and the current density is 24mA/cm in 3-cycle treatment²The power consumption is reduced to 47mW/cm²And the result in the 4-cycle processing is almost the same as the value in the 3-cycle processing.

Example 3

The chemical reaction apparatus prepared in the same manner as in example 1 was examined for changes in reactivity with the amount of oxygen coexisting to inhibit the reaction and the concentration of nitrogen oxides in the object to be treated. Under the same experimental conditions as in example 1, (a) when the oxygen content was increased from 2% to 10%, and (b) when the nitrogen oxide concentration was decreased from 1000ppm to 500ppm, the current density and the required power at 50% decomposition were measured as (a) current density: 55mA/cm²Required power: 150mW/cm². (b) Current density: 20mA/cm²Required power: 37mW/cm²，It is obvious that the chemical reaction apparatus of the present invention has an improved relative treatment ability even when the amount of oxygen coexists is large, and has a remarkably improved performance against nitrogen oxides of a lean concentration.

Next, an embodiment of the invention 2 will be described with reference to the drawings. FIG. 1 is a schematic diagram of a chemical reaction apparatus according to an embodiment of the present invention. A chemical reaction site 6 constituting a chemical reaction apparatus 7 facing a gas flow of an object to be treated includes a working electrode layer 2, a cathode (reduction phase) 3, an ion conductive phase 4,and an anode (oxidation phase) 5, which are disposed in order from an upstream side, respectively, and a barrier layer 1 is disposed at an upstream side of the chemical reaction site 6. That is, the gas to be processed passes through the gas processing apparatus from 1 to 5 in sequence.

Hereinafter, the case where nitrogen oxide is used as the substance to be treated will be specifically described.

Example 4

Stabilized zirconia (containing yttria) was used as the ion-conducting phase 4, and was formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The reducing phase 3 is a mixed layer of platinum and zirconia, and the working electrode layer 2 is aThe layer is a film composed of a mixture of nickel oxide and stabilized zirconia (containing yttria). The platinum film is screen-printed on one side of the ion-conducting phase 4 to a thickness of about 1.8cm²And then formed by heat treatment at 1200 ℃. A mixed film of nickel oxide and stabilized zirconia (containing yttria) was formed by screen printing on a platinum film to the same area, and then heat treating at 1450 ℃. The mixing ratio (molar ratio) of nickel oxide to stabilized zirconia (containing yttrium oxide) was 6: 4. Screen-printed about 1.8cm on the other side of the ionically conductive phase 4 forming the reduced phase²The platinum film was then subjected to a heat treatment at 1200 ℃ to form an oxide phase 5. The barrier layer 1, which was formed on the upper portion of the working electrode layer 2 by screen printing and heat treatment at 1400 c using stabilized zirconia (containing yttria), was about 3 μm thick. Further, the temperature was raised to 650 ℃ while applying a current of 1.2V to 25mA between the cathode 3 and the anode 5, and the temperature was maintained for 1 hour, and then the current application was stopped to gradually cool the cathode.

The method for treating nitrogen oxides by means of the chemical reactor of the invention thus constituted is explained below. The chemical reaction apparatus 7 is disposed in the gas to be treated, fixed to the reduction phase 3 and the oxidation phase 5 by using a platinum wire as a lead wire, connected to a DC power supply, and energized by applying a DC voltage. The apparatus was evaluated at a reaction temperature of 600 ℃ when energized and at a reaction temperature of 350 ℃ when not energized. So that one of the compounds contains NO1000ppm and O ₂2% balance helium sample combustion exhaust gasThe gas (as a gas to be treated) was flowed at a flow rate of 50 ml/min. The concentration of nitrogen oxides in the gas to be treated before and after flowing into the chemical reactor was measured by a chemiluminescence NOx meter; the concentrations of nitrogen and oxygen were determined by gas chromatography. After the removal rate of nitrogen oxides was determined from the reduction in nitrogen oxides, the current density and the power consumption were measured at a removal rate of 50%.

At the start of the measurement, the chemical reactor was heated to a reaction temperature of 600 ℃ and the chemical reaction site was energized. In this case, the removal rate of nitrogen oxides was improved with the increase of the amount of current, and the current density was 31mA/cm²61mW/cm power consumption²The nitrogen oxide is reduced to 50%.

In this chemical reaction apparatus, the energization was stopped 1 hour after the start of energization, the measurement of the decomposition rate of nitrogen oxides was continued as it was, the decomposition rate of nitrogen oxides was decreased by about 10% immediately after the energization was stopped, the tendency of the decrease was indicated, and the continuous measurement for a total period of 5 days (120 hours) "decrease" was stopped at 5% or less, and itwas judged that the removal rate was decreased with the lapse of time. If the results are compared with the calculated values of the removal rate of 35%, it can be confirmed that the power consumption for 120 hours in total of removal of nitrogen oxides is reduced to about 1/84 at least as compared with the case of continuous energization of the present invention.

Example 5

To examine how the same chemical reaction apparatus as in example 4 was adapted to practical conditions, the removal performance of nitrogen oxides was examined by increasing the oxygen content from 2% to 10% and reducing the nitrogen oxide concentration from 1000ppm to 500 ppm. The energization for 10 minutes was repeated 3 times under the same temperature and power conditions as in example 4. As shown in fig. 5, the decomposition rate of nitrogen oxides decreased by 15% or more at the beginning of the measurement, and also decreased to a level of 30% at about 20 hours after the start of the measurement, and then gradually decreased, and almost reached an equilibrium state from the time of 100 hours. After 200 hours had passed, the same energization treatment was performed again to show a nitrogen oxide decomposition rate with time substantially the same as that of the 1 st cycle.

Example 6

Activation by the reducing atmosphere treatment was evaluated under the same chemical reaction apparatus configuration conditions as in example 4. 2% of oxygen coexisting, 650 ℃ of plant operating temperature, 1000ppm of nitrogen oxide, and about 68mW/cm of power required for 50% decomposition of nitrogen oxide²The chemical reaction apparatus (4) raises the temperature to 800 ℃ at a time of 48 hours (the decomposition rate of nitrogen oxides is reduced to about 38%) after the stop of energization, and flows a reducing gas (hydrogen 5%, argon 95%) for 10 hoursThereafter, the nitrogen oxide removal performance was measured, and the improvement in performance was judged to be about 2%.

Mode 3 of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 7

Stabilized zirconia (containing yttria) was used as a solid electrolyte having oxygen ion conductivity, and was formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The electrode layer is a composite of platinum and stabilized zirconia (containing yttria) in a 40: 60 volume ratio. The reduction body layer is a composite body of iron, platinum and stabilized zirconia (containing yttrium oxide) with the volume ratio of 30: 40, and is made into the upper layer of the electrode layer. The electrode layer to be the counter electrode was a composite of platinum and stabilized zirconia (containing yttria) in a volume ratio of 60: 40, and was formed on the reverse side of the solid electrolyte plate in the same area.

The redox reactor thus prepared, at 10% CO₂In the coexistence of H₂Reduction of O to H₂. At a temperature of 400 to 800 ℃, even in the presence of CO by means of an electrical current between the electrodes₂In the presence of (2), H can also be converted at a conversion of 90%₂Selective reduction of O to H₂. After the electrode is energized and the reduced body is regenerated, the energization is stopped, and the same H is converted at a conversion rate of 50 to 80%₂Selective reduction of O to H₂When the conversion rate is reduced to 50% or less, the reduced body is regenerated by applying current between electrodes, and then the application of current is stopped, and the reaction is performed in the same manner as above, so that H can be produced again at a conversion rate of 50 to 80%₂。

Example 8

Stabilized zirconia (containing yttria) was used as a solid electrolyte having oxygen ion conductivity, and formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The electrode layer is a composite of platinum and stabilized zirconia (containing yttria) in a volume ratio of 40: 60. The nitrogen oxide reducing agent layer is a composite body of nickel oxide and stabilized zirconia (containing yttrium oxide) with the volume ratio of 40: 60, and is made into the upper layer of the electrode layer. The electrode layer to be the counter electrode was a composite of platinum and stabilized zirconia (containing yttria) in a volume ratio of 60: 40, and was formed on the reverse side of the solid electrolyte plate in the same area. The nickel oxide of the nitrogen oxide-reducing layer was partially reduced to metal nickel particles of 100nm in size by applying electricity between electrodes at 500 ℃ to form the final nitrogen oxide-reducing layer.

The redox reactor thus prepared, at 5% O₂Implementation of nitrogen oxides in the coexistence(NO, 1000ppm) reduction removal. At a temperature of 400 to 700 ℃, by means of an electric current between electrodes, even in the presence of O₂Can also selectively reduce NO at a conversion of 70%. After the electrode is energized and the reduced body is regenerated, the energization is stopped, the same NO is selectively reduced at a conversion rate of 50 to 80%, and when the conversion rate falls to 50% or less, the reduced body is regenerated by the energization between the electrodes. After regeneration, the energization is stopped, and the same reaction as described above is carried out, whereby NO can be reduced again at a conversion rate of 50 to 80%.

Example 9

Stabilized zirconia (containing yttria) was used as a solid electrolyte having oxygen ion conductivity, and formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The electrode layer is a composite of lanthanum manganite and stabilized zirconia (containing yttrium oxide) in a volume ratio of 50: 50. The nitrogen oxide reducing body layer is a composite body of nickel oxide and stabilized zirconia (containing yttrium oxide) with the volume ratio of 40: 60, and is used as the upper layer of the electrode layer. An electrode layer La-Sr-Ca-Fe-O serving as a counter electrode is formed on the reverse surface of the solid electrolyte plate in the same area. The nickel oxide of the nitrogen oxide-reducing layer was partially reduced to metallic nickel particles of 50nm size by applying electricity between electrodes at 500 c to form the final nitrogen oxide-reducing layer.

The redox reactor thus prepared, at 10% O₂The reductive removal of nitrogen oxides (NO, 1000ppm) was carried out in the presence of co-catalyst. At a temperature of 400 to 700 ℃, by means of an electric current between electrodes, even in the presence of O₂Also in the presence of (b), NO was selectively reduced at a conversion rate of 65%. After the electrode is energized and the reduced body is regenerated, the energization is stopped, the same NO is selectively reduced at a conversion rate of 50 to 80%, and when the conversion rate falls to 50% or less, the reduced body is regenerated by the energization between the electrodes. After regeneration, the energization is stopped, and the same reaction as described above is carried out, whereby NO can be reduced again at a conversion rate of 50 to 80%.

Example 10

Stabilized zirconia (containing yttria) was used as a solid electrolyte having oxygen ion conductivity, and formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The electrode layer is a composite of platinum and a stable (containing yttrium oxide) with the volume ratio of 40: 60. The oxide layer is a composite of silver oxide, platinum and stabilized zirconia (containing yttrium oxide) in a volume ratio of 30: 40, and is formed as an upper layer of the electrode layer. The electrode layer to be the counter electrode was a composite of platinum and stabilized zirconia (containing yttria) in a volume ratio of 60: 40, and was formed on the reverse side of the solid electrolyte plate in the same area.

The redox reactor thus prepared, consists of CH in the CO-presence of 5% of CO₄To CH₃And (5) OH. By applying electricity between electrodes under the temperature condition of 400-600 ℃, CH can be converted at 95% even in the presence of CO₄Is selectively oxidized to CH₃And (5) OH. And, the electrode is energized, and after the regeneration of the oxidized body, the energization is stopped, and the same CH is added at a conversion rate of 60 to 80%₄Is selectively oxidized to CH₃When the conversion rate of OH is reduced to 60% or less, the oxidized body is regenerated by applying current between the electrodes. Stopping the energization, performing the same reaction as above, and producing CH again at a conversion rate of 60 to 80%₃OH。

Example 11

Stabilized zirconia (containing yttria) was used as a solid electrolyte having oxygen ion conductivity, and formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The electrode layer is a composite of platinum and stabilized zirconia (containing yttria) in a volume ratio of 40: 60. The oxide layer is a composite of copper oxide, platinum and stabilized zirconia (containing yttrium oxide) in a volume ratio of 40: 30, and is formed as an upper layer of the electrode layer. The electrode layer to be the counter electrode was a composite of lanthanum manganite and stabilizedzirconia (containing yttria) in a volume ratio of 60: 40, and was formed on the reverse side of the solid electrolyte plate in the same area.

The redox reactor thus prepared oxidatively decomposes dioxin in the coexistence of 10% of CO. Under the temperature condition of 400-600 ℃, by means of the electricity supply between electrodes, dioxin can be selectively oxidized and decomposed with the conversion rate of 80 percent even in the presence of CO. Further, the electrodes are energized, the energization is stopped after the regeneration of the oxidizing agent, the same dioxin is selectively oxidized and decomposed at a conversion rate of 40 to 70%, and when the conversion rate falls below 40%, the energization is stopped after the oxidizing agent is regenerated by the energization between the electrodes, and the same reaction as above is carried out, and the dioxin is again oxidized and decomposed at a conversion rate of 40 to 70%.

Example 12

Stabilizing and sizing CeO₂The oxide (containing Sm) was used as a solid electrolyte having oxygen ion conductivity and was formed into a disk shape having a diameter of 20mm and a thickness of 0.5 mm. The electrode layer is lanthanum manganite and stable CeO₂Is a composite of an oxide (containing Sm) and 50: 50 by volume. The oxide layer is a silver oxide, tungsten oxide, stable CeO₂A composite of an oxide (containing Sm) and an oxide in a volume ratio of 20: 30, to form an upper layer of the electrode layer. Become counter electrodeThe electrode layer is lanthanum manganite and stable CeO₂A composite body of a system oxide (containing Sm) and having a volume ratio of 60: 40 was formed on the reverse side of the solid electrolyte sheet in the same area.

The redox reactor thus prepared, at 5% CH₄In coexistence with CH₃CH₂Partial oxidation of OH to CH₃COOH. At a temperature of 400 to 600 ℃, by means of the electric current between the electrodes, even in CH₄In the presence of (2), CH can also be converted at a conversion rate of 70%₃CH₂Selective partial oxidation of OH to CH₃COOH. And, the electrode is energized, and after the regeneration of the oxidized body, the energization is stopped, and the same CH is added at a conversion rate of 50 to 70%₃CH₂Selective partial oxidation of OH to CH₃COOH, when the conversion rate is reduced to 50% or less, regeneration of the oxide by energization between electrodes and then stopping energization, and the same reaction as described above is carried out, and CH can be produced again at a conversion rate of 50 to 70%₃COOH。

Industrial applicability of the invention

As described above, according to the 1 st aspect of the present invention, the following effects can be obtained:

(1) provided is a chemical reaction apparatus capable of efficiently treating a substance to be treated even when oxygen which prevents the substance to be treated from chemically reacting is excessive.

(2) The amount of current required for decomposing nitrogen oxides can be reduced, and nitrogen oxides can be efficiently removed with a small amount of power consumption.

(3) The micro reaction region where a single stage of the object to be treated undergoes redox reaction can be introduced into a part of the chemical reaction site of the chemical reaction apparatus.

(4) A chemical reaction apparatus is provided which comprises a chemical reaction site which is an interface formed by a metal phase portion of an electron-conducting phase on a contact of the electron-conducting phase and an ion-conducting phase, an oxygen-deficient portion of the ion-conducting phase, and a micro-void portion (cavity) around the contact.

Further, according to the 2 nd aspect of the present invention, the following effects can be obtained:

(1) provided is a chemical reaction apparatus capable of efficiently treating a substance to be treated with a small amount of electric power consumption even when oxygen gas that prevents the substance to be treated from chemically reacting is excessive.

(2) Can remove nitrogen oxides efficiently by small power consumption.

(3) The chemical reaction apparatus can be reactivated.

(4) The energy-saving electrochemical reaction device can be reused by intermittently electrifying or applying an electric field to activate the chemical reaction part.

Further, the 3 rd aspect of the present invention relates to a reaction method of oxidation-reduction reaction, and according to the present invention, the following effects can be obtained:

(1) a highly selective oxidation or reduction reaction method is provided which employs a redox reactor that does not require the supply and replacement of a reducing agent and an oxidizing agent.

(2) The reaction method using the redox reactor of the present invention selects substances suitable for the reaction, which can oxidize or reduce the target substance with high selectivity, from the following substances having oxidizing and reducing abilities. For example, organic compounds, organic chlorine compounds, hydrogen, carbon monoxide, nitrogen oxides, ammonia, and the like.

(3) The present invention is suitable for, for example, synthesis of useful substances such as hydrogen, methanol and acetic acid, removal of impurities, removal of harmful substances such as dioxin and nitrogen oxide in exhaust gas, and the like.

(4) The method of the present invention can regenerate the reducing body or the oxidizing body by means of electrification, so that the method does not need to be replaced, and the burden of equipment maintenance is not long.

Claims

1. A chemical reaction system for chemically reacting a substance to be treated, comprising an oxygen ion conductor (ion conductive phase) and two chemical reaction sites each having a cathode (reduction phase) and an anode (oxidation phase) which are opposed to each other with the ion conductor interposed therebetween as a basic unit, wherein a minute reaction region for causing an oxidation-reduction reaction of the substance to be treated is introduced into a part of the chemical reaction sites at a position on a contact point of the ion conductive phase and the ion conductive phase, which contact point is formed by an arbitrary combination of the ion conductor, the electron conductor, and a mixed conductor at the chemical reaction sites, by passing an electric current, applying an electric field, or performing a heat treatment in a reducing atmosphere or under reduced pressure.

2. The chemical reaction system according to claim 1, wherein as the minute reaction region, an interface composed of a metal phase portion of the electron-conducting phase, an oxygen-deficient portion of the ion-conducting phase, and a small gap (cavity) around the contact thereof is formed on the contact of the electron-conducting phase and the ion-conducting phase.

3. A chemical reaction system according to claim 1, wherein a minute reaction region where the oxidation-reduction takes place is introduced into the cathode.

4. The chemical reaction system according to claim 1, wherein a working electrode layer for controlling a redox reaction is formed on an upper portion of the cathode, and a nano-to micro-sized minute reaction region where the redox reaction occurs is introduced into the working electrode layer.

5. A chemical reaction system according to claim 1, wherein all or a part of the substance constituting the minute reaction region has an oxidizing and reducing action on the substance to be treated.

6. The chemical reaction system according to claim 1, wherein the metal phase is composed of ultrafine particles of a metal phase generated by oxidation-reduction and generated in a part or the whole of the electron conductor or the mixed conductor by conducting a current to the chemical reaction system or by heat treatment in a reducing atmosphere.

7. The chemical reaction system according to claim 1, wherein the oxygen deficient portion is constituted by an oxygen deficient layer generated by oxidation-reduction and generated over a part or the whole of the ion conductor or the mixed conductor by conducting a current to the chemical reaction apparatus or by heat treatment in a reducing atmosphere.

8. A chemical reaction system according to claim 1, wherein the minute reaction region is constituted such that at least 1 part of the ion conductor and the electron conductor is in direct contact with each other or is in contact with each other during the production thereof.

9. A chemical reaction system according to claim 1, wherein a barrier layer capable of blocking the electron conductive substance is provided in a path to which the substance to be treated reaches from the surface of the electrochemical cell to the gap of the chemical reaction.

10. A chemical reaction system according to claim 1, characterised in that the chemical reaction is a matter or energy shift reaction.

11. A chemical reaction system according to claim 1, wherein the substance to be treated is nitrogen oxide.

12. A chemical reaction system according to claim 10, characterised in that the chemical reaction is a reductive decomposition reaction of nitrogen oxides.

13. A chemical reaction system according to claim 9, wherein a chemical reaction represented by the following general formula occurs in the chemical reaction apparatus:

；

(M: metal, O: oxygen atom, e: electron)

14. The method for producing a chemical reaction system according to any one of claims 1 to 13, wherein a minute reaction region for causing a redox reaction of a substance to be treated is introduced into the chemical reaction site by conducting or heat treatment in a reducing atmosphere to a contact point of an ion conducting phase and an ion conducting phase formed by an arbitrary combination of an ion conductor, an electron conductor, and a mixed conductor at the chemical reaction site.

15. A method according to claim 14, characterised in that either or both of the two are in a reduced state when forming the interface with which the material is in contact.

16. The method for activating a chemical reaction system according to claim 1, wherein the metallic phase portion of the electron conducting phase or the mixed conducting phase is coupled to the oxygen deficient portion of the ion conducting phase or the mixed conducting phase by passing an electric current.

17. A chemical reaction system for chemically reacting a substance to be treated, characterized in that it comprises 1) an oxygen ion conductor (ion conductive phase), a cathode (reduction phase) and an anode (oxidation phase) which are opposed to each other with the ion conductor interposed therebetween, and 2) a chemical reaction site comprising an oxidation and/or reduction catalyst as a basic unit, and the desorption capability is activated by ionizing oxygen adsorbed to the chemical reaction site and inhibiting the reaction by applying an electric field or applying an electric field to the chemical reaction site or by heating under a reducing atmosphere or reduced pressure.

18. A chemical reaction system according to claim 17, wherein as the chemical reaction site, there are used a chemical reaction site provided with a reducing phase selective to oxygen and the substance to be treated, respectively, and having pores of a size of less than a desired micrometer for the treatment for efficiently supplying the substance to be treated to the reducing phase.

19. A chemical reaction system characterized in that as the chemical reaction site, a minute reaction region for causing a material to be treated to undergo an oxidation-reduction reaction is introduced into a part of the chemical reaction site by conducting or heat treating in a reducing atmosphere to a contact point of an electron conducting phase and an ion conducting phase, which is formed by an arbitrary combination of an ion conductor, an electron conductor, and a mixed conductor.

20. The chemical reaction system according to claim 19, wherein as the minute reaction region, an interface composed of a metal phase portion of the electron-conducting phase, an oxygen-deficient portion of the ion-conducting phase, and a small gap portion (cavity) around the contact thereof is formed on the contact of the electron-conducting phase and the ion-conducting phase.

21. A chemical reaction system according to claim 19, wherein as the chemical reaction site, a minute reaction region where the redox reaction takes place is introduced into the cathode.

22. A chemical reaction system according to claim 17, wherein a working electrode layer for controlling a redox reaction is provided as the chemical reaction site on the upper portion of the cathode, and a nano-to micro-sized minute reaction region for effecting the redox reaction is introduced into the working electrode layer.

23. A chemical reaction system according to claim 17, wherein the substance to be treated is nitrogen oxide.

24. A chemical reaction system according to claim 22, characterised in that the chemical reaction is a reductive decomposition reaction of nitrogen oxides.

25. Use of a chemical reaction system for chemical reaction of a substance to be treated according to any one of claims 17 to 24, wherein the temperature of the chemical reaction apparatus is maintained at 400 to 700 ℃ or the temperature is raised or lowered within the same temperature range, and the chemical reaction site is activated by applying electricity or an electric field for a predetermined time.

26. The method according to any one of claims 17 to 24, wherein the temperature of the chemical reaction apparatus is maintained at 400 to 700 ℃ or the temperature is raised or lowered within the same temperature range, and the cathode and the anode are energized for 1 minute to 3 hours or subjected to an external electric field.

27. The method for activating a chemical reaction apparatus according to claim 26, wherein the electrochemical reaction is caused to occur by applying an electric voltage of 5mV to 1A or applying an external voltage of 0.5V to 2.5V.

28. The activation method for chemical reaction apparatus according to claim 26, wherein the energization or the electric field treatment is carried out under an oxygen partial pressure of 0% to 21% (in the atmosphere).

29. The method according to any one of claims 17 to 24, wherein the temperature of the chemical reaction apparatus is maintained at 500 ℃ or higher, or the temperature is raised or lowered in the same temperature range, and the heat treatment is performed in a reducing atmosphere or under reduced pressure.

30. A reaction method, which is a redox method of a redox reactor formed by a solid electrolyte of oxygen ion conductor and at least 1 kind of electronic conductor electrode, is characterized in that a cathode is providedAdding a reducing agent (R) by the reaction formula By redox reaction of the oxide (AOx) with a reducing agent (R) to form a reduced product AOx-y (y is greater than 0 and less than or equal to x), or by adding an oxidizing agent (R' Ox) to the anode by means of the reaction formula The redox reaction of compound a with an oxidizing agent (R' Ox) to produce an oxidation product AOy.

31. Reaction process according to claim 30, characterised in that a reducing body (R) made of a metal or a base oxide is applied to the cathode, (1) the oxide AOx (x being the 1/2 oxidation number for A) is introduced into the reactor according to the reaction formula The oxide AOx and the reducing agent (R) are subjected to redox reaction to generate a reduction product AOx-y (y is more than 0 and less than or equal to x), (2) the electrode is electrified according to the reaction formula (cathode) a, The electrochemical reaction (anode) reduces the oxidized reducing agent (ROy) to regenerate the reducing agent (R).

32. The reaction process according to claim 31, wherein the reducing agent (R) is regenerated by energizing the electrode after or simultaneously with the oxidation-reduction reaction of the oxide (AOx) with the reducing agent (R) to produce a reduction product AOx-y (0<y.ltoreq.x).

33. The reaction process according to claim 32, characterized in that the reducing agent (R) is a nitrogen oxide according to the formula The nitrogen oxide reducing agent and the nitrogen oxide NOx to generate a reduction product N₂And NOx is removed.

34. The reaction process of claim 33, wherein the redox reactor comprises: the solid electrolyte comprises nitrogen oxide reducing agent made of metal or suboxide (containing more than 50%) of more than 1 element selected from Ni, Cu and Fe, electrode made of more than 1 electron conductor selected from Au, Pt, Ag, Pd, Ni oxide, Cu oxide, Fe oxide and Mn oxide group, and oxygen ion conductor made of zirconium oxide.

35. Reaction process according to claim 33 or 34, characterised in that the particle size of the nitrogen oxide reducing agent is between 10nm and 1 μm.

36. The reaction process according to claim 33, wherein 1 or more oxide-based electron conductors selected from the group consisting of Ni oxide, Cu oxide, Fe oxide and Mu oxide are brought into contact with the solid electrolyte of the oxygen ion conductor, and a cathodic current is applied to the electron conductor to reduce a part of the oxide-based electron conductor to form a nitrogen oxide reducing agent having a size of 10nm to 1 μm.

37. Reaction process according to claim 30, characterised in that the anode is provided with an oxide-forming oxide (R' Ox), (1) the compound A is introduced into the reactor according to the reaction scheme The redox reaction of compound A with an oxide (R' Ox) to form an oxidation product AOy, (2) energizing the electrode according to the reaction formula yO^2-+R’Ox-y→R’Ox+y2e^-(anode) of the anode, the electrochemical reaction (at the cathode) oxidizes the reduced oxide R 'Ox-y to regenerate the oxide (R' Ox).

38. The reaction process according to claim 37, characterized in that the oxide (R 'Ox) is regenerated by energizing the electrode after or simultaneously with the redox reaction of the compound a with the oxide (R' Ox) to form an oxidation product AOy.

39. The reaction process according to claim 37 or 38, characterized in that the compound A is a hydrocarbon or an organochlorine compound.