OXIDIZING DEVICE WITH INCREASED OXIDIZING PERFORMANCE AND METHOD OF MANUFACTURING THE SAME

Abstract

An oxidizing device and an oxidizing method for oxidizing a carbon-containing component in a gaseous mixture containing H2O and the carbon-containing component are disclosed having a proton conductive body and an electrode member placed on the proton conductive body. The electrode member has an anode electrode and a cathode electrode held in contact with each other and the proton conductive body has electric conductivity of 0.01 Scm−1 or more at a temperature of 400° C. or less. The anode electrode separates a proton (H+) from H2O at a boundary portion between the anode electrode and the proton conductive body to facilitate a reaction to introduce the proton into the proton conductive body. The cathode electrode facilitates a reduction reaction in the presence of the proton supplied from the proton conductive body at a boundary portion between the cathode electrode and the proton conductive body.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2008-85238, filed on Mar. 28, 2008, the content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to oxidizing devices or more particularly, to an oxidizing device for oxidizing a carbon-containing component and a method of oxidizing the carbon-containing component.

2. Description of the Related Art

In the related art, attempts have heretofore been made to provide an exhaust gas purifying system as a catalyst converter system for purifying exhaust gases emitted from an internal combustion engine such as an automotive engine or the like. The exhaust gas purifying system incorporates therein an exhaust gas purifying catalyst body, located in an exhaust pipe of the internal combustion engine, which has a carrier (catalyst carrier) carrying thereon catalyst components. This causes oxidation and reduction reactions to take place for purifying HC, CO and NO_x in exhaust gases.

For such a catalyst body, a ceramic carrier body (monolith carrier body) is formed in a honeycomb structure having, for instance, a large number of cells and used as a base material, on which a catalyst component such as noble metal is carried.

For the catalyst component of noble metal, it is a usual practice to use Pt, Pd and Rh, etc.

When using a plurality of kinds of noble metals in combination, it is significantly effective to remove plural harmful components in exhaust gases.

Japanese Patent Application Publication No. 2001-70797 discloses an exhaust-gas purifying electrochemical catalyst composed of a mixture of a first catalyst having a NO_x absorbing substance and a NO_x reduction catalyst, a second catalyst having a hydrocarbon absorbing substance and a hydrocarbon oxidizing catalyst, an electron conductive substance and an ion conductive substance.

With an exhaust-gas purifying electrochemical catalyst, electrons are caused to transfer between the first and second catalysts via the electron conductive substance while causing ion to transfer through the electron conductive substance. When this takes place, an electrochemical reduction reaction occurs in the first catalyst and an electrochemical oxidizing reaction occurs in the second catalyst. These reactions occur independently from each other and the reduction of absorbed NO_x is rapidly initiated using absorbed hydrocarbon.

However, with such a technology proposed in the related art described above, an active oxygen species can be produced merely from a cathode electrode with a resultant disadvantage in which the catalyst has inadequate oxidizing capability for carbon containing substances like carbon or CH₄ that are chemically stable. Further, the active oxygen species reacts rapidly with reduction gases such as H₂ and HC under the same atmosphere, causing an issue to arise with a difficulty of producing the active oxygen species.

SUMMARY OF THE INVENTION

The present invention has been completed with a view to addressing the above issue and has an object to provide an oxidizing device, which can use H₂O in a gaseous mixture, containing H₂O and a carbon-containing component, as a reactant with an effect of having a capability of oxidizing the carbon-containing component with increased oxidizing performance, and a method of oxidizing the carbon-containing component.

To achieve the above object, one aspect of the present invention provides an oxidizing device for oxidizing a carbon-containing component in a gaseous mixture containing H₂O and the carbon-containing component, the oxidizing device comprising: a proton conductive body; and an electrode member placed on the proton conductive body; the electrode member having an anode electrode portion and a cathode electrode portion held in contact with each other; the proton conductive body having an electric conductivity of 0.01 Scm⁻¹ or more at a temperature of 400° C. or less; the anode electrode portion separating a proton (H⁺) from H₂O at a boundary portion between the anode electrode portion and the proton conductive body to facilitate a reaction to introduce the proton into the proton conductive body; and the cathode electrode portion facilitating a reduction reaction in the presence of the proton supplied from the proton conductive body at a boundary portion between the cathode electrode portion and the proton conductive body.

With the oxidizing device according to the present invention, the electrode member is placed on the proton conductive body having the specified electric conductivity with the anode electrode portion and the cathode electrode portion held in contact the proton conductive body. This structure enables H₂O in the gaseous mixture, containing H₂O and the carbon-containing component, to be used as the reactant, resulting in a capability of oxidizing the carbon-containing component with increased oxidizing performance.

With the oxidizing device of such a structure, the anode electrode portion facilitates the reaction to separate the proton (H⁺) from H₂O held in contact with the boundary portion between the anode electrode portion and the proton conductive body and introduce the proton into the proton conductive body.

The anode electrode portion serves as an electrode material to expedite an anode reaction. As set forth above, the proton conductive body has a property to pass the proton and an electric conductivity as high as 0.01 Scm⁻¹ or more at a relatively low temperature of 400° C. or less.

Therefore, if H₂O in the gaseous mixture is brought into contact with the boundary portion between the anode electrode portion and the proton conductive body, reactions occur on three-phase interfaces (oxidizing sites) of the proton conductive body, the anode electrode and H₂O as expressed by H₂O→H⁺+OH⁻ and H₂O→2H⁺+O²⁻, etc. This causes active oxygen species (such as, for instance, O²⁻, OH⁻, O₂⁻, O₂²⁻, etc.) to be generated at the anode electrode portion. When this takes place, the proton conductive body takes the resulting proton.

The active oxygen species, generated from the anode reaction, has a high oxidizing capability and immediately after generation, the active oxygen species reacts to oxidize the carbon-containing component in the gaseous mixture. For instance, this enables the oxidation from C to CO or CO₂, CH₄ to CH₃OH, CO₂ and CO or the like, and HC to CO₂ or the like. That is, with such an oxidation site mentioned above, the anode reactions (2H₂O+C→CO₂+4H⁺4e⁻ and 2_xH₂O+C_xH_y→C_xO_2x+(4_x-y) H⁺+4xe⁻ or the like) will take place.

Further, electrons, generated when oxidizing the carbon-containing component freely move about in the anode electrode portion and the cathode electrode portion when held in contact therewith.

Since the proton conductive body has the high electric conductivity, the proton conductive body autonomously takes in the protons separated from H₂O in contact with the boundary portion between the anode electrode portion and the proton conductive body. The captured protons freely move about in the proton conductive body.

The cathode electrode portion allows the protons, supplied from the proton conductive body, to facilitate the reduction reaction at the boundary portion between the cathode electrode portion and the proton conductive body.

The cathode electrode portion serves as an electrode material for expediting a cathode reaction and the proton conductive body is placed in a condition under which the protons, taken during the reaction at the oxidizing site as set forth above, are present.

Therefore, reduction reactions (cathode reactions) of reaction gas occur on the interfaces (oxidizing sites) of the proton conductive body, the cathode electrode portion and reaction gases (like NO, NO₂ and O₂, etc) due to the proton. More particularly, if NO, NO₂ and O₂ are present in an area in the vicinity to the cathode electrode, these components can be reduced to H₂O (i.e., 2NO+4H⁺+4e⁻→N₂+2H₂O, and 1/2O₂+2H⁺+2e⁻→H₂O, etc.). Furthermore, if H₂O or O₂ are present in the vicinity of the cathode electrode, H₂O₂ and active oxygen species (such as, for instance, O₂H and H₃O⁺, etc.) occur (as expressed as O₂+2H⁺+2e⁻→H₂O₂, etc.). The active oxygen species induces a reaction to oxidize the carbon-containing component in the gaseous mixture immediately after the active oxygen species has been produced.

In such a way set forth above, the present invention contemplates the use of H₂O in the gaseous mixture as the reactant to enable both of the anode electrode and the cathode electrode to generate the active oxygen species. The active oxygen species, generated at both the electrodes, can oxidize the carbon-containing substance in the gaseous mixture, thereby making it possible to perform the oxidation with increased oxidizing capability. In addition, due to the existence of high oxidizing performance, the generation of the active oxygen species and the oxidation of the carbon-containing substance autonomously occur even at a relatively low temperature of 400° C. or less. Moreover, not only the oxidation of the carbon-containing substance but also the reduction of NO and NO₂ or the like can be expedited.

Form this, it turns out that the present invention can provide an oxidizing device that can use H₂O in a gaseous mixture, containing H₂O and a carbon-containing component, as a reactant for thereby enabling the oxidation of carbon-containing substance with increased oxidizing performance.

Another aspect of the present invention provides a method of oxidizing a carbon-containing component in a gaseous mixture containing H₂O and one carbon-containing component, the method comprising: preparing a proton conductive body having an electric conductivity of 0.01 Scm⁻¹or more at a temperature of 400° C. or less; preparing an electrode member having an anode electrode portion and a cathode electrode portion held in contact with each other; mixing the proton conductive body and the electrode member to locate the electrode member on the proton conductive body such that the anode electrode portion and the cathode electrode portion are held in contact with the proton conductive body; contacting H₂O with the anode electrode portion at a boundary portion between the anode electrode portion and the proton conductive body for separating a proton (H⁺) from H₂O to introduce the proton into the proton conductive body through which the proton moves; and causing a reduction reaction to occur on the cathode electrode portion at a boundary portion between the cathode electrode portion and the proton conductive body in the presence of the proton supplied from the proton conductive body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative view showing an oxidizing device of a first embodiment according to the present invention.

FIG. 2 is a graph showing the relationships between temperatures and the amount of generated CO₂ resulting from tests conducted using the oxidizing device of the embodiment shown in FIG. 1.

FIG. 3 is a graph showing the relationships between temperatures and the amount of generated CO₂ resulting from tests conducted on an oxidizing device of a second embodiment according to the present invention.

FIG. 4 is a graph showing the relationships between temperatures and the amount of generated CO₂ resulting from tests conducted on an oxidizing device of a third embodiment according to the present invention.

FIG. 5 is a graph showing the relationships between temperatures and the amount of generated CO₂ resulting from tests conducted on an oxidizing device of a fourth embodiment according to the present invention.

FIG. 6 is a spectrum obtained upon conducting Raman spectroscopy on an oxidizing device of a fifth embodiment according to the present invention.

FIG. 7 is a graph showing the relationships between temperatures and the amount of generated CO₂ resulting from tests conducted on an oxidizing device of a sixth embodiment according to the present invention.

FIG. 8 is a graph showing the relationships between temperatures and conversion rates of HC resulting from tests conducted on an oxidizing device of a seventh embodiment according to the present invention.

FIG. 9 is a graph showing the relationships between the inverse numbers of temperatures and electric conductivities resulting from tests conducted on an oxidizing device of an eighth embodiment according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Now, oxidizing devices of various embodiments according to the present invention and a method of oxidizing carbon-containing material are described below with reference to the embodiments shown in the accompanying drawings. However, the present invention is construed not to be limited to such embodiments described below and technical concepts of the present invention may be implemented in combination with other known technologies or the other technology having functions equivalent to such known technologies.

An oxidizing device, implementing the present invention, includes a proton conductive body, and an electrode member placed on the proton conductive body.

The oxidizing device may suffice to take the form of a structure placed in a status under which the proton conductive body and the electrode member are placed in contact with each other. For instance, examples of such a status include a state under which granular proton conductive bodies and granular electrode member are mixed in contact with each other.

If none of the proton conductive body and the electrode member is placed in contact with each other, no reactions are expedited at the oxidizing site and the reduction site mentioned above. Thus, no active oxygen species can be obtained at adequate generation rates. This causes difficulty of obtaining oxidizing performance to oxidize the carbon-containing substance in the gaseous mixture.

An example of a method of manufacturing the oxidizing device mentioned above may include, for instance, a method of obtaining the oxidizing device by physically mixing the proton conductive body and various electrode materials expediting anode and cathode reactions in a manner described below using a mortar or the like.

In an alternative, the oxidizing device may be obtained by causing materials, forming the anode electrode portion and the cathode electrode portion, to be carried on the proton conductive body in a solution technique such as a coprecipitation method or the like and mixing these components.

Further, the proton conductive body may be suffice to have one point in an electric conductivity of 0.01 Scm⁻¹or more at a temperature (room temperature or more) in a temperature range of 400° C. or less.

The proton conductive body can have permeating property varying such that the higher the electric conductivity, the easier will be to permeate the proton and has a capability of facilitating reactions at the oxidizing site and the reduction site to allow the oxidizing device to have increased oxidizing performance.

If the proton conductive body has the electric conductivity of 0.01 Scm⁻¹ or less even at any temperatures of 400° C. or less, the anode reaction and the cathode reaction become hard to take place with a resultant adequate amount of generated active oxygen species. This results in an issue of a difficulty occurring to obtain oxidizing performance to oxidize the carbon-containing substance.

Further, the electric conductivity is a value obtained by a calculation conducted using a formula described below. To execute the calculation, various kinds of proton conductive bodies were formed in pellets each with a thickness of L [cm] with both surfaces applied with electrically conductive paste of Pt and the like or electrically conductive foils, thereby preparing cells. Then, electric resistances of the cells were measured by using an alternating current impedance method to obtain ohmic resistances R_ohmic [Ω] of the respective cells to be used for the calculation expressed below.

α=L/(S *R_ohmic)

The proton conductive body may include any one of those having a property to permeate the proton while having an electric conductivity of 0.01 Scm⁻¹or more at a temperature of 400° C. or less. The proton conductive body may include, for instance, inorganic phosphate compound (MP₂O₇: M=Tetravalent Metal), BaCe_0.85Y_0.15O_3-α, and Nafion high-polymer film, etc.

Among these, the proton conductive body may be preferably composed of an inorganic phosphate compound expressed by MP₂O₇ where M represents tetravalent metal.

The inorganic phosphate compound is particularly suited as the proton conductive body because it has a high electric conductivity.

Examples of the inorganic phosphate compound may include, for instance, SnP₂O₇, and TiP₂O₇, etc.

Further, the inorganic phosphate compound may preferably have an M-site to which a dopant is added.

Such a structure enables the proton conductive body to have increased electric conductivity, thereby making it possible to produce a large amount of active oxygen species at lower temperatures.

As used herein, the term “dopant” refers to a substance of trivalent metal that generates holes in a lattice upon substitution to an M-site of MP₂O₇ to provide improved proton conductivity.

Examples of the dopant may preferably include, for instance, Al³⁺ and In³⁺, etc.

Examples of the inorganic phosphate compound having the M-site to which the dopant is added may include, for instance, Sn_1-xIn_xP₂O₇, Sn_1-xAl_xP₂O₇, Ti_1-xIn_xP₂O₇, and Ti_1-xAl_xP₂O₇, etc.

Further, the electrode member includes the anode electrode portion and the cathode electrode portion held in contact with each other.

When the anode electrode portion and the cathode electrode portion are not held in contact with each other, no exchange of electrons is achieved between the electrodes and no reaction takes place at the reduction site. This results in an issue of difficulty of adequately achieving the oxidation of the carbon-containing substance. In addition, no reductions of NO and NO₂, etc., can be accomplished.

The anode electrode portion may include any of those which facilitate the anode reaction as set forth above and are composed of material having electric conductivity. Examples of the anode electrode portion include, for instance, a metallic material selected from the group consisting of Pt, Ag, Cu, Fe, Cr, Ir, Ni, Co, Au, W and Mo or a metallic alloy material, etc.

The cathode electrode portion may include any of those which facilitate the cathode reaction as set forth above and are composed of material having electric conductivity. Examples of the anode electrode portion include, for instance, a metallic material selected from the group consisting of Pt, Ag, Cu, Fe, Cr, Ir, Ni, Co, Au, W and Mo or a metallic alloy material, etc.

Moreover, the anode electrode portion and the cathode electrode portion may be made of different materials or same materials.

If the anode electrode portion and the cathode electrode portion are made of different materials, it may suffice for the electrode member to include a mixture of the anode electrode portion and the cathode electrode portion.

If the anode electrode portion and the cathode electrode portion are made of the same materials, one kind of material may suffice to be prepared for the electrode member with the anode electrode portion and the cathode electrode portion remained undifferentiated. In is case, the electrode member has an oxidizing site formed in an area constituting three-phase interfaces between the proton conductive body and H₂O, thereby facilitating the anode reaction mentioned above. Meanwhile, the electrode member has a reduction site formed in an area constituting three-phase interfaces between the proton conductive body and reaction gas, thereby facilitating the cathode reaction mentioned above.

EMBODIMENTS

First Embodiment

An oxidizing device of a first embodiment according to the present invention will be described below with reference to FIG. 1 of the accompanying drawings.

As shown in FIG. 1, the oxidizing device 1 of the present embodiment includes a proton conductive body 2 and an electrode member 3 placed on the proton conductive body 2 for oxidizing a carbon-containing component 5 in a gaseous mixture containing H₂O 4 and a carbon-containing component 5.

The proton conductive body 2 has a conducting rate of 0.01 Scm⁻¹or more at a temperature of 400° C. or less.

The electrode member 3 includes an anode electrode portion 31 and a cathode electrode portion 32 held in contact with each other. The electrode member 3 allows a proton (H⁺) to be separated from H₂O 4 placed in contact with a boundary portion between the anode electrode portion 31 and the proton conductive body 2 to facilitate a reaction introducing the proton into the proton conductive body 2. Further, the electrode member 3 allows the cathode electrode portion 32 to facilitate reduction reaction due to the proton supplied from the proton conductive body 2 at a boundary between the cathode electrode portion 32 and the proton conductive body 2.

With the oxidizing device 1 of such a structure, when H₂O 4 in the gaseous mixture is brought into contact with the boundary portion between the anode electrode portion 31 and the proton conductive body 2, reactions such as, for instance, H₂O→H⁺+OH⁻ and H₂O→2H⁺+O²⁻ or the like take place at tree-phase interfaces (oxidizing sites) of the proton conductive body 2, the anode electrode portion 31 and H₂O 4. This causes active oxygen species O* (such as, for instance, O²⁻, OH⁻, O₂⁻, O₂²⁻, etc.) to generate at the anode electrode portion 31.

The active oxygen species O*, occurring due to anode reaction, have high oxidizing capability and, immediately after the generation, a reaction takes place to oxidize the carbon-containing component 5 in the gaseous mixture. For instance, this enables the oxidation from C to CO or CO₂, CH₄ to CH₃OH, CO₂ and CO or the like, and HC to CO₂ or the like. That is, with such an oxidation site mentioned above, the anode reactions (2H₂O+C→CO₂+4H⁺+4e⁻ and 2_xH₂O+C_xH_y→CxO_2x+(4_x-y) H⁺+4xe⁻ or the like) will take place.

Further, reduction reactions (cathode reactions) of reaction gas occur on the interfaces (oxidizing sites) of the proton conductive body 2, the cathode electrode portion 32 and reaction gases (not shown) (like NO, NO₂ and O₂, etc) due to the proton H⁺. More particularly, if NO, NO₂ and O₂ are present in an area in the vicinity to the cathode electrode, these components can be reduced to H₂O (i.e., 2NO+4H⁺+4e⁻→N₂+2H₂O, and 1/2O₂+2H⁺+2e⁻→H₂O, etc.), Furthermore, if H₂O or O₂ are present in the vicinity of the cathode electrode, active oxygen species O* (such as, for instance, O₂H and H₃O⁺, etc.) occur (O₂+2H⁺+2e⁻→H₂O₂, etc.).

Next, description will be provided of a method of manufacturing the oxidizing device 1.

First, Pt was prepared as the electrode materials 3 (the anode electrode portion and the cathode electrode portion). With the present embodiment, although the anode electrode portion 31 and the cathode electrode portion 32 of the electrode materials 3 will be described as having structure made of Pt, it will be appreciated that the anode electrode portion 31 and the cathode electrode portion 32 may be made of other materials different from each other.

Next, the proton conductive body 2 and the electrode member 3 were physically mixed using a mortar or the like, thereby obtaining a structure of the oxidizing device 1 of the present embodiment. The oxidizing device 1 was prepared to have a composition 10% by mass of the electrode material 3 and 90% by mass of the proton conductive body 2.

With the present embodiment, moreover, although the oxidizing device 1 was prepared by the physically mixing method, the oxidizing device 1 may be prepared by causing an anode electrode material and a cathode electrode material to be carried on a proton conductive body in a solution technique like a coprecipitation method and by mixing these materials.

Subsequently, 100 mg of the resulting oxidizing device and 30 mg of carbon black (CB) are physically added to each other to obtain a test sample, which was then tested as described below.

The test sample was raised in temperature at a rate of 5° C./min and a stream of air containing 3% of H₂O is caused to pass through the test sample at a rate of 30 ml/min at each temperature. During such operation, the amount of CO₂ in outlet gas was measured upon gas chromatography measurement to evaluate a generation start temperature and the amount of generated active oxygen. Further, for comparison purposes, start temperatures of generating active oxygen and the amounts of generated active oxygen were similarly evaluated on only CB, CB and Pt, and CB and SnP₂O₇. The results were shown in FIG. 2.

In FIG. 2, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates the amount (μmol/min) of generated CO₂.

It turns out from FIG. 2 that the oxidizing device (Pt+SnP₂O₇+CB) of the present embodiment lead the lowest CO₂ generating temperature and SnP₂O₇+CB, Pt+CB and CB had CO₂ generating temperatures lower in this order.

Carbon black (CB), which is one kind of carbon, began to oxidize at a temperature close proximity to 450° C. in atmosphere to completely oxidize at temperatures of 550 to 600° C.

When using only Pt forming the electrode material in the present embodiment, the combustion start temperature is slightly hastened but complete combustion is initiated at temperatures of 550 to 600° C. and nearly the same result as that of natural combustion can be merely obtained.

When using only SnP₂O₇ forming the proton conductive body in the present embodiment, combustion begins at a temperature in the vicinity of 300° C.

When using an oxidizing device wherein Pt, forming the electrode member, and SnP₂O₇ forming the proton conductive body, are held in contact with each other, such an oxidizing device oxidizes at a temperature in the vicinity of 200° C. and is completely oxidized at temperatures ranging from 450 to 500° C.

This result strongly gives a suggestion based on a current proposed doctrine that an active oxygen species is generated.

Second Embodiment

With the present embodiment, three kinds of oxidizing devices are prepared in structures including the proton conductive bodies of the first embodiment containing compositions of TiP₂O₇, Ba Ce_0.85Y_0.15O_3-α and La_0.9Sr_0.1Sc_3-α, respectively.

The proton conductive bodies had electric conductivities of MP₂O₇ (M=Sn, Ti) (under a condition of 250° C., the electric conductivities can be described as 5.8×10⁻² Scm⁻¹>>BaCe_0.85Y_0.15O_3-α (under a condition of 400° C., the electric conductivities can be described as 1.0×10⁻² Scm⁻¹)>>La_0.9Sr_0.1ScO_3-α) (under a condition of 500° C., the electric conductivities can be described as 1.4×10⁻³ Scm⁻¹) in this order.

Further, tests were conducted to evaluate generation start temperatures of generating active oxygen and the amounts of generated active oxygen in the same methods conducted in the tests of the first embodiment. Results are indicated in FIG. 3. For comparison purposes, tests were also conducted on oxidizing devices incorporating the proton conductive bodies having compositions of SnP₂O₇ and only CB, with results being indicated in FIG 3.

In FIG. 3, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates the amount (μmol/min) of generated CO₂.

It turns out from FIG. 3 that the amount of generated CO₂ varies such that the greater the electric conductivity of proton, the lower will be the temperature for active oxygen to be generated. That is, it turns out that the proton electric conductivity is important.

The CO₂ is prominently generated at 200° C. or more due to active oxygen when using TiP₂O₇ and SnP₂O₇ as electrolytes and in the neighborhood of 400° C. when using BaCe_0.85Y_0.15O_3-α as electrolyte. It can be said from such results that the present proposal needs to have a proton conductive body having the proton electric conductivity of at least 0.01 Scm⁻¹ or more.

When using La_0.9Sr_0.1ScO_3-α with the electric conductivity of 0.01 Scm⁻¹ or less under a condition at 500° C., nearly the equivalent result as that, obtained when causing CB to naturally combust was obtained.

It can be said from such results that the present proposal needs to have a proton conductive body having the proton electric conductivity of at least 0.01 Scm⁻¹ or more at 400° C. or less.

Third Embodiment

With the present embodiment, oxidizing devices are prepared using proton conductive bodies (Sn_0.9In_0.1P₂O₇ (under a condition of 250° C., the electric conductivity is 0.194 Scm⁻¹) and Ti_0.95Al_0.5P₂O₇ (under a condition of 250° C., the electric conductivity is 0.181 Scm⁻¹)) having improved electric conductivities by adding In and Al as dopants to metallic sites of SnP₂O₇ and TiP₂O₇ of the proton conductive bodies.

Further, tests were conducted to evaluate generation start temperatures of generating active oxygen and the amounts of generated active oxygen in the same methods conducted in be tests of the first embodiment. Results are indicated in FIG. 4. For comparison purposes, tests were also conducted on oxidizing devices employing SnP₂O₇ and only CB, respectively, with results being indicated in FIG. 4.

In FIG. 4, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates the amount (μmol/min) of generated CO₂.

It turns out from FIG. 4 that the amount of generated CO₂ increases at 200° C. and complete combustion takes place at temperatures ranging from 350 to 400° C. From such a result, it is predictable such that the higher the proton electric conductivity, the higher will be the effect of the present embodiment.

Fourth Embodiment

With the present embodiment, an oxidizing device was prepared using Sn_0.9In_0.1P₂O₇ as the proton conductive body in the third embodiment in which the tests were conducted using the stream of air containing 3% of H₂O. With the present embodiment, tests were conducted using streams of air with contents of H₂O set to values of 0.6% and 10%, respectively. Results are indicated in FIG. 5. For comparison purposes, tests were also conducted on oxidizing devices prepared using Sn_0.9In_0.1P₂O₇ and only CB, respectively, upon using the stream of air containing 3% of H₂O with results being indicated in FIG 5.

In FIG. 5, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates the amount (μmol/min) of generated CO₂.

It turns out from FIG. 5 that as a feeding rate of H₂O increased, both the generation start temperature of generating CO₂ due to active oxygen species and a temperature of complete combustion was lowered. That is, it turns out that the existence of H₂O resulted in the formation of active oxygen.

From such a result, it can be said that the active oxygen species is generated from H₂O.

This result demonstrates that the presently proposed mechanism is supported by evidence.

Fifth Embodiment

With the present embodiment, a test sample was prepared using 100 mg of the oxidizing device prepared using Sn_0.9In_0.1P₂O₇ as the proton conductive body in the third embodiment and tests were conducted to confirm the expression of active oxygen species upon conducting Raman spectroscopy.

The confirmation of the active oxygen species based on Raman spectroscopy was conducted by observing Raman spectrum of a sample with the present oxidizing device placed on a glass plate using a Raman spectrometer.

For comparison purposes, tests were also conducted on a first sample using Sn_0.9In_0.1P₂O₇ as the proton conductive body to which CB was added, a second sample having an electrode member to which CB was added, and a third sample in which only CB was used, respectively, to similarly confirm the expression of active oxygen species. Resulting spectrums are indicated in FIG. 6.

It turns out from FIG. 6 that the oxidizing device added with CB demonstrated a spectrum having a peak of O₂⁻ at an intensity of 1233 cm⁻¹ and a peak of O₂²⁻ at an intensity of 678 cm⁻¹, respectively. Meanwhile, none of the peaks O²⁻ and O₂²⁻ was found in the first sample in which CB was added to Sn_0.9In_0.1P₂O₇, the second sample in which CB was added to Pt and the third sample in which only CB was added.

From such a result, the expression of the active oxygen species can be confirmed.

Sixth Embodiment

With the present embodiment, an oxidizing device was prepared using Mo, Ni, Ag, Fe and Pt as electrode materials (for an anode and a cathode) and using Sn_0.9In_0.1P₂O₇ (having an electric conductivity of 0.194 Scm⁻¹ at a temperature of 250° C.) as a proton conductive body.

The inclusion of any of Mo, Ni, Ag, Fe and Pt results in an increase in response of an anode reaction and a cathode reaction while providing electric conductivity.

Tests were conducted on the resulting oxidizing device in the same test method as that conducted in the first embodiment to evaluate a generation start temperature of active oxygen and the amount of resulting active oxygen. Results are shown in FIG. 7. For comparison purpose, a result on an oxidizing device using only CB is also indicated.

In FIG. 7, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates the amount (μmol/min) of generated CO₂.

It will be understood from FIG. 7 that with the oxidizing devices having the electrode materials using Mo, Ni, Ag, Fe and Pt, all of the oxidizing devices have increased oxidizing performances.

Seventh Embodiment

With the present embodiment, the oxidizing device was prepared in the third embodiment using Sn_0.9In_0.1P₂O₇ as a proton conductive body to provided a test sample, which is then subjected to tests as described below.

For conducting the tests, model gas was prepared containing 1000 ppm of C, 1% of O₂, 3% of H₂O and a balance of N₂ and caused to pass through the test sample, thereby obtaining a varying rate of HC before and after the model gas has passed at various temperatures.

Results are indicated in FIG. 8. In FIG. 8, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates a conversion rate (%) of HC.

It turns out from FIG. 8 that the oxidizing device was capable of oxidizing HC at lower temperatures than those achieved with the oxidizing device of the related art due to the generation of active oxygen species in a low temperature region.

Eighth Embodiment

With the present embodiment, a dopant was added to the M-site of the proton conductive body to clarify an effect of the inclusion of the dopant.

With the present embodiment, In was added as the dopant to the M-site of the proton conductive body of the first embodiment, thereby preparing four kinds of proton conductive bodies (Sn_0.8In_0.2P₂O₇, Sn_0.9In_0.1P₂O₇, Sn_0.95In_0.05P₂O₇ and Sn_0.97In_0.03P₂O₇).

Electric conductivities of the resulting proton conductive bodies were measured.

For measuring the electric conductivities, the respective resulting proton conductive bodies are formed in pellets each having a thickness L [cm] and having both surfaces applied with conductive paste of Pt, etc., or electrically conductive foils, thereby forming cells. Ohmic resistances R_ohmic [Ω] of the respective cells were measured in air using an alternating-current impedance method and subjected to calculations using a formula described below. Results are shown in FIG. 9.

α=L/(S*R_ohmic)

In FIG. 9, the abscissa axis indicates a temperature (° C.) and the ordinate axis indicates the electric conductivity (Scm⁻¹).

It will be understood from FIG. 9 that adding the dopant to the proton conductive body of the oxidizing device results in an increase in electric conductivity.

While the specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limited to the scope of the present invention, which is to be given the full breadth of the following claims and all equivalents thereof.

Claims

1. An oxidizing device for oxidizing a carbon-containing component in a gaseous mixture containing H2O and the carbon-containing component, the oxidizing device comprising:

a proton conductive body; and

an electrode member placed on the proton conductive body;

the electrode member having an anode electrode portion and a cathode electrode portion held in contact with each other;

the proton conductive body having an electric conductivity of 0.01 Scm−1 or more at a temperature of 400° C. or less;

the anode electrode portion separating a proton (H+) from H2O at a boundary portion between the anode electrode portion and the proton conductive body to facilitate a reaction to introduce the proton into the proton conductive body; and

the cathode electrode portion facilitating a reduction reaction in the presence of the proton supplied from the proton conductive body at a boundary portion between the cathode electrode portion and the proton conductive body.

2. The oxidizing device according to claim 1, wherein:

the proton conductive body is composed of an inorganic phosphate compound expressed by MP2O7 where M represents tetravalent metal.

3. The oxidizing device according to claim 2, wherein:

the inorganic phosphate compound has an M-site to which a dopant is added.

4. The oxidizing device according to claim 1, wherein:

the proton conductive body is made of a material selected from an inorganic phosphate compound, BaCe0.85Y0.15O3-α, and Nafion high-polymer film.

5. The oxidizing device according to claim 4, wherein:

the inorganic phosphate compound includes at least one of SnP2O7, and TiP2O7.

6. The oxidizing device according to claim 3, wherein:

the inorganic phosphate compound having the M-site to which the dopant is added includes Sn1-xInxP2O7, Sn1-xAlxP2O7, Ti1-xInxP2O7, and Ti1-xAlxP2O7.

7. The oxidizing device according to claim 1, wherein:

the anode electrode portion is made of a metallic material selected from the group consisting of Pt, Ag, Cu, Fe, Cr, Ir, Ni, Co, Au, W and Mo or a metallic alloy material.

8. The oxidizing device according to claim 1, wherein:

the cathode electrode portion is made of a metallic material selected from the group consisting of Pt, Ag, Cu, Fe, Cr, Ir, Ni, Co, Au, W and Mo or a metallic alloy material.

9. A method of oxidizing a carbon-containing component in a gaseous mixture containing H2O and the carbon-containing component, the method comprising:

preparing a proton conductive body having an electric conductivity of 0.01 Scm−1 or more at a temperature of 400° C. or less;

preparing an electrode member having an anode electrode portion and a cathode electrode portion held in contact with each other;

mixing the proton conductive body and the electrode member to locate the electrode member on the proton conductive body such that the anode electrode portion and the cathode electrode portion are held in contact with the proton conductive body;

contacting H2O with the anode electrode portion at a boundary portion between the anode electrode portion and the proton conductive body for separating a proton (H+) from H2O to introduce the proton into the proton conductive body through which the proton moves; and

causing a reduction reaction to occur on the cathode electrode portion at a boundary portion between the cathode electrode portion and the proton conductive body in the presence of the proton supplied from the proton conductive body.