JP2013015398A - Selective hydrogen oxidation catalyst and gas sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen selective oxidation catalyst capable of selectively oxidizing hydrogen from gas mixture, and a gas sensor element using the same.SOLUTION: The hydrogen selective oxidation catalyst for selectively removing Hfrom a gas mixture by selectively reacting Hwith O, and a gas sensor element using the same are provided. The hydrogen oxidation catalyst includes SnO. The gas sensor element 1 includes: a solid electrolyte 11 with oxygen ion conductivity; a measuring electrode 12 and a reference electrode 13 provided on one surface 111 and the other surface 112 thereof respectively; a porous diffusion resistance layer 14 that is superposed on the surface where the measuring electrode 12 is disposed in the solid electrolyte 11 and allows measuring object gas to permeate therethrough; and a porous catalyst support layer 15 formed on the outside surface thereof. The catalyst support layer 15 includes the hydrogen selective oxidation catalyst.

Description

  The present invention relates to a hydrogen selective oxidation catalyst that selectively oxidizes hydrogen from a mixed gas and a gas sensor element using the same.

An exhaust system such as an internal combustion engine for a vehicle is provided with a gas sensor that detects a specific gas concentration such as an oxygen concentration in a gas to be measured such as exhaust gas.
In order to detect a specific gas concentration, as shown in FIG. 8, the gas sensor includes a solid electrolyte body 91 having oxygen ion conductivity, and a measurement provided on one surface 911 and the other surface 912 of the solid electrolyte body. An electrode 92 and a reference electrode 93, a porous diffusion resistance layer 94 that is laminated on the surface 911 of the solid electrolyte body 91 on which the measurement electrode 92 is disposed, and allows the gas to be measured to pass therethrough; A gas sensor element 9 having a porous catalyst support layer 95 formed on the side surface 940 is incorporated.

In the gas sensor element 9, a gas to be measured such as an exhaust gas containing CO, HC, H ₂ , O ₂ , NO, etc. enters from the catalyst support layer 95 and is disposed in the gas chamber 920 to be measured through the diffusion resistance layer 94. The measurement electrode 92 is reached. The measurement electrode 92 detects the concentration of a specific gas such as oxygen in the exhaust gas. However, hydrogen having a small molecular weight contained in the exhaust gas is more easily diffused in the porous diffusion resistance layer 94 than other gas components such as oxygen and easily reaches the measurement electrode 92. For this reason, the hydrogen concentration may be detected high, and the concentration of a specific gas such as oxygen in the measurement gas may be detected low. In particular, in an air-fuel ratio sensor that detects an oxygen concentration as a specific gas concentration, if it is determined that the hydrogen concentration increases and the oxygen concentration decreases, the air-fuel ratio in the actual measured gas (exhaust gas) However, the output signal may be judged on the rich side.

  Therefore, in a gas sensor such as an air-fuel ratio sensor, measures are taken to remove hydrogen in the gas to be measured before reaching the measurement electrode 92. Specifically, a catalyst such as a noble metal is supported on the catalyst support layer 95. Thereby, hydrogen in the gas to be measured can be oxidized, and hydrogen can be removed from the exhaust gas before the exhaust gas reaches the measurement electrode 92.

  However, a catalyst made of a noble metal is oxidized in a high-temperature oxidizing atmosphere, and the noble metal oxide is easily melted and evaporated. As a result, the catalyst carrying layer 95 carrying a catalyst made of a noble metal has a problem that its catalytic performance deteriorates. In addition, noble metals have a problem of high cost. Therefore, development of a catalyst that replaces the noble metal catalyst is desired.

  To date, it has been proposed to use, for example, a base metal oxide having a perovskite structure as a catalyst in place of a noble metal (see Patent Document 1). By using a base metal oxide having a perovskite structure, it is possible to suppress deterioration in catalyst performance in the catalyst support layer. Base metal oxides having a perovskite structure exhibit excellent hydrogen combustion performance particularly in a lean atmosphere.

JP 2010-38600 A

  However, a base metal oxide having a perovskite structure is insufficient as a catalyst for selectively removing hydrogen. That is, a base metal oxide having a perovskite structure can effectively oxidize (combust) hydrogen in a lean atmosphere in which oxygen is excessive, but in an atmosphere near the stoichiometric air-fuel ratio (stoichiometric), Oxygen necessary for combustion is insufficient, and sufficient hydrogen combustion performance cannot be exhibited. This is because the base metal oxide having a perovskite structure consumes oxygen and burns CO contained in the exhaust gas in preference to hydrogen, so that the amount of oxygen necessary for the oxidation of hydrogen gas cannot be secured.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a hydrogen selective oxidation catalyst capable of selectively oxidizing hydrogen from a mixed gas and a gas sensor element using the same.

One aspect of the present invention is a hydrogen selective oxidation catalyst that selectively removes H ₂ by selectively reacting H ₂ and O ₂ from a mixed gas,
A hydrogen selective oxidation catalyst characterized by containing SnO ₂ (Claim 1).

Another aspect of the present invention includes an oxygen ion conductive solid electrolyte body, a measurement electrode and a reference electrode provided on one surface and the other surface of the solid electrolyte body, and the measurement electrode in the solid electrolyte body, respectively. Is a gas sensor element having a porous diffusion resistance layer that is laminated on the surface on which the gas is measured and permeates the gas to be measured, and a porous catalyst support layer formed on the outer surface of the diffusion resistance layer. ,
In the gas sensor element, the catalyst supporting layer contains a hydrogen selective oxidation catalyst containing SnO ₂ .

The hydrogen selective oxidation catalyst containing SnO ₂ can selectively oxidize and remove hydrogen gas from a mixed gas containing not only hydrogen but also other gas components such as CO. In the hydrogen selective oxidation catalyst, SnO ₂ can selectively adsorb hydrogen from a mixed gas such as exhaust gas on the surface of its particles. Therefore, the hydrogen selective oxidation catalyst can preferentially burn hydrogen even in a mixed gas in which hydrogen and another combustible gas coexist.

In the gas sensor element, the catalyst supporting layer contains a hydrogen selective oxidation catalyst containing SnO ₂ . Therefore, in the gas sensor element, hydrogen contained in the measurement gas such as exhaust gas is oxidized and removed in the catalyst support layer. Therefore, the gas to be measured containing almost no hydrogen can be sent from the catalyst support layer through the diffusion resistance layer to the measurement electrode, and hydrogen having a small molecular weight passes through the diffusion layer preferentially. Can be prevented. Therefore, the gas sensor element can accurately measure the specific gas concentration in the gas to be measured.

FIG. 3 is an explanatory view showing a honeycomb structure in Example 1. FIG. 3 is an explanatory diagram showing a cross-sectional structure of a honeycomb structure in Example 1. Explanatory drawing which shows the relationship between the temperature of each catalyst (sample 1 and sample 2) in Example 1, and the purification rate with respect to hydrogen, carbon monoxide, and a hydrocarbon. Explanatory drawing which shows the purification rate with respect to the hydrogen in the temperature of 600 degreeC of each catalyst (sample 1-sample 7) in Example 1, carbon monoxide, and a hydrocarbon. FIG. 4 is an explanatory diagram showing a cross-sectional configuration of a stacked gas sensor element in Example 2. Explanatory drawing which expands and shows the outer peripheral surface periphery of the diffused resistance layer of a laminated | stacked type gas sensor element in Example 2. FIG. In Example 2, illustrates the relationship between the sensor output and the O ₂ flow rate (air-fuel ratio) of the gas sensor element (elements A through C). Explanatory drawing which shows the cross-sectional structure of a laminated | stacked type gas sensor element in background art.

Next, a preferred embodiment of the present invention will be described.
The hydrogen selective oxidation catalyst is used for selectively removing H ₂ by selectively reacting H ₂ and O ₂ from a mixed gas.
The mixed gas preferably contains at least H ₂ , O ₂ and CO.
In this case, the hydrogen selective oxidation catalyst can burn H ₂ in preference to CO, and can fully exhibit the selective oxidation performance of the hydrogen selective oxidation catalyst with respect to hydrogen.

The mixed gas preferably contains CO, HC, H ₂ , O ₂ , and NO (Claim 2). Specific examples of such a mixed gas include exhaust gas.
Even in this case, the hydrogen selective oxidation catalyst can burn H ₂ in preference to CO, HC, and NO. Therefore, the selective oxidation performance with respect to hydrogen of the hydrogen selective oxidation catalyst can be more fully exhibited.

  Next, the gas sensor element includes the solid electrolyte body, the measurement electrode and the reference electrode, the diffusion resistance layer, and the catalyst support layer. The catalyst support layer contains the hydrogen selective oxidation catalyst. The hydrogen selective oxidation catalyst can be supported on the porous catalyst support layer.

The solid electrolyte body can be made of an oxygen ion conductive ceramic. Specifically, it can be composed of partially stabilized zirconia, ceria or the like in which a stabilizer is added to a main component composed of zirconia or zirconia.
Further, the measurement electrode and the reference electrode formed on the solid electrolyte body can be made of, for example, a noble metal.

  The diffusion resistance layer is a porous body that allows the gas to be measured to pass through, and can be composed of porous ceramics. Specifically, for example, it can be composed of porous zirconia, alumina or the like. The diffusion resistance layer can be formed so as to cover the measurement electrode. In addition, a gas chamber to be measured can be formed inside the diffusion resistance layer, which is a cavity into which the gas to be measured is introduced.

The catalyst support layer is formed on the outer surface of the diffusion resistance layer. In the gas sensor element, a measurement gas such as exhaust gas is supplied from the porous catalyst support layer to the measurement electrode through the diffusion resistance layer. Since the catalyst-carrying layer contains a hydrogen selective oxidation catalyst containing SnO ₂ , in the gas sensor element, the gas to be measured from which hydrogen has been removed by oxidation in the catalyst-carrying layer passes through the diffusion resistance layer. Supplied to the measurement electrode.

Preferably, the catalyst support layer has a porous body made of alumina, and the hydrogen selective oxidation catalyst is supported on the porous body.
In this case, the heat resistance of the catalyst support layer can be improved, and as a result, the durability of the gas sensor element can be improved.
In this case, since the surface area of the catalyst support layer can be increased, the hydrogen selective oxidation catalyst can easily come into contact with the exhaust gas, and the hydrogen contained in the exhaust gas can be oxidized more efficiently. become.
Further, in this case, the catalyst support layer can play a role of trapping poisoning components contained in the measurement gas such as exhaust gas. The poisoning component is a component that poisons and degrades a measurement electrode made of, for example, a noble metal. For example, when the gas to be measured is exhaust gas, the poisoning components include P, Si, and Ca contained in oil. And compounds formed from components such as Zn.

The porous body can be composed of alumina particles having an average particle diameter of 1 to 10 μm. And the said hydrogen selective oxidation catalyst with an average particle diameter of 0.1-5 micrometers can be carry | supported to an alumina particle.
The average particle size of the alumina particles and the hydrogen selective oxidation catalyst can be defined by the particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method.

The porous body is preferably made of γ-alumina or θ-alumina.
In this case, the particles constituting the porous body of the catalyst support layer itself become porous, and the catalyst support layer can have a large surface area. Therefore, poisoning components in the measurement gas such as exhaust gas, for example, compounds generated from components such as P, Si, Ca, and Zn contained in the oil can be easily trapped in the catalyst support layer. Therefore, poisoning of the measurement electrode due to poisoning components can be further prevented. More preferably, the porous body is made of θ-alumina.

The content of the hydrogen selective oxidation catalyst in the catalyst support layer is preferably 10% by mass or more (Claim 6).
In this case, the oxidation performance for hydrogen by the hydrogen selective oxidation catalyst can be further improved. More preferably, the content of the hydrogen selective oxidation catalyst in the catalyst support layer is preferably 10% by mass or more, and more preferably 30% by mass or more.
Further, when the ratio of the hydrogen selective oxidation catalyst is increased, gas diffusibility in the catalyst supporting layer may be impaired. Therefore, the content of the hydrogen selective oxidizing catalyst in the catalyst supporting layer is preferably 50% by mass or less.

Further, the catalyst support layer is preferably formed with a thickness of 5 to 2000 μm.
In this case, it becomes possible to support the catalyst supporting layer with a sufficient amount of the hydrogen selective oxidation catalyst capable of sufficiently exhibiting oxidation performance against hydrogen, and to maintain the porosity of the catalyst supporting layer sufficiently. The flow of the gas to be measured in the catalyst support layer can be prevented from being hindered. More preferably, the thickness of the catalyst support layer is 20 to 1000 μm, and more preferably 100 to 200 μm.

  In the gas sensor element, a trap layer made of alumina or the like can be formed on the outer surface of the catalyst support layer. Thereby, poisoning components in the measurement gas can be removed in the trap layer. Further, the thickness of the catalyst support layer can be increased to, for example, 100 μm or more, and the catalyst support layer can serve as a trap layer for trapping poisoning components.

The gas sensor element preferably includes a heater for heating the gas sensor element.
In this case, the gas sensor element can be easily heated to the operating temperature by the heater.

  The gas sensor element is disposed in an exhaust system such as an internal combustion engine for a vehicle, for example, and is based on a limiting current flowing between electrodes depending on a specific gas concentration (oxygen concentration) in a gas to be measured (exhaust gas). An air-fuel ratio sensor (A / F sensor) for detecting an air-fuel ratio (A / F) of an air-fuel mixture supplied to a gas, a specific gas concentration (oxygen concentration) between a measured gas (exhaust gas) and a reference gas (atmosphere) The present invention can be applied to an oxygen sensor or the like that detects an air-fuel ratio based on an electromotive force generated between electrodes depending on the ratio.

The gas sensor element is preferably used for an air-fuel ratio sensor.
In this case, the performance of the hydrogen selective oxidation catalyst that can selectively oxidize hydrogen can be fully utilized. That is, the hydrogen selective oxidation catalyst can burn hydrogen with excellent selectivity from a mixed gas not only in a lean atmosphere but also in an atmosphere near the stoichiometric air-fuel ratio (stoichiometric). Therefore, the gas sensor element provided with the hydrogen selective oxidation catalyst in the catalyst support layer has a concentration of a specific gas such as O ₂ from a mixed gas such as exhaust gas not only in a lean atmosphere but also in an atmosphere near the theoretical air-fuel ratio. It can be detected accurately. Therefore, the gas sensor element is suitable for an air-fuel ratio sensor.

  The gas sensor element can be a so-called stacked gas sensor element formed by stacking the solid electrolyte body and the diffusion resistance layer, for example. Further, the gas sensor element may be a so-called cup-type gas sensor element having the cup-type solid electrolyte body with a distal end closed and a proximal end opened.

Example 1
Next, examples of the hydrogen selective oxidation catalyst will be described.
In this example, the selective oxidation performance for hydrogen is evaluated for a hydrogen selective oxidation catalyst containing SnO ₂ .
The SnO ₂ according to the embodiment of this example was prepared SnO ₂ powder commercially available. This is designated as Sample 1.

  Next, a honeycomb structure (volume: about 0.035 L) having a diameter of 30 mm and a length of 50 mm was prepared. As shown in FIGS. 1 and 2, the honeycomb structure 5 includes an outer peripheral wall 51, porous cell walls 52 arranged in a square lattice pattern in the outer peripheral wall 51, and compartments in these cell walls 52. And a large number of cells 53 extending along the axial direction of the columnar honeycomb structure. The cell walls 52 are arranged in a square lattice shape, and the cells 53 are square in the cross section perpendicular to the axial direction of the cylindrical honeycomb structure 5 and in the end face 54 of the honeycomb structure 5. The honeycomb structure 5 is made of porous cordierite and has a cylindrical shape.

Next, the hydrogen selective oxidation catalyst of Sample 1 was supported on the honeycomb structure.
Specifically, first, Sample 1 was dispersed in water to prepare a catalyst slurry. Next, after the honeycomb structure was immersed in the catalyst slurry and pulled up, excess water was blown off by air blowing. Next, the honeycomb structure was fired under conditions of a temperature of 600 ° C. for 3 hours, and the catalyst of Sample 1 was baked.
Thus, a honeycomb structure carrying 3.5 g of the hydrogen selective oxidation catalyst of Sample 1 was obtained.

Next, a mixed gas corresponding to an air-fuel ratio of 14.6 (air / fuel, mass ratio) is flowed into the cell from one end surface side to the other end surface of the honeycomb structure supporting the hydrogen selective oxidation catalyst of Sample 1. It was distributed at 20 L / min. Gas mixture, 4600ppm of CO, HC (hydrocarbons) to 1600 ppm, 2500 ppm of NO, O ₂ and 0.5 vol%, the H ₂ 5000 ppm, of H ₂ O containing 13.6vol%.
Then, while increasing the temperature of the hydrogen selective oxidation catalyst (sample 1) supported on the honeycomb structure from 200 ° C. to 700 ° C. at a rate of temperature increase of 20 ° C./min, H ₂ contained in the gas that has passed through the honeycomb structure. The concentration of each component of CO, HC was measured with an analyzer. From the measurement results, the H ₂ purification rate, the CO purification rate, and the HC purification rate at each temperature were calculated by the following equations. The result is shown in FIG.
H ₂ purification rate (%) = (1− (concentration of H _{2 in} mixed gas that has passed through honeycomb structure (ppm) / 5000 (ppm)) × 100
CO purification rate (%) = (1− (concentration of CO in mixed gas that has passed through honeycomb structure (ppm) / 4600 (ppm)) × 100
HC purification rate (%) = (1− (concentration of HC in the mixed gas that has passed through the honeycomb structure (ppm) / 1600 (ppm)) × 100

Next, for comparison with Sample 1, a catalyst made of a base metal oxide having a perovskite structure made of LaFeO ₃ was prepared.
Specifically, first, lanthanum nitrate and iron nitrate were mixed at a molar ratio of 1: 1 in water to prepare a nitrate aqueous solution. Then, the aqueous nitrate solution was heated with stirring until the water was completely evaporated. The solid obtained after drying was sufficiently pulverized in an agate mortar and mixed uniformly, and then baked at a temperature of 800 ° C. for 5 hours. This gave a catalyst comprising LaFeO _3. This is designated as Sample 2. For sample 2, the H ₂ purification rate, the CO purification rate, and the HC purification rate at temperatures of 200 ° C. to 700 ° C. were measured in the same manner as for sample 1. The result is shown in FIG.
In FIG. 3, the horizontal axis represents the catalyst temperature (° C.), and the vertical axis represents the purification rate (%) of each gas component (H ₂ , CO, HC).

As can be seen from FIG. 3, sample 1 made of tin oxide can preferentially oxidize H ₂ over CO, HC, and the like. The sample 1 can be oxidized with hydrogen in a high temperature region of, for example, 500 ° C. or more with particularly excellent selectivity and oxidation performance. Further, the sample 1 can be oxidized with priority over H ₂ over other gases even in a low temperature region.

On the other hand, it can be seen that Sample 2 made of a metal oxide having a perovskite structure preferentially oxidizes CO over H ₂ . That is, the selectivity for hydrogen is low. Therefore, Sample 2, preferentially oxidize CO, in O ₂ concentration environment with limited becomes insufficient O ₂ required for oxidizing H _2, it is possible to sufficiently oxidize hydrogen There is a risk that it will not be possible.

Further, in this example, for comparison with Sample 1, five types of catalysts (samples 3 to 7) made of metal oxides having a perovskite structure were prepared, and the purification rate was evaluated.
Sample 3 is a catalyst made of LaCoO ₃ powder. Sample 3 was prepared in the same manner as Sample 2 described above, except that cobalt nitrate was used instead of iron nitrate.
Sample 4 is a catalyst made of LaMnO ₃ powder. Sample 4 was prepared in the same manner as Sample 2 described above, except that manganese nitrate was used instead of iron nitrate.

Sample 5 is a catalyst made of LaCu _0.2 Co _0.8 O ₃ powder. Sample 5 was prepared by mixing lanthanum nitrate and iron nitrate in water at a 1: 1 molar ratio, but lanthanum nitrate, copper nitrate, and cobalt nitrate in water at a molar ratio of 1: 0.2: 0.8, respectively. It was produced in the same manner as Sample 2 described above except for the mixed point.
Sample 6 is a catalyst made of LaCu _0.2 Mn _0.8 O ₃ powder. Sample 6 was prepared by mixing lanthanum nitrate and iron nitrate in water at a 1: 1 molar ratio, but lanthanum nitrate, copper nitrate, and manganese nitrate in water at a molar ratio of 1: 0.2: 0.8, respectively. It was produced in the same manner as Sample 2 described above except for the mixed point.
Sample 7 is a catalyst made of LaCu _0.2 Fe _0.8 O ₃ powder. Instead of mixing lanthanum nitrate and iron nitrate in water at a 1: 1 molar ratio, sample 7 was prepared by mixing lanthanum nitrate, copper nitrate, and iron nitrate in water at a molar ratio of 1: 0.2: 0.8, respectively. It was produced in the same manner as Sample 2 described above except for the mixed point.

Next, for Sample 3 to Sample 7, the H ₂ purification rate, the CO purification rate, and the HC purification rate at temperatures of 200 ° C. to 700 ° C. were measured in the same manner as Sample 1. FIG. 4 shows the purification rates of the component gases (H ₂ , CO, and HC) at a temperature of 600 ° C. In the figure, the purification rates (temperature 600 ° C.) of the component gases of the sample 1 and the sample 2 are also shown.

  As can be seen from FIG. 4, it can be seen that the catalysts (samples 2 to 7) made of an oxide having a perovskite structure oxidize carbon monoxide preferentially over hydrogen. On the other hand, the catalyst (sample 1) made of tin oxide oxidizes hydrogen preferentially over other component gases, and is found to be excellent in selective oxidation performance with respect to hydrogen.

Thus, according to this example, it can be seen that the hydrogen selective oxidation catalyst containing SnO ₂ can selectively remove H ₂ by selectively reacting H ₂ and O ₂ from the mixed gas.

(Example 2)
Next, an embodiment of a gas sensor element using a hydrogen selective oxidation catalyst will be described with reference to FIGS.
As shown in FIG. 5, the gas sensor element 1 of this example includes an oxygen ion conductive solid electrolyte body 11, a measurement electrode 12 and a reference electrode 13 provided on one surface 111 and the other surface 112, respectively, A porous diffusion resistance layer 14 that is laminated on the surface 111 of the electrolyte body 11 on which the measurement electrode 12 is disposed and transmits the gas to be measured, and a porous catalyst support layer 15 formed on the outer surface of the porous diffusion resistance layer 14. Have. As shown in FIGS. 5 and 6, the catalyst support layer 15 contains a hydrogen selective oxidation catalyst 155 containing SnO ₂ .

The gas sensor element 1 of this example includes the following element components in addition to the solid electrolyte body 11, the measurement electrode 12, the reference electrode 13, the diffusion resistance layer 14, and the catalyst support layer 15 described above.
That is, as shown in FIG. 5, the gas sensor element 1 includes a dense shielding layer 16 that covers the surface of the diffusion resistance layer 14 opposite to the solid electrolyte body 11, and a gas chamber to be measured that includes a space for introducing the gas to be measured. 120, a reference gas chamber 130 including a space for introducing a reference gas, a reference gas chamber forming layer 17 for forming the reference gas, and a heater substrate 182 on which a heat generating portion 181 that generates heat when energized is printed. And a heater 18.

Hereinafter, the gas sensor element 1 will be described in detail.
The gas sensor element 1 of this example is an air-fuel ratio sensor element (A / F sensor element) that is installed in an exhaust pipe of an automobile engine and used for an exhaust gas feedback system. The gas sensor element 1 is a so-called laminated gas sensor element.

A measurement electrode 12 made of platinum is arranged on one surface 111 of the solid electrolyte body 11 made of partially stabilized zirconia or the like, and a reference electrode 13 made of platinum is arranged on the other surface 112.
The shielding layer 16 is laminated on the surface 111 of the solid electrolyte body 11 on the side where the measurement electrode 12 is disposed, with the measured gas chamber 120 and the diffusion resistance layer 14 interposed therebetween.

The diffusion resistance layer 14 is made of a gas-permeable alumina porous body, is laminated on the measurement electrode 12 side of the solid electrolyte body 11, and is formed so as to cover the measurement electrode 12. A measurement gas chamber 120 is formed inside the diffusion resistance layer 14, and a measurement electrode 12 is formed on the surface of the solid electrolyte body 11 in the measurement gas chamber 120. A gas under measurement (exhaust gas) that has passed through the porous diffusion resistance layer 14 is introduced into the gas measurement chamber 120.
The shielding layer 16 is formed on the surface of the diffusion resistance layer 14 opposite to the solid electrolyte body 11. The shielding layer 16 is made of alumina having electrical insulation and being dense and impermeable to gas.

  On the other hand, the heat generating portion 181 and the heat generating portion 181 are printed on the surface 112 of the solid electrolyte body 11 on the side where the reference electrode 13 is disposed through a dense reference gas chamber forming layer 17 made of alumina. A heater 18 including the formed heater substrate 182 is laminated. The heat generating portion 181 is for heating the gas sensor element 1 to the activation temperature by generating heat when energized.

  As shown in FIG. 5 and FIG. 6, the catalyst supporting layer 15 is configured to pass the gas to be measured on the outer surface 140 of the diffusion resistance layer 14 in the portion not facing the shielding layer 16 and the solid electrolyte body 11, that is, the diffusion resistance layer 14. It is formed on the gas introduction outer surface 140 to be introduced. In this example, the catalyst support layer 15 is formed with a film thickness of 150 μm. The film thickness d of the catalyst support layer 15 can be defined by the maximum value of the thickness of the catalyst support layer 15 in the direction perpendicular to the outer surface 140 of the diffusion resistance layer 14 (see FIG. 5).

  As shown in FIG. 6, the catalyst support layer 15 is composed of a porous layer made of ceramic particles 151 having θ-alumina as a main component and having an average particle diameter of 1 to 2 μm. A hydrogen selective oxidation catalyst 155 having an average particle size of 0.1 to 0.5 μm is supported on the catalyst support layer 15. In this example, the content of the hydrogen selective oxidation catalyst 155 in the catalyst support layer 15 is 50 wt%. As the hydrogen selective oxidation catalyst 155, the sample 1 of Example 1 was used.

The catalyst supporting layer 15 of this example is prepared by adding a binder to a mixed powder obtained by mixing the hydrogen selective oxidation catalyst of Sample 1 prepared in Example 1 and the θ-alumina powder at a weight ratio of 1: 1, It was formed by applying to the outer surface 140 of the diffusion resistance layer 14 and drying.
The gas sensor element having the above configuration is referred to as an element A.

Next, the sensor characteristics of the gas sensor element (element A) of this example were evaluated.
Specifically, first, the gas sensor element 1 was heated to a temperature of 700 ° C. by the built-in heater 18 (see FIG. 5). Next, exhaust gas model gas was supplied from the catalyst support layer 15 of the gas sensor element 1. At this time, a mixed gas containing N ₂ , CO, H ₂ , O ₂ , and C ₃ H ₈ was used as the model gas. In supplying the model gas, the flow rate of each component gas is adjusted to N ₂ : 2980 cc / min, CO: 58 cc / min, H ₂ : 12 cc / min, C ₃ H ₈ : 15 cc / min, and an air-fuel ratio ( The flow rate of O ₂ was adjusted between 25.7 and 171.3 cc / min so that the air / fuel ratio was 0.3 to 2.0. And the limiting current value output from a gas sensor element was measured. FIG. 7 shows the relationship between the O ₂ flow rate (air-fuel ratio) and the sensor output.
In the figure, the horizontal axis indicates the O ₂ flow rate (cc / min) and the air-fuel ratio (air / fuel), and the vertical axis indicates the sensor output (limit current value) (mA).

Further, in this example, for comparison with the element A, a gas sensor element using the sample 2 of Example 1 as a catalyst to be supported on the catalyst supporting layer was produced. This is element B. The element B has the same configuration as the element A except that the sample 2 is used instead of the sample 1.
For the element B, the relationship between the O ₂ flow rate (air-fuel ratio) and the sensor output was measured in the same manner as the element A. The result is shown in FIG.

In this example, as a comparison with the element A, a gas sensor element in which no catalyst was supported on the catalyst support layer was produced. This is element C. The element C has the same configuration as the element A except that the catalyst is not supported on the catalyst support layer. In the element C, the catalyst supporting layer is composed only of a porous layer made of ceramic particles whose main component is θ-alumina.
For the element C, the relationship between the O ₂ flow rate (air-fuel ratio) and the sensor output was measured in the same manner as the element A. The result is shown in FIG.

As is known from FIG. 7, in the gas sensor element of the element C in which the catalyst is not supported on the catalyst support layer, even if the supplied model gas has an air-fuel ratio λ of 1, the sensor output is negative and the air-fuel ratio is rich. It is shown that. On the other hand, in the element A and the element B in which the sample 1 made of SnO ₂ and the sample 2 made of LaFeO ₃ are supported on the catalyst supporting layer as catalysts, the sensor output is improved as compared with the element C. Output deviation (decrease in output) due to ₂ is suppressed.

In particular, in the device A using the sample 1 excellent in selective oxidation performance with respect to H ₂ , when the air-fuel ratio λ of the supplied model gas is about 1, the senna output shows 0, and the device B It can be seen that the output deviation is further suppressed as compared with that.

Thus, according to this example, it can be seen that by supporting the hydrogen selective oxidation catalyst made of SnO ₂ on the catalyst support layer, output deviation due to hydrogen can be suppressed and the detection performance of the gas sensor element can be improved.

DESCRIPTION OF SYMBOLS 1 Gas sensor element 11 Solid electrolyte 12 Measuring electrode 13 Reference electrode 14 Diffusion resistance layer 15 Catalyst support layer

Claims (8)

A hydrogen selective oxidation catalyst for selectively removing H ₂ by selectively reacting H ₂ and O ₂ from a mixed gas,
A hydrogen selective oxidation catalyst comprising SnO ₂ . 2. The hydrogen selective oxidation catalyst according to claim 1, wherein the mixed gas contains CO, HC, H ₂ , O ₂ , and NO. Layered on the surface of the solid electrolyte body, the measurement electrode and the reference electrode provided on one surface and the other surface of the solid electrolyte body, and the surface of the solid electrolyte body on which the measurement electrode is disposed A porous diffusion resistance layer that allows the gas to be measured to permeate and a porous catalyst support layer formed on the outer surface of the diffusion resistance layer,
The gas sensor element, wherein the catalyst support layer contains a hydrogen selective oxidation catalyst containing SnO ₂ .   4. The gas sensor element according to claim 3, wherein the catalyst supporting layer has a porous body made of alumina, and the hydrogen selective oxidation catalyst is supported on the porous body.   The gas sensor element according to claim 4, wherein the porous body is made of γ-alumina or θ-alumina.   6. The gas sensor element according to claim 4, wherein the content of the hydrogen selective oxidation catalyst in the catalyst support layer is 10% by mass or more.   7. The gas sensor element according to claim 3, wherein the catalyst support layer is formed with a thickness of 5 to 2000 μm.   The gas sensor element as described in any one of Claims 3-7 is used for an air fuel ratio sensor, The gas sensor element characterized by the above-mentioned.

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