JP2019211376A - Catalyst unit and breath sensor - Google Patents

Abstract

To provide a catalyst unit which can suppress adsorption of NOby the carrier of the catalyst.SOLUTION: The present invention relates to a catalyst unit for a breath sensor for measuring the concentration of Nox in the breath. The catalyst unit includes: a catalyst part for converting the NO in the breath into NO; a base part containing the catalyst part; and a heater having a heat transfer surface for heating the catalyst part. The catalyst part contains a catalyst in which a noble metal is carried by an H-type zeolite.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a catalyst unit and an expiration sensor.

As a sensor for measuring the concentration of NOx contained in exhaled breath, a sensor that detects NO ₂ by a sensor element after converting nitric oxide (NO) in exhaled breath into nitrogen dioxide (NO ₂ ) using a catalyst is known. .

  As the catalyst, a catalyst in which a noble metal such as platinum (Pt) is supported on zeolite is known (see Patent Document 1 and Patent Document 2).

US Pat. No. 6,765,591 Special table 2010-519514

In a conventional catalyst for a sensor, Na-type zeolite using sodium cation (Na ⁺ ) is used as a carrier. However, when Na-type zeolite is used as a carrier, NO ₂ converted from NO by the catalytic reaction is adsorbed by sodium contained in the Na-type zeolite.

For this reason, in the catalyst using Na-type zeolite, a part of NO ₂ converted from exhaled NO is adsorbed immediately after the exhaled air is introduced, so that the output of the sensor decreases. In addition, after the introduction of exhalation, a certain time is required until the output of the sensor is saturated.

An object of one aspect of the present disclosure is to provide a catalyst unit for an exhalation sensor that can suppress adsorption of NO ₂ by a carrier of the catalyst, and an exhalation sensor including such a catalyst unit.

One aspect of the present disclosure is a catalyst unit for an expiration sensor that measures the concentration of NOx contained in expiration. The catalyst unit includes a catalyst part that converts NO contained in exhaled air into NO ₂ , a base part in which the catalyst part is disposed, and a heater having a heat transfer surface that heats the catalyst part. The catalyst portion includes a catalyst in which a noble metal is supported on H-type zeolite.

According to such a configuration, adsorption of NO ₂ by the support can be suppressed by using H-type zeolite using proton (H ⁺ ) instead of Na-type zeolite as the support of the catalyst. As a result, a decrease in the output of the expiration sensor immediately after the introduction of expiration is suppressed. Moreover, the time until the output of the breath sensor is saturated is shortened.

Further, since the NO ₂ desorption temperature of the H-type zeolite is lower than the NO ₂ desorption temperature of the Na-type zeolite, the catalyst can be used at a lower heating temperature than when the Na-type zeolite is used. As a result, the ratio of NO ₂ / NO is increased by thermodynamic chemical equilibrium, so that the output of the breath sensor can be increased.

In one aspect of the present disclosure, the base portion may have an inner wall that constitutes an exhalation flow path. The catalyst part may be arranged in layers on the inner wall of the base part. According to such a configuration, since the exhaled air can be efficiently brought into contact with the catalyst portion, the NO ₂ / NO ratio after conversion can be further increased.

  In one aspect of the present disclosure, at least a part of the exhalation flow path in the base portion may extend along the heat transfer surface of the heater. According to such a structure, the catalyst part arrange | positioned at the inner wall of a base | substrate part can be heated efficiently.

  In one embodiment of the present disclosure, the H-type zeolite may have a Y-type crystal structure. According to such a configuration, the adhesion strength between the catalyst portion containing H-type zeolite and the base portion can be increased.

In one aspect of the present disclosure, the heating temperature of the catalyst portion by the heater may be 200 ° C. or more and 500 ° C. or less. According to such a configuration, it is possible to promote the catalytic reaction by the catalyst portion while increasing the NO ₂ / NO ratio.

Another aspect of the present disclosure is an exhalation sensor that measures the concentration of NOx contained in exhaled breath. The exhalation sensor includes the catalyst unit and a sensor element whose electrical characteristics change according to the concentration of NO ₂ in exhaled gas that has passed through the catalyst unit.

According to such a configuration, as described above, the adsorption of NO ₂ by the catalyst carrier can be suppressed, so that a decrease in the output of the expiration sensor immediately after the introduction of expiration is suppressed. Moreover, the time until the output of the breath sensor is saturated is shortened. Furthermore, since the NO ₂ / NO ratio increases due to thermodynamic chemical equilibrium, the output of the breath sensor can be increased.

It is a typical sectional view showing a gas sensor of an embodiment. It is typical sectional drawing which shows the catalyst unit of the gas sensor of FIG. It is a graph showing the relationship between the amount of released temperatures and NO ₂ in the Na-type zeolite and H-type zeolite. A gas containing NO ₂ is a graph showing temporal changes in the concentration of NO ₂ in the filter outlet when passed through a catalyst filter. It is a graph which shows the relationship between NO density | concentration of the gas supplied to the expiration sensor, and the output of an expiration sensor.

Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings.
[1. First Embodiment]
[1-1. Constitution]
The breath sensor 1 shown in FIG. 1 is a gas sensor for measuring the concentration of nitrogen oxide (NOx) contained in the breath G.

The exhalation sensor 1 can be suitably used particularly for measurement of exhalation including NOx (specifically NO) having an extremely low concentration of several ppb to several hundreds of ppb, specifically for asthma diagnosis.
As shown in FIG. 1, the breath sensor 1 includes a catalyst unit 2, a sensor unit 3, and three pipes 6, 7, and 8.

<Catalyst unit>
As shown in FIG. 2, the catalyst unit 2 includes a base portion 2A, a catalyst portion 2C, a sheet body 2D, and a heater 5.

(Base part)
The base portion 2A is a box-shaped member having an inner wall 2B that constitutes a flow path of the exhalation G. The base portion 2A is an integral product mainly composed of ceramic. Here, the “main component” means a component contained by 80% by mass or more. In the present embodiment, alumina (Al ₂ O ₃ ) is used as the ceramic constituting the base portion 2A. The ceramic constituting the base portion 2A is not limited to alumina, and aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), zirconium oxide (ZrO ₂ ), or the like may be used.

  Specifically, the base portion 2A is a fired body that is integrally fired in a state where three or more unsintered sheets (so-called ceramic green sheets) mainly composed of ceramic are stacked. In other words, the base portion 2A has a configuration in which three or more unsintered sheets (ceramic green sheets) are fired at the same time in a state of being overlaid. Some of the plurality of sheets constituting the base portion 2A are each provided with an opening. The inner wall 2B of the base portion 2A is configured by the inner surfaces of the plurality of openings being continuous.

  The base portion 2A is fixed to the surface of a sensor carrier 3B of the sensor unit 3 described later by an adhesive portion 2E. The base portion 2A is disposed at a position facing a heater 5 described later with the sensor carrier 3B interposed therebetween. In addition, as the bonding part 2E, an inorganic adhesive or glass can be used.

  The base portion 2 </ b> A has an exhalation G flow path 10 configured such that the exhalation G introduced from the first pipe 6 is discharged from the second pipe 7. The inner wall 2B constituting the flow path 10 of the exhalation G has a plurality of detour walls 12A and 12B for detouring the exhalation G flowing from the gas introduction position 10A to the gas discharge position 10B of the flow path 10 to lengthen the flow path 10. , 12C, 12D, 12E, 12F, 12G, 12H, and 12I.

  As a result, the exhalation G flowing from the gas introduction position 10A toward the gas discharge position 10B bypasses without flowing at the shortest distance from the gas introduction position 10A to the gas discharge position 10B due to the presence of the detour walls 12A-12I. become.

  The flow path 10 constituted by the inner wall 2B including the bypass walls 12A-12I is directed from the first pipe 6 toward the heater 5 along the sheet stacking direction (that is, the direction perpendicular to the surface of the sensor carrier 3B). Branching into multiple branches connected in parallel. The plurality of tributaries extend along the heat transfer surface 5 </ b> A of the heater 5. Further, in the flow path 10, a plurality of tributaries are merged at a portion extending toward the second pipe 7 so as to be separated from the heater 5 along the sheet stacking direction.

(Catalyst part)
The catalyst unit 2C chemically changes the components contained in the exhalation G. The chemical change by the catalyst unit 2C includes converting a certain component into another component and burning a certain component. Specifically, the catalyst unit 2C converts the NO contained in the exhaled G to NO _2, combusting components exhalation sensor 1 does not measure the concentration (i.e. miscellaneous gas component). In the case of asthma diagnosis, the catalyst unit 2C burns a small amount of miscellaneous gas components contained in the exhaled breath G, such as CO, H ₂ , and VOC.

  The catalyst part 2C includes a catalyst in which a noble metal is supported on H-type zeolite. “H-type zeolite” is a zeolite in which more than half of the total number of cations introduced into the zeolite are protons.

The crystal structure of the H-type zeolite can be Y-type, ZSM-5 type, or β-type. Among these, Y type is preferable. Y-type zeolite has high adhesion strength with the base 2A. Therefore, by using Y-type zeolite, the catalyst portion 2C can be brought into close contact with the base portion 2A at a relatively low temperature, which is advantageous from the viewpoint of productivity and suppression of catalyst deterioration. Examples of the H-type zeolite having a Y-type crystal structure include “320HOA” manufactured by Tosoh Corporation.

  Examples of the noble metal supported on the H-type zeolite include platinum, rhodium, palladium, and gold. The amount of noble metal supported is, for example, 2% by mass or more and 15% by mass or less with respect to 100% by mass of the H-type zeolite.

Figure 3 is a catalyst supported platinum on H-type zeolites, adsorbed to saturation NO ₂ in the catalyst supported platinum to Na zeolite, then the amount of released NO ₂ when the catalyst was heated Represents. In FIG. 3, the solid line is test data using H-type zeolite, and the broken line is test data using Na-type zeolite.

As shown in FIG. 3, the catalyst using Na-type zeolite needs to be heated to 400 ° C. or higher in order to sufficiently desorb NO ₂ . On the other hand, with a catalyst using H-type zeolite, NO ₂ can be desorbed at 340 ° C. or lower.

  As shown in FIG. 2, the catalyst part 2C is arranged in layers on the inner wall 2B of the base part 2A. In the present embodiment, the entire surface of the inner wall 2B of the base portion 2A is covered with the catalyst portion 2C. That is, the catalyst portion 2C forms a layer that covers the inner surface of the flow path 10 in the base portion 2A. In addition, in the flow path 10 in the base 2A, there may be a portion that is not covered with the catalyst 2C.

  The catalyst part 2C can be formed, for example, by the following procedure. First, a noble metal is supported on zeolite powder to obtain a catalyst powder. As a method for supporting the noble metal, an ion exchange method, an impregnation method or the like can be used.

  Next, this catalyst powder is mixed with a binder to obtain a catalyst paste. This catalyst paste is attached to the inner wall 2B of the base portion 2A by dipping to form a catalyst film. The catalyst part 2C is obtained by baking this catalyst film.

  The baking conditions can be selected according to the heat resistance of the catalyst and the required adhesion strength, and are, for example, 500 ° C. or higher and 800 ° C. or lower in an air atmosphere. If the baking temperature is too high, the noble metal particles may aggregate and the function of the catalyst may be reduced. If the baking temperature is too low, the adhesion strength to the base portion 2A will be low, and the catalyst portion 2C may be easily peeled when subjected to an impact.

  Alternatively, a catalyst paste may be printed on each ceramic green sheet constituting the base portion 2A to form a catalyst film, and the catalyst film may be fired together with a plurality of laminated ceramic green sheets.

(Sheet body)
The sheet body 2D is a sheet mainly composed of ceramic. The sheet body 2D is provided with a first opening 2F and a second opening 2G. A first pipe 6 is connected to the first opening 2F, and a second pipe 7 is connected to the second opening 2G.

  The sheet body 2D is bonded to the surface of the base portion 2A by the bonding portion 2H. The sheet body 2D is disposed so that the first opening 2F and the second opening 2G communicate with the flow path 10 of the base portion 2A.

In the present embodiment, alumina (Al ₂ O ₃ ) is used as the ceramic constituting the sheet body 2D.
Is used. The ceramic constituting the sheet body 2D is not limited to alumina, and aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), zirconium oxide (ZrO ₂ ), or the like may be used.

  The ceramic material constituting the sheet body 2D is preferably the same as the ceramic material constituting the base portion 2A. When the base part 2A and the sheet body 2D are made of the same material, the base part 2A and the sheet body 2D have the same coefficient of thermal expansion, and thus the base part 2A and the sheet body 2D are repeatedly heated and cooled. In addition, it is possible to suppress the sheet body 2D from being detached from the base portion 2A. The same adhesive part 2H as the adhesive part 2E can be used.

  The exhaled gas G introduced from the gas introduction position 10A into the base body 2A through the first opening 2F of the sheet body 2D from the first pipe 6 passes through the flow path 10 while being in contact with the catalyst part 2C, and the gas discharge position 10B and the second opening 2G of the sheet body 2D are discharged to the second pipe 7.

(heater)
The heater 5 heats the catalyst unit 2C and the sensor unit 3 simultaneously. In this embodiment, the heater 5 is arrange | positioned in the sensor element 3A, as shown in FIG. By disposing the heater 5 in the sensor element 3A, it is possible to control the temperature of the sensor element 3A that needs to be controlled with higher accuracy and higher temperature than the catalyst unit 2C. In addition, when the resistance element for temperature measurement is provided in the sensor element 3A, the temperature control of the sensor element 3A is made highly accurate by performing energization control of the heater 5 using the output from the resistance temperature detector. It is also possible to do.

  The heater 5 is configured by metal wiring (that is, load resistance) such as platinum. The heater 5 is electrically connected to the wiring formed on the sensor carrier 3B by bonding or the like, and generates heat when electric power is supplied from the outside.

  The heater 5 has a heat transfer surface 5A configured to heat the catalyst unit 2C and the sensor unit 3. The “heat transfer surface” is, for example, the surface of the base material on which the metal wiring constituting the heater 5 is arranged. Further, as shown in FIG. 2, the heater 5 is disposed on the opposite side to the sheet body 2D with the base portion 2A interposed therebetween.

  As described above, a part of the flow path 10 in the base portion 2A (that is, a plurality of branch portions after branching) is along the heat transfer surface 5A of the heater 5 (that is, in a direction parallel to the heat transfer surface 5A). ) Stretched.

  Further, the flow path 10 in the base portion 2A is provided at a position overlapping the heater 5 when viewed from the direction perpendicular to the heat transfer surface 5A of the heater 5 (that is, the heat transfer direction with respect to the base portion 2A). Therefore, the catalyst part 2C can be efficiently heated.

The heating temperature of the catalyst part 2C by the heater 5 is preferably 200 ° C. or higher and 500 ° C. or lower. If the heating temperature is too high, the ratio of NO ₂ / NO becomes small and the output of the breath sensor 1 may be reduced. If the heating temperature is too low, the catalyst may not function sufficiently.

  In the present embodiment, since the catalyst unit 2C and the sensor unit 3 can be simultaneously heated by one heater 5, the power consumption of the breath sensor 1 can be reduced. Moreover, the structure of the breath sensor 1 can be simplified.

<Sensor unit>
As shown in FIG. 1, the sensor unit 3 includes a sensor element 3A whose electrical characteristics change according to the concentration of NO ₂ in the exhaled gas G that has passed through the catalyst unit 2, and a sensor carrier 3B that houses the sensor element 3A. And a cap 3C.

  The sensor element 3A has a mixed potential type detection body, and the detection body is mounted on a base substrate made of ceramic. The sensor element 3A may further include a temperature measuring resistor. The hybrid potential type detector is well known and will not be described in detail. For example, it has a solid electrolyte body made of zirconia and electrodes made of different materials, and the potential difference (that is, electromotive force) between these electrodes is determined. It has the structure which outputs as a sensor signal. The detector and the temperature measuring resistor are electrically connected to the wiring formed on the sensor carrier 3B by bonding or the like, and are connected to an external circuit (not shown).

  Note that the detection element of the sensor element 3A is not limited to this, and a detection element made of a metal oxide semiconductor whose resistance is changed by the presence of a gas component to be detected, or a capacitance change type detection element is used. May be.

The output of the sensor element 3 </ _b > A varies according to the NO ₂ concentration in the exhaled breath G in which the electrical characteristics of the sensor element 3 </ _b > A (for example, an electromotive force in the case of a hybrid potential type detector) have passed through the catalyst unit 2. Since the NO ₂ / NO ratio in the exhaled gas G that has passed through the catalyst unit 2 becomes a constant value based on the thermodynamic chemical equilibrium, the total amount of NOx in the exhaled gas G can be measured based on the output of the sensor element 3A. Note that the total amount of NOx in the exhalation G can be measured by calculating with an external circuit (not shown) to which the output of the sensor element 3A is input.

  The sensor carrier 3B, together with the cap 3C, constitutes a casing that houses the sensor element 3A. The sensor element 3A is bonded to the bottom surface surrounded by the side wall of the sensor carrier 3B by the bonding portion 3D.

Further, as described above, the base portion 2A of the catalyst unit 2 is fixed to the surface of the sensor carrier 3B opposite to the bottom surface where the sensor element 3A is disposed.
In the present embodiment, the heater 5 is integrated with the sensor element 3A, and the heater 5 is bonded to the sensor carrier 3B.

  The cap 3C is disposed so as to face the sensor element 3A, and is bonded to the side wall of the sensor carrier 3B by an adhesive portion 3E. A space for storing the sensor element 3A is defined by the cap 3C and the sensor carrier 3B.

  The cap 3C is provided with two openings, and the second pipe 7 and the third pipe 8 are connected to these openings. The exhalation G introduced into the sensor unit 3 from the second pipe 7 is discharged from the third pipe 8 to the outside of the sensor unit 3 (specifically, outside the exhalation sensor 1 system) while contacting the sensor element 3A. The

The sensor carrier 3B is made of a material whose main component is ceramic. In the present embodiment, alumina (Al ₂ O ₃ ) is used as the ceramic constituting the sensor carrier 3B. The ceramic constituting the sensor carrier 3B is not limited to alumina, and aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), zirconium oxide (ZrO ₂ ), or the like may be used.

  The ceramic material constituting the sensor carrier 3B is preferably the same as the ceramic material constituting the base portion 2A. When the base 2A and the sensor carrier 3B are made of the same material, the base 2A and the sensor carrier 3B have the same coefficient of thermal expansion, and thus the base 2A and the sensor carrier 3B are repeatedly heated and cooled. In addition, the separation of the sensor carrier 3B from the base portion 2A can be suppressed.

  The cap 3C may be made of a metal material such as aluminum or stainless steel (SUS), or may be made of a material mainly composed of ceramic such as alumina. Further, the same bonding parts 3D and 3E as the bonding part 2E can be used.

<Piping>
The first pipe 6 supplies exhalation G to the catalyst unit 2. The second pipe 7 supplies the expiratory gas G that has passed through the catalyst unit 2 into the sensor unit 3. The third pipe 8 discharges the exhaled breath G in the sensor unit 3.

[1-2. effect]
According to the embodiment detailed above, the following effects can be obtained.
(1a) Adsorption of NO ₂ by the carrier can be suppressed by using H-type zeolite using protons as a catalyst carrier instead of Na-type zeolite. As a result, a decrease in the output of the expiration sensor 1 immediately after the introduction of the expiration G is suppressed. Further, the time until the output of the breath sensor 1 is saturated is shortened.

(1b) Since the NO ₂ desorption temperature of H-type zeolite is lower than the NO ₂ desorption temperature of Na-type zeolite, the catalyst can be used at a lower heating temperature than when Na-type zeolite is used. As a result, the ratio of NO ₂ / NO is increased due to thermodynamic chemical equilibrium, so that the output of the breath sensor 1 can be increased.

  Furthermore, since the catalyst can be used at a temperature lower than that of a sensor using Na-type zeolite, the sensor structure and the selection range of constituent members are widened. As a result, the breath sensor 1 can be reduced in size and cost.

(1c) Since the catalyst part 2C is arranged in layers on the inner wall 2B of the base part 2A, the exhalation G can be efficiently brought into contact with the catalyst part 2C. As a result, the ratio of NO ₂ / NO after conversion can be further increased.

  (1d) At least a part of the flow path 10 of the exhalation G in the base 2A extends along the heat transfer surface 5A of the heater 5 so that the catalyst 2C disposed on the inner wall 2B of the base 2A is efficiently heated. can do.

[2. Other Embodiments]
As mentioned above, although embodiment of this indication was described, it cannot be overemphasized that this indication can take various forms, without being limited to the above-mentioned embodiment.

  (2a) The structure of the base 2A in the breath sensor 1 of the above embodiment is an example. The shape of the base portion 2A is not limited as long as the catalyst portion 2C can be held inside. For example, the flow path 10 constituted by the inner wall 2B of the base portion 2A does not necessarily have to be branched into a plurality of tributaries. Further, the flow path 10 may have a zigzag shape.

  Furthermore, the base 2A does not necessarily have to have the inner wall 2B that constitutes the flow path 10 of the exhalation G, and the inside may be a cavity. Moreover, the catalyst part 2C does not necessarily need to be layered, and may be a block body.

  Further, the sheet body 2D is not an essential component for the present disclosure, and can be omitted. That is, you may connect the 1st piping 6 and the 2nd piping 7 directly to the opening which comprises the gas introduction position 10A of the base | substrate part 2A, and the opening which comprises the gas discharge position 10B.

  (2b) In the breath sensor 1 of the above embodiment, the heater 5 is not necessarily integrated with the sensor element 3A. For example, the heater 5 may be disposed inside the sensor carrier 3B. Moreover, the heater 5 may be arrange | positioned on the surface facing the sensor carrier 3B in the base | substrate part 2A. Further, the heater 5 may be disposed on the surface of the sensor carrier 3B facing the sensor element 3A, the surface of the sensor carrier 3B facing the base portion 2A, the inside of the base portion 2A, or the like.

  The breath sensor 1 may include a plurality of heaters 5 for heating the catalyst part 2C, a first heater for heating the catalyst part 2C, and a second heater for heating the sensor element 3A. And may be provided.

  (2c) The functions of one component in the above embodiment may be distributed as a plurality of components, or the functions of a plurality of components may be integrated into one component. Moreover, you may abbreviate | omit a part of structure of the said embodiment. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

[3. Example]
Below, the content of the test conducted in order to confirm the effect of this indication and its evaluation are demonstrated.

<Example>
Using an ion exchange method, 9.2% by mass of platinum was supported on an H-type zeolite having a crystal structure of Y-type (“320HOA” manufactured by Tosoh Corporation) with respect to the H-type zeolite to obtain a catalyst powder. Note that Pt (NH ₃ ) ₄ Cl ₂ powder was used as a raw material for platinum.

  The catalyst powder was mixed with a binder prepared by dissolving ethosel with butyl carbitol and kneaded to prepare a catalyst paste. This catalyst paste was attached to the inner wall 2B of the base 2A shown in FIG. 2 by dipping, thereby forming a catalyst film. The catalyst film was baked at 600 ° C. in an air atmosphere to form the catalyst part 2C in the base part 2A, thereby obtaining the catalyst filter of the example.

<Comparative example>
A catalyst filter of a comparative example was obtained in the same procedure as in the example except that Na type zeolite was used instead of H type zeolite.

<Test 1>
In each of the catalyst filters of Examples and Comparative Examples, the NO ₂ concentration at the catalyst filter outlet when a test gas containing NO was supplied into the catalyst filter was measured by a NOx analyzer. The result is shown in FIG. The solid line in FIG. 4 is an example, and the broken line is a comparative example. A test gas having a gas composition of 200 ppb NO, 16% oxygen, and the balance nitrogen was used, and the test gas was supplied to the catalyst filter at a flow rate of 50 cc / min. In this test, the test gas is supplied to the catalyst filter 50 seconds after the start of measurement, and the atmosphere (oxygen concentration 21%) is supplied to the catalyst filter before the test gas is supplied.

In the catalyst filter, the function of converting NO into NO ₂ is exhibited. As shown in FIG. 4, in the example using H-type zeolite, the NO ₂ concentration is around 150 ppb, compared with the comparative example using Na-type zeolite. Rose quickly. In this test, the test gas is supplied 50 seconds after the start of measurement.

<Test 2>
The catalyst filter of the example and the comparative example is incorporated in the breath sensor 1 of FIG. The amount of change was measured. The result is shown in FIG. The solid line in FIG. 5 is an example, and the broken line is a comparative example. In addition, as for components other than NO of each test gas, oxygen is 16% and the balance is nitrogen. In addition, before supplying the test gas, the atmosphere is supplied to the breath sensor. Further, the change amount of the sensor output in FIG. 5 is a value based on the sensor output when the atmosphere is supplied to the breath sensor (that is, 0 mV).

As shown in FIG. 5, in the example using H-type zeolite, a higher sensor output was obtained than in the comparative example using Na-type zeolite. That is, in the example, the adsorption of NO ₂ by the carrier was suppressed, and the concentration of NO ₂ reaching the sensor element increased rapidly.

  In FIG. 5, the output is negative when the NO concentration is low because the oxygen concentration (16%) of the test gas is lower than the oxygen concentration (21%) in the atmosphere. is there.

DESCRIPTION OF SYMBOLS 1 ... Exhalation sensor, 2 ... Catalyst unit, 2A ... Base | substrate part, 2B ... Inner wall, 2C ... Catalyst part,
2D ... sheet body, 2E ... bonding part, 2F ... first opening, 2G ... second opening, 2H ... bonding part,
3 ... Sensor unit, 3A ... Sensor element, 3B ... Sensor carrier, 3C ... Cap,
3D: Adhering part, 3E ... Adhering part, 5 ... Heater, 5A ... Heat transfer surface, 6 ... First piping,
7 ... 2nd piping, 8 ... 3rd piping, 10 ... flow path, 12A-12I ... detour wall.

Claims (6)

A catalyst unit for an exhalation sensor that measures the concentration of NOx contained in exhalation,
A catalyst part for converting NO contained in the exhalation into NO ₂ ;
A base portion in which the catalyst portion is disposed;
A heater having a heat transfer surface for heating the catalyst unit;
With
The catalyst unit includes a catalyst in which a noble metal is supported on H-type zeolite. The base portion has an inner wall that constitutes the flow path of the breath,
The catalyst unit according to claim 1, wherein the catalyst part is arranged in a layered manner on the inner wall of the base part.   The catalyst unit according to claim 2, wherein at least a part of the flow path of the exhalation in the base portion extends along the heat transfer surface of the heater.   The catalyst unit according to any one of claims 1 to 3, wherein the H-type zeolite has a Y-type crystal structure.   The catalyst unit according to any one of claims 1 to 4, wherein a heating temperature of the catalyst portion by the heater is 200 ° C or higher and 500 ° C or lower. An exhalation sensor that measures the concentration of NOx contained in exhalation,
The catalyst unit according to any one of claims 1 to 5,
A sensor element whose electrical characteristics change according to the concentration of NO _{2 in} the exhaled air that has passed through the catalyst unit;
A breath sensor.