JP2018054593A - Gas sensor and gas detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor or gas detection device, which offers enhanced catalytic site performance and improved sensitivity to both methane and carbon monoxide.SOLUTION: A gas detection device 100 comprises a gas detection layer 10, a catalytic layer 11, a heater layer 6, a heating controller 12 that energizes the heater layer 6, and a gas detection unit 13 configured to measure a property of the gas detection layer 10 to detect a detection target gas. The heating controller 12 is configured to perform a first heating operation for heating the heater layer to first temperature for carbon monoxide detection and a second heating operation for heating the heater layer to second temperature that is higher than the first temperature. The catalytic layer 11 consists of a catalytic support for carrying a catalytic metal which includes at least one substance selected from the group comprising palladium, iridium, platinum, and rhodium. The catalytic support is principally made of a transition metal oxide.SELECTED DRAWING: Figure 1

Description

  The present invention includes a gas detection portion whose characteristics change by contact with the detection target gas, a catalyst portion provided to cover at least a part of the gas detection portion, and a heater portion that heats the gas detection portion and the catalyst portion. The present invention relates to a gas detection device including a gas sensor, the above-described gas sensor, a heating control unit that controls heating by a heater part, and a gas detection part that measures a characteristic of the gas detection part and detects a detection target gas.

  In such a gas detection device, the heating control unit controls the heating by the heater part, thereby heating the gas detection part to an appropriate temperature according to the type of the detection target gas and maintaining this temperature. The detection target gas is detected on the basis of the characteristics (electric resistance value, voltage value, etc.) of the gas detection part.

In the gas detection device of Patent Document 1, a sintered material in which Pd (palladium) is supported on Al ₂ O ₃ (alumina) as a catalyst is used as a catalyst portion. The catalyst part is heated to a high temperature by the heater part and burns reducing gases such as CO (carbon monoxide) and H ₂ (hydrogen) and other miscellaneous gases, and is inert CH ₄ (methane), C ₃ H. ₈ Permeate and diffuse combustible gas such as (propane) to reach the gas detection site. Thus, CH ₄ (methane), the detection accuracy of the combustible gas, such as C ₃ H ₈ (propane) is enhanced. And a gas detection device hold | maintains a heater site | part at high temperature (400-500 degreeC), detects combustible gas, such as methane, hold | maintains at low temperature (about 100-200 degreeC), and detects CO, so-called combustibility. It can also be operated as a gas (eg methane) / CO one sensor.

JP 2013-190232 A

  When the above-described combustible gas / CO one sensor detection is performed, by burning hydrogen, CO, alcohol, etc. other than the combustible gas that is the detection target gas at a high temperature and allowing the combustible gas to permeate without being burned. It is supposed to detect flammable gas selectively. At a low temperature, the catalyst site detects CO by allowing it to permeate without burning CO. However, the inventors conducted experiments on the above-mentioned materials that are generally used as catalyst sites. As a result, alumina supporting Pd does not sufficiently suppress the combustion removal activity of flammable gas at high temperature and CO at low temperature. It has been found that the concentration of methane and carbon monoxide reaching the gas detection unit decreases and gas sensitivity decreases, so that it is not necessarily an optimal material for realizing the combustible gas / CO one sensor detection.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to improve the performance of the catalytic site, optimize the temperature dependence of the reactivity at both the catalytic site of the combustible gas and CO, and An object of the present invention is to provide a gas detection device having improved sensitivity and selectivity at both detection temperatures of CO and CO.

<Configuration 1>
The characteristic configuration of the gas detection device for achieving the above object is as follows:
A gas detection region whose characteristics change due to contact with the detection target gas;
A catalyst portion provided to cover at least a part of the gas detection portion;
A heater part for heating the gas detection part and the catalyst part;
A heating control unit for controlling heating by the heater part;
A gas detection device having a gas detection unit that detects a gas to be detected by measuring characteristics of the gas detection site;
The heating controller is
A first heating operation for controlling heating by the heater part to heat the gas detection part and the catalyst part to a first temperature for detecting carbon monoxide;
A second heating operation for controlling the heating by the heater part to heat the gas detection part and the catalyst part to a second temperature higher than the first temperature;
The catalyst portion is configured by supporting a catalyst metal on a carrier, the catalyst metal includes at least one substance selected from the group consisting of palladium, iridium, platinum and rhodium, and the main component of the carrier is transitioned It is a metal oxide.

The inventors of the present invention have used methane as a sintered material (Pd / alumina), which is conventionally used as a catalyst part and has Pd (palladium) as a catalyst supported on a support mainly composed of Al ₂ O ₃ (alumina). (Example of combustible gas) and reactivity with CO were confirmed by experiments. Then, it was found that the reaction rate with methane becomes a high value of 85 to 88% regardless of humidity at 400 ° C. corresponding to the detection temperature of methane which is a combustible gas in the combustible gas / CO one sensor. That is, at 400 ° C., 85 to 88% of the methane that has reached the gas detection device burns at the catalytic site, and only 12 to 15% of the methane reaches the gas detection site, contributing to methane detection. It is. On the other hand, it was found that at 150 ° C. corresponding to the CO detection temperature, the reaction rate with CO varies from 42 to 85% depending on the humidity, and becomes a high value of 85% in high humidity. That is, most of Pd / alumina reacts at the catalytic site at the detection temperature of methane and CO in the methane / CO one sensor, particularly in high humidity. Also, the CO reaction rate varies greatly with humidity.

  Therefore, the inventors examined various substances as materials for the catalytic site. When at least one substance selected from the group consisting of palladium, iridium, platinum and rhodium is used as the catalyst metal, selectivity for each gas by the catalytic site at the detection temperature of combustible gas and CO (gas to be detected) It has been found that the reactivity of other gases increases. Then, the present invention has been completed using a transition metal oxide as a support for the catalyst site and using at least one substance selected from the group consisting of palladium, iridium, platinum and rhodium as the catalyst metal.

<Configuration 2>
That is, according to the above characteristic configuration, the catalytic site is configured by supporting a catalytic metal on a support, and the catalytic metal includes at least one substance selected from the group consisting of palladium, iridium, platinum, and rhodium. To increase the selectivity of carbon monoxide at the first temperature (for detecting carbon monoxide) and the selectivity of the flammable gas at the second temperature (for detecting flammable gas) at the catalytic site. Therefore, the selectivity of the gas detection device at each detection temperature of carbon monoxide and combustible gas can be improved. If the catalyst metal contains at least two substances selected from the group consisting of palladium, iridium, platinum and rhodium, it will be possible to pursue higher levels of selectivity for both carbon monoxide and combustible gases. It is more preferable because the control of the property becomes easy.

<Configuration 3>
Another characteristic configuration of the gas detector according to the present invention is that the catalyst metal is a mixture containing iridium and platinum, the iridium content in the catalyst site is 0.3 mass% or more, and the platinum content is It exists in the point which is 0.3 mass% or more.

  According to said characteristic structure, a catalyst metal is a mixture containing iridium and platinum, the iridium content rate in a catalyst part is 0.3 mass% or more, and the platinum content rate is 0.3 mass% or more. By this, compared with the conventional palladium catalyst, the gas detection apparatus with high selectivity which improved the selectivity (reactivity of gas other than detection object gas) of the combustible gas and CO in the detection of combustible gas or CO is provided. be able to.

<Configuration 4>
Another characteristic configuration of the gas detection device according to the present invention is that the catalyst metal is a mixture containing iridium and platinum, and the iridium content in the catalyst site is 0.01% by mass or more and 5% by mass or less. The content of is in the range of 0.01 mass% to 7 mass%.

  According to the above characteristic configuration, the catalyst metal is a mixture containing iridium and platinum, the iridium content in the catalytic site is 0.01% by mass or more and 5% by mass or less, and the platinum content is 0.01% by mass. % Or more and 7% by mass or less can reduce the CO combustion removal reactivity at the catalyst site at the time of CO detection and the methane combustion removal reactivity at the catalyst site at the time of methane detection compared with the conventional palladium catalyst. . Therefore, the sensitivity with respect to both methane and CO can be improved, and a highly sensitive gas detection apparatus can be provided. Note that the sensitivity of methane and CO is higher than before under various conditions in which the carrier is zirconium oxide, the iridium content is 0.5 to 3% by mass, and the platinum content is 0.5 to 5% by mass. This has been confirmed by experiments.

<Configuration 5>
Another characteristic configuration of the gas detector according to the present invention is that the catalyst metal is a mixture containing palladium and platinum, the palladium content in the catalyst site is 0.3% by mass or more, and the platinum content is It exists in the point which is 0.3 mass% or more.

  According to said characteristic structure, a catalyst metal is a mixture containing palladium and platinum, the content rate of palladium in a catalyst part is 0.3 mass% or more, and the content rate of platinum is 0.3 mass% or more. By this, compared with the conventional palladium catalyst, the gas detection apparatus with high selectivity which improved the selectivity (reactivity of gas other than detection object gas) of the combustible gas and CO in the detection of combustible gas or CO is provided. be able to.

<Configuration 6>
Another characteristic configuration of the gas detection device according to the present invention is that the catalyst metal is a mixture containing palladium and platinum, and the content of palladium in the catalyst portion is 0.01% by mass or more and 5% by mass or less. The content of is in the range of 0.01 mass% to 7 mass%.

  According to the above characteristic configuration, the catalyst metal is a mixture containing palladium and platinum, the palladium content in the catalyst site is 0.01% by mass or more and 5% by mass or less, and the platinum content is 0.01% by mass. % Or more and 7% by mass or less can reduce the CO combustion removal reactivity at the catalyst site at the time of CO detection and the methane combustion removal reactivity at the catalyst site at the time of methane detection compared with the conventional palladium catalyst. . Therefore, the sensitivity with respect to both methane and CO can be improved, and a highly sensitive gas detection apparatus can be provided. Note that the reactivity of methane and CO was significantly higher than before under various conditions where the support was zirconium oxide, the palladium content was 0.5-3 mass%, and the platinum content was 0.5-2 mass%. It has been confirmed by experiments that the value is low.

<Configuration 7>
Another characteristic configuration of the gas detector according to the present invention is a mixture in which the catalytic metal contains palladium and iridium, a palladium content in the catalytic site is 0.3 mass% or more, and an iridium content is It exists in the point which is 0.3 mass% or more.

  According to said characteristic structure, a catalyst metal is a mixture containing palladium and iridium, the content rate of palladium in a catalyst part is 0.3 mass% or more, and the content rate of iridium is 0.3 mass% or more. By this, compared with the conventional palladium catalyst, the gas detection apparatus with high selectivity which improved the selectivity (reactivity of gas other than detection object gas) of the combustible gas and CO in the detection of combustible gas or CO is provided. be able to.

<Configuration 8>
Another characteristic configuration of the gas detector according to the present invention is a mixture in which the catalytic metal contains palladium and iridium, and the palladium content in the catalytic site is 0.01% by mass or more and 5% by mass or less, and iridium The content of is in the range of 0.01 mass% or more and 5 mass% or less.

  According to the above characteristic configuration, the catalyst metal is a mixture containing palladium and iridium, the palladium content in the catalytic site is 0.01% by mass or more and 5% by mass or less, and the iridium content is 0.01% by mass. % Or more and 5% by mass or less can reduce the CO combustion removal reactivity at the catalyst site at the time of CO detection and the methane combustion removal reactivity at the catalyst site at the time of methane detection, as compared with the conventional palladium catalyst. . Therefore, the sensitivity with respect to both methane and CO can be improved, and a highly sensitive gas detection apparatus can be provided. It should be noted that the reactivity of methane and CO may be significantly lower than in the past under a plurality of conditions in which the support is zirconium oxide, the palladium content is 1 to 3% by mass, and the iridium content is 1 to 2% by mass. It has been confirmed by experiments.

<Configuration 9>
Another characteristic configuration of the gas detection device according to the present invention is that the catalyst metal includes one or more metals selected from the group consisting of palladium, platinum, and iridium, and the content of the metal in the catalyst site. The total is 0.3% by mass or more.

  The inventor diligently examined and experimented on the composition of the catalyst metal, and according to the catalyst metal according to the above-described configuration, selectivity for the detection target gas at the time of detecting methane and CO (reactivity of gases other than the detection target gas) It was found that it can be improved. According to said characteristic structure, combustion removal reactivity of gas other than the detection target gas at the time of methane and CO detection can be improved by making content of the said metal into 0.3 mass% or more. For this reason, the selectivity of the detection object gas at the time of methane and CO detection can be improved.

<Configuration 10>
Another characteristic configuration of the gas detection device according to the present invention is that the catalyst metal includes one or more metals selected from the group consisting of palladium, platinum, and iridium, and the content of the metal in the catalyst site. It exists in the point whose sum total is 0.01 mass% or more and 6 mass% or less.

  The inventor diligently studied and experimented on the composition of the catalyst metal, and according to the catalyst metal according to the above-described configuration, the sensitivity of the gas detection device with respect to methane at the time of methane detection and carbon monoxide at the time of carbon monoxide detection has been improved. Also found that it can be enhanced. According to the above characteristic configuration, by setting the noble metal content to be 0.01% by mass or more and 6% by mass or less, the methane combustion removal reaction rate in the catalyst site at the time of methane detection and the catalyst site at the time of carbon monoxide detection The combustion removal reaction rate of carbon monoxide in can be reduced. For this reason, the methane sensitivity at the time of methane detection and the carbon monoxide sensitivity at the time of carbon monoxide detection can be improved conventionally.

<Configuration 11>
Another characteristic configuration of the gas detection device according to the present invention is that the platinum content in the catalyst portion is 0.3% by mass or more.

  It has been found that the selectivity of the detection target gas at the time of detecting methane and CO can also be increased by setting the platinum content to 0.3 mass% or more. According to said characteristic structure, the combustion removal reactivity of gas other than the detection target gas at the time of methane and CO detection can be improved. For this reason, the selectivity of the detection object gas at the time of methane and CO detection can be improved.

<Configuration 12>
Another characteristic configuration of the gas detector according to the present invention is that the platinum content in the catalyst portion is 0.01% by mass or more and 6% by mass or less.

  The inventors have diligently studied and experimented on the composition of the catalyst metal, and found that the sensitivity of the gas detection device for methane during methane detection can be improved by making the platinum content 6% by mass or less. It was. According to said characteristic structure, the combustion removal reaction rate of the methane in the catalyst site | part at the time of methane detection can be reduced by making platinum content into 6 mass% or less. For this reason, the methane sensitivity at the time of methane detection can be raised.

<Configuration 13>
Another characteristic configuration of the gas detector according to the present invention is that the total content of platinum and iridium is 0.3% by mass or more.

  The inventors have studied and experimented on the composition of the catalyst metal, and according to the catalyst metal according to the above-described configuration, even when the total content of platinum and iridium is 0.3% by mass or more, methane and CO It was found that the selectivity of the detection target gas at the time of detection can be enhanced. According to said characteristic structure, the reactivity of gas other than the detection target gas at the time of methane and CO detection can be improved. For this reason, the selectivity of the detection object gas at the time of methane and CO detection can be improved.

<Configuration 14>
Another characteristic configuration of the gas detector according to the present invention is that the total content of platinum and iridium in the catalyst portion is 0.01% by mass or more and 4.5% by mass or less.

  The inventors have studied and experimented on the composition of the catalyst metal, and found that the sensitivity of the gas detection device to both carbon monoxide and combustible gas can be further enhanced by the catalyst metal according to the above-described configuration. That is, by making the total content of platinum and iridium 0.01% by mass or more and 4.5% by mass or less, the methane combustion removal reactivity at the catalyst site at the time of methane detection is suppressed, and at the time of carbon monoxide detection It has been found that the carbon monoxide combustion removal reactivity at the catalytic site can also be suppressed. According to said characteristic structure, the sensitivity of the gas detection apparatus with respect to both carbon monoxide and combustible gas can be improved more. In the case where importance is attached to methane sensitivity, the concentration of platinum should be increased (only platinum is acceptable), and in the case where sensitivity to carbon monoxide is important, the iridium concentration should be increased. This is considered to be because platinum has carbon monoxide reactivity when carbon monoxide is detected, and iridium has an action of suppressing platinum carbon monoxide reactivity.

  The total content of platinum and iridium in the catalyst portion may be 0.01% by mass or more and 2.5% by mass or less.

  The inventors have studied and experimented on the composition of the catalyst metal, and found that the sensitivity of the gas detection device to methane can be further enhanced by the catalyst metal according to the above-described configuration. That is, the sensitivity of methane and carbon monoxide can be increased by containing platinum and iridium, but if the catalyst concentration is high, the methane combustion removal reactivity at the catalytic site at the methane detection temperature is increased, thereby suppressing the methane sensitivity. I found out. When the total content of platinum and iridium in the catalyst part is 0.01% by mass or more and 2.5% by mass or less, the combustion removal reactivity of the methane in the catalyst part at the methane detection temperature is greatly suppressed, and the gas detection device The methane sensitivity of can be further increased.

<Configuration 15>
Another characteristic configuration of the gas detection device according to the present invention is that the iridium content in the catalyst portion is 0.3% by mass or more.

  The inventors have studied and experimented on the composition of the catalytic metal, and by containing 0.3% by mass or more of iridium, the combustion removal reactivity at the catalytic site for carbon monoxide at the heating temperature at which carbon monoxide is detected is suppressed. I found out that I can do it. According to said characteristic structure, the sensitivity of the gas detection apparatus with respect to carbon monoxide can be improved further.

  The platinum content in the catalyst portion may be 0.7% by mass or more.

  The inventors have studied and experimented on the composition of the catalyst metal, and found a means for suppressing the expression of hydrogen sensitivity at the heating temperature at which carbon monoxide is detected depending on the composition of the catalyst metal. When the platinum content in the catalyst portion is 0.7% by mass or more, the development of hydrogen sensitivity can be suppressed by the high hydrogen combustion action of platinum.

The catalytic metal described above can be suitably applied to a catalytic site using a transition metal oxide as a support.
The inventors have found that when a transition metal oxide is used as the support, the humidity dependency of the combustion removal reaction rate of methane and CO at the detected temperature of methane and CO is smaller than that of a conventionally used alumina support. In particular, it has been found that the effect is remarkable if it is at least one oxide among Group 3 element oxide, Group 4 element oxide, and Group 5 element oxide. Zirconium oxide or titanium oxide is preferable and more preferable for supporting noble metals such as palladium, platinum, iridium, rhodium and the like because they can be supported in a highly dispersed state and have high thermal stability.

<Configuration 16>
The catalyst portion described above can be suitably used for a gas detection device having a first temperature of 250 ° C. or lower, more preferably 150 ° C. or lower, and a second temperature of 300 ° C. or higher, more preferably 400 ° C. or higher. . When the first temperature exceeds 250 ° C., the reactivity of carbon monoxide at the catalytic site increases, and the sensitivity of carbon monoxide is greatly reduced. In addition, when the second temperature is lower than 300 ° C., the reaction between the surface adsorbed oxygen and the combustible gas at the gas detection site does not proceed, so that the combustible gas sensitivity does not appear.

  Moreover, the catalyst site | part described above can be applied suitably with respect to the gas detection apparatus whose main component of a gas detection site | part is a tin oxide. Note that indium oxide, zinc oxide, tungsten oxide, composite oxide, or the like may be used as the main component of the gas detection site.

  In addition, the present invention can be suitably applied to a gas detection device that is provided so as to cover at least the entire part of the gas detection part that can contact the detection target gas of the gas detection part, thereby ensuring the selectivity of the detection target gas. Can be obtained.

<Configuration 17>
Further, the present invention is more suitably applied to a gas detection device in which the heating control unit is configured to perform a heating operation for performing heating by the heater part and a non-heating operation for stopping heating by the heater part. Is done.

<Configuration 18>
Further, the gas detection part, the catalyst part, and the heater part are provided, the catalyst part is configured by supporting a catalyst metal on a carrier, and the catalyst metal is configured by palladium, iridium, platinum, and rhodium. A gas sensor including at least one substance selected from the group consisting of: a carbon monoxide selectivity at a first temperature (for detecting carbon monoxide); and a combustible gas at a second temperature (for detecting a flammable gas). Since the selectivity of the reactive gas can be made higher than before, it is suitable for application as a gas sensor that can improve the selectivity of each of carbon monoxide and combustible gas.

Schematic showing the outline of the gas detector Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example a Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example b Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example c Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example d Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example e Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example f Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example g Schematic showing the structure of the gas detector Schematic showing the structure of the gas detector Graph showing the temperature dependence and humidity dependence of methane and CO sensitivity in Example h Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example i Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example j Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example k Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example l Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example m Graph showing the temperature dependence and humidity dependence of methane and CO sensitivity in Example n Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example o Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example p Graph showing the temperature dependence and humidity dependence of methane and CO sensitivity in Example q Graph showing temperature dependence and humidity dependence of methane and CO sensitivity in Experimental Example r Graph showing experimental results of CO sensitivity and methane sensitivity of experimental examples a, b, c, e, f, g, h, i, j, k, l, m, n, p, q, and r Graph showing experimental results of CO sensitivity and methane sensitivity of Experimental Examples a, f, g, i, j, k, l, n, p, and r Graph showing experimental results of CO sensitivity and methane sensitivity of Experimental Examples f, g, i, j, k, l, and n Graph showing experimental results of CO sensitivity and methane sensitivity of Experimental Examples f, g, i, j, l, and n

  A gas detection apparatus 100 according to this embodiment will be described with reference to FIG. The gas detection device 100 includes a sensor element 20, a heating control unit 12, and a gas detection unit 13. The sensor element 20 includes a gas detection layer 10 (an example of a gas detection part), a catalyst layer 11 (an example of a catalyst part), and a heater layer 6 (an example of a heater part).

  The gas detection device 100 heats the gas detection layer 10 to an appropriate temperature according to the type of the detection target gas by energizing the heater layer 6 with the heating control unit 12, and maintains this temperature. The detection target gas is detected based on the characteristics (electric resistance value, voltage value, etc.) of the gas detection layer 10 in FIG. In this embodiment, methane and carbon monoxide are assumed as detection target gases.

The catalyst layer 11 is heated by the heater layer 6 to a high temperature, combusts a combustible gas that is active (combusts) at that temperature, and permeates and diffuses the inflammable gas that is inactive at that temperature, thereby detecting the gas detection layer. 10 is reached. Thus, the detection target gas by appropriately controlling the heating temperature (for example, CH ₄ (methane), C ₃ H ₈ (propane), etc.) the detection accuracy of the combustible gas is enhanced. In other words, the catalyst layer 11 burns reducing gas (non-detection target gas) such as hydrogen gas and alcohol gas other than the detection target gas so as not to reach the gas detection layer 10, and the gas detection device 100 selects the gas. It has the function to give sex. Therefore, when performing methane / CO one-sensor detection, the detection accuracy of methane is increased at high temperatures (400 ° C or higher) (hydrogen, CO, alcohol, etc. other than methane are burned and removed, and only methane is permeated), and low temperatures (150 ° C) In the following, it is necessary to optimize the catalyst metal composition so as to increase CO detection accuracy (combustion and removal of hydrogen, alcohol, etc. other than CO, and CO is not combusted). Note that methane is not burned and removed in the catalyst layer 11 at a low temperature (150 ° C. or less), but does not react in the temperature range of the gas detection layer 10 (it does not react unless the temperature is 300 ° C. or higher), and thus reaches the gas detection layer 10. Even if it does, it is not detected.

(Sensor element)
The sensor element 20 has a diaphragm structure in which the end portion of the support layer 5 is supported by the silicon substrate 1. The support layer 5 is formed by sequentially laminating a thermal oxide film 2, a Si ₃ N ₄ film 3, and a SiO ₂ film 4. A heater layer 6 is formed on the support layer 5, an insulating layer 7 is formed to cover the entire heater layer 6, a pair of bonding layers 8 is formed on the insulating layer 7, and the bonding layer 8 is formed on the bonding layer 8. An electrode layer 9 is formed. The heater layer 6 generates heat when energized to heat the gas detection layer 10 and the catalyst layer 11. The sensor element 20 may have a bridge structure, and the heater layer 6 may also serve as an electrode.

A gas detection layer 10 is formed between the pair of electrode layers 9 on the insulating layer 7. The gas detection layer 10 is a semiconductor layer mainly composed of a metal oxide. In the present embodiment, a mixture containing tin oxide (SnO ₂ ) as a main component is used as the gas detection layer 10. The electric resistance value of the gas detection layer 10 changes due to contact with the detection target gas.

  A catalyst layer 11 is formed on the gas detection layer 10 so as to cover the gas detection layer 10. The catalyst layer 11 is configured by supporting a catalyst metal on a carrier whose main component is a metal oxide. Specifically, a metal oxide carrying a catalyst metal is bonded to each other through a binder. The gas detection layer 10 may be a thin film having a thickness of about 0.2 to 1.6 μm or a film (thick film) having a thickness exceeding 1.6 μm.

As the catalyst metal, a metal that is a catalyst capable of oxidizing and removing an interference gas (reducing gas or other miscellaneous gas such as ethanol or H ₂ (hydrogen)) that may cause erroneous detection when detecting the detection target gas is used. Palladium (Pd), platinum (Pt), rhodium (Rh), iridium (Ir), etc. can be used as the catalyst metal. In this embodiment, the catalyst metal contains at least one of palladium, platinum, iridium, and rhodium. Is used.

Conventionally, alumina (Al ₂ O ₃ ) has been mainly used as a carrier for supporting a catalytic metal. In the present embodiment, at least one oxide among transition metal oxides, in particular, Group 3 element oxides, Group 4 element oxides, and Group 5 element oxides is used. For example, zirconium oxide (ZrO ₂ ), yttrium oxide (Y ₂ O ₃ ), cerium oxide (CeO ₂ ), lanthanum oxide (La ₂ O ₃ ), titanium oxide (TiO ₂ ), hafnium oxide (HfO ₂ ), niobium oxide (Nb ₂ O ₅ ) or tantalum oxide (Ta ₂ O ₅ ) can be used.

  As the binder for binding the carrier, metal oxide fine powders such as zirconium oxide, silica fine powder, silica sol, magnesia and the like can be used. If it is used in a very small amount as a binder, it is possible to use alumina fine powder or alumina sol as long as the function of the catalyst layer 11 is not impaired.

  Any of the above-described catalyst metals, metal oxides as supports, and binders may be used alone or in combination of two or more.

  The amount of the catalyst metal contained in the catalyst layer 11 is preferably 0.3 to 9% by mass with respect to the total mass of the catalyst metal and the support, and more preferably with respect to the total mass of the catalyst metal and the support. It is good to set it as 0.5 mass%-6 mass%.

  The catalyst metal contained in the catalyst layer 11 preferably contains one or more metals selected from the group consisting of palladium, platinum and iridium. In this case, it is preferable that the total content of the metal in the catalyst portion is 0.3% by mass or more and 6% by mass or less. It has been confirmed by experiments to be described later that the sensitivity of the gas detection device with respect to carbon monoxide and methane can be increased by setting the total content of the metal in the catalyst portion to 1% by mass or more and 5% by mass or less.

  In addition, it is preferable that the platinum content in the catalyst portion is 0.3% by mass or more. It has been confirmed by experiments to be described later that the platinum content in the catalyst portion is 0.5% by mass or more, whereby the sensitivity of the gas detection device to combustible gas (methane or the like) can be increased. The platinum content in the catalyst portion is preferably 6% by mass or less. If the platinum content in the catalyst portion exceeds 6% by mass, it is expected that the reactivity of methane at the time of methane detection increases and the methane is burned to greatly reduce the methane sensitivity. It has been confirmed by an experiment described later that the platinum content in the catalyst portion is 5% by mass, and the methane sensitivity is lower than that in the platinum content of 3% by mass.

  The catalyst metal contained in the catalyst layer 11 contains iridium or platinum, and the total content of the metals in the catalyst portion is 0.3% by mass or more, desirably 0.7% by mass or more, 4.5% by mass. The following is more preferable. The platinum content in the catalyst portion is 0.5 mass% or more, and the total content of the metals is 1 mass% or more and 4 mass% or less, so that carbon monoxide at the time of carbon monoxide detection is obtained. It has been confirmed by experiments described later that both the reactivity and the reactivity of methane at the time of methane detection can be suppressed, and the sensitivity of the gas detection device to carbon monoxide and methane can be further increased.

  The catalyst metal contained in the catalyst layer 11 contains iridium or platinum, and the total content of the metals in the catalyst portion is 0.3% by mass or more, desirably 0.7% by mass or more, 2.5% by mass. The following is even more preferable. The platinum content in the catalyst portion is 0.5% by mass or more, and the total content of the metals is 1% by mass or more and 2% by mass or less to further increase the reactivity of methane at the time of methane detection. It has been confirmed by experiments to be described later that it can be suppressed and the sensitivity of the gas detector to methane can be further increased.

  Further, it is preferable that the content of iridium in the catalyst portion is 0.3% by mass or more. One or more metals selected from the group consisting of palladium, platinum, and iridium are included, the total content of the metals in the catalyst portion is 1% by mass or more and 4% by mass or less, and the iridium content is 0.00. It is confirmed by an experiment described later that the reactivity of carbon monoxide at the time of detecting carbon monoxide can be suppressed and the sensitivity of the gas detection device with respect to carbon monoxide can be further increased by setting the amount to 5% by mass or more. ing

  Moreover, it is suitable when the content rate of platinum in the said catalyst site | part shall be 0.7 mass% or more. By making the platinum content in the catalyst site 1% by mass or more, the reactivity of hydrogen gas at the time of detecting carbon monoxide can be increased, and the sensitivity of hydrogen gas at the time of detecting carbon monoxide can be suppressed. This has been confirmed by the experiment described below.

(Heating control unit)
The heating control unit 12 performs an energization operation for energizing the heater layer 6 (heating operation for heating by the heater part) and a non-energization operation for not energizing the heater layer 6 (non-heating operation for stopping the heating by the heater part). It is configured as follows. The heating control unit 12 is configured to vary the temperature of the heater layer 6, and is configured to be able to heat the temperature of the heater layer 6 to a set arbitrary temperature.

  Specifically, the heating control unit 12 receives power supply from a power source such as a battery (not shown) and energizes the heater layer 6 of the sensor element 20 to heat the sensor element 20. The heating temperature, that is, the ultimate temperature of the gas detection layer 10 and the catalyst layer 11 is controlled, for example, by changing the voltage applied to the heater layer 6.

(Gas detection part)
The gas detection unit 13 detects the detection target gas by measuring the characteristics of the gas detection layer 10. In the present embodiment, the gas detection unit 13 measures the resistance value of the gas detection layer 10 by measuring the electrical resistance value (electrical characteristic) between the pair of electrode layers 9, and detects the detection target gas from the change. The concentration of is detected.

(Detection of detection target gas)
An operation in detecting the detection target gas in the gas detection device 100 configured as described above will be described.

First, the case where the gas detection device 100 detects a combustible gas (detection target gas) such as CH ₄ (methane) or C ₃ H ₈ (propane) will be described. The heater control unit 12 energizes the heater layer 6 to heat the gas detection layer 10 and the catalyst layer 11 to 300 ° C. to 500 ° C. for 0.05 seconds to 0.5 seconds. During this time, the gas detection unit 13 measures the resistance value of the gas detection layer 10 and detects the concentration of combustible gas such as CH ₄ (methane) or C ₃ H ₈ (propane) from the measured value. Thereafter, power supply to the heater layer 6 is stopped.

During this time, in the catalyst layer 11 that has become hot, the catalytic metal serves as a catalyst, and reducing gases such as CO (carbon monoxide) and H ₂ (hydrogen) and other miscellaneous gases burn. The inflammable gas such as inert CH ₄ (methane) and C ₃ H ₈ (propane) permeates and diffuses through the catalyst layer 11 to reach the gas detection layer 10, and the metal oxide of the gas detection layer 10. Reacts with (tin oxide) to change the resistance value. As described above, the gas detector 100 detects flammable gases (detection target gases) such as CH ₄ (methane) and C ₃ H ₈ (propane).

  Next, the case where CO (carbon monoxide) is detected by the gas detector 100 will be described. The energization to the heater layer 6 is controlled to set the gas detection layer 10 and the catalyst layer 11 to 50 ° C. to 250 ° C., and the temperature is maintained for 0.05 seconds to 0.5 seconds. During this time, the gas detection unit 13 measures the resistance value of the gas detection layer 10 and detects the concentration of CO (carbon monoxide) from the measured value. Thereafter, power supply to the heater layer 6 is stopped. As described above, CO (carbon monoxide, detection target gas) is detected by the gas detection device 100.

  These energization operations are repeatedly performed with a low-temperature operation (a heating operation or a pause operation at a temperature lower than the carbon monoxide detection temperature) interposed therebetween. In this embodiment, the gas detection device 100 is configured as a methane / CO one sensor that detects methane and carbon monoxide with one sensor, performs an energization operation of heating to 400 ° C., then performs a low temperature operation, and then An energization operation of heating to 150 ° C. is performed, a low temperature operation is performed again, and the above operation is repeated. Further, the energization operation time, the low temperature operation time, the heating temperature, and the like can be changed as appropriate, the low temperature operation may not be required, and the appearance frequency of 400 ° C. heating and 150 ° C. heating may not be constant (for example, 400 ° C. heating 1 The heating at 150 ° C. is repeated 5 times for each time).

(Methane, CO sensitivity temperature dependency, humidity dependency)
In order to clarify the temperature dependence and humidity dependence of sensor sensitivity for methane and CO, samples with different types of carriers and types and amounts of catalytic metals were created, and changes in CO and methane gas sensitivity with temperature and humidity were measured. did. The measurement objects are the following seven types of samples.
(Experimental example a) A sample in which 1% by mass of palladium, 1% by mass of iridium and 1% by mass of platinum are supported on zirconium oxide as a carrier,
(Experimental example b) Sample in which 3% by mass of iridium and 2% by mass of platinum are supported on zirconium oxide as a carrier,
(Experimental example c) Sample in which 3% by mass of palladium and 2% by mass of platinum are supported on zirconium oxide as a carrier,
(Experimental example d) Sample in which 3% by mass of palladium and 2% by mass of iridium are supported on zirconium oxide as a carrier,
(Experimental example e) Sample in which 2% by mass of iridium and 5% by mass of platinum are supported on zirconium oxide as a carrier,
(Experimental example f) Sample in which 2% by mass of iridium and 5% by mass of platinum are supported on alumina as a carrier, and (Experimental example g) A sample in which 7% by mass of palladium is supported on alumina as a carrier.

Specifically, the CO sensitivity at the heating temperature of 150 ° C., which is the CO detection temperature and 400 ° C., which is the methane detection temperature (the resistance value in the Air when heated at 150 ° C. is the 100 ppm CO ) And methane sensitivity (resistance value in Air when heated at 400 ° C. divided by resistance value in 3000 ppm of CH ₄ when heated at 400 ° C.), low humidity (water vapor concentration) : 0.1%) and in high humidity (water vapor concentration: 2.3%).

  2 to 8 show CO and methane sensitivities at 150 ° C. and 400 ° C. of Experimental Examples a to g. When performing methane / CO one-sensor detection, ideally, there is no methane and hydrogen sensitivity at 150 ° C and high CO sensitivity, and at 400 ° C, there is no CO and hydrogen sensitivity and methane sensitivity is increased. It has the characteristic that there is no sensitivity fluctuation by. Compared to the case where only palladium was used as the catalyst metal (FIG. 7: Experimental Example f and FIG. 8: Experimental Example g), the other configuration (Experimental examples a to e) had a CO sensitivity of 150 ° C., 400 ° C. It can be seen that the methane sensitivity of the methane / CO one sensor is larger, and is more suitable for performing methane / CO one sensor detection.

  It can also be seen that the humidity dependence is hardly exhibited in the case of a zirconium oxide support.

  That is, according to the above experimental results, zirconium oxide is used as the support of the catalyst layer 11, and the catalyst metal component contains at least iridium or platinum among palladium, iridium or platinum (that is, other than those composed only of palladium). ), The reactivity of methane at the first temperature (for detecting methane) in the catalyst layer 11 and the reactivity of carbon monoxide at the second temperature (for detecting carbon monoxide) (especially in high humidity). It has been shown that the sensitivity of the gas detection device 100 to both methane and CO can be improved.

  Even if the same catalyst metal is used, the zirconium oxide support can suppress the decrease in sensitivity at high humidity compared to the alumina support. Thus, it is considered that the catalyst layer can be more suitable for detection of methane / CO one sensor than in the past.

(Change in humidity dependence due to carrier)
In order to confirm the change in humidity dependence due to the carrier, a sample with only the carrier type changed was prepared, and the change in CO / methane gas sensitivity due to the heating temperature and ambient humidity was measured. The measurement objects are the following 10 types of samples.
(Experimental example 1) A sample in which 2% by mass of iridium and 5% by mass of platinum are supported on zirconium oxide (ZrO ₂ ) as a support,
(Experimental example 2) Sample in which 2% by mass of iridium and 5% by mass of platinum are supported on yttrium oxide (Y ₂ O ₃ ) as a carrier,
(Experimental example 3) A sample in which 2% by mass of iridium and 5% by mass of platinum are supported on cerium oxide (CeO ₂ ) as a carrier,
(Experimental Example 4) Sample in which 2% by mass of iridium and 5% by mass of platinum were supported on lanthanum oxide (La ₂ O ₃ ) as a carrier,
(Experimental Example 5) Sample in which 2% by mass of iridium and 5% by mass of platinum are supported on titanium oxide (TiO ₂ ) as a carrier,
(Experimental example 6) A sample in which 2% by mass of iridium and 5% by mass of platinum are supported on hafnium oxide (HfO ₂ ) as a carrier,
(Experimental example 7) A sample in which 2% by mass of iridium and 5% by mass of platinum are supported on niobium oxide (Nb ₂ O ₅ ) as a carrier,
(Experimental Example 8) Sample in which 2% by mass of iridium and 5% by mass of platinum are supported on tantalum oxide (Ta ₂ O ₅ ) as a carrier,
(Experimental example 9) A sample in which 2% by mass of iridium and 5% by mass of platinum are supported on alumina (Al ₂ O ₃ ) as a support, and (Experimental example 10) _{2 in} silicon oxide (SiO ₂ ) as a support A sample carrying mass% iridium and 5 mass% platinum.

Specifically, the CO sensitivity at the heating temperature of 150 ° C., which is the CO detection temperature and 400 ° C., which is the methane detection temperature (the resistance value in Air when heated at 150 ° C. is the CO sensitivity of 100 ppm when heated at 150 ° C. ) And methane sensitivity (resistance value in Air when heated at 400 ° C. divided by resistance value in 3000 ppm of CH ₄ when heated at 400 ° C.), low humidity (water vapor concentration) : 0.1%) and in high humidity (water vapor concentration: 2.3%).

  Table 1 below shows the sensitivity of CO and methane at 150 ° C. and 400 ° C. in Experimental Examples 1 to 10. The sensitivity of each sample and each gas in low humidity is 1.

  As shown in Table 1, in Experimental Examples 1 to 8 in which the carrier is a Group 3 to Group 5 transition metal oxide, neither CO sensitivity nor methane sensitivity shows almost any change in sensitivity due to humidity fluctuations. . In contrast, in Experimental Example 9 (carrier is alumina) and Experimental Example 10 (carrier is silicon oxide), the CO sensitivity greatly fluctuated due to humidity fluctuations.

The inventors have discovered that this factor is due to the following. When SiO ₂ or Al ₂ O ₃ is used as a carrier, since the interaction with water is strong, the condensed water tends to accumulate due to capillary condensation, and a large amount accumulates at high humidity. After this, water is blown off by purging (heating treatment at a high temperature for cleaning the sensor surface. When heating control including low temperature operation is performed, the heating time at a high temperature becomes a finite time) In some cases, it cannot be completely blown off, and OH groups remain on the surface. This is particularly noticeable when a low temperature operation including a finite time for heating to a predetermined temperature or more is included. The inventors have found that this OH group expresses the effect of promoting CO adsorption, and the CO oxidation in the catalyst layer is promoted, so that the CO reaching the detection layer is reduced and the CO sensitivity is lowered. it is conceivable that.
On the other hand, when a transition metal oxide belonging to Group 3 to Group 5 is used as a carrier, capillary condensation during low-temperature operation is unlikely to occur, and since there is little condensed water, moisture can be sufficiently removed by purging, and OH group There will be no survival. For this reason, since CO oxidation in the catalyst layer is not promoted, the CO sensitivity is higher than that in the case where SiO ₂ and Al ₂ O ₃ are used as a carrier, and the CO sensitivity does not depend on humidity.

(Methane, CO sensitivity temperature dependency, humidity dependency, hydrogen sensitivity)
In order to investigate in more detail the temperature dependence and humidity dependence of sensor sensitivity for methane and CO, samples with different types and amounts of catalytic metals were prepared, and changes in CO / methane gas sensitivity with temperature and humidity were measured. The measurement objects are 11 types of samples shown in Table 2 below. In addition to temperature dependency and humidity dependency, hydrogen sensitivity was also measured.

The measurement was performed in the same manner as the above experiment. CO sensitivity at a heating temperature of 150 ° C. as the CO detection temperature and 400 ° C. as the methane detection temperature (the resistance value in Air when heated at 150 ° C. is divided by the resistance value in 100 ppm of CO when heated at 150 ° C. Methane sensitivity (resistance value in Air when heated at 400 ° C. divided by resistance value in 3000 ppm of CH ₄ when heated at 400 ° C.) in low humidity (water vapor concentration: 0.1%) And in high humidity (water vapor concentration: 2.3%).

The hydrogen sensitivity is a sensitivity at 1000 ppm of hydrogen, and the hydrogen sensitivity in carbon monoxide detection is a value obtained by dividing the resistance value in Air when heated at 150 ° C. by the resistance value in 1000 ppm of H ₂ when heated at 150 ° C. It is. The hydrogen sensitivity at the time of methane detection is a value obtained by dividing the resistance value in Air at 400 ° C. heating by the resistance value in 1000 ppm of H ₂ at 400 ° C. heating. When the hydrogen sensitivity exceeded 1, the hydrogen sensitivity was expressed as “present”. In addition, the hydrogen sensitivity at the time of methane detection (hydrogen sensitivity at the time of heating at 400 ° C.) was “none” in any sample. The hydrogen sensitivity was measured in a low humidity (water vapor concentration: 0.1%) environment.

  From the above experimental results, hydrogen sensitivity at the time of methane detection was not developed regardless of the type and amount of any catalyst metal. From this, when one or more metals selected from the group consisting of palladium, platinum, and iridium are included, and the total content of the metals in the catalyst portion is 1% by mass or more, hydrogen at the time of methane detection It was shown that the sensitivity was suppressed and the methane selectivity during methane detection was enhanced. Further, it is expected that the same effect can be expected by setting the total content of the metal in the catalyst portion to 0.3 mass% or more.

  11 to 21 show the CO and methane sensitivities at 150 ° C. and 400 ° C. of Experimental Examples hr. When performing methane / CO one-sensor detection, ideally, the characteristic is that there is no methane sensitivity and large CO sensitivity at 150 ° C, and there is no CO sensitivity and large methane sensitivity at 400 ° C. It has no characteristics. Both samples have higher CO sensitivity of 150 ° C. and methane sensitivity of 400 ° C., and it is understood that these samples are more suitable for performing methane / CO one sensor detection.

  Compared to the CO sensitivity (16 to 18.4, low humidity) and the methane sensitivity (9.3 to 10.3, low humidity) of the experimental examples e to g (see FIGS. 6 to 8), the experimental examples a to d (FIG. 2). -5) and experimental examples hr (see FIGS. 11 to 21) have high CO sensitivity (19.9 to 24.6, low humidity) and methane sensitivity (11.3 to 15.2, low humidity). Here, focusing on the total content of palladium, iridium, and platinum in the catalytic site, the experimental examples eg exceeded 5% by mass, whereas the experimental examples ad and hr had 1 mass. % To 5% by mass. That is, from the above experimental results, the catalyst metal contains one or more metals selected from the group consisting of palladium, platinum and iridium, and the total content of the metals in the catalyst site is 1% by mass or more 5 It was shown that the sensitivity of carbon monoxide and methane can be increased by adjusting the content to less than mass%. Further, it is expected that the same effect can be expected by setting the total content of the metal in the catalyst portion to 0.7 mass% or more and 6 mass% or less.

  FIG. 22 shows a sample in which the horizontal axis represents CO sensitivity (low humidity), the vertical axis represents methane sensitivity (low humidity), and the platinum content in the catalytic site is 0.3 mass% or more and 6 mass% or less (Experimental example a, b, c, e, h, i, j, k, l, m, n, p, q, and r; see FIGS. 2-4, 6, 11-17, and 19-21) on a conventional alumina support These are plotted in comparison with the samples (Experimental Examples f and g; see FIGS. 7 and 8). Both samples have higher CO sensitivity and methane sensitivity than conventional alumina support samples. That is, it turns out that it is suitable for making CO sensitivity and methane sensitivity higher than before by setting it as the composition containing platinum. In addition, the CO sensitivity (18.4, low humidity) and methane sensitivity (10.3, low humidity) of the sample (Experiment e; see FIG. 6) containing 5% by mass of platinum with the same carrier are platinum platinum. Is lower than the CO sensitivity (19.9, low humidity) and methane sensitivity (16.2, low humidity) of the sample containing 3% by mass (Experimental Example p; see FIG. 19). From this, it is considered that when the platinum content increases, the reactivity of CO and methane increases, and the sensitivity of CO and methane decreases. Therefore, it is expected that the platinum content is preferably 0.3% by mass or more and 6% by mass or less.

  In FIG. 23, the horizontal axis represents CO sensitivity (low humidity), the vertical axis represents methane sensitivity (low humidity), the platinum content in the catalytic site is 0.3 mass% or more, and the total content of platinum and iridium is Samples of 0.3 mass% or more and 4.5 mass% or less (Experimental examples a, i, j, k, l, n, p, and r; see FIGS. 2, 12 to 15, 17, 19, and 21) FIG. 8 is a plot in comparison with a conventional alumina carrier sample (Experimental Examples f and g; see FIGS. 7 and 8). By making the platinum content in the catalyst portion 0.3 mass% or more and the total content of platinum and iridium 0.3 mass% or more and 4.5 mass% or less, carbon monoxide is detected at the time of carbon monoxide detection. Both the reactivity of carbon and the reactivity of methane during methane detection can be suppressed, and it has been shown that it is preferable to further increase the sensitivity of the gas detector to carbon monoxide and methane.

  In FIG. 24, the horizontal axis represents CO sensitivity (low humidity), the vertical axis represents methane sensitivity (low humidity), the platinum content in the catalytic site is 0.3 mass% or more, and the total content of platinum and iridium is Samples of 0.3% by mass or more and 2.5% by mass or less (Experimental Examples i, j, k, l, and n; see FIGS. 12 to 15 and 17) were replaced with conventional alumina support samples (Experimental Example f). , G; see FIGS. 7 and 8). Reactivity of methane at the time of methane detection by setting the platinum content in the catalytic site to 0.3 mass% or more and the total content of platinum and iridium to 0.3 mass% to 2.5 mass% It can be further suppressed, and it has been shown that it is more preferable to increase the sensitivity of the gas detection device to methane.

  In FIG. 25, the horizontal axis represents CO sensitivity (low humidity), the vertical axis represents methane sensitivity (low humidity), the platinum content in the catalyst portion is 0.3% by mass or more, and the total content of platinum and iridium is Samples of 0.3 mass% or more and 2.5 mass% or less and the iridium content is 0.3 mass% or more (Experimental examples i, j, l, and n; see FIGS. 12, 13, 15, and 17) ) Is plotted in comparison with a conventional alumina support sample (Experimental Examples f and g; see FIGS. 7 and 8). The platinum content in the catalyst portion is 0.3% by mass or more, the total content of platinum and iridium is 0.3% by mass or more and 2.5% by mass or less, and the iridium content is 0.3% by mass or more. By doing so, the reactivity of carbon monoxide at the time of carbon monoxide detection can be further suppressed, and it has been shown that it is more preferable to increase the sensitivity of the gas detection apparatus with respect to carbon monoxide.

  As shown on the right side of Table 2, the hydrogen sensitivity at the time of carbon monoxide detection was such that the experimental examples h, i, and j exhibited “sensitivity” of hydrogen sensitivity, and the other samples exhibited “absence” of hydrogen sensitivity. Here, focusing on the platinum content in the catalytic site, the experimental examples h, i, and j are 0.5% by mass, whereas the platinum content is 1% by mass or more (experimental examples k, l, In m, n, p, q and r), the expression of hydrogen sensitivity is “none”. That is, from the above experimental results, it was shown that the expression of hydrogen sensitivity can be suppressed by setting the platinum content to 1% by mass or more. It is also expected that the expression of hydrogen sensitivity can be suppressed by setting the platinum content in the catalyst portion to 0.7 mass% or more.

  From the above results, in order to increase the methane sensitivity and methane selectivity at the time of methane detection and to increase the CO sensitivity and CO selectivity at the time of CO detection, the platinum content in the catalyst site is set to 0.7% by mass or more. When the total content of iridium and iridium is 1% by mass or more and 2.5% by mass or less, and the iridium content is 0.3% by mass or more, the highest effect is obtained.

(Other embodiments)
In the above-described embodiment, the structure of the gas detection device 100 is the so-called substrate type shown in FIG. 1, but other structures are possible. For example, a structure in which the insulating layer 7 covering the heater layer 6 is not provided and the heater layer 6 also serves as the electrode layer 9 is possible. For example, as shown in FIG. 9, a structure is formed in which a gas detection portion 23 made of an oxide semiconductor is formed around the coil 22 of the electrode wire 21 serving as an electrode and a heater portion, and a catalyst layer 24 is formed around the gas detection portion 23. Is also possible. Further, as shown in FIG. 10, another electrode 33 is arranged at the center of the coil 32 of the electrode wire 31 serving both as an electrode and a heater part, and a gas detection part 34 made of an oxide semiconductor is provided around the coil 32. A structure in which the catalyst layer 35 is formed around it is also possible.
Further, in the above-described embodiments, examples using zirconium oxide as a support have been given. However, similar effects can be obtained when titanium oxide is used, and when other transition metal oxides are also used. Can also be obtained.

  Note that the configurations disclosed in the above-described embodiments (including the other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in the other embodiments unless there is a contradiction. The embodiments disclosed in this specification are exemplifications, and the embodiments of the present invention are not limited thereto, and can be appropriately modified without departing from the object of the present invention.

6: Heater layer (heater part)
10: Gas detection layer (gas detection part)
11: catalyst layer (catalyst site)
12: Heating control unit 13: Gas detection unit 21: Electrode wire (heater part)
23: Gas detection part 24: Catalyst layer (catalyst part)
31: Electrode wire (heater part)
34: Gas detection part 35: Catalyst layer (catalyst part)
100: Gas detection device

Claims (18)

A gas detection region whose characteristics change due to contact with the detection target gas;
A catalyst portion provided to cover at least a part of the gas detection portion;
A heater part for heating the gas detection part and the catalyst part;
A heating control unit for controlling heating by the heater part;
A gas detection device having a gas detection unit that detects a gas to be detected by measuring characteristics of the gas detection site;
The heating controller is
A first heating operation for controlling heating by the heater part to heat the gas detection part and the catalyst part to a first temperature for detecting carbon monoxide;
A second heating operation for controlling the heating by the heater part to heat the gas detection part and the catalyst part to a second temperature higher than the first temperature;
The catalyst portion is configured by supporting a catalyst metal on a carrier, the catalyst metal includes at least one substance selected from the group consisting of palladium, iridium, platinum and rhodium, and the main component of the carrier is transitioned A gas detector that is a metal oxide.   The gas detection device according to claim 1, wherein the catalyst metal includes at least two substances selected from the group consisting of palladium, iridium, platinum, and rhodium.   3. The catalyst metal according to claim 1 or 2, wherein the catalyst metal is a mixture containing iridium and platinum, the iridium content in the catalyst portion is 0.3 mass% or more, and the platinum content is 0.3 mass% or more. The gas detector described.   The catalyst metal is a mixture containing iridium and platinum, the iridium content in the catalyst portion is 0.01% by mass or more and 5% by mass or less, and the platinum content is 0.01% by mass or more and 7% by mass or less. The gas detection device according to claim 1 or 2.   The catalyst metal is a mixture containing palladium and platinum, the palladium content in the catalyst site is 0.3% by mass or more, and the platinum content is 0.3% by mass or more. The gas detector described.   The catalyst metal is a mixture containing palladium and platinum, the palladium content in the catalyst portion is 0.01% by mass or more and 5% by mass or less, and the platinum content is 0.01% by mass or more and 7% by mass or less. The gas detection device according to claim 1 or 2.   3. The catalyst metal according to claim 1 or 2, wherein the catalyst metal is a mixture containing palladium and iridium, the palladium content in the catalytic site is 0.3 mass% or more, and the iridium content is 0.3 mass% or more. The gas detector described.   The catalyst metal is a mixture containing palladium and iridium, the palladium content in the catalyst portion is 0.01% by mass to 5% by mass, and the iridium content is 0.01% by mass to 5% by mass. The gas detection device according to claim 1 or 2.   The catalyst metal includes one or more metals selected from the group consisting of palladium, platinum, and iridium, and the total content of the metals in the catalyst portion is 0.3% by mass or more. The gas detection device according to any one of 8.   The catalyst metal includes one or more metals selected from the group consisting of palladium, platinum, and iridium, and the total content of the metals in the catalyst site is 0.01% by mass or more and 6% by mass or less. The gas detection device according to any one of claims 1 to 8.   The gas detection device according to any one of claims 1 to 8, wherein a platinum content in the catalyst portion is 0.3 mass% or more.   The gas detector according to any one of claims 1 to 8, wherein a platinum content in the catalyst portion is 0.01 mass% or more and 6 mass% or less.   The gas detection device according to any one of claims 1 to 8, wherein a total content of platinum and iridium in the catalyst portion is 0.3 mass% or more.   The gas detection device according to any one of claims 1 to 8, wherein a total content of platinum and iridium in the catalyst portion is 0.01% by mass or more and 4.5% by mass or less.   The gas detector according to any one of claims 1 to 14, wherein a content of iridium in the catalyst portion is 0.3% by mass or more.   The gas detection device according to any one of claims 1 to 15, wherein the first temperature is 250 ° C or lower and the second temperature is 300 ° C or higher.   The gas according to any one of claims 1 to 16, wherein the heating control unit is configured to perform a heating operation for heating by the heater part and a non-heating operation for stopping the heating by the heater part. Detection device. A gas detection region whose characteristics change due to contact with the detection target gas;
A catalyst portion provided to cover at least a part of the gas detection portion;
A heater part for heating the gas detection part and the catalyst part;
A gas sensor, wherein the catalyst portion is configured by supporting a catalyst metal on a carrier, and the catalyst metal includes at least one substance selected from the group consisting of palladium, iridium, platinum, and rhodium.

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