JPH0313854A - NOx gas detection element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a NOx gas detection element for detecting the concentration of NOx gas contained in a mixed gas, and in particular, to a NOx gas detection element for detecting the concentration of NOx gas contained in a mixed gas. The present invention relates to a NOx gas detection element that is effective for detecting such high concentration NOx gas.

[Conventional technology and problems]

Conventionally, methods such as chemiluminescence, infrared absorption, and electrolysis have been used to measure Noxlf levels.
Implementation of these methods requires large equipment, which is expensive, and maintenance is difficult.

In order to solve these problems, we have developed a compact and maintenance-free NOx gas detection element using metal oxide semiconductors such as SnO□ and Ago-■205, and organic semiconductors such as phthalocyanine complexes.
Gas detectors have been considered by many researchers.

Such a NOx gas detector measures the amount of NOx by connecting a pair of electrodes to a NOx gas sensing element and measuring a change in resistance that occurs when the NOx gas sensing element adsorbs NOx.

However, the conventional NOx gas detector described above is
The following problems have arisen due to the characteristics of the Ox gas detection element.

(1) Because the sensitivity to NO is low, more than 90% of the NOx contained in exhaust gas from internal combustion engines is
It is difficult to accurately measure the NOx concentration for those dominated by O.

(2) Since the upper limit of the NOx concentration that can be quantified is as low as several hundred ppm, it cannot be used when the NOx concentration reaches several thousand ppm, such as in exhaust gas from internal combustion engines.

Because of the relatively high sensitivity, it is difficult to accurately measure the NOx concentration when NOx gas is contaminated with these gases.

[Means for solving problems]

In order to solve the above-mentioned problems, the inventors of the present invention have discovered that by using it as a method, it shows equal and high sensitivity to No and NO2, and also has a high upper limit of measurable NOx gas concentration. In addition, the present inventors have discovered that the sensitivity to contaminant gases other than NOx is extremely low and exhibits excellent characteristics such that the influence of the contaminant gases is small, leading to the completion of the present invention.

The following margin The present invention has a non-stoichiometric parameter (δ) of 0.01
Forms (a) TiOz, (b) composite oxide of metal and titanium in solid solution with TiO2, and (c) oxide of titanium and provskite structure, which have oxygen defects of <δ<0.5. At least one metal oxide selected from the group consisting of composite oxides of metal and titanium (
This is a NOx gas detection element made of a titanium-containing oxide (hereinafter also referred to as a titanium-containing oxide).

Note that in the present invention, the non-stoichiometric parameter (δ)
The values are the values measured using ESCA (X-ray photoelectron spectroscopy) under mA conditions after performing Ar sputtering at lkV and 25 mA for 30 seconds.

The No. gas sensing element of the present invention has a non-chemical IgA parameter (δ) of o, oi<δ<0.5, preferably
It has 0.04 to 0.2 oxygen vacancies. (a) TiOt
.

At least one member selected from the group consisting of (b) a composite oxide of metal and titanium that forms a solid solution with TiOt, and (c) a composite oxide of titanium and a metal that forms an oxide with titanium and a perovskite structure. N
This is necessary to exhibit high sensitivity selectively to O. That is, in the present invention, when the non-stoichiometric parameter (δ) of the titanium-containing oxide is smaller than the above range, the sensitivity to oxygen becomes high and the sensitivity to No.

decreases significantly. Furthermore, when the non-stoichiometric parameter (δ) is larger than the above range, the sensitivity to all gases decreases.

Typical examples of such titanium-containing oxides include TjOz-J as the titania in (a), Mamei #l
Engraving of the book (no change in content) General formula AXT++-xoz as the composite oxide of (b)
-δ (however, eight is A l, Nbs Tas sb
, 85% Indicates at least one element selected from the group consisting of Ga, In-5c, Mg and Y, and 0<x<
1) is further represented by the general formula BTiO*-j (where B is Pb
sCa, Sr, Cd5Zn.

Examples include oxides represented by (representing at least one element selected from the group consisting of Ln and Ba).

Specific examples of the titanium-containing oxide represented by the above general formula A)ITil□02-t include A IX'ri, -,
o□I, Nb++Ti+-xo t-1' % Tax
Ti+-++O*-j -SbJ' 1-XOt -J
%^5llTi1-Xo z-1, GaXTi 1-
XO! -J-, In, T', -1lo t-t, 5
CXTI +-xOz-J-, Y, ITi+-xo
t-J −, MgxTr l-Xo *-j %N
,,Nb,,ri (1-XI-N2) Ot-J ,
In Lux+Stl+tTi (1-xi-N2), X is 0<X<L, preferably O<x≦0.5,
Sentence 1, N2 is 0<(X1+X2)<1, preferably O<(XI+X2)≦0.5.

In addition, the general titanium-containing acid represented by 2B T i O3 ”°, specific examples of which are CaT i
O3-t %5rTiOff-7', BaTi0. l-
1, PbTtOz-7, CdTi0ff45, ZnTi
0: +-5% LaTiO3-J, BaTi0ff4
, NdTi0=4, Sr, Ba-yTiOx-j,
BayLat-yTi 03- (, Ca, Sr+-y
Examples include T, i 0 x-J, and the like.

In the above formula, y satisfies Q<y<l, and these titanium-containing oxides constitute the NoX gas detection element alone or in combination with other titanium-containing oxides.

The titanium-containing oxide which is the NO gas detection element of the present invention is
Although it is shown by the above chemical formula, in order to increase the reactivity with NOX, it is generally used in the range of 200 to 7
It is preferred to heat to 400-600°C.

No. of the present invention, the shape of the gas sensing element is not particularly limited,
The NO formed using the gas detection element may be appropriately determined depending on the structure of the gas detector.For example, a general formula is a chip shape, a film shape, etc.

The method for producing a titanium-containing oxide having such a shape is not particularly limited, but representative methods include methods such as a sintering method, a sintering method, a vapor deposition method, and a thermal decomposition method.

Among the above methods, the sintering method is used for forming titanium-containing oxides in the form of chips and films, and the centering method, vapor deposition method, and pyrolysis methods are used for forming film-like titanium oxides with blank spaces below. suitable. A specific manufacturing method is illustrated below. First, as a manufacturing method using the sintering method,
A preferred method is to fill a cavity having a predetermined shape with titanium-containing oxide powder, compression mold it, or heat and sinter it simultaneously with the compression molding. The pressure in the compression molding is 200'fJ9/cm2 to 1t7c
m2, generally 300-700kl? /α2 is appropriate. Furthermore, the sintering temperature and sintering atmosphere are particularly important since they determine the non-stoichiometric parameter (δ). In a non-reducing atmosphere (N2, Ar, etc.), the sintering temperature (T) may be in the range of 900°C<T<melting point. In addition, when using an atmosphere of reducing gas such as CO2H2, the suitable sintering temperature varies depending on the type and concentration of the gas, but for example, in N2 containing 5% CO2, the suitable sintering temperature is 700℃ to T (1000℃ Preferably, 600°C (T (900°C) is preferable in N2 containing H2S. Also, of course, combinations of the above sintering conditions, such as sintering in a non-reducing atmosphere followed by treatment in a reducing atmosphere, etc. You may also use this method.

Another method of sintering is to mix titanium-containing oxide powder with a dispersion medium to form a paste.

An example of this method is to print a film on an insulating substrate by screen printing, and then sinter it at the above-mentioned sintering temperature.

In the above-described sintering method, a compound such as a titanium-containing hydroxide or alkoxide may be used instead of the methane-containing oxide as a starting material, and the compound may be oxidized and sintered.

In addition, as a sputtering method, for example, titanium metal is used as a target material, and sputtering is performed on an insulating substrate such as alumina in the presence of oxygen to form a thin film, and then the thin film is coated in air with a A method of obtaining a TiO2 thin film by firing at 800° C. is exemplified.

Furthermore, as a vapor deposition method, for example, metal titanium is deposited at an oxygen pressure of 0.
．． A method of forming a T r 02 thin film by evaporating under 5 to 3 Torr and depositing the vapor on an insulating substrate such as alumina can be mentioned.

Furthermore, as a thermal decomposition method, a solution of an organometallic compound such as a metal alkoxide constituting the target titanium-containing oxide is applied to a substrate such as alumina, and then the solution is heated in a non-reducing atmosphere such as air or in a reducing atmosphere. A method of forming a TiO2 thin film by thermal decomposition at a temperature of 500° C. to below the melting point is mentioned.

As mentioned above, T by sputtering method, vapor deposition method, thermal decomposition method, etc.
Although a method for producing a thin film of iO2 has been shown, thin films of other titanium-containing oxides can also be produced according to the above method.

Although the sensitivity to blank gas is extremely low, if the concentration of the contaminant gas in the NOx gas to be measured is extremely high, such as 11,000 pp or more, a phenomenon occurs in which the measured value decreases to some extent.

Even in such a case, the inventors have determined that the NO
We conducted repeated research to measure the v gas concentration. the result,
By providing a layer containing an oxidation catalyst on at least the surface of the element made of the titanium-containing oxide described above, the NOx gas concentration can always be accurately measured even in the presence of a low to high concentration of contaminant gas. I discovered that.

That is, in the present invention, the non-stoichiometric parameter (δ) is 0.
．． 01<6<0.5 oxygen defects (81-10
□, selected from the group consisting of (b) a composite oxide of a metal and titanium that forms a solid solution with TiOt, and (c) a composite oxide of a metal and titanium that forms an oxide of titanium and a perovskite structure. The present invention also provides a gas sensing element that is made of one type of metal oxide and has a layer containing an oxidation catalyst on at least the surface.

Description of Specification (No change in content) In the present invention, the oxidation catalyst is not particularly limited as long as it can exhibit its performance as an oxidation catalyst at the operating temperature of the gas detection element. For example, PL, Ph, Pd
Noble metal-based oxidation catalysts such as Old, Metal-based oxidation catalysts such as Fe, etc.
LaC0:+% LaNi0:+, La5ro, 3
Typical examples include metal oxide-based oxidation catalysts such as Coo and 703. Among these, noble metal oxidation catalysts are particularly suitable.

The oxidation catalyst may be present as a layer containing the oxidation catalyst on at least the surface of the element made of the titanium-containing oxide described above. That is, as embodiments in which a layer containing an oxidation catalyst is present at least on the surface of an element made of a titanium oxide, there are two methods: (1) B in which the oxidation catalyst is dispersed throughout the element, and (2) the oxidation catalyst is present in the element. Examples include a mode in which the oxidation catalyst is partially dispersed including the surface layer portion of the element, and a mode in which a layer containing an oxidation catalyst is provided on the surface of the element. Of these,■
The embodiments (1) and (2) are particularly preferred. In the embodiment (2) above, the layer containing the oxidation catalyst may be formed by carrier particles carrying the oxidation catalyst, or in some cases, the layer containing the oxidation catalyst may be formed by the oxidation catalyst alone. good.

The above embodiments (1) and (2) are suitable for the above-mentioned noble metal oxidation catalyst and metal oxidation catalyst. In this case, the concentration of the noble metal oxidation catalyst in the oxidation-containing catalyst matrix of the titanium-containing oxide is preferably 10 to 101000 pp.
The concentration of the metal oxidation catalyst is generally 100 to 600 ppm, and the concentration of the metal oxidation catalyst is generally 0.1 to 5% by weight, preferably 0.5 to 3% by weight.

Further, the embodiment (2) can be applied to all oxidation catalysts. In particular, it is preferable to support noble metal oxidation catalysts and metal-based oxidation catalysts on carrier particles to form a layer, and in this case, the concentration of the oxidation catalyst on the surface of the carrier particles is
The concentrations in the oxidized catalyst matrix described above are preferred. Further, it is preferable that the metal oxide-based metal catalyst forms a layer by itself. In the above embodiments (1) and (2), the thickness of the layer containing the oxidation catalyst is preferably 1 μm or more at -1fQ.

In the present invention, the method for forming a layer containing an oxidation catalyst on an element made of a titanium-containing oxide is particularly described in the specification (
(No change in content) No restrictions. For example, in the embodiment (2) above, when producing a titanium-containing oxide by a sintering method, a pyrolysis method, etc., an oxidation catalyst is contained in the raw material, or an oxidation catalyst is generated by heating during sintering or pyrolysis. It is preferable to use a method in which a compound is blended in advance. In addition, in the embodiment (■), the titanium-containing oxide includes:
After impregnation with a solution of a compound that produces an oxidation catalyst upon heating,
A heating method is preferred. Compounds that generate oxidation catalysts by such heating include the above-mentioned noble metals or soluble salts of metals such as chlorides, nitrates, and organic acid salts.

Furthermore, in the aspect (2), a method of attaching an oxidation catalyst to the surface of an element made of titanium oxide by a method such as a sputtering method, a vapor deposition method, a sintering method, or a thermal decomposition method, Tie, A.
I! z O3, Mg O・^1. l z Ox, 5
For example, a method may be mentioned in which the oxidation catalyst' is supported on carrier particles such as No. 40, and then the particles are attached to the surface of an element made of a titanium-containing oxide by means such as sintering.

The following is a blank space for the present invention. As for the NOx gas detector using the NOx gas detection element, any known structure may be adopted without particular limitation.

Figure 1 shows NOx detection using a square chip NOx gas detection element.
FIG. 2 is a perspective view showing a typical aspect of an x-gas detector. That is, in the NOx gas detector, the NOx gas sensing element 1 is mounted on a support base made of an insulating substrate 3 with at least a portion thereof exposed, and the NOx gas sensing element 1 is provided with a pair of electrodes spaced apart from each other. The electrode 2 is connected, and the NOx gas detection element 1
It has a structure in which a heater 4 (the heater electrode is not shown) is provided so as to be located near the heater. In the above NOx gas detector, the insulating substrate 3 is the NOx gas sensing element 1.
, the heater 4, and the electrode 2, and any material that is insulative and heat resistant to the heating temperature of the heater 4 can be used without particular limitation. Such materials include alumina, MgO-At203. AtN etc. are suitable. Further, the heater 4 is used to enhance the reactivity with NOx by controlling the NOx gas detection element 1.

The heater 4 described above is preferably provided near the NOx gas detection element 1 so as to be able to heat the NOx gas detection element 1 via the insulating substrate 3. Specifically, as shown in FIG. 1, it is preferable to embed it in an insulating substrate near the KNOx gas detection element 1, or to attach it to a surface other than the exposed surface of the NOx gas detection element 1. Furthermore, the material of the heater 4 is not particularly limited as long as it can be heated to a desired temperature by energization. Examples of suitable materials include platinum, tungsten, ruthenium oxide, silicon carbide, etc. .

FIG. 2 shows a typical circuit diagram of a NOx gas measuring device incorporating a NOx gas detector. That is, NOx
The gas detector 5 is connected to a circuit power supply 6 and a voltmeter 7 via electrodes.
connected in series with Further, a load resistor 8 is connected in parallel with the voltmeter 7. On the other hand, the heater 4 is connected to the heater power source 9
connected to.

With the NOx gas measuring device, the NOx gas concentration is measured by activating the heater 4 and heating the NOx gas detection element 1 to a predetermined temperature, for example, 400 to 600°C.
The Ox gas detection element 1 is placed in the gas to be measured, and the voltage at that time is measured with a voltmeter 7.

That is, the voltage ■ of the circuit power supply 6. and resistance RL of load resistance 8
, the output voltage Voud″ measured by the voltmeter 7, and NOx
The following relationship exists between the resistance R8 of the sensing element and Vo.
By measuring wt, R8 can be easily determined from equation (1) below.
It is possible to calculate.

R3= Rt, (V, -Voit-)/Vowt
(11) When the element temperature is constant, the NOx gas detection element of the present invention exhibits a certain resistance depending on the degree of Noxa in the atmosphere. Therefore, from R8 above, the NOx
By determining the gas concentration from a calibration curve prepared in advance,
It is possible to know the NOx gas concentration in the gas to be measured.

〔effect〕

The NOx gas detection element of the present invention has the following features: (11The sensitivity to both NO and No2 is high and equivalent, (2) It has sufficient sensitivity even to high concentration NOx gas, (3) The influence of contaminant gas It has characteristics such as being hardly affected by

Therefore, it is possible to accurately measure the Noxn degree in a mixed gas containing NOx over a wide range.

The NOx gas detection element of the present invention detects N in a general mixed gas.
It is possible to detect Ox concentration, but even higher concentrations of NO
Since the sensitivity to It is suitable for monitoring the NOx concentration from beginning to end. Furthermore, it is also possible to develop a feedback system that tracks changes in resistance of elements and changes the operating conditions of internal combustion engines etc. in the event of an abnormality.

〔Example〕

Examples are shown below to specifically explain the present invention, but the present invention is not limited to these Examples.

In addition, Oite, No., No. 2.02 and Co.
Sensitivity was determined by the following method.

m No, No2 sensitivity; 0□5% and Noxlo
Resistance R1 in an atmosphere containing opFl and 025% and N
Ratio Lo to resistance R2 in an atmosphere containing Ox1000pa
It was expressed as g(R2/R1).

(2) 0□ Sensitivity: Resistance R1 in an atmosphere containing NOx 1000p and 021% and NOx 1000p and 021%
Ratio to resistance R2 in an atmosphere containing 0%Lo g (R
2/R1).

(31Co sensitivity; 0□5%, Noxloool) - and resistance R1 and 025 in an atmosphere containing CO10pIn
%, the ratio Zo g (R2/R
+).

It can be said that the larger the value expressed by log(R2hiko), the higher the sensitivity to the gas.

Example I T Ammonium sulfate aqueous solution and ammonia were added to the 1C64 aqueous solution, and the resulting precipitate was filtered through the mouth, washed, and incubated in air for 90 minutes.
It was baked at 00°C for 1 hour. The obtained fired powder was put into a cavity, and Pt @ electrodes were embedded in both ends of the cavity, and then compression molded to form a chip having the shape shown in FIG. 1. Next, this chip-shaped molded body was fired in air at 1200° C. for 4 hours to obtain a sintered body of T 1O2-6. The value of δ of TiO2-δ of the obtained sintered body was 0.05.

A NOx gas detector having the structure shown in FIG. 1 was constructed using the above T 102-δ chip. In this NOx gas detector, the insulating substrate was made of At203, and the heater was made of platinum.

Using the NOx gas detector thus obtained, sensitivity to various gases was measured. The measurement was performed by heating the NOx gas detection element to 500° C. with a heater and placing it in a predetermined gas.

The results are shown in Table 1.

Examples 2 to 16 General 2AxTi, -xO□ (A is At, V, Nb
.

Ta, Sb, As, Ga, In,
The production of a titanium-containing oxide containing at least one element selected from the group consisting of Sc and Y and consisting of Q (x (1)) involves combining the oxide of A and T i O The mixture was mixed in a molar ratio and calcined in air at 1000°C for 1 hour.Also, uTto, (B is Mg
, Ca, Sr.

Ba, Pb, Cd, Ni, Cr, Co, M
In order to produce a titanium-containing oxide containing at least one element selected from the group consisting of n, Zn, Fe, and Ln, the carbonate of B and TiO□ are mixed at a predetermined molar ratio, and then air This was carried out by baking at 1200° C. for 1 hour.

The obtained oxides and mixtures thereof were formed into chips in the same manner as in Example 1, and then fired in air at 1200°C for 4 hours to obtain chip-shaped sintered bodies shown in Table 1. . Table 1 shows the non-stoichiometric parameters of the obtained chip-shaped sintered body. Furthermore, the NOx sensitivity, 02 sensitivity, and CO sensitivity were measured for this chip-shaped sintered body in the same manner as in Example 1. The results are shown in Table 1.

These results show that the NOx gas detection element according to the present invention has high sensitivity to high concentrations of NOx, and is not affected by contaminants.

Comparative Example I S nO2 powder was molded into chips in the same manner as in Example 1, and calcined in air at 1200°C for 4 hours to obtain the non-chemical all-ring shape and rammeter (δ) shown in Table 1. A chip-shaped sintered body having the following properties was obtained. Regarding the obtained chip-shaped sintered body, the sensitivity to various gases was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 In Example I, the firing temperature of the chip-shaped molded body was set to 120
A chip-shaped sintered body was obtained in the same manner except that the temperature was changed from 0° C. to 150° C. and the firing time was changed from 4 hours to 11 hours. The values of the non-stoichiometric parameter (δ) in this case are o, oo
It was s. This chip-shaped sintered body was used as a NOx gas detection element, and the sensitivity to various gases was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 In Comparative Example 2, the firing conditions for the chip-shaped compact were changed to Co
A chip-shaped sintered body was obtained in the same manner except that it was fired at 1000° C. for 4 hours in N2 containing 5%. The resulting chip-shaped sintered body had a non-stoichiometric matrix rammeter (δ) of 0.55. This was used as a NOx gas detection element to measure the sensitivity of various gases. The results are shown in Table 1.

Example 17 The NOx level in automobile exhaust gas was analyzed using the NOx gas detector and chemiluminescence NOx meter of Examples 1 to 16 and Comparative Example 1. The engine operating conditions adopted at this time were a rotational speed of 150 rpm.

l was in the range of 13-20. As a result of comparing the analytical values of each detector, it was found that the analytical values of the chemiluminescent NOx meter and the analytical values of the detectors using titanium-containing oxides of Examples 1 to 16 were in good agreement. 0 in exhaust gas
2. It was found that NOx gas can be detected accurately up to high concentrations without being affected by changes in the concentration of contaminant gases such as Co and HC. On the other hand, the analytical value of the detector using SnO2 of Comparative Example 1 showed a value that was significantly different from the NOx concentration analytical value of the chemiluminescence NOx meter.

In Examples 18 to 31, N01C◯, R2, and HC sensitivity were each determined by the following methods.

(1) No sensitivity; resistance R in an atmosphere containing 0.025%
It was expressed as the ratio log (R2/R+) between I and resistance R2 in an atmosphere containing 025% and No. 11000pp.

(2) Go sensitivity - 25%, resistance R1 in an atmosphere containing No 500ppm and Co 50PPm, and 0
25%, resistance R2 in an atmosphere containing 500 ppm NO and 5000 ppm GO, l o g (R2/
R1).

(3) R2 sensitivity; resistance R1 and 025 in an atmosphere containing O25%, No 500ppm and H250ppm
%, the ratio to the resistance R2 in an atmosphere containing No 500 ppm and H25000 Ppm,], og(R2/R
+ ).

(4) HC sensitivity; ○25%, NO500ppm and C
Resistance R1 in an atmosphere containing 50 ppm of zHa and 02
5%, resistance R2 in an atmosphere containing 500 ppm NO and 5000 ppm C3Ha, l o g (R2
/R1).

It can be said that the larger the value expressed by log(R2), the higher the sensitivity to the gas.

Example 18 An aqueous ammonium sulfate solution and ammonia were added to an aqueous T i Cl 4 solution, and the resulting precipitate was filtered, washed, and then calcined in air at 900°C for 1 hr. The obtained fired powder is put into the cavity, and Ptf! is placed on both ends of the cavity. After embedding the poles, compression molding was performed to form a chip having the shape shown in FIG. Next, this chip-shaped molded body was heated in air for 12 hours.
It was fired at 00'C for 4 hours to obtain a sintered body of T i O2-δ. The value of δ of T i O2-δ of the obtained sintered body was 0.05.

An NOx gas detector having the structure shown in FIG. 1 was constructed using the above T i O2-δ chip. In this NOx gas detector, Al 203 was used for the insulating substrate and platinum was used for the heater.

Using the NOx gas detector obtained in this way,
Sensitivity to various gases was measured. The measurement was performed by heating the NOx gas detection element to 500'C using a heater and placing it in a predetermined gas.

The results are shown in Table 2.

Examples 19 to 21 Ammonium sulfate aqueous solution and ammonia were added to the T i CI J aqueous solution, and the resulting precipitate was filtered, washed, and then calcined in air at 900'C for 1 hr. Then, R2PtC1a, H2P dCl a, Rh
Aqueous solution of Cl 3-4H20 with Pt, Pd, Rh
Add to iO2 so that it is 300 ppm each,
After drying, it was fired at 500'C for 1 hour. The obtained powder was molded into chips in the same manner as in Example 18, and then fired in air at 1200''C for 4 hours.

This chip-shaped sintered body was treated in the same manner as in Example 18,
Sensitivity to various gases was measured.

The results are shown in Table 2.

Example 22 After applying the Pt/TiO2 powder obtained in Example 19 to the surface of the TiO2-δ chip obtained in Example 1, it was heated in air at 1200'C for 1 hr. ,
Fired. The sensitivity of this chip-shaped sintered body to various gases was measured in the same manner as in Example 18.

The results are shown in Table 2.

Examples 23-29 General formula AxT i I XO2 (where A is A1.N
b, Ta, Sb, As, Ga, In, SC, M
In order to produce a titanium-containing oxide containing at least one element selected from the group consisting of Mix at 1000'C in air for 1 hr.

This was done by firing. Also, BTiO3 (B is Ca
, representing at least one element selected from the group consisting of Sr, Ba, Pb, Cd, Zn, and Ln). This was carried out by mixing at a ratio of 100 to 1000 ml and calcining in air at 1200'C for 1 hour. The obtained oxides and their mixtures were formed into chips in the same manner as in Example 18, and then fired in air at 1200'C for 4 hours to obtain the chip-shaped sintered bodies shown in Table 1. Ta. P t / obtained in Example 19 was applied to the surface of the obtained chip-shaped sintered body.
After applying TiO2 powder, it was heated to 1200°C in air.
hr.

Fired. The sensitivity of this chip-shaped sintered body to various gases was measured in the same manner as in Example 18.

The results are shown in Table 2.

Example 3O NiO was mixed with TiO2 at a concentration of 1%, and the mixture was fired in air at 1200°C for 1 hour.

The obtained powder was converted into T i O2-δ obtained in Example 18.
After coating the surface of the chip, it was baked in air at 1200°C for 1 hour. The sensitivity of this chip-shaped sintered body to various gases was measured in the same manner as in Example 18.

The results are shown in Table 2.

Example 31 LaC○3 and Co (cH3COO)2 = 1
Mix at a molar ratio of
It was baked for 1 hour. The obtained powder was used in Example 1.
After coating the surface of the TiO2-δ chip obtained in step 8, it was fired in air at 1000'C for 1 hour. The sensitivity of this chip-shaped sintered body to various gases was measured in the same manner as in Example 18.

The results are shown in Table 2.

Margin below

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a typical embodiment in which the NOx gas detection element of the present invention is used in a NOx gas detector, and FIG.
- The figure shows a typical circuit diagram of a NO-, gas measuring device incorporating a NOx gas detector. In the figure, 1 is a NOx force detection element, 2 is an electrode, and 3
is an insulating substrate, 4 is a heater, and 1 is a NOx detector 1
, 6 is a circuit power supply, 7 is a voltmeter, 8 is a load resistance, and 9 is a heater power supply.

Claims (1)

[Claims] 1) Non-stoichiometric parameter (δ) is 0.01<δ<
(a) TiO_2, (b) composite oxide of metal and titanium in solid solution with TiO_2, and (c) metal and titanium forming an oxide with titanium and provskite structure, each having 0.5 oxygen vacancies. A NOx gas detection element made of at least one metal oxide selected from the group consisting of composite oxides with. 2) The NOx gas detection element according to claim 1, which has a layer containing an oxidation catalyst on at least the surface thereof.