JPS5952782B2 - gas sensing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas-sensitive element, and particularly to a gas-sensitive element having a catalyst layer provided on the surface thereof to improve sensitivity selectivity, aging characteristics, and the like.

This invention relates to a gas-sensitive element with improved properties. Gas-sensitive elements are known that utilize the fact that the specific resistance of the surface of an oxide semiconductor changes when gas comes into contact with the surface of the oxide semiconductor.

For example, ZnO, SnO2, and Fe exhibiting N-type semiconductor properties. O
. When a reducing gas comes into contact with the material, the resistance value decreases, and when an oxidizing gas comes into contact with the material, the resistance value increases. In addition, in an oxide semiconductor exhibiting P-type semiconductivity, increases and decreases in resistance value exhibit an inverse relationship. In the above-mentioned oxide semiconductors, the reactivity with various gases, that is, the selectivity, is determined by the semiconductor surface temperature, surface electron level structure, porosity, pore size, etc.; As a result, the sensitivity is low and the selectivity is not sufficient. Therefore, attempts have been made to increase the sensitivity by adding a catalyst such as Pt or Pd to the oxide semiconductor, but this method has the following drawbacks. In other words, since the oxide semiconductor and the catalyst, which are the main components, have different optimal firing temperatures, it has been extremely difficult to select a firing temperature that fully brings out the characteristics of both. Furthermore, when used as a gas-sensitive element under high temperature conditions (
In order to increase the sensitivity of the gas-sensitive element, it is preferable to provide a heating section and use the oxide semiconductor surface to maintain it at 300°C.)
However, the catalyst is dissolved in the oxide semiconductor, causing a decrease in sensitivity and an increase in changes over time. The present invention improves the above-mentioned drawbacks of the conventional element, and includes 99.85 to 20 mol% of ZnO and 0.1 to 50 mol% of Me2O3 (However, Me is Sc , Y, La) and Me'.

00 to 0.05 to 30 mol% (however, Me' is Ga, B
, In, Fe, Al, and Cr) and ptcl as an additive to the silica-alumina compound.

The object of the present invention is to provide a gas-sensitive element comprising a catalyst layer containing 0.01 to 10 wt. Note that the composition range in the present invention was limited for the following reasons.

That is, when ZnO exceeds 99.85 mol%, Me.
O. When ZnO is less than 0.1 mol% and when Me″203 is less than 0.05 mol%, the change in resistance due to gas adsorption is small, and when ZnO is less than 20 mol%, Me2O3 is less than 50 mol%. If exceeded and Me″2
When 03 exceeds 30 mol%, the change in resistance due to gas adsorption is small, and the change in resistance with respect to temperature becomes large, so this range was set. Furthermore, the amount of Ptcl2 added to the silica alumina system was set at 0.01 to 10% because Ptcl2 is necessary from the viewpoint of improving the aging characteristics, and if it is less than 0.01% by weight, the effect is small.
If it exceeds % by weight, the change in resistance value due to gas adsorption becomes small, so this range was set. The present invention will be explained in detail below with reference to Examples.

First, the gas-sensitive element according to the present invention has a pair of electrodes 2 on the outer peripheral surface of a cylindrical insulating base 1, as shown in cross section in FIG. A gas sensitive body 3 is provided. Furthermore, a catalyst layer 4 made of a silica-alumina compound containing Ptcl2 is provided on the surface of the gas sensitive body 3. Further, the gas-sensitive element constructed as described above is assembled on a pin leg, for example, as shown perspectively in FIG. Note that 5 in the figure is the lead wire, and 6 is the lead wire.
indicates an insulating plate, and 7 indicates a heater. The heater 7 is provided to improve the sensitivity of the gas sensitive element, and can be provided as appropriate if necessary. Note that the catalyst layer 4 does not necessarily need to completely cover the surface of the gas sensitive body 3. The gas-sensitive element according to the present invention is manufactured, for example, as follows.

That is, ZnO, Me2O3 (Me is Sc, Y, La
) and Me″203 (Me is G
At least one of a, B, In, Fe, Al, Cr) is weighed out in a predetermined composition ratio, mixed, water or a binder is added to form a paste, and a pair of electrodes 2 are provided as shown in Figure 1. 600 to 1 after drying.
It is fired at 000°C to form a gas sensitive body. On the other hand, the silica-alumina compound is ground into a fine powder using a grinder such as a planetary mill or a pot mill.

Next, this fine powder and platinum chloride (Ptcl2) are weighed out in a predetermined composition ratio, mixed, and dried to obtain a catalyst. This catalyst is coated on the gas sensitive member 3 and dried, and then
C. to obtain a gas-sensitive element.

Next, various characteristic examples of the gas-sensitive element according to the present invention are shown in FIGS. 3 to 9.

First, Figures 3 to 5 show Me2O3 (
However, at least one of Me-Sc, Y, La) and Me″203 (however, M6 is Ga, B, In, Fe)
Sensitivity (RO/Rg
). A silica-alumina compound containing 0.2% by weight of Ptcl2 was used as the catalyst layer, and curve 1 in the figure shows Ga2O3, B2O3, Fe2O3, c
Resistance value in case of r2O3, curve 2 is B2O3, In2O
3. Resistance value in case of cr2O3, and curve 3 is Al2O
3 and Fe2O3 are shown, respectively. FIG. 3 shows the case where SC2O3 is used as Me2O3, FIG. 4 shows the case where Y2O3 is used, and FIG. 5 shows the case where La2O3 is used.

Curves 1'', 2'' and 3'' indicate sensitivities corresponding to curves 1, 2 and 3, respectively.As is clear from FIGS. 3 to 5, the gas-sensitive element according to the present invention always has excellent sensitivity. Further, Figures 6 to 8 show the relationship between the amount of Ptcl2 added to the silica alumina compound when the amount of Me2O3 added was fixed at 2 mol% for curve 1 in Figures 3 to 5. Indication of temporal change characteristics.

The measurement shows the rate of change in resistance value after 5000 hours of energization, and the dotted line shows the case where Pt and Pt oxide catalysts were used as a comparative example.
, FIG. 7 shows the case using Y2O3, and FIG. 8 shows the case using La2O3. As a result, as is clear from Figs. 6 to 8,
In the gas-sensitive element according to the present invention, a decrease of only about 5% at most was observed during long-term use. Like this P
The reason why the rate of change over time of the gas-sensitive element added with tcl2 is small is considered to be due to the following reason.

First, due to the two-layer structure in which the gas sensitive material and the catalyst layer are separated, the catalyst Ptcl2 does not dissolve solidly in the gas sensitive material.
This is thought to be because the catalyst performance does not deteriorate. In addition, Pt, Pd, etc., or their oxides, which have been conventionally used as catalysts, cause grain growth and reduce the surface area of the catalyst, but catalysts made from a combination of Ptcl2 and silica-alumina compounds are chloride-based. This is thought to be because grain growth is less likely to occur, and the surface area is maintained in a large state because it is supported on a heat-resistant silica-alumina compound. FIG. 9 shows CO, H2, C2H6, C3H8, C4Hl obtained using the gas-sensitive element according to the present invention.
It shows the rate of change in resistance value with respect to O gas concentration, and as a result, it is clear that it has excellent selectivity.

As described above, the gas-sensitive element according to the present invention has excellent sensitivity selectivity and temporal change characteristics, and has excellent features never seen before.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view showing a configuration example of the present invention, FIG. 2 is a perspective view showing an example of an apparatus using a gas-sensitive element according to the present invention, and FIGS. 3 to 5 are Me2O3 A curve diagram showing the relationship between resistance value and sensitivity with respect to the amount of addition. Figures 6 to 8 are curve diagrams showing changes over time depending on the amount of Ptcl2 added when the amount of Me2O3 added is fixed at 2 mol%. FIG. 3 is a curve diagram showing the selectivity of the gas-sensitive element according to the invention. 2... Electrode, 3... Gas sensitive body, 4... Catalyst layer.

Claims (1)

[Claims] 1 A pair of electrodes and 99.85 to 20 mol % of ZnO and 0.1 to 5 mol % of Me_2O_3 provided between a pair of electrodes.
0 mol%. (However, Me is at least one of Sc, Y, and La)
and 0.05 to 30 mol% of Me'_2O_3 (where Me' is at least one of Ga, B, In, Fe, Al, and Cr); A gas-sensitive element comprising a catalyst layer made of a silica-alumina compound containing .01 to 10% by weight of PtCl_2.