JPH0611400B2 - Combustion catalyst with deterioration detection function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst body for exhaust gas purification and low temperature combustion, which has a deterioration detection mechanism.

2. Description of the Related Art Conventionally, a catalyst of this type in which a white metal is supported on an oxide such as activated alumina has been used. These not only oxidize reducing gases such as CO and HC, but also NO
It is said to be a three-way catalyst because reduction of oxidizing gas such as ₂ is also performed at the same time. Further, although catalysts using CuO-Mn ₂ O ₃ and rare earth oxides are also used, these are different from three-way catalysts in that they only oxidize the reducing gas.
Even if these catalysts deteriorate, there is no significant change in the physical properties of the catalyst, which is an indicator of deterioration. Therefore, it is necessary to install a sensor to detect the increase of incomplete combustion components (reducing gas) in the exhaust gas. It was necessary to provide another detection means such as a sensor for detecting the temperature decrease of the. However, even if these sensors are provided separately, they cannot be put to practical use for a long time because they are used at high temperatures, and in reality, a catalyst without a deterioration detection mechanism is used, which is harmful to the human body. Outgassing was happening.

The inventors (Me: at least one element selected from Fe, Mn, Cr, and V, 0 ≦ x ≦ 1, 0 <δ <0.5) is reversible at high temperature as a redox catalyst or equivalent point sensor. We found that it showed excellent performance, and filed a patent application,
I have also clarified the reason.

After that, when the second component SrMe′O ₃ (M′e: Ti, Zr, Hf) is added, it enters the grain boundary of the first component and increases the O ²⁻ ion transport number, which improves the catalyst and sensor performance. Not only is it significantly improved, but the coefficient of expansion is reduced to the same level as that of other metals and ceramic materials, making it easier to attach and support these materials, and the effect of eliminating the temperature dependence of the sensor is added. I found that I could do it. Furthermore, the catalytic performance, sensor sensitivity, and responsiveness are governed mainly by O ² -ion conductivity, and a small amount of Pd does not decrease at low temperatures.
Has been found to be improved by the addition of Pt, and it is possible to prevent the drawback that the catalytic effect of Pd and Pt is significantly reduced at high temperatures, and we have applied for a patent for these. However, at this point in time, it was not found that the catalyst was inevitably accompanied by a rapid increase in resistance when it deteriorated, so no application was filed to utilize the increase in resistance for deterioration detection.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention focuses on the fact that these catalyst bodies are accompanied by a sudden increase in electrical resistance when they deteriorate, and when they deteriorate, which is a problem with conventional combustion catalysts. Provided are a catalyst and a method for preventing the emission of gases harmful to the human body.

Means for solving problems The catalyst mainly composed of has the ability as a three-way catalyst equivalent to a conventional noble metal catalyst, and has the property that when deteriorated, the crystal form changes to increase the electric resistance. The present invention is intended to solve the problems that cannot be achieved by the conventional catalyst by detecting the change in the electric resistance and knowing the deterioration.

Action ^Has mixed conductivity of electrons and O ²⁻ ions. Mixed conductivity takes the electrons to reducing substances such as fuels and CO give O ^2- ions and oxidizing them, the electronic O ₂ or NO
_{It is} useful for giving an oxidizing substance such as _x to reduce these to take in O ²⁻ ion, and again providing to the reducing substance for mediating, in other words, exhibiting an oxidation-reduction catalytic action. Since the electronic conductivity of this substance alone is 10 ⁴ to 10 ⁵ times higher than the O ²⁻ ion conductivity, the catalytic action is
It is rate-controlled by O ^2- ion conductivity. Therefore, even if the electronic conductivity is suppressed to some extent, if the ionic conductivity is promoted, the catalytic ability becomes large. The addition of the second component SrM'eO ₃ serves in this way to increase the catalytic capacity. Electronic conduction is mainly performed in the crystal grains, whereas ionic conduction is performed at the grain boundaries, but SrM'eO ₃ is separated into two phases. This is because it helps to create the grain boundaries of. Even in this case, at a low temperature of 500 ° C. or lower, the ionic conductivity is lowered and the catalytic ability is lowered. The decrease in the ionic conductivity occurs because the charge transfer reaction on the surface is delayed, and the improvement can be seen by the addition of a small amount of the platinum group element. The conventional noble metal three-way catalyst deteriorates rapidly at high temperatures, but it can be considerably improved by using the first component and the second component together.
Since it works strongly as an O ² -ion donor, it is considered to prevent sintering, which is a cause of deterioration of the noble metal catalyst.
In the catalyst body of the present invention, O ^{2 −} ion conduction is carried out through defects, so that the more defects there are, the higher the O ^{2 −} ion conductivity and the greater the catalytic ability. This substance is stable even if it has more defects than other oxides, and reversibly takes in and out oxygen according to the oxygen concentration in the atmosphere. However, the allowable amount of defects is still limited, and if it exceeds 0.5, the crystal collapses and the repair becomes extremely slow, which is the cause of catalyst deterioration.

On the other hand, the electrical resistance of the catalytic body is dominated by electronic conduction, and at high temperatures where catalytic activity appears, the transition metals (Co, Fe, M
n, Cr, V, Ti, Zr, Hf) is determined by the ion and O conductivity vs. Me ^3- -O-Me number of ⁴⁺ composed ^2- ions. When oxygen is released and defects occur, an electrically neutral condition is maintained,
Me ⁴⁺ becomes Me ³⁺ , the conductive pair disappears, and the electric resistance increases. When the crystal collapses δ> 0.5, such a conductive pair disappears altogether and the resistance significantly increases. The deterioration mode of this catalyst is only that this conductive pair disappears at all and the crystal collapses. In that case, the electric resistance inevitably increases rapidly, and therefore the deterioration of the catalyst can be known from the increase in the resistance.

Example Next, the effect of the present invention will be described based on an example.

<Reference Example> The effect of the first component alone will be described. Add oxides to each metal element Sr _0.5 La _0.5 CoC ₃ , Sr _0.65 La _0.35 Co _0.7 Fe _0.3 O ₃ , Sr
_0.8 La _0.2 Co _0.4 Fe _0.6 O ₃ and SrFeO ₃ are mixed to have a composition, and the mixture is heated and reacted at 1200 ° C. for 4 hours in air to prepare a compound, and 1.5 g of the compound is supported on 2.0 g of silica-alumina fiber, Fill the central part of the tubular furnace made of quartz glass,
On the other hand, as shown in Fig. 1 (a side view, b is a top view), the same material was used to mold a pellet 2 in which a platinum lead 1 for resistance measurement was embedded to form a combustion catalyst body with deterioration detection function. Near its catalyst-packed layer, and excisional the inlet side, notwithstanding et keeping the temperature markedly deteriorate 850 ° C. The atmosphere in the usual of a noble metal catalyst, CO1000ppm, O ₂ 500ppm (remainder N ₂₎ a space velocity of 20,000 h ^- CO at the outlet of the pipe at a rate of ¹
The concentration and the electric resistance of the pellet were measured, and changes in the CO removal rate and the electric resistance were obtained. This test was continued until the CO removal rate reached 50%.

The change in CO removal rate and the change in electric resistance were as shown in FIG. Depending on the composition of the sample, for example, the CO removal rate has a maximum around x = 0.3 in the initial stage, the life is longer when x is larger, and there is a difference as shown in the previous application regarding the catalytic activity. It can be seen that for all samples it can be said that the electrical resistance rapidly increases when deterioration occurs.

<Example 1> The first component, taken up _{Sr 0.65 Lc 0.35 Co 0.7 Fe 0.3} O 3-δ, a SrTiO ₃ as the second component to the powder 0,20,4
Mixing was carried out at a ratio of 0, 60, 80 mol%, and the resistance measuring part formed a combustion catalyst body with deterioration detecting function as shown in FIG. 1 as in the reference example. Also, the catalyst part was molded into a large pellet, heated and baked in air at 1350 ° C. for 2 hours, and then re-ground to carry 1.5 g of it on 2.0 g of silica-alumina fiber,
Otherwise, the catalyst carrier and pellets for resistance measurement were set in the center of the quartz glass tube furnace in the same manner as in Example 1, and CO 150 ppm NO ₂ 40 ppm (remaining N ₂ ) was passed through at a space velocity of 8000 h ⁻¹ . On the other hand, the CO removal rate and the N ₂ production rate were determined while heating in an electric furnace and changing the ambient temperature for control, and subsequently, the change in the CO removal rate and the change in electrical resistance were determined under the same conditions as in Example 1.

The CO removal rate and N ₂ production rate at each temperature obtained at the beginning are the third
The result of the deterioration test was as shown in FIG. 5.

From this, the addition of SrTiO ₃ as a catalytic ability is 40 to 70 mol.
It can be seen that the percentage of% is excellent, but it is recognized that a sharp increase in electrical resistance occurs when deterioration occurs in any composition.

Further, the thermal expansion coefficient of the first component alone was larger than that of heat-resistant metal materials and ceramic materials, making it difficult to support, but the addition of the second component SrTiO ₃ made it smaller as shown in the table. Approaching the coefficient of thermal expansion of ceramic materials,
There is an advantage that attachment and support become easy.

Example 2 A mixture of Sr _0.65 La _0.35 Co _0.7 Fe _0.3 O _3−δ with 60 mol% of SrTiO ₃ mixed and a mixture of this mixture with Pd further added to 0.6% 3 to 100 parts each Cylindrical honeycomb (outer diameter 50 mm, length 80 mm) made of porous alumina by mixing 100 parts of binder made by adding No. water glass and aluminum dihydrogen tripolyphosphate at a ratio of 10: 1 into a slurry shape , Apparent aperture ratio 25%), and heated and solidified at 120 ° C. for 30 minutes. The amount of these catalysts deposited was about 10 g, which was the same for both the samples and the honeycomb weight of 20 g. Separately, 0.6 part of Pd black was added to 100 parts of the above-mentioned binding part, and the honeycomb was dipped in a slurry and heated repeatedly to prepare a product carrying only Pd of about the same weight as that of the above Pd black addition. As shown in FIG. 6, a kerf 2 was formed in the peripheral portion of the honeycomb 1, and Pt paste was applied so as to face each other, and baked at 900 ° C. for 30 minutes to form an electrode 3 for resistance measurement.

Then, the temperature dependence of the catalytic ability and the deterioration test were conducted under the same conditions and methods as in Example 2.

The CO removal rate and N ₂ production rate that were initially obtained are shown in FIGS. 7 and 8, and the CO removal rate and the change in electric resistance in the deterioration test are shown in FIG. 9.

The addition of Pd significantly improves the low temperature catalytic ability. Further, the combined use of the perovskite composite material and Pd has an effect of preventing deterioration at high temperature, which is a drawback of using only Pd. In general, it is recognized that the catalyst material of the present invention inevitably accompanies a sudden increase in electric resistance even when it deteriorates.

The combustion catalyst may be a mixture or a sinter.

In any of the above examples, when the catalyst deteriorates, the resistance is rapidly increased. Therefore, it can be known that the deterioration has occurred by observing the change in the electric resistance of the catalyst itself. A conventional catalyst supporting only Pd is also shown in Example 3, but since the conventional catalyst hardly causes such a change, even if it deteriorates and emits a harmful gas to the human body, I could not know.

In addition, in Example 1, only the case where Fe was added to Me in the first component was shown, but the deterioration mode is limited to 0.5 <δ and the crystal form is changed, and the crystal form is not changed.
The same applies to the case of substitution with an element other than Fe.

Although only the case where SrTiO ₃ is added as the second component is described in Example 2, the addition of the second component causes the phase separation of the second component from the first component to act as a grain boundary forming agent, and O ^{2 −} ion The purpose is to increase the catalytic ability in order to increase the transport number, and when Zr and Hf are added to'Me, it also plays a similar role, and when deterioration occurs, it changes to electrical resistance. Not considered.

Furthermore, in Example 3, the effect of the addition of Pd as the third component was shown, but this is for promoting the charge transfer reaction at low temperature and improving the catalytic ability at low temperature, and it has the same function. Although the addition of a platinum group element to improve the low-temperature catalytic activity is also useful, the increase in electrical resistance due to deterioration can be expected as in the case of Pd.

In the above examples, the mixture, the sintered product, and the binder of the mixture and the sintered product were used as the catalyst body, and there was a difference in the catalytic ability depending on the processing method, but the deterioration was Was also accompanied by a surge in electrical resistance. The essence of deterioration is 0.5
This is because the crystal collapse and the disappearance of the conductive pair due to <δ are considered to mean that the deterioration can be detected by measuring the electric resistance regardless of the binding of the catalyst body and the supporting method.

EFFECTS OF THE INVENTION As described above, the combustion catalyst body with deterioration detecting function of the present invention can detect deterioration of the catalyst as a change in resistance value in use.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a sintered pellet for resistance measurement used in a combustion catalyst body having a deterioration detecting function according to an embodiment of the present invention.
FIG. 3 is a change diagram of CO removal rate and electric resistance in the reference example, and FIG. 3 is SrTiO 3 in the first embodiment of the present invention.
_{3 is} a change diagram of the CO removal rate depending on the addition amount, FIG. 4 is a change diagram of the N ₂ production rate according to the addition amount of SrTiO ₃ in the first embodiment, and FIG. 5 is a CO change according to the addition amount of SrTiO _{3 in the} first embodiment. FIG. 6 is a change diagram of the removal rate and the electric resistance, FIG. 6 is a configuration diagram of the catalyst-supporting honeycomb and the electric resistance measuring body in the second embodiment of the present invention, and FIG. 7 is the second embodiment in comparison with the conventional example. FIG. 8 is a diagram showing the effect of the sample of the example on the catalytic ability by the CO removal rate, FIG. 8 is a diagram showing the same N ₂ production rate,
FIG. 9 is a diagram showing changes in the CO removal rate and electric resistance.

Continuation of front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B01J 23/84 301 M 8017-4G A 8017-4G 311 M 8017-4G A 8017-4G 23/86 M 8017- 4G ZAB A 8017-4G F23D 14/18 Z G01N 27/00 L 7414-2J

Claims (2)

[Claims] 1. A chemical formula (Me: at least one element selected from Fe, Mn, Cr, V, 0 ≦ x ≦ 1, 0 ≦ δ ≦ 0.5) as a main component and SrMe′O ₃ (Me ′: Ti, Zr) as the second component , At least one element selected from Hf) and, if necessary, at least one element of the platinum group, and a lead provided separately from the catalyst body. A combustion catalyst body with a deterioration detecting function, characterized in that a change in the catalyst body is detected by measuring an electric resistance between the leads. 2. A combustion catalyst body with a deterioration detecting function according to claim 1, wherein the second component is added in a proportion of 40 to 70 mol%.