JPS60110336A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To provide a catalyst for removing CO, NOx or the like excellent in heat resistance, life and SO2-poisoning resistance, obtained by supporting a platimum group element or a rare earth element by a support containing calcium aluminate and a specific amount of zirconium oxide. CONSTITUTION:Alumina cement >35% as calcium aluminate and 5-60% of ZrO2 or composite oxide containing ZrO2 such as ZrO2-SiO2, ZrO2-CaO or ZrO2- MgO as ZrO2 are mixed with water in fine powdery form. Or, a proper amount of a heat resistant base aggregate material such as a silica, a silica-alumina or an alumina type aggregate material is further added to and mixed with the slurry in a fine powdery form. This mixture is molded into an arbitrary form while the molded one is aged, dried and solidified to prepare a catalyst carrier. This carrier is allowed to support 0.001-0.1% of a platinum group metal such as Pt, Pd, Ru, Rh or Ir in an aqueous solution of chloride or nitrate and a rare earth element such as La, Ce or Sm in an oxalate form.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to automobile exhaust gases and household combustion equipment such as carbon monoxide and nitrogen generated from equipment such as kerosene stoves, kerosene fan heaters, and table roaster-1 electric ovens. The present invention relates to a catalyst body that purifies exhaust gas such as oxides.

Conventional configurations and their problems Most conventional catalyst configurations use alumina, cosilite, cane earth, or magnesia as catalyst carriers, and these are formed into formed bodies such as honeycomb structures. The mainstream is a catalyst body formed into a pellet or granule, on which a catalytic metal is supported. In addition, examples of the catalytic metal supported on the tactile support, which is a catalytic metal supported on a support made of lime aluminate and titanium oxide, include platinum group metals and rare earth elements.

Next, problems with these conventional catalyst bodies will be described. The disadvantages of alumina (γ-A22o3), cordierite, cinnabar earth, and magnesia catalyst carriers are that they have poor heat resistance, and their specific surface area decreases due to nontaling when used at high temperatures. For example, γ-A2203'lf: For example, when used at high temperatures, stable α from 203 to γ-8
-8 to 203, and along with this, the specific surface area decreases due to sintering, causing catalyst deterioration. Also,
Regarding the causes of deterioration of catalytic metals on supports, (1) a mechanism in which one to several atoms separate from metal particles and move on the surface (
(2) A mechanism in which the entire particle moves on the surface while overcoming the strong carrier-metal interaction due to metal-metal interaction (particle transfer theory); (3) A mechanism in which the entire particle moves on the surface while overcoming the strong carrier-metal interaction (particle transfer theory); For example, there are mechanisms for moving the particles on a carrier or a carrier.

According to the above theory, metal catalysts on conventional catalyst carriers gradually agglomerate, resulting in a decrease in activity due to a decrease in specific surface area. The carrier that promotes the growth of metal particles in this way is
γ-Af! , 203, etc., and the same applies to those made of lime aluminate and titanium oxide. The type of carrier on which the catalytic metal is supported greatly influences the catalytic properties.

OBJECTS OF THE INVENTION The object of the present invention is to provide a catalyst having excellent heat resistance, long life, and resistance to SO2 toxicity.

Structure of the Invention The present invention is characterized in that the needle containing zirconium oxide, which contains at least lime aluminate and zirconium oxide, contains 5 to 60% by weight of zirconium oxide.
At least one selected from the group consisting of platinum group elements and rare earth elements is supported on a carrier.

DESCRIPTION OF THE EMBODIMENTS The binder of the catalyst support used in the present invention is alumina cement, which is distinguished from Portland cement.

Alumina cement bar is generally mAIV, 2o3・nca
It is represented by o, Voltland Cement Ha, m'si○
2・n'cao Portland cement, which is expressed as
It has the disadvantages of poor spalling properties, slow curing speed, and is easily attacked by sulfate ions. On the other hand, alumina cement has high heat resistance and a fast curing speed, and can be said to be a preferable cement from the viewpoint of catalyst production.

When the alumina cement u lime content exceeds 40% by weight,
Although the mechanical strength of the carrier increases, its heat resistance decreases and it reacts with heavy metal oxides at high temperatures, leading to thermal destruction of the catalyst. On the other hand, if the lime content is low, heat resistance will improve, but
Mechanical strength decreases, curing time during molding increases, and productivity also deteriorates. When the alumina content is less than 35% by weight, the heat resistance decreases. On the other hand, as the alumina content increases, the heat resistance improves.

The preferred composition of alumina cement is lime content of 15 to 50.
% by weight, especially 20-40% by weight, alumina content 36-85
Weight%, especially 30 to 60% by weight is optimal. The optimum particle size of the crushed lime aluminate is 100 microns or less, preferably 60 microns or less.

The content of lime aluminate in the catalyst carrier is required to be at least 35% by weight in view of mechanical strength.

Next, as the zirconium oxide, not only zirconium oxide alone but also a composite oxide containing zirconium oxide may be used. Among zirconium oxides, in addition to ZrO2, which exists most stably, several lower oxides have been reported, but there is no clear crystal form. ZrO2 is
This material has excellent thermal stability and is commonly used in the porcelain and refractory industries. Composite oxide of zirconium oxide (ZrO2-8102, ZrO2-CaO1Z
r02-”10% ZrO2-H King02, ZrO2-
Examples include Y2O2.

Zr02ij: It has a high melting point of 2716°C, and when used as a catalyst carrier material, has the effect of suppressing the reduction in surface area due to sintering and the growth of catalyst metal particles.

A suitable content of zirconium oxide in the carrier is 5-6
It is 0% by weight. If it is less than 6% by weight, no effect of adding zirconium oxide can be expected.

On the other hand, if the amount exceeds 60 M%, the amount of lime aluminate decreases and the bonding strength weakens, making it unusable. Also,
From the viewpoint of formability, etc., the particle size of zirconium oxide is 10
It is 0 micron or less, particularly preferably 60 micron or less.

This zirconium oxide is mixed with lime aluminate as a binder by adding enough water for molding, molded into an arbitrary shape, and then cured and dried to solidify. A catalyst carrier is thus obtained. In this production method, the addition of zirconium oxide has the effect of improving moldability, particularly the fluidity of the material, and is suitable for catalyst supports using lime aluminate as a binder.

By mixing zirconium oxide, which has excellent heat resistance and poisoning resistance, with lime aluminate, this catalyst carrier suppresses particle growth of the supported catalyst metal due to non-talling, etc. Furthermore, it is resistant to SO2 poisoning. Due to the influence of zirconium oxide, which is strong against sulfur, the catalyst metal itself becomes resistant to sulfur poisoning. In other words, in the past, sulfur compounds were first captured in lime aluminate and then internally diffused to poison metal oxides, but zirconium oxide is supported on zirconium oxide because it has excellent resistance to sulfur poisoning. Catalytic metals are also no longer susceptible to sulfur poisoning.

The catalyst support of the present invention can be used with just lime aluminate and zirconium oxide, but in order to further increase the mechanical strength, transverse rupture strength, and heat resistance against cracking of the catalyst, a heat-resistant group is added. It is better to add aggregate. As the heat-resistant base aggregate, silica base aggregate, silica/alumina base aggregate, alumina base aggregate, silicate minerals, mullite, corantum, sillimanite, and magnesia minerals can be used. Depending on the temperature at which the shredded catalyst is used, low temperatures (300~
700°C), it is preferable to use a general granular aggregate, and for high temperatures (70°C or higher), it is preferable to use a heat-resistant granular base aggregate.

To explain in more detail, there are silica stones and the like as silica-based substrates. These base aggregates are mainly composed of SiO2, and silica-alumina base aggregates include chamotte, waxite, high alumina, etc., and SiO2-A2203
is the main component. α-AL2 as alumina base aggregate
03. β-AI! , 203. γ-Afi203. p-
A℃203 etc. Further, common major mineral phases such as shite, silicate minerals, mullite, corundum, sillimanite, and β-alumina are used. These base aggregates can be crushed to a certain extent, or base aggregates such as commercially available conical silica sand, alumina, and chamotte can be used.Generally, commercially available silica sand or chamotte is used. It is convenient to do so.

Furthermore, for the purpose of increasing heat resistance, it is optional to add dealkalized glass fiber, fibrous iron wire, silica/alumina fiber, asbestos, etc.

In addition, carboxymethyl cellulose,
Addition of clay minerals such as methylcellulose, holvinyl alcohol, alcohol, and bentonite makes molding easier.

Next, a description will be given of the catalyst supported on the catalyst carrier having the above-mentioned composition.

The supported catalyst is mainly a platinum group metal, including platinum, palladium, ruthenium, rhodium, iridium, and Al, and their salts are preferably chlorides or nitrates. Typical examples include tetrachloroplatinic acid, hexachloroplatinic acid, and palladium chloride. These metal salts are used after being dissolved in a solvent such as water or alcohol. The concentration varies depending on the amount deposited and the supporting method, but if the solution is too concentrated, the dispersibility of the catalyst particles will deteriorate, so the optimum concentration is determined depending on the purpose of use, shape, etc.

Especially when platinum group metals are used, compared to conventional platinum catalysts,
When the amount of platinum supported is 0.001 to 0.1% by weight, a catalyst body with excellent initial performance and lifetime performance can be obtained. In other words, conventional platinum catalysts use carriers such as alumina and cordierite, and the amount of platinum supported is 0.5 to 0.1% by weight.When the amount of platinum supported is less than 0.1% by weight, the life performance is particularly deteriorated. is large, and the amount supported is common knowledge.

- When using the catalyst carrier of Rikiki's invention, high performance is achieved even if the amount of platinum supported is minute.

As described above, when the catalyst carrier of the present invention is used, a high-performance catalyst body can be obtained in which only a small amount of platinum or the like is supported.

This is because a part of the aluminate lime constituting the carrier absorbs water and Aflt20. This is because <ncao is partially dissolved and Cadi is partially liberated, and the solution exhibits alkalinity. On the other hand, raw materials for noble metal catalysts are mostly chlorides; for example, in the case of chloroplatinic acid, when dissolved in water, Pt (462- ion
PtCf! , 6(OH)k is formed. This salt PtCf
16(OH) It is generated near the surface of the Id carrier and does not reach deep into the pores. Therefore, the solidity distribution of the catalyst metal of the present invention is concentrated on the surface and does not diffuse into the interior of the carrier.

That is, as described above, the catalytic metal ions turn into hydroxides on the surface of the carrier and adhere to Zr02 as they are. Furthermore, since the carrier is alkaline, the catalytic metal cations and a part of the carrier surface form a compound and firmly adhere to the carrier. In this way, it is possible to support only the surface layer, so the amount supported can be reduced. A high-performance catalyst can be obtained even with a small amount.

Although the above discussion has focused on platinum group metals, the same applies to the support of catalytic metals such as rare earth elements, lanthanum, cerium, samarium, and yttrium on the carrier. Typical salts of these catalytic metals are oxalates, nitrates, and hydroxides.0 There is a strong relationship between the amount of supported catalyst and performance, and normally, as the amount of supported catalyst increases, performance improves accordingly. If the amount is too large, problems such as drop-off of the catalyst and non-uniform dispersion of the catalyst may occur. Furthermore, by supporting two or more types of various metals and metal oxides in addition to the amount of the catalyst, the purpose of use, shape, low-temperature activity, life, etc. can be improved.

Example 1 A disk with a diameter of 1541B and a thickness of 15 knits made of lime aluminate, zirconium oxide, and silica dust as a heat-resistant base aggregate,
A honeycomb-shaped carrier was prepared in which 745 holes with a diameter of 4.1M were provided in the thickness direction.The manufacturing method for this carrier was as follows. That is, to 100 parts by weight of the above raw materials mixed in various proportions as shown in Table 1, 30 to 40 parts by weight of water, 4 parts by weight of alkali-resistant glass fiber, and methyl cellulose (
(0.5 parts by weight was added and wet-mixed, press-molded, dried, poured in a water bath at 90''C, and dried. PT, PA, and Ce were used as catalysts. pt is a chloroplatinic acid aqueous solution <1.9/1 oocC)-1, carrier 1
-romji phase 6 (0,028% by weight) as pt per piece, Pd is expressed as palladium chloride aqueous solution (0,5, V/
100CC)'f: used, equivalent to 35■ as Pd (0,
014C)' and 14(llp phase 4 (
0,056% by weight) and dried at 500″C for 1
Pt--Pd--Ce was supported by heat treatment for several hours.

The performance of the thus obtained catalyst body was as follows: at 200″G, space velocity 10.000 hr″, Co inlet concentration 300p.
The CO purification ability was measured and compared under pm conditions. The presence or absence of heat resistance was determined by comparing the performance after heating at 700'C for 1 hour and the performance after heating at 900°C for 50 hours.

As is clear from the Examples in Table 1, the effect of Zr02 appears when the content in the carrier is 5 to 60% by weight.

If it exceeds 60% by weight, the amount of lime aluminate decreases and moldability becomes impossible.

Example 2 In Example 1, Zr02 was replaced with ZrO2 with a composition of &6.
Z r02-5 i02 , which is a composite oxide of Z
r02-T102.

ZzO2-CaO, ZrO2-MgO, Zr02-Hf
The CO purification ability was measured with respect to what was changed to O2, Zr02-Y2O2.

All 100%, 900° after heating at 700″C for 1 hour
After heating at C for 60 hours, the results were 97%, 98%, and 22 ga, respectively.

They were 99%, 98%, 98%.

Example 3 The composition of black 6 in Example 1 and its Z r
02 was extruded using rutile type TiO2 and the moldability was compared. show. 1 is a rectangular gas passage hole, 2 is a partition wall 0 extrusion molding conditions are partition wall 2
The condition is that the dimension of the width a is 1.0 to 0.1 mm.

These 8 dimensions are the same as the opening diameter of the molded product outlet of the Ni-Cam die.

In addition, the lime aluminate, zirconium oxide,
The particle size of the titanium oxide powder is as follows.

Lime aluminate...Zirconium oxide below 50 microns...Titanium oxide below 20 microns...
Below 20 microns Table 2 shows the results of moldability in this case.0 Table 2 (Note) ○...Moldable ×...Not moldable As is clear from the examples, the carrier composition of the present invention was When used, honeycomb structures with extremely thin wall thicknesses are obtained.

This means that it is possible to increase the porosity and surface area of the catalyst, and this f'L greatly contributes to improving the performance of the catalyst.

Example 4 A with a composition of 6 in Example 1 and its Z r0
Regarding B, which uses TlO2 instead of 2, the SO resistance
2. A toxicity test was conducted. The results are shown in FIG. The test method is to apply a catalyst heated to 400°C at 70°C).
Air mixed with ppm of So2 gas and 1100 ppm of CO gas was passed through, and the C◯ purification rate was measured every 10 hours, and the degree of deterioration of the catalyst by the S◯2 gas was measured.

As is clear from FIG. 2, the product of the present invention is different from the conventional TiO
Compared to a catalyst body using a 7-based carrier, the inferiority is small.

Effects of the Invention As described above, the catalyst of the present invention has excellent heat resistance, stability in terms of life, and excellent resistance to S02 poisoning.

In addition, when producing a catalyst carrier, it has good moldability and can be easily molded into complex shapes, which also improves production yield.

[Brief explanation of drawings]

Figure 1 is a plan view of a catalyst carrier in an example, and Figure 2 is a C
O showing a comparison of O purification rates

Claims (1)

[Scope of Claims] 0) A catalyst body for exhaust gas purification, characterized in that it supports at least one catalyst metal selected from the group consisting of lime aluminate and elemental zirconia oxide. (2) The exhaust gas purifying catalyst body according to claim 1, wherein the zirconium oxide is a composite oxide containing zirconium oxide.