CN1137945A

CN1137945A - Catalyst for purifying exhaust gases

Info

Publication number: CN1137945A
Application number: CN 96104057
Authority: CN
Inventors: 坂野幸次; 杉浦正洽; 熊井叶子
Original assignee: Catala Industrial Co ltd; Toyota Motor Corp
Current assignee: Catala Industrial Co ltd; Toyota Motor Corp
Priority date: 1995-01-17
Filing date: 1996-01-17
Publication date: 1996-12-18
Also published as: JPH08252459A

Abstract

A catalyst for purifying exhaust gases comprises a catalyst carrier made of potassium titanate and a noble metal loaded on the catalyst carrier. The catalyst carrier is substantially free from alumina. This catalyst can oxidize at least hydrocarbons in exhaust gases at a high catalytic activity even at low temperatures, and at the same time can suppress SO2 from converting into sulfates. This catalyst does not employ substance like alumina exhibiting solid acidity as a catalyst carrier. Further, this catalyst can be used for purifying exhaust gases from diesel engines to suppress particulates and sulfates from being emitted, and to improve conversions of hydrocarbons and-carbon monoxide.

Description

Exhaust gas purifying catalyst

The present invention relates to an exhaust gas purifying catalyst which suppresses sulfur dioxide (SO) in combustion exhaust gas discharged from an automobile internal combustion engine, boiler, etc₂) While oxidizing and removing Hydrocarbons (HC) and oxygen in the exhaust gasCarbon (CO) is converted. The invention also relates to a trap or open-flow catalyst for removing carbon monoxide (CO), Hydrocarbons (HC) and Soluble Organic Fractions (SOF) from diesel exhaust gases.

One of the catalysts disclosed in Japanese unexamined patent publication (KOKAI) No. 52-29487, which comprises a porous catalyst carrier such as alumina and a noble metal such as platinum supported on the carrier, is generally referred to as an oxidation catalyst. In such oxidation catalysts, solid acidity and large BET surface area of the porous catalyst support have been considered. However, the oxidation performance of these catalysts is not good enough. In practice, for use as catalysts for purifying automobile exhaust gases, catalysts having higher catalytic performance even at lower temperatures have been demanded.

During this period, the inventors of the present application have filed a patent application on an oxidation catalyst for oxidizing Hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas, which is prepared by the following method: heat-treating a clay mineral having a double-chain structure at a temperature of 400-800 ℃ to make at least a portion of the clay mineral amorphous; exchanging magnesium ions and/or aluminum ions on the clay mineral with iron ions; platinum and/or palladium is supported to the clay mineral (Japanese unexamined patent publication No. 4-363138). The oxidation catalyst achieves improved catalytic activity for conversion of 50% hydrocarbons at lower temperatures of 100 ℃ to 200 ℃.

Further, Japanese unexamined patent publication (KOKAI) No. 61-54238 discloses an exhaust gas purifying catalyst comprising a catalyst carrier comprising calcium aluminate and fibrous potassium titanate and at least one catalyst component selected from platinum group elements and rare earth elements supported on the carrier.

The exhaust gas purifying catalyst comprises 0.5 to 50 wt% of fibrous potassium titanate as a melting inhibitor for stabilizing calcium aluminate at a high temperature of 900 to 1000 ℃. The disclosure demonstrates that the catalyst is effective in purifying carbon monoxide and nitrogen oxides.

For gasoline engines, internal combustion engines, various technologies developed to meet stringent exhaust gas regulations have reduced the harmful components in the exhaust gas. However, in the field of diesel engines, since harmful components are mainly discharged in the form of particles, regulations and technical developments in reducing toxic substances in exhaust gas have lagged behind those of gasoline engines. It has been desired to develop a device for safely purifying exhaust gas discharged from a diesel engine.

Devices developed to date for purifying the exhaust gases of diesel engines use either a trap (with or without catalyst) or an open SOF decomposition catalyst.

Devices utilizing a catalyst-free trap suppress the emission of particulates contained in diesel engine exhaust by trapping particulates. One problem with such devices is that the trap breaks or the like, since it is generally necessary to heat the trap during regeneration, burning off the trapped SOF particles and solid soot.

Devices utilizing a trap with a catalyst not only purify carbon monoxide and hydrocarbons, but also purify particulates from the exhaust gas emitted by a diesel engine. For example, Japanese examined patent publication No.5-58775 discloses a catalyst for purifying exhaust gas, which carries at least one member selected from the group consisting of palladium, praseodymium, neodymium, and samarium. During long-term use, the pores of the trap with the catalyst are clogged according to the kind of the supported catalyst, and thus there may be caused a problem that the purification efficiency is lowered.

On the other hand, Japanese examined patent publication No.3-38255 discloses an open type SOF decomposition catalyst in which an oxidation catalyst component such as a platinum group element is supported on a catalyst supporting layer such as activated alumina in the same manner as that for the support of an exhaust gas purifying catalyst for a gasoline engine. Thereby purifying the soluble organic fraction and carbon monoxide and hydrocarbons in the particles by means of oxidation reactions. Although these open type SOF decomposition catalysts have a disadvantage in that the solid soot cannot be sufficiently removed, research and development has been conducted on such catalysts because the amount of soot is reduced with improvements to diesel engines and fuels themselves, and further, because one advantage of these catalysts is that there is no need for a device for regenerating the trap.

Despite the above-mentioned oxidationCatalysts, i.e. catalysts in which at least one platinum group element and a rare earth element are supported on a catalyst carrier comprising calcium aluminate and fibrous potassium titanate, can purify carbon monoxide and nitrogen oxides, but contain sulfur dioxide (SO) in the exhaust gas₂) In the case of (a), the problem arises that the catalyst oxidizes sulphur dioxide to anhydrous sulphuric acid and forms sulphates. When SO₂By oxidation with SO₃When exhausted to the atmosphere in the form of SO₃One problem that arises is that it interacts with atmospheric H₂Reaction of O to sulfuric acid (H)₂SO₄). On the other hand, when SO₂In its own form, i.e. as SO₂When formally discharged, SO₂With O in the atmosphere₃Reaction to form SO₃Due to SO₂And O₃There is little chance of reaction in the atmosphere, SO₂Require a certain time to convert into SO₃. Therefore, with emission of SO to the atmosphere₃In contrast, SO is emitted to the atmosphere₂The severity of the problem is somewhat worse. Therefore, it is desirable to minimize the emission of SO to the atmosphere₃。

In SO₂In the oxidation process, the alumina component such as calcium aluminate enhances SO according to the reaction₂By oxidation to SO₃And H₂SO₄Catalytic activity of noble metal:

(1)

(2)SO₃and H₂SO₄Is undesirable.

Further, the above oxidation catalyst, i.e., a catalyst in which at least one platinum group element and a rare earth element are supported on a catalyst carrier comprising calcium aluminate and fibrous potassium titanate, has insufficient catalyst performance at a relatively low exhaust temperature.

Incidentally, conventional catalysts for purifying exhaust gas of diesel engines are ineffective in reducing the amount of particulate emissions. That is, the active alumina layer used in the conventional catalyst has adsorptionWith SO₂Performance of SO contained in exhaust gas of diesel engine₂Adsorbed by the active alumina layer, and when the catalyst temperature rises, the adsorbed SO is catalyzed by the catalyst metal₂And (4) oxidizing. Thereby causing SO₂With SO₃Form discharge, increase SO₃The amount of particles. SO is readily produced as a result of the abundance of oxygen in exhaust gases, particularly diesel exhaust gases₂Oxidation reaction of (3). Generated SO₃And easily reacts with water vapor existing in a large amount in the exhaust gas to generate sulfuric acid mist.

An object of the present invention is to provide an exhaust gas purifying catalyst which can oxidize at least hydrocarbons and carbon monoxide in exhaust gas at a relatively low temperature with a relatively high catalytic activity and, at the same time, can suppress the conversion of sulfur dioxide into sulfuric acid.

It is another object of the present invention to provide a catalyst which is particularly suitable for purifying the exhaust gases of diesel engines.

An exhaust gas purifying catalyst comprises a catalyst carrier comprising a noble metal represented by the formula K₂O·nTiO₂(wherein n is an integer selected from 4 to 8) and is substantially free of alumina.

An exhaust gas purifying catalyst comprises a catalyst carrier and a heat-resistant inorganic oxide coating layer formed on the carrier. The heat-resistant inorganic oxide layer comprises a material represented by the formula K₂O·nTiO₂(wherein n is an integer selected from 4 to 8) and at least one member selected from the group consisting of silicon dioxide, titanium dioxide and zirconium dioxide and a noble metal supported thereon. The refractory inorganic oxide layer is substantially free of alumina.

The potassium titanate is K₂O and TiO₂A complex compound of (1). When n is less than 4, K₂O readily dissolves into an acidic solution. This narrows the selection of noble metal-loaded solutions for preparing the catalyst. It is not desirable that n be less than 4.

Further, when n is less than 2, potassium titanate does not have a regular crystal structure, and potassium is adsorbed and supported on the surface thereof. Therefore, when n is less than 2, potassium is washed out by water and the like contained in the exhaust gas, so that the catalyst cannot maintain the desired catalytic activity. In addition, the eluted excessive potassium covers a noble metal catalyst component such as platinum, resulting in further reduction of catalytic activity.

On the other hand, when n is more than 8, the effect of potassium on suppressing the generation of sulfuric acid is insufficient, and the catalytic activity required for purifying exhaust gas is also insufficient. So n is not desired to be greater than 8. Thus, when potassium titanate is represented by the formula K₂O·nTiO₂When represented, n is preferably 4 to 8.

Making potassium oxide (K)₂O) and titanium dioxide (TiO)₂) The solid phase reaction can generate potassium titanate, and the potassium in the compound exists in a stable state.

If the catalyst support is prepared, K is simply added₂O supported on TiO₂As opposed to using potassium titanate, K is easily converted from water in the exhaust gas₂O is eluted to load K₂The effect of O is drastically diminished. In addition, when preparing the catalyst carrier, potassium is loaded on other catalyst carriers such as SiO₂And Al₂O₃In addition, water or the like in the exhaust gas may elute potassium, resulting in failure to exert the effect of loading potassium. Further, if potassium is supported on SiO₂The washed out potassium reacts with SiO at high temperature₂Unfavorably react to form a vitreous body.

Preferably, the catalyst support of the first aspect of the present invention consists solely of potassium titanate. In other words, it is preferable to use potassium titanate in powder or porous pellets. It is noted that the potassium titanate can be shaped with a binder. Examples of suitable binders include silica-based materials, titania-based materials, zirconia-based materials, and ceria-based materials.

As mentioned above, it is preferred not to use alumina as one component of the catalyst support, since alumina will bind SO₂By oxidation to SO₃And H₂SO₄. For this reason, the catalyst of the present invention is substantially free of alumina. The term "substantially" refers to a catalyst that does not exclude alumina as an impurity.

Load including the present inventionThe catalyst component on the catalyst carrier of potassium titanates is preferably a noble metal, in particular one of the platinum group elements platinum (Pt), palladium (Pd) and rhodium (Rh). Of these noble metal catalyst components, platinum is most preferable because platinum has a strong ability to decompose Hydrocarbon (HC) even at a small amount of K₂This elution has little detrimental effect on the ability of O to decompose hydrocarbons when eluted from potassium titanate.

The platinum group element loading is preferably 0.2 to 10g per 100g of potassium titanate. When the supporting amount is less than 0.2g, the catalyst performance is insufficient. On the other hand, when the supporting amount is more than 10g, not only the catalytic action is impaired by the aggregation of the metal, but also the production cost of the catalyst is increased. The loading amount of more than 10g is not preferred.

According to thesecond aspect of the present invention, in the exhaust gas purifying catalyst, the heat-resistant inorganic oxide coating layer is substantially free of alumina and includes potassium titanate and at least one of silica, titania and zirconia. Silicon dioxide, titanium dioxide and zirconium dioxide are preferably used in the heat-resistant inorganic oxide layer in the form of a powder and/or a sol. Although it is sufficient to use either one of the powder and the sol, it is desirable to use a mixture of the powder and the sol. The particle diameter of the inorganic oxide is preferably 60 μm or less. When the inorganic oxide is larger than 60 μm, the catalyst, i.e., the catalyst in which at least one catalyst component of platinum, palladium and rhodium is supported on these inorganic oxides, cannot exhibit sufficient catalytic activity.

By having the heat-resistant inorganic oxide coating layer with the above-described constitution, the catalyst can suppress the emission of sulfate, while improving the conversion rate of hydrocarbon and carbon monoxide in a lower temperature range.

The potassium titanate loading in the heat resistant inorganic oxide coating is preferably in the range of 20 to 60g/L of catalyst. When the potassium titanate loading is less than 20g/L, a sufficient catalytic activity cannot be achieved. On the other hand, when the potassium titanate loading amount is more than 60g/L, the more the potassium titanate loading amount is increased, not only the catalytic activity cannot be correspondingly improved but also the production cost is unduly increased. Particularly preferred loadings are 30 to 40g/L from both catalytic activity and cost considerations.

The amount of one or more selected from the group consisting of silicon dioxide, titanium dioxide and zirconium dioxide constituting the refractory inorganic oxide coating layer coated on the carrier is preferably 40 to 80g/L of the catalyst. When the coating amount is less than 40g/L, a sufficient catalytic activity cannot be obtained. On the other hand, when the coating amount is more than 80g/L, the more the coating amount is increased, not only the catalytic activity cannot be correspondingly improved but also the production cost is increased. From the viewpoint of both catalytic activity and production cost, a more preferable coating amount is 60 to 70 g/L.

The refractory inorganic oxide coating can include a zeolite. When zeolites are included, it is preferred that the silica to alumina ratio be up to about 30/1-100/1 or more silica.

The amount of platinum as the catalyst component to be supported is preferably 0.01 to 5.0 g/L. When the amount of platinum is less than 0.01g/L, a sufficient catalytic activity cannot be obtained. On the other hand, when the amount of platinum is more than 5.0g/L, the amount of the supported platinum is much increased and the catalytic activity is not improved accordingly, which rather unduly increases the production cost. In particular, from the viewpoint of catalytic activity and production cost, the platinum loading amount is more preferably 0.1 to 3.0 g/L.

The palladium loading is preferably 0.1 to 5.0g/L of catalyst. When the palladium supporting amount is less than 0.1g/L, a sufficient catalytic activity cannot be obtained. On the other hand, when the palladium supporting amount exceeds 5.0g/L, the increase in the palladium supporting amount is much larger and the catalytic activity is not improved accordingly, but the production cost is unduly increased. Particularly, the palladium loading amount is more preferably 0.5 to 3.0g/L from the viewpoint of both the catalytic activity and the production cost.

The rhodium loading is preferably from 0.01 to 1.0 g/L. When the rhodium loading is less than 0.01g/L, a sufficient catalytic activity cannot be obtained. On the other hand, when the rhodium loading is more than 1.0g/L, the rhodium loading is much increased and the catalytic activity is not improved accordingly, which rather unduly increases the production cost. Particularly, the rhodium loading is more preferably 0.05 to 0.5g/L from the viewpoint of both the catalytic activity and the production cost.

According to the present invention, potassium titanate in the heat-resistant inorganic oxide coating layer can effectively suppress the generation of sulfate, and can greatly improve the ability to remove harmful components such as hydrocarbons, carbon monoxide and soluble organic fractions at low temperatures.

Besides, in the exhaust gas purifying catalyst according to the second aspect of the present invention, the heat-resistant inorganic oxide coating layer preferably comprises potassium titanate and at least one member selected from the group consisting of silicon dioxide, titanium dioxide and zirconium dioxide. The heat-resistant inorganic oxide coating comprising potassium titanate and at least one of silicon dioxide, titanium dioxide and zirconium dioxide hardly adsorbs SO₂Thus, SO₂SO formed by reaction with catalyst components, e.g. platinum₃The amount is also small.

As mentioned above, alumina is not preferred as a component of the refractory inorganic oxide coating because alumina adsorbs more SO₂，SO₂Then reacting with a catalyst component such as platinum to produce a large amount of SO₃。

According to the second aspect of the present invention, the particle size of silicon dioxide, titanium dioxide and/or zirconium dioxide in the heat-resistant inorganic oxide coating layer is preferably 60 μm or less. When the particle diameter is larger than 60 μm, sufficient catalytic activity cannot be achieved. The mechanism is not clear, but the following reasoning can be made:

the exhaust gas purifying catalyst according to the second aspect of the present invention comprises a mixed coating layer containing potassium titanate and at least one of silica, titania and zirconia, and a catalyst component selected from at least one of palladium, platinum and rhodium supported on the mixed coating layer. The hybrid coating is comprised of a homogeneous mixture of potassium titanate and at least one of silicon dioxide, titanium dioxide, and zirconium dioxide. I.e., potassium titanate and at least one of silicon dioxide, titanium dioxide and zirconium dioxideA powder contact and/or at least one of silicon dioxide, titanium dioxide and zirconium dioxide powder is disposed about or in contact with the potassium titanate. The catalyst component supported on the mixed coating layer thus constituted is supported on potassium titanate and at least one of silicon dioxide, titanium dioxide and zirconium dioxide. Alkaline component K stably existing in potassium titanate₂O changes the electronic state of the catalyst component supported on potassium titanate, resulting in SO₂The oxidation reaction of (2) hardly occurs. Further, since at least one of silica, titania and zirconia is in contact with potassium titanate, at least one of silica, titania and zirconia is supported onThe electronic state of most of the catalyst components on the seed is represented by K in potassium titanate₂O is changed SO that SO can be suppressed₂Oxidation reaction of (3).

In contrast, if the catalyst component such as platinum in the catalyst is supported on at least one of silicon dioxide, titanium dioxide and zirconium dioxide which are not mixed with potassium titanate, hydrocarbons and SO in the exhaust gas₂By oxidation with a catalyst component such as platinum, the hydrocarbons are purified and at the same time SO is formed₂To form sulfate. Therefore, when the content of at least one of silicon dioxide, titanium dioxide and zirconium dioxide is more than 70g/L, it does not react with K in potassium titanate₂The fraction of O contact increases and the amount of sulfate produced increases. Further, if the particle diameter of at least one of silica, titania and zirconia is larger than 60 μm, the portion thereof not in contact with potassium titanate increases, and a large amount of sulfate is generated by the catalyst component for the same reason as the effect produced by the increase in the content of one of silica, titania and zirconia.

As described above, the exhaust gas purifying catalyst according to the second aspect of the present invention is a catalyst in which the catalyst component is supported on a coating layer formed by uniformly mixing and contacting potassium titanate and at least one of silicon dioxide, titanium dioxide and zirconium dioxide with each other. Therefore, the catalyst can purify hydrocarbons in exhaust gas even at a relatively low temperature while hardly generating sulfates at a high temperature.

The exhaust gas purifying catalyst according to the second aspect of the invention substantially does not include alumina as a heat-resistant inorganic oxide coating component, except for the case where the catalyst contains alumina as an impurity.

A most preferable catalyst in the exhaust gas purifying catalyst according to the second aspect of the invention is a catalyst in which at least one catalyst component of platinum, palladium and rhodium is supported on a heat-resistant inorganic oxide coating layer which is substantially free from alumina and includes potassium titanate and silica.

The function of the exhaust gas purifying catalyst of the present invention will be explained below.

Becausealumina is not used as a catalyst carrier, the catalyst of the invention can oxidize at least hydrocarbon in the exhaust gas with higher catalytic activity at lower temperature, and can inhibit SO2 from being converted into sulfate.

The noble metal catalyst component loaded on the catalyst carrier can oxidize hydrocarbons in the exhaust gas into harmless substances, and the reaction is as follows:

at the same time, the sulfur dioxide in the exhaust gas is oxidized as follows:

however, since the support of the present invention does not substantially contain alumina, the oxidation reaction rate is slow. As a result, the production of sulfuric acid is suppressed.

As described above, by supporting a noble metal on the potassium titanate of the present invention, the conversion of hydrocarbons is mainly improved, and the process of generating sulfuric acid by oxidation of sulfur dioxide can be suppressed.

Therefore, in the exhaust gas purifying catalyst according to the second aspect of the present invention, since the heat-resistant inorganic oxide coating layer includes potassium titanate and at least one selected from the group consisting of silica, titania and zirconia, the catalyst can suppress the emission of sulfate while improving the conversion of hydrocarbons and carbon monoxide at a lower temperature.

The catalyst for purifying waste gas of the present invention has the advantages of high catalytic activity, high oxidation rate of hydrocarbon in waste gas, and low sulfur dioxide converting reaction to sulfate.

Further, the configuration in which the heat-resistant inorganic oxide coating layer comprises potassium titanate and at least one selected from the group consisting of silica, titania and zirconia allows the conversion of carbon monoxide and hydrocarbons at lower temperatures to be increased while improving the efficiency of removing particles when purifying exhaust gases, particularly diesel exhaust gases.

Other objects and features of the present invention will become more apparent to those skilled in the art from the following description of the preferred embodiments of the present invention.

In examples 1 and 2 and comparative examples 1 to 4 according to the present invention, compositions of a catalyst carrier having substantially catalytic activity and a noble metal supported thereon, and compositions of a catalyst carrier, a noble metal and a binder were prepared, and the catalytic activity of these compositions was evaluated. Therefore, when the catalysts of examples 1 and 2 of the present invention are used as catalytic devices for purifying exhaust gas discharged from internal combustion engines of automobiles, it is necessary to coat the compositions of examples 1 and 2, respectively, on the surface of a substrate such as a honeycomb carrier, or to form the compositions of examples 1 and 2 into pellets each having a predetermined particle size. It should be noted that in examples 1 and 2 of the present invention, only the catalytic activities of the composition of the catalyst carrier and the noble metal supported thereon and the composition of the catalyst carrier, the noble metal and the binder were evaluated.

Examples 3-8 are examples of catalysts comprising honeycomb supports for the purification of diesel exhaust gases.

Example 1

Potassium titanate produced by OTSUKA CHEMICAL coHas a chemical formula of K₂O·nTiO₂Wherein nis 4, 6 and 8.

100ml of acetone were added to 20g each of potassium titanate, and each mixture was ground with a planetary ball mill and filtered. Powder with the diameter not larger than 100 meshes is used as a catalyst carrier.

Platinum as a platinum group element was supported on each of the potassium titanate catalyst carriers as a catalyst component. The platinum used was a dinitroso platinum nitrate solution (Pt-P salt) prepared by ltd. The platinum loading is from 0.1 to 10g per 100g of potassium titanate catalyst support. Platinum was loaded using the following method: a predetermined amount of a diluted solution of a Pt-P salt and 100ml of water was added to each of 20g of the potassium titanate catalyst carriers. Stirring at a temperature of 120 ℃ to 150 ℃ while the mixture is evaporated to dryness. The resultant was further dried at 110 ℃ for 15 hr. Calcining in air at 350 deg.C for 3hr, grinding, and filtering to obtain particles with diameter of 6-10 meshes. Thus, the catalyst of the present invention was prepared.

Using the above method, but changing the titanium content n in the potassium titanate to 8, 6, and 4, while changing the platinum loading, catalyst samples 1-12 were made.

The catalytic performance of these catalysts was evaluated in a conventional flow system using a tubular fixed bed reactor, each of which was charged with 7cc of each of the above catalyst particles. The simulated exhaust gas used comprised propylene (C) as the hydrocarbon₃H₆) The amounts are expressed in terms of carbon as 600ppm, 10% oxygen, 1000ppm carbon monoxide, 5% carbon dioxide, 25ppm sulphur dioxide, 10% water, the remainder being nitrogen. The temperature at 50% propylene conversion was measured by changing the gas inlet temperature from 500 ℃ to 150 ℃ while calculating the SO at a simulated gas temperature of 400 ℃ using the following formula₂Conversion (%):

(SO in the Outlet gas)₂concentration/SO in inlet gas₂Concentration) × 100%

The results are shown in Table 1.

TABLE 1

Sample number	K₂O·nTiO₂ N value of (1)	pt amount (g)/100g K₂O·nTiO₂	Catalytic performanceCan be used for
Sample number	K₂O·nTiO₂ N value of (1)	pt amount (g)/100g K₂O·nTiO₂	Catalytic performanceCan be used for					50％C₃H₆ Conversion temperature (. degree.C.)	At 400 deg.C SO₂Conversion (%)
1	8	2	220	24				50％C₃H₆ Conversion temperature (. degree.C.)	At 400 deg.C SO₂Conversion (%)
1	8	2	220	24	2	8	6	232	18
3	8	8	235	18	2	8	6	232	18
3	8	8	235	18	4	8	10	240	17
5	8	2.5	216	26	4	8	10	240	17
5	8	2.5	216	26	6	8	0.2	245	10
7	6	4	228	22	6	8	0.2	245	10
7	6	4	228	22	8	6	O.5	240	10
9	6	2	222	23	8	6	O.5	240	10
9	6	2	222	23	10	4	2	218	12
11	4	6	241	10	10	4	2	218	12
11	4	6	241	10	12	4	8	243	10

As shown in table 1, the 50% hydrocarbon conversion temperature in samples 1-12 was 216 c to 245 c, and the sulfur dioxide conversion at 400 c did not exceed 26%. Therefore, the catalyst of example 1 of the present invention can suppress SO without impairing the performance of the catalyst₂The transformation of (3).

Comparative example 1

Using the method of example 1, the compound of formula K₂O·nTiO₂Wherein n is 2, by supporting platinum on titanic acid in an amount of 2g/100g of the potassium titanate catalyst carrierPreparing the catalyst on a potassium catalyst carrier.

The catalyst performance was evaluated in the same manner as in example 1. The results are shown in table 2 in the column for sample 101. When sample 101 is compared to sample 1 of example 1 having the same platinum content, the hydrocarbon conversion temperature of sample 101 is about 60 ℃ higher and the sulfur dioxide conversion at 400 ℃ is about 14% higher than that of sample 1.

Comparative example 2

Using no K₂TiO of O₂As a catalyst carrier, platinum is loaded according to the dosage of 2g/100g of titanium dioxide catalyst carrier to prepare the catalyst. The catalyst performance was evaluated in the same manner as in example 1. The results are shown in table 2 under sample 102. Although sample 102 converted hydrocarbons, the sulfur dioxide conversion at 400 ℃ was 85% due to the absence of K₂O, sulfuric acid is easily generated.

Comparative example 3

According to the proportion of 0.25-0.5mol/1mol TiO₂In an amount of KNO₃Solution of K₂O on TiO₂The above. Then 2g/100g (TiO)₂+K₂O) amount of platinum supported on each catalyst support, catalyst samples 103-107 were prepared. The performance of these comparative catalysts was evaluated in the same manner as in example 1.

The results are shown in Table 2 under sample 103 and column 107. Some of samples 103-107 had 50% hydrocarbon conversion temperatures above 300 deg.C and conversion to sulfuric acid at 400 deg.C was higher than samples 1-2 of example 1 of the present invention.

TABLE 2

Sample number	mK₂O·nTiO₂In M: n of	Amount of Pt (g)/100g K₂O·nTiO₂	Performance of catalyst
Sample number	mK₂O·nTiO₂In M: n of	Amount of Pt (g)/100g K₂O·nTiO₂	Performance of catalyst					50％C₃H₆ Transition temperature (℃)	At 400 ℃ C SO₂Conversion rate (％)
101	1∶2	2	286	38				50％C₃H₆ Transition temperature (℃)	At 400 ℃ C SO₂Conversion rate (％)
101	1∶2	2	286	38	102	1∶0	2	231	85
103	0.25∶1	2	285	35	102	1∶0	2	231	85
103	0.25∶1	2	285	35	104	0.3∶1	2	295	35
105	0.4∶1	2	310	30	104	0.3∶1	2	295	35
105	0.4∶1	2	310	30	106	0.5∶1	2	310	30
107	0.45∶1	2	305	30	106	0.5∶1	2	310	30

Is apparent, wherein K₂Simple O loading on TiO₂The above comparative catalysts have a 50% hydrocarbon conversion temperature and a conversion to sulfuric acid at 400 c higher than the catalyst of example 1 of the present invention. That is, it is clear that the catalyst performance of these comparative catalysts is not good enough.

Example 2

Silicon dioxide (SiO) each manufactured by NISSAN CHEMICAL co, ltd₂) Sol, titanium dioxide (TiO)₂) Sol or zirconium dioxide (ZrO)₂) Sol as a binderAn agent added in a solid content of 1 to 10 parts by weight (as shown in Table 3) to 100 parts by weight of potassium titanate (K) manufactured by OTSUKACHEMICAL CO., LTD₂O·8TiO₂) In (1). After vigorous stirring, each mixture was calcined at 500 ℃. Further, platinum was supported on each of the calcined carriers in an amount of 2g per 100 parts by weight of potassium titanate in the same manner as in example 1. Each carrying a catalystThe roasted carrier of the components is ground and filtered to obtain particles with the diameter of 6-10 meshes. Thus, 8 catalysts of samples 13-20 were prepared.

The performance of these catalysts was evaluated in the same manner as in example 1. The results are shown in Table 3.

TABLE 3

Sample number	Inorganic binder	Catalyst Performance
Sample number	Inorganic binder	Catalyst Performance				50％C₃H₆ Conversion temperature (. degree.C.)	At 400 deg.C SO₂Conversion rate%
13	SiO₂1 part of	223	25			50％C₃H₆ Conversion temperature (. degree.C.)	At 400 deg.C SO₂Conversion rate%
13	SiO₂1 part of	223	25	14	SiO₂5 portions of	225	25
15	SiO₂10 portions of	225	28	14	SiO₂5 portions of	225	25
15	SiO₂10 portions of	225	28	16	TiO₂1 part of	222	26
17	TiO₂5 portions of	228	26	16	TiO₂1 part of	222	26
17	TiO₂5 portions of	228	26	18	TiO₂10 portions of	226	24
19	ZrO₂1 part of	227	24	18	TiO₂10 portions of	226	24
19	ZrO₂1 part of	227	24	20	ZrO₂10 portions of	226	26

As shown in Table 3, the hydrocarbon conversion temperatures of samples 13-20 ranged from 222 deg.C to 228 deg.C, and the sulfur dioxide conversion at 400 deg.C ranged from 24 to 28%. Thus, the catalyst of example 2 can suppress SO without impairing catalytic performance₂And (4) transformation.

Comparative example 4

Alumina (Al) prepared as in example 2, but using the method of Japan NISSAN CHEMICAL CO₂O₃) The sol was used as a binder in an amount of 1 to 10 parts by weight of solid per 100 parts by weight of potassium titanate, as shown in Table 4, in place of the binder used in example 2, to prepare catalyst sample 108-110.

TABLE 4

Sample number	Inorganic binder	Catalyst Performance
Sample number	Inorganic binder	Catalyst Performance		50％C₃H₆ Conversion temperature (. degree.C.)	At 400 ℃ C SO₂Conversion rate%
108 109 110	Al₂O₃1 part of Al₂O₃5 portions of Al₂O₃10 portions of	225 223 230	48 56 82	50％C₃H₆ Conversion temperature (. degree.C.)	At 400 ℃ C SO₂Conversion rate%

The catalyst performance of samples 108-110 was evaluated in the same manner as in example 1. The results are shown in Table 4.

As shown in Table 4, the 50% hydrocarbon conversion temperatures for samples 108, 109, and 110 were 223 deg.C to 230 deg.C. That is, sample 108-110 exhibited very good catalyst performance. However, the sulfur dioxide conversion of sample 108-110 reached very high values of 48-82%at 400 ℃. That is, sample 108-110 was unable to inhibit SO₂The transformation of (3). Such SO₂The conversion cannot be suppressed and the formation of large amounts of harmful sulfates is undesirable.

Example 3

A monolithic carrier composed of cordierite and having 400 pores per square inch, a diameter of 80mm and a length of 95mm was coated with a slurry containing 40g of silica powder having an average particle diameter of 10 μm, 40g of potassium titanate having an average minimum axial diameter of 0.5 μm and an average maximum axial diameter of 15 μm, and 20g of silica sol containing solid silica and 100g of deionized water. After coating, the monolith was dried and calcined at 500 ℃ for 1hr, thereby forming a heat-resistant inorganic oxide coating layer comprising silica and potassium titanate on the monolith support. The heat resistant inorganic oxide coating comprised (60g silica +40g potassium titanate)/L catalyst.

The prepared carrier was immersed in an aqueous chloroplatinic acid solution to load 1.0g of platinum/L catalyst. Thus, a catalyst sample 51 shown in Table 5 was produced.

TABLE 5

	Catalyst and process for preparing same Sample number	Heat resistant inorganic oxide coating	Catalyst gold Genus (g/L)		Conversion (%) was 250 ℃			Conversion of the granules% At 350 DEG C
	Catalyst and process for preparing same Sample number	Heat resistant inorganic oxide coating	Catalyst gold Genus (g/L)		Conversion (%) was 250 ℃			Conversion of the granules% At 350 DEG C				Pt	Pd	Rh	HC	CO
Example 3 Example 4 Example 5 Example 6 Example 7 Example 8	51 52 53 54 55 56	SiO₂K₂O·8TiO₂ TiO₂K₂O·8TiO₂ ZrO₂K₂O·8TiO₂ SiO₂K₂O·8TiO₂ TiO₂K₂O·8TiO₂ SiO₂K₂O·8TiO₂	1.0 - - 1.0 - 0.5	- 1.0 - - 1.0 0.5	- - 1.0 0.2 0.2 0.2	92 75 45 82 71 85	94 81 44 85 80 92	29 25 20 27 24 26				Pt	Pd	Rh	HC	CO
Example 3 Example 4 Example 5 Example 6 Example 7 Example 8	51 52 53 54 55 56		1.0 - - 1.0 - 0.5	- 1.0 - - 1.0 0.5	- - 1.0 0.2 0.2 0.2	92 75 45 82 71 85	94 81 44 85 80 92	29 25 20 27 24 26	Comparative example 5 Comparative example 6 Comparative example 7 Comparative example 8 Comparative example 9 Comparative example 10 Comparative example 11 Comparative example 12 Comparative example 13	A B C D E F G H I	Al₂O₃ SiO₂ TiO₂ ZrO₂ Al₂O₃ SiO₂ TiO₂ Al₂O₃ SiO₂	1.0 1.0 - - 1.0 1.0 - 0.5 0.5	- - 1.0 - - - 1.0 0.5 0.5	- - - 1.0 0.2 0.2 0.2 0.2 0.2	83 80 81 35 72 71 69 69 91	94 92 91 30 71 79 71 71 87	-43 -37 -50 2 -23 -22 -1 -5 -10

Example 4

A monolithic support composed of cordierite and having 400 pores per square inch, a diameter of 80mm and a length of 95mm was coated with a slurry comprising 40g of a titanium dioxide powder having an average particle diameter of 0.7 μm, 40g of potassium titanate having an average minimum axial diameter of 0.5 μm and an average maximum axial diameter of 15 μm, a titanium oxide sol containing 20g of solid titanium dioxide, and 100g of deionized water. The coated support was dried and calcined at 500 c for 1 hour, thereby forming a heat-resistant inorganic oxide coating layer comprising titanium dioxide and potassium titanate on the monolithic support. The heat resistant inorganic oxide coating comprised (60g titanium dioxide +40g potassium titanate)/L catalyst.

The coated carrier was immersed in a palladium nitrate solution to support 1.0g of palladium per liter of the catalyst. Thus, catalyst samples 52 shown in Table 5 were produced. The catalyst composition is shown in table 5.

Example 5

A monolithic support of cordierite having 400 pores per square inch, a diameter of 80mm and a length of 95mm was coated with a slurry containing 80g of zirconium dioxide powder having an average particle diameter of 0.5 μm, 50g of potassium titanate having an average minimum axial diameter of 0.5 μm and an average maximum axial diameter of 15 μm, a zirconium oxide sol containing 20g of solid zirconium dioxide and 150g of deionized water. Drying the coated carrier, and roasting at 500 deg.C for 1h to form a heat-resistant inorganic oxide coating on the whole carrier. The heat-resistant inorganic oxide coating comprised (100g of zirconia +50g of potassium titanate)/L of catalyst.

The coated carrier was immersed in a rhodium nitrate solution to carry 1.0g of rhodium per liter of the catalyst. Thus, a catalyst sample 53 shown in Table 5 was produced.

Example 6

The catalyst sample 51 prepared in example 3 was further immersed in a rhodium nitrate solution to load 0.2g of rhodium per liter of the catalyst. Thus, a catalyst sample 54 shown in Table 5 was prepared.

Example 7

A catalyst sample 53 prepared in example 4 was immersed in a rhodium nitrate solution to carry 0.2g of rhodium per liter of the catalyst. Thus, a catalyst sample 55 shown in Table 5 was prepared.

Example 8

The monolithic support coated with the heat-resistant inorganic oxide coating layer of example 3 was immersed in an aqueous chloroplatinic acid solution, then in a palladium nitrate solution, and then in a rhodium nitrate solution so as to carry 0.5g of platinum, 0.5g of palladium, and 0.2g of rhodium per liter of the catalyst. Thus, a catalyst sample 56 shown in Table 5 was prepared.

Comparative example 5

A monolithic cordierite substrate having 400 pores per square inch, 80mm in diameter and 95mm in length was coated with a slurry containing 100g of activated alumina having an average particle size of 5 μm, 5g of hydrated alumina and 150g of deionized water. The coated support was dried and calcined at 500 c for 1 hour, thereby forming a heat-resistant inorganic oxide coating layer comprising activated alumina on the entire support.

The monolithic support having the above heat-resistant inorganic oxide coating was immersed in an aqueous chloroplatinic acid solution to carry 1.0g of platinum per liter of the catalyst. Thus, catalyst sample A shown in Table 5 was prepared.

Comparative example 6

A monolithic support composed of cordierite and having a diameter of 80mm and a length of 95mm and 400 cells per square inch was coated with a slurry containing 100g of a silica powder having an average particle diameter of 5 μm, a silica sol containing 50g of solid silica and 100g of deionized water. The coated support is dried and calcined at 500 ℃ for 1h to form a silica-containing refractory inorganic oxide coating on the monolithic support.

The carrier with the heat-resistant inorganic oxide coating was immersed in an aqueous chloroplatinic acid solution to carry 1.0g of platinum per liter of the catalyst. Thus, catalyst sample B shown in Table 5 was prepared.

Comparative example 7

A monolithic support composed of cordierite and having a diameter of 80mm and a length of 95mm and having 400 cells per square inch was coated with a slurry containing 100g of titania having an average particle diameter of 0.7 μm, a titania sol containing 20g of solid titania, and 200g of deionized water. The coated support is then dried and calcined at 500 ℃ for 1 hour to form a heat-resistant inorganic oxide coating containing titanium dioxide on the support.

The carrier with the heat-resistant inorganic oxide coating was immersed in an aqueous palladium nitrate solution to support 1.0g of palladium per liter of the catalyst. Thus, catalyst sample C shown in Table 5 was prepared.

Comparative example 8

A monolithic support composed of cordierite and having a diameter of 80mm and a length of 95mm and 400 cells per square inch was coated with a slurry containing 100g of zirconia having an average particle diameter of 0.7 μm, 20g of a zirconia sol containing solid zirconia and 200g of deionized water. The coated support was dried and calcined at 500 ℃ for 1h to form a refractory inorganic oxide coating comprising zirconium dioxide on the entire support. The carrier with the heat-resistant inorganic oxide coating was immersed in an aqueous rhodium nitrate solution to carry 1.0g/L of rhodium/L of the catalyst. Thus, catalyst sample D shown in Table 5 was prepared.

Comparative example 9

The catalyst sample A prepared in comparative example 5 was further immersed in a rhodium nitrate solution to load 0.2g of rhodium per liter of the catalyst. Thus, catalyst sample E shown in Table 5 was prepared.

Comparative example 10

The catalyst sample B prepared in comparative example 6 was immersed in a rhodium nitrate solution so as to load 0.2g of rhodium per liter of the catalyst. Thus, a catalyst sample F shown in Table 5 was prepared.

Comparative example 11

The catalyst C prepared in comparative example 7 was immersed in a rhodium nitrate solution to load 0.2g of rhodium per liter of the catalyst. Thus, a catalyst sample G shown in Table 5 was prepared.

Comparative example 12

The platinum loading of catalyst sample A prepared in comparative example 5 was halved and the catalyst was then immersed in a palladium nitrate solution and a rhodium nitrate solution to load 0.5g of platinum, 0.5g of palladium and 0.2g of rhodium per liter of catalyst. Thus, catalyst sample H shown in Table 5 was prepared.

Comparative example 13

The platinum loading of catalyst sample B prepared in comparative example 6 was halved and the catalyst was thenimmersed in a palladium nitrate solution and a rhodium nitrate solution to load 0.5g of platinum, 0.5g of palladium and 0.2g of rhodium per liter of catalyst. Thus, catalyst sample I shown in Table 5 was prepared.

Evaluation experiment

Each of the catalysts prepared above was charged into an exhaust pipe of a direct injection diesel engine having an exhaust gas amount of 3.6 l. The engine was first run at a determined full speed for 500 h. Next, when the engine was operated at 2500rpm and 8KW of rotational torque, the hydrocarbons and carbon monoxide in the catalyst bed inlet and outlet gases were measured, and the conversion (%) was calculated using the following formula 1. The inlet gas temperature was 250 ℃.

Formula 1:

conversion (%) - (concentration of inlet exhaust gas constituent-concentration of outlet exhaust gas constituent) —

Inlet exhaust gas component concentration x 100

Next, the engine torque was adjusted to 25KW, the temperature of the inlet gas to the catalyst bed was controlled at 350 deg.C, the amount of particles in the inlet and outlet gases of the catalyst bed was analyzed, and the conversion (%) was calculated using equation 1. For particle analysis, the particles were collected on a filter using a dilution tube and the composition of the particles on the filter was measured using a Soxhlet extractor.

The results are shown in Table 5.

As shown in Table 5, samples 51-56 of inventive examples 3-8 exhibited higher hydrocarbon and carbon monoxide conversion at 250 ℃ and excellent particle conversion at 350 ℃. On the other hand, in samples A to I of comparative examples 5 to 13 in which potassium titanate was not present, but the catalyst component loadings were the same as in samples 51 to56, the conversion of hydrocarbon and carbon monoxide at 250 ℃ was as high as the corresponding conversion of samples 51 to 56 of examples 3 to 8 of the present invention, but the particle conversions were all negative. This indicates SO₂Is oxidized into SO by oxygen in the exhaust gas of the diesel engine₃. This is because of SO₂Not measured in particle form, and SO₃But measured in particle form. In particular, in the catalyst using platinum as a catalyst component, the oxidation reaction is promoted, so that the particle conversion rate has a large negative value.

Further, as shown in Table 5, the heat-resistant inorganic oxide layer thereof included SiO₂The catalyst has higher capability of purifying hydrocarbon and carbon monoxide than other catalysts, and has high particle conversion rate.

As described above, in the exhaust gas purifying catalysts of examples 3 to 8 of the present invention, the conversion rate of particles was improved by adding potassium titanate (40g/L) to the heat-resistant inorganic oxide layer. Therefore, these catalysts can suppress particle emission.

Obviously, many modifications and variations of the present invention are possible within the scope of the above description. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

1. An exhaust gas purifying catalyst comprising:

a catalyst carrier comprises a catalyst carrier of formula K₂O·nTiO₂Wherein n is an integer selected from 4 to 8, said catalyst support being substantially free of alumina; and

a noble metal supported on the support.

2. An exhaust gas purifying catalyst according to claim 1, wherein said noble metal is at least one member selected from the group consisting of platinum, palladium and rhodium.

3. An exhaust gas purifying catalyst according to claim 1, wherein a supported amount of said noble metal is 0.2 to 10g per 100g of said potassium titanate.

4. An exhaust gas purifying catalyst according to claim 1, further comprising Silica (SiO)₂) Sol, titanium dioxide (TiO)₂) Sol and zirconium dioxide (ZrO)₂) At least one binder of the sol.

5. An exhaust gas purifying catalyst comprising:

a catalyst support; and

a refractory inorganic oxide coating formed on the support, the refractory inorganic oxide coating comprising a coating of formula K₂O·nTiO₂Wherein n is an integer selected from 4 to 8, and represents potassium titanate and at least one member selected from the group consisting of silicon dioxide, titanium dioxide and zirconium dioxide and a noble metal supported thereon,

the refractory inorganic oxide coating is substantially free of alumina.

6. The exhaust gas purifying catalyst according to claim 5, wherein the noble metal is at least one member selected from the group consisting of platinum, palladium and rhodium.

7. The exhaust gas purifying catalyst according to claim 5, wherein the content of potassium titanate is 20 to 60 g/L.

8. The exhaust gas purifying catalyst according to claim 5, wherein the heat-resistant inorganic oxide coating layer comprises the potassium titanate and silica.