JP3436765B2 - Diesel engine exhaust gas purification catalyst - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine exhaust gas purifying catalyst. Specifically, for purification of diesel engine exhaust gas that can remove carbonaceous fine particles, unburned hydrocarbons, carbon monoxide, and other harmful components in diesel engine exhaust gas from low temperatures, while suppressing the formation of sulfur dioxide into sulfate. It relates to a catalyst.

[0002]

2. Description of the Related Art In recent years, particularly fine particles in diesel engine exhaust gas (mainly solid carbon fine particles, sulfur fine particles such as sulfate, liquid or solid polymer hydrocarbon fine particles, etc. These are collectively referred to as "particulate matter"), which is a problem in terms of environmental hygiene.
The reason is that these fine particle substances have a particle diameter of almost 1 micron or less, and thus are easily suspended in the atmosphere and easily taken into the human body by respiration. Therefore, studies are being conducted in the direction of tightening regulations on the emission of these particulate materials from diesel engines.

On the other hand, the amount of particulate matter discharged from the diesel engine has been reduced to some extent with the improvement of the high pressure fuel injection of the diesel engine and the improvement of the control of the fuel injection timing. However, the reduction is not yet sufficient, and it is included in the particulate matter. Organic solvent-soluble components consisting mainly of liquid high molecular weight hydrocarbons (S
OF) cannot be removed by the above engine improvement, resulting in an increase in the SOF ratio in the particulate matter. Since this SOF contains harmful components such as carcinogenic substances, the removal of SOF together with the particulate matter has become an important issue.

As a method for removing fine particle substances, carbonaceous fine particles are added to a refractory three-dimensional structure such as ceramic foam, wire mesh, metal foam, plugged type ceramic honeycomb, open flow type ceramic honeycomb, and metal honeycomb. Using a catalyst supporting a combustible catalytic substance, while capturing particulate matter in the exhaust gas of a diesel engine, under the exhaust gas emission conditions (gas composition and temperature) obtained under normal diesel engine running conditions, Alternatively, a catalyst system for removing carbonaceous fine particles by using a heating means such as an electric heater has been studied.

In general, as a catalyst for purifying exhaust gas of a diesel engine, (a) a high efficiency of burning and removing harmful components such as unburned hydrocarbons and carbon monoxide from low temperatures in addition to carbonaceous fine particles, (b) fuel Dioxide (SO ₂ ) generated from sulfur components contained in large amounts in diesel oil used as
Has a low ability to oxidize sulfur trioxide (SO ₃ ), and can suppress the formation of sulfate (sulfur dioxide is oxidized to sulfur trioxide or sulfuric acid mist), and (c) continuous operation under high load. It is desired to have the capability of enduring even under low temperatures, that is, having high so-called high temperature durability.

Various proposals have hitherto been made for the purpose of improving the efficiency of burning and removing carbonaceous fine particles. For example, in JP-A-55-24597, as a platinum group element-based catalyst, rhodium (7.5%) platinum alloy, platinum / palladium (50/50) mixture, tantalum oxide or cerium oxide is supported with palladium. And alloys of palladium and 75% by weight or less of platinum, and these catalysts are said to be effective for removing SOF.

In addition, in JP-A-61-129030, JP-A-61-149222 and JP-A-61-146314, palladium and rhodium are used as main active components, and an alkali metal, an alkaline earth metal and copper are further added. A catalyst composition containing lanthanum, zinc, manganese, etc. is also disclosed in JP-A-59-82944. At least one selected from copper, alkali metal, molybdenum and vanadium and platinum, rhodium and palladium are selected. A catalyst composition in combination with at least one is disclosed.

Further, S in the exhaust gas of the diesel engine
As a catalyst for removing OF, an open-type honeycomb-shaped noble metal-based oxidation catalyst having through-holes parallel to the gas flow has been reported (SAE Paper, 81026).
3).

[0009]

However, all of the above-mentioned conventional catalysts are effective to some extent for removing carbonaceous fine particles by burning or for removing SOF, but since they have a high oxidizing ability of sulfur dioxide, they produce sulfate. There is a drawback that the amount is increased and the removal rate of the whole particulate matter is decreased, and this sulfate causes a new environmental problem.

That is, the performance required for the catalyst for purifying the exhaust gas of the diesel engine of the above (a) to (c),
Furthermore, a catalyst having sufficient SOF removal performance has not yet been found.

Therefore, one object of the present invention is to provide a catalyst for purifying diesel engine exhaust gas, which can efficiently remove particulate matter in diesel engine exhaust gas.

Another object of the present invention is to have a capability of burning and removing not only carbonaceous fine particles in diesel engine exhaust gas but also harmful components such as unburned hydrocarbons and carbon monoxide from a low temperature, and having an oxidizing ability of sulfur dioxide. To provide a catalyst for purifying a diesel engine, which has a low sulfur content and suppresses the formation of sulfate.

Another object of the present invention is to provide a diesel engine exhaust gas purifying catalyst capable of efficiently removing SOF in a diesel engine exhaust gas.

Another object of the present invention is to provide a diesel engine purifying catalyst which has good durability at high temperature and can be mounted on a diesel vehicle without causing any problems in practical use.

[0015]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a catalyst component containing palladium, copper oxide and a refractory inorganic oxide is converted into a refractory three-dimensional structure. A supported catalyst comprising palladium and acid
The weight ratio (Pd / CuO value) of copper oxide (CuO conversion) is 0.
Within the range of 1 to 2.0, the fire resistant three-dimensional structure.
Palladium is 0.01 to 1.0 per liter
g, copper oxide (CuO equivalent) 0.1 to 2.0 (less than) g
It has been found that the above object can be achieved in a catalyst for purifying diesel engine exhaust gas, which is characterized by being carried, and the present invention has been completed based on this finding. Hereinafter, the present invention will be described in detail.

A catalyst in which a catalyst component containing palladium, copper oxide, and a refractory inorganic oxide is supported on a refractory three-dimensional structure, and per 1 liter of the refractory three-dimensional structure,
0.01 to 1.0 g of palladium and 0.1 to 2.0 (less than) g of copper oxide (as CuO) are supported, and the weight ratio of palladium and copper oxide (as CuO) (Pd / C).
The catalyst for purifying exhaust gas from diesel engine is characterized by having a uO value) of 0.1 to 2.0.

The catalyst component may contain rare earth elements, if necessary.
It is preferable to add an oxide of at least one element selected from the group consisting of alkali metals, alkaline earth metals, vanadium, niobium, and tungsten.

The amount of palladium carried must be 0.01 to 1.0 g per liter of the three-dimensional structure. If the supported amount is less than 0.01 g, the oxidizing ability of harmful components such as SOF from a low temperature is remarkably lowered, and if the supported amount exceeds 1.0 g, the oxidizing ability is no longer improved. This is because it is not possible and economically unfavorable.

In the preparation of the catalyst of the present invention, palladium starting material may be palladium nitrate, palladium chloride, palladium tetramine chloride, palladium sulfide complex salt or the like.

On the other hand, the supported amount of copper oxide (CuO) must be 0.1 to 2.0 (less than) g per liter of the structure. When the supported amount is 2.0 g or more , the copper-dependent sulfur dioxide oxidizing ability is drastically improved, which is not preferable, and when the supported amount is less than 0.1 g, it is no longer compatible with palladium. This is because the synergistic effect is not exhibited.

In the preparation of the catalyst of the present invention, as the copper starting material, commercially available oxides, chlorides, nitrates, acetates, carbonates and the like are preferably used.

Further, the loading amount of each of palladium and copper per liter of the three-dimensional structure is 0.01 to.
Weight ratio (Pd ) of supported palladium / copper oxide even in the range of 1.0 g and 0.1-2.0 (less than) g
/ CuO value) is required to be 0.1 to 2.0. When it is less than 0.1, the purification ability of SOF, unburned hydrocarbons and the like is lowered, which is not preferable. Because.

The refractory inorganic oxide according to the present invention includes
Activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, zeolite, etc. are used, of which zirconia is sulfur dioxide of palladium and copper. As a suitable base material having the effect of suppressing the oxidation of

The amount of the refractory inorganic oxide supported is not particularly limited, but when applied to exhaust gas of a diesel engine, it is in the range of 1 to 80 g, preferably 5 to 60 g per liter of the three-dimensional structure. Is preferred.

The fire-resistant three-dimensional structure includes ceramic foam, open-flow ceramic honeycomb,
A wall-flow type honeycomb monolith, an open-flow metal honeycomb, a metal foam or a metal mesh can be used. In particular, diesel engine exhaust gas contains 100 mg or less of particulate matter per 1 m ^{3 of} exhaust gas, and the SOF content in this particulate matter is 20.
When it is at least%, an open flow type ceramic honeycomb or metal honeycomb is preferably used.

In order to improve high-temperature durability and control oxidation ability, rare earth elements such as scandium, yttrium, lanthanum, cerium, praseodymium and neodymium, alkali metals such as lithium, sodium and potassium may be added to the above-mentioned catalyst component, if necessary. , At least one element selected from the group consisting of alkaline earth metals such as beryllium, magnesium, and calcium, vanadium, niobium, and tungsten (hereinafter referred to as additional components). The amount of the element added to this catalyst component is preferably 10 g or less per liter of the refractory three-dimensional structure as an oxide.

The method for preparing the catalyst of the present invention is not particularly limited, and the catalyst can be prepared, for example, by the following method.

(1) The refractory inorganic oxide powder is wet pulverized to form a slurry, and the refractory three-dimensional structure is immersed in this slurry to remove excess slurry, and then 80 to 25
Dry at 0 ° C and then bake at 300-850 ° C. Next, the refractory three-dimensional structure is immersed in an aqueous solution containing a predetermined amount of palladium and copper to remove excess solution, dried at 80 to 250 ° C., and then 300 to 850.
The target catalyst is obtained by calcining at ℃.

(2) Titania is put into an aqueous solution containing a predetermined amount of palladium and copper to impregnate it, and
It is dried at 250 ° C and then calcined at 300 to 850 ° C to disperse and carry the noble metal component on the titania. Next, the titania powder carrying the above noble metal component is wet pulverized to form a slurry, the refractory three-dimensional structure is immersed in this slurry, excess slurry is removed, and then dried at 80 to 250 ° C., Then, it is calcined at 300 to 850 ° C. to obtain the desired catalyst.

[0030]

INDUSTRIAL APPLICABILITY The catalyst of the present invention is excellent in the ability to remove carbonaceous fine particles as well as harmful components such as unburned hydrocarbons and carbon monoxide from low temperatures, and has a low oxidizing ability of sulfur dioxide. Generation can be suppressed.
Therefore, the catalyst of the present invention is excellent in reducing particulate matter in diesel engine exhaust gas, and by using the catalyst of the present invention, diesel engine exhaust gas can be efficiently purified.

When palladium is used alone, it has the ability to purify SOF, unburned hydrocarbons, carbon monoxide, etc. from low temperatures, but has a high sulfur dioxide oxidizing ability, especially when diesel engine exhaust gas rises. Sulfate is generated at a high temperature, which rather leads to an increase in particulate matter, but when copper oxide is made to coexist with palladium at a specific ratio, SOF, unburned hydrocarbons, carbon monoxide, etc. from a low temperature are generated. It has a purifying ability and exhibits excellent performance in which the oxidizing ability of sulfur dioxide is suppressed.

Therefore, the present invention is also very effective in purifying diesel engine exhaust gas, since it is also excellent in SOF removing ability.

Further, since the catalyst of the present invention is excellent in high temperature durability, it can be mounted on a diesel vehicle without causing any practical problems.

As described above, the catalyst of the present invention is extremely useful as a diesel engine exhaust gas purification catalyst.

[0035]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 1 kg of alumina having a specific surface area of 118 m ² / g and 12.5 g of palladium contained palladium nitrate and copper nitrate 2
2.8 g and was added to an aqueous solution prepared by dissolving in deionized water, thoroughly stirred, dried at 150 ° C. for 1 hour, and further baked at 500 ° C. for 2 hours to disperse palladium and copper oxide (CuO). A supported alumina powder was obtained. 1 kg of this alumina powder was wet pulverized into a slurry.

A cylindrical cordierite honeycomb having a diameter of 5.66 inches and a length of 6.00 inches, which has about 400 open-flow gas flow cells per square inch in cross-section, is added to the slurry thus obtained. After immersing the carrier and removing excess slurry, it was dried at 150 ° C. for 2 hours and then calcined at 500 ° C. for 1 hour to obtain a catalyst.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 0.3 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 1.7. .

Example 2 A catalyst was obtained in the same manner as in Example 1 except that 38 g of copper nitrate was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 0.5 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 1.0. .

Example 3 A catalyst was obtained in the same manner as in Example 1 except that 76 g of copper nitrate was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 1.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.5. .

Example 4 A catalyst was obtained in the same manner as in Example 1 except that 114 g of copper nitrate was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 1.5 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.33. .

Example 5 A catalyst was obtained in the same manner as in Example 3 except that palladium nitrate containing 5 g of palladium was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.2 g and 1.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.2. .

Example 6 A catalyst was obtained in exactly the same manner as in Example 3, except that palladium nitrate containing 20 g of palladium was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.8 g and 1.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.8. .

Example 7 In Example 3, the specific surface area was 55 m instead of alumina.
^A catalyst was obtained in exactly the same manner as in Example 3 except that zirconia having ² / g was used.

The amounts of zirconia, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 1.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.5. .

Example 8 1 kg of alumina-silica powder (Al ₂ O ₆ / SiO ₂ molar ratio 3/7) having a specific surface area of 182 m ² / g, and 12.5 g of palladium contained palladium nitrate and copper nitrate 76 g.
And are dissolved in deionized water to prepare an aqueous solution, thoroughly stirred, dried at 150 ° C. for 1 hour, and further 500
Palladium and copper oxide (CuO) after firing at ℃ for 2 hours
Alumina-silica powder having dispersed therein was obtained. 1 kg of this alumina-silica powder was wet pulverized to form a slurry.

A cylindrical honeycomb carrier made of stainless steel having a diameter of 5.66 inches and a length of 6.00 inches, which has about 300 open-flow gas flow cells per square inch in cross section in the slurry thus obtained. Was dipped to remove excess slurry, dried at 150 ° C. for 2 hours, and then calcined at 500 ° C. for 1 hour to obtain a catalyst.

The amounts of alumina-silica, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 1.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.5. there were.

Example 9 1 kg of alumina-zirconia powder consisting of 200 g of alumina having a specific surface area of 24 m ² / g and 800 g of zirconia having a specific surface area of 55 m ² / g was wet pulverized to form a slurry.

The same stainless steel honeycomb carrier as used in Example 8 was immersed in the slurry thus obtained to remove excess slurry, followed by drying at 150 ° C. for 1 hour and then at 400 ° C. for 1 hour. It was calcined to obtain a structure supporting alumina-zirconia.

This structure was converted into palladium tetramine chloride containing 10.5 g of palladium and copper chloride 35.
g, 95 g of lanthanum chloride and 73 g of cerium carbonate are immersed in 2.5 liters of an aqueous solution prepared by dissolving in deionized water to remove excess solution, followed by drying at 150 ° C. for 3 hours and then at 650 ° C. for 1 hour. The catalyst was obtained by firing.

Alumina, zirconia in this catalyst,
The amounts of palladium, copper oxide, lanthanum oxide and ceria supported were 10 g and 40 g, respectively, per liter of the structure.
0.5 g, 1.0 g, 2 g and 2.0 g, with a palladium / copper oxide weight ratio of 0.5.

Example 10 Palladium chloride containing 25 g of palladium and 75 g of copper nitrate containing 1 kg of zirconia having a specific surface area of 82 m ² / g.
And were added to an aqueous solution prepared by dissolving in deionized water, thoroughly stirred, dried at 150 ° C. for 1 hour, and further 500
Palladium and copper oxide (CuO) after firing at ℃ for 2 hours
A zirconia powder having dispersed therein was obtained. 1 kg of this alumina powder was wet pulverized into a slurry.

In the slurry thus obtained, the number of bubbles formed in the ceramic skeleton was about 12 in 1 inch.
5.6, which has a number of cells which is about 90%.
A 6 inch diameter × 6.00 inch length of cylindrical cordierite ceramic foam was dipped to remove excess slurry, and then dried at 150 ° C. for 2 hours, then 500
Firing at 1 ° C. for 1 hour gave a structure supporting zirconia, palladium and copper oxide.

This structure was prepared by mixing 69 g of ammonium metavanadate with deionized water while stirring with oxalic acid 82.
5 g was gradually added and immersed in a dissolved solution of 2 liters to remove excess solution, dried at 150 ° C. for 3 hours and then calcined at 500 ° C. for 1 hour to obtain a catalyst.

The supported amounts of zirconia, palladium, copper oxide and vanadium oxide in this catalyst were 20 g, 0.5 g, 0.6 g and 3 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was. It was 0.83.

Comparative Example 1 A catalyst was obtained in exactly the same manner as in Example 1 except that 3.8 g of copper nitrate was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 0.05 g, respectively, per liter of the structure, and the weight ratio of palladium / copper oxide was 10.

Comparative Example 2 A catalyst was obtained in the same manner as in Example 1 except that 228 g of copper nitrate was dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 0.5 g and 3.0 g per liter of the structure, respectively, and the palladium / copper oxide weight ratio was 0.17. .

Comparative Example 3 A catalyst was obtained in exactly the same manner as in Example 1 except that palladium nitrate containing 50 g of palladium and 76 g of copper nitrate were dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 2.0 g and 1.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 2.0. .

Comparative Example 4 A catalyst was obtained in the same manner as in Example 1 except that palladium nitrate containing 50 g of palladium and 228 g of copper nitrate were dissolved in deionized water.

The amounts of alumina, palladium and copper oxide supported on this catalyst were 40 g, 2.0 g and 3.0 g, respectively, per liter of the structure, and the palladium / copper oxide weight ratio was 0.66. .

Table 1 shows the amount of each component supported in the catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 4.

[0071]

[Table 1]

(Evaluation of Catalyst) The diesel engine exhaust gas purification performance of each catalyst was evaluated by the following method.

In this method, a supercharged direct injection diesel engine (4 cylinders, 2800 cc) and diesel fuel having a sulfur content of 0.38% by weight were used.

Each catalyst was attached to an exhaust gas pipe from the above engine, and a durability test was carried out for 300 hours under conditions of a full load of an engine speed of 2500 rpm and a catalyst inlet temperature of 600 ° C.

Next, after aeration of the catalyst for 1 hour under the conditions of an engine speed of 2000 rpm, a torque of 3.0 kg · m and a catalyst inlet temperature of 200 ° C., the operating conditions were engine speed of 2000 rpm and torque of 14.0 kg · m. change,
The content of the particulate matter in the exhaust gas before entering the catalyst bed (inlet) and after exiting the catalyst bed (exit) under conditions where the catalyst inlet temperature was stable at 400 ° C was determined by the usual dilution tunnel method. The measurement was performed to determine the purification rate (%) of the particulate matter.

Further, the particulate matter captured using the dilution tunnel was extracted with a dichloromethane solution, and the SOF emission amount was measured from the weight change of the particulate matter before and after the extraction to obtain the SOF purification rate. .

Further, the sulfur dioxide, gaseous hydrocarbons and carbon monoxide in the exhaust gas before entering the catalyst bed and in the exhaust gas after passing through the catalyst bed were also analyzed at the same time, and the conversion rate (%)
I asked. The results are shown in Table 2.

[0078]

[Table 2]

Claims (2)

(57) [Claims] 1. A catalyst in which a catalyst component containing palladium, copper oxide and a refractory inorganic oxide is supported on a refractory three-dimensional structure , wherein the weight of palladium and copper oxide (CuO equivalent) is increased.
Within the range where the quantity ratio (Pd / CuO value) is 0.1 to 2.0
In 1 liter of the fire-resistant three-dimensional structure.
0.01 to 1.0 g of radium, copper oxide (CuO equivalent)
Is supported by 0.1 to 2.0 (less than) g, and a catalyst for purifying exhaust gas from a diesel engine. 2. A catalyst component carrying an oxide of at least one element selected from the group consisting of rare earths, alkali metals, alkaline earth metals, vanadium, niobium, and tungsten. catalyst.