JPH0442063B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a catalyst for purifying exhaust gas from a diesel engine and a method for producing the same. Specifically, the present invention relates to a catalyst for purifying diesel engine exhaust gas that has excellent performance in burning and removing carbon-based particulates present in diesel engine exhaust gas, and a method for producing the catalyst. In recent years, particulate matter in diesel engine exhaust gas (mainly consisting of solid carbon particles, sulfur-based particles such as sulfates, and high molecular weight hydrocarbon particles in liquid or solid form) has tended to become an environmental health problem. . This is because most of these fine particles have particle diameters of 1 micron or less and are easily suspended in the atmosphere and easily taken into the human body through breathing. Therefore, efforts are being made to tighten regulations on the emission of these particulates from diesel engines. By the way, as a method for removing these fine particles,
There are two main methods as follows. One is to use a heat-resistant gas filter (ceramic foam, wire mesh, metal foam, sealed type ceramic honeycomb, etc.) to pass through the exhaust gas and capture fine particles, and if the pressure drop increases, the particles may be accumulated in a burner, etc. One method is to burn the fine particles to regenerate the filter, and the other is to carry a catalyst substance on a carrier with this heat-resistant gas filter structure and perform over-operation as well as combustion operation to reduce the frequency of the above-mentioned combustion regeneration. This is a method of increasing the combustion activity of the catalyst to such an extent that regeneration is not necessary. In the former case, the higher the particle removal effect, the faster the pressure drop will rise and the more frequently the regeneration will occur, which will be cumbersome and economically disadvantageous. In comparison, the latter method is considered to be a much better method if a catalytic material that can maintain catalytic activity under the exhaust conditions (gas composition and temperature) of diesel engine exhaust gas is employed. However, the exhaust gas temperature of a diesel engine is much lower than that of a gasoline engine, and since light oil is used as fuel, the amount of SO ₂ in the exhaust gas is also large. Therefore, it has almost no ability to generate sulfate (SO ₂ is further oxidized to SO ₃ or sulfuric acid mist), and it can effectively ignite and burn accumulated particulates within the temperature obtained under normal engine running conditions. Although there is a demand for a catalyst with performance that satisfies this requirement, the current situation is that no catalyst has been proposed that satisfactorily meets this requirement. The object of the present invention is to provide a catalyst that satisfies this requirement. Specifically, diesel engine exhaust gas purification has good combustion behavior of particulates within the diesel engine exhaust gas temperature range obtained during normal city driving, with a gradual rise in pressure drop, and where combustion regeneration occurs promptly when a predetermined exhaust gas temperature is reached. The purpose is to provide a catalyst for That is, the present invention is specified as follows. (1) On a porous inorganic base supported on a refractory three-dimensional structure having a gas filter function, (a) selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium and silver; (b) an oxide of at least one metal selected from the group consisting of sodium, potassium and cesium; and (c) an oxide of at least one metal selected from the group consisting of platinum, rhodium and palladium. and at least one metal and represented by groups (a) and (b),
The atomic ratio of these metals is in the range of (a)/(b) = 0.25 to 9.0, and the oxides and metals shown in groups (b) and (c) have an atomic ratio of (b) /(c)=4
A catalyst for exhaust gas purification that is dispersedly supported in the range of ~80%. (2) The porous inorganic substrate contains 5 to 250 g of oxide per finished catalyst, and the oxide of group (a) contains 2
~100g, 2~100g of oxides shown in group (b),
The catalyst according to claim 1, further comprising 0.1 to 4.0 g of a metal represented by group (c). (3) The catalyst according to claim 1 or 2, wherein the refractory three-dimensional structure is a ceramic foam, a wire mesh, a metal foam, or a sealed ceramic honeycomb. (4) On a porous inorganic base supported on a refractory three-dimensional structure having a gas filter function, (a) a material selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium and silver; (b) a compound containing at least one metal;
(c) a compound containing at least one metal selected from the group consisting of sodium, potassium and cesium; and (c) a compound containing at least one metal selected from the group consisting of platinum, rhodium and palladium; The compounds shown in groups (a) and (b) are
(a)/(b)=0.25 to 9.0, and (b) and (c)
By dispersing and supporting the compounds represented by the group in an atomic ratio of metals (b)/(c) in the range of 4 to 80, and heat-treating this at a temperature in the range of 700 to 1000°C, (a ) and (b) are oxides, and (c) is a metal. The present inventors found that the exhaust gas temperature from a diesel engine is extremely low, and the exhaust gas temperature during city driving does not reach 450℃ even at the manhold exit, so it is 350℃.
The combustion behavior of carbon-based fine particles is good even below, and the pressure equilibrium temperature (the temperature at which the pressure increase due to accumulation of fine particles is equal to the pressure drop due to combustion of fine particles) is 330~
We have discovered a catalyst system that has the characteristics of a catalyst that is as low as 350°C, starts combustion of accumulated particulates below 400°C, and rapidly reduces pressure drop, and has the characteristics that almost no sulfate formation is observed even at 450°C. Normally, with catalysts that use only base metals, the combustion behavior of fine particles is such that the pressure drop increases quickly until a predetermined temperature is reached, and if the regeneration temperature is not reached under normal running conditions, external forced regeneration is required frequently. It needs to be done expensively and lacks practicality. On the other hand, catalysts containing precious metals have the ability to oxidize carbon monoxide (CO) and hydrocarbons (HC), but at the same time
Oxidation of SO ₂ also occurs, producing sulfate, which is undesirable. However, even in the low temperature range, some of the combustible components in the fine particles burn, so the pressure drop increases slowly, and the pressure equilibrium temperature is also lower than when only base metals are used. The present invention provides a catalyst composition that compensates for the above-mentioned drawbacks and does not impair the advantages of each catalyst component. According to the findings of the present inventors, in the above-mentioned catalyst component dispersed and supported on an inorganic substrate, the alkali metal of group (b) acts extremely closely on the noble metal of group (c), and the sulfate that originally contains Demonstrates the effect of effectively suppressing generation capacity. Of course, group (b) alkali metals have the same fine particle combustion performance as group (a) metals. In particular, the effect is fully exhibited when supporting and firing alkali metals and noble metals is carried out at a high temperature of 700 to 1000°C. Moreover, the coexistence ratio of alkali metals/noble metals (molar ratio) is 4.
It has been found that the sulfate-forming ability is most suppressed in the range of 80 to 80, preferably 8 to 50. The inorganic bases used in the present invention include alumina, silica, titania, which are usually used as carrier bases,
Zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia and the like are preferably used, but are not limited thereto. The specific method for preparing the catalyst according to the present invention is as follows. First, the above-mentioned inorganic base is formed into a three-dimensional structure having a gas filter type structure (e.g., ceramic foam, wire mesh, metal foam, sealed type ceramic honeycomb).
The slurry is made into a slurry and coated with wash to form a support layer.
Compounds containing at least one metal selected from the group consisting of iron, cobalt, vanadium, and silver, compounds containing at least one metal selected from the group consisting of potassium, cesium, and sodium, and further platinum, rhodium, and palladium. A compound containing at least one metal selected from the group consisting of at least one metal is supported in the form of an aqueous or organic solvent (alcohol etc.) solution or dispersion by an impregnation or dipping method. The above compounds include inorganic compounds such as oxides, hydroxides, nitrates, carbonates, phosphates, sulfates, halides, and metal salts, and organic compounds such as carboxylates and complex compounds such as acetates and formates. Although it is appropriately selected from among these, it is preferable to use one that is easily soluble in water or an alcoholic organic solvent. It is also possible to adopt a method in which the inorganic base material and each catalyst component group are mixed in advance, and this is washed coated, dried, and fired to form a finished catalyst.
These compromise methods may also be adopted as appropriate. Hereinafter, the present invention will be explained in more detail by showing Examples and Comparative Examples. Example 1 1 kg of alumina powder contains 12.86 g of platinum (Pt)
A nitric acid solution of dinitrodiammine platinum containing Pt and a rhodium nitrate aqueous solution containing 1.286 g of rhodium (Rh) were added and mixed thoroughly, dried at 150°C for 3 hours, fired at 500°C for 2 hours, and crushed to obtain Pt, Rh
An alumina powder containing . The powder was made into a slurry using a wet mill and supported on a commercially available cordierite foam (bulk density 0.35
g/cm ³ , porosity 87.5%, volume 1.7), and the excess slurry was shaken off to obtain a cordierite foam having an alumina coat layer containing platinum-rhodium. Next, 265 g of lead nitrate and 124.4 g of cesium nitrate were dissolved in ion exchange water to obtain 2. The foam was immersed in this, the excess solution was shaken off, and the foam was dried at 150°C for 3 hours and then baked at 750°C for 2 hours. At this time, the supported amount of Pt and Rh was 0.90g/− carrier,
The supported amounts of 0.09 g/-carrier, lead, and cesium were 20 g/-carrier and 10 g/-carrier, respectively, in terms of oxides. The composition of the finished coating layer is 69.3% by weight of alumina, 19.8% by weight of PbO, 9.9% by weight of Cs ₂ O,
Pt+Rh (Pt/Rh=10/1) was 0.99% by weight. Example 2 Titanium tetrachloride 10 containing 959g of titanium as TiO ₂
180.2 g of silicon as SiO ₂ in a wt% aqueous solution
Contains Snowtex-0 (product containing 20% by weight)
A mixed solution of about 3.9% and 28% ammonium water was added under stirring, and the resulting cake was washed with water and heated to 150°C.
After drying for 5 hours at 500°C, it was fired for 2 hours. The fired product was pulverized to obtain titania-silica powder with a TiO ₂ /SiO ₂ molar ratio of 8/2. The surface area was 160 m ² /g. Next, 868 g of copper nitrate Cu ₍ NO ₃ ) 2.3H ₂ O, 307 g of potassium nitrate KNO ₃ , a chloroplatinic acid aqueous solution containing 12.86 g as Pt, and a rhodium chloride aqueous solution containing 1.286 g as Rh were mixed to give about 1. To this solution, 1 kg of the titania-silica powder was mixed and uniformly dispersed. After drying at 150℃ for 3 hours,
Sintered at 500℃ for 2 hours and crushed to produce CuO, K ₂ O, Pt,
Titania-silica powder containing Rh was obtained. 1 kg of the powder is made into a slurry using a wet mill to make a slurry of 1.7 kg.
The slurry was dipped and supported on a capacity cordierite foam, and after removing excess slurry, it was dried at 150°C for 3 hours and fired at 800°C for 2 hours. The amount of titania-silica supported at this time was 70g/
-The amount of Pt and Rh supported on the carrier is 0.90 each.
g/-carrier and 0.09 g/-carrier, and copper and potassium were 20 g/-carrier and 10 g/-carrier, respectively, in terms of oxides. The composition of the finished coating layer is titania-silica.
69.3 wt%, CuO19.8 wt%, _K2O9.9 wt%, Pt
+Rh (Pt/Rh=10/1) was 0.99% by weight. Example 3 Catalysts 3-a, 3-b, 3-c, 3-e, 3-
For g, 3-j, 3-m and 3-n, the method according to Example 1, 3-d, 3-f, 3-h, 3
For -i, 3-k and 3-l, catalysts made of cordierite foam having a coat layer having the following catalyst composition were obtained in the same manner as in Example 2. The numbers in parentheses indicate the amount of each component supported (g/-carrier).

[Table] Comparative Example 1 Except for not using Pt and Rh in Example 1,
All catalysts were prepared in the same way, Al ₂ O ₃ 70g/-
Support, PbO20g/-support, Cs ₂ 10g/-support,
A supported cordierite foam catalyst was obtained. Comparative Example 2 A catalyst was prepared in the same manner as in Example 1 except that cesium was not used, and 70 g of Al ₂ O ₃ /- support, 20 g of PbO /- support, 0.90 g of Pt /- support,
Rh0.09g/- carrier, supported cordierite foam was obtained. Comparative Example 3 A catalyst was prepared in the same manner as in Example 2 except that copper nitrate was not used, and titania-silica 70
g/- carrier, K ₂ O 10 g/- carrier, Pt 0.90 g/
- Carrier, Rh 0.09 g/- Carrier, supported cordierite foam was obtained. Comparative Example 4 A catalyst was prepared in the same manner as in Example 1 except that the final calcination temperature was changed to 600°C. Example 4 In Example 1, except that the cordierite foam was replaced with a sealed type honeycomb structure in which adjacent holes on both end faces were alternately closed with a honeycomb structure to allow gas to pass only from the partition wall.
A catalyst was prepared using exactly the same method. Example 5 The catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 2 were evaluated using a 4-cylinder diesel engine with a displacement of 2300 c.c. Particulate capture was carried out for approximately 2 hours under the conditions of engine rotation speed 2500 rpm and torque 4.0 kg・m, and then the torque was
The pressure drop change in the catalyst layer was continuously recorded by increasing the pressure at 0.5 kg/m intervals every 5 minutes, and as the exhaust gas temperature rose on the catalyst, the pressure increased due to the accumulation of fine particles and the pressure due to the combustion of fine particles. The temperature at which the drop is equal (Te) and the temperature at which ignition and combustion occur and the pressure drop rapidly increases (Ti) were determined. In addition, the value of ΔP (mmHg/H) was determined by calculating the change in pressure drop over time when capturing fine particles at 2500 rpm and a torque of 4.0 Kg·m from a chart of the amount of change in pressure drop per hour. In addition, the conversion rate of SO ₂ to SO ₃ was determined at an exhaust gas temperature of 450°C. The conversion rate of SO ₂ is determined by the inlet gas and outlet gas.
The SO ₂ concentration was analyzed using a non-dispersive infrared analyzer (NDIR method), and the conversion rate (%) to SO ₂ was determined using the following calculation formula. SO conversion rate (%) = Inlet SO ₂ concentration (ppm) - Outlet SO ₂ concentration (ppm) / Inlet SO ₂ concentration (ppm) x 100 The results are shown in Table 1 below. The catalysts obtained in Examples 1 to 3 and Comparative Examples 1 to 3
Table 2 shows the (a)/(b) values and (b)/(c) values.

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Claims (1)

[Scope of Claims] 1. On a porous inorganic base supported on a refractory three-dimensional structure having a gas filter function, (a) a material made of copper, manganese, molybdenum, lead, iron, cobalt, vanadium, and silver; (b) an oxide of at least one metal selected from the group consisting of sodium, potassium and cesium; and (c) platinum, rhodium and palladium. at least one metal selected from the group, and (a)
The oxides and metals shown in groups (b) and (c) have an atomic ratio of (a)/(b) = 0.25 to 9.0. A catalyst for exhaust gas purification is prepared by dispersing and supporting these metals in an atomic ratio of (b)/(c)=4 to 80. 2. The porous inorganic base contains 5 to 250 g of oxide per finished catalyst, and the oxide of group (a) contains 2 to 250 g of oxide.
2. The catalyst according to claim 1, which contains 100 g of the oxide of group (b), 2 to 100 g of the oxide of group (b), and 0.1 to 4.0 g of the metal of group (c). 3. Claim 1, wherein the fire-resistant three-dimensional structure is ceramic foam, wire mesh, metal foam, or sealed ceramic honeycomb.
or the catalyst described in 2. 4. On a porous inorganic base supported on a refractory three-dimensional structure having a gas filter function, (a) a material selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium and silver; (b) a compound containing at least one metal selected from the group consisting of sodium, potassium, and cesium; and (c) at least one selected from the group consisting of platinum, rhodium, and palladium. and a compound containing one kind of metal, and the compound represented by groups (a) and (b) has an atomic ratio of those metals (a)/(b)=0.25 to 9.0.
The compounds shown in groups (b) and (c) are dispersed and supported at an atomic ratio of (b)/(c) = 4 to 80, and this is carried out at 700 to 1000°C. A method for producing a catalyst for exhaust gas purification, characterized in that the compounds (a) and (b) are converted into oxides, and the compound (c) is converted into metals by heat treatment at a temperature in the range of .