JPS6078640A - Catalyst for purifying exhaust gas and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain a catalyst for burning and removing fine carbonaceous particles in exhaust gas of an diesel engine, by dispersing and supporting copper, Na and platinum or the like by a porous inorg. substrate supported by a refractory three-dimensional structure before heat treatment. CONSTITUTION:A compound (a) containing at least one metal selected from a group consisting of copper, Mn, Mo, lead, iron, Co, V and Ag, a compound (b) containing at least one metal selected from a group consisting of Na, K and Cs and, further, a compound (c) containing at least one metal selected from a group consisting of platinum, Rh and Pd are dispersed in and supported by a porous inorg. substrate such as alumina supported by a refractory three-dimentional structure having gas filter function such as ceramic foam and heat treated at 700-1,000 deg.C. As a result, the title catalyst, wherein combustion behavior of fine particles is good in an engine exhaust gas temp. range and the rising in pressure loss is slow as well as combustion regeneration is rapidly generated from the catalyst reaches a predetermined exhaust gas temp., is obtained.

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 same.

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. . Most of these fine particles have a particle size of 1 micron or less,
This is because they easily float in the atmosphere and are easily taken into the human body through breathing. Therefore, studies are underway to tighten the regulations on emissions of these particulates from diesel engines.

By the way, as a method for removing these particulates, there are gas filters (ceramic foam, wire mesh, metal foam, sealed type ceramic honeycomb, etc.)
is used to filter the exhaust gas and capture particulates, and if the pressure drop increases, the accumulated particulates are combusted with a burner, etc.
In addition to the method of regenerating the filter, there is also a method of supporting a catalyst material on a carrier having this heat-resistant gas filter structure, and performing a combustion operation as well as a heating operation to reduce the frequency of the combustion regeneration. This method increases the combustion activity of the catalyst to such an extent that it is not necessary.

In the former case, if the removal effect of fine particles is enhanced, the pressure drop will increase rapidly, and the baking mold will have to be regenerated frequently, which will be 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 S02 in the exhaust gas is also large. Therefore, the catalyst has almost no ability to generate sulfate (SO7, which is further oxidized to SO3 or sulfuric acid mist), and has the ability to successfully ignite and burn accumulated particulates within the temperature range obtained under normal engine running conditions. However, to date, no catalyst has been proposed that satisfies this requirement.

The object of the present invention is to provide a catalyst that satisfies this requirement. Specifically, the diesel engine exhaust gas purification method has good combustion behavior of particulates within the diesel engine exhaust gas temperature range obtained during normal running in cloth, and has a gradual increase in pressure drop, and when a predetermined exhaust gas temperature is reached, combustion regeneration occurs quickly. The purpose is to provide a catalyst for

That is, the present invention is specified as follows.

(1) At least one member selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium, and silver on a porous inorganic base coated on a refractory monolithic carrier. (b) a compound of at least one metal selected from the group consisting of sodium, potassium, and cesium; and (c) at least one metal selected from the group consisting of platinum, rhodium, and palladium. An exhaust gas purification catalyst comprising a dispersed support of a compound.

(2) The compounds represented by groups (a) and (b) have a molar ratio of (a)/(b) = 0.25 to 9.0, preferably 0.4 to 5, (b) and (
The molar ratio of the compounds in group c) is (b)/(c) =
4 to so, preferably 8 to 50 (1)
Catalysts as described.

(3) The porous inorganic substrate has an oxide content of 5 to 250 f, preferably 10 to 200 f, per finished catalyst iI. , (a
) The compound represented by group (b) has an oxide of 2 to 100 F, preferably 4 to 501, the compound represented by group (b) has an oxide of 2 to 100 F, preferably 4 to 50 F, and the compound represented by group (c) is 0.1 to 4 as a metal element
．． Of, preferably 0.3 to 3. The catalyst according to (1) or (2), which contains a range of Of.

(4) a compound containing at least one metal selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium, and silver on an inorganic carrier; and (b)
A compound containing at least one metal selected from the group consisting of sodium, potassium and cesium;
) A catalyst for exhaust gas purification, characterized in that a compound containing at least one metal selected from the group consisting of platinum, rhodium and palladium is dispersed and supported, and the catalyst is heat-treated at a temperature in the range of 700 to 1000°C. Manufacturing method.

The present inventors found that the exhaust gas temperature from a diesel engine is extremely low, and the exhaust gas temperature during city driving is not far from 450°C even at the manhold exit, so the combustion behavior of carbon-based particulates is good even below 350°C, and the pressure equilibrium temperature (The temperature at which the pressure increase due to the accumulation of fine particles is equal to the pressure drop due to the combustion of fine particles) is as low as 330 to 350°C, and the accumulated fine particles are 4
We have discovered a catalyst system that starts combustion at temperatures below 00°C and exhibits a rapid drop in pressure drop, and has the characteristic that almost no sulfate formation is observed even at 450°C.

Normally, in catalysts using 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, forced regeneration from the outside is required. It is not practical because it needs to be done frequently. On the other hand, in the case of a catalyst containing noble metals, -carbon oxide (
CO).

Although it has the ability to oxidize hydrocarbons (HC), it also oxidizes 802, producing sulfate, which is undesirable. However, even in the low-temperature region, some of the combustible components in the fine particles burn, so the increase in pressure drop is gradual, 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 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, the alkali metals of group (b) are also recognized to have the same fine particle combustion performance as the metals of group (,). In particular, supporting firing of alkali metals and noble metals is carried out at 700 to 1000℃.
The effect is fully demonstrated when the process is carried out at high temperatures. Moreover, it has been found that the ability to generate sulfate is most suppressed when the coexisting ratio of alkali metal/noble metal (molar ratio) is in the range of 4 to 80, preferably in the range of 8 to 50.

The inorganic base used in the present invention is preferably alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, etc., which are usually used as carrier bases. but are not limited to these.

A specific method for preparing such a catalyst according to the present invention is as follows. First, the above-mentioned inorganic base is slurried into a three-dimensional structure having a gas filter type structure (for example, ceramic foam, wire mesh, metal foam, sealed type ceramic honeycomb) and washed with a wash cordon to form a support layer. A compound containing at least one metal selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium, and silver, at least one selected from the group consisting of potassium, cesium, and sodium.
Impregnation or immersion method with a compound containing a certain metal and a compound containing at least one metal selected from the group consisting of platinum, rhodium, and palladium in the form of an aqueous or organic solvent (alcohol etc.) solution or dispersion. It is carried by 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. Appropriate selection is made from among
It is preferable to use a material 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, washed coated, dried, and fired to obtain a finished catalyst, and a compromise between these methods can also be adopted as appropriate.

Hereinafter, the present invention will be explained in more detail by showing Examples and Comparative Examples.

Example 1 Alumina powder 1kl? 12.86 as platinum (Pi)
A nitric acid solution of dinitrodiammine platinum containing F and a rhodium nitrate aqueous solution containing 1.2869 as rhodium (ah) were added and mixed thoroughly, dried at 150°C for 3 hours, calcined at 500°C for 2 hours, and crushed. Alumina powder containing Pt and Rh was obtained.

The powder was made into a slurry using a wet mill and supported, and then ion-exchanged with 265 g of lead nitrate and 124.4 F of cesium nitrate. Dissolve in water 2
It was set to 1. Dip the foam into this and shake off the excess solution.

After drying at 150°C for 3 hours, it was fired at 750°C for 2 hours.

The amount of Pt and Rh supported at this time is o, sor/l-carrier.

The supported amount of 0.09r/A'-carrier, lead, and cesium is 20f/'l-carrier, 10 t/l in oxide equivalent Teso, respectively.
- It was a carrier. The composition of the finished coat layer was 69.3% by weight of alumina, 19.8% by weight of PbO, and C8!09.
9% by weight, Pt 10 h (Pt/lung = ”/1) 0.9
It was 9% by weight.

Example 2 Titanium tetrachloride 10 containing 959f titanium as TiO2
Weight of silicon in an aqueous solution of 8i01 and 1B0.2
A mixed solution of about 3.91 of Snowtex-○ (containing 20% by weight) containing f and 28 thiammonia water was added under stirring, and the resulting cake was washed with p water, dried at 150°C for 5 hours, and then heated to 500°C. It took two hours. Crush the fired product,
A titania-silica powder of T s OH/5i025i02/2 was obtained. The surface area is 160 n? /f.

Next, copper nitrate cu(No, ), -3H,0868t and potassium nitrate KN0.30? 12.8 as 9% Pt
Chloroplatinic acid aqueous solution containing 6f and 1,28 as Rh
An aqueous rhodium chloride solution containing 6F was mixed to obtain a solution of about 11, and 1 volume of the titania-silica powder was mixed therewith and uniformly dispersed. After drying at 150℃ for 3 hours, 5
Calcined at 00℃ for 2 hours and crushed to produce CuO, K2O, Pt
, a titania-silica powder containing slenderness was obtained.

1kl of the powder? was made into a slurry using a wet mill, immersed and supported on a 1.71 volume cordierite foam, and after removing the excess slurry, it was dried at 150°C for 3 hours to form a SOO°C
It was baked for 2 hours.

The amount of titania-silica supported at this time was 709/l-carrier, and the amount of supported Pt and Rh was 0.90 f/l- each.
The carrier is 0.09 f/13-carrier, copper and potassium are each 2 oy/l-carrier and 10
f/l-carrier.

The composition of the finished coat layer is titania-silica 69.3
"fr (Amount 'Is, CuO19, 8 weight N%, K, 09
．． 9% by weight, Pt + Rh (Pjt/Rh-10/
1) 0.99% by weight.

Example 3 A catalyst made of a cordierite foam having a coating layer having the following catalyst composition was obtained by a method according to Examples 1 and 2.

The numbers in parentheses indicate the supported amount of each component (t/It-carrier).

Comparative Example 1 One carrier, Pb020 f/l- carrier, Cs2010
A t/1-support, supported cordierite foam catalyst was obtained.

Comparative Example 2 A catalyst was prepared in the same manner as in Example I except that cesium was not used, and kl, 0370 t/1-support,
Pb020 t/l-carrier, pto, sor/J-
-Support, Rh 0.09 f/l -Support, 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 70t/13-support, KtO 10f/11-support, Pto, 9ot/l-
A carrier, Rh 0.09 f/lj-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 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 illegally in exactly the same way.

Example 5 Regarding the catalysts found in Examples 1 to 4 and Comparative Examples 1 to 2,
A catalyst evaluation test was conducted using a 4-cylinder diesel engine with an exhaust of 2300 cc.

Engine speed 2500y'pm, torque 4.0kg
・Particle capture was carried out for about 2 hours under the conditions of m, and then the torque was increased every 5 minutes at o, sky・m intervals,
The change in pressure drop in the catalyst layer is continuously recorded, and as the temperature of the exhaust gas increases as the particulates move on the catalyst, the temperature (T
The temperature at which Ti
). Also 2 500 rpm, torque 4. OKG
The change in pressure drop over time when capturing particulates with am
The value of tmllg/H) was calculated.

The conversion rate of SO6 to SO8 was determined at an exhaust gas temperature of 450°C. The conversion rate of SO2 was calculated by analyzing the SO concentration of the inlet gas and outlet gas using a non-dispersive infrared analyzer (NDIR method), and calculating the conversion rate of SO2 using the following calculation formula.

The results are shown in Table 1 below.

Continuing from page 1 ■Int, CI, 4 Identification code Internal office reference number // B
01 D 46102 7636-4D@Inventor Satoshi Ono 53-1 Higashisonoda-cho, Amagasaki City

Claims (5)

[Claims] (1) On a porous inorganic base supported on a refractory three-dimensional structure having a gas filter function, (a)
(b) at least one metal compound selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium and silver; and (b) at least one metal compound selected from the group consisting of sodium, potassium and cesium. An exhaust gas purifying catalyst comprising a metal compound and (c) a compound of at least one metal selected from the group consisting of platinum, rhodium and palladium. (2) The compounds represented by groups (-) and (b) have a molar ratio of (a)/(b) = 0.25 to 9.0, and the compounds represented by groups (b) and (c) The catalyst according to claim (1), wherein the molar ratio of the compound (b)/(c) is in the range of 4 to 80. (3) Per finished catalyst 11, the porous inorganic base is 5 to 250 f as an oxide, the compound shown in group (a) is 2 to 1 o ot as an oxide, and the compound shown in group (b) is as an oxide. 2 to 100f, and further K, the compound represented by group (c) is 0.1 to 4. The catalyst according to claim (1) or (2), which contains a range of Of. (4) The catalyst according to claim (1), (2) or (3), wherein the refractory three-dimensional structure is a ceramic foam, wire mesh, metal foam, or sealed ceramic honeycomb. (5) On an inorganic substrate, (a) a compound containing at least one metal selected from the group consisting of copper, manganese, molybdenum, lead, iron, cobalt, vanadium, and silver;
) A compound containing at least one metal selected from the group consisting of sodium, potassium and cesium, and further (
C) A compound containing at least 1 fffl of a metal selected from the group consisting of platinum, rhodium and palladium is dispersed and supported, and this is heat-treated at a temperature in the range of 700 to 1000°C. −〇Contest: Manufacturing method for exhaust gas purification catalysts.