JPH05345133A - Production of exhaust gas purifying material - Google Patents

Abstract

PURPOSE:To produce an exhaust gas purifying material capable of efficiently burning and removing the particulate contained in the exhaust gas largely changed in its oxygen concn. discharged from a diesel engine and capable of keeping good purifying characteristics even with respect to SO2-containing exhaust gas and capable of effectively removing nitrogen oxide at the same time. CONSTITUTION:In a method for producing an exhaust gas purifying material by forming a ceramic layer having a catalyst having active seeds consisting of one or more kind of an alkali metal element, a Cu element, a V element and one or more kind of an rare earth element supported thereon on a heat- resistant porous filter, respective compounds of the Cu element and the V element are infiltrated and baked in separate processes when the respective active seeds of the catalyst are supported on the ceramic powder forming the ceramic layer or the ceramic layer formed on the filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing an exhaust gas purifying material, and more specifically, it is possible to simultaneously remove nitrogen oxides (hereinafter referred to as NOx) and particulate matter in exhaust gas from diesel engines and the like. The present invention relates to a method for preparing an exhaust gas purification material that can maintain good exhaust gas purification characteristics even if the exhaust gas contains a relatively large amount of SO ₂ .

[0002]

2. Description of the Related Art In recent years,
Particulate matter (mainly composed of solid carbon fine particles, called particulates), NOx, and the like in exhaust gas discharged from diesel engines and the like have become problems as environmentally harmful substances. In particular, since particulates have an average particle size of 0.1 to 1 μm and are easily suspended in the air, they are easily taken into the human body by breathing, and recent clinical test results also indicate that they also contain carcinogens. Has been confirmed.

As a method of removing particulates, the following two methods are roughly studied. One of them is a method of trapping particulates by filtering exhaust gas using a heat resistant filter, and burning the trapped particulates with a burner, an electric heater, etc. to regenerate the filter when the pressure loss due to this is increased. Is. The heat-resistant filters used include honeycomb-type ceramic filters, foam-type ceramic filters having a three-dimensional mesh structure, steel wool, wire mesh and the like.

The other one is a method of filtering particulates by the above-mentioned filter and causing the trapped particulates to self-combust by the action of the oxidation catalyst carried by the filter.

In the former case, the higher the effect of removing particulates, the faster the pressure loss rises, and the more frequently the filter is regenerated. Therefore, high reliability is required for regeneration, and it is considered to be economically disadvantageous.

On the other hand, the latter method is considered to be a far superior method if there is a catalyst that can retain the catalytic activity under the exhaust gas emission conditions (gas composition and temperature) of the diesel engine. However, since the diesel engine uses light oil as a fuel, it contains a large amount of SO ₂ in the exhaust gas, which causes problems such as poisoning of the catalyst and secondary pollution.

[0007] For example, the oxidation catalysts for particulates in the exhaust gas of diesel engines, etc., which have been proposed so far, are roughly classified into noble metal base metals and base metal base catalysts.
Noble metal-based catalysts have high durability and high oxidation characteristics such as CO and unburned hydrocarbons (hereinafter referred to as HC), but on the other hand, they easily convert SO ₂ present in exhaust gas into SO ₃ , It is highly likely to cause pollution. There is also a drawback that the combustion characteristics of the soot in the particulates are deteriorated. On the other hand, a base metal catalyst is effective as a particulate purification catalyst, but has a problem in durability. That is, SO ₂ in the exhaust gas easily deteriorates the characteristics of the catalyst supported on the filter.

As described above, an effective method for trapping particulates in exhaust gas with a filter and igniting and burning this to regenerate an exhaust gas purification filter has not yet been established.

Most of the exhaust gas purifying catalysts and purifying agents proposed so far are focused on reducing the ignition temperature of particulates, and the oxygen concentration in the exhaust gas is generally high or the oxygen concentration is high. The removal of NOx contained in the exhaust gas of a diesel engine or the like, which changes greatly, remains unsolved.

Therefore, an object of the present invention is to efficiently burn and remove particulates contained in exhaust gas having a large change in oxygen concentration such as that emitted from a diesel engine, and also to be good for exhaust gas containing SO _2. An object of the present invention is to provide a method for preparing an exhaust gas purification material that can maintain purification characteristics and at the same time effectively remove nitrogen oxides.

[0011]

In view of the above-mentioned problems, the present inventor carried a catalyst composed of an alkali metal, a copper element, a vanadium element, and a rare earth element on a heat-resistant porous filter. As a result of earnest research on a purification material having a ceramic layer, in the preparation of this purification material, if the copper element and the vanadium element are supported in separate steps,
The present invention has been completed by discovering that an exhaust gas purification material having good purification characteristics for a long time can be obtained.

That is, on the heat resistant porous filter,
(A) one or more alkali metal elements, and (b)
One or two of Cu element and V element, and (c) rare earth element
The method of the present invention for preparing an exhaust gas purifying material in which a ceramic layer carrying a catalyst having an active species consisting of one or more kinds is formed is a ceramic powder forming the ceramic layer, or a ceramic formed on the filter. When each active species of the catalyst is supported on the layer, the respective compounds of Cu element and V element are impregnated and fired in separate steps.

In a particularly preferred embodiment, in the above-mentioned preparation, the ceramic layer is 1 to 15 parts by weight and the catalytically active species is 1 to 20 parts by weight per 100 parts by weight of the filter.

The present invention will be described in detail below. Since the filter used in the present invention treats exhaust gas at high temperature, its forming material needs to be porous and have high heat resistance, particularly high thermal shock resistance. Moreover, it is necessary that the pressure loss be within an allowable range while maintaining the required particulate collection performance. Materials for forming such filters include ceramics such as alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, cordierite. Is mentioned.

The porosity of the filter may be 40-80%. The shape and size of the filter can be variously changed according to the purpose.

In the present invention, a ceramic layer carrying a catalyst, which will be described later, is provided on the filter made of the above-mentioned material. As the ceramic forming the ceramic layer, porous ceramics having a large surface area such as titania, alumina, silica, titania-alumina, and titania-silica can be used. Of these, titania is particularly preferable.

As the active species of the catalyst supported on the above filter through the ceramic layer having a large surface area as described above, (a) one or more alkali metal elements and (b) Cu and V are used. And (c) one or more rare earth elements.

Examples of the alkali metal element (a) include lithium, sodium, potassium, and cesium. Among them, cesium and potassium are particularly preferable. As the rare earth element (c), cerium, lanthanum, neodymium, praseodymium and the like are preferable, and among them, cerium and lanthanum are particularly preferable.

In the present specification, the components (a), (b) and (c) of the respective catalytically active species are used for simplification of description.
Is indicated by a metal element, but these components (catalyst active species) exist in the state of oxides under normal use temperature conditions of the purification material.

By using the catalyst composed of the above components, the particulates in the exhaust gas can be ignited and burned at a relatively low temperature, and NOx can be effectively removed. That is, since the particulates in the exhaust gas coexist with oxygen on the surface of the catalyst in the filter, the ignition temperature of the particulates is lowered, and the particulates are burned (oxidized) near 400 ° C.

At the same time, the particulates act as a reducing agent to reduce NOx, and the exhaust gas is effectively purified. Thus, the reason why NOx is efficiently reduced at a relatively low temperature is due to the synergistic effect of the simultaneous presence of the particulates in the exhaust gas and the respective catalytically active species (a), (b) and (c). It seems to be.

Simultaneous removal of NOx and particulates is a catalyst composed of an alkali metal element, a transition metal and a rare earth element, particularly when Cu is used as the transition metal, its purifying ability is excellent at the initial stage of use. However, if the combination of the above three elements (alkali metal element, Cu as transition metal element, rare earth element) is combined, the purification characteristics of the catalyst gradually increase due to the presence of sulfur and its oxides contained in the exhaust gas. Will decrease. In particular, since exhaust gas has a high temperature, sulfur oxides such as SO ₂ cause a rapid deterioration of the purification characteristics of the catalyst. Therefore, in the present invention, Cu and V are used as the (b) transition metal element. V
Addition (ie by the combination of alkali metals, Cu and V, rare earth elements) is not expected to significantly improve the initial characteristics of catalytically active species, but stable simultaneous NOx and particulate removal characteristics over a long period of time. Is obtained.

The amount of each catalytically active species (a), (b) and (c) compounded is (a):
(B): (c) is 0.5 to 1: 1.5 to 10: 0.1
It should be ~ 1. More preferably, this ratio is 0.5-
1: 1.5-8: 0.2-1.

Further, the ratio of Cu to V in (b) (Cu /
V) is preferably about 1/15 to 5/1 by weight. If this ratio is less than 1/15, the exhaust gas purification characteristics are significantly reduced. On the other hand, when it exceeds 5/1, the amount of V becomes small, and the decrease of the catalytic ability due to SO ₂ becomes large.

The amount of the catalyst supported is preferably 1 to 20 parts by weight (metal content conversion) per 100 parts by weight of the filter. If the catalyst amount is less than 1 part by weight, it becomes difficult to remove particulates and NOx simultaneously. On the other hand, even if the catalyst is loaded in an amount of more than 20 parts by weight, the exhaust gas purification performance is not significantly improved. A more preferred amount of catalyst is 5 to 15 parts by weight.

The amount of the ceramic layer serving as a carrier for catalytically active species is 1 to 15 parts by weight per 100 parts by weight of the filter. When the amount of the ceramic layer is less than the above lower limit,
It is not preferable because a sufficient amount of catalyst cannot be supported.
On the other hand, when the amount of the ceramic layer exceeds the above upper limit value, the pressure loss in the purification material becomes too large. The preferred amount of ceramic layer is 2 to 10 parts by weight.

Each of the above-mentioned catalytically active species is carried on the filter through the ceramic layer by the washcoat method or the like. In the preparation of the exhaust gas purifying material by the washcoat method, (1) the salt of the catalytically active species is used as the starting material. As described above, the above-mentioned ceramic powder such as titania is impregnated with the active species in advance, and then the filter is immersed in a slurry of the ceramic powder carrying the active species and then dried and fired, or (2) the carrier This is performed by coating a filter with a slurry of ceramic powder forming a layer to form a ceramic layer for supporting a catalyst, impregnating this layer with a solution of a salt of a catalytically active species, drying and firing. You can However, the Cu element and the V element are supported in separate steps, as will be described later. In the above two methods, the firing temperature is preferably about 600 to 800 ° C., and particularly about 700 ° C. The firing time in each step is about 120 to 300 minutes.

As the metal salt or compound of the catalytically active species, any kind such as carbonate, nitrate, acetate and hydroxide can be used as long as it is soluble in water. For loading V, a solution of NH ₄ VO ₃ and oxalic acid can be used.

In the present invention, in any of the above two methods, Cu element and V element are supported on the ceramics (ceramic powder or ceramic layer) in a separate step. That is, a ceramic is impregnated with a solution of a compound of one of Cu element and V element (for example, a water-soluble salt), dried and fired, and then impregnated with a solution of another compound (for example, a water-soluble salt). Then, it is dried and baked again.
In this case, either Cu element or V element may be supported first. Further, the loading of the component (a) (alkali metal element) and the component (c) (rare earth element) in the catalyst is carried out simultaneously in any of the step of loading the Cu element and the step of loading the V element. Good.

[0030]

EXAMPLES The present invention will be explained in more detail by the following specific examples. Example 1 Cordierite ceramic foam (apparent volume 2
0 ml, density 0.65 g / ml) and Ti sol 10% by weight
After coating (converted to TiO ₂ ), firing was performed to form a ceramic layer made of TiO ₂ . This ceramic foam was made to have a predetermined concentration of CuCl ₂ , La (NO ₃ ) ₃ , CsN.
Immerse in order in the O ₃ aqueous solution, dry and heat to 700 ° C.,
Firing was performed by holding for 3 hours.

Next, this ceramic foam was immersed in a mixed aqueous solution of NH ₄ VO ₃ and oxalic acid of a predetermined concentration, dried, heated to 700 ° C., and held for 3 hours for firing.

In the exhaust gas purifying material comprising the filter thus obtained, the total amount of Cu, La, Cs and V (metal-equivalent amount) was 10% by weight with respect to the filter. Also, the molar ratio Cs: C of each component in the catalyst
u: V: La was 1: 0.5: 5: 1.

This exhaust gas purifying material trapped only 100 mg of particulates in the diesel exhaust gas and set it in a flow reaction system.

Next, 800 ppm of NO, 10% of H ₂ O, 10% of O ₂ and SO ₂ were added to the exhaust gas purifying material.
The temperature at which the particulate matter trapped in the exhaust gas purifying material ignites was obtained by passing the simulated exhaust gas consisting of 100 ppm and the balance nitrogen while gradually raising the temperature. The ignition temperature was determined by changing the concentration of carbon dioxide in the exhaust gas downstream of the exhaust gas purifying material (check of carbon dioxide production).
The above evaluation test (test for determining the ignition temperature of particulates) was repeated a plurality of times for the purpose of examining the durability of the purification material. The results are shown in Figure 1.

Example 2 The same ceramic foam as used in Example 1 was used.
After coating 10% by weight of TiO _{2 in the same} manner as in Example 1, this was immersed in a mixed aqueous solution of a predetermined concentration of NH ₄ VO ₃ and oxalic acid, dried and heated to 700 ° C. and kept for 3 hours. Firing was performed.

Next, this ceramic foam was successively dipped in an aqueous solution of CuCl ₂ , La (NO ₃ ) ₃ and CsNO ₃ having a predetermined concentration, dried, heated to 700 ° C. and held for 3 hours for firing.

In the exhaust gas purifying material comprising the filter thus obtained, the total amount of Cu, La, Cs and V (metal-equivalent amount) was 10% by weight with respect to the filter. Further, the molar ratio of each component in the catalyst Cs: Cu: V:
La was 1: 0.5: 5: 1.

With respect to this exhaust gas purifying material, the ignition temperature of particulates was determined by the same method as in Example 1.
This evaluation test was repeated in the same manner as in Example 1.
The results are shown in Figure 1.

Comparative Examples 1 and 2 Using the same filters as in Example 1, 10% by weight of TiO ₂ was coated in the same manner as in Example 1, and then L having a predetermined concentration
a (NO ₃ ) ₃ aqueous solution and CsNO ₃ aqueous solution
La and Cs were supported on the O ₂ layer.

Next, Cu and V were simultaneously loaded using a mixed aqueous solution of CuCl ₂ aqueous solution, NH ₄ VO ₃ and oxalic acid (Comparative Example 1).

Contrary to Comparative Example 1, 10% of TiO ₂ was added.
Weight% coated filters, first of all, CuCl ₂
Cu and V are simultaneously loaded using an aqueous solution and a mixed aqueous solution of NH ₄ VO ₃ and oxalic acid, and then La (NO ₃ ) ₃
A purification material was obtained by supporting La and Cs using an aqueous solution and an aqueous CsNO ₃ solution (Comparative Example 2).

With respect to the obtained purifying material, the ignition temperature of the trapped particulates was determined by the same method as in Example 1. The results are shown in Figure 1.

As is apparent from FIG. 1, Examples 1 and 2
In the exhaust gas purifying material, the combustion of particulates in the presence of SO ₂ occurs at a relatively low temperature. On the other hand, in the purification material of the comparative example in which Cu and V are simultaneously loaded, the ignition temperature of particulates increases as the number of evaluations increases.

[0044]

As described above, when the exhaust gas purifying material according to the method of the present invention is used, even if the exhaust gas contains a relatively large amount of SO ₂ , the purifying characteristics thereof are not deteriorated and the performance at a temperature as low as about 400 ° C. is maintained. The curate can be ignited and burned.

Further, the purifying material according to the present invention is capable of simultaneously performing excellent NOx and particulate removal simultaneously.

The purifying material according to the present invention is suitable for purifying exhaust gas from diesel engines and the like.

[Brief description of drawings]

FIG. 1 is an example 1, an example 2, a comparative example 1, and a comparative example 2.
3 is a graph showing the ignition temperature of particulates in FIG.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kozo Ogasawara 4-14-1, Suehiro, Kumagaya-shi, Saitama Stock company Riken Kumagaya Works (72) Inventor Kiyohide Yoshida 4--14, Suehiro, Kumagaya, Saitama No. 1 Stock company Riken Kumagaya Works (72) Inventor Tomoaki Honma 1-26 Takitanihonmachi, Niitsu City, Niigata JGC Chemical Co., Ltd. Niitsu Works

Claims (3)

[Claims] 1. A heat-resistant porous filter comprising (a) one or more alkali metal elements, (b) Cu and V elements, and (c) one or more rare earth elements. A method of preparing an exhaust gas purifying material, wherein a ceramic layer supporting a catalyst having an active species is formed, comprising: a ceramic powder forming the ceramic layer, or a ceramic layer formed on the filter of the catalyst. A method for preparing an exhaust gas purifying material, which comprises impregnating and firing respective compounds of Cu element and V element in separate steps when supporting each active species. 2. The preparation method according to claim 1, wherein one ceramic layer is added per 100 parts by weight of the filter.
.About.15 parts by weight and 1 to 20 parts by weight of the catalytically active species.
An exhaust gas purification material, characterized in that the amount is parts by weight. 3. The exhaust gas purifying material according to claim 1 or 2, wherein the ceramic layer supporting the catalyst is TiO ₂ .