JPS63182036A - Preparation of catalyst for removing nitrogen oxide in exhaust gas - Google Patents

Abstract

PURPOSE:To enhance not only moldability but also mechanical strength by adding titania and water to zeolite having copper supported thereby to knead both of them with said zeolite and subsequently adding an inorg. fiber to the kneaded mixture. CONSTITUTION:In a method for preparing a catalyst catalytically reducing and removing nitrogen oxide in exhaust gas by ammonia, 10-90wt.% of titania is added to zeolite having copper supported as an active metal component thereby and water is added to said zeolite to be kneaded therewith. After the moisture of this kneaded mixture is adjusted to 23-43wt.%, 5-30% by wt. of a total catalyst amount of an inorg. fiber is added to and mixed with said mixture and the resulting composition is molded, dried and baked. By this method, the catalyst reduced a deterioration due to the catalytic poison substance such as arsenic or sulphurous acid gas contained in exhaust gas is obtained and the zeolite-titanium type catalyst sufficiently developing the effect of the inorg. fiber being a binder and having good moldability and excellent mechanical strength can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a catalyst for removing nitrogen oxides in exhaust gas by catalytic reduction with ammonia, and particularly relates to a method for producing a catalyst for removing nitrogen oxides in exhaust gas by catalytic reduction, and in particular, This invention relates to a method for producing a catalyst that is resistant to deterioration and has excellent formability and mechanical strength.

(Prior Art) Nitrogen oxides contained in various combustion furnace exhaust gases are not only harmful to the human body, but also cause air pollution such as photochemical smog. In order to remove (tax control) these nitrogen oxides, a catalytic reduction method (selective reduction) using ammonia is currently widely used. The catalyst currently in practical use for this purpose is JP-A-50-5
1966 and JP-A-52-122293, titania (T t O□) is the main component, and vanadium (V), molybdenum (Mo), and tungsten (
This is a catalyst to which W) and the like are added. These catalysts had high activity, little deterioration due to sulfur oxides in the exhaust gas, and were excellent in terms of service life.
It has been found that the presence of volatile substances such as S), selenium (Se), and tellurium (Te) causes poisoning and causes deterioration of activity.

The present inventors have demonstrated that catalysts mainly composed of zeolite have excellent toxicity resistance against these volatile catalyst poisons, and that zeolite catalysts supporting copper in particular have high activity and maintain high activity for a long period of time. Found this and filed a patent application in 1986-1574.
The application was filed as No. 48.

(Problems to be Solved by the Invention) However, the above-mentioned zeolite catalysts are insufficient in terms of moldability and mechanical strength, and it has been desired to obtain catalyst molded bodies with sufficient strength.

The present invention has been made to solve the above problems, and includes a method for producing a catalyst for removing nitrogen oxides in exhaust gas by catalytic reduction using ammonia. 10 to 90% by weight of titania on zeolite supporting copper
After adding water to this and kneading to make the moisture content of this mixed wire 23 to 43% by weight, inorganic fibers are added and mixed in an amount of 5 to 30% by weight based on the total amount of catalyst, and after molding, drying and baking. The present invention provides a method for producing a catalyst for removing nitrogen oxides from exhaust gas, which is characterized by the following.

(Function) According to the present invention, by mixing inorganic fibers into the catalyst composition, individual catalyst particles are crosslinked with each other, and mechanical strength can be increased. Here, in order to fully exhibit the effects of the inorganic fibers, it is important to cut the fibers appropriately, and the degree of cutting is largely controlled by the softness of the catalyst mixture when the fibers are added and mixed. If the kneaded material is hard, the fibers will be cut excessively, making it impossible to expect the desired effect. On the other hand, if it is too soft,
The fibers are hardly cut, which reduces the fluidity of the kneaded material, impairing the moldability. If fibers are added and mixed into the mixed material having the softness specified by the water content limited in the present invention, it is possible not only to obtain practically sufficient mechanical strength without impairing the moldability, but also to It has the effect of improving the particle size distribution of objects and further improving moldability.

(Example) In the method for producing the catalyst of the present invention, as the zeolite, mordenite, ferrierite, pentasil type zeolite ZSM-5 manufactured by Mobil Oil Co., etc. can be used, but the Si○2/Al2O3 ratio is 10 or more. , the average pore diameter is preferably 10 Å or less. As a method for supporting the active metal component, methods such as substitution using various metal salt aqueous solutions, kneading, and impregnation may be employed. The supported amount is 0. Although a range of O1 to 20% by weight can be adopted, it is preferable to keep it below the cation exchange capacity of the zeolite. Further, as the titania, any of metatitanic acid, chlorine-processed titania, etc. may be used, but fine particles having a specific surface area of 20 rrf/g or less and an average particle size of 2 μm or less are preferable.

The mixing ratio of zeolite and titania may be 1/9 to 9/1 in terms of zeolite/titania weight ratio. If this ratio is too small, the catalytic performance of the zeolite will not be utilized, and if the ratio is too large, the strength-imparting effect and particle size improving effect of titania will not be significant. Therefore, the zeolite/titania weight ratio should be 3/7 to 8/ 2 is more preferred.

The amount of inorganic fiber added is suitably 5 to 30% by weight based on the total amount of the catalyst, since too much will reduce the catalyst activity, life and moldability, and too little will not improve the strength.

The catalyst paste obtained by this production method is cylindrical, cylindrical,
A catalyst molded body can be obtained by extrusion molding into a honeycomb shape, or by coating and molding on metal, ceramic woven fabric, or the like.

Zeolite has significant glatancy and the mechanical strength of the particles is extremely low. Giratancy occurs when the particle sizes are relatively uniform. Adding strong, fine particles like titania can widen the particle size distribution,
It is expected that titania can eliminate giratancy and improve moldability, and at the same time, titania acts as a matrix and improves mechanical strength. However, since the binding force between zeolite and titania, different types of particles, or particles of the same type is not strong, a binder or the like is required. Inorganic fibers are used for this purpose, but depending on the method of introduction during the catalyst production stage, this effect may not be fully exerted or may even have an adverse effect.

In the present invention, after adjusting the moisture content of the kneaded product of zeolite and titania to 23 to 43% by weight, inorganic fibers are mixed. If the water content is outside this range, the kneaded material will not have appropriate softness as described above, the degree of cutting of the ta-free fibers will be insufficient, and a catalyst with excellent moldability and mechanical strength will not be obtained. .

When inorganic fibers are added during wet kneading, if the fibers are cut excessively, the crosslinking function between particles by the fibers will be reduced, and no strength improvement effect can be expected. On the other hand, if the fibers are not cut too much, the plasticity of the catalyst kneaded product will be reduced and the moldability will be sacrificed. In particular, when the catalyst mixture is pressure-coated and molded onto a wire-mesh-like fully curved lath plate using a roller, the paste does not penetrate well into the mesh of the lath plate, making it impossible to form a plate-shaped catalyst.

The present inventors have discovered that the degree of cutting of inorganic fibers is largely controlled by the softness of the catalyst kneaded material when the fibers are added and mixed.

According to the method for producing a catalyst according to the present invention, after zeolite and titania are thoroughly mixed and kneaded in advance, inorganic fibers are added and mixed into the kneaded material of appropriate softness, so that the fibers are appropriately cut and molded. This makes it possible to obtain a catalyst with excellent properties and mechanical strength.

If zeolite and inorganic fibers are mixed and kneaded and then titania is added and mixed in, or if zeolite, titania, and inorganic fibers are mixed and kneaded simultaneously, it is difficult to control the degree of cutting of the fibers.

Hereinafter, the present invention will be explained in more detail using Examples.

Example I Aqueous solution of copper acetate (Cu(CH3Coo)z) was added to 1.2 pupil of hydrogen-type synthetic mordenite powder with SiOz/Aβ20 ratio of 23 and average pore diameter of 7.
(Cu concentration 2.1 g/j) was added and stirred, copper was supported on mordenite by a substitution method, and then dried at 180°C and then fired at 500°C for 2 hours. 500 g of the obtained powder of copper-supported mordenite was wet-kneaded for 30 minutes by adding water using a Neegu.

Next was CR-50, which is titania for pigments manufactured by Ishiya Sangyo.
A specific surface area of 10.7 rrr/g) was added and kneaded for 1 hour. Add water appropriately to reduce the moisture content of the kneaded product to 33.
．． After making it 4%, add 150g of Kao wool as inorganic fiber.
Then 10g of Metrose was added and kneaded for 40 minutes.
After addition and kneading for 30 minutes, a catalyst paste was obtained. This paste was formed into a plate by applying it with a roller onto a wire-mesh lath plate made of stainless steel 5US304 that had been thermally sprayed with alumina in an oxygen atmosphere, air-dried at room temperature for about 8 hours, and then heated at 500℃ for 2 hours. A plate-shaped catalyst was obtained by firing for a period of time.

Example 2.3 In Example 1, a plate-shaped catalyst was obtained under the same conditions as in Example 1, except that the moisture content of the catalyst mixed material when inorganic fibers were added was 38.6% and 25.1%, respectively.

Comparative Example 1.2 In Example 1, plate-shaped catalysts were prepared with the moisture content of the catalyst mixed material at the time of addition of inorganic fibers being 22.5% and 40.8%, respectively, and the other conditions being the same.

Comparative Example 3.4 In Example 1, the catalyst was prepared by setting the amount of inorganic fibers added to 1% and 33% by weight of the total amount of catalyst, and keeping the other conditions the same.

Experimental Example 1 The catalysts of Examples 1 to 3 and Comparative Examples 1 to 4 were tested on a grid (Noso Kogyo WMGH-70) 8k under constant temperature and humidity conditions.
1100X1 with g tilted at an angle of 45° from a height of 500cm
The sample was dropped onto a No. 00 catalyst (plate-shaped) test piece, and the amount of wear was measured.

Table 1 shows the wear amount of each of the above catalysts. When the water content of the catalyst paste is around 23% by weight when inorganic fibers are added, the paste becomes hard rapidly, so the fibers become severed, the strength improvement effect decreases, and the amount of wear increases rapidly. When the paste water content is 23 to 40, the paste maintains appropriate softness, so the amount of wear can be suppressed to a small level. Paste moisture content is 4
If it exceeds 0%, the paste becomes extremely softened and almost no inorganic fibers can be cut, and long fibers remain, making it impossible to convert them into plate-like catalysts.

Further, in Comparative Example 3, the amount of inorganic fiber added was too small, resulting in little strength improvement effect and large amount of wear. In Comparative Example 4, the amount of inorganic fiber added was too large, making it difficult to form a plate-shaped catalyst.

Table 1 (Effects of the Invention) According to the present invention, it is possible to obtain a catalyst that is less susceptible to catalyst poisonous substances such as arsenic and sulfur dioxide contained in exhaust gas, and to improve the effect of inorganic fibers as a binder during catalyst production. It is possible to obtain a zeolite-titanium-based catalyst that can exhibit sufficient performance, has good moldability, and has excellent mechanical strength.

Claims (1)

[Claims] In a method for producing a catalyst that removes nitrogen oxides in exhaust gas by catalytic reduction with ammonia, 10 to 90% by weight of titania is added to zeolite supporting copper as an active metal component, water is added to this, and the mixture is kneaded. After adjusting the water content of the kneaded product to 23 to 43% by weight, inorganic fibers were added to 5% of the total amount of catalyst.
A method for producing a catalyst for removing nitrogen oxides from exhaust gas, which comprises adding and mixing up to 30% by weight, molding, drying, and firing.