JPS596180B2 - Plate-shaped denitrification catalyst for high temperatures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst used in a reaction for selectively catalytically reducing nitrogen oxides (hereinafter referred to as NOx) in exhaust gas with NH3.

Since NOx in exhaust gas is considered to be a causative agent of photochemical smog, an effective means for treating it is desired.

Among the exhaust gas denitrification methods that have been proposed in the past, N
The NOx catalytic reduction method using H3 as a reducing agent selectively converts NH3 into N even if the exhaust gas contains more than 1 volume of oxygen.
Since it reacts with Ox, it is considered to be an advantageous method in that it requires less reducing agent.

Generally, in exhaust gas denitrification, a method with low pressure loss is desired without exception.

A honeycomb-shaped denitration catalyst is said to be suitable for meeting this demand.In particular, since the exhaust gas from power plants and sintering furnaces has a large volume, it is necessary to have a large size and strong enough to prevent damage during filling. A honeycomb-shaped catalyst is required.

As a honeycomb structure catalyst, one in which an active ingredient is attached to a honeycomb structure made of ceramics or metal has been proposed.

However, when using metal as a material for a honeycomb structure, it is necessary to make the surface of the metal porous through a complicated process in order to increase the adhesion of the catalyst component.
Furthermore, when ceramics are used, it is necessary to thicken the walls and harden them at high temperatures in order to increase the strength of the structure.

Under these circumstances, the first object of the present invention is to provide a denitrification catalyst that can be made large-sized, can be easily formed into a honeycomb structure, and has excellent strength. .

Furthermore, when waste heat of exhaust gas is used, exhaust gas denitration needs to be performed at a high temperature.

Therefore, the second object of the present invention is to achieve high humidity, for example, 500°C.
The object of the present invention is to provide a denitrification catalyst that exhibits excellent activity in the above aspects as well.

This invention was made to achieve these objects, and its gist is that powdered titania is held in a wire mesh made of aluminum wire or aluminum-coated metal wire with a binder. +ThTh
Wet plate-shaped denitrification catalyst.

Aluminum does not exhibit NH3 oxidative decomposition activity at temperatures above 500°C.

Steel has the above-mentioned NH3 oxidative decomposition activity, tin, zinc, etc. have poor heat resistance, and molybdenum, tungsten, etc. are expensive and their oxides have sublimation properties, so none of them are preferable.

Wires made of these metals coated with aluminum are preferred.

The wire diameter of the wire mesh may be large enough that the structure formed into a predetermined shape will not be deformed during catalyst production or product use.

The size of the mesh is not limited, although it is better to make it smaller.

Usually about 10 to 100 meshes is sufficient.

The shape of the wire mesh is, for example, one made of a single flat wire mesh, one made by stacking multiple layers of flat wire mesh, and one made by bending or bending a flat wire mesh into a corrugated, zigzag, or pleated shape. , and even those formed into a honeycomb structure by combining these curved or bent wire meshes with flat wire meshes.

It is also possible to manufacture catalysts from curved or bent wire meshes and flat wire meshes, respectively, and to combine these catalysts to form a honeycomb-structured catalyst.

The shape of the segments of the honeycomb structure may also be arbitrarily selected, such as a triangle, square, or hexagon, depending on the size of dust in the exhaust gas.

Titania is a substance that has high denitrification catalytic activity even at temperatures of 500°C or higher.

As a binder, A1(OH)3. S t (O
H) Preferably used are alumina sol, silica sol, titania sol, phosphoric acid, boric acid, etc., which can undergo dehydration condensation upon drying or firing to form a strong three-dimensional network structure.

None of these substances exhibits oxidative decomposition activity of NH3 at temperatures above 500°C and does not lose its ability as a binder.

The thinner the catalyst, the better.

Usually it is 0.5 to 20 fights.

The catalyst according to the present invention is produced, for example, by the following method.

a) A method in which a slurry consisting of powdered titania and a binder is applied to both sides of a wire mesh, dried, and fired if necessary.

b) A method in which a slurry consisting of a powdery porous carrier carrying an active ingredient, that is, titania, and a binder is applied to both sides of a wire mesh, dried, and fired if necessary.

In methods a) and b) above, in order to speed up drying after applying the slurry and increase the porosity of the formed wallboard, substances that volatilize, decompose or burn out during drying or baking, such as organic solvents, polymer emulsions, It is advisable to add carbon fiber or the like to the binder.

Further, the drying and firing conditions are all according to conventional methods.

Preferably, drying is carried out at 70-120°C for 0.5-2 hours, and calcination is carried out at 200-500°C for 1-5 hours.

Since the plate-shaped denitrification catalyst according to the present invention is constructed as described above, the area of the catalyst can be increased as much as desired, and catalysts having various desired shapes such as a honeycomb structure can be obtained.

Further, the powdered titania is firmly held on the wire mesh by a strong three-dimensional network structure produced by dehydration condensation polymerization of the binder.

Therefore, this catalyst is satisfactory in terms of strength and does not require sintering for strength reinforcement.

Therefore, high porosity is maintained and high activity is exhibited.

Furthermore, the thickness of the catalyst can be changed as appropriate by adjusting the amount of slurry applied, making it possible to form a thin catalyst with high effectiveness, which is extremely advantageous in terms of cost efficiency when using expensive catalyst components. becomes.

In addition, since the wire mesh is made of aluminum wire or metal wire coated with aluminum, it has the characteristics of TiO2, which shows no oxidative decomposition activity of NH3 at high humidity of 500°C or higher, and has high denitrification activity at high humidity. There's nothing to lose.

Production of Example Catalyst Commercially available titania powder (fineness 44μ or less, surface area 150
m/g) and 100 parts of commercially available silica sol (containing about 20 tm of SiO2) were mixed thoroughly to form a slurry.

This slurry is shown in the drawing as aluminum wire wire mesh 1 (size: 301 m x 50 mm, mesh: 20 mesh, wire diameter:
0.5 mm) and dried at 100° C. for 1 hour.

In this way, a plate-shaped titania catalyst 2 of 0.8 mm was obtained.

Activity Measurement A flow-through type reaction tube having a rectangular catalyst-filled part with a height of 50 mm and openings at both ends of 5 mm x 35 mm was used, and the above-mentioned plate-shaped titania catalyst was filled in the filled part.

Then, the reaction humidity was adjusted to 450° C., and the prepared exhaust gas for testing shown in Table 1 was passed through the reaction tube at a flow rate of 11/min (standard state).

The denitrification rate was determined from the population of the reaction tube and the amount of change in NO concentration at the outlet.

By the same operation, the denitrification rates at reaction humidity of 500°C, 550°C, and 600°C were determined.

The results are shown in Table 2. Comparative Example Except for using a wire mesh made of SUS 304 steel wire,
The same operation as in the example was performed to obtain a plate-shaped chikunya catalyst.

The activity of this catalyst was also measured by the same procedure as in the example.

The results are shown in Table 2. As can be seen from the table, the catalysts of the examples exhibit higher denitrification activity at temperatures of 500° C. or higher than those of the comparative examples.

[Brief explanation of drawings]

The drawing is a partially perspective view of a plate-shaped catalyst showing an embodiment of the present invention.

Claims (1)

[Claims] 1. A high-temperature deck-shaped denitrification catalyst in which powdered titania is held in a binder by a wire mesh made of aluminum wire or metal wire coated with aluminum.