JPS5945418B2 - Catalyst for nitrogen oxide reduction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for reducing nitrogen oxides, particularly nitrogen oxides (hereinafter referred to as NOx) in exhaust gas from internal combustion engines, etc.
The object of the present invention is to provide a catalyst having an excellent reducing action against oxidants, and a simple and durable manufacturing method for producing the catalyst.

Conventionally, this type of catalyst for reducing nitrogen oxides, for example, a catalyst for reducing NOx in exhaust gas from internal combustion engines, not only requires excellent catalytic performance, but also has different performance as a catalyst depending on the manufacturing method even if the composition is the same. Since there is a difference in
A manufacturing method that is simple and provides stable performance is required, and in view of its intended use, a manufacturing method that is suitable for mass production is also required.

The present invention has been made with attention to these points, and the substrate constituting the catalyst is formed of a heat-resistant material of 1000°C or higher, and the surface of the substrate is coated with the periodic table 1 Va, Va, VI.
The content is a catalyst for reducing nitrogen oxides, which is provided with a coating layer of one or more types of metal carbides of group a.

In this case, IVa group metals mean Ti, Zr, Hf, and Va group metals mean V, Nb, Ta.

Further, Vla group metal means Cr, Mo, and W.

The material of the substrate in the present invention may be metal, folded metal, ceramic, or any other material as long as it has heat resistance of 1000° C. or higher and can be processed into the shape described below.

However, if the coating method is electrodeposition, electrical conductivity is further required.

In particular, if the substrate is one or more metals or alloys (including solid solutions) of copper, nickel, iron, and cobalt, the substrate material solid-diffuses and becomes a binding material for the carbide when coating the carbide. This is particularly advantageous.

The shape of the substrate in the present invention needs to have a large contact area with gas, and there are several types of specific shapes.

It may be granular, in which case the particle size is 10. It is preferably less than mm.

It may also be an air-permeable sintered body obtained by adding a sublimable substance such as naphthalene or zinc to a powdered raw material in the form of a powder, plate, rod, wire, or other arbitrary structure and heat-treating this.

It can be in the shape of a block, plate, rod, wire, pipe, filament, net, or honeycomb (and it can also be machined such as drilling, grooving, etc., or it can be bent, stretched, crushed, etc.) may be modified (or may be combined by overlapping, gluing, welding, etc.).

It is preferable to have a porosity of 40 to 90% based on the total capacity.

It may be in the form of whiskers, fibers, or cloth.

Although other coating methods may be used in the present invention, vapor deposition and electrodeposition are particularly preferred.

If one or more of copper, nickel, iron, or cobalt is included in electrodeposition, carbide is electrodeposited with the metal or alloy (including solid solution) using a conductive substrate. It will be done.

This is particularly advantageous since the carbide is fixed to the substrate by a film of metal or the like.

In addition, the method of coating metals in the form of metals, alloys, solid solutions, or inorganic compounds or organic compounds that become metals, alloys, or solid solutions by thermal decomposition, and then heat-treating them together with carbide coating is a method that uniformly coats metals with powders, suspensions, solutions, etc. This is particularly advantageous because it allows the coating to be carried out by selecting a shape that is easy to coat.

The catalyst according to the present invention has high mechanical strength, excellent wear resistance, and high contact rate with exhaust gas.

According to the manufacturing method of the present invention, catalysts with complex shapes can also be manufactured, less manufacturing equipment is required, and the catalyst can be manufactured simply and inexpensively in a short time.

The catalyst according to the present invention may be packed in a stainless steel or other heat-resistant basket and integrated by heat treatment.

At the time of filling, a heat-resistant banking material such as glass fiber and alumina fiber may also be filled.

Further, the catalyst according to the present invention may be filled into a mold made of alumina, carbon, etc. of a predetermined shape and integrated by heat treatment with a load of 1000 kg/cr4 or less applied, or without applying any load.

These are suitable for coating granular substrates by vapor deposition.

It is even more effective to add 0.0005% by weight or more of one or both of ruthenium and rhodium to the catalyst according to the present invention.

Further, the catalyst according to the present invention may be heat-treated at a temperature of 1000°C or higher and lower than the substrate's heat resistance temperature, preferably 1300 to 1400°C.

Next, the content of the present invention will be explained more specifically and in detail by showing experimental examples, but the present invention is not limited to these experimental examples.

Experimental Example 1 A 30-mesh commercially available stainless steel mesh was coated with titanium carbide by chemical vapor deposition under the following conditions.

Reaction gas composition: titanium tetrachloride ('l"1c14) 3%,
Hydrogen 93.1%, Methane 3.9% Temperature: 1100°C Time: 3 hours After coating titanium carbide under the above conditions, the stainless steel net was cut and the cut surface of the wire was observed under a microscope.
The average thickness of the coating layer was 20μ.

0.01% by weight of ruthenium was added to the surface of the stainless steel net, the surface of which was coated with titanium carbide, manufactured by such a method, for immersion.

Regarding this catalyst (Ti catalyst), NO0 is used as the reaction gas.
,1%, H21,0%, diluent gas N2, normal pressure G
The NO reduction activity was measured at H8V30,000 volume/volume/hour.

As a result, in the case without the addition of ruthenium, a reaction was observed at 450°C, and the reaction rate was 87% at 500°C, whereas in the case of the addition of ruthenium, the reaction rate was 30% at 350°C, and the reaction rate was 87% at 500°C. A reaction rate of 75% at 450°C and 97% was obtained at 450°C.

Experimental Example 2 A porous alumina material (commercially available α-alumina) was coated with titanium carbide and zirconium carbide by chemical vapor deposition under the following conditions.

Titanium tetrachloride (TiC14) 1.5% Zirconium tetrachloride (ZrC14) 1.8% Hydrogen 93% Methane 3.7% Temperature: 1100°C Time: 3 hours After coating, microscopic observation of the cut surface revealed the coating layer. The thickness was 16μ.

In addition, when we analyzed the components of this coating layer, we found that TiC
62%, ZrC 38%.

Using this method, 0.01% by weight of rhodium was added to the surface of the alumina material coated with a double carbide of Ti and Zr for immersion.

The NO reduction performance of this TiC, ZrC catalyst was investigated under the same conditions as in Experimental Example 1.

As a result, the NO reaction rate was 48% at 450°C, 91% at 500°C, and 98% at 550°C without rhodium addition, whereas it was 35% with rhodium addition.
It showed 35% at 0°C, 78% at 400°C, and 98% at 450°C, showing almost the same activity as Experimental Example 1, but the amount of by-product ammonia was less than 1/2 compared to Experimental Example 1. , compared to the TiC catalyst (Experimental Example 1), the TiC-Z of this example
The rC catalyst** catalyst was said to be an even better catalyst.

Experimental example 3 A stainless steel wire with a diameter of 0.5♂ψ is 2 mm.
Further, they were stacked on top of each other at intervals of 2 mvt in the direction perpendicular to this to form a net, and this was coated with chromium carbide by thermal spraying.

After coating, the cut surface was observed under a microscope, and the average thickness of the coating layer was 0.8 mm.

Note that the stainless steel wires were bonded together by coated chromium carbide to form a net.

The surface of the net produced in this way has a 0.0% immersion property.
Ruthenium was added at 5% by weight of OO.

Regarding this catalyst, NO reduction activity using various reducing agents was measured.

The results obtained are shown in Table 1. A mesh-like stainless steel-supported carbide was produced in a similar manner, and 0.005% by weight of ruthenium was added to the surface of the mesh for immersion.

For this catalyst, NQo, 1%, H2 as reaction gas
The NO reduction activity was measured at normal pressure GH8V 3000 volume/volume/hour using diluent gas N2 at 1.0%.As a result, the NO reaction rate as shown in Table 2 was obtained.

Experimental Example 4 Chromium carbide powder was electrodeposited with nickel on a 30-mesh stainless steel screen using an electrodeposition apparatus under the following conditions.

Nickel sulfate (NiSO4.6H20) 450 g/l Nickel chloride (NiCl26 H2O) 75 fl/73 Boric acid (IE (a BO4) 60 ft/l Electrolyte pH: 4 Current density: 20 A/di Liquid temperature: 45°C In this manner, 0.005% by weight of ruthenium was added by dipping to the surface of a stainless steel mesh on which chromium carbide was electrodeposited with nickel.

The catalyst prepared in this way was prepared at 1170°C under hydrogen atmosphere for 4
Heat treated for hours.

The resulting catalyst was in the form of a ternary catalyst of chromium carbide (Crs C2), nickel (NC), and ruthenium (Ru) supported on a stainless steel mesh.

Regarding this catalyst, a reaction gas (
Using simulated automobile exhaust gas, normal pressure, GH8V30
The NO reduction activity was measured under the conditions of 000 volume/volume/hour.

As a result, the NO reaction rate was as follows without the addition of ruthenium.
24% at 500℃, 92% at 550℃, g at 600℃
While it was 100%, in the case of ruthenium addition,
28% at 400℃, 95% at 450℃, 10% at 500℃
A value of 0% was obtained.

Furthermore, with this catalyst, almost no NH3 by-product was observed, and at most only 25% of NHa was produced.

Taking these points together, this catalyst can be said to be fully suitable for practical use.

Experimental Example 5 The surface of alumina granules having an average diameter of 3 mm was coated with nickel by electroless plating under the following conditions.

Palladium chloride (PdC1) 0.1 Hydrochloric acid (HCI) 17717 Water (H2O) IJ Nickel chloride (NiCl 26H20) 60P/J Sodium hypophosphite (NaHP02H20) 30 ? /l Ammonium chloride (NH2Cl) 100P/l Ammonium citrate [C6H5O□(NH,i) 3] 30 g/l Liquid PH: 9 (Adjusted with NH30H) Liquid temperature:
90°C Several alumina grains coated with nickel using the above method were placed in a carbon mold and heat treated at 1350°C in a hydrogen stream to bond the grains together with nickel.

Next, this surface was coated with titanium carbide by chemical vapor deposition under the following conditions.

Titanium tetrachloride (TiC14) 3% Hydrogen 93.1% Methane 3.9% Temperature: 1000°C Time: 2 hours Alumina supported titanium carbide produced by the above method.
0.01% by weight of rhodium was added to nickel for immersion properties.

Regarding this catalyst, the NO
Decreased activity was investigated.

As a result, when rhodium was not added, N
O reduction started and a No reduction rate of 98% was obtained at 400°C, whereas in the case of rhodium addition, NO reduction started at a low temperature of around 100°C and reached 98% at 300°C.
% No reduction rate was obtained.

Thus, this catalyst had high NO reduction activity at a very low temperature and exhibited performance that was sufficiently satisfactory for practical use.

Experimental Example 6 A mesh made of nickel metal was heat treated with the following mixed powder to coat the surface of the mesh with chromium carbide.

Composition of mixed powder Chromium dioxide (Cr203) 74% Graphite (C) 26% Carrier gas: Hydrogen Temperature: 1400°C Time: 2 hours Through this heat treatment, chromium oxide and graphite react to form chromium carbide, which is combined with nickel. This causes a eutectic phenomenon, and as a result, a composite of chromium carbide and nickel is formed on the surface of metallic nickel.

The surface produced by this method is immersible into a nickel mesh made of a composite of chromium carbide and nickel.
0.005% by weight of ruthenium was added.

Regarding this catalyst, the NO
As a result of examining the reduction activity, the NO reaction rate was 12% at 500°C without the addition of ruthenium, 80% at 550°C, and 60% at 550°C.
98% at 500°C, whereas in the case of ruthenium addition, the values were 72% at 450°C and 98% at 500°C, which were slightly lower than those in Experimental Example 4.

However, overall, it showed a very similar tendency to Experimental Example 4, including extremely little NH3 by-product.

Experimental Example 7 A mesh of about 30 meshes was made from a nickel-iron alloy wire, and its surface was coated with titanium carbide by chemical vapor deposition.

The vapor deposition conditions at this time are as follows.

Titanium tetrachloride (TiCl4) 3% Hydrogen 93.1% Methane 3.9% Temperature: 1000°C Time: 2 hours Due to the immersion property of the nickel-iron alloy mesh coated with titanium carbide, 0.01 weight % rhodium was added.

The NO reduction activity of the catalyst produced in this manner was measured in the same manner as in Experimental Example 5.

As a result, this catalyst showed an activity comparable to that of the catalyst shown in Experimental Example 5, and the reaction rate was 100% at 400°C in the case without the addition of rhodium, whereas in the case of the addition of rhodium, A reaction rate of 100% was already shown at 300°C.

Furthermore, this catalyst produced only a small amount of NH3 as a by-product and only showed a maximum NH3 production rate of 40% at around 320°C.

On the other hand, when no rhodium was added, the maximum production rate was 37% at around 420°C.

Furthermore, even when this catalyst was exposed to CFR engine exhaust using commercially available regular gasoline for 150 hours, its activity hardly changed.

Experimental Example 8 Similar to Experimental Example 2, chemical vapor deposition was performed on the alumina material.
Coated with TiC-ZrC.

Based on this coated material, 0.01% by weight depending on immersion properties.
of ruthenium and rhodium were added and used as a catalyst.

The NO reduction performance of this catalyst was investigated under the same conditions as in Experimental Example 2.

As a result, the No reaction rate was 48% at 350℃, 90% at 400℃, and 450℃ in the case of the ruthenium-added catalyst.
It was 100%.

In the case of rhodium-added catalyst, 65% at 350°C, 400%
An activity of 86% at 450°C and 100% at 450°C was obtained.

Further, the amount of by-product ammonia was almost the same as that of the catalyst to which ruthenium and rhodium were not added.

As explained above, in the present invention, the substrate is formed of a heat-resistant material, and the surface thereof is coated with one or more metal carbides of groups ①, ②, and ② of the periodic table. Furthermore, since it provides a catalyst in which at least one of ruthenium and rhodium is added in an amount of 0.005% by weight or more, it has the advantage of effectively purifying NOx in the exhaust gas of internal combustion engines. .

Claims (1)

[Claims] A substrate made of a heat-resistant material of 11,000°C or higher, the surface of this substrate coated with one or more metal carbides of Groups 1 Va, Va, and VIa of the periodic table, and 0.01 to 0.05% in the coating layer or on its surface. A catalyst for reducing nitrogen oxides, characterized in that at least one of ruthenium and rhodium is added in an amount of 5% by weight or more.