JPS5945417B2 - Catalyst for nitrogen oxide reduction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for reducing nitrogen oxides, and in particular provides a catalyst with excellent performance and durability, and a manufacturing method for reliably and easily obtaining the catalyst, thereby purifying exhaust gas from an internal combustion engine. It is suitable as a catalyst for

Conventionally, this type of catalyst for reducing nitrogen oxides, such as a catalyst for purifying exhaust gas from an internal combustion engine, has required on the one hand a catalyst with excellent catalytic performance and durability, and on the other hand, even if the composition is the same, it has been Because of the differences in performance as catalysts, a manufacturing method that is simple and provides stable performance is required, and considering its use, a low-cost manufacturing method that is suitable for mass production is also required. There is.

Therefore, there is a need for the development of a catalyst that has excellent performance and durability that satisfies these requirements, and a manufacturing method that can easily produce this catalyst with stable performance.

The present invention has been made with attention to these points, and the substrate constituting the catalyst is made of one or more metals, alloys, and oxidation of these metals of Group 1 Va, Va, and VIa elements of the periodic table. It contains a carbide-based catalyst selected from substances and obtained by carbonizing the surface thereof.

An example of the catalyst for reducing nitrogen oxides of the present invention will be described below.

The material of the substrate in the present invention is the material of the first Va of the periodic table.

It is made of one or more metals, alloys, and oxides of these metals of group Va and VIa elements, and may be in the form of a mixture, compound, or solid solution.

In this case, it is preferable to use a powder metallurgy method in which component metal powders are mixed, molded, and sintered.

In this case, the IVaVa group metals are Ti, Zr, and Hf, and the Va group metals are V, Nb, Ta, and V
Group Ia metal GζCrlMo, W.

Therefore, these alloys include, for example, Cr-M
Examples of these metal oxides include TiO2 and MeO2.

The shape of the base in the present invention preferably has a large contact area with gas, and in the case of purifying internal combustion engine exhaust gas, it is desirable that gas flow is good and that the back pressure of the internal combustion engine is not increased. There are several types of specific shapes.

It may be in the form of particles with a particle size of 0.2 mvtJU or more.

It may also be an air-permeable sintered body obtained by adding a sublimated 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 sintering this.

It may be in the shape of a block, plate, rod, wire, pipe, filament, or net, and may also be subjected to drilling, grooving, or machining, or may be combined by stacking, gluing, welding, etc. Good too.

It is preferable to have voids of 40 to 90% of the total capacity.

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

In the present invention, any method may be used to carbonize at least the surface of the substrate, but the following three methods can be used:
Types of methods are preferred.

First, as a solid phase carbonization method, the substrate is charged into a container made of alumina, carbon, etc., and the voids are filled with carbon powder, blocks, etc.
There is a method of heating by burying it in plates, rods, pipes, filaments, nets, etc.

There is also a vapor phase carbonization method in which the substrate is heated in a carbonizing atmosphere.

A mixed atmosphere of a hydrocarbon such as methane, propane, or butane and hydrogen, a mixed atmosphere of carbon monoxide and hydrogen, or a mixed atmosphere of hydrocarbon, carbon monoxide, and hydrogen is suitable.

Further, as a special carbonization method, there is a method in which the surface of the substrate is coated with a carbonized substance by vapor deposition or the like and then heated.

If the catalyst according to the present invention contains 0.0005% by weight or more of one or both of ruthenium and rhodium in the form of a metal, an inorganic compound, or an organic compound by a method such as vapor deposition, the catalytic ability will be further increased. Become.

In addition, when the catalyst according to the present invention is in the form of powder, it can be filled into a mold made of alumina, carbon, etc.
Heat treatment is also performed with or without applying a load under kglcvtJU to bond and integrate the particles.

Furthermore, the catalyst produced by the production method of the present invention may be filled into a heat-resistant basket made of stainless steel or the like, and at this time, a heat-resistant banking material such as glass fiber or alumina fiber may also be filled.

The present invention configured as described above has the following great effects.

First, according to the production method of the present invention, an excellent catalyst can be obtained.

Since the catalyst produced by the production method of the present invention is a hard metal carbide, it has high mechanical strength, and is rich in impact resistance, abrasion resistance, and heat resistance, and therefore is rich in durability.

This is important as an internal combustion engine exhaust purification catalyst used in an environment with large vibrations.

Further, since the catalyst according to the production method of the present invention is produced by applying powder metallurgy technology, etc., various shapes can be obtained, and shapes with a high contact rate with exhaust gas and shapes with reduced weight can be easily obtained.

Further, the manufacturing method of the present invention is excellent as a manufacturing method itself.

The manufacturing method of the present invention is simple and requires few human steps,
The equipment used is simple and requires only a small amount of equipment.

Furthermore, the occurrence of defects is low and there is no loss of material, so the overall manufacturing cost is low.

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 mesh of 30 meshes was prepared from a tungsten wire having a diameter of 0.5 m/m, and this was heat-treated together with graphite powder under the following conditions to carbonize the surface of the mesh.

Carrier gas: Hydrogen Temperature: 1900° C. Time = 30 minutes The tungsten wire network after carbonization was cut and observed under a microscope to measure the thickness of the carbide layer, which was approximately 20 μm.

Ruthenium in an amount of 0.01% by weight was added to the surface of the tungsten carbide network produced by this method by a seeding method.

Then, this added material becomes the total catalyst, and NO0,1 is added to this.
%, COI, and nitrogen gas containing 0% at normal pressure and a gas hourly space velocity (GH8V) of 30,000 volume/volume/hour.

The reduction rate was measured.

As a result, in the case of no addition of ruthenium, 50% at 600℃
, and about 90% at 70°C, whereas in the case of ruthenium addition, reduction rates of 45% at 450°C and 93% at 550°C were obtained.

Although this performance cannot necessarily be said to be sufficient, if the thickness of the tungsten wire used and the size of the mesh are considered, it can be seen as a considerably high performance.

Experimental Example 2 A tungsten mesh prepared in the same manner as in Experimental Example 1 was heat-treated together with graphite powder under the following conditions to obtain tungsten carbide.

Carrier gas: Hydrogen Temperature: 200°C Time: 2 hours When the structure of the tungsten carbide thus obtained was analyzed by X-ray diffraction, it was found that the wire mesh was completely carbonized to the center of the strands and turned into a carbide. confirmed.

0.01% by weight of rhodium was added to the surface of the tungsten carbide mesh thus obtained by a seeding method.

Using tungsten carbide produced by this method as a catalyst, the NO reduction performance was measured under the same conditions as in Experimental Example 1, and it was found that when no rhodium was added, the NO reduction performance was approximately 5% at 600°C.
0% and about 90% at 700℃, while at 450℃
An NO reduction rate of about 40% was obtained at 550°C and 92% at 550°C.

Experimental Examples 1 and 2 show that with a catalyst characterized by carbonizing a tungsten wire network at high temperature using graphite powder, even when only the surface layer was carbonized, the center of the wire was completely carbonized. It was also revealed that almost no change was observed in the NO reduction performance.

: Experimental Example 3 When the surface of a tungsten net prepared in the same manner as Experimental Example 1 was vapor-phase carbonized under the following conditions, the surface layer of the catalyst was approximately 0.1 m.
The carbide formed over a thickness of m.

Reaction gas composition: 35% methane & 65% hydrogen Temperature: 190
0° C. Time: 1 hour 0.01% by weight of rhodium was added to the surface of this surface-carburized tungsten wire network by a seeding method.

Using the tungsten wire network obtained by such a method as a catalyst, NO reduction performance was measured under the same conditions as in Experimental Example 1.

As a result, almost the same performance as the results of Experimental Example 1 or Experimental Example 2 was obtained.

Experimental Example 4 A mesh of 30 meshes was prepared from a chromium-molybdenum alloy wire having a diameter of LOm/m, and vapor-phase carbonized under the following conditions.

Reaction gas composition dimethane 35% & hydrogen 65% Temperature: 145
0°C Time: 30 minutes to 2 hours 0.005% by weight of ruthenium was added to the surface of the three types of chromium-molybdenum double carbide nets with different carbonization times by a seeding method.

Regarding these three types of catalysts, under the same conditions as Experimental Example 1,
Its NO reduction activity was investigated.

The results obtained are shown in Table 1.

As shown in Table 1, the activity of this catalyst does not change depending on the carbonization time, and therefore, it is clear that if even the surface of the alloy wire is carbonized, there is no need to further carbonize the center. .

Experimental example 5 Chromium titanium (CrTi) with a diameter of 1.0 m/m
) A mesh of 30 meshes was prepared from a solid solution wire, and this mesh was fired and carbonized together with graphite powder at 1550° C. in a hydrogen atmosphere.

A catalyst was prepared by adding 0.005% by weight of ruthenium to the surface of the chromium-titanium double carbide steel thus produced by a seeding method.

About this catalyst Nitrogen monoxide 0.1% Carbon monoxide 1.0% Hydrogen
0.3% Methane 200 ppm Propylene 100 ppm Benzene
50 ppm carbon dioxide gas
lO% water vapor 10% oxygen
0.25% Balance: Using simulated automobile exhaust gas consisting of nitrogen, normal pressure, GH8
The NO reduction performance was measured under the conditions of V30,000 volume/volume/hour and catalyst amount of 6 ml.

As a result, in the case of no addition of ruthenium, 3
0%, 85% at 600°C, and 97% at 700°C, while in the case of ruthenium addition, it was 45% at 450°C.
, a No reaction rate of 98% was obtained at 600°C, and the production of NH3 was also relatively small at 15% at 450°C and 45% at 600°C.

Experimental Example 6 Add and mix 25% by weight of naphthalene granules (#80 to #40) to chromium oxide (Cr2O3) powder.
After press molding at a pressure of 000 kg/crA, heat treatment is performed at a temperature of 1700° C. in the atmosphere.

The porous chromium oxide (Cr2o3) substrate thus produced was carbonized in a vapor phase under the following conditions.

Reaction gas composition dimethane 35% & hydrogen 65% Temperature: 120
0°C Time: 2 hours The chromium carbide granules produced by this method were
．． 0.1% by weight of ruthenium was added and used as a catalyst.

The performance of this catalyst was evaluated under the same conditions as in Experimental Example 1, and it was found that when no ruthenium was added, it was 90% at 500°C.
% and 100% at 550°C, while in the case of ruthenium addition, it was 85% at 350°C and 100% at 400°C.
%, and the activity was sufficiently satisfactory from a practical standpoint.

In addition, the carbide produced by the same method was used by the seeding method.
Table 2 shows the performance evaluation results for the catalyst to which 0.01% by weight of ruthenium was added.

Experimental Example 7 A mesh of 30 meshes was prepared from a nichrome wire having a diameter of 1.0X, and this was heat-treated together with graphite powder at 1100° C. in a hydrogen atmosphere to perform carbonization.

0.01% by weight of rhodium was added to the surface of the nickel-chromium double carbide net produced by this method by an insemination method, and this was used as a catalyst.

The performance of this catalyst was evaluated under the conditions shown in Experimental Example 5, and it was found that in the case of no rhodium addition, 35% at 500°C
, 90% at 550°C and 100% at 600°C, while in the case of rhodium addition &ζ 40% at 350°C, 40%
An NO reaction rate of 91% at 0°C and 100% at 450°C was obtained, and NH3 was only produced at a maximum of 35% (at 400°C), demonstrating excellent NO purification performance.

Furthermore, this catalyst was tested using commercially available regular gasoline.
When we evaluated its performance in the exhaust of an FR engine, we found that a NO reduction rate of almost 100% was obtained at around 600°C, and even after 150 hours of use, the performance decreased only slightly. It wasn't.

Experimental Example 8 0.01% by weight of ruthenium (Ru) and rhodium (Rh) were added to chromium carbide (Cr3C2)-nickel (N1)K prepared in the same manner as in Experimental Example 7 by the Sarani immersion method. Using this as a catalyst, an experiment similar to Experimental Example 7 was conducted.

As a result, in the case of the ruthenium-added catalyst, 4
5%, 93% at 400°C, 100% at 450°C, 60% at 350°C, 8% at 400°C for rhodium-added catalyst.
5%, 100% NO reaction rate was obtained at 450 °C, and NH
In the case of the ruthenium-added catalyst, the production of 3 is at most 17
% (400℃), 25% (for rhodium-added catalyst)
400°C), demonstrating excellent NO purification performance.

Furthermore, when we evaluated the performance of these additive catalysts in FR engine exhaust gas using commercially available regular gasoline, we found that a NO reduction rate of 100% was obtained at 450°C, and even after 150 hours of use. Even in
Its performance was extremely low (only slightly degraded).

As explained above, the present invention provides a catalyst with excellent catalytic performance and a manufacturing method that is simple and provides stable performance. Therefore, the present invention is suitable for purifying exhaust gas from internal combustion engines, and its industrial value is high. It has the advantage of being thick.

Claims (1)

[Claims] 1 At least the surface of the substrate constituting the catalyst is carbonized,
Moreover, its composition is in the periodic table 1 V a, V a,
Nitrogen consisting of L type or two or more metals, alloys, and oxides of these metals of group VIa elements, and containing 0.0005% by weight or more of one or two of ruthenium and rhodium. Catalyst for oxide reduction.