JPS5945420B2 - 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 more particularly to a catalyst suitable for purifying exhaust gas from internal combustion engines, etc., and an advantageous method for producing the catalyst.

Catalysts for reducing nitrogen oxides in exhaust gas from internal combustion engines are required to have good catalytic performance;
Depending on the manufacturing method, there are often differences in catalyst performance even with the same composition.

In addition, this catalyst must be produced by a manufacturing method that is low cost and suitable for mass production in view of its intended use.

The present invention has been made in view of the above points, and provides a metal carbide catalyst for reducing nitrogen oxides having excellent performance.

The material of the substrate in the present invention is rVa, Va of the periodic table.
It is composed of one or more metals, alloys, and oxides of these metals in the family of elements, and its state may be a mixture, a compound, or a solid solution.

Particularly preferred are those obtained by a powder metallurgy method in which powders of component metals are mixed, molded, and sintered.

In this case, the IVaVa group metals are Ti, Zr, and Hf, the Va group metals are V, Nb, and 'ra, and the family metals are Cr, Mo, and W.

Therefore, these alloys include, for example, Cr-M
Examples of these metal oxides include TiO2 and MoO2.

Further, the entire substrate does not need to be made of the above-mentioned material, as long as the surface condition becomes the same as that of the above-mentioned material by carbonization.

That is, one or more of copper, nickel, iron, and cobalt is applied in the form of a metal, alloy, inorganic compound, or organic compound on the surface of one or more of metals in Groups Na, Va, and VIa of the periodic table. It may be coated by vapor deposition or electroless plating, or instead of the coating, it may be immersed in a solution of one or more inorganic or organic compounds of copper, nickel, iron, and cobalt dissolved in an appropriate solvent. , or may be coated by coating.

The shape of the base body in the present invention needs to have a large contact area with the gas, and it is desirable that the gas flow is good and the bank pressure of the internal combustion engine is not increased. There is.

It may be in the form of particles with a particle size of 0.2 mi or more. It may also be an air-permeable sintered body obtained by adding a sublimable substance such as naphthalene or zinc to a powder 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 machining such as drilling or grooving, or may be deformed by bending, stretching, crushing, etc. Alternatively, they may be introduced by overlapping, gluing, welding, etc.

It is preferable to have a space 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 are suitable.

First, as a solid phase carbonization method, there is a method in which a substrate is placed in a container made of alumina, carbon, etc., and the space is filled with carbon powder blocks, plates, rods, pipes, filaments, nets, etc., and then heated.

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 carbon material by vapor deposition or the like and then heated.

If the catalyst produced by the production method of 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 can be further improved. It gets expensive.

Further, when the catalyst according to the present invention is in the form of powder, it is filled into a mold made of alumina, carbon, etc.
Heat treatment is also performed with or without applying a load under kg/caJJ to bond and integrate the granules.

Moreover, the catalyst according to the present invention is also filled in a heat-resistant basket made of stainless steel or the like, and at that time, a heat-resistant backing material such as glass fiber or alumina fiber is also filled together.

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

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

Since the catalyst according to the present invention is a hard metal carbide, it has high mechanical strength, and is rich in impact resistance, abrasion resistance, and heat resistance.
Therefore, it is highly durable.

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

Further, since the catalyst according to the present invention is manufactured by applying powder metallurgy technology, etc., various shapes can be obtained, and shapes that have a high contact rate with exhaust gas and shapes that are lightweight can be easily obtained.

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

According to the manufacturing method of the present invention, the number of steps is small and simple, and the equipment used can be simple and small.

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 titanium basket was filled with several chromium metal particles having an average diameter of 3 mm, and plated with nickel under the following conditions.

Nickel sulfate (Ni SO4・6H20) 2401/l Nickel chloride (NiC12・6H20) 45 g/l Boric acid (H3BO3) 30P/J PH of liquid:
pH 4-0 Current density: 4 A/di Temperature: 60° C. After coating, the chromium grains were each bonded by nickel to form a high porosity substrate.

This was heat treated together with graphite powder under the following conditions to carbonize the chromium.

Carrier gas: Hydrogen temperature: 1250°C The Cr-Ni carbide catalyst produced in this manner was used in an atmospheric pressure flow reactor to obtain a NO of 0.1%.

COI, 0%, H20, 3%, CH4200ppm.

C3H6100ppm, C6H650ppm, C0
The NO conversion activity of the catalyst was measured under a simulated automobile exhaust gas atmosphere having a composition of 7210%, H2O 10%, 020.25%].

As a result, this catalyst showed 50% at 500°C and 9% at 550°C.
It showed an NO conversion rate of 5% or more, and the amount of ammonia by-product was very small at a maximum of 20% (550°C).

Moreover, the activity of this catalyst is not affected much by the gas flow rate (GH8V), and even under the conditions of GH8V 100,000 volume/volume/hour, the GH8V
It showed almost the same level of activity as when it was 30,000Ω.

Experimental Example 2 25% by weight of naphthalene granules (#80 to #140) were added and mixed to chromium oxide (Cr203) powder, and this was added to 1
000 at a pressure of 91 crl, and then heat-treated at 1700° C. in the atmosphere.

The surface of this porous chromium oxide substrate was coated with nickel by electroless plating under the following conditions.

Palladium chloride (PdC12) O11g Hydrochloric acid (H
CI) 1.0ml water (H20)
1.01 Nickel chloride (NiC12.6H20) 60 g/1 hypophosphorous acid (NaH2PO2, H2O) 301/l Ammonium chloride 1°o? /1 (NH4C1) Ammonium citrate 309/l (Ca Hs 07 (NH4) s) pH of solution:
pH 9 (adjusted with NH40H) Liquid temperature: 90°C Next, this was carbonized in vapor phase under the following conditions.

Reaction gas composition: 35% methane, 65% hydrogen Temperature:
1000° C. The NO conversion activity of the C r —N i -based carbide catalyst produced in this manner was measured under the same conditions as shown in Experimental Example 1.

As a result, although the reaction generally proceeded at a low temperature of 20 to 30°C, the tendency was almost the same as the result shown in Experimental Example 1.

The reason why the catalyst of Experimental Example 2 had higher performance than that of Experimental Example 1 was thought to be due to the difference in surface area or porosity of the catalyst.

Similarly, porous metal oxides were created using various oxides as starting material powders, coated with nickel by electroless plating under the conditions described above, and then carbonized in vapor phase, and used as catalysts. .

The results of performance evaluation of the catalyst thus obtained are shown in the following table.

Experimental Example 3 The surface of a net made from a chromium-molybdenum alloy wire was plated with nickel under the same conditions as described in Experimental Example 1.

Next, this was heat-treated together with graphite powder under the following conditions to effect carbonization.

Carrier gas: Hydrogen temperature: 1350° C. The Cr MO—Ni-based carbide catalyst thus obtained was treated with N under the same conditions as in Experimental Example 1.

When the conversion activity was measured, it was 35% at 500°C and 550%.
The No reaction rate is 90% at ℃ and almost 100% at 600℃, and the ammonia by-product is also up to 26% (at 550℃).
There were relatively few.

Comparing this result with the results of Experimental Example 1, it can be said that Experimental Example 3 is not necessarily superior to Experimental Example 1.
It became clear that the effect of adding molybdenum was not necessarily significant.

Similarly, a mesh of 30 meshes was made from a chromium-titanium wire having a diameter of 1.0 mm, and its surface was plated with cobalt under the same conditions as in Experimental Example 1.

Next, the obtained plated wire is mixed with graphite powder.
The catalyst was carbonized by heat treatment at 1550° C. in a hydrogen atmosphere to produce a catalyst.

When the No conversion activity of this catalyst was measured, it was found to be 30% at 500°C, 85% at 600°C, and 85% at 700°C.
A 97% No reaction rate was obtained.

Experimental example 4 Nickel was added to the surface of a net made from tungsten wire.
An iron alloy was coated using a vacuum evaporation method, and this was vapor-phase carbonized under the following conditions.

Reaction gas composition 2: 35% methane & 65% hydrogen mixture:
1050°C When the No conversion activity of this catalyst was measured under the same conditions as in Experimental Example 1, a No reaction rate of 68% was already obtained at 500°C, and although the NO reaction activity was high at low temperatures, Even when the temperature increases, the increase in NO reaction activity is small: 79% at 550°C, 86% at 600°C, and 9% at 700°C.
Only 0% No reaction rate was obtained.

Experimental Example 5 Tungsten wire rods were arranged at 2 mm intervals, and then stacked on top of each other at right angles to each other at 2 mm intervals, and coated with nickel and copper solid solution 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.

After coating, the tungsten wires were bonded together by the coated nickel/copper solid solution and formed into a thin shape.

Next, this was heat-treated under the following conditions to vapor-phase carbonize the surface of the coating layer.

Reaction gas composition: 35% methane & 65% hydrogen Temperature:
1ooo<0>C Regarding the W--Ni--Cu-based carbide catalyst manufactured by such a method, the No conversion activity was measured under the same conditions as in Experimental Example 1.

As a result, as in Experimental Example 4, the NO reaction activity was high in the low temperature range, but it was insufficient in the high temperature range.
That is, at 500°C and 550°C, 60% and 76
% reaction rate was obtained, but only 85% reaction rate was obtained even at 600°C and 93% reaction rate was obtained even at 700°C.

Experimental Example 6 0.01% by weight of ruthenium (Ru) and rhodium (Rh) were further added by dipping to a carbonized nickel-plated chromium wire prepared in the same manner as in Experimental Example 3, and this was used as a catalyst. An experiment similar to Experimental Example 3 was conducted.

In the case of ruthenium-added catalyst, 45% at 350°C, 40%
93% at 0 °C, 100% at 450 °C, 60% at 350 °C, 85% at 400 °C, 45
A 100% No reaction rate was obtained at 0°C.

The production of NH3 is at most 17% (at 400°C) for the ruthenium-doped catalyst and 2% for the rhodium-doped catalyst.
Only 5% (at 400°C) was produced, demonstrating very excellent NO purification performance.

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

As explained above, the present invention provides a metal carbide catalyst for reducing nitrogen oxides having excellent performance, and in particular,
It has the advantage of being suitable for purifying internal combustion engine exhaust gas.

Claims (1)

[Scope of Claims] 1. A substrate composed of one or more metals, alloys, and oxides of these metals of Group IVa, Va, and VIa elements of the periodic table, and at least a portion of which is carbonized; A nitrogen oxide characterized by being formed as a coating on the surface of the substrate and comprising a coating layer composed of one or more metals, alloys, or compounds of these metals selected from copper, nickel, iron, and cobalt. Catalyst for reduction. 2. The substrate is characterized in that it is made of a net-like, linear, granular, block-like, plate-like, rod-like, pipe-like, filament-like, whisker-like, fiber-like, and cloth-like material with a large specific surface area. A catalyst for reducing nitrogen oxides according to claim 1. 3 The coating layer has 0. The catalyst for reducing nitrogen oxides according to claim 1 or 2, which contains one or both of ruthenium and rhodium in an amount of OO5% by weight or more.