JPS5945419B2 - 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 to a catalyst that has an excellent reducing effect on nitrogen oxides (hereinafter referred to as NOx) in exhaust gas from internal combustion engines and the like. This provides an advantageous manufacturing method.

Conventionally, catalysts for reducing NOx in exhaust gas from internal combustion engines, etc., have not only required excellent catalytic performance, but also required a manufacturing method that is simple and provides stable performance. A manufacturing method suitable for production is required.

The present invention has been made in view of these requirements, and the substrate constituting the catalyst is made of a heat-resistant material of 1000° C. or higher, and the surface of the substrate is coated with materials such as Va, Va, and V of the periodic table.
A nitrogen oxide reduction catalyst comprising one or more metals, alloys, and oxides of these metals of group IA elements, and comprising a coating layer in which at least a portion of the metal is carbonized. It is something to do.

The material of the substrate in the present invention may be metal, nonmetal, 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.

The shape of the base 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, and in that case, the particle size is preferably 10yx.

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 powder, plate, rod, wire, or any other structure and then heat-treating this may also be used.

It may be in the shape of a block, plate, rod, wire, pipe, filament, net, or two-cam shape, and may also be machined by drilling, grooving, etc., or may be bent, stretched, etc. They may be deformed by crushing, etc., or they 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.℃・0 The coating layer is made of one or more metals, alloys, or oxides of these metals of Group 1 Va, Va, and VIa elements of the periodic table. It is something.

In this case, the IVa group metals are Ti, Zr, Hf,
The Va group metals are V, Nb, and Ta, and the Vla group metals are Cr, Mo, and W.

Therefore, these alloys include, for example, Cr-M
Examples of these metal oxides include TiO2 and MoO3.

Preferred coating methods in the present invention include vapor deposition, electrodeposition, thermal spraying, etc., but other methods may also be used.

The coating layer may contain one or more metals such as copper, nickel, iron, and cobalt, alloys, and metal compounds thereof; in this case, as a conductive substrate, It may be coated by electrodeposition.

In addition, the method of coating in the form of a metal, alloy, inorganic compound or organic compound as a solid solution, and then heat-treating it can be selected as appropriate, such as suspension or solution, and is advantageous because a uniform coating layer can be obtained.

In the present invention, solid-phase carbonization and gas-phase carbonization are suitable as a method for carbonizing the coating layer formed on the surface of the substrate, but other methods may also be used.

As a method of solid phase carbonization, a substrate provided with the coating layer,
The method is to charge the material into a container made of alumina, carbon, etc., fill the space with carbon powder, blocks, plates, rods, pipes, filaments, nets, etc., and heat it.

In addition, gas phase carbonization can be carried out in a mixed atmosphere of a hydrocarbon such as methane, propane, or butane and hydrogen, or in a mixed atmosphere of carbon monoxide and hydrogen, or in a mixed atmosphere of hydrocarbon, carbon monoxide, and hydrogen. A method of heating is used.

Furthermore, as a special method, a method can be considered in which the surface of the coating layer of the substrate is coated with a carbon material by vapor deposition or the like and then heated.

In addition, the said coating layer has the periodic table 1 Va, Va, and VIa.
One or more metals, alloys, and oxides of these metals may be coated alone (
These groups may be coated with one or more metals selected from copper, nickel, iron, and cobalt, alloys, and metal compounds in a laminated or mixed state.

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 and can be manufactured rationally in a short time.

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

During this filling, a backing material such as glass fiber or alumina fiber is used.

Alternatively, the catalyst according to the present invention may be filled into a mold made of alumina, carbon, etc. of a desired shape and integrated by heat treatment.

In this case, a load may be applied.

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 stainless steel mesh was plated with chromium under the following conditions.

Electrolytic bath composition: CrO3300? /13 &H2SO4
4 g/l Electrolytic bath temperature: 80° C. Current density: 80 A/di Next, this was heat treated together with graphite powder under the following conditions to carbonize the coated chromium.

Carrier gas: Hydrogen temperature: 1400° C. The NO reduction activity of the chromium carbide catalyst produced by such a method was investigated in a nitrogen gas atmosphere containing 0.1% NO and 1.0% CO.

As a result, the reaction of this catalyst started at 300°C, and the reaction started at 40°C.
NO reduction rates of 30 to 40% at 0°C and 90% or more at 500°C were obtained.

When this activity was compared with that of other commercially available catalysts, it was found to be much higher than that of a commercially available alumina-supported platinum catalyst measured under the same conditions.

Experimental Example 2 A wire mesh made of mild steel film was coated with Ti-MO alloy under the following conditions,
Furthermore, this was mixed with graphite in a hydrogen atmosphere for 14
The coating was heat treated at 00° C. for several hours to carbonize the coating.

Equipment used: Vapor phase plating equipment for binary alloys Vaporization chamber (1): Insert titanium tetrachloride (2): Insert molybdenum pentachloride Plating chamber: Insert wire mesh with mild steel film Heating temperature: Vaporization chamber (1,) 80℃ vaporization chamber (21200℃ plating chamber 1000℃ carrier gas: hydrogen gas flow rate: vaporization chamber (1) 70 rul/mvr vaporization chamber (2) 3omi/= Ti-Mo based carbide catalyst prepared by such method (
The No reduction activity of the mild steel wire mesh supported catalyst was measured under the same conditions as in Experimental Example 1.

As a result, 18% at 400℃ and 86% at 500℃550
A reduction rate of 96% or more was obtained at °C.

Although this activity was somewhat lower than the activity of the chromium carbide catalyst shown in Experimental Example 1, it was still much higher than that of the commercially available alumina-supported platinum catalyst.

Experimental Example 3 A net made of a nickel-iron alloy wire was coated with chromium oxide (Cr2O5) to an average thickness of 0.5% by thermal spraying.

The thickness was measured by microscopic observation.

Next, this was heat-treated under the following conditions to vapor-phase carbonize the entire coating layer to obtain a catalyst.

Reaction gas: methane 35 vol 1% & hydrogen 65% Temperature: 1
050°C Time: 3 hours It was confirmed by X-ray diffraction that the surface coating layer of this catalyst was entirely carbide.

First, the No reduction activity of this catalyst was examined under the same conditions as those shown in Experimental Example 1, and it showed a No reduction rate of 50% or more at 400°C, 85% at 450°C,
At 500°C, the No reduction rate was approximately 100%.

Next, regarding this catalyst, further No. 0.1%,
COl, 0%, H20, 3%, CH4200ppm, C
3H6100ppmSC6H650ppm, CO2]
The No reduction activity was investigated under a simulated automobile exhaust gas atmosphere containing -00% H2O 10% and 020-0.5%.

As a result, the activity under such an atmosphere is lower than that of NO and CO.
Although the activity was much lower than that in the single system, the activity was still 35% at 500°C and 68% at 550°C.
%, showed an activity of 97% at 600°C, and the amount of ammonia by-product was as low as 23% at maximum.

In a similar manner, a net made of nickel-iron alloy wire was coated with various metal oxides to an average thickness of 0.5 mm, and a catalyst was carbonized under the same conditions as in Experimental Example 1. The No reduction activity was examined under the following conditions.

The results are shown in the table below. Experimental Example 4 The surface of a porous alumina material was coated with a nickel, chromium, and molybdenum alloy by vacuum deposition.

After coating, the thickness of the coating layer was determined to be 11 μm when measured using a Betascope.

This was heat-treated together with graphite under the following conditions to make the entire coating layer a carbide.

It was confirmed by X-ray diffraction that the entire coating layer was made of carbide.

When the No reduction activity of this catalyst was measured using the simulated automobile exhaust gas shown in Experimental Example 3, it was found that 600
The NO reduction rate was approximately 100% at ℃.

Moreover, this activity remained unchanged even after 100 hours of exposure to CFR engine exhaust using commercially available gasoline.

Experimental example 5 A 2 mm stainless steel wire with a diameter of 0.5 to ψ
They were arranged at intervals of 2 mm, and then stacked on top of each other at 2 mm intervals in a direction perpendicular to the above to form a net, which was then coated with a chromium-titanium (Cr2Ti) solid solution by thermal spraying.

After coating, the cut surface was observed under a microscope, and the average thickness of the coating layer was 0.9%.

After coating, the stainless steel wires were each bonded by the coated chromium-titanium solid solution to form a net.

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: 110
After the heat treatment at 0° C. for 1 hour, microscopic observation was performed and the thickness of the carbonized material was measured, and the average thickness was 1.4 μm.

Regarding the Cr-Ti based carbide catalyst prepared by such a method, the No reduction activity was measured using the simulated automobile exhaust gas shown in Experimental Example 3 under the conditions of 5V30,000 volume/volume/hour.

As a result, an NO reduction rate of 100% was already obtained at 600°C.

Experimental Example 6 A nickel mesh was heat-treated with chromium chloride (CrC1□) under the following conditions, and the surface of the mesh was coated with chromium by chemical vapor deposition.

Reaction gas composition S Hydrogen chloride 10% & Hydrogen 90% Temperature: 10
50°C Next, the coated chromium was carbonized in vapor phase under the following conditions.

Reaction gas composition: 735% meta & 65% hydrogen Temperature: 10
00°C Regarding the catalyst prepared by such a method, the No reduction activity was examined under the same conditions as in Experimental Example 5.

As a result, 35% at 500℃ and 95% at 550℃
The NO reduction rate was obtained.

Moreover, with this catalyst, the production of ammonia is small, with only around 20% (550°C) of NHs being produced at maximum, 15% at 600°C, and 3% at 700°C.
Only H3 production was observed.

Experimental Example 7 Chromium oxide (Cr203) powder was electrodeposited with nickel on a stainless steel mesh using an electrodeposition device under the following conditions.

'Nickel sulfate (NiSO4.6H20) 450 g/l Nickel chloride (NiC12・6H20) 75? /73 Boric acid (H3BO3) 60g/l Liquid pH: PH4,0 Current density: 20A/dm Liquid temperature: 45℃ Next, this was carbonized in a vapor phase using a conventional method in Experimental Example 1.

The activity of the catalyst prepared by this method was almost equal to that of Experimental Example 6.

Moreover, even when this catalyst is exposed to CFR engine exhaust at temperatures of 600 to 700°C, its activity does not decrease, and even after up to 200 hours of exposure, it has almost the same activity as a new catalyst. Was.

Experimental Example 8 Alumina particles having an average diameter of 3X were coated with nickel by electroless plating under the following conditions.

Palladium chloride (PdC12) 0.11 Hydrochloric acid (HCl) 177 Il Water 1. O1 Nickel chloride NiCl2・6H20) 60g/1 Sodium hypophosphite (Na H2PO2・H20) 30 ? /l Ammonium chloride (NH4Cl) 100 g/l Ammonium citrate (C6H507(NH4)s) 30 g/l Liquid pH: pH 9 (adjusted with NH40H) Liquid temperature: 90°C Furthermore, on this surface, as described in Experimental Example 1, Chromium plating was applied by the method described above, and several of the granules were placed in a carbon mold and heat treated at a temperature of 1250° C. in a hydrogen stream to bond each granule.

Then, this was carbonized in a vapor phase in the same manner as in Experimental Example 5.

The Cr3C2-Ni-based catalyst prepared in this manner also showed almost the same activity as Experimental Examples 6 and 7 in terms of reaction activity, and no performance deterioration was observed when exposed to engine exhaust. There wasn't.

Furthermore, this catalyst was exposed to commercial automobile exhaust, and approximately 1
After driving for the equivalent of 10,000 km, the catalyst was taken out and its NO reduction activity was measured under the conditions shown in Experimental Example 5. As a result, there was almost no change in the NO reduction rate, and no ammonia formation, which was slightly observed with the new catalyst, was observed. It was gone.

As explained above, in the present invention, the base body is formed of a heat-resistant material of 1000° C. or higher, and the surface of the base body is composed of metal oxides of elements of groups 1 Va, Va, and Vla of the periodic table, and at least Since the present invention provides a carbide-based catalyst including a coating layer in which a portion of the coating layer is carbonized, it has the advantage of effectively purifying NOx in the exhaust gas of an internal combustion engine. have

Claims (1)

[Claims] i. A substrate made of a heat-resistant material of 1000° C. or higher, and a metal or alloy formed on the surface of the substrate, the composition of which is one or more of the group IV elements of group IV a, Va, and Via of the periodic table, A catalyst for reducing nitrogen oxides, comprising a coating layer made of these metal oxides and having at least a portion of its surface carbonized.