JPH1182005A - Catalyst structure and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently purify a gas to be purified by forming a gas passing port so as to have a tapered form in which its passage sectional area is contracted from the inlet part toward the outlet part in a catalyst structure having a catalyst layer on the inside surface of a number of gas passing holes provided substantially in parallel to each other at prescribed intervals. SOLUTION: A catalyst structure 1 has a number of gas passing ports 2 provided substantially in parallel to each other at prescribed intervals. The gas passing port 2 is formed to have a tapered form in which the passage sectional area is contracted from an inlet part 2a toward an outlet part 2b. Thus, since the gas pressure can be kept in the whole gas passing port 2 area, or gradually raised toward the downstream side even if a passing gas is cooled in the gas passing port 2 and reduced in volume, the gas penetration to a catalyst component 5 can be promoted in the whole gas passing port 2 area. Since a mixture of the passing gas with a reducing agent can be efficiently brought into contact with the catalyst component 5 to promote the chemical reaction, thus, the purifying performance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst structure used by incorporating a reducing agent or an oxidizing agent into a gas such as an exhaust gas of an internal combustion engine and purifying the gas by utilizing a catalytic action. It is about the body.

[0002]

2. Description of the Related Art Various researches and proposals have been made on catalyst devices for reducing and removing NOx from exhaust gas of internal combustion engines such as diesel engines and some gasoline engines and for purifying various combustion gases. I have. This catalytic device promotes the reaction by helping the chemical change without changing itself,
It utilizes a function of a catalyst for purifying gas by oxidizing or reducing HC, CO, and NOx, and a catalyst structure mounted on a catalyst device generally includes an active component (catalytic component),
It is composed of a carrier (a catalyst carrier) and additional components such as a co-catalyst and a stabilizer.

The active component of this catalyst is a noble metal such as Pt (platinum) or Pd (palladium) or a mixture thereof in the case of an oxidation catalyst, and Pt-Rh in the case of a three-way catalyst.
(Rhodium) and Pt-Pd-Rh-based mixtures are generally used. In addition, the carrier supporting the active ingredient is generally activated alumina or ceramic, and in shape,
There are two types, a pellet catalyst in which an active component is supported on the surface of a granular carrier, and a monolith (honeycomb) catalyst in which a catalyst layer is provided on a carrier having an integral honeycomb structure.

[0004] In a monolithic catalyst that occupies the mainstream, a catalyst structure 11 is disposed in a catalytic converter C as shown in FIG. Reference numeral 11 denotes a catalyst layer 15 made of alumina or the like containing an active metal species formed on the inner surface of a cell 11e of a carrier 14 made of cordierite ceramic or the like formed in a lattice (honeycomb) shape as shown in FIG. Have been.

As another form of the monolith catalyst, there is a catalyst structure made of a solid catalyst that maintains a shape by adding a binder to a catalyst material and binding the catalyst material without using a carrier that hinders gas penetration. The structure of the solid catalyst is usually manufactured by extrusion. NOx in exhaust gas by the catalyst structure as described above
In the case of reducing and removing, it is necessary to mix a reducing agent (reducing component) into a gas to be purified such as exhaust gas,
As the reducing agent, unburned HC (hydrocarbon) discharged from the combustion chamber of the internal combustion engine or fuel injected and supplied into the exhaust pipe is used. Depending on the catalyst component, C or C is used.
O may be used in some cases.

When the gas to be purified containing the reducing agent passes through each cell (gas flow hole) of the catalyst structure and comes into contact with the active component of the catalyst, the chemical reaction between NOx and the reducing agent is promoted, and NOx is reduced. Is reduced to N2, so that the gas is purified. The overall diameter and length of the catalyst structure are adjusted so that a contact area with the catalyst component commensurate with the flow rate of the gas to be purified can be obtained while taking into account the flow pressure loss and the like when disposing the catalyst. It is manufactured by setting the number and the size and number of flow holes (cells).

[0007]

However, even if the dimensions of the catalyst structure are set as described above, the purification performance as expected cannot be obtained, and the purification performance decreases relatively early.
In addition, there is a problem that clogging occurs. One of the causes is that the gas does not enter the catalyst layer 15 on the downstream side, and the catalytic action is not performed efficiently. That is, the passing gas generally enters the catalyst structure 11 at a high temperature, is cooled in the flow hole 12 and gradually decreases in volume, but the gas flow hole 12 is formed into a cylindrical shape having a constant passage cross-sectional area. As a result, the gas pressure decreases on the downstream side. Even if the gas temperature does not decrease, the gas pressure decreases on the downstream side due to gas flow resistance. Therefore, the gas is less likely to sneak into the catalyst layer 15 on the downstream side, and the catalytic action in this portion is reduced.

[0008] Another cause is considered to be a shortage of reducing agent on the downstream side. That is, as shown in FIG. 7, the gas flow flowing into the flow hole 12 is substantially layered with respect to the wall surface (catalyst layer) 15 of the flow hole 12, that is, in the case of a cylinder, the gas flow is like a concentric straw shape. Ga, G
b and Gc. Therefore, most of the reducing agent such as HC in the gas flow portion Ga in contact with the catalyst layer 15 of the flow hole 12 is consumed on the upstream side near the inlet 12a of the flow hole 12,
Since the gas flow portion Ga directly flows downstream along the wall surface, the reducing agent runs short on the downstream side, and almost no reduction reaction occurs.

On the other hand, the central portion Gc of the gas stream containing the unreacted reducing agent flows to the outlet 12b side almost without contacting the catalyst layer. It does not contribute to the reduction reaction on the side and is exhausted wastefully, leading to gas pollution by the reducing agent and deterioration of fuel efficiency. Further, in order to promote a downstream reduction reaction, HC
Even if a large amount of a reducing agent such as is supplied, the concentration of the reducing agent becomes excessive on the upstream side of the catalyst structure 11, thereby lowering the catalytic activity, and the reducing agent adheres to the inner surface of the flow hole 12 and precipitates. As a result, precipitated carbon (caulking) 3 is generated, and the amount of the reducing agent in the gas is reduced by the precipitation of the carbon, so that the reducing agent remains insufficient on the downstream side.

[0010] Further, as shown in FIG.
The gas adheres and grows on the wall surface on the inlet 12a side, so that the gas is prevented from contacting the active component of the catalyst layer 15 upstream of the catalyst structure 11, so that the reduction reaction is further reduced. In addition, since the passage of the gas itself is hindered by the clogging of the flow holes 12, the contact with the catalyst layer 15 is further reduced, and the catalyst structure 11
As a result, the reduction reaction as a whole becomes inactive, and the purification performance as expected cannot be obtained.

In general, as the cross-sectional area of the gas flow holes 12 is reduced, the contact area of the catalyst layer 15 is increased, but the pressure loss during the flow is increased and clogging is liable to occur. In addition, there is a problem that manufacturing becomes difficult. These phenomena occur in the same manner in the honeycomb catalyst and the solid catalyst, so that the same problem occurs in the solid catalyst device.

In addition, since the structure of the solid catalyst is manufactured by extrusion molding that pressurizes the catalyst raw material, there is a problem that the gap between the catalyst layers is crushed by the pressurization, and the gas squeezing effect is reduced. Furthermore, extrusion molding has a problem that the shape that can be molded is limited, and the diameter, shape, arrangement, and the like of the flow holes in the catalyst structure are limited. The present invention has been made in order to solve the above-described problem, and an object of the present invention is to form a shape of a flow hole of a gas to be purified into a special shape, so that a gas to be purified and a reducing agent or an oxidizing agent are formed. It is an object of the present invention to provide a catalyst structure capable of efficiently contacting an active component of a catalyst, promoting a chemical reaction such as reduction or oxidation, and efficiently purifying a purification target gas.

Another object of the present invention is to provide a method for easily producing the catalyst structure of the first object.

[0014]

A catalyst structure for achieving the above-mentioned object has a large number of gas flow holes provided substantially in parallel at predetermined intervals, and an inner periphery of the gas flow hole. In a gas purifying catalyst structure having a catalyst layer formed on its surface,
The gas flow hole is formed in a tapered shape in which the passage cross-sectional area is reduced from the inlet portion to the outlet portion, and the gas flow is maintained by maintaining the gas pressure in the entire flow hole or gradually increasing the pressure toward the downstream side. In addition to promoting the effect of infiltration of the gas into the catalyst layer in the entire area of the hole, a flow toward the central axis of the flow passage hole is generated to disturb the flow of the passing gas, and the entire passing gas is substantially uniformly exposed to the catalyst component. Thus, the gas and the reducing agent (or the oxidizing agent) can be efficiently brought into contact with the catalyst component in the entire catalyst structure to promote the chemical reaction.

Preferably, the gas flow holes are formed such that the cross-sectional hole diameter of the inlet portion is 1 to 3 mm and the cross-sectional hole diameter of the outlet portion is 0.8 to 1.5 mm. By forming the catalyst structure with a solid catalyst, the wall of the carrier (honeycomb) that prevents the purification target gas from sneaking into the catalyst is omitted, the effect of escaping the passing gas is increased, and the catalytically active component is increased. Increase contact with

Further, a cylindrical female mold which forms the outer peripheral surface of the catalyst structure by enclosing the catalyst raw material of the catalyst structure, and is inserted and arranged below the female mold, and the gas flow through the substrate is carried out. A preparation step of assembling a molding die with a male mold in which needle-shaped projections for forming holes are arranged at the predetermined intervals, a step of adding a binder to a catalyst raw material and kneading the mixture to form a sol, A step of pouring into a molding die, and inserting a carrier having a number of parallel through holes disposed with a gap between the needle-like projections into the sol-like kneaded material in the molding die. A step of drying and solidifying the sol-state kneaded material in the molding die, and a step of forming the catalyst structure by decomposing the molding die after the drying and solidification to release the mold, A honeycomb catalyst structure is manufactured.

Also, a cylindrical female mold enclosing the catalyst raw material of the catalyst structure and forming the outer peripheral surface of the catalyst structure, and inserted and disposed below the female mold, and the gas flow A preparation step of assembling a molding die with a male mold in which needle-shaped projections for forming holes are arranged at the predetermined intervals, a step of adding a binder to a catalyst raw material and kneading the mixture to form a sol, A step of pouring into a mold, a step of drying and solidifying the sol-like kneaded material in the mold, and a step of forming the catalyst structure by decomposing the mold after punching and drying and solidifying. The catalyst structure formed of the solid catalyst is manufactured by the following manufacturing method.

By employing these manufacturing methods,
The diameter and the shape of the hole of the gas passage of the catalyst structure can be relatively freely formed, and the catalyst structure having the special shape described above can be easily manufactured. In addition, since there is no pressing step at the time of manufacture, the gap in the catalyst layer can be prevented from being collapsed, so that the gas to be purified is more easily sunk, and the contact with the catalytically active component is increased, thereby improving the purification performance of the catalyst structure. I do.

Further, specific examples of the catalyst raw material include:
Platinum (P), which is a catalytically active component, is added to alumina (Al2 O3).
t) is carried out in the form of a powder and the sol is added to the powder, and a binder containing silicon dioxide (SiO2) as a main component is added thereto. Instead, the catalyst raw material may be a generally known one, and the binder may be freely selected and used, such as an alumina-based or resin-based binder, corresponding to the catalyst raw material to be used. Further, the present invention can be applied not only to a reducing agent such as HC, but also to a catalyst raw material to which another reducing agent is added.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a catalyst structure according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, a catalyst structure according to an embodiment of the present invention is a catalyst structure 1 or 1A having a cylindrical outer shape, and is provided substantially in parallel with a predetermined interval therein. Many gas circulation holes 2
The gas Gin to be purified is taken in from the inlet 2a at one end of the gas flow hole 2, and the gas is catalyzed inside the gas flow hole 2 to be purified gas Gout from the outlet 2b at the other end. And then, as shown in FIG.
The catalyst structure 1 is formed such that the cross-sectional area of the gas flow hole 2 formed by the catalyst component 5 supported on the support 4 is reduced from the inlet 2a toward the outlet 2b. Or,
As shown in FIG. 3, a catalyst structure 1A made of a solid catalyst in which a wall of a carrier (honeycomb) that hinders the gas infiltration effect is removed is used, and the cross-sectional area of the gas flow hole 2 is changed from the inlet 2a to the outlet 2b. It is formed so as to shrink toward.

The shape of the flow hole 2 may be not only a conical shape with a cut end but also a polygonal pyramid such as a square pyramid with a cut end. According to the catalyst structures 1 and 1A having the gas flow holes 2 having this shape, the following effects can be obtained. By forming the passage cross-sectional area of the gas flow holes 2 of the catalyst structures 1 and 1A into a tapered shape that is reduced from the inlet 2a side to the outlet 2b side, the passing gas is cooled in the gas flow holes 2 to reduce the volume. However, since the gas pressure can be maintained in the entire flow hole 2 or gradually increased toward the downstream side, the gas infiltration S into the catalyst component 5 can be promoted in the entire flow hole 2.

Further, since the gas flow hole 2 is formed in a tapered shape which decreases toward the outlet 2b, a flow in the direction R perpendicular to the central axis of the gas flow hole 2 is generated, and concentric circles of the passing gas are generated. Can disturb the layered flow of
The entire passing gas can be almost uniformly exposed to the catalyst component 5. The gas and reducing agent can be efficiently exposed to the catalyst component 5 by the above-described sneaking effect and mixing effect, so that it is not necessary to add an excessive reducing agent, and the coking by suppressing the carbon deposition reaction from the reducing agent is suppressed. Can be prevented, and clogging near the entrance 2a can be prevented. Therefore, a gas passage can be secured, and the gas and the reducing agent can flow from the inlet 2a to the outlet 2b, so that the reducing agent can be uniformly added to the catalyst component 5, and the gas flow can be reduced. The reduction reaction can be efficiently performed in the entire area of the hole 2.

Accordingly, in the entire catalyst structure 1, 1A, the mixture of the passing gas and the reducing agent can be efficiently brought into contact with the catalyst component 5 to promote the chemical reaction by the catalytic action, so that the purification performance for the passing gas can be remarkably improved. Can be improved.
Further, since the exhaust gas and the reducing agent can be brought into contact with the active component of the catalyst almost equally, the poisoning substances such as SOx and CO contained in the exhaust gas also have the same effect on the catalyst structures 1, 1A. Since it can be dispersed throughout, it is possible to suppress a decrease in the catalytic action due to the poisoning substance.

In addition, in the case of exhaust gas treatment of automobiles, fuel efficiency can be improved because fuel as a reducing agent can be efficiently used. Further, the gas flow holes 2 of the catalyst structures 1 and 1A are formed to have an inlet hole diameter of about 3 to 1 mm and an outlet hole diameter of about 1.5 to 0.8 mm. When used in a diesel engine, the diameter of the outlet hole is set to about 1 mm to prevent the gas flow hole 2 from being clogged.

By forming the gas flow holes 2 to this size, the gas which can sufficiently obtain the effect of sneaking into the catalyst component 5 can be obtained while maintaining the relationship between the gas flow rate and the total pressure loss of the gas flow holes 2 in an appropriate range. By realizing the pressure distribution, the contact between the exhaust gas, the reducing agent, and the catalyst component 5 can be favorably maintained in the entire region of the gas flow hole 2, and the catalytic action can be efficiently exhibited.

Then, the catalyst structure 1 is formed with the solid catalyst.
By forming A, it is possible to omit the carrier that hinders the gas spill-in effect, so that the gas spill-in effect in the catalyst can be further increased and the purification efficiency can be significantly improved. Next, a method for manufacturing the above-described catalyst structures 1 and 1A will be described below with reference to FIGS.

First, in the case of the catalyst structure 1 having the carrier 4, as a preparation step, a cylindrical female mold 21 including the catalyst raw material of the catalyst structure 1 and forming the outer peripheral surface of the catalyst structure 1 is formed. ,
The molding die 20 is assembled with the male die 22 which is inserted and arranged below the female die 21 and has needle-like projections for forming the gas flow holes 2 arranged on the substrate at predetermined intervals. Next, a certain ratio of a liquid binder is added to the sol-shaped catalyst raw material, mixed well, and kneaded,
As shown in FIG. 4 (a), this sol-form catalyst raw material 5a is
From the pouring passage 23, the sol-like kneaded material 5a in the mold 20 is poured into the mold 20 as shown in FIG.
After the carrier 4 having a large number of parallel through holes disposed with a gap between the needle-like projections is inserted therein, the sol-like kneaded material 5a in the mold 20 is heated by the heater 30. To evaporate the water to dry and solidify.

Then, as shown in FIG. 4C, after drying and solidification, the male mold 22 is pulled out from the female mold 21 and the solidified catalyst structure 1 is removed. Further, depending on the shape of the catalyst structure 1, the catalyst structure 1 may be extruded by pushing the male mold 22 upward. Then, as necessary, as shown in FIG. 4D, the surplus member 7 is cut off along the cut line 8 to manufacture the catalyst structure 1.

That is, the catalyst portion 5 is manufactured by a die-cutting molding method utilizing only the adhesive force of a binder or the like without performing extrusion molding in which a gap is crushed by pressing the catalyst portion 5. In the case of the catalyst structure 1A of the solid catalyst, the forming die 20 is assembled in the same manner as above in preparation. Then, a certain ratio of a liquid binder is added to the sol-shaped catalyst raw material, and the mixture is sufficiently stirred and kneaded.
As shown in (a), the sol-like kneaded material 5a in the molding die 20 is heated by the heater 30 to evaporate the moisture and solidify by drying.

Next, as shown in FIG. 5B, after being dried and solidified, the female mold 21 and the male mold 22 are decomposed to remove the solidified catalyst structure 1A. Then, if necessary, as shown in FIG. 5C, the surplus member 7 is cut off along the cut line 8 to manufacture the catalyst structure 1. The following effects can be obtained by these manufacturing methods. That is, since the catalyst structures 1 and 1A can be manufactured while maintaining the gap of the catalyst portion 5 without being crushed, the gas sunk effect can be further improved, the gas sunk ability is high, and the contact area of the catalyst with the active component is reduced. Large catalyst structures 1 and 1A can be obtained.

Further, the diameter and shape of the gas flow holes 2 of the catalyst structures 1 and 1A can be relatively freely formed.
The catalyst structures 1 and 1A having the special shapes as described above can be easily manufactured.

[0032]

As described above, according to the present invention, the passage cross-sectional area of the gas flow hole of the catalyst structure is formed in a tapered shape decreasing from the inlet to the outlet.
The gas pressure can be maintained in the entire flow hole or the pressure can be gradually increased toward the downstream side, and the effect of gas sneaking into the catalyst layer can be promoted in the entire flow hole.

Further, since the gas flow passage is formed in a tapered shape which is reduced toward the outlet side, a flow toward the central axis of the gas flow hole can be generated to disturb the flow of the passing gas. In addition, the entire passing gas can be substantially uniformly exposed to the catalyst layer. Therefore, the gas and the reducing agent (or the oxidizing agent) can be efficiently brought into contact with the catalyst component in the entire catalyst structure, and the chemical reaction can be promoted. Therefore, the purification performance of the catalyst structure is improved, and the purification target gas is improved. Can be efficiently purified. Moreover, since the chemical reaction can be efficiently promoted, the reducing agent can be used effectively.

By forming the above-mentioned catalyst structure with a solid catalyst, the wall of the carrier (honeycomb) can be omitted, so that the effect of the gas sneaking into the catalyst can be further increased and the purification efficiency can be further improved. it can. In addition, by adopting a manufacturing method based on a die-cutting molding method in which molding is performed by utilizing the adhesive force of a binder or the like, a catalyst structure having a special shape as described above can be easily manufactured. Since there is no pressure step and the gap of the catalyst layer can be prevented from being crushed, the effect of gas sneaking into the catalyst layer can be largely maintained, and the contact between the gas, the reducing agent and the catalytically active component can be increased. The gas purification performance of the body can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a catalyst structure according to the present invention.

FIG. 2 is a side sectional view showing a flow hole portion of the catalyst structure according to the present invention.

FIG. 3 is a side sectional view showing a flow hole portion of a catalyst structure using a solid catalyst according to the present invention.

FIG. 4 is a side sectional view showing a method for producing a catalyst structure according to the present invention, wherein (a) shows a state where a catalyst material is packed in a mold;
(B) shows a state in which the carrier is inserted, (c) shows a state in which the carrier is cut out, and (d) shows a state in which the surplus member is cut.

FIGS. 5A and 5B are side sectional views showing a method for producing a catalyst structure using a solid catalyst according to the present invention, wherein FIG. 5A shows a state in which a catalyst material is packed in a mold material, FIG. ,
(C) shows the state where the surplus member was cut.

FIG. 6 is a perspective view showing a catalytic converter having a catalyst structure.

FIG. 7 is a cross-sectional view showing a cell portion of a conventional catalyst structure.

FIG. 8 is a schematic diagram showing the state of soot and carbon deposits in a cell portion of a conventional catalyst structure.

[Explanation of symbols]

1, 1A, 11 Catalyst structure 1e, 11e Cell 2 Gas flow hole (flow passage) 2a Inlet 2b outlet 3 Soot and deposited carbon 4 Carrier (support) 5 Catalyst layer 7 Surplus member 8 Cut line 20 Mold 21 Female 22 Male type 23 Inflow passage 30 Heater 31 Exhaust temperature sensor C Catalytic converter Gin Purified gas Gout Purified gas S Sink

Claims (5)

[Claims] 1. A gas purification catalyst structure having a plurality of gas flow holes provided substantially in parallel at predetermined intervals and having a catalyst layer formed on an inner peripheral surface of the gas flow holes. A catalyst structure in which a flow hole is formed in a tapered shape in which a passage cross-sectional area decreases from an inlet to an outlet. 2. The gas flow hole according to claim 1, wherein a diameter of a cross section of an inlet portion is 1 to 3 mm, and a diameter of a cross section of the outlet portion is 0.
The catalyst structure according to claim 1, wherein the catalyst structure is formed to have a thickness of 8 to 1.5 mm. 3. The catalyst structure according to claim 1, wherein the catalyst structure is formed of a solid catalyst. 4. A cylindrical female mold that includes a catalyst material of the catalyst structure and forms an outer peripheral surface of the catalyst structure, and is inserted and arranged below the female mold, and the gas flow through the substrate. A preparation step of assembling a molding die with a male mold in which needle-shaped projections for forming holes are arranged at the predetermined intervals, a step of adding a binder to a catalyst raw material and kneading the mixture to form a sol, A step of pouring into a molding die, and inserting a carrier having a number of parallel through holes disposed with a gap between the needle-like projections into the sol-like kneaded material in the molding die. A step of drying and solidifying the sol-like kneaded material in the molding die; and a step of disassembling the molding die after the drying and solidifying to form a die and molding the catalyst structure. 3. The method for producing a catalyst structure according to item 2. 5. A cylindrical female mold that forms the outer peripheral surface of the catalyst structure by enclosing the catalyst raw material of the catalyst structure, and is inserted and arranged below the female mold, and the gas flow through the substrate. A preparation step of assembling a molding die with a male mold in which needle-shaped projections for forming holes are arranged at the predetermined intervals, a step of adding a binder to a catalyst raw material and kneading the mixture to form a sol, A step of pouring into a mold, a step of drying and solidifying the sol-like kneaded material in the mold, and a step of forming the catalyst structure by decomposing the mold after punching and drying and solidifying. The method for producing a catalyst structure according to claim 3.