WO2021075276A1 - Catalyst for purification of exhaust gas - Google Patents

Abstract

The present invention provides a catalyst that is for purifying exhaust gas and that comprises a substrate and a catalyst layer provided on the substrate. The catalyst layer contains silver, and an AlTi-containing oxide containing elemental aluminum and elemental titanium. When the AlTi-containing oxide is observed using a transmission electron microscope (observation magnification: x2,000,000), and elemental mapping is performed by energy-dispersive X-ray spectroscopy, the elemental titanium is detected, and the ratio (S_Al/S_{Al, Ti}) of the area (S_Al) of the elemental aluminum with respect to the total area (S_{Al, Ti}) of the elemental aluminum and the elemental titanium is 0.85 or more.

Description

Exhaust gas purification catalyst

The present invention relates to a catalyst for purifying exhaust gas. More specifically, the present invention relates to an exhaust gas purification catalyst that is arranged in an exhaust path of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine.
This application claims priority based on Japanese Patent Application No. 2019-190810 filed on October 18, 2019, and the entire contents of the application are incorporated herein by reference. There is.

Exhaust gas emitted from internal combustion engines such as vehicles contains harmful components such as nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO). In order to efficiently react and remove these harmful components from the exhaust gas, an exhaust gas purification catalyst has been conventionally used. Patent documents 1 to 3 are mentioned as prior art documents related to exhaust gas purification.

For example, Patent Document 1 discloses an exhaust gas purification system provided with an SCR catalyst (Selective Catalytic Reduction) effective for purifying NOx. The exhaust gas purification system disclosed in Patent Document 1 includes an SCR catalyst and a fuel addition device provided on the upstream side in the exhaust gas flow direction with respect to the SCR catalyst and spraying atomized fuel (HC) on the exhaust gas. I have. In the exhaust gas purification system of Patent Document 1, a partial oxide of HC (for example, HCO) is produced from the fuel sprayed by the fuel addition device. The produced partial oxide functions as a reducing agent for purifying NOx. That is, when the partial oxide reacts with NOx in the exhaust gas on the SCR catalyst, NOx is converted into nitrogen and water, and the exhaust gas is purified.

Japanese Patent Application Publication No. 2016-17495 Japanese Patent Application Publication No. 2007-7607 Japanese Patent Application Publication No. 2005-28271

As described above, the SCR catalyst uses a partial oxide of HC as a reducing agent. However, according to the studies by the present inventors, the amount of fuel that is completely oxidized increases in a high temperature environment (for example, in an environment of 400 ° C. or higher, particularly 450 ° C. or higher). As a result, the amount of partial oxide produced may decrease, and the SCR catalyst may run out of reducing agent. When the activity of the SCR catalyst is lowered due to this, for example, as can be seen from the test example of Patent Document 1, there is a problem that the purification performance of NOx deteriorates in a high temperature environment.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purification catalyst having improved NOx purification performance in a high temperature environment.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided an exhaust gas purification catalyst which is arranged in an exhaust path of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine. The exhaust gas purification catalyst includes a base material and a catalyst layer arranged on the base material. The catalyst layer contains silver and an AlTi-containing oxide containing an aluminum element and a titanium element. When the AlTi-containing oxide was observed with a transmission electron microscope (TEM, observation magnification 2 million times) and elemental mapping was performed by energy dispersive X-ray analysis (EDS), the titanium element was detected and TEM. -In the EDS image, the ratio (S _Al / S _{Al, Ti} ) of the area (S _Al ) of the aluminum element to the total area (S _{Al, Ti} ) of the aluminum element and the titanium element is 0.85 or more. is there.

The above ratio (S _Al / S _{Al, Ti} ) is a variable in the range of 0 to 1, and is one index showing the distribution state of Ti elements. The above ratio (S _Al / S _{Al, Ti} ) indicates that the closer the value is to 1, the higher the probability that the Ti element is at the same position as the Al element (exists in an overlapping manner). Further, the farther the value is from 1 (smaller), the more the Ti element is at a different position from the Al element (exists separately). By setting the above ratio (S _Al / S _{Al, Ti} ) to a predetermined value or more, the effect of containing the Ti element can be fully exhibited. As a result, the NOx purification performance in a high temperature environment (for example, an environment of 400 ° C. or higher, particularly 450 ° C. or higher) can be improved.

In a preferred embodiment, the ratio (S _Al / S _{Al, Ti} ) is 0.9 or more. Thereby, the NOx purification performance in a high temperature environment can be further improved.

In a preferred embodiment, when the total amount of the AlTi-containing oxide is 100% by mass, the ratio of the titanium element in terms of oxide is 0.1% by mass or more. As a result, the above ratio (S _Al / S _{Al, Ti} ) can be easily adjusted to 0.9 or more, and the NOx purification performance in a high temperature environment can be further improved.

In a preferred embodiment, when the total amount of the AlTi-containing oxide is 100% by mass, the ratio of the titanium element in terms of oxide is 5% by mass or less. Thereby, the NOx purification performance in a high temperature environment can be further improved.

In a preferred embodiment, when the AlTi-containing oxide is measured by an X-ray diffraction method, a diffraction peak derived from the titanium element is not detected. Thereby, the NOx purification performance in a high temperature environment can be further improved.

In a preferred embodiment, the oxide-equivalent content ratio of the titanium element is 0.1% by mass or more and 5% by mass or less, assuming that the entire catalyst layer is 100% by mass. As a result, the amount of partial oxides produced can be efficiently increased in a high temperature environment, and the NOx purification performance can be further improved.

Further, according to the present invention, an exhaust gas purification system provided with the exhaust gas purification catalyst and a supply mechanism for supplying hydrocarbons to the exhaust gas on the upstream side in the exhaust gas flow direction with respect to the exhaust gas purification catalyst is provided. Will be done. The internal combustion engine can be a diesel engine. This exhaust gas purification system has excellent heat resistance and sulfur resistance. Therefore, excellent NOx purification performance can be exhibited even in a high temperature environment. In addition, the catalytic activity can be maintained for a long period of time even when exposed to exhaust gas containing a sulfur component.

Further, according to the present invention, there is provided a method for manufacturing an exhaust gas purification catalyst which is arranged in an exhaust path of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine. In the above-mentioned production method, an AlTi-containing compound produced by an alkoxide method in which an aluminum alkoxide and a titanium alkoxide are hydrolyzed is prepared, and a silver element source and the above-mentioned AlTi-containing compound are applied to a base material and fired. Including what to do. According to this method, an exhaust gas purification catalyst having excellent NOx purification performance in a high temperature environment can be suitably produced.

FIG. 1 is a schematic view of an exhaust gas purification system according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing the second catalyst. FIG. 3 is a partial cross-sectional view of the second catalyst cut in the tubular axis direction. FIG. 4A is an XRD chart of Comparative Example 1, Example 2, and Example 3. FIG. 4B is an enlarged view in the range of 2θ = 20 to 30 °. FIG. 5 is a TEM-EDS image of Example 2. FIG. 6A is a TEM-EDS image of Comparative Example 4. FIG. 6B is a red separated image obtained by RGB separation. FIG. 6C is a binary image when calculating _{the area S Al of the Al element.} FIG. 6D is a monochrome image obtained by monochrome imaging. FIG. 6E is a binary image when calculating _{the total area S Al and Ti} of the Al element and the Ti element. FIG. 7 is _{a graph showing the relationship between the TiO 2} content ratio and the NOx purification rate. FIG. 8 is a graph showing the relationship between the Al—Ti distribution coefficient and the NOx purification rate. FIG. 9 is a graph showing the relationship between the durability time and the NOx purification rate. FIG. 10 is a graph showing the amount of sulfur deposited after 100-hour endurance.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. Further, in the following drawings, members / parts having the same action may be designated by the same reference numerals, and duplicate description may be omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in each figure do not necessarily reflect the actual dimensional relationships. Further, in the present specification, the notation of "A to B" (A and B are arbitrary numerical values) indicating the range means "preferably larger than A" and "preferably smaller than B" with the meaning of A or more and B or less. Including the meaning of.

≪Exhaust gas purification system≫
FIG. 1 is a schematic view of an exhaust gas purification system 1. The exhaust gas purification system 1 includes an internal combustion engine (engine) 2, an exhaust gas purification device 3, and an engine control unit (ECU) 4. The exhaust gas purification system 1 is configured to purify harmful components such as NOx, HC, and CO contained in the exhaust gas discharged from the internal combustion engine 2 by the exhaust gas purification device 3. The exhaust gas purification system 1 is configured to purify NOx in the exhaust gas mainly by the HC (hydrocarbon) -SCR (selective catalytic reduction) method. Unlike the urea SCR method, the exhaust gas purification system 1 of the present embodiment does not have a tank for storing a reducing agent such as ammonia or urea water. Therefore, it is compact and has excellent mountability and mountability. The arrow in FIG. 1 indicates the flow direction of the exhaust gas. Further, in the following description, the side close to the internal combustion engine 2 is referred to as an upstream side, and the side away from the internal combustion engine 2 is referred to as a downstream side along the flow of exhaust gas.

The internal combustion engine 2 of the present embodiment is mainly composed of a diesel engine of a vehicle. However, the internal combustion engine 2 may be an engine other than a diesel engine, for example, an engine mounted on a gasoline engine of a vehicle or a hybrid vehicle. The internal combustion engine 2 includes a plurality of combustion chambers (not shown). Each combustion chamber is connected to a fuel tank (not shown). Diesel fuel (light oil) is stored in the fuel tank of this embodiment. However, the fuel stored in the fuel tank may be gasoline or the like. In the combustion chamber, the fuel gas supplied from the fuel tank is burned. The combustion chamber communicates with the exhaust port 2a. The exhaust port 2a communicates with the exhaust gas purification device 3. The burned fuel gas becomes exhaust gas and is discharged to the exhaust gas purification device 3.

The exhaust gas purification device 3 includes an exhaust path 5 communicating with the internal combustion engine 2, a fuel supply mechanism 6, a pressure sensor 8, a first catalyst 9, and a second catalyst 10. The exhaust path 5 is an exhaust gas channel through which exhaust gas flows. The exhaust path 5 of the present embodiment includes an exhaust manifold 5a and an exhaust pipe 5b. The upstream end of the exhaust manifold 5a is connected to the exhaust port 2a of the internal combustion engine 2. The end on the downstream side of the exhaust manifold 5a is connected to the exhaust pipe 5b. The first catalyst 9 and the second catalyst 10 are arranged in the middle of the exhaust pipe 5b in order from the upstream side.

The first catalyst 9 may be the same as the conventional one, and is not particularly limited. The first catalyst 9 is, for example, a diesel particulate filter (DPF: Diesel Particulate Filter) that removes PM contained in exhaust gas; a diesel oxidation catalyst (DOC: Diesel Oxidation Catalyst) that purifies HC and CO contained in exhaust gas; exhaust gas. A three-way catalyst that simultaneously purifies NOx, HC, and CO contained in the fuel; stores NOx during normal operation (under lean conditions) and reduces HC and CO when injecting a large amount of fuel (under rich conditions). It may be a NOx adsorption reduction (NSR: NOx Storage-Reduction) catalyst that purifies NOx. The first catalyst 9 may have a function of raising the temperature of the exhaust gas flowing into the second catalyst 10, for example. The first catalyst 9 is not an essential configuration and may be omitted.

The second catalyst 10 is an SCR catalyst. The second catalyst 10 is an example of the exhaust gas purification catalyst disclosed herein. The configuration of the second catalyst 10 will be described in detail later. The arrangement of the first catalyst 9 and the second catalyst 10 may be arbitrarily variable. Further, the number of the first catalyst 9 and the second catalyst 10 is not particularly limited, and a plurality of each may be provided. For example, the first catalyst 9 may be provided with DOC and DPF in order from the upstream side. Further, a third catalyst (not shown) may be further arranged on the downstream side of the second catalyst 10.

The fuel supply mechanism 6 is a mechanism that directly injects diesel fuel into the exhaust gas. The fuel supply mechanism 6 includes a pressurizing section 6a, a flow path 6b, and a discharging section 6c. The pressurizing unit 6a pressurizes the diesel fuel and supplies it to the discharge unit 6c. The pressurizing unit 6a is, for example, a pressurizing pump. The pressurizing unit 6a is connected to a fuel tank (not shown) of diesel fuel used in the internal combustion engine 2. The pressurizing unit 6a is electrically connected to the ECU 4. The flow path 6b communicates the diesel fuel tank with the discharge portion 6c. The flow path 6b is, for example, a easily deformable tube. The discharge portion 6c is provided on the upstream side of the second catalyst 10. The discharge unit 6c is electrically connected to the ECU 4. The discharge unit 6c injects the diesel fuel pressurized by the pressurizing unit 6a in the form of mist. As a result, diesel fuel is mixed with the exhaust gas. Exhaust gas mixed with diesel fuel is circulated through the second catalyst 10 located on the downstream side of the discharge portion 6c of the exhaust path.

The ECU 4 controls the internal combustion engine 2 and the exhaust gas purification device 3. The ECU 4 is electrically connected to the internal combustion engine 2 and the exhaust gas purification device 3. The ECU 4 is electrically connected to, for example, a pressurizing portion 6a and a discharging portion 6c of the fuel supply mechanism 6 and sensors (for example, a pressure sensor 8) installed at each portion of the exhaust gas purification device 3. .. The configuration of the ECU 4 may be the same as the conventional one, and is not particularly limited. The ECU 4 is, for example, a processor or an integrated circuit. The ECU 4 includes an input port (not shown) and an output port (not shown). The ECU 4 receives, for example, information such as the operating state of the vehicle, the amount of exhaust gas discharged from the internal combustion engine 2, the temperature of the exhaust gas, the pressure of the exhaust gas, and the like via the input port. The ECU 4 receives the information detected by the sensor (for example, the pressure measured by the pressure sensor 8) via the input port.

The ECU 4 transmits a control signal via the output port, for example, based on the received information. The ECU 4 controls operations such as fuel injection control, ignition control, and intake air amount adjustment control of the internal combustion engine 2. The ECU 4 controls the drive and stop of the exhaust gas purification device 3 based on, for example, the operating state of the internal combustion engine 2. The ECU 4 controls the pressurizing unit 6a and the discharge unit 6c based on information such as the amount of exhaust gas discharged from the internal combustion engine 2, and adjusts the discharge of diesel fuel, for example, the discharge amount and the discharge timing. For example, when the exhaust gas discharged from the internal combustion engine 2 is the first exhaust gas amount, the pressurizing unit 6a is controlled so that the diesel fuel having the first discharge amount is discharged from the discharge unit 6c, and the internal combustion engine 2 controls the exhaust gas. When the exhaust gas discharged is a second exhaust gas amount larger than the first exhaust gas amount, the diesel fuel having a second discharge amount larger than the first discharge amount is pressurized so as to be discharged from the discharge unit 6c. The unit 6a is controlled.

FIG. 2 is a perspective view schematically showing the second catalyst 10. The arrow in FIG. 2 indicates the flow of exhaust gas. That is, in FIG. 2, the left side is the upstream side of the exhaust path 5 relatively close to the internal combustion engine 2, and the right side is the downstream side of the exhaust path relatively far from the internal combustion engine 2. Further, in FIG. 2, reference numeral X represents the axial direction of the second catalyst 10. The second catalyst 10 is installed in the exhaust path 5 so that the axial direction X is along the flow direction of the exhaust gas. In the following, of the tubular axis directions X, one direction X1 is referred to as an upstream side (also referred to as an exhaust gas inflow side and a front side), and the other direction X2 is referred to as a downstream side (also referred to as an exhaust gas outflow side and a rear side). Sometimes. However, this is merely a direction for convenience of explanation, and does not limit the installation form of the second catalyst 10 in any way.

The second catalyst 10 has a function of purifying NOx in the exhaust gas. The second catalyst 10 includes a base material 11 having a straight flow structure and a catalyst layer 20 (see FIG. 3). The end of one direction X1 of the second catalyst 10 is the exhaust gas inlet 10a, and the end of the other direction X2 is the exhaust gas outlet 10b. The outer shape of the second catalyst 10 of the present embodiment is a cylindrical shape. However, the outer shape of the second catalyst 10 is not particularly limited, and may be, for example, an elliptical cylinder shape, a polygonal cylinder shape, a pipe shape, a foam shape, a pellet shape, a fibrous shape, or the like.

The base material 11 constitutes the framework of the second catalyst 10. The base material 11 is not particularly limited, and various materials and forms used in conventional applications of this type can be used. The base material 11 may be, for example, a ceramic carrier composed of ceramics such as cordierite, aluminum titanate, and silicon carbide, stainless steel (SUS), Fe—Cr—Al alloy, and Ni—Cr—. It may be a metal carrier composed of an Al-based alloy or the like. As shown in FIG. 2, the base material 11 of the present embodiment has a honeycomb structure. The base material 11 includes a plurality of cells (cavities) 12 regularly arranged in the axial direction X, and a partition wall (rib) 14 for partitioning the plurality of cells 12. Although not particularly limited, the volume of the base material 11 (apparent volume including the volume of the cell 12) may be approximately 0.1 to 10 L, for example, 1 to 5 L. Further, the length (total length) of the base material 11 along the tubular axis direction X may be approximately 10 to 500 mm, for example, 50 to 300 mm.

Cell 12 serves as a flow path for exhaust gas. The cell 12 extends in the axial direction X. The cell 12 is a through hole that penetrates the base material 11 in the axial direction X. The shape, size, number, etc. of the cells 12 may be designed in consideration of, for example, the flow rate and components of the exhaust gas supplied to the second catalyst 10. The shape of the cross section of the cell 12 orthogonal to the tubular axis direction X is not particularly limited. The cross-sectional shape of the cell 12 is, for example, a rectangle such as a square, a parallelogram, a rectangle, or a trapezoid, or various geometric shapes such as other polygons (for example, a triangle, a hexagon, an octagon), a waveform, or a circle. You can. The partition wall 14 faces the cell 12 and separates the adjacent cells 12. Although not particularly limited, the thickness of the partition wall 14 (dimensions in the direction orthogonal to the surface; the same applies hereinafter) is approximately 10 to 500 μm from the viewpoint of improving mechanical strength and reducing pressure loss. For example, it may be 20 to 100 μm.

FIG. 3 is a partial cross-sectional view schematically showing a part of a cross section of the second catalyst 10 cut along the axial direction X. The catalyst layer 20 of the present embodiment is provided on the surface of the base material 11, specifically, on the partition wall 14. However, a part or all of the catalyst layer 20 may permeate the inside of the catalyst layer 20. The catalyst layer 20 of this embodiment has a single layer structure. The catalyst layer 20 is a porous body having a large number of communicating voids. The catalyst layer 20 is a place for purifying exhaust gas. The exhaust gas that has flowed into the second catalyst 10 comes into contact with the catalyst layer 20 while flowing in the flow path (cell 12) of the second catalyst 10. As a result, NOx in the exhaust gas is purified. For example, a partial oxide of HC (for example, HCO) is produced from the fuel injected from the discharge unit 6c. When this partial oxide reacts with NOx in the exhaust gas on the catalyst layer 20, NOx is reduced and converted to nitrogen.

The catalyst layer 20 is a reaction field that purifies NOx in the exhaust gas. The catalyst layer 20 of the present embodiment contains silver (Ag) and an AlTi-containing oxide. Silver is a catalytic metal for purifying NOx in exhaust gas. Silver is typically supported on the surface of AlTi-containing oxides. Silver is typically particulate. From the viewpoint of increasing the contact area with exhaust gas and reducing agents, silver has an average particle size (average value based on the number of particle sizes required by transmission electron microscope (TEM) observation) of approximately 1 to 15 nm. For example, it is preferably 10 nm or less, and further preferably 5 nm or less.

The AlTi-containing oxide contains an aluminum (Al) element, a titanium (Ti) element, and an oxygen element (O) as essential elements. The AlTi-containing oxide can function as a supporting material for supporting silver. AlTi-containing oxides are typically particulate. The AlTi-containing oxide is preferably an inorganic porous body having a large specific surface area. The AlTi-containing oxide may be composed of an Al element, a Ti element, and an oxygen element, and may further contain other elements. As an example, AlTi-containing oxides include alkaline earth metal elements such as magnesium (Mg) and calcium (Ca), transition metal elements such as iron (Fe), rare earth metal elements such as lanthanum (La), and silicon (Si). Etc. may be included.

The AlTi-containing oxide is a Ti-containing alumina composed mainly of the Al element (a component occupying the largest proportion in the mass ratio, preferably a component occupying 50% by mass or more; the same applies hereinafter) in terms of oxide. You may. Although not particularly limited, when the total amount of the AlTi-containing oxide is 100% by mass, the oxide-equivalent ratio of the Al element is approximately 80% by mass or more, typically 90% by mass or more, for example. It is preferably 95% by mass or more and approximately 99.99% by mass or less, typically 99.95% by mass or less, for example, 99.9% by mass or less. Further, when the total amount of AlTi-containing oxide is 100% by mass, the ratio of Ti element in terms of oxide (for example, _{the ratio as TiO 2} ) is approximately 0.01% by mass or more, typically 0. 05% by mass or more, for example 0.1% by mass or more, 0.2% by mass or more, approximately 20% by mass or less, typically 10% by mass or less, 7% by mass or less, for example 5% by mass or less, 1 It is preferable that it is mass% or less, 0.5 mass% or less, and 0.4 mass% or less.

The AlTi-containing oxide may have a crystal structure in which some Al elements constituting aluminum oxide (alumina) are substituted with at least a Ti element. However, when the Ti element is highly dispersed in the AlTi-containing oxide as described later, and when the proportion of the Ti element is as small as about 10% by mass or less, for example, 5% by mass or less, X-rays are emitted. It is difficult for a diffractometer (XRD: X-ray diffraction) to detect a diffraction peak derived from a Ti element, for example, a single Ti or a diffraction peak of a Ti-containing oxide such as _{TiO 2} or Al ₂ TiO _5. .. Therefore, even if the AlTi-containing oxide is analyzed by XRD, for example, only the diffraction peak of alumina can be detected, and the Ti element can be below the lower limit of detection.

The surface of AlTi-containing oxides is observed with a transmission electron microscope (TEM, observation magnification 2 million times), and elemental mapping is performed with Energy Dispersive X-ray Spectroscopy (EDS) to obtain TEM. -When the EDS image is analyzed, the following conditions: (1) Ti element is detected. That is, in the TEM-EDS image, the Ti element exceeds the lower limit of detection. (2) _{Al—Ti distribution represented by S Al} / S _{Al, Ti} (where S _Al is the area of the Al element, and S _{Al, Ti} is the total area of the Al element and the Ti element). The coefficient is 0.85 or more; all of them are satisfied. The detailed method for obtaining the Al—Ti distribution coefficient will be described later in the section of Test Example I. As the Al—Ti distribution coefficient, it is preferable to acquire and analyze TEM-EDS images at a plurality of points (for example, N = 5 or more) of the catalyst layer 20 and adopt the arithmetic mean value thereof.

The Al—Ti distribution coefficient is one index showing the distribution state of the Ti element with respect to the Al element. The Al—Ti distribution coefficient indicates that the closer the value is to 1, the higher the probability that the Ti element is in the same position as the Al element (exists), and the farther the value is from 1 (smaller), the higher the probability. It indicates that the Ti element is in a different position (exists separately) from the Al element. Although the detailed mechanism has not been clarified, the above ratio (S _Al / S _{Al, Ti} ) should be set to a predetermined value or more, in other words, the Ti element should be present at the same position as the Al element with a probability of a predetermined value or higher. Therefore, the catalytic activity of the catalyst layer 20 is improved, and excellent NOx purification performance can be realized in a high temperature environment. From the viewpoint of better improving the NOx purification performance in a high temperature environment, the Al—Ti distribution coefficient is preferably 0.9 or more, more preferably 0.93 or more, for example 0.95 or more. Further, the Al—Ti distribution coefficient may be less than 1, for example, 0.999 or less, 0.995 or less, and 0.99 or less.

Although not particularly limited, when the whole catalyst layer 20 is 100% by mass, the content ratio (supporting ratio) of Ag is approximately 0.1% by mass or more, typically 0.5% by mass. As mentioned above, for example, it is preferable that it is 1% by mass or more and 2% by mass or more and is approximately 10% by mass or less, typically 7% by mass or less, for example, 6% by mass or less and 5% by mass or less. Further, when the whole catalyst layer 20 is 100% by mass, the content ratio of the AlTi-containing oxide is approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more, and is approximately approximately 80% by mass or more. It is preferably 99.9% by mass or less, typically 99.5% by mass or less, for example, 99% by mass or less, 98% by mass or less.

Further, when the whole of the catalyst layer 20 is 100% by mass, the content ratio of Ti element in terms of oxide (for example, _{the content ratio as TiO 2} ) is approximately 0.01% by mass or more, typically 0. 0.05% by mass or more, for example 0.1% by mass or more, 0.2% by mass or more, approximately 20% by mass or less, typically 10% by mass or less, 7% by mass or less, for example 5% by mass or less, It is preferable that it is 1% by mass or less, 0.5% by mass or less, and 0.4% by mass or less. The oxide-equivalent content ratio of the Ti element is typically smaller than the Ag content ratio described above. However, the oxide-equivalent content ratio of the Ti element may be larger than the Ag content ratio. The ratio of the content ratio of Ti element to the content ratio of Ag (Ti / Ag) is approximately 0.05 or more, typically 0.01 or more, for example 0.015 or more, 0.03 or more, and is approximately 1. It may be .5 or less, typically 1.0 or less, for example 0.75 or less, and even 0.5 or less, 0.05 or less.

The catalyst layer 20 may be composed of silver and an AlTi-containing oxide. For example, depending on the intended use, the catalyst layer 20 may contain other optional components in addition to the silver and the AlTi-containing oxide. The catalyst layer 20 may be composed mainly of an AlTi-containing oxide. The catalyst layer 20 may contain a catalyst metal other than silver, which is known to function as an oxidation catalyst and / or a reduction catalyst in purifying exhaust gas. As an example, platinum group metals such as rhodium (Rh), palladium (Pd) and platinum (Pt), and transition metals such as Ti, iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) are available. Can be mentioned. These may be used individually by 1 type, and may be used in combination of 2 or more type.

Further, as another example, the catalyst layer 20 further contains a metal oxide other than the AlTi-containing oxide and a solid solution thereof, for example, as a supporting material on which the catalyst metal is supported or as a non-supporting material on which the catalyst metal is not supported. It may be. As an example, alumina without Ti element, rare earth metal oxides such as titanium oxide (titania), zirconium oxide (zirconia), silicon oxide (silica), cerium oxide (ceria), alkalis such as magnesium oxide (MgO, magnesia) earth metal oxides, and these solid solutions, for example, _CeO 2 -ZrO ₂ composite oxide containing ceria and zirconia, and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.

As another example, the catalyst layer 20 includes alkaline earth metal elements such as calcium (Ca) and barium (Ba), rare earth metal elements such as yttrium (Y), lanthanum (La), and neodymium (Nd), and NOx. It may contain a NOx adsorbent having a storage capacity or the like. In some embodiments, the catalyst layer 20 is preferably free of alkali metal elements such as sodium (Na) and potassium (K). Thereby, the production of silver oxide can be suppressed.

Although not particularly limited, the coating amount (molding amount) of the catalyst layer 20 is approximately 50 g or more, preferably 100 g or more, for example 200 g or more, per 1 L of the volume of the second catalyst 10 (volume of the base material 11). It may be approximately 500 g or less, preferably 300 g or less, for example 250 g or less. By satisfying the above range, it is possible to improve the NOx purification performance in a high temperature environment and reduce the pressure loss at a high level. In addition, in this specification, a "coating amount" means the mass of solid content contained in a unit volume.

The thickness and length of the catalyst layer 20 may be designed in consideration of, for example, the size of the cell 12 of the base material 11 and the flow rate of the exhaust gas supplied to the second catalyst 10. In some embodiments, the thickness of the catalyst layer 20 is approximately 1 to 500 μm, such as 5 to 200 μm, 10 to 100 μm. Further, the catalyst layer 20 may be provided over the entire length of the base material 11 in the tubular axis direction X, or approximately 20% or more of the total length of the base material 11 continuously or intermittently in the tubular axis direction X. For example, it may be provided in a portion corresponding to 50% or more, preferably 80% or more. As a result, the effects of the techniques disclosed herein can be exerted at a higher level.

The second catalyst 10 may include a plurality of (two or more layers) catalyst layers having different compositions and properties. In this case, at least one of them may satisfy the above-mentioned structure of the catalyst layer 20. The second catalyst 10 may include a catalyst layer other than the catalyst layer 20, a layer that is not a catalyst layer, for example, a layer that does not contain a catalyst metal. Further, the catalyst layer 20 in FIG. 3 has a single-layer structure, but the second catalyst 10 has a structure of two or more layers having another catalyst layer different from the catalyst layer 20 above or below the catalyst layer 20. You may. Further, the second catalyst 10 may include, for example, another catalyst layer different from the catalyst layer 20 in the axial direction X. In some embodiments, the second catalyst 10 may be provided with catalyst layers having different compositions for each portion of the base material 11, for example, on the upstream side X1 and the downstream side X2 in the axial direction X. In that case, the catalyst layer 20 may be in any portion. The catalyst layer 20 may be provided, for example, from the exhaust gas inflow port 10a along the tubular axis direction X, or may be provided from the exhaust gas outlet 10b along the tubular axis direction X.

≪Manufacturing method of catalyst for exhaust gas purification≫
Although not particularly limited, the second catalyst 10 is described in the following step: (step S1) preparation step of preparing the AlTi-containing compound; (step S2) catalyst layer forming step of forming the catalyst layer 20 on the base material 11. It can be produced by a method including; in this order. In one example, in the preparation step (step S1), for example, an AlTi-containing hydroxide produced by an alkoxide method is prepared. As long as the AlTi-containing hydroxide is produced by the alkoxide method, a commercially available product may be purchased. Alternatively, it may be prepared by itself by a method including the following steps: (step S1A) alkoxide preparation step; (step S1B) hydrolysis step; in this order. Hereinafter, each step will be described in order.

(Step S1A) In the alkoxide preparation step, aluminum alkoxide and titanium alkoxide are prepared as starting materials. As the aluminum alkoxide, for example, a compound represented by the following formula: Al (OR) ₃ (where R is an alkyl group); or a derivative thereof can be used. Examples of aluminum alkoxides include aluminum triethoxyde, aluminum trin-propoxide, aluminum triisopropoxide, aluminum trin-butoxide, aluminum triisobutoxide, and the like. As the titanium alkoxide, for example, a compound represented by the following formula: Ti (OR) ₄ (where R is an alkyl group); or a derivative thereof can be used. Examples of titanium alkoxides include titanium tetraethoxydo, titanium tetra n-propoxide, titanium tetraisopropoxide, titanium tetra n-butoxide, and the like.

Next, the aluminum alkoxide and the titanium alkoxide are mixed in a predetermined ratio to prepare a mixture of alkoxides. The mixing ratio of titanium alkoxide to aluminum alkoxide is appropriately adjusted so that the molar ratio is approximately 0.001 to 1, for example, 0.01 to 0.5, and the AlTi-containing oxide has the above-mentioned mass ratio. It is good to do. For example, the molar ratio of the Al element to the Ti element may be adjusted to be approximately 99.99 to 0.01 to 80:10, for example, 99.95: 0.05 to 90:10.

(Step S1B) In the hydrolysis step, first, a hydrophobic solvent is prepared. As the hydrophobic solvent, for example, benzene, cyclohexane, toluene, chloroform, carbon tetrachloride, 1,2-dichloroethane, and the like can be used. Next, typically, in a temperature environment of room temperature to below the boiling point of the solvent, the mixture of alkoxide prepared in step S1A and water are continuously supplied and stirred in the solvent. In the solvent, the alkoxide reacts with water and the alkoxide is hydrolyzed. As a result, AlTi hydroxide such as Ti-containing boehmite (alumina monohydrate, AlOOH) is precipitated in the solvent as a hydrolysis product. The AlTi hydroxide can be amorphous nanoparticles. AlTi hydroxides are typically particulate. Then, the precipitated AlTi hydroxide is separated from the solvent and dried to obtain the AlTi hydroxide as an AlTi-containing compound.

(Step S2) In the catalyst layer forming step, first, the base material 11 and the catalyst layer forming slurry for forming the catalyst layer 20 are prepared. The catalyst layer forming slurry contains a silver element source (for example, a solution containing silver ions) and an AlTi-containing compound (for example, the AlTi hydroxide obtained in step S1B) as essential components, and other optional components. For example, a binder, various additives, and the like may be prepared by dispersing them in a dispersion medium. The catalyst layer 20 can be formed by a conventionally used method such as an impregnation method or a wash coat method. In one example, the prepared catalyst layer forming slurry is flowed into the cell 12 from the end portion of the base material 11 and supplied to a predetermined length along the axial direction X.

Next, the base material 11 to which the slurry is supplied is dried and fired at a predetermined temperature. The firing temperature is generally 450 to 1000 ° C., for example, 500 to 700 ° C. The firing may be performed in an oxygen-containing atmosphere (for example, in the atmosphere). By setting the firing temperature to 450 ° C. or higher, the AlTi-containing compound (for example, AlTi hydroxide) undergoes a heat change in dehydration, and Ti-containing alumina having a crystal structure such as γ-alumina, θ-alumina, or α-alumina changes. Can be generated. In this way, each component is sintered on the partition wall 14 to form a catalyst layer 20 containing silver and an AlTi-containing oxide. As described above, the second catalyst 10 can be obtained.

In the AlTi-containing oxide obtained by the alkoxide method, the Al element and the Ti element are mixed at the elemental level, and both are highly dispersed. As a result, in the AlTi-containing oxide of the catalyst layer 20, the value of the Al—Ti distribution coefficient represented by _{the ratio (S Al} / S _{Al, Ti) becomes large (close to 1).} That is, there is a high probability that the Ti element overlaps with the Al element at the same position. As a result, the catalytic activity of the catalyst layer 20 is improved, and excellent NOx purification performance can be realized in a high temperature environment. The detailed mechanism of this reason has not been clarified, but the present inventors consider it as follows.

That is, for alumina, there are two methods of filling oxygen elements, six-way dense filling and cubic dense filling, and there are also two methods of coordinating Al elements. Therefore, the structure of alumina becomes diverse. According to the inference of the present inventors, in the AlTi-containing oxide having a large Al—Ti distribution coefficient, the Ti element is mixed in the crystal structure of the alumina, and the Ti element is mixed with some Al elements constituting the alumina. It is considered that they are bonded via an oxygen element. At this time, since the Ti element takes 6 coordinations, the Al element easily takes 4 coordinations with high solid acidity. In addition, the crystal structure of alumina may be distorted. As a result, the AlTi-containing oxide has improved solid acidity and easily functions as a so-called Lewis acid. As a result, it is considered that the second catalyst 10 suppresses the oxidation of the fuel in a high temperature environment and promotes the production of partial oxides. It is considered that the second catalyst 10 can enhance the catalytic activity and realize excellent NOx purification performance in a high temperature environment by the above actions.

In general, when the second catalyst 10 is _{exposed to exhaust gas containing a sulfur (S) component such as SO 2} for a long period of time, the sulfur component adheres to the catalyst layer 20, and Ag as a catalyst metal is poisoned. Catalytic activity tends to decrease. However, the Ti element contained in the AlTi-containing oxide is an element having solid acidity by itself and can also function to improve sulfur resistance. For example, by including the Ti element in the AlTi-containing oxide, the adhesion of sulfur to the catalyst layer 20 can be effectively suppressed. In addition, the grain growth of Ag can be suppressed and the size (dispersibility) of Ag can be maintained. As a result, it is possible to suppress a decrease in catalytic activity due to sulfur poisoning. That is, it is possible to improve sulfur resistance (S resistance) and maintain sufficiently high catalytic activity for a long period of time.

Note that Patent Document 1 describes a catalyst for purifying exhaust gas including a catalyst layer containing alumina and titanium or titanium oxide as a simple substance. However, as shown in Test Example I described later, even if alumina and titanium are mixed in the process of forming the catalyst layer (in other words, after the crystal structure of alumina is determined), the Al—Ti distribution coefficient is set to 0. It cannot be increased above 85. An Al—Ti distribution coefficient of 0.85 or more is realized only by mixing the Al element and the Ti element before the formation of the AlTi-containing oxide, as in the technique disclosed herein. That is, the conventional exhaust gas purification catalyst cannot obtain the effects of the techniques disclosed herein.

The second catalyst 10 includes vehicles such as automobiles and trucks, marine products such as motorcycles and motorized bicycles, ships, tankers, personal watercraft, personal watercraft, and outboard motors, grass mowers, chainsaws, and trimmers. It can be suitably used for purifying exhaust gas emitted from gardening products such as, golf carts, leisure products such as four-wheel buggies, power generation equipment such as cogeneration systems, and internal combustion engines such as garbage incinerators. Among them, it can be suitably used for small to medium-sized trucks.

Hereinafter, test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the following test examples.

≪Test Example I≫
(Comparative Example 1) No Titanium Addition First, silver nitrate (9.6 g as Ag) and boehmite (230 g as γ-alumina) were mixed to prepare a slurry. This slurry was introduced into the cell from the end of the monolith honeycomb carrier as a base material, and coated on the surface of the base material with the same length as the total length of the partition wall. Then, the substrate coated with the slurry was dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to form a catalyst layer, thereby obtaining the SCR catalyst of Comparative Example 1. The coating amount of the catalyst layer of Comparative Example 1 was 239.6 g (of which Ag was 9.6 g), and the final composition ratio of the catalyst layer of Comparative Example 1 was 4% by mass of Ag and alumina in the others. is there.

(Comparative Example 2) Use of titania sol (TiO ₂ : 0.1% by mass)
Comparative Example 1 above, except that silver nitrate (9.6 g as Ag), boehmite (230 g as γ-alumina), and titania sol (anatase type, _{0.24 g as TiO 2} ) were mixed to prepare a slurry. In the same manner as above, the SCR catalyst of Comparative Example 2 was obtained. The coating amount of the catalyst layer of Comparative Example 2 was 239.84 g (of which, Ag was 9.6 g and TiO ₂ was 0.24 g), and the final composition ratio of the catalyst layer of Comparative Example 2 was 4 for Ag. Mass%, TiO ₂ is 0.1% by mass, and the others are alumina.

(Comparative Example 3) Use of titania sol (TiO ₂ : 0.2% by mass)
The SCR catalyst of Comparative Example 3 was obtained in the same manner as in Comparative Example 2 except that the amount of titania sol _{was doubled (0.48 g as TiO 2).} The coating amount of the catalyst layer of Comparative Example 3 was 240.08 g (of which, Ag was 9.6 g and TiO ₂ was 0.48 g), and the final composition ratio of the catalyst layer of Comparative Example 3 was 4 Ag. Mass%, TiO ₂ is 0.2 mass%, and the others are alumina.

(Comparative Example 4) Use of titania sol (TiO ₂ : 0.4% by mass)
The SCR catalyst of Comparative Example 4 was obtained in the same manner as in Comparative Example 2 except that the amount of titania sol was quadrupled ( _{0.96 g as TiO 2).} The coating amount of the catalyst layer of Comparative Example 4 was 240.56 g (of which, Ag was 9.6 g and TiO ₂ was 0.96 g), and the final composition ratio of the catalyst layer of Comparative Example 4 was 4 Ag. Mass%, TiO ₂ is 0.4% by mass, and the others are alumina.

(Example 1) Use of Ti-containing boehmite (TiO ₂ : 0.1% by mass)
First, Ti-containing boehmite produced by the alkoxide method (TIO ₂ was 0.1% by mass) was prepared. Next, the SCR of Example 1 was carried out in the same manner as in Comparative Example 1 above, except that silver nitrate (9.6 g as Ag) and Ti-containing boehmite (230 g as γ-alumina) were mixed to prepare a slurry. Obtained a catalyst. The coating amount of the catalyst layer of Example 1 was 239.6 g (of which, Ag was 9.6 g and TiO ₂ was 0.24 g), and the final composition ratio of the catalyst layer of Example 1 was 4% by mass of Ag. , TiO ₂ is 0.1% by mass, and the others are alumina.

(Example 2) Use of Ti-containing boehmite (TiO ₂ : 0.2% by mass)
The SCR catalyst of Example 2 was obtained in the same manner as in Example 1 above except that Ti-containing boehmite (TIO _{2 was 0.2% by mass) was prepared.} The coating amount of the catalyst layer of Example 2 was 240.08 g (of which, Ag was 9.6 g and Ti was 0.48 g), and the final composition ratio of the catalyst layer of Example 2 was 4% by mass of Ag. TiO ₂ is 0.2% by mass, and the others are alumina.

(Example 3) Use of Ti-containing boehmite (TiO ₂ : 0.4% by mass)
The SCR catalyst of Example 3 was obtained in the same manner as in Example 1 above except that Ti-containing boehmite (TIO _{2 was 0.4% by mass) was prepared.} The coating amount of the catalyst layer of Example 3 was 240.56 g (of which, Ag was 9.6 g and TiO ₂ was 0.96 g), and the final composition ratio of the catalyst layer of Example 3 was 4% by mass of Ag. , TiO ₂ is 0.4% by mass, and the others are alumina.

(Example 4) Use of Ti-containing boehmite (TiO ₂ : 5% by mass)
The SCR catalyst of Example 4 was obtained in the same manner as in Example 1 above except that Ti-containing boehmite (TiO _{2 was 5% by mass) was prepared.} The coating amount of the catalyst layer of Example 4 was 240.8 g (of which Ag was 9.6 g and TiO ₂ was 1.2 g), and the final composition ratio of the catalyst layer of Example 4 was Ag. Mass%, TiO ₂ is 5.0 mass%, and the others are alumina.

[Detection of Ti using XRD]
First, in Comparative Examples 2 to 4, it was obtained by calcining γ-alumina obtained by adding titania sol at the stage of forming the catalyst layer and firing, and in Examples 1 to 4, Ti-containing boehmite was calcined. Γ-Alumina was used as a measurement sample. Next, the X-ray diffraction pattern of the measurement sample was measured under the following conditions using an X-ray diffractometer (XRD) manufactured by Rigaku Co., Ltd., model "RINT-2500". As an example, FIG. 4A shows the XRD charts of Comparative Example 1, Example 2, and Example 3. Further, FIG. 4B shows an enlarged view of FIG. 4A in the range of 2θ = 20 to 30 °. Then, the presence or absence of the Ti-derived diffraction peak (here, the diffraction peak of 2θ = 25.280 ° of _{TiO 2) in the XRD chart was confirmed.} The results are shown in Table 1. In Table 1, "ND" indicates that the intensity of the peak was below the lower limit of detection, and "detection" indicates that the intensity of the peak exceeded the lower limit of detection.
Tube (X-ray): CuKα ray, tube voltage; 40 kV, tube current; 250 mA
Divergent slit; 1 deg, Scattering slit; 1 deg, Light receiving slit; 3 deg
Measuring angle 8 to 65 °

[Detection of Al element and Ti element using TEM-EDS]
First, in Comparative Examples 2 to 4, it was obtained by calcining γ-alumina obtained by adding titania sol at the stage of forming the catalyst layer and firing, and in Examples 1 to 4, Ti-containing boehmite was calcined. Γ-Alumina was used as an observation sample. Next, using a transmission electron microscope (TEM) manufactured by JEOL Ltd. and the model "JEM-ARM200F", observe the above-mentioned γ-alumina powder under the following conditions, and obtain a TEM observation image (observation magnification 2 million times). Obtained.
Acceleration voltage: 200kV
Beam irradiation: Spot size 1C, aperture diameter 40μm

Next, using the energy dispersive X-ray analyzer (EDS) manufactured by JEOL Ltd. and the model "JED-2300T", the TEM observation image was analyzed with ^{a "dry SD100GV" (detection area 100 mm 2) detector.} , Al element and Ti element were mapped with different colors. Here, the Al element is mapped in red and the Ti element is mapped in green. The number of integrations was 30. As an example, FIG. 5 shows a TEM-EDS image of Example 2. Then, the presence or absence of the Ti element was confirmed from the TEM-EDS image. The results are shown in Table 1. In Table 1, "ND" indicates that the Ti element was below the lower limit of detection, and "detection" indicates that the intensity of the peak exceeded the lower limit of detection.

[Analysis of TEM-EDS images]
First, the TEM-EDS image is taken into the two-dimensional image analysis software Winroof (registered trademark), the processing range is set to the catalyst layer _{, and the area S Al} of the Al element and the Al element and Ti element are determined by the following procedure. The total areas S _{Al and Ti} were calculated. Further, the ratio of the area S _{Al of the Al} element to the total area S Al of the Al element and the Ti element (Al—Ti distribution coefficient, S _Al / S _{Al, Ti} ) was determined. The results are shown in Table 1.
-Calculation of the area S _Al of the Al element (Procedure A1) RGB separation was performed on the image display, and a red separated image was extracted.
(Procedure A2) The red separated image was automatically binarized by the mode method to obtain a binary image.
(Procedure A3) The black part of the binary image was regarded as the Al element, and the area S _Al (nm ² ) of the Al element was calculated.
-Calculation of total area S _{Al and Ti} of Al element and Ti element (Procedure B1) Monochrome image was obtained by image display.
(Procedure B2) A monochrome image was automatically binarized by the mode method to obtain a binary image.
(Procedure B3) The black part of the binary image was regarded as the sum of the Al element and the Ti element, and the total area S _{Al and Ti} (nm ² ) of the Al element and the Ti element were calculated.

Note that FIGS. 6A to 6E show the analysis results of Comparative Example 4 as an example. That is, FIG. 6A is a TEM-EDS image of Comparative Example 4. FIG. 6B is a red separated image obtained by RGB-separating the TEM-EDS image of FIG. 6A (in step A1) in calculating _{the area S Al of the Al element.} FIG. 6C is a binary image obtained by automatically binarizing the separated image of FIG. 6B (in procedure A2). FIG. 6D is a monochrome image obtained by converting the TEM-EDS image of FIG. 6A into a monochrome image (in step B1) in calculating _{the total areas S Al and Ti} of the Al element and the Ti element. FIG. 6E is a binary image obtained by automatically binarizing the monochrome image of FIG. 6D (in step B2).

[Measurement of NOx purification performance using model gas]
First, an exhaust gas generator for testing using a diesel engine as an internal combustion engine was prepared, and the SCR catalyst produced above was connected to the exhaust path of the diesel engine to supply a lean model gas (without sulfur). Further, on the upstream side of the SCR catalyst, vaporized model gas was sprayed as a reducing agent at a concentration of 4000 ppmC. Then, under the high temperature condition of the SCR catalyst temperature of 450 ° C., the NOx concentration of the model gas on the outlet side of the SCR catalyst was measured, and the NOx purification rate was calculated. The results are shown in Table 1, FIGS. 7 and 8.

[About Ti detection using XRD and TEM-EDS]
As shown in Table 1, FIGS. 4A and 4B, in Examples 1 to 4 using Ti-containing boehmite, _{the diffraction peak of 2θ = 25.280 ° of TiO 2} was not detected (below the lower limit of detection) by XRD. .. Further, in Comparative Examples 2 to 4 using the titania sol, _{the diffraction peak of TiO 2} was not detected by XRD. It is considered that this is because the ratio of Ti was as small as 5% by mass or less. On the other hand, as shown in Table 1, in the TEM-EDS image, the presence of the Ti element could be confirmed in Examples 1 to 4 and Comparative Examples 2 to 4, respectively.

[About Al-Ti distribution coefficient]
As shown in Table 1, in Comparative Examples 2 to 4 in which Ti was added as the titanium sol, the Al—Ti distribution coefficient was relatively low, and the maximum was 0.81 of Comparative Example 2 (Tio in terms of oxide of Ti element). _The content ratio (as 2) was 0.1% by mass). On the other hand, in Examples 1 to 4 in which Ti-containing boehmite was used, the Al—Ti distribution coefficient was relatively high. Further, when the titanium sol was used and the Ti-containing boehmite was used, the Al—Ti distribution coefficient tended to decrease as the content ratio of _{TiO 2 increased.} It is considered that this is _{because the higher the content ratio of TiO 2,} the larger the ratio of Ti separately present. Further, when Ti-containing boehmite is used, it is considered that when the content ratio of Ti element is high, it becomes difficult for Ti element to be contained in the crystal structure of alumina, and the ratio of Ti separately present is increased.

Although not shown in the table, in Comparative Example 1 in which titanium was not added, the area S _Al of the Al element and the total area S _{Al, Ti of the} Al element and the Ti element were calculated by the above method, and Al. When the -Ti distribution coefficient was calculated, it exceeded 0.99 (it was approximately 1). Therefore, it can be judged that the above analysis method is a highly accurate analysis.

[About NOx purification performance]
FIG. 7 is _{a graph showing the relationship between the TiO 2} content ratio and the NOx purification rate. As shown in Table 1 and FIG. 7, in Comparative Examples 2 to 4 in which Ti was added as the titania sol, the NOx purification performance in a high temperature (450 ° C.) environment was lower than that in Comparative Example 1 in which titanium was not added. That is, the addition of titania sol reduced the NOx purification performance. In particular, as _{the content ratio of TiO 2 in} the SCR catalyst increases, the NOx purification rate at high temperature (450 ° C.) tends to decrease. It is considered that the reason for this is that the addition of titanium increases the amount of fuel that is completely oxidized in a high temperature environment and reduces the amount of partial oxide that functions as a reducing agent, resulting in a decrease in catalytic activity.

FIG. 8 is a graph showing the relationship between the Al—Ti distribution coefficient and the NOx purification rate. As shown in Table 1 and FIG 8, between the Al-Ti distribution coefficient and NOx purification rate, the correlation coefficient ^{(R 2)} was observed positive correlation of 0.7 or more. Examples 1 to 4 having a high Al—Ti distribution coefficient had a relatively high NOx purification rate as compared with Comparative Examples 2 to 4. The reason for this is that the solid acidity of the catalyst improved with the increase in the Al—Ti distribution coefficient, so that the complete oxidation of the fuel in a high temperature environment was suppressed, and the production of partial oxides functioning as a reducing agent was promoted. Can be considered.

≪Test Example II≫
The sulfur resistance was further evaluated using the SCR catalysts of Comparative Examples 1 and 3 of Test Example I. Specifically, first, an SCR catalyst was installed in the exhaust path of the diesel engine (displacement 4 L) of the actual vehicle, and light oil fuel (sulfur concentration 5 ppm) was supplied. Further, vaporized gas oil fuel was sprayed at a concentration of 2000 ppmC as a reducing agent on the upstream side of the SCR catalyst. Then, the engine speed was 900 to 3000 rpm, the temperature of the exhaust gas on the inlet side of the catalyst was 450 ° C., the NOx concentration on the outlet side of the SCR catalyst was measured, and the NOx purification rate was calculated. The measurement was performed every 20 hours until the total endurance time reached 100 hours. The results are shown in FIG.

In addition, it was measured how much sulfur (S) contained in the diesel fuel adhered to the SCR catalyst that had been subjected to the durability test for 100 hours. Specifically, the amount of sulfur deposited was measured using a carbon / sulfur analyzer manufactured by LECO, model "CS744". The results are shown in FIG.

FIG. 9 is a graph showing the relationship between the durability time and the NOx purification rate. FIG. 10 is a graph showing the amount of sulfur deposited after 100-hour endurance. As shown in FIG. 9, in Example 3 containing titanium, the decrease in NOx purification performance was suppressed to be smaller than in Comparative Example 1 in which titanium was not added. That is, high NOx purification performance was maintained even after durability. The reason for this is considered to be that the inclusion of the Ti element suppressed the adhesion of sulfur as shown in FIG. 10 and suppressed the decrease in catalytic activity due to sulfur poisoning.

Although some embodiments of the present invention have been described above, the above embodiments are only examples. The present invention can be implemented in various other forms. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. The techniques described in the claims include various modifications and modifications of the embodiments illustrated above. For example, it is possible to replace a part of the above-described embodiment with another modification, and it is also possible to add another modification to the above-described embodiment. Further, if the technical feature is not explained as essential, it can be deleted as appropriate.

1 Exhaust gas purification system 2 Internal combustion engine 3 Exhaust gas purification device 6 Fuel supply mechanism 10 Second catalyst (catalyst for exhaust gas purification)
11 Base material 12 cells 14 partition wall 20 catalyst layer

Claims (9)

1. An exhaust gas purification catalyst that is placed in the exhaust path of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine.
   A base material and a catalyst layer arranged on the base material are provided.
   The catalyst layer contains silver and an AlTi-containing oxide containing an aluminum element and a titanium element.
   When the AlTi-containing oxide was observed with a transmission electron microscope (observation magnification 2 million times) and element mapping was performed by energy dispersive X-ray analysis, the titanium element was detected, and the aluminum element and the titanium An exhaust gas purification catalyst in which the ratio (S _Al / S _{Al, Ti} ) of the area (S _Al ) of the aluminum element to the total area (S _{Al, Ti) with the elements is 0.85 or more.}
2. The ratio (S _Al / S _{Al, Ti} ) is 0.9 or more.
   The catalyst for purifying exhaust gas according to claim 1.
3. When the total amount of the AlTi-containing oxide is 100% by mass, the ratio of the titanium element in terms of oxide is 0.1% by mass or more.
   The catalyst for purifying exhaust gas according to claim 1 or 2.
4. When the total amount of the AlTi-containing oxide is 100% by mass, the ratio of the titanium element in terms of oxide is 5% by mass or less.
   The catalyst for purifying exhaust gas according to any one of claims 1 to 3.
5. When the AlTi-containing oxide is measured by an X-ray diffraction method, a diffraction peak derived from the titanium element is not detected.
   The catalyst for purifying exhaust gas according to any one of claims 1 to 4.
6. When the whole catalyst layer is 100% by mass, the content ratio of the titanium element in terms of oxide is 0.1% by mass or more and 5% by mass or less.
   The catalyst for purifying exhaust gas according to any one of claims 1 to 5.
7. The exhaust gas purification catalyst according to any one of claims 1 to 6 and
   A supply mechanism that supplies hydrocarbons to the exhaust gas on the upstream side of the exhaust gas purification catalyst in the exhaust gas flow direction.
   Exhaust gas purification system equipped with.
8. The internal combustion engine is a diesel engine.
   The exhaust gas purification system according to claim 7.
9. It is a method for manufacturing an exhaust gas purification catalyst that is arranged in the exhaust path of an internal combustion engine and purifies the exhaust gas discharged from the internal combustion engine.
   To prepare an AlTi-containing compound produced by an alkoxide method in which an aluminum alkoxide and a titanium alkoxide are hydrolyzed, and
   Applying the silver element source and the AlTi-containing compound to the base material and firing.
   A method for producing a catalyst for purifying exhaust gas, including the above.

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