JP2012075992A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas, in which accumulation of a sulfur component can be sufficiently suppressed and which can exhibit sufficiently high catalytic activity even after exposed to high temperature for a long period of time.SOLUTION: The catalyst for cleaning exhaust gas includes: a carrier comprising a metal oxide on which at least one additive component selected from the group consisting of phosphorus and tungsten is deposited; and palladium and iron which are deposited on the carrier. In terms of the metal, the deposited amount of the additive component is 0.3-9.0 parts mass, that of the palladium is 0.1-10 parts mass and that of the iron is 0.06-2.0 parts mass based on 100 parts mass of the metal oxide.

Description

  The present invention relates to an exhaust gas purifying catalyst.

Various exhaust gas purification catalysts have been conventionally used to remove harmful components such as hydrocarbon gas (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) in exhaust gas from automobile engines. It was. In such an exhaust gas purifying catalyst, the sulfur (S) component contained in the exhaust gas is occluded and gradually accumulated (sulfur poisoning) at the time of use, and the accumulation of the sulfur component is suppressed. Various attempts have been made to do this. For example, in Japanese Patent Application Laid-Open No. 2008-279319 (Patent Document 1), a carrier containing alumina on which an acidic oxide composed of an oxide of at least one metal selected from W, Ti, Si, P and Mo is supported. And an exhaust gas purifying catalyst including the noble metal supported on the carrier. Then, in Patent Document 1, there is a description to the effect that the adsorption of the SO _x is prevented by such acidic oxide. However, in such a conventional exhaust gas purifying catalyst as described in Patent Document 1, the catalytic activity after being exposed to a high temperature for a long time is not always sufficient, and the accumulation of sulfur components and the catalytic activity are suppressed. However, it was not always sufficient in terms of compatibility with high temperature durability.

  Further, various studies have been made on exhaust gas purification catalysts from the viewpoint of catalytic activity. For example, in JP-A-2005-185959 (Patent Document 2), a noble metal and at least one transition metal compound selected from Mn, Fe, Co, Ni, Cu and Zn are supported on a carrier, An exhaust gas purifying catalyst in which a noble metal and a transition metal compound form a composite is disclosed. However, such an exhaust gas purifying catalyst as described in Patent Document 2 is not necessarily sufficient in terms of suppressing the accumulation of sulfur components.

JP 2008-279319 A JP 2005-185959 A

  The present invention has been made in view of the above-described problems of the prior art, can sufficiently suppress the accumulation of sulfur components in the catalyst, and is sufficiently advanced even after being exposed to a high temperature for a long period of time. An object is to provide an exhaust gas purifying catalyst capable of exhibiting catalytic activity.

  As a result of intensive studies to achieve the above object, the present inventors have used, as a support, a metal oxide on which at least one additive component selected from the group consisting of phosphorus and tungsten is supported. Palladium and iron are supported, and the supported amounts of the additive component and the palladium and iron are each 0.3 to 9.0 parts by mass (additional component) with respect to 100 parts by mass of the metal oxide in terms of metal. 0.1 to 10 parts by mass (palladium) and 0.06 to 2.0 parts by mass (iron) of the exhaust gas purifying catalyst can sufficiently suppress the accumulation of sulfur components in the catalyst, and the temperature is high. It has been found that a sufficiently high catalytic activity can be exhibited even after being exposed to a long period of time, and the present invention has been completed.

That is, the exhaust gas purifying catalyst of the present invention comprises a carrier made of a metal oxide carrying at least one additive component selected from the group consisting of phosphorus and tungsten, and palladium and iron carried on the carrier. Prepared,
The supported amount in terms of metal is that the supported amount of the additive component is 0.3 to 9.0 parts by mass and the supported amount of palladium is 0.1 to 10 parts by mass with respect to 100 parts by mass of the metal oxide. And the supported amount of iron is 0.06 to 2.0 parts by mass,
It is characterized by.

  In such an exhaust gas purification catalyst of the present invention, the metal oxide preferably contains alumina.

In addition, as the carrier according to the present invention, a carrier having a base point amount of 17.8 to 38 μmol-CO ₂ / g determined on the basis of the amount of CO ₂ desorbed per gram of the carrier measured by CO ₂ temperature programmed desorption measurement. Is preferred.

  In the exhaust gas purifying catalyst of the present invention, it is preferable that a part of the iron is dissolved in a part of the palladium.

  Furthermore, it is preferable that the exhaust gas purifying catalyst of the present invention further includes an oxide having oxygen absorption / release capability.

The exhaust gas purifying catalyst of the present invention can sufficiently suppress the accumulation of sulfur components in the catalyst, and can exhibit sufficiently high catalytic activity even after being exposed to high temperatures for a long period of time. The reason for this is not necessarily clear, but the present inventors infer as follows. That is, first, in the present invention, a metal oxide on which at least one additive component selected from the group consisting of phosphorus (P) and tungsten (W) is supported is used as the support. By supporting such an added component on the metal oxide, the base point that is the adsorption site of the sulfur component of the metal oxide is reduced. Therefore, accumulation of sulfur components can be sufficiently suppressed by using a metal oxide carrying such added components as a carrier. Even when used as an additive component for Mo, Ti, and Si as described in Patent Document 1, it is possible to reduce the base point of the metal oxide itself. However, first, regarding Mo, since Mo evaporates at a high temperature, a sufficient effect is not necessarily obtained after being exposed to a high temperature for a long time. Further, regarding Ti, when used together with Fe, it easily reacts with Fe to form FeTiO _3, and therefore, in a catalyst system supporting Fe, the effect obtained by supporting Fe can be obtained. The catalytic activity cannot be sufficiently maintained after being exposed to a high temperature for a long time. In addition, Si easily reacts with a metal oxide (for example, alumina) to significantly reduce the specific surface area. On the other hand, P and W do not have the problem of easily evaporating under high temperature conditions or easily reacting with Fe, and without reacting with the metal oxide of the carrier and significantly reducing the specific area. By using P and / or W, it is possible to sufficiently reduce the base point and to sufficiently suppress the accumulation of sulfur components. As a result of intensive research, the present inventors have found the above-mentioned knowledge regarding the additive component, and select P and W from various components as additive components supported on the metal oxide in the catalyst system supporting Fe. It is used as. Moreover, in this invention, the load of such an additional component is 0.3-9.0 mass parts with respect to 100 mass parts of said metal oxides. By setting the loading amount of the additive component within the above range, it is possible to sufficiently maintain the specific surface area while sufficiently reducing the amount of the base point of the metal oxide, so that the sulfur component is accumulated in the catalyst. It is possible to sufficiently suppress a decrease in catalyst activity even after being exposed to a high temperature for a long time while sufficiently suppressing the above.

  Moreover, in this invention, palladium (Pd) is carry | supported by the support | carrier in the ratio used as 0.1-10 mass parts with respect to 100 mass parts of said metal oxides. By using palladium in this way, it is possible to develop sufficient exhaust gas purification performance for the resulting catalyst. Moreover, in this invention, iron (Fe) is carry | supported by the support | carrier with the ratio used as 0.06-2.0 mass part with respect to 100 mass parts of said metal oxides with Pd. Thus, in the present invention, since Fe is present in the vicinity of Pd, the effect of facilitating the oxidation and reduction of Pd is obtained, and the catalytic activity becomes sufficiently high. In such a catalyst, when exposed to a high temperature, Fe and Pd are dissolved (alloyed) to form a solid solution (alloy) of Fe and Pd. The Fe dissolved in this way forms Fe—O—Pd bonds on the surface of the Pd particles, and the grain growth (sintering) of the Pd particles accompanying the evaporation of Pd is sufficiently suppressed. In addition, Fe dissolved in Pd forms an Fe—OM bond with a metal on the surface of the metal oxide (hereinafter, simply referred to as “M”) so that Pd is bound to M. Therefore, the grain growth accompanying the movement of Pd on the surface of the carrier is sufficiently suppressed. As described above, in the present invention, the transpiration of Pd and the surface movement of Pd on the carrier are sufficiently suppressed by Fe, and thus the decrease in catalytic activity is sufficiently suppressed even after being exposed to a high temperature for a long time. The present inventors infer that. As described above, in the present invention, a metal oxide carrying a specific amount of additive components (P, W) is used as a carrier, and a specific amount of Pd and Fe is carried on the carrier. The present inventors speculate that it is possible to exhibit sufficiently high catalytic activity even after being exposed to a high temperature for a long period of time while sufficiently suppressing the accumulation of components.

  According to the present invention, there is provided an exhaust gas purifying catalyst capable of sufficiently suppressing the accumulation of sulfur components in a catalyst and exhibiting a sufficiently high catalytic activity even after being exposed to a high temperature for a long time. It becomes possible to provide.

It is a graph which shows the specific surface area of the metal oxide obtained by manufacture example 1 and the metal oxide which carry | supported Fe obtained by manufacture example 2-4.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

The exhaust gas purifying catalyst of the present invention comprises a support made of a metal oxide on which at least one additive component selected from the group consisting of phosphorus and tungsten is supported, and palladium and iron supported on the support,
The supported amount in terms of metal is that the supported amount of the additive component is 0.3 to 9.0 parts by mass and the supported amount of palladium is 0.1 to 10 parts by mass with respect to 100 parts by mass of the metal oxide. And the supported amount of iron is 0.06 to 2.0 parts by mass,
It is characterized by.

  Such a metal oxide is not particularly limited as long as it is a metal oxide that can be used as a carrier for an exhaust gas purification catalyst. For example, lanthanum (La), cerium (Ce), praseodymium (Pr) , Neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) , Oxides of metals such as ytterbium (Yb), ruthenium (Lu), yttrium (Y), zirconium (Zr), aluminum (Al), magnesium (Mg), vanadium (V), and mixtures of these metal oxides A solid solution of these metal oxides or a composite oxide of these metals can be used as appropriate. Among such metal oxides, those containing alumina are preferable from the viewpoint that the specific surface area can be more sufficiently maintained under high temperature conditions. As such a metal oxide containing alumina, a known metal oxide containing alumina such as alumina, lanthanum-stabilized activated alumina, alumina-ceria-zirconia, alumina-zirconia, alumina-ceria, etc. may be appropriately used. However, alumina, lanthanum stabilized activated alumina, and alumina-ceria are more preferable because higher effects can be obtained. Moreover, the manufacturing method in particular of such a metal oxide is not restrict | limited, A well-known method is employable suitably. Furthermore, as such a metal oxide, a commercially available product may be used.

Examples of such metal oxides, it is preferable that the specific surface area of 200~50m ² / g, more preferably 200~100m ² / g. When the specific surface area exceeds the upper limit, sulfur component adhesion sites tend to increase, and the sulfur component tends to accumulate. On the other hand, when the specific surface area is less than the lower limit, the catalyst performance tends to decrease. Such a specific surface area can be calculated as a BET specific surface area from an adsorption isotherm using a BET isotherm adsorption formula. In addition, such a BET specific surface area can be calculated | required using a commercially available apparatus.

  In the carrier according to the present invention, at least one additive component selected from the group consisting of phosphorus and tungsten is supported on the metal oxide. Thus, in the present invention, phosphorus and / or tungsten is used as an additive component. However, by supporting such an additive component, the specific surface area of the carrier is decreased, and iron and the additive component react. The amount of the base point of the carrier can be sufficiently reduced while sufficiently suppressing the above. Therefore, such an additive component can be obtained by supporting iron while sufficiently reducing the amount of base points of the metal oxide and suppressing the accumulation of sulfur components on the support at a sufficiently high level. It is possible to maintain a sufficiently high effect and obtain a sufficiently high catalytic activity. In addition, at least one additive component selected from the group consisting of phosphorus and tungsten may be supported as an oxide.

  Moreover, the load of such an additional component is 0.3-9.0 mass parts with respect to 100 mass parts of said metal oxides in metal conversion. If the amount supported is less than the lower limit, the amount of base points cannot be sufficiently reduced, and accumulation of sulfur components cannot be sufficiently suppressed. On the other hand, if the upper limit is exceeded, the specific surface area decreases. In addition, since active site poisoning occurs, the catalytic activity decreases. In addition, the loading amount of such an additive component is similar in terms of obtaining a higher effect, that is, exhibiting a balance between the ability to sufficiently suppress the accumulation of sulfur components in the resulting catalyst and the catalyst activity. From the viewpoint of making the additive component phosphorus, the supported amount is more preferably 0.3 to 2.0 parts by mass with respect to 100 parts by mass of the metal oxide in terms of metal, -1.8 is particularly preferred. Further, when the additive component is tungsten, the supported amount is more preferably 0.3 to 3.0 parts by mass with respect to 100 parts by mass of the metal oxide in terms of metal. Particularly preferred is 3.0. If the amount of phosphorus or tungsten supported is less than the lower limit, sulfur component accumulation tends not to be sufficiently suppressed. On the other hand, if the upper limit is exceeded, catalyst activity tends to decrease. In the present specification, the loading amount is calculated considering the phosphorus (P) element as a metal element. Among these additive components, P is preferable from the viewpoint of the stability of the oxide under high temperature conditions.

In the carrier adding components such a metal oxide is formed by carrying, it is preferable that the base point of the carrier is _{17.8~38μmol-CO 2 / g, 20~30μmol} -CO 2 / g It is more preferable that If the amount of the base point is less than the lower limit, the catalytic activity tends to be reduced, and the catalyst activity and the sulfur component accumulation preventing performance tend not to be exhibited in a well-balanced manner. It tends to be difficult to sufficiently suppress the accumulation of components. The value of the basic point amount is within the range in which the supported amount of the additive component is 0.3 to 9.0 parts by mass with respect to 100 parts by mass of the metal oxide, depending on the type of the carrier, A desired value can be obtained by appropriately changing the loading amount. Here, the “base point” is a value measured as the amount of CO ₂ desorbed per 1 g of carrier in CO ₂ temperature-programmed desorption measurement. Hereinafter, a method for measuring the “base point amount” in the present invention using CO ₂ temperature programmed desorption measurement will be described.

In such a “base point amount” measurement method, first, 1 g of a carrier is prepared as a measurement sample. Next, a rich gas composed of H ₂ (4 vol%) and N ₂ (96 vol%) and a lean gas composed of O ₂ (4 vol%) and N ₂ (96 vol%) are switched every 60 seconds. The gas (the rich gas and the lean gas) is brought into contact with the carrier while being alternately supplied. At this time, the temperature of the gas (the rich gas and the lean gas) brought into contact with the carrier is increased to 600 ° C. with an initial temperature of 90 ° C. and a temperature increase rate of 40 ° C./min. Then, after the temperature of the gas reaches 600 ° C., the gas temperature is maintained at 600 ° C., and the lean gas and the rich gas are alternately supplied while being switched every 10 seconds, and the gas ( The rich gas and the lean gas) are contacted for 10 minutes. Thereafter, the supply of the rich gas and the lean gas is stopped, N ₂ gas at 90 ° C. is supplied for 30 minutes, and N ₂ gas is brought into contact with the carrier. Next, a gas composed of 90 ° C. CO ₂ (0.5% by volume) and N ₂ (99.5% by volume) is supplied for 10 minutes, and a gas containing CO ₂ is brought into contact with the carrier. Then, CO ₂ is adsorbed on the carrier (CO ₂ adsorption treatment). Thereafter, the initial temperature is set to 90 ° C., N ₂ gas is supplied while raising the temperature to 600 ° C. at a rate of 40 ° C./min, and the N ₂ gas is brought into contact with the carrier to desorb CO ₂ from the carrier. (CO ₂ desorption treatment). In such CO ₂ desorption treatment, the amount of CO _{2 in} the output gas from the time when the temperature of the N ₂ gas begins to rise until the gas temperature reaches 600 ° C. is measured (CO ₂ temperature rise). Desorption measurement). For measurement of such gas concentration, a commercially available gas measuring device (trade name “MEXA-4300FT” manufactured by Horiba, Ltd.) can be used as the measuring device. The amount of CO ₂ measured per 1 g of the carrier in this way is defined as “base point amount” in the present invention. In such a “base point amount” measurement method, the flow rate of the gas brought into contact with the carrier is 5 L / min with respect to 1 g of the carrier. Moreover, you may utilize the reaction apparatus as described in Unexamined-Japanese-Patent No. 2002-311013 for the measurement of such a basic point amount.

  Further, the method for supporting the additive component on the metal oxide is not particularly limited, and a known method capable of supporting P and / or W can be appropriately employed. As such a method, for example, when P is supported, the solution is dried by bringing the solution into contact with a metal oxide using a solution in which a phosphorus compound is dissolved in a solvent such as water or alcohol (for example, phosphoric acid aqueous solution). In the case of supporting W, the solution is made into a metal oxide using a solution in which a tungsten compound (for example, ammonium paratungstate) is dissolved in a solvent such as water or alcohol. The method of baking after making it contact and drying is mentioned. In addition, the conditions in the case of such drying and baking are not restrict | limited in particular, Well-known conditions can be employ | adopted suitably, For example, as drying conditions, the conditions heated about 80-140 degreeC for about 1 to 24 hours, As the firing conditions, conditions of heating at 200 to 700 ° C. for about 0.5 to 5 hours may be employed.

  In the present invention, palladium is supported on the carrier. The supported amount of palladium is 0.1 to 10 parts by mass in terms of metal with respect to 100 parts by mass of the metal oxide. When the supported amount of palladium is less than the lower limit, it becomes difficult to exhibit sufficient catalytic activity. On the other hand, when the upper limit is exceeded, palladium sintering is easily promoted by an increase in supported density, and the activity is increased. Saturation increases costs. The amount of palladium supported is 0.1 to 5 parts by mass with respect to 100 parts by mass of the metal oxide in terms of metal from the viewpoint of obtaining a higher effect in the same manner as described above. It is more preferable that the content is 0.1 to 3 parts by mass. Such palladium may be supported as an oxide.

In addition, the crystallite size of palladium thus supported on the carrier is preferably 0.1 to 100 nm (more preferably 2 to 20 nm). If the crystallite diameter is less than the lower limit, the metalation rate tends to be slow, whereas if it exceeds the upper limit, sufficient catalytic activity tends not to be obtained. In addition, such a crystallite diameter of palladium is based on Scherrer's formula on the basis of a half-value width of a peak derived from a (111) plane of a palladium crystal obtained by measurement by X-ray diffraction (XRD):
D = 0.9λ / βcos θ
(In the formula, D represents the particle diameter, λ represents the used X-ray wavelength, β represents the half width of the XRD measurement sample, and θ represents the diffraction angle)
Can be obtained by calculating. As a method of X-ray diffraction measurement when confirming such a crystallite diameter, as a measuring device, a trade name “RINT-TTR” manufactured by Rigaku Corporation is used, a scan step of 0.01 °, divergence and scattering. A method of measuring under the conditions of slit 1/2 deg, light receiving slit 0.15 mm, CuKα ray, 40 kV, 30 mA, scan speed 2θ = 0.25 ° / min is adopted.

  In addition, the method for supporting palladium on the carrier is not particularly limited, and a known method can be appropriately employed. For example, a palladium compound (for example, a palladium salt such as nitrate, chloride, acetate, A method in which the carrier is brought into contact with a solution in which a palladium complex or the like is dissolved in a solvent such as water or alcohol, and then dried and fired may be employed. In addition, the conditions in the case of such drying and baking are not restrict | limited in particular, Well-known conditions can be employ | adopted suitably, For example, as drying conditions, the conditions heated about 80-140 degreeC for about 1 to 24 hours, As the firing conditions, conditions of heating at 200 to 700 ° C. for about 0.5 to 5 hours may be employed.

  In the present invention, iron is supported on the carrier. As described above, in the catalyst of the present invention, iron is supported along with palladium on the carrier. Therefore, iron is present in the vicinity of palladium, and the oxidation and reduction of palladium is facilitated and the catalyst is sufficiently advanced. Activity can be obtained, and it is possible to sufficiently suppress the grain growth of palladium under high temperature conditions, and the catalytic activity can be sufficiently maintained even after long-term use at high temperature. Further, when iron is supported on the carrier in this way, the reducibility of the catalyst is sufficiently improved, and higher catalyst performance can be obtained. Such iron may be supported as an oxide.

  The amount of iron supported is 0.06 to 2.0 parts by mass with respect to 100 parts by mass of the metal oxide in terms of metal. If the amount of iron supported is less than the lower limit, the effect obtained by supporting iron becomes insufficient, and it becomes difficult to sufficiently suppress the grain growth of palladium under high-temperature conditions, while exceeding the upper limit. When the substrate is exposed to a high temperature for a long time, the specific surface area of the support is lowered and sufficient catalytic activity cannot be obtained. Moreover, as a load of such iron, it is more preferable that it is 0.1-1.7 mass part from the same viewpoint, and it is especially preferable that it is 0.5-1.0 mass part.

  Further, the state of supporting the iron supported on the carrier is not particularly limited, but it is preferable that the iron is supported closer to the palladium. By supporting iron closer to palladium, the effect of suppressing the grain growth of palladium tends to be further improved.

  In addition, the method for supporting such iron on a carrier is not particularly limited. For example, iron compounds (for example, iron salts such as carbonate, nitrate, citrate, acetate, sulfate, and iron complexes) ) Is dissolved in a solvent such as water or alcohol, the carrier is brought into contact with the substrate, and then dried and fired. In addition, the conditions in the case of such drying and baking are not restrict | limited in particular, Well-known conditions can be employ | adopted suitably, For example, as drying conditions, the conditions heated about 80-140 degreeC for about 1 to 24 hours, As the firing conditions, conditions of heating at 200 to 700 ° C. for about 0.5 to 5 hours may be employed. In addition, such iron loading may be performed simultaneously with the palladium loading. For example, a mixed solution of an aqueous solution of palladium salt and an aqueous solution of iron salt is brought into contact with the carrier, dried, and further fired. You may employ | adopt the method of employ | adopting a method. In the case where iron and palladium are separately supported on the carrier, the order in which these are supported is not particularly limited.

  In the exhaust gas purifying catalyst of the present invention, it is preferable that a part of the iron is dissolved in a part of the palladium supported on the carrier. This solid solution of iron sufficiently suppresses palladium from evaporating under high temperature conditions, and the iron in the solid solution can also bind to the surface of the metal oxide, so palladium moves on the support. Since this is sufficiently suppressed by iron, the grain growth of palladium can be suppressed to a higher degree. Such a solid solution can be produced by reduction treatment at 800 ° C. or higher, and a catalyst supporting iron and palladium is used for 1 to 5 hours under high temperature conditions (for example, temperature conditions of 800 ° C. or higher). Can also be generated. Note that when the exhaust gas purification catalyst of the present invention is used, for example, to purify automobile exhaust gas, a solid solution can be formed even in the environment of use. Therefore, the exhaust gas purification catalyst of the present invention is durable. As a high catalyst, it can be suitably used as a catalyst for purifying automobile exhaust gas. Further, the presence of such a solid solution is obtained by measuring a peak derived from the (111) plane of the palladium crystal in the same manner as the X-ray diffraction measurement when measuring the crystallite diameter of palladium, and obtaining the lattice constant. This can be confirmed. Furthermore, when X-ray diffraction measurement is performed on the solid solution in this way, it is also possible to determine the amount of iron dissolved in the solution based on the Vegard law from the change in the lattice constant. The amount of iron solid-dissolved in palladium thus obtained is preferably 0.1 to 20 at% based on the total metal in the solid solution. If the amount of solid solution of iron is less than the lower limit, sintering tends not to be sufficiently suppressed at a higher level. On the other hand, if the upper limit is exceeded, the number of exposed Pd decreases and the catalyst is reduced. The activity tends to decrease.

Moreover, it is preferable that the exhaust gas purifying catalyst of the present invention further includes an oxide having oxygen absorbing / releasing ability as another component. By further providing such an oxide having oxygen absorbing / releasing capability, the exhaust gas atmosphere can be stably maintained in the vicinity of the stoichiometric range, and higher catalytic activity can be obtained. As such an oxide having oxygen absorbing / releasing ability, it can absorb oxygen in a lean atmosphere, absorb oxygen in a lean atmosphere, and release oxygen in a rich atmosphere due to the oxygen absorbing / releasing ability (OSC ability). It is preferable that In addition, as the oxide having such an oxygen absorption / release ability, a known metal oxide used as a so-called OSC material in the catalyst field can be appropriately used, and is not particularly limited. For example, ceria (CeO _2), ceria - zirconia _(CeO 2 -ZrO ₂₎ include composite oxides and the like. In addition, the oxide having such oxygen absorption / release ability may be one in which a rare earth element such as lanthanum, yttrium, neodymium, or praseodymium is supported. Thus, by using what carry | supported the rare earth elements, it exists in the tendency which can fully suppress the fall of the specific surface area under high temperature conditions.

  Further, the content of the oxide (second component) having such an oxygen absorption / release capacity is 100 parts by mass of the catalyst (first component) composed of the carrier and the palladium and iron supported on the carrier. The amount is preferably 1 to 500 parts by mass, and more preferably 100 to 300 parts by mass. If the content of the oxide (second component) having oxygen absorption / release capacity is less than the lower limit, the effect of adjusting the atmosphere due to OSC performance tends not to be obtained sufficiently. Pressure loss tends to increase with increasing layer thickness. A commercially available oxide may be used as the oxide having such oxygen storage / release capability.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Production Examples 1-4)
Using γ-alumina (La stabilized activated alumina) containing ₃ % by mass of La as a metal oxide (1.5% by mass as La ₂ O ₃ ), Production Example 1 (Fe loading 0.00 parts by mass) In Example 1, the metal oxide was used as it was without supporting Fe on the metal oxide. In Production Examples 2 to 4, the supported amount of iron with respect to the metal oxide is shown in Table 1 below. After the metal oxide was dispersed in the iron nitrate aqueous solution so as to have a ratio of water, it was heated to evaporate water, dried at 120 ° C. for 5 hours, and dried in the atmosphere at 500 ° C. for 1 hour. Firing was performed to obtain metal oxides (Fe-supported bodies) on which Fe was supported.

[Evaluation of characteristics of metal oxide (Production Example 1) and Fe carrier (Production Examples 2 to 4)]
The specific surface area was measured using the metal oxide obtained in Production Example 1 and the Fe carrier obtained in Production Examples 2 to 4, respectively. That is, first, an endurance test (I) in which the metal oxide obtained in Production Example 1 and the Fe carrier obtained in Production Examples 2 to 4 are heated in the atmosphere at 1000 ° C. for 5 hours. After the measurement, the specific surface area was determined based on the BET isotherm adsorption method using a trade name “Fully Automatic Surface Area Meter” manufactured by Microdata Corporation as a measuring device. The obtained results are shown in FIG.

As is clear from the results shown in FIG. 1, even after the durability test (I), from the viewpoint of sufficiently maintaining the specific surface area (for example, maintaining the specific surface area at 90 m ² / g or more), Fe It was found that it was necessary to make the loading amount of 2.0 2.0 parts by mass or less with respect to 100 parts by mass of the metal oxide in terms of metal.

(Production Examples 5-7)
First, a metal oxide (La stabilized activated alumina) was obtained by employing the same method as that employed in Production Example 1. Next, the metal oxide is dispersed in a phosphoric acid aqueous solution so that the amount of phosphorus (P) supported on the metal oxide is in the ratio shown in Table 2 below, and then heated to evaporate the water. Then, it was dried at 120 ° C. for 5 hours and calcined in the atmosphere at a temperature condition of 500 ° C. for 1 hour to obtain a metal oxide (P carrier) carrying P thereon.

(Production Examples 8 to 10)
First, a metal oxide (La stabilized activated alumina) was obtained by employing the same method as that employed in Production Example 1. Next, the metal oxide was dispersed in an aqueous solution of ammonium paratungstate so that the supported amount of tungsten (W) with respect to the metal oxide was in the ratio shown in Table 3 below, and then heated to remove water. After evaporation, it was dried at 120 ° C. for 5 hours, and calcined in the atmosphere at a temperature condition of 500 ° C. for 1 hour, thereby obtaining W-supported metal oxides (W carrier).

[Evaluation of characteristics of metal oxide (Production Example 1) and P or W carrier (Production Examples 5 to 10)]
1 g each of the metal oxide obtained in Production Example 1, the P carrier obtained in Production Examples 5 to 7 and the W carrier obtained in Production Examples 8 to 10 were prepared, and the above-described method for measuring the amount of base points The amount of base points was measured using the same method as described above. In this method of measuring the amount of base points, the product name “MEXA-4300FT” manufactured by HORIBA, Ltd. was used as a measuring device for measuring the gas concentration. The obtained measurement results are shown in Table 4.

Example 1
First, using the metal oxide supporting P obtained in Production Example 5 as a support, palladium (Pd) is supported on the support and then iron (Fe) is supported on the support as described below. After the production of one component), the resulting catalyst (first component) was mixed with ceria-zirconia composite oxide (second component) containing lanthanum and yttrium to obtain an exhaust gas purification catalyst. That is, first, the support is dispersed in an aqueous palladium nitrate solution and heated so that the supported amount of palladium is 1.00 parts by mass (in terms of metal) with respect to 100 parts by mass of the metal oxide in the support. After evaporating the water, it was dried at 120 ° C. for 5 hours, and subjected to a step of firing in the atmosphere at 500 ° C. for 1 hour (palladium loading step) to obtain a carrier carrying palladium. Next, the palladium-supported carrier is dispersed in an iron nitrate aqueous solution so that the amount of iron supported is 0.54 parts by mass (as metal) with respect to 100 parts by mass of the metal oxide in the carrier. , After evaporating the water by heating, drying at 120 ° C. for 5 hours, firing in the atmosphere at 500 ° C. for 1 hour (iron loading step), A catalyst (first component) on which was supported was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

Subsequently, with respect to the obtained catalyst (first component), CeO ₂ (60 wt%), ZrO ₂ (30 wt%), La ₂ O ₃ ( 3 wt%) and Pr ₂ O ₃ (7 wt%) ceria-zirconia composite oxide was mixed to obtain an exhaust gas purification catalyst.

(Example 2)
Exhaust gas purification in the same manner as in Example 1 except that the metal oxide supporting P obtained in Production Example 6 was used as a carrier instead of the metal oxide supporting P obtained in Production Example 5. A catalyst was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Example 3)
Exhaust gas purification in the same manner as in Example 1 except that the metal oxide supporting P obtained in Production Example 7 was used as a support instead of the metal oxide supporting P obtained in Production Example 5. A catalyst was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

Example 4
Exhaust gas purification in the same manner as in Example 1 except that the metal oxide supporting W obtained in Production Example 8 was used as a support instead of the metal oxide supporting P obtained in Production Example 5. A catalyst was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 1)
The metal oxide obtained in Production Example 1 was used as a carrier instead of the metal oxide on which P obtained in Production Example 5 was supported, and only palladium was supported on the carrier without performing the iron loading step. Except that, an exhaust gas purifying catalyst for comparison was obtained in the same manner as in Example 1. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 2)
Exhaust gas purifying catalysts for comparison were obtained in the same manner as in Example 1 except that only the palladium was supported on the support without carrying out the iron supporting step. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 3)
The metal oxide carrying P supported in Production Example 6 was used as a carrier instead of the metal oxide carrying P obtained in Production Example 5, and the carrier was carried out without carrying out the iron loading step. Exhaust gas purification catalyst for comparison was obtained in the same manner as in Example 1 except that only palladium was supported on the catalyst. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 4)
The metal oxide carrying P supported in Production Example 7 was used as a carrier instead of the metal oxide carrying P obtained in Production Example 5, and the carrier was carried out without carrying out the iron loading step. Exhaust gas purification catalyst for comparison was obtained in the same manner as in Example 1 except that only palladium was supported on the catalyst. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 5)
Instead of the metal oxide carrying P supported in Production Example 5, the metal oxide carrying W obtained in Production Example 8 was used as a carrier, and the carrier was carried out without carrying out the iron loading step. Exhaust gas purification catalyst for comparison was obtained in the same manner as in Example 1 except that only palladium was supported on the catalyst. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 6)
Instead of the metal oxide supporting P obtained in Production Example 5, the metal oxide carrying W obtained in Production Example 9 was used as a carrier, and the carrier was supported without carrying out the iron loading step. Exhaust gas purification catalyst for comparison was obtained in the same manner as in Example 1 except that only palladium was supported on the catalyst. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 7)
Instead of the metal oxide carrying P supported in Production Example 5, the metal oxide carrying W obtained in Production Example 10 was used as a carrier, and the carrier was carried out without carrying out the iron loading step. Exhaust gas purification catalyst for comparison was obtained in the same manner as in Example 1 except that only palladium was supported on the catalyst. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 8)
Exhaust gas purification for comparison in the same manner as in Example 1 except that the metal oxide obtained in Production Example 1 was used as a support instead of the metal oxide on which P obtained in Production Example 5 was supported. A catalyst was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 9)
A comparative example was made in the same manner as in Example 1 except that the metal oxide supporting W obtained in Production Example 9 was used as a support instead of the metal oxide supporting P obtained in Production Example 5. An exhaust gas purifying catalyst was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

(Comparative Example 10)
A comparative example was made in the same manner as in Example 1 except that the metal oxide supporting W obtained in Production Example 10 was used as a support instead of the metal oxide supporting P obtained in Production Example 5. An exhaust gas purifying catalyst was obtained. Table 5 shows the amount of each component in the catalyst (first component) thus obtained with respect to 100 parts by mass of the metal oxide.

[Evaluation of characteristics of exhaust gas purification catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 10]
<Durability test (II)>
Using each of the exhaust gas purifying catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 10, a durability test (II) was performed as follows. That is, with respect to 2.5 g of each catalyst, H ₂ (5% by volume), H ₂ O (3% by volume), and N are set so that the gas flow rate is 0.5 L / min under a temperature condition of 1000 ° C. _And alternately supplying a rich gas composed of ₂ (remainder) and a lean gas composed of O ₂ (5% by volume), H ₂ O (3% by volume) and N ₂ (remainder) every 5 minutes, Gases (rich gas and lean gas) were contacted with each catalyst for 5 hours.

<Measurement test of NOx purification activity>
1 g of each of the exhaust gas purifying catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 10 after carrying out the durability test (II) was used, and the NOx 20% purification temperature was measured as follows. That is, first, O ₂ (0.43% by volume), NO (0.12% by volume), CO (1.12% by volume), C ₃ H ₆ (0.17% by volume C) per 1 g of catalyst. (Capacity% in terms of carbon atoms)), H ₂ O (10% by volume), CO ₂ (10% by volume) and N ₂ (remainder) from 110 ° C. (initial temperature) at a flow rate of 20 L / min. Contact with heating at a rate of 12 ° C./min, measure the concentration of NOx in the gas (outgas) after contacting the catalyst, and determine the amount of NOx in the gas before contacting the catalyst. As a reference, a temperature at which NOx was purified by 20% (NOx 20% purification temperature) was determined. Table 5 shows the NOx 20% purification temperature of each catalyst.

<Measurement of accumulated sulfur content>
1 g of each of the exhaust gas purifying catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 10 after carrying out the durability test (II) was used, and the amount of accumulated sulfur components was measured as follows. That is, first, a gas composed of H ₂ O (10% by volume), CO ₂ (10% by volume), and N ₂ (remainder) was brought into contact with 1 g of the catalyst at a flow rate of 25 L / min. The gas temperature at this time is 90 ° C. as the initial temperature, the temperature is increased to 780 ° C. at a rate of temperature increase of 40 ° C./min, held at 780 ° C. for 20 minutes, and then the gas temperature is increased to 480 ° C. Changed and held for 5 minutes (pretreatment).

_Next, H 2 (0.3 _volume%), O 2 (0.1 _volume%), H 2 O (10 volume%), _CO 2 (10 _volume%), SO 2 (20ppm) and _{N 2} (balance ) Rich gas, H ₂ (0.2% by volume), O ₂ (0.15% by volume), H ₂ O (10% by volume), CO ₂ (10% by volume), SO ₂ (20 ppm) and N ₂ (remainder) and the lean gas are alternately supplied every 15 seconds for 15 minutes while maintaining the gas temperature at 480 ° C., and gas (at a flow rate of 25 L / min with respect to 1 g of the pretreated catalyst) The rich gas and the lean gas were contacted (sulfur poisoning treatment). Then, during such sulfur poisoning treatment, the amount of SO ₂ in the gas (outgas) after contact with the catalyst is continuously measured, and an integrated amount of the amount of SO ₂ in the outgas is obtained to obtain SO _2. The amount of SO ₂ accumulated in the catalyst was calculated based on the difference between the total supply amount and the integrated amount, and the accumulation amount (μmol / g) of sulfur (S) was measured.

  As is clear from the results shown in Table 5, when the exhaust gas purifying catalyst of the present invention is used (Examples 1 to 4), the NOx 20% purification temperature is a sufficiently low temperature of 414.8 ° C. or less. In addition, since the accumulated amount of sulfur component is as low as 40.4 μmol / g or less, the catalyst activity and the accumulation of sulfur component are maintained even after the high temperature endurance test (endurance test (II)). It was confirmed that the ability to suppress can be exhibited in a sufficiently high level with a good balance.

On the other hand, when the exhaust gas purifying catalyst for comparison is used (Comparative Examples 1 to 10), the high temperature durability of the catalytic activity and the performance of suppressing the accumulation of sulfur components can be exhibited in a balanced manner. I found it impossible. In particular, when the metal oxide (Production Example 1) that does not carry the additive components (P and W) is used as a carrier (in the case of the exhaust gas purification catalyst obtained in Comparative Examples 1 and 8), the sulfur component It was found that the accumulation amount of sulfur was 60.0 μmol / g or more, and accumulation of sulfur components could not be sufficiently suppressed. In addition, from the results of the exhaust gas purifying catalysts obtained in Comparative Examples 1 to 7, when palladium and additive components (P and W) were supported without supporting Fe, the catalytic activity after the durability test decreased. As a result, it was found that the high-temperature durability of the catalytic activity is lowered. Moreover, when the support | carrier (manufacture examples 8 and 9) with which the load of the addition component (P and W) exceeded 9.0 mass parts was used (comparative examples 6-7 and comparative examples 9-10). In the case of an exhaust gas purifying catalyst), the NOx 20% purification temperature is 464.8 ° C. or higher even when iron is supported on the carrier (Comparative Examples 9 to 10), and the high temperature durability of the catalytic activity is sufficient. I knew it wouldn't be. Further, based on the results of the exhaust gas purification catalyst obtained in Comparative Examples 2 to 5 in which Fe is not supported on the carrier and the exhaust gas purification catalyst of the present invention obtained in Examples 1 to 4, the same carrier is used. When the difference in the effect is investigated, Fe is supported together with the additive components (P and W), and the high-temperature durability of the catalytic activity and the performance of suppressing the accumulation of sulfur components are improved in a balanced manner at a higher level. I found out that From these results, while supporting iron, the loading amount of the additive components (P and W) is 0.3 to 9.0 parts by mass, so that the high temperature durability of the catalytic activity and the accumulation amount of the sulfur component can be reduced. It has been found that a sufficiently reduced performance can be achieved in a well-balanced manner. If the results shown in Table 5 and the results shown in FIG. 1 are taken into consideration, Fe is a metal oxide in terms of metal from the viewpoint of sufficiently maintaining the specific surface area while sufficiently obtaining the effect of supporting iron. It turns out that it is necessary to carry | support at least 0.06 mass part or more with respect to 100 mass parts. Furthermore, when the results shown in Table 5 and the results shown in Table 4 are taken into consideration, it is confirmed that the base point amount of the metal oxide is reduced by supporting the additive components (P and W). When iron is supported using a carrier (Production Examples 5 to 8) in the range of 17.8 to 40.0 μmol-CO ₂ / g, the high temperature durability of the catalytic activity and the amount of accumulated sulfur components are sufficiently reduced. It was also found that the performance to be achieved is balanced.

<X-ray diffraction (XRD) measurement>
Exhaust gas purifying catalyst obtained in Example 1 (Fe carrying amount: 0.54 parts by mass) and exhaust gas purifying catalyst obtained in Comparative Example 1 not carrying Fe (Fe carrying amount: 0.004) After the above durability test (II) was carried out on each catalyst using the respective parts by mass), the XRD pattern attributed to the (111) plane of palladium in each catalyst was measured, and the half-value width of the XRD pattern was measured. Based on this, the crystallite diameter of palladium in each catalyst and the solid solution ratio of iron in palladium (the content of Fe with respect to all atoms in the solid solution) were calculated. In addition, the measurement of the XRD pattern by such an X-ray diffraction uses a scanning name of 0.01 °, a divergence and scattering slit 1/2 deg, using a trade name “RINT-TTR” manufactured by Rigaku Corporation as a measuring device. The measurement was performed under the conditions of a light receiving slit of 0.15 mm, CuKα ray, 40 kV, 30 mA, scan speed 2θ = 0.25 ° / min. The results obtained are shown in Table 6. The solid solution rate of Fe was calculated based on the Vegard law.

  As is clear from the results shown in Table 6, in the exhaust gas-purifying catalyst obtained in Example 1 in which 0.54 parts by mass of Fe was supported on 100 parts by mass of the metal oxide, the crystallite diameter of palladium was Is 30 nm, whereas in the exhaust gas purifying catalyst obtained in Comparative Example 1 that does not carry Fe, the crystallite diameter of palladium is 41 nm. It was confirmed that grain growth (sintering) can be sufficiently suppressed. In the exhaust gas purifying catalyst obtained in Example 1, the solid solution rate of Fe (the content of Fe with respect to all atoms in the solid solution) was 3.4 at%. From these results, Fe—O—Pd bonds are formed on the surface of the Pd particles by the dissolved Fe, and Fe—OM bonds are formed on the metal (M) on the surface of the metal oxide. , Fe binds Pd to M, Pd evaporation and Pd grain growth associated with Pd moving on the surface of the support are sufficiently suppressed, and a sufficiently advanced catalyst even after long-term exposure to high temperatures The present inventors speculate that it is possible to show activity.

As described above, according to the present invention, accumulation of sulfur components in the catalyst can be sufficiently suppressed, and sufficiently high catalytic activity can be exhibited even after long-term exposure to high temperatures. It is possible to provide an exhaust gas purifying catalyst. As described above, the exhaust gas purifying catalyst of the present invention is excellent in high temperature durability and can sufficiently prevent sulfur poisoning, and thus is particularly useful as a catalyst for purifying exhaust gas from automobiles.

Claims (5)

A support made of a metal oxide on which at least one additive component selected from the group consisting of phosphorus and tungsten is supported, and palladium and iron supported on the support,
The supported amount in terms of metal is that the supported amount of the additive component is 0.3 to 9.0 parts by mass and the supported amount of palladium is 0.1 to 10 parts by mass with respect to 100 parts by mass of the metal oxide. And the supported amount of iron is 0.06 to 2.0 parts by mass,
An exhaust gas purifying catalyst characterized by.   The exhaust gas purifying catalyst according to claim 1, wherein the metal oxide contains alumina. The carrier is a carrier having a base point amount of 17.8 to 38 μmol-CO ₂ / g determined on the basis of CO ₂ desorption amount per gram of carrier measured by CO ₂ temperature-programmed desorption measurement. The exhaust gas-purifying catalyst according to claim 1 or 2.   The exhaust gas-purifying catalyst according to any one of claims 1 to 3, wherein a part of the iron is dissolved in a part of the palladium.   The exhaust gas-purifying catalyst according to any one of claims 1 to 4, further comprising an oxide having an oxygen absorption / release capability.

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