JP5131053B2 - Precious metal supported catalyst and catalyst device - Google Patents

Description

  The present invention relates to a noble metal supported catalyst and a catalyst device in which the noble metal supported catalyst is coated on a base material.

  In a noble metal-supported catalyst in which noble metal particles are supported on a carrier as a catalyst component, the noble metal particles are finely supported on a carrier in order to improve the activity. This is to make the specific surface area of the catalyst component as wide as possible. However, if the particle size of the catalyst component is reduced, its surface energy increases, and therefore it becomes easier to sinter (sinter) each other. In particular, in the exhaust gas purification catalyst, the noble metal-supported catalyst is exposed to a high temperature of several hundred degrees due to the heat of the exhaust gas and the heat generated by the reaction, so that the sintering of the noble metal particles proceeds and the particle size increases and becomes active. Tends to decrease.

  Many studies have been made on the prevention of sintering of precious metals as described below.

  Patent Document 1 proposes an exhaust gas purification catalyst in which a white metal catalyst metal is supported as large colloidal particles on a highly active ceria powder. In Patent Document 1, according to this exhaust gas purification catalyst, sintering of catalyst metals and solid solution with ceria powder can be prevented.

In Patent Document 2, the general formula (La _a-x M _x ) (Si _6-y N _y ) O _27-z (wherein M represents Ca, Al, Ce, Ba, Sr, Li, Nd, and Pr). N represents a cation such as Fe, Cu and Al, 8 ≦ a ≦ 10, 0 ≦ x ≦ 5, 0 ≦ y ≦ 3, and 0 ≦ z. An exhaust gas purifying catalyst characterized in that it comprises a composite oxide having an apatite structure represented by ≦ 2 and a noble metal component that is solid solution or supported on the composite oxide.

  Patent Document 3 proposes a support composed of a composite oxide of an electron-accepting element such as lanthanum, neodymium, yttrium, or magnesium and another element such as silicon, aluminum, zirconium, or titanium. . In the carrier of Patent Document 3, electrons contained in the noble metal element are coordinated to the composite oxide constituting the carrier, thereby preventing or suppressing the movement of the noble metal and sintering caused by the noble metal. Patent Document 4 proposes a method for producing a composite metal oxide that can be used as such a carrier.

  In Patent Document 5, a rare earth element, an alkaline earth element, zirconium, and a noble metal are included, and the atomic ratio of the alkaline earth element to the sum of the rare earth element and zirconium is not less than 0.1 atomic% and less than 10 atomic%. Proposed a catalyst for exhaust gas purification in which part of the element and part of zirconium form a composite oxide with at least part of the alkaline earth element, and the composite oxide and part of the noble metal form a solid solution. doing.

  Patent Document 6 proposes a catalyst containing a perovskite complex oxide in which a noble metal is dissolved.

In Patent Document 7, wherein _{Ca 10-z (HPO 4)} z (PO 4) 6-z X 2-z · nH 2 O ( wherein, z = 0~1, n = 0~1 , X is OH or In the apatite compound represented by (halogen element), an exhaust gas purifying catalyst in which Pt is incorporated at the position of Ca ion is proposed.

  That is, in each of Patent Documents 1 to 7, a certain kind of bond is generated between the carrier and the noble metal supported thereon, thereby preventing or suppressing the movement of the noble metal and sintering caused by the bond.

As the noble metal-supported catalyst, it has also been proposed to use a catalyst supporting a plurality of types of noble metals. For example, in an exhaust gas purification catalyst, platinum having excellent properties with respect to oxidation of NO for storing NO _x , and CO In addition, it has been proposed to use in combination with rhodium which has excellent properties with respect to the oxidation of HC, particularly with respect to HC. In this regard, as described in Patent Document 8, when platinum and rhodium are used in combination, the surface of platinum is covered with rhodium during the use of the catalyst, thereby reducing the NO oxidation ability by platinum. There was a problem.

Therefore, as a method for solving this problem, in Patent Document 8, platinum, a relatively low concentration of rhodium, and a first carrier particle carrying a NO _x storage material such as an alkali metal, and a relatively high concentration of rhodium are used. An exhaust gas purification catalyst is proposed in which the second carrier particles supported are mixed. Here, in the first carrier particles, platinum and rhodium are used in combination while preventing the problem that the surface of platinum is covered with rhodium because the supported amount of rhodium relative to the supported amount of platinum is relatively small. Have gained that.

JP-A-4-180835 JP 2007-144212 A JP 2007-144393 A JP 2008-24529 A JP 2006-346586 A JP 2006-346602 A JP-A-11-197507 JP 2008-104924 A

  As described above, a noble metal supported catalyst, particularly a noble metal supported catalyst used at a relatively high temperature, such as an exhaust gas purification catalyst, causes some kind of bond between the support and the noble metal supported thereon. Therefore, it has been proposed to prevent or suppress the movement of the noble metal and the sintering of the noble metal resulting therefrom.

  Although prevention or suppression of sintering of the noble metal by some kind of bond between the support and the noble metal is effective for keeping the particle size of the noble metal small, this bond between the noble metal and the support is effective. It is conceivable that the noble metal has an oxide-like property, so that the original characteristics of the noble metal cannot be sufficiently exhibited. In particular, when the noble metal is held in solid solution in the support, it is considered that the noble metal cannot sufficiently exhibit the activity as a catalyst in an oxidizing atmosphere.

  The present invention has been made paying attention to the above technical problem, while preventing the sintering of the noble metal supported on the carrier, particularly platinum, while mitigating the influence of the bond between the noble metal and the carrier, The purpose is to fully exhibit the original characteristics of noble metals.

  The present inventor has found that the above-described problems can be solved by the present invention described below.

[1] having a carrier and platinum supported on the carrier;
The carrier further carries another noble metal selected from the group consisting of rhodium, palladium, gold, and combinations thereof; and the carrier is selected from the group consisting of lanthanum, neodymium, yttrium, and combinations thereof. an electron accepting element is silicon, aluminum, titanium and is composed of a composite oxide containing other elements selected from the group consisting a combination thereof, and the electron accepting element and said other The molar ratio of the electron-accepting element to the total with the element is 0.3 or more;
A noble metal-supported catalyst for exhaust gas purification or oxidation at the cathode of a fuel cell .

  [2] The above-mentioned [1], wherein the molar ratio of the supported amount of the other noble metal to the supported amount of platinum and the other noble metal supported on the carrier is 0.001 to 0.500. Noble metal supported catalyst.

  [3] The noble metal-supported catalyst according to the above [1] or [2], wherein the supported amount of platinum and the other noble metal supported on the carrier is 1% by mass or less based on the carrier. .

[4] The other element is silicon, and a molar ratio of the electron accepting element to a total of the electron accepting element and the other element is 0.5 to 0.7.
The noble metal-supported catalyst according to any one of [1] to [3] above.

[5] The other elements, aluminum, selected from the group consisting of titanium, and combinations thereof, and the molar ratio of the electron accepting element to a total of the said electron accepting element and said other elements, 0 .3-0.7,
The noble metal-supported catalyst according to any one of [1] to [3].

  [6] A catalyst device comprising a base material coated with the noble metal-supported catalyst according to any one of [1] to [5].

  [7] The catalyst device according to the above [6], wherein the supported amount of platinum and the other noble metal supported on the substrate is 1.0 g / substrate-L or less in total.

  According to the noble metal-supported catalyst of the present invention, it is possible to reduce the influence of the bond between platinum and the carrier while preventing sintering of platinum supported on the carrier, and to fully exhibit the original characteristics of platinum. it can. Therefore, according to the noble metal supported catalyst of the present invention, sufficient catalytic activity can be obtained even when the total amount of noble metal used in the noble metal supported catalyst is relatively small.

[Precious metal supported catalyst of the present invention]
The noble metal-supported catalyst of the present invention is a noble metal-supported catalyst for exhaust gas purification or oxidation at the cathode of a fuel cell , and has a support and platinum supported on the support, and the support includes rhodium, palladium, gold And other noble metals selected from the group consisting of combinations thereof. Here carrier, lanthanum, neodymium, yttrium, and an electron accepting element is selected from the group consisting a combination thereof, silicon, aluminum, and other elements selected from the group consisting of titanium and combinations thereof And a molar ratio of the electron-accepting element to the total of the electron-accepting element and other elements is 0.3 or more.

[Carrier]
Carriers used in the noble metal loaded catalyst of the present invention, the selection of lanthanum, neodymium, yttrium, and an electron accepting element is selected from the group consisting a combination thereof, silicon, aluminum, from the group consisting of titanium and combinations thereof It is comprised from the complex oxide containing other elements to be made.

  Here, these electron-accepting elements are selected as elements that have an electron-accepting property for accepting electrons from platinum when platinum approaches or comes into contact with them, and whose valence does not change in a normal oxidation-reduction reaction. It is considered that the electron acceptability of these elements is provided by the fact that there is a lot of space in the 4d, 4f or 5d orbit of the inner shell. It is preferable that the valence of the electron-accepting element does not change in a normal oxidation-reduction reaction in order to stably fix platinum to the support in both the oxidation atmosphere and the reduction atmosphere. In this regard, the noble metal-supported catalyst of the present invention is a conventional noble metal-supported catalyst as proposed in Patent Document 1, that is, a conventional noble metal-supported catalyst that prevents platinum sintering with ceria that has a tendency to change its oxidation number. It is different from the catalyst.

  As described in Patent Document 3 above, in a carrier that uses an element that accepts electrons from platinum when platinum approaches or contacts, and that does not change valence in a normal oxidation-reduction reaction. 2, platinum (Pt) supplies electrons to the electron-accepting element (La) in a coordinated manner by the mechanism shown for lanthanum (La) as the electron-accepting element and silicon (Si) as the other element. Thus, it is considered that they are bound to the carrier and fixed on the carrier.

  In particular, as shown in FIG. 2, when the other element is an element having a high electronegativity as a metal oxide such as silicon (Si) or titanium (Ti), the lanthanum (La) is used. An electron is strongly attracted from an electron-accepting element, thereby increasing the effect of stabilizing the ion (La ion) of the electron-accepting element.

In the present invention, since “electronegativity as a metal oxide” is simple, the electronegativity due to poling of the metal elements constituting the metal oxide and oxygen is determined based on these elements contained in the metal oxide. The weighted average value is set according to the ratio. Thus, for example, the electronegativity of silica (SiO ₂ ) as a metal oxide is calculated as follows:
{1.90 (Electronegativity of silicon) × 1 + 3.44 (Electronegativity of oxygen) × 2} / 3
≒ 2.93

  For reference, the electronegativity as metal oxide for some metals is shown in Table 1 below:

Regarding the mechanism shown in FIG. 2, according to XPS analysis (X-ray photoelectron spectroscopic analysis) after reduction of H ₂ at 400 ° C. on the lanthanum oxide-silica support, platinum is oxidized despite the reduction. The result which supports is obtained.

Also, lanthanum oxide carrying from 1% platinum with respect to the support - silica _{(La 10} Si _{6 O 27)} carrier, and neodymium oxide carrying from 1% platinum with respect to the support - zirconia _{(NdZrO 3.5} ) The support was calcined in air at 800 ° C. for 2 hours, after which XPS analysis was performed. According to this, platinum was supported in a tetravalent and divalent oxidized state on a lanthanum oxide-silica support and a neodymium oxide-zirconia support, despite being formed by supporting platinum on the support. I understood.

  On the other hand, according to the same XPS analysis on the ceria-zirconia (Ce: Zr = 1: 1 (molar ratio)) support carrying 1% by mass of platinum with respect to the support, Was supported in a divalent or zero-valent state, and it was found that platinum supported in a tetravalent state was substantially absent. Furthermore, the result of XPS analysis with alumina attached to platinum nanoparticles shows that most of platinum is not oxidized. That is, platinum is supported as a metal in a normal carrier. (RM Navarro et al., Applied Catalysis B: Environmental 55 (2005) 229-241).

  The effect of preventing platinum sintering for the support considered to be used in the noble metal-supported catalyst of the present invention is shown in Table 2 below, cited from Patent Document 3.

  The carriers used in connection with this Table 2 were obtained using the microemulsion method, and after loading 1% by weight of platinum particles on these carriers and calcining in air at 800 ° C. for 2 hours, The particle size of platinum is measured.

As is clear from Table 2, the support used in the noble metal-supported catalyst of the present invention has a clear effect on alumina, zirconia, titania and silica with respect to the suppression of sintering of platinum particles. Supports that have a particularly large sintering suppression effect include lanthanum oxide-silica composite oxide (La ₁₀ Si ₆ O ₂₇ ), neodymium oxide-silica composite oxide (Nd ₁₀ Si ₆ O ₂₇ ), neodymium oxide-zirconia composite oxide ( NdZrO _3.5 ) and yttrium oxide-silica composite oxide (Y ₁₀ Si ₆ O ₂₇ ).

[Mole ratio of carrier-electron-accepting element]
Conventionally, when an element such as neodymium or lanthanum is added to an oxide of another element such as zirconium, the molar ratio of the electron-accepting element to the sum of the element such as neodymium and the other element is 0.01 to 0.3. It is generally known that when it is about the degree, oxides of other elements are stabilized by an element such as neodymium and the heat resistance as a carrier is improved.

  However, unexpectedly, the molar ratio of elements such as neodymium is relatively large, for example, 0.3 or more, particularly 0.4 or more, thereby reducing the heat resistance of the support and reducing the surface area of the support. Even in this case, sintering of the noble metal supported on the carrier is prevented by the affinity between the element such as neodymium and the noble metal.

  Therefore, in the carrier used in the noble metal-supported catalyst of the present invention, the electron-accepting element is selected from the group consisting of lanthanum, neodymium, yttrium, and combinations thereof, and the other elements are silicon, aluminum, zirconium, titanium, and the like. And the molar ratio of the electron-accepting element to the total of the electron-accepting element and other elements is 0.3 or more, particularly 0.4 or more, so that it is supported on the carrier. Prevents platinum sintering.

[Carrier-apatite complex oxide]
In the carrier used in the noble metal-supported catalyst of the present invention, the carrier can be stabilized by making the complex oxide constituting the carrier constitute an apatite type complex oxide.

  When using the apatite-type composite oxide, for example, in the support used in the noble metal-supported catalyst of the present invention, the electron-accepting element is selected from the group consisting of lanthanum, neodymium, yttrium, and combinations thereof, and the other elements are silicon. And the molar ratio of the electron-accepting element to the total of the electron-accepting element and other elements is 0.5 to 0.7. In this case, particularly, the electron-accepting element is lanthanum, the other element is silicon, and the molar ratio of lanthanum to the total of lanthanum and silicon (La / (La + Si)) is 0.5 to 0.7. It is.

  Such apatite-type composite oxides, particularly apatite-type composite oxides composed of lanthanum oxide and silica, exhibit particularly favorable properties with respect to platinum sintering prevention, and thus, for example, at temperatures up to 1,000 ° C. It can be preferably used when a noble metal supported catalyst is used.

[Carrier-pyrochlore type or perovskite type complex oxide]
Further, in the carrier used in the noble metal-supported catalyst of the present invention, the carrier can be stabilized by making the complex oxide constituting the carrier constitute a pyrochlore type or perovskite type complex oxide.

  When using a pyrochlore-type or perovskite-type composite oxide, for example, in the support used in the noble metal-supported catalyst of the present invention, the electron-accepting element is selected from the group consisting of lanthanum, neodymium, yttrium, magnesium, and combinations thereof, The other element is selected from the group consisting of aluminum, zirconium, titanium, and combinations thereof, and the molar ratio of the electron accepting element to the sum of the electron accepting element and the other elements is 0.3 to 0.7. It is. In this case, particularly, the electron accepting element is neodymium, the other element is zirconium, and the molar ratio of neodymium to the total of neodymium and zirconium (Nd / (Nd + Zr)) is 0.3 to 0.7. It is.

  Such pyrochlore-type or perovskite-type composite oxides, particularly pyrochlore-type composite oxides composed of neodymium oxide and zirconia, exhibit particularly preferable properties with respect to platinum sintering prevention. When using the noble metal supported catalyst of the invention, it can be preferably used.

[Carrier-other components]
In the carrier used in the noble metal-supported catalyst of the present invention, as long as the characteristics as the carrier are not lost, the above-described electron-accepting element and other elements than the other elements are contained in the composite oxide, Elements other than the electron-accepting element and other elements may replace the electron-accepting element and other elements.

[Carrier-use form]
In the support used in the noble metal-supported catalyst of the present invention, a composite oxide containing an electron accepting element and another element can be used in the form of particles.

  Further, as described in Patent Document 3, the composite oxide can be supported on other carrier particles having higher heat resistance than the composite oxide, for example, alumina carrier particles. According to this, even if it is a case where it exposes to high temperature by comprising as an exhaust gas purification catalyst etc., it is easy to maintain the structure of said composite oxide, As a result, heat resistance can further be improved. .

[Precious metal]
In the noble metal-supported catalyst of the present invention, platinum and other noble metals selected from the group consisting of rhodium, palladium, gold, and combinations thereof are supported on the support.

  The work function and melting point of other noble metals such as rhodium are shown in Table 3 below.

  As shown in Table 3, other noble metals such as rhodium have a somewhat lower work function than platinum. Here, the fact that the work function of a metal is large means that the tendency for electrons to be taken away from the crystal surface is small.

Therefore, in the noble metal-supported catalyst (10) of the present invention, as shown in FIG. 2, for example, platinum is bonded by a covalent bond between the support (La ₁₀ Si ₆ O ₂₇ ) and platinum (Pt) supported thereon. As shown in FIG. 1, other noble metals such as rhodium (Rh) donate electrons (free electrons, that is, metallic electrons) to platinum (Pt), while achieving the sintering prevention or suppression method. This is considered to improve the mobility of oxygen on platinum (Pt).

  In addition, other noble metals, such as rhodium used here, can keep platinum in a metallic state by contacting with platinum. Therefore, when other metals that always form oxides under the use conditions of the noble metal supported catalyst are used instead of other noble metals such as rhodium, it is not possible to achieve the donation of electrons to platinum, and therefore the noble metal of the present invention. The same effect as the supported catalyst cannot be obtained.

  Among other noble metals supported on the support together with platinum, rhodium has a relatively high melting point, and thus has high heat resistance. Therefore, rhodium is preferably used as the other noble metal in the use of a noble metal-supported catalyst that requires relatively high heat resistance, for example, the use of an exhaust gas purification catalyst. However, when the temperature at which the noble metal-supported catalyst of the present invention is used is relatively low, the melting point of these other noble metals may not be a problem. In such applications, it may be preferable to use palladium (Pd) or gold (Au) as the other noble metal.

  Further, in addition to or instead of the above mechanism, the noble metal-supported catalyst of the present invention supports rhodium or the like by supporting other noble metals such as rhodium having a somewhat lower work function than platinum together with platinum. It is also conceivable that other noble metals are sacrificially oxidized to suppress the oxidation of platinum. Furthermore, in addition to or instead of the above mechanism, in the noble metal-supported catalyst of the present invention, when other noble metals such as rhodium are oxidized, the oxide becomes relatively acidic, thereby causing hydrocarbon components. It is conceivable that the adsorption performance of (HC) is improved.

[Molar ratio of precious metal-supported amount]
In the noble metal-supported catalyst of the present invention, the molar ratio of the supported amount of other noble metals such as rhodium to the supported amount of other noble metals such as platinum and rhodium supported on the carrier depends on the characteristics of the desired noble metal-supported catalyst. Can be determined based on. That is, when this molar ratio is large, the influence of the bond between platinum (Pt) and the carrier can be alleviated and the original characteristics of platinum can be promoted. On the other hand, if this molar ratio is too large, problems due to the abundance of these other noble metals, for example in the case of rhodium, rhodium coats the surface of the platinum during the use of the noble metal supported catalyst, resulting in catalytic activity. It is conceivable that a problem of lowering will occur. In addition, if the total amount of noble metals supported on the support is kept constant and this molar ratio is reduced, the amount of platinum supported is reduced as a result, and it is possible that the catalytic activity by platinum is not sufficiently obtained.

  In this regard, for example, when rhodium is used as another noble metal for the purification of exhaust gas from an internal combustion engine such as an automobile, a relatively high operating temperature is taken into consideration, so this molar ratio is made relatively small so that noble metal is supported. It would be preferable to prevent the problem of rhodium coating the surface of platinum during use of the catalyst. In contrast, when the noble metal-supported catalyst of the present invention is used for reforming a fuel for a relatively low temperature application, for example, a fuel cell, even if rhodium is used as another noble metal, a comparison is made. It is considered that this molar ratio can be made relatively large because a relatively low use temperature is considered.

  Specifically, in the noble metal-supported catalyst of the present invention, the molar ratio of the supported amount of other noble metal to the supported amount of platinum and other noble metals supported on the carrier is 0.001-1.000, 0.001. ˜0.500, or 0.01 to 0.30, or 0.01 to 0.20.

[Noble metal-loading]
As described above, the noble metal-supported catalyst of the present invention can sufficiently exhibit the original characteristics of platinum while preventing platinum sintering. Therefore, in the noble metal-supported catalyst of the present invention, the amount of noble metal used can be reduced as compared with conventional noble metal-supported catalysts. The specific amount of noble metal used can be determined based on the use conditions of the noble metal-supported catalyst, the desired catalytic activity, the price of the noble metal, and the like.

  For example, a noble metal-supported catalyst of the present invention is obtained by supporting a noble metal on a support, and then a base material such as a cordierite honeycomb substrate is coated with the noble metal-supported catalyst of the present invention, and an internal combustion engine such as an automobile When used for purification of exhaust gas from the carrier, the total amount of platinum and other noble metals supported on the carrier is 1% by mass or less, 0.7% by mass or less, 0.5% by mass with respect to the carrier. % Or less.

  Further, for example, the carrier is coated on a substrate such as a cordierite honeycomb substrate, and then the noble metal is supported on the carrier coated on the substrate to obtain the noble metal-supported catalyst of the present invention. When used for purifying exhaust gas from internal combustion engines, the total amount of platinum and other noble metals supported on the carrier is 1.0 g / base-L or less, 0.7 g / base-L Hereinafter, it can be 0.5 g / base-L or less.

[Precious metal-supported catalyst and catalyst device production method of the present invention]
The carrier used in the noble metal-supported catalyst of the present invention can be produced by any method, for example, a coprecipitation method as used in Patent Document 2, a microemulsion method as used in Patent Document 3, It can be produced by a method using colloidal particles and a salt as proposed in Patent Document 4.

  In addition, the production of the noble metal-supported catalyst of the present invention by supporting the noble metal on the carrier can be performed by any method. In order to obtain the catalyst device of the present invention in which the noble metal-supported catalyst of the present invention is supported on a substrate, for example, a honeycomb substrate such as a cordierite honeycomb substrate, the noble metal is supported on a carrier. Obtaining a noble metal supported catalyst of the invention and then coating the noble metal supported catalyst of the present invention on a substrate, or coating a support on a substrate, and then on the support coated on the substrate Precious metals can be supported.

  Here, in order to obtain the catalyst device of the present invention, when a carrier is coated on a substrate, and then a noble metal is supported on the carrier coated on the substrate, the surface portion of the coating layer on the substrate That is, it is possible to increase the concentration of a noble metal in a portion where there is a high probability of contact with a fluid such as exhaust gas treated by the catalyst device of the present invention, and thus it is possible to efficiently use a noble metal such as platinum.

[Use of noble metal supported catalyst of the present invention]
The noble metal-supported catalyst of the present invention can be used in any application that requires catalytic activity with platinum, particularly oxidation activity with platinum. Therefore, for example, the use of the noble metal-supported catalyst of the present invention includes an exhaust gas purification catalyst for purifying exhaust gas from an internal combustion engine such as an automobile such as a gasoline engine and a diesel engine, and an oxidation catalyst at the cathode of a fuel cell. it can.

  Below, this invention is demonstrated using an Example and a comparative example. However, these examples and comparative examples do not limit the present invention in any way.

(Examples 1-4)
A lanthanum oxide-silica composite oxide (La ₁₀ Si ₆ O ₂₇ ) having an apatite structure was obtained by a method using colloidal particles of silica and a lanthanum salt as described in Patent Document 4. Here, the firing temperature of the lanthanum oxide-silica composite oxide was 900 ° C. This lanthanum oxide-silica composite oxide as a support is made into a slurry using a basic silica sol as a binder, and coated on a honeycomb substrate made of cordierite, fired, and lanthanum oxide-silica composite oxidation as a support. A substrate coated with the product was obtained. Here, the coating amount on the honeycomb substrate was 120 g / substrate-L, and the portion derived from the silica sol as the binder in the coating amount was about 8% by mass.

  The base material obtained as described above was immersed in a mixed solution of a dinitrodiammine platinum aqueous solution and a rhodium nitrate aqueous solution for 1 hour, thereby supporting platinum and rhodium on the support, and supporting the noble metal of Examples 1 to 4. A catalyst was obtained. Table 4 shows the supported amounts of platinum and rhodium in each of the noble metal-supported catalysts of Examples 1 to 4.

(Comparative Example 1)
The alumina carrier obtained by firing at 900 ° C. is made into a slurry using an aqueous solution containing alumina sol and aluminum nitrate as a binder, and then coated on a honeycomb substrate made of cordierite and fired to coat the alumina carrier. A substrate was obtained. Here, the coating amount on the honeycomb substrate was 120 g / substrate-L, and the portion derived from the binder in the coating amount was about 8% by mass.

  The base material obtained as described above was immersed in a dinitrodiammine platinum aqueous solution for 1 hour, whereby platinum was supported on a support, and a noble metal-supported catalyst of Comparative Example 1 was obtained. The amount of platinum supported on the noble metal-supported catalyst of Comparative Example 1 was 1.5 g / base material-L.

(Comparative Example 2)
Instead of the alumina support obtained by firing at 900 ° C., a lanthanum oxide-silica-zirconia composite oxide (La _0.07 Ce _0.40 Zr _0.53 O _x ) obtained by firing at 900 ° C. was used. A noble metal-supported catalyst of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that.

(Comparative Example 3)
Comparison except that the lanthanum oxide-silica composite oxide (La ₁₀ Si ₆ O ₂₇ ) having the same apatite structure as in Examples 1 to 4 was used instead of the alumina support obtained by firing at 900 ° C. In the same manner as in Example 1, a noble metal supported catalyst of Comparative Example 3 was obtained.

(Comparative Example 4)
A noble metal-supported catalyst of Reference Example was obtained in the same manner as in Examples 1 to 4 except that rhodium was not supported. The amount of platinum supported on the noble metal-supported catalyst of Comparative Example 4 was 0.5 g / base material-L.

(Comparative Example 5)
In the same manner as in Comparative Example 1, a noble metal-supported catalyst of Comparative Example 5 was obtained. Therefore, in the noble metal-supported catalyst of Comparative Example 5, the supported amount of platinum was 1.5 g / base material-L.

(Comparative Example 6)
A noble metal-supported catalyst of Comparative Example 6 was obtained in the same manner as in Comparative Example 1, except that a mixed solution of a dinitrodiammine platinum aqueous solution and a rhodium nitrate aqueous solution was used instead of the dinitrodiammine platinum aqueous solution. In the noble metal-supported catalyst of Comparative Example 6, the supported amount of platinum was 1.5 g / substrate-L, and the supported amount of rhodium was 0.15 g / substrate-L.

(Comparative Example 7)
A noble metal-supported catalyst of Comparative Example 7 was obtained in the same manner as in Comparative Example 1 except that a mixed solution of a dinitrodiammine platinum aqueous solution and a rhodium nitrate aqueous solution was used instead of the dinitrodiammine platinum aqueous solution. In the noble metal-supported catalyst of Comparative Example 7, the supported amount of platinum was 1.5 g / substrate-L, and the supported amount of rhodium was 0.30 g / substrate-L.

(Evaluation)
For the catalysts of Examples 1 to 4 and Comparative Examples 1 to 4, using a model gas corresponding to an air-fuel ratio (A / F ratio) = 21, in an electric furnace, 2 hours at 800 ° C. or 5 hours at 1,000 ° C. Durability treatment was performed over the entire time. In addition, the catalysts of Comparative Examples 5 to 7 were subjected to an endurance treatment at 650 ° C. for 2 hours using a model gas corresponding to an air-fuel ratio (A / F ratio) = 21. The composition of the model gas used here is shown in Table 4 below.

  With respect to the catalysts of Examples 1 to 4 and Comparative Examples 1 to 7 subjected to endurance treatment, the above model gas was supplied while increasing the temperature, and the HC 50% purification temperature (HC purification rate reached 50%). Catalyst temperature), and the NO oxidation rate at 250 ° C. was measured. The results are shown in Table 5. The low HC 50% purification temperature obtained here and the high NO oxidation rate mean that the activity as a catalyst is high. The reason why the NO oxidation rate was obtained at a relatively low temperature of 250 ° C. is that NO oxidation becomes an equilibrium reaction at a relatively high temperature (about 350 ° C. or higher), and the catalytic activity cannot be measured.

  As is clear from Table 5, the catalysts of Examples 1 to 4 of the present invention showed significantly superior results with respect to the HC 50% purification temperature and NO oxidation compared to the catalysts of Comparative Examples 1 to 4. In particular, when compared with the catalysts of Comparative Examples 1 to 3, the catalysts of Examples 1 to 4 of the present invention showed significantly superior results even though the total supported amount of noble metal (Pt + Rh) was 1/3. It was. In addition, the total supported amount of the carrier and the noble metal used (Pt + Rh) is the same as that of the catalysts of Examples 1 to 4 of the present invention, but in addition to the catalyst of Comparative Example 4 that does not support rhodium, in addition to platinum. The benefits of loading rhodium are obvious.

  In Examples 1 to 4 of the present invention, as the molar ratio of rhodium to the total supported amount of noble metal (Rh / Pt + Rh) increased from 0.019 to 0.174, the HC50 purification temperature was improved. As shown in Comparative Examples 5 to 7, when a general alumina carrier is used, when rhodium is added to platinum, rhodium covers the surface of platinum as the platinum particles become coarse due to durability treatment. By doing so, it is known that the catalytic activity decreases. Therefore, in Examples 1 to 4 of the present invention, the HC 50% purification temperature was improved as the ratio of rhodium to the total supported amount of noble metal (Rh / Pt + Rh) was increased. Met.

  In the catalysts of Examples 1 to 4 of the present invention, as the ratio of rhodium to the total supported amount of noble metal (Rh / Pt + Rh) increased, the NO oxidation rate slightly decreased. However, in any case of Examples 1-4, compared with the catalyst of the comparative example 4 which is the same as that of Example 1-4 except not carrying | supporting rhodium, the outstanding NO oxidation rate is shown. It was.

  In general, NO oxidation occurs after HC oxidation. Therefore, in the catalysts of Examples 1 to 4 of the present invention, as the ratio of rhodium to the total supported amount of noble metal (Rh / Pt + Rh) is increased, the NO oxidation is improved in spite of the improved activity against HC oxidation. The phenomenon that the rate decreases suggests that the NO oxidation ability is greatly decreased with the increase of the Rh addition amount.

  Although described in Patent Document 3, the lanthanum oxide-silica support can suppress platinum sintering, and thus in Examples 1 to 4 and Comparative Examples 3 and 4 using this support. The difference in catalyst performance between the case where the durability treatment is performed at 800 ° C. for 2 hours and the case where the durability treatment is performed at 1,000 ° C. for 5 hours is small.

It is a figure which shows notionally the mechanism of the noble metal carrying | support catalyst of this invention. It is a figure which shows notionally the platinum sintering prevention mechanism by the support | carrier used in the noble metal carrying | support catalyst of this invention.

Explanation of symbols

10 Noble Metal Supported Catalyst of the Present Invention Pt Platinum Rh Rhodium Si Silicon La Lanthanum La ₁₀ Si ₆ O ₂₇ Lanthanum Oxide-Silica Composite Oxide (Support)

Claims (7)

Having a support and platinum supported on said support;
The carrier further carries another noble metal selected from the group consisting of rhodium, palladium, gold, and combinations thereof; and the carrier is selected from the group consisting of lanthanum, neodymium, yttrium, and combinations thereof. an electron accepting element is silicon, aluminum, titanium and is composed of a composite oxide containing other elements selected from the group consisting a combination thereof, and the electron accepting element and said other The molar ratio of the electron-accepting element to the total with the element is 0.3 or more;
A noble metal-supported catalyst for exhaust gas purification or oxidation at the cathode of a fuel cell .   2. The noble metal-supported catalyst according to claim 1, wherein a molar ratio of the amount of the other noble metal supported to the amount of platinum and the other noble metal supported on the carrier is 0.001 to 0.500.   3. The noble metal-supported catalyst according to claim 1, wherein the total amount of platinum and the other noble metal supported on the carrier is 1% by mass or less based on the carrier. The other element is silicon, and the molar ratio of the electron accepting element to the total of the electron accepting element and the other element is 0.5 to 0.7.
The noble metal carrying | support catalyst as described in any one of Claims 1-3. The other elements, aluminum, selected from the group consisting of titanium, and combinations thereof, and the molar ratio of the electron accepting element and the electron accepting element to a total of the said other elements, 0.3 0.7,
The noble metal carrying | support catalyst as described in any one of Claims 1-3. The catalyst apparatus with which the noble metal carrying | support catalyst as described in any one of Claims 1-5 is coated by the base material.   The catalyst device according to claim 6, wherein the total amount of platinum and the other noble metal supported on the base material is 1.0 g / base material-L or less.

Images