JP2002177788A - Exhaust gas cleaning catalyst and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst capable of efficiently cleaning the hydrocarbon, carbon monoxide and SOF in an exhaust gas of an internal combustion engine including a diesel engine and to provide its manufacturing method. SOLUTION: The exhaust gas cleaning catalyst is obtained by coating a catalyst component on an integrated structure type carrier, and the catalyst component contains a hydrocarbon adsorbing marital and a noble metal deposited on a heat resistant inorganic oxide carrier, and in which particles different in noble metal particle size coexist. In the manufacturing method for the exhaust gas cleaning catalyst, an organic acid is contained in a noble metal salt aqueous solution so that a molar ratio of the organic acid and the noble metal may be a fixed range, and the noble metal is deposited on the heat resistant inorganic oxide carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for purifying exhaust gas and a method for producing the same. More specifically, the present invention relates to a catalyst for purifying exhaust gas immediately after starting an engine of an internal combustion engine under an oxygen-excess atmosphere of 350 ° C. or less. More particularly, the present invention relates to an exhaust gas purifying catalyst for purifying hydrocarbon, carbon monoxide and organic solvent soluble components in exhaust gas with high efficiency and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, for the purpose of purifying hydrocarbons (HC), carbon monoxide (CO) and the like in exhaust gas of an internal combustion engine,
Exhaust gas purification catalysts using noble metals as purification components have been developed. In particular, H in diesel engine exhaust
For the purpose of purifying C, CO and organic solvent soluble components (SOF), development of ordinary monolithic catalysts such as those used in gasoline vehicles has been advanced.

In general, catalysts for purifying diesel engine exhaust gas include (1) a high efficiency of purifying and removing harmful components such as HC, CO and SOF from low temperatures;
Sulfur trioxide (SO ₃ ) of sulfur dioxide (SO ₂ ) generated from a large amount of sulfur components contained in light oil used as fuel
(3) the ability to suppress the production of sulfate (sulfur dioxide is oxidized into sulfur trioxide or sulfuric acid mist) is low, (3) the performance decrease due to the sulfur component of the active ingredient is small, and (4) A catalyst is desired that has a performance such that the performance degradation is small even when particulate matter adheres to the catalyst surface, and (5) the so-called high-temperature durability that can withstand continuous operation under a high load. .

[0004] Conventionally, HC, CO and SOF,
Various proposals have been made for the purpose of increasing the efficiency of burning and removing carbon-based particulate matter and the like. For example, JP-A-55-245
No. 97 discloses, as a platinum group element-based catalyst, rhodium (7.5%) platinum alloy, platinum / palladium (50/5).
0) A mixture, one in which palladium is supported on tantalum oxide or cerium oxide, and an alloy composed of palladium and 75% or less of platinum are disclosed.

In addition, JP-A-61-129030, JP-A-61-149222, and
JP-A-146314 discloses a catalyst composition containing palladium and rhodium as main active components and further adding an alkali metal, an alkaline earth metal, copper, lanthanum, zinc, manganese and the like. 59-82944
The publication discloses a catalyst composition in which copper, an alkali metal, molybdenum or vanadium and a metal according to any combination thereof are combined.

[0006]

However, the conventional catalyst as described above removes HC, CO, and SOF in a low-temperature, oxygen-excess atmosphere of diesel engine exhaust gas, and removes particulate matter in a low-temperature region. There is a problem that the suppression of the decrease in the activity of the active ingredient or the suppression of the decrease in the performance of the active component due to sulfur is insufficient. That is, HC, CO and SOF are used as a catalyst for purifying diesel engine exhaust gas.
There has not yet been found a catalyst capable of purifying methane with high efficiency.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide HC, CO, and CO contained in exhaust gas of an internal combustion engine including a diesel engine exhaust gas. An object of the present invention is to provide an exhaust gas purifying catalyst capable of efficiently purifying SOF and a method for producing the same.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by mixing noble metal particles having different particle sizes on a heat-resistant inorganic oxide carrier, The inventors have found that the problem can be solved, and have completed the present invention.

That is, an exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst comprising a catalyst component coated on a monolithic carrier, wherein the catalyst component comprises an HC adsorbent and a heat-resistant inorganic material. And a precious metal supported on an oxide carrier, wherein particles having different particle diameters of the noble metal are mixed.

Further, a preferred embodiment of the exhaust gas purifying catalyst of the present invention is characterized in that the noble metal includes small particles having a diameter of 1 nm or more and less than 5 nm and large particles having a diameter of 5 nm or more and 20 nm or less. I do.

In the method for producing an exhaust gas purifying catalyst according to the present invention, in producing the exhaust gas purifying catalyst, the aqueous solution of the noble metal salt may contain at least one kind selected from the group consisting of citric acid, acetic acid and oxalic acid. Wherein the molar ratio between the noble metal and the organic acid is such that the total number of moles of the organic acid / the number of moles of the noble metal is 0.25 to 2.0.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In addition, "%" shows a mass percentage unless otherwise specified. The exhaust gas purifying catalyst of the present invention is obtained by coating a catalyst component on a monolithic carrier. The catalyst component contains an HC adsorbent and a noble metal supported on a heat-resistant inorganic oxide carrier. Examples of the noble metal include platinum (Pt), palladium (Pd), and rhodium (Rh). These noble metals include CO, HC, and nitrogen oxides (NOx) in exhaust gas.
And redox reaction of SOF components and the like. In particular, in a diesel engine exhaust gas purifying catalyst, it is preferable to use Pt.

The noble metal is supported on the heat-resistant inorganic oxide in the form of fine particles. These particles are mixed with particles having different particle sizes, and are small particles (DS) and large particles (D).
L). Transmission electron microscope (TE
In the measurement according to M), it is preferable that particles having a particle size of 1 nm or more and less than 5 nm are DS, and particles having a particle size of 5 nm or more and 20 nm or less are DL, and these are dispersed and supported. As described above, by allowing DS and DL to coexist on the heat-resistant inorganic oxide carrier, the oxidation reaction of CO easily occurs on DS, and the oxidation reaction of unburned HC easily occurs on DL.

When the area occupied by DS and DL is measured by TEM with DS and DL supported on the heat-resistant inorganic oxide carrier, the total area of DS / DL
Is preferably 1/4 to 4/1. That is, the total area ratio of DS and DL when the noble metal particles are projected on a plane when the heat-resistant inorganic oxide carrier is viewed from above, in other words, when DS and DL are cut into a spherical crown, D
It is preferable that the total cross-sectional area ratio of S and DL is 1/4 to 4/1. If the area ratio between DS and DL is out of the above range, HC, CO and S in a low temperature and oxygen excess atmosphere
OF removal efficiency may be reduced. Specifically, when DS / DL is less than 1/4, DS is small,
It is presumed that HC / CO purification is mainly performed on the DL, and sufficient HC / CO purification performance is not exhibited. When DS / DL is 1/1, HC / CO purification is performed on both DS and DL, and DL becomes a heat spot, so that even if the exhaust gas is at a low temperature and the catalyst is not easily heated, the purification activity can be maintained. it can. When DS / DL is more than 4/1, the amount of DS is too large for DL, the heat spot effect of DL is weakened, the catalyst is hardly heated, and sufficient HC / CO purification performance cannot be obtained. is there.

Further, as described above, the catalyst component is HC
In the low temperature range of 200 ° C. or less immediately after the start of the engine, liquid SOF is preferentially captured by the HC adsorbent. Further, since the HC adsorbent and the noble metal particles coexist in the catalyst component, it is possible to prevent SOF from being adsorbed on the noble metal particles and to suppress the deterioration of the noble metal particles from being activated. At the same time, it is possible to promote the development of a purification reaction between the precious metal such as Pt and the unburned HC and CO. Further, DL in which the oxidation reaction of unburned HC occurs becomes a heat spot,
It is presumed that the oxidation reaction of the SOF captured by the adsorbent can be promoted. Thus, HC, C in the catalyst
By providing a reaction field where the oxidation reaction of O and SOF easily occurs, HC,
CO and SOF can be efficiently removed.

Further, the HC adsorbent is preferably a zeolite according to ZSM5, mordenite, USY or β-zeolite and any combination thereof.
Even immediately after the start of the engine, the liquid SOF can be preferentially captured by the HC adsorbent even in a low temperature range of 200 ° C. or less. Further, the content of the zeolite is 5% of the catalyst component.
It is preferably 0% to 90%. If the content is less than 50%, the effect as an HC adsorbent is not sufficiently exhibited, and
%, The effect as an HC adsorbent is saturated, and even if the amount is further increased, the effect may not be improved. Further, when the content is within the range, the trapping efficiency of SOF is increased, the adsorption of SOF on the noble metal particles such as Pt is suppressed, and the purification reaction between the noble metal and CO / unburned HC is promoted. be able to.

The heat-resistant inorganic oxide carrier contained in the catalyst component is represented by the following formula: W _X Zr _1-X O ₂ (wherein W is tungsten, and X is 0.05 to 0. 2
5)). X is preferably 0.05 to 0.25, and 0.05
If it is less than W, the effect of W will not be sufficiently exhibited. Conversely, if it exceeds 0.25, the effect of W may be saturated. Furthermore,
As the heat-resistant inorganic oxide carrier, a zirconium oxide represented by the following formula S _X Zr _1-X O 2 (where S represents sulfur and X represents 0.05 to 0.25) is used. These zirconium oxides may be used as a mixture. X is in the range of 0.
If it is less than 0.05, the effect of S is not sufficiently exhibited, and if it exceeds 0.25, the effect of S may be saturated. By using these zirconium oxide for the heat-resistant inorganic oxide carrier,
Even in a low-temperature, oxygen-excess atmosphere, the active site Pt
HC components which are hardly adsorbed on the noble metal particles can be preferentially adsorbed and oxidized and removed.

Further, the heat-resistant inorganic oxide carrier is preferably a titanium oxide (titanium dioxide) having a particle diameter of 100 nm or less, and preferably 50% or more of the titanium oxide has an anatase structure. By using a titanium oxide, CO can be oxidized and removed at a low temperature and in an oxygen-excess atmosphere on a noble metal particle such as Pt which is an active site. When the particle size exceeds 100 nm, the effect of promoting the low-temperature CO oxidation reaction of titanium oxide is reduced,
When the content of the anatase type structure is less than 50%, low temperature C
The effect of promoting the O oxidation reaction may be reduced.

In producing the exhaust gas purifying catalyst of the present invention, when the above-mentioned noble metal is supported on the above-mentioned refractory inorganic oxide carrier, an aqueous solution of a water-soluble noble metal salt contains citric acid, acetic acid or oxalic acid and any of these. And the molar ratio of the noble metal and the organic acid is preferably 0.25 to 2.0 in total moles of the organic acid / moles of the noble metal. In order to support the noble metal particles on the refractory inorganic oxide carrier, usually, an aqueous solution of the noble metal is prepared, and then dried by impregnating the aqueous solution with the refractory inorganic oxide carrier.
A method of firing and leaving only noble metal is adopted. If the organic acid is contained in the aqueous solution of the noble metal at the above molar ratio, the loading of the noble metal can be controlled so that the area ratio of DS and DL becomes 1/4 to 4/1. If the molar ratio exceeds 2.0, the heat generated during decomposition and combustion of the organic acid is large, and the distribution of the noble metal particle diameter cannot be set within a predetermined range. Similarly, the distribution of the noble metal particle diameter may not be set in a predetermined range.

The total amount of the catalyst component supported is preferably 10 to 350 g / L per liter of the refractory monolithic carrier, and the supported amount of the HC adsorbent is 5 to 20 g / L.
0 g / L, the loading amount of the heat-resistant inorganic oxide carrier is 1-2.
00 g / L, supported amount of the above-mentioned noble metal is 0.1 to 10 g / L
It is preferred that

The above-mentioned monolithic carrier is preferably a carrier structure made of a heat-resistant material, such as a ceramic open-flow or wall-flow carrier structure.
An iC carrier or a metal carrier can also be used.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Example 1) An aqueous solution in which platinum dinitrodiamminate and citric acid were dissolved in powder of titanium oxide (anatase type structure is 80% or more) having an average particle diameter of 30 nm (total moles of organic acid / moles of platinum) = 1.0) and 15
After drying at 0 ° C. for 24 hours, the mixture was calcined at 300 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain Pt-supported titanium oxide powder (powder a). The Pt concentration of this powder a was 15.0%
Met. Pt-supported titanium oxide powder (powder a) 26
7 g, β-zeolite powder 1000 g, activated alumina powder 483 g, nitric acid acidic alumina sol 50 g (sol obtained by adding 10% nitric acid to 10% boehmite alumina) and 2000 g of pure water are put into a magnetic ball mill, and mixed and ground. Thus, a slurry liquid was obtained. This slurry liquid was attached to a cordierite-based monolithic carrier (400 cells / 8 mil, 1.3 L), excess slurry in the cells was removed by air flow, dried, and baked at 400 ° C. for 1 hour to form a coating layer. The coating operation was repeated until the weight reached 180 g / L to obtain Catalyst-a of this example.

(Example 2) An aqueous solution in which platinum dinitrodiamminate and citric acid were dissolved in a titanium oxide powder having an average particle diameter of 30 nm (anatase type structure is 80% or more) (total number of moles of organic acid / number of moles of platinum) = 1.0) and 15
After drying at 0 ° C. for 24 hours, the mixture was calcined at 300 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain Pt-supported titanium oxide powder (powder b). The Pt concentration of this powder b was 5.0%. Pt-supported titanium oxide powder (powder b) 800
g, β-zeolite powder 980 g, nitric acid acidic alumina sol 20 g (sol obtained by adding 10% nitric acid to 10% boehmite alumina) and pure water 2000
g was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (400 cells / 8 mil, 1.3 L), and the excess slurry in the cells was removed by an air stream and dried.
It was baked at 00 ° C. for 1 hour, and the coating operation was repeated until the coat layer weight became 180 g / L, to obtain Catalyst-b of this example.

Example 3 The same operation as in Example 1 was repeated except that the total number of moles of organic acid / the number of moles of platinum was 1.5, to obtain a catalyst-c of this example.

Example 4 The same operation as in Example 1 was repeated except that the total number of moles of organic acid / the number of moles of platinum was 2.0, to obtain a catalyst-d of this example.

Example 5 The same operation as in Example 1 was repeated except that the total number of moles of organic acid / the mole number of platinum was 0.5, to obtain a catalyst-e of this example.

(Example 6) Instead of titanium oxide powder having an average particle diameter of 30 nm (anatase type structure is 80% or more) powder, W _0.1 Zr _0.9 O ₂ powder was used, and platinum dinitrodiamminate and citric acid were used. Impregnated with an aqueous solution of an acid (total moles of organic acid / moles of platinum = 1.0)
After drying for 4 hours, at 300 ° C. for 1 hour, then 600 ° C.
C. for 1 hour to obtain Pt-supported zirconium oxide powder (powder c). The Pt concentration of this powder c was 15.0%. Pt-supported zirconium oxide powder (powder c) 2
67 g, β-zeolite powder 1000 g, activated alumina powder 483 g, nitric acid acidic alumina sol 50 g (sol obtained by adding 10% nitric acid to 10% boehmite alumina) and 2000 g of pure water are put into a magnetic ball mill and mixed and pulverized. Thus, a slurry liquid was obtained. This slurry liquid is applied to a cordierite monolithic carrier (400 cells / 8
Mill, 1.3 L), the excess slurry in the cell was removed by an air stream, dried, baked at 400 ° C. for 1 hour, and the coating operation was repeated until the coat layer weight became 180 g / L. Of catalyst-f was obtained.

(Example 7) The same operation as in Example 6 was repeated except that S _0.1 Zr _0.9 O ₂ powder was used instead of W _0.1 Zr _0.9 O ₂ powder. , The catalyst of this example-
g was obtained.

Example 8 β-zeolite powder 1000
g instead of β-zeolite powder 700 g, ZSM5
The same operation as in Example 1 was repeated, except that 300 g of the powder was used, to obtain a catalyst-h of this example.

Example 9 β-zeolite powder 1000
Catalyst-i of this example was obtained in the same manner as in Example 1, except that 400 g of β-zeolite powder, 200 g of mordenite powder, 200 g of ZSM5 powder, and 200 g of USY powder were used instead of g.

Example 10 The same operation as in Example 1 was carried out except that 134 g of powder a and 134 g of ZrO ₂ powder supporting 15.0% of Pt were used instead of 267 g of powder a, to obtain catalyst-j of this example. Was.

(Example 11) Instead of 267 g of powder a, 134 g of powder a and W _0.1 Zr carrying 15.0% Pt were used.
Except that 134 g of _0.9 O ₂ powder was used, the same operation as in Example 1 was performed to obtain Catalyst-k of this example.

Example 12 Instead of 267 g of powder a, 134 g of powder a and S _0.1 Zr carrying 15.0% Pt were used.
Except for using 134 g of _0.9 O ₂ powder, the same operation as in Example 1 was performed to obtain Catalyst 1 of this example.

(Example 13) Instead of powder a, powder a
220 g, Pt 1.0% supported β-zeolite powder 700
Except for using g, the same operation as in Example 1 was performed to obtain Catalyst-m of this example.

Example 14 β-zeolite powder 100
The same operation as in Example 1 was carried out except that 700 g of β-zeolite powder was used instead of 0 g, and the catalyst-n of this example was used.
I got

Example 15 β-zeolite powder 100
The same operation as in Example 1 was carried out except that 1500 g of β-zeolite powder was used instead of 0 g, and the catalyst of the present example was used.
o was obtained.

Example 16 The same operation as in Example 1 was carried out except that acetic acid was used instead of citric acid, to obtain a catalyst-p of this example.

Example 17 The same operation as in Example 1 was carried out except that oxalic acid was used instead of citric acid, to obtain a catalyst q of this example.

Example 18 The same operation as in Example 1 was performed except that titanium oxide having an average particle diameter of 100 nm was used.
Catalyst-r of this example was obtained.

Comparative Example 1 The same operation as in Example 1 was carried out except that β-zeolite was not used.
aa was obtained.

Comparative Example 2 Instead of 267 g of powder a, P
Except for using 267 g of β-zeolite carrying t15%,
The same operation as in Example 1 was performed to obtain catalyst-bb of this example.

Comparative Example 3 The same operation as in Example 1 was carried out except that no organic acid was used, to obtain a catalyst-cc of this example.

(Comparative Example 4) The same operation as in Example 1 was carried out except that the total number of moles of organic acid / the number of moles of platinum was set to 10,
The catalyst-dd of this example was obtained.

Comparative Example 5 The same operation as in Example 1 was carried out except that titanium oxide having an average particle size of 100 nm and a rutile structure was used, to obtain a catalyst-ee of this example.

Table 1 shows the specifications of the exhaust gas purifying catalysts of the above Examples and Comparative Examples.

[0047]

[Table 1]

For each of the above Examples and Comparative Examples, HC and CO purification characteristics were evaluated (ECE + EUDC in Europe) using the evaluation system shown in FIG. 1 under the following evaluation conditions.

<Endurance conditions> Engine displacement 2500cc Fuel JIS No. 2 light oil Catalyst inlet gas temperature 600 ° C Endurance time 100 hours

<Performance evaluation conditions> Catalyst capacity Catalyst 1.3L Evaluation vehicle Nissan Motor Co., Ltd. V type 6
Cylinder 2.5L diesel engine

Further, regarding the purification rates of HC and CO,
The following equation and HC purification rate (%) = ([catalyst inlet HC concentration] − [catalyst outlet HC concentration]) / [catalyst inlet HC concentration] × 100 CO purification rate (%) = ([catalyst inlet CO concentration] − [Catalyst outlet CO concentration]) / [Catalyst inlet CO concentration] × 100 An expression was obtained, and the results are shown in Table 2.

[0052]

[Table 2]

Each of the above Examples is different from each of the above Comparative Examples.
All have high catalytic activity, unburned HC, CO and SOF
Has excellent purifying performance from low temperatures, and it has been confirmed that HC, CO and SOF can be purified with high efficiency as a catalyst for purifying diesel engine exhaust gas.

[0054]

According to the catalyst of the present invention, noble metal particles having different particle diameters are mixed on the heat-resistant inorganic oxide carrier. A catalyst capable of efficiently purifying CO and SOF can be provided.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an evaluation system for an exhaust gas purifying catalyst.

[Explanation of symbols]

 1 engine 2 catalyst

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 37/02 301 F01N 3/08 A F01N 3/08 3/10 A 3/10 3/24 E 3 / 24 B01D 53/36 104B 104Z F-term (reference) 3G091 AA02 AA18 AA28 AB01 AB10 BA00 BA03 BA14 BA15 BA19 BA39 FA02 FA04 FB02 FB10 FC04 FC07 GA06 GB01X GB05W GB06W GB07W GB09Y GB10X GB16X GB19X HA18 4A048 A03 BA18 BA11X BA27X BA30X BA31Y BA32Y BA33Y BA41X BA42X BA46X BB02 BB17 DA03 DA06 EA04 4G066 AA61B BA05 CA51 DA02 FA03 FA14 FA21 FA22 FA37 4G069 AA03 AA08 AA09 BC01A BA01B BA04A BA04BBA10BBABBBABBABAB BC75A BC75B BE08C EA19 EB18X EB18Y EC22Y FA01 FA06 FB14 FB16 FC04 FC08 ZA05A ZA06A ZA11A ZA 19A ZA19B

Claims (8)

[Claims] An exhaust gas purifying catalyst comprising a catalyst component coated on a monolithic carrier, wherein the catalyst component comprises an HC adsorbent and a noble metal supported on a heat-resistant inorganic oxide carrier. An exhaust gas purifying catalyst comprising: a mixture of particles having different particle diameters of the noble metal. 2. The particle size of the noble metal is 1 nm or more and 5 nm or more.
The exhaust gas purifying catalyst according to claim 1, comprising small particles having a particle size of less than 10 nm and large particles having a size of 5 nm or more and 20 nm or less. 3. The total cross-sectional area ratio of small particles and large particles of a noble metal supported on the heat-resistant inorganic oxide carrier is 1/4 to 4 /
The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is 1. 4. The exhaust gas purification according to claim 1, wherein the noble metal is at least one noble metal selected from the group consisting of platinum, palladium and rhodium. Catalyst. 5. The heat-resistant inorganic oxide carrier comprises zirconium oxide, wherein the zirconium oxide is
Equation _{W X Zr 1-X O 2} ... (W in the formula, tungsten, X is 0.05 to 0.2
5) and / or the following formula S _X Zr _1-X O ₂ (wherein S represents sulfur and X represents 0.05 to 0.25). The exhaust gas purifying catalyst according to any one of claims 1 to 4. 6. The heat-resistant inorganic oxide carrier contains a titanium oxide, and the titanium oxide has a particle size of 100 nm or less.
Item 5. The exhaust gas purifying catalyst according to any one of Items 5 to 5. 7. The HC adsorbent is at least one zeolite selected from the group consisting of ZSM5, mordenite, USY and β-zeolite, and the content of the HC adsorbent is 50 to 50% of the catalyst component. The exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein the catalyst is 90%. 8. The method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 7, wherein the aqueous solution of the noble metal salt contains at least one selected from the group consisting of citric acid, acetic acid, and oxalic acid. Kinds of organic acids, and the molar ratio of the noble metal to the organic acid is the total number of moles of the organic acid /
A method for producing an exhaust gas purifying catalyst, wherein the number of moles of the noble metal is from 0.25 to 2.0.