JP2012201553A - Amorphous silica zirconium composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel porous body which has pores suited for carrying a noble metal catalyst such as a platinum group metal etc. and which is produced at an extremely low cost.SOLUTION: In the amorphous silica zirconium composite, a ratio Zr/(Si+Zr) is in a range of 0.5 to 15.0 mol%, a pore volume at a pore diameter of 2 to 50 nm is 0.2 to 1.0 cm/g, and desorption of NHmeasured by an NH-TPD method is 0.05 mmol/g or more.

Description

  The present invention relates to an amorphous silica-zirconium composite, and more particularly to an amorphous silica-zirconium composite that is suitably used as a catalyst support for diesel exhaust gas purification.

  Platinum group metals typified by platinum, palladium, and rhodium have a function as exhaust gas purifying catalysts, and those in which such a platinum group metal is supported on a porous carrier are, for example, in automobile exhaust gas. It is used as a catalyst for purifying contained hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) (see Patent Document 1).

  By the way, the platinum group metal as described above is a noble metal and is very expensive. Therefore, the platinum group metal must be held on a porous carrier (catalyst carrier) so that its catalytic function is efficiently exhibited. Accordingly, various proposals have been made for porous carriers that are suitably used as catalyst carriers.

For example, Patent Document 1 proposes that at least one selected from the group consisting of alumina, ceria, zirconia, titania, silica, zeolite, and mesoporous silica is used as a catalyst carrier for supporting the platinum group metal. Has been.
Patent Document 2 proposes that a composite oxide of SiO ₂ and ZrO ₂ is used as a catalyst carrier for an exhaust gas purification catalyst.
Further, Patent Document 3 proposes to use mesoporous silica having uniform mesopores having a regular periodic structure and having Si—O—Zr bonds at a certain ratio as a catalyst carrier.

JP 2004-148166 A JP 7-108137 A Japanese Patent Laid-Open No. 2002-241123

  Among the various catalyst supports described above, mesoporous silica having uniform mesopores having a regular periodic structure can be uniformly dispersed and held without agglomerating the platinum group metal particles. Attention has been paid.

  However, this type of mesoporous silica requires the use of an expensive surfactant in order to form uniform mesopores, and this surfactant is removed by thermal decomposition. There is a problem that can not be done. That is, such mesoporous silica is extremely expensive, and an exhaust gas purifying catalyst in which a platinum group metal is supported is extremely expensive, which hinders its practical application. It is.

Accordingly, an object of the present invention is to provide a novel porous body that has pores suitable for supporting a noble metal catalyst such as a platinum group metal and can be manufactured at a very low cost.
Another object of the present invention is to provide an exhaust gas purifying catalyst carrier comprising the above porous body and an exhaust gas purifying characteristic equivalent to that obtained by supporting a platinum group metal on the carrier and using a conventionally known mesoporous silica as the carrier. The present invention provides an exhaust gas purifying catalyst.

According to the invention, Zr / (Si + Zr) is in the range of 0.5 to 15.0 mol% and the pore volume at a pore diameter of 2 to 50 nm is 0.2 to 1.0 cm ³ / The amorphous silica-zirconium composite is characterized in that the amount of NH ₃ desorbed by the NH ₃ -TPD method is 0.05 mmol / g or more.
In general, the amorphous silica-zirconium composite of the present invention has an average pore diameter of 2.0 to 12.0 nm as measured by a nitrogen adsorption method.

According to the present invention, there is also provided an exhaust gas purifying catalyst carrier comprising the above amorphous silica zirconium composite.
According to the present invention, there is further provided an exhaust gas purifying catalyst comprising a platinum group metal supported on the catalyst carrier.

In the amorphous silica-zirconium composite of the present invention, pores having a certain size (pore diameter of 2.0 to 50 nm) are formed with a constant volume (0.2 to 1.0 cm ³ / g). Therefore, for example, a platinum group metal catalyst that functions suitably as an exhaust gas purifying catalyst can be efficiently supported.

Further, as understood from the fact that this complex exhibits a large NH ₃ desorption amount (0.05 mmol / g or more) measured by the NH ₃ -TPD method, many acid sites are formed on the particle surface. As a result, the exhaust gas-purifying catalyst in which a platinum group metal is supported on the composite exhibits excellent hydrocarbon decomposition characteristics. That is, it is considered that hydrocarbons decomposed and activated on the platinum group metal are adsorbed on the acid sites, and the decomposition is promoted.

Further, the exhaust gas purifying catalyst in which the platinum group metal is supported on the amorphous silica-zirconium composite of the present invention has good heat resistance and excellent catalytic activity even after aging at 750 ° C. for 50 hours. Indicates. That is, as shown in the examples described later, the temperature (T ₅₀ ) for achieving a conversion rate of 50% indicating oxidization activity for decane hardly increased even after the aging treatment, and therefore excellent. It can be seen that the catalytic activity is not impaired by aging. Thus, the reason why the exhaust gas purifying catalyst in which the platinum group metal is supported on this amorphous silica-zirconium composite exhibits excellent heat resistance is not clearly elucidated, but Zr is probably Si. It is presumed that the thermal contraction of the pores is suppressed in connection with being introduced into a part of the —O—Si bond.

  As described above, the exhaust gas purifying catalyst in which the platinum group metal is supported on the amorphous silica-zirconium composite of the present invention exhibits excellent catalytic activity. For example, the platinum group metal is supported on a carrier such as known mesoporous silica. The catalytic activity is equal to or higher than that of the exhaust gas purification catalyst.

  The greatest advantage of the present invention is that this amorphous silica-zirconium composite is amorphous, so it does not require heating at a significantly high temperature for crystallization, and is as expensive as known mesoporous silica. There is no need to use a surfactant or the like, and it can be manufactured at a very low cost. This makes it possible to realize a significant cost reduction for the exhaust gas purifying catalyst.

Furthermore, since the amorphous silica-zirconium composite of the present invention is amorphous and is not formed using a surfactant, in its X-ray diffraction measurement, diffraction peaks derived from the crystal structure and periodically Diffraction peaks derived from regularly arranged mesopores are not observed. For example, in the mesoporous silica disclosed in Patent Document 3, a Zr component is introduced into the SiO ₂ component as in the amorphous silica-zirconium composite of the present invention, and diffraction derived from periodic mesopores. Although a peak is observed, in the present invention, such a diffraction peak is not observed at all.

The amorphous silica-zirconium composite of the present invention is composed of a SiO ₂ component and a Zr component, and is different from, for example, a simple mixture of a SiO ₂ sol and a ZrO ₂ sol. This is understood from comparison with Examples and Comparative Examples described later. That is, in Comparative Example 1 using SiO ₂ gel to which zirconium was not added as a catalyst carrier and Comparative Example 2 using a mixture of SiO ₂ sol and ZrO ₂ sol as a catalyst carrier, measurement was performed by the NH ₃ -TPD method. The amount of NH ₃ desorbed is very small, few acid sites are formed, and the decane conversion 50% achievement temperature (T ₅₀ ) after the aging treatment is remarkably increased from before the aging treatment, and the heat resistance is low. On the other hand, in the embodiment using the amorphous silica zirconium complexes of the present invention as a catalyst carrier, often NH ₃ desorption amount measured by NH ₃ -TPD method, moreover, little difference before and after the T ₅₀ is also the aging process However, the fact is that the amorphous silica-zirconium composite of the present invention is not a simple mixture of SiO ₂ sol and ZrO ₂ sol, but is formed by incorporating Zr into a part of the Si—O—Si bond to form a composite. It shows that.

The X-ray-diffraction figure of the amorphous silica zirconium composite_body | complex (Example 3) of this invention. The X-ray diffraction small angle scattering diagram of the amorphous silica zirconium composite of the present invention (Example 3). The figure which shows the pore distribution by the nitrogen adsorption method (BJH method desorption branch side) of the amorphous silica zirconium composite (Example 3) of this invention.

<Production of amorphous silica-zirconium composite>
As explained above, the amorphous silica-zirconium composite of the present invention is produced without using an expensive agent such as a surfactant and heating at an extremely high temperature (for example, 500 ° C. or more). Is done.
Specifically, an acidic sol of silicic acid and a zirconium salt are mixed to perform gelation, and the resulting gel is treated with aqueous ammonia and washed with water to fix zirconium to the gelated product, and then treated with ammonium chloride. It is manufactured by removing alkali metals such as Na by ion exchange with, and finally adjusting pores by hydrothermal treatment.

1. Acidic sols and zirconium salts;
As the acidic sol of silicic acid used in the above method, water glass sodium silicate or potassium silicate standardized by JIS as an industrial product is used.

In addition, this acidic sol is prepared by reacting an alkali metal hydroxide solution with easily reactive silica recovered from clayey raw materials such as acidic clay, and preparing alkali silicate. It can also be produced by adding a mineral acid.
For example, a sodium silicate aqueous solution containing 21 to 23% by weight of SiO ₂ and a sulfuric acid aqueous solution having a concentration of 42 to 45% by weight are continuously mixed at a high speed in an amount of about 4: 1 by volume ratio to thereby adjust the pH. By adjusting so that it may become the range of 1.6 thru | or 2.2, the acidic sol used by this invention can be obtained.

As the zirconium salt to be mixed with the acidic sol, zirconium nitrate, zirconium sulfate, zirconium chloride and the like can be used, but zirconium nitrate is most preferable from the viewpoint of reactivity and cost.
Such zirconium salt is in such a ratio that Zr is in the range of 0.5 to 15.0 mol%, particularly 3.0 to 6.0 mol%, with respect to the total of Si in the acidic sol and Zr to be added. used. That is, by setting the molar percentage of Zr / (Si + Zr) in this range, the pore distribution and average pore diameter of the finally obtained amorphous silica zirconium composite are within a predetermined range, and a certain amount or more. Thus, it is possible to ensure a solid acid amount such that the amount of NH ₃ desorbed is expressed.

2. Gelation and ammonium treatment;
Zirconium salt is added and mixed in the above amount in the acidic sol for gelation, then treated with aqueous ammonium and washed with water. Thereby, precipitation of a zirconium salt can be avoided and a zirconium ion can be fixed in a gel. Since a certain amount of zirconium ions is present in this gel, pores can be formed by hydrothermal treatment described later so as to exhibit the characteristics as a predetermined catalyst carrier.
The gelation reaction temperature may generally be 10 to 50 ° C.

3. Ion exchange treatment;
Next, the gel obtained above is subjected to an ion exchange treatment using an aqueous ammonium chloride solution and washed with water. Thus, Na content is removed, finally obtained can improve the heat resistance of the amorphous silica zirconium complexes, for example, suppress a reduction in catalytic activity due to aging treatment at a high temperature (increase in T ₅₀₎ It becomes possible to do. That is, if a large amount of Na is contained, the degree of pore shrinkage increases due to heat treatment at high temperature, resulting in a decrease in heat resistance, but the Na content is removed by ion exchange by ammonium chloride treatment. Thus, pore shrinkage due to heat treatment at high temperature can be effectively suppressed, and heat resistance can be enhanced.

The ammonium chloride aqueous solution used for the above ion exchange treatment is usually used in a concentration of 1 to 10% by weight, so that the amount of Na ₂ O per 100 parts by weight of SiO ₂ is 0.3 parts by weight or less. It is preferable to perform processing.

4). Hydrothermal treatment;
Hydrothermal treatment is performed after removal of the Na content by the ion exchange treatment. This is performed to adjust the pores, and is generally performed at a temperature of 80 to 180 ° C. and preferably performed in a sealed state such as an autoclave. Usually, a pore distribution suitable as a catalyst carrier can be obtained in a treatment time of about 6 to 120 hours.
After the hydrothermal treatment, the target amorphous silica zirconium composite can be obtained by drying.

<Amorphous silica-zirconium composite>
The amorphous silica-zirconium composite obtained as described above has a Zr / (Si + Zr) content of 0.5 to 15.0 mol%, particularly 3.0, according to the amount of the acidic sol and zirconium salt used. To 6.0 mol%, and based on such a composition, characteristics such as predetermined pore distribution and solid acid amount are exhibited.

Furthermore, in this amorphous silica-zirconium composite, it is preferable that the amount of Na ₂ O per 100 parts by weight of SiO ₂ is adjusted to 0.3 parts by weight or less from the viewpoint of heat resistance. The Na 2 _O content can be adjusted by ion-exchange treatment with ammonium chloride as already mentioned, it is expressed excellent heat resistance by Na 2 _O amount is reduced, heat treatment at a high temperature The shrinkage of the pores due to the is suppressed, and excellent characteristics as a catalyst carrier are exhibited.

The amorphous silica-zirconium composite has a pore volume of 2 to 50 nm and a pore volume of 0.2 to 1.0 cm ³ / g, particularly 0.4 to 0.8 cm ³ / g. is there. Furthermore, the average pore diameter measured by the nitrogen adsorption method is generally in the range of 2.0 to 12.0 nm, particularly 2.5 to 7.5 nm.
That is, as understood from the pore distribution as described above, the amorphous silica-zirconium composite of the present invention has mesopores having a pore diameter of 2 to 50 nm in addition to macropores having a pore diameter of 50 nm or more. As a result, it has excellent characteristics as a carrier for supporting a noble metal catalyst such as a platinum group metal. This is because such noble metals can be uniformly dispersed and held without agglomerating, and the catalytic function can be maximized.

  In addition, the amorphous silica-zirconium composite is amorphous and is manufactured without using an agent for forming pores such as a surfactant. Are not regularly and periodically formed. Therefore, in the X-ray diffraction measurement of this composite, no diffraction peak derived from the crystal structure or periodic pores is formed as shown in FIG. (In FIG. 1, the broad peak formed in the region of 2θ = 20 to 30 degrees is known to be a peculiar peak observed for amorphous silica. In other words, from this X-ray diffraction characteristic, this amorphous silica-zirconium composite is clearly different from a sintered body of composite oxide of silica and zirconia, and It is understood that this is different from mesoporous silica produced using a surfactant.

The amorphous silica-zirconium composite of the present invention has a large specific surface area in connection with the porous structure as described above, and generally has a BET specific surface area of 300 to 650 m ² / g. , Preferably in the range of 430 to 650 m ² / g.

Furthermore, amorphous silica zirconium complexes of the present invention has a characteristic as a solid _acid, NH ₃ amount desorbed 0.05 mmol / g or more as measured by NH 3 -TPD method, in particular 0.07 mmol / It is in the range of g or more. That is, a large NH ₃ desorption amount indicates that there are many acid sites that adsorb NH ₃ . Such a characteristic as a solid acid is formed on the particle surface of the composite in a manner other than Si—O—Si bond, Zr—O—Si bond, or Zr—O—Zr bond, resulting in an unbalanced charge. In addition, it is shown that a group exhibiting characteristics as a solid acid such as Si—OH exists.
The NH ₃ desorption amount tends to increase with an increase in the Zr content. However, an increase in the Zr content more than necessary has an adverse effect on the pore distribution. Therefore, the molarity of Zr / (Si + Zr) % Should be within the above-mentioned range.

<Application>
The amorphous silica-zirconium composite having the above characteristics is extremely inexpensive, and can efficiently and uniformly disperse and support the catalyst, so that it is particularly useful as a support for a noble metal catalyst such as a platinum group metal. It is extremely suitable, and a significant cost reduction can be achieved by using a noble metal catalyst as a catalyst for exhaust gas purification.
In particular, the above-described pore distribution is advantageous in uniformly and stably dispersing and supporting the noble metal catalyst without agglomerating, and the characteristics as a solid acid can improve the decomposition characteristics of hydrocarbons. Therefore, it is advantageous in enhancing the catalytic function of exhaust gas purification.

  Amorphous silica-zirconium composite used as a catalyst carrier is formed into various shapes such as a cylindrical shape, a granular shape, and a tablet by a known method such as extrusion molding and granulation molding, and the catalyst is supported on this. For use as a catalyst.

  As the noble metal catalyst to be supported, a platinum group metal known as an exhaust gas purifying catalyst, for example, platinum, palladium, rhodium, iridium, ruthenium can be exemplified. Since the present invention has a high effect with a small amount supported compared to the conventional amount supported, the amount of catalyst used can be reduced, which leads to a reduction in cost, so that only a particularly expensive noble metal catalyst is supported. Most advantageous in case. Of course, other metals that function as catalysts such as hydrorefining catalysts, hydrodesulfurization catalysts, hydrodenitrogenation catalysts, such as chromium, molybdenum, tungsten, iron, cobalt, nickel, osmium, molybdenum-cobalt, molybdenum -Nickel, tungsten-nickel, molybdenum-cobalt-nickel, tungsten-cobalt-nickel, molybdenum-tungsten-cobalt-nickel, or the like may be supported as necessary.

  As a method for supporting the metal catalyst, the above-described amorphous silica-zirconium composite molded body (support) is immersed in a solution of a soluble salt of the catalyst metal and the metal component is introduced into the support, In the production, a known method such as a coprecipitation method in which metal components are simultaneously precipitated can be employed. However, it is preferable to use an impregnation method that is easy in operation and convenient for maintaining stable catalyst characteristics. For example, the support may be immersed in an impregnation solution at room temperature or above and kept under conditions where the desired component is sufficiently impregnated in the support. The amount and temperature of the impregnating solution can be appropriately adjusted so that a desired amount of the catalytic metal component is supported. Further, the amount of the carrier immersed in the impregnation solution can be determined by the desired loading amount of the catalytic metal component.

  In order to support two or more types of catalytic metal components, a one-component impregnation method in which two or more types of catalytic metal components are mixed in advance and simultaneously impregnated from the mixed solution can be adopted. A two-component impregnation method in which the above metal component solutions are separately prepared and sequentially impregnated can also be employed.

As described above, the amorphous silica-zirconium composite of the present invention is particularly preferably used as an exhaust gas purifying catalyst that supports a platinum group metal, and supports the platinum group metal efficiently and uniformly. It can be efficiently expressed. For example, exhaust gas from automobiles and the like can be purified cleanly by hydrocarbon decomposition, NOx and carbon oxidation, and the like. In particular, the exhaust gas purifying catalyst in which a platinum group metal is supported on the amorphous silica-zirconium composite of the present invention has good heat resistance, and as shown in the examples described later, T ₅₀ (temperature at which the conversion becomes 50%) is stably maintained even after the aging treatment at 750 ° C.

In addition, the amorphous silica-zirconium composite of the present invention has a unique porous structure (pore distribution) and at the same time is extremely inexpensive. Can be used for
For example, because of its porous structure and solid acid characteristics, it has excellent adsorption characteristics for moisture and various gases (especially, bad odor basic gases such as ammonia), so it is also suitable as a humidity control agent and deodorant. It can also be used as a filler for resin or papermaking, etc., depending on its use form, by appropriate particle size adjustment, molding, etc., powder, granules, rods, pellets, honeycombs, etc. It can also be added to various materials by coating, impregnation, scouring, etc.

The present invention will be described in detail by the following experimental examples.
Various measurement methods used in the following experiments are as follows.

(1) Chemical analysis Si is measured according to JIS. M.M. Measured according to 8852. Zr was determined from analysis by ICP using iCAP6300Duo manufactured by Thermo Fisher Scientific. The sample used for ICP was prepared by removing impurities using sulfuric acid, hydrofluoric acid, and hydrochloric acid so that the liquid became 1% hydrochloric acid.

(2) BET specific surface area, pore volume, and pore distribution Measurement was performed by a nitrogen adsorption method using TriStar II 3020 manufactured by Micromeritics. The pore volume was determined by integrating the pore volumes with pore diameters of 2.0 nm to 50 nm in the pore distribution determined by the BJH method from the desorption branch side nitrogen adsorption isotherm. The specific surface area was analyzed by a BET method from an adsorption branch side nitrogen adsorption isotherm having a specific pressure of 0.05 to 0.20. The pore diameter was calculated by calculating from 4 V / A, where V is the nitrogen adsorption amount of less than P / Po = 0.975 and A is the specific surface area.

(3) X-ray diffraction X-ray diffraction measurement was performed in the range of 2θ = 5 to 70 deg using Cu-Kα under the following conditions using a SmartLab manufactured by Rigaku Corporation.
Target: Cu
Filter: Kβ
Detector: SC
Voltage: 40 kV
Current: 30mA
Step size: 0.01 °
Counting time: Continuous 1 ° / min
Slit: DS1 / 10 ° RS0.3mm SS1 / 10 °

(4) X-ray diffraction (small angle scattering)
Using an X-ray diffractometer SmartLab manufactured by Rigaku Corporation, measurement was performed in the range of 2θ = 0.5 to 5 deg with Cu-Kα under the following conditions.
Target: Cu
Filter: Kβ
Detector: D / tex (semiconductor detector)
Voltage: 40 kV
Current: 30mA
Step size: 0.01 °
Counting time: Continuous 10 ° / min
Slit: IS 1/3 ° (0.1 ° = 0.3 mm), RS1 8 °, RS2 16
mm

(5) NH ₃ desorption amount (NH ₃ -TPD method)
The sample was treated in a He atmosphere at 500 ° C. for 1 hour, cooled to 100 ° C., exposed to 0.1% NH ₃ / He, purged with He, heated at a rate of 5 ° C./min, and desorbed. The amount of NH ₃ released was measured.

(6) Catalyst preparation A solution obtained by impregnating and supporting a dinitrodiammine platinum nitric acid solution at 1 wt% Pt with respect to the amorphous silica-zirconium composite, reduced in hydrogen at 400 ° C., and treated in air at 500 ° C. for 1 hour. A sample before aging was used, and a sample after aging at 750 ° C. for 50 hours in air was used as a sample after aging.

(7) Decane oxidation activity (T ₅₀ )
It was carried out by a normal pressure fixed bed flow reaction method. Catalyst 200ppmNO + 200ppm decane +10 vol% H ₂ O + 5 vol% O ₂ (N ₂ dilution) was 400 mL · ^{min -1} flow as adjusted samples 40mg simulated exhaust gas, the temperature was lowered stepwise from 500 ° C., the activity at each temperature measured, the conversion rate of 50% temperature was _{T 50.}

Example 1
Sodium silicate (SiO ₂ 22.5 wt%, Na ₂ O 7.2 wt%, SG 1.295 / 15 ° C.) and 45 wt% sulfuric acid aqueous solution (SG 1.343 / 25 ° C.) were used as raw materials. Then, the sodium silicate 7.5 L / min and the sulfuric acid aqueous solution 2.0 L / min were supplied to a device capable of instantaneous contact with both to generate an acidic silica sol. 1.5 kg of this silica sol was poured into 22.8 g of a 43.8 wt% zirconium nitrate solution to produce a silica zirconium sol. The silica zirconium sol was allowed to stand and gelled, then treated with aqueous ammonia, and then washed with pure water. Next, an ion exchange treatment was performed with a 2.3 wt% ammonium chloride solution, and washing was again performed with pure water. 1.1 times the amount of pure water was added to the silica zirconium gel and hydrothermal treatment was performed at 130 ° C. for 12 hours. Then, it dried at 110 degreeC and obtained the amorphous silica zirconium composite. The physical properties of the obtained sample were measured, and the results are shown in Table 1.

(Example 2)
A sample was obtained in the same manner as in Example 1 except that the amount of the 43.8 wt% zirconium nitrate solution was changed to 45.6 g. The results of physical property measurement are shown in Table 1.

(Example 3)
A sample was obtained in the same manner as in Example 1 except that the amount of the 43.8 wt% zirconium nitrate solution was 91.2 g. The results of physical property measurement are shown in Table 1. FIG. 1 shows the result of X-ray diffraction, FIG. 2 shows the result of X-ray diffraction (small angle scattering), and FIG. 3 shows the pore distribution diagram by the BJH method (desorption side).

Example 4
A sample was obtained in the same manner as in Example 1 except that the amount of the 43.8% by weight zirconium nitrate solution was 182.4 g. The results of physical property measurement are shown in Table 1.

(Example 5)
A sample was obtained in the same manner as in Example 1 except that the amount of the 43.8 wt% zirconium nitrate solution was changed to 364.8 g. The results of physical property measurement are shown in Table 1.

(Comparative Example 1)
The steps until the acidic silica sol was produced in Example 1 were similarly performed. The acidic silica sol was allowed to stand and gelled, and then washed with pure water. 1.1 times the amount of pure water was added to the acidic silica gel, and hydrothermal treatment was performed at 130 ° C. for 12 hours. Subsequently, drying was performed at 110 ° C. to obtain a sample. The results of physical property measurement are shown in Table 1.

(Comparative Example 2)
A sample was obtained in the same manner as in Example 1 except that 26.9 g of 40 wt% zirconia sol was used instead of the 43.8 wt% zirconium nitrate solution in Example 1. The results of physical property measurement are shown in Table 1.

Claims (4)

Zr / (Si + Zr) is in the range of 0.5 to 15.0 mol%, the pore volume at a pore diameter of 2 to 50 nm is 0.2 to 1.0 cm ³ / g, and NH An amorphous silica-zirconium composite, wherein the NH ₃ desorption amount measured by a _3- TPD method is 0.05 mmol / g or more.   The amorphous silica-zirconium composite according to claim 1, wherein the average pore diameter measured by a nitrogen adsorption method is 2.0 to 12.0 nm.   An exhaust gas purifying catalyst carrier comprising the amorphous silica-zirconium composite according to claim 1.   An exhaust gas purifying catalyst obtained by supporting a platinum group metal on the catalyst carrier according to claim 3.

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