CN110526290B

CN110526290B - Nano cerium-zirconium composite oxide and application thereof in catalyzing NOXApplication in reduction reaction

Info

Publication number: CN110526290B
Application number: CN201910728939.2A
Authority: CN
Inventors: 宋锡滨; 邢晶; 刘洪升; 潘光军
Original assignee: Shandong Sinocera Functional Material Co Ltd
Current assignee: Shandong Sinocera Functional Material Co Ltd
Priority date: 2019-08-08
Filing date: 2019-08-08
Publication date: 2021-11-02
Anticipated expiration: 2039-08-08
Also published as: WO2021022593A1; CN110526290A

Abstract

The invention provides a nano cerium-zirconium composite oxide, which comprises cerium oxide, zirconium oxide and at least one oxide of rare earth metal elements except cerium, wherein the ratio of the mass fraction of the cerium oxide to the mass fraction of the zirconium oxide contained in the composite oxide is less than 1; the composite oxide has a particle diameter of 5-20nm and at least 1.10mmol [ O ] after heat treatment at 750 ℃ for 4-8 hours]Oxygen storage per gram. The nanometer cerium-zirconium composite oxide obtained by the invention has proper microscopic nanometer grain size and higher oxygen storage capacity. Experiments show that the T of the nano cerium-zirconium composite oxide obtained by the invention after being calcined for 4 hours at 750 DEG C₅₀、T₉₀Respectively T after aging at 150 ℃ and 200 ℃ and high temperature of 1100 ℃ for 4 hours₅₀And T₉₀The catalyst shows excellent low-temperature catalytic activity and ageing resistance activity at about 170 ℃ and 220 ℃.

Description

Nano cerium-zirconium composite oxide and application thereof in catalyzing NOXApplication in reduction reaction

Technical Field

The invention relates to the technical field of mobile source tail gas purification catalysis, in particular to a nano cerium-zirconium composite oxide and application thereof in catalyzing NO_XApplication in reduction reaction.

Background

The mobile source isFor short, mobile air pollution sources can produce a large amount of pollutants, for example, during the cold start of an engine, a large amount of nitrogen compounds, such as Nitric Oxide (NO) and nitrogen dioxide (NO), can be emitted₂) Equal Nitrogen Oxides (NO)_X) And ammonia (NH)₃) And the like. At present, the main means for solving the problem of cold start exhaust is to install a purifier with a built-in catalyst at the exhaust emission part of the automobile.

The cerium-zirconium composite oxide is widely applied to the field of automobile exhaust catalysis. Besides participating in catalytic reaction, the cerium-zirconium composite oxide also has the function of a carrier, not only plays a role in supporting and dispersing catalytic active metal, but also provides a proper place for catalytic reaction of reactant molecules.

The physical and chemical properties of the cerium-zirconium solid solution are greatly dependent on the microstructure of the cerium-zirconium solid solution, such as morphology, size, specific surface, pore channel structure and the like. The size is one of the important factors influencing the physical and functional indexes of the cerium-zirconium solid solution. The cerium-zirconium solid solution with the nano porous structure can meet the requirement of the material on efficient adsorption of pollutants, and simultaneously, because the nano structure material has the characteristic of higher surface energy, the pollutants adsorbed by the nano structure material are more easily activated, so that the ignition temperature of the pollutants is reduced.

The cerium-zirconium solid solution with the nano structure can also increase the specific surface area of the material, increase the surface active sites of the carrier and improve the catalytic efficiency of pollutants. In practice, however, the solid solution should be of a suitable size. The size is too small, the surface activity is too high, and the particles are easy to agglomerate, so that the specific surface after high-temperature aging is sharply reduced; the catalyst has the advantages of overlarge size, overlow initial specific surface, less active sites, lower surface active energy and influence on the conversion efficiency of the catalyst to pollutants due to the two factors. Therefore, how to prepare and obtain the cerium-zirconium solid solution with the proper size structure is very important.

The invention takes the grain diameter of the cerium-zirconium solid solution as an entry point to carry out a series of research works to determine the grain diameter of the cerium-zirconium solid solution and NO_XThe relationship of catalysis.

Disclosure of Invention

In order to solve the above problems, the present invention aims to provide a nano-sized cerium-zirconium composite oxide having a suitable particle size, which has a high oxygen storage amount, and also exhibits excellent low-temperature catalytic activity and high-temperature stability, and is particularly suitable for catalytic purification of nitrogen oxides.

In one aspect, the present invention provides a nano cerium-zirconium composite oxide comprising an oxide of cerium oxide, zirconium oxide and at least one rare earth metal element selected from the group consisting of cerium and other elements, wherein:

the ratio of the mass fraction of cerium oxide to the mass fraction of zirconium oxide contained in the composite oxide is less than 1; the composite oxide has a particle diameter of 5 to 20nm and an oxygen storage amount of at least 1.10mmol [ O ]/g after heat treatment at 750 ℃ for 4 to 8 hours.

As a preferred embodiment, the heat treatment may be calcination, otherwise known as roasting, sintering. As another preferred embodiment, the ratio of the mass fraction of cerium oxide to the mass fraction of zirconium oxide is greater than 0.15, more preferably, said ratio is comprised between 0.20 and 0.90.

Further, the composite oxide has a particle diameter of 8 to 15nm, preferably 9 to 13nm, after heat treatment at 750 ℃ for 4 to 8 hours. More preferably, the particle size of the composite oxide after heat treatment at 750 ℃ for 4 to 8 hours may be 9.3nm, 11.5nm, 12.7 nm.

Further, the composite oxide has an oxygen storage amount of at least 1.12 mmol [ O ]/g, preferably at least 1.15mmol [ O ]/g, after heat treatment at 750 ℃ for 4 to 8 hours.

Nano cerium-zirconium composite oxide with above grain size and/or oxygen storage for catalytic reduction of NO_XThe catalyst has lower ignition temperature and complete conversion temperature, shows better low-temperature catalytic activity, still has good purification catalytic effect after high-temperature aging, has smaller difference of catalytic effect before and after aging, and shows more advantageous high-temperature aging resistant effect.

In the present application, the grain size of the nano cerium-zirconium composite oxide is mainly controlled by adjusting the concentration of the oxide, but the cerium-zirconium composite oxide with the appropriate grain size is not limited by the preparation method, and can be obtained by adjusting other process parameters or using other methods, for example, the grain size of the cerium-zirconium composite oxide obtained after hydrothermal treatment can be adjusted by controlling hydrothermal time, hydrothermal temperature, pH or viscosity of the hydrothermal system, adding a mineralizer, and the like.

Further, the at least one oxide of a rare earth metal element other than cerium is selected from one or more of lanthanum oxide, yttrium oxide and praseodymium oxide; preferably comprising lanthanum oxide and yttrium oxide.

Furthermore, the composite oxide contains 20-40 wt% of cerium oxide, 45-80 wt% of zirconium oxide, 2-10 wt% of lanthanum oxide and 2-10 wt% of yttrium oxide.

Preferably, the cerium oxide is 28 wt%, the zirconium oxide is 62 wt%, the lanthanum oxide is 5 wt%, and the yttrium oxide is 5 wt%.

Further, the particle size of the composite oxide after being subjected to heat treatment at 750 ℃ for 4-8h is 15-24nm, preferably 17-23nm after being aged at 1100 ℃ for 4-8 h; the oxygen storage amount is at least 1.08mmol [ O ]/g, preferably at least 1.10mmol [ O ]/g.

Further, the composite oxide also comprises a noble metal loaded on the composite oxide, wherein the loading amount of the noble metal is 1-2 wt%, preferably 1.5 wt% of the composite oxide; the noble metal is selected from one or more of platinum, rhodium and palladium.

On the other hand, the invention also provides the application of the nano cerium-zirconium composite oxide in catalytic reduction of NO_XThe use of (1); preferably, the NO is_XIncluding NO.

On the other hand, the invention also provides a method for preparing the nano cerium-zirconium composite oxide, which comprises the step of carrying out hydrothermal treatment on a mixed solution obtained by dissolving the raw materials, wherein the concentration of the mixed oxide is 40-140g/L, and is preferably 80-120 g/L.

Preferably, the preparation method adopts a hydrothermal method, and specifically comprises the following steps: respectively dissolving cerium, zirconium and rare earth metal salt, mixing, fixing the volume, adjusting the concentration of the mixed oxide to 40-140g/L, adjusting the pH value to acidity, and reacting for a period of time; then adjusting the pH value to be alkaline, reacting for a period of time, and calcining at high temperature for a period of time to obtain the catalyst.

Further, the acidic pH is 1-3, preferably 1.5-2, the reaction temperature is 100-.

Further, the alkaline pH is 8-11, preferably 9-10, the reaction temperature is 100-300 ℃, preferably 120-220 ℃, preferably 130-180 ℃, more preferably 150 ℃, and the reaction time is 5-30 h.

Further, the high-temperature calcination condition is 500-900 ℃ for 2-10h, preferably 750 ℃ for 4-8 h.

Further, in the above method, the salt of cerium and zirconium is nitrate. Preferably, the raw materials are zirconium nitrate, ammonium ceric nitrate, lanthanum nitrate and yttrium nitrate, wherein the yttrium nitrate is prepared by dissolving yttrium oxide in concentrated nitric acid. Preferably, the cerium salt may also be cerium nitrate, cerium chloride, cerium sulfate, cerium carbonate; the zirconium salt may be zirconium carbonate, zirconium oxychloride, zirconium sulfate, or zirconium acetate.

As a preferred embodiment, the above preparation method comprises:

s1, respectively dissolving cerium, zirconium and rare earth metal salts, wherein the total oxide concentration is 40-140 g/L;

s2, dropwise adding an alkaline precipitator into the solution, wherein the alkaline precipitator is one or more of ammonia water, sodium hydroxide and amines, preferably mainly ammonia water, and adjusting the pH value of the solution to 1-3;

s3, introducing the solution into a high-pressure reaction kettle, and carrying out high-temperature hydrolysis reaction at 120-220 ℃ for 10-20 h;

s4, dropwise adding an alkaline precipitator into the precursor slurry obtained in the step S3 to adjust the pH value to 8-11;

s5, introducing the precursor slurry obtained in the step S4 into a high-pressure kettle, and carrying out hydrothermal reaction at the temperature of 120-220 ℃ for 6-10 h;

s6, pumping and filtering, pulping and washing, drying the filter cake for 10h, and calcining at 500-900 ℃ for 4-8 h.

Further, a noble metal component is supported by an isovolumetric impregnation method on the cerium-zirconium composite oxide. Taking noble metal palladium as an example, the specific steps of loading the noble metal component by using the isometric impregnation method are as follows:

with chloropalladate solution (H)₂PdCl₄) Is precursor impregnation liquid, wherein the loading amount of palladium is 1.5 wt%; the loaded cerium-zirconium composite oxide slurry is dried in a rotary evaporator, then is dried in a forced air drying oven at 110 ℃ for 3 hours, and is calcined in a calcining furnace at 500 ℃ for 3 hours in an air atmosphere.

On the other hand, the invention also provides a method for reducing NO at low temperature by using the nano cerium-zirconium composite oxide as a catalyst_XThe method comprises the step of using the nano cerium zirconium composite oxide to react NO at low temperature_XThe low temperature is a temperature not higher than 250 ℃.

Preferably, the nano cerium-zirconium composite oxide can be subjected to NO treatment for 4-8h at 750-1100 DEG C_XCatalysis of (3). More preferably, it can be used for NO after calcination at 750 ℃ for 4 hours_XCatalysis of (3).

The nanometer cerium-zirconium composite oxide is calcined for 4 hours at 750 ℃ and then NO is treated_XWhen the catalysis is carried out: NO_XTemperature T at 50% conversion efficiency₅₀Can be as low as 170 ℃ or below and can be as low as 147 ℃; NO_XTemperature T at 90% conversion efficiency₉₀Can be as low as below 230 ℃ and can be as low as 199 ℃ at least.

In addition, the nanometer cerium-zirconium composite oxide is calcined at 750 ℃ for 4 hours and then aged at 1100 ℃ for 4 hours to react with NO_XWhen the catalysis is carried out: NO_XT of₅₀Can be as low as below 190 ℃ and can be as low as 167 ℃; t is₉₀Can be as low as 250 ℃ or below, and can be as low as 218 ℃ at least.

The invention has the beneficial effects that:

the nanometer cerium-zirconium composite oxide obtained by the invention has proper microscopic nanometer grain size and higher oxygen storage amount, and simultaneously shows excellent low-temperature catalytic activity and high-temperature stability, especially on nitrogen oxide tableShows excellent catalytic advantages and can still keep good catalytic effect after high-temperature aging. Experiments show that the nanometer cerium-zirconium composite oxide provided by the invention has T after being calcined for 4 hours at 750 DEG C₅₀、 T₉₀Respectively T after aging at 150 ℃ and 200 ℃ and high temperature of 1100 ℃ for 4 hours₅₀And T₉₀The research on the purifying agent for treating the mobile source tail gas containing the nano cerium-zirconium composite oxide is significant at about 170 ℃ and 220 ℃ respectively.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

FIG. 1 is a transmission electron microscope image of a nano-sized cerium-zirconium composite oxide (calcined at 750 ℃ for 4 hours) prepared in example 1;

FIG. 2 is a transmission electron microscope image of the nano-sized cerium-zirconium composite oxide (calcined at 750 ℃ for 4 hours) prepared in example 2;

FIG. 3 is a transmission electron microscope image of the nano-sized Ce-Zr composite oxide (calcined at 750 ℃ for 4h) prepared in example 3;

FIG. 4 is a transmission electron microscope image of the nano-sized cerium-zirconium composite oxide (calcined at 750 ℃ for 4 hours) prepared in example 4;

FIG. 5 is a transmission electron microscope image of the nano-sized cerium-zirconium composite oxide (calcined at 750 ℃ for 4 hours) prepared in example 5;

FIG. 6 is a transmission electron micrograph of the nano-cerium-zirconium composite oxide (calcined at 750 ℃ for 4 hours) prepared in example 6.

Detailed Description

In order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. It will be apparent, however, to one skilled in the art, that the present application may be practiced without one or more of these specific details. In other instances, well-known features of the art have not been described in order to avoid obscuring the present application.

In the following examples, raw materials for preparing cerium-zirconium composite oxides are commercially available, unless otherwise specified; wherein the containers used in the hydrothermal reaction are a pressure soluble bomb with a polytetrafluoroethylene lining and a titanium high-pressure reaction kettle with a capacity specification of 10L, which are provided by special chemical equipment limited company on the cigarette bench side and a capacity specification of 10L; the structural representation and the particle size measurement of the obtained composite oxide adopt a transmission electron microscope with the model number of HT7800 provided by Hitachi company, and a ChemBET-3000 instrument of Kangta company is used for analyzing the oxygen storage capacity of the cerium-zirconium solid solution; the catalytic activity test uses an infrared flue gas analyzer with model number HN-CK21 provided by Taiyuan Hainan instruments and meters Co.

The embodiment of the invention provides a preparation method of a nano cerium-zirconium composite oxide, which comprises the following specific steps:

s1, respectively dissolving cerium, zirconium, lanthanum, praseodymium or yttrium salts, fixing the volume to the total concentration of 40-140g/L, stirring to be clear, and continuing to stir at a low speed for 0.5 h;

s2, dropwise adding an alkaline precipitator into the solution, wherein the alkaline precipitator is one or more of ammonia water, sodium hydroxide and amines, preferably mainly ammonia water, and then adjusting the pH value of the solution to 1.5-2;

s3, introducing the solution into a high-pressure reaction kettle, and hydrolyzing under the temperature of 150 ℃ for 10-20 h;

s4, dropwise adding an alkaline precipitator into the precursor slurry obtained in the step S3 to adjust the pH value to 8-10;

s5, introducing the precursor slurry obtained in the step S4 into an autoclave, and carrying out hydrothermal reaction for 6-10h at 150 ℃;

and S6, carrying out suction filtration, pulping and washing, drying the obtained filter cake for 10h, and calcining at 700-800 ℃ for 4-8h to obtain the nano cerium-zirconium composite oxide.

Unless otherwise specified, the following examples were prepared by the above-described method.

Example 1

Example 1 provides a composition based on cerium oxide, zirconium oxide, lanthanum oxide, yttrium oxide, in proportions by weight of oxides of CeO₂ 28％，ZrO₂ 62％，La₂O₃ 5％，Y₂O₃ 5％。

The equipment used in this example was a 10L polytetrafluoroethylene lined autoclave, the solution fill was 80%, the total oxide concentration was 40g/L, and the preparation method was as follows:

dissolving 574g of zirconyl nitrate and 54.2g of yttrium nitrate in 2000ml of deionized water until the solution is clear to obtain a solution A;

adding 278.5g of ammonium ceric nitrate and 42.7g of lanthanum nitrate into the solution A, stirring until the solution A is clear, adjusting the pH value of the solution A to 1.5-1.6 by using ammonia water under the condition of 50 ℃ water bath, fixing the volume to 8000ml, introducing the solution A into a polytetrafluoroethylene lining pressure bomb, carrying out hydrothermal hydrolysis reaction at 150 ℃ for 20 hours, cooling to the normal temperature, adjusting the pH value to 9.5-9.7 by using ammonia water, and obtaining slurry B;

and transferring the slurry B into a titanium material kettle, and carrying out hydrothermal reaction at 150 ℃ for 8h under the condition that the rotating speed is 200 r/min. Filter-pressing the slurry after hydrothermal treatment, washing for 3 times by 50L of deionized water, washing for 2 times by 40L of lauric acid alkali liquor with the concentration of 5g/L to obtain a final filter cake, and calcining at high temperature for degumming, wherein the calcining conditions are as follows: the temperature is raised to 750 ℃ by adopting a temperature programming mode, the temperature raising rate is 2 ℃/min, the gas flow of the furnace body is controlled to be 10-20L (air)/min/kg (oxide), and after the calcination is carried out for 4 hours, the material is sieved by a 200-fold and 250-mesh sieve, thus obtaining the nano cerium-zirconium composite oxide.

Examples 2 to 6 were prepared in the same manner as in example 1, except that the concentrations of the precursor oxides of the respective examples were different, and a series of cerium-zirconium solid solutions having different grain sizes were obtained, and the concentrations of the precursor oxides of the respective specific examples are shown in table 1.

TABLE 1 concentration of precursor oxides for examples 1-6

Examples of the invention	Precursor oxide concentration (g/l)
		Example 1	40
Example 2	60
		Example 3	80
Example 4	100
		Example 5	120
Example 6	140

Evaluation of Performance

First, structural characterization

The nano-cerium-zirconium composite oxides obtained in examples 1 to 6 were subjected to characterization of the nanostructure and measurement of the particle size by Transmission Electron Microscopy (TEM) respectively during fresh preparation (calcination at 750 ℃ for 4 hours) and after aging at high temperature (aging at 1100 ℃ for 4 hours). The particle size of the nano structure is measured by randomly measuring 50 crystal grains according to an equipment scale and taking the average number to obtain the particle size.

Meanwhile, the oxygen storage amount of the samples of each example before and after aging is also measured by the following method: 0.2g of a sample was held at 600 ℃ for 1 hour in high purity oxygen, and then heated from 100 ℃ to 1000 ℃ in a 5% hydrogen-argon gas flow (100sccm) at a heating rate of 10 ℃/min, and the consumed hydrogen was continuously measured by a quadrupole mass spectrometer to obtain a temperature-water vapor amount curve, and the amount of oxygen released, i.e., the oxygen storage amount of the sample, was measured from the curve and its area.

Among the above characterization results, TEM characterization results of fresh samples of examples 1-6 are shown in FIGS. 1-6, and the measured particle size and oxygen storage amount results are shown in Table 2.

Table 2 shows the particle size and oxygen storage amount of each of the examples in the fresh state and after aging at high temperature

As can be seen from the results shown in fig. 1 to 6 and table 2, the cerium-zirconium composite oxides with different grain sizes can be prepared by adjusting the concentration of the precursor oxide in the preparation method, and not only the grain sizes of the cerium-zirconium composite oxides obtained in examples 1 to 6 are greatly different, but also the corresponding oxygen storage properties are significantly different. Among them, as can be seen from the data of table 2, the nano cerium zirconium composite oxides of examples 3 to 5 exhibited more excellent oxygen storage capacity.

II, testing catalytic activity

The catalytic active component palladium is loaded on the prepared nano cerium-zirconium composite oxide by an isometric impregnation method, and the specific method comprises the following steps:

with chloropalladate solution (H)₂PdCl₄) The catalyst is used as precursor impregnation liquid, and is used for impregnating and loading the nano cerium-zirconium composite oxide, wherein the loading amount is 1.5 wt%; the loaded slurry was dried in a rotary evaporator, then dried in a forced air drying oven at 110 ℃ for 3 hours, and then calcined in a calciner at 500 ℃ for 3 hours in an air atmosphere.

Of these, examples 1 to 6 in which 1.5 wt% of palladium was supported were each identified as CZ1-CZ6, and the above examples were subjected to a test of catalytic activity when freshly prepared (calcined at 750 ℃ for 4 hours) and when aged at high temperature (calcined at 1100 ℃ for 4 hours) to evaluate the catalysts obtained for NO_XThe reduction catalytic effect of (1), wherein the test method is as follows:

a small sample evaluation reaction device self-made by a U-shaped quartz reaction tube is adopted, a small group of quartz cotton is plugged at the bottom of one side of the U-shaped quartz reaction tube, a weighed catalyst sample is placed, and mixed gas is introduced for temperature rise determination. Wherein the mixed gas consists of NH₃(520ppm)、NO(520ppm)、H₂O (6%) and O₂(14%) in pure N₂As a mixed balance gas, to35000mL·h^-1The reaction was carried out at a flow rate of 150 ℃ and 400 ℃ through a sample of 0.1g at 5 ℃/min. Detecting the composition of the gas after passing through the catalyst with a gas concentration detector, and calculating NO of the catalyst by analyzing the change of the gas concentration before and after_XThe conversion of (a).

The catalytic effect of each example is shown in Table 3, where T₅₀And T₉₀Each means NO_XThe lower the temperature, the better the catalytic effect, the lower the temperature required for the same catalytic efficiency, where T₅₀Known as the light-off temperature, T₉₀Referred to as the complete removal temperature.

TABLE 3 NO for each example_XEffect of catalytic reduction

As can be seen from table 3, the catalytic reduction effect of the cerium-zirconium composite oxides on nitrogen oxides is greatly different for different grain sizes, and the low-temperature reduction effect of the cerium-zirconium composite oxides tends to increase first and then decrease as the grain size of the sample decreases. Particularly, the examples 3 to 5 show more remarkable low-temperature catalytic effect of nitrogen oxides, and the T of the freshly prepared (calcined at 750 ℃ for 4 hours) nano cerium-zirconium composite oxide loaded with noble metal₅₀As low as 147 ℃ T₉₀As low as 199 deg.c.

Meanwhile, the loaded noble metal of the nano cerium-zirconium composite oxide in each embodiment still has good low-temperature catalytic effect of nitrogen oxide after high-temperature aging (aging at 1100 ℃ for 4 hours), and T is₅₀The temperature can be as low as below 190 ℃ and can reach 167 ℃ at the lowest; t is₉₀Can be as low as 250 ℃ or lower, can reach 218 ℃ at least, has small difference before and after aging, and shows good high-temperature aging resistant activity.

The nano cerium-zirconium composite oxide has high oxygen storage capacity, and also shows excellent low-temperature catalytic activity and high-temperature stability to nitrogen oxides, and particularly, when the grain size of the nano cerium-zirconium composite oxide is 9-13nm, the oxygen storage capacity, the catalytic purification activity and the anti-aging performance of the nano cerium-zirconium composite oxide are optimal.

The above description is only an example of the present application and is not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A nano-cerium-zirconium composite oxide comprising a cerium oxide, a zirconium oxide and an oxide of at least one rare earth metal element other than cerium,

the ratio of the mass fraction of cerium oxide to the mass fraction of zirconium oxide contained in the composite oxide is less than 1;

the composite oxide has a particle diameter of 9 to 13nm and an oxygen storage amount of 1.15 to 1.26mmol [ O ]/g after heat treatment at 750 ℃ for 4 to 8 hours;

in the composite oxide, the content of cerium oxide is 20-40 wt%, the content of zirconium oxide is 45-80 wt%, the content of lanthanum oxide is 2-10 wt%, and the content of yttrium oxide is 2-10 wt%;

the preparation method of the composite oxide comprises the step of carrying out hydrothermal treatment on a solution obtained by dissolving and mixing raw materials, wherein the concentration of a precursor oxide in the mixed solution is 80-120 g/L.

2. The composite oxide according to claim 1, wherein the cerium oxide is contained in an amount of 28 wt%, the zirconium oxide is contained in an amount of 62 wt%, the lanthanum oxide is contained in an amount of 5 wt%, and the yttrium oxide is contained in an amount of 5 wt%.

3. The composite oxide according to claim 1, wherein the composite oxide after heat treatment at 750 ℃ for 4 to 8 hours has a particle diameter of 15 to 24nm and an oxygen storage amount of 1.08 to 1.15mmol [ O ]/g after aging at 1100 ℃ for 4 to 8 hours.

4. The composite oxide according to claim 1, further comprising a noble metal supported on the composite oxide, the noble metal being supported at a content of 1 to 2 wt% of the composite oxide; the noble metal is selected from one or more of platinum, rhodium and palladium.

5. The composite oxide according to claim 4, wherein a loading amount of the noble metal is 1.5 wt% of the composite oxide.

6. The use of the nano-sized cerium-zirconium composite oxide as claimed in any one of claims 1 to 5 in the catalytic reduction of NO_XThe use of (1).

7. Use according to claim 6, wherein said NO is_XIncluding NO.

8. Catalytic reduction of NO at low temperature_XThe method of (2), which comprises subjecting a nano cerium-zirconium composite oxide as claimed in any one of claims 1 to 5 to a reaction containing NO at a low temperature_XThe low temperature is a temperature not higher than 250 ℃.