Cerium-zirconium surface-supported noble metal catalyst and method for preparing the same

Abstract

The application discloses a catalyst with a cerium-zirconium surface loaded with noble metal and a preparation method thereof. D / I F2g is 0.2-1.2, preferably 0.5-1.0; and the defects of the cerium-zirconium composite oxide are loaded with the noble metal. Through parameters control of precipitation, aging, atmosphere roasting and acid etching, a non-uniform rare earth element doping structure is constructed, the radius effect and valence balance principle of the rare earth doping elements in the structure are utilized, the cerium-zirconium crystal lattice is induced to be distorted, the step and zigzag defects are generated, the valence change of Ce and the formation of oxygen vacancies are promoted, the pinning effect is formed, the surface energy is reduced, the cerium-zirconium oxygen storage performance and high-temperature stability are improved, the noble metal is anchored, the migration, agglomeration and growth of the noble metal in a high-temperature environment are inhibited, the high-temperature dispersibility of the noble metal is improved, and the catalytic activity is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of supported metal catalysts, in particular to a catalyst with a noble metal supported on a cerium-zirconium surface and a preparation method thereof. BACKGROUND

[0002] With the increasing number of global car ownership, automobile exhaust pollution has become the primary source of urban air pollution, and the environmental problems caused by automobile exhaust emissions are becoming increasingly serious. Automobile exhaust catalytic converter is an effective solution for automobile exhaust purification, and the core is a three-way catalyst with noble metal supported. Generally, the automobile exhaust three-way catalyst is composed of a honeycomb carrier, a noble metal, an active coating, etc., and its service life is mainly determined by the active coating material and the preparation process of the three-way catalyst. The active coating material includes cerium-zirconium-based composite oxides, and the noble metal is supported on the cerium-zirconium-based composite oxides. Due to the high environmental temperature of automobile exhaust three-way catalysts in practical applications, sometimes it can reach more than 900℃. Due to particle migration and coalescence (PMC) and Ostwald ripening effect, thermodynamically unstable noble metals are prone to migrate and aggregate to form large particles, resulting in reduced utilization of noble metals and catalytic activity. SUMMARY

[0003] The purpose of the embodiments of the present application is to provide a catalyst with a noble metal supported on a cerium-zirconium surface and a preparation method thereof. By controlling the parameters of precipitation, aging, atmosphere calcination and acid etching, a non-uniform rare earth element doping structure is constructed. By using the radius effect and valence balance principle of the rare earth doping elements in the structure, the cerium-zirconium lattice is induced to distort, producing defects such as step and sawtooth, which anchor the noble metal, inhibit the migration, aggregation and growth of the noble metal in a high-temperature environment, improve the high-temperature dispersibility and improve the catalytic activity.

[0004] To solve the above technical problems, the first aspect of the embodiments of the present application provides a catalyst with a noble metal supported on a cerium-zirconium surface, comprising: a cerium-zirconium-based composite oxide and a noble metal; the number of surface defect characteristic value I D / I F2g of the cerium-zirconium-based composite oxide is 0.2-1.2, preferably 0.5-1.0;

[0005] The defects of the cerium-zirconium-based composite oxide are loaded with noble metals.

[0006] Further, the chemical formula of the cerium-zirconium-based composite oxide is Ce x Zr y M z O 2-α D δwherein M is a cationic doping element, D is an anionic doping element, 0.1 < x < 0.9, 0.1 < y < 0.9, 0 < z < 0.3 in terms of mole number, and x + y + z = 1; 0 ≤ α ≤ 0.1; 0 ≤ δ ≤ 0.1.

[0007] Further, the noble metal is in a metallic state and / or an oxidized state.

[0008] The noble metal comprises at least one of Pt, Pd, Rh, Ir, Os, Ru, Au and Ag; preferably, the noble metal comprises at least one of Pt, Pd, Rh and Ru.

[0009] The loading amount of the noble metal is 0.01% to 3% in terms of mass fraction; preferably, the loading amount of the noble metal is 0.1% to 2% in terms of mass fraction.

[0010] Further, the defects of the cerium-zirconium-based composite oxide comprise stepped defects and / or zigzag defects.

[0011] Further, the size of the noble metal loaded on the defect sites is 3 nm or less before high-temperature aging treatment, preferably, the size of the noble metal is 2 nm or less.

[0012] After 1000℃ / 4h high-temperature aging treatment, the size of the noble metal is 5 nm or less, preferably, the size of the noble metal is 3 nm or less.

[0013] Further, the cerium-zirconium-based composite oxide has an element gradient distribution structure, and the content of cerium and / or M element in the surface layer is higher than the content of the corresponding element in the interior, and the content of the above elements gradually increases from the interior to the exterior in terms of mole ratio.

[0014] Or,

[0015] The cerium-zirconium-based composite oxide has a core-shell structure, and the content of cerium and / or M element in the surface layer is 1.5 times to 3.5 times the content of the corresponding element in the cerium-zirconium-based composite oxide in terms of mole ratio.

[0016] Further, the cationic doping element M comprises at least one of non-cerium rare earth elements, transition metal elements other than zirconium and rare earth elements, alkaline earth metal elements, Al, Si, Ga, Sn and Bi.

[0017] Optionally, the non-cerium rare earth element comprises at least one of La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y; preferably, the non-cerium rare earth element comprises at least one of La, Pr, Nd, Sm, Eu, Gd, Tm, Yb and Y.

[0018] Optionally, the transition metal element comprises at least one of Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Hf, Ta and W; preferably, the transition metal element comprises at least one of Ti, Mn, Fe, Co, Ni, Cu, Nb, Hf, W and Mo.

[0019] Optionally, the alkaline earth metal element comprises at least one of Be, Mg, Ca, Sr and Ba; preferably, the alkaline earth metal element comprises at least one of Mg, Sr and Ba.

[0020] Further, the anion doping element D comprises at least one of anions N, F and P.

[0021] Correspondingly, a second aspect of the embodiment of the present application provides a preparation method of a cerium-zirconium surface loaded noble metal catalyst, for preparing the above-mentioned cerium-zirconium surface loaded noble metal catalyst, comprising the following steps:

[0022] mixing the cerium-zirconium based composite oxide with a noble metal liquid salt in one or more steps, and drying;

[0023] performing heat treatment on the dried product under a preset atmosphere to obtain the noble metal loaded catalyst.

[0024] Further, the noble metal liquid salt comprises at least one of molten salt or aqueous solution of chloride salt, nitrate salt and acetate salt.

[0025] The preset atmosphere comprises at least one of air, CO, N2 or H2.

[0026] Further, before the cerium-zirconium based composite oxide is mixed with the noble metal liquid salt uniformly, the method further comprises:

[0027] The required cerium, zirconium and M salt solutions are prepared according to the stoichiometric ratio, and a precipitation reaction is performed with an alkaline substance, preferably a multi-step precipitation reaction;

[0028] The obtained precipitate slurry is filtered, washed, dried and calcined;

[0029] Optionally, the precipitate slurry is subjected to aging treatment before filtration, preferably aging treatment in a hydrothermal environment; and / or, the dried precipitate slurry is subjected to calcination treatment under a certain atmosphere; and / or, the calcined cerium-zirconium based composite oxide is subjected to acid etching treatment;

[0030] The cerium-zirconium based composite oxide with surface defects is obtained.

[0031] Further, the basic substance comprises at least one of sodium hydroxide, ammonium hydroxide, potassium hydroxide, urea, ammonium bicarbonate, sodium carbonate, sodium bicarbonate;

[0032] The atmosphere comprises air or at least one of CO, N2, H2;

[0033] The aqueous solution of the cerium ion and the cation doping element comprises at least one of nitrate solution, chloride solution, sulfate solution, acetate solution;

[0034] The aqueous solution of the zirconium ion comprises at least one of zirconyl nitrate solution, zirconyl sulfate solution, zirconyl oxychloride solution, zirconium acetate;

[0035] The calcination temperature ranges from 600 DEG C to 1200 DEG C.

[0036] Correspondingly, the third aspect of the embodiment of the present application provides an application of the cerium-zirconium surface loaded noble metal catalyst in the fields of motor vehicle exhaust purification, industrial organic waste gas treatment, natural gas catalytic combustion, petroleum chemical industry, hydrogen energy and batteries.

[0037] The above technical solution of the embodiment of the present application has the following beneficial technical effects:

[0038] By controlling the parameters of precipitation, aging, atmosphere calcination and acid etching, a non-uniform rare earth element doping structure is constructed, the radius effect and valence balance principle of the rare earth doping element in the structure are utilized, the cerium-zirconium lattice is induced to be distorted, the defects such as step type and zigzag type are generated, the anchoring effect on the noble metal is generated, the migration, agglomeration and growth of the noble metal in the high temperature environment are inhibited, the high temperature dispersibility of the noble metal is improved, and the catalytic activity is improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a preparation method flow chart of the cerium-zirconium surface loaded noble metal catalyst provided by the embodiment of the present application.

[0040] Figure 2a It is a Raman test result of the cerium-zirconium surface loaded noble metal catalyst provided by the embodiment of the present application.

[0041] Figure 2b It is a HAADF-STEM electron microscope graph of the cerium-zirconium surface loaded noble metal catalyst provided by the embodiment of the present application. DETAILED DESCRIPTION

[0042] In order to make the objects, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application with reference to the specific embodiments and the accompanying drawings. It should be understood that the description is only exemplary and is not intended to limit the scope of the present application. In addition, in the following description, the description of the well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application.

[0043] In order to ensure the conversion efficiency of the automobile exhaust catalyst and maintain the catalytic activity of the cerium-zirconium-based composite oxide supported noble metal catalyst, the high-temperature sintering of the cerium-zirconium supported noble metal should be prevented as much as possible in a high-temperature environment, and one of the important ways is to form a steric hindrance by regulating the defect structure of the cerium-zirconium carrier surface, to enhance the anchoring effect of the cerium-zirconium carrier and the noble metal, and to prevent the migration, agglomeration and growth of the noble metal particles at high temperature to reduce the catalytic activity. The noble metal catalysts are also required to have high high-temperature stability in the fields of natural gas catalytic combustion, organic waste gas treatment, reforming hydrogen production, etc.

[0044] The first aspect of the embodiment of the present application provides a catalyst of cerium-zirconium surface supported noble metal, comprising: a cerium-zirconium-based composite oxide and a noble metal; the number characteristic value I of the surface defects of the cerium-zirconium-based composite oxide is 0.2-1.2, preferably 0.5-1.0; the defects of the cerium-zirconium-based composite oxide are loaded with the noble metal. D / I F2g The number characteristic value I of the surface defects of the cerium-zirconium-based composite oxide is 0.2-1.2, preferably 0.5-1.0; the defects of the cerium-zirconium-based composite oxide are loaded with the noble metal. Figure 2b

[0045] Further, the chemical formula of the cerium-zirconium-based composite oxide is Ce x Zr y M z O 2-α D δ , wherein M is a cation doping element, D is an anion doping element, the molar number of 0.1

[0046] Further, the noble metal is in a metallic state and / or an oxidized state, the form of the noble metal is related to the calcination atmosphere; optionally, the noble metal includes at least one of Pt, Pd, Rh, Ir, Os, Ru, Au and Ag; preferably, the noble metal includes at least one of Pt, Pd, Rh and Ru; optionally, the loading amount of the noble metal is 0.01%-3% by mass fraction; preferably, the loading amount of the noble metal is 0.1%-2% by mass fraction.

[0047] ​Further, the defects of the cerium-zirconium-based composite oxide include one or more of oxygen vacancy defects, step defects, and zigzag defects; and the defects of the cerium-zirconium-based composite oxide are loaded with noble metals. Specifically, the defects of the cerium-zirconium-based composite oxide have the following advantages: 1. The unsaturated coordination environment of the defect structure promotes the valence change of Ce and the formation of oxygen vacancies, and increases the oxygen storage capacity of cerium-zirconium; 2. The pinning effect of rare earth elements around the defects reduces the surface energy and inhibits the migration and fusion of cerium-zirconium crystal faces, thereby improving the high-temperature stability of cerium-zirconium; 3. The defects facilitate the strong interaction between cerium-zirconium and noble metals, anchor the noble metals, inhibit the migration and agglomeration of noble metals at high temperatures, accelerate the generation of "active oxygen" species, and synergistically improve the high-temperature dispersibility and catalytic activity of noble metals, so as to meet the use requirements of catalysts for mobile vehicle exhaust purification, VOC treatment, or catalytic combustion.

[0048] Preferably, the cerium-zirconium-based composite oxide forms step defects and / or zigzag defects, and has the following special effects with respect to oxygen defects: 1. The coordination number of the step defect or zigzag defect structure is smaller, and the unsaturation degree of the coordination environment is greater, which is more conducive to promoting the valence change of Ce and the formation of oxygen vacancies, and increasing the oxygen storage capacity of cerium-zirconium; 2. The step defect or zigzag steric hindrance is greater, which is conducive to enhancing the strong interaction between cerium-zirconium and noble metals, anchoring the noble metals, inhibiting the migration and agglomeration of noble metals at high temperatures, and the unsaturated coordination environment of the defects is more conducive to accelerating the generation of "active oxygen" species and synergistically improving the catalytic activity.

[0049] The surface defect quantity characteristic value I of the cerium-zirconium-based composite oxide D / I F2g is 0.2-1.2, preferably 0.5-1.0. D / I F2g is used to quantitatively describe the relative size of the surface defect quantity of the cerium-zirconium-based composite oxide, and I D / I F2g is controlled within a reasonable range to ensure that the surface contains a certain amount of defects, promotes the valence change of Ce, accelerates the generation of "active oxygen" species, synergistically improves the catalytic activity and oxygen storage capacity, and prevents the surface defect quantity from being too large to cause unstable surface structure and reduce high-temperature thermal stability.

[0050] Further, I D / I F2g is calculated as follows: a laser with a wavelength of 532 nm is used for excitation, and the range is 100-3000 cm -1 . Two Raman characteristic peaks, F2g-peak and D-peak, of the cerium-zirconium-based composite oxide are distinguished, the F2g-peak represents the strong vibration peak of the main phase structure, and the D represents the resonance Raman peak generated by the ultraviolet laser and the defect structure, which represents the defects of the lattice atoms. I is obtained by calculating the ratio of the peak strengths of the two peaks.D / I F2g .

[0051] Further, the size of the noble metal loaded on the defect site is less than 3 nm before high-temperature aging treatment, preferably less than 2 nm; and the size of the noble metal is less than 5 nm after 1000℃ / 4h high-temperature aging treatment, preferably less than 3 nm.

[0052] Further, the cerium-zirconium-based composite oxide has an element gradient distribution structure, the content of cerium and / or M element in the surface layer is higher than that in the internal corresponding element, and the content of the above elements gradually increases from the inside to the outside; or, the cerium-zirconium-based composite oxide has a core-shell structure, the content of cerium and / or M element in the surface layer is 1.5-3.5 times of the content of the corresponding element in the cerium-zirconium-based composite oxide; or, the cerium-zirconium-based composite oxide has a grain boundary doping structure, and the cerium-zirconium-based composite oxide grain boundary and surface contain a doping element M.

[0053] Specifically, the cerium-zirconium-based composite oxide includes: an element gradient distribution cerium-zirconium-based composite oxide, a core-shell structure cerium-zirconium-based composite oxide, and / or a grain boundary doping structure. By forming an element gradient distribution, a core-shell structure and / or a grain boundary doping structure, it is beneficial to reduce the surface energy and increase the surface Ce 3+ content, promote the formation of surface defects, improve the cerium-zirconium high-temperature stability and oxygen storage capacity, and synergistically improve the high-temperature stability and catalytic activity of the noble metal.

[0054] According to the differences in element surface energy and defect formation energy calculated by theory, the element types, distribution and content in the gradient, core-shell and / or grain boundary doping structure are designed and controlled to regulate the I D / I F2g Within a reasonable range, the thermal stability and oxygen storage and release performance of the cerium-zirconium-based composite oxide are comprehensively improved.

[0055] The specific surface area of the above cerium-zirconium-based composite oxide after calcination at 1000℃ for 10 hours is ≥52m 2 / g, the static oxygen storage capacity is ≥600μmol O2 / g, preferably the specific surface area is ≥55m 2 / g, and the static oxygen storage capacity is ≥650μmol O2 / g; the specific surface area of the above cerium-zirconium-based composite oxide after calcination at 1100℃ for 10 hours is ≥28m 2 / g, and the static oxygen storage capacity is ≥500μmol O2 / g, preferably the specific surface area is ≥31m 2 / g, and the static oxygen storage capacity is ≥550μmol O2 / g.

[0056] Further, the cation-doped element M includes at least one of a non-cerium rare earth element, a transition metal element except for zirconium and rare earth, an alkaline earth metal element, Al, Si, Ga, Sn and Bi;

[0057] Optionally, the non-cerium rare earth element includes at least one of La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y; preferably, the non-cerium rare earth element includes at least one of La, Pr, Nd, Sm, Eu, Gd, Tm, Yb and Y.

[0058] Optionally, the transition metal element includes at least one of Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Hf, Ta and W; preferably, the transition metal element includes at least one of Ti, Mn, Fe, Co, Ni, Cu, Nb, Hf, W and Mo.

[0059] Optionally, the alkaline earth metal element includes at least one of Be, Mg, Ca, Sr and Ba; preferably, the alkaline earth metal element includes at least one of Mg, Sr and Ba.

[0060] Further, the anion-doped element D includes at least one of anions N, F and P.

[0061] Correspondingly, a second aspect of the embodiment of the present application provides a preparation method of a cerium-zirconium surface loaded noble metal catalyst, for preparing the above-mentioned cerium-zirconium surface loaded noble metal catalyst, including the following steps:

[0062] In step S200, the cerium-zirconium based composite oxide is mixed with a noble metal liquid salt in one or more steps, and is dried, so as to adsorb and fix the noble metal to the defects by using the steric hindrance effect of the defects. Preferably, the proportion of the added part of the noble metal is 10%-40%.

[0063] In step S400, the dried product is heat treated under a preset atmosphere, so as to obtain the noble metal loaded catalyst.

[0064] Further, the noble metal liquid salt includes at least one of a molten salt or an aqueous solution of a chloride salt, a nitrate salt and an acetate salt; the preset atmosphere includes at least one of air, CO, N2 or H2, and the case where air and H2 exist simultaneously is not included on the premise of considering safety factors.

[0065] Further, before the step S200 of mixing the cerium-zirconium-based composite oxide and the noble metal liquid salt uniformly, the method further comprises: preparing a cerium, zirconium and M salt solution according to a stoichiometric ratio, and performing a precipitation reaction with an alkaline substance, preferably a multi-step precipitation reaction; filtering, washing, drying and calcining the obtained precipitate slurry; optionally, the precipitate slurry is subjected to aging treatment before filtering, preferably aging treatment in a hydrothermal environment; and / or, the dried precipitate slurry is subjected to calcination treatment in a certain atmosphere; and / or, the calcined cerium-zirconium-based composite oxide is subjected to acid etching treatment; to obtain the cerium-zirconium-based composite oxide with surface defects.

[0066] Further, the alkaline substance comprises at least one of sodium hydroxide, ammonium hydroxide, potassium hydroxide, urea, ammonium bicarbonate, sodium carbonate, sodium bicarbonate; the atmosphere comprises at least one of air or CO, N2, H2; the aqueous solution of cerium ions and cation-doped elements comprises at least one of nitrate solution, chloride solution, sulfate solution, acetate solution; the aqueous solution of zirconium ions comprises at least one of zirconyl nitrate solution, zirconyl sulfate solution, zirconyl oxychloride solution, zirconium acetate; the calcination temperature ranges from 600℃ to 1200℃. The precipitation pH value is controlled in the range of 4.5 to 14, preferably 5 to 11; the precipitation end point pH value is controlled in the range of 8 to 13, preferably 9 to 11; the precipitation reaction temperature is 0℃ to 120℃, preferably 20℃ to 80℃.

[0067] In the combination of the above atmospheres, in order to improve the safety of the preparation process, the mixed gas of air and H2 is generally not used.

[0068] Further, the mixed solution contains complexing agent ions; optionally, the complexing agent ions are sulfate anions; optionally, the molar ratio of the complexing agent ions to the zirconium ions is 0.2 to 3.0; preferably, the molar ratio of the complexing agent ions to the zirconium ions is 0.5 to 2.5.

[0069] Correspondingly, the third aspect of the embodiment of the present application provides an application of the cerium-zirconium surface-supported noble metal catalyst in the fields of motor vehicle exhaust purification, industrial organic waste gas treatment, natural gas catalytic combustion, petrochemical industry, hydrogen energy and batteries.

[0070] The following specific preparation processes are described by means of several preparation method comparative examples and examples:

[0071] Comparative Example 1:

[0072] According to the molar ratio of the cerium-zirconium-based composite oxide Ce 0.52 Zr 0.36 La 0.05 Y 0.07O2A mixture solution of 250 mL of Ce(NO3)3, ZrO(NO3)2, La(NO3)3, Y(NO3)3, each having a total metal ion molar concentration of 1.5 mol / L, is prepared. The mixture solution is mixed with an aqueous ammonia solution having a concentration of 2.5 mol / L to perform a precipitation reaction. The precipitation temperature is 20-50°C, the pH value during the precipitation process is 10±2, and the pH value at the end of the precipitation is 11±1. The precipitate is subjected to post-treatment such as filtration and washing to obtain a precursor. The precursor is then dried at 110°C for 10 hours and calcined at 800°C for 5 hours to obtain a fresh sample of cerium-zirconium-based composite oxide. The fresh sample is further calcined at 1000°C and 1100°C for 10 hours, respectively, to obtain aged samples of cerium-zirconium-based composite oxide.

[0073] A certain volume of a palladium nitrate solution and a platinum nitrate solution are taken in such a manner that the loading of palladium is 0.9% and the loading of platinum is 0.3%. The solution is mixed with the above-mentioned Ce 0.52 Zr 0.36 La 0.05 Y 0.07 The fresh sample of the cerium-zirconium-supported noble metal catalyst is further calcined at 1000°C for 4 hours to obtain an aged sample of the cerium-zirconium-supported noble metal catalyst.

[0074] Comparative Examples 2-4

[0075] Unless otherwise indicated below, the same procedure as in Comparative Example 1 is followed. The composition and process parameters of the comparative examples are shown in Table 1.

[0076] Example 1

[0077] This example relates to the preparation of Ce 0.52 Zr 0.36 La 0.05 Y 0.07 O2.

[0078] Two mixed chloride solutions were prepared, one was chloride mixed solution A containing 22 mol% cerium, 48 mol% zirconium and 8 mol% yttrium in total. The other was chloride mixed solution B containing the rest of cerium, zirconium, lanthanum and yttrium in the designed distribution. Solution A was added to an appropriate amount of sodium hydroxide solution for precipitation. After the addition of solution A was completed, solution B was added to the mixture, and sodium hydroxide solution was added for precipitation. The precipitation process was controlled at pH = 8 ± 2. The precipitate was filtered and washed to obtain a composite hydroxide precipitate containing cerium, zirconium or cerium, zirconium and optionally one or more than one metal of rare earth salt other than Ce and non-rare earth metal salt other than Zr. The obtained precipitate was reslurried, and the obtained slurry was placed in an autoclave, so that the temperature of the slurry reached 120°C for 2 hours. A modifier was added, and the mixture was stirred for a period of time and then filtered. The obtained filter cake was calcined at 600°C for 3 hours and roasted at 800°C for 5 hours to obtain a fresh sample of cerium-zirconium-based composite oxide, which was further roasted at 1000°C and 1100°C for 10 hours, respectively, to obtain an aged sample of cerium-zirconium-based composite oxide.

[0079] A certain volume of palladium nitrate and platinum nitrate solutions were taken with a loading of 0.9% palladium and 0.3% platinum, and two mixed noble metal salt solutions were prepared in proportion, one was noble metal salt mixed solution C containing 12 mol% palladium and 15 mol% platinum in total, and the other was mixed solution D containing the rest of palladium and platinum. Solution C was first added to the above Ce 0.52 Zr 0.36 La 0.05 Y 0.07 O2 powder fresh sample was mixed uniformly, and solution D was added to the mixture after stirring for 30 minutes. The sample was dried at 110°C for 4 hours, and then the dried sample was roasted at 600°C in an air atmosphere for 5 hours to obtain a fresh sample of cerium-zirconium-supported noble metal catalyst. Further roasting at 1000°C for 4 hours obtained an aged sample of cerium-zirconium-supported noble metal catalyst.

[0080] Examples 2-44:

[0081] Unless otherwise indicated below, the same procedures as in Example 1 were used. The specific compositions and process parameters of the examples are shown in Table 1. The defect structure characteristic values and performance test results of the comparative examples and examples are shown in Table 2.

[0082] Table 1 Specific compositions and process parameters of comparative examples and examples

[0083]

[0084]

[0085]

[0086]

[0087] Table 2 Summary of Defect Structural Characteristic Values ​​and Performance Test Results for Comparative Examples and Embodiments

[0088]

[0089]

[0090]

[0091] PM in the table above refers to precious metals.

[0092] Figure 2(a) shows Ce in Example 23 0.33 Zr 0.57 La 0.04 Y 0.06 The Raman test results show that the F2g- and D- peaks of the cerium-zirconium-based composite oxide can be distinguished from the figure. The ratio of the intensities of the two peaks is further calculated to obtain I. D / I F2g It is 0.95.

[0093] Figure 2(b) shows the PM / Ce ratio in Example 23. 0.33 Zr 0.57 La 0.04 Y 0.06 The HAADF-STEM test results show that the defects in the cerium-zirconium-based composite oxide are loaded with the noble metal Pt.

[0094] This invention aims to protect a catalyst with a cerium-zirconium surface loaded with a noble metal and its preparation method, wherein the catalyst comprises: a cerium-zirconium-based composite oxide and a noble metal; and the surface defect quantity characteristic value I of the cerium-zirconium-based composite oxide. D / I F2g The content is 0.2-1.2, preferably 0.5-1.0; the defects in the cerium-zirconium based composite oxide are loaded with noble metals. The above technical solution has the following effects:

[0095] By controlling the parameters of precipitation, aging, atmosphere roasting, and acid etching, a non-uniform doped structure of rare earth elements is constructed. Utilizing the radius effect and valence charge balance principle of the rare earth dopants in this structure, distortion of the cerium-zirconium lattice is induced, producing defects such as step-like and serrated shapes. This anchors the noble metals, inhibits their migration, aggregation, and growth under high-temperature conditions, improves their high-temperature dispersibility, and enhances their catalytic activity.

[0096] It should be understood that the foregoing detailed description of the application, rather than limiting the application, is intended to explain and describe the current implementation of the application. Therefore, any modification, equivalent replacement or improvement made without departing from the spirit and scope of the application should be included in the protection scope of the application. In addition, the appended claims of the application are intended to cover all changes and modifications falling within the scope and boundary of the appended claims, or the equivalent form of such scope and boundary.

Claims

1. A catalyst with a cerium-zirconium surface-supported noble metal, characterized in that, include: Cerium-zirconium-based composite oxides and noble metals; the characteristic value I of the number of surface defects in the cerium-zirconium-based composite oxides. D / I F2g The value is 0.2-1.2; the defects in the cerium-zirconium based composite oxide include: stepped defects and / or serrated defects; The defects in the cerium-zirconium-based composite oxide are loaded with noble metals; The general chemical formula of the cerium-zirconium-based composite oxide is Ce. x Zr y M z O 2-α D δ Where M is a cation dopant and D is an anion dopant, in molar terms, 0.1 < x < 0.9, 0.1 < y < 0.9, 0 < z < 0.3, and x + y + z = 1; 0 ≤ α ≤ 0.1; 0 ≤ δ ≤ 0.

1.

2. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 1, characterized in that, The characteristic value of the number of surface defects in the cerium-zirconium-based composite oxide is I. D / I F2g It ranges from 0.5 to 1.

0.

3. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 1, characterized in that, The noble metal is in a metallic state and / or an oxidized state; The precious metals include at least one of Pt, Pd, Rh, Ir, Os, Ru, Au and Ag; The loading of the precious metal is 0.01%-3% by mass fraction.

4. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 3, characterized in that, The precious metals include at least one of Pt, Pd, Rh, and Ru; The loading of the precious metal is 0.1%-2% by mass fraction.

5. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 1, characterized in that, Before the high-temperature aging treatment, the size of the noble metal loaded at the defect site is less than 3 nm; After high-temperature aging treatment at 1000℃ for 4 hours, the size of the precious metal is less than 5nm.

6. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 5, characterized in that, Before the high-temperature aging treatment, the size of the noble metal loaded at the defect site is less than 2 nm; After high-temperature aging treatment at 1000℃ for 4 hours, the size of the precious metal is less than 3nm.

7. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 1, characterized in that, The cerium-zirconium-based composite oxide has an elemental gradient distribution structure. In terms of molar ratio, the content of cerium and / or M elements on the surface is higher than that of the corresponding elements inside, and the content of the above elements gradually increases from the inside to the outside. or, The cerium-zirconium-based composite oxide has a core-shell structure, and the content of cerium and / or M elements on its surface is 1.5 to 3.5 times the content of the corresponding elements in the cerium-zirconium-based composite oxide, in molar ratio.

8. The catalyst with noble metal supported on the cerium-zirconium surface according to any one of claims 1-7, characterized in that, The cation doping element M includes: non-cerium rare earth elements, transition metal elements other than zirconium and rare earth elements, alkaline earth metal elements, and at least one of Al, Si, Ga, Sn and Bi.

9. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 8, characterized in that, The non-cerium rare earth elements include at least one of the following: La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; The transition metal element includes at least one of the following: Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Hf, Ta, and W; The alkaline earth metal element includes at least one of Be, Mg, Ca, Sr and Ba.

10. The catalyst with noble metal supported on the cerium-zirconium surface according to claim 9, characterized in that, The non-cerium rare earth elements include at least one of La, Pr, Nd, Sm, Eu, Gd, Tm, Yb, and Y; The transition metal element includes at least one of the following: Ti, Mn, Fe, Co, Ni, Cu, Nb, Hf, W, and Mo; The alkaline earth metal element includes at least one of Mg, Sr and Ba.

11. The catalyst with noble metal supported on the cerium-zirconium surface according to any one of claims 1-7, characterized in that, The anion doping element D includes at least one of the anions N, F, and P.

12. A method for preparing a catalyst with noble metal supported on a cerium-zirconium surface, characterized in that, The catalyst for preparing the cerium-zirconium surface-supported noble metal as described in any one of claims 1-11 comprises the following steps: The cerium-zirconium-based composite oxide is mixed with a noble metal liquid salt in one or more steps and then dried. The dried product was heat-treated under a preset atmosphere to obtain a catalyst loaded with noble metals.

13. The method for preparing a cerium-zirconium surface-supported noble metal catalyst according to claim 12, characterized in that, The noble metal liquid salt includes: a molten salt or aqueous solution of at least one of chloride salts, nitrate salts and acetates; The preset atmosphere includes at least one of air, CO, N2, or H2.

14. The method for preparing a cerium-zirconium surface-supported noble metal catalyst according to claim 12, characterized in that, Before uniformly mixing the cerium-zirconium-based composite oxide with the noble metal liquid salt, the process further includes: Prepare the required cerium, zirconium, and M salt solutions according to the stoichiometric ratio, and then carry out a precipitation reaction with alkaline substances; The resulting precipitate slurry was filtered, washed, dried, and calcined. The precipitate slurry is aged before filtration; and / or the dried precipitate slurry is calcined under a certain atmosphere; and / or the calcined cerium-zirconium-based composite oxide is acid-etched. The cerium-zirconium-based composite oxide with surface defects is obtained.

15. The method for preparing a cerium-zirconium surface-supported noble metal catalyst according to claim 14, characterized in that, The required cerium, zirconium, and M salt solutions are prepared according to stoichiometric ratios and then subjected to a multi-step precipitation reaction with alkaline substances.

16. The method for preparing a cerium-zirconium surface-supported noble metal catalyst according to claim 14, characterized in that, Before filtration, the precipitate slurry is aged in a hydrothermal environment.

17. The method for preparing a cerium-zirconium surface-supported noble metal catalyst according to claim 14, characterized in that, The alkaline substance includes at least one of the following: sodium hydroxide, ammonium hydroxide, potassium hydroxide, urea, ammonium bicarbonate, sodium carbonate, and sodium bicarbonate. The atmosphere includes: air or at least one of CO, N2, and H2; The aqueous solution of cerium ions and the cation doping element includes at least one of the following: nitrate solution, chloride solution, sulfate solution, and acetate solution; Aqueous solutions of zirconium ions include at least one of the following: zirconium oxynitrate solution, zirconium oxysulfate solution, zirconium oxychloride solution, and zirconium acetate. The roasting temperature ranges from 600℃ to 1200℃.

18. The application of the cerium-zirconium surface-supported noble metal catalyst as described in any one of claims 1-11 in the fields of motor vehicle exhaust purification, industrial organic waste gas treatment, natural gas catalytic combustion, petrochemicals, hydrogen energy, and batteries.

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