A tightly coupled SCR post-treatment composite catalyst, its preparation method and application

Abstract

The present invention provides a tightly coupled SCR post-treatment composite catalyst, a preparation method thereof and an application. The composite catalyst comprises a metal oxide loaded with noble metal single atoms and nanoclusters and Cu-SSZ-13 zeolite with a mass ratio of 1:(0.1-30); the metal oxide loaded with noble metal single atoms and nanoclusters uses the metal oxide as a carrier and the noble metal as an active component, and the noble metal is dispersed on the metal oxide in the form of single atoms and nanoclusters. The preparation method of the composite catalyst comprises: mixing the metal oxide loaded with noble metal single atoms and Cu-SSZ-13 zeolite, and then calcining to partially convert the noble metal single atoms into nanoclusters and disperse them on the metal oxide together, so as to obtain the tightly coupled SCR post-treatment composite catalyst. The composite catalyst provided by the present invention has excellent catalytic activity and nitrogen selectivity in a low-temperature environment (<150 °C).

Description

Technical Field

[0001] The present invention relates to a tightly coupled SCR post-treatment composite catalyst, a preparation method thereof, and an application thereof, belonging to the technical field of tail gas treatment. Background Art

[0002] Nitrogen oxides (NO x ) emitted from diesel engine tail gas can cause ozone formation, acid rain formation, and respiratory diseases. The traditional selective catalytic reduction (SCR) technology has been widely used to reduce NO x emissions, and the Cu-SSZ-13 molecular sieve catalyst is a commercial SCR catalyst for the national VI stage. However, the Cu-SSZ-13 molecular sieve catalyst cannot meet the future national VII standard in a low-temperature environment (<150 °C).

[0003] Tightly coupled SCR (CCSCR) has been developed to overcome some limitations of traditional SCR technology due to its relatively mature technical route, good durability, and low cost, and is also an ideal choice for solving the low-temperature NO x emission problem. The key issue of CCSCR technology is the selection of the catalyst. Since the Cu-SSZ-13 catalyst has been widely used, the most ideal solution is to modify the traditional Cu-SSZ-13 catalyst to make it have excellent low-temperature activity.

[0004] There are mainly two possible ways being explored in the prior art to improve the low-temperature activity of Cu-SSZ-13. One way is to dope a second metal element into Cu-SSZ-13, and the other way is to add a second component. Among them, the loading of the second metal element has little effect on the low-temperature activity of Cu-SSZ-13 and cannot significantly reduce the low-temperature activity of Cu-SSZ-13. Ideally, the second component added to Cu-SSZ-13 has strong oxidizing properties and can oxidize NO to NO2 under low-temperature conditions to promote the fast SCR reaction in Cu-SSZ-13 (i.e., NO + NO2 + 2NH3 → 2N2 + 3H2O), thereby improving the low-temperature activity of the Cu-SSZ-13 catalyst.

[0005] CN102869427B and CN116422364A respectively disclose modified molecular sieves loaded with bimetals / polymetals and a preparation method thereof. CN116550376A discloses a Cu-SSZ-13 composite catalyst loaded with rare earth metal oxides or transition metal oxides and a preparation method thereof. The catalysts disclosed in these documents cannot achieve ideal low-temperature activity.

[0006] In addition, the addition method of the second component is a technical problem. If the second component is too tightly combined with Cu-SSZ-13, the second component will block the pores of Cu-SSZ-13, resulting in a decrease in catalytic activity. However, if the combination is not tight, NO2 will not be able to fully participate in the rapid SCR reaction. Moreover, the selection of the second component is also a technical problem. If its oxidizing property is too strong, NH3 will be oxidized in the low temperature section, causing a sharp decrease in catalytic activity. On the contrary, NO cannot be oxidized to NO2 in the low temperature section, and the low temperature activity of Cu-SSZ-13 cannot be promoted.

[0007] Therefore, developing a tightly coupled SCR post-treatment composite catalyst and a preparation method thereof is still one of the problems to be solved urgently in the art. Summary of the invention

[0008] In order to solve the above technical problems, the purpose of the present invention is to provide a close-coupled SCR post-treatment composite catalyst and its preparation method and application. The present invention can improve the catalytic activity of the composite catalyst in a low temperature environment (<150°C).

[0009] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a tightly coupled SCR post-treatment composite catalyst, which comprises a metal oxide loaded with noble metal single atoms and nanoclusters and a Cu-SSZ-13 molecular sieve in a mass ratio of 1:(0.1-30); wherein the metal oxide loaded with noble metal single atoms and nanoclusters uses metal oxide as a carrier and noble metal as an active component, and the noble metal is co-dispersed on the metal oxide in the form of single atoms and nanoclusters.

[0010] According to a specific embodiment of the present invention, preferably, the composite catalyst is prepared by at least the following steps: mixing a metal oxide loaded with noble metal single atoms and a Cu-SSZ-13 molecular sieve and then calcining the mixture, so that the noble metal single atoms in the metal oxide loaded with noble metal single atoms are partially converted into nanoclusters and dispersed together on the metal oxide to obtain the composite catalyst; wherein the calcination comprises: using a mixed gas of N2 and O2 as a calcination atmosphere, in the calcination atmosphere, heating the mixture of the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve to a calcination temperature, maintaining the temperature for a period of time, and then cooling it to room temperature within 1-10 minutes.

[0011] The inventors of this case found through extensive research that after calcining a mixture of a metal oxide loaded with single-atom noble metal and Cu-SSZ-13 zeolite in a mixed gas of N2 and O2 and then rapidly cooling it to room temperature, part of the single-atom noble metal in the metal oxide loaded with single-atom noble metal can be converted into nanoclusters and dispersed on the metal oxide; at the same time, in the catalyst material obtained by calcining the composite of the metal oxide loaded with single-atom noble metal and Cu-SSZ-13 zeolite, the interfacial effect between the nanoclusters formed by the cooperation of single-atom noble metal and part of the single atoms and the metal oxide promotes the occurrence of the fast SCR reaction in Cu-SSZ-13 zeolite, thus greatly promoting the low-temperature activity of the NH3-SCR reaction; therefore, the composite catalyst of the present invention has improved catalytic activity and excellent nitrogen selectivity in a low-temperature environment (<150°C).

[0012] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, during the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 20-80 Vol.% N2 and 80-20 Vol.% O2. More preferably, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 80 Vol.% N2 and 20 Vol.% O2.

[0013] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, during the calcination process, it is cooled to room temperature within 1-5 minutes.

[0014] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, during the calcination process, the method of cooling to room temperature within 1-10 minutes includes cooling with a cooling medium outside the calcination device or directly taking out the powder in the calcination device and exposing it to room temperature.

[0015] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, during the calcination process, the calcination temperature is 300-600°C, and the constant temperature maintenance time is 1-6 hours.

[0016] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, the mass ratio of the metal oxide loaded with single-atom noble metal and nanoclusters to the Cu-SSZ-13 zeolite is 1:(0.1-10).

[0017] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, the particle size of the nanoclusters of the noble metal is 1-3 nm.

[0018] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, based on the total mass of the metal oxide loaded with noble metal single atoms and nanoclusters being 100%, the content of the noble metal therein is 0.01-10%, more preferably 0.5-5%; the content of the noble metal nanoclusters is 0.01-5%, more preferably 0.02-1%.

[0019] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, the noble metal includes one or a combination of several of Pt, Pd, Rh, Ru, Ir, Au, Ag, etc. More preferably, the noble metal is Rh.

[0020] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, the metal oxide includes a single metal oxide formed by one element among Ce, Fe, Mn, V, W, Ti, Sn, Zr, etc. and / or a composite oxide formed by several elements. More preferably, the metal oxide includes a cerium-zirconium composite oxide.

[0021] In the above-mentioned close-coupled SCR aftertreatment composite catalyst, preferably, the metal oxide loaded with noble metal single atoms and nanoclusters is M x -Ce y -Zr 1-y -O z , where M is a noble metal, x is the mass content of the noble metal, y is the mass fraction of Ce in the CeZrO support based on the total mass of Ce and Zr being 1, z is the number of oxygen atoms, x = 0.01-10%, y = 0.01-0.99, z = 1-5; more preferably, the metal oxide loaded with noble metal single atoms and nanoclusters is M x -Ce y -Zr 1-y -O z , where M is a noble metal, x is the mass content of the noble metal, y is the mass fraction of Ce in the CeZrO support based on the total mass of Ce and Zr being 1, z is the number of oxygen atoms, x = 0.5-5%, y = 0.5-0.8, z = 1-2.

[0022] The second aspect of the present invention provides a preparation method of the above-mentioned close-coupled SCR aftertreatment composite catalyst, which includes the following steps:

[0023] Mix the metal oxide loaded with noble metal single atoms and Cu-SSZ-13 zeolite, and then calcine it to convert part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms into nanoclusters and disperse them on the metal oxide together, thus obtaining the tight-coupling SCR post-treatment composite catalyst; wherein, the calcination includes: using a mixed gas of N2 and O2 as the calcination atmosphere, in the calcination atmosphere, after heating the mixture of the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 zeolite to the calcination temperature, keep it at a constant temperature for a period of time, and then cool it to room temperature within 1 - 10 min.

[0024] In the above preparation method, preferably, during the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 20 - 80 Vol.% N2 and 80 - 20 Vol.% O2. More preferably, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 80 Vol.% N2 and 20 Vol.% O2.

[0025] In the above preparation method, preferably, during the calcination process, cool it to room temperature within 1 - 5 min.

[0026] In the above preparation method, preferably, during the calcination process, the method of cooling it to room temperature within 1 - 10 min includes using a cooling medium to cool outside the calcination device or directly taking out the powder in the calcination device and exposing it to room temperature.

[0027] In the above preparation method, preferably, during the calcination process, the calcination temperature is 300 - 600 °C, and the time for maintaining at a constant temperature is 1 - 6 h.

[0028] In the above preparation method, preferably, the metal oxide loaded with noble metal single atoms is prepared at least through the following steps: uniformly mix the precursor solution of the noble metal with the metal oxide, and then obtain the metal oxide loaded with noble metal single atoms after at least drying and calcination.

[0029] In the above preparation method, preferably, in the preparation step of the metal oxide loaded with noble metal single atoms, the precursor of the noble metal includes one or a combination of several of nitrate, chloride, acetate, sulfate, etc. of the noble metal. More preferably, the precursor of the noble metal includes nitrate and / or chloride, etc. of the noble metal.

[0030] In the above preparation method, preferably, the Cu-SSZ-13 molecular sieve is prepared through the following steps: (a) uniformly mixing an aluminum source, an alkali metal compound, a structure-directing agent, a silicon source, and SSZ-13 molecular sieve seeds in a solvent, then performing crystallization, and then subjecting the product obtained by crystallization to at least drying and calcination to obtain a molecular sieve containing an alkali metal; (b) adding the molecular sieve containing an alkali metal to an ammonium salt aqueous solution for an ion exchange reaction, and subjecting the product to at least drying and calcination to obtain an H-type molecular sieve; (c) contacting the H-type molecular sieve with a copper salt for an ion exchange reaction, and subjecting the product to at least drying and calcination to obtain the Cu-SSZ-13 molecular sieve.

[0031] In the above preparation method, preferably, in the preparation step of the Cu-SSZ-13 molecular sieve, the aluminum source includes sodium aluminate, the alkali metal compound includes potassium hydroxide, the structure-directing agent includes N,N,N-trimethyl-1-adamantylammonium hydroxide, and the silicon source includes silica sol; the mixing mass ratio of the aluminum source, the alkali metal compound, the structure-directing agent, the silicon source, and the SSZ-13 molecular sieve seeds is (1-5):(1-5):(1-20):(10-30):(0.01-0.03).

[0032] In the above preparation method, preferably, in the preparation step of the Cu-SSZ-13 molecular sieve, the concentration of the ammonium salt aqueous solution is 0.01-5 mol / L. The mixing ratio of the ammonium salt aqueous solution and the molecular sieve containing an alkali metal can be routinely adjusted by those skilled in the art on the basis of ensuring the smooth progress of the reaction.

[0033] In the above preparation method, preferably, in the preparation step of the Cu-SSZ-13 molecular sieve, the mass ratio of the copper salt to the H-type molecular sieve is 1:(1-100).

[0034] In the above preparation method, preferably, in the preparation step of the Cu-SSZ-13 molecular sieve, the temperature of the crystallization is 150-200 °C, and the time is 6-24 h.

[0035] In the above preparation method, preferably, in the preparation step of the Cu-SSZ-13 molecular sieve, the temperature for adding the molecular sieve containing an alkali metal to the ammonium salt aqueous solution for an ion exchange reaction is 20-100 °C, and the time is 3-24 h.

[0036] In the above preparation method, preferably, in the preparation step of the Cu-SSZ-13 molecular sieve, the temperature for contacting the H-type molecular sieve with the copper salt for an ion exchange reaction is 20-90 °C, and the time is 1-12 h.

[0037] In the above preparation method, preferably, the method of mixing the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve includes one or a combination of several of mechanical mixing, pneumatic mixing, impulse mixing, etc., and more preferably mechanical mixing.

[0038] The third aspect of the present invention provides the application of the above-mentioned close-coupled SCR aftertreatment composite catalyst in the selective catalytic reduction of NO at low temperature x as a catalyst.

[0039] In the above application, preferably, the low temperature is above 100 °C. More preferably, the low temperature is 125-150 °C.

[0040] In the above application, preferably, the selective catalytic reduction of NO x includes automotive exhaust treatment.

[0041] The present invention provides a close-coupled SCR aftertreatment composite catalyst, its preparation method and application. The present invention composes a metal oxide loaded with noble metal single atoms and Cu-SSZ-13 molecular sieve, and by controlling the calcination atmosphere and cooling process of the mixture of the two, part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms are converted into nano-clusters and are dispersed on the metal oxide together. The composite catalyst of the present invention has a synergistic effect and is more active than the single metal oxide loaded with noble metal single atoms or the single Cu-SSZ-13 molecular sieve alone. This synergistic effect includes: nitric oxide (NO) undergoes a NO oxidation reaction on the metal oxide loaded with noble metal single atoms and nano-clusters to generate nitrogen dioxide (NO2) (NO + 1 / 2O2 → NO2), and due to the synergistic effect between the noble metal single atoms and the partially converted nano-clusters, it has excellent catalytic activity; then NO2 undergoes a fast SCR reaction on the Cu-SSZ-13 molecular sieve (2NO + 4NH3 + 2NO2 → 4N2 + 6H2O). Since the fast SCR reaction is faster than the standard SCR reaction (4NO + 4NH3 + O2 → 4N2 + 6H2O), the reaction can proceed rapidly in a low-temperature environment (<150 °C). At the same time, the oxidizing property of the metal oxide loaded with noble metal single atoms and nano-clusters of the present invention and the tightness of its combination with the Cu-SSZ-13 molecular sieve are both very suitable, enabling the reaction to proceed smoothly in a low-temperature environment.

[0042] Compared with the prior art, the technical method of the present invention has at least the following beneficial effects:

[0043] (1) After calcining the mixture of metal oxide loaded with noble metal single atoms and Cu-SSZ-13 zeolite in a mixed gas of N2 and O2 and then rapidly cooling it to room temperature, part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms can be converted into nano-clusters and co-dispersed on the metal oxide, and the synergistic effect between the noble metal single atoms and nano-clusters and the interfacial effect with the metal oxide greatly promotes the low-temperature activity of the NH3-SCR reaction.

[0044] (2) The preparation process of the composite catalyst of the present invention is simple, and only steps such as mixing and calcining can achieve the effect of 1+1>2, greatly promoting the low-temperature activity of SCR.

[0045] (3) The composite catalyst of the present invention can solve the problem of tail gas pollutant emissions caused by the low temperature in the low-temperature cold start stage of automobiles. At the same time, the composite catalyst has excellent N2 selectivity and strong practicability.

[0046] In summary, the close-coupled SCR post-treatment composite catalyst provided by the present invention has excellent catalytic activity and nitrogen selectivity in a low-temperature environment. Brief Description of the Drawings

[0047] Figure 1 is the aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of Rh-CZO in Preparation Example 1.

[0048] Figure 2 is the TEM image of the Rh-CZO / Cu-SSZ-13 composite catalyst in Example 1.

[0049] Figure 3 is the aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of the Rh-CZO / Cu-SSZ-13 composite catalyst in Example 1.

[0050] Figure 4 is the X-ray absorption fine structure spectrum of the Rh-CZO / Cu-SSZ-13 composite catalyst in Example 1.

[0051] Figure 5 is the XPS image of Ce element and Rh element of Rh-CZO in Preparation Example 1 and the Rh-CZO / Cu-SSZ-13 composite catalyst in Example 1.

[0052] Figure 6 is the XRD image of the products of Preparation Example 1, Preparation Example 5, Example 1 and Comparative Example 1.

[0053] Figure 7 is the N2 adsorption-desorption isotherm of the products of Preparation Example 1, Preparation Example 5, Example 1 and Comparative Example 1.

[0054] Figure 8 It is the catalytic activity diagram of the products of Preparation Examples 1-4.

[0055] Figure 9 It is the catalytic activity diagram of the products of Preparation Example 5, Examples 1-2 and Comparative Examples 1-4.

[0056] Figure 10 It is the nitrogen selectivity diagram of the products of Preparation Example 5, Examples 1-2 and Comparative Examples 1-4. Detailed implementation manners

[0057] For a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0058] The first aspect of the present invention provides a close-coupled SCR post-treatment composite catalyst, and the composite catalyst comprises a metal oxide loaded with noble metal single atoms and nanoclusters and Cu-SSZ-13 molecular sieve with a mass ratio of 1:(0.1-30); wherein, the metal oxide loaded with noble metal single atoms and nanoclusters uses the metal oxide as a carrier and the noble metal as an active component, and the noble metal is dispersed in the metal oxide in the form of single atoms and nanoclusters.

[0059] According to the specific implementation manner of the present invention, the composite catalyst is prepared at least through the following steps: mixing the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve and then calcining, so that part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms is converted into nanoclusters and are dispersed in the metal oxide together to obtain the composite catalyst; wherein, the calcination includes: using a mixed gas of N2 and O2 as the calcination atmosphere, in the calcination atmosphere, after heating the mixture of the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve to the calcination temperature, maintaining a constant temperature for a period of time, and then cooling to room temperature within 1-10 minutes.

[0060] In some specific implementation manners, the mass ratio of the metal oxide loaded with noble metal nanoclusters and the Cu-SSZ-13 molecular sieve is 1:(0.1-10), for example, it can be 1:1.

[0061] In some specific implementation manners, the particle size of the noble metal nanoclusters is 1-3 nm.

[0062] In some specific embodiments, based on the total mass of the metal oxide loaded with noble metal single atoms and nanoclusters being 100%, the content of the noble metal therein is 0.01 - 10%, preferably 0.5 - 5%, the content of the noble metal nanoclusters is 0.01 - 5%, preferably 0.02 - 1%.

[0063] Those skilled in the art can understand that in the metal oxide loaded with noble metal single atoms and nanoclusters, the balance other than the content of the noble metal should be the metal oxide.

[0064] In some specific embodiments, the noble metal includes one or a combination of several of Pt, Pd, Rh, Ru, Ir, Au, Ag, etc. Preferably, the noble metal is Rh.

[0065] In some specific embodiments, the metal oxide includes a single metal oxide formed by one element among Ce, Fe, Mn, V, W, Ti, Sn, Zr, etc. and / or a composite oxide formed by several elements. Preferably, the metal oxide includes a cerium-zirconium composite oxide.

[0066] In some specific embodiments, the metal oxide loaded with noble metal single atoms and nanoclusters is M x -Ce y -Zr 1-y -O z , where M is a noble metal, x is the mass content of the noble metal, y is the mass fraction of Ce in the CeZrO support with the total mass of Ce and Zr being 1, z is the number of oxygen atoms, x = 0.01 - 10%, y = 0.01 - 0.99, z = 1 - 5; preferably, the metal oxide loaded with noble metal single atoms and nanoclusters is M x -Ce y -Zr 1-y -O z , where M is a noble metal, x is the mass content of the noble metal, y is the mass fraction of Ce in the CeZrO support with the total mass of Ce and Zr being 1, z is the number of oxygen atoms, x = 0.5 - 5%, y = 0.5 - 0.8, z = 1 - 2.

[0067] The second aspect of the present invention provides a preparation method of the above-mentioned close-coupled SCR post-treatment composite catalyst, which includes the following steps:

[0068] Mix the metal oxide loaded with noble metal single atoms and Cu-SSZ-13 molecular sieve, and then calcine it, so that part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms is converted into nano-clusters and co-dispersed on the metal oxide, and the tight-coupled SCR post-treatment composite catalyst is obtained; wherein, the calcination includes: using a mixed gas of N2 and O2 as the calcination atmosphere, in the calcination atmosphere, after the mixture of the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve is heated to the calcination temperature, keep it at a constant temperature for a period of time, and then cool it to room temperature within 1-10 minutes.

[0069] In some specific embodiments, during the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 20-80 Vol.% N2 and 80-20 Vol.% O2. Preferably, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 80 Vol.% N2 and 20 Vol.% O2.

[0070] In some specific embodiments, during the calcination process, cool it to room temperature within 1-5 minutes.

[0071] In some specific embodiments, during the calcination process, the method of cooling it to room temperature within 1-10 minutes includes using a cooling medium to cool outside the calcination device or directly taking out the powder in the calcination device and exposing it to room temperature. Among them, the calcination device used can be a conventional device in the art, such as but not limited to a quartz tube. The cooling medium used is, for example but not limited to, cooling water.

[0072] In some specific embodiments, during the calcination process, the calcination temperature is 300-600 °C, such as 550 °C, and the time for maintaining the constant temperature is 1-6 h, such as 4 h.

[0073] In some preferred specific embodiments, the preparation method of the tight-coupled SCR post-treatment composite catalyst includes the following steps:

[0074] Mix at least the metal oxide loaded with noble metal single atoms and Cu-SSZ-13 molecular sieve to obtain a semi-finished composite catalyst, put the semi-finished composite catalyst into a quartz tube, and in an atmosphere of a mixed gas of 80 Vol.% N2 and 20 Vol.% O2, at 2-10 °C·min -1The heating rate is from room temperature to the calcination temperature, the calcination temperature is 300 - 600 °C, and it is maintained at a constant temperature for 1 - 6 h. Then, it is cooled to room temperature within 1 - 5 min by using a cooling medium to cool the outside of the quartz tube or directly taking out the powder in the quartz tube and exposing it to room temperature, so that part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms are converted into nanoclusters and are jointly dispersed on the metal oxide, obtaining the tight-coupling SCR post-treatment composite catalyst described above.

[0075] In some specific embodiments, the metal oxide loaded with noble metal single atoms is prepared at least through the following steps: uniformly mixing the precursor solution of the noble metal with the metal oxide, and then obtaining the metal oxide loaded with noble metal single atoms after at least drying and calcination.

[0076] In some specific embodiments, in the preparation step of the metal oxide loaded with noble metal single atoms, the precursor of the noble metal includes one or a combination of several of nitrates, chlorides, acetates, sulfates, etc. of the noble metal. Preferably, the precursor of the noble metal includes nitrates and / or chlorides, etc. of the noble metal.

[0077] In some specific embodiments, in the preparation step of the metal oxide loaded with noble metal single atoms, the mixing mass ratio of the precursor of the noble metal to the metal oxide is (0.01 - 10):(1 - 20).

[0078] In some specific embodiments, in the preparation step of the metal oxide loaded with noble metal single atoms, the drying temperature is 50 - 100 °C and the time is 6 - 24 h.

[0079] In some specific embodiments, in the preparation step of the metal oxide loaded with noble metal single atoms, the calcination temperature is 300 - 600 °C and the time is 2 - 8 h. Specifically, the calcination includes: placing the dried product in a muffle furnace and heating it from room temperature to 300 - 600 °C at a heating rate of 2 - 10 °C·min -1 and calcining for 2 - 8 h, the calcination atmosphere is an air atmosphere, and after the calcination is completed, it is cooled to room temperature at a cooling rate of 2 - 5 °C·min -1

[0080] In some specific embodiments, the preparation step of the metal oxide loaded with noble metal single atoms may further include conventional steps such as solid-liquid separation and washing, and those skilled in the art can make conventional adjustments to these steps.

[0081] In some specific embodiments, the specific surface area of the metal oxide loaded with noble metal single atoms is 10 - 50 m 2 ​ / g, with a pore diameter of 0.3 - 100 nm and a total pore volume of 0.001 - 5 cm 3 / g.

[0082] In some specific embodiments, the Cu-SSZ-13 molecular sieve is prepared through the following steps: (a) uniformly mixing an aluminum source, an alkali metal compound, a structure directing agent, a silicon source, and SSZ-13 molecular sieve seeds in a solvent, then carrying out crystallization, and then subjecting the product obtained from crystallization to at least drying and calcination to obtain a molecular sieve containing an alkali metal; (b) adding the molecular sieve containing an alkali metal to an aqueous ammonium salt solution for an ion exchange reaction, and subjecting the product to at least drying and calcination to obtain an H-type molecular sieve; (c) contacting the H-type molecular sieve with a copper salt for an ion exchange reaction, and subjecting the product to at least drying and calcination to obtain the Cu-SSZ-13 molecular sieve.

[0083] In some specific embodiments, in the preparation steps of the Cu-SSZ-13 molecular sieve, the aluminum source includes sodium aluminate, the alkali metal compound includes potassium hydroxide, the structure directing agent includes N,N,N-trimethyl-1-adamantylammonium hydroxide, and the silicon source includes silica sol; the mixing mass ratio of the aluminum source, the alkali metal compound, the structure directing agent, the silicon source, and the SSZ-13 molecular sieve seeds is (1 - 5):(1 - 5):(1 - 20):(10 - 30):(0.01 - 0.03).

[0084] In some specific embodiments, in the preparation steps of the Cu-SSZ-13 molecular sieve, the ammonium salt is, for example but not limited to, ammonium nitrate, etc.

[0085] In some specific embodiments, in the preparation steps of the Cu-SSZ-13 molecular sieve, the concentration of the aqueous ammonium salt solution is 0.01 - 5 mol / L. The mixing ratio of the aqueous ammonium salt solution and the molecular sieve containing an alkali metal can be routinely adjusted by those skilled in the art on the basis of ensuring the smooth progress of the reaction.

[0086] In some specific embodiments, in the preparation steps of the Cu-SSZ-13 molecular sieve, the copper salt is, for example but not limited to, copper nitrate, etc.

[0087] In some specific embodiments, in the preparation steps of the Cu-SSZ-13 molecular sieve, the mass ratio of the copper salt to the H-type molecular sieve is 1:(1 - 100).

[0088] In some specific embodiments, in the preparation step (a) of the Cu-SSZ-13 molecular sieve, the temperature of the crystallization is 150 - 200 °C, and the time is 6 - 24 h.

[0089] In some specific embodiments, in the preparation step (a) of the Cu-SSZ-13 molecular sieve, the drying temperature is 50-100 °C and the time is 6-12 h.

[0090] In some specific embodiments, in the preparation step (a) of the Cu-SSZ-13 molecular sieve, the calcination temperature is 300-600 °C and the time is 2-6 h. Specifically, the calcination includes: placing the dried product in a muffle furnace and heating from room temperature to 300-600 °C at a heating rate of 2-10 °C·min -1 and calcining for 2-6 h. The calcination atmosphere is an air atmosphere. After the calcination is completed, it is cooled to room temperature at a cooling rate of 2-5 °C·min -1 .

[0091] In some specific embodiments, in the preparation step (b) of the Cu-SSZ-13 molecular sieve, when adding the alkali metal-containing molecular sieve to the ammonium salt aqueous solution for the ion exchange reaction, the temperature is 20-100 °C, preferably 30-80 °C, and the time is 3-24 h, preferably 6-12 h.

[0092] In some specific embodiments, in the preparation step (b) of the Cu-SSZ-13 molecular sieve, the drying temperature is 50-100 °C and the time is 6-12 h.

[0093] In some specific embodiments, in the preparation step (b) of the Cu-SSZ-13 molecular sieve, the calcination temperature is 300-600 °C and the time is 2-6 h. Specifically, the calcination includes: placing the dried product in a muffle furnace and heating from room temperature to 300-600 °C at a heating rate of 2-10 °C·min -1 and calcining for 2-6 h. The calcination atmosphere is an air atmosphere. After the calcination is completed, it is cooled to room temperature at a cooling rate of 2-5 °C·min -1 .

[0094] In some specific embodiments, in the preparation step (c) of the Cu-SSZ-13 molecular sieve, when contacting the H-type molecular sieve with a copper salt for the ion exchange reaction, the temperature is 20-90 °C, preferably 20-80 °C, and the time is 1-12 h, preferably 3-12 h.

[0095] In some specific embodiments, in the preparation step (c) of the Cu-SSZ-13 molecular sieve, the drying temperature is 50-110 °C and the time is 6-12 h.

[0096] In some specific embodiments, in the preparation step (c) of the Cu-SSZ-13 molecular sieve, the calcination temperature is 300-600 °C and the time is 2-6 h. Specifically, the calcination includes: placing the dried product in a muffle furnace and heating it from room temperature to 300-600 °C at a heating rate of 2-10 °C·min -1 to calcine for 2-6 h in an air atmosphere, and then cooling it to room temperature at a cooling rate of 2-5 °C·min -1 .

[0097] In some specific embodiments, the preparation steps of the Cu-SSZ-13 molecular sieve may further include conventional solid-liquid separation, washing and other steps, and those skilled in the art can make conventional adjustments to these steps.

[0098] In some specific embodiments, the silicon-aluminum ratio of the Cu-SSZ-13 molecular sieve is Si:Al = 5-30, the specific surface area is 100-800 m 2 / g, the pore diameter is 0.3-0.5 nm, the micropore volume is 0.001-5 cm 3 / g, and the total pore volume is 0.001-5 cm 3 / g.

[0099] In some specific embodiments, the method of mixing the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve includes one or a combination of several of mechanical mixing, pneumatic mixing, impulse mixing, etc., and more preferably mechanical mixing. Specifically, the mechanical mixing is grinding.

[0100] In some preferred embodiments of the present invention, the preparation method of the close-coupled SCR post-treatment composite catalyst may include the following steps:

[0101] (1) Prepare a metal oxide loaded with noble metal single atoms

[0102] Dissolve 0.01-10 g of the noble metal precursor in an appropriate amount of deionized water and stir vigorously. Under stirring conditions, add 1-20 g of the metal oxide powder, continuously stir until there is no precipitate in the visual mixture, dry it at 50-100 °C for 6-24 h, and then place it in a muffle furnace and heat it from room temperature to 300-600 °C at a heating rate of 2-10 °C·min -1 to calcine for 2-8 h in an air atmosphere, and then cool it to room temperature at a cooling rate of 2-5 °C·min -1 to obtain the metal oxide loaded with noble metal single atoms; wherein, the noble metal precursor includes noble metal nitrates and / or chlorides, etc.;

[0103] (2) Preparation of Cu-SSZ-13 molecular sieve

[0104] (a) Dissolve 1 - 5 g of sodium aluminate (NaAlO₂) and 1 - 5 g of potassium hydroxide (KOH, purity 98 wt.%) in 5 - 30 g of deionized water; then add 1 - 20 g of N,N,N-trimethyl-1-adamantylammonium hydroxide (TMAdaOH, purity 25 wt.%) as a structure-directing agent (SDA), stir vigorously for 0.5 - 2 h, then dropwise add 10 - 30 g of silica sol (purity 30 wt.%), continue to stir vigorously for 0.5 - 2 h, then add 0.01 - 0.03 g of SSZ-13 molecular sieve as seeds and continue stirring. After mixing evenly, a gel mixture is obtained. Transfer the gel mixture to a 100 mL Teflon-lined autoclave, crystallize at 150 - 200 °C for 6 - 24 h. After the obtained product is filtered and washed, dry it overnight at 50 - 100 °C (specifically, it can be 6 - 12 h), and then place it in a muffle furnace and heat it from room temperature to 300 - 600 °C at a heating rate of 2 - 10 °C·min -1 and calcine for 2 - 6 h in an air atmosphere. After the calcination is completed, cool it to room temperature at a cooling rate of 2 - 5 °C·min -1 to obtain a molecular sieve containing Na + and K + ;

[0105] (b) Add 5 - 10 g of the molecular sieve containing Na + and K + to an aqueous solution of ammonium salt (such as NH₄NO₃) with a volume of 500 - 1000 mL, and carry out an ion exchange reaction at 30 - 80 °C under stirring conditions. The concentration of the ammonium salt aqueous solution is 0.01 - 5 mol / L, and the reaction time is 6 - 12 h to remove Na + and K + to obtain an NH₄ + type molecular sieve. Dry the NH₄ + type molecular sieve at 50 - 100 °C for 6 - 12 h, and then place it in a muffle furnace and heat it from room temperature to 300 - 600 °C at a heating rate of 2 - 10 °C·min -1 and calcine for 2 - 6 h in an air atmosphere. After the calcination is completed, cool it to room temperature at a cooling rate of 2 - 5 °C·min -1 to obtain an H-type molecular sieve;

[0106] (c) The H-type molecular sieve is subjected to an ion exchange reaction with an aqueous solution of a copper salt (such as Cu(NO3)2·3H2O) at room temperature (generally 20 - 30 °C) under stirring conditions. The mass ratio of the copper salt to the H-type molecular sieve is 1:(1 - 100), and the reaction time is 3 - 12 h. Then, the obtained product is filtered, washed, dried at 50 - 110 °C for 6 - 12 h, and then placed in a muffle furnace and heated from room temperature to 300 - 600 °C at a heating rate of 2 - 10 °C·min -1 and calcined for 2 - 6 h in an air atmosphere. After the calcination, it is cooled to room temperature at a cooling rate of 2 - 5 °C·min -1 to obtain the Cu-SSZ-13 molecular sieve;

[0107] (3) The metal oxide loaded with noble metal single atoms prepared in step (1) and the Cu-SSZ-13 molecular sieve prepared in step (2) are mixed evenly at a mass ratio of 1:(1 - 30), then poured into an agate jar, and then dipropanol is added. It is ground with ZrO2 grinding beads at 70 rpm, and then dried overnight at 50 - 100 °C (specifically 6 - 12 h) to obtain a semi-finished composite catalyst. Subsequently, the semi-finished composite catalyst is loaded into a quartz tube and heated from room temperature to the calcination temperature at a heating rate of 2 - 10 °C·min -1 in an atmosphere of a mixture of 80Vol.% N2 and 20Vol.% O2. The calcination temperature is 300 - 600 °C, and it is maintained at a constant temperature for 1 - 6 h. Then, it is cooled to room temperature within 1 - 5 min by directly taking out the powder in the quartz tube and exposing it to room temperature, so that part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms are converted into nano-clusters and are jointly dispersed on the metal oxide to obtain the close-coupled SCR post-treatment composite catalyst.

[0108] The technical solutions of the present invention are specifically described below through examples and comparative examples. However, the present invention is not limited to these examples, and of course, various deformations can be carried out within the scope of the key points of the present invention.

[0109] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods used are all conventional methods unless otherwise specified.

[0110] Preparation Example 1

[0111] This preparation example provides a metal oxide loaded with noble metal single atoms, and its preparation method includes the following steps:

[0112] Dissolve 0.0508 g of RhCl3·3H2O in 10 mL of deionized water and stir vigorously. Under stirring conditions, add 10 g of CeZrO powder (the cerium-zirconium composite oxide is Ce 0.6 Zr 0.4 O2). Continuously stir for 1 h until there is no precipitate in the mixture visually, then place it in an oven and dry at 80 °C for 12 h. Then, place it in a muffle furnace and heat from room temperature to 550 °C at a heating rate of 5 °C·min -1 . Calcinate for 4 h, and the calcination atmosphere is an air atmosphere. After the calcination is completed, cool to room temperature at a cooling rate of 5 °C·min -1 to obtain a metal oxide powder loaded with noble metal single atoms, denoted as Rh-CZO.

[0113] Detected by inductively coupled plasma atomic emission spectrometry (ICP-AES), based on the total mass of Rh-CZO being 100%, the content of Rh in it is 3%.

[0114] Detected by a nitrogen physical adsorption and desorption instrument (BET), the specific surface area of Rh-CZO is 48.3742 m 2 / g, the pore diameter is 0.787 nm, and the total pore volume is 0.021248 cm 3 / g.

[0115] Detected by a spherical aberration corrected high-angle annular dark field scanning transmission electron microscope (AC-HAADF-STEM), as Figure 1 shown, it can be seen that Rh in Rh-CZO is dispersed as single atoms on the CZO support.

[0116] Preparation Example 2

[0117] This preparation example provides a metal oxide loaded with noble metal single atoms. Its preparation method is basically the same as that of Preparation Example 1, except that: replace 0.0508 g of RhCl3·3H2O in Preparation Example 1 with 0.0908 g of Pt(NO3)3, and the remaining steps are the same as those in Preparation Example 1 to obtain a metal oxide powder loaded with noble metal single atoms, denoted as Pt-CZO.

[0118] Detected by inductively coupled plasma atomic emission spectrometry (ICP-AES), based on the total mass of Pt-CZO being 100%, the content of Pt in it is 3%.

[0119] Detected by a nitrogen physical adsorption and desorption instrument (BET), the specific surface area of Pt-CZO is 47.4246 m 2 / g, the pore diameter is 0.7894 nm, and the total pore volume is 0.020580 cm 3 / g.

[0120] Preparation Example 3

[0121] This preparation example provides a metal oxide loaded with noble metal single atoms. Its preparation method is basically the same as that of Preparation Example 1, except that: 0.0508 g of RhCl3·3H2O in Preparation Example 1 is replaced with 0.0626 g of PdCl2, and the remaining steps are the same as those in Preparation Example 1, obtaining a metal oxide powder loaded with noble metal single atoms, denoted as Pd-CZO.

[0122] Detected by inductively coupled plasma atomic emission spectrometry (ICP-AES), based on the total mass of Pd-CZO being 100%, the content of Pd in it is 3%.

[0123] Detected by a nitrogen physical adsorption and desorption instrument (BET), the specific surface area of Pd-CZO is 49.1241 m 2 / g, the pore diameter is 0.7862 nm, and the total pore volume is 0.020276 cm 3 / g.

[0124] Preparation Example 4

[0125] This preparation example provides a metal oxide loaded with noble metal single atoms. Its preparation method is basically the same as that of Preparation Example 1, except that: 0.0508 g of RhCl3·3H2O in Preparation Example 1 is replaced with 0.3137 g of Ru(NO)(NO3)3, and the remaining steps are the same as those in Preparation Example 1, obtaining a metal oxide powder loaded with noble metal single atoms, denoted as Ru-CZO.

[0126] Detected by inductively coupled plasma atomic emission spectrometry (ICP-AES), based on the total mass of Ru-CZO being 100%, the content of Ru in it is 3%.

[0127] Detected by a nitrogen physical adsorption and desorption instrument (BET), the specific surface area of Ru-CZO is 48.7916 m 2 / g, the pore diameter is 0.7841 nm, and the total pore volume is 0.021244 cm 3 / g.

[0128] Preparation Example 5

[0129] This preparation example provides a Cu-SSZ-13 molecular sieve, and its preparation method includes the following steps:

[0130] (a) Dissolve 1.64 g of sodium aluminate (NaAlO₂) and 1.34 g of potassium hydroxide (KOH, purity 98 wt%) in 14 g of deionized water; then add 10 g of N,N,N-trimethyl-1-adamantylammonium hydroxide (TMAdaOH, purity 25 wt.%) as a structure-directing agent (SDA). After vigorously stirring for 1 h, add 30 g of silica sol (purity 30 wt.%) dropwise, continue to stir vigorously for 1 h, then add 0.02 g of SSZ-13 zeolite as a seed crystal and continue to stir for 1 h to mix evenly, obtaining a gel mixture. Transfer the gel mixture to a 100 mL Teflon-lined autoclave, crystallize at 160 °C for 12 h. After filtering the obtained product, wash it three times with deionized water, then dry it overnight at 100 °C (specifically, it can be 12 h), and then place it in a muffle furnace and heat it from room temperature to 550 °C at a heating rate of 5 °C·min -1 and then calcine for 4 h at a heating rate of 5 °C·min -1 from room temperature to 550 °C, with the calcination atmosphere being an air atmosphere. After the calcination is completed, cool it to room temperature at a cooling rate of 5 °C·min + to obtain a zeolite containing Na + and K

[0131] (b) Add 10 g of the zeolite containing Na + and K + to 1000 mL of a 2 mol·L -1 NH₄NO₃ aqueous solution and carry out an ion exchange reaction at 80 °C under stirring conditions for 8 h to remove Na + and K + , obtaining an NH₄ + type SSZ-13 zeolite. Dry the NH₄ + type SSZ-13 zeolite at 80 °C for 12 h, then place it in a muffle furnace and heat it from room temperature to 550 °C at a heating rate of 5 °C·min -1 and calcine for 4 h, with the calcination atmosphere being an air atmosphere. After the calcination is completed, cool it to room temperature at a cooling rate of 5 °C·min -1 to obtain an H-type SSZ-13 zeolite;

[0132] (c) Mix 5 g of the H-type SSZ-13 zeolite with 800 mL of a 0.002 mol·L -1 Cu(NO₃)₂ aqueous solution and carry out an ion exchange reaction at room temperature (generally 20 - 30 °C) under stirring conditions for 4 h. Then, after filtering and washing the obtained product, dry it at 110 °C for 12 h, and then place it in a muffle furnace and heat it from room temperature to 550 °C at a heating rate of 5 °C·min -1 and calcine for 4 h, with the calcination atmosphere being an air atmosphere. After the calcination is completed, cool it to room temperature at a cooling rate of 5 °C·min -1The cooling rate is reduced to room temperature to obtain the Cu-SSZ-13 molecular sieve.

[0133] Detected by inductively coupled plasma atomic emission spectrometry (ICP-AES), the silicon-aluminum ratio of the Cu-SSZ-13 molecular sieve is 10.

[0134] Detected by a nitrogen physical adsorption and desorption instrument (BET), the specific surface area of the Cu-SSZ-13 molecular sieve is 549.9649 m 2 / g, the pore diameter is 0.34 nm, the micropore volume is 0.270319 cm 3 / g, and the total pore volume is 0.277940 cm 3 / g.

[0135] Example 1

[0136] This example provides a close-coupled SCR aftertreatment composite catalyst, and its preparation method includes the following steps:

[0137] Mix the Rh-CZO prepared in Preparation Example 1 and the Cu-SSZ-13 molecular sieve prepared in Preparation Example 5 evenly at a mass ratio of 1:1, then pour them into an agate jar, then add 6 g of dipropanol, and add 40 g of ZrO2 grinding beads, grind for 3 h under the condition of 70 rpm, and then dry overnight at 60 °C (specifically, it can be 12 h) to obtain a composite catalyst semi-finished product; subsequently, load the composite catalyst semi-finished product into a quartz tube, and in an atmosphere of a mixed gas of 80 Vol.% N2 and 20 Vol.% O2, heat from room temperature to the calcination temperature at a heating rate of 5 °C·min -1 The heating rate is raised to the calcination temperature, the calcination temperature is 550 °C, and it is kept at a constant temperature for 4 h. Then, it is cooled to room temperature within 2 min by directly taking out the powder in the quartz tube and exposing it to room temperature, so that part of the Rh single atoms in Rh-CZO are converted into nano-clusters and are jointly dispersed on CZO to obtain the close-coupled SCR aftertreatment composite catalyst, denoted as the Rh-CZO / Cu-SSZ-13 composite catalyst.

[0138] Based on the total mass of the Rh-CZO / Cu-SSZ-13 composite catalyst being 100%, the content of Rh in it is 1.5%.

[0139] Figure 2 is the TEM image of the Rh-CZO / Cu-SSZ-13 composite catalyst in this example. Among them, the black cube with a particle size of about 1 μm is the Cu-SSZ-13 molecular sieve, and the small particles with an outer surface particle size of about 20 nm are metal oxides loaded with noble metal single atoms and nano-clusters. It can be observed that the metal oxides loaded with noble metal single atoms and nano-clusters are uniformly attached to the surface of the Cu-SSZ-13 molecular sieve.

[0140] Figure 3 It is the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) image of the Rh-CZO / Cu-SSZ-13 composite catalyst of this example. It can be observed that Rh exists in the form of single atoms and nanoclusters.

[0141] Figure 4 It is the X-ray absorption fine structure spectrum (EXAFS) image of the Rh-CZO / Cu-SSZ-13 composite catalyst of this example, which can confirm that Rh exists in the form of single atoms and nanoclusters. Figure 5 It is the XPS images of Ce element and Rh element of Rh-CZO in Preparation Example 1 and the Rh-CZO / Cu-SSZ-13 composite catalyst of this example. Among them, the change in the binding energy of XPS indicates that the coordination environment of atoms changes. Shifting towards the low binding energy direction indicates that the atom is more likely to participate in the reaction. From Figure 5 it can be seen that the binding energies of both Ce and Rh elements shift towards the low value, which indicates that by calcining the mixture of Rh-CZO and Cu-SSZ-13 molecular sieve in a specific atmosphere and controlling the cooling process, in the composite catalyst of this example, the coordination environment between Rh and the CeZrO support is changed compared with that in Rh-CZO, and a Rh x -Ce y -Zr 1-y -O z -interface is formed, which can greatly improve the low-temperature activity of the composite catalyst.

[0142] Example 2

[0143] This example provides a close-coupled SCR post-treatment composite catalyst, and its preparation method is basically the same as that of Example 1, except that: Rh-CZO in Example 1 is replaced by Pt-CZO in Preparation Example 2, and the remaining steps are the same as those in Example 1 to obtain a Pt-CZO / Cu-SSZ-13 composite catalyst. Calculated based on the total mass of the Pt-CZO / Cu-SSZ-13 composite catalyst being 100%, the content of Pt therein is 1.5%.

[0144] Example 3

[0145] This example provides a close-coupled SCR post-treatment composite catalyst, and its preparation method is basically the same as that of Example 1, except that: Rh-CZO in Example 1 is replaced with Pd-CZO in Preparation Example 3, and the remaining steps are the same as those in Example 1, to obtain a Pd-CZO / Cu-SSZ-13 composite catalyst. Based on the total mass of this Pd-CZO / Cu-SSZ-13 composite catalyst being 100%, the content of Pd therein is 1.5%.

[0146] Example 4

[0147] This example provides a close-coupled SCR post-treatment composite catalyst, and its preparation method is basically the same as that of Example 1, except that: Rh-CZO in Example 1 is replaced with Ru-CZO in Preparation Example 4, and the remaining steps are the same as those in Example 1, to obtain a Ru-CZO / Cu-SSZ-13 composite catalyst. Based on the total mass of this Ru-CZO / Cu-SSZ-13 composite catalyst being 100%, the content of Ru therein is 1.5%.

[0148] Comparative Example 1

[0149] This comparative example provides a composite catalyst, and its preparation method is basically the same as that of Example 1, except that: Rh-CZO in Example 1 is replaced with CeZrO powder (the cerium-zirconium composite oxide is Ce 0.6 Zr 0.4 O2), and the remaining steps are the same as those in Example 1, to obtain a CZO / Cu-SSZ-13 composite catalyst.

[0150] Comparative Example 2

[0151] This comparative example provides a composite catalyst, and its preparation method is basically the same as that of Example 1, except that: the mixed gas of 80Vol.% N2 and 20Vol.% O2 in Example 1 is used as the calcination atmosphere and changed to pure N2 as the calcination atmosphere, and the remaining steps are the same as those in Example 1, and the obtained composite catalyst is denoted as Rh-CZO / Cu-SSZ-13-N2.

[0152] Comparative Example 3

[0153] This comparative example provides a composite catalyst, and its preparation method is basically the same as that of Example 1, except that: the mixed gas of 80Vol.% N2 and 20Vol.% O2 in Example 1 is used as the calcination atmosphere and changed to a mixed gas of 5Vol.% H2 and 95Vol.% N2 as the calcination atmosphere, and the remaining steps are the same as those in Example 1, and the obtained composite catalyst is denoted as Rh-CZO / Cu-SSZ-13-H2.

[0154] Comparative Example 4

[0155] This comparative example provides a composite catalyst, and its preparation method is basically the same as that of Example 1, except that: the method of directly taking out the powder in the quartz tube and exposing it to room temperature in Example 1 to reduce the temperature to room temperature within 2 minutes is changed to reducing the temperature at a rate of 2 °C·min -1 to room temperature, and the remaining steps are the same as those in Example 1. The obtained composite catalyst is denoted as Rh-CZO / Cu-SSZ-13-S.

[0156] Test Example

[0157] XRD analysis, N2 adsorption-desorption test, catalytic activity and nitrogen selectivity test were carried out on the products of the above preparation examples, examples and comparative examples.

[0158] Among them, the test methods for the conversion rate of nitrogen oxides (i.e., catalytic activity) and nitrogen selectivity include: carried out in a quartz fixed-bed reactor, and a Fourier transform infrared gas analyzer (Thermo Fisher IGS) was used to continuously analyze the concentrations of NO, NO2, N2O and NH3 in the product gas. The experimental conditions include: space velocity 30000h -1 , temperature 50 °C - 300 °C, and the total flow rate of the reaction gas is 500 mL·min -1 . The composition of the reaction gas includes: 500 ppm NO, 500 ppm NH3 and 5% O2, with N2 as the balance gas. The catalyst filling amount is: 1 mL (40 - 60 mesh).

[0159] NO x The conversion rate and N2 selectivity are calculated by the following formulas:

[0160]

[0161]

[0162] Figure 6 are the XRD patterns of the products of Preparation Example 1, Preparation Example 5, Example 1 and Comparative Example 1. It can be seen from Figure 6 that Preparation Example 1 shows the characteristic peaks standardly attributed to the CeZrO structure (θ = 28.87°, 33.471°, 48.049°, 57.012°), Preparation Example 5 shows the characteristic peaks standardly attributed to the CHA structure (θ = 9.635°, 13.082°, 14.195°, 16.282°, 18.051°, 19.354°, 20.939°, 22.363°, 22.763°, 23.429°, 25.335°, 26.351°, 31.135°, 31.589°), and Example 1 and Comparative Example 1 show both characteristic peaks of the CeZrO structure and the CHA structure.

[0163] Figure 7 is the N2 adsorption - desorption curve of the products of Preparation Example 1, Preparation Example 5, Example 1 and Comparative Example 1. As can be seen from Figure 7 it, all samples showed a typical Type - I isotherm of microporous materials, indicating that all materials are microporous materials.

[0164] The NO x conversion rate and N2 selectivity data of the products of Preparation Examples 1, 2, 5, Examples 1 - 4 and Comparative Examples 1 - 4 are shown in Table 1 and Table 2.

[0165] Table 1

[0166]

[0167] Table 2

[0168]

[0169] Figure 8 is the catalytic activity diagram of CeZrO loaded with different noble metals prepared in Preparation Examples 1 - 4 as a catalyst. As can be seen from Figure 8 it, the activity temperature window (i.e., the interval where the NOx conversion rate is close to 100%) of the simple noble - metal - loaded CeZrO catalyst is very narrow, only in the range of 175°C - 250°C, while the SCR catalyst to meet the national VI standard in the future requires the NO x conversion rate to be close to 100% in the low - temperature range (<150°C).

[0170] Figure 9 is the catalytic activity diagram of the products of Preparation Example 5, Examples 1 - 2 and Comparative Examples 1 - 4. As can be seen from Figure 9 and Table 1, the activity interval of the composite catalyst provided by the examples of the present invention is 125°C - 300°C. In particular, the Rh - CZO / Cu - SSZ - 13 composite catalyst prepared in Example 1 has a NO x conversion rate that can reach more than 99% at 125°C. Therefore, the close - coupled SCR after - treatment composite catalyst of the present invention has excellent low - temperature catalytic performance.

[0171] Figure 10 is the nitrogen selectivity diagram of the products of Preparation Example 5, Examples 1 - 2 and Comparative Examples 1 - 4. Nitrogen selectivity is the ability of the catalyst to selectively convert NO x into N2 rather than other NO x s. As can be seen from Figure 10 and Table 2, at 150°C, the N2 selectivity of the composite catalyst provided by the examples of the present invention is more than 98%. Therefore, the close - coupled SCR after - treatment composite catalyst of the present invention has excellent nitrogen selectivity.

[0172] In summary, the close-coupled SCR after-treatment composite catalyst provided by the present invention has excellent catalytic activity and nitrogen selectivity in a low-temperature environment. This composite catalyst can be applied to low-temperature selective catalytic reduction of NO x , especially for automotive exhaust treatment.

Claims

1. A tightly-coupled SCR aftertreatment composite catalyst, wherein the composite catalyst comprises a metal oxide loaded with noble metal single atoms and nanoclusters and Cu-SSZ-13 molecular sieve with a mass ratio of 1:(0.1 - 30); wherein, The metal oxide loaded with noble metal single atoms and nanoclusters uses the metal oxide as a carrier and the noble metal as an active component, and the noble metal is dispersed on the metal oxide in the form of single atoms and nanoclusters; The composite catalyst is prepared at least through the following steps: mixing the metal oxide loaded with noble metal single atoms and Cu-SSZ-13 zeolite and then calcining, so that part of the noble metal single atoms in the metal oxide loaded with noble metal single atoms are converted into nanoclusters and are dispersed on the metal oxide together, to obtain the composite catalyst; wherein, the calcination includes: using a mixed gas of N2 and O2 as the calcination atmosphere, in the calcination atmosphere, after heating the mixture of the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 zeolite to the calcination temperature, maintaining a constant temperature for a period of time, and then cooling to room temperature within 1-10 min.

2. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, During the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 20-80 Vol.% N2 and 80-20 Vol.% O2.

3. The tightly-coupled SCR aftertreatment composite catalyst according to claim 2, wherein, During the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 80 Vol.% N2 and 20 Vol.% O2.

4. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, During the calcination process, the method of cooling to room temperature within 1-10 min includes using a cooling medium to cool outside the calcination device or directly taking out the powder in the calcination device and exposing it to room temperature.

5. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, During the calcination process, cool to room temperature within 1-5 min.

6. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, During the calcination process, the calcination temperature is 300-600 °C, and the time for maintaining a constant temperature is 1-6 h.

7. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, The mass ratio of the metal oxide loaded with noble metal single atoms and nanoclusters to the Cu-SSZ-13 zeolite is 1:(0.1-10).

8. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, The particle size of the noble metal nanoclusters is 1-3 nm.

9. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, Based on the total mass of the metal oxide loaded with noble metal single atoms and nanoclusters being 100%, the content of the noble metal therein is 0.01-10%; the content of the noble metal nanoclusters is 0.01-5%.

10. The tightly-coupled SCR aftertreatment composite catalyst according to claim 9, wherein, Based on the total mass of the metal oxide loaded with noble metal single atoms and nanoclusters being 100%, the content of the noble metal therein is 0.5-5%; the content of the noble metal nanoclusters is 0.02-1%.

11. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, The noble metal includes one or a combination of several of Pt, Pd, Rh, Ru, Ir, Au, and Ag.

12. The tightly-coupled SCR aftertreatment composite catalyst according to claim 11, wherein, The noble metal is Rh.

13. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, The metal oxide includes a single metal oxide formed by one element among Ce, Fe, Mn, V, W, Ti, Sn, and Zr and / or a composite oxide formed by several elements.

14. The tightly-coupled SCR aftertreatment composite catalyst according to claim 13, wherein, The metal oxide includes a cerium-zirconium composite oxide.

15. The tightly-coupled SCR aftertreatment composite catalyst according to claim 1, wherein, The metal oxide loaded with noble metal single atoms and nanoclusters is M x -Ce y -Zr 1-y -O z , where M is a noble metal, x is the mass content of the noble metal, y is the mass fraction of Ce in the CeZrO support with the total mass of Ce and Zr being 1, z is the number of oxygen atoms, x = 0.01 - 10%, y = 0.01 - 0.99, and z = 1 - 5.

16. The tightly-coupled SCR aftertreatment composite catalyst according to claim 15, wherein, The metal oxide loaded with noble metal single atoms and nanoclusters is M x -Ce y -Zr 1-y -O z , where M is a noble metal, x is the mass content of the noble metal, y is the mass fraction of Ce in the CeZrO support based on the total mass of Ce and Zr being 1, z is the number of oxygen atoms, x = 0.5 - 5%, y = 0.5 - 0.8, and z = 1 - 2.

17. The preparation method of the close-coupled SCR after-treatment composite catalyst according to any one of claims 1-16, comprising the following steps: Mix the metal oxide loaded with noble metal single atoms and Cu-SSZ-13 molecular sieve, and then calcine it to partially convert the noble metal single atoms in the metal oxide loaded with noble metal single atoms into nanoclusters and co-disperse them on the metal oxide, thereby obtaining the tight-coupled SCR post-treatment composite catalyst; wherein, the calcination includes: using a mixed gas of N2 and O2 as the calcination atmosphere, in the calcination atmosphere, after heating the mixture of the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve to the calcination temperature, keep it at a constant temperature for a period of time, and then cool it to room temperature within 1 - 10 min.

18. The preparation method according to claim 17, wherein During the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 20 - 80 Vol.% N2 and 80 - 20 Vol.% O2.

19. The preparation method according to claim 18, wherein During the calcination process, based on the total volume of the mixed gas of N2 and O2 being 100%, it includes 80 Vol.% N2 and 20 Vol.% O2.

20. The preparation method according to claim 17, wherein During the calcination process, cool it to room temperature within 1 - 5 min.

21. The preparation method according to claim 17, wherein During the calcination process, the method of cooling it to room temperature within 1 - 10 min includes using a cooling medium to cool outside the calcination device or directly taking out the powder in the calcination device and exposing it to room temperature.

22. The preparation method according to claim 17, wherein During the calcination process, the calcination temperature is 300 - 600 °C, and the time for maintaining the constant temperature is 1 - 6 h.

23. The preparation method according to claim 17, wherein The metal oxide loaded with noble metal single atoms is prepared at least through the following steps: uniformly mix the precursor solution of the noble metal with the metal oxide, and then obtain the metal oxide loaded with noble metal single atoms after at least drying and calcination.

24. The preparation method according to claim 23, wherein In the preparation step of the metal oxide loaded with noble metal single atoms, the precursor of the noble metal includes one or a combination of several of nitrate, chloride, acetate, and sulfate of the noble metal.

25. The preparation method according to claim 17, wherein The Cu-SSZ-13 molecular sieve is prepared through the following steps: (a) uniformly mix the aluminum source, alkali metal compound, structure-directing agent, silicon source, and SSZ-13 molecular sieve seeds in a solvent, then crystallize, and then obtain the alkali metal-containing molecular sieve after at least drying and calcination of the crystallized product; (b) add the alkali metal-containing molecular sieve to an ammonium salt aqueous solution for an ion exchange reaction, and obtain the H-type molecular sieve after at least drying and calcination of the product; (c) contact the H-type molecular sieve with a copper salt for an ion exchange reaction, and obtain the Cu-SSZ-13 molecular sieve after at least drying and calcination of the product.

26. The preparation method according to claim 25, wherein In the preparation step of the Cu-SSZ-13 molecular sieve, the aluminum source includes sodium aluminate, the alkali metal compound includes potassium hydroxide, the structure-directing agent includes N,N,N-trimethyl-1-adamantylammonium hydroxide, and the silicon source includes silica sol; the mixing mass ratio of the aluminum source, the alkali metal compound, the structure-directing agent, the silicon source, and the SSZ-13 molecular sieve seeds is (1 - 5):(1 - 5):(1 - 20):(10 - 30):(0.01 - 0.03).

27. The preparation method according to claim 26, wherein In the preparation step of the Cu-SSZ-13 molecular sieve, the concentration of the ammonium salt aqueous solution is 0.01-5 mol / L.

28. The preparation method according to claim 26, wherein In the preparation step of the Cu-SSZ-13 molecular sieve, the mass ratio of the copper salt to the H-type molecular sieve is 1:(1-100).

29. The preparation method according to claim 26, wherein In the preparation step of the Cu-SSZ-13 molecular sieve, the crystallization temperature is 150-200 °C and the time is 6-24 h.

30. The preparation method according to claim 26, wherein In the preparation step of the Cu-SSZ-13 molecular sieve, the temperature for the ion exchange reaction by adding the alkali metal-containing molecular sieve into the ammonium salt aqueous solution is 20-100 °C and the time is 3-24 h.

31. The preparation method according to claim 26, wherein In the preparation step of the Cu-SSZ-13 molecular sieve, the temperature for the ion exchange reaction by contacting the H-type molecular sieve with the copper salt is 20-90 °C and the time is 1-12 h.

32. The preparation method according to claim 17, wherein The method for mixing the metal oxide loaded with noble metal single atoms and the Cu-SSZ-13 molecular sieve includes one or a combination of several of mechanical mixing, pneumatic mixing and impulse mixing.

33. The application of the close-coupled SCR after-treatment composite catalyst according to any one of claims 1-16 in the low-temperature selective catalytic reduction of NO x as a catalyst.

34. The application according to claim 33, wherein The low temperature is above 100 °C.

35. The application according to claim 33, wherein The selective catalytic reduction of NO x includes the treatment of automotive exhaust gases.

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