A three-way catalyst capable of suppressing dynamic air-fuel ratio, its preparation method and application in exhaust gas purification

Abstract

The present invention discloses a three-way catalyst capable of suppressing dynamic air-fuel ratio, its preparation method and application in motor vehicle exhaust treatment. The three-way catalyst consists of a main catalyst Rh / CeO2-ZrO2-Al2O3 and a promoter Mn x Fe 3‑x O4 composite oxide, wherein the mass percentage of Mn x Fe 3‑x O4 is 1% to 30%, and the mass percentage of the Rh / CeO2-ZrO2-Al2O3 catalyst is 70% to 99%. The three-way catalyst is obtained by mechanically mixing the above promoter and the main catalyst; the Rh / CeO2-ZrO2-Al2O3 uses a CeO2-ZrO2-Al2O3 composite oxide with high thermal stability as a carrier, and is prepared by a co-precipitation method, and the mass ratio of Ce, Zr, and Al is controlled to be 4:3:3 or 1:2:7 or 2:2:6; the Mn x Fe 3‑ x O4 is prepared by a co-precipitation method, and the molar ratio of Mn and Fe is controlled to be 1:1 or 1:5 or 5:1. The three-way catalyst obtained by the present invention is used for the treatment of CO, HC and NO x in automobile exhaust, can suppress the fluctuation of the air-fuel ratio, broaden the working window, significantly improve the conversion efficiency of NO x and C3H8 under dynamic conditions, and at the same time improve the conversion ability of NO x during lean combustion.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of solid catalysts for heterogeneous catalytic reaction systems, and specifically relates to the preparation of catalysts for purifying motor vehicle exhaust gas. Background Art

[0002] Motor vehicles include gasoline vehicles, diesel vehicles, gas vehicles, motorcycles, etc. The combustion modes of motor vehicles are divided into two types: stoichiometric air-fuel ratio (14.7:1) and lean combustion. Among them, the combustion mode of the stoichiometric air-fuel ratio is that air (oxygen) and fuel are configured and burned in a stoichiometric ratio, while lean combustion is that air (oxygen) and fuel are configured and burned in a ratio greater than the stoichiometric ratio. Gasoline vehicles mainly adopt the combustion mode of the stoichiometric air-fuel ratio. Currently, automotive companies such as Honda and Mazda have developed lean-burn gasoline engines from different technical routes in order to improve the thermal efficiency of the engine.

[0003] The three-way catalyst is a monolithic catalyst, which mainly uses a metal honeycomb substrate or a ceramic honeycomb substrate to carry the supported catalyst powder. The working principle of the three-way catalyst is that at a certain temperature (>250 °C), the CO, HC, and NO in the exhaust gas of gasoline vehicles x under the action of the catalyst, three types of harmful substances undergo redox chemical reactions and become CO2, H2O, and N2 that are harmless to humans, so it is named the three-way catalyst. The main reactions occurring in the three-way catalytic system are: CO and HC oxidation reactions, NO reduction reactions, water-gas shift reactions, and steam reforming reactions, etc. The occurrence of these reactions requires a certain temperature range and an oxidation or reduction atmosphere. When the exhaust gas atmosphere of gasoline vehicles is biased towards an oxidation atmosphere, it is beneficial to the oxidation of CO and HC, but x unfavorable for the reduction of NO; when the exhaust gas atmosphere of gasoline vehicles is biased towards a reduction atmosphere, it is beneficial to the reduction of NO x but unfavorable for the oxidation of CO and HC. In order to maximize the conversion of the above three pollutants, it is necessary to control the atmosphere of the vehicle exhaust, that is, to control the ratio of air and fuel supply to the stoichiometric air-fuel ratio. At this time, the stoichiometric ratio of the oxidizing and reducing substances in the exhaust gas is 1, and the efficient purification of the three harmful substances can be achieved.

[0004] However, the actual working conditions of automobile engines are complex, and the air-fuel ratio fluctuates around the theoretical air-fuel ratio. The combustion mode of the engine is sometimes lean and sometimes rich, and the proportion of exhaust gas components is also fluctuating. Especially when driving on urban roads, frequent starts, stops and turns are required, and the engine working conditions are in a dynamic state of change. Due to the narrow working window of the existing three-way catalyst, the conversion of pollutants in the exhaust gas is not ideal; at the same time, in order for the three-way catalyst to work stably, that is, the air-fuel ratio is the theoretical air-fuel ratio, the posture and habits of the driver are also required to be high. Therefore, in order for the three-way catalyst to play a good role in different working conditions and when switching between different working conditions, it is necessary to develop a high-performance three-way catalyst that can autonomously smooth out air-fuel ratio fluctuations. Furthermore, under the lean combustion conditions of gasoline vehicle engines, the oxidized exhaust atmosphere is not conducive to NO x In addition, in order to achieve fuel economy and improve engine thermal efficiency, automobile companies have developed lean-burn engines. Such engines have a large air-fuel ratio and a high oxygen concentration in the exhaust gas. The exhaust gas is always oxygen-rich, which is very unfavorable to NO x of restoration.

[0005] In summary, designing and developing a three-way catalyst with good catalytic performance, wide working window and high economy is of great significance in the catalytic purification technology of motor vehicle exhaust. Summary of the invention

[0006] The purpose of the present invention is to provide a high-performance three-way catalyst that can autonomously stabilize the dynamic air-fuel ratio and its preparation method and application in motor vehicle exhaust treatment to obtain a series of Rh / CeO2-ZrO2-Al2O3+ Mn x Fe 3-x O4 (abbreviated as Rh / CZA+MF) three-way catalyst, and used for CO, HC and NO in automobile exhaust. x The treatment can smooth the fluctuation of air-fuel ratio, broaden the working window and significantly improve NO x and C3H8 conversion efficiency under dynamic conditions, while improving NO x Conversion capacity during lean combustion.

[0007] The three-way catalyst provided by the present invention comprises a main catalyst Rh / CeO2-ZrO2-Al2O3 (abbreviated as Rh / CZA) and a co-catalyst Mn x Fe 3-x O4 composite oxide (abbreviated as MF), in which Mn x Fe 3-x The value range of x in O4 is 0.5~2.5, the mass percentage of MF is 1%~30%, and the mass percentage of Rh / CZA catalyst is 70%~99%.

[0008] Mn-containing spinel structure x Fe 3-x O4 composite oxide (where the value range of x is 0.5 - 2.5) has excellent thermal stability and excellent oxygen storage capacity (about 10 times higher than that of CeO2-ZrO2 composite oxide), as well as NO adsorption and activation ability. At present, there are not many studies on such oxides. In the present invention, such oxides are applied to the field of catalytic purification of gasoline vehicle exhaust, and relevant research on applying such non-noble metal oxides in three-way catalysts is carried out.

[0009] The preparation method of the above-mentioned three-way catalyst provided by the present invention, the three-way catalyst is obtained by mechanically mixing a promoter MF with a Rh / CZA catalyst; the Rh / CZA catalyst uses a CeO2-ZrO2-Al2O3 composite oxide with high thermal stability (abbreviated as CZA) as a carrier, and is prepared by a co-precipitation method, and controlling the mass ratio of Ce, Zr, and Al to be 4:3:3 or 1:2:7 or 2:2:6; the MF is prepared by a co-precipitation method, and controlling the molar ratio range of Mn and Fe to be 0.2 - 5, preferably 1:1 or 1:5 or 5:1.

[0010] In the technical solution of the preparation method of the three-way catalyst described in the present invention, further, the preparation method of the Rh / CZA catalyst is as follows:

[0011] (1) Weigh the corresponding precursor Ce(NO3)3·6H2O solid, Zr(NO3)4·6H2O solid, and Al(NO3)3·9H2O solid according to the mass ratio of Ce, Zr, and Al in CZA being 4:3:3 or 1:2:7 or 2:2:6 in turn;

[0012] (2) Dissolve each precursor in deionized water to form a precursor solution, mix the precursor solutions and mix them evenly by stirring and ultrasonic waves in turn to prepare a CeZrAl mixed solution with a total cation concentration of 0.01 - 0.10 mol / L;

[0013] (3) Under the conditions of room temperature and stirring, slowly add the obtained CeZrAl mixed solution dropwise to a reactor together with a precipitant composed of ammonia water and ammonium carbonate solution for co-precipitation reaction, and control the pH range during the titration process to be 8.5 - 9.0;

[0014] (4) After the precipitation is complete, continue to stir for 0.5 - 2 h and stand for 24 - 48 h;

[0015] (5) Filter, wash the precipitate with deionized water until the pH of the filtrate is neutral, and dry the precipitate obtained by filtration;

[0016] (6) Bake the dried solid in a muffle furnace at 450 - 600 °C for 3 - 5 h to obtain the CZA support powder.

[0017] (7) Use the equal-volume saturation impregnation method to load the noble metal Rh onto the CZA support. The loading amount of Rh is 0 - 1 wt.% and not 0 to obtain the Rh / CZA material; after drying the Rh / CZA material, bake it in a muffle furnace at 450 - 600 °C for 3 - 5 h to obtain the Rh / CZA catalyst.

[0018] In the preparation method of the above Rh / CZA catalyst, in step (2), stir rapidly for 0.5 h and perform ultrasonic treatment on the solution for 10 min; in steps (5) and (7), drying is carried out at 98 °C for 10 - 24 h.

[0019] In the preparation method of the above Rh / CZA catalyst, the pH of the precipitant > 9.

[0020] In the technical solution of the preparation method of the three-way catalyst described in the present invention, the promoter Mn x Fe 3-x The preparation method of the O4 composite oxide is as follows:

[0021] (1) Weigh the precursor Fe(NO3)3·9H2O solid and Mn(NO3)2 solution successively according to the molar ratio of Mn x Fe 3-x in the O4 composite oxide.

[0022] (2) Dissolve the precursor in deionized water to prepare a mixed solution of Mn and Fe with a total cation concentration of 0.01 - 0.10 mol / L, and then add citric acid or polyvinyl alcohol or ethylene glycol accounting for 5 - 30% of the mass of the Mn x Fe 3-x O4 composite oxide to be prepared, and mix well to obtain a mixed solution.

[0023] (3) At room temperature and under stirring conditions, slowly add the above mixed solution dropwise to the reactor with a precipitant (pH > 9) formed by mixing ammonia water and ammonium carbonate solution, and control the pH range during the titration to be 8.5 - 9.0.

[0024] (4) After complete precipitation, continue to stir for 0.5 h and let it stand for 48 h.

[0025] (5) Filter and wash the precipitate with deionized water until the pH of the filtrate is neutral.

[0026] (6) Add to the precipitate obtained by filtration the amount of Mn x Fe 3-x5 to 30% by mass of polyethylene glycol, ethylene glycol or polyvinyl alcohol of the O4 composite oxide is thoroughly mixed and then dried. Then, it is calcined in a tube furnace at 600 to 900 °C for 3 to 5 h to obtain the MF promoter powder.

[0027] In the above method for preparing the MF promoter, in step (2), it is rapidly stirred for 0.5 h by stirring and ultrasonic treatment, and the solution is ultrasonically treated for 10 min.

[0028] In the above method for preparing the MF promoter, the mass concentration of the Mn(NO3)2 solution in step (1) is 50%.

[0029] In the above method for preparing the MF promoter, the drying in step (6) is carried out at 98 °C for 10 to 24 h.

[0030] The present invention also provides a method for preparing the above three-way catalyst into a monolithic catalyst, and the method includes the following steps:

[0031] (1) A cordierite ceramic substrate with 400 cpis is used as the coating substrate and soaked in water for about 6 to 12 h;

[0032] (2) The above three-way catalyst of the present invention and a binder are formulated into a uniformly mixed coating slurry by ball milling, and the pH value of the slurry is controlled in the acidic range with an acetic acid solution having a volume fraction of 5 to 40%. The solid mass content in the slurry is 20 to 50%; the binder is selected from one or more of pseudoboehmite, aluminum sol, silica sol and zirconia sol;

[0033] (3) After the slurry is formulated, one end of the substrate is dipped into the slurry, and then the slurry is blown by an air compressor to make it evenly distributed in the pores of the substrate; the same operation is carried out on the other end of the substrate, and it is dried after coating; during the coating process, the loading amount of the coating on the dried substrate is controlled to be 120 to 160 g / L;

[0034] (4) The coated and dried substrate is calcined in a muffle furnace at 600 to 900 °C for 3 to 5 h to obtain the monolithic catalyst.

[0035] In the above method for preparing the monolithic three-way catalyst, further, the amount of the binder is 1% to 5% of the mass of the coating slurry.

[0036] In the above method for preparing the monolithic three-way catalyst, further, in step (4), the sample is dried at 98 °C for 10 h.

[0037] The present invention also provides the three-way catalyst monolithic catalyst prepared by the above method.

[0038] The present invention also provides the application of the above-mentioned three-way catalyst in the treatment of motor vehicle exhaust. The specific application is for the treatment of CO, HC and NO in automobile exhaust x , achieving the purpose of suppressing the fluctuation of air-fuel ratio, broadening the working window, and significantly improving the conversion efficiency of NO x and C3H8 under dynamic conditions, and at the same time improving the conversion ability of NO x during lean combustion.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The three-way catalyst prepared by the present invention contains the main catalyst Rh / CZA and the promoter MF. Its characteristic lies in combining the advantages of the mainstream CZA material-supported noble metal catalyst and the MF oxygen storage material, which not only improves the catalyst activity, but also broadens the adaptation range of the catalyst to the air-fuel ratio fluctuation, and also improves the conversion activity of NO x during lean combustion of the engine. The activity results show that the three-way catalyst containing the promoter Mn x Fe 3-x O4, compared with the three-way catalyst containing only the main catalyst Rh / CeO2-ZrO2-Al2O3 and the commercially available three-way catalyst at the same level, firstly, the former has an obvious property of suppressing the air-fuel ratio fluctuation, secondly, the former significantly improves the conversion efficiency of NO x during lean combustion, and thirdly, due to the addition of the promoter Mn x Fe 3-x O4, the dosage of the main catalyst Rh / CeO2-ZrO2-Al2O3 is reduced, the content of noble metal is decreased, and the cost is also reduced accordingly. Therefore, the three-way catalyst prepared by the present invention has good catalytic performance, a wide air-fuel ratio window, and a relatively low noble metal content, and has better performance.

[0041] 2. The present invention mixes MF species into the main catalyst, which has an effect on improving the thermal stability and prolonging the service life. Moreover, the coating process adopted by the present invention can uniformly coat the catalyst on the substrate, and at the same time reduce the phenomenon of high-temperature catalyst shedding.

[0042] 3. Compared with the catalysts on the market, the three-way catalyst prepared by the present invention not only shows better catalytic performance, but also has a simple production process, reduces the use of noble metals, and lowers the cost, and is suitable for industrial requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 are the three views of the cordierite ceramic substrate used in the examples.

[0044] Figure 2 are the steady-state activity results.

[0045] Figure 3 It is the XRD pattern of the promoter MF.

[0046] Figure 4 It is the HRTEM image of the Rh / CZA+MF catalyst.

[0047] Figure 5 It is the dynamic activity result.

[0048] Figure 6 It is the single reaction activity results of the Rh / CZA(a) and Rh / CZA+MF(b) catalysts and the comparison of NO x conversion rate (c).

[0049] Figure 7 It is the relationship between the CO, NO x and HC conversion curves of the Rh / CZA(a) and Rh / CZA+MF(b) catalysts at 400 °C and λ. Specific Embodiments

[0050] The present invention will be further described below in conjunction with specific embodiments. The specific embodiments are further explanations of the principle of the present invention and do not limit the present invention in any way. Embodiments identical or similar to the present invention do not exceed the scope of protection of the present invention.

[0051] Example 1

[0052] Preparation of Rh / CZA catalyst:

[0053] (1) Weigh the corresponding precursors Ce(NO3)3·6H2O solid, Zr(NO3)4·6H2O solid and Al(NO3)3·9H2O solid in accordance with the mass ratio of Ce, Zr, and Al in CZA being 1:2:7 in sequence;

[0054] (2) Dissolve each precursor in deionized water to form a precursor solution. Mix the precursor solutions and stir rapidly for 0.5 h, and then perform ultrasonic treatment for 10 min to mix evenly, so as to prepare a CeZrAl mixed solution with a total cation concentration of 0.01 - 0.10 mol / L;

[0055] (3) Under the conditions of room temperature and stirring, slowly add the obtained CeZrAl mixed solution dropwise to the reactor together with a precipitant (pH>9) formed by mixing ammonia water and ammonium carbonate solution for coprecipitation reaction, and control the pH range during the titration process to be 8.5 - 9.0;

[0056] (4) After the precipitation is complete, continue to stir for 0.5 - 2 h and let it stand for 24 - 48 h;

[0057] (5) Filtration: Wash the precipitate with deionized water until the pH of the filtrate is neutral, and dry the filtered precipitate at 98 °C for 24 h;

[0058] (6) Calcinate the dried solid in a muffle furnace at 450 - 600 °C for 3 - 5 h to obtain the CZA support powder.

[0059] (7) Load the noble metal Rh onto the CZA support by the equal-volume saturation impregnation method. The loading amount of Rh is 0.4 wt.% (mass percentage) and not zero to obtain the Rh / CZA material; dry the Rh / CZA material at 98 °C for 24 h, and then calcine it in a muffle furnace at 550 °C for 5 h to obtain the Rh / CZA catalyst.

[0060] Prepare the co-catalyst for MF:

[0061] (1) Weigh the precursor Fe(NO3)3·9H2O solid and Mn(NO3)2 (mass concentration 50%) solution according to the molar ratio of Mn to Fe in MF being 1:1;

[0062] (2) Dissolve the precursors in deionized water to prepare a mixed solution of Mn and Fe with a total cation concentration of 0.01 - 0.10 mol / L, and then add 5% of the mass of the MF oxide to be prepared of citric acid or polyvinyl alcohol or ethylene glycol. Stir rapidly for 0.5 h and then ultrasonically treat for 10 min to mix evenly to obtain a mixed solution;

[0063] (3) Under the conditions of room temperature and stirring, slowly add the precipitant (pH > 9) formed by mixing the above mixed solution with ammonia water and ammonium carbonate solution dropwise to the reactor, and control the pH range during the titration to be 8.5 - 9.0;

[0064] (4) Continue to stir for 0.5 h after the precipitation is complete and let it stand for 48 h;

[0065] (5) Filtration: Wash the precipitate with deionized water until the pH of the filtrate is neutral;

[0066] (6) Add 5% of the mass of the MF to be prepared of polyethylene glycol or ethylene glycol or polyvinyl alcohol to the filtered precipitate, mix evenly, and then dry at 98 °C for 24 h. After drying, calcine it in a tube furnace at 900 °C for 3 - 5 h to obtain the MF co-catalyst powder.

[0067] Mechanically mix the prepared Rh / CZA and MF according to the mass ratios of 100:0 and 90:10 respectively to obtain the Rh / CZA and Rh / CZA + MF three-way catalysts.

[0068] Then both Rh / CZA and Rh / CZA+MF were made into monolithic catalysts:

[0069] (1) Take 2.5 mL of cordierite support (see the three-view drawing in Figure 1 ), and use a cordierite ceramic matrix with 400 cpis as the coating matrix, and soak it in water for about 6 - 12 h;

[0070] (2) Prepare a uniformly mixed coating slurry by ball-milling the above-mentioned three-way catalyst of the present invention and a binder, and control the pH value of the slurry in the acidic range with an acetic acid solution with a volume fraction of 5 - 40%. The solid mass content in the slurry is 40%; the binder is selected from one or more of pseudoboehmite, aluminum sol, silica sol, and zirconium sol;

[0071] (3) After the slurry is prepared, dip one end of the matrix into the slurry, and then blow the slurry with an air compressor to make it evenly distributed in the matrix pores; perform the same operation on the other end of the matrix, and dry it after coating; during the coating process, control the loading of the coating on the dried matrix to be 0.4 g, about 157 g / L.

[0072] (4) Bake the coated and dried matrix in a muffle furnace at 900 °C for 5 h to obtain the monolithic catalyst.

[0073] Place the coated monolithic catalyst in a self-assembled fixed-bed continuous flow reactor for steady-state (non-dynamic, that is, a state where the simulated exhaust gas composition does not change) activity testing. The simulated exhaust gas conditions are shown in Table 1.

[0074] The activity results are as shown in Figure 2 . It can be seen from this that the Rh / CZA+MF catalyst has different degrees of improvement in the steady-state catalytic activity of various pollutants compared with the Rh / CZA catalyst. The 90% conversion temperature of CO and NO is reduced by about 15 °C, the conversion activity of C3H8 has no obvious change, and the 90% conversion temperature of C3H6 is reduced by about 10 °C.

[0075] The XRD technology was used to analyze the phase structure of the promoter, and the results are as shown in the appendix Figure 3 . The characteristic peaks of MF belong to the spinel structure of manganite (PDF 38-0430), and there are no diffraction peaks of other substances, indicating that it is relatively pure manganite spinel.

[0076] Appendix Figure 4 is the HRTEM image of the Rh / CZA+MF catalyst. As shown in the marked area in the figure, the lattice fringes of Rh and MF are staggered, deformed, and the intersection becomes blurred, indicating that Rh and MF interact to form a Rh(200) / MF(311) interface. In such an interface, O atoms are easily oxidized to form a large number of oxygen vacancies (Ov ),O v As an active site, it can promote the activation and migration of O, thereby promoting the progress of the catalytic reaction.

[0077] Table 1 Steady-state simulated tail gas conditions

[0078]

[0079] Example 2

[0080] The main catalyst Rh / CZA (the loading of noble metal Rh is 0.4 wt. %, and the mass ratio of Ce, Zr, and Al in the carrier is 1:2:7) and the promoter MF (the molar ratio of Mn and Fe is 1:1) were prepared according to the method of Example 1. Rh / CZA and MF were mechanically mixed at a mass ratio of 100:0 and 90:10 respectively to obtain the three-way catalysts Rh / CZA and Rh / CZA+MF.

[0081] Then both Rh / CZA and Rh / CZA+MF were made into monolithic catalysts. During the coating process, a cordierite carrier with a volume of 2.5 mL was used, and the solid content was 40%. Coating was carried out according to the above coating steps, and the final loading was 0.4 g.

[0082] The coated monolithic catalysts were placed in a self-assembled fixed-bed continuous flow reactor for dynamic activity testing. The simulated tail gas conditions are shown in Table 2, which can achieve the fluctuation of the simulated tail gas within the range of the excess air coefficient λ = 0.98 - 1.02, and the switching frequency between lean-burn and rich-burn conditions is 10 s.

[0083] The activity results are as Figure 3 shown. It can be seen from it that NO and C3H8 are very sensitive to the change of atmosphere, resulting in a sharp drop or sharp increase in their conversion rates with the change of the air-fuel ratio, while CO and C3H6 can quickly adapt to this air-fuel ratio fluctuation situation and the conversion rates no longer fluctuate with the change of the air-fuel ratio; the Rh / CZA catalyst could not achieve the complete conversion of pollutants at 540 °C, while the Rh / CZA+MF catalyst achieved the complete conversion of pollutants and reached the conversion equilibrium at 440 °C (about 100 °C earlier than Rh / CZA), showing excellent dynamic activity and the ability to suppress the fluctuation of the air-fuel ratio.

[0084] Table 2 Dynamic simulated tail gas conditions

[0085]

[0086] a Simulated tail gas content under lean-burn condition

[0087] b Simulated tail gas content under rich-burn condition

[0088] Example 3

[0089] The main catalyst, Rh / CZA (the loading amount of noble metal Rh is 0.4 wt.%, and the mass ratio of Ce, Zr, and Al in the carrier is 1:2:7), and the promoter MF (the molar ratio of Mn and Fe is 1:1) were prepared by the method of Example 1. Rh / CZA and MF were mechanically mixed at a mass ratio of 100:0 and 90:10, respectively, to obtain Rh / CZA and Rh / CZA+MF three-way catalysts.

[0090] Then both Rh / CZA and Rh / CZA+MF were made into monolithic catalysts. During the coating process, a cordierite carrier with a volume of 2.5 mL was used, and the solid content was 40%. Coating was carried out according to the above coating steps, and the final loading amount was 0.4 g.

[0091] The coated monolithic catalyst was placed in a self-assembled fixed-bed continuous flow reactor for single-reaction activity testing of CO+NO+O2 under lean combustion conditions (λ = 1.02). The simulated exhaust gas conditions are shown in Table 3.

[0092] Activity results and NO x Conversion rate comparison is as Figure 4 shown. It can be seen from this that complete conversion of CO was achieved for both catalysts. The Rh / CZA+MF catalyst showed higher NO conversion ability under lean combustion conditions, with higher conversion efficiency, a longer temperature range maintaining high conversion rate, and a significant reduction in the amount of NO generated in the high-temperature section. At the same time, the generation rate of NO also slowed down significantly. This shows that the catalyst prepared by the present invention can achieve efficient conversion of NO under dynamic operating conditions, especially under lean combustion conditions.

[0093] Table 3 Single-reaction simulated exhaust gas conditions

[0094]

[0095] Example 4

[0096] The main catalyst Rh / CZA (the loading amount of noble metal Rh is 0.4 wt.%, and the mass ratio of Ce, Zr, and Al in the carrier is 1:2:7) and the promoter MF (the molar ratio of Mn and Fe is 1:1) were prepared according to the method of Example 1. Rh / CZA and MF were mechanically mixed at a mass ratio of 100:0 and 90:10, respectively, to obtain Rh / CZA and Rh / CZA+MF three-way catalysts.

[0097] Then both Rh / CZA and Rh / CZA+MF were made into monolithic catalysts. During the coating process, a cordierite support with a volume of 2.5 mL was used, and the solid content was 40%. Coating was carried out according to the above coating steps, and the final loading amount was 0.4 g.

[0098] The coated monolithic catalyst was placed in a self-assembled fixed-bed continuous flow reactor for three-way working window testing. At a constant temperature of 400 °C, the excess air coefficient (λ) was simulated and regulated by changing the O2 content in the simulated exhaust gas. λ can be calculated according to the following formula, and the contents of the remaining exhaust gas components are shown in Table 1. Record the conversion of CO, NO, C3H8, and C3H6 at the corresponding λ, obtain the relationship diagram between the pollutant conversion rate and λ, and define the λ range where the pollutant conversion rate reaches more than 80% as the three-way working window. λ = 1 is the theoretical air-fuel ratio condition, λ<1 is the rich combustion condition, and λ>1 is the lean combustion (dilute combustion) condition.

[0099] λ=(2[CO2]+[H2O]+[CO]+2[O2]+[NO]) / (2[CO2]+[H2O]+2[CO]+[H2]+9[C3H6]+10[C3H8]

[0100] The relationship between the CO, NO x and HC conversion curves of Rh / CZA and Rh / CZA+MF catalysts at 400 °C and λ is as Figure 5 shown. The results show that with the change of λ, Rh / CZA and Rh / CZA+MF catalysts exhibit the same conversion law, that is, rich combustion conditions are beneficial to NO conversion, and lean combustion conditions are beneficial to CO and C3H6 conversion. Possibly due to the conversion characteristics of Rh-based catalysts, the conversion of C3H8 is only within a certain range. The addition of MF broadens the three-way working window of the Rh / CZA catalyst, enabling it to better adapt to λ fluctuations.

Claims

1. A high-performance three-way catalyst capable of suppressing dynamic air-fuel ratio, characterized in that, Composed of the main catalyst Rh / CeO2-ZrO2-Al2O3 and the cocatalyst Mn x Fe 3-x O4 composite oxide, where the value range of x in Mn x Fe 3-x O4 is 0.5 to 2.5, and the mass percentage of the Mn x Fe 3-x O4 composite oxide is 1% to 30%, and the mass percentage of the Rh / CeO2-ZrO2-Al2O3 catalyst is 70% to 99%.

2. The preparation method of the three-way catalyst according to claim 1, characterized in that, The promoter Mn x Fe 3-x O4 composite oxide is obtained by mechanically mixing with the main catalyst Rh / CeO2-ZrO2-Al2O3; the main catalyst Rh / CeO2-ZrO2-Al2O3 uses the CeO2-ZrO2-Al2O3 composite oxide with high thermal stability as the carrier, and is prepared by the co-precipitation method, and controlling the mass ratio of Ce, Zr, and Al to be 4:3:3 or 1:2:7 or 2:2:6; the Mn x Fe 3-x O4 composite oxide is prepared by the co-precipitation method, and controlling the molar ratio range of Mn and Fe to be 0.2 to 5; The preparation method of the Rh / CeO2-ZrO2-Al2O3 is as follows: (1) Weigh the corresponding precursor solids of Ce(NO3)3·6H2O, Zr(NO3)4·6H2O, and Al(NO3)3·9H2O according to the mass ratio of Ce, Zr, and Al in the CeO2-ZrO2-Al2O3 composite oxide being 4:3: or 1:2:7 or 2:2:6 in turn; (2) Dissolve each precursor in deionized water to form a precursor solution, mix the precursor solutions, and mix them uniformly by stirring and ultrasonic treatment in turn to prepare a CeZrAl mixed solution with a total cation concentration of 0.01 - 0.10 mol / L; (3) Under the conditions of room temperature and stirring, slowly add the precipitant formed by mixing the obtained CeZrAl mixed solution with ammonia water and ammonium carbonate solution dropwise to the reactor for coprecipitation reaction, and control the pH range during the titration process to be 8.5 - 9.0; (4) After the precipitation is complete, continue stirring for 0.5 - 2 h and stand for 24 - 48 h; (5) Filter, wash the precipitate with deionized water until the pH of the filtrate is neutral, and dry the filtered precipitate; (6) Calcinate the dried solid in a muffle furnace at 450 - 600 °C for 3 - 5 h to obtain CZA support powder; (7) Load the noble metal Rh onto the CZA support by the equal-volume saturation impregnation method, and the loading amount of Rh is 0 - 1 wt.% and not 0 to obtain Rh / CZA material; after drying the Rh / CZA material, calcine it in a muffle furnace at 450 - 600 °C for 3 - 5 h to obtain the Rh / CeO2-ZrO2-Al2O3 catalyst; The promoter Mn x Fe 3-x The preparation method of the O4 composite oxide is as follows: (1) According to the molar ratio of Mn x Fe 3-x in the MnFe₂O₄ composite oxide, weigh the precursor Fe(NO₃)₃·9H₂O solid and Mn(NO₃)₂ solution in sequence; (2) Dissolve the precursor in deionized water to prepare a mixed solution of Mn and Fe with a total cation concentration of 0.01 - 0.10 mol / L, and then add citric acid or polyvinyl alcohol or ethylene glycol in an amount of 5 - 30% of the mass of the Mn x Fe 3-x O4 composite oxide, and mix well to obtain a mixed solution; (3) Under the conditions of room temperature and stirring, slowly add the precipitant with pH > 9 formed by mixing the above mixed solution with ammonia water and ammonium carbonate solution dropwise to the reactor, and control the pH range during the titration process to be 8.5 - 9.0; (4) After the precipitation is complete, continue stirring for 0.5 h and stand for 48 h; (5) Filter, wash the precipitate with deionized water until the pH of the filtrate is neutral; (6) Add polyethylene glycol or ethylene glycol or polyvinyl alcohol in an amount of 5 to 30% of the mass of the Mn x Fe 3-x O4 composite oxide to the filtered precipitate, mix thoroughly, and then dry. After drying, calcine in a tubular furnace at 600 to 900 °C for 3 to 5 h to obtain the Mn x Fe 3-x O4 promoter powder.

3. The preparation method of the three-way catalyst according to claim 2, characterized in that, In the preparation method of Rh / CeO2-ZrO2-Al2O3, in step (2), stir rapidly for 0.5 h and perform ultrasonic treatment on the solution for 10 min; in steps (5) and (7), drying is carried out at 98 °C for 10 - 24 h.

4. The preparation method of the three-way catalyst according to claim 2, characterized in that, Promoter Mn x Fe 3-x In the preparation method of the Fe3O4 composite oxide, the mass concentration of the Mn(NO3)2 solution described in step (1) is 50%.

5. The preparation method of the three-way catalyst according to claim 2, characterized in that, Promoter Mn x Fe 3-x In the preparation method of the O4 composite oxide, the drying described in step (6) is carried out at 98 °C for 10 to 24 h.

6. A preparation method of an integral catalyst, characterized in that, It includes the following steps: (1) Use a cordierite ceramic substrate of 400 cpsi as the coating substrate and soak it in water for 6 - 12 h; (2) Prepare a uniformly mixed coating slurry by ball milling the three-way catalyst described in claim 1 and a binder, and control the pH value of the slurry in the acidic range with an acetic acid solution with a volume fraction of 5 - 40%. The solid mass content in the slurry is 20 - 50%; the binder is selected from one or more of pseudoboehmite, aluminum sol, silicon sol, and zirconium sol; (3) After the slurry is prepared, dip one end of the substrate into the slurry, and then blow the slurry with an air compressor to make it evenly distributed in the pore channels of the substrate; perform the same operation on the other end of the substrate, and dry it after coating; during the coating process, control the loading amount of the coating on the dried substrate to be 120 - 160 g / L; (4) Bake the coated and dried substrate in a muffle furnace at 600 - 900 °C for 3 - 5 h to obtain the monolithic catalyst.

7. A monolithic catalyst prepared by the method according to claim 6.

8. An application of the three-way catalyst according to claim 1 in motor vehicle exhaust treatment.

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