Highly heat stable low precious metal loading single pt three-way catalyst and method of making and use thereof

Abstract

The application discloses a single-Pt three-effect catalyst with high thermal stability and low noble metal loading, a preparation method and application thereof, and adopts a simple one-pot method (reduction sol method) to load Pt on Ce x Zr 1‑x O2 carrier phase, and through control of an inducing temperature and a Ce x Zr 1‑x O2 carrier, a migration driving force of Pt from the bulk phase to the surface is regulated, and then a three-effect catalyst Pt / Ce x Zr 1‑x O2 carrier with high thermal stability and low noble metal loading is prepared. The catalyst is used in exhaust treatment of a gasoline engine, and can improve the high-temperature stability of the catalyst and reduce the noble metal consumption.

Description

Technical Field

[0001] This invention belongs to the field of monolithic catalyst preparation technology for heterogeneous catalytic reaction systems, specifically relating to the preparation and application of three-way catalysts for purifying motor vehicle exhaust. Background Technology

[0002] In recent years, vehicle exhaust pollution has become increasingly prominent. Exhaust pollution has become one of the main sources of air pollution, and the difficulty of controlling gasoline vehicle exhaust emissions has increased dramatically.

[0003] Three-way catalytic converters (TWCs) are currently the most effective end-of-pipe control method for purifying gaseous pollutants in gasoline vehicle exhaust. They can simultaneously reduce CO and NO emissions near the stoichiometric air-fuel ratio. x And HCs are converted into non-toxic and harmless CO2, H2O and N2. Pt is beneficial for the catalytic conversion of CO and HCs and its price is significantly lower than Rh and Pd, so it is often preferred as the active component with the largest amount used. Cerium-zirconium based oxygen storage material Ce x Zr 1-x O2 (CZ) can smooth out air-fuel ratio fluctuations caused by frequent start-stop cycles and is the most commonly used carrier for three-way catalysts; the combination of the two to construct Pt / Ce x Zr 1-x O2-based three-way catalysts have been extensively studied. However, Pt phase is more prone to sintering and agglomeration during thermal aging compared to Pd and Rh, thus severely reducing catalytic activity. Currently, optimizing Pt / Ce... x Zr 1-x The main methods for improving the activity and high-temperature stability of O2 catalysts focus on optimizing the support-noble metal interaction through methods such as additive doping and support modification, to form Pt / Ce. x Zr 1-x The strong interaction with O2 suppresses Pt sintering at high temperatures, which improves the high-temperature stability of the catalyst to some extent. Although the impregnation method currently used is simple to prepare and can optimize the high-temperature stability of the catalyst to a certain extent, the ultra-long-cycle high-speed operation and extreme harsh service conditions of gasoline vehicles, as well as the future zero-emission standards, place higher demands on TWCs technology. At the same time, the high price of precious metals and the prominent supply-demand imbalance require reducing the amount of precious metals loaded and lowering costs. Therefore, developing new preparation methods to design and construct TWCs with high activity, high thermal stability, and low precious metal loading is crucial for the control of gasoline vehicle exhaust emissions. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a single Pt three-way catalyst with high thermal stability and low precious metal loading, along with its preparation method and application. This invention improves the high-temperature stability of the catalyst while reducing the amount of precious metals used, thus ensuring catalytic activity.

[0005] This invention employs a reduction-sol-gel method, by adjusting the reducing agent, gelation conditions, and carrier element ratio, to load Pt onto Ce. x Zr 1-x In the O2 support phase, an atmospheric thermal induction method is then used, by controlling the induction temperature and Ce... x Zr 1-x By adjusting the Ce:Zr ratio in the O2 support, the migration driving force of Pt from the bulk phase to the surface is controlled, thereby preparing a three-way catalyst Pt / Ce with high thermal stability and low noble metal loading. x Zr 1-x O2 improves the high-temperature stability of the catalyst; when this series of catalysts is used in the treatment of gasoline engine exhaust gas, it can improve the high-temperature stability of the catalyst, and under low precious metal loading, it still has a significant performance advantage compared with the impregnation method, and has the prospect of development and application for reducing precious metal loading.

[0006] This invention provides a high thermal stability, low noble metal loading single-Pt three-way catalyst (Pt / Ce). x Zr 1-x The method for preparing O2 includes the following steps:

[0007] (1) According to cerium zirconium oxide Ce x Zr 1-x The molar ratio of Ce to Zr in O2 (0≤x≤1) is determined by weighing the corresponding precursors Ce(NO3)3·6H2O and Zr(NO3)4·5H2O solids.

[0008] (2) Dissolve each precursor separately in deionized water to form a precursor mixed solution, and mix thoroughly to prepare a Ce solution with a total cation concentration of 0.01–0.10 mol / L. 3+ Zr 4+ Mixed solutions;

[0009] (3) Add citric acid (C6H8O7) to the mixed solution obtained in step (2), and the ratio of the total amount of Ce and Zr to the amount of C6H8O7 is 1:(2~5).

[0010] (4) Continue to add Pt nanoparticles and stir at 50-80°C until a gel is formed;

[0011] (5) The obtained gel was dried and calcined in a muffle furnace at 300-550℃ for 3-5 hours to obtain Pt / Ce. x Zr 1-x O2 catalyst.

[0012] In the above technical solution of the present invention, the Pt nanoparticles are prepared by the following method:

[0013] (1) Prepare a Pt(NO3)2 solution;

[0014] (2) Use a mixed solution of glycerol, ethylene glycol and ethanol as a mixed reducing agent with strong and weak reducing agents;

[0015] (3) Heat the mixed reducing agent solution in step (2) to 50-90°C and maintain it for 3-4 hours;

[0016] (4) Add the mixed reducing agent solution to the Pt(NO3)2 solution obtained in step (1) and pass N2 for protection;

[0017] (5) Heat the mixed solution obtained in step (4) to 90-120°C and stir for 4-8 hours until the solution becomes a black colloidal solution.

[0018] (6) Add polyvinylpyrrolidone (K30) to the black colloidal solution. The molar ratio of Pt to K30 is 1:(5-50). Stir at 100-150℃ for 1-4 hours and centrifuge to obtain Pt nanoparticles.

[0019] Furthermore, in the preparation of the above Pt nanoparticles, the concentration of the Pt(NO3)2 solution in step (1) is 0.01 g / mL.

[0020] Furthermore, in the preparation of the above Pt nanoparticles, the molar ratio of glycerol, ethylene glycol and ethanol in step (2) is preferably 1:1:1, 2:1:1 or 3:1:1.

[0021] Furthermore, in the preparation of the above Pt nanoparticles, in step (4), a constant flow pump is used and the titration rate is controlled at 2 mL / min to add the mixed reducing agent solution dropwise into the Pt(NO3)2 solution in step (1).

[0022] Furthermore, in the preparation of the above-mentioned Pt three-way catalyst, the amount of Pt nanoparticles added is such that Pt is added to cerium zirconium oxide (Ce) x Zr 1-x The loading amount on the O2 carrier is 0.3% to 1.0% of the carrier mass.

[0023] Furthermore, in the preparation of the above-mentioned Pt three-way catalyst, step (4) involves stirring in a water bath at temperatures of 60, 70, and 80°C for 0.5 to 2 hours until a gel state is formed.

[0024] Furthermore, in the preparation of the above Pt three-way catalyst, the molar ratio of Ce:Zr in step (1) can be 0:10, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or 10:0.

[0025] Furthermore, in the preparation of the above-mentioned Pt three-way catalyst, the amount of citric acid C6H8O7 added in step (2) is 1:2, 1:3, 1:4 or 1:5 according to the ratio of the total amount of Ce and Zr to the amount of C6H8O7.

[0026] The high thermal stability and low noble metal loading of the single-Pt three-way catalyst Pt / Ce provided by the method of the present invention x Zr 1-x O2.

[0027] The present invention also provides a Pt-based monolithic three-way catalyst for gasoline vehicles, comprising the above-mentioned Pt / Ce x Zr 1-x O2 catalyst and cordierite, the Pt / Ce x Zr 1-x An O2 catalyst is coated onto cordierite. This monolithic catalyst exhibits good catalytic activity and high-temperature stability, and is used for gasoline vehicle exhaust purification.

[0028] This invention also provides a method for preparing the above-mentioned Pt-based monolithic three-way catalyst for gasoline vehicles, wherein the above-mentioned Pt / Ce x Zr 1-x O2 catalyst powder was added to pseudoboehmite, acetic acid, and deionized water, mixed and ball-milled to form a slurry, which was then coated onto cordierite. After drying, the mixture was calcined at 300–550°C for 3–5 hours, and then aged in flowing air at 900°C for 5 hours to obtain a monolithic catalyst, wherein Pt / Ce... x Zr 1-x The loading of O2 catalyst was 160 g / L.

[0029] Furthermore, the drying temperature is 70°C.

[0030] The present invention also provides the above-mentioned Pt / Ce x Zr 1-x The application of O2 catalysts in the purification of gasoline vehicle exhaust specifically involves the purification of CO, HCs, and NO.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. This invention employs a simple and controllable one-pot method (reduction-gel method) to prepare Pt / Ce. x Zr 1-x An O2 triple-effect catalyst utilizes the uniform dispersion of gels to complex cerium-zirconium cations, forming a stable sol system in solution. During heating and stirring, the sol slowly polymerizes, forming a three-dimensional network structure. The spaces between the gel networks are filled with solvent that has lost its flowability, thus forming a gel. The gel is then dried and sintered to solidify, yielding a sub-nanostructured Ce. x Zr1-x O2 materials.

[0033] 2. This method utilizes a liquid-phase reduction method with a combination of strong and weak reducing agents to prepare low-valence Pt nanoparticles. Pt nanoparticles are then obtained by coating them with a non-ionic polymer copolymer. During the continuous reduction process, a citric acid-complexed cerium-zirconium support solution is added, ensuring sufficient contact between the coated Pt nanoparticles and the complexed precursor salt solution, thus enhancing the interaction between the metal and the support. In the subsequent calcination process, the coated Pt nanoparticles migrate from the bulk phase or interior of the oxide support to the surface under thermal drive. By controlling the preparation conditions, the Pt nanoparticles settle into a stable "semi-coated structure," achieving small-particle-size, highly dispersed, and strongly interacting Pt / Ce nanoparticles. x Zr 1-x Preparation of O2 catalyst. After aging in flowing air at 900℃, it exhibited excellent catalytic performance and good thermal stability.

[0034] 3. The single-Pt three-way catalyst Pt / Ce prepared by this invention x Zr 1-x O2 is used to remove CO, HCs, and NO from vehicle exhaust. x The treatment not only exhibits excellent catalytic performance and thermal stability, but also, compared with impregnation and other common supported catalyst preparation methods, this method has the advantages of controllable operating conditions, easy process scale-up, and environmental friendliness. The single Pt catalyst obtained by this preparation method outperforms commercial catalysts that simultaneously support three noble metals, Pt, Pd, and Rh, significantly reducing catalyst costs and meeting industrial needs. Attached Figure Description

[0035] Figure 1 (a) CO activity conversion curves of Comparative Examples 1 and 2 and Examples 1, 2 and 3;

[0036] Figure 1 (b) The activity conversion curves of NO in Comparative Examples 1 and 2 and Examples 1, 2 and 3;

[0037] Figure 1 (c) The activity conversion curves of C3H8 in Comparative Examples 1 and 2 and Examples 1, 2 and 3;

[0038] Figure 1 (d) shows the activity conversion curves of C3H6 in Comparative Examples 1 and 2 and Examples 1, 2 and 3;

[0039] Figure 2 (a) shows the CO activity conversion curves of Comparative Examples 3 and 4 and Example 1;

[0040] Figure 2 (b) shows the activity conversion curves of NO in Comparative Examples 3 and 4 and Example 1;

[0041] Figure 2 (c) The activity conversion curves of C3H8 in Comparative Examples 3 and 4 and Example 1;

[0042] Figure 2 (d) shows the activity conversion curves of C3H6 in Comparative Examples 3 and 4 and Example 1;

[0043] Figure 3 (a) is the activity conversion curve of CO in Comparative Example 5 and Example 1;

[0044] Figure 3 (b) is the activity conversion curve of NO in Comparative Example 5 and Example 1;

[0045] Figure 3 (c) is the activity conversion curve of C3H8 in Comparative Example 5 and Example 1;

[0046] Figure 3 (d) shows the activity conversion curves of C3H6 in Comparative Example 5 and Example 1;

[0047] Figure 4 (a) is the activity conversion curve of hydrogen thermal induction at different temperatures in Comparative Example 6 and CO in Example 1.

[0048] Figure 4 (b) is the activity conversion curve of hydrogen thermal induction at different temperatures in Comparative Example 6 and NO in Example 1.

[0049] Figure 4 (c) is the activity conversion curve of C3H8 from Example 1 with hydrogen thermal induction at different temperatures in Comparative Example 6.

[0050] Figure 4 (d) shows the activity conversion curves of C3H6 from Example 1 and hydrogen thermal induction at different temperatures in Comparative Example 6.

[0051] Figure 5 (a) is the activity conversion curve of CO in Comparative Example 7 with different Ce:Zr ratios and in Example 1;

[0052] Figure 5 (b) is the activity conversion curve of NO in Example 1 with different Ce:Zr ratios in Comparative Example 7;

[0053] Figure 5 (c) is the activity conversion curve of different Ce:Zr ratios in Comparative Example 7 and C3H8 in Example 1;

[0054] Figure 5 (d) shows the activity conversion curves of different Ce:Zr ratios in Comparative Example 7 and C3H6 in Example 1.

[0055] In the picture:

[0056] Example 1 - 1 wt% Pt / Ce prepared by reduction sol-gel method x Zr 1-x O2 catalyst

[0057] Example 2 - 0.8 wt% Pt / Ce loaded by reduction sol-gel method x Zr 1-x O2 catalyst

[0058] Example 3 - 0.5 wt% Pt / Ce loaded by reduction sol-gel method x Zr 1-x O2 catalyst

[0059] Comparative Example 1 - 1 wt% Pt / Ce prepared by impregnation method x Zr 1-x O2 catalyst

[0060] Comparative Example 2 - 1 wt% Pt / CeO2-ZrO2-La2O3-Pr2O3 catalyst prepared by commercial carrier impregnation method; Comparative Example 3 - R-1 wt% Pt / CeO2-ZrO2-La2O3-Pr2O3 catalyst prepared by impregnation method after Pt reduction. x Zr 1-x O2 catalyst

[0061] Comparative Example 4 - N-1wt% Pt Ce prepared by direct sol-gel method from non-reduced Pt precursor x Zr 1-x O2 catalyst

[0062] Comparative Example 5 - Commercial National VIb three-way catalyst (Pt:Pd:Rh = 5:3:2, total precious metal loading 1wt%)

[0063] Comparative Example 6 - Hydrogen thermal induction treatment at different temperatures using the reduction sol-gel method

[0064] Comparative Example 7 - Different Ce:Zr Ratios Using Reduction Solvent Method Detailed Implementation

[0065] The present invention will be further described below with reference to specific embodiments. These specific embodiments are further explanations of the principles of the present invention and are not intended to limit the present invention in any way. Embodiments that are the same as or similar to the present invention do not exceed the scope of protection of the present invention.

[0066] Example 1

[0067] The Pt / Ce provided in this embodiment x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0068] (1) Add Pt(NO3)2 solution to deionized water to prepare a solution with a concentration of 0.01 g / mL;

[0069] (2) Using a combination of strong and weak reducing agents, a mixed solution of glycerol, ethylene glycol and ethanol is prepared. The solution is mixed by stirring and ultrasonic mixing to prepare a mixed reducing agent solution with a molar ratio of 1:1:1.

[0070] (3) Heat the mixed reducing agent solution in step (2) to 90°C and maintain it for 3 hours;

[0071] (4) Use a constant flow pump to control the titration rate at 2 mL / min, add the mixed reducing agent solution from step (3) to the solution obtained in step (1), and immediately pass high-purity nitrogen gas for protection after titration.

[0072] (5) Heat the mixed solution in step (4) to 90°C and stir in an oil bath for 5 hours until the solution becomes a black colloidal solution.

[0073] (6) Add polyvinylpyrrolidone K30 to the black colloidal solution, with a Pt:K30 molar ratio of 1:5, stir at 150℃ for 1 h, and centrifuge to obtain noble metal Pt nanoparticles.

[0074] (7) According to Ce x Zr 1-x The molar ratio of Ce and Zr in O2 is 1:1. Weigh out the corresponding precursors Ce(NO3)3·6H2O solid and Zr(NO3)4·5H2O solid.

[0075] (8) Dissolve each precursor separately in deionized water to form a precursor solution. Mix the precursor solutions and stir rapidly for 0.5 h. Then, sonicate the solution for 10 min to mix thoroughly, and prepare a Ce solution with a total cation concentration of 0.10 mol / L. 3+ Zr 4+ Mixed solutions;

[0076] (9) In the obtained Ce 3+ Zr 4+ Solid citric acid C6H8O7 was added to the mixed solution and stirred until homogeneous. The ratio of the amount of C6H8O7 to the total amount of Ce and Zr was 2:1.

[0077] (10) After adding the Pt nanoparticles from step (6) to the mixed solution obtained in step (9), the amount of Pt nanoparticles added is 1 wt% of the mass loading of Pt on the cerium zirconium oxide support. Stir for 30 min at each temperature range of 60℃, 70℃ and 80℃ until a gel state is formed.

[0078] (11) The obtained gel was dried in an oven at 80°C for 24 hours and calcined in a muffle furnace at 550°C for 3 hours to obtain Pt / Ce. x Zr 1-x O2 catalyst;

[0079] (12) The catalyst powder obtained in step (11) is coated on cordierite and dried at 80°C for 5 hours and calcined at 550°C for 3 hours.

[0080] (13) The monolithic catalyst was prepared by aging it in a tube furnace at 900°C with flowing air for 5 hours, and denoted as Pt / Ce. x Zr 1-x O2, with a catalyst loading of 160 g / L.

[0081] Example 2

[0082] The Pt / Ce provided in this embodiment x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0083] (1) Control the loading of Pt to 0.8 wt%. Take the corresponding mass of Pt(NO3)2 solution and add deionized water to prepare a solution with a concentration of 0.01 g / mL.

[0084] (2) Prepare noble metal Pt particles according to steps (2)-(6) in Example 1.

[0085] (3) Prepare monolithic Pt / Ce according to steps (7)-(13) in Example 1. x Zr 1-x O2 catalyst is denoted as 0.8% -Pt / Ce x Zr 1-x O2;

[0086] Example 3

[0087] The Pt / Ce provided in this embodiment x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0088] (1) Control the loading of Pt to 0.5 wt%. Take the corresponding mass of Pt(NO3)2 solution and add deionized water to prepare a solution with a concentration of 0.01 g / mL.

[0089] (2) Prepare noble metal Pt particles according to steps (2)-(6) in Example 1.

[0090] (3) Prepare monolithic Pt / Ce according to steps (7)-(13) in Example 1. x Zr 1-xO2 catalyst, denoted as 0.5%-Pt / Ce x Zr 1-x O2.

[0091] Comparative Example 1

[0092] This comparative example provides a gel carrier impregnated with Pt / Ce. x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0093] (1) According to Ce x Zr 1-x The molar ratio of Ce to Zr in O2 is 1:1. Weigh out the corresponding precursors Ce(NO3)3·6H2O solid and Zr(NO3)4·5H2O solid.

[0094] (2) Dissolve each precursor in deionized water to form a precursor solution. Mix the precursor solutions and stir rapidly for 0.5 h. Then, sonicate the solution for 10 min to mix evenly and prepare a mixed solution with a total cation concentration of 0.01 mol / L.

[0095] (3) Add solid citric acid C6H8O7 to the Ce and Zr mixed solution in step (2) and stir until homogeneous. The ratio of the amount of C6H8O7 to the total amount of Ce and Zr is 2:1. Stir the mixed solution in a water bath at 60℃, 70℃ and 80℃ for 0.5h each until a gel is formed.

[0096] (4) Dry in an oven at 80℃ for 24 hours, and calcine in a muffle furnace at 550℃ for 3 hours to obtain Ce. x Zr 1-x O2 carrier;

[0097] (5) Control the loading of Pt to 1 wt% of the carrier, take the corresponding mass of Pt(NO3)2 solution, add deionized water to prepare a solution with a concentration of 0.01 g / mL;

[0098] (6) Using the traditional impregnation method, weigh a certain mass of Ce from step (4). x Zr 1-x O2 carrier was added to the solution obtained in step (5), and the mixture was stirred rapidly and continuously. The mixture was then placed in a water bath at 70°C for 5 hours and calcined in a muffle furnace at 550°C for 3 hours to prepare powdered Pt / Ce. x Zr 1-x O2 catalyst, denoted as Pt / Ce x Zr 1-x O2;

[0099] (7) The obtained catalyst powder was coated on cordierite and dried at 80°C for 5 hours and calcined at 550°C for 3 hours.

[0100] (8) The monolithic catalyst was prepared by aging it in a tube furnace at 900°C with flowing air for 5 hours, denoted as Pt / Ce. x Zr 1-x O2, with a catalyst loading of 160 g / L.

[0101] Comparative Example 2

[0102] The preparation method of the commercially available supported Pt / CeO2-ZrO2-La2O3-Pr2O3 (Pt / CZLP) catalyst provided in this comparative example includes the following steps:

[0103] (1) Solvay's commercial CeO2-ZrO2-La2O3-Pr2O3 (S BET =72m 2 / g);

[0104] (2) In the same step (5) as in control sample 1, a noble metal colloidal solution is obtained;

[0105] (3) The Pt(NO3)2 solution from step (2) was impregnated onto the CZLP commercial support from step (1), and the mixture was placed in a water bath at 70°C for 5 hours and then calcined at 550°C in a muffle furnace for 3 hours to obtain the Pt / CZLP catalyst.

[0106] (4) The catalyst powder obtained in step (3) is coated on cordierite and dried at 80°C for 5 hours and calcined at 550°C for 3 hours.

[0107] (5) The catalyst was aged in a tube furnace at 900°C with flowing air for 5 hours to obtain an integral catalyst, denoted as Pt / CZLP, with a catalyst loading of 160 g / L.

[0108] Comparative Example 3

[0109] This comparative example provides a reduction impregnation of R-Pt / Ce. x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0110] (1) Ce was prepared in Comparative Example 1 (1)-(4). x Zr 1-x O2 carrier powder;

[0111] (2) Pt colloidal nanoparticles were prepared in the same manner as in Example 1 (1)-(6);

[0112] (3) Add a certain amount of deionized water to the Pt colloidal nanoparticles obtained in step (2) to prepare a solution. Using the traditional impregnation method, weigh the Ce obtained in step (1) in proportion to the amount of water. x Zr 1-xO2 carrier was added and stirred rapidly and continuously. The mixture was then in a 70°C water bath for 5 hours and calcined in a muffle furnace at 550°C for 3 hours to obtain R-Pt / Ce. x Zr 1-x O2 catalyst.

[0113] (4) The catalyst powder obtained in step (3) is coated on cordierite and dried at 80°C for 5 hours and calcined at 550°C for 3 hours.

[0114] (5) The monolithic catalyst was prepared by aging it in a tube furnace at 900°C with flowing air for 5 hours, and denoted as R-Pt / Ce. x Zr 1-x O2, with a catalyst loading of 160 g / L.

[0115] Comparative Example 4

[0116] The comparative example provides N-1wt%Pt / Ce prepared by direct sol-gel method using a non-reduced Pt precursor. x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0117] (1) Prepare the carrier mixture solution according to steps (1)-(3) of Comparative Example 1;

[0118] (2) Control the loading of Pt to 1 wt% of the carrier, take the corresponding mass of Pt(NO3)2 solution, add deionized water to prepare a solution with a concentration of 0.01 g / mL;

[0119] (3) The Pt(NO3)2 solution from step (2) is added dropwise to the mixed solution obtained in step (1) above. The titration rate is controlled by a constant flow pump at 2 mL / min. Then, the solution is stirred in a water bath at 60℃, 70℃ and 80℃ for 0.5 h until a gel is formed.

[0120] (4) Dry in an oven at 80℃ for 24 hours and calcine in a muffle furnace at 550℃ for 3 hours to obtain N-1wt% Pt / Ce x Zr 1-x O2 catalyst;

[0121] (5) Coat the catalyst powder obtained in step (4) onto cordierite, and dry it at 80°C for 5 hours and calcine it at 550°C for 3 hours.

[0122] (6) The catalyst was aged in a tube furnace at 900°C with flowing air for 5 hours to obtain a monolithic catalyst, denoted as N-1wt%Pt / Ce. x Zr 1-x O2, with a catalyst loading of 160 g / L.

[0123] Comparative Example 5

[0124] The main parameters of the China VIb commercial three-way catalyst provided in this comparative example are as follows:

[0125] Precious metal loading capacity 60g / ft 3 The catalyst loading was 220 g / L, and the molar ratio of Pt:Pd:Rh was 5:3:2.

[0126] The carrier and additive components are unknown. The material was aged in a tube furnace at 900°C with flowing air for 5 hours.

[0127] Comparative Example 6

[0128] The Pt / Ce ratio of the hydrogen thermally induced post-treatment H2-T (T = 500, 600, 700, 800, 900℃) provided in this comparative example is... x Zr 1-x The method for preparing an O2 catalyst includes the following steps:

[0129] (1) Pt / Ce was prepared in the same manner as in Example 1, step (1-11). x Zr 1-x O2 catalyst powder;

[0130] (2) Place the powder in a tube furnace, introduce 5% H2 / N2, and control the temperature rise to the target temperature (500, 600, 700, 800, 900℃) with a heating rate of 5℃ / min, and maintain the target temperature for 5h.

[0131] (3) The catalyst powder obtained in step (2) is coated on cordierite, dried at 80°C for 5 hours and calcined at 550°C for 3 hours to obtain an integral catalyst, denoted as H2-T (T = 500, 600, 700, 800, 900°C), with a catalyst loading of 160 g / L.

[0132] Comparative Example 7

[0133] This comparative example provides different Ce:Zr ratios to adjust Pt / Ce. x Zr 1-x O2 preparation method includes the following steps:

[0134] (1) Noble metal Pt nanoparticles were prepared in the same manner as in Example 1 (1-6).

[0135] (2) Prepare precursor solutions with different molar ratios of Ce and Zr, namely 0:10, 2:8, 8:2, and 10:0, by weighing the corresponding precursor Ce(NO3)3·6H2O solid and Zr(NO3)4·5H2O solid.

[0136] (3) Dissolve each precursor in deionized water to form a precursor solution. Mix the precursor solutions and stir rapidly for 0.5 h. Then, sonicate the solution for 10 min to mix evenly and prepare a Ce and Zr mixed solution with a total cation concentration of 0.10 mol / L.

[0137] (4) Add solid citric acid C6H8O7 to the Ce and Zr mixed solution obtained in step (2) and stir until homogeneous. The ratio of the amount of C6H8O7 to the total amount of Ce and Zr is 2:1.

[0138] (5) After adding the Pt nanoparticles from step (1) to the mixed solution obtained in step (4), stir for 30 min at each temperature range of 60℃, 70℃ and 80℃ until a gel state is formed.

[0139] (6) The obtained gel was dried in an oven at 80°C for 24 hours and then calcined in a muffle furnace at 550°C for 3 hours to obtain Pt / Ce. x Zr 1- x O2 (m = 1, 0.8, 0.5, 0.2, 0) catalyst;

[0140] (7) The catalyst powder obtained in step (6) is coated on cordierite and dried at 80°C for 5 hours and calcined at 550°C for 3 hours.

[0141] (8) The monolithic catalyst was prepared by aging it in a tube furnace at 900°C with flowing air for 5 hours, denoted as Pt / Ce. x Zr 1-x O2, with a catalyst loading of 160 g / L.

[0142] Activity evaluation experiment

[0143] The catalyst activity was tested using a laboratory-assembled fixed-bed continuous flow reactor. The catalyst was immobilized in the reactor, and the gas hourly space velocity (GHSV) was controlled at 50,000 h⁻¹. -1 The composition of the simulated exhaust gas is shown in Table 1. Before the activity test, the catalyst was pretreated in a simulated exhaust gas atmosphere at 550℃ for 1 hour, and then cooled to the Tconversion of pollutants. 10 Below the temperature at which the pollutant conversion rate is 10%. Subsequently, under continuous heating conditions, the analyzer outlet detected a decrease in the concentration of each pollutant, and the T values ​​for each pollutant were recorded. 50 and T 90 (Tempers at 50% and 90% pollutant conversion rates) were used to evaluate catalyst activity. Test results are as follows: Figure 1-5 And Table 2.

[0144] Table 1 Simulated exhaust gas conditions

[0145]

[0146] Table 2 Catalytic activity T of each pollutant 50 and T 90

[0147]

[0148]

[0149] Dispersion and particle size estimation

[0150] The dispersion of the catalyst was tested using a laboratory-assembled chemical pulse adsorption method. Utilizing the selective chemical adsorption of CO on the surface of a noble metal, and the existence of a stoichiometric relationship between the adsorbed molecules and the atoms on the metal surface, the dispersion of the loaded noble metal was measured, and the particle size of the noble metal at the corresponding dispersion was estimated.

[0151] Test Procedure: Weigh 0.25g of sample and mix with quartz sand, place in a U-tube and put in a heating furnace. Reduce with hydrogen gas at 450℃ for 1 hour. After reduction, cool and test at -77℃ to eliminate the influence of Ce on CO adsorption. After the chromatogram reaches baseline, pulse CO onto the sample until the peak area remains unchanged. The calculation formula is as follows:

[0152] Dispersion calculation:

[0153] Particle size calculation:

[0154] V0 – Pulse CO consumption

[0155] M Pt —Molar mass of Pt

[0156] W—Catalyst mass

[0157] P – The amount of Pt loaded in the catalyst

[0158] Table 3 provides the dispersion and particle size of some catalysts.

[0159] Table 3 Dispersion and Particle Size

[0160]

[0161] Results analysis:

[0162] 1. Figure 1 and Figure 2 The results showed that the fresh activity of Example 1 and Comparative Example 3 was similar, but the activity of Example 1 was superior to that of Comparative Example 3, indicating that the present invention uses the method of first reducing and preparing Pt nanoparticles, and then introducing Ce as a support. x Zr1-x O2 solution, obtained Pt / Ce x Zr 1-x The O2 catalyst exhibits excellent thermal stability under aging conditions of 900℃, which is not only superior to gel supports loaded by impregnation and reduction methods, but also comparable to commercially available impregnation-loaded supports.

[0163] 2. Figure 3 The results show that the single-Pt catalyst prepared by this invention has a significant activity advantage compared with a commercial three-way catalyst with the same noble metal loading (Pt:Pd:Rh = 5:3:2), meaning that the catalyst of this invention can reduce the amount of noble metals used while maintaining the same activity. Considering that the three noble metals Pt, Pd, and Rh are affected by market fluctuations, the amount and ratio of noble metals directly affect the catalyst cost. Among the noble metals, Pt has the lowest price. Therefore, the method of this invention is beneficial for developing single-Pt catalysts with high activity and thermal stability, and has great industrial application value.

[0164] 3. Due to the high-temperature operating conditions of three-way catalysts, good thermal stability is required. This method utilizes a combination of strong and weak reducing agents in liquid-phase reduction to prepare Pt nanoparticles, which are then encapsulated with a non-ionic polymer copolymer to prevent aggregation. During continuous reduction, a citric acid-complexed cerium-zirconium support solution is added, ensuring sufficient contact between the Pt nanoparticles and the complexed precursor salt solution, enhancing the interaction between the metal support. In the subsequent calcination process, the encapsulated Pt nanoparticles are thermally driven to detach in situ from the oxide support, exhibiting excellent anti-aging properties after aging. Combined with the results in Table 3, the catalyst prepared by this invention can inhibit noble metal sintering. Compared to methods that use surface-loaded noble metals, Pt exhibits better dispersion and a smaller particle size.

[0165] 4. Figure 4 The results show that the catalyst performance is significantly improved by atmospheric thermal hydrogen-induced treatment. Under hydrogen atmospheres at different temperatures, Pt nanoparticles are further reduced, exposing more active sites. Hydrogen pretreatment can be used as a catalyst pretreatment method to further enhance catalytic activity.

[0166] 5. Figure 5 Catalysts prepared with Ce:Zr supports of different ratios were shown, and it was found that the best activity was observed when the Ce:Zr ratio was kept at 1:1.

Claims

1. A process for the preparation of a high thermal stability low precious metal loading mono-Pt three-way catalyst, characterized in that, The method comprises the following steps: S1, according to cerium zirconium oxide Ce x Zr 1-x The solid precursors Ce(N03)3-6H20 and Zr(N03)4-5H20 are weighed according to the molar ratio of Ce to Zr in 02; wherein the molar ratio of Ce:Zr is 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:

2. S2, each precursor is dissolved in deionized water to form a precursor mixed solution, and the total cation concentration of the prepared Ce 3+ , Zr 4+ mixed solution is 0.01 ~ 0.10 mol / L; S3, adding citric acid into the mixed solution obtained in step S2, and the ratio of the total mass of Ce and Zr to the mass of citric acid is 1: (2-5) ; S4, continue to add Pt nanoparticles and stir at 50 ~ 80 ℃ until a gel state is formed; the amount of Pt nanoparticles added is such that the Pt content in the cerium-zirconium oxide Ce x Zr 1-x The loading amount on the O2 carrier is 0.3 ~ 1.0% of the mass of the carrier; S5, the obtained gel is dried and calcined at 300-550 ℃ in a muffle for 3-5 h to obtain Pt / Ce x Zr 1-x O2catalyst The Pt nanoparticles are prepared by the following method: (1) preparing a Pt(NO3)2 solution; (2) using a mixed solution of glycerol, ethylene glycol and ethanol as a mixed reducing agent of strong and weak reducing agents; the mass ratio of glycerol, ethylene glycol and ethanol is 1:1:1, 2:1:1 or 3:1:1; (3) heating the mixed reducing agent solution in step (2) to 50-90 ℃ and keeping for 3-4 h; (4) adding the mixed reducing agent solution into the Pt(NO3)2 solution obtained in step (1) and protecting by N2; (5) heating the mixed solution obtained in step (4) to 90-120 ℃, stirring for 4-8 h until the solution completely turns into a black colloidal solution; (6) adding polyvinylpyrrolidone into the black colloidal solution, the mass ratio of Pt to polyvinylpyrrolidone is 1: (5-50), stirring at 100-150 ℃ for 1-4 h, and centrifuging to obtain Pt nanoparticles.

2. The method of claim 1, wherein In the preparation of the Pt nanoparticles, the concentration of the Pt(NO3)2 solution in step (1) is 0.01 g / mL.

3. The method of claim 1, wherein In the preparation of the Pt nanoparticles, a constant flow pump is used in step (4) to drop the mixed reducing agent solution into the Pt(NO3)2 solution in step (1) at a titration rate of 2 mL / min.

4. The method of claim 1, wherein In step S2, the amount of citric acid added is determined according to the ratio of the total mass of Ce and Zr to the mass of citric acid, which is 1:2, 1:3, 1:4 or 1:

5.

5. The high thermal stable low noble metal loading single Pt three-way catalyst Pt / Ce prepared by the preparation method of any one of claims 1-4 x Zr 1-x O2.

6. A Pt-based monolithic three-way gasoline vehicle catalyst characterized by comprising a Pt-based three-way catalyst composition according to any one of claims 1 to 5. comprising the Pt / Ce of claim 5 x Zr 1-x O2catalyst and cordierite, the Pt / Ce x Zr 1-x O2catalyst coated on cordierite.

7. Application of the high-thermal-stability low-noble-metal-loading single-Pt three-way catalyst in claim 5 to purification of exhaust gas of a gasoline vehicle.

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