Preparation and application of PtCu alloy three-way catalyst with core-shell structure

Abstract

The invention discloses preparation and application of a core-shell structure PtCu alloy three-way catalyst, and belongs to the technical field of catalysis. The CeO2-loaded core-shell structure PtCu alloy catalyst is prepared by using nano CeO2 as a carrier and loading Pt and Cu metals by adopting an impregnation method, wherein the nano CeO2 is formed by carrying out hydrothermal reaction on cerous nitrate and a nitrogen-containing compound. Compared with a commercial Pt-Rh-Pd / cordierite catalyst, the catalyst prepared by the invention not only has an excellent purification effect on nitrogen oxide (NOx), propylene (C3H6) and carbon monoxide (CO) discharged from tail gas of an extended-range engine, but also has relatively good catalytic stability, and the catalyst has the advantages of simple process, relatively wide catalytic window and good commercial application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis technology, and in particular relates to the preparation and application of a core-shell structured PtCu alloy three-way catalyst. Background Art

[0002] Automobile exhaust pollutants have become one of the main sources of urban pollution. Gasoline engine exhaust gas pollutants mainly contain carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO x As a precursor to acid rain, photochemical smog and haze, NO x Hydrocarbons and HC not only harm the environment but also pose serious risks to human health. Despite significant research progress, current three-way catalysts still suffer from low efficiency, high reaction temperatures, and poor stability, making them inadequate for the range-extended engines currently being developed in China. Therefore, developing new three-way catalysts with higher efficiency, improved stability, and lower conversion temperatures holds significant economic value.

[0003] Cerium dioxide is widely used in environmental catalysis due to its unique high oxygen storage capacity, abundant oxygen vacancies, and multiple redox states. However, pure CeO2 is greatly limited in practical applications due to its poor thermal stability and small specific surface area. Pt metal catalysts, due to their high oxidation activity, low oxidation temperature, and resistance to poisoning, can efficiently degrade NO, CO, and C3H6 under relatively mild conditions, and have great application potential in air purification. Some studies have attempted to enhance its catalytic oxidation ability by loading Pt on the CeO2 surface, reduce the reaction temperature, and improve catalyst activity. However, since Pt metal particles easily agglomerate during the reaction, the catalyst still has problems such as poor stability and high Pt metal dosage. Summary of the Invention

[0004] The present invention aims to provide a core-shell structured PtCu alloy three-way catalyst and its preparation method and application. The preparation process is simple, the obtained catalyst has excellent performance, a wide catalytic window, and good commercial application prospects.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The invention discloses a core-shell structured PtCu alloy three-way catalyst, which is composed of nano CeO2 as a carrier and a PtCu alloy loaded thereon.

[0006] Furthermore, the contents of Pt and Cu in the catalyst are both 0.05-1 wt%.

[0007] The preparation method of the core-shell structure PtCu alloy three-way catalyst comprises the following steps: (1) Add cerium nitrate hexahydrate to an ethylene glycol solution of a nitrogen-containing compound. After complete dissolution, transfer the mixed solution to a reactor for hydrothermal reaction. After the reaction is completed, filter, wash, dry, calcine, and grind into powder to obtain nano-CeO2. (2) The obtained nano-CeO2 was ultrasonically dispersed uniformly in water, and then tetraammine platinum nitrate and copper nitrate were added. The mixture was ultrasonically stirred for 2 hours, and then dried, calcined and heat-treated to obtain a CeO2-loaded core-shell structure PtCu alloy catalyst.

[0008] Furthermore, the nitrogen-containing compound in step (1) is any one of polyvinylpyrrole, urea or ammonium carbonate.

[0009] Furthermore, the mass ratio of the nitrogen-containing compound used in step (1) to cerium nitrate hexahydrate is (0.38-0.42):1.

[0010] Furthermore, the temperature of the hydrothermal reaction in step (1) is 160-180°C, and the time is 8 hours.

[0011] Furthermore, the calcination in step (1) is first carried out at 400°C for 2 h in an air atmosphere, and then at 500°C for 2 h in a hydrogen atmosphere.

[0012] Furthermore, the drying temperature in step (2) is 100°C and the drying time is 12 h.

[0013] Furthermore, the calcination in step (2) is first carried out at 400°C in an air atmosphere for 2 h, and then at 500°C in a hydrogen atmosphere for 2 h.

[0014] Furthermore, the heat treatment in step (2) is performed at 500° C. in an environment containing 0.1 vol % water vapor for 2 h.

[0015] The core-shell structure PtCu alloy three-way catalyst is effective for the reduction of nitrogen oxides (NO x ), propylene (C3H6) and carbon monoxide (CO) have excellent purification effects and can therefore be used for exhaust gas treatment in range-extended engines.

[0016] The beneficial effects of the present invention are: (1) Based on the traditional Pt / CeO2, the present invention introduces Cu as the second metal phase to form PtCu alloy nanoparticles, which can increase the contact area between the catalyst and the reactants, disperse and stabilize the Pt particles, increase the exposed atoms on their surface, and thus reduce the total loading of precious metals. At the same time, by regulating the electronic effect between the Pt and CeO2 carrier, the high activity and high stability of low-load Pt-based three-way catalysts can be achieved, solving the problems of low catalytic activity of traditional metal oxides and poor stability and high cost of supported Pt-based catalysts.

[0017] (2) The core-shell structure PtCu / CeO2 catalyst prepared by the present invention has excellent low-temperature three-way catalytic performance, and the raw materials used are cheap and easily available. The preparation method is fast and can be produced on a large scale, which has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a transmission electron microscope image of CeO2 nanospheres prepared in Example 1. It can be seen from the image that they are nanospheres.

[0019] Figure 2 Pt1Cu prepared in Example 4 0.5 Transmission electron microscopy image of the / CeO2 nanosphere catalyst. From the image, it can be seen that there are PtCu particles on its surface.

[0020] Figure 3 Pt1Cu prepared in Example 4 0.5 HAADF-STEM image and mapping (a) of the Pt / CeO2 nanosphere catalyst, along with EDX line profiles of Pt and Cu (b). The HAADF-STEM image shows higher contrast in the core region than in the shell region, indicating that the core region is enriched in Pt and the shell region is enriched in Cu. This is consistent with the elemental mapping information and confirms the core-shell structure of the PtCu particles. EDX line scans further confirm that the core of the PtCu particles is primarily enriched in Pt, while the shell is primarily enriched in Cu.

[0021] Figure 4 The X-ray diffraction patterns of the catalysts prepared in Examples 4 and 5 and Comparative Examples 1 and 2 show no diffraction peaks of the alloy particles, indicating that the alloy particles in the core-shell structure are small and uniformly dispersed.

[0022] Figure 5 The conversion efficiency of CeO2 nanospheres prepared in Example 1 and the catalysts prepared in Examples 4, 5, and Comparative Examples 1 and 2 in removing carbon monoxide, propylene, and nitrogen oxides is shown in Figure 1, where a is the conversion rate curve of carbon monoxide, b is the conversion rate curve of propylene, and c is the conversion rate curve of nitrogen oxides. x Cu y / CeO2 catalyst has a high conversion efficiency in removing nitrogen oxides, propylene and carbon monoxide, among which Pt1Cu 0.5 / CeO2 nanosphere catalyst has the best performance.

[0023] Figure 6 Pt1Cu prepared in Example 4 0.5 / CeO2 nanosphere catalyst stability test results. As can be seen from the figure, Pt1Cu 0.5 / CeO2 nanosphere catalysts showed excellent catalytic stability in three-way catalysis for 50 h. DETAILED DESCRIPTION

[0024] A core-shell structure PtCu alloy three-way catalyst, the preparation method of which comprises the following steps: (1) Cerium nitrate hexahydrate was added to an ethylene glycol solution of a nitrogen-containing compound. After complete dissolution, the mixed solution was transferred to a reactor and subjected to a hydrothermal reaction at 160-180 °C for 8 h. After the reaction, the product was filtered and washed, dried, and then calcined at 400 °C for 2 h in an air atmosphere, and then calcined at 500 °C for 2 h in a hydrogen atmosphere, and then ground into powder to obtain a CeO2 nanosphere carrier. (2) The obtained CeO2 nanosphere carrier was ultrasonically dispersed uniformly in water, and then tetraammine platinum nitrate and copper nitrate were added, and ultrasonic stirring was continued for 2 h. After drying at 100 °C for 12 h, it was first calcined at 400 °C in an air atmosphere for 1 h, then calcined at 500 °C in a hydrogen atmosphere for 2 h, and then heat-treated at 500 °C in an environment containing 0.1 vol% water vapor for 2 h to obtain a CeO2-supported core-shell structure PtCu alloy catalyst, which was recorded as Pt x Cu y / CeO2, where x and y are the mass percentages (%) of Pt and Cu in the catalyst, respectively, and the values ​​range from 0.05 to 1.

[0025] The nitrogen-containing compound is any one of polyvinylpyrrole, urea or ammonium carbonate. The mass ratio of the nitrogen-containing compound to cerium nitrate hexahydrate is (0.38-0.42):1.

[0026] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] Example 1 Preparation of CeO2 Nanospheres 0.5 g of cerium nitrate hexahydrate was dissolved in 75 ml of ethylene glycol solution containing 0.2 g of polyvinylpyrrole. After complete dissolution, the mixed solution was transferred to a 100 ml reactor and tightened. The reactor was placed in a 160 °C oven for 8 h. The product was filtered and washed three times with distilled water. It was then placed in an 80 °C oven for 12 h. The dried sample was then placed in a tube furnace and heated to 400 °C at a rate of 10 °C / min under air atmosphere. The temperature was kept at this temperature for 2 h. Then, the atmosphere was replaced with hydrogen and calcined at 500 °C for 2 h. The resulting product was then ground into powder to obtain CeO2 nanospheres.

[0029] Example 2 Preparation of CeO2 Nanoblocks The 75 ml ethylene glycol solution containing 0.2 g polyvinylpyrrole in Example 1 was replaced with 75 ml aqueous solution containing 0.2 g urea. Other operations were the same as in Example 1 to obtain porous CeO2 nanoblocks.

[0030] Example 3 Preparation of CeO2 Nanosheets The 75 ml ethylene glycol solution containing 0.2 g polyvinylpyrrole in Example 1 was replaced with 75 ml ethylene glycol solution containing 1.25 g ammonium carbonate. Other operations were the same as in Example 1 to obtain CeO2 nanosheets.

[0031] Example 4Pt1Cu 0.5 Preparation of CeO2 nanospheres 2 g of CeO2 nanospheres prepared in Example 1 were weighed and placed in a 50 mL beaker. 15 mL of distilled water was added and the CeO2 was uniformly dispersed in the water by ultrasound. Then 0.04 g of tetraammine platinum nitrate and 0.03 g of copper nitrate were added and ultrasonic stirring was continued for 2 h. The mixture was then placed in an oven at 100 °C and dried for 12 h. The mixture was then calcined at 400 °C in a flowing air atmosphere for 1 h and then at 500 °C in a hydrogen atmosphere for 2 h. Finally, the mixture was heat treated at 500 °C in an environment containing 0.1 vol% water vapor for 2 h to obtain a core-shell structure alloy catalyst Pt1Cu 0.5 / CeO2.

[0032] Example 5 Preparation of Pt1Cu1 / CeO2 Nanospheres 2 g of CeO2 nanospheres prepared in Example 1 were weighed and placed in a 50 mL beaker. 15 mL of distilled water was added and the CeO2 was evenly dispersed in the water by ultrasound. Then 0.04 g of tetraammine platinum nitrate and 0.06 g of copper nitrate were added and ultrasonic stirring was continued for 2 h. The mixture was then placed in a 100 °C oven and dried for 12 h. The mixture was then calcined at 400 °C in a flowing air atmosphere for 1 h and then at 500 °C in a hydrogen atmosphere for 2 h. Finally, the mixture was heat treated at 500 °C in an environment containing 0.1 vol% water vapor for 2 h to obtain a core-shell structure alloy catalyst Pt1Cu1 / CeO2.

[0033] Example 6Pt1Cu 0.5 Preparation of CeO2 nanoblocks The CeO2 nanospheres used in Example 4 were replaced with the porous CeO2 nanoblocks prepared in Example 2. Other operations were the same as in Example 4 to obtain a core-shell structure alloy catalyst Pt1Cu 0.5 / CeO2-N.

[0034] Example 7Pt1Cu 0.5 Preparation of CeO2 nanosheets The CeO2 nanospheres used in Example 4 were replaced with CeO2 nanosheets prepared in Example 3, and other operations were the same as in Example 4 to obtain a core-shell structure alloy catalyst Pt1Cu 0.5 / CeO2-S.

[0035] Comparative Example 1 Preparation of Pt1 / CeO2 Nanospheres 2 g of CeO2 nanospheres prepared in Example 1 were weighed and placed in a 50 mL beaker. 15 mL of distilled water was added and the CeO2 was evenly dispersed in the water by ultrasound. Then 0.04 g of tetraammineplatinum nitrate was added and ultrasonic stirring was continued for 2 h. The mixture was then placed in an oven at 100 °C and dried for 12 h. The mixture was then calcined at 400 °C in a flowing air atmosphere for 1 h and then at 500 °C in a hydrogen atmosphere for 2 h. Finally, the mixture was heat treated at 500 °C in an environment containing 0.1 vol% water vapor for 2 h to obtain a core-shell structure alloy catalyst Pt1 / CeO2.

[0036] Comparative Example 2Cu 0.5 Preparation of CeO2 nanospheres 2 g of CeO2 nanospheres prepared in Example 1 were weighed and placed in a 50 mL beaker. 15 mL of distilled water was added and ultrasonicated to uniformly disperse CeO2 in the water. 0.03 g of copper nitrate was then added and ultrasonically stirred for 2 h. The mixture was then placed in an oven at 100 °C and dried for 12 h. The mixture was then calcined at 400 °C in a flowing air atmosphere for 1 h and then at 500 °C in a hydrogen atmosphere for 2 h. Finally, the mixture was heat treated at 500 °C in an environment containing 0.1 vol% water vapor for 2 h to obtain a core-shell structure alloy catalyst Cu 0.5 / CeO2.

[0037] Application Examples The catalytic performance of different catalysts prepared in the examples and comparative examples in removing carbon monoxide, propylene and nitrogen oxides (NO x conversion rate, C3H6 conversion rate, CO conversion rate and catalyst stability), the specific operation is as follows: The catalytic reaction was carried out in a quartz reactor with a fixed bed and continuous gas flow, with a diameter of 10 mm. The catalyst particle size was 40-60 mesh and the dosage was 0.5 g. The gas space velocity during the reaction was 100,000 h -1 The reaction gas concentrations were 500 ppm NO, 1000 ppm C3H6, 1 vol% CO, 1.25 vol% O2, and the balance gas was N2. The catalytic reaction was carried out at 160-400 °C, and the activity data were collected after reaction A stabilized. NO x , CO were collected by German MRU flue gas analyzer, and C3H6 were collected by Shimadzu GC-2014c.

[0038] Table 1 Comparison of catalyst activity

[0039] The experimental results show that: Pt1Cu 0.5 The lowest temperatures for the conversion of CO, C3H6 and NO to 90% for Pt1Cu / CeO2 nanospheres are 160 ℃, 190 ℃ and 220 ℃, respectively. 0.5 / CeO2 nanospheres can achieve higher triple-effect reaction performance at lower temperatures. 0.5 The overall purification effect of the / CeO2 nanosphere catalyst is better than that of the currently reported three-way catalyst.

[0040] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a core-shell structured PtCu alloy three-way catalyst, characterized by: The following steps are involved: (1) Add cerium nitrate hexahydrate to an ethylene glycol solution of a nitrogen-containing compound, and after it is completely dissolved, transfer it to a reactor for hydrothermal reaction. After the reaction is completed, filter and wash the product, dry it, calcine it, and grind it into powder to obtain nano-CeO2; (2) The obtained nano-CeO2 was ultrasonically dispersed uniformly in water, and then tetraammine platinum nitrate and copper nitrate were added and ultrasonically stirred for 2 hours. Then, the catalyst was dried, calcined and heat-treated to obtain a CeO2-loaded core-shell structure PtCu alloy catalyst.

2. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1, wherein: The mass ratio of the nitrogen-containing compound used in step (1) to cerium nitrate hexahydrate is (0.38-0.42):

1.

3. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1 or 2, wherein: The nitrogen-containing compound is any one of polyvinylpyrrole, urea or ammonium carbonate.

4. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1, wherein: The temperature of the hydrothermal reaction in step (1) is 160-180°C and the time is 8 hours.

5. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1, wherein: The calcination in step (1) is first carried out at 400°C for 2 h in an air atmosphere, and then at 500°C for 2 h in a hydrogen atmosphere.

6. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1, wherein: The calcination in step (2) is first carried out at 400°C in an air atmosphere for 2 h, and then at 500°C in a hydrogen atmosphere for 2 h.

7. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1, wherein: The heat treatment in step (2) is carried out at 500°C in an environment containing 0.1 vol% water vapor for 2 h.

8. The method for preparing a core-shell structured PtCu alloy three-way catalyst according to claim 1, wherein: The contents of Pt and Cu in the obtained catalyst are both 0.05-1 wt%.

9. A core-shell structured PtCu alloy three-way catalyst prepared by the method of claim 1.

10. Use of the core-shell structured PtCu alloy three-way catalyst according to claim 9 in exhaust gas treatment of a range-extended engine.

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