Segmented-coating three-way catalyst combined by noble metal and cerium-zirconium solid solution and preparation method of segmented-coating three-way catalyst

Abstract

The invention provides a three-way catalyst formed by combining precious metal and a cerium-zirconium solid solution through segmented coating and a preparation method of the three-way catalyst. The three-way catalyst comprises a honeycomb ceramic carrier, the oxidation type catalyst and the reduction type catalyst are loaded on the honeycomb ceramic carrier in a sectional manner; the oxidation type catalyst is a platinum-neodymium doped cerium-zirconium solid solution; the reduction type catalyst is a rhodium-praseodymium doped cerium-zirconium solid solution; the mass ratio of the oxidation type catalyst to the reduction type catalyst is 9: (0.95-1.05). The combination of the noble metal and the cerium-zirconium solid solution which are coated in sections is used as an active component of the three-way catalyst for tail gas purification of gasoline cars and hybrid vehicles, and the activity of the combined three-way catalyst is basically kept unchanged before and after hydrothermal aging.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a three-way catalyst composed of a segmented-coated noble metal and a cerium-zirconium solid solution, and a preparation method thereof. Background Art

[0002] Automobile exhaust is a mixture composed of unburned carbon monoxide, hydrocarbons, and nitrogen oxides, which has become the main source of air pollution and has had a non-negligible impact on the environment.

[0003] In the prior art, through the action of a catalyst, CO, HC, and NO X are respectively oxidized and reduced to carbon dioxide (CO2), nitrogen (N2), and water vapor (H2O) that are harmless to human health. During the conversion process, if the catalyst can simultaneously catalyze and purify the three harmful substances of CO, HC, and NO x such a catalyst is called a three-way catalyst.

[0004] For the currently commonly used three-way catalysts, their active components are usually mainly palladium and rhodium, and the active components of alkane oxidation catalysts are mainly platinum. Traditional catalysts directly add noble metal solutions to the coating slurry, resulting in uneven distribution of noble metals, and they are prone to sintering at high temperatures, showing agglomeration of noble metals, which will cause a decrease in the utilization rate of noble metals and a decline in activity. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a three-way catalyst composed of a segmented-coated noble metal and a cerium-zirconium solid solution, and a preparation method thereof. In this three-way catalyst, the oxidation catalyst first contacts the automobile exhaust, releases oxygen, and promotes the oxidation reaction of carbon monoxide and hydrocarbons; the reduction catalyst then contacts the exhaust gas treated by the oxidation catalyst. The reduction catalyst can quickly store oxygen and assist the reduction reaction of nitrogen oxides; the activity of this oxidation-reduction segmented combined catalyst remains basically unchanged before and after hydrothermal aging, and it is expected to be widely used in the field of automobile exhaust.

[0006] The present invention provides a three-way catalyst composed of a segmented-coated noble metal and a cerium-zirconium solid solution, including a honeycomb ceramic carrier;

[0007] The oxidation catalyst and the reduction catalyst that are segmentally loaded on the honeycomb ceramic carrier;

[0008] The oxidation catalyst is a cerium-zirconium solid solution doped with platinum and neodymium;

[0009] The reduction catalyst is a cerium-zirconium solid solution doped with rhodium and praseodymium;

[0010] The mass ratio of the oxidation catalyst to the reduction catalyst is 9:(0.95 - 1.05).

[0011] The present invention proposes a construction strategy for a combined three-way catalyst, which is particularly suitable for the synergistic application of oxidation-type and reduction-type catalysts. Platinum and palladium are loaded on a neodymium-doped cerium-zirconium solid solution with excellent oxygen evolution performance to ensure the rapid release of oxygen when the oxygen content in the exhaust gas is low, promoting the oxidation reactions of carbon monoxide and hydrocarbons; while rhodium is loaded on a praseodymium-doped cerium-zirconium solid solution with excellent oxygen storage performance to quickly store oxygen when the oxygen content in the exhaust gas is high, facilitating the reduction reaction of nitrogen oxides. The oxidation-type catalyst of platinum-neodymium-doped cerium-zirconium solid solution contacts the exhaust gas first, and the reduction-type catalyst of rhodium-praseodymium-doped cerium-zirconium solid solution contacts the exhaust gas later for sectional coating. The obtained oxidation-type-reduction-type sectional combined catalyst basically maintains its activity before and after hydrothermal aging, which is of great significance for reducing air pollution and protecting the ecological environment.

[0012] In the present invention, the mass ratio of the oxidation-type catalyst to the reduction-type catalyst is 9:(0.95 - 1.05), preferably 9:1. The coating densities of the oxidation-type catalyst and the reduction-type catalyst are basically the same. In the present invention, the coating lengths of the oxidation-type catalyst and the reduction-type catalyst on the honeycomb ceramic carrier are positively correlated with their mass ratio.

[0013] In the present invention, the platinum content in the platinum-neodymium-doped cerium-zirconium solid solution is 1.25 - 1.35 wt%; specifically, the platinum content is 1.25 wt%, 1.26 wt%, 1.27 wt%, 1.28 wt%, 1.29 wt%, 1.30 wt%, 1.31 wt%, 1.32 wt%, 1.33 wt%, 1.34 wt% or 1.35 wt%. Preferably, the platinum content in the platinum-neodymium-doped cerium-zirconium solid solution is 1.3 wt%.

[0014] In the present invention, the rhodium content in the rhodium-praseodymium-doped cerium-zirconium solid solution is 0.65 - 0.75 wt%; specifically, the rhodium content is 0.65 wt%, 0.66 wt%, 0.67 wt%, 0.68 wt%, 0.69 wt%, 0.70 wt%, 0.71 wt%, 0.72 wt%, 0.73 wt%, 0.74 wt% or 0.75 wt%. Preferably, the rhodium content in the rhodium-praseodymium-doped cerium-zirconium solid solution is 0.7 wt%.

[0015] In the present invention, the molar ratio of neodymium, cerium and zirconium in the platinum-neodymium-doped cerium-zirconium solid solution is (1.8 - 2.1):18:(4.5 - 5.5). Preferably, the molar ratio of neodymium, cerium and zirconium in the platinum-neodymium-doped cerium-zirconium solid solution is 2:18:5.

[0016] In the rhodium-praseodymium doped cerium zirconium solid solution of the present invention, the molar ratio of praseodymium, cerium and zirconium is (1.8 - 2.1):18:(4.5 - 5.5). Preferably, the molar ratio of praseodymium, cerium and zirconium in the rhodium-praseodymium doped cerium zirconium solid solution is 2:18:5.

[0017] The present invention provides a preparation method of a three-way catalyst combined with a segmented coated noble metal and a cerium zirconium solid solution, comprising the following steps:

[0018] Mix an aqueous solution of a mixture of NdCl3·6H2O, CeCl3·7H2O and ZrOCl2·8H2O with a surfactant, add ammonia water, adjust the pH value to 11 - 12, stir for 55 - 65 min, perform crystallization treatment to obtain a precipitate; wash and dry the precipitate, and calcine to obtain a neodymium doped cerium zirconium solid solution;

[0019] Mix an aqueous solution of a mixture of PrCl3·6H2O, CeCl3·7H2O and ZrOCl2·8H2O with a surfactant, add ammonia water, adjust the pH value to 11 - 12, stir for 55 - 65 min, perform crystallization treatment to obtain a precipitate; wash and dry the precipitate, and calcine to obtain a praseodymium doped cerium zirconium solid solution;

[0020] Mix water, the neodymium doped cerium zirconium solid solution and chloroplatinic acid, heat until evaporated to dryness, calcine the obtained precipitate to obtain a platinum-neodymium doped cerium zirconium solid solution; mix water, the praseodymium doped cerium zirconium solid solution and rhodium chloride solution, heat until evaporated to dryness, calcine the obtained precipitate to obtain a rhodium-praseodymium doped cerium zirconium solid solution;

[0021] Coat the platinum-neodymium doped cerium zirconium solid solution on one end of a honeycomb ceramic carrier, and coat the rhodium-praseodymium doped cerium zirconium solid solution on the other end of the honeycomb ceramic carrier, and the mass ratio of the platinum-neodymium doped cerium zirconium solid solution to the rhodium-praseodymium doped cerium zirconium solid solution is 9:(0.95 - 1.05) to obtain a three-way catalyst combined with a segmented coated noble metal and a cerium zirconium solid solution.

[0022] In the present invention, the surfactant is an aqueous solution of cetyltrimethylammonium bromide with a concentration of 0.1 mol / L. The temperature of the crystallization treatment is 85 - 95 °C and the time is 6.5 - 7.5 days; in a specific embodiment, the temperature of the crystallization treatment is 90 °C and the time is 7 days. The calcination temperature is 480 - 520 °C and the calcination time is 2.5 - 3.5 h; in a specific embodiment, the calcination temperature is 500 °C and the time is 3 h.

[0023] The present invention provides a three-way catalyst composed of a segmented coating of noble metal and cerium-zirconium solid solution, including a honeycomb ceramic carrier; an oxidation catalyst and a reduction catalyst that are segmentally loaded on the honeycomb ceramic carrier; the oxidation catalyst is a cerium-zirconium solid solution doped with platinum and neodymium; the reduction catalyst is a cerium-zirconium solid solution doped with rhodium and praseodymium; the mass ratio of the oxidation catalyst to the reduction catalyst is 9:(0.95-1.05). The present invention uses the above combination of segmented coating of noble metal and cerium-zirconium solid solution as the active component of the three-way catalyst for purifying the exhaust gas of gasoline vehicles and hybrid vehicles, and the activity of this combined three-way catalyst remains basically unchanged before and after hydrothermal aging. Description of the Drawings

[0024] Figure 1 is the oxygen storage performance of cerium-zirconium solid solution doped with different elements before and after hydrothermal aging in Example 1;

[0025] Figure 2 is the oxygen release performance of cerium-zirconium solid solution doped with different elements before and after hydrothermal aging in Example 1;

[0026] Figure 3 is the activity of the oxidation-reduction combined catalyst prepared in Example 1 before and after hydrothermal aging. Detailed Description of the Invention

[0027] To further illustrate the present invention, the following describes in detail a three-way catalyst composed of a segmented coating of noble metal and cerium-zirconium solid solution provided by the present invention and its preparation method in combination with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0028] Example 1

[0029] Prepare 100 mL of 0.1 M cetyltrimethylammonium bromide solution and 80 mL of a mixed aqueous solution containing 0.008 M NdCl3·6H2O, 0.072 M CeCl3·7H2O, and 0.02 M ZrOCl2·8H2O. While continuously stirring, slowly drop the CTAB aqueous solution into the mixed solution containing cerium and zirconium ions, and continue stirring for 15 minutes to ensure thorough mixing. Slowly add concentrated ammonia water dropwise to the mixed solution to adjust the pH value to 11.5. Maintain the stirring state and continue stirring for 60 minutes. Transfer the obtained solution to a reaction kettle and perform crystallization treatment at 90°C for 7 days. After the crystallization is completed, filter the precipitate, wash it with water, and dry it. Calcinate the dried product at 500°C for 3 hours to obtain neodymium-doped cerium-zirconium solid solution.

[0030] Prepare 100 mL of 0.1 M aqueous CTAB solution and 80 mL of a mixed aqueous solution containing 0.008 M PrCl3·6H2O, 0.072 M CeCl3·7H2O, and 0.02 M ZrOCl2·8H2O. While continuously stirring, slowly add the CTAB aqueous solution dropwise to the mixed solution containing cerium and zirconium ions, and continue stirring for 15 minutes to ensure thorough mixing. Add concentrated ammonia water dropwise to the mixed solution to adjust the pH value to 11.5. Maintain the stirring state and continue stirring for 60 minutes. Transfer the resulting solution to a reaction kettle and crystallize it at 90 °C for 7 days. After crystallization, filter the precipitate, wash it with water, and dry it. Calcinate the dried product at 500 °C for 3 hours to obtain praseodymium-doped cerium zirconium solid solution.

[0031] Take 226.5 mL of water, add 6 g of the above-mentioned neodymium-doped cerium zirconium solid solution and 87.7 mg of chloroplatinic acid to it, and mix well. Heat and stir the mixed solution at 80 °C until it is evaporated to dryness. Place the resulting precipitate in a furnace and calcine it at 500 °C for 1 hour to obtain platinum-neodymium-doped cerium zirconium solid solution.

[0032] Figure 1 The oxygen storage performance of cerium zirconium solid solution doped with different elements before and after hydrothermal aging; the oxygen storage capacity of the cerium zirconium solid solution doped with the doping element is the area under the curve of the cerium zirconium solid solution containing the doping element minus the area under the curve of zirconia; (a) is the oxygen storage performance curve before hydrothermal aging, and (b) is the oxygen storage performance curve after hydrothermal aging.

[0033] Take 114.4 mL of water, add 8.1 g of praseodymium-doped cerium zirconium solid solution and 19.6 μL of 2 M rhodium chloride solution to it, and mix well. Heat and stir the mixed solution at 80 °C until it is evaporated to dryness. Place the resulting precipitate in a furnace and calcine it at 500 °C for 1 hour to obtain rhodium-praseodymium-doped cerium zirconium solid solution.

[0034] Figure 2 The oxygen release performance of cerium zirconium solid solution doped with different elements before and after hydrothermal aging in Example 1; the oxygen release amount of the cerium zirconium solid solution doped with the doping element is the area above the curve of the cerium zirconium solid solution containing the doping element minus the area above the curve of zirconia; (a) is the oxygen release performance curve before hydrothermal aging, and (b) is the oxygen release performance curve after hydrothermal aging.

[0035] Two catalysts, namely platinum-neodymium doped cerium-zirconium solid solution and rhodium-praseodymium doped cerium-zirconium solid solution, are respectively coated on a honeycomb ceramic carrier. One end of the honeycomb ceramic carrier is impregnated with a load of an oxidation catalyst, and the other end is impregnated with a load of a reduction catalyst. The coating length ratio of the oxidation catalyst to the reduction catalyst is 9:1. The oxidation catalyst is placed at the end of the reactor (an 8-mm inner diameter quartz tube) close to the reaction gas inlet, and the reduction catalyst is placed at the end close to the outlet to form a combined catalyst. A reaction gas with the composition of [C3H8]=300 ppm, [C3H6]=800 ppm, [H2]=0.2%, [CO]=3.5%, [NO]=800 ppm, [O2]=the air-fuel ratio is 1, [CO2]=10%, [H2O]=10%, and N2 as the balance gas and a space velocity of 50000 h -1 is passed through from the inlet end to the outlet end for the catalyst activity test. The catalyst aging conditions are 950 °C, a time of 20 h, [H2O]=10%, air as the balance gas, and a space velocity of 50000 h -1 .

[0036] Figure 3 It is the activity curve graph of the combined catalyst prepared in Example 1 before and after hydrothermal aging. As can be seen from Figure 3 it: The activity of the combined catalyst basically remains unchanged before and after hydrothermal aging, and it has good stability.

[0037] As can be seen from the above examples, the present invention provides a three-way catalyst combined with a noble metal and a cerium-zirconium solid solution with segmented coating, including a honeycomb ceramic carrier; an oxidation catalyst and a reduction catalyst that are segmentally loaded on the honeycomb ceramic carrier; the oxidation catalyst is a platinum-neodymium doped cerium-zirconium solid solution; the reduction catalyst is a rhodium-praseodymium doped cerium-zirconium solid solution; the mass ratio of the oxidation catalyst to the reduction catalyst is 9:(0.95-1.05). The activity of the three-way catalyst basically remains unchanged before and after hydrothermal aging.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A three-way catalyst composed of a segmented coated noble metal and cerium zirconium solid solution, characterized in that, It includes a honeycomb ceramic carrier; An oxidation catalyst and a reduction catalyst which are segmentally loaded on the honeycomb ceramic carrier; The oxidation catalyst is a platinum-neodymium doped cerium zirconium solid solution; The reduction catalyst is a rhodium-praseodymium doped cerium zirconium solid solution; The mass ratio of the oxidation catalyst to the reduction catalyst is 9:(0.95 - 1.05).

2. The three-way catalyst of the combination of the segmented-coated noble metal and cerium-zirconium solid solution according to claim 1, characterized in that, The platinum content in the platinum-neodymium doped cerium zirconium solid solution is 1.25 - 1.35 wt%.

3. The three-way catalyst of the combination of the segmented-coated noble metal and cerium-zirconium solid solution according to claim 1, characterized in that, The platinum content in the platinum-neodymium doped cerium zirconium solid solution is 1.3 wt%.

4. The three-way catalyst of the combination of the segmented-coated noble metal and cerium-zirconium solid solution according to claim 1, characterized in that, The rhodium content in the rhodium-praseodymium doped cerium zirconium solid solution is 0.65 - 0.75 wt%.

5. The three-way catalyst of the segmented-coated noble metal and cerium-zirconium solid solution combination according to claim 1, characterized in that The rhodium content in the rhodium-praseodymium doped cerium zirconium solid solution is 0.7 wt%.

6. The three-way catalyst of the segmented-coated noble metal and cerium-zirconium solid solution combination according to claim 1, characterized in that The molar ratio of neodymium, cerium and zirconium in the platinum-neodymium doped cerium zirconium solid solution is (1.8 - 2.1):18:(4.5 - 5.5).

7. The three-way catalyst of the segmented coated combination of noble metal and cerium-zirconium solid solution according to claim 1, characterized in that, The molar ratio of neodymium, cerium and zirconium in the platinum-neodymium doped cerium zirconium solid solution is 2:18:

5.

8. The three-way catalyst of the segmented coated noble metal and cerium zirconium solid solution combination according to claim 1, characterized in that, The molar ratio of praseodymium, cerium and zirconium in the rhodium-praseodymium doped cerium zirconium solid solution is (1.8 - 2.1):18:(4.5 - 5.5).

9. The three-way catalyst of the combination of the segmented-coated noble metal and cerium-zirconium solid solution according to claim 1, characterized in that, The molar ratio of praseodymium, cerium and zirconium in the rhodium-praseodymium doped cerium zirconium solid solution is 2:18:

5.

10. A preparation method of a three-way catalyst combined with a segmented coated noble metal and a cerium zirconium solid solution, comprising the following steps: Mix an aqueous solution mixture of NdCl3·6H2O, CeCl3·7H2O and ZrOCl2·8H2O with a surfactant, add ammonia water, adjust the pH value to 11 - 12, stir for 55 - 65 min, perform crystallization treatment to obtain a precipitate; wash and dry the precipitate, and calcine it to obtain a neodymium doped cerium zirconium solid solution; Mix an aqueous solution mixture of PrCl3·6H2O, CeCl3·7H2O and ZrOCl2·8H2O with a surfactant, add ammonia water, adjust the pH value to 11 - 12, stir for 55 - 65 min, perform crystallization treatment to obtain a precipitate; wash and dry the precipitate, and calcine it to obtain a praseodymium doped cerium zirconium solid solution; Mix water, the neodymium doped cerium zirconium solid solution and chloroplatinic acid, heat until it is evaporated to dryness, calcine the obtained precipitate to obtain a platinum-neodymium doped cerium zirconium solid solution; mix water, the praseodymium doped cerium zirconium solid solution and rhodium chloride solution, heat until it is evaporated to dryness, calcine the obtained precipitate to obtain a rhodium-praseodymium doped cerium zirconium solid solution; Coat the platinum-neodymium doped cerium zirconium solid solution on one end of the honeycomb ceramic carrier, and coat the rhodium-praseodymium doped cerium zirconium solid solution on the other end of the honeycomb ceramic carrier, and the mass ratio of the platinum-neodymium doped cerium zirconium solid solution to the rhodium-praseodymium doped cerium zirconium solid solution is 9:(0.95 - 1.05), to obtain a three-way catalyst combined with a segmented coated noble metal and a cerium zirconium solid solution.

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