Patent Application
20230256418
The present invention relates to the application of catalysis technology and the environmental protection field related to air pollution control, particularly to a three-way catalyst having low NH3 formation and preparation method therefor.
For vehicles with equivalence ratio combustion, three-way catalyst (TWC) is usually installed on the exhaust pipe to purify Hydrocarbon (HC), nitrogen oxides (NOx) and carbon monoxide (CO) in the exhaust gas. The purpose of installing vehicles exhaust purification catalyst is to convert three main pollutants, such as CO, HC and NOx, into harmless substances such as CO2, N2 and H2O, while avoiding the generation of new harmful substances. When the vehicle is running under different working conditions, the concentration, flow rate, temperature and air-fuel ratio of pollutants in the exhaust gas fluctuate greatly, and TWC usually has multiple main reactions and side reactions. Part of the main reaction and side reaction (main reaction: CO+H2O→CO2+H2, HC+H2O → CO2+H2; Side reaction: NO+H2→NH3+H2O, CO+NO+H2→NH3+H2O) will lead to the formation of new pollutant NH3 on TWC. NH3 is a colorless, irritating and foul-smelling gas, which is harmful to human skin, eyes and respiratory organs. GB17691-2018 “Emission Limits and Measurement Methods of Pollutants from Heavy Diesel Vehicles (China’s Sixth Stage)” stipulates that NH3 emitted from vehicles exhaust should not exceed 10 ppm.
The literature (Applied Thermal Engineering 130 (2018) 1363-1372) reported the NH3 emission of a heavy-duty natural gas engine (equivalence ratio combustion) equipped with TWC. In WHTC (World Harmonized Transient Cycle) test, the NH3 emission exceeded 100 ppm, with the highest exceeding 450 ppm; under more than 80% of the working conditions. The steady state 13 operating point test shows that in 11 of the 13 operating point conditions, the NH3emissionexceeds 100 ppm, with the highest exceeding 300 ppm. The literature (Atmospheric Environment 97 (2014) 43-53) compares and verifies seven light gasoline vehicles equipped with TWC (equivalence ratio combustion). The test results of NEDC (New European Driving Cycle, New European Cycle Test) show that the highest NH3 emission is 108 ppm, and the lowest NH3 emission is 6 ppm. The NH3 emission of different vehicles is quite different, which is mainly related to vehicle emission control system and after-treatment catalyst. Literature (Science of the Total Environment 616-617 (2018) 774-784) compares the NH3 emissions of diesel vehicles with DOC+DPF (lean combustion) and natural gas vehicles with TWC (equivalence ratio combustion) in different test cycles. The results show that the NH3 emissions of diesel vehicles are all lower than 10 mg/km, but the NH3 emissions of natural gas vehicles are 13-24 mg/km. The above literature shows that it is a common phenomenon that the equivalent combustion car with TWC has higher NH3 emission. It is necessary to solve the problem that the equivalent combustion car with TWC has higher NH3 emission than that with TWC by installing other catalysts to purify NH3 or by reducing the amount of TWC NH3generated (improving the selectivity of TWC N2). Chinese patent (CN109225316 A) introduces a kind of TWC+AOC (ammonia oxidation catalyst, AOC for short), which can purify the byproduct NH3 generated by TWC through AOC. TWC+AOC can effectively purify CO, HC and NOx, and at the same time reduce NH3 emission to below 10 ppm. This technical route is widely used in the national six heavy-duty natural gas vehicles in China. Through AOC, the problem of NH3 emission exceeding the standard of equivalent combustion vehicle with TWC can be solved. However, after adding AOC, the calibration difficulty of engine after-treatment system increases, the volume of exhaust purification catalytic converter increases and the cost increases to a certain extent.
The purpose of the present invention is to provide a three-way catalyst with low NH3 formation, aiming at the problems in the prior art that the excess NH3 emission of equivalent combustion vehicles equipped with TWC can be solved by AOC, but after the AOC is added, the calibration difficulty of the engine after-treatment system increases, the volume of the exhaust purification catalytic converter increases and the cost increases to a certain extent. In this catalyst, by adding ruthenium metal or ruthenium oxide into TWC, the N2 selectivity of TWC is improved, and the NH3formation is reduced. This scheme is a new and more effective technical scheme to solve the problem of NH3 emission exceeding the standard.
In order to achieve the above object, the technical scheme adopted by the present invention is:
A three-way catalyst having low NH3 formation, which consists of a carrier and a coating material;
The three-way catalyst having low NH3 formation of the present invention improves the N2 selectivity of TWC by adding metallic ruthenium (Ru) and/or ruthenium oxide into the coating material, and inhibits the NH3formation of TWC byproduct. The NH3formation is reduced from the source, and part of the generated NH3 is decomposed into N2 and H2 on Ru catalyst, which greatly reduces the NH3 formation, reduces the volume and cost of catalytic converter, and more effectively solves the problem of NH3 emission exceeding the standard. Among them, platinum, palladium and rhodium are commonly used precious metals of three-way catalysts.
As a preferred scheme of the present invention, the content of Ru is 1 ~ 100 g/ft3 in terms of simple substance.
When the content of ruthenium is in the range of 1 ~ 100 g/ft3, the NH3formation is all lower than 10 ppm, and the NH3formation is very low, showing high N2 selectivity.
As a preferred scheme of the present invention, the content of Ru is 5 ~ 40 g/ft3 in terms of simple substance.
As the content of ruthenium increases, the NH3formation gradually decreases. When the content of ruthenium is too high, the production cost increases. In the above range, it shows high N2 selectivity and reduces the cost.
When the content of ruthenium is not 0, it can all play a role in reducing the NH3 formation. With the increase of ruthenium content, the NH3formation decreases. The ruthenium content is 0.05, 0.1, 0.2, 0.3, 0.5, 0.8, 1, 2, 2.5, 3, 5, 10, 20, 25, 30, 40, 50, etc., and the unit is g/ft3.
As a preferred scheme of the present invention, the Ru composition contains metallic ruthenium and/or ruthenium oxide.
The content and proportion of the second precious metal active component, the coating loading amount, etc., are the conventional dosage of commercial TWC.
As a preferred scheme of the present invention, the catalytic material comprises an oxygen storage material and an alumina material.
As a preferred scheme of the present invention, the oxygen storage material comprises CeO2, CeO2—ZrO2, CeO2—ZrO2—Y2O3, CeO2—ZrO2—La2O3—Y2O3, CeO2—ZrO2—La2O3—Pr2O3, CeO2—ZrO2—La2O3—La2O3.
As a preferred scheme of the present invention, the alumina material comprises pure alumina; At least one of modified alumina such as La and Ce.
As a preferred scheme of the present invention, the carrier is a ceramic carrier or a metal carrier. The ceramic carrier is a cordierite ceramic carrier.
The present invention also provides a preparation method of the three-way catalyst having low NH3 formation as described above, comprising the following steps,
S1, preparation of coating material;
loading the salt solution of the first precious metal active component and the salt solution of the second precious metal active component onto a catalytic material; Drying and calcining to obtain a coating material;
S2, preparation of coating material slurry;
mixing the coating material, water, and binder, and ball milling slurry is obtained to obtain coating material slurry;
S3, prepares three-way catalyst;
Coating the coating material slurry on the carrier, and drying and calcining to obtain the three-way catalyst.
The preparation method of the invention is that Ru and other precious metal active components are loaded on oxygen storage materials and alumina together, then dried, calcined and solidified, and finally slurry is coated on cordierite ceramic carriers or metal carriers.
To sum up, due to the adoption of the above-mentioned technical scheme, the beneficial effects of the present invention are:
1. The three-way catalyst having low NH3 formation of the present invention by adding metallic ruthenium, in which the content of Ru is 1-100 g/ft3, more preferably 5-40 g/ft3improves the N2 selectivity of TWC. Compared with the existing three-way catalyst, it can achieve a high-efficiency purification equivalence ratio of CO/HC/NOx in the combustion of vehicles exhaust, and at the same time, the amount of NH3 generated is also greatly reduced, avoiding the use of AOC and other methods to remove the NH3formation, reducing the volume of the catalytic converter.
2. The preparation method of the three-way catalyst adopted by the invention avoids the mixed preparation of multiple catalysts, and the process is simpler. This preparation method is the traditional preparation process of vehicles exhaust purification catalyst, which greatly reduces the production cost and is easier to scale up and industrialize.
The following describes the present invention in detail with reference to the drawings.
In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further explained in detail below with reference to the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not for limiting the present invention.
S1, preparation of coating material;
The Pd(NO3)2 and Rh(NO3)2 solutions were loaded on Al2O3 and CeO2—ZrO2 materials by dipping method, dried at 80° C. for 6 h, and calcined at 500° C. for 2 h to obtain a coating material, denoted as M1.
S2, preparation of coating material slurry;
Mix M1 with water and a binder to obtain a coating material slurry, denoted as N1.
S3, prepares three-way catalyst;
The N1 is coated on the cordierite ceramic carrier, and the carrier size is Φ25.4*101.6/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pd and Rh is 35 g/ft3, and the ratio of Pd and Rh is 9:1. The prepared catalyst is denoted as C1-1.
The N1 is coated on the cordierite ceramic carrier, and the carrier size is Φ304.8*152.4/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pd and Rh is 35 g/ft3, and the ratio of Pd and Rh is 9:1. The prepared catalyst is denoted as C1-2.
S1, preparation of coating material;
The Pt(NO3)2, Pd(NO3)2 and Rh(NO3)2 solutions were loaded onto the La—Al2O3 and CeO2—ZrO2 materials by dipping, dried at 80° C. for 6 h, and calcined at 500° C. for 2 h to obtain a coating. Layer material, denoted as M2.
S2, preparation of coating material slurry;
The M2 is mixed with water and a binder to obtain a coating material slurry, which is denoted as N2.
S3, prepares three-way catalyst;
The N2 is coated on the cordierite ceramic carrier, and the carrier size is 25.4+101.6/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pt, Pd and Rh is 35 g/ft3, and the ratio of Pt, Pd and Rh is 3:6:1. The prepared catalyst was denoted as C2-1.
N2 is applied to the cordierite ceramic carrier, the carrier size is Φ304.8*152.4/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pt, Pd and Rh is 35 g/ft3, and the ratio of Pt, Pd and Rh is 3:6:1. The prepared catalyst is denoted as C2-2.
S1, preparation of coating material;
The Pd(NO3)2, Rh(NO3)2 and Ru(NO3)2 solutions were loaded onto Al2O3 and CeO2—ZrO2 materials by impregnation method, dried at 80° C. for 6 h, and calcined at 500° C. for 2 h to obtain a coating material, denoted as M3.
S2, preparation of coating material slurry;
The M3 is mixed with water and a binder to obtain a coating material slurry, which is denoted as N3.
S3, prepares three-way catalyst;
The N3 is coated on the cordierite ceramic carrier, the carrier size is Φ25.4*101.6/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pd and Rh is 35 g/ft3, the ratio of Pd and Rh is 9:1, and the content of Ru is 5 g/ft3. The prepared catalyst was denoted as C3-1.
The N3 is coated on the cordierite ceramic carrier, and the carrier size is Φ304.8*152.4/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pd and Rh is 35 g/ft3, the ratio of Pd and Rh is 9:1, and the content of Ru is 5 g/ft3. The prepared catalyst is denoted as C3-2.
S1, the preparation of coating material;
Pt(NO3)2, Pd(NO3)2, Rh(NO3)2 and Ru(NO3)2 solutions were loaded onto La—Al2O3 and CeO2—ZrO2 materials by impregnation method, dried at 80° C. for 6 h, 500° C. calcined for 2 h to obtain a coating material, denoted as M4.
S2, preparation of coating material slurry;
The M4 is mixed with water and a binder to obtain a coating material slurry, which is denoted as N4.
S3, prepares three-way catalyst;
The N4 is coated on a cordierite ceramic carrier with a carrier size of 25.4*101.6/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pt, Pd and Rh is 35 g/ft3, the ratio of Pt, Pd and Rh is 3:6:1, and the Ru content is 20 g/ft3. The prepared catalyst is denoted as C4-1.
The N4 is coated on the cordierite ceramic carrier, the carrier size is Φ304.8*152.4/400 cpsi. After drying at 80° C. for 6 h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pt, Pd and Rh is 35 g/ft3, the ratio of Pt, Pd and Rh is 3:6:1, and the Ru content is 20 g/ft3. The prepared catalyst is denoted as C4-2.
S1, the preparation of coating material;
Pt(NO3)2, Pd(NO3)2, Rh(NO3)2 and Ru(NO3)2 solutions were loaded onto La—Al2O3 and CeO2—ZrO2 materials by impregnation method, dried at 80° C. for 6 h, and calcined at 500° C. for 2 h to obtain a coating material, which is denoted as M5.
S2, preparation of coating material slurry;
The M5 is mixed with water and a binding agent to obtain a coating material slurry, denoted as N5.
S3, prepares three-way catalyst;
The N5 is coated on a cordierite ceramic carrier with a carrier size of Φ25.4*101.6/400 cpsi. After drying at 80° C. for 6h and calcining at 500° C. for 2h, the coating amount is 200 g/L, the total content of Pt, Pd and Rh is 35 g/ft3, the ratio of Pt, Pd and Rh is 3:6:1, and the Ru content is 40 g/ft3. The prepared catalyst was denoted as C5-1.
The N5 is coated on the cordierite ceramic carrier, the carrier size is Φ304.8*152.4/400 cpsi. After drying at 80° C. for 6h and calcining at 500° C. for 2 h, the coating amount is 200 g/L, the total content of Pt, Pd and Rh is 35 g/ft3, the ratio of Pt, Pd and Rh is 3:6:1, and the Ru content is 40 g/ft3. The prepared catalyst is denoted as C5-2. Test example 1
Catalyst C1-1, C2-1, C3-1, C4-1 and C5-1 obtained in above-mentioned comparative example and embodiment are carried out activity evaluation test on vehicles exhaust sample simulation device, test condition is as follows:
Simulated atmosphere: HC (CH4): 1000 ppm; CO: 4000 ppm; NO: 1000 ppm; O2: 3500 ppm; H2O: 10%; CO2: 10%; N2 is the balance gas, and the airspeed is 40,000 h-1 (the airspeed calculated according to the volume of TWC). The patent of the present invention adopts CH4 with the most stable structure to represent HC in vehicles exhaust gas; NOx is adopted to represent NOx (including NOx such as NO and NO2) in vehicles exhaust gas. The catalysts were tested for the conversion efficiency of CO, CH4 and NO at 300-600° C. (the main temperature range of vehicles exhaust) under the simulated atmosphere.
The results of
The results of
The catalysts C1-1, C2-1, C3-1, C4-1 and C5-1 obtained in the comparative examples and embodiments are verified different lambda NH3 on the vehicles exhaust sample simulation device (N2 Selectivity), The test conditions are as follows:
Simulated atmosphere: HC (CH4): 1000 ppm; CO: 4000 ppm; NO: 1000 ppm; H2O: 10%; CO2: 10%; N2 is the balance gas, and the airspeed is 40,000 h-1 (the airspeed calculated according to the volume of TWC). O2 content is determined according to the Lambda value. The patent of the present invention adopts CH4 with the most stable structure to represent HC in vehicles exhaust gas; NOx is adopted to represent NOx (including NOx such as NO and NO2) in vehicles exhaust gas. The catalyst was tested at 500° C. in a simulated atmosphere (this temperature is the temperature at which the TWC NH3formation is relatively high, and the average exhaust temperature of the vehicles exhaust is also near this, so it is more representative to choose this temperature test),The NH3formation of each comparative example and embodiment at different Lambdas. Lambda is the equivalent air-fuel ratio.
The results of
The catalyzer C1-2, C2-2, C3-2, C4-2 and C5-2 that above-mentioned comparative example and embodiment are obtained are in the gas engine bench of heavy-duty equivalence ratio combustion, according to the test method specified inGB17691-2016″Diesel Vehicle Pollutant Emission Limits and Measurement Methods (China Phase VI)″ validates the WHTC test cycle conditions, comparative examples and implementation of CO, HC (CH4), NOx and NH3 emission values.
Table 1 shows results of the corresponding catalysts C1-2, C2-2, C3-2, C4-2 and C5-2 of comparative example 1, comparative example 2, embodiment 1, embodiment 2 and embodiment 3 according to WHTC cycle and the CO, HC(CH4), NOx and NH3 emission values of the operating conditions test.
The results in Table 1 show that the three pollutants of embodiment and Comparative Example, CO, HC(CH4) and NOx, are all purified to within 50% of the national six limit, showing very high pollutant purification efficiency. The NH3formation of comparative example 1 and comparative example 2 is more than three times of the national six limit, and the emission exceeds the standard; the NH3formationof embodiment 1, embodiment 2 and embodiment 3 are all lower than 10 ppm, the NH3formationis very low, showing high N2 selectivity. The above results show that, while embodiment 1, embodiment 2 and embodiment 3 efficiently purify CO, CH4 and NOx, NH3 emission is greatly reduced and N2 selectivity is greatly improved.
The above discusses preferred embodiments of the present invention, and is not intended to limit the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110173740.5 | Feb 2021 | CN | national |
This application is a national phase application of International Application No. PCT/CN2021/078494, filed Mar. 1, 2021, pending, which claims the benefit of Chinese Pat. Appl. No. CN202110173740.5, filed Feb. 6, 2021, both of which are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2021/078494 | Mar 2021 | WO |
| Child | 18307141 | US |
