WO2020073666A1 - 一种尾气处理催化剂及其制备方法和用途 - Google Patents

一种尾气处理催化剂及其制备方法和用途 Download PDF

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WO2020073666A1
WO2020073666A1 PCT/CN2019/089171 CN2019089171W WO2020073666A1 WO 2020073666 A1 WO2020073666 A1 WO 2020073666A1 CN 2019089171 W CN2019089171 W CN 2019089171W WO 2020073666 A1 WO2020073666 A1 WO 2020073666A1
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catalyst
active component
exhaust gas
gas treatment
hours
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PCT/CN2019/089171
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English (en)
French (fr)
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王云
淡宜
杜洪仪
朱赞
罗甜甜
张艳华
王勤
李云
陈启章
程永香
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中自环保科技股份有限公司
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Priority to US17/040,523 priority Critical patent/US11596932B2/en
Priority to EP19871878.5A priority patent/EP3778016A4/en
Publication of WO2020073666A1 publication Critical patent/WO2020073666A1/zh

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Definitions

  • the invention relates to the technical field of tail gas treatment, in particular to a tail gas treatment catalyst and a preparation method and application thereof.
  • TWC Three Way Catalyst
  • the three pollutants CO, HC and NO x can be purified to below the national six limit by TWC, but in the vicinity of the theoretical air-fuel ratio, especially under rich conditions, CO, NO and H 2 react to form NH 3 and H 2 O
  • the emissions of the newly added by-product NH 3 far exceed the requirements of the National Six emission regulations (discharges are more than 5-10 times the limit), and the newly added by-product NH 3 must be purified to meet the requirements of the regulations.
  • NH 3 is an unstable compound. It is easily oxidized under certain temperature conditions. The oxidation products are usually N 2 , N 2 O and NO. The difficulty of this reaction is the selectivity of NH 3 to N 2 oxidation.
  • Ammonia Oxidation Catalyst (AOC) has been used in the aftertreatment of diesel vehicles. Compared with diesel vehicles, the equivalent combustion of natural gas vehicles under the same working conditions, the exhaust temperature is generally about 200 °C higher than diesel vehicles, The ammonia oxidation catalyst used in diesel vehicles, as the temperature rises above 450 °C, the selectivity of NH 3 to N 2 will be significantly reduced. Therefore, the ammonia oxidation catalyst used in natural gas vehicles will oxidize NH 3 at high temperatures. The requirements for the selectivity of N 2 are significantly increased.
  • a post-treatment catalyst In order to make the exhaust of heavy natural gas vehicles meet the national VI regulations, a post-treatment catalyst must be developed, which can simultaneously purify the HC, CO, NOx, PM and NH 3 in the exhaust to the national VI limits.
  • the purpose of the present invention is to overcome the defect that the existing exhaust gas treatment catalyst cannot effectively purify the newly added by-product NH 3 of the exhaust gas, and to provide an effective purification treatment of hydrocarbon compounds, carbon monoxide, nitrogen oxides, particulate matter and newly added by-products in the exhaust gas NH 3 tail gas treatment catalyst, and preparation method and use of the tail gas treatment catalyst.
  • the catalyst is composed of a carrier, a first catalyst and a second catalyst.
  • the first catalyst and the second catalyst are provided at both ends of the carrier.
  • the first catalyst can purify and treat CH 4 and NMHC in the exhaust gas , CO and NO x ;
  • the second catalyst can purify the by-product NH 3 after purification treatment of the first catalyst and some pollutants that have not been completely purified by the first catalyst;
  • the second catalyst has a double-layer structure, and the lower layer is composed of an oxygen storage material, alumina and a second active component,
  • the second active component is a combination of Pt and Pd, or a combination of Ce, Fe, Ni, and Cu;
  • the upper layer consists of molecular sieve and the third active component
  • the third active component is Cu, or a combination of Cu and Fe.
  • the above-mentioned exhaust gas treatment catalyst may be a monopolar staged catalyst or a bipolar catalyst, which is composed of three catalyst functional regions.
  • the front section (or front pole) of the catalyst is composed of a carrier material and a first catalyst.
  • the first catalyst is a three-way catalyst, which mainly purifies methane, non-methane hydrocarbons, carbon monoxide, nitrogen oxides and particulate matter in the exhaust gas into carbon dioxide , Nitrogen and water;
  • the rear stage (or rear pole) of the catalyst is composed of a carrier material and a second catalyst, where the second catalyst is divided into upper and lower layers:
  • the lower layer is an ammonia oxidation catalyst, which mainly oxidizes ammonia gas to nitrogen and a small part Nitric oxide,
  • the upper layer is a passive selective reduction catalyst, which mainly converts ammonia and nitric oxide into nitrogen and water.
  • the rear end (or rear pole) of the catalyst mainly converts the original ammonia gas in the tail gas or the front stage of the catalyst (or front Pole)
  • the newly added by-product ammonia gas after purification treatment and the unpurified methane, non-methane hydrocarbon, nitrogen oxides, carbon monoxide and other pollutants in the previous section (or front pole) of the catalyst are purified by carbon dioxide, nitrogen and water.
  • the total loading capacity of the upper and lower layers of the second catalyst is 50-200 g / L, wherein the ratio of the loading capacity of the upper layer and the lower layer is (0.1-10): 1.
  • the loading amount of the lower coating of the second catalyst is 0.1-150 g / L
  • the loading amount of the upper coating is 0.1-150 g / L
  • the total loading of the upper and lower layers is 50-200 g / L.
  • the loading amount of the second catalyst lower layer coating is 10-100 g / L
  • the loading amount of the upper layer coating is 10-100 g / L
  • the total loading amount of the upper and lower layers is 100-180 g / L.
  • the loading amount of the second catalyst lower layer coating is 30-80 g / L
  • the loading amount of the upper layer coating is 50-100 g / L
  • the total loading amount of the upper and lower layers is 150-180 g / L.
  • the weight ratio of Pt and Pd is (10 ⁇ 1): (1 ⁇ 0).
  • the weight ratio of Pt and Pd is (10 to 1): (1 to 0.5).
  • the weight ratio of Pt and Pd is (10 to 5): (1 to 0.5).
  • the content of the second active component in the lower layer of the second catalyst is 0.1-10 g / ft 3 .
  • the content of the second active component in the lower layer of the second catalyst is 1-10 g / ft 3 .
  • the content of the second active component in the lower layer of the second catalyst is 1 to 5 g / ft 3 .
  • the molecular sieve is one or a combination of several small pore molecular sieves such as Beta, ZSM-5, SSZ-13, or SAPO-34.
  • the second catalyst under the conditions of the theoretical air-fuel ratio or slightly lean (excess oxygen), uses a lower layer of precious metal and an upper layer of molecular sieve to form a layered coating.
  • Pt underlayer single or Pt, Pd bimetallic catalyst consisting of a noble metal based or transition metal Ce, Fe, Ni, Cu and the like catalyst, NH 3 converted mainly of NH 3 and the resulting sub-three-way catalyst for engine exhaust N 2 ; and part of the CO, CH 4 and NMHC that have not been converted by the three-way catalyst into CO 2 and H 2 O;
  • the upper layer uses Cu or Cu, Fe as the active component, Beta, ZSM-5, SSZ-13 or one kind of small pore molecular sieve and SAPO-34 or more as the carrier, the catalyst prepared, the occurrence of HC-SCR NH3-SCR reaction and the NH3, NO x, CH 4 and the like is converted to N 2, CO 2 and H 2 O.
  • the first catalyst is composed of an oxygen storage material, alumina, an auxiliary agent, and a first active component; the first active component is a combination of Pt, Pd, and Rh.
  • the weight ratio of Pt, Pd and Rh in the first active component is (0-50): (1-100): (1-10).
  • the weight ratio of Pt, Pd and Rh in the first active component is (10-50): (20-100): (3-10).
  • the weight ratio of Pt, Pd and Rh in the first active component is (20-50): (50-100): (3-8).
  • the loading amount of the dry-based coating of the first catalyst is 100-250 g / L, and the content of the first active component is 50-200 g / ft 3 .
  • the first catalyst is a Pt / Pd / Rh three-way catalyst with Pt, Pd and Rh as the main active components or a Pd / Rh three-way catalyst with Pd and Rh as the main active components
  • CH 4 , NMHC, CO, NO x and particulate matter in the exhaust gas are converted into CO 2 , N 2 and H 2 O.
  • the content, proportion and active load of the first catalyst can be adjusted according to the actual exhaust emission characteristics of the engine.
  • volume ratio of the first catalyst to the second catalyst is (0.5-10): 1.
  • the volume ratio of the first catalyst to the second catalyst is (0.5-5): 1.
  • the volume ratio of the first catalyst to the second catalyst is (1-3): 1.
  • the carrier is preferably a cordierite carrier
  • the catalytic material is preferably an oxygen storage material and alumina
  • the auxiliary agent is cerium nitrate, barium nitrate, or the like.
  • the Pt component mainly plays the role of oxidizing CO and HC in the catalyst. It has a certain reducing ability to NO, but its effect is not Rh when the concentration of CO is high or SO 2 is present. Good; the Rh component is the main component of catalytic reduction of nitrogen oxides.
  • the main reduction product In the presence of oxygen, the main reduction product is N 2 and only a small amount of NH 3 is produced; when the oxygen-free or oxygen content is lower than the stoichiometric ratio, the reduction product is divided by N 2 In addition, the production of NH 3 is greatly increased; Pd component is mainly used to convert CO and hydrocarbons, which is slightly less effective for saturated hydrocarbons, poor resistance to S poisoning, and easy to sinter at high temperature, but its stability is high and it ignites Sex is good.
  • the additives themselves are additives with no catalytic effect or low activity, which can greatly improve the activity, selectivity and life of the catalyst.
  • Cerium oxide is the most important additive for automobile exhaust purification catalysts. Its main functions are: storage and release of oxygen; improve the dispersion of precious metals, inhibit the formation of inactive solid solutions of precious metal particles and alumina; improve the anti-poisoning ability of the catalyst; increase The stability of the catalyst, etc.
  • the invention also provides a preparation method of the above-mentioned tail gas treatment catalyst, which includes the following steps:
  • the precursor of the first active component is impregnated on the surface of the oxygen storage material and alumina, and then dried at 60 to 120 ° C for 2 to 10 hours, and fired in an air atmosphere at 350 to 600 ° C for 2 to 5 hours to obtain M- 1; exemplarily, drying at 90 ° C for 6 hours and firing in an air atmosphere of 475 ° C for 3.5 hours to obtain M-1;
  • the first active component precursor is impregnated on the surface of the oxygen storage material and the alumina by an equal volume impregnation method, and the amount of impregnation is controlled so that the single active component accounts for 0 to 6%;
  • the adhesive includes but is not limited to aluminum sol and silica sol. During the ball milling process, the solid content of the resulting slurry is controlled to be 25-50%;
  • the precursor of the second active component is impregnated on the surface of the oxygen storage material and alumina, and then dried at 60 to 120 ° C for 2 to 10 hours, and baked in an air atmosphere at 350 to 600 ° C for 2 to 5 hours to obtain M- 2; exemplarily, drying at 90 ° C for 6 hours and firing in an air atmosphere of 475 ° C for 3.5 hours to obtain M-2;
  • the adhesive includes but is not limited to aluminum sol and silica sol. During the ball milling process, the solid content of the resulting slurry is controlled to be 25-50%;
  • the precursor of the third active component is exchanged into the molecular sieve framework by ion exchange, filtered, washed, and then dried at 60 to 120 ° C for 2 to 10 hours, and baked at 350 to 650 ° C in an air atmosphere for 2 to 8 hours To obtain M-3; exemplarily, drying at 90 ° C for 6 hours and firing in an air atmosphere at 500 ° C for 5 hours to obtain M-3;
  • the adhesive includes but is not limited to aluminum sol and silica sol. During the ball milling process, the solid content of the resulting slurry is controlled to be 25-50%;
  • the active component precursor refers to a nitrate, tetraamine nitrate or other inorganic salt of each active component.
  • the active component precursor is platinum nitrate, palladium nitrate, Rhodium nitrate, tetraamine platinum nitrate, tetraamine palladium nitrate, chloroplatinic acid, etc.
  • the active component precursor solution may be a single active component precursor solution, or a mixed solution of multiple active component precursor solutions, or a mixed solution of the precursor solution and the auxiliary salt solution.
  • the invention also provides the use of the above-mentioned exhaust gas treatment catalyst in purification and treatment of natural gas automobile exhaust gas.
  • the first catalyst can purify NO, HC and CO in the exhaust gas
  • the second catalyst can purify the exhaust gas exhaust and the first catalyst reaction by-product NH 3 , and the unreacted NO in the previous stage, HC and CO, with high purification efficiency, can significantly reduce the content of various pollutant gases in the exhaust gas, especially the newly added by-product NH 3 , so that it can meet the emission requirements of China VI.
  • FIG. 1 is a schematic diagram of the structure of a monopolar segmented exhaust gas treatment catalyst in an embodiment of the present invention.
  • FIG. 2 is a schematic structural diagram of a bipolar exhaust gas treatment catalyst in an embodiment of the present invention.
  • Figure 3 shows the effect of different coating loadings of the first catalyst on the CH 4 light- off temperature (T 50 ).
  • Figure 4 shows the effect of different precious metal contents of the first catalyst on the CH 4 light- off temperature (T 50 ).
  • Figure 5 shows the effect of different Pt / Pd ratios of the second catalyst on the NH 3 light- off temperature (T 50 ).
  • Fig. 6 is the effect of different contents of the second catalyst precious metal on the NH 3 light- off temperature (T 50 ).
  • the labels in the figure are: 1-support, 2-first catalyst, 3-second catalyst, 31-second catalyst lower layer, 32-second catalyst upper layer.
  • the instruments and raw materials used in the embodiments of the present invention are known commercially available products, which are obtained by purchasing commercially available products.
  • an exhaust gas treatment catalyst is composed of a carrier, a first catalyst and a second catalyst.
  • the first catalyst and the second catalyst are provided at both ends of the carrier, and the first catalyst can be purified Treatment of CH 4 , NMHC, CO and NO x in the exhaust gas; the second catalyst can purify the by-product NH 3 after purification treatment of the first catalyst and partial pollutants that have not been completely purified by the first catalyst;
  • the second catalyst 3 has a double-layer structure, and the lower layer 31 is composed of an oxygen storage material, alumina, and a second active component.
  • the second active component is a combination of Pt and Pd, or Ce, Fe, Ni, A composition of transition metals such as Cu;
  • the upper layer 32 is composed of a molecular sieve and a third active component, where the third active component is Cu, or a combination of Cu and Fe.
  • the type of the first catalyst 2 is not particularly limited, as long as it can purify and process pollutants such as methane, non-methane hydrocarbons, carbon monoxide, nitrogen oxides, and particulate matter in the exhaust gas into carbon dioxide, nitrogen, and water.
  • the first catalyst 2 is a three-way catalyst, which is composed of an oxygen storage material, alumina, an auxiliary agent, and a first active component; the first active component is a combination of Pt, Pd, and Rh, The weight ratio of Pt, Pd and Rh is (0-50): (1-100): (1-10).
  • the weight ratio of Pt, Pd and Rh in the first active component is ( 10-50): (20-100): (3-10), preferably, the weight ratio of Pt, Pd and Rh in the first active component is (20-50): (50-100): (3 ⁇ 8).
  • the weight ratio of Pt, Pd and Rh in the first active component may be 0: 1: 1, 50: 100: 10, 15: 35: 3, 35: 75: 5, etc .; the first The catalyst 2 is coated on the surface of the carrier 1, the dry base coating has a loading of 100 to 250 g / L, and the content of the first active component is 50 to 200 g / ft 3.
  • the dry base coating has a loading of 100 to 250 g / L
  • the content of the first active component is 50 to 200 g / ft 3.
  • the first catalyst 2 is compared loading the coating is 100g / L, 150g / L, 200g / L, CH -off temperature (T 50) 4 of 250g / L time;
  • FIG. 4 the first active component of the first comparative catalyst 2
  • the content is the light-off temperature (T 50 ) of CH 4 at 50 g / ft 3 , 100 g / ft 3 , 150 g / ft 3 , and 200 g / ft 3 .
  • the total loading capacity of the upper and lower layers of the second catalyst 3 is 50-200 g / L, wherein the ratio of the loading capacity of the upper layer and the lower layer is (0.1-10): 1.
  • the loading capacity of the coating layer of the second catalyst lower layer 31 is 0-150 g / L
  • the loading capacity of the coating layer of the upper layer 32 is 0-150 g / L
  • the total loading capacity of the upper and lower layers is 50-200 g / L.
  • the loading capacity of the coating layer of the second catalyst lower layer 31 is 10-100 g / L
  • the loading capacity of the coating layer of the upper layer 32 is 10-100 g / L
  • the total loading capacity of the upper and lower layers is 100-180 g / L .
  • the loading capacity of the coating layer of the second catalyst lower layer 31 is 30-80 g / L
  • the loading capacity of the coating layer of the upper layer 32 is 50-100 g / L
  • the total loading capacity of the upper and lower layers is 150-180 g / L .
  • the total uploading capacity of the upper and lower layers of the second catalyst 3 is 100 g / L, the uploading capacity of the upper layer 32 is 50 g / L, and the uploading capacity of the lower layer 31 is 50 g / L; or, the total uploading of the upper and lower layers of the second catalyst 3
  • the amount is 130g / L, the upper layer 32 is 75g / L, and the lower layer 31 is 55g / L; or, the total amount of the upper and lower layers of the second catalyst 3 is 165g / L and the upper layer 32 is 85g / L
  • the loading capacity of the lower layer 31 is 80g / L; or, the total loading capacity of the upper and lower layers of the second catalyst 3 is 180g / L, the loading capacity of the upper layer 32 is 100g / L, and the loading capacity of the lower layer 31 is 80g / L; or, the second The total loading of the upper and lower layers of the catalyst 3 is 80 g / L, the loading of the upper layer 32 is 50 g /
  • the weight ratio of Pt and Pd is (10 to 1): (1 to 0).
  • the weight ratio of Pt and Pd is (10 to 1): (1 to 0.5).
  • the weight ratio of Pt and Pd is (10 to 5): (1 to 0.5).
  • the weight ratio of Pt and Pd in the second active component may be 10: 1, 5: 0, 2: 1, 1: 1, or 1: 5.
  • FIG. 5 compares the light-off of NH 3 when the weight ratio of the second active components Pt and Pd in the second catalyst lower layer 31 is 10: 1, 5: 0, 2: 1, 1: 1 and 1: 5 Temperature (T 50 ).
  • the content of the second active component in the second catalyst lower layer 31 is 0.1 to 10 g / ft 3 .
  • the content of the second active component in the lower layer of the second catalyst is 1-10 g / ft 3 .
  • the content of the second active component in the second catalyst lower layer 31 is 1 to 5 g / ft 3 .
  • the content of the second active component in the second catalyst lower layer 31 may be 1 g / ft 3 , 2 g / ft 3 , 3 g / ft 3 , 5 g / ft 3 or 10 g / ft 3 .
  • the ratio of the second active components Pt and Pd in the second catalyst lower layer 31 is 2: 1 and the total amount is 1g / ft 3 , 2g / ft 3 , 3g / ft 3 , 5g / ft NH 3 light -off temperature (T 50 ) at 3 and 10 g / ft 3 .
  • the molecular sieve in the second catalyst upper layer 32 is one or a combination of several small pore molecular sieves such as Beta, ZSM-5, SSZ-13 or SAPO-34.
  • the molecular sieve may be Beta or a combination of ZSM-5 and SSZ-13.
  • the second catalyst 3 is layered and coated with the lower precious metal and the upper molecular sieve to form a catalyst under the condition of theoretical air-fuel ratio or slightly lean (excess oxygen).
  • the lower layer 31 adopts a noble metal catalyst mainly composed of single Pt or Pt, Pd bimetal or a transition metal catalyst composed of Ce, Fe, Ni, Cu, etc., which mainly converts NH 3 emitted by the engine and NH 3 produced by the side reaction of the three-way catalyst into N 2 ; and part of the CO, CH 4 and NMHC that have not been converted by the three-way catalyst into CO 2 and H 2 O;
  • the upper layer 32 uses Cu or Cu, Fe as the active component, Beta, ZSM-5, SSZ- one kind of small pore molecular sieves are SAPO-34, etc.
  • the catalyst prepared occurs HC-SCR NH3-SCR reaction and the NH3, NO x, CH 4 and the like is converted to N 2, CO 2, and H 2 O.
  • the content, proportion and active load of the second catalyst can be adjusted according to the actual exhaust emission characteristics of the engine.
  • the volume ratio of the first catalyst 2 to the second catalyst 3 is (0.5-10): 1.
  • the volume ratio of the first catalyst to the second catalyst is (0.5-5): 1.
  • the volume ratio of the first catalyst 2 to the second catalyst 3 is (1 to 3): 1.
  • the volume ratio of the first catalyst 2 to the second catalyst 3 may be 1: 2, 1: 1, 2: 1, 3: 1 or 5: 1.
  • the above-mentioned exhaust gas treatment catalyst may be a monopolar segmented catalyst or a bipolar catalyst, which is composed of three kinds of catalysts.
  • FIG. 1 shows a monopolar segmented catalyst
  • FIG. 2 shows a bipolar catalyst.
  • the front stage (or front pole) of the catalyst is composed of the carrier material 1 and the first catalyst 2.
  • the first catalyst 2 is a three-way catalyst, which mainly purifies methane, non-methane hydrocarbons, carbon monoxide, nitrogen oxides and particulate matter in the exhaust gas.
  • the rear stage (or back electrode) of the catalyst is composed of the carrier material 1 and the second catalyst 3, wherein the lower layer of the second catalyst 3 is an ammonia oxidation catalyst, mainly oxidizing ammonia gas to nitrogen and a small part Nitric oxide, the upper layer is a passive selective reduction catalyst, which mainly converts ammonia and nitric oxide into nitrogen and water.
  • the lower layer of the second catalyst 3 is an ammonia oxidation catalyst, mainly oxidizing ammonia gas to nitrogen and a small part Nitric oxide
  • the upper layer is a passive selective reduction catalyst, which mainly converts ammonia and nitric oxide into nitrogen and water.
  • the rear end (or rear pole) of the catalyst mainly converts the original ammonia gas in the tail gas or the front stage of the catalyst (or front Pole)
  • the newly added by-product ammonia gas after purification treatment and the unpurified methane, non-methane hydrocarbon, nitrogen oxides, carbon monoxide and other pollutants in the previous section (or front pole) of the catalyst are purified by carbon dioxide, nitrogen and water.
  • the carrier 1 is preferably a cordierite carrier
  • the catalytic material is preferably an oxygen storage material and alumina
  • the auxiliary agent is cerium nitrate, barium nitrate, or the like.
  • the Pt component mainly plays the role of oxidizing CO and HC in the catalyst, and it has a certain reducing ability to NO x , but when the concentration of CO is high or SO 2 is present, its effect is not Rh is good; the Rh component is the main component of catalytic reduction of nitrogen oxides.
  • the main reduction product In the presence of oxygen, the main reduction product is N 2 and only a small amount of NH 3 is produced; when the oxygen-free or oxygen content is lower than the stoichiometric ratio, the reduction product is divided by N 2.
  • the production of NH 3 is greatly increased; the Pd component is mainly used to convert CO and hydrocarbons, which is slightly less effective for saturated hydrocarbons, poor resistance to S poisoning, and easy to sinter at high temperatures, but its stability is higher. Good flammability.
  • the additives themselves are additives with no catalytic effect or low activity, which can greatly improve the activity, selectivity and life of the catalyst.
  • Cerium oxide is the most important additive for automobile exhaust purification catalysts. Its main functions are: storage and release of oxygen; improve the dispersion of precious metals, inhibit the formation of inactive solid solutions of precious metal particles and alumina; improve the anti-poisoning ability of the catalyst; increase The stability of the catalyst, etc.
  • the palladium nitrate and rhodium nitrate solutions were loaded on the oxygen storage material (OSM) and alumina (Al 2 O 3 ) by equal volume impregnation method, dried at 80 °C for 6h, and calcined at 500 °C for 2h, where the palladium material was recorded as M1- 1.
  • the rhodium material is recorded as M1-2;
  • Coat N1-1 on the cordierite carrier the specification of the cordierite carrier is ⁇ 25.4 * 50.8 / 400cpsi-4mil, dried at 80 °C for 6h, and calcined at 500 °C for 2h to obtain catalyst C1-1, coating amount 120g / L , Precious metal content 145g / ft 3 ;
  • the coating amount of upper layer is 60g / L
  • the content of precious metal in upper layer is 5g / ft 3
  • the total coating amount of catalyst C1 is 180g / L
  • the total precious metal content is 150g / ft 3 .
  • the palladium nitrate and rhodium nitrate solutions were loaded on the oxygen storage material (OSM) and alumina (Al 2 O 3 ) by equal volume impregnation method, dried at 80 °C for 6h, and calcined at 500 °C for 2h, where the palladium material was recorded as M1- 1.
  • the rhodium material is recorded as M1-2;
  • the platinum nitrate solution was loaded on alumina (Al 2 O 3 ) by equal volume impregnation method, dried at 80 °C for 6h, and calcined at 500 °C for 2h, which was recorded as M2-1;
  • the size of the cordierite carrier is ⁇ 25.4 * 101.6 / 400cpsi-4mil, dry at 80 °C for 6h, and calcinate at 500 °C for 2h to obtain catalyst C2-1, coated
  • the amount is 120g / L, and the precious metal content is 145g / ft 3 ;
  • the coating amount of the upper layer is 60g / L, and the content of the precious metal in the upper layer is 5g / ft 3 .
  • the amount is 180g / L, the total precious metal content is 150g / ft 3 ;
  • N2-2 was coated on the upper layer of C2-3, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C2-4 with a coating amount of 120g / L and a total coating amount of 180g / L in the subsequent stage.
  • the N1-1 in Example 1 was applied to the front 2/3 of the cordierite carrier.
  • the size of the cordierite carrier was ⁇ 25.4 * 76.2 / 400cpsi-4mil, dried at 80 °C for 6h, and calcined at 500 °C for 2h to obtain catalyst C3- 1.
  • the coating amount is 120g / L, and the precious metal content is 145g / ft 3 ;
  • Example 1 N1-2 in Example 1 was applied to the upper layer of C3-1, dried at 80 ° C for 6 hours, and calcined at 500 ° C for 2 hours to obtain catalyst C3-2.
  • the coating amount of the upper layer was 60 g / L, and the content of the precious metal in the upper layer was 5 g / ft 3 .
  • the total coating amount of the catalyst is 180g / L, and the total precious metal content is 150g / ft 3 ;
  • Example 1 N2-1 in Example 1 was applied to the rear 1/3 of the cordierite carrier, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C3-3, coating amount 60g / L, precious metal content 3g / ft 3 ;
  • Example 1 N2-2 in Example 1 was applied to the upper layer of C3-3, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C3-4 with a coating amount of 120g / L and a total coating amount of 180g / L in the subsequent stage .
  • Example 1 The N1-1 in Example 1 was applied to the front 2/3 of the cordierite carrier, the size of the cordierite carrier was ⁇ 25.4 * 76.2 / 400cpsi-4mil, dried at 80 °C for 6h, and calcined at 500 °C for 2h to obtain catalyst C4- 1.
  • the coating amount is 120g / L, and the precious metal content is 145g / ft 3 ;
  • the total coating amount of the catalyst is 180g / L, and the total precious metal content is 150g / ft 3 ;
  • Example 1 N2-1 in Example 1 was applied to the rear 1/3 of the cordierite carrier, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C4-3, coating amount 60g / L, precious metal content 3g / ft 3 ;
  • Example 1 N2-2 in Example 1 was applied to the upper layer of C4-3, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C4-4 with a coating amount of 150g / L and a total coating amount of 210g / L .
  • N1-1 in Example 1 was coated on a cordierite carrier with a carrier size of ⁇ 25.4 * 50.8 / 400cpsi-4mil, dried at 80 °C for 6h, and calcined at 500 °C for 2h to obtain catalyst C5-1 with a coating amount of 120g / L, precious metal content 145g / ft 3 ;
  • Example 1 N1-2 in Example 1 was applied to the upper layer of C5-1, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C5-2.
  • the amount of coating on the upper layer was 60g / L, and the content of precious metal on the upper layer was 5g / ft 3 .
  • the total coating amount of the polar catalyst is 180g / L, and the total precious metal content is 150g / ft 3 ;
  • Example 1 N2-1 in Example 1 was coated on a cordierite carrier with a carrier size of ⁇ 25.4 * 25.4 / 400cpsi-4mil, dried at 80 °C for 6h, and calcined at 500 °C for 2h to obtain catalyst C5-3 with a coating amount of 60g / L, precious metal content 3g / ft 3 ;
  • Example 1 N2-2 in Example 1 was applied to the upper layer of C5-3, dried at 80 ° C for 6h, and calcined at 500 ° C for 2h to obtain catalyst C5-4 with a coating amount of 150g / L and a total rear electrode coating amount of 210g / L, precious metal content 3g / ft 3 ;
  • Simulated natural gas engine exhaust gas volume composition CH 4 : 1000 ppm; CO: 4000 ppm; NO: 1000 ppm; O 2 : 3500 ppm; H 2 O: 10%; CO 2 : 10%; N 2 is the balance gas; space velocity 40000h -1 (Airspeed calculated from the volume of TWC).
  • the conversion rate of each pollutant at 450 °C is shown in Table 1.
  • the catalyst C1 prepared in the comparative example has a high conversion efficiency for the three pollutants CO, CH 4 and NO, with an average conversion rate exceeding 90%, but the NH 3 emission by-product of the reaction of the catalyst C1 is higher, which greatly exceeds the national The emission limits of the six regulations (10ppm);
  • the silver catalyst C2 adds a second catalyst, and the emission of NH 3 is significantly reduced;
  • the above experiment shows that in the exhaust gas treatment catalyst of the present invention, the first catalyst and the second catalyst work in conjunction with each other.
  • the first catalyst can purify NO, HC, CO, and PM in the exhaust gas
  • the second catalyst can purify the exhaust gas
  • a catalyst catalyzes the by-product NH 3 and the unreacted NO, HC and CO in the pre-purification stage, with high purification efficiency, which can significantly reduce the content of various pollutant gases in the exhaust gas, especially the newly added by-product NH 3 , so that it can meet Emission requirements for China VI.
  • the coating volumes of the first catalyst and the second catalyst in Example 1 were changed, and an activity evaluation test was conducted.
  • the experimental conditions are as follows:
  • Simulated natural gas engine exhaust gas volume composition CH 4 : 1000 ppm; CO: 4000 ppm; NO: 1000 ppm; O 2 : 3500 ppm; H 2 O: 10%; CO 2 : 10%; N 2 is the balance gas; space velocity 40000h -1 (Airspeed calculated from the volume of TWC).
  • the test conditions and the amount of ammonia produced are shown in Table 2.
  • the volume ratio of the first catalyst to the second catalyst is preferably (1 to 3): (1 to 2).

Abstract

本发明公开了一种尾气处理催化剂，该催化剂由载体、第一催化剂和第二催化剂组成，所述第一催化剂和第二催化剂设于所述载体两端，第一催化剂能净化处理尾气中的污染物，第二催化剂能净化处理第一催化剂净化处理后的副产物氨气以及第一催化剂未净化完全的部分污染物；其中，所述第二催化剂为双层结构，下层由储氧材料、氧化铝和第二活性组分组成，所述第二活性组分为Pt与Pd的组合物，或者Ce、Fe、Ni、Cu的组合物；上层由分子筛和第三活性组分组成，所述第三活性组分为Cu，或者Cu、Fe的组合物。本发明的尾气处理催化剂，净化处理效率高，能够显著减少尾气中CH 4、CO和NO x的排放，特别是减少副产物NH 3的含量，使其能满足国六的排放要求。

Description

一种尾气处理催化剂及其制备方法和用途 技术领域
本发明涉及尾气处理技术领域，特别涉及一种尾气处理催化剂及其制备方法和用途。
背景技术
重型天然气汽车从国五到国六，发动机的燃烧方式从稀薄燃烧升级到当量比燃烧，相应地，后处理催化剂从氧化性催化剂(Methane Oxidation Catalyst,MOC)升级到三效催化剂(Three Way Catalyst,TWC)。TWC在当量燃烧条件下，能将尾气中的HC(包括CH 4和NMHC)、CO、和NO x转化为N 2、CO 2和H 2O，但在该催化转化过程中，会产生副产物NH 3。
GB17691-2018《重型柴油车污染物排放限值及测量方法(中国第六阶段)》，该标准适用于重型天然气汽车和重型柴油车，其中天然气汽车从2019年7月1日起实施该标准。该标准在GB17691-2005的基础上，气态污染物除进一步降低CO、HC和NO x的限值外，还新增了NH 3的限值要求。
CO、HC、NO x三种污染物通过TWC可以净化到国六限值以下，但在理论空燃比附近，特别是偏浓的条件下，CO、NO和H 2反应生成NH 3和H 2O，新增的副产物NH 3的排放量远远超过了国六排放法规的要求(排放量是限值的5-10倍以上)，必须净化新增副产物NH 3以满足法规要求。
NH 3是一种不稳定的化合物，在一定的温度条件下，很容易被氧化，氧化产物通常是N 2、N 2O和NO。该反应的难点是NH 3氧化为N 2的选择性。氨氧化催化剂(Ammonia Oxidation Catalyst,简称AOC)在柴油车后处理中已有应用，相对于柴油车，当量燃烧的天然气汽车在相同的工作条件下，尾气温度一般要比柴油车高200℃左右，而用于柴油车的氨氧化催化剂，随着温度升高到450℃以上，NH 3氧化为N 2的选择性会明显降低，因此，用于天然气汽车的氨氧化催化剂，高温时对NH 3氧化为N 2的选择性方面的要求显著提高。
为使重型天然气汽车尾气排放满足国六法规，必须开发一种后处理催化剂，可同时将尾气中的HC、CO、NOx、PM和NH 3净化到国六限值内。
发明内容
本发明的目的在于克服现有尾气处理催化剂不能有效净化处理尾气新增副产物NH 3的缺陷，提供一种能够有效净化处理尾气中烃类化合物、一氧化碳、氮氧化物、颗粒物以及新增副产物NH 3的尾气处理催化剂，以及该尾气处理催化剂的制备方法和用途。
为实现上述发明目的，本发明提供了以下技术方案：
一种尾气处理催化剂，该催化剂由载体、第一催化剂和第二催化剂组成，所述第一催化剂和第二催化剂设于所述载体两端，第一催化剂能净化处理尾气中的CH 4、NMHC、CO和NO x；第二催化剂能净化处理第一催化剂净化处理后的副产物NH 3以及第一催化剂未净化完全的部分污染物；其中，
所述第二催化剂为双层结构，下层由储氧材料、氧化铝和第二活性组分组成，
所述第二活性组分为Pt与Pd的组合物，或者Ce、Fe、Ni、Cu的组合物；
上层由分子筛和第三活性组分组成，
所述第三活性组分为Cu，或者Cu、Fe的组合物。
上述尾气处理催化剂可以为单极分段催化剂或者两极催化剂，由三种催化剂功能区域组成。催化剂前段(或前极)由载体材料和第一催化剂组成，第一催化剂为三效催化剂，主要将尾气中的甲烷、非甲烷碳氢、一氧化碳、氮氧化物和颗粒物等污染物净化处理成二氧化碳、氮气和水；催化剂后段(或后极)由载体材料和第二催化剂组成，其中，第二催化剂分为上下两层：下层为氨氧化催化剂，主要将氨气氧化为氮气和少部分的一氧化氮，上层为被动选择还原型催化剂，主要将氨气和一氧化氮转化为氮气和水，本催化剂后端(或后极)主要将尾气中的原排氨气或者催化剂前段(或前极)净化处理后的新增副产物氨气和催化剂前段(或前极)未净化处理的甲烷、非甲烷碳氢、氮氧化物、一氧化碳等污染物净化处理为二氧化碳、氮气和水。
进一步地，所述第二催化剂上、下两层的总上载量为50～200g/L，其中，上层与下层上载量之比为(0.1～10)：1。
优选地，所述第二催化剂下层涂层上载量为0.1～150g/L，上层涂层上载量为0.1～150g/L，上、下两层的总上载量为50～200g/L。
更优选地，所述第二催化剂下层涂层上载量为10～100g/L，上层涂层上载量为10～100g/L，上、下两层的总上载量为100～180g/L。
更优选地，所述第二催化剂下层涂层上载量为30～80g/L，上层涂层上载量为50～100g/L，上、下两层的总上载量为150～180g/L。
进一步地，所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～1)：(1～0)。
优选地，所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～1)：(1～0.5)。
更优选地，所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～5)： (1～0.5)。
进一步地，所述第二催化剂下层中第二活性组分含量为0.1～10g/ft 3。
优选地，所述第二催化剂下层中第二活性组分含量为1～10g/ft 3。
更优选地，所述第二催化剂下层中第二活性组分含量为1～5g/ft 3。
进一步地，所述分子筛为Beta、ZSM-5、SSZ-13或SAPO-34等小孔分子筛中的一种或几种的组合物。
第二催化剂，在理论空燃比条件或略微偏稀(氧气过量)的条件下，采用下层贵金属和上层分子筛分层涂覆形成催化剂。下层采用单Pt或Pt、Pd双金属为主组成的贵金属催化剂或以Ce、Fe、Ni、Cu等过渡金属催化剂，将发动机排放的NH 3和三效催化剂副反应产生的NH 3主要转化为N 2；以及将部分未被三效催化剂转化的CO、CH 4和NMHC转化为CO 2和H 2O；上层采用以Cu或Cu、Fe为活性组分，Beta、ZSM-5、SSZ-13或SAPO-34等小孔分子筛中的一种或多种为载体，制备的催化剂，发生HC-SCR和NH3-SCR反应，将NH3、NO x、CH 4等转化为N 2、CO 2和H 2O。第二催化剂的活性组分含量、比例以及涂层上载量可根据发动机的实际尾气排放特点作相应调整。
进一步地，所述第一催化剂由储氧材料、氧化铝、助剂和第一活性组分组成；所述第一活性组分为Pt、Pd和Rh的组合物。
进一步地，所述第一活性组分中Pt、Pd和Rh的重量配比为(0～50)：(1～100)：(1～10)。
优选地，所述第一活性组分中Pt、Pd和Rh的重量配比为(10～50)：(20～100)：(3～10)。
优选地，所述第一活性组分中Pt、Pd和Rh的重量配比为(20～50)：(50～100)：(3～8)。
所述第一催化剂的干基涂层上载量为100～250g/L，第一活性组分的含量为50～200g/ft 3。
第一催化剂是采用以Pt、Pd、Rh三种贵金属为主要活性组分的Pt/Pd/Rh型三效催化剂或以Pd、Rh两种贵金属为主要活性组分的Pd/Rh型三效催化剂，在理论空燃比附近，将尾气中的CH 4、NMHC、CO、NO x和颗粒物转化为CO 2、N 2和H 2O。第一催化剂的活性组分含量、比例以及涂层上载量可根据发动机的实际尾气排放特点作相应调整。
进一步地，所述第一催化剂与第二催化剂的体积比为(0.5～10):1。
优选地，所述第一催化剂与第二催化剂的体积比为(0.5～5):1。
优选地，所述第一催化剂与第二催化剂的体积比为(1～3):1。
在上述尾气处理催化剂中，所述载体优先为堇青石载体，所述催化材料优选为储氧材料和氧化铝，所述助剂为硝酸铈、硝酸钡等。在所述活性组分中，Pt组分在催化剂中主要起氧 化CO和HC的作用，它对NO有一定的还原能力，但是CO的浓度较高或者有SO 2存在时，它的效果没有Rh好；Rh组分是催化还原氮氧化物的主要成分，在有氧时，主要还原产物是N 2，仅生成少量NH 3；无氧或氧含量低于化学计量比时，还原产物除N 2外，NH 3的生成量大幅提高；Pd组分主要用来转化CO和烃类，对于饱和烃类效果稍差，抗S中毒能力差，易高温烧结，但它的稳定性较高，起燃性好。助剂本身是一些没有催化作用或者活性较低的添加物，能大大提高催化剂的活性、选择性和寿命。铈氧化物是汽车尾气净化催化剂最主要的助剂，其主要作用有：贮存及释放氧气；提高贵金属的分散性，抑制贵金属颗粒与氧化铝形成无活性的固溶体；提高催化剂的抗中毒能力；增加催化剂的稳定性等。
本发明还提供了上述尾气处理催化剂的制备方法，包括如下步骤：
1)第一催化剂制备：
S01.将第一活性组分前躯体浸渍到储氧材料和氧化铝表面，然后于60～120℃干燥2～10小时，在350～600℃的空气气氛中焙烧2～5小时，得到M-1；示例性地，在90℃干燥6小时，在475℃的空气气氛中焙烧3.5小时，得到M-1；
以等体积浸渍法将第一活性组分前驱体浸渍到储氧材料和氧化铝表面，控制浸渍的量使第一活性组分单质占比为0～6％；
S02.将M-1与1～5wt.％的粘接剂混合，球磨制浆，添加0～5wt.％的助剂，所述助剂添加量以助剂氧化物计，即得第一催化剂浆料N-1；示例性地，粘接剂的添加量为3％，助剂的添加量为2.5％；
所述粘接剂包括但不限于铝溶胶和硅溶胶，球磨过程中，控制所得浆料固含量为25～50％；
2)第二催化剂制备：
S01.将第二活性组分前躯体浸渍到储氧材料和氧化铝表面，然后于60～120℃干燥2～10小时，在350～600℃的空气气氛中焙烧2～5小时，得到M-2；示例性地，在90℃干燥6小时，在475℃的空气气氛中焙烧3.5小时，得到M-2；
以等体积浸渍法将第二活性组分前驱体浸渍到储氧材料和氧化铝表面，控制浸渍的量使第二活性组分单质占比为0～1％；
S02.将M-2与1～5wt.％的粘接剂混合，球磨制浆，添加0～5wt.％的助剂，所述助剂添加量以助剂氧化物计，即得第二催化剂下层浆料N-2；示例性地，粘接剂的添加量为3％，助剂的添加量为2.5％；
所述粘接剂包括但不限于铝溶胶和硅溶胶，球磨过程中，控制所得浆料固含量为25～50％；
S03.将第三活性组分前躯体以离子交换法交换到分子筛骨架内，过滤，洗涤，然后于60～120℃干燥2～10小时，在350～650℃的空气气氛中焙烧2～8小时，得到M-3；示例性地， 在90℃干燥6小时，在500℃的空气气氛中焙烧5小时，得到M-3；
控制离子交换的量，使第三活性组分单质占比为0～3％；
S04.将M-3与1～5wt.％的粘接剂混合，球磨制浆，添加0～5wt.％的助剂，所述助剂添加量以助剂氧化物计，即得第二催化剂上层浆料N-3；示例性地，粘接剂的添加量为3％，助剂的添加量为2.5％；
所述粘接剂包括但不限于铝溶胶和硅溶胶，球磨过程中，控制所得浆料固含量为25～50％；
3)尾气处理催化剂制备：在载体一端涂覆浆料N-1，在载体另一端一次涂覆浆料N-2和浆料N-3，然后于60～120℃干燥2～10小时，并在350～600℃的空气气氛中焙烧2～8小时，即得尾气处理催化剂。示例性地，在90℃干燥6小时，并在475℃的空气气氛中焙烧5小时，即得尾气处理催化剂。
在上述制备方法中，所述活性组分前驱体是指各活性组分的硝酸盐、硝酸四胺盐或其它无机盐，示例性地，所述活性组分前驱体为硝酸铂、硝酸钯、硝酸铑、硝酸四胺铂、硝酸四胺钯、氯铂酸等。所述活性组分前驱体溶液可以是单一的活性组分前驱体溶液，也可以是多种活性组分前驱体溶液的混合溶液，或者前驱体溶液与助剂盐溶液的混合溶液。
本发明还提供了上述尾气处理催化剂在净化处理天然气汽车尾气中的用途。
与现有技术相比，本发明的有益效果：
本发明的尾气处理催化剂，第一催化剂能净化处理尾气中的NO、HC和CO，第二催化剂能净化处理尾气原排和第一催化剂反应副产物NH 3，以及净化前段未反应完全的NO、HC和CO，净化处理效率高，能够显著减少尾气中各污染性气体特别是新增副产物NH 3的含量，使其能满足国六的排放要求。
附图说明：
图1为本发明实施例中单极分段尾气处理催化剂结构示意图。
图2为本发明实施例中两极尾气处理催化剂结构示意图。
图3为第一催化剂不同涂层上载量对CH 4起燃温度(T 50)的影响。
图4为第一催化剂不同贵金属含量对CH 4起燃温度(T 50)的影响。
图5为第二催化剂不同Pt/Pd比例对NH 3起燃温度(T 50)的影响。
图6为第二催化剂贵金属不同含量对NH 3起燃温度(T 50)的影响。
图中标记：1-载体，2-第一催化剂，3-第二催化剂，31-第二催化剂下层，32-第二催化剂上层。
具体实施方式
下面结合试验例及具体实施方式对本发明作进一步的详细描述。但不应将此理解为本发明上述主题的范围仅限于以下的实施例，凡基于本发明内容所实现的技术均属于本发明的范围。
本发明实施例中所使用的仪器和原料均为已知市售产品，通过购买市售产品获得。
基础实施例
如图1或2所示，一种尾气处理催化剂，该催化剂由载体、第一催化剂和第二催化剂组成，所述第一催化剂和第二催化剂设于所述载体两端，第一催化剂能净化处理尾气中的CH 4、NMHC、CO和NO x；第二催化剂能净化处理第一催化剂净化处理后的副产物NH 3以及第一催化剂未净化完全的部分污染物；其中，
所述第二催化剂3为双层结构，下层31由储氧材料、氧化铝和第二活性组分组成，所述第二活性组分为Pt与Pd的组合物，或者Ce、Fe、Ni、Cu等过渡金属的组合物；上层32由分子筛和第三活性组分组成，所述第三活性组分为Cu，或者Cu、Fe的组合物。
所述第一催化剂2的种类不作特别限定，只要其能将尾气中的甲烷、非甲烷碳氢、一氧化碳、氮氧化物和颗粒物等污染物净化处理成二氧化碳、氮气和水即可。示例性地，所述第一催化剂2为三效催化剂，由储氧材料、氧化铝、助剂和第一活性组分组成；所述第一活性组分为Pt、Pd和Rh的组合物，Pt、Pd和Rh的重量配比为(0～50)：(1～100)：(1～10)，优选地，所述第一活性组分中Pt、Pd和Rh的重量配比为(10～50)：(20～100)：(3～10)，优选地，所述第一活性组分中Pt、Pd和Rh的重量配比为(20～50)：(50～100)：(3～8)。示例性地，第一活性组分中Pt、Pd和Rh的重量配比可以为0:1:1、50:100:10、15：35:3、35:75:5等；所述第一催化剂2涂覆与载体1表面，干基涂层上载量为100～250g/L，第一活性组分的含量为50～200g/ft 3，示例性地，如图3对比了第一催化剂2的涂层上载量是100g/L、150g/L、200g/L、250g/L时CH 4的起燃温度(T 50)；如图4，对比了第一催化剂2的第一活性组分的含量是50g/ft 3、100g/ft 3、150g/ft 3、200g/ft 3时CH 4的起燃温度(T 50)。
所述第二催化剂3上、下两层的总上载量为50～200g/L，其中，上层与下层上载量之比为(0.1～10)：1。
优选地，所述第二催化剂下层31涂层上载量为0～150g/L，上层32涂层上载量为0～150g/L，上、下两层的总上载量为50～200g/L。
更优选地，所述第二催化剂下层31涂层上载量为10～100g/L，上层32涂层上载量为10～100g/L，上、下两层的总上载量为100～180g/L。
更优选地，所述第二催化剂下层31涂层上载量为30～80g/L，上层32涂层上载量为50～100g/L，上、下两层的总上载量为150～180g/L。
示例性地，第二催化剂3上下两层的总上载量为100g/L，上层32上载量为50g/L，下层31上载量为50g/L；或者，第二催化剂3上下两层的总上载量为130g/L，上层32上载量为75g/L，下层31上载量为55g/L；或者，第二催化剂3上下两层的总上载量为165g/L，上层32上载量为85g/L，下层31上载量为80g/L；或者，第二催化剂3上下两层的总上载量为180g/L，上层32上载量为100g/L，下层31上载量为80g/L；或者，第二催化剂3上下两层的总上载量为80g/L，上层32上载量为50g/L，下层31上载量为30g/L。
所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～1)：(1～0)。
优选地，所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～1)：(1～0.5)。
更优选地，所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～5)：(1～0.5)。
示例性地，所述第二活性组分中Pt与Pd的重量配比可以为10:1、5:0、2:1、1:1或者1:5。图5对比了所述第二催化剂下层31中第二活性组分Pt与Pd的重量配比是10:1、5:0、2:1、1：1和1：5时NH 3的起燃温度(T 50)。
所述第二催化剂下层31中第二活性组分含量为0.1～10g/ft 3。
优选地，所述第二催化剂下层中第二活性组分含量为1～10g/ft 3。
更优选地，所述第二催化剂下层31中第二活性组分含量为1～5g/ft 3。
示例性地，所述第二催化剂下层31中第二活性组分含量可以为1g/ft 3、2g/ft 3、3g/ft 3、5g/ft 3或者10g/ft 3。如图6，对比了所述第二催化剂下层31中第二活性组分Pt与Pd比例为2：1且总量为为1g/ft 3、2g/ft 3、3g/ft 3、5g/ft 3和10g/ft 3时NH 3的起燃温度(T 50)。
所述第二催化剂上层32中分子筛为Beta、ZSM-5、SSZ-13或SAPO-34等小孔分子筛中的一种或几种的组合物。示例性地，所述分子筛可以为Beta或者ZSM-5与SSZ-13的组合物。
第二催化剂3，在理论空燃比条件或略微偏稀(氧气过量)的条件下，采用下层贵金属和上层分子筛分层涂覆形成催化剂。下层31采用单Pt或Pt、Pd双金属为主组成的贵金属催化剂或以Ce、Fe、Ni、Cu等过渡金属催化剂，将发动机排放的NH 3和三效催化剂副反应产生的NH 3主要转化为N 2；以及将部分未被三效催化剂转化的CO、CH 4和NMHC转化为CO 2和H 2O；上层32采用以Cu或Cu、Fe为活性组分，Beta、ZSM-5、SSZ-13或SAPO-34等小孔分子筛中的一种或多种为载体，制备的催化剂，发生HC-SCR和NH3-SCR反应，将NH3、NO x、CH 4等转化为N 2、CO 2和H 2O。第二催化剂的活性组分含量、比例以及涂层上载量可根据发动机的实际尾气排放特点作相应调整。
所述第一催化剂2与第二催化剂3的体积比为(0.5～10):1。
优选地，所述第一催化剂与第二催化剂的体积比为(0.5～5):1。
更优选地，所述第一催化剂2与第二催化剂3的体积比为(1～3):1。
示例性地，所述第一催化剂2与第二催化剂3的体积比可以是1:2、1:1、2:1、3:1或者5：1等。
上述尾气处理催化剂可以为单极分段催化剂或者两极催化剂，由三种催化剂组成，图1所示为单极分段催化剂，图2所示为两极催化剂。催化剂前段(或前极)由载体材料1和第一催化剂2组成，第一催化剂2为三效催化剂，主要将尾气中的甲烷、非甲烷碳氢、一氧化碳、氮氧化物和颗粒物等污染物净化处理成二氧化碳、氮气和水；催化剂后段(或后极)由载体材料1和第二催化剂3组成，其中，第二催化剂3下层为氨氧化催化剂，主要将氨气氧化为氮气和少部分的一氧化氮，上层为被动选择还原型催化剂，主要将氨气和一氧化氮转化为氮气和水，本催化剂后端(或后极)主要将尾气中的原排氨气或者催化剂前段(或前极)净化处理后的新增副产物氨气和催化剂前段(或前极)未净化处理的甲烷、非甲烷碳氢、氮氧化物、一氧化碳等污染物净化处理为二氧化碳、氮气和水。
在上述尾气处理催化剂中，所述载体1优先为堇青石载体，所述催化材料优选为储氧材料和氧化铝，所述助剂为硝酸铈、硝酸钡等。在所述活性组分中，Pt组分在催化剂中主要起氧化CO和HC的作用，它对NO x有一定的还原能力，但是CO的浓度较高或者有SO 2存在时，它的效果没有Rh好；Rh组分是催化还原氮氧化物的主要成分，在有氧时，主要还原产物是N 2，仅生成少量NH 3；无氧或氧含量低于化学计量比时，还原产物除N 2外，NH 3的生成量大幅提高；Pd组分主要用来转化CO和烃类，对于饱和烃类效果稍差，抗S中毒能力差，易高温烧结，但它的稳定性较高，起燃性好。助剂本身是一些没有催化作用或者活性较低的添加物，能大大提高催化剂的活性、选择性和寿命。铈氧化物是汽车尾气净化催化剂最主要的助剂，其主要作用有：贮存及释放氧气；提高贵金属的分散性，抑制贵金属颗粒与氧化铝形成无活性的固溶体；提高催化剂的抗中毒能力；增加催化剂的稳定性等。
对比例
将硝酸钯和硝酸铑溶液，以等体积浸渍法分别负载到储氧材料(OSM)和氧化铝(Al 2O 3)上，80℃干燥6h，500℃焙烧2h，其中钯材料记为M1-1,铑材料记为M1-2；
将M1-1与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量45％的浆料N1-1；
将M1-2与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量45％的浆料N1-2；
将N1-1涂覆至堇青石载体上，堇青石载体规格为Φ25.4*50.8/400cpsi-4mil，经80℃干燥6h，500℃焙烧2h，得到催化剂C1-1，涂覆量120g/L，贵金属含量145g/ft 3；
将N1-2涂覆至C1-1上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C1，上层涂覆量60g/L,上层贵金属含量5g/ft 3，催化剂C1总涂敷量180g/L，总贵金属含量150g/ft 3。
实施例1
将硝酸钯和硝酸铑溶液，以等体积浸渍法分别负载到储氧材料(OSM)和氧化铝(Al 2O 3)上，80℃干燥6h，500℃焙烧2h，其中钯材料记为M1-1,铑材料记为M1-2；
将硝酸铂溶液，以等体积浸渍法分别负载到氧化铝(Al 2O 3)上，80℃干燥6h，500℃焙烧2h，记为M2-1；
将硝酸铜溶液，以离子交换法负载到SSZ-13分子筛上，80℃干燥6h，500℃焙烧2h，记为M2-2；
将M1-1与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量45％的浆料N1-1；
将M1-2与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量45％的浆料N1-2；
将M2-1与铝溶胶混合，球磨10min，粘接剂占比3％，得到固含量40％的浆料N2-1；
将M2-2与铝溶胶混合，球磨10min，粘接剂占比5％，得到固含量40％的浆料N2-2；
将N1-1涂覆至堇青石载体的前段1/2，堇青石载体尺寸为Φ25.4*101.6/400cpsi-4mil，经80℃干燥6h，500℃焙烧2h，得到催化剂C2-1，涂覆量120g/L,贵金属含量145g/ft 3；
将N1-2涂覆至C2-1上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C2-2，上层涂覆量60g/L,上层贵金属含量5g/ft 3，前端催化剂总涂敷量180g/L，总贵金属含量150g/ft 3；
将N2-1涂覆至堇青石载体的后段1/2，经80℃干燥6h，500℃焙烧2h，得到催化剂C2-3,涂覆量60g/L,贵金属含量3g/ft 3；
将N2-2涂覆至C2-3的上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C2-4,涂覆量120g/L,后段总涂敷量180g/L。
将以上制备好的催化剂记为C2。
实施例2
将实例1中的N1-1涂覆至堇青石载体的前段2/3，堇青石载体尺寸为Φ25.4*76.2/400cpsi-4mil，经80℃干燥6h，500℃焙烧2h，得到催化剂C3-1,涂覆量120g/L,贵金属含量145g/ft 3；
将实例1中的N1-2涂覆至C3-1上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C3-2，上层涂覆量60g/L,上层贵金属含量5g/ft 3，前端催化剂总涂敷量180g/L，总贵金属含量150g/ft 3；
将实例1中的N2-1涂覆至堇青石载体的后段1/3，经80℃干燥6h，500℃焙烧2h，得到催化剂C3-3,涂覆量60g/L,贵金属含量3g/ft 3；
将实例1中的N2-2涂覆至C3-3的上层，经80℃干燥6h，500℃焙烧2h，得到催化剂 C3-4,涂覆量120g/L,后段总涂敷量180g/L。
将以上制备好的催化剂记为C3。
实施例3
将实例1中的N1-1涂覆至堇青石载体的前段2/3，堇青石载体尺寸为Φ25.4*76.2/400cpsi-4mil，经80℃干燥6h，500℃焙烧2h，得到催化剂C4-1,涂覆量120g/L,贵金属含量145g/ft 3；
将实例1中的N1-2涂覆至C4-1上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C4-2，上层涂覆量60g/L,上层贵金属含量5g/ft 3，前端催化剂总涂敷量180g/L，总贵金属含量150g/ft 3；
将实例1中的N2-1涂覆至堇青石载体的后段1/3，经80℃干燥6h，500℃焙烧2h，得到催化剂C4-3,涂覆量60g/L,贵金属含量3g/ft 3；
将实例1中的N2-2涂覆至C4-3的上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C4-4,涂覆量150g/L,后段总涂敷量210g/L。
将以上制备好的催化剂记为C4。
实施例4
将实例1中的N1-1涂覆至堇青石载体，载体尺寸为Φ25.4*50.8/400cpsi-4mil，经80℃干燥6h，500℃焙烧2h，得到催化剂C5-1,涂覆量120g/L,贵金属含量145g/ft 3；
将实例1中的N1-2涂覆至C5-1上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C5-2，上层涂覆量60g/L,上层贵金属含量5g/ft 3，前极催化剂总涂敷量180g/L，总贵金属含量150g/ft 3；
将实例1中的N2-1涂覆至堇青石载体，载体尺寸为Φ25.4*25.4/400cpsi-4mil，经80℃干燥6h，500℃焙烧2h，得到催化剂C5-3,涂覆量60g/L,贵金属含量3g/ft 3；
将实例1中的N2-2涂覆至C5-3的上层，经80℃干燥6h，500℃焙烧2h，得到催化剂C5-4,涂覆量150g/L,后极催化剂总涂敷量210g/L，贵金属含量3g/ft 3；
将以上制备好的催化剂记为C5。
将上述实施例及对比例制备的催化剂进行活性评价试验，试验条件如下所示：
模拟天然气发动机尾气气体体积组成：CH 4:1000ppm；CO:4000ppm；NO:1000ppm；O 2:3500ppm；H 2O:10％；CO 2:10％；N 2为平衡气；空速40000h -1(根据TWC的体积计算的空速)。在450℃时各污染物的转化率如表1所示。
表1不同实施例制备的催化剂在450℃时对各污染物的转化率
Figure PCTCN2019089171-appb-000001
Figure PCTCN2019089171-appb-000002
从表1可以看出：
1)对比例中制备的催化剂C1对CO、CH 4和NO三种污染物均有很高的转化效率，平均转化率超过90％，但是催化剂C1反应副产物NH 3排放较高，大幅超过国六法规的排放限值(10ppm)；
2)增加了第二催化剂后，催化剂C1、C2、C3和C4的反应副产物NH 3的生成量均降至10ppm以下，并且由于第二催化剂对CH 4和CO有一定的转化效率，催化剂C1、C2、C3和C4对CH4和CO的转化率有一定程度的提高，但由于第二催化剂氧化NH 3的产物有一定量的NO生成，因此，催化剂C1、C2、C3和C4对NO的转换率哟略微降低；
3)实施例1制备的催化剂C2和对比例制备的催化剂C1比较，银催化剂C2增加了第二催化剂，NH 3的排放量显著降低；
4)实施例1制备的催化剂C2和实施例2制备的催化剂C3比较，调整第一催化剂和第二催化剂的提及占比，当增加第二催化剂和第一催化剂的比例后，NH 3的排放量略微降低，同时CO、CH 4和NO的转化率略微升高；
5)实施例2制备的催化剂C3和实施例3制备的催化剂C4比较，调整第二催化剂上层和下层层的含量比例，当增加上层的含量后，NH 3的排放量略微降低，同时NO的转化率略微升高，但CO和CH 4的转化率略微降低；
6)实施例3制备的催化剂C4和实施例4制备的催化剂C5比较，单极分段催化剂和两极催化剂对比，在氧气含量一样的条件下，活性基本相当，对各污染性气体的转化率基本相同。
上述实验说明：本发明的尾气处理催化剂，第一催化剂与第二催化剂相互配合工作，第一催化剂能净化处理尾气中的NO、HC、CO和PM，第二催化剂能净化处理尾气原排和第一催化剂催化副产物NH 3，以及净化前段未反应完全的NO、HC和CO，净化处理效率高，能够显著减少尾气中各污染性气体特别是新增副产物NH 3的含量，使其能满足国六的排放要求。
实验例
改变实施例1中第一催化剂和第二催化剂的涂覆体积，并进行活性评价试验，实验条件如下所示：
模拟天然气发动机尾气气体体积组成：CH 4:1000ppm；CO:4000ppm；NO:1000ppm；O 2:3500ppm；H 2O:10％；CO 2:10％；N 2为平衡气；空速40000h -1(根据TWC的体积计算的空速)。试验条件及氨气生成量如表2所示。
表2第一催化剂和第二催化剂体积比对NH 3生成量的影响
Figure PCTCN2019089171-appb-000003
从表3可以看出，改变第一催化剂和第二催化剂的体积比，将会影响氨气生成量，第一催化剂与第二催化剂体积比优选为(1～3):(1～2)。

Claims (10)

  1. 一种尾气处理催化剂，其特征在于，所述催化剂由载体、第一催化剂和第二催化剂组成，所述第一催化剂和第二催化剂设于所述载体两端，第一催化剂能净化处理尾气中的CH 4、NMHC、CO和NO x；第二催化剂能净化处理第一催化剂净化处理后的副产物NH 3以及第一催化剂未净化完全的部分污染物；其中，
    所述第二催化剂为双层结构，下层由储氧材料、氧化铝和第二活性组分组成，
    所述第二活性组分为Pt与Pd的组合物，或者Ce、Fe、Ni、Cu的组合物；
    上层由分子筛和第三活性组分组成，
    所述第三活性组分为Cu，或者Cu、Fe的组合物。
  2. 如权利要求1所述的尾气处理催化剂，其特征在于，所述第二催化剂上、下两层的总上载量为100～300g/L，其中，上层与下层上载量之比为(0.1～10)：1。
  3. 如权利要求1所述的尾气处理催化剂，其特征在于，所述第二活性组分为Pt、Pd的组合物时，Pt与Pd的重量配比为(10～1)：(1～0)。
  4. 如权利要求1所述的尾气处理催化剂，其特征在于，所述第二催化剂下层中第二活性组分含量为0.1～10g/ft 3。
  5. 如权利要求1所述的尾气处理催化剂，其特征在于，所述分子筛为Beta、ZSM-5、SSZ-13或SAPO-34等小孔分子筛中的一种或几种的组合物。
  6. 如权利要求1所述的尾气处理催化剂，其特征在于，所述第一催化剂由储氧材料、氧化铝、助剂和第一活性组分组成；所述第一活性组分为Pt、Pd和Rh的组合物。
  7. 如权利要求6所述的尾气处理催化剂，其特征在于，所述第一活性组分中Pt、Pd和Rh的重量配比为(0～50)：(1～100)：(1～10)。
  8. 如权利要求1所述的尾气处理催化剂，其特征在于，所述第一催化剂与第二催化剂的体积比为(0.5～10):1。
  9. 权利要求1～8任一项所述的尾气处理催化剂的制备方法，其特征在于，包括如下步骤：
    1)第一催化剂制备：
    S01.将第一活性组分前躯体浸渍到储氧材料和氧化铝表面，然后于60～120℃干燥2～10小时，在350～600℃的空气气氛中焙烧2～5小时，得到M-1；
    S02.将M-1与1～5wt.％的粘接剂混合，球磨制浆，添加0～5wt.％的助剂，所述助剂添加量以助剂氧化物计，即得第一催化剂浆料N-1；
    2)第二催化剂制备：
    S01.将第二活性组分前躯体浸渍到储氧材料和氧化铝表面，然后于60～120℃干燥2～10小时，在350～600℃的空气气氛中焙烧2～5小时，得到M-2；
    S02.将M-2与1～5wt.％的粘接剂混合，球磨制浆，添加0～5wt.％的助剂，所述助剂添加量以助剂氧化物计，即得第二催化剂下层浆料N-2；
    S03.将第三活性组分前躯体以离子交换法交换到分子筛骨架内，过滤，洗涤，然后于60～120℃干燥2～10小时，在350～650℃的空气气氛中焙烧2～8小时，得到M-3；
    S04.将M-3与1～5wt.％的粘接剂混合，球磨制浆，添加0～5wt.％的助剂，所述助剂添加量以助剂氧化物计，即得第二催化剂上层浆料N-3；
    3)尾气处理催化剂制备：在载体一端涂覆浆料N-1，在载体另一端依次涂覆浆料N-2和浆料N-3，然后于60～120℃干燥2～10小时，并在350～600℃的空气气氛中焙烧2～8小时，即得尾气处理催化剂。
  10. 权利要求1～8任一项所述的尾气处理催化剂在净化处理天然气汽车尾气中的用途。
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