CN111957342B - Small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in tail gas of diesel vehicles at low temperature and preparation method and application thereof - Google Patents

Small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in tail gas of diesel vehicles at low temperature and preparation method and application thereof Download PDF

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CN111957342B
CN111957342B CN202010653519.5A CN202010653519A CN111957342B CN 111957342 B CN111957342 B CN 111957342B CN 202010653519 A CN202010653519 A CN 202010653519A CN 111957342 B CN111957342 B CN 111957342B
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molecular sieve
ssz
temperature
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nitrogen oxides
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CN111957342A (en
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陈培榕
陈冬冬
付名利
叶代启
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South China University of Technology SCUT
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/74—Noble metals
    • B01J29/743—CHA-type, e.g. Chabazite, LZ-218
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/30—Ion-exchange
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/20—After treatment, characterised by the effect to be obtained to introduce other elements in the catalyst composition comprising the molecular sieve, but not specially in or on the molecular sieve itself

Abstract

The invention discloses a small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in tail gas of diesel vehicles at low temperature, and a preparation method and application thereof. The method comprises the following steps: (1) pretreatment of commercial small pore molecular sieve H-SSZ-13; (2) uniformly loading a Pd component on the surface of the treated molecular sieve by adopting an ion exchange or impregnation mode to prepare a Pd-based single-component molecular sieve system; (3) and doping the second component Ce into the Pd-SSZ-13 system by means of ion exchange to prepare the bimetallic supported molecular sieve PNA system. The method of the invention can not only provide more NOxAdsorption sites to promote NO at low temperature for PNA systemxThe adsorption efficiency of (A) and the anti-poisoning ability of the molecular sieve type PNA system can be effectively improved, thereby effectively realizing NO at low temperaturexThe method can be widely applied to the field of atmospheric pollution treatment.

Description

Small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in tail gas of diesel vehicles at low temperature and preparation method and application thereof
Technical Field
The invention relates to a preparation method of a small pore molecular sieve loaded Pd and Ce bimetallic material (PdCe-SSZ-13) and a method for removing nitrogen oxide at low temperatureSubstance (NO)x) Belonging to the technical field of thermal catalytic materials.
Background
As is well known, NOxThe method is an important precursor for the formation of fine particulate matters (PM 2.5) in the atmospheric environment, and the large emission of the fine particulate matters can cause serious urban dust-haze pollution problems and also can cause serious environmental pollution events such as acid rain, photochemical smog and the like. And, NOxIt causes severe damage to the ozone layer and is also a major gas forming the greenhouse effect. NO in the atmospherexThe source of (A) is mainly divided into two aspects: on one hand, the nitrogen is generated by the nature and discharged into the environment, including the nitrogen fixation process of nitrogen-fixing bacteria and the natural lightning process; on the other hand, the human body is generated by human activities, and mainly comprises various life and production processes. NO from naturexCan be naturally digested and utilized without serious pollution. However, with the development of economy and society, the living standard of people is continuously improved due to the emission of NO into the atmosphere by human activitiesxThe total amount is rising, which poses a serious threat to human survival and physical health. NO produced by high-temperature combustion of fuels of thermal power plants, various industrial furnaces, diesel vehicles and the likexNO emitted during human activitiesxThe total content is up to more than 90%. Wherein the diesel vehicle is city atmosphere NOxThe most dominant source of emissions.
Currently on diesel vehicles NOxMainly comprises nitrogen oxide storage reduction (NSR) and selective catalytic reduction (NH)3-SCR，H2-SCR, etc.) wherein the effective operating temperature of the NSR is above 250 ℃, SCR also has to be above 200 ℃. However, under cold-start conditions (within 200 s before the start of the vehicle engine), the exhaust aftertreatment system temperature does not quickly reach the effective operating windows of NSR and SCR. NO produced at this stagexDirectly discharged into the atmospheric environment without treatment, and causes non-negligible harm to the environment and the human health. Under the increasingly severe background of emission policy, the bottleneck of the traditional method is broken through, and a new technical means is found for realizing NO in the cold start processxIs subjected to innocent treatmentThe method is extremely important in theoretical significance and strategic necessity, and accords with the struggle target of building an ecological civilized society in China.
Research reports that the Pd-based molecular sieve system can efficiently adsorb NO under low-temperature conditions (at the cold start stage of an automobile)xRelease of NO within the temperature window of NSR and SCR operationxEventually to reach NOxConversion to harmless N2And H2And (4) purpose of O. The system shows excellent low temperature NO removalxThe property of (A) is that NO more regular Chinese name exists for the material at present, and the English name is passive NOxabsorber, abbreviated PNA. At present, most studied PNA systems mainly include transition metal oxides carrying noble metals and molecular sieves carrying noble metals, and compared with transition metal oxides, molecular sieve systems have more excellent sulfur poisoning resistance at low temperature, and thus are receiving more extensive attention. Pd-supported molecular sieve catalyst as an important component of PNA system in NOxPlays an increasingly important role in low-temperature harmless removal.
Disclosure of Invention
The invention aims to provide a bimetallic supported molecular sieve catalyst (PdCe-SSZ-13) and a preparation method thereof, and the catalyst is used for diesel vehicle tail gas NO under the condition of low temperaturexAnd (4) removing.
The technical scheme of the invention is as follows.
A preparation method of a small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in tail gas of diesel vehicles at low temperature is characterized in that rare earth element cerium (Ce) rich in China is added into a traditional Pd-based molecular sieve, so that the low-temperature removal of nitrogen oxides in tail gas of diesel vehicles by a system can be greatly improved, the use amount of noble metal Pd is reduced, the hydrothermal stability of the material can be improved, and the service life of the material is prolonged; the preparation method of the material comprises the following steps: the method is characterized in that a commercial H-SSZ-13 molecular sieve with sufficient supply is used as a substrate material, a Pd-SSZ-13 material is prepared by adopting a simple ion exchange or impregnation method, and finally rare earth metal Ce is introduced into a Pd-SSZ-13 system by using an ion exchange method.
The method comprises the following steps:
a. placing a commercial proton type molecular sieve H-SSZ-13 in a tubular furnace at a high temperature of 500-600 ℃ for calcining for 10-12H, adding the calcined product into an ammonium sulfate solution, stirring at room temperature, filtering the stirred turbid solution, washing with deionized water and absolute ethyl alcohol for several times, and then transferring the slurry sample into an oven for drying at the drying temperature of 50-220 ℃ for 12-24H;
b. Pd-SSZ-13 is prepared by adopting one of the following methods; the preparation of Pd-SSZ-13 by the ion exchange method is the step (1) in the following steps, and the preparation of Pd-SSZ-13 by the impregnation method is the step (2) in the following steps.
(1) Weighing 1-15 g of the molecular sieve product in the step a, placing the molecular sieve product in a tube furnace for pretreatment, adding the calcined product into a round-bottom flask (the volume is 50-250 mL) containing a palladium nitrate solution with the concentration of 0.01-0.15 mol/L, fully mixing, transferring the product into an oil bath pot, heating and stirring at 50-100 ℃ for 10-24 hours to complete an ion exchange process, cooling and protecting by using a condensation reflux device in the heating process, and preventing the water in the bottle from being evaporated to dryness to obtain Pd-SSZ-13;
(2) weighing 2-10 g of the product obtained in the step a, adding the product into a palladium nitrate solution with the concentration of 0.01-0.15 mol/L, uniformly stirring (stirring by a glass rod for about 5-20 min), standing at room temperature for 12-36 h, and completing the impregnation process to obtain Pd-SSZ-13;
c. filtering the product subjected to ion exchange in the step b, washing the product with deionized water for several times, then placing the product in an oven for drying for 12-18 h (the impregnated sample is directly transferred to the oven for drying under the same conditions), and placing the dried product in a tubular furnace for calcining to obtain an initial Pd-SSZ-13 catalyst;
d. weighing 10-30 mL of deionized water, weighing cerium acetate monohydrate, dissolving into the deionized water, and stirring for several minutes until solid substances are completely dissolved to obtain a cerium acetate solution;
e. weighing a certain amount of the initial Pd-SSZ-13 catalyst in the step c, adding the initial Pd-SSZ-13 catalyst into the cerium acetate solution prepared in the step d, wherein the mass ratio of Pd to Ce is 1/1-10/1, and stirring at room temperature to ensure that Ce ions are fully exchanged;
f. and e, filtering the product subjected to ion exchange in the step e, washing the product for a plurality of times by using deionized water, transferring the slurry product obtained by filtering into a drying oven, and drying to obtain the small pore molecular sieve loaded bimetallic material for removing the nitrogen oxides in the tail gas of the diesel vehicle at low temperature.
In the method, in the step a, the concentration of the ammonium sulfate is 0.1-10 mol/L; the stirring speed is 600-900 r/min; the stirring time is 0.1-10 h.
In the method, in the step b, the pretreatment temperature is 500-600 ℃, and the time is 1-5 h.
In the method, in the step c, the temperature in the oven is 100-220 ℃; the temperature in the tubular furnace is 500-600 ℃, and the calcining time is 1-5 h.
In the method, in the step d, the concentration of the cerium acetate solution is 0.1-10 mol/L.
In the method, in the step e, the stirring time is 30-120 min, and the stirring speed is as follows: 600 to 900 r/min.
In the above method, in step f, the drying is: drying for 5-20 h at 50-100 ℃.
The utility model provides a low temperature gets rid of little pore molecular sieve load bimetallic material of diesel vehicle tail gas nitrogen oxide, little pore molecular sieve load bimetallic material can high-efficiently get rid of the nitrogen oxide at low temperature, the absorption of little pore molecular sieve load bimetallic material to the nitrogen oxide is the dibit point absorption, and the introduction of rare earth element Ce can effectively promote the anti hydrothermal ability of material moreover, prolongs the life of material. The small pore molecular sieve loaded bimetallic material is applied to removal of nitrogen oxides discharged in the initial starting stage of a diesel vehicle engine, wherein the initial starting stage of the engine is 0-200 seconds from the start, the temperature is lower than 200 ℃, and the process is called as a cold start process.
According to the technical scheme provided by the invention, the preparation method can provide more NOxAdsorption sites, enhancement of PNA system to NO at low temperaturexThe adsorption performance of (c); meanwhile, the Ce is added to inhibit the agglomeration of active species in the reaction process, and the PNA system is promoted to be used in the actual diesel vehicleTail gas NOxService life in decontamination applications.
The invention has the beneficial effects that:
(1) the invention obtains the bimetallic supported molecular sieve catalyst PdCe-SSZ-13 by a two-step method. On one hand, the addition of Ce can increase more adsorption sites, and is beneficial to improving NO of PNA system at low temperaturexThe adsorption efficiency of (a); on the other hand, the excellent oxygen storage capacity of the rare earth element Ce can be beneficial to converting NO into NO in the high-temperature desorption process2For late NH3-NO in SCR ProcessxThe improvement of the removal efficiency has great promotion effect.
(2) The invention obtains the bimetallic supported molecular sieve catalyst PdCe-SSZ-13 by a two-step method, wherein the addition of Ce can improve the performances of the catalyst in the aspects of high temperature water resistance, phosphorus poisoning resistance and the like, can effectively inhibit the agglomeration of active species caused by the dealumination of the molecular sieve under harsh conditions, and can provide technical basis and theoretical support for the practical application of a PNA system.
Drawings
FIG. 1 is a transmission electron micrograph of the molecular sieve supported active component catalyst prepared in example 2 (PdCe-SSZ-13 catalyst, molecular sieve/palladium nitrate mass ratio of 23/1, Pd/Ce mass ratio of 5/1); wherein (a): 50 nm, (b): 20 nm, (c): 200 nm, (d) elemental profile (Pd);
FIG. 2 is a phase structure representation of the molecular sieve supported active component catalyst (Pd supported by ion exchange) prepared in example 1;
FIG. 3 is a phase structure representation of the molecular sieve supported active component catalyst (Pd supported by impregnation) prepared in example 2;
FIG. 4 shows the adsorption at low temperature and the desorption at high temperature of NO for the molecular sieve supported bimetallic active component catalyst (ion exchange supported Pd) prepared in example 1xPerformance graph of (a);
FIG. 5 adsorption at low temperature and desorption at high temperature of NO for the molecular sieve supported bimetallic active component catalyst (Pd supported by impregnation method) prepared in example 2xPerformance graph of (2).
Detailed Description
The technical solutions in the embodiments are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and these are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
（1）NH4Preparation of the-SSZ-13 catalyst
(1-1) weighing 5-20 g of commercial H-SSZ-13, placing the commercial H-SSZ-13 in a tube furnace, and calcining the commercial H-SSZ-13 for 12 hours at the temperature of 520 ℃ under the condition of dry air for later use; adding 20g of ammonium sulfate into a proper amount of water (the solution concentration is 8 mol/L, the solution volume is 250mL), and stirring for several minutes under the ultrasonic condition until the ammonium nitrate is completely dissolved; 40g of the high-temperature calcined H-SSZ-13 molecular sieve is weighed and added into the ammonium sulfate solution, then the mixed solution is transferred to a magnetic stirrer to be stirred for 2.5H (800 r/min) at normal temperature, and the stirred mixed solution is filtered to obtain white solid which is washed by deionized water for several times. Repeating the above process for 3 times, placing the obtained white solid in an oven, and drying at 160 deg.C for 20 hr to obtain NH4-SSZ-13。
(1-2) a preparation method of Pd-SSZ-13 (ion exchange method), which is one of the following steps A) and B): A) pretreatment of a carrier: 11.5g of NH in (1-1) was weighed4SSZ-13 and transferred to a tube furnace, calcined at 520 ℃ for 3 h under dry air conditions;
B) pd ion exchange: NH pretreated at high temperature in A)4-SSZ-13 is poured into a flask (volume 100 mL) containing 30 g of deionized water, 0.5 g of palladium nitrate dihydrate (molecular sieve/palladium nitrate mass ratio: 23/1) is weighed into a beaker and vigorously stirred (with a condensation circulation device) at 60 ℃ for 15 h until the ion exchange process is completed, the stirred mixture is filtered and washed with deionized water several times to obtain a brown mud-like sample, which is then transferred to an oven for drying at 120 ℃ for 15 h, and the dried sample is calcined at 550 ℃ for 2 h to obtain the Pd-SSZ-13 sample.
C) Active component Ce loading: weighing 3 g of Pd-SSZ-13 calcined at high temperature, 20g of deionized water and 0.037 g of cerium acetate monohydrate (the mass ratio of Pd to Ce is 5/1) in a beaker, stirring strongly (needing a condensation circulation device) at room temperature for 90min (the stirring rate is 800 r/min) until the ion exchange process is completed, filtering the stirred mixed solution, washing the mixed solution for several times by using the deionized water, transferring the obtained brown sample into an oven, and drying the brown sample at 80 ℃ for 12 h to prepare a PdCe-SSZ-13 sample;
(2) and (2) calcining the PdCe-SSZ-13 prepared in the step (1) for 6 hours at 550 ℃ in dry air for later use. Phase structure characterization is carried out on Pd-SSZ-13 and PdCe-SSZ-13, and the result is shown in FIG. 2, and it can be seen from the figure that the structure of the molecular sieve is well preserved after Pd and Ce are introduced, and no obvious characteristic peaks of Pd and Ce appear, which indicates that the bimetallic has high dispersity on the molecular sieve;
(3) the PNA experiment is carried out, and the reaction temperature is 100-500 ℃. 50 mg of PdCe-SSZ-13 calcined at high temperature and 0.45 g of quartz sand (60-80 meshes) are uniformly mixed in a self-made reaction bed layer (arranged in a quartz glass tube); ② in 10 percent of O2Is pretreated for 1 h at 500 ℃, and is cooled to room temperature, and then the atmosphere is converted into 200 ppm NO and 6% O2The mixed atmosphere of (3); carrying out temperature programmed reaction: the temperature is raised from room temperature to 100 ℃ at the temperature raising rate of 5 ℃/min and is kept for 10 min, and then the temperature is raised from 100 ℃ to 500 ℃ at the speed of 10 ℃/min, and the experiment is completed.
The molecular sieve supported active component catalyst (PdCe-SSZ-13) prepared in the example is used for NO at low temperaturexThe removal reaction of (1). NOxThe concentration is 200 ppm, the space velocity is 240,000 ml h-1 g-1The reaction activity curve is shown in FIG. 4.
Example 2
（1）NH4Preparation of the-SSZ-13 catalyst
(1-1) weighing 5-20 g of commercial H-SSZ-13, placing the commercial H-SSZ-13 in a tube furnace, and calcining the commercial H-SSZ-13 for 12 hours at the temperature of 520 ℃ under the condition of dry air for later use; adding 20g of ammonium sulfate into a proper amount of water (the solution concentration is 8 mol/L, the solution volume is 250mL), and stirring for several minutes under the ultrasonic condition until the ammonium nitrate is completely dissolved; weighingAdding 40g of the high-temperature calcined H-SSZ-13 molecular sieve into the ammonium sulfate solution, then transferring the mixed solution onto a magnetic stirrer, stirring at normal temperature for 2.5H (800 r/min), filtering the stirred mixed solution to obtain a white solid, and washing with deionized water for several times. Repeating the above process for 3 times, placing the obtained white solid in an oven, and drying at 160 deg.C for 20 hr to obtain NH4-SSZ-13。
(1-2) a preparation method of Pd-SSZ-13 (impregnation method), which is one of the following steps A) and B): 11.5g of NH in (1-1) was weighed4-SSZ-13 is transferred to a tube furnace and calcined at 520 ℃ for 3 h under dry air conditions;
B) pd impregnation: 5g of NH calcined at high temperature are weighed4Pouring the-SSZ-13 and 0.208 g of palladium nitrate dihydrate (the mass ratio of the molecular sieve to the palladium nitrate is 23/1) into a beaker filled with 10g of deionized water, stirring the mixture by a glass rod for 15min, standing the mixture at room temperature for 24h, transferring the sample into a drying oven, baking the sample for 15 h at 120 ℃, and calcining the dried sample for 2 h at 550 ℃ to prepare the Pd-SSZ-13 sample. In fig. 1, it can be observed that the bimetallic Pd and Ce has been successfully supported on the cubic small-pore molecular sieve, and the distribution is relatively uniform, so that the bimetallic Pd and Ce can be used as an active site for removing NOx at low temperature.
C) Active component Ce loading: weighing 3 g of Pd-SSZ-13 calcined at high temperature, 20g of deionized water and 0.037 g of cerium acetate monohydrate (the mass ratio of Pd to Ce is 5/1) in a beaker, stirring strongly (needing a condensation circulation device) at room temperature for 90min (the stirring rate is 800 r/min) until the ion exchange process is completed, filtering the stirred mixed solution, washing the mixed solution for several times by using the deionized water, transferring the obtained brown sample into an oven, and drying the brown sample at 80 ℃ for 12 h to prepare a PdCe-SSZ-13 sample;
(2) and (2) calcining the PdCe-SSZ-13 prepared in the step (1) for 6 hours at 550 ℃ in dry air for later use. Phase structure characterization results of Pd-SSZ-13 and PdCe-SSZ-13 are shown in FIG. 3, and from the figure, it can be observed that the introduction of bimetallic Pd and Ce does not change the structure of the molecular sieve, and the dispersion of bimetallic on the molecular sieve is high;
(3) the PNA experiment is carried out, and the reaction temperature is 100-500 ℃. 50 mg of the extractThe PdCe-SSZ-13 after high-temperature calcination and 0.45 g of quartz sand (60-80 meshes) are uniformly mixed in a self-made reaction bed layer; ② in 10 percent of O2Is calcined at 500 ℃ for 1 h, cooled to room temperature and then converted to 200 ppm NO and 6% O2The mixed atmosphere of (3); carrying out temperature programmed reaction: raising the temperature from room temperature to 100 ℃ at a temperature raising rate of 5 ℃/min, keeping the temperature for 10 min, and raising the temperature from 100 ℃ to 500 ℃ at a temperature of 10 ℃/min.
The molecular sieve supported active component catalyst (PdCe-SSZ-13) prepared in the example is used for NO at low temperaturexThe removal reaction of (1). NOxThe concentration is 200 ppm, and the space velocity is 240,000 ml h-1 g-1The reaction activity curve is shown in FIG. 5.
The phase characterization of the materials referred to in examples 1 and 2 above was carried out on an Ultima type IV X-ray diffractometer manufactured in japan, measuring in the range of 5 ° to 70 °, and the sample was sufficiently dried and ground to be powdery before the test. The microstructure of the material is characterized by adopting an FEI Talos F200X type transmission electron microscope, the accelerating voltage is 200 kV during testing, a sample is subjected to ultrasonic dispersion in absolute ethyl alcohol for 5-10 minutes before testing, then a liquid transfer gun is used for taking suspended liquid to be dropped on a copper net attached with a carbon film, and finally the suspended liquid is placed under an infrared lamp to be dried for 20 min and then tested.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention in any way
Any modification, equivalent replacement, improvement and the like made within the principle should be included in the protection scope of the present invention.

Claims (2)

1. A preparation method of a small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in tail gas of diesel vehicles at low temperature is characterized in that rare earth element cerium (Ce) is added into a Pd-based molecular sieve, so that the low-temperature removal of nitrogen oxides in tail gas of diesel vehicles by a system can be greatly improved, the use amount of noble metal Pd is reduced, the hydrothermal stability of the material can be improved, and the service life of the material is prolonged; the preparation method of the material comprises the following steps: taking an H-SSZ-13 molecular sieve with sufficient supply as a substrate material, preparing a Pd-SSZ-13 material by adopting a simple ion exchange or impregnation method, and finally introducing rare earth metal Ce into a Pd-SSZ-13 system by using an ion exchange method;
the method comprises the following steps:
a. placing a proton type molecular sieve H-SSZ-13 in a tubular furnace at a high temperature of 500-600 ℃ for calcining for 10-12H, adding the calcined product into an ammonium sulfate solution, stirring at room temperature, filtering the stirred turbid solution, washing the turbid solution with deionized water and absolute ethyl alcohol for several times, then transferring the slurry sample into a drying oven for drying at the drying temperature of 50-220 ℃ for 12-24H;
b. Pd-SSZ-13 is prepared by adopting one of the following methods; the preparation of Pd-SSZ-13 by the ion exchange method is a step (1) in the following steps, and the preparation of Pd-SSZ-13 by the impregnation method is a step (2) in the following steps;
(1) weighing 1-15 g of the molecular sieve product in the step a, placing the molecular sieve product in a tubular furnace for pretreatment, then adding the calcined product into a round-bottom flask containing a palladium nitrate solution with the concentration of 0.01-0.15 mol/L, fully mixing, transferring the mixture into an oil bath kettle, heating and stirring at 50-100 ℃ for 10-24 hours to complete an ion exchange process, cooling and protecting by using a condensation reflux device in the heating process, and preventing the water in the bottle from being evaporated to dryness to obtain Pd-SSZ-13;
(2) weighing 2-10 g of the product obtained in the step a, adding the product into a palladium nitrate solution with the concentration of 0.01-0.15 mol/L, uniformly stirring, standing at room temperature for 12-36 h, and completing the impregnation process to obtain Pd-SSZ-13;
c. filtering the product subjected to ion exchange in the step b, washing the product with deionized water for several times, then placing the product in an oven for drying for 12-18 h, directly transferring the impregnated sample into the oven for drying under the same conditions, and placing the dried product in a tubular furnace for calcining to obtain an initial Pd-SSZ-13 catalyst;
d. weighing 10-30 mL of deionized water, weighing cerium acetate monohydrate, dissolving into the deionized water, and stirring for several minutes until solid substances are completely dissolved to obtain a cerium acetate solution;
e. weighing a certain amount of the initial Pd-SSZ-13 catalyst in the step c, adding the initial Pd-SSZ-13 catalyst into the cerium acetate solution prepared in the step d, wherein the mass ratio of Pd to Ce is 1/1-10/1, and stirring at room temperature to ensure that Ce ions are fully exchanged;
f. e, filtering the product subjected to ion exchange in the step e, washing the product for a plurality of times by using deionized water, transferring the slurry product obtained by filtering into a drying oven, and drying to obtain a small pore molecular sieve loaded bimetallic material for removing nitrogen oxides in the tail gas of the diesel vehicle at low temperature;
the small pore molecular sieve loaded bimetallic material can efficiently remove nitrogen oxides at low temperature, the adsorption of the small pore molecular sieve loaded bimetallic material on the nitrogen oxides is double-site adsorption, and the introduction of the rare earth element Ce can effectively improve the heat and water resistance of the material and prolong the service life of the material;
the small pore molecular sieve loaded bimetallic material is applied to removal of nitrogen oxides discharged in the initial starting stage of a diesel vehicle engine, wherein the initial starting stage of the engine is 0-200 seconds from the start, the temperature is lower than 200 ℃, and the process is called as a cold start process;
in the step b, the temperature of the pretreatment is 500-600 ℃, and the time is 1-5 h;
in the step c, the temperature in the oven is 100-220 ℃; the temperature in the tubular furnace is 500-600 ℃, and the calcining time is 1-5 h;
in the step d, the concentration of the cerium acetate solution is 0.1-10 mol/L;
in the step e, the stirring time is 30-120 min, and the stirring speed is as follows: 600-900 r/min;
in step f, the drying is as follows: drying for 5-20 h at 50-100 ℃.
2. The preparation method of the small pore molecular sieve loaded bimetallic material for removing the nitrogen oxides in the tail gas of the diesel vehicle at low temperature according to claim 1, wherein in the step a, the concentration of the ammonium sulfate is 0.1-10 mol/L; the stirring speed is 600-900 r/min; the stirring time is 0.1-10 h.
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