CN110975800A - Pd-based NOXAdsorbent and preparation method and application thereof - Google Patents

Abstract

The invention discloses Pd-based NO_XThe preparation method of the adsorbent comprises the following steps: s1, carrying out ammonium ion exchange on the zeolite molecular sieve to obtain an ammonium type molecular sieve; s2, performing palladium ion exchange on the ammonium molecular sieve to obtain a first precursor; s3, dropwise adding a water solution containing palladium ions into the first precursor, uniformly mixing, standing, soaking and drying to obtain a second precursor; s4, roasting the second precursor, and carrying out hydrothermal activation to obtain Pd-based NO_XAn adsorbent. The invention also discloses Pd-based NO_XAdsorbent according to the above Pd-based NO_XThe preparation method of the adsorbent. The invention also discloses the Pd-based NO_XThe application of the adsorbent in adsorbing automobile exhaust. Pd-based NO prepared by the invention_XAdsorbent for low-temperature efficient and rapid adsorption and storage of NO_XAnd high temperature thermal desorptionNO_XCan realize NO in the cold start stage of the diesel engine_XAnd (4) innocent treatment.

Description

Pd-based NOXAdsorbent and preparation method and application thereof

Technical Field

The invention relates to the technical field of adsorbents, in particular to Pd-based NO_XAn adsorbent and a preparation method and application thereof.

Background

Since 2015, automobile emission problems have been continuously fermented under the continuous aggravation of domestic atmospheric pollution. In order to reduce tail gas pollution, the hard requirement on tail gas emission is accelerated in recent years in China, the national fourth standard is pushed out in 2014, and all heavy diesel vehicles manufactured, imported, sold and registered in China need to meet the national fifth standard requirement in 2017, 7 month and 1 day. As early as 2016, the ministry of environmental protection and the national quality control agency jointly issued "emission limits of light-duty automotive pollutants" and measurement methods (sixth stage of china "), which were classified into two emission limit schemes a and b and started to be implemented in 2020 and 2023, respectively. The time span is less than 3 years from the implementation of the national five standards, and the time interval is greatly shortened compared with the conventional time interval. After the implementation of the six national standards, the exhaust emission of motor vehicles will be reduced by about 40-60% on average, and the standard of emission limits of light vehicle pollutants and measurement methods (the sixth stage of china) will become one of the strictest emission standards of light vehicles in the world.

The catalytic purification of automobile tail gas means that CO, HC and NO in the tail gas are reduced by means of some effective technical measures_XThe harmful substances in the tail gas are oxidized or reduced to generate nontoxic CO₂、H₂O and N₂. At present, the main measures for controlling the automobile exhaust emission comprise three measures, namely a pre-measure, an in-measure and an after-measure, wherein the pre-measure and the in-measure have high technical difficulty and limited emission reduction effect, and the after-measure adopts measures including air injection, an oxidation type reactor, a three-way catalyst and the like to purify the exhaust emission, so that the method is the most mainstream and effective exhaust treatment method at present, and the catalyst is the key of the purification effect.

Because the emission limit value of light automobile pollutants and the measurement method (sixth stage of China) standard of the light automobile pollutants greatly improve the requirements on the emission limit of the tail gas of the motor vehicle and the test cycle, the emission limit value of the light automobile pollutants and the measurement method are particularly highIn particular to NO in tail gas_XAnd (4) controlling. With increasingly stringent emissions regulations, increased fuel efficiency, and decreased engine exhaust temperatures, exhaust emission control during engine cold start emissions will become more difficult.

Prior to the official implementation of standards for emission limits and measurement methods for pollutants for light-duty automobiles (sixth stage of China), the industry generally used vanadium-based SCR catalysts to convert NO into NO_XReduction to N₂So as to realize the standard emission of the tail gas of the motor vehicle. Vanadium-based SCR catalyst for NO_XThe conversion rate of the vanadium-containing catalyst reaches more than 90%, the working temperature window is narrow (250 ℃ C. and 450 ℃ C.), and certain vanadium loss can exist. Emission standard of light automobile pollutant emission limit and measurement method (sixth stage of China) to be implemented greatly reduces NO_XThe emission limit requirement is that the vanadium-based SCR catalyst can not meet the NO of the cold start stage of the engine_XResulting in a cold start phase NO of the vehicle_XThe emission exceeds the standard.

The existing research shows that the copper-based catalyst taking the molecular sieve material as the carrier is a relatively ideal SCR catalyst, and has a wider working temperature window compared with a vanadium-based SCR catalyst, for example, Cu-SSZ-13 is taken as the example, NO of the catalyst_XThe working temperature window when the conversion reaches 90% is 200-550 ℃, but when the flue gas temperature is lower than 200 ℃, such as in the cold start stage of an automobile or in a low-speed running state for a long time, at the moment, the copper-based SCR molecular sieve catalyst is difficult to play a role, and the emission limit of light automobile pollutants and the NO in the measurement method (the sixth stage in China) cannot be reached in the full-temperature stage_XEmission limit requirements.

Due to the novel Cu-based SCR catalyst for catalyzing and reducing NO_XThe temperature requirement is generally not lower than 200 ℃, so that the development of a high-efficiency low-temperature adsorption-high-temperature desorption NO is needed_XAdsorbing material, can realize NO in cold start stage of diesel engine_XAnd (4) innocent treatment. The function of the Cu-based SCR catalyst at the rear end of the tail gas post-treatment device is combined, and the total temperature section NO of the diesel vehicle can be finally realized_XThe emission control of (1).

Pd-based NO as presently disclosed in the literature_XThe synthesis technique of the adsorbentIn the technical route, an ion exchange method, an isometric impregnation method, an excess impregnation method, a solid-state ion exchange method and the like are mainly adopted, the ion exchange method can cause that the Pd ion exchange rate is too low, most Pd ions remain in the reaction liquid, loss and environmental pollution are caused, and the recovery is difficult; the isovolumetric impregnation method and the excess impregnation method can cause the aggregation of Pd ions, so that part of Pd is oxidized into PdO and the adsorption-desorption NO is lost_XThe ability of (c); the solid ion exchange method is difficult to operate and is not beneficial to large-scale production.

Disclosure of Invention

Based on the technical problems in the background art, the invention provides Pd-based NO_XAdsorbent, preparation method and application thereof, and Pd-based NO prepared by using adsorbent_XAdsorbent (abbreviated as Pd-LNA, LNA is Low-temperature NO)_XAcronym for Adsorber) with low temperature, efficient and fast adsorption for storage of NO_XAnd high temperature thermal desorption of NO_XCan realize NO in the cold start stage of the diesel engine_XAnd (4) innocent treatment. The function of the Cu-based SCR catalyst at the rear end of the tail gas post-treatment device is combined, and the total temperature section NO of the diesel vehicle can be finally realized_XThe emission control of (1).

The invention provides Pd-based NO_XThe preparation method of the adsorbent comprises the following steps:

s1, carrying out ammonium ion exchange on the zeolite molecular sieve to obtain an ammonium type molecular sieve;

s2, performing palladium ion exchange on the ammonium molecular sieve to obtain a first precursor;

s3, dropwise adding a water solution containing palladium ions into the first precursor, uniformly mixing, standing, soaking and drying to obtain a second precursor;

s4, roasting the second precursor, and carrying out hydrothermal activation to obtain Pd-based NO_XAn adsorbent.

Preferably, in S1, the zeolite molecular sieve is a sodium type molecular sieve.

Preferably, in S1, the framework structure of the zeolite molecular sieve is one of CHA, MFI, BEA.

The CHA, MFI and BEA framework structures are the conventional framework structures of molecular sieves.

Preferably, in S1, the zeolite molecular sieve has a silica to alumina ratio of 10 to 50.

Preferably, at least two ammonium ion exchanges are performed in S1.

Preferably, in S2 and S3, the same amount of palladium ions is used, and the palladium ions account for Pd-based NO_X0.45-0.55% of the total weight of the adsorbent.

Preferably, in S2, the temperature of palladium ion exchange is 75-85 ℃ and the time is 10-14 h.

Preferably, in S3, the temperature for standing and soaking is room temperature, and the time for standing and soaking is 10-14 h.

Preferably, in S4, the calcination temperature is 720-770 ℃, and the calcination time is 1.5-2.5 h.

Preferably, in S4, the temperature of hydrothermal activation is 720-770 ℃, and the time of hydrothermal activation is 20-30 h.

Preferably, in S4, the hydrothermal activation is performed in a mixed gas stream of water vapor, oxygen, and nitrogen.

Preferably, the volume ratio of water vapor, oxygen and nitrogen is 9-11: 4-6: 83-87.

Preferably, the flow rate of the mixed gas flow is 150-250 mL/min.

Preferably, in S1, the temperature of ammonium ion exchange is 60-70 ℃ and the time is 1.5-2.5 h.

Preferably, in S1, the zeolite molecular sieve is dried and calcined for use.

The drying treatment of the zeolite molecular sieve is mainly used for removing impurities such as water and the like adsorbed in the preparation, storage and transportation processes of the molecular sieve; the roasting treatment is mainly used for removing template agents, adsorbed impurities and the like added in the preparation process of the molecular sieve.

Preferably, the drying temperature is 75-85 ℃ and the drying time is 10-14 h.

Preferably, the roasting temperature is 550-650 ℃, the roasting time is 10-14h, and the roasting is carried out in the air atmosphere.

Preferably, in S1, the specific steps of ammonium ion exchange are: and adding the zeolite molecular sieve into an ammonium salt aqueous solution for ammonium ion exchange, and then carrying out suction filtration, washing and drying to obtain the ammonium type molecular sieve.

Preferably, NH in aqueous ammonium salt solution₄ ⁺The concentration of (A) is 0.4-0.6 mol/L.

Preferably, the ammonium salt is ammonium carbonate, ammonium chloride, ammonium nitrate or ammonium sulfate.

Preferably, in S2, the specific steps of palladium ion exchange are: and adding the ammonium molecular sieve into a water solution containing palladium ions to perform palladium ion exchange, then performing suction filtration, washing and drying to obtain a first precursor.

The water is distilled water.

The invention also provides Pd-based NO_XAdsorbent according to the above Pd-based NO_XThe preparation method of the adsorbent.

The invention also provides the Pd-based NO_XThe application of the adsorbent in adsorbing automobile exhaust.

Preferably, the adsorption of NO in automobile exhaust_XThe use of (1).

Has the advantages that:

1. the invention selects the zeolite molecular sieve as a carrier, selects one of three framework structures of CHA, MFI and BEA, has the silicon-aluminum ratio of 10-50, can improve the hydrothermal stability of the adsorbent, and can improve the load efficiency of Pd in a proper range;

2. the invention adopts multiple ammonium ion exchange to reduce Na in zeolite molecular sieve as much as possible⁺Content of NH, increase₄ ⁺The content of the sodium type molecular sieve is converted into the ammonium type molecular sieve, thereby obviously increasing the available Pd²⁺Loading on exchange sites on molecular sieves to increase Pd²⁺Exchange efficiency; the method adopts the ammonium molecular sieve to carry out Pd loading, does not need to be changed into a hydrogen type, and simplifies the process;

3. pd-based NO is prepared by adopting a method combining a palladium ion exchange method and an isometric impregnation method_XAdsorbent significantly improved Pd over palladium ion exchange or impregnation alone²⁺Reduced Pd²⁺Is lost, and increases Pd²⁺While the utilization rate of the catalyst is obviously improved²⁺The dispersibility on the molecular sieve carrier reduces the adsorptionCost of synthesis of reagents and Pd²⁺The cost of environmental protection recovery treatment;

4. pd-based NO prepared by the invention_XThe adsorbent has low temperature (below 200 ℃) for adsorbing NO_XAnd high temperature (above 250 ℃) desorption of NO_XThe function of (a);

5. pd-based NO prepared by the invention_XThe adsorbent can realize NO in the tail gas of the diesel vehicle engine_XThe high-efficiency low-temperature adsorption-high-temperature desorption function of the automobile solves the NO problem in the cold start stage of the automobile_XAnd (4) the problem of excessive emission. The function of the Cu-based SCR catalyst at the rear end of the tail gas post-treatment device is combined, and the total temperature section NO of the diesel vehicle can be finally realized_XThe emission control of (1).

Drawings

FIG. 1 shows an ammonium CHA molecular sieve and Pd-based NO_XSEM image of adsorbent, wherein NH₄ ⁺-CHA is ammonium CHA molecular sieve, and Pd-CHA is Pd-based NO_XAn adsorbent.

FIG. 2 shows an ammonium MFI molecular sieve and Pd-based NO_XSEM image of adsorbent, wherein NH₄ ⁺-MFI is an ammonium MFI molecular sieve, and Pd-MFI is Pd-based NO_XAn adsorbent.

FIG. 3 shows ammonium BEA molecular sieve and Pd-based NO_XSEM image of adsorbent, wherein NH₄ ⁺-BEA is ammonium BEA molecular sieve, Pd-BEA is Pd radical NO_XAn adsorbent.

FIG. 4 shows Pd-based NO prepared in example 1 and comparative examples 1 and 2_XAdsorbent for NO_XAdsorption profile, wherein Pd-LNA-Na⁺Comparative example 1, Pd-LNA-H⁺Comparative example 2, Pd-LNA-NH₄ ⁺Example 1 was used.

FIG. 5 shows Pd-based NO prepared in example 1 and comparative examples 1-2_XAdsorbent for NO_XDesorption profile of (2), wherein, Pd-LNA-Na⁺Comparative example 1, Pd-LNA-H⁺Comparative example 2, Pd-LNA-NH₄ ⁺Example 1 was used.

FIG. 6 is Pd-based NO prepared in example 1 and comparative examples 3 to 5_XAdsorbent for NO_XAdsorption profile, wherein Pd-LNA-NH₄ ⁺ION is a comparative example3，Pd-LNA-NH₄ ⁺IWI is comparative example 4, Pd-LNA-NH₄ ⁺-ION + ION is comparative example 5, Pd-LNA-NH₄ ⁺Example 1 for ION + IWI.

FIG. 7 shows Pd-based NO prepared in example 1 and comparative examples 3 to 5_XAdsorbent for NO_XDesorption profile of (2), wherein, Pd-LNA-NH₄ ⁺Comparative example 3, Pd-LNA-NH-ION₄ ⁺IWI is comparative example 4, Pd-LNA-NH₄ ⁺-ION + ION is comparative example 5, Pd-LNA-NH₄ ⁺Example 1 for ION + IWI.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to specific examples.

Example 1

Pd-based NO_XThe preparation method of the adsorbent comprises the following steps:

s1, carrying out ammonium ion exchange on the sodium zeolite molecular sieve for 2 times to obtain the ammonium molecular sieve, wherein the ammonium ion exchange comprises the following specific steps: adding sodium zeolite molecular sieve into NH₄ ⁺In 0.5mol/L ammonium chloride aqueous solution, performing ammonium ion exchange at 65 ℃ for 2h, then performing suction filtration, washing with water, and drying in a forced air drying oven at 80 ℃ overnight to obtain the ammonium type molecular sieve;

the framework structure of the sodium type zeolite molecular sieve is CHA, and the silica-alumina ratio of the sodium type zeolite molecular sieve is 20;

drying the sodium zeolite molecular sieve in a constant-temperature oven at 80 ℃ for 12h, then placing the dried sodium zeolite molecular sieve in a muffle furnace, and roasting the sodium zeolite molecular sieve at 600 ℃ for 12h in an air atmosphere;

s2, adding an ammonium molecular sieve into an aqueous solution containing palladium ions, uniformly mixing, placing the mixture in a constant-temperature oil bath kettle at the temperature of 80 ℃, carrying out palladium ion exchange for 12 hours by magnetic stirring, then carrying out suction filtration, washing with water, and drying in a forced air drying oven at the temperature of 80 ℃ for 12 hours to obtain a first precursor, wherein the dosage of the palladium ions accounts for Pd-based NO_X0.5% of the total weight of the adsorbent;

s3, slowly and uniformly dripping the water solution containing palladium ions into the first precursor, stirring while dripping, uniformly stirring, standing and soaking at room temperature for 12h, and then, drum-soaking at 80 DEG CDrying in an air drying oven for 12h to obtain a second precursor, wherein the dosage of palladium ions accounts for Pd-based NO_X0.5% of the total weight of the adsorbent;

s4, placing the second precursor in a muffle furnace, roasting at the constant temperature of 750 ℃ for 2h in the air atmosphere, and introducing water vapor, oxygen and nitrogen at the temperature of 750 ℃ in a volume ratio of 10: 5: 85 mixed gas flow is subjected to hydrothermal activation for 25 hours to obtain Pd-based NO_XAnd the adsorbent is used for adsorbing the gas, wherein the flow rate of the mixed gas flow is 200 mL/min.

Taking the ammonium CHA molecular sieve and Pd-based NO in example 1_XScanning the adsorbent with an electron microscope, and obtaining the result shown in figure 1, wherein figure 1 shows ammonium CHA molecular sieve and Pd-based NO_XSEM image of adsorbent, wherein NH₄ ⁺-CHA is ammonium CHA molecular sieve, and Pd-CHA is Pd-based NO_XAn adsorbent; as can be seen from FIG. 1, Pd-based NO is compared with the ammonium-type CHA molecular sieve before loading_XThe crystal morphology of the adsorbent is basically not changed, and the dispersibility of the adsorbent is relatively uniform.

Example 2

Pd-based NO_XThe preparation method of the adsorbent comprises the following steps:

s1, carrying out ammonium ion exchange on the sodium zeolite molecular sieve for 2 times to obtain the ammonium molecular sieve, wherein the ammonium ion exchange comprises the following specific steps: adding sodium zeolite molecular sieve into NH₄ ⁺The ammonium chloride aqueous solution with the concentration of 0.4mol/L is subjected to ammonium ion exchange for 1.5h at the temperature of 70 ℃, then is subjected to suction filtration and water washing, and is dried in a forced air drying oven at the temperature of 80 ℃ overnight to obtain the ammonium type molecular sieve;

the framework structure of the sodium zeolite molecular sieve is MFI, and the silica-alumina ratio of the sodium zeolite molecular sieve is 50;

drying the sodium zeolite molecular sieve in a constant-temperature oven at 75 ℃ for 14h, then placing the dried sodium zeolite molecular sieve in a muffle furnace, and roasting the sodium zeolite molecular sieve at 550 ℃ for 14h in an air atmosphere;

s2, adding an ammonium molecular sieve into an aqueous solution containing palladium ions, uniformly mixing, placing the mixture in a constant-temperature oil bath kettle at the temperature of 75 ℃, carrying out palladium ion exchange for 14 hours by magnetic stirring, then carrying out suction filtration, washing with water, and drying in a forced air drying oven at the temperature of 80 ℃ for 12 hours to obtain a first precursor, wherein the dosage of the palladium ions accounts for Pd-based NO_X0.45% of the total weight of the adsorbent;

s3, slowly and uniformly dripping an aqueous solution containing palladium ions into the first precursor, stirring while dripping, uniformly stirring, standing and soaking at room temperature for 14h, and drying in a forced air drying oven at 80 ℃ for 12h to obtain a second precursor, wherein the dosage of the palladium ions accounts for Pd-based NO_X0.45% of the total weight of the adsorbent;

s4, placing the second precursor in a muffle furnace, roasting at 770 ℃ for 1.5h in an air atmosphere, and introducing water vapor, oxygen and nitrogen at 770 ℃ in a volume ratio of 9: 6: 85 mixed gas flow is subjected to hydrothermal activation for 20 hours to obtain Pd-based NO_XAnd the adsorbent is used for adsorbing the gas, wherein the flow rate of the mixed gas flow is 250 mL/min.

Taking the ammonium MFI molecular sieve and Pd-based NO in example 2_XScanning the adsorbent with an electron microscope, and obtaining results shown in figure 2, wherein figure 2 shows the ammonium MFI molecular sieve and Pd-based NO_XSEM image of adsorbent, wherein NH₄ ⁺-MFI is an ammonium MFI molecular sieve, and Pd-MFI is Pd-based NO_XAn adsorbent; as can be seen from FIG. 2, Pd-based NO is compared with the ammonium MFI molecular sieve before loading_XThe crystal morphology of the adsorbent is basically not changed, and the dispersibility of the adsorbent is relatively uniform.

Example 3

Pd-based NO_XThe preparation method of the adsorbent comprises the following steps:

s1, carrying out ammonium ion exchange on the sodium zeolite molecular sieve for 2 times to obtain the ammonium molecular sieve, wherein the ammonium ion exchange comprises the following specific steps: adding sodium zeolite molecular sieve into NH₄ ⁺The ammonium nitrate solution with the concentration of 0.6mol/L is subjected to ammonium ion exchange for 2.5h at the temperature of 60 ℃, then is subjected to suction filtration and water washing, and is dried in a forced air drying oven at the temperature of 80 ℃ overnight to obtain the ammonium type molecular sieve;

the framework structure of the sodium zeolite molecular sieve is BEA, and the silica-alumina ratio of the sodium zeolite molecular sieve is 10;

drying the sodium zeolite molecular sieve in a constant-temperature oven at 85 ℃ for 10h, then placing the dried sodium zeolite molecular sieve in a muffle furnace, and roasting the sodium zeolite molecular sieve at 650 ℃ for 10h in an air atmosphere;

s2, adding ammonium type molecular sieve into palladium ion-containingMixing the above solutions, placing in a constant temperature oil bath at 85 deg.C, performing palladium ion exchange for 10 hr under magnetic stirring, vacuum filtering, washing with water, and drying in a forced air drying oven at 80 deg.C for 12 hr to obtain a first precursor, wherein the amount of palladium ions is Pd-based NO_X0.55% of the total weight of the adsorbent;

s3, slowly and uniformly dripping an aqueous solution containing palladium ions into the first precursor, stirring while dripping, uniformly stirring, standing and soaking at room temperature for 10h, and drying in a forced air drying oven at 80 ℃ for 12h to obtain a second precursor, wherein the dosage of the palladium ions accounts for Pd-based NO_X0.55% of the total weight of the adsorbent;

s4, placing the second precursor in a muffle furnace, roasting at the constant temperature of 720 ℃ for 2.5h in the air atmosphere, and introducing water vapor, oxygen and nitrogen at the temperature of 720 ℃ in a volume ratio of 11: 4: 85 mixed gas flow is subjected to hydrothermal activation for 30 hours to obtain Pd-based NO_XAnd the adsorbent is used for adsorbing the gas, wherein the flow rate of the mixed gas flow is 150 mL/min.

Taking the ammonium BEA molecular sieve and Pd-based NO in example 3_XScanning the adsorbent with an electron microscope, and obtaining the result shown in FIG. 3, wherein FIG. 3 shows the ammonium BEA molecular sieve and Pd-based NO_XSEM image of adsorbent, wherein NH₄ ⁺-BEA is ammonium BEA molecular sieve, Pd-BEA is Pd radical NO_XAn adsorbent; as can be seen from FIG. 3, Pd-based NO is compared with the ammonium BEA molecular sieve before loading_XThe crystal morphology of the adsorbent is basically not changed, and the dispersibility of the adsorbent is relatively uniform.

Comparative example 1

Pd-based NO prepared by sodium type molecular sieve_XAn adsorbent, the preparation of which comprises the steps of: the same procedure as in example 1 was repeated except that the sodium type zeolite molecular sieve was used in place of the ammonium type zeolite, and the same procedure as in example 1 was repeated.

Comparative example 2

Pd-based NO prepared by hydrogen type molecular sieve_XAn adsorbent, the preparation of which comprises the steps of: placing the ammonium type molecular sieve in the embodiment 1 in a muffle furnace, and roasting at the constant temperature of 600 ℃ for 12h in a nitrogen atmosphere to obtain a hydrogen type molecular sieve; then, using a hydrogen type molecular sieve instead of an ammonium type molecular sieve, the method was carried out in the same manner as the method of S2-S4 in example 1Pd-based NO prepared by H-type molecular sieve_XAn adsorbent.

Taking the Pd-based NO prepared in example 1, comparative example 1 and comparative example 2_XThe performance of the adsorbent is detected, and the result is shown in fig. 4 and fig. 5;

FIG. 4 shows Pd-based NO prepared in example 1 and comparative examples 1 and 2_XAdsorbent for NO_XAdsorption profile, wherein Pd-LNA-Na⁺Comparative example 1, Pd-LNA-H⁺Comparative example 2, Pd-LNA-NH₄ ⁺Example 1 was used; as can be seen from FIG. 4, Pd-based NO was obtained using an ammonium type molecular sieve_XThe adsorbent has NO_XLarger adsorption interval, indicating NO_XThe adsorption capacity is higher, the duration of 100% adsorption is longer, the adsorption efficiency is higher, and the adsorption effect is better; pd-based NO prepared from sodium type molecular sieve and hydrogen type molecular sieve_XThe adsorption performance of the adsorbent is relatively poor;

FIG. 5 shows Pd-based NO prepared in example 1 and comparative examples 1-2_XAdsorbent for NO_XDesorption profile of (2), wherein, Pd-LNA-Na⁺Comparative example 1, Pd-LNA-H⁺Comparative example 2, Pd-LNA-NH₄ ⁺Example 1 was used; as can be seen from FIG. 5, the Pd-based NO produced by the ammonium-type molecular sieve_XThe initial desorption temperature of the adsorbent is above 250 ℃, and the instantaneous maximum NO is about 400 DEG C_XDesorption amount, at which temperature the back-end SCR catalyst has reached an optimum near 100% NO_XTreatment effect; NO_XThe desorption duration and the temperature zone are also longer, and the instantaneous release amount is within the concentration range which can be treated by the SCR catalyst; pd-based NO prepared by sodium type molecular sieve and hydrogen type molecular sieve_XThe initial desorption temperature of the adsorbent is high, the adsorbent slips to a high-temperature area, the optimal treatment temperature area of the SCR catalyst can be missed, and the desorption amount is small.

Comparative example 3

Pd-based NO prepared by single palladium ion exchange method_XAn adsorbent, the preparation of which comprises the steps of: without the step of S3, in S2, the dosage of palladium ions accounts for Pd-based NO_XThe same as example 1 except that 1% by weight of the total adsorbent was used.

Comparative example 4

Pd-based NO prepared by single impregnation method_XAn adsorbent, the preparation of which comprises the steps of: without the step of S2, in S3, the dosage of palladium ions accounts for Pd-based NO_XThe same as example 1 except that 1% by weight of the total adsorbent was used.

Comparative example 5

Pd-based NO prepared by twice palladium ion exchange method_XAn adsorbent, the preparation of which comprises the steps of: the same procedure as in example 1 was repeated except that the step S3 was replaced with the step S2.

Taking the Pd-based NO prepared in example 1, comparative example 3, comparative example 4 and comparative example 5_XThe performance of the adsorbent is detected, and the result is shown in fig. 6 and 7;

FIG. 6 is Pd-based NO prepared in example 1 and comparative examples 3 to 5_XAdsorbent for NO_XAdsorption profile, wherein Pd-LNA-NH₄ ⁺Comparative example 3, Pd-LNA-NH-ION₄ ⁺IWI is comparative example 4, Pd-LNA-NH₄ ⁺-ION + ION is comparative example 5, Pd-LNA-NH₄ ⁺ION + IWI is example 1; as can be seen from FIG. 6, Pd-based NO was produced by combining the palladium ion exchange method and the equal-volume impregnation method_XThe adsorbent has NO_XLarger adsorption interval, indicating NO_XThe adsorption capacity is higher, the duration of 100% adsorption is longer, the adsorption efficiency is higher, and the adsorption effect is better; pd-based NO prepared by single palladium ion exchange method, single impregnation method and double palladium ion exchange method_XThe adsorption performance of the adsorbent is poorer than that of Pd-based adsorption prepared by combining a palladium ion exchange method and an isometric impregnation method;

FIG. 7 shows Pd-based NO prepared in example 1 and comparative examples 3 to 5_XAdsorbent for NO_XDesorption profile of (2), wherein, Pd-LNA-NH₄ ⁺Comparative example 3, Pd-LNA-NH-ION₄ ⁺IWI is comparative example 4, Pd-LNA-NH₄ ⁺-ION + ION is comparative example 5, Pd-LNA-NH₄ ⁺ION + IWI is example 1; as can be seen from FIG. 7, Pd-based NO was produced by combining the palladium ion exchange method and the equal-volume impregnation method_XThe initial temperature of desorption of the adsorbent is above 250 ℃ and in the region of 400-450 DEG CWith instantaneous maximum NO in between_XDesorption amount, at which temperature the back-end SCR catalyst has reached an optimum near 100% NO_XTreatment effect; NO_XThe desorption duration and the temperature zone are also longer, and the instantaneous release amount is within the concentration range which can be treated by the SCR catalyst; pd-based NO prepared by single palladium ion exchange method, single impregnation method and double palladium ion exchange method_XAdsorbent mainly NO_XThe desorption area misses the optimal treatment temperature area of the SCR catalyst, and the desorption amount is small.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (10)

1. Pd-based NO_XThe preparation method of the adsorbent is characterized by comprising the following steps:

s1, carrying out ammonium ion exchange on the zeolite molecular sieve to obtain an ammonium type molecular sieve;

s2, performing palladium ion exchange on the ammonium molecular sieve to obtain a first precursor;

s3, dropwise adding a water solution containing palladium ions into the first precursor, uniformly mixing, standing, soaking and drying to obtain a second precursor;

s4, roasting the second precursor, and carrying out hydrothermal activation to obtain Pd-based NO_XAn adsorbent.

2. Pd-based NO according to claim 1_XThe preparation method of the adsorbent is characterized in that in S1, the zeolite molecular sieve is a sodium type molecular sieve; preferably, in S1, the framework structure of the zeolite molecular sieve is one of CHA, MFI, BEA.

3. Pd-based NO according to claim 1 or 2_XThe preparation method of the adsorbent is characterized in that in S1, the silica-alumina ratio of the zeolite molecular sieve is 10-50; preferably, in S1At least two ammonium ion exchanges.

4. Pd-based NO according to any one of claims 1 to 3_XA process for producing an adsorbent, characterized in that in S2 and S3, the same amount of palladium ions is used, both occupying Pd-based NO_X0.45-0.55% of the total weight of the adsorbent; preferably, in S2, the temperature of palladium ion exchange is 75-85 ℃ and the time is 10-14 h; preferably, in S3, the temperature for standing and soaking is room temperature, and the time for standing and soaking is 10-14 h.

5. Pd-based NO according to any one of claims 1 to 4_XThe preparation method of the adsorbent is characterized in that in S4, the roasting temperature is 720-770 ℃, and the roasting time is 1.5-2.5 h; preferably, in S4, the temperature of hydrothermal activation is 720-770 ℃, and the time of hydrothermal activation is 20-30 h.

6. Pd-based NO according to any one of claims 1 to 5_XA method for producing an adsorbent, characterized by comprising performing hydrothermal activation in a mixed gas stream of water vapor, oxygen and nitrogen in S4; preferably, the volume ratio of water vapor, oxygen and nitrogen is 9-11: 4-6: 83-87; preferably, the flow rate of the mixed gas flow is 150-250 mL/min.

7. Pd-based NO according to any one of claims 1 to 6_XThe preparation method of the adsorbent is characterized in that in S1, the temperature of ammonium ion exchange is 60-70 ℃ and the time is 1.5-2.5 h; preferably, in S1, the zeolite molecular sieve is dried and roasted for use; preferably, the drying temperature is 75-85 ℃, and the drying time is 10-14 h; preferably, the roasting temperature is 550-650 ℃, the roasting time is 10-14h, and the roasting is carried out in the air atmosphere.

8. Pd-based NO according to any one of claims 1 to 7_XThe preparation method of the adsorbent is characterized in that in S1, the ammonium ion exchange comprises the following specific steps: adding zeolite molecular sieve into ammonium salt water solution for ammonium ion exchange, then carrying out suction filtration, washing and drying to obtain the zeolite molecular sieveAn ammonium type molecular sieve; preferably, NH in aqueous ammonium salt solution₄ ⁺The concentration of (A) is 0.4-0.6 mol/L; preferably, the ammonium salt is ammonium carbonate, ammonium chloride, ammonium nitrate or ammonium sulfate; preferably, in S2, the specific steps of palladium ion exchange are: and adding the ammonium molecular sieve into a water solution containing palladium ions to perform palladium ion exchange, then performing suction filtration, washing and drying to obtain a first precursor.

9. Pd-based NO_XAdsorbent, characterized in that Pd-based NO according to any one of claims 1 to 8_XThe preparation method of the adsorbent.

10. The Pd-based NO of claim 9_XThe application of the adsorbent in adsorbing automobile exhaust; preferably, the adsorption of NO in automobile exhaust_XThe use of (1).

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