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CN-117696002-B - Preparation method of nitrogen oxide passive adsorbent

CN117696002BCN 117696002 BCN117696002 BCN 117696002BCN-117696002-B

Abstract

A preparation method of a passive adsorbent for trapping nitrogen oxides. The passive adsorbent is a load-type material composed of noble metal palladium and a molecular sieve. The adsorbent is obtained after being compounded with a metal Pd precursor through a molecular sieve and being subjected to low-temperature plasma/microwave treatment, and shows extremely high adsorption quantity on nitrogen oxides as passive adsorption, and is applied to passive adsorption of nitrogen oxides in a cold start stage of a mobile source.

Inventors

  • YU QINGJUN
  • Cheng Haodan
  • TANG XIAOLONG
  • YI HONGHONG
  • ZHAO SHUNZHENG
  • GAO FENGYU
  • Pan Rouxing

Assignees

  • 北京科技大学

Dates

Publication Date
20260508
Application Date
20230609

Claims (20)

  1. 1. A method for passively adsorbing nitrogen oxides comprises that under the condition that the temperature is lower than 200 ℃, nitrogen oxide-containing gas is adsorbed by an adsorbent, and the adsorbent is a metal Pd-loaded molecular sieve which is processed by plasma or microwave; The molecular sieve comprises one or more of CHA type zeolite molecular sieve, AEI type zeolite molecular sieve, MFI type zeolite molecular sieve, MEL type zeolite molecular sieve, BEA type zeolite molecular sieve and FAU type zeolite molecular sieve.
  2. 2. The method of claim 1 wherein the molecular sieve is a MEL-type zeolite molecular sieve.
  3. 3. The method according to claim 2, wherein the molecular sieve is a MEL-type zeolite molecular sieve, and the supported metal Pd is present in an amount of less than 5wt%.
  4. 4. The method according to claim 2, wherein the molecular sieve is a MEL-type zeolite molecular sieve, and the content of the supported metal Pd is 0.5-2 wt%.
  5. 5. The method of any one of claims 1 to 4, wherein the plasma treatment conditions are a mixture of O 2 and N 2 or an atmosphere of N 2 , and the treatment power density is 100 to 200W/g.
  6. 6. The method of claim 5, wherein the plasma treatment has a power density of 150W/g.
  7. 7. The method according to claim 5, wherein the amount of treated gas is 20-500 ml/min.
  8. 8. The method according to claim 5, wherein the amount of treated gas is 50-150 ml/min.
  9. 9. The method of claim 5, wherein the volume content of O 2 in the plasma processing atmosphere is no more than 21v%.
  10. 10. The method of claim 5, wherein the volume of the mixed gas O 2 and N 2 is 5:95-21:79.
  11. 11. The method of claim 1, wherein the microwave treatment conditions include a power density of 300-2250W/g.
  12. 12. The method according to claim 11, wherein the microwave treatment is carried out at a power density of 900-2000W/g.
  13. 13. The method according to claim 11, characterized in that the microwave treatment is carried out at a power density of 1250-1750W/g.
  14. 14. A method according to claim 1 or 11, characterized in that in the microwave treatment the temperature is kept between 50 and 170 ℃.
  15. 15. A method according to claim 1 or 11, characterized in that in the microwave treatment the temperature is kept between 80 and 100 ℃.
  16. 16. The method according to claim 1 or 11, wherein a mixed gas containing O 2 and N 2 is continuously introduced during the microwave treatment.
  17. 17. The method of claim 16, wherein the amount of the gas mixture of O 2 and N 2 is 20-500 ml/min.
  18. 18. The method of claim 16, wherein the amount of O 2 and N 2 mixed gas treated is 50-150 ml/min.
  19. 19. The method according to any one of claims 1 to 4, wherein the method for producing the Pd-supported MEL-type zeolite molecular sieve comprises: Uniformly mixing a silicon element-containing substance, a template agent and water to obtain a first mixture; Uniformly mixing a substance containing aluminum element, alkali metal hydroxide and water to obtain a second mixture; Adding the second mixture into the first mixture under the stirring condition, crystallizing at 120-180 ℃, separating solid matters from mother liquor after crystallization, washing the separated solid matters to be neutral by deionized water, drying, and finally removing a template agent by roasting to obtain the MEL type zeolite molecular sieve; The MEL zeolite molecular sieve is converted into an H-type MEL zeolite molecular sieve after ion exchange; And (3) dropwise adding the Pd-containing soluble salt aqueous solution onto the H-type MEL zeolite molecular sieve, or carrying out ion exchange on the Pd-containing soluble salt aqueous solution and the H-type MEL zeolite molecular sieve, and drying and roasting to obtain the Pd-loaded MEL zeolite molecular sieve.
  20. 20. The method according to claim 19, wherein the crystallization process comprises crystallizing the obtained mixture at a temperature of 60-120deg.C, and then continuing the static crystallization at a temperature of 150-200deg.C; the template agent is tetrabutylammonium bromide.

Description

Preparation method of nitrogen oxide passive adsorbent Technical Field The invention relates to a method for treating nitrogen oxides, in particular to a method for preparing a passive nitrogen oxide adsorbent. Background As a main vehicle for human beings, the motor vehicles bring convenience to the life of the human beings, and the pollution problem caused by the motor vehicles is increasingly prominent, so that the motor vehicles become one of important sources of air pollution. Facing the improvement of the emission limit standard of the motor vehicle, the following is an omnibearing challenge to the emission control technology of the motor vehicle. The lean-burn engine has the advantages of high combustion efficiency, good fuel economy, low content of tail gas HCs, CO, CO 2 and the like, and is the engine technology with the most development prospect. However, the high air-fuel ratio of the engine results in a significant increase in the amount of NO x discharged from the exhaust gas, which is one of the most difficult problems to be solved by the current commercial lean-burn engines. Diesel engines are typically lean-burn engines that employ Selective Catalytic Reduction (SCR), NO x storage reduction catalytic technology (LNT or NSR) to eliminate NO x from the exhaust off-board. The two technologies can effectively remove NO x, but can only play a role in catalytic conversion after the tail gas temperature reaches the ignition temperature (> 200 ℃) of the catalyst, and the denitration activity is low below an activity temperature window. Thus, the NO x emitted from the stage (cold start stage 1-3 min) from the start of the motor vehicle to the rise of the exhaust gas temperature to the catalyst activation temperature is directly emitted into the air without any substantial treatment, and the emission amount thereof occupies 80% of the total engine emission amount. NO x generated during the cold start phase has attracted attention in the industry for the effect of engine exhaust quality. Thus, NO x Passive adsorbents (PNAs) have been developed and are currently being studied. The composition of PNA materials generally includes an active component (noble metal, rare earth metal, etc.) and a carrier (metal oxide, molecular sieve), wherein supported PNAs prepared by supporting noble metal Pd on molecular sieve have been confirmed as the optimal PNAs composition. However, the noble metal Pd is expensive and has low utilization efficiency, so that the preparation cost of PNAs is too high, and the method becomes one of the important challenges facing the current PNAs research. The novel preparation method is developed, the Pd utilization efficiency is improved, the high-efficiency NOx passive adsorbent is obtained, the storage of NO x in the cold start stage is realized, and the method is very important for reducing the NOx emission in the cold start stage of the lean-burn engine. Disclosure of Invention An object of the present application is to provide a method for preparing a passive adsorbent for nitrogen oxides, in which nitrogen oxides are adsorbed by using a molecular sieve loaded with metal Pd by plasma treatment or microwave treatment, and the adsorption performance for nitrogen oxides is remarkably improved. The application also aims to provide a preparation method of the nitrogen oxide passive adsorbent, which improves the utilization rate of the metal Pd by using the molecular sieve loaded with the metal Pd through plasma treatment or microwave treatment to be applied to the passive adsorption of the nitrogen oxide. It is still another object of the present application to provide a method for passively adsorbing nitrogen oxides, in which the molecular sieve loaded with metal Pd is subjected to plasma treatment or microwave treatment to be easily desorbed after passively adsorbing nitrogen oxides, so that the molecular sieve has good performance of passively adsorbing nitride after repeated passive adsorption and desorption of nitrogen oxides. The method for passively adsorbing the nitrogen oxides comprises the step that under the condition that the temperature is lower than 200 ℃, the gas containing the nitrogen oxides is adsorbed by an adsorbent, and the adsorbent is a molecular sieve which is treated by plasma or microwave and is loaded with metal Pd. The molecular sieve includes, but is not limited to, CHA type zeolite molecular sieve, AEI type zeolite molecular sieve, MFI type zeolite molecular sieve, MEL type zeolite molecular sieve, BEA type zeolite molecular sieve, FAU type zeolite molecular sieve After the molecular sieve loaded with the metal Pd is subjected to plasma or microwave treatment, the adsorption quantity of nitrogen oxides can be remarkably improved, and the utilization efficiency of Pd metal is improved. Drawings FIG. 1 is a graph of adsorption performance of Pd/molecular sieves prepared in example 4 of the present invention against NOx FIG. 2 is a graph of Pd/molecular sieve