A method for the preparation of a passive adsorbent for nitrogen oxides

Abstract

A preparation method of a passive adsorbent for capturing nitrogen oxides. The passive adsorbent is a supported material composed of noble metal palladium and molecular sieve. The adsorbent is obtained by compounding the molecular sieve with a metal Pd precursor and then subjected to low-temperature plasma / microwave treatment, and exhibits extremely high adsorption capacity for nitrogen oxides as a passive adsorbent, and is applied to passive adsorption of nitrogen oxides in the cold start stage of a mobile source.

Description

Technical Field

[0001] This invention relates to a method for treating nitrogen oxides, and more specifically, to a method for preparing a passive adsorbent for nitrogen oxides. Background Technology

[0002] Motor vehicles, as a primary means of transportation, bring convenience to people's lives, but the pollution they cause is becoming increasingly prominent, making them a significant source of air pollution. The tightening of emission limits for motor vehicles presents a comprehensive challenge to vehicle exhaust emission control technologies. Lean-burn engines, with their advantages of high combustion efficiency, good fuel economy, and low levels of HCs, CO, and CO2 in exhaust gases, represent the most promising engine technology. However, their high air-fuel ratio leads to higher NO content in exhaust gases. x The emissions increase significantly, which is one of the most difficult problems to solve for commercial lean-burn engines.

[0003] Diesel engines, as typical lean-burn engines, usually employ selective catalytic reduction (SCR) and NO2. x Storage-reduction catalytic technology (LNT or NSR) for NO in exhaust gas x External removal is performed. Both of these technologies can effectively remove NO. x However, catalytic conversion only occurs after the exhaust gas temperature reaches the catalyst's ignition temperature (>200℃). Below the active temperature window, the denitrification activity is very low. Therefore, NO emissions during the period from vehicle start-up to the exhaust gas temperature rising to the catalyst's active temperature (cold start phase 1-3 minutes) are very high. x NOx is emitted directly into the air without any treatment, accounting for 80% of the total engine emissions. NOx produced during the cold start phase... x The impact of NO on engine exhaust quality has already attracted industry attention. Therefore, NO x Passive adsorbent (Passive NO) x PNAs (pure metal adsorbers) have emerged and become a current research hotspot. PNA materials generally consist of an active component (noble metal, rare earth metal, etc.) and a support (metal oxide, molecular sieve). Among these, supported PNAs prepared by loading the noble metal Pd onto molecular sieves have been proven to be the optimal PNA composition. However, the high price and low utilization efficiency of Pd result in excessively high PNA preparation costs, becoming one of the major challenges currently facing PNA research. Developing novel preparation methods to improve Pd utilization efficiency and obtain highly efficient passive NOx adsorbents is crucial for achieving NOx adsorption during the cold start phase. x Storage is crucial for reducing NOx emissions during the cold start phase of lean-burn engines. Summary of the Invention

[0004] One objective of this application is to provide a method for preparing a passive adsorbent for nitrogen oxides, in which a molecular sieve loaded with metal Pd is used for adsorbing nitrogen oxides by plasma treatment or microwave treatment, which significantly improves the adsorption performance of nitrogen oxides.

[0005] Another objective of this application is to provide a method for preparing a passive adsorbent for nitrogen oxides, wherein molecular sieves loaded with metal Pd are subjected to plasma treatment or microwave treatment and then applied to passively adsorb nitrogen oxides, thereby improving the utilization rate of metal Pd.

[0006] Another objective of this application is to provide a method for passively adsorbing nitrogen oxides. After passively adsorbing nitrogen oxides, the molecular sieve loaded with metal Pd is relatively easy to desorb after being treated with plasma or microwave. Thus, the molecular sieve still has good passive adsorption performance of nitrogen oxides after repeated passive adsorption and desorption.

[0007] This application discloses a method for passively adsorbing nitrogen oxides, comprising: under conditions of temperature below 200°C, a gas containing nitrogen oxides is adsorbed by an adsorbent, wherein the adsorbent is a molecular sieve loaded with metal Pd that has been treated by plasma or microwave.

[0008] The molecular sieves mentioned include, but are not limited to, CHA-type zeolite molecular sieves, AEI-type zeolite molecular sieves, MFI-type zeolite molecular sieves, MEL-type zeolite molecular sieves, BEA-type zeolite molecular sieves, and FAU-type molecular sieves.

[0009] The molecular sieves loaded with metal Pd prepared in this application can significantly increase the adsorption capacity of nitrogen oxides after plasma or microwave treatment, thereby improving the utilization efficiency of Pd metal. Attached Figure Description

[0010] Figure 1 This is a graph showing the NOx adsorption performance of the Pd / molecular sieve prepared in Example 4 of this invention.

[0011] Figure 2 This is a graph showing the NOx adsorption capacity of the Pd / molecular sieve prepared in Example 4 of this invention.

[0012] Figure 3 These are the NH3-TPD curves of the Pd / molecular sieves prepared in Examples 4 and 5 of this application and Comparative Example 1.

[0013] Figure 4 These are the XPS spectra of the Pd / molecular sieves prepared in Examples 4 and 5 and Comparative Example 1 of this application.

[0014] Figure 5 This is a graph showing the NOx adsorption performance of the Pd / molecular sieve prepared in Example 5 of this invention.

[0015] Figure 6 This is a graph showing the NOx adsorption capacity of the Pd / molecular sieve prepared in Example 5 of this invention.

[0016] Figure 7 These are the H2-TPR curves of the Pd / molecular sieves prepared in Example 5 and Comparative Example 1 of this application.

[0017] Figure 8 The attached diagram shows the NOx adsorption-desorption process of the Pd / molecular sieve prepared in Example 5 of this invention.

[0018] Figure 9 These are X-ray powder diffraction patterns of the Pd / molecular sieves prepared in Example 6 and Comparative Example 2 of this invention. Detailed Implementation

[0019] The preparation method of a passive adsorbent for nitrogen oxides according to the present invention is described in further detail below. This does not limit the scope of protection of this application, which is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.

[0020] Unless the context otherwise requires, the terms “comprising” and “including” in the specification and claims shall be understood as open-ended and inclusive, meaning “including, but not limited to”.

[0021] The terms "implementation," "an implementation," "another implementation," or "certain implementations" used in this specification refer to specific features, structures, or characteristics described in relation to the implementation, which are included in at least one implementation. Therefore, "implementation," "an implementation," "another implementation," or "certain implementations" do not necessarily all refer to the same implementation. Furthermore, specific features, structures, or characteristics can be combined in any way within one or more implementations. Each feature disclosed in this specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0023] The units in the weight-volume percentages of this invention are well known to those skilled in the art, for example, referring to the weight of the solute in 100 ml of solution.

[0024] In this invention, the concentration unit "M" of the solution represents mol / L.

[0025] Nitrogen oxides refer to compounds composed solely of nitrogen and oxygen, including various compounds such as nitrous oxide (N₂O), nitric oxide (NO), nitrogen dioxide (NO₂), nitrous oxide (N₂O₃), nitrous oxide (N₂O₄), and nitrous oxide (N₂O₅). Therefore, mixtures of several gases encountered in the environment are often referred to as fumes, primarily composed of nitric oxide and nitrogen dioxide, with nitrogen dioxide being the dominant component. All nitrogen oxides exhibit varying degrees of toxicity.

[0026] The term "molecular sieve" refers to a synthetic hydrated aluminosilicate (zeolite) or natural zeolite that has the function of screening molecules.

[0027] MEL is a five-membered ring molecular sieve made of Pentasil.

[0028] Microwaves are electromagnetic waves with frequencies between 300MHz and 300GHz.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0030] In this application, a method for preparing a passive adsorbent for nitrogen oxides includes: subjecting a molecular sieve loaded with metal Pd to plasma treatment or microwave treatment to obtain a passive adsorbent for nitrogen oxides.

[0031] The molecular sieves mentioned include, but are not limited to, CHA type zeolite molecular sieves, AEI type zeolite molecular sieves, MFI type zeolite molecular sieves, MEL type zeolite molecular sieves, BEA type zeolite molecular sieves, and FAU type molecular sieves.

[0032] The plasma treatment or microwave treatment steps in this application are carried out after the palladium metal is loaded onto the molecular sieve through steps such as drying and calcination.

[0033] According to the inventors' analysis, by treating the Pd-loaded molecular sieve with plasma or microwaves, the number of Pd species serving as effective adsorption sites for nitrogen oxides increases, and / or the molecular sieve structure creates local defects, while simultaneously increasing the number of acidic sites on the molecular sieve. This increases the adsorption capacity for nitrogen oxides.

[0034] Plasma processing

[0035] In some embodiments, the low-temperature plasma treatment conditions are a mixture of O2 and N2 or an N2 atmosphere, and the treatment power density is 100-200 W / g.

[0036] In an atmosphere containing a mixture of O2 and N2, the concentration of oxygen shall not exceed 21v.

[0037] Preferably, the volume ratio of the mixed gas O2 to N2 is 5:95 to 21:79.

[0038] For example, approximately 0.1 g of Pd-loaded MEL molecular sieves can be treated with low-temperature plasma at a voltage of 10-50 V, preferably 25-35 V.

[0039] The processing gas flow rate is 20-500 ml / min, preferably 50-150 ml / min, and the treatment time is 15-120 min.

[0040] In some embodiments, the molecular sieve is a MEL-type zeolite molecular sieve, and the content of the supported metal Pd is less than 5 wt%.

[0041] In a preferred embodiment, the molecular sieve is a MEL-type zeolite molecular sieve, and the content of the supported metal Pd is less than 0.5-2 wt%.

[0042] In some embodiments, the MEL-type zeolite molecular sieve is preferably a ZSM-11 molecular sieve.

[0043] In this application, by treating the Pd-loaded ZSM-11 molecular sieve with a mixture of O2 and N2 or N2 plasma working gas, more acidic sites are generated, thereby improving the passive adsorption of nitrogen oxides.

[0044] On the one hand, the Pd-loaded ZSM-11 molecular sieve, after plasma treatment, allows more Pd to be released. 2+ It was produced. Before plasma treatment, the Pd-loaded ZSM-11 molecular sieve, after calcination, contained Pd in ​​both divalent and tetravalent states. The divalent Pd mainly existed as Pd... 2+ While tetravalent Pd exists in the form of PdO, it is entirely PdO2. The increase in divalent Pd content after plasma treatment indicates that tetravalent Pd has been converted to divalent Pd. On the other hand, the number of acidic sites in the molecular sieve increases accordingly. There may also be other unexplained reasons. All these factors combined result in a significant improvement in the adsorption performance of plasma-treated molecular sieves, especially ZSM-11 molecular sieves, as passive adsorbents for low-temperature nitrogen oxides.

[0045] The content of the loaded metal Pd in ​​this application refers to the ratio of palladium metal to the total weight of the molecular sieve.

[0046] In some embodiments, when the plasma-treated Pd-loaded MEL-type zeolite molecular sieve is used as a passive adsorbent for nitrogen oxides, the water content of the nitrogen oxides is about 5% v.

[0047] Microwave processing

[0048] In some embodiments, the microwave processing conditions include performing microwave processing at a power density of 300-2250 W / g.

[0049] In microwave processing, the temperature is maintained between 50-170℃.

[0050] After microwave treatment, the molecular sieve loaded with Pd has an increased number of acidic sites due to the change in Pd species and / or the defects caused by the breaking or formation of some chemical bonds in the molecular sieve, thereby increasing its ability to passively adsorb nitrogen oxides.

[0051] In some implementations, microwave processing is performed at a power density of 900-2000 W / g.

[0052] In microwave processing, the temperature is maintained at 80-100℃.

[0053] Under microwave conditions, especially when treating Pd-loaded MEL-type zeolite molecular sieves as passive adsorbents for nitrogen oxides, the increased number of Pd ions allows them to retain a relatively large number of effective NOx adsorption sites even in humid environments, demonstrating high passive adsorption performance for nitrogen oxides.

[0054] In some embodiments, a mixture of O2 and N2 gas or a gas containing N2 is continuously introduced during microwave processing.

[0055] Optionally, the processing flow rate of the O2 and N2 mixture or the gas containing N2 is 20-500 ml / min.

[0056] In the process of microwave treatment of Pd-loaded molecular sieves, introducing a mixed gas containing O2 and N2 or a gas containing N2 at the above-mentioned treatment rate, and performing microwave treatment under this atmosphere, is more conducive to improving the passive adsorption capacity of nitrogen oxides of molecular sieves.

[0057] Preferably, the processing flow rate of the O2 and N2 mixed gas or the gas containing N2 is 50-150 ml / min.

[0058] In some implementations, the microwave treatment time is controlled between 15 min and 90 min.

[0059] In some embodiments, when microwave-treated Pd-loaded MEL-type zeolite molecular sieves are used as passive adsorbents for nitrogen oxides, the water content of the nitrogen oxides is approximately 5% v.

[0060] Even in humid environments, this passive adsorbent for nitrogen oxides exhibits high adsorption performance. Generally, in humid environments, the adsorption sites of various Pd-loaded zeolite molecular sieves are affected, leading to a decrease in their passive adsorption performance for nitrogen oxides. However, microwave-treated Pd-loaded MEL-type zeolite molecular sieves (such as ZSM-11 molecular sieve) still retain a relatively large number of effective NOx adsorption sites and exhibit high passive adsorption performance for nitrogen oxides even in humid environments.

[0061] MEL type molecular sieve

[0062] The X-ray diffraction pattern of the MEL-type molecular sieve in this application shows characteristic peaks at 2θ degrees of 11.2±0.2, 10.1±0.2, and 3.72±0.1.

[0063] Preferably, the MEL type molecular sieve uses ZSM-11 type zeolite molecular sieve.

[0064] ZSM-11 type zeolite molecular sieve has a nanorod intercalation structure.

[0065] The lower the silicon-to-aluminum ratio of ZSM-11 zeolite molecular sieve, the better. The preferred ratio is Si / Al = 15-35.

[0066] The silicon-to-aluminum ratio refers to the ratio of the amount of silicon to aluminum in a molecular sieve.

[0067] ZSM-11 zeolite molecular sieves loaded with Pd have a nanorod intercalation structure, and after the above-mentioned plasma treatment or microwave treatment, the acidic sites are significantly increased.

[0068] In some embodiments, the grain size of ZSM-11 zeolite molecular sieve is between 100 nm and 10 μm.

[0069] Compared with MEL molecular sieves before plasma / microwave treatment, the passive adsorption efficiency of Pd-loaded MEL molecular sieves after the above-mentioned plasma / microwave treatment is increased by several times.

[0070] According to the inventors' speculation, in addition to changes in structure and species, plasma-treated Pd-loaded MEL molecular sieves may also have altered electronegativity, thereby improving their adsorption capacity for nitrogen oxides under low-temperature conditions.

[0071] In particular, the Pd-loaded ZSM-11 molecular sieve prepared by the following method has a high passive adsorption performance of nitrogen oxides, and its desorption performance is also improved. After desorption, the content of residual nitrogen oxides is extremely low.

[0072] In one embodiment, a method for preparing Pd-loaded MEL molecular sieves employs the following technical solution:

[0073] The silicon-containing raw material, template agent, and water are mixed evenly to obtain the first mixture;

[0074] Aluminum-containing substances, alkali metal hydroxides, and water are mixed evenly to obtain a second mixture;

[0075] Under stirring conditions, the second mixture is added to the first mixture. The resulting mixture is first crystallized at a temperature of 60-120℃, and then statically crystallized at a temperature of 150-200℃. After crystallization, the solid material is separated from the mother liquor. The separated solid material is washed with deionized water until neutral and dried. Finally, the template agent is removed by calcination to obtain MEL molecular sieve.

[0076] MEL zeolite molecular sieves are transformed into H-type MEL molecular sieves after ion exchange.

[0077] Pd-containing soluble saline solution is added dropwise to H-type MEL molecular sieve, or Pd-containing soluble saline solution is exchanged with H-type MEL molecular sieve; after drying and calcination, Pd-loaded MEL molecular sieve is obtained.

[0078] The template agent is tetrabutylammonium bromide, and the amount of tetrabutylammonium bromide used is calculated as (TBA)2O.

[0079] In some implementations, the molar ratio of Si to Al is (15-∞):1.

[0080] In the preferred embodiment, the molar ratio of Si to Al is (17-100):1.

[0081] Alkali metal hydroxides are calculated based on their oxides, with the molar ratio of alkali metal oxides to Si being (0.08-0.4):1.0.

[0082] The molar ratio of template agent (TBA)₂O to Si element is (0.01-0.5): 1.

[0083] The molar ratio of silicon to water is 1:10-100.

[0084] The silicon-containing substances include one or a mixture of two or more of the following: silica sol, water glass, tetraethyl orthosilicate, silica fume, and silica gel microspheres.

[0085] The aluminum-containing substances include one or a mixture of two or more of aluminum sulfate, sodium aluminate, aluminum nitrate, aluminum chloride, and aluminum isopropoxide.

[0086] The alkali metal hydroxide includes one or a mixture of two or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0087] In this application, unless otherwise specified, the calcination temperature is controlled between 500-600℃ in the steps of preparing MEL molecular sieves, preparing H-type MEL molecular sieves, or loading Pd.

[0088] The ion exchange in this application refers to the exchange of MEL molecular sieves with ammonium ions to form hydrogen ions.

[0089] The Pd-loaded MEL molecular sieves prepared by the above method, such as ZSM-11 molecular sieve, have a nanorod intercalation structure.

[0090] In another embodiment, the method for preparing Pd-loaded MEL molecular sieve involves adding seed crystals during the preparation of the MEL molecular sieve. The mixture containing the seed crystals is crystallized at a temperature of 120-180°C, and then dried and calcined to obtain the MEL molecular sieve. For example, seed crystals are added to a mixture of the first mixture and the second mixture, followed by crystallization, drying, and calcination to obtain the MEL molecular sieve.

[0091] In the method for preparing Pd-loaded MEL molecular sieves using seed crystals, the types and amounts of raw materials, as well as other process steps or parameters, follow the same conditions as those for preparing Pd-loaded MEL molecular sieves without seed crystals. These will not be repeated here.

[0092] Pd can be impregnated onto the MEL molecular sieve after it has been prepared into an H-type MEL molecular sieve. Alternatively, Pd can be first loaded onto seed crystals, and then crystallized, dried, and calcined to obtain the final Pd-loaded MEL molecular sieve.

[0093] Regardless of whether H-type MEL molecular sieves are prepared with or without seed crystals, their passive adsorption performance for nitrogen oxides is improved after plasma or microwave treatment. H-type MEL molecular sieves prepared with seed crystals exhibit a more significant improvement in their passive adsorption performance for nitrogen oxides.

[0094] The H-type MEL molecular sieves (such as ZSM-11 molecular sieve) loaded with Pd metal obtained by this method, after plasma treatment as described above, exhibit a high passive adsorption capacity for nitrogen oxides (PNAs) at temperatures below 200°C. Compared to H-type MEL molecular sieves loaded with Pd metal without plasma treatment, the passive adsorption of PNAs by the plasma-treated H-type MEL molecular sieve is increased by more than 10 times. Compared to H-type MEL molecular sieves loaded with Pd metal without microwave treatment, the passive adsorption of PNAs by the microwave-treated H-type MEL molecular sieve is increased by more than 20 times. On the other hand, at high temperatures (above 400-500°C), the adsorbed nitrogen oxides can be rapidly and thoroughly desorbed, meaning that very low levels of nitrogen oxides remain on the molecular sieve, thereby increasing the number of times the molecular sieve can be used to adsorb nitrogen oxides.

[0095] On the other hand, a method for passively adsorbing nitrogen oxides includes: adsorbing nitrogen oxide-containing gas by an adsorbent at a temperature below 200°C, wherein the adsorbent is a molecular sieve loaded with metal Pd that has been treated by plasma or microwave.

[0096] The preparation method and performance of the passive adsorbent for adsorbing nitrogen oxides of the present invention are further illustrated below with reference to specific embodiments.

[0097] Example 1

[0098] 0.14 g of Pd(NH3)4(NO3)2 was dissolved in 3.33 g of water to prepare a clear solution. 5 g of commercially available H-type ZSM-11 molecular sieve (Si / Al = 17.5) was weighed. The above solution was mixed with an equal volume of the molecular sieve, stirred vigorously until homogeneous, and then slowly evaporated to remove moisture, yielding a dried product. This product was then calcined in air at 500℃ for 4 h and cooled to room temperature to obtain Pd / ZSM-11 molecular sieve. 0.1 g of the Pd / ZSM-11 molecular sieve was placed in a discharge apparatus for plasma treatment. A mixture of nitrogen and oxygen (oxygen volume 10%) was introduced at a flow rate of 50 ml / min, a space velocity of 60,000 mL / (hg), a discharge voltage of 15 V, and a power of 15 W. After treatment for 30 min, the treated Pd / ZSM-11 molecular sieve was obtained.

[0099] Example 2

[0100] 0.14 g of Pd(NH3)4(NO3)2 was dissolved in 3.33 g of water to prepare a clear solution. 5 g of H-type ZSM-11 molecular sieve (Si / Al = 17.5) was weighed and placed in the solution. After vigorous stirring for 24 h, the solution was filtered to obtain a solid product. This solid product was dried and then calcined in air at 500 °C for 4 h, then cooled to room temperature to obtain Pd / ZSM-11 molecular sieve. Subsequently, 0.1 g of the Pd / ZSM-11 molecular sieve was placed in a discharge apparatus for plasma treatment. A mixture of nitrogen and oxygen (oxygen volume 10%) was introduced at a flow rate of 100 mL / min, a space velocity of 60,000 mL / (hg), a discharge voltage of 25 V, and a power of 15 W. After treatment for 30 min, Pd / ZSM-11 molecular sieve was obtained.

[0101] Example 3

[0102] Dissolve 0.19g of Pd(NH3)4(NO3)2 in 5g of water to prepare a clear solution. The mixture was stirred vigorously with silicon source, aluminum source, template agent, and alkali source according to the synthesis ratio of ZSM-11 (Na2O:Al2O3:SiO2:(TBA)2O:H2O = 12.5:1.6:55:0.83:1650) until a uniform gel was formed. Then, it was placed in a crystallization vessel and placed in an oven for hydrothermal crystallization. The obtained product was calcined at 500℃ in air for 2 hours to remove the template agent. Then, it was subjected to three ion exchanges with ammonium chloride solution and dried and calcined to obtain Pd / ZSM-11 molecular sieve. Finally, 0.1g of Pd / ZSM-11 molecular sieve was placed in a discharge device, and a mixed gas of nitrogen and oxygen (oxygen volume was 10%) was introduced at a gas flow rate of 100ml / min, a space velocity of 60,000 mL / (hg), a discharge voltage of 20V, and a power of 15W. After treatment for 30 min, Pd / ZSM-11 molecular sieve was obtained.

[0103] The seed crystals used in the preparation of H-type ZSM-11 molecular sieves in Examples 4-8 below are prepared using the method of preparing MEL molecular sieves disclosed in the inventor's previous patent (i.e., Example 1 with patent number ZL201210003750.5).

[0104] Example 4

[0105] Preparation method of H-type ZSM-11 molecular sieve:

[0106] Mixture I: Add 15g of silica sol (40% SiO2, 60% H2O, the same below), 0.97g of tetrabutylammonium bromide (99%), and 18.9g of deionized metals to a beaker and mix thoroughly; then add 0.4g of powdered ZSM-11 seed crystals (10wt%) (Si / Al = 17.5) and stir vigorously until evenly dispersed;

[0107] Mixture II: A homogeneous solution prepared from 1.90g aluminum sulfate, 1.81g sodium hydroxide and 25g deionized water;

[0108] Mixture II was slowly added to mixture I under constant stirring, and the mixture was stirred vigorously until homogeneous. The molar ratio of the resulting reaction mixture was Na₂O:Al₂O₃:SiO₂:(TBA)₂O:H₂O = 12.5:1.6:55:0.83:1650. The initial gel was aged at room temperature for 5 days, and then crystallized at approximately 170°C for 48 hours. After cooling, the solid was separated from the mother liquor. The solid was washed with deionized water until neutral, dried in air at 120°C, and then calcined at 550°C for 4 hours to remove the template agent, yielding ZSM-11 molecular sieve.

[0109] ZSM-11 molecular sieve was subjected to ion exchange with a 0.1M ammonium chloride solution, and then dried at 120℃ and calcined at 550℃ for 2 hours to obtain H-type ZSM-11 molecular sieve.

[0110] 0.14 g of Pd(NH3)4(NO3)2 was dissolved in 5 g of water to obtain a clear solution. The above solution was mixed with 5 g of H-type ZSM-11 molecular sieve, stirred vigorously until homogeneous, and then slowly evaporated to remove moisture to obtain a dried product. After calcination in air at 500℃ for 4 h and cooling to room temperature, Pd-loaded ZSM-11 molecular sieve was obtained.

[0111] Plasma treatment of Pd-loaded ZSM-11 molecular sieves:

[0112] The Pd-loaded ZSM-11 molecular sieve described above was placed in a discharge apparatus, and a mixture of nitrogen and oxygen (oxygen volume 10%) was introduced at a gas flow rate of 50 ml / min, a space velocity of 60,000 mL / (hg), and a discharge voltage of 15 V. After treatment for 30 min, the treated Pd / ZSM-11 molecular sieve was obtained. The final product powder appeared... Figure 9 (b) X-ray diffraction pattern.

[0113] Example 5

[0114] The preparation of Pd-loaded ZSM-11 molecular sieves in this embodiment is described in Example 4. The obtained Pd-loaded ZSM-11 molecular sieve samples were subjected to microwave treatment.

[0115] A 0.1 g sample of Pd-loaded ZSM-11 molecular sieve was placed in a microwave processor for microwave irradiation under a nitrogen and oxygen mixed gas atmosphere (oxygen volume 10%), a gas flow rate of 50 ml / min, and a power of 120-175 W at a macroscopic temperature of 90 °C for 30 min, yielding 1 wt% Pd-MEL molecular sieve. The final product powder appeared... Figure 9 (a) X-ray diffraction pattern.

[0116] Comparative Example 1

[0117] The other raw material ratios and process flow in this embodiment are the same as in embodiment 4. The difference is that the obtained Pd-loaded ZSM-11 molecular sieve sample is not subjected to plasma treatment, but is placed in a tube furnace and heat-treated at 500°C for 1 hour in an air atmosphere.

[0118] Example 6

[0119] Preparation of Pd-supported H-type ZSM-11 molecular sieves:

[0120] Mixture I: Add 18.99g of silica sol (40% SiO2, 60% H2O, the same below), 2.04g of tetrabutylammonium bromide (99%), and 17.5g of deionized water to a beaker and mix well;

[0121] Mixture II: Mix 0.93g of seed crystals with 10g of water and then ultrasonically disperse in an ultrasonic oscillator for 10 min.

[0122] Mixture II: A homogeneous solution prepared from 2.61 g sodium hydroxide, 2.41 g aluminum sulfate (Al2(SO4)3·18H2O) and 10 g deionized water;

[0123] Mixture IV: Dissolve 0.141 g of Pd(NH3)4(NO3)2 in 3.33 g of water to prepare a clear solution.

[0124] Mixture II was slowly added to mixture I under constant stirring. After vigorous stirring for 30 minutes, mixture IV was added dropwise, and vigorous stirring continued until homogeneous. Then, mixture III was added, and stirring continued for a period of time. The resulting reaction mixture was transferred to a reaction vessel with a polytetrafluoroethylene liner, sealed, and placed in a hydrothermal synthesis oven for crystallization at 170°C for 24 hours. After cooling, the solid was separated from the mother liquor. The solid was washed with deionized water until neutral, dried at 120°C, calcined at 550°C, and then subjected to ion exchange with a 0.1M ammonium chloride solution. After drying at 120°C and calcining at 550°C for 2 hours, it was converted to the H-type. 5g of the H-type ZSM-11 molecular sieve was weighed, and mixture IV was slowly added dropwise onto the molecular sieve. After drying and calcination at 500°C for 4 hours, Pd-loaded ZSM-11 molecular sieve was obtained.

[0125] Microwave treatment of Pd-loaded ZSM-11 molecular sieves:

[0126] 0.1 g of the Pd-loaded ZSM-11 molecular sieve was placed in a microwave processor for microwave irradiation treatment. The treatment was carried out under an atmosphere of nitrogen and oxygen mixture (oxygen volume 10%) at a flow rate of 50 ml / min, at a power of 125-175 W and a macroscopic temperature control of 90℃ for 30 min, yielding 1 wt% Pd-MEL molecular sieve. The final product appears as follows... Figure 1 X-ray diffraction analysis of the product powder is as follows: Figure 9 (a).

[0127] Example 7

[0128] Preparation of Pd-supported H-type ZSM-11 molecular sieves:

[0129] Mixture I: Add 18.99g of silica sol (40% SiO2, 60% H2O, the same below), 2.04g of tetrabutylammonium bromide (99%), and 17.5g of deionized water to a beaker and mix thoroughly.

[0130] Mixture II: 0.1653g Pd(NH3)4(NO3)2 was mixed with 10g water to form a clear solution. Then 0.93g seed crystals were added to the solution and stirred for 30min. The solution was then ultrasonically dispersed in an ultrasonic oscillator for 10min.

[0131] Mixture II: A homogeneous solution prepared from 2.61 g sodium hydroxide, 2.41 g aluminum sulfate (Al2(SO4)·18H2O) and 10 g deionized water;

[0132] Mixture II was slowly added to mixture I under constant stirring. After vigorous stirring for 30 min, mixture III was added dropwise, and vigorous stirring continued until homogeneous. The resulting reaction mixture was transferred to a reaction vessel with a polytetrafluoroethylene liner, sealed, and placed in a hydrothermal synthesis oven. Crystallization was carried out at 90℃ for 48 h, followed by crystallization at 170℃ for 48 h. After cooling of the reaction vessel, the solid was separated from the mother liquor. The solid was washed with deionized water until neutral, dried at 120℃, calcined at 550℃, and then subjected to ion exchange with a 0.1M ammonium chloride solution. After drying at 120℃ and calcining at 550℃ for 2 h, it was converted to the H-type. Pd-loaded ZSM-11 molecular sieve was obtained.

[0133] Microwave treatment of Pd-loaded ZSM-11 molecular sieves:

[0134] 0.1 g of Pd-loaded ZSM-11 molecular sieve was placed in a microwave processor and subjected to microwave radiation treatment without the introduction of additional mixed gas. The treatment was carried out for 30 min at a power of 125-175 W and a macroscopic temperature of 90 °C to obtain 1 wt% Pd-MEL molecular sieve.

[0135] Example 8

[0136] Preparation of Pd-supported H-type ZSM-11 molecular sieves:

[0137] Mixture I: Add 18.99g of silica sol (40% SiO2, 60% H2O, the same below), 2.04g of tetrabutylammonium bromide (99%), and 17.5g of deionized water to a beaker and mix thoroughly.

[0138] Mixture II: 0.15g Pd(NO3)2 and 0.556g water were mixed to form a clear solution. The solution was then impregnated onto 0.65g seed crystals and calcined at 500℃ for 4h to obtain modified seed crystals. Subsequently, the modified seed crystals were mixed with 10g water and then ultrasonically dispersed in an ultrasonic oscillator for 10 min.

[0139] Mixture II: A homogeneous solution prepared from 2.61 g sodium hydroxide, 2.41 g aluminum sulfate (Al2(SO4)·18H2O) and 10 g deionized water;

[0140] Mixture II was slowly added to mixture I under constant stirring. After vigorous stirring for 30 min, mixture III was added dropwise, and vigorous stirring continued until homogeneous. The resulting reaction mixture was transferred to a reaction vessel with a polytetrafluoroethylene liner, sealed, and placed in a hydrothermal synthesis oven for crystallization at 170 °C for 24 h. After the reaction vessel cooled, the solid was separated from the mother liquor. The solid was washed with deionized water until neutral, dried at 120 °C, calcined at 550 °C, and then subjected to ion exchange with a 0.1 M ammonium chloride solution. After drying at 120 °C and calcining at 550 °C for 2 h, it was converted to the H-type.

[0141] Microwave treatment of Pd-loaded ZSM-11 molecular sieves:

[0142] 0.1 g of Pd-loaded ZSM-11 molecular sieve was placed in a microwave processor and subjected to microwave radiation treatment without the introduction of additional mixed gas. The treatment was carried out for 30 min at a power of 125-175 W and a macroscopic temperature of 90 °C to obtain 1 wt% Pd-MEL molecular sieve.

[0143] Experimental Example 1

[0144] This experimental example illustrates the passive adsorption of NOx by the Pd / ZSM-11 molecular sieve prepared in Example 4 of this invention and the Pd / ZSM-11 molecular sieve prepared in Comparative Example 1.

[0145] A gas containing nitrogen oxides was continuously passed into a molecular sieve-filled tube. The gas composition was 200 ppm NO and 10% O2. 2、 With N2 (as a balance gas), total gas flow rate: 100 ml / min, gas temperature: 100 °C o C, space velocity: 300,000 mL / (hg). Purge until the inlet and outlet NO concentrations are equal, then heat to desorb the adsorbed nitrogen oxides from the Pd / ZSM-11 molecular sieve, as shown in the attached diagram. Figure 1 As shown, the amount of nitrogen oxides adsorbed by the Pd / ZSM-11 molecular sieve in Example 4 (curve b) is much greater than that of the Pd / ZSM-11 molecular sieve in Comparative Example 1 (curve a).

[0146] like Figure 2 The Pd / ZSM-11 shown in Example 1 of this invention passively adsorbs NOx at a rate 10 times higher than that of the Pd / ZSM-11 sample in the comparative example. Figure 1 , Figure 2 ).

[0147] Experiment Example 2

[0148] This experimental example involves the detection of acidic sites in Pd / ZSM-11 molecular sieves prepared by plasma treatment or microwave treatment in Examples 4 and 5 of this invention, and in Pd / ZSM-11 molecular sieves prepared in Comparative Example 1, as shown in the appendix. Figure 3 The NH3-TPD spectrum. Figure 3 In the figure, curve a represents the Pd / ZSM-11 molecular sieve of Comparative Example 1, curve b represents the Pd / ZSM-11 molecular sieve after microwave treatment in Example 5, and curve c represents the Pd / ZSM-11 molecular sieve after plasma treatment in Example 4.

[0149] From the appendix Figure 3 It is evident that the Pd / ZSM-11 molecular sieves prepared in Examples 4 and 5 have significantly more acidic sites than those prepared in Comparative Example 1. In particular, the Pd / ZSM-11 molecular sieves treated with microwaves exhibit a very significant increase in acidity, with both weak acids (generally considered to be physically adsorbed NH3 or L acids, provided by Al or other metals such as Pd that can donate lone pairs of electrons) and strong acids (generally considered to be Brønsted acids, formed from the Al framework of the molecular sieve) showing a marked increase.

[0150] Experimental Example 3

[0151] This experimental example demonstrates the X-ray photoelectron spectroscopy (XPS) analysis of Pd / ZSM-11 molecular sieves prepared by plasma treatment or microwave treatment in Examples 4 and 5 of this invention, and the Pd / ZSM-11 molecular sieve prepared in Comparative Example 1. (See attached...) Figure 4 As shown. Among them, Figure 4 (a) is the XPS image of Pd / ZSM-11 molecular sieve in Comparative Example 1. Figure 4 (b) is the XPS image of the Pd / ZSM-11 molecular sieve in Example 5. Figure 4 (c) is the XPS diagram of Pd / ZSM-11 molecular sieve in Example 4.

[0152] From the appendix Figure 4 As can be seen from the data, after plasma / microwave treatment, the proportion of divalent Pd in ​​the total Pd of Pd / ZSM-11 molecular sieves significantly increased. Especially after microwave treatment, the increase in the proportion of valence Pd in ​​the total Pd was even greater.

[0153] Experiment Example 4

[0154] This experimental example illustrates the passive adsorption of NOx by the Pd / ZSM-11 molecular sieve prepared in Example 5 of this invention and the Pd / ZSM-11 molecular sieve prepared in Comparative Example 1.

[0155] A gas containing nitrogen oxides was continuously passed into a molecular sieve-filled tube. The gas composition was 200 ppm NO and 10% O2. 2、 With N2 (as a balance gas), total gas flow rate: 100 ml / min, gas temperature: 100 °C o C, space velocity: 300,000 mL / (hg). Purge until the inlet and outlet NO concentrations are equal, then heat to desorb the adsorbed nitrogen oxides from the Pd / ZSM-11 molecular sieve, as shown in the attached diagram. Figure 5 As shown, the amount of nitrogen oxides adsorbed by the Pd / ZSM-11 molecular sieve in Example 5 (curve b) is much greater than that of the Pd / ZSM-11 molecular sieve in Comparative Example 1 (curve a).

[0156] like Figure 6 The image shows Pd / ZSM-11 after microwave treatment provided in Example 5 of the present invention. The passive NOx adsorption amount of Pd / ZSM-11 is 26 times higher than that of the Pd / ZSM-11 sample in Comparative Example 1. Figure 5 , Figure 6 ).

[0157] Experimental Example 5

[0158] This experimental example involves H2-TPR (temperature-programmed reduction) characterization of the Pd / ZSM-11 molecular sieves prepared by plasma or microwave treatment in Examples 4 and 5 of this invention, and the Pd / ZSM-11 molecular sieve prepared in Comparative Example 1. The composition of Pd species loaded on the molecular sieves was analyzed, as shown in the appendix. Figure 7 H2-TPR spectrum. Figure 7In the figure, curve a represents the Pd / ZSM-11 molecular sieve of Comparative Example 1, and curve b represents the Pd / ZSM-11 molecular sieve after microwave treatment in Example 5.

[0159] From the appendix Figure 7 It can be seen that the Pd on the Pd / ZSM-11 molecular sieve after microwave treatment... n+ The number of ions (which are the main sites for NO adsorption, especially in humid environments, where they are the only adsorption sites) increases dramatically.

[0160] Experimental Example 6

[0161] Multiple adsorption-desorption experiments were conducted on the microwave-treated Pd / ZSM-11 molecular sieve of Example 5. The specific experimental procedure is detailed in Example 1. (See attached...) Figure 8 As shown, after five cycles of adsorption-desorption, the release of Pd / ZSM-11 molecular sieve decreased to a very low degree. In other words, nitrogen oxides adsorbed on Pd / ZSM-11 molecular sieve can be effectively desorbed, thereby increasing the service life of Pd / ZSM-11 molecular sieve.

[0162] Experimental Example 7

[0163] For the passive adsorption of NOx by Pd / ZSM-11 molecular sieves prepared by plasma treatment or microwave treatment in other Examples 1-3 and 6-8, the specific methods are the same as in Experimental Example 1. The results are shown in the table below.

[0164]

[0165] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for passively adsorbing nitrogen oxides, comprising: Under conditions below 200°C, gases containing nitrogen oxides are adsorbed by an adsorbent, which is a molecular sieve loaded with metal Pd that has been treated by plasma or microwave. The molecular sieves include one or a mixture of more than one of the following: CHA type zeolite molecular sieves, AEI type zeolite molecular sieves, MFI type zeolite molecular sieves, MEL type zeolite molecular sieves, BEA type zeolite molecular sieves, and FAU type molecular sieves.

2. The method according to claim 1, characterized in that, The molecular sieve mentioned is a MEL-type zeolite molecular sieve.

3. The method according to claim 2, characterized in that, The molecular sieve is a MEL-type zeolite molecular sieve, and the content of the supported metal Pd is less than 5 wt%.

4. The method according to claim 2, characterized in that, The molecular sieve is a MEL-type zeolite molecular sieve with a Pd content of 0.5-2 wt%.

5. The method according to any one of claims 1-4, characterized in that, The plasma treatment conditions are a mixture of O2 and N2 or an N2 atmosphere, with a treatment power density of 100-200 W / g.

6. The method according to claim 5, characterized in that, The power density of plasma treatment is 150 W / g.

7. The method according to claim 5, characterized in that, The gas flow rate is 20-500 ml / min.

8. The method according to claim 5, characterized in that, The gas flow rate is 50-150 ml / min.

9. The method according to claim 5, characterized in that, In the plasma treatment atmosphere, the volume content of O2 is not higher than 21v.

10. The method according to claim 5, characterized in that, The volume ratio of the mixed gas O2 to N2 is 5:95 to 21:

79.

11. The method according to claim 1, characterized in that, The conditions for microwave treatment include microwave treatment at a power density of 300-2250 W / g.

12. The method according to claim 11, characterized in that, Microwave processing was performed at a power density of 900-2000 W / g.

13. The method according to claim 11, characterized in that, Microwave processing was performed at a power density of 1250-1750 W / g.

14. The method according to claim 1 or 11, characterized in that, In microwave processing, the temperature is maintained between 50-170℃.

15. The method according to claim 1 or 11, characterized in that, In microwave processing, the temperature is maintained at 80-100℃.

16. The method according to claim 1 or 11, characterized in that, During the microwave processing, a mixture of O2 and N2 gas is continuously introduced.

17. The method according to claim 16, characterized in that, The processing flow rate of the O2 and N2 mixed gas is 20-500 ml / min.

18. The method according to claim 16, characterized in that, The processing flow rate of the O2 and N2 mixed gas is 50-150 ml / min.

19. The method according to any one of claims 1-4, characterized in that, The preparation method of Pd-loaded MEL-type zeolite molecular sieves includes: The silicon-containing raw material, template agent, and water are mixed evenly to obtain the first mixture; Aluminum-containing substances, alkali metal hydroxides, and water are mixed evenly to obtain a second mixture; Under stirring conditions, the second mixture is added to the first mixture and crystallized at a temperature of 120-180℃. After crystallization, the solid material is separated from the mother liquor. The separated solid material is washed with deionized water until neutral and dried. Finally, the template agent is removed by calcination to obtain MEL-type zeolite molecular sieve. MEL-type zeolite molecular sieves are transformed into H-type MEL zeolite molecular sieves after ion exchange. A Pd-containing soluble salt solution is added dropwise to an H-type MEL-type zeolite molecular sieve, or an ion exchange is performed between a Pd-containing soluble salt solution and an H-type MEL-type zeolite molecular sieve; after drying and calcination, a Pd-loaded MEL-type zeolite molecular sieve is obtained.

20. The method according to claim 19, characterized in that, The crystallization process includes: the resulting mixture is first crystallized at a temperature of 60-120℃, and then statically crystallized again at a temperature of 150-200℃; The template agent is tetrabutylammonium bromide.

21. The method according to claim 19, characterized in that, The preparation method of Pd-loaded MEL-type zeolite molecular sieves includes: Seed crystals are added during the preparation of MEL-type zeolite molecular sieves. The mixture containing the seed crystals is crystallized at a temperature of 120-180℃, and after drying and calcination, MEL-type zeolite molecular sieves are obtained.

22. The method according to claim 21, characterized in that, The method for preparing seed crystals includes the following steps: The silicon-containing raw material, template agent, and water are mixed evenly to obtain the first mixture; Aluminum-containing substances, alkali metal hydroxides, and water are mixed evenly to obtain a second mixture; Under stirring conditions, the second mixture is added to the first mixture, and crystallization is carried out in two stages at temperatures of 60-120℃ and 150-180℃. After crystallization, the solid material is separated from the mother liquor. The separated solid material is washed with deionized water until neutral and dried. Finally, the template agent is removed by calcination to obtain seed crystals.

23. The method according to claim 22, characterized in that, The template agent is tetrabutylammonium bromide.

24. The method according to claim 1 or 11, characterized in that, During the microwave processing, a gas containing N2 is continuously introduced.

25. The method according to claim 24, characterized in that, The processing flow rate of gas containing N2 is 20-500 ml / min.

26. The method according to claim 24, characterized in that, The processing flow rate of gas containing N2 is 50-150 ml / min.

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