Single-atom palladium-modified hierarchical porous molecular sieve adsorbents, their preparation methods and applications

Abstract

This invention provides a single-atom palladium-modified hierarchical porous molecular sieve adsorbent, its preparation method, and its application, comprising the following steps: S1. Adding a palladium complex to a molecular sieve gel and mixing evenly; S2. Crystallizing the product obtained in step S1 at a certain temperature for a certain time, and then washing, drying, and calcining to obtain the single-atom palladium-modified hierarchical porous molecular sieve adsorbent. In the preparation method of this invention, the palladium complex is used simultaneously as both a palladium source and a pore-forming agent, enabling the in-situ synthesis of the single-atom palladium-modified hierarchical porous molecular sieve adsorbent via a one-step method. The palladium species are anchored at ion exchange sites in an isolated single-atom ionic state, resulting in more effective adsorption sites with a more uniform distribution and higher NO content. x capacity.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve synthesis technology, specifically to a single-atom palladium-modified hierarchical porous molecular sieve adsorbent, its preparation method, and its application in the low-temperature adsorption of nitrogen oxides in motor vehicle exhaust. Background Technology

[0002] Currently, urea-selective catalytic reduction (Urea-SCR) is the method to meet the NO emission standards for diesel vehicles meeting China VI emission standards. x Urea solution is the most mainstream purification technology; however, the decomposition temperature of urea solution into the reducing agent ammonia is generally above 180℃. Therefore, at exhaust gas temperatures below 180℃, the catalyst cannot effectively perform its denitrification function, resulting in NO emissions. x Escape emissions. Furthermore, the catalytic activity of currently available commercial SCR catalysts, such as Cu-SSZ-13 molecular sieves, rapidly declines below 200°C in exhaust gas temperature, and its denitrification efficiency below 150°C fails to meet emission reduction requirements. Therefore, the mainstream Urea-SCR technology cannot meet the future ultra-low emission regulations for motor vehicles regarding NO2 during cold starts. x Emission reduction requirements (CN 110740810 A).

[0003] Currently NO x The mainstream solution for low-temperature air purification is to add NO2 devices before the exhaust gas is emitted. x Passive adsorbent (passive NO) x Adsorbent nanoparticles (PNA) are used to remove NO from exhaust gases when the exhaust temperature is low during a cold start of a car. x Adsorption occurs when the exhaust gas temperature rises during normal engine operation, causing the adsorbed NO to be absorbed. x Desorption, desorption NO x In subsequent SCR units, the NH3 from urea decomposition is used for reduction and purification (CN108368762 A, US 20150266002A1). Among them, palladium (Pd) modified molecular sieves such as CHA and FER (Pd-SSZ-13 and Pd-FER) are considered to be the most promising PNA materials (CN 105813717 B, Angew.Chem.Int.Edit.134(2022)e202107554). In palladium modified molecular sieve materials, isolated Pd anchored on ion exchange sites... 2+ The ion was considered to be NO xEffective adsorption sites (Chemical Engineering Journal, 2013, 222: 172-179, Applied Catalysis B: Environmental 212(2017) 140-149). Therefore, the preparation of single-atom dispersed Pd-modified molecular sieves is crucial. However, in the traditional "two-step method" for preparing Pd-modified molecular sieves, the hydrolysis of Pd ions produces hydrated palladium ions and palladium hydroxide precipitates, which prevents Pd species from smoothly entering the pores of the small-pore molecular sieve and forming isolated Pd at the ion exchange sites. 2+ NO ions x Effective adsorption sites; simultaneously, due to their small pore size, small-pore molecular sieves exhibit good adsorption properties in NO. x During the desorption stage, the confinement effect of the orifice restricts NO production. x The desorption temperature is relatively high, preventing high-ratio desorption in a single step and hindering good coupling with the active temperature window of the NH3-SCR catalyst. Therefore, solving the NO problem requires... x Rapid, one-time, high-ratio desorption is another challenge faced by traditional palladium-modified small-pore molecular sieve materials. Summary of the Invention

[0004] To address the challenges posed by traditional methods for preparing palladium-based small-pore molecular sieve materials, such as the ease with which palladium ions hydrolyze and their difficulty in entering the sieve channels, as well as the strong pore confinement effect of small-pore molecular sieves, NO... x Addressing the two major technical challenges of rapid, high-proportion desorption in a single step, this invention provides a single-atom palladium-modified hierarchical porous molecular sieve adsorbent, its preparation method, and its application. A palladium complex is added to the molecular sieve gel, serving as both a palladium source and a pore-forming agent, enabling a one-step in-situ synthesis of the single-atom palladium-modified hierarchical porous molecular sieve adsorbent.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a single-atom palladium-modified hierarchical porous molecular sieve adsorbent, comprising the following steps:

[0007] S1. Add the palladium complex to the molecular sieve gel and mix thoroughly;

[0008] S2. The product obtained in step S1 is crystallized at a certain temperature for a certain time, and then washed, dried and calcined to obtain a single-atom palladium-modified hierarchical porous molecular sieve adsorbent.

[0009] According to the above scheme, the palladium complex is one or more of palladium cyanide, bis(acetonitrile)palladium chloride, bis(ethylenediamine)palladium chloride, bis(acetonitrile)p-toluenesulfonate palladium(II), palladium-ethylenediamine, and palladium-pentaethylenehexamine, preferably bis(acetonitrile)p-toluenesulfonate palladium(II) and / or palladium-pentaethylenehexamine.

[0010] According to the above scheme, in step S1, after the palladium complex is added to the molecular sieve gel and mixed evenly, it is aged for 2 to 48 hours under static or stirring conditions.

[0011] According to the above scheme, hydrothermal crystallization is carried out in step S2. The crystallization temperature is 100-180℃ and the time is 24-336h. The crystallization method is static or dynamic crystallization.

[0012] According to the above scheme, the washing liquid in step S2 is deionized water and / or ethanol, the drying temperature is 80-120℃, the calcination temperature is 400-700℃, and the calcination atmosphere is air.

[0013] According to the above scheme, the molecular sieve is one of Pd-SSZ-13, Pd-ZSM-35, Pd-SSZ-39, Pd-LTA, Pd-AFX, Pd-KFI, Pd-RHO, Pd-RTH, Pd-ZSM-5 or Pd-Beta.

[0014] According to the above scheme, when the molecular sieve is Pd-SSZ-13, Pd-ZSM-35 or Pd-SSZ-39, the preparation method of molecular sieve gel is as follows: dissolve the alkali source in water, add the aluminum source to dissolve and obtain solution A, dissolve the silicon source in water, add the template agent and stir evenly to obtain solution B, slowly add solution A to solution B, stir evenly, and obtain molecular sieve gel.

[0015] According to the above scheme, the alkali source is Na2O;

[0016] The aluminum source is one or more of sodium aluminate, aluminum isopropoxide, boehmite, and boehmite.

[0017] The silicon source is one of silica sol, water glass, fumed silica, and tetraethyl orthosilicate.

[0018] The template agents for molecular sieve Pd-SSZ-13 are N,N,N-trimethyladamantylammonium hydroxide and choline chloride. The molar ratio of each component of the molecular sieve gel with added palladium complex is (1~100)SiO2:Al2O3:6Na2O:4R:1600H2O:(0.001~0.5)Pd, where R represents the template agent.

[0019] The template agent for molecular sieve Pd-ZSM-35 is one or more of cyclohexylamine, hexamethyleneimine, ethylenediamine, and pyridine. The molar ratio of each component in the molecular sieve gel with added palladium complex is 1.0SiO2:(0.025~0.1)Al2O3:0.1Na2O:0.2R:40H2O:(0.001~0.5)Pd, where R represents the template agent.

[0020] The template agent for molecular sieve Pd-SSZ-39 is N,N-diethyl-2,6-dimethylpiperidinium hydroxide or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide. The molar ratio of each component in the molecular sieve gel with added palladium complex is 1.0SiO2:(0.025~0.1)Al2O3:0.2Na2O:0.2R:15H2O:(0.001~0.5)Pd, where R represents the template agent.

[0021] In some other implementations, the silicon and aluminum sources of the molecular sieve Pd-SSZ-39 are both derived from USY molecular sieves and obtained through a crystallization method.

[0022] Secondly, this invention provides a single-atom palladium-modified hierarchical porous molecular sieve adsorbent prepared by the above-described method. Since the molecular sieve itself has pores, and the palladium complex acts as a pore-forming agent, it secondary-forms pores within the molecular sieve, resulting in a molecular sieve adsorbent with hierarchical pores. The palladium (Pd) loading in this single-atom palladium-modified hierarchical porous molecular sieve adsorbent is 0.01 wt% to 3.0 wt%, preferably 0.1 wt% to 2.0 wt%.

[0023] This invention provides the application of the above-mentioned single-atom palladium-modified hierarchical porous molecular sieve adsorbent as a passive adsorbent for nitrogen oxides during cold starts of motor vehicles.

[0024] The beneficial effects of this invention are:

[0025] Compared with palladium molecular sieves prepared by the traditional two-step liquid-phase method, the palladium species of this invention are anchored at ion exchange sites in an isolated monatomic ionic state, resulting in more effective adsorption sites and a more uniform distribution. This leads to the synthesized monatomic palladium-modified hierarchical porous molecular sieve adsorbent exhibiting higher NO content. x capacity;

[0026] Compared with the traditional two-step method for preparing palladium molecular sieves, this method avoids multiple ammonium exchange, drying and calcination processes, and overcomes the disadvantage of the traditional two-step synthesis method which requires a later active species loading process. This makes the synthesis method simple and environmentally friendly.

[0027] This invention is the first to utilize a palladium source as a pore-forming agent. The in-situ synthesized hierarchical porous single-atom palladium-modified hierarchical porous molecular sieve adsorbent exhibits better NO adsorption than ordinary palladium molecular sieves in the temperature range of 200–300°C. x The one-time rapid desorption rate is higher. Detailed Implementation

[0028] The principles and features of the present invention are described below with reference to specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] This invention provides a method for preparing a single-atom palladium-modified hierarchical porous molecular sieve adsorbent, comprising the following steps:

[0030] S1. Add the palladium complex to the molecular sieve gel and mix thoroughly;

[0031] S2. The product obtained in step S1 is crystallized at a certain temperature for a certain time, and then washed, dried and calcined to obtain a single-atom palladium-modified hierarchical porous molecular sieve adsorbent.

[0032] According to the above scheme, the palladium complex is one or more of palladium cyanide, bis(acetonitrile)palladium chloride, bis(ethylenediamine)palladium chloride, bis(acetonitrile)p-toluenesulfonate palladium(II), palladium-ethylenediamine, and palladium-pentaethylenehexamine, preferably bis(acetonitrile)p-toluenesulfonate palladium(II) and / or palladium-pentaethylenehexamine.

[0033] The palladium-based small-pore molecular sieve adsorbent materials mentioned in the background technology face challenges in traditional preparation methods, such as the easy hydrolysis of Pd ions making it difficult for them to enter the molecular sieve channels, and the strong pore confinement effect of small-pore molecular sieves affecting NO production. x Addressing the two major technical challenges of rapid, high-ratio desorption in a single step, this invention proposes a one-step in-situ synthesis of a single-atom palladium-modified hierarchical porous molecular sieve adsorbent by adding a palladium complex to the molecular sieve gel, which serves as both a palladium source and a pore-forming agent. The palladium species are anchored at ion exchange sites in an isolated single-atom ionic state, resulting in more effective adsorption sites with a more uniform distribution. Furthermore, by utilizing the palladium source as a pore-forming agent, the prepared single-atom palladium-modified hierarchical porous molecular sieve adsorbent exhibits multi-level pore sizes, leading to higher NO adsorption capacity. x Storage capacity, and NO content is higher than that of ordinary palladium molecular sieves in the temperature range of 200℃~300℃. x A higher rate of rapid desorption in a single step.

[0034] According to the above scheme, in step S1, after the palladium complex is added to the molecular sieve gel and mixed evenly, it is aged for 2 to 48 hours under static or stirring conditions.

[0035] According to the above scheme, hydrothermal crystallization is carried out in step S2. The crystallization temperature is 100-180℃ and the time is 24-336h. The crystallization method is static or dynamic crystallization.

[0036] According to the above scheme, the washing liquid in step S2 is deionized water and / or ethanol, the drying temperature is 80-120℃, the calcination temperature is 400-700℃, and the calcination atmosphere is air.

[0037] According to the above scheme, the molecular sieve is one of Pd-SSZ-13, Pd-ZSM-35, Pd-SSZ-39, Pd-LTA, Pd-AFX, Pd-KFI, Pd-RHO, Pd-RTH, Pd-ZSM-5 or Pd-Beta.

[0038] According to the above scheme, when the molecular sieve is Pd-SSZ-13, Pd-ZSM-35 or Pd-SSZ-39, the preparation method of molecular sieve gel is as follows: dissolve the alkali source in water, add the aluminum source to dissolve and obtain solution A, dissolve the silicon source in water, add the template agent and stir evenly to obtain solution B, slowly add solution A to solution B, stir evenly, and obtain molecular sieve gel.

[0039] According to the above scheme, the alkali source is Na2O;

[0040] The aluminum source is one or more of sodium aluminate, aluminum isopropoxide, boehmite, and boehmite.

[0041] The silicon source is one of silica sol, water glass, fumed silica, and tetraethyl orthosilicate.

[0042] The template agents for molecular sieve Pd-SSZ-13 are N,N,N-trimethyladamantylammonium hydroxide and choline chloride. The molecular sieve gel with added palladium complex has the following composition by mass ratio: (1-100)SiO2:Al2O3:6Na2O:4R:1600H2O:(0.001-0.5)Pd, where R represents the template agent.

[0043] The template agent for molecular sieve Pd-ZSM-35 is one or more of cyclohexylamine, hexamethyleneimine, ethylenediamine, and pyridine. The molecular sieve gel with added palladium complex has the following composition by mass ratio: 1.0SiO2:(0.025~0.1)Al2O3:0.1Na2O:0.2R:40H2O:(0~0.5)Pd, where R represents the template agent.

[0044] The template agent for molecular sieve Pd-SSZ-39 is N,N-diethyl-2,6-dimethylpiperidinium hydroxide or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide. The molecular sieve gel with added palladium complex has the following composition by mass ratio: 1.0SiO2:(0.025~0.1)Al2O3:0.2Na2O:0.2R:15H2O:(0.001~0.5)Pd, where R represents the template agent.

[0045] In some other implementations, the silicon and aluminum sources of the molecular sieve Pd-SSZ-39 are both derived from USY molecular sieves and obtained through a crystallization method.

[0046] Compared with the traditional two-step synthesis method, this preparation method avoids multiple ammonium exchange, drying and calcination processes, and overcomes the disadvantage of the traditional two-step synthesis method which must go through the later active species loading process. This makes the synthesis method simple and environmentally friendly.

[0047] This invention also provides the application of the above-mentioned single-atom palladium-modified hierarchical porous molecular sieve adsorbent as a passive adsorbent for nitrogen oxides during cold starts of motor vehicles.

[0048] The following are specific embodiments.

[0049] Example 1: In-situ synthesis of single-atom palladium-modified hierarchical porous Pd-SSZ-13 molecular sieve adsorbent

[0050] 0.9 g of sodium hydroxide was dissolved in 22 g of deionized water. After complete dissolution, 0.51 g of sodium aluminate was added and stirred until fully dissolved to obtain solution A. 15 g of silica sol was dissolved in 10 g of deionized water, followed by the addition of 3 g of N,N,N-trimethyladamantyl ammonium hydroxide. The mixture was stirred thoroughly to obtain solution B. Solution B was slowly added to solution A while stirring. 0.2 g of palladium(II) bis(acetonitrile)-p-toluenesulfonate was slowly added in batches to the mixed solution of A and B, and stirred for 4 h. The mixture was then placed in a reactor and crystallized at 160 °C for 96 h. The resulting product was washed with deionized water, filtered, dried at 110 °C for 12 h, and then calcined at 550 °C for 6 h to remove the organic template agent and complexing agent, thus obtaining the single-atom dispersed hierarchical porous Pd-SSZ-13 molecular sieve, with the adsorbent designated as Pd1-SSZ-13.

[0051] Example 2: In-situ synthesis of single-atom palladium-modified hierarchical porous Pd-ZSM-35 molecular sieve adsorbent

[0052] 0.8 g of sodium hydroxide was dissolved in 30 g of deionized water. After complete dissolution, 0.50 g of sodium aluminate was added and stirred until fully dissolved to obtain solution A. 20 g of silica sol was dissolved in 10 g of deionized water, followed by the addition of 3.48 g of cyclohexylamine. The mixture was stirred thoroughly to obtain solution B. Solution B was slowly added to solution A while stirring. 0.2 g of palladium(II) bis(acetonitrile)-p-toluenesulfonate was slowly added in batches to the mixed solution of A and B, and stirred for 4 h. The mixture was then placed in a reactor and crystallized at 160 °C for 72 h. The resulting product was washed with deionized water, filtered, dried at 110 °C for 12 h, and then calcined at 550 °C for 6 h to remove the organic template agent and complexing agent, thus obtaining the single-atom dispersed hierarchical porous Pd-ZSM-35 molecular sieve, with the adsorbent designated as Pd1-ZSM-35.

[0053] Example 3: In-situ synthesis of single-atom palladium-modified hierarchical porous Pd-SSZ-39 molecular sieve adsorbent

[0054] 0.67 g of sodium hydroxide was dissolved in 15.6 g of deionized water and stirred until fully dissolved to obtain solution A. 12.9 g of USY molecular sieve was added to 10 g of deionized water and stirred until homogeneous. Then, 24.6 g of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide was added and stirred thoroughly to obtain solution B. Solution B was slowly added to solution A while stirring. 0.2 g of bis(acetonitrile)-p-toluenesulfonate palladium(II) was slowly added in batches to the mixture of solutions A and B, and stirred for 4 h. The mixture was then placed in an autoclave and crystallized at 135 °C for 168 h. The resulting product was washed with deionized water, filtered, dried at 110 °C for 12 h, and then calcined at 600 °C for 6 h to remove the organic template agent and complexing agent, yielding a single-atom dispersed hierarchical porous Pd-SSZ-39 molecular sieve, with the adsorbent designated as Pd1-SSZ-39.

[0055] Comparative Example 1

[0056] Using commercial H-SSZ-13 molecular sieve as a carrier and precious metal Pd as the active component, the loading of Pd element in the adsorbent is 1 wt%, based on the mass of the carrier being 100%.

[0057] Preparation method of adsorbent: Place molecular sieve support in a beaker, add a certain concentration of palladium nitrate solution to the molecular sieve, and stir thoroughly before the liquid phase appears; transfer it to an oven for drying overnight, and then calcine at 550℃ for 6 hours to obtain the adsorbent with a Pd loading of 1wt%, and the adsorbent is designated as Pd-SSZ-13.

[0058] Comparative Example 2

[0059] The preparation method is the same as that of Comparative Example 1, except that the commercial H-SSZ-13 molecular sieve support is replaced with the commercial ZSM-35 support, and the adsorbent is referred to as Pd-ZSM-35.

[0060] Comparative Example 3

[0061] The preparation method is the same as that of Comparative Example 1, except that the commercial H-SSZ-13 molecular sieve support is replaced with the commercial SSZ-39 support, and the adsorbent is referred to as Pd-SSZ-39.

[0062] Determination of NO in the molecular sieve adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 x The adsorption performance is evaluated using the following methods:

[0063] Pd-zeolite molecular sieve NO xThe adsorbent powder sample was pressed into tablets and sieved to obtain 40-60 mesh particles. 0.1 g of catalyst particles were weighed and placed in a fixed-bed activity evaluation device. The simulated flue gas composition was 200 ppm NO, 200 ppm CO2, 15% O2, and 5% H2O, with a reaction space velocity of 100,000 h⁻¹. -1 The NO content of the molecular sieve adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 was determined respectively. x The adsorption performance results are shown in Table 1 below.

[0064] Table 1

[0065] <![CDATA[Pd1-SSZ-13]]> 85 180～350 <![CDATA[Pd1-ZSM-35]]> 78 150～320 <![CDATA[Pd1-SSZ-39]]> 82 190～370 Pd-SSZ-13 63 200～400 Pd-ZSM-35 60 180～370 Pd-SSZ-39 78 220～435

[0066] As can be seen from Table 1, the single-atom palladium-modified hierarchical porous molecular sieve adsorbent prepared by the method of this invention exhibits higher NO content compared to the palladium-modified molecular sieve adsorbent prepared by the traditional two-step method. x Storage capacity, NO content of the prepared single-atom palladium-modified hierarchical porous Pd-SSZ-13 molecular sieve adsorbent and single-atom palladium-modified hierarchical porous Pd-ZSM-35 molecular sieve adsorbent x The storage capacity is increased by more than 30% compared to molecular sieves prepared by the traditional two-step method, and the NO content is also higher. x The desorption temperature is even lower.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a single-atom palladium-modified hierarchical porous molecular sieve adsorbent, characterized in that, Includes the following steps: S1. Add the palladium complex to the molecular sieve gel and mix thoroughly; S2. The product obtained in step S1 is crystallized at 100~180℃ for 24~336h, and then washed, dried and calcined at 400~700℃ to obtain a single-atom palladium modified hierarchical porous molecular sieve adsorbent. The palladium complex is bis(acetonitrile)-p-toluenesulfonate palladium(II) and / or palladium-pentaethylenehexamine; The molecular sieve is one of Pd-SSZ-13, Pd-ZSM-35, Pd-SSZ-39, Pd-LTA, Pd-AFX, Pd-KFI, Pd-RHO, Pd-RTH, Pd-ZSM-5 or Pd-Beta. The single-atom palladium-modified hierarchical porous molecular sieve adsorbent is used as a passive adsorbent for nitrogen oxides during cold starts of motor vehicles.

2. The method for preparing the single-atom palladium-modified hierarchical porous molecular sieve adsorbent according to claim 1, characterized in that, In step S1, the palladium complex is added to the molecular sieve gel and mixed evenly, and then aged for 2 to 48 hours under static or stirring conditions.

3. The method for preparing the single-atom palladium-modified hierarchical porous molecular sieve adsorbent according to claim 1, characterized in that, Hydrothermal crystallization is carried out in step S2, and the crystallization method is static or dynamic crystallization.

4. The method for preparing the single-atom palladium-modified hierarchical porous molecular sieve adsorbent according to claim 1, characterized in that, The washing solution in step S2 is deionized water and / or ethanol, the drying temperature is 80~120℃, and the calcination atmosphere is air.

5. The method for preparing the single-atom palladium-modified hierarchical porous molecular sieve adsorbent according to claim 1, characterized in that, When the molecular sieve is Pd-SSZ-13, Pd-ZSM-35 or Pd-SSZ-39, the preparation method of the molecular sieve gel is as follows: dissolve the alkali source in water, add the aluminum source to dissolve and obtain solution A, dissolve the silicon source in water, add the template agent and stir evenly to obtain solution B, slowly add solution A to solution B, stir evenly, and obtain molecular sieve gel. The alkali source is Na2O; The aluminum source is one or more of sodium aluminate, aluminum isopropoxide, boehmite, and boehmite. The silicon source is one of silica sol, water glass, fumed silica, and tetraethyl orthosilicate. The aluminum and silicon sources for molecular sieve Pd-SSZ-39 can also be derived from USY molecular sieve; The template agent for molecular sieve Pd-SSZ-13 is N,N,N-trimethyladamantylammonium hydroxide and / or choline chloride. The molar ratio of each component of the molecular sieve gel with added palladium complex is (1~100) SiO2:Al2O3:6Na2O:4R:1600H2O:(0.001~0.5)Pd, where R represents the template agent; The template agent for molecular sieve Pd-ZSM-35 is one or more of cyclohexylamine, hexamethyleneimine, ethylenediamine, and pyridine. The molar ratio of each component in the molecular sieve gel with added palladium complex is 1.0 SiO2: (0.025~0.1) Al2O3: 0.1 Na2O: 0.2 R: 40H2O: (0.001~0.5) Pd, where R represents the template agent; The template agent for molecular sieve Pd-SSZ-39 is N,N-diethyl-2,6-dimethylpiperidinium hydroxide or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide. The molar ratio of each component of the molecular sieve gel with added palladium complex is 1.0 SiO2: (0.025~0.1) Al2O3: 0.2 Na2O: 0.2 R: 15 H2O: (0.001~0.5) Pd, where R represents the template agent.

6. A single-atom palladium-modified hierarchical porous molecular sieve adsorbent, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.