CN111001435B - Hollow Cu-SSZ-13 molecular sieve catalyst and application thereof - Google Patents

Abstract

The invention discloses a preparation method of a hollow structure Cu-SSZ-13 molecular sieve and selective catalysis of NH ₃ A method of reducing NO comprising the steps of: firstly, fully mixing a silicon source, an aluminum source, inorganic base, a microporous template agent and an organic additive to form gel, and directly preparing the hollow single crystal SSZ-13 molecular sieve through one-step hydrothermal crystallization; then separately carrying out NH ₄ ⁺ And Cu ²⁺ Ion exchange, centrifugal washing, drying and roasting to prepare the hollow structure Cu-SSZ-13 molecular sieve; finally, under the catalytic action of the hollow structure Cu-SSZ-13 molecular sieve, NH is utilized ₃ Selective reduction of NO to N as a reducing agent ₂ . Compared with the traditional two-step acid-base treatment method, the method for preparing the SSZ-13 molecular sieve with the hollow structure by using the one-step hydrothermal method is more economic, simpler and efficient; meanwhile, in the NO reduction reaction, the mass transfer diffusion of each reaction molecule is facilitated, so that the NO reduction activity is effectively improved, the activity window is widened, and the method is more suitable for the NO reduction reaction under the condition of high airspeed.

Description

A kind of hollow Cu-SSZ-13 molecular sieve catalyst and its application

technical field

The invention relates to the removal of nitrogen oxide gas pollutants contained in fixed source flue gas such as boilers, incinerators, and exhaust gas from diesel vehicles, that is, the field of denitrification molecular sieve catalyst reaction, and specifically relates to the preparation of hollow Cu-SSZ-13 molecular sieve catalysts and apply.

Background technique

In recent years, as air pollution has become more and more serious, people have paid more and more attention to the emission of air pollutants. NO _X has been clearly listed as a class of pollutants subject to total amount control. Its emission density is high and the emission is concentrated. The harm caused It is very serious and is one of the most difficult pollutants to remove. During the operation of diesel vehicles, a large amount of NO _X will be produced, causing serious pollution to the atmosphere. NH ₃ Selective Catalytic Reduction of NO _X (NH ₃ -SCR) is a mature and effective diesel vehicle exhaust NO _X purification technology. Its principle is to use NH ₃ as a reducing agent to reduce NO _X under the action of a special denitrification catalyst into N ₂ , realizing green and pollution-free. At present, there are many materials used as catalysts for the NH ₃ -SCR reaction, which can be divided into three categories: noble metal catalysts, metal oxide catalysts, and molecular sieve catalysts. _The traditional V ₂ O _{5 -WO 3} (MO ₃ ) ₃ /TiO ₂ catalyst has a narrow activity temperature window, poor N ₂ selectivity and thermal stability, and is easy to deactivate. ₂ has defects such as strong catalytic oxidation performance, which limits its application. Molecular sieve has a large specific surface area, excellent thermal stability and anti-aging ability, and high reactivity, and is currently the preferred catalyst for purifying diesel vehicle exhaust. At present, the commonly used molecular sieve denitration catalysts mainly include Cu-ZSM-5, Fe-ZSM-5, Cu-SAPO-34, Cu-Beta, Cu-SSZ-13 and so on.

According to the latest research publications, catalysts supported by Chabazite (CHA) molecular sieves (Cu-SSZ-13, Cu-SAPO-34) have attracted widespread attention due to their superior NH ₃ -SCR reactivity. SSZ-13 has a relatively developed pore structure, its specific surface can reach up to 700m ² /g, and there are many exchangeable cations and surface proton acid centers, and the range of silicon-aluminum ratio can be adjusted well, so it is determined that it can be used as an adsorption agent and catalyst or catalyst carrier. Peden et al. found that the Cu-exchanged SSZ-13 molecular sieve had better catalytic activity and selectivity than the traditional Cu-ZSM-5 and Cu-Beta molecular sieve catalysts. And after long-term hydrothermal aging treatment at high temperature, Cu-SSZ-13 can still maintain the skeleton structure well and still exhibit excellent activity, while Cu-Y, Cu-ZSM-5, and Cu-Beta have skeleton collapse. Activity reduction or even inactivation phenomenon. (Kwak, Ja Hun, et al."Excellent activity and selectivity of Cu-SSZ-13in the selective catalytic reduction of NO _X ,with NH ₃ ."Journal of Catalysis275.2(2010):187-190; Kwak, Ja Hun , et al. "Effects of hydrothermal aging on NH ₃ -SCR reaction over Cu/zeolites." Journal of Catalysis 287.3(2012):203-209.). QYe et al. found that Cu-CHA has better resistance to HCs poisoning, better low-temperature NO _X removal efficiency, and a wider high-conversion temperature window than Cu-ZSM-5. It also exhibits excellent hydrothermal stability (Q Ye, L.Wang, and RTYang. "Activity, propene poisoning resistance and hydrothermal stability of copperexchanged chabazite-like zeolite catalysts for SCR of NO with ammonia incomparison to Cu/ZSM -5."Applied Catalysis A General 427-428.1(2012):24-34.). It also makes it a new research direction for molecular sieve SCR catalysts.

However, the traditional Cu-SSZ-13 is a microporous molecular sieve. During the reaction process, the mass transfer and diffusion efficiency of various reaction molecules in the internal tiny pores is low. At the same time, the accessibility of the active sites inside the crystal is low, and the crystal utilization rate decreased, thereby reducing the catalytic activity. Especially under the conditions of low temperature and high space velocity, the diffusion of various reaction gases is slow, and the contact time with the catalyst is shortened, which greatly reduces the denitrification performance of the catalyst. At present, the mainstream methods to solve this problem are mainly to introduce mesopores, reduce particle size and prepare molecular sieves with hollow structures. The introduction of mesopores may destroy the framework structure and crystallinity of molecular sieves. It is a more reasonable method at present. However, the traditional hollow structure is mainly treated by two-step acid-base treatment, which is complicated in procedure, high in cost, and easy to damage the molecular sieve structure. Therefore, how to improve the catalytic activity of Cu-SSZ-13 molecular sieve catalysts at low temperature and high space velocity has become a hot topic in the field of denitrification.

Contents of the invention

In order to solve the shortcomings of the existing technology, the present invention provides a single-crystal SSZ-13 molecular sieve with a single-step synthesis with a hollow structure, which has a uniform and regular outer wall and an inner hollow structure, fast mass transfer, high catalytic activity, and can effectively improve NO activity. Reaction performance at window and high space velocity.

In order to achieve the above object, the present invention adopts the following technical solutions:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add polyethylenimine to the mixture, stir well and mix well, then add aluminum source and mix and stir; add silicon source to the mixed solution and stir evenly. Put the above mixed solution into a hydrothermal kettle, crystallize at 100-200°C for 2-8 days, centrifuge, wash, dry, and roast at 450-700°C for 2-10h to prepare hollow single crystal Na-SSZ-13 Molecular sieve. The prepared hollow single crystal Na-SSZ-13 molecular sieve has a cuboid structure, its size is 0.1-10 μm, and the wall thickness accounts for 1%-30% of the side length

(2) Stir Na-type molecular sieves and liquid ammonium solution at 40-90°C for 1-12 hours, perform ammonium exchange, centrifuge washing, and after drying, repeat the above steps for secondary ammonium exchange, and obtain hollow ammonium NH ₄ - SSZ-13 molecular sieve.

(3) Stir the ammonium NH ₄ -SSZ-13 molecular sieve and liquid copper solution at 40-90°C for 1-12h, perform copper exchange, centrifugally wash, dry, and roast at 400-700°C for 2-10h to obtain a hollow copper base Cu-SSZ-13 molecular sieve.

(4) Place the hollow Cu-SSZ-13 molecular sieve prepared above in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, heat the reactor to a certain reaction temperature, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the NO concentration of the reaction tail gas.

As a preference of the above technical solution, in the reaction system of step (1), the organic additive is polyethyleneimine (PEIM). The molar ratio of each component in the system is: (30-100) H ₂ O: (0.23-0.36) NaOH: (0.1-0.8) TMAda-OH: (0.08-0.4) PEIM: (0.01-0.1) Al ₂ O ₃ : 1SiO ₂ . The molar ratio of each component is preferably: (40-80) H ₂ O: (0.3-0.36) NaOH: (0.2-0.5) TMAda-OH: (0.1-0.3) PEIM: (0.04-0.08) Al ₂ O ₃ : 1SiO ₂ .

As a preference of the above technical solution, in the reaction system of step (1), the aluminum source is aluminum hydroxide solid powder, and the molecular weight of polyethyleneimine is preferably Mw=1600-6000, more preferably Mw=1700-2500.

As a preference for the above technical solution, in the reaction system of step (1), the crystallization temperature is 100-200°C, preferably 120-180°C, more preferably 150-160°C; the crystallization time is 2-8 days, preferably 3-5 days sky

As a preference of the above technical solution, in step (2), the exchange temperature is 40-90° C., preferably 60-80° C., and stirred for 1-12 hours, preferably 3-8 hours.

As a preference of the above technical solution, in step (3), the calcination temperature is 400-700°C, preferably 500-600°C, and the calcination time is 2-10h, preferably 5-8h.

As a preference of the above technical solution, in step (4), during the reaction process of selective reduction of NO by NH ₃ , the reaction space velocity of the total mixed gas is 4000-500,000h ^-1 , preferably 20,000-200,000h ^-1 , more preferably Preferably it is 30,000-150,000h ^-1 .

The present invention has the following advantages:

The present invention prepares SSZ-13 molecular sieve with hollow structure by one-step hydrothermal method, which is more economical, simple and efficient compared with the traditional two-step acid-base treatment method; at the same time, in the NO reduction reaction, it is beneficial to the mass transfer and diffusion of each reaction molecule , thereby effectively improving the activity of NO reduction, broadening the activity window, and being more suitable for NO reduction reaction under high space velocity conditions.

The present invention prepares the hollow single crystal SSZ-13 molecular sieve through a one-step synthesis method, the preparation method is simple, the efficiency is high, and the cost is low. It has a uniform and regular thin-walled structure with a wall thickness of about 0.1-0.5 μm, and the molecular sieve particles are in the shape of a cuboid. The side length is 0.8-2 μm. The hollow catalyst has high catalytic activity, and when used in NH ₃ -SCR catalytic reaction, the mass transfer resistance suffered by the diffusion of reaction gas molecules is small, and the catalytic activity window and high space velocity catalytic activity are effectively improved.

Description of drawings

Figure 1: SEM and TEM photos of hollow SSZ-13 molecular sieve (Example 1), (a) SEM image of hollow SSZ-13, (b) TEM image of hollow SSZ-13 (scale bars are 1 μm and 0.2 μm);

Figure 2: SEM and TEM photographs of hollow SSZ-13 molecular sieves (Example 2), (a) SEM image of hollow SSZ-13, (b) TEM image of hollow SSZ-13 (scale bars are 1 μm and 0.2 μm)

Figure 3: SEM and TEM photos of hollow SSZ-13 molecular sieves (Example 3), (a) SEM image of hollow SSZ-13, (b) TEM image of hollow SSZ-13 (scale bars are 1 μm and 0.5 μm)

Figure 4: SEM and TEM images of solid SSZ-13 molecular sieve (comparative example 1), (a) SEM image of solid SSZ-13, (b) TEM image of solid SSZ-13 (scale bars are 0.5 μm and 1 μm)

Figure 5: SEM and TEM images of solid SSZ-13 molecular sieve (comparative example 2), (a) SEM image of solid SSZ-13, (b) TEM image of solid SSZ-13 (scale bars are 5 μm and 2 μm)

Figure 6: SEM and TEM images of solid SSZ-13 molecular sieve (comparative example 3), (a) SEM image of solid SSZ-13, (b) TEM image of solid SSZ-13 (scale bars are 5 μm and 2 μm)

Figure 7: SEM and TEM images of solid SSZ-13 molecular sieve (comparative example 4), (a) SEM image of solid SSZ-13, (b) TEM image of solid SSZ-13 (scale bars are 0.5 μm and 0.2 μm)

Figure 8: Comparison of SCR reactivity of hollow Cu-SSZ-13 molecular sieve and solid Cu-SSZ-13 molecular sieve catalysts;

Accompanying drawing 9: Hollow SSZ-13 molecular sieve (embodiment 1) and solid SSZ-13 molecular sieve (comparative example 1) catalyst N ₂ adsorption-desorption curves

Attached Table 1: _N2 adsorption and desorption parameters of catalysts of hollow SSZ-13 molecular sieve (Example 1) and solid SSZ-13 molecular sieve (Comparative Example 1)

detailed description

The features of the present invention are described below by examples, but the present invention is not limited to the following examples.

Example 1

The preparation of hollow Cu-SSZ-13 molecular sieve catalyst and its application in NH ₃ -SCR reaction include the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add polyethyleneimine (Mw=1800, the same as the following examples), stir well and mix well, then add Al(OH) ₃ solid powder and mix and stir; add silica sol dropwise to the mixed solution and stir evenly. The above mixed solution was put into a hydrothermal kettle, crystallized at 160°C for 3 days, washed by centrifugation, dried, and calcined at 600°C for 8 hours to obtain a hollow single crystal SSZ-13 molecular sieve; wherein, the molar ratio of each component in the system For: 62H ₂ O: 0.3NaOH: 0.2TMAda: 0.16PEIM: 0.048Al ₂ O ₃ : 1Si ₂ O.

(2) Stir Na-type molecular sieve and ammonium chloride solution at 80° C. for 6 hours, perform ammonium exchange, centrifugally wash, dry, and repeat the above steps for secondary ammonium exchange to obtain ammonium-type molecular sieve.

(3) Stir the ammonium molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain copper-based Cu-SSZ-13 molecular sieve.

(4) The hollow Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8 ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above is a cuboid with a hollow structure, the shell thickness is about 0.1-0.3 μm, and the side length is about 1-2 μm. The results of scanning and transmission electron microscopy are shown in Figure 1. The catalyst has a microporous structure as a whole, and the synthesis process does not cause structural damage to it, with a large specific surface area and a small external surface area. The results are shown in Figure 9 and Table 1.

Using the above catalysts, the NO conversion rate in the NH ₃ -SCR reaction can reach up to 100%, and the NO conversion rate can reach more than 95% at 200°C-500°C, and the catalyst is still Maintain a certain activity, as shown in Figure 8a.

Example 2

The preparation of hollow Cu-SSZ-13 molecular sieve catalyst and its application in NH ₃ -SCR reaction, compared with Example 1, increased the content of NaOH, including the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add polyethyleneimine to the mixture, stir and mix well, then add Al(OH) ₃ solid powder and mix and stir; add silica sol drop by drop to the mixed solution and stir evenly. The above mixed solution was put into a hydrothermal kettle, crystallized at 160°C for 3 days, washed by centrifugation, dried, and calcined at 600°C for 8 hours to obtain a hollow single-crystal SSZ-13 molecular sieve; wherein, the molar ratio of feeding was: 62H ₂ O: 0.34NaOH: 0.2TMAda: _0.16PEIM : _0.048Al2O3 : _1Si2O .

(2) Stir Na-type molecular sieve and ammonium chloride solution at 80° C. for 6 hours, perform ammonium exchange, centrifugally wash, dry, and repeat the above steps for secondary ammonium exchange to obtain ammonium-type molecular sieve.

(3) Stir the ammonium-type molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain a hollow copper-based Cu-SSZ-13 molecular sieve.

(4) The hollow Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8 ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above is a cuboid with a hollow structure, and some molecular sieves are damaged, with a shell thickness of about 0.1-0.2 μm and a side length of about 1-2 μm. The results of scanning and transmission electron microscopy are shown in Figure 2.

Using the above catalysts, the NO conversion rate in the NH ₃ -SCR reaction can reach up to 100%, and the NO conversion rate can reach more than 95% at 200°C-500°C, and the catalyst is still Maintain a certain activity, as shown in Figure 8a.

Example 3

The preparation of hollow Cu-SSZ-13 molecular sieve catalyst and its application in NH ₃ -SCR reaction, compared with Example 1, increased the dosage of polyethyleneimine, including the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add polyethyleneimine to the mixture, stir and mix well, then add Al(OH) ₃ solid powder and mix and stir; add silica sol drop by drop to the mixed solution and stir evenly. The above mixed solution was put into a hydrothermal kettle, crystallized at 160°C for 3 days, washed by centrifugation, dried, and calcined at 600°C for 8 hours to obtain a hollow single-crystal SSZ-13 molecular sieve; wherein, the molar ratio of feed was: 62H ₂ O:0.3 _NaOH : 0.2TMAda: _0.19PEIM : _0.048Al2O3 : 1Si2O.

(2) Stir Na-type molecular sieve and ammonium chloride solution at 80° C. for 6 hours, perform ammonium exchange, centrifugally wash, dry, and repeat the above steps for secondary ammonium exchange to obtain ammonium-type molecular sieve.

(3) Stir the ammonium-type molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain a hollow copper-based Cu-SSZ-13 molecular sieve.

(4) The hollow Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8 ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above is a cuboid with a hollow structure, and some molecular sieves are damaged, with a shell thickness of about 0.3-0.5 μm and a side length of about 1.2-2.2 μm. The results of scanning and transmission electron microscopy are shown in Figure 3.

Using the above catalysts, the NO conversion rate in the NH ₃ -SCR reaction can reach up to 100%, and the NO conversion rate can reach more than 95% at 200°C-500°C, and the catalyst is still Maintain a certain activity, as shown in Figure 8.

Comparative example 1

The synthesis catalyst adopts the synthesis process in Example 1, wherein the usage amount of NaOH is reduced. Include the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add polyethylenimine to the mixture, stir and mix well, then add Al(OH)3 solid powder and mix and stir; add silica sol drop by drop into the mixed solution and stir evenly. Put the above mixed solution into a hydrothermal kettle, crystallize at 160°C for 3 days, centrifuge wash, dry, and roast at 600°C for 8 hours to obtain a solid SSZ-13 molecular sieve; wherein, the molar ratio of feed is: 62H ₂ O:0.15NaOH: 0.2TMAda: _0.16PEIM : _0.048Al2O3 : _1Si2O .

(2) Stir Na-type molecular sieve and ammonium chloride solution at 80° C. for 6 hours, perform ammonium exchange, centrifugally wash, dry, and repeat the above steps for secondary ammonium exchange to obtain ammonium-type molecular sieve.

(3) Stir the ammonium molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain copper-based Cu-SSZ-13 molecular sieve.

(4) The Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above does not have a hollow structure (solid) cuboid, and the side length is about 0.5-1.5 μm. The results of scanning and transmission electron microscopy are shown in Figure 4. The catalyst structure is a microporous structure, and the results are shown in Figure 9 and Table 1.

Attached Table 1: Catalyst _N2 adsorption and desorption parameters of hollow SSZ-13 molecular sieve (Example 1) and solid SSZ-13 molecular sieve (Comparative Example 1)

Among them: S _BET represents the specific surface area; S _ext represents the external surface area; S _micro represents the micropore surface area; V _tot represents the total pore volume; V _meso represents the mesopore volume; V _micr represents the micropore volume.

Using the above catalysts in the NH ₃ -SCR reaction, the activity window of NO _x conversion >95% is reduced to 250°C-400°C, and compared with the hollow sample, the catalyst activity is poor at both low and high temperature conditions, such as Figure 8 shows.

Comparative example 2

The synthetic catalyst adopts the synthesis process in Example 1, wherein the dosage of the organic additive polyethyleneimine is reduced. Include the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add Al(OH) ₃ solid powder and mix and stir; add silica sol dropwise to the mixed solution and stir evenly. The above mixed solution was put into a hydrothermal kettle, crystallized at 160°C for 3 days, washed by centrifugation, dried, and calcined at 600°C for 8 hours to obtain a hollow single-crystal SSZ-13 molecular sieve; wherein, the molar ratio of feed was: 62H ₂ O:0.3 _NaOH : 0.2TMAda: _0.06PEIM : _0.048Al2O3 : 1Si2O.

(2) Na-type molecular sieve and ammonium chloride solution were stirred at 80° C. for 6 h, ammonium exchange was performed, centrifugal washing, drying, and the above steps were repeated for a second ammonium exchange to obtain ammonium-type NH ₄ -SSZ-13 molecular sieve.

(3) Stir the ammonium molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain copper-based Cu-SSZ-13 molecular sieve.

(4) The Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above is a cuboid without a hollow structure (solid), with a side length of about 1.5-3 μm and severe agglomeration. The results of scanning and transmission electron microscopy are shown in Figure 5.

Using the above catalysts in the NH ₃ -SCR reaction, the activity window of NO _x conversion >95% is reduced to 200°C-400°C, and compared with the hollow sample, the catalyst activity is poor under high temperature conditions, as shown in Figure 8 Show.

Comparative example 3

The synthetic catalyst adopts the synthesis process in Example 1, wherein no organic additive polyethyleneimine is added. Include the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add Al(OH) ₃ solid powder and mix and stir; add silica sol dropwise to the mixed solution and stir evenly. The above mixed solution was put into a hydrothermal kettle, crystallized at 160°C for 3 days, washed by centrifugation, dried, and calcined at 600°C for 8 hours to obtain a hollow single-crystal SSZ-13 molecular sieve; wherein, the molar ratio of feed was: 62H ₂ O:0.3 NaOH: 0.2TMAda: 0.048Al ₂ O ₃ : 1Si ₂ O.

(2) Na-type molecular sieve and ammonium chloride solution were stirred at 80° C. for 6 h, ammonium exchange was performed, centrifugal washing, drying, and the above steps were repeated for a second ammonium exchange to obtain ammonium-type NH ₄ -SSZ-13 molecular sieve.

(3) Stir the ammonium molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain copper-based Cu-SSZ-13 molecular sieve.

(4) The Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above is a cuboid without a hollow structure (solid), and the side length is about 1-3 μm. The results of scanning and transmission electron microscopy are shown in Figure 6.

Using the above catalysts in the NH ₃ -SCR reaction, the activity window of NO _x conversion >95% is reduced to 200°C-400°C, and compared with the hollow sample, the catalyst activity is poor under high temperature conditions, as shown in Figure 8 Show.

Comparative example 4

The catalyst was synthesized using the synthesis process in Example 1, wherein the aluminum source was Al(NO ₃ ) ₃ ·9H ₂ O. Include the following steps:

(1) After mixing and stirring deionized water and NaOH evenly, add an aqueous solution of N,N,N-trimethyl-1-adamantyl ammonium hydroxide with a mass fraction of 25%, and obtain a mixed solution after fully stirring; Add Al(NO ₃ ) ₃ ·9H ₂ O and mix and stir; add silica sol dropwise to the mixed solution and stir evenly. The above mixed solution was put into a hydrothermal kettle, crystallized at 160°C for 3 days, washed by centrifugation, dried, and calcined at 600°C for 8 hours to obtain a hollow single crystal SSZ-13 molecular sieve; among them, deionized water, NaOH, N,N, The molar ratio of N-trimethyl-1-adamantyl ammonium hydroxide aqueous solution, polyethyleneimine, aluminum hydroxide, and silica sol is: 62H ₂ O: 0.3NaOH: 0.2TMAda: 0.048Al ₂ O ₃ : 1Si ₂ O.

(2) Na-type molecular sieve and ammonium chloride solution were stirred at 80° C. for 6 h, ammonium exchange was performed, centrifugal washing, drying, and the above steps were repeated for a second ammonium exchange to obtain ammonium-type NH ₄ -SSZ-13 molecular sieve.

(3) Stir the ammonium molecular sieve and cupric chloride solution at 80°C for 6h, perform copper exchange, centrifugally wash, dry, and roast at 550°C for 6h to obtain copper-based Cu-SSZ-13 molecular sieve.

(4) The Cu-SSZ-13 (0.1 ml) molecular sieve prepared above was placed in a miniature fixed-bed reactor. Feed the NH ₃ +NO+O ₂ +N ₂ mixed reaction raw material gas with a fixed total flow rate and molar ratio, and the reaction raw material gas conditions are: [NH ₃ ]=0.1ml/min, [NO]=0.1ml/min, [ O ₂ ]=6ml/min, [N ₂ ]=193.8ml/min, heat the reactor from 150°C to 550°C, carry out the chemical reaction of NH ₃ selective reduction of NO, and monitor the concentration of NO in the reaction tail gas. The reaction space velocity of the mixed gas was adjusted to 120,000h ^-1 by changing the catalyst filling amount, and the chemical reaction of NH ₃ selective reduction of NO was carried out, and the concentration of NO in the reaction tail gas was monitored.

The Cu-SSZ-13 molecular sieve obtained above is a cuboid without a hollow structure (solid), and the side length is about 0.5-1 μm. The results of scanning and transmission electron microscopy are shown in Figure 7.

Using the above catalysts, the activity window of _NOx conversion >95% in NH ₃ -SCR reaction is reduced to 250°C-500°C. Hollow sample, as shown in Figure 8.

According to the analysis, the NO conversion rate of Cu-SSZ-13 molecular sieve with hollow structure can reach more than 95% in the NH ₃ -SCR reaction at 200°C-500°C. Compared with the solid sample, the catalyst activity window is wider. In the low temperature section, the catalytic activity is better than that of the solid sample, as shown in Figure 8.

Result analysis:

The hollow Cu-SSZ-13 molecular sieve prepared in the present invention, compared with the solid sample, the hollow structure can reduce the mass transfer resistance in the crystal, enhance the accessibility of the Cu active site, and improve the utilization rate of the crystal, so that NH ₃ -SCR reaction efficiency is greatly improved.

Claims (14)

1. A hollow Cu-SSZ-13 molecular sieve catalyst is characterized in that the catalyst preparation process may further comprise the steps: (1) Mix and stir deionized water and inorganic alkali source evenly, then add N,N,N-trimethyl-1-adamantyl ammonium hydroxide TMAda-OH aqueous solution, stir well to obtain a mixed solution; add to the mixed solution Add organic additives, stir and mix well, then add aluminum source and mix; add silicon source to the mixed solution and stir evenly; put the above mixed solution into a hydrothermal kettle, crystallize at 100-200 °C for 2-7 days, centrifuge Washing, drying, and roasting at 450-800°C for 2-10 hours; (2) Stir Na-type molecular sieves and liquid ammonium solution at 40-90°C for 1-12 hours, perform ammonium exchange, centrifuge washing, and after drying, repeat the above steps for more than two ammonium exchanges, and obtain hollow ammonium NH after drying ₄ - SSZ-13 molecular sieve; (3) Stir the ammonium NH ₄ -SSZ-13 molecular sieve and liquid copper solution at 40-90 °C for 1-12 hours, perform copper exchange, centrifugal washing, drying, and roasting at 400-700 °C for 2-10 hours to obtain a hollow Copper-based Cu-SSZ-13 molecular sieve; In the reaction system of step (1), the inorganic base is NaOH, the organic additive is polyethyleneimine PEIM, the aluminum source is Al(OH) ₃ solid powder, and the silicon source is silica sol and/or tetraethylorthosilicate Ester TEOS; the molar ratio of each component in the system is: (30-100) H ₂ O: (0.23-0.36) NaOH: (0.1-0.8) TMAda-OH: (0.08-0.4) PEIM: (0.01-0.1 ) Al ₂ O ₃ : 1SiO ₂ ; the aluminum source is counted as Al ₂ O ₃ ; the silicon source is counted as SiO ₂ . 2. The catalyst according to claim 1, characterized in that: the molar ratio of each component is: (40-80) H ₂ O: (0.3-0.36) NaOH: (0.2-0.5) TMAda-OH: ( 0.1-0.3) PEIM: (0.04-0.08) Al ₂ O ₃ : 1 SiO ₂ . 3. The catalyst according to claim 1, characterized in that: in step (1), the crystallization temperature is 140-180 °C, and the crystallization time is 2-5 days; In step (1), the roasting temperature is 500-650 °C, and the roasting time is 4-8 h. 4. The catalyst according to claim 1, characterized in that: in step (2) and/or step (3), the ion exchange temperature is 60-80 °C, and the exchange time is 5-8 h; step (1) reaction In the system, the molecular weight of polyethyleneimine Mѡ=1600-6000; Step (1) prepares a hollow single crystal Na-SSZ-13 molecular sieve, which is a cuboid structure with a side length of 0.3-10 μm; the wall thickness accounts for 1% of the side length %-30%. 5. The catalyst according to claim 1, characterized in that: in step (3), the calcination temperature is 500-600 °C, and the calcination time is 4-8 h. 6. The catalyst according to claim 1, characterized in that: the side length of the cuboid structure is 0.5-2 μm; the wall thickness accounts for 5%-20% of the side length. 7. _A method for selective catalytic reduction of NO by NH , the catalyst used is the catalyst according to any one of claims 1-5. 8. The method of claim 7, wherein: The hollow Cu-SSZ-13 molecular sieve is placed in a fixed bed reactor; the mixed reaction raw material gas of NH ₃ +NO+O ₂ +N ₂ with a fixed total flow rate and molar ratio is introduced, and the reactor is heated to 150-550 ℃ for reaction temperature, the degree of chemical reaction to carry out the selective reduction of NO by _NH3 . 9. The method according to claim 8, characterized in that: the reaction raw material gas conditions are [NH ₃ ]=0.02-0.5mL/min, [NO]=0.02-0.5mL/min, [O ₂ ]=1- 12mL/min, [ _N2 ]=100-300mL/min. 10. The method according to claim 7, characterized in that: during the selective reduction of NO by NH ₃ , the reaction temperature is 200°C-500°C. 11. The method according to claim 8, characterized in that: during the selective reduction of NO by NH ₃ , the reaction space velocity of the mixed reaction raw material gas is 4000-500,000 h ^-1 . 12. The method according to claim 9, characterized in that: the reaction raw material gas conditions are [NH ₃ ]=0.05-0.2 mL/min, [NO]=0.05-0.2 mL/min, [O ₂ ]=3- 8mL/min, [ _N2 ]=160-220mL/min. 13. The method according to claim 11, characterized in that: the reaction space velocity of the mixed reaction raw material gas is 20,000-200,000 h ^-1 . 14. The method according to claim 13, characterized in that: the reaction space velocity of the mixed reaction raw material gas is 30,000-150,000 h ^-1 .

Images