Method for post-processing OP-Fe-MCM-22 molecular sieve by hydrochloric acid and application of OP-Fe-MCM-22 molecular sieve in high-temperature NH3-SCR catalytic reaction

Abstract

The invention relates to a method for post-treating an OP-Fe-MCM-22 molecular sieve by hydrochloric acid, which comprises the following steps: sequentially carrying out water bath heating and condensation reflux on a mixture of HC (Hydrocarbon) l and the OP-Fe-MCM-22 molecular sieve to optimize the distribution of iron species of the molecular sieve, so as to obtain OP-Fe-MCM-22-F-xHC l; x represents the concentration of an HC 1 pair used for acid treatment, and the unit is mol / L; f represents a fresh sample. The OP-Fe-MCM-22-F-xHC is subjected to hydrothermal aging treatment, OP-Fe-MCM-22-A-xHCl is obtained, and A represents a hydrothermal aging sample. The invention relates to an application of OP-Fe-MCM-22-F-xHC l or OP-Fe-MCM-22-F-xHC l in a high-temperature NH3-SCR (Selective Catalytic Reduction) catalytic reaction. The method has the beneficial effect that the activity and hydrothermal stability of the iron-based molecular sieve in NH3-SCR catalytic reaction are effectively improved.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to a method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid and an application of the method in a high-temperature NH3-SCR catalytic reaction. Background Art

[0002] MCM-22 is a layered zeolite with an MWW topology, used as a catalyst for the liquid phase alkylation of benzene to synthesize cumene and ethylbenzene (Journal of Catalysis, 2016, 333: 17-28). In 1998, Corma et al. (Catalysis Communications, 2004, 5 (4): 191-194) found that Cu and Co exchanged MCM-22 molecular sieves are active and selective catalysts for the selective catalytic reduction of NO by propane. In addition, Rutkowska et al. (Applied Catalysis B Environmental, 2015) compared several molecular sieves with MWW topology (MCM-22, ITQ-2 and MCM-36) with copper and iron exchanged molecular sieves and found that Cu / MCM-22 is a potential catalyst for NH3-SCR reaction with high activity and good hydrothermal stability (Catalysis Communications, 2004, 5(4): 191-194.). Analyzing the previous research results on MWW type materials, we believe that metal-modified MCM-22 should be a potential catalyst in NH3-SCR reaction.

[0003] Since iron can be directly introduced into MCM-22 by a one-pot synthesis method (Microporous & Mesoporous Materials, 1999, 30(1)), Fe / MCM-22 molecular sieve is expected to become an efficient catalyst for NH3-SCR reaction.

[0004] It has been reported that the NH3-SCR performance of iron-containing zeolites is mainly determined by the active iron species in the catalyst. As for the active Fe sites, it is generally believed that isolated Fe 3+ Species and oligomeric Fe x O y It is the main active site of NH3-SCR, while iron oxide particles can only provide limited activity at relatively high temperatures, and highly aggregated iron oxide particles are the main active sites of ammonia oxidation reaction. In addition, Brandenberger et al. (Appl. Catal, B, 2010, 95, 348–357) found that there is a strong correlation between the reaction temperature and the relative activity of various Fe sites of Fe / ZSM-5 catalyst in NH3-SCR, especially isolated Fe 3+The site provides most of the activity at temperatures below 300 °C; as the temperature increases, the dimer Fe 3+ species, namely [HO-Fe-O-Fe-OH] 2+ sites, which are responsible for high-temperature (>300°C) NH3-SCR activity and NH3 oxidation side reactions. Therefore, considering the main active iron species, preparing Fe-containing zeolites with more isolated, dimerized and oligomeric Fe sites and fewer large particles of Fe2O3 is beneficial to promote NH3-SCR activity.

[0005] Acid treatment is a commonly used post-treatment method in the preparation of molecular sieves. A large number of studies have shown (journal of Catalysis, 33 (2016) 17-28) that moderate acid treatment can remove some metal oxide species in the molecular sieve pores and increase the pore diffusion performance of the molecular sieve. This is because inorganic (hydrochloric acid, sulfuric acid, nitric acid, etc.) or organic (oxalic acid, acetic acid, etc.) acids can react with metal oxide species in the molecular sieve pores, dissolve them and carry them out of the molecular sieve pores. This shows that acid treatment is a potential method to remove iron oxide species, thereby regulating the distribution of iron species in the catalyst and then changing the NH3-SCR performance of the catalyst. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid and its application in high-temperature NH3-SCR catalytic reaction in order to overcome the above-mentioned deficiencies in the prior art.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: a method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid, comprising the following steps:

[0008] The mixture of HCl and OP-Fe-MCM-22 molecular sieve is sequentially heated in a water bath and condensed under reflux to optimize the iron species distribution of the molecular sieve to obtain OP-Fe-MCM-22-F-xHCl;

[0009] Wherein, x represents the concentration of HCl used for acid treatment, in mol / L; F represents the fresh sample.

[0010] Based on the above technical solution, the present invention can also be improved as follows.

[0011] Furthermore, the method further comprises: subjecting OP-Fe-MCM-22-F-xHCl to hydrothermal aging treatment to obtain OP-Fe-MCM-22-A-xHCl, wherein A represents a hydrothermal aging sample.

[0012] Furthermore, the synthesis method of OP-Fe-MCM-22 molecular sieve is as follows: an alkali source, water, an aluminum source, a silicon source and an iron source are mixed and stirred by a one-pot hydrothermal synthesis method, and then a template agent and MWW seed crystals are added to form an initial gel, and then the initial gel is treated by aging, static crystallization, centrifugal washing, and calcination to remove the template agent to obtain a molecular sieve; the molecular sieve and NH4NO3 are ammonium exchanged in a water bath, and then centrifugal washing and calcination are performed to obtain OP-Fe-MCM-22.

[0013] Furthermore, the alkali source, water, aluminum source, silicon source, iron source and template agent are respectively sodium hydroxide, ultrapure water, sodium aluminate, silica sol, ferric nitrate nonahydrate and hexamethyleneimine (HMI).

[0014] Furthermore, the synthesis ratio of SiO2:Al2O3:Fe(NO3)3:HMI:NaOH:H2O is 1:0.017:0.05:0.5:0.4:45, and the seed content is 0% to 5% of the mass of the non-aqueous matter in the gel.

[0015] Further, the synthesis method of OP-Fe-MCM-22 molecular sieve is as follows:

[0016] The initial gel was prepared by a one-pot hydrothermal synthesis method by mixing alkali source, water, aluminum source, silicon source, iron source, template agent and MWW seed crystals in sequence.

[0017] Then the initial gel is aged for 2h to 4h, then statically crystallized at 140°C to 190°C for 0 to 72h, centrifugally washed and dried, and then calcined at 550°C for 10h to remove the template agent to obtain a molecular sieve;

[0018] Then, ammonium exchange was carried out twice with 1 g molecular sieve and 30 mL NH 4 NO 3 in a water bath at 80° C., each time for 4 h, followed by centrifugal washing, and then calcined at 550° C. for 5 h to obtain OP-Fe-MCM-22-F-0HCl.

[0019] Furthermore, the aging time is 4 h; the static crystallization temperature is 150°C and the time is 72 h.

[0020] Furthermore, the molar ratio of silicon to aluminum is 10-70, and the molar ratio of silicon to iron is 5-80.

[0021] Furthermore, the molar ratio of silicon to aluminum is 20-40, and the molar ratio of silicon to iron is 20-60.

[0022] Furthermore, the molar ratio of silicon to aluminum is 30, and the molar ratio of silicon to iron is 20.

[0023] Further, 1 g OP-Fe-MCM-22: 30 mL HCl was heated in a water bath at 60° C., wherein the molar concentration of HCl was 0.25 to 1 mol / L, and then condensed and refluxed for 4 h to optimize the iron species distribution of the molecular sieve, and centrifuged and dried to obtain OP-Fe-MCM-22-F-xHCl.

[0024] Furthermore, the molar concentration of HCl is 0.25 mol / L, 0.5 mol / L, 0.75 mol / L or 1 mol / L.

[0025] Furthermore, the molar concentration of HCl is 1 mol / L.

[0026] Further, the hydrothermal aging treatment of OP-Fe-MCM-22-F-xHCl is specifically as follows:

[0027] First, take OP-Fe-MCM-22-F-xHCl with a particle size of 40-60 mesh and place it in a quartz tube, and then place the whole in the constant temperature zone of a tube furnace. The N2 flow rate is controlled to be 100 ml / min by a mass flow meter, and a water bubbler is passed through, and the water vapor content is 10%. After N2 starts to be introduced into the tube furnace, the temperature is raised to 750°C and maintained for 16 hours to obtain OP-Fe-MCM-22-A-xHCl.

[0028] Based on the above technical solution, the present invention also provides an application of OP-Fe-MCM-22-F-xHCl prepared by the above preparation method in a high-temperature NH3-SCR catalytic reaction.

[0029] Based on the above technical solution, the present invention also provides an application of OP-Fe-MCM-22-F-xHCl prepared by the above preparation method in a high-temperature NH3-SCR catalytic reaction.

[0030] The beneficial effects of the present invention are:

[0031] 1) The active species Fe in the catalyst is introduced during the one-pot hydrothermal synthesis of the molecular sieve, and then hydrochloric acid is used as the post-treatment acid solution, and OP-Fe-MCM-22 is used for water bath heating and condensation reflux in sequence to optimize the distribution of iron species in OP-Fe-MCM-22, thereby obtaining OP-Fe-MCM-22-F-xHCl, which effectively improves the catalytic activity and hydrothermal stability of the iron-based molecular sieve catalyst for NH3-SCR, and has a NOx conversion activity of about 80% in the range of 400°C to 550°C;

[0032] 2) OP-Fe-MCM-22-F-xHCl is hydrothermally aged to obtain OP-Fe-MCM-22-A-xHCl, which can further improve the high temperature (400°C to 550°C) NH3-SCR catalytic activity after hydrothermal aging, and has a NOx conversion activity of more than 80% in the range of 400°C to 550°C;

[0033] 3) The molecular sieve is prepared by a one-step method, and the preparation process is simple and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the UV-visible absorption spectrum of the sample OP-Fe-MCM-22-F-0HCl of the present invention;

[0035] Figure 2 It is the UV-visible absorption spectrum of the sample OP-Fe-MCM-22-F-0.25HCl of the present invention;

[0036] Figure 3 It is the UV-visible absorption spectrum of the sample OP-Fe-MCM-22-F-0.5HCl of the present invention;

[0037] Figure 4 It is the UV-visible absorption spectrum of the sample OP-Fe-MCM-22-F-0.75HCl of the present invention;

[0038] Figure 5 It is the UV-visible absorption spectrum of the sample OP-Fe-MCM-22-F-1HCl of the present invention;

[0039] Figure 6 It is a scanning electron microscope image of the sample OP-Fe-MCM-22-F-0HCl of the present invention. DETAILED DESCRIPTION

[0040] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0041] Example 1

[0042] A method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid, comprising the following steps:

[0043] Divide the calculated water volume into two parts:

[0044] Take beaker A, add 3.0812g of sodium hydroxide (NaOH) particles, 128.73g of water (H2O), stir to dissolve, 1.2283g of sodium aluminate, 47.39g of silica sol (JN-40) and slowly add dropwise to prepare solution A;

[0045] Take beaker B, add 6.55g of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and 100.17g of water (H2O) in turn, stir and dissolve to make solution B;

[0046] After the A and B solutions are fully stirred, the solution in beaker B is placed in a separatory funnel and slowly added to beaker A while stirring. After the addition is complete, the mixture is stirred for 1 hour. 15.88 g of template (HM I) is added and continued to be stirred. Then, 0.5768 g of 3% iron seed (i.e., OP-Fe-MCM-22 molecular sieve with 3% iron content is used as seed) is added. The mixture is aged for 4 hours and finally placed in a stainless steel autoclave lined with polytetrafluoroethylene. The mixture is statically crystallized for 72 hours at 150°C, washed by centrifugation, dried at 100°C overnight, and then calcined in a muffle furnace at 550°C for 10 hours to remove the template.

[0047] Then, 1 g molecular sieve: 30 mL NH4NO3 (1 mL / mol) was used for ammonium exchange twice in a water bath at 80 °C, each time for 4 h, and after centrifugal washing, it was calcined in a muffle furnace at 550 °C for 5 h to obtain OP-Fe-MCM-22, which is recorded as OP-Fe-MCM-22-F-0HCl for the convenience of description;

[0048] Acid treatment 1:

[0049] First, prepare 100 mL of 0.25 mol / L HCl solution, and weigh 2.4563 g of concentrated HCl (mass percentage is 37%, if converted to molar concentration is 12.1 mol / L), add water to prepare 100 mL of acid solution for use;

[0050] Then, 2 g OP-Fe-MCM-22-F-0HCl and 60 mL acid solution were heated in a water bath at 60°C with stirring in a ratio of 1 g:30 mL, and treated under condensation reflux for 4 h. The above solution was centrifuged to retain the solid part, which was placed in an oven at 100°C for overnight drying and ground to obtain OP-Fe-MCM-22-F-0.25HCl.

[0051] Example 2

[0052] The difference between this example and example 1 is the acid treatment. In this example, the acid treatment 2 is similar to the acid treatment 1, except that a 0.5 mol / L HCl solution is used during the treatment, and the obtained product is named OP-Fe-MCM-22-F-0.5HCl.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is the acid treatment. In this embodiment, acid treatment 3 is similar to acid treatment 1, except that a 0.75 mol / L HCl solution is used during the treatment, and the obtained product is named OP-Fe-MCM-22-F-0.75HCl.

[0055] Example 4

[0056] The difference between this embodiment and embodiment 1 is the acid treatment. In this embodiment, acid treatment 4 is similar to acid treatment 1, except that a 1 mol / L HCl solution is used during the treatment, and the obtained product is named OP-Fe-MCM-22-F-1HCl.

[0057] Example 5

[0058] This example is to take the OP-Fe-MCM-22-F-0HCl in Example 1 for hydrothermal aging, specifically as follows:

[0059] 0.3 g of OP-Fe-MCM-22-F-0HCl catalyst with a particle size of 40 to 60 mesh was placed in a quartz tube and placed in the constant temperature zone of a tube furnace. The N2 flow rate was controlled to be 100 ml / min by a mass flow meter, and a bubbler filled with water was used (the water vapor content was controlled by heating in a water bath, the water bath temperature was 48°C, and the water vapor content was about 10%). After N2 was introduced into the tube furnace, the temperature was increased to 750°C at 10°C / min and maintained for 16 hours to obtain the hydrothermally aged sample OP-Fe-MCM-22-A-0HCl.

[0060] Example 6

[0061] The difference between this embodiment and embodiment 5 is that in this embodiment, OP-Fe-MCM-22-F-0.25HCl in embodiment 1 is subjected to hydrothermal aging, and the sample after hydrothermal aging is named OP-Fe-MCM-22-A-0.25HCl.

[0062] Example 7

[0063] The difference between this embodiment and embodiment 5 is that in this embodiment, OP-Fe-MCM-22-F-0.5HCl in embodiment 2 is subjected to hydrothermal aging, and the sample after hydrothermal aging is named OP-Fe-MCM-22-A-0.5HCl.

[0064] Example 8

[0065] The difference between this embodiment and embodiment 5 is that in this embodiment, OP-Fe-MCM-22-F-0.75HCl in embodiment 3 is subjected to hydrothermal aging, and the sample after hydrothermal aging is named OP-Fe-MCM-22-A-0.75HCl.

[0066] Example 9

[0067] The difference between this embodiment and embodiment 5 is that in this embodiment, OP-Fe-MCM-22-F-1HCl in embodiment 4 is subjected to hydrothermal aging, and the sample after hydrothermal aging is named OP-Fe-MCM-22-A-1HCl.

[0068] Application examples:

[0069] A certain amount of 40-60 mesh catalyst was placed in a fixed bed microreactor. The simulated flue gas consisted of NO, NH3, O2 and N2, where NO: 500ppm, NH3: 600ppm, O2: 5.5%, and the balance gas was N2. The reaction temperature was 400℃-550℃, and the space velocity was 36000h -1 ,The smoke components before and after the reaction were detected and analyzed by an ultraviolet smoke analyzer.

[0070] It can be seen from Table 1 that compared with OP-Fe-MCM-22-F-0HCl, the high-temperature NH3-SCR performance of other hydrochloric acid treated samples has increased, indicating that hydrochloric acid treatment of OP-Fe-MCM-22 has improved its high-temperature NH3-SCR activity.

[0071] Table 1 shows the high temperature NH3-SCR performance of OP-Fe-MCM-22-F-xHCl

[0072]

[0073] It can be seen from Table 2 that compared with OP-Fe-MCM-22-A-0HCl, the high-temperature NH3-SCR performance of other samples has increased, indicating that hydrochloric acid post-treatment improves the hydrothermal stability of OP-Fe-MCM-22 molecular sieve.

[0074] Table 2 shows the high temperature NH3-SCR performance of OP-Fe-MCM-22-A-xHCl

[0075]

[0076] As shown in Table 3, after hydrochloric acid treatment, the total surface area and total pore volume of the molecular sieve increased, indicating that the hydrochloric acid post-treatment eliminated some of the large-particle metal oxides that blocked the molecular sieve pores and increased the total surface area and total pore volume.

[0077] Table 3 Pore volume and specific surface area of ​​fresh samples treated with acid

[0078]

[0079] Depend on Figure 1 to Figure 5It can be seen that the UV absorption peak at 220nm~280nm can be attributed to the independent Fe 3+ ions, the absorption peak at around 380nm belongs to the small cluster (Fe x O y ) 3+ ions, while the absorption peak at around 500nm can be attributed to larger iron oxides, such as ferric oxide nanoparticles; it can be seen from the figure that the post-treatment with HCl at a concentration of 0.25 mol / L optimizes the Fe species distribution of the sample, increases the dimeric iron species, and higher concentrations eliminate the dimeric iron species, convert them into independent iron species, and aggregate them into highly polymerized iron species, thereby improving the high-temperature NH3-SCR performance.

[0080] Depend on Figure 6 It can be seen that from the SEM image of one of the samples OP-Fe-MCM-22-F-0HCl, the molecular sieve is a uniform lamellar molecular sieve, aggregated into spheres, with a lamellar size of about 1 um and a thickness of about 50-100 nm, which is a typical MCM-22 molecular sieve morphology.

[0081] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid, characterized in that: It includes the following steps: The mixture of HCl and OP-Fe-MCM-22 molecular sieve is sequentially heated in a water bath and condensed under reflux to optimize the iron species distribution of the molecular sieve to obtain OP-Fe-MCM-22-F-xHCl; Wherein, x represents the concentration of HCl used for acid treatment, in mol / L; F represents the fresh sample.

2. The method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 1, characterized in that: Also includes: OP-Fe-MCM-22-F-xHCl is subjected to hydrothermal aging treatment to obtain OP-Fe-MCM-22-A-xHCl, wherein A represents a hydrothermally aged sample.

3. A method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 1 or 2, characterized in that: The synthesis method of OP-Fe-MCM-22 molecular sieve is as follows: using a one-pot hydrothermal synthesis method to mix and stir an alkali source, water, an aluminum source, a silicon source and an iron source, then adding a template agent and MWW seed crystals to prepare an initial gel, and then sequentially subjecting the gel to aging, static crystallization, centrifugal washing, and calcination to remove the template agent to obtain a molecular sieve; The molecular sieve and NH4NO3 were subjected to ammonium exchange in a water bath, followed by centrifugal washing and calcination to obtain OP-Fe-MCM-22.

4. The method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 3, characterized in that: The alkali source, water, aluminum source, silicon source, iron source and template agent are respectively sodium hydroxide, ultrapure water, sodium aluminate, silica sol, ferric nitrate nonahydrate and hexamethyleneimine.

5. The method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 3 or 4, characterized in that: The synthesis method of OP-Fe-MCM-22 molecular sieve is as follows: The initial gel was prepared by a one-pot hydrothermal synthesis method by fully mixing alkali source, water, aluminum source, silicon source, iron source, template agent and MWW seed crystals in sequence; Then the initial gel is aged for 2h to 4h, then statically crystallized at 140°C to 190°C for 0 to 72h, centrifugally washed and dried, and then calcined at 550°C for 10h to remove the template agent to obtain a molecular sieve; Then, ammonium exchange was carried out twice with 1 g molecular sieve and 30 mL NH 4 NO 3 in a water bath at 80° C., each time for 4 h, followed by centrifugal washing, and then calcined at 550° C. for 5 h to obtain OP-Fe-MCM-22-F-0HCl.

6. The method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 1 or 2, characterized in that: 1 g OP-Fe-MCM-22: 30 mL HCl was heated in a water bath at 60° C., wherein the molar concentration of HCl was 0.25 to 1 mol / L, and then condensed and refluxed for 4 h to optimize the iron species distribution of the molecular sieve. The mixture was centrifuged and dried to obtain OP-Fe-MCM-22-F-xHCl.

7. The method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 6, characterized in that: The molar concentration of HCl is 0.25 mol / L, 0.5 mol / L, 0.75 mol / L or 1 mol / L.

8. The method for post-treating OP-Fe-MCM-22 molecular sieve with hydrochloric acid according to claim 2, characterized in that: The hydrothermal aging treatment of OP-Fe-MCM-22-F-xHCl is as follows: First, take OP-Fe-MCM-22-F-xHCl with a particle size of 40-60 mesh and place it in a quartz tube, and then place the whole in the constant temperature zone of a tube furnace. The N2 flow rate is controlled to be 100 ml / min by a mass flow meter, and a water bubbler is filled with water with a water vapor content of 10%. After N2 starts to be introduced into the tube furnace, the temperature is raised to 750°C and maintained for 16 hours to obtain OP-Fe-MCM-22-A-xHCl.

9. Use of OP-Fe-MCM-22-F-xHCl prepared by the preparation method according to any one of claims 1 or 3 or 4 to 7 in high temperature NH3-SCR catalytic reaction.

10. Use of OP-Fe-MCM-22-F-xHCl prepared by the preparation method according to any one of claims 2 to 8 in high temperature NH3-SCR catalytic reaction.

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