SAPO-34 molecular sieve with controllable morphology and preparation method

Abstract

The invention belongs to the technical field of molecular sieve preparation, and particularly relates to a shape-controllable SAPO-34 molecular sieve and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing metal salt, organic acid and water, and reacting to obtain a metal compound; the metal salt comprises one or more of zinc salt, chromium salt, aluminum salt and zirconium salt; mixing an aluminum source, a phosphorus source, a silicon source, a template agent, the metal compound and water, and stirring to form a gel mixture; and aging, reacting, separating and drying the gel mixture to obtain the SAPO-34 molecular sieve with controllable morphology. The morphology and size of the SAPO-34 can be regulated and controlled by adjusting the metal type of the metal compound.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and particularly relates to a morphology-controllable SAPO-34 molecular sieve and a preparation method thereof. Background Art

[0002] SAPO-34 molecular sieve has a CHA topological structure, and the skeleton structure is composed of parallel double six-membered rings stacked in an ABC manner. The skeleton has an eight-membered ring pore and a three-dimensional cross-channel structure. The molecular sieve pore size is 0.38nm×0.38nm, and an ellipsoidal CHA cage with a cage size of 1.0nm×0.67nm×0.67nm is formed at the intersection of the eight-membered ring channels. SAPO-34 is a small-pore molecular sieve with a medium-strength acid center. Therefore, SAPO-34 molecular sieve is widely used in the fields of catalytic conversion of low-carbon substances to olefins, cracking of C4~C8 straight-chain olefins / alkanes to produce low-carbon olefins, automobile exhaust purification, catalyst carriers, membrane separation materials and luminescent materials.

[0003] The performance of molecular sieves in catalysis, adsorption and separation is closely related to their morphology. For example, large-sized molecular sieve crystals are excellent materials for preparing optical devices; nano-thin sheet-like molecular sieves show high activity and long service life in catalytic reactions; small-particle crystals are easy to prepare into molecular sieve membranes for separation and adsorption. Regarding the research on SAPO-34 morphology regulation, in addition to the conventional cubic morphology, patent CN202110611879.3 discloses the one-pot synthesis of a La-SAPO-34 molecular sieve with a nano-sheet morphology under hydrothermal synthesis conditions using tetraethylammonium hydroxide as a template and aluminum isopropoxide as an aluminum source. Patent CN202010279730.5 discloses that a SAPO-34 molecular sieve with a composite morphology is prepared by controlling the use of auxiliary agents and the synthesis steps. Patent CN201410557543.3 discloses adding a specific organic additive to a gel mixed with an aluminum source, a phosphorus source, a silicon source, a template and water, stirring evenly, and then adding a nano SAPO-34 molecular sieve as a seed, and preparing a sheet-like nano SAPO-34 molecular sieve by temperature-variable crystallization. Patent CN201410444908.1 discloses a method for preparing a SAPO-34 molecular sieve with a thin layer morphology by adding a double-headed amine cationic surfactant to a hydrothermal synthesis system. Patent CN201310002665.1 discloses a nano SAPO-34 molecular sieve with a spherical or flaky morphology prepared by microwave heating. Patent CN201910309290.0 discloses a loose porous spherical SAPO-34 molecular sieve. Patent CN201610389108.3 discloses a method for preparing a lamellar SAPO-34 molecular sieve.

[0004] In summary, the types of SAPO-34 morphologies are limited, and one synthesis scheme can basically only synthesize molecular sieves with one morphology, and the synthesis scheme has limitations in morphology control. Summary of the invention

[0005] To address the deficiencies of the prior art, the present invention provides a method for preparing a morphology-controllable SAPO-34 molecular sieve, which uses a metal composite and can regulate the morphology and size of SAPO-34 by adjusting the different metal types of the metal composite.

[0006] The invention also provides a SAPO-34 molecular sieve with controllable morphology.

[0007] In order to solve the deficiencies of the prior art, the technical solution provided by the present invention is:

[0008] A method for preparing a morphology-controllable SAPO-34 molecular sieve, comprising:

[0009] Step S1: uniformly mixing a metal salt, an organic acid and water to obtain a metal complex; the metal salt includes one or more of a zinc salt, a chromium salt, an aluminum salt and a zirconium salt;

[0010] Step S2: mixing an aluminum source, a phosphorus source, a silicon source, a template, the metal complex and water, and stirring to form a gel mixture;

[0011] Step S3: The gel mixture is aged, reacted, separated, and dried to obtain a SAPO-34 molecular sieve with controllable morphology.

[0012] Preferably, in step S1, the metal salt includes one or more of zinc nitrate, chromium nitrate, aluminum nitrate and zirconium nitrate.

[0013] Preferably, in step S1, the organic acid is citric acid.

[0014] Preferably, in step S1, the molar ratio of the organic acid to the metal salt is (0.1-30):1, more preferably (0.1-20):1.

[0015] Preferably, in step S1, the reaction temperature is 180-275° C., more preferably 180-250° C.; the reaction time is 1-20 hours, more preferably 3-17 hours.

[0016] Preferably, in step S2, the mass ratio of the metal complex to the gel mixture is (0.01-0.8):1; more preferably (0.01-0.5):1.

[0017] Preferably, in step S2, the aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, and the silicon source is calculated as SiO2, and the molar ratio of the silicon source, the aluminum source, the phosphorus source, the template, and water is (0.1-1.0):1.0:(0.5-3):(1.0-4.0):(30-100).

[0018] Preferably, in step S3, the gel mixture is aged at room temperature for 5-120 minutes.

[0019] Preferably, in step S3, the reaction temperature is 170-200° C., and the reaction time is 24-72 hours.

[0020] A SAPO-34 molecular sieve with controllable morphology is prepared by the above-mentioned method for preparing the SAPO-34 molecular sieve with controllable morphology.

[0021] Beneficial effects of the present invention:

[0022] The method for preparing the morphology-controllable SAPO-34 molecular sieve provided by the present invention adopts a metal composite for preparation, and the method is simple, and the morphology and size of SAPO-34 can be regulated by adjusting different metal types of the metal composite. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD patterns of the SAPO-34 molecular sieves obtained in Comparative Example 1 and Examples 1 to 8 of the present invention;

[0024] Figure 2 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Comparative Example 1 of the present invention;

[0025] Figure 3 This is a SEM magnified image of the morphology of the SAPO-34 molecular sieve obtained in Comparative Example 1 of the present invention;

[0026] Figure 4 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 1 of the present invention;

[0027] Figure 5 This is a SEM magnified image of the morphology of the SAPO-34 molecular sieve obtained in Example 1 of the present invention;

[0028] Figure 6 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 2 of the present invention;

[0029] Figure 7 This is a SEM magnified image of the morphology and structure of the SAPO-34 molecular sieve obtained in Example 2 of the present invention;

[0030] Figure 8This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 3 of the present invention;

[0031] Fig. 9 This is a SEM magnified image of the morphology of the SAPO-34 molecular sieve obtained in Example 3 of the present invention;

[0032] Fig.10 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 4 of the present invention;

[0033] Fig.11 This is a SEM magnified image of the morphology of the SAPO-34 molecular sieve obtained in Example 4 of the present invention;

[0034] Fig.12 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 5 of the present invention;

[0035] Fig.13 This is a SEM magnified image of the morphology and structure of the SAPO-34 molecular sieve obtained in Example 5 of the present invention;

[0036] Fig.14 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 6 of the present invention.

[0037] Fig.15 This is a SEM magnified image of the morphology of the SAPO-34 molecular sieve obtained in Example 6 of the present invention;

[0038] Fig.16 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 7 of the present invention;

[0039] Fig.17 This is a SEM magnified image of the morphology of the SAPO-34 molecular sieve obtained in Example 7 of the present invention;

[0040] Fig.18 This is a SEM image of the morphology of the SAPO-34 molecular sieve obtained in Example 8 of the present invention.

[0041] Fig.19 This is a SEM magnified image of the morphology and structure of the SAPO-34 molecular sieve obtained in Example 8 of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0043] The embodiment of the present invention provides a method for preparing a morphology-controllable SAPO-34 molecular sieve, comprising:

[0044] Step 1: Add metal salt and citric acid to 100 mL of water in a certain molar ratio, stir in a 90°C water bath for 30-180 minutes until completely dissolved, and react at 180-275°C (preferably 180-250°C) for 1-20 hours (preferably 3-17 hours) to directly obtain a solid metal composite. The reaction container is an oven or a muffle furnace. The metal composite is crushed and ground for later use.

[0045] The metal salt includes one or more of zinc salt, chromium salt, aluminum salt and zirconium salt. The metal salt is preferably nitrate, that is, the metal salt includes one or more of zinc nitrate, chromium nitrate, aluminum nitrate and zirconium nitrate.

[0046] The molar ratio of citric acid to nitrate is (0.1-30):1, preferably (0.1-20):1.

[0047] Step 2: Disperse the aluminum source, phosphorus source, silicon source, template, and metal complex into water in sequence, mix and stir to form a gel mixture:

[0048] The aluminum source can be selected from Al2O3, such as pseudo-boehmite, the phosphorus source can be selected from P2O5, such as phosphoric acid, the silicon source can be selected from SiO2, such as silica sol, and the template can be selected from triethylamine. The aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, and the silicon source is calculated as SiO2. The molar ratio of the silicon source, the aluminum source, the phosphorus source, the template, and water is (0.1-1.0):1.0:(0.5-3):(1.0-4.0):(30-100). The mass ratio of the metal complex to the gel mixture is (0.01-0.8):1, preferably (0.01-0.5):1.

[0049] Step 3: The gel mixture is aged by stirring at room temperature for 5-120 minutes:

[0050] Step 4: The aged gel mixture is transferred into a stainless steel synthesis reactor with a polytetrafluoroethylene liner and reacted at 170-200°C for 24-72 hours to obtain a mixture:

[0051] Step 5: The mixture is separated (such as filtered or centrifuged), washed, and dried to obtain a SAPO-34 molecular sieve with controllable morphology.

[0052] The embodiment of the present invention further provides a morphology-controllable SAPO-34 molecular sieve, which is prepared by the aforementioned method for preparing the morphology-controllable SAPO-34 molecular sieve.

[0053] In the following examples, pseudo-boehmite was purchased from Shandong Aluminum Co., Ltd., with an Al2O3 content of 70wt%. Phosphoric acid was purchased from Tianjin Komiou Chemical Reagent Co., Ltd., with an H3PO4 concentration of 85wt%. Silica sol was purchased from Qingdao Jiyida Silica Gel Reagent Co., Ltd., with an SiO2 content of 30wt%. Triethylamine was purchased from Tianjin Komiou Chemical Reagent Co., Ltd., with a triethylamine content of 99wt%. Zinc nitrate (Zn(NO3)2·6H2O), chromium nitrate (Cr(NO3)3·9H2O), aluminum nitrate (Al(NO3)3·9H2O), zirconium nitrate (Zr(NO3)4·5H2O) and citric acid were all analytically pure and purchased from Aladdin.

[0054] Comparative Example 1

[0055] Preparation of conventional cubic morphology SAPO-34 molecular sieve: Weigh 10.12g of pseudo-boehmite and stir evenly with 51.7g of deionized water, then slowly add 16.14g of phosphoric acid, 2.75g of silica sol, and 20.25g of triethylamine in sequence, and continue stirring until a uniform gel is formed. Transfer the resulting gel into a 150mL stainless steel synthesis kettle with a polytetrafluoroethylene liner and react at 200°C for 40h. After the reaction is completed, cool the synthesis kettle to room temperature with water. The resulting product is centrifuged and washed until neutral, and placed in an oven at 110°C for overnight drying to obtain conventional cubic morphology SAPO-34 molecular sieve raw powder with a size of about 5-20μm. The scanning electron microscope results are as follows Figure 2 , Figure 3 See Figure 1 As shown in Comparative Example 1, the characteristic diffraction peaks at 9.51°, 12.87°, 16.03°, 20.57°, etc. appearing in the XRD spectrum prove that the synthesized sample belongs to the SAPO-34 structure.

[0056] Example 1

[0057] Preparation of ZnCrAl composite: Add 13.4g zinc nitrate, 12g chromium nitrate, 11.25g aluminum nitrate and 19.1g citric acid into 100mL water, stir in a 90°C water bath for 90min until completely dissolved, then place in a 180°C oven for reaction for 17 hours to obtain the ZnCrAl composite, grind and set aside.

[0058] Preparation of polygonal SAPO-34 molecular sieve: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of ZnCrAl complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30min, then transfer it into a 150mL stainless steel synthesis kettle with polytetrafluoroethylene lining, and react at 200℃ for 40h. After the reaction, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and then placed in an oven at 110℃ for drying overnight to obtain polygonal SAPO-34 molecular sieve raw powder with a size of about 10μm. The scanning electron microscope results are as follows Figure 4 , Figure 5 As shown. Figure 1 As shown in Example 1, the characteristic diffraction peaks at 9.51°, 12.81°, 15.16°, 20.48°, etc. appearing in the XRD spectrum prove that the synthesized sample belongs to the SAPO-34 structure.

[0059] Example 2

[0060] Preparation of ZnCr complex: Add 17.9 g zinc nitrate, 16 g chromium nitrate and 16.91 g citric acid to 100 mL water, stir in a 90°C water bath for 90 min until completely dissolved, then place in a 180°C oven for reaction for 17 hours to obtain a ZnCr complex, grind and set aside.

[0061] Preparation of SAPO-34 molecular sieve with flower ball morphology: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of ZnCr complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30min, then transfer it into a 150mL stainless steel synthesis kettle with polytetrafluoroethylene lining, and react at 200℃ for 40h. After the reaction is completed, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and then placed in a 110℃ oven to dry overnight to obtain the raw powder of SAPO-34 molecular sieve with flower ball morphology, with a size of about 15μm. The scanning electron microscope results are as follows Figure 6 , Figure 7 The XRD spectrum is shown in Figure 1 As shown in Example 2, the XRD peak position of the result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0062] Example 3

[0063] Preparation of Zn complex: Add 31.24g zinc nitrate and 14.8g citric acid into 100mL water, stir in a 90°C water bath for 90min until completely dissolved, then place in a 180°C oven for reaction for 17 hours to obtain Zn complex, grind and set aside.

[0064] Preparation of SAPO-34 molecular sieve with low-angle morphology: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of Zn complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30min, then transfer it into a 150mL stainless steel synthesis kettle with polytetrafluoroethylene lining, and react at 200℃ for 40h. After the reaction, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and placed in a 110℃ oven to dry overnight to obtain the raw powder of SAPO-34 molecular sieve with low-angle morphology, with a size of about 2-5μm. The scanning electron microscope results are as follows Figure 8 , Fig. 9 The XRD spectrum is shown in Figure 1 As shown in Example 3, the XRD peak position of the result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0065] Example 4

[0066] Preparation of Al complex: Add 22.5 g aluminum nitrate and 12.7 g citric acid into 100 mL water, stir in a 90° C. water bath for 90 min until completely dissolved, then place in a 180° C. oven for reaction for 17 hours to obtain the Al complex, grind and set aside.

[0067] Preparation of plate-like SAPO-34 molecular sieve: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of Al complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30min, then transfer it into a 150mL stainless steel synthesis kettle with a polytetrafluoroethylene liner, and react at 200°C for 40h. After the reaction is completed, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and placed in a 110°C oven to dry overnight to obtain a plate-like SAPO-34 molecular sieve raw powder. The scanning electron microscopy results are as follows Fig.10 , Fig.11 The XRD spectrum is shown in Figure 1 As shown in Example 4, the XRD peak position of the result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0068] Example 5

[0069] Preparation of Cr complex: Add 28 g of chromium nitrate and 14.8 g of citric acid into 100 mL of water, stir in a 90° C. water bath for 90 min until completely dissolved, then place in a 180° C. oven for reaction for 17 hours to obtain the Cr complex, grind it, and set aside.

[0070] Preparation of small cubic SAPO-34 molecular sieve: weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of Cr complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30 minutes, then transfer it into a 150mL stainless steel synthesis kettle with a polytetrafluoroethylene liner, and react at 200°C for 40 hours. After the reaction is completed, the synthesis kettle is cooled to room temperature with water. The obtained product is centrifuged and washed until neutral, and then placed in an oven at 110°C for overnight drying to obtain small cubic SAPO-34 molecular sieve raw powder with a size of about 2-3μm. The scanning electron microscope results are as follows Fig.12 , Fig.13 The XRD spectrum is shown in Figure 1 As shown in Example 5, the peak position of the XRD result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0071] Example 6

[0072] Preparation of ZnZr composite: Add 19.6g zirconium nitrate, 0.85g zinc nitrate and 12.3g citric acid into 100mL water, stir in a 90℃ water bath for 90min until completely dissolved, then place in a 180℃ oven for reaction for 4 hours to obtain ZnZr composite, grind and set aside.

[0073] Preparation of porous rectangular SAPO-34 molecular sieve: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of ZnZr complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30min, then transfer it into a 150mL stainless steel synthesis kettle with a polytetrafluoroethylene liner, and react at 200°C for 40h. After the reaction is completed, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and then placed in an oven at 110°C for overnight to obtain a porous rectangular SAPO-34 molecular sieve raw powder. The scanning electron microscope results are shown as follows Fig.14 , Fig.15As shown, it can be seen that the SAPO-34 molecular sieve prepared in this embodiment has a porous surface compared with the comparative example and other embodiments. Figure 1 As shown in Example 6, the XRD peak position of the result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0074] Example 7

[0075] Preparation of ZnCrAl composite: Add 13.4g zinc nitrate, 12g chromium nitrate, 11.25g aluminum nitrate and 19.1g citric acid into 100mL water, stir in a 90°C water bath for 90min until completely dissolved, then place in a 250°C muffle furnace for reaction for 4 hours to obtain the ZnCrAl composite, grind and set aside.

[0076] Preparation of polygonal SAPO-34 molecular sieve: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of ZnCrAl complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30min, then transfer it into a 150mL stainless steel synthesis kettle with polytetrafluoroethylene lining, and react at 200℃ for 40h. After the reaction, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and then placed in an oven at 110℃ for drying overnight to obtain polygonal SAPO-34 molecular sieve raw powder with a size of about 5μm. The scanning electron microscope results are as follows Fig.16 , Fig.17 The XRD spectrum is shown in Figure 1 As shown in Example 7, the XRD peak position of the result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0077] Example 8

[0078] Preparation of Zn complex: Add 31.24g zinc nitrate and 14.8g citric acid into 100mL water, stir in a 90°C water bath for 90min until completely dissolved, then place in a 275°C muffle furnace for reaction for 3 hours to obtain Zn complex, grind and set aside.

[0079] Preparation of SAPO-34 molecular sieve with low-angle morphology: Weigh 10.12g of pseudo-boehmite and mix it evenly with 51.7g of deionized water, then add 16.14g of phosphoric acid, 2.75g of silica sol, 20.25g of triethylamine, and 5g of Zn complex in sequence, mix evenly to obtain a gel mixture, stir and age it at room temperature for 30 minutes, then transfer it into a 150mL stainless steel synthesis kettle with polytetrafluoroethylene lining, and react at 200°C for 40h. After the reaction, cool the synthesis kettle to room temperature with water. The obtained product is centrifuged and washed until neutral, and placed in an oven at 110°C for overnight drying to obtain the raw powder of SAPO-34 molecular sieve with low-angle morphology, with a size of about 2-5μm. The scanning electron microscope results are as follows Fig.18 , Fig.19 The XRD spectrum is shown in Figure 1 As shown in Example 8, the XRD peak position of the result is similar to that of Comparative Example 1, and the relative peak intensity of each peak is slightly different with the change of the metal composite, indicating that the synthesized product is SAPO-34 molecular sieve.

[0080] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a morphology-controlled SAPO-34 molecular sieve, characterized in that: include, Step S1: uniformly mixing a metal salt, an organic acid and water to obtain a metal complex; the metal salt includes one or more of a zinc salt, a chromium salt, an aluminum salt and a zirconium salt; Step S2: mixing an aluminum source, a phosphorus source, a silicon source, a template, the metal complex and water, and stirring to form a gel mixture; Step S3: The gel mixture is aged, reacted, separated, and dried to obtain a SAPO-34 molecular sieve with controllable morphology.

2. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In the step S1, the metal salt includes one or more of zinc nitrate, chromium nitrate, aluminum nitrate, and zirconium nitrate.

3. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In the step S1, the organic acid is citric acid.

4. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In the step S1, the molar ratio of the organic acid to the metal salt is (0.1-30):

1.

5. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In the step S1, the reaction temperature is 180-275° C., and the reaction time is 1-20 hours.

6. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In the step S2, the mass ratio of the metal complex to the gel mixture is (0.01-0.8):

1.

7. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In step S2, the aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, and the silicon source is calculated as SiO2. The molar ratio of the silicon source, the aluminum source, the phosphorus source, the template, and water is (0.1-1.0):1.0:(0.5-3):(1.0-4.0):(30-100).

8. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In step S3, the gel mixture is aged at room temperature for 5-120 minutes.

9. The method for preparing the morphology-controlled SAPO-34 molecular sieve according to claim 1, characterized in that: In step S3, the reaction temperature is 170-200° C., and the reaction time is 24-72 hours.

10. A morphology-controllable SAPO-34 molecular sieve, characterized in that: The morphology-controllable SAPO-34 molecular sieve is prepared by the preparation method of any one of claims 1 to 9.

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