Metal-loaded mcm-41 molecular sieve, its preparation method and application

Abstract

The present application relates to the technical field of molecular sieve preparation, and provides a metal-loaded MCM-41 molecular sieve, a preparation method and application thereof.The preparation method comprises the following steps: mixing MCM-41 molecular sieve raw powder, a metal source, a first silicon source and an alkali solution to obtain a mixture, and then performing molding and drying on the mixture to obtain a molecular sieve A; mixing an organic template agent R, water, a second silicon source and an alkali source to obtain a solution B; adding the solution B into the molecular sieve A, and then performing hydrothermal crystallization, filtration, washing, drying and calcination to obtain the metal-loaded MCM-41 molecular sieve.The preparation method is simple, and the molding and metal impregnation process are completed in one step; the metal-loaded MCM-41 molecular sieve prepared has a silicon dioxide film covering the outside of the molecular sieve, so that the metal active sites are not easy to be lost in the reaction process, and the service life and activity of the catalyst are effectively prolonged.The metal-loaded MCM-41 molecular sieve is used in the reaction of the directional conversion of methanol into DMM, and the conversion rate of methanol and the selectivity of DMM can be obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve preparation, and more specifically to a metal-loaded MCM-41 molecular sieve, a preparation method thereof, and applications thereof. Background Art

[0002] Due to the rapid development of coal-to-methanol industry in my country, methanol has an overcapacity problem. The utilization of methanol and its derivatives is becoming more and more valuable for research. Dimethoxymethane (DMM) is one of the important derivatives of methanol and an important raw material for synthesizing organic matter. It has good performance and great application value. The process of direct oxidation of methanol to DMM is a new method for synthesizing DMM. This method solves the problems of complex process, high economic cost, and corrosion equipment in the traditional two-step process of preparing DMM by alcohol-aldehyde condensation, and has good development prospects. The process reaction requires the catalyst to have both oxidation center and acid center. Studies have shown that vanadium-based and titanium-based catalysts have good reaction performance, and the selection of a suitable carrier is crucial to the performance of the catalyst.

[0003] MCM-41 molecular sieve is a suitable catalyst carrier due to its large specific surface area, large pore volume, regular and orderly pore structure, uniform and adjustable pore size, and adjustable acidity. Traditional supported catalysts are generally obtained by post-processing to obtain pure silicon mesoporous molecular sieves, and then bonding the hydroxyl groups on the surface of the mesoporous molecular sieve to heteroatoms through soaking and calcination. Since the metal in the catalyst obtained by this direct impregnation method is on the surface of the molecular sieve, it is very easy to cause the loss of metal components during the reaction, resulting in a shortened catalyst life and reduced catalytic effect. Summary of the Invention

[0004] The purpose of the present invention is to provide a metal-loaded MCM-41 molecular sieve and a preparation method thereof, so as to solve the technical problem in the prior art that the metal components in the catalyst are dispersed on the surface of the molecular sieve, resulting in the easy loss of metal components during the reaction, thereby shortening the service life of the catalyst and reducing the catalytic effect.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a method for preparing a metal-loaded MCM-41 molecular sieve, comprising:

[0007] S1. The MCM-41 molecular sieve powder, the metal source, the first silicon source and the alkaline solution are mixed to obtain a mixture, and the mixture is formed and dried to obtain a molecular sieve A;

[0008] S2. The organic template R, water, a second silicon source and an alkali source are mixed to obtain a solution B;

[0009] S3. Solution B was added to molecular sieve A, hydrothermal crystallization, filtration, washing, drying, and calcination to obtain the metal-loaded MCM-41 molecular sieve;

[0010] The metal source includes a vanadium source and / or a titanium source.

[0011] In the preparation method of the metal-loaded MCM-41 molecular sieve provided by the present invention, the first silicon source is hydrolyzed under the action of an alkaline solution to generate a viscous silica gel net, and the viscous silica gel net bonds the molecular sieve particles to each other. After extrusion, the viscous silica gel net transforms a silicon dioxide film under the conditions of high-temperature roasting, covering the silicon hydroxyl structure on the outer surface of the molecular sieve, due to the skeleton structure silicon oxygen structure type of the silicon dioxide film and the molecular sieve itself, the outer surface of the molecular sieve will not be covered with blockage, and in actual applications, reactants will enter the outer surface of the molecular sieve from the silicon dioxide film in the form of diffusion. However, due to the presence of metal distribution on the outer surface of the molecular sieve, the silicon dioxide film formed will have a gap in the position of the metal, and hydrothermal crystallization is carried out by adding a mixed solution of an organic template agent R, water, a second silicon source and an alkali source, and the position of the gap is crystallized and grown so that the outer surface of the molecular sieve is formed into a complete silicon dioxide film. These silica films can improve the mechanical strength of the molecular sieve and provide a protective film for the molecular sieve structure itself. Since this protective film has a similar structure to the silica in the molecular sieve skeleton structure, it will not affect the activity and diffusion performance of the molecular sieve itself. It can also prevent the metal active sites from being lost during the reaction, effectively extending the life and activity of the catalyst.

[0012] According to some embodiments of the present invention, the vanadium source includes at least one of vanadium oxide, vanadic acid, and vanadate.

[0013] According to some embodiments of the present invention, the titanium source includes at least one of an inorganic titanium compound and an organic titanium compound.

[0014] According to some embodiments of the present invention, the inorganic compound of titanium includes at least one of titanium oxide, titanium intermetallic compound, and titanium halide.

[0015] According to some embodiments of the present invention, the first silicon source includes at least one of tetraethyl orthosilicate (TEOS), silica sol, and water glass, preferably tetraethyl orthosilicate.

[0016] According to some embodiments of the invention, the base in the alkaline solution comprises NaOH.

[0017] According to some embodiments of the present invention, the organic template R includes at least one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, and cetyltriethylammonium bromide, preferably cetyltrimethylammonium chloride.

[0018] According to some embodiments of the present application, the second silicon source comprises at least one of white carbon black, tetraethyl orthosilicate (TEOS), sodium silicate, silica sol, preferably TEOS.

[0019] According to some embodiments of the present application, the alkali source comprises at least one of sodium hydroxide, tetramethylammonium hydroxide, aqueous ammonia, preferably aqueous ammonia.

[0020] According to some embodiments of the present application, the mass ratio of the metal source to the MCM-41 molecular sieve raw powder is 1-10:100.

[0021] According to some embodiments of the present application, the mass ratio of the first silicon source to the MCM-41 molecular sieve raw powder is 1-2:5.

[0022] According to some embodiments of the present application, the molar ratio of the alkali in the alkali solution to the first silicon source in terms of OH - According to some embodiments of the present application, the molar ratio of the alkali in the alkali solution to the first silicon source in terms of OH

[0023] According to some embodiments of the present application, the molar ratio of the components in the solution B is SiO2:d H2O:e R:c OH - , wherein the value of d is 80-160, preferably 100-140, the value of e is 0.1-0.7, preferably 0.2-0.5, and the value of c is 2-7, preferably 4-5.

[0024] According to some embodiments of the present application, the mixture in the step S1 is dried first, and then the dried mixture is mixed with water and shaped.

[0025] According to some embodiments of the present application, the mass of the water mixed with the dried mixture is 10%-30%, preferably 15%-25% of the mass of the dried mixture.

[0026] According to some embodiments of the present application, the drying temperature in the step S1 is 100-150°C, preferably 120-130°C.

[0027] According to some embodiments of the present application, the crystallization temperature in the step S3 is 110-140°C, preferably 120-130°C, and the crystallization time is 72-108h, preferably 84-100h.

[0028] According to some embodiments of the present application, the drying temperature in the step S3 is 100-150°C, preferably 120-130°C.

[0029] According to some embodiments of the present application, the calcination temperature in the step S3 is 400-600°C, and the calcination time is 2-10h.

[0030] In a second aspect, the present invention provides a metal-loaded MCM-41 molecular sieve prepared by the preparation method described in the first aspect.

[0031] According to some embodiments of the present invention, the surface of the metal-loaded MCM-41 molecular sieve includes a silica shell layer.

[0032] According to some embodiments of the present invention, the particle size of the metal-loaded MCM-41 molecular sieve is 50 to 120 nm.

[0033] In a third aspect, the present invention provides the use of the metal-loaded MCM-41 molecular sieve described in the second aspect in the directional conversion of methanol into DMM.

[0034] According to some embodiments of the present invention, the metal-loaded MCM-41 molecular sieve is subjected to activation pretreatment before being used in the directed conversion of methanol to DMM.

[0035] According to some embodiments of the present invention, the activation pretreatment includes: activating at 350-450° C. for 1-4 hours in an atmosphere with a molar ratio of O 2 to N 2 of 1:3-5.

[0036] According to some embodiments of the present invention, the reaction temperature is 185-195°C.

[0037] According to some embodiments of the present invention, the methanol is gasified and mixed with O2, and reacts under the action of the metal-loaded MCM-41 molecular sieve.

[0038] According to some embodiments of the present invention, the molar ratio of methanol to O2 is (1.5-2.5):1.

[0039] The beneficial effects of the present invention are at least:

[0040] The metal-loaded MCM-41 molecular sieve provided by the present invention has a simple preparation method. A metal source is directly added during the molecular sieve forming stage, eliminating the need for impregnation of the molecular sieve with a metal solution. The forming and metal impregnation processes are completed in a single step. The prepared metal-loaded MCM-41 molecular sieve is coated with a silicon dioxide film, providing a protective layer for the molecular sieve structure, preventing the loss of metal active sites during the reaction, and effectively extending the life and activity of the catalyst. The metal-loaded MCM-41 molecular sieve can be used in the directed conversion of methanol to dimethyl methyl sulfide (DMM) to significantly improve methanol conversion and DMM selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a scanning electron microscope image of the catalyst prepared in Example 3.

[0042] Figure 2 This is the XPS graph of vanadium atoms in the catalyst prepared in Example 3. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to illustrate this patent in detail and do not limit the scope of protection of the present invention in any way.

[0044] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following examples, etc., are all commercially available or can be obtained by existing methods; the reagent amounts used, unless otherwise specified, are the amounts used in conventional experimental procedures; and the experimental methods described, unless otherwise specified, are all conventional methods.

[0045] Among them, XPS uses Thermo's ESCALAB 250spectrometer X-ray photoelectron spectrometer to measure the bonding situation of metal particles.

[0046] The scanning electron microscope was a Hitachi S-4700 scanning electron microscope.

[0047] The sodium silicate used in each embodiment and comparative example is hydrated sodium silicate with crystal water, and has a molecular weight of 284.2.

[0048] Example 1

[0049] S1. Add 40g of MCM-41 molecular sieve powder, 0.8g of sodium pyrovanadate, 8g of tetraethyl orthosilicate (TEOS), and 0.4L of 0.1mol / L NaOH solution into a mortar and mix. After mixing evenly, dry the mixture at 100°C. Then, take 30g of the dried sample and place it into an extruder. Add 3g of deionized water and stir evenly before forming. The formed molecular sieve is dried at 100°C and recorded as molecular sieve A.

[0050] S2. 4.4 g of hexadecyltrimethylammonium bromide (CTAB) and 38.9 g of deionized water were added to the reactor in sequence, stirred evenly, and 5 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise. Finally, 4.8 g of NaOH was added to obtain Solution B. The molar ratio of the components in Solution B was SiO2: 90 H2O: 0.5 R: 5 OH. - .

[0051] S3. Solution B and molecular sieve A were mixed and transferred to a crystallization kettle. The temperature was raised to 110°C and crystallized at this constant temperature for 72 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 100°C. Finally, the final sample was obtained after calcination at 400°C for 3 hours.

[0052] Example 2

[0053] S1. Add 40g of MCM-41 molecular sieve powder, 1.6g of sodium orthovanadate, 12g of silica sol (SW-25, with a silica content of 25wt%) and 0.9L of 0.1mol / L NaOH solution into a mortar and mix them. After mixing evenly, dry them at 110°C. Then take 30g of the dried sample and put it into an extruder. Add 6g of deionized water and stir evenly before starting to shape it. The formed molecular sieve is dried at 110°C and recorded as molecular sieve A.

[0054] S2. 1.8 g of hexadecyltrimethylammonium chloride (CTAC) and 20.3 g of deionized water were added to the reactor in sequence, stirred evenly, and 4 g of sodium silicate was slowly added dropwise. Finally, 3.4 g of NaOH was added to obtain Solution B. The molar ratio of the components in Solution B was SiO2: 80 H2O: 0.4 R: 6 OH. - .

[0055] S3. Solution B and molecular sieve A were mixed and transferred to a crystallization reactor. The temperature was raised to 120°C and crystallized at this constant temperature for 80 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 110°C. Finally, the final sample was obtained by calcining at 450°C for 4 hours.

[0056] Example 3

[0057] S1. Add 40g of MCM-41 molecular sieve powder, 3.2g of ammonium metavanadate, 12g of tetraethyl orthosilicate (TEOS) and 1.2L of 0.1mol / L NaOH solution into a mortar and mix them. After mixing evenly, dry them at 120°C. Then, take 30g of the dried sample and put it into an extruder. Add 7.5g of deionized water and stir evenly before starting to shape it. The formed molecular sieve is dried at 120°C and recorded as molecular sieve A.

[0058] S2. 1.4 g of hexadecyltrimethylammonium chloride (CTAC) and 25.9 g of deionized water were added to the reactor in sequence and stirred evenly. 3 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, and finally 2.0 g of ammonia was added to obtain Solution B. The molar ratio of the components in Solution B was SiO2:100H2O:0.3R:4OH. - .

[0059] S3. Solution B and molecular sieve A were mixed and transferred to a crystallization reactor. The temperature was raised to 130°C and crystallized at this constant temperature for 90 hours. After complete crystallization, the temperature was lowered to room temperature. The reaction mixture was separated, washed, and dried at 120°C. Finally, the final sample was obtained after calcination at 500°C for 5 hours.

[0060] SEM images of the samples are shown in Figure 1 , the state of vanadium atoms in the molecular sieve is analyzed by XPS Figure 2 .

[0061] Depend on Figure 1 and Figure 2 It can be seen that the metal in the sample is distributed on the outer surface of the molecular sieve in the form of oxides (the peak of vanadium pentoxide in XPS is 524.5 eV). Figure 1 It can be clearly seen that the outer surface of the sample is a silicon dioxide film, and no metal oxides can be seen in the entire field of view, indicating that the metal oxides are distributed on the outer surface of the molecular sieve within the silicon dioxide film. Since the outer surface of the molecular sieve is protected by the silicon dioxide film, the metal on the outer surface of the molecular sieve is not easily lost during the reaction, thereby extending the service life of the catalyst.

[0062] Example 4

[0063] The test process refers to Example 3, and the only difference from Example 3 is that 3.2 g of ammonium metavanadate is replaced by 3.2 g of tetrabutyl titanate.

[0064] Comparative Example 1

[0065] 40g of MCM-41 molecular sieve powder and 14.2g of pseudo-boehmite (Al2O3 content of 70%) were added to a mixer and mixed. After mixing evenly, 25.8g of dilute nitric acid (HNO3 content of 6.3%) was added and kneaded, followed by adding 15.5g of deionized water and continuing to knead. The kneaded material was then placed in an extruder for molding. The molded molecular sieve was dried at 120°C and then calcined at 500°C for 5h. The calcined molecular sieve was then mixed with 3.2g of ammonium metavanadate for 4h, dried at 120°C, and then calcined at 500°C for 5h to obtain a V / MCM-41 molecular sieve sample.

[0066] Comparative Example 2

[0067] The experimental process refers to Example 3, and the only difference from Example 3 is that the amount of 0.1 mol / L NaOH solution is changed from 1.2 L to 2.1 L.

[0068] Catalytic effect evaluation

[0069] The molecular sieve samples prepared in each embodiment and comparative example were used for the directional conversion of methanol into DMM reaction, and the specific process was as follows:

[0070] The targeted conversion of methanol to DMM was carried out in a fixed-bed reactor. A 1g sample of molecular sieve was placed in the middle constant-temperature section of the fixed-bed reactor, and the remaining sections of the reactor were filled with quartz sand. This facilitated uniform heat dissipation in the reactor and prevented catalyst overheating and sintering. Prior to the reaction, the catalyst was pretreated and activated at 400°C for 2 hours in an atmosphere of O₂:N₂ at a molar ratio of 1:4. After catalyst conditioning, methanol was supplied via a dual-plunger micropump. The vaporized methanol was mixed with O₂ in a molar ratio of 2:1 (methanol:O₂, 2:1) and introduced into the reactor. The reaction was carried out at 190°C. The product was cooled in a cooling tank, and the resulting liquid product was analyzed by gas chromatography. The experimental results are shown in Table 1.

[0071] Table 1 Results of the reaction of methanol directional conversion to DMM

[0072] Methanol conversion rate (%) DMM selectivity (%) Example 1 86.1 98.2 Example 2 86.9 98.5 Example 3 88.3 99.4 Example 4 87.5 99.0 Comparative Example 1 50.4 78.1 Comparative Example 2 4.7 5.5

[0073] The above test results show that the catalyst prepared by the preparation method provided by the present invention exhibits excellent catalytic performance in terms of methanol conversion rate and DMM selectivity.

[0074] Comparative Example 1 uses a traditional molding method. Firstly, due to the addition of adhesive during the molding process, the catalyst prepared by the traditional method has relatively fewer active sites among catalysts of the same mass. Secondly, due to the lack of protection of the outer surface silica film, the metal on the surface of the molecular sieve is very likely to be lost during the reaction, which will cause the catalyst activity to decrease.

[0075] In Comparative Example 2, due to the addition of too much base, the molecular sieve skeleton itself collapsed while the silicon source was hydrolyzed to form a silicon dioxide film and a sticky network, resulting in very low catalytic activity.

[0076] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing metal-loaded MCM-41 molecular sieve, characterized in that: include: S1. Mixing MCM-41 molecular sieve powder, a metal source, a first silicon source, and an alkaline solution to obtain a mixture, and forming and drying the mixture to obtain molecular sieve A; S2. Mixing the organic template R, water, a second silicon source, and an alkaline source to obtain a solution B; S3. adding solution B to molecular sieve A, hydrothermally crystallizing, filtering, washing, drying, and calcining to obtain the metal-loaded MCM-41 molecular sieve; The metal source includes a vanadium source and / or a titanium source; the first silicon source includes at least one of ethyl orthosilicate, silica sol, and water glass; the alkali solution contains OH - The ratio of the molar amount of the base calculated as SiO2 to the molar amount of the first silicon source calculated as SiO2 is 0.8~2.2:

1.

2. The preparation method according to claim 1, characterized in that The vanadium source includes at least one of vanadium oxide, vanadic acid, and vanadate; And / or, the titanium source includes at least one of an inorganic titanium compound and an organic titanium compound; And / or, the first silicon source is tetraethyl orthosilicate; And / or, the alkali in the alkali solution comprises NaOH.

3. The preparation method according to claim 2, characterized in that The inorganic titanium compound includes at least one of titanium oxide, titanium intermetallic compound, and titanium halide.

4. The preparation method according to any one of claims 1 to 3, characterized in that The organic template R includes at least one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, and cetyltriethylammonium bromide; And / or, the second silicon source includes at least one of white carbon black, ethyl orthosilicate, sodium silicate, and silica sol; And / or, the alkaline source includes at least one of sodium hydroxide, tetramethylammonium hydroxide, and ammonia water.

5. The preparation method according to claim 4, characterized in that The organic template R is hexadecyltrimethylammonium chloride; And / or, the second silicon source is tetraethyl orthosilicate; And / or, the alkaline source is aqueous ammonia.

6. The preparation method according to any one of claims 1 to 3, characterized in that The mass ratio of the metal source to the MCM-41 molecular sieve raw powder is 1-10:100; And / or, the mass ratio of the first silicon source to the MCM-41 molecular sieve raw powder is 1-2:

5.

7. The preparation method according to any one of claims 1 to 3, characterized in that The molar ratio of each component in the solution B is SiO2:d H2O:e R:c OH - , where the value of d is 80~160, the value of e is 0.1~0.7, and the value of c is 2~7.

8. The preparation method according to claim 7, characterized in that The value of d is 100-140, and / or the value of e is 0.2-0.5, and / or the value of c is 4-5.

9. The preparation method according to any one of claims 1 to 3, characterized in that The mixture in step S1 is first dried, and then the dried mixture is mixed with water and then formed.

10. The preparation method according to claim 9, characterized in that The mass of water mixed with the dried mixture is 10% to 30% of the mass of the dried mixture.

11. The preparation method according to claim 10, characterized in that: The mass of water mixed with the dried mixture is 15% to 25% of the mass of the dried mixture.

12. The preparation method according to any one of claims 1 to 3, characterized in that The drying temperature in step S1 is 100-150°C; And / or, the crystallization temperature in step S3 is 110-140° C.; the crystallization time is 72-108 h; And / or, the drying temperature in step S3 is 100-150° C.; And / or, the calcination temperature in step S3 is 400-600° C., and the calcination time is 2-10 hours.

13. The preparation method according to claim 12, characterized in that The drying temperature in step S1 is 120-130°C; And / or, the crystallization temperature in step S3 is 120-130° C.; and / or the crystallization time is 84-100 h; And / or, the drying temperature in step S3 is 120-130°C.

14. A metal-loaded MCM-41 molecular sieve prepared by the preparation method according to any one of claims 1 to 13.

15. The metal-loaded MCM-41 molecular sieve according to claim 14, characterized in that The surface of the metal-loaded MCM-41 molecular sieve includes a silicon dioxide shell layer.

16. Use of the metal-loaded MCM-41 molecular sieve according to claim 14 or 15 in the directed conversion of methanol to DMM.

17. The use according to claim 16, characterized in that The reaction temperature is 185-195°C; And / or, the methanol is gasified and mixed with O2, and reacts under the action of the metal-loaded MCM-41 molecular sieve.

18. The use according to claim 17, characterized in that The molar ratio of methanol to O2 is (1.5~2.5):1.

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