Metal-loaded MCM-41 molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to the technical field of molecular sieve preparation, and provides a metal-loaded MCM-41 molecular sieve as well as 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 molding and drying 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; and adding the solution B into the molecular sieve A, carrying out hydrothermal crystallization, filtering, washing, drying and roasting to obtain the metal-loaded MCM-41 molecular sieve. The preparation method provided by the invention is simple, and the forming and metal dipping processes are completed by a one-step method; according to the prepared metal-loaded MCM-41 molecular sieve, a silicon dioxide film is covered outside the molecular sieve, so that metal active sites are not easy to lose in the reaction process, and the service life and the activity of the catalyst are effectively prolonged. When the metal-loaded MCM-41 molecular sieve is used in a reaction for directionally converting methanol into DMM, the conversion rate of methanol and the selectivity of DMM can be obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieve preparation, and more specifically to a metal-loaded MCM-41 molecular sieve and a preparation method and application 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 an oxidation center and an acid center. Studies have shown that vanadium-based 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 can be selected as a catalyst carrier because of its large specific surface area, large pore volume, regular and orderly pore structure, uniform pore size and adjustable size, and adjustable acidity. Traditional supported catalysts are generally obtained by post-processing to obtain pure silicon mesoporous molecular sieves, and then the hydroxyl groups on the surface of the mesoporous molecular sieves are bonded to heteroatoms by soaking, burning, etc. The catalyst obtained by this direct impregnation method is very easy to cause the loss of metal components during the reaction process because the metal is on the surface of the molecular sieve, resulting in a reduction in the service life of the catalyst and a reduction in the 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, which easily causes the loss of the 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. 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 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. adding solution B to molecular sieve A, hydrothermally crystallizing, filtering, washing, drying, and calcining 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 mesh, and the viscous silica mesh bonds the molecular sieve particles to each other. After extrusion molding, the viscous silica mesh 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, and due to the silicon dioxide film and the skeleton structure silicon oxygen structure type of the molecular sieve itself, the outer surface of the molecular sieve will not be covered and blocked, and in practical applications, the reactant will enter the outer surface of the molecular sieve from the silicon dioxide film in the form of diffusion. However, due to the metal distribution on the outer surface of the molecular sieve, the silicon dioxide film formed will have a gap at 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 forms 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 compound of titanium and an organic compound of titanium.

[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 hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyltriethylammonium bromide, preferably hexadecyltrimethylammonium chloride.

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

[0019] According to some embodiments of the present invention, the alkali source includes at least one of sodium hydroxide, tetramethylammonium hydroxide, and ammonia water, preferably ammonia water.

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

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

[0022] According to some embodiments of the present invention, 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 to 2.2:1.

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

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

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

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

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

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

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

[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 comprises 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 reaction of directed conversion of methanol to DMM.

[0035] According to some embodiments of the present invention, the activation pretreatment comprises: 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 preparation method of the metal-loaded MCM-41 molecular sieve provided by the present invention is simple. The metal source is directly added in the molecular sieve forming stage, and the molecular sieve does not need to be impregnated with a metal solution. The forming and metal impregnation processes are completed in one step. The prepared metal-loaded MCM-41 molecular sieve is covered with a silicon dioxide film on the outside of the molecular sieve, which provides a protective film for the structure of the molecular sieve itself, so that the metal active sites are not easily lost during the reaction process, and the life and activity of the catalyst are effectively extended. The metal-loaded MCM-41 molecular sieve is used in the reaction of directional conversion of methanol to DMM, which can significantly improve the conversion rate of methanol and the selectivity of DMM. 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 explain 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 those generally understood by those skilled in the art to which the present 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., can all be purchased on the market or can be obtained by existing methods; the reagent amounts, unless otherwise specified, are the reagent amounts used in conventional experimental operations; the experimental methods, unless otherwise specified, are all conventional methods.

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

[0046] The scanning electron microscope used was 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 the molecular weight is 284.2.

[0048] Example 1

[0049] S1. Add 40g MCM-41 molecular sieve powder, 0.8g sodium pyrovanadate, 8g tetraethyl orthosilicate (TEOS) and 0.4L 0.1mol / L NaOH solution into a mortar and mix. After mixing evenly, dry and dry at 100°C. Then take 30g of the dried sample and put it into an extruder. Add 3g deionized water and stir evenly to start molding. The molded 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, 5 g of tetraethylorthosilicate (TEOS) was slowly added dropwise, and finally 4.8 g of NaOH was added to obtain solution B. The molar ratio of each component in solution B was SiO2: 90H2O: 0.5R: 5OH - .

[0051] S3. After mixing solution B and molecular sieve A, transfer them to a crystallization kettle, raise the temperature to 110°C, and crystallize at a constant temperature for 72 hours. After the crystallization is complete, wait for the temperature to drop to room temperature, separate and wash the reaction mixture, dry it at 100°C, and finally calcine it at 400°C for 3 hours to obtain the final sample.

[0052] Example 2

[0053] S1. Add 40g MCM-41 molecular sieve powder, 1.6g sodium orthovanadate, 12g silica sol (SW-25, silicon dioxide content is 25wt%) and 0.9L 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 deionized water and stir evenly before starting to shape it. Dry the formed molecular sieve at 110°C and record it 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, 4 g of sodium silicate was slowly added dropwise, and finally 3.4 g of NaOH was added to obtain solution B. The molar ratio of each component in solution B was SiO2: 80H2O: 0.4R: 6OH - .

[0055] S3. After mixing solution B and molecular sieve A, transfer them to a crystallization kettle, raise the temperature to 120°C, and crystallize at a constant temperature for 80 hours. After the crystallization is complete, wait for the temperature to drop to room temperature, separate and wash the reaction mixture, dry it at 110°C, and finally calcine it at 450°C for 4 hours to obtain the final sample.

[0056] Example 3

[0057] S1. Add 40g MCM-41 molecular sieve powder, 3.2g ammonium metavanadate, 12g tetraethyl orthosilicate (TEOS) and 1.2L 0.1mol / L NaOH solution into a mortar and mix. After mixing evenly, dry and dry at 120°C. Then take 30g of the dried sample and put it into an extruder. Add 7.5g 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, stirred evenly, 3 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise, and finally 2.0 g of ammonia water was added to obtain solution B. The molar ratio of each component in solution B was SiO2: 100H2O: 0.3R: 4OH - .

[0059] S3. After mixing solution B and molecular sieve A, transfer them to a crystallization kettle, raise the temperature to 130°C, and crystallize at a constant temperature for 90 hours. After the crystallization is complete, wait for the temperature to drop to room temperature, separate and wash the reaction mixture, dry it at 120°C, and finally calcine it at 500°C for 5 hours to obtain the final sample.

[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 is 70%) are added to a mixer and mixed. After mixing evenly, 25.8g of dilute nitric acid (HNO3 content is 6.3%) is added for kneading, and then 15.5g of deionized water is added for further kneading. The kneaded material is then put into an extruder for molding. The molded molecular sieve is dried at 120°C, and then calcined at 500°C for 5h. The calcined molecular sieve is 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 test 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 directional conversion of methanol to DMM reaction is carried out in a fixed bed reactor. Weigh 1g of molecular sieve sample and load it into the middle constant temperature section of the fixed bed reactor, and fill the rest of the reactor with quartz sand, which is conducive to uniform heat dissipation of the reactor and avoids overheating and sintering of the catalyst. The catalyst is pretreated before the reaction: pretreatment and activation at 400°C for 2h in an atmosphere with a molar ratio of O2 and N2 of 1:4. After the catalyst is treated, methanol is supplied by a double plunger micropump. After methanol is gasified, it is mixed with O2 gas in a molar ratio of 2:1 (n(methanol):n(O2) is 2:1) and enters the reactor to react at 190°C. After the product is cooled in a cooling tank, the obtained liquid product is analyzed by gas chromatograph. The test 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] It can be seen from the above test results 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 easy 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 alkali, the framework of the molecular sieve itself will collapse while the silicon source is hydrolyzed to form a silicon dioxide film and a sticky network, so the catalytic activity is very low.

[0076] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to 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 functions.

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 a molecular sieve A; S2. The organic template R, water, a second silicon source and an alkali source are mixed 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.

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 compound of titanium and an organic compound of titanium, preferably, the inorganic compound of titanium includes at least one of an oxide of titanium, an intermetallic compound of titanium, and a halide of titanium; and / or, the first silicon source comprises at least one of tetraethyl orthosilicate, silica sol, and water glass, preferably tetraethyl orthosilicate; And / or, the alkali in the alkali solution comprises NaOH.

3. The preparation method according to claim 1 or 2, characterized in that: The organic template R comprises at least one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyltriethylammonium bromide, preferably hexadecyltrimethylammonium chloride; and / or, the second silicon source comprises at least one of white carbon black, tetraethyl orthosilicate, sodium silicate, and silica sol, preferably tetraethyl orthosilicate; And / or, the alkali source includes at least one of sodium hydroxide, tetramethylammonium hydroxide and ammonia water, preferably ammonia water.

4. 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 to 10:100; And / or, the mass ratio of the first silicon source to the MCM-41 molecular sieve raw powder is 1 to 2:5; And / or, the alkaline 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 to 2.2:

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The molar ratio of each component in the solution B is SiO2: d H2O: e R: c OH - , wherein the value of d is 80 to 160, preferably 100 to 140, the value of e is 0.1 to 0.7, preferably 0.2 to 0.5, and the value of c is 2 to 7, preferably 4 to 5.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The mixture in step S1 is first dried, and then the dried mixture is mixed with water and then formed; Preferably, the mass of water mixed with the dried mixture is 10% to 30%, preferably 15% to 25% of the mass of the dried mixture.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The drying temperature in step S1 is 100-150°C, preferably 120-130°C; And / or, the crystallization temperature in step S3 is 110-140° C., preferably 120-130° C.; the crystallization time is 72-108 h, preferably 84-100 h; And / or, the drying temperature in step S3 is 100-150° C., preferably 120-130° C.; And / or, the calcination temperature in step S3 is 400-600° C., and the calcination time is 2-10 hours.

8. A metal-loaded MCM-41 molecular sieve prepared by the preparation method according to any one of claims 1 to 7.

9. The metal-loaded MCM-41 molecular sieve according to claim 8, characterized in that: The surface of the metal-loaded MCM-41 molecular sieve includes a silicon dioxide shell layer.

10. Use of the metal-loaded MCM-41 molecular sieve according to claim 8 or 9 in the directional conversion of methanol into DMM.

11. The use according to claim 10, 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; preferably, the molar ratio of the methanol to O2 is (1.5-2.5):1.

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