A bifunctional catalyst encapsulating ni@h-mcm-22 molecular sieve and a preparation method thereof

Abstract

The application discloses a kind of bifunctional catalysts of encapsulating Ni@H-MCM-22 molecular sieve, it is characterized in that, the particle of encapsulating Ni is uniformly distributed in nanometer scale, particle size is 0.1~3nm, the mass content of encapsulating Ni is 0.1~3% of the catalyst, Na + The mass content is not higher than 0.05%. The catalyst is uniformly mixed with MCM-22 molecular sieve, metal Ni precursor, nitrogen-containing organic base, structure directing agent and deionized water, the obtained mixture is hydrothermally crystallized, and the crystallization product and the reduction process obtained, different from the method of the prior art to realize metal encapsulation by sacrificing the crystallinity of molecular sieve.

Description

Technical Field

[0001] This invention relates to a bifunctional catalyst and its preparation method, and more specifically to a bifunctional catalyst encapsulated with Ni@H-MCM-22 molecular sieve and its preparation method. Background Technology

[0002] Bifunctional catalysts are a typical example of catalysts, possessing two different catalytically active centers or capable of catalyzing two different chemical reactions to obtain the target product. The concept and applications of bifunctional catalysts are found in numerous fields, including petrochemicals, new energy, and organic synthesis. In recent years, combining the advantages of metals and molecular sieves, the development of metal / molecular sieve bifunctional catalysts has become a research hotspot. Metal / molecular sieve bifunctional catalysts are of great significance in important reactions such as biomass catalytic conversion, phenol catalytic deoxygenation, and catalytic reforming.

[0003] When preparing metal / molecular sieve bifunctional catalysts using impregnation, deposition, and ion exchange methods, problems such as uneven dispersion of metal particles on the molecular sieve, non-uniform particle size, easy agglomeration, and easy loss can easily occur, ultimately leading to poor catalyst stability. The Ni / H-MCM-49 bifunctional catalyst exhibits excellent catalytic performance in the hydrodeoxygenation-acid catalysis (moderate cracking and isomerization) of long-chain fatty acids, but its poor catalytic stability is caused by uneven dispersion, non-uniform particle size, easy migration, and coking of Ni particles.

[0004] In recent years, selective encapsulation of metals into specific structures of molecular sieves has become an effective method for constructing structurally homogeneous bifunctional catalysts (metal@molecular sieves), possessing significant scientific and practical value. Currently, research focuses more on the successful encapsulation of noble metals, while studies on the encapsulation of non-noble metals and the selectivity of encapsulation sites are quite limited. In 2017, Corma A et al. successfully utilized this property of MCM-22(P) to selectively encapsulate Pt into the supercage and outer surface twelve-membered ring "cup" structure of pure silicon MCM-22 molecular sieves (Nat. Mater. 2017, 16, 132-138). In 2018, US9938157B2 reported the encapsulation of noble metals into small-pore molecular sieves such as SOD or GIS using a molecular sieve transcrystalline method; in 2019, Professor Gong Jinlong et al. reported the encapsulation of Pd into SOD cages (Angew. Chem. Int. Ed. 2019, 58, 7668-7672). CN 107020147A (2017) discloses an MFI structured layered molecular sieve catalyst encapsulating metal oxides or metal nanoparticles, its preparation method, and its uses. The preparation method involves first synthesizing a layered MFI structured molecular sieve, then using silicon support pillars to support the layered MFI structured molecular sieve and encapsulating metal oxides or metal nanoparticles between the layers. This is equivalent to using a post-processing modification method to achieve the encapsulation of metal oxides or metal nanoparticles in the MFI structured molecular sieve. The content of metal oxides in the entire catalyst is 0.1-5 wt%. The preparation method involves many steps and is time-consuming.

[0005] The above molecular sieve encapsulation of metals only utilizes the pore structure characteristics of molecular sieves to encapsulate metals. Molecular sieves do not have acid catalysis function and cannot achieve the dual function of metal hydrogenation / dehydrogenation and acid catalysis.

[0006] Compared to MFI structured molecular sieves, MCM-22 molecular sieves with MWW structure possess unique layered structure advantages. The synthesized MCM-22 raw powder, also known as MCM-22(P), exhibits structural diversity and plasticity due to its weaker interlayer bonding. Under the action of expanding agents / modifiers, the interlayer distance can be altered, such as through exfoliation (partial or complete exfoliation), as well as post-treatments like intercalation, pore expansion, and pillaring. This allows for the production of catalytic materials that retain the basic MWW layered structural units while possessing large pore sizes and high specific surface areas. Furthermore, post-treatment of MCM-22 molecular sieves often focuses on inorganic alkali treatment with NaOH. Due to the strong alkalinity of NaOH, the controllability of desilication is poor. Even with selective protection of the molecular sieve framework by introducing organic amines, the damage to the molecular sieve framework by NaOH is still unavoidable.

[0007] Ni, a non-precious metal, has a competitive advantage as a future industrial catalyst. However, avoiding the destruction of the molecular sieve framework and achieving highly dispersed encapsulation of Ni is a very difficult challenge. Summary of the Invention

[0008] One objective of this invention is to provide a bifunctional catalyst for encapsulated Ni@H-MCM-22 molecular sieves that is different from existing technologies and has a uniform distribution of Ni nanoparticles. Another objective of this invention is to provide a method for obtaining the bifunctional catalyst for encapsulated Ni@H-MCM-22 molecular sieves of this invention through post-processing of MCM-22. This method is completely different from existing technologies that achieve metal encapsulation by sacrificing the crystallinity of the molecular sieve.

[0009] To achieve the objectives of this invention, the first aspect of this invention provides a bifunctional catalyst encapsulated with Ni@H-MCM-22 molecular sieve, characterized in that the encapsulated Ni particles are uniformly distributed at the nanoscale with a particle size of 0.1–3 nm, and the mass content of the encapsulated Ni is 0.1–3% of the catalyst. + The mass content is not higher than 0.05%.

[0010] The catalyst of this invention has a BET specific surface area of ​​470-510 m². 2 / g, with a micropore area of ​​370-430m² 2 / g, total pore volume is 0.56-0.68cm³ 3 / g. The encapsulated Ni particles have an average particle size of 1.50-2.50 nm.

[0011] To achieve the objectives of this invention, the second aspect of this invention provides a method for preparing a bifunctional catalyst encapsulated with Ni@H-MCM-22 molecular sieve, characterized in that MCM-22 molecular sieve is uniformly mixed with a metallic Ni precursor, an organic base, a structure directing agent, and deionized water, and the resulting mixture is subjected to hydrothermal crystallization, recovery of crystallization products, and reduction processes to obtain the bifunctional catalyst encapsulated with Ni@H-MCM-22 molecular sieve.

[0012] In the preparation method of this invention, the MCM-22 molecular sieve is either uncalcined MCM-22 molecular sieve raw powder without template removal, or calcined MCM-22 molecular sieve after template removal, preferably uncalcined MCM-22 molecular sieve raw powder. The template is hexamethyleneimine or a mixture of hexamethyleneimine and aniline; in the MCM-22 molecular sieve, the SiO2 / Al2O3 ratio is 20–500 (molar). In the preparation method of this invention, when the MCM-22 molecular sieve is obtained from uncalcined MCM-22 molecular sieve raw powder, the raw MCM-22 molecular sieve raw powder can be obtained by the direct hydrothermal synthesis method described in US4954325 (Mobil) and CN103771435A (RIPP).

[0013] In the preparation method of this invention, the metallic Ni precursor can be selected from a complex solution of metallic nickel, which does not produce significant precipitation in an alkaline system. For example, the metallic Ni precursor is a Ni-ethylenediamine complex solution.

[0014] In the preparation method of the present invention, the nitrogen-containing organic base is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, dimethyldiethylammonium hydroxide, monomethyltriethylammonium hydroxide, monomethyltripropylammonium hydroxide, dimethyldipropylammonium hydroxide, monoethyltrimethylammonium hydroxide, diethyldipropylammonium hydroxide, monoethyltripropylammonium hydroxide, monopropyltrimethylammonium hydroxide, and monopropyltriethylammonium hydroxide. Preferably, the nitrogen-containing organic base is selected from tetraethylammonium hydroxide or dimethyldiethylammonium hydroxide.

[0015] In the preparation method of this invention, the structure-directing agent is selected from pentamethyleneimine, hexamethyleneimine, heptamethyleneimine, 1,4-diazacycloheptane, cycloheptaneamine, cyclohexaneamine, cyclopentylamine, aniline, piperidine, piperazine, N,N,N-trimethyladamantylammonium hydroxide, Me3N + (CH2)5N + Me3 and (Me2CH)2HN + (CH2)5NH + At least one of (Me2CH)2, wherein Me represents a methyl group. Preferably, the structure directing agent is selected from hexamethyleneimine or piperidine.

[0016] In the preparation method of the present invention, the molar ratio of the mixture is SiO2 / Al2O3 = 20-500, H2O / SiO2 = 5-50, S / SiO2 = 0.05-0.5, R / SiO2 = 0.05-0.5, and Ni / SiO2 = 0.01-0.03, wherein S represents a structure-directing agent and R represents an organic base; preferably, the molar ratio of the mixture is H2O / SiO2 = 5-50, R / SiO2 = 0.05-0.5, Ni / SiO2 = 0.015-0.03, and S / SiO2 = 0.05-0.3; more preferably, the molar ratio of the mixture is H2O / SiO2 = 10-25, R / SiO2 = 0.05-0.2, Ni / SiO2 = 0.02-0.03, and S / SiO2 = 0.05-0.1.

[0017] In the preparation method of the present invention, the hydrothermal crystallization is preferably carried out at a temperature of 100-170°C for 8-24 hours; more preferably, at a temperature of 120-150°C for 12-16 hours.

[0018] In the preparation method of this invention, the process of recovering the crystallized product is familiar to those skilled in the art and basically includes solid-liquid separation, washing, drying, and calcination. For example, calcination is carried out at a temperature of 400–600°C for 3–8 hours. One specific process for recovering the crystallized product, exemplified but not limited to this, involves lowering the reaction system temperature to room temperature after hydrothermal crystallization, separating the crystallized product from the mother liquor, washing the solid with deionized water until the pH value is close to 7, drying it at 100°C, and then calcining it at 550°C for 5 hours at a heating rate of 2°C / min. The reduction process is preferably carried out at 400–600°C for 4–10 hours under a hydrogen atmosphere.

[0019] The preparation method of this invention involves post-processing and modifying MCM-22 molecular sieves and encapsulating them with Ni. This preparation method exhibits a significant degree of ion exchange, resulting in a low Na content in the product sample. + When the concentration is reduced to below 0.05 wt%, no further ion exchange is required, and the encapsulated Ni@H-MCM-22 molecular sieve bifunctional catalyst can be obtained directly by calcination and reduction without undergoing an ammonium exchange process.

[0020] The encapsulated Ni@H-MCM-22 molecular sieve bifunctional catalyst provided by this invention has metallic Ni of approximately 0.1–3 nm, with uniformly distributed and sized nanoparticles. The mass content of metallic Ni nanoparticles accounts for 0.1–3% of the total catalyst mass, and Na… + The mass content is not higher than 0.05 wt%.

[0021] The preparation method provided by this invention improves both the specific surface area and pore volume while maintaining the high crystallinity of H-MCM-22 molecular sieve, and also has lower Na+ content. + With a mass content ≤0.05%, the acid catalytic function is basically met, and further ion exchange is unnecessary. Therefore, the encapsulation of metallic Ni particles and the treatment of Na are achieved during the post-processing modification of MCM-22(P) molecular sieves. + Ion exchange. After a process including calcination to recover the crystallized products and a reduction process, a Ni@H-MCM-22 bifunctional catalyst can be obtained with a relative crystallinity of over 95%, which is completely different from the existing technology that sacrifices crystallinity (70-80%) to achieve Ni encapsulation. Attached Figure Description

[0022] Figure 1 The images show the XRD patterns of the samples in each embodiment and comparative example.

[0023] Figure 2 TEM analysis of sample D-12.

[0024] Figure 3 TEM analysis of sample A-1.

[0025] Figure 4 TEM analysis of sample A-2.

[0026] Figure 5 TEM analysis of sample D-22.

[0027] Figure 6 TEM analysis of sample A-3.

[0028] Figure 7 TEM analysis of sample A-4.

[0029] Figure 8 TEM analysis of sample A-5.

[0030] Figure 9 TEM analysis of sample D-3. Detailed Implementation

[0031] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0032] In the examples and comparative examples, the X-ray diffraction (XRD) phase patterns of the samples were measured using a Siemens D5005 X-ray diffractometer. The crystallinity of the sample relative to the reference sample was expressed as the ratio of the sum of the diffraction intensities (peak heights) of the characteristic diffraction peaks between 2θ and 25.0°, i.e., the relative crystallinity (with Comparative Example 1 sample as the reference sample, its crystallinity was 100%).

[0033] In the examples and comparative examples, the TEM analysis instrument for the samples was a FEI Tecnai G2F20 (200 kV) transmission electron microscope. Test conditions: Sample preparation was performed using the suspension method. A very small amount of sample (approximately 0.01 g) was placed in a 2 mL glass bottle; dispersed in anhydrous ethanol and shaken thoroughly; a drop was taken and placed on a 3 mm diameter sample grid; after the sample dried, it was placed in the sample injector; finally, it was inserted into the electron microscope for observation. The average particle size of the encapsulated Ni particles was measured at 100 test points based on the HRTEM results, and a particle size distribution curve was plotted, with the most concentrated distribution value being recorded.

[0034] In the examples and comparative examples, the catalyst BET analysis instrument was a Quantachrome Autosorb-iQ-MP static nitrogen adsorption analyzer. Test conditions: The sample was placed in the sample processing system and evacuated to a vacuum of 1.33 × 10⁻⁶ at 350°C. -2 The sample was purified by maintaining the temperature and pressure at 20 h. At liquid nitrogen temperature -196℃, the adsorption and desorption of nitrogen on the purified sample under different specific pressures p / p0 were measured, yielding nitrogen adsorption-desorption isotherms. The BET specific surface area was then calculated using the BET formula, and the micropore specific surface area of ​​the sample was calculated using the t-plot method. The total pore volume was calculated based on the adsorption amount at p / p0 = 0.98.

[0035] Comparative Example 1

[0036] This comparative example illustrates the process of synthesizing SiO2 / Al2O3=3 MCM-22 molecular sieves using hexamethyleneimine as a structure directing agent according to the method in US4954325, and the preparation of Ni / H-MCM-22 bifunctional catalysts by the conventional impregnation method.

[0037] (1) MCM-22 molecular sieve with SiO2 / Al2O3 = 30:

[0038] Sodium aluminate (Sinopharm Group, analytical grade) and sodium hydroxide (Beijing Reagent Company, analytical grade) were dissolved in deionized water and stirred until completely dissolved. Solid silica gel (Qingdao Ocean Chemical Plant, 97% dry basis) was added to the above solution, followed by hexamethyleneimine (HMI). After stirring until homogeneous, the colloidal molar ratio of the resulting mixture was: 0.18NaOH:SiO2:0.033Al2O3:0.30HMI:15H2O. The resulting mixture was then transferred to a sealed crystallization vessel and crystallized at 145℃ for 72 hours. After cooling, the product was removed, filtered, washed, dried, and calcined to obtain the sample.

[0039] The XRD diffraction pattern of the test sample is as follows Figure 1As shown, the 2θ angle is 5 to 35°, and the product is MCM-22 molecular sieve, labeled D-11. The crystallinity of this D-11 sample is set to 100%. Figure 1 The relative crystallinity data for subsequent example samples were based on this. XRF analysis showed that its Na₂O content was 0.65 wt.%. BET analysis showed that the BET specific surface area of ​​D-11:MCM-22C was 456 m². 2 / g, micropore area is 374 m² 2 / g, total pore volume is 0.55cm³. 3 / g.

[0040] (2) Preparation of Ni / H-MCM-49 bifunctional catalyst by conventional impregnation method:

[0041] Ion exchange: The MCM-22 raw powder was subjected to ion exchange in a 90℃ water bath for 2 hours. Afterward, it was removed, filtered, and dried for later use. The ammonium ion precursor was ammonium nitrate. The exchange solution ratio was: 1g molecular sieve : 1g ammonium nitrate : 20g deionized water. The ion exchange process was repeated twice to achieve Na+ exchange. + The content was less than 0.05 wt%; the obtained sample was named MCM-22C.

[0042] Ni / H-MCM-22 bifunctional catalyst was prepared by impregnation method: Nickel nitrate (Ni(NO3)2·6H2O) was dissolved in deionized water, and then MCM-22 molecular sieve was added to the above solution. The mixture was stirred at room temperature for 4 h to achieve a homogeneous consistency. The mass ratio of the resulting mixture was MCM-22C:0.02Ni:10H2O. The resulting mixture was dried, calcined, and reduced at 105℃ to obtain the Ni@H-MCM-22 bifunctional catalyst, named D-12.

[0043] XRD diffraction pattern can be seen in... Figure 1 Compared to D-11, D-12 has a lower relative crystallinity of 80%. Characteristic diffraction peaks of Ni species at 2θ of 44.3° and 52.7° (indicated by asterisks) were clearly observed, indicating that the Ni particles prepared by the impregnation method are relatively large and unevenly dispersed on the surface of MCM-22, and obvious Ni species can be observed.

[0044] TEM analysis such as Figure 2 As shown in (D-12), Ni particles were also clearly observed. The Ni particles were about 20-50 nm in size, and their distribution was uneven and their size was not uniform.

[0045] XRF analysis of Na in D-12 + The contents were 0.02 wt.% and Ni content was 2.20 wt.%.

[0046] BET analysis shows that the BET specific surface area of ​​D-12 is 401 m². 2 / g, micropore area is 325m² 2 / g, total pore volume is 0.48cm³ 3 / g. It exhibits a significant pore-blocking effect.

[0047] Example 1

[0048] This embodiment illustrates the bifunctional catalyst and its preparation method of the present invention.

[0049] Tetraethylammonium hydroxide solution (TEAOH, 25 wt.%) was added to deionized water, followed by the uncalcined MCM-22P containing hexamethyleneimine from Comparative Example 1. Finally, a complex solution of nickel nitrate and ethylenediamine was added as a precursor for metallic Ni, and the mixture was stirred until homogeneous. The resulting mixture had a molar ratio of SiO2:0.033Al2O3:0.1TEAOH:0.02Ni:15H2O. The mixture was transferred to a sealed crystallization vessel and crystallized at 145℃ for 12 hours. After cooling, the product was removed, filtered, washed, dried, calcined, and reduced to obtain sample Ni@H-MCM-22, designated A-1.

[0050] The XRD diffraction pattern obtained from the A-1 test is shown below. Figure 1 It exhibits characteristic diffraction peaks of MCM-22 molecular sieve, with a relative crystallinity of 103%, and no obvious Ni species diffraction peaks, indicating that the Ni particles are small and uniformly distributed within the MCM-22 crystal.

[0051] TEM analysis such as Figure 3 As shown, the Ni nanoparticles have a size of 1–3 nm and an average particle size of approximately 1.94 nm.

[0052] XRF analysis showed that its Na + The contents were 0.02 wt.% and the Ni content was 2.1 wt%.

[0053] BET analysis shows that the BET specific surface area of ​​A-1 is 485 m². 2 / g, micropore area is 376m² 2 / g, total pore volume is 0.61cm³ 3 / g.

[0054] As can be seen from the crystallinity, specific surface area, and pore volume data above, A-1 significantly improves the specific surface area and pore volume while maintaining the high crystallinity of MCM-22 molecular sieve.

[0055] Example 2

[0056] This embodiment illustrates the bifunctional catalyst and its preparation method of the present invention.

[0057] Tetraethylammonium hydroxide solution (TEAOH, 25 wt.%) was added to deionized water, followed by the calcined MCM-22C from Comparative Example 1. Finally, a complex solution of piperidine (PI), nickel nitrate, and ethylenediamine was added as a Ni precursor, and the mixture was stirred until homogeneous. The resulting mixture had a molar ratio of SiO2:0.033Al2O3:0.1TEAOH:0.02Ni:15H2O:0.05PI. The mixture was transferred to a sealed crystallization vessel and crystallized at 145℃ for 12 hours. After cooling, the product was removed, filtered, washed, dried, calcined, and reduced to obtain sample Ni@H-MCM-22, designated A-2.

[0058] The XRD diffraction pattern obtained from the A-2 test is shown below. Figure 1 It exhibits characteristic diffraction peaks of MCM-22 molecular sieve, with a relative crystallinity of 100%, and no obvious Ni species diffraction peaks appear, indicating that the Ni particles are small and uniformly distributed within the MCM-22 crystal.

[0059] TEM analysis such as Figure 4 As shown: Ni nanoparticles have a size of 1–3 nm and an average particle size of approximately 2.17 nm.

[0060] XRF analysis showed that its Na + The contents were 0.02 wt.% and the Ni content was 2.1 wt%.

[0061] BET analysis shows that the BET specific surface area of ​​A-2 is 495 m². 2 / g, micropore area is 416m² 2 / g, total pore volume is 0.57cm³ 3 / g.

[0062] As can be seen from the crystallinity, specific surface area, and pore volume data above, A-2 significantly improves the specific surface area and pore volume while maintaining the high crystallinity of MCM-22 molecular sieve.

[0063] Comparative Example 2

[0064] This comparative example illustrates the process of synthesizing MCM-22 molecular sieves with SiO2 / Al2O3=30 using hexamethyleneimine and aniline as template agents according to the method in Example 1 of CN103771435A, as well as the preparation process of Ni / H-MCM-22 bifunctional catalysts prepared by the conventional impregnation method.

[0065] (1) MCM-22 molecular sieve with SiO2 / Al2O3 = 30:

[0066] Sodium aluminate (Sinopharm Group, analytical grade) and sodium hydroxide (Beijing Reagent Company, analytical grade) were dissolved in deionized water and stirred until completely dissolved. Solid silica gel (Qingdao Ocean Chemical Plant, 97% dry basis) was added to the above solution, followed by hexamethyleneimine (HMI) and aniline (AN). After stirring evenly, the colloidal molar ratio of the resulting mixture was: 0.18NaOH:SiO2:0.033Al2O3:0.10HMI:0.20AN:15H2O. The resulting mixture was then transferred to a sealed crystallization vessel and crystallized at 145℃ for 72 hours. After cooling, the product was removed, filtered, washed, dried, and calcined to obtain sample D-21.

[0067] The XRD diffraction pattern of test sample D-21 is shown below. Figure 1 The 2θ angle was 5 to 35°, and the product was MCM-22 molecular sieve with a relative crystallinity of 105%. XRF analysis showed that its Na₂O content was 0.66 wt.%. BET analysis showed that the BET specific surface area of ​​D-21:MCM-22C was 466 m². 2 / g, micropore area is 375m² 2 / g, total pore volume is 0.56cm³ 3 / g.

[0068] (2) Ni / H-MCM-22 bifunctional catalyst prepared by conventional impregnation method:

[0069] The traditional impregnation method is similar to that in Comparative Example 1 (2), and the resulting sample is named D-22.

[0070] The XRD diffraction pattern of the D-22 sample was obtained, see [link / reference]. Figure 1 The relative crystallinity of D-22 was 76%, and characteristic diffraction peaks of Ni species with 2θ of 44.3° and 52.7° were clearly observed.

[0071] TEM analysis of sample D-22 is shown in Figure 5 As shown: There are obvious Ni particles, which are about 20-50 nm in size, and their distribution is uneven and their size is non-uniform.

[0072] XRF analysis of Na in D-22 + The contents were 0.01 wt.% and Ni content was 2.12 wt.%.

[0073] BET analysis shows that the BET specific surface area of ​​D-22 is 416 m². 2 / g, micropore area is 322m² 2 / g, total pore volume V is 0.49cm³ 3 / g.

[0074] Example 3

[0075] This embodiment illustrates the bifunctional catalyst and its preparation method of the present invention.

[0076] Tetraethylammonium hydroxide solution (TEAOH, 25 wt.%) was added to deionized water, followed by the uncalcined MCM-22P containing hexamethyleneimine and aniline from Comparative Example 2. Finally, a complex solution of nickel nitrate and ethylenediamine was added as a precursor for metallic Ni, and the mixture was stirred until homogeneous. The resulting mixture had a molar ratio of SiO2:0.033Al2O3:0.1TEAOH:0.02Ni:15H2O. The mixture was transferred to a sealed crystallization vessel and crystallized at 145℃ for 16 h. After cooling, the product was removed, filtered, washed, dried, calcined, and reduced to obtain sample Ni@H-MCM-22, designated A-3.

[0077] The XRD diffraction pattern obtained from test A-3 is shown below. Figure 1 It exhibits characteristic diffraction peaks of MCM-22 molecular sieve, with a relative crystallinity of 106%, and no obvious Ni species diffraction peaks, indicating that the Ni particles are small and uniformly distributed within the MCM-22 crystal.

[0078] TEM analysis of A-3, such as Figure 6 As shown, the Ni particles are uniformly distributed and have a uniform particle size, with the Ni nanoparticle size ranging from 1 to 3 nm and an average particle size of approximately 1.74 nm.

[0079] XRF analysis showed that its Na + The contents were 0.01 wt.% and the Ni content was 1.81 wt.%.

[0080] BET analysis shows that the BET specific surface area of ​​A-3 is 501 m². 2 / g, micropore area is 410m² 2 / g, total pore volume is 0.65cm³ 3 / g.

[0081] As can be seen from the crystallinity, specific surface area, and pore volume data above, A-3 significantly improves the specific surface area and pore volume while maintaining the high crystallinity of MCM-22 molecular sieve.

[0082] Example 4

[0083] This embodiment illustrates the bifunctional catalyst and its preparation method of the present invention.

[0084] First, a dimethyl diethyl ammonium hydroxide solution (DEDMAOH, 25 wt.%) was added to deionized water. Then, uncalcined MCM-22P containing hexamethyleneimine and aniline from Comparative Example 2 was added. Finally, a complex solution of nickel nitrate and ethylenediamine was added as a precursor for metallic Ni, and the mixture was stirred until homogeneous. The resulting mixture had a molar ratio of SiO2:0.033Al2O3:0.1DEDMAOH:0.03Ni:15H2O. The mixture was transferred to a sealed crystallization vessel and crystallized at 145℃ for 12 hours. After cooling, the product was removed, filtered, washed, dried, calcined, and reduced to obtain sample Ni@H-MCM-22, designated A-4.

[0085] The XRD diffraction pattern of A-4 is shown below. Figure 1 It exhibits characteristic diffraction peaks of MCM-22 molecular sieve, with a relative crystallinity of 97%, and no obvious Ni species diffraction peaks, indicating that the Ni particles are small and uniformly distributed within the MCM-22 crystal.

[0086] TEM analysis of A-4, such as Figure 7 As shown, the Ni nanoparticles are uniformly distributed, have a uniform particle size, and the nanoparticle size is 1-3 nm, with an average particle size of about 1.86 nm.

[0087] XRF analysis showed that its Na + The contents were 0.02 wt.% and the Ni content was 2.81 wt.%.

[0088] BET analysis shows that the BET specific surface area of ​​A-4 is 474 m². 2 / g, micropore area is 387m² 2 / g, total pore volume is 0.59cm³ 3 / g.

[0089] As can be seen from the crystallinity, specific surface area, and pore volume data above, A-4 significantly improves the specific surface area and pore volume while maintaining the high crystallinity of MCM-22 molecular sieve.

[0090] Example 5

[0091] This embodiment illustrates the bifunctional catalyst and its preparation method of the present invention.

[0092] Tetraethylammonium hydroxide solution (TEAOH, 25 wt.%) was added to deionized water. Then, uncalcined MCM-22 raw powder containing hexamethyleneimine and aniline (SiO2 / Al2O3 = 50, synthesized according to the method of Example 1 in CN103771435A using hexamethyleneimine and aniline as template agents, SiO2 / Al2O3 = 50) was added to the above solution. Finally, a complex solution of nickel nitrate and ethylenediamine was added as a precursor of metallic Ni, and the mixture was stirred until homogeneous. The molar ratio of the resulting mixture was SiO2:0.02Al2O3:0.1TEAOH:15H2O:0.01Ni. The resulting mixture was then transferred to a sealed crystallization vessel, crystallized at 145℃ for 8 hours, and after cooling, the product was removed. After filtration, washing, drying, and calcination, the modified molecular sieve raw powder was obtained, sample number A-5.

[0093] The XRD diffraction pattern of A-5 is shown below. Figure 1 The relative crystallinity of MCM-22 molecular sieve is 105%, and there are no obvious characteristic diffraction peaks of Ni species.

[0094] TEM analysis of A-5, such as Figure 8 As shown, the Ni nanoparticles are uniformly distributed and have a uniform particle size, with a particle size of 1–3 nm and an average particle size of approximately 1.68 nm.

[0095] XRF analysis showed that its Na + The content was 0.01 wt.%; the Ni content was 1.04 wt.%.

[0096] BET analysis shows that the BET specific surface area of ​​A-5 is 495m². 2 / g, micropore area is 416m² 2 / g, total pore volume is 0.67cm³ 3 / g.

[0097] As can be seen from the crystallinity, specific surface area, and pore volume data above, A-5 significantly improves the specific surface area and pore volume while maintaining the high crystallinity of MCM-22 molecular sieve.

[0098] Comparative Example 3

[0099] In this comparative example, the traditional inorganic alkali sodium hydroxide (NaOH) was used as the alkali source. The method of Comparative Example 2 was used to synthesize MCM-22 molecular sieves with hexamethyleneimine and aniline as template agents, and then post-processing modification was carried out to realize the encapsulation process of metal Ni nanoparticles.

[0100] Sodium hydroxide (Beijing Reagent Company, analytical grade) was dissolved in deionized water and stirred until completely dissolved. Uncalcined MCM-22P molecular sieve powder and metallic Ni precursor from Comparative Example 2 were added and stirred until homogeneous. The resulting colloid had a molar ratio of 0.10 NaOH:SiO2:0.033 Al2O3:0.02 Ni:15 H2O. The colloid mixture was transferred to a crystallization vessel for crystallization at 145℃ under autogenous pressure and a stirring speed of 300 rpm for 12 hours. After cooling, the product was removed, filtered, washed, dried, subjected to ion exchange, calcined, and reduced to obtain sample D-3.

[0101] The XRD diffraction pattern of D-3 is shown below. Figure 1 The relative crystallinity of MCM-22 molecular sieve is 70%.

[0102] TEM analysis such as Figure 9 As shown, Ni particles are relatively uniform in distribution and size, but Ni nanoparticles are significantly larger than those in A-1, A-2, A-3, A-4 and A-5, ranging from approximately 14 to 30 nm, with an average particle size of approximately 20 nm.

[0103] XRF analysis of Na + The content is 0.04 wt.%; the Ni content is 2.04 wt.%.

[0104] BET analysis shows that the BET specific surface area of ​​D-3 is 434 m². 2 / g, micropore area is 326m² 2 / g, total pore volume is 0.68cm³ 3 / g.

Claims

1. A bifunctional catalyst encapsulating Ni@ H-MCM-22 molecular sieve, characterized in that, The encapsulated Ni particles are uniformly distributed in nanometer scale, the particle size is 0.1-3 nm, the mass content of encapsulated Ni is 0.1-3% of the catalyst, and the mass content of Na + is not higher than 0.05%; the catalyst is obtained by uniformly mixing MCM-22 molecular sieve, metal Ni precursor, nitrogen-containing organic base, structure directing agent and deionized water, hydrothermally crystallizing the obtained mixture, recovering the crystallization product and reducing.

2. Catalyst according to claim 1, characterized in that BET specific surface area of 470-510 m 2 / g, micropore area of 370-430 m 2 / g, total pore volume of 0.56-0.68 cm 3 / g.

3. The catalyst according to claim 1, characterized in that, The encapsulated Ni particles have an average particle size of 1.50-2.50 nm.

4. A process for preparing the bifunctional catalyst encapsulating Ni@ H-MCM-22 molecular sieves according to claim 1, characterized in that, MCM-22 molecular sieve was mixed with a metallic Ni precursor, a nitrogen-containing organic base, a structure directing agent, and deionized water. The resulting mixture was then subjected to hydrothermal crystallization. The crystallization products and reduction process were then recovered to obtain a bifunctional catalyst encapsulated with Ni@H-MCM-22 molecular sieve.

5. The method of claim 4, wherein, The MCM-22 molecular sieve is raw MCM-22 molecular sieve powder that has not been calcined to remove the template agent.

6. The method of claim 4, wherein, The MCM-22 molecular sieve is the MCM-22 molecular sieve after calcination to remove the template agent.

7. The method according to claim 5 or 6, characterized in that, The template agent is hexamethyleneimine or a mixture of hexamethyleneimine and aniline.

8. The method according to claim 4, characterized in that, In the MCM-22 molecular sieve, the SiO2 / Al2O3 ratio is 20~500 in molar terms.

9. The method according to claim 4, characterized in that, The metallic Ni precursor is selected from a complex solution of metallic nickel.

10. The method according to claim 9, characterized in that, The metallic Ni precursor is a Ni-ethylenediamine complex solution.

11. The method according to claim 4, characterized in that, The nitrogen-containing organic base is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, dimethyldiethylammonium hydroxide, monomethyltriethylammonium hydroxide, monomethyltripropylammonium hydroxide, dimethyldipropylammonium hydroxide, monoethyltrimethylammonium hydroxide, diethyldipropylammonium hydroxide, monoethyltripropylammonium hydroxide, monopropyltrimethylammonium hydroxide, and monopropyltriethylammonium hydroxide.

12. The method according to claim 4, characterized in that, The nitrogen-containing organic base is selected from tetraethylammonium hydroxide or dimethyldiethylammonium hydroxide.

13. The method according to claim 4, characterized in that, The structure-directing agent is selected from at least one of pentamethyleneimine, hexamethyleneimine, heptamethyleneimine, 1,4-diazacycloheptane, cycloheptaneamine, cyclohexaneamine, cyclopentylamine, aniline, piperidine, piperazine, and N,N,N-trimethyladamantylammonium hydroxide, wherein Me represents methyl.

14. The method according to claim 4, characterized in that, The structure directing agent is selected from hexamethyleneimine or piperidine.

15. The method according to claim 4, characterized in that, The molar ratio of the mixture is SiO2 / Al2O3 = 20-500, H2O / SiO2 = 5-100, R / SiO2 = 0.01-5, Ni / SiO2 = 0.01-0.03, and S / SiO2 = 0.05-0.5, where S represents a structure directing agent and R represents an organic base.

16. The method according to claim 15, characterized in that, The molar ratio of the mixture is H2O / SiO2 = 5-50, R / SiO2 = 0.05-0.5, Ni / SiO2 = 0.015-0.03, and S / SiO2 = 0.05-0.

3.

17. The method according to claim 16, characterized in that, The molar ratio of the mixture is H2O / SiO2 = 10-25, R / SiO2 = 0.05-0.2, Ni / SiO2 = 0.02-0.03, and S / SiO2 = 0.05-0.

1.

18. The method according to claim 4, characterized in that, The hydrothermal crystallization is carried out at a temperature of 100~170℃ for 8~24 hours.

19. The method according to claim 4, characterized in that, The hydrothermal crystallization is carried out at a temperature of 120~150℃ for 12~16 h.

20. The method according to claim 4, characterized in that, The reduction is carried out at 400-600°C for 4-10 hours in a hydrogen atmosphere.

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