Ni-based silicalite-1 molecular sieve as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of molecular sieve catalyst preparation, and particularly relates to a Ni-based silicalite-1 molecular sieve as well as a preparation method and application thereof. According to the method, the Ni-based silicalite-1 molecular sieve is prepared under the assistance of ethanol, so that the Ni nanoparticles can be effectively and uniformly anchored in the pore channels of the molecular sieve in a dispersed manner, the problem of relatively poor metal dispersity in a traditional impregnation method and a deposition-precipitation method is solved, high dispersion of the Ni nanoparticles is realized, and the interaction between the Ni nanoparticles and the silicalite-1 is enhanced. According to the Ni-based silicaltie-1 molecular sieve provided by the invention, the size of Ni nanoparticles is relatively small, the pore channel confinement effect of the silicaltie-1 molecular sieve on metal Ni is beneficial to enhancing the metal-carrier interaction between Ni active species and the molecular sieve, and the Ni-based silicaltie-1 molecular sieve shows relatively good sintering resistance and carbon deposition resistance in a catalytic methane dry reforming reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve catalyst preparation, and specifically relates to a Ni-based silicalite-1 molecular sieve and a preparation method and application thereof. Background Art

[0002] Molecular sieve materials have been developed into ideal carriers of confined metal nanoparticles due to their unique pore structure, adjustable acidity, large specific surface area and good thermal / hydrothermal stability. They are widely used in important industrial catalysis fields such as acid catalysis. In recent years, the dry reforming of methane to produce synthesis gas (CH4+CO2→2CO+2H2) has attracted extensive attention from researchers. Since the dry reforming of methane can simultaneously convert two greenhouse gases, methane and carbon dioxide, into synthesis gas, and synthesis gas with hydrogen and carbon monoxide as the main components is an important type of raw gas, this reaction is of great significance. However, since the DRM reaction temperature (873-1073K) is higher than the Tammann temperature of metal Ni (863K), high-loaded Ni-based catalysts are prone to sintering during the reaction; more serious is the existence of side reactions, including CH4 deep cracking (CH4→2H2+C) and CO disproportionation (2CO→CO2+C) to produce coke deposition, which leads to catalyst deactivation.

[0003] Among the 255 existing molecular sieves, MFI molecular sieve Silicalite-1 with a ten-membered ring pore structure is a relatively common metal-loaded material. In particular, the Ni-Silicalite-1 molecular sieve catalyst is obtained by loading metal Ni into the Silicalite-1 molecular sieve. Its regular pore structure is conducive to the formation of dispersed small-sized Ni nanoparticles and inhibits their leaching or sintering during the reaction. At the same time, the good thermal stability and hydrothermal stability of the Silicalite-1 molecular sieve are also conducive to improving the methane dry reforming activity.

[0004] The commonly used preparation methods of Ni-Silicalite-1 molecular sieves include impregnation method or deposition precipitation method, wherein in the Ni / Silicalite-1 molecular sieve synthesized by the deposition precipitation method, Ni nanoparticles are mainly distributed on the outer surface of Silicalite-1, and the Ni nanoparticles are relatively large in size. Although the metal Ni can be encapsulated into the microporous channels of Silicalite-1 when the Ni / Silicalite-1 molecular sieve is prepared by the impregnation method, the metal solution cannot evenly enter the pores of the molecular sieve, resulting in poor dispersion of the Ni nanoparticles and uneven distribution inside and outside the channels. In summary, how to obtain a Ni-based Silicalite-1 molecular sieve with highly dispersed Ni nanoparticles is a problem to be solved in this field. Summary of the invention

[0005] The object of the present invention is to provide a Ni-based silicalite-1 molecular sieve and a preparation method and application thereof. The Ni nanoparticles in the Ni-based silicalite-1 molecular sieve provided by the present invention are highly dispersed.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a Ni-based silicalite-1 molecular sieve, comprising the following steps:

[0008] Silicalite-1 molecular sieve, nickel salt, ethanol and water are mixed and then dried, calcined and reduced in sequence. The reduction reaction is carried out in a reducing atmosphere to obtain the Ni-based silicalite-1 molecular sieve.

[0009] Preferably, the nickel salt is nickel nitrate hexahydrate.

[0010] Preferably, the mass ratio of the Silicalite-1 molecular sieve to ethanol is 1:2-4; the mass ratio of the nickel salt to ethanol is 0.26:2-4; and the mass ratio of the ethanol to water is 2-4:1.

[0011] Preferably, the calcination temperature is 450-500° C., and the heat preservation calcination time is 4-5 hours.

[0012] Preferably, the reduction reaction temperature is 650-700° C., and the insulation reaction time is 3-5 hours.

[0013] Preferably, the preparation method of the Silicalite-1 molecular sieve is: mixing a silicon source, a template, an alcohol solvent and water, performing a hydrothermal crystallization reaction and then calcining.

[0014] Preferably, the temperature of the hydrothermal crystallization reaction is 160-180° C., and the insulation reaction time is 48-96 hours.

[0015] The present invention also provides a Ni-based silicalite-1 molecular sieve obtained by the preparation method described in the above scheme, comprising a silicatie-1 molecular sieve and Ni nanoparticles distributed in the pores of the silicatie-1 molecular sieve; the particle size of the Ni nanoparticles is 0.8 to 2.0 nm.

[0016] Preferably, the loading amount of Ni nanoparticles in the Ni-based silicalite-1 molecular sieve is 3 to 10 wt%.

[0017] The present invention also provides the use of the Ni-based silicalite-1 molecular sieve described in the above scheme in carbon dioxide hydrogenation, furfural hydrogenation or methane dry reforming reaction.

[0018] The present invention provides a method for preparing a Ni-based silicalite-1 molecular sieve. The present invention uses ethanol to assist in preparing the Ni-based silicalite-1 molecular sieve. Compared with the traditional impregnation method and the deposition precipitation method, the preparation method provided by the present invention can effectively anchor Ni nanoparticles in the molecular sieve pores in a uniformly dispersed manner, solves the problem of poor metal dispersion in the traditional impregnation method and the deposition precipitation method, realizes high dispersion of Ni nanoparticles, enhances the interaction between Ni nanoparticles and silicalite-1, improves the methane dry reforming activity of Ni-based silicalite-1, and is simple to operate.

[0019] The present invention also provides a Ni-based silicalite-1 molecular sieve obtained by the preparation method described in the above scheme. The Ni-based silicatie-1 molecular sieve provided by the present invention is a metal-loaded molecular sieve catalyst, and the size of the Ni nanoparticles is relatively small, only 1.5nm (the existing ones are between 3 and 15nm), which is beneficial to improve the catalytic activity of the Ni-based silicalite-1 molecular sieve and reduce the agglomeration of Ni; the pore confinement effect of the silicalite-1 molecular sieve on the metal Ni is beneficial to enhance the metal-carrier interaction between the Ni active species and the molecular sieve, so that the Ni-based silicalite-1 molecular sieve of the present invention is used as a catalyst, and exhibits good sintering resistance and carbon deposition resistance in the catalytic methane dry reforming reaction. After the methane dry reforming reaction, the size of the Ni nanoparticles is only slightly increased to 2.5nm, the catalytic stability is high, the raw material conversion rate is high, and the effective utilization rate of the metal Ni is greatly improved, which reduces the Ni loading required in the methane dry reforming reaction, and only 5wt% is required.

[0020] The present invention also provides the use of the Ni-based silicalite-1 molecular sieve described in the above scheme in the carbon dioxide hydrogenation, furfural hydrogenation or methane dry reforming reaction. The Ni-based silicalite-1 molecular sieve provided by the present invention is used as a catalyst, and exhibits good sintering resistance and carbon deposition resistance in catalytic methane dry reforming and other reactions, has high catalytic stability, and a catalytic life of 200 hours, and after the reaction, the conversion rates of CH4 and CO2 are 89% and 94% respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 X-ray diffraction patterns of Ni-based silicalite-1 molecular sieves prepared in Examples 1 to 3;

[0023] Figure 2 High-angle annular dark-field scanning transmission electron microscopy photographs of Ni-based silicalite-1 molecular sieves prepared in Example 1 (a and d), Example 2 (b and e) and Example 3 (c and f);

[0024] Figure 3 N2 adsorption / desorption isotherms of the Ni-based silicalite-1 molecular sieve prepared in Examples 1 to 3;

[0025] Figure 4 X-ray diffraction patterns of the molecular sieves prepared in Comparative Examples 1 to 2;

[0026] Figure 5 High-angle annular dark-field scanning transmission electron microscopy photographs of the molecular sieves prepared in Comparative Example 1 (a and c) and Comparative Example 2 (b and d);

[0027] Figure 6 The conversion rates of CH4 and CO2 in the methane dry reforming reaction using the molecular sieves prepared in Examples 1 to 3 and Comparative Examples 1 to 2;

[0028] Figure 7 The molar ratio of H2 / CO in the methane dry reforming reaction of the molecular sieves prepared in Examples 1 to 3 and Comparative Examples 1 to 2. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing a Ni-based silicalite-1 molecular sieve, comprising the following steps:

[0030] Silicalite-1 molecular sieve, nickel salt, ethanol and water are mixed and then dried, calcined and reduced in sequence to obtain the Ni-based silicalite-1 molecular sieve.

[0031] The present invention mixes Silicalite-1 molecular sieve, nickel salt, ethanol and water (referred to as first water) (referred to as first mixing). In the present invention, the preparation method of the Silicalite-1 molecular sieve is preferably as follows: silicon source, template, alcohol solvent and water (referred to as second water) are mixed (referred to as second mixing) and subjected to hydrothermal crystallization reaction and then calcined (referred to as second calcination).

[0032] In the present invention, the silicon source is preferably tetraethyl orthosilicate. In a specific embodiment of the present invention, the tetraethyl orthosilicate is preferably purchased from Tianjin Fuchen Company.

[0033] In the present invention, the template is preferably tetrapropylammonium hydroxide. In a specific embodiment of the present invention, the tetrapropylammonium hydroxide is preferably purchased from Sinopharm Reagent Company.

[0034] In the present invention, the molar ratio of the silicon source (calculated as SiO2) to the template is preferably 1:0.25-0.40, specifically 1:0.25, 1:0.27, 1:0.30, 1:0.32, 1:0.35, 1:0.38 or 1:0.40.

[0035] In the present invention, the alcohol solvent is preferably anhydrous ethanol. In a specific embodiment of the present invention, the anhydrous ethanol is preferably purchased from Tianjin Guangfu Company.

[0036] In the present invention, the molar ratio of the template to the alcohol solvent is preferably 0.25 to 0.40:1, specifically 0.25:1, 0.27:1, 0.28:1, 0.30:1, 0.32:1, 0.35:1, 0.37:1, 0.39:1 or 0.40:1.

[0037] In the present invention, the second water is preferably deionized water.

[0038] In the present invention, the molar ratio of the alcohol solvent to the second water is preferably 1:20-30, specifically 1:20, 1:21, 1:23, 1:25, 1:27, 1:29 or 1:30.

[0039] In the present invention, the second mixing is preferably: the template, the alcohol solvent and the second water are stirred and mixed to obtain a premixed liquid, and then the silicon source is dropped into the premixed liquid while stirring.

[0040] In the present invention, the hydrothermal crystallization reaction is preferably carried out in a reactor; the temperature of the hydrothermal crystallization reaction is preferably 160-180°C, specifically 160°C, 165°C, 170°C, 175°C or 180°C, and the insulation reaction time is preferably 48-96h, specifically 48h, 60h, 72h, 82h or 96h.

[0041] In the present invention, after the hydrothermal crystallization reaction, it is preferred that the obtained product is sequentially subjected to solid-liquid separation, washing and drying (referred to as the second drying); the solid-liquid separation is preferably centrifugation; the washing reagent is preferably distilled water, preferably until washed to neutrality (pH value = 7); the temperature of the second drying is preferably 80-100°C, specifically 80°C, 85°C, 90°C, 95°C or 100°C, and the heat preservation and drying time is preferably 8-12h, specifically 8h, 9h, 10h, 11h or 12h.

[0042] In the present invention, the second calcination temperature is preferably 550-600°C, specifically 550°C, 560°C, 570°C, 580°C, 590°C or 600°C, and the heat preservation calcination time is preferably 5-6h, specifically 5h, 5.3h, 5.5h, 5.7h or 6h.

[0043] In the present invention, the nickel salt is preferably nickel nitrate hexahydrate. In a specific embodiment of the present invention, the nickel nitrate hexahydrate is preferably purchased from Sinopharm Reagent Company.

[0044] In the present invention, the first water is preferably deionized water.

[0045] In the present invention, the mass ratio of the Silicalite-1 molecular sieve to ethanol is preferably 1:2-4, specifically 1:2, 1:2.3, 1:2.7, 1:3, 1:3.2, 1:3.5, 1:3.7 or 1:4; the mass ratio of the nickel salt to ethanol is preferably 0.26:2-4, specifically 0.26:2, 0.26:2.4, 0.26:2.7, 0.26:3, 0.26:3.5, 0.26:3.8 or 0.26:4; the mass ratio of the ethanol to the first water is preferably 2-4:1, specifically 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1.

[0046] In the present invention, the first mixing is preferably stirring mixing; and the temperature of the first mixing is preferably room temperature.

[0047] After the first mixing, the present invention sequentially dries (referred to as the first drying), calcines (referred to as the first calcination) and reduces the obtained mixture to obtain the Ni-based silicalite-1 molecular sieve. In the present invention, the temperature of the first drying is preferably 40 to 80°C, specifically 40°C, 45°C, 50°C, 55°C, 60°C, 70°C or 80°C; the equipment for the first drying preferably includes an infrared heater and a drying oven; the first drying preferably includes sequentially performing infrared heating drying and constant temperature drying; the heat preservation drying time of the infrared heating drying is preferably 3 to 5 hours, specifically 4 hours; the infrared heating drying is preferably carried out under stirring conditions; the temperature of the constant temperature drying is preferably 40 to 80°C, specifically 40°C, 45°C, 50°C, 55°C, 60°C, 70°C or 80°C, and the heat preservation drying time is preferably 8 to 12 hours, specifically 10 hours.

[0048] In the present invention, the temperature of the first calcination is preferably 450-500°C, specifically 450°C, 465°C, 480°C, 490°C or 500°C, and the heat preservation calcination time is preferably 4-5h, specifically 4.5h.

[0049] In the present invention, the reduction reaction is preferably carried out in a reducing atmosphere; the reducing atmosphere is preferably hydrogen; the temperature of the reduction reaction is preferably 650-700°C, specifically 650°C, 660°C, 670°C, 680°C, 690°C or 700°C, and the insulation reaction time is preferably 3-5h, specifically 4h.

[0050] The present invention also provides a Ni-based silicalite-1 molecular sieve obtained by the preparation method described in the above scheme, comprising a silicatie-1 molecular sieve and Ni nanoparticles distributed in the pores of the silicatie-1 molecular sieve; the particle size of the Ni nanoparticles is 0.8 to 2.0 nm, specifically 1 nm, 1.2 nm, 1.5 nm or 1.8 nm.

[0051] In the present invention, the loading amount of Ni nanoparticles in the Ni-based silicalite-1 molecular sieve is preferably 3-10wt%, specifically 4wt%, 5wt%, 7wt% or 9wt%.

[0052] The Ni-based silicatie-1 molecular sieve provided by the present invention is a metal-loaded molecular sieve catalyst. The size of Ni nanoparticles is relatively small, only 1.5 nm (the existing size is between 3 and 15 nm), which is beneficial to improving the catalytic activity of the Ni-based silicatie-1 molecular sieve and reducing Ni agglomeration. The pore confinement effect of the silicatie-1 molecular sieve on the metal Ni is beneficial to enhancing the metal-carrier interaction between the Ni active species and the molecular sieve, so that the Ni-based silicatie-1 molecular sieve of the present invention, as a catalyst, exhibits good sintering resistance and carbon deposition resistance in the catalytic methane dry reforming reaction. After the methane dry reforming reaction, the size of the Ni nanoparticles is only slightly increased to 2.5 nm, the catalytic stability is high, the raw material conversion rate is high, the effective utilization rate of the metal Ni is greatly improved, and the Ni loading required in the methane dry reforming reaction is reduced to only 5wt%.

[0053] The present invention also provides the use of the Ni-based silicalite-1 molecular sieve described in the above scheme in carbon dioxide hydrogenation, furfural hydrogenation or methane dry reforming reaction.

[0054] The Ni-based silicaltie-1 molecular sieve provided by the present invention is used as a catalyst, and exhibits good resistance to sintering and carbon deposition in reactions such as catalytic methane dry reforming, has high catalytic stability, a catalytic life of 200 hours, and after the reaction, the conversion rates of CH4 and CO2 are 89% and 94% respectively.

[0055] In order to further illustrate the present invention, the scheme of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0056] In the specific embodiments, comparative examples and test examples of the present invention, the XRD test adopts the RigakuDMax 2550 instrument of Rigaku Company, with a scanning range of 4-40° and a scanning speed of 9° / min; the morphology and structure of the molecular sieve and the size and distribution of the metal Ni are tested using a JEM-2100F transmission electron microscope; the element content of the metal Ni is tested on a Perkin-Elmer Optima 3300DV; the specific surface area and pore volume are characterized by N2 adsorption / desorption, and the test is completed on a MicromeriticASAP 2020Plus adsorption instrument.

[0057] Example 1

[0058] First, the Silicalite-1 molecular sieve was dried in a vacuum drying oven at 80°C for 12 h to remove impurities such as water adsorbed in the pores of the Silicalite-1 molecular sieve; then 0.4 g of the dried Silicalite-1 molecular sieve, 0.1044 g of Ni(NO3)2·6H2O, 1 g of ethanol and 1 g of deionized water were mixed and stirred at room temperature for 3 h to obtain a reaction mixture; then stirring was continued for 4 h under an infrared heater until the ethanol and water were completely evaporated, and the mixture was placed in a drying oven at 80°C overnight to obtain a solid sample; the obtained solid sample was calcined at 500°C for 4 h; finally, the temperature was programmed to 700°C in a hydrogen atmosphere for reduction for 4 h to obtain a Ni-based Silicalite-1 molecular sieve, recorded as Ni@Silicalite-1-1.

[0059] The Ni-based Silicalite-1 molecular sieve prepared in this example has a Ni nanoparticle loading of 5 wt %.

[0060] Example 2

[0061] The preparation method of this embodiment is the same as that of Example 1, except that the loading amount of Ni nanoparticles is reduced from 5wt% to 3wt%. The mass ratio of the raw materials in the reaction mixture of this embodiment is Silicalite-1:Ni(NO3)2·6H2O:EtOH:H2O=1:0.156:2.5:2.5, and a Ni-based Silicalite-1 molecular sieve is obtained, which is recorded as Ni@Silicalite-1-2.

[0062] Example 3

[0063] The preparation method of this embodiment is the same as that of Example 1, except that the loading amount of Ni nanoparticles is increased from 5wt% to 10wt%. The mass ratio of the raw materials in the reaction mixture of this embodiment is Silicalite-1:Ni(NO3)2·6H2O:EtOH:H2O=1:0.522:2.5:2.5, and a Ni-based Silicalite-1 molecular sieve is obtained, which is recorded as Ni@Silicalite-1-3.

[0064] Comparative Example 1

[0065] Preparation of Ni-based Silicalite-1 molecular sieve by traditional impregnation method:

[0066] 0.4 g of Silicalite-1 molecular sieve, 0.1044 g of Ni(NO3)2·6H2O and 2 g of deionized water were mixed and stirred at room temperature for 3 h; then placed in a vacuum drying oven at 80°C for overnight drying to obtain a solid; the obtained solid was calcined at 500°C for 4 h; finally, the temperature was programmed to 700°C in a hydrogen atmosphere and reduced for 4 h to obtain a Ni-based Silicalite-1 molecular sieve, denoted as Ni / Silicalite-1-D1, with a metal Ni loading of 5 wt%.

[0067] Comparative Example 2

[0068] Preparation of Ni / Silicalite-1 molecular sieve by sedimentation precipitation method:

[0069] In a 70°C oil bath, 0.4g of Silicalite-1, 0.1044g of Ni(NO3)2·6H2O and 2g of deionized water were mixed and stirred; then 1.26g of urea was dissolved in 8g of deionized water to prepare a solution, and the solution was added dropwise to the above solution in three times; then stirred in a 90°C oil bath for 10h; then centrifuged and washed, dried overnight, and calcined at 500°C for 6h; finally, the temperature was raised to 700°C in a hydrogen atmosphere and reduced for 4h to obtain a Ni / Silicalite-1 molecular sieve, denoted as Ni / Silicalite-1-D2, with a metal Ni loading of 5wt%.

[0070] Test Example 1

[0071] The Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 were subjected to X-ray diffraction analysis. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 all exhibit characteristic diffraction peaks of the MFI topological structure in the range of 4 to 40°, indicating that the embedding of metal Ni nanoparticles does not damage the crystal structure of the nano Silicalite-1 molecular sieve, and no characteristic peaks of metal Ni appear in the spectrum, indicating that there are no agglomerated metal particles and the particle size of metal Ni is relatively small.

[0072] The Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 were analyzed by high-angle annular dark-field scanning transmission electron microscopy. The results are as follows: Figure 2 As shown. Figure 2It can be seen that in the Ni-based Silicalite-1 molecular sieves prepared in Examples 1 and 2, the Ni element is uniformly distributed inside the Silicalite-1 molecular sieve crystals, and the size of the Ni nanoparticles is about 1.5 nm. In the Ni-based Silicalite-1 molecular sieve prepared in Example 3, most of the metal Ni nanoparticles are uniformly distributed in the Silicalite-1 crystals in a smaller size, but it is obvious that some metal particles aggregate, and the nanoparticles aggregate into nanoparticles with a size of about 10 nm.

[0073] The Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 were subjected to N2 adsorption / desorption isotherm tests. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 all present type I isotherms, indicating good crystallinity and microporous properties of the molecular sieves, indicating that the embedding of metal Ni does not significantly destroy the pore structure of the molecular sieves.

[0074] The molecular sieves prepared in Comparative Examples 1 and 2 were subjected to X-ray diffraction analysis, and the results were as follows: Figure 4 As shown. Figure 4 It can be seen that the molecular sieves prepared in Comparative Examples 1 to 2 show obvious diffraction peaks at diffraction angles of 44.5°, 51.8° and 76.4°, corresponding to the (111), (200) and (220) planes of metallic Ni, respectively, indicating that the particle size of metallic Ni in the molecular sieves prepared in Comparative Examples 1 to 2 is larger.

[0075] The molecular sieves prepared in Comparative Examples 1 and 2 were analyzed by high-angle annular dark field scanning transmission electron microscopy. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that in the molecular sieve prepared in Comparative Example 1, most of the metal Ni is distributed inside the Silicalite-1 molecular sieve crystals, but a small part is on its outer surface, and the size of the metal Ni nanoparticles is uneven, with an average size of 2.5 nm; in the molecular sieve prepared in Comparative Example 2, the metal Ni nanoparticles are mainly distributed on the outer surface of Silicalite-1, the particle size is larger, about 4.5 nm, and the distribution is uneven.

[0076] Test Example 2

[0077] The metal content and pore properties of the Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were tested, and the Ni content was measured by ICP-AES; S BET is the total specific surface area, calculated by the BET method; S micro is the micropore specific surface area, S extis the external specific surface area, calculated by the t-plot method; the results are shown in Table 1.

[0078] Table 1 Metal content and pore properties of Ni-based Silicalite-1 molecular sieves of Examples 1 to 3 and Comparative Examples 1 to 2

[0079] project <![CDATA[Ni a (wt%)]]> <![CDATA[S BET b (m 2 g -1 )]]> <![CDATA[S micro c (m 2 g -1 )]]> <![CDATA[S ext c (m 2 g -1 )]]> Silicalite-1 / 391 242 149 Ni@Silicalite-1-1 2.32 298 210 88 Ni@Silicalite-1-2 4.78 284 195 89 Ni@Silicalite-1-3 9.26 266 183 83 Ni / Silicalite-1-D1 4.52 291 194 97 Ni / Silicalite-1-D2 4.11 333 214 119

[0080] It can be seen from Table 1 that the contents of metallic Ni in the Ni-based Silicalite-1 molecular sieves prepared in Examples 1 to 3 are 2.32wt%, 4.78wt% and 9.26wt%, respectively, and the micropore specific surface area is reduced compared with that of Silicalite-1, and the degree of reduction is more obvious as the Ni loading amount increases, indicating that the metallic Ni nanoparticles are embedded in the interior of the molecular sieve crystals, and the amount of embedding increases as the loading amount increases.

[0081] Test Example 3

[0082] The molecular sieves prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were used for methane dry reforming reaction (reaction conditions: feed ratio CH4:CO2=1:1, space velocity of 30 L·g -1 ·h -1 , catalyst dosage is 0.1g, temperature is 800℃, pressure is 1atm), test CH4 and CO2 conversion rate, the results are as follows Figure 6 As shown. Figure 6It can be seen that the molecular sieve prepared in Example 2 has a small Ni loading of only 3wt%, and the small amount of Ni active species makes the reaction activity low. After 40h of reaction, the conversion rates of methane and carbon dioxide rapidly decrease from the initial 85% and 92% to 58% and 74%; the molecular sieve prepared in Example 2 has the best stability. After 200h of continuous reaction, the conversion rates of methane and carbon dioxide slightly decrease from the initial 92% and 96% to 88% and 94%, which is mainly attributed to the uniform dispersion and small size of Ni nanoparticles, which increase the interaction between metal and carrier, and give the catalyst higher resistance to carbon deposition and sintering. Although the molecular sieve prepared in Example 3 contains more metallic Ni and the loading amount is increased to 10wt%, the sample begins to deactivate rapidly after 20h of reaction, and the conversion of methane and carbon dioxide decreases. The conversion rate dropped sharply from the initial 92% and 96% to 37% and 54%, which was mainly attributed to the metal agglomeration phenomenon; for the molecular sieve prepared in comparative example 1, the methane and carbon dioxide conversion rates remained high at 91% and 96% after 100 hours of reaction, and then the molecular sieve began to deactivate at a slow rate. After 200 hours of continuous reaction, the methane and carbon dioxide conversion rates decreased to 69% and 81%, respectively. Although its activity was also very high, due to the insufficient dispersion of metal Ni, its activity was still lower than that of the molecular sieve prepared in Example 2; for the molecular sieve prepared in comparative example 2, the initial conversion rates of methane and carbon dioxide were 91% and 96%, respectively, and the conversion rate dropped significantly after 40 hours of reaction. When the reaction was carried out for 100 hours, the methane and carbon dioxide conversion rates had seriously dropped to 74% and 84%.

[0083] The molecular sieves prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were used for methane dry reforming reaction (reaction conditions: feed ratio CH4:CO2=1:1, space velocity of 30 L·g -1 ·h -1 , catalyst dosage is 0.1g, temperature is 800℃, pressure is 1atm), test the molar ratio of H2 / CO, the results are as follows Figure 7 As shown. Figure 7It can be seen that the initial H2 / CO ratio of the molecular sieve prepared in Example 1 is only 0.92, which decreases to 0.80 after 40 hours of reaction; the H2 / CO ratio of the molecular sieve prepared in Example 2 is always maintained at about 0.99, without obvious changes, indicating that no obvious reverse water gas conversion reaction (CO2+H2→CO+H2O) occurs in the catalytic methane dry gas reforming reaction; the H2 / CO ratio of the molecular sieve prepared in Example 3 decreases rapidly to 0.80 after 20 hours of reaction, indicating that the larger Ni nanoparticles cause a more obvious reverse water gas conversion reaction to occur therein; the H2 / CO ratio of the molecular sieve prepared in Comparative Example 1 is always maintained at 0.99 within 100 hours before the reaction, and slowly decreases after 100 hours of reaction, and decreases to 0.94 at 200 hours; the H2 / CO ratio of the molecular sieve prepared in Comparative Example 2 is always maintained at 0.9 within 100 hours of reaction.

[0084] It can be seen from the above embodiments that the Ni nanoparticles in the Ni-based silicalite-1 molecular sieve provided by the present invention are highly dispersed, the size of the Ni nanoparticles is small, and they exhibit good resistance to sintering and carbon deposition in the catalytic methane dry reforming reaction, high catalytic stability, high raw material conversion rate, and greatly improved effective utilization of metal Ni, thereby reducing the Ni loading required in the methane dry reforming reaction.

[0085] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a Ni-based silicalite-1 molecular sieve, characterized in that: The following steps are involved: Silicalite-1 molecular sieve, nickel salt, ethanol and water are mixed and then dried, calcined and reduced in sequence. The reduction reaction is carried out in a reducing atmosphere to obtain the Ni-based silicalite-1 molecular sieve.

2. The preparation method according to claim 1, characterized in that: The nickel salt is nickel nitrate hexahydrate.

3. The preparation method according to claim 1 or 2, characterized in that: The mass ratio of the Silicalite-1 molecular sieve to ethanol is 1:2-4; The mass ratio of the nickel salt to ethanol is 0.26:2-4; The mass ratio of the ethanol to water is 2 to 4:

1.

4. The preparation method according to claim 1, characterized in that: The calcination temperature is 450-500° C., and the heat preservation calcination time is 4-5 hours.

5. The preparation method according to claim 1 or 4, characterized in that: The temperature of the reduction reaction is 650-700° C., and the heat preservation reaction time is 3-5 hours.

6. The preparation method according to claim 1, characterized in that: The preparation method of the Silicalite-1 molecular sieve comprises: mixing a silicon source, a template agent, an alcohol solvent and water, performing a hydrothermal crystallization reaction and then calcining.

7. The preparation method according to claim 6, characterized in that: The temperature of the hydrothermal crystallization reaction is 160-180° C., and the heat preservation reaction time is 48-96 hours.

8. The Ni-based silicalite-1 molecular sieve obtained by the preparation method according to any one of claims 1 to 7, characterized in that: It comprises a silicatie-1 molecular sieve and Ni nanoparticles distributed in the pores of the silicatie-1 molecular sieve; the particle size of the Ni nanoparticles is 0.8-2.0 nm.

9. The Ni-based silicalite-1 molecular sieve according to claim 8, characterized in that The loading amount of Ni nanoparticles in the Ni-based silicalite-1 molecular sieve is 3-10 wt %.

10. Use of the Ni-based silicalite-1 molecular sieve according to any one of claims 8 to 9 in carbon dioxide hydrogenation, furfural hydrogenation or methane dry reforming reaction.

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