A supported ruthenium catalyst for 2,2-bipyridine and its preparation method, regeneration method and application

Abstract

This invention relates to the fields of heterogeneous catalytic materials and organic synthesis technology, and particularly to a supported ruthenium catalyst for 2,2-bipyridine, its preparation method, regeneration method, and applications. The preparation method provided by this invention is based on the principle of "metal-directed assembly," constructing a novel catalyst structure. This invention constructs a rigid "columnar" confined structure on the support surface, firmly anchoring the ruthenium active centers in a highly dispersed and spatially open manner, thereby preparing a highly efficient, stable, and regenerable supported ruthenium catalyst for 2,2-bipyridine. The supported ruthenium catalyst for 2,2-bipyridine prepared by this invention has a stable structure, highly dispersed and spatially open active centers, and simultaneously improves activity, selectivity, and stability in direct dehydrogenation coupling reactions. It exhibits high catalytic efficiency and can be economically and regenerated, effectively overcoming the fundamental defects of existing catalysts.

Description

Technical Field

[0001] This invention relates to the fields of heterogeneous catalytic materials and organic synthesis technology, and in particular to a supported ruthenium catalyst for 2,2-bipyridine, its preparation method, regeneration method and application. Background Technology

[0002] 2,2-Bipyridine, as one of the isomers of bipyridine, is a key intermediate in the preparation of herbicides (such as 1,1'-ethylidene-2,2-bipyridine dibromide, traded as diquat). Developing a high-yield, low-cost, safe, and low-pollution green synthesis method for 2,2-bipyridine not only has significant application prospects and market value, but also encourages enterprises to reduce pollution, rationally utilize resources, and promote cleaner production, resulting in significant economic, social, and environmental benefits.

[0003] Currently, the industrial synthesis of 2,2-bipyridine mainly relies on the Ullmann coupling reaction, which uses halogenated pyridines as raw materials and carries out the coupling reaction in the presence of a copper catalyst. However, this method has inherent drawbacks such as poor atom economy, the use of expensive halogenated precursors, and the generation of large amounts of halide pollution.

[0004] In contrast, the direct dehydrogenation coupling of pyridine, a widely available and inexpensive raw material, to synthesize 2,2'-bipyridine is a highly attractive, green, and atom-economical route. However, this method faces significant challenges in its direct dehydrogenation coupling reaction: the aromatic ring of pyridine is very stable, and the CH bond activation barrier is high. Therefore, the direct dehydrogenation coupling reaction must be carried out at high temperatures (typically >200°C) and is prone to side reactions such as over-dehydrogenation or polymerization, resulting in low selectivity for the target product. Therefore, the realization of this route is highly dependent on catalysts that possess high activity, high selectivity, and excellent stability.

[0005] Currently, homogeneous catalysts used for direct dehydrogenation coupling reactions (such as ruthenium complexes and iridium complexes) exhibit certain activity, but they mainly rely on physical adsorption or simple grafting to immobilize metal complexes on supports. This has the following fundamental drawbacks: the active centers are randomly distributed on the support surface and are prone to agglomeration, resulting in low density and accessibility of active sites. Summary of the Invention

[0006] In view of this, the present invention provides a supported ruthenium catalyst for 2,2-bipyridine, its preparation method, regeneration method and application. The supported ruthenium catalyst for 2,2-bipyridine prepared by the present invention has a high degree of dispersion of ruthenium active centers, open space, and high efficiency and stability.

[0007] This invention provides a method for preparing a supported ruthenium catalyst for 2,2-bipyridine, comprising the following steps: (1) The carrier is calcined to obtain a pretreated carrier; (2) The pretreated carrier is covalently grafted with a bissilane compound and a first organic solvent to obtain an intermediate compound; the intermediate compound includes a carrier and a bissilane compound bonded to silanol groups on the surface of the carrier. (3) The intermediate compound is mixed with a silane coupling agent with a terminally modified dipyridine group, ruthenium trichloride (RuCl3·xH2O) and a second organic solvent, and then subjected to metal-directed assembly, solid-liquid separation, washing, Soxhlet extraction and drying to obtain the active precursor. (4) The active precursor is reduced to obtain the supported ruthenium catalyst for 2,2-bipyridine.

[0008] Preferably, the carrier is silica; the silica is ordered mesoporous silica; and the specific surface area of ​​the carrier is greater than 500 m². 2 / g.

[0009] Preferably, the calcination is carried out in an air or oxygen atmosphere; the calcination includes sequentially performing heating calcination, isothermal calcination, and cooling; the heating rate of the heating calcination is 1~5℃ / min; the temperature of the isothermal calcination is 500~600℃, and the holding time is 4~6 hours; the cooling is natural cooling; the final temperature of the cooling is below 80℃.

[0010] Preferably, the bissilane compound is one or more of 1,4-bis(triethoxysilyl)benzene and bis(triethoxysilyl)ethane.

[0011] Preferably, the silane coupling agent with a terminal modified dipyridine group is (3-triethoxysilylpropyl)-2,2′-bipyridine; the molar ratio of ruthenium trichloride to the silane coupling agent with a terminal modified dipyridine group is 0.8~1.2:1.

[0012] Preferably, the process after drying and before reduction further includes performing a post-grafting metal exchange on the obtained product. The post-grafting metal exchange includes the following steps: mixing the active precursor, alcohol solvent, and cobalt salt to perform a post-grafting metal exchange reaction.

[0013] Preferably, the reduction is carried out in a reducing atmosphere; the reduction includes sequential heating reduction and isothermal reduction; the heating rate of the heating reduction is 2~5℃ / min; the temperature of the isothermal reduction is 250~350℃, and the holding time is 1~3 hours.

[0014] The present invention also provides a supported ruthenium catalyst for 2,2-bipyridine obtained by the preparation method described above.

[0015] The present invention also provides the application of the supported ruthenium catalyst described above for 2,2'-bipyridine in the preparation of 2,2'-bipyridine.

[0016] The present invention also provides a method for regenerating the supported ruthenium catalyst for 2,2-bipyridine as described above, comprising the following steps: (A) The deactivated supported ruthenium catalyst for 2,2-bipyridine was impregnated in acid to obtain a regenerated intermediate compound; (B) The regenerated intermediate compound is mixed with a silane coupling agent with a terminally modified dipyridine group, ruthenium trichloride (RuCl3·xH2O), and a second organic solvent for metal-directed assembly and reduction.

[0017] Preferably, the acid solution is an aqueous solution of an inorganic acid; the inorganic acid solution includes one or more of nitric acid and hydrochloric acid; and the concentration of the acid solution is 0.5~2 mol / L.

[0018] This invention provides a method for preparing a supported ruthenium catalyst for 2,2-bipyridine. The preparation method provided by this invention, based on the principle of "metal-directed assembly," constructs a novel catalyst structure. This invention constructs a rigid "columnar" confined structure on the support surface, firmly anchoring the ruthenium active centers in a highly dispersed and spatially open manner, thereby preparing a highly efficient, stable, and regenerable supported catalyst.

[0019] This invention also provides a supported ruthenium catalyst for 2,2-bipyridine prepared by the method described above. The supported ruthenium catalyst for 2,2-bipyridine prepared by this invention has a stable structure, highly dispersed and spatially open active centers, and simultaneously improves activity, selectivity, and stability (not easily deactivated at high temperatures) in direct dehydrogenation coupling reactions. It exhibits high catalytic efficiency and is economically renewable.

[0020] This invention also provides the application of the supported ruthenium catalyst for 2,2'-bipyridine described above in the preparation of 2,2'-bipyridine. The supported ruthenium catalyst for 2,2'-bipyridine provided by this invention can be used as a catalyst to prepare 2,2'-bipyridine, catalyzing the direct dehydrogenation coupling reaction of pyridine to synthesize 2,2'-bipyridine, exhibiting high catalytic efficiency, good selectivity, and stable catalytic activity.

[0021] This invention also provides a method for regenerating the supported ruthenium catalyst for 2,2-bipyridine as described above. The regeneration method provided by this invention is simple to operate, low in cost, and offers significant economic and social benefits.

[0022] Existing homogeneous catalysts for direct dehydrogenation coupling reactions suffer from the following drawbacks: 1) Under harsh high-temperature dehydrogenation reaction conditions, active centers are prone to migration, sintering, or loss from the support, resulting in rapid catalyst deactivation; 2) The deactivated catalyst structure is usually destroyed, making it difficult to restore activity through simple methods, leading to short catalyst lifetime and high cost. Compared to existing technologies, this invention achieves the following beneficial effects overall: 1) Targeted and Highly Efficient Catalysis: The supported ruthenium catalyst for 2,2'-bipyridine provided by this invention can specifically catalyze the direct dehydrogenation coupling reaction of pyridine. Its unique "columnar" structure fully exposes the active sites, greatly promoting the adsorption and activation of pyridine molecules. Under reaction conditions of 220~240℃, the pyridine conversion can reach 45~55%, and the selectivity for 2,2'-bipyridine is as high as 90~96%, which is significantly better than traditional supported catalysts.

[0023] 2) Excellent thermal stability and cycle performance: The rigid covalently linked "columnar" structure is extremely stable under high-temperature reaction conditions, effectively preventing the migration and sintering of ruthenium active centers. The supported ruthenium catalyst for 2,2-bipyridine provided by this invention exhibits less than 15% activity decay after five consecutive reaction cycles.

[0024] 3) Revolutionary Renewability (Core Advantage): When the supported ruthenium catalyst for 2,2-bipyridine provided by this invention slowly deactivates due to long-term use, the regeneration method provided by this invention can achieve "in-situ renewal" of the active center without completely destroying the macroscopic structure of the support and the columnar organic framework. The performance of the regenerated supported ruthenium catalyst for 2,2-bipyridine can be restored to 90-95% of its initial level, and the regeneration process can be repeated more than once, fundamentally breaking through the bottleneck of the existing catalyst's "single-use" limitation, and has extremely high economic value.

[0025] 4) Clear structure-activity relationship of active sites: The "metal-guided assembly" method ensures the structural uniformity and controllability of active sites, providing an ideal model system for in-depth study of reaction catalysis mechanism and further improvement of catalyst performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of this invention, the accompanying drawings used in the embodiments of this invention or in the prior art are briefly described below. For those skilled in the art, other drawings can be derived from the following drawings without creative effort, and all such drawings are within the protection scope of this invention.

[0027] Figure 1 The image shows a scanning electron microscope (SEM) image of the supported ruthenium catalyst for 2,2-bipyridine prepared according to the present invention. Detailed Implementation

[0028] This invention provides a method for preparing a supported ruthenium catalyst for 2,2-bipyridine, comprising the following steps: (1) The carrier is calcined to obtain a pretreated carrier; (2) The pretreated carrier is covalently grafted with a bissilane compound and a first organic solvent to obtain an intermediate compound; the intermediate compound includes a carrier and a bissilane compound bonded to silanol groups on the surface of the carrier. (3) The intermediate compound is mixed with a silane coupling agent with a terminally modified dipyridine group, ruthenium trichloride (RuCl3·xH2O), and a second organic solvent for metal-directed assembly to obtain an active precursor; (4) The active precursor is reduced to obtain the supported ruthenium catalyst for 2,2-bipyridine.

[0029] This invention involves calcining a carrier to obtain a pretreated carrier. In this invention, the carrier is preferably silica; the silica is preferably ordered mesoporous silica, specifically ordered mesoporous silica SBA-15; the specific surface area of ​​the carrier is preferably greater than 500 m². 2 / g, more preferably 500~700m 2 / g. The carrier used in this invention has one-dimensional straight channels and high thermal stability.

[0030] In this invention, the calcination equipment preferably includes a muffle furnace; the calcination is preferably carried out in an air or oxygen atmosphere; the calcination preferably includes sequentially performing heating calcination, isothermal calcination, and cooling.

[0031] In this invention, the heating rate of the calcination is preferably 1~5℃ / min, more preferably 2~3℃ / min. By employing the above heating rate, this invention can gently decompose and remove the template agent within the carrier pores, effectively avoiding violent outgassing and structural collapse caused by rapid thermal decomposition, thereby maximizing the preservation of the carrier's high specific surface area and highly ordered mesoporous structure.

[0032] In this invention, the temperature of the constant-temperature calcination is preferably 500~600℃, more preferably 550℃, and the holding time is preferably 4~6 hours, more preferably 5 hours.

[0033] In this invention, the cooling is preferably natural cooling; the final temperature of the cooling is preferably below 80°C, more preferably 20~60°C.

[0034] Through the above-mentioned calcination, the present invention can strengthen the silicon skeleton of the carrier and generate surface silanol groups (-SiOH) with moderate density and uniform distribution, which lays an indispensable structural foundation for the uniform and high-density covalent grafting of "molecular bridges" in subsequent steps.

[0035] After obtaining the pretreated carrier, the present invention covalently grafts the pretreated carrier with a bissilane compound and a first organic solvent (denoted as the first mixture) to obtain an intermediate compound. In the present invention, the bissilane compound is preferably one or more of 1,4-bis(triethoxysilyl)benzene and bis(triethoxysilyl)ethane.

[0036] In this invention, the mass ratio of the pretreatment carrier to the bissilane compound is preferably 1:1.3 to 2.5, more preferably 1:1.5 to 2.2, and even more preferably 1:2.

[0037] In this invention, the first organic solvent preferably includes one or more of toluene and xylene; the toluene is preferably anhydrous toluene.

[0038] In this invention, the mass ratio of the pretreatment carrier to the first organic solvent is preferably 1:60~150, more preferably 1:80~145, and even more preferably 1:144.

[0039] In this invention, the first mixing preferably includes the following steps: adding the pretreated carrier to a first organic solvent and stirring magnetically to obtain a premixed solution, and then adding 1,4-bis(triethoxysilyl)benzene dropwise to the premixed solution.

[0040] In this invention, the preferred rate of adding the drop is 1 drop every 2 to 4 seconds.

[0041] In this invention, the covalent grafting is preferably performed in a protective atmosphere; the protective atmosphere is preferably an inert atmosphere or nitrogen; the covalent grafting is preferably performed under reflux conditions; the covalent grafting time is preferably 8-16 hours, more preferably 10-14 hours, and even more preferably 12 hours. This invention, through covalent grafting, bonds one end of a bissilane compound to the silanol groups on the surface of a carrier, forming a first layer of "bridge piers".

[0042] In this invention, the covalent grafting process preferably further includes sequentially performing solid-liquid separation, washing, and drying of the resulting product; the solid-liquid separation is preferably vacuum filtration; the gauge pressure of the vacuum filtration is preferably -0.1 to -0.08 MPa; the washing preferably includes sequential washing with toluene and acetone; the number of washing cycles is preferably 3 to 5 times, more preferably 4 times. This invention effectively removes physically adsorbed raw materials and byproducts through washing.

[0043] In this invention, the drying temperature is preferably 60~90℃, more preferably 70~80℃, the vacuum degree is preferably below -0.09MPa, and the heat preservation time is preferably 4~8 hours, more preferably 6 hours.

[0044] After obtaining the intermediate compound, the present invention mixes the intermediate compound with a silane coupling agent with a terminally modified bipyridine group, ruthenium trichloride, and a second organic solvent for metal-directed assembly to obtain an active precursor.

[0045] In this invention, the silane coupling agent with a terminal modified dipyridine group is preferably (3-triethoxysilylpropyl)-2,2′-bipyridine; the (3-triethoxysilylpropyl)-2,2′-bipyridine is preferably a commercially available product or prepared in-house; the in-house preparation preferably includes the following steps: under an inert atmosphere, reacting 2,2′-bipyridine with sodium hydride in tetrahydrofuran to generate an anion, then reacting it with (3-chloropropyl)triethoxysilane, and then purifying it.

[0046] In this invention, the mass ratio of the intermediate compound to the silane coupling agent with a terminal modified dipyridine group is preferably 1:1.2 to 2, more preferably 1:1.4 to 1.8, and even more preferably 1:1.6.

[0047] In this invention, the molar ratio of ruthenium trichloride to the silane coupling agent with a terminal bispyridine group is preferably 0.8 to 1.2:1, more preferably 0.9 to 1.1:1, and even more preferably 1:1.

[0048] In this invention, the second organic solvent preferably includes one or more of N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP).

[0049] In this invention, the mass ratio of the intermediate compound to the second organic solvent is preferably 1:40 to 80, more preferably 1:50 to 70, and even more preferably 1:68.

[0050] In this invention, the metal guiding assembly is preferably carried out under a protective atmosphere and stirring conditions; the protective atmosphere is preferably an inert atmosphere or nitrogen; the temperature of the metal guiding assembly is preferably 90~100℃, more preferably 93~96℃, and the holding time is preferably 30~48 hours, more preferably 35~42 hours, and even more preferably 37 hours.

[0051] In this invention, the metal-guided assembly preferably further includes sequentially performing solid-liquid separation, washing, purification, and drying on the resulting product.

[0052] In this invention, the solid-liquid separation is preferably filtration; the washing preferably includes sequential amide washing and alcohol washing; the reagent used for amide washing is preferably N,N-dimethylformamide (DMF); the reagent used for alcohol washing is preferably methanol; the number of washings is preferably 3 to 5 times, more preferably 4 times; the purification is preferably Soxhlet extraction; the extractant used for Soxhlet extraction is preferably a low-boiling-point alcohol; the low-boiling-point alcohol preferably includes one or more of methanol and ethanol; the Soxhlet extraction preferably includes the following steps: placing the washed solid in a Soxhlet extractor for extraction; the extraction time is preferably 18 to 36 hours, more preferably 24 hours; the drying temperature is preferably 60 to 80°C, the vacuum degree is preferably below -0.09 MPa, and the heat preservation time is preferably 8 to 12 hours, more preferably 10 hours.

[0053] In this invention, the process after drying and before reduction preferably includes post-grafting metal exchange of the obtained product.

[0054] In this invention, the post-grafting metal exchange preferably includes the following steps: mixing an active precursor, an alcohol solvent, and a cobalt salt to carry out a post-grafting metal exchange reaction.

[0055] In this invention, the alcohol solvent is preferably ethanol; the ethanol is preferably anhydrous ethanol.

[0056] In this invention, the mass ratio of the active precursor to the alcohol solvent is preferably 1:40~60, more preferably 1:48~50.

[0057] In this invention, the cobalt salt is preferably cobalt nitrate; the cobalt nitrate is preferably cobalt nitrate hexahydrate (Co(NO3)2·6H2O).

[0058] In this invention, the mass ratio of the active precursor to the cobalt salt is preferably 1:0.01 to 0.1, more preferably 1:0.05.

[0059] In this invention, the temperature of the post-grafting metal exchange reaction is preferably 55~65℃, more preferably 60℃, and the holding time is preferably 11~13 hours, more preferably 12 hours; the post-grafting metal exchange reaction is preferably carried out under stirring conditions; the post-grafting metal exchange reaction is preferably carried out in a protective atmosphere; the protective atmosphere is preferably nitrogen.

[0060] In this invention, the post-grafting metal exchange reaction preferably further includes sequentially subjecting the obtained product to solid-liquid separation, alcohol washing, and drying; the solid-liquid separation is preferably filtration; the alcohol used for alcohol washing is preferably ethanol; the drying temperature is preferably 55~65℃, more preferably 60℃, the vacuum degree is preferably below -0.095MPa (gauge pressure), and the heat preservation time is preferably more than 6 hours.

[0061] After obtaining the active precursor, the present invention reduces the active precursor to obtain the supported ruthenium catalyst for 2,2-bipyridine. In the present invention, the reduction apparatus preferably includes a tubular furnace; the reduction is preferably carried out in a reducing atmosphere; the reducing atmosphere is preferably a mixture of hydrogen and a protective gas; the protective gas is preferably an inert gas or nitrogen; the inert gas is preferably argon; the volume fraction of hydrogen in the mixture is preferably 5-10%, more preferably 7%.

[0062] In this invention, the reduction preferably includes sequential heating reduction and isothermal reduction; the heating rate of the heating reduction is preferably 2~5℃ / min, more preferably 3~4℃ / min; the temperature of the isothermal reduction is preferably 250~350℃, more preferably 300℃, and the holding time is preferably 1~3 hours, more preferably 2 hours. This invention, through reduction, transforms Ru... 3+ It is reduced in situ to a highly active, low-valence ruthenium species.

[0063] This invention utilizes covalent grafting to construct rigid "molecular bridge piers," followed by Ru... 3+ Guided synchronous assembly of active layers yields pre-assembled columnar active precursors, followed by reduction and activation of active centers to construct Ru. 3+ Ion-guided columnar pre-assembled layer.

[0064] The present invention also provides a supported ruthenium catalyst for 2,2-bipyridine obtained by the preparation method described above.

[0065] The supported ruthenium catalyst for 2,2-bipyridine prepared in this invention is a columnar supported ruthenium catalyst. The ruthenium active center is chemically bonded and anchored to the surface of the support and the inner wall of the pores in a vertical columnar morphology through a "ruthenium-bipyridine" (Ru-Bipy) complex unit via rigid piers derived from bissilane compounds, forming a spatially open and highly dispersed array of active sites.

[0066] In this invention, the structure of the supported ruthenium catalyst for 2,2-bipyridine is shown in Formula I or Formula II: Formula I: SBA-O-Si-(C6H4)-Si-O-(CH2)3-Bipy-Ru; Formula II: SBA-O-Si-(CH2)2-Si-O-(CH2)3-Bipy-Ru; In this context, SBA represents the support, and Ru-Bipy represents the ruthenium-bipyridine complex unit.

[0067] The present invention also provides the application of the supported ruthenium catalyst described above for 2,2'-bipyridine in the preparation of 2,2'-bipyridine.

[0068] The supported ruthenium catalyst for 2,2'-bipyridine provided by this invention can be used as a catalyst to prepare 2,2'-bipyridine, catalyzing the direct dehydrogenation coupling reaction of pyridine to synthesize 2,2'-bipyridine. It has high catalytic efficiency, good selectivity and stable catalytic effect.

[0069] The supported ruthenium catalyst for 2,2-bipyridine provided by this invention can be recycled when used in the direct dehydrogenation coupling reaction of pyridine. When the conversion rate of pyridine drops to 75-85% of the initial value after 4-6 consecutive cycles, it indicates that the supported ruthenium catalyst for 2,2-bipyridine has been deactivated to the point where it needs to be regenerated.

[0070] The present invention also provides a method for regenerating the supported ruthenium catalyst for 2,2-bipyridine as described above, comprising the following steps: (A) The deactivated supported ruthenium catalyst for 2,2-bipyridine was impregnated in acid to obtain a regenerated intermediate compound; (B) The regenerated intermediate compound is mixed with a silane coupling agent with a terminally modified dipyridine group, ruthenium trichloride (RuCl3·xH2O), and a second organic solvent for metal-directed assembly and reduction.

[0071] This invention involves impregnating a deactivated supported ruthenium catalyst for 2,2-bipyridine in an acidic solution to obtain a regenerated intermediate compound. In this invention, the acidic solution is preferably an aqueous solution of an inorganic acid; the inorganic acid in the aqueous solution preferably includes one or more of nitric acid and hydrochloric acid.

[0072] In this invention, the concentration of the acid solution is preferably 0.5~2 mol / L, more preferably 1~1.5 mol / L.

[0073] In this invention, the impregnation temperature is preferably room temperature (20-38 degrees Celsius), and the impregnation time is preferably 4-8 hours, more preferably 5-7 hours; the impregnation is preferably carried out under stirring conditions. This invention removes inactivated ruthenium species through impregnation, while maintaining the integrity of its columnar organic framework.

[0074] In this invention, the impregnation process preferably further includes sequentially filtering, washing with water, and drying the resulting product.

[0075] After obtaining the regenerated intermediate compound, the present invention mixes the regenerated intermediate compound with a silane coupling agent with a terminally modified bipyridine group, ruthenium trichloride, and a second organic solvent for metal-directed assembly and reduction.

[0076] In this invention, the steps and parameters of metal-directed assembly and reduction are preferably the same as those of the preparation method of the supported ruthenium catalyst for 2,2-bipyridine described above, and will not be repeated here.

[0077] The regeneration method provided by this invention can restore the catalytic activity to more than 90% of that of a fresh (before first use) supported ruthenium catalyst for 2,2-bipyridine.

[0078] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments.

[0079] In the specific embodiments of the present invention, unless otherwise specified, all raw materials and reagents used are commercially available products.

[0080] Example 1: This embodiment prepared a supported ruthenium catalyst for 2,2-bipyridine (denoted as Ru-Bipy-Column@SBA-15): 1) Pretreatment of the carrier: Weigh 2.0 g of ordered mesoporous silica SBA-15 and place it in a quartz boat, then place it in a muffle furnace. Under static air, heat to 550 °C at a programmed heating rate of 2 °C / min, and calcine at this temperature for 5 hours. Then, turn off the heating and allow the muffle furnace to cool naturally to below 80 °C. Remove the calcined carrier and place it in a desiccator for later use. This step thoroughly and gently removes the template agent and forms a surface silanol group with moderate density and uniform distribution.

[0081] 2) Construct Ru 3+ Ion-guided columnar pre-assembled layer: 2.1) Construction of rigid "molecular bridges": 1.5 g of pretreated SBA-15 was added to a 250 mL three-necked flask containing 100 mL of anhydrous toluene. Dry nitrogen gas was introduced for protection, and the mixture was magnetically stirred. 2.0 mL of 1,4-bis(triethoxysilyl)benzene was slowly added dropwise (1 drop every 2-4 seconds) using a constant-pressure dropping funnel. The mixture was heated to 110 °C and refluxed for 12 hours. After the reaction was complete, the mixture was cooled to room temperature and filtered under reduced pressure (gauge pressure controlled at -0.1 to -0.08 MPa) using a G4 sintered glass funnel. The resulting solid was washed thoroughly with anhydrous toluene (3 × 20 mL) and acetone (3 × 20 mL) to completely remove physically adsorbed silane reagents and their hydrolysis byproducts. The solid was transferred to a vacuum drying oven and dried at 80 °C and a vacuum below -0.095 MPa for 6 hours to obtain the intermediate SBA-Ph. Thermogravimetric analysis showed that the organic layer gained 9.5 wt%.

[0082] 2.2) Ru 3+Guided simultaneous assembly of the active layer: All obtained SBA-Ph was transferred to a 250 mL three-necked flask containing 80 mL of anhydrous N,N-dimethylformamide (DMF). Under nitrogen protection and stirring, 2.2 g of (3-triethoxysilylpropyl)-2,2′-bipyridine (prepared in-house, preparation method described below) and 0.12 g of RuCl3·3H2O were added simultaneously. The mixture was heated to 95 °C and reacted for 36 hours. After the reaction was complete, the mixture was cooled and filtered. The solid was washed successively with hot DMF (50 °C, 3 × 15 mL) and methanol (3 × 20 mL). Subsequently, the solid was placed in a Soxhlet extractor (250 mL, with matching extraction sleeve) and extracted continuously for 24 hours using 200 mL of boiling methanol as the extractant. After extraction, the solid was dried at 70 °C and a vacuum degree below -0.095 MPa for 10 hours to obtain a dark brown active precursor.

[0083] 3) Reduction and activation of active centers: The obtained active precursor was uniformly spread in a quartz boat and placed in the isothermal zone of a tube furnace. Under a 10% (v / v) H₂ / Ar (volume ratio) gas flow at a rate of 5 °C / min, the temperature was programmed to rise to 300 °C and isothermally reduced for 2 hours. After reduction, the catalyst was allowed to cool naturally to room temperature under an H₂ / Ar atmosphere, then purged with pure argon for 10 minutes to obtain a supported ruthenium catalyst for 2,2-bipyridine, denoted as Cat-1. Inductively coupled plasma atomic emission spectrometry (ICP-AES) determined its ruthenium (Ru) loading to be 0.38 mmol / g.

[0084] 4) Catalytic performance testing (for the direct synthesis of 2,2′-bipyridine from pyridine): In a 50 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), 10 g of pyridine (0.13 mol) and 50 mg of Cat-1 catalyst were added. After purging the air three times with nitrogen, a nitrogen atmosphere of 1.0 MPa was introduced as an inert atmosphere. The high-pressure reactor was placed in a magnetically stirred heater and heated to 220 °C, and the reaction was continuously stirred (600 rpm) at this temperature for 24 hours. After the reaction was completed, the high-pressure reactor was cooled to room temperature, the reaction mixture was removed, and the supported ruthenium catalyst for 2,2-bipyridine was recovered by centrifugation.

[0085] The clarified liquid was quantitatively analyzed using a gas chromatograph equipped with an FID detector (internal standard method), and the main product was confirmed as 2,2′-bipyridine by GC-MS. The test results showed that the conversion rate of pyridine was 51.2%, the selectivity of 2,2′-bipyridine was 94.7%, and the yield was 48.5%.

[0086] In this embodiment, the preparation steps of the silane coupling agent (3-triethoxysilylpropyl)-2,2′-bipyridine are as follows: Under nitrogen protection, 2,2′-bipyridine (3.12 g, 20.0 mmol) was dissolved in 50 mL of anhydrous tetrahydrofuran (THF) in a dry 250 mL three-necked flask. Under ice-water bath cooling, 60% sodium hydride (NaH, 0.88 g, 22.0 mmol) was added in two batches, and the mixture was stirred at room temperature until no bubbles were generated. The reaction solution was cooled again to 0 °C, and (3-chloropropyl)triethoxysilane (4.97 g, 21.0 mmol) was slowly added dropwise (1 drop every 2-4 seconds). After the addition was complete, the ice bath was removed, and the mixture was stirred at room temperature for 12 hours. After the reaction was complete, methanol was added to quench excess NaH until no obvious bubbles were generated, which was the endpoint. Under water bath conditions of 30–40 °C and a vacuum of -0.095–-0.08 MPa (gauge pressure), the product was rotary evaporated under reduced pressure until no fraction was effluent to remove THF. The residue was extracted with dichloromethane, and the organic phase was washed with water and saturated brine, then dried over anhydrous sodium sulfate. After filtration, the solvent was removed under reduced pressure to -0.1–-0.08 MPa (gauge pressure) to obtain the crude product. Purification was achieved by silica gel column chromatography (eluent: ethyl acetate / petroleum ether = 1:4) to give a pale yellow oily liquid product, (3-triethoxysilylpropyl)-2,2′-bipyridine, with a mass of 5.2 g and a yield of 78%.

[0087] The supported ruthenium catalyst for 2,2-bipyridine prepared in this example was characterized using scanning electron microscopy, and the results are as follows: Figure 1 As shown. According to Figure 1 As can be seen from the morphology preservation: the supported ruthenium catalyst for 2,2-bipyridine completely retained the original rod-shaped morphology of SBA-15, with uniform particle size, indicating that the pretreatment and subsequent covalent grafting process did not damage the macroscopic structure of the support. Regarding the absence of surface agglomeration: obvious ruthenium metal particle agglomerates were observed on the surface of the supported ruthenium catalyst for 2,2-bipyridine, indicating that the active centers prepared by the "metal-directed synchronous assembly" method exist in the form of particle agglomerates.

[0088] Example 2: This embodiment prepared a supported ruthenium catalyst for 2,2-bipyridine based on "pier" structure regulation: 1) Pretreatment of the carrier: Same as in Example 1.

[0089] 2) Construction of flexible "molecular bridges": Same as step 2.1 in Example 1, except that 1,4-bis(triethoxysilyl)benzene is replaced with 2.2 mL of bis(triethoxysilyl)ethane. The intermediate SBA-BTESE is obtained.

[0090] 3) Ru 3+Guided synchronous assembly of active layer: Same as step 2.2 in Example 1.

[0091] 4) Reduction and activation: Same as step 3 in Example 1, to obtain a supported ruthenium catalyst for 2,2-bipyridine, denoted as Cat-A.

[0092] 5) Performance testing: Under standard reaction conditions (same as Example 1), Cat-A achieved a pyridine conversion of 48.1%, a selectivity of 95.5%, and a yield of 45.9%. Its selectivity is slightly higher than that of Cat-1.

[0093] Example 3: This embodiment prepares a supported ruthenium catalyst for 2,2-bipyridine based on "post-grafting metal exchange": 1) Preparation of active precursor: Same as steps 1 and 2 in Example 1, to prepare unreduced precursor containing Ru 3+ Columnar active precursors.

[0094] 2) Post-grafting metal exchange treatment: Take 1.0 g of the above active precursor and disperse it in 50 mL of anhydrous ethanol. Add 0.05 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and stir the reaction at 60 °C for 12 hours under nitrogen protection. After the reaction, filter, wash thoroughly with ethanol, and dry under vacuum at 60 °C and below -0.095 MPa (gauge pressure) for 6 hours.

[0095] 3) Reduction and activation: Same as step 3 in Example 1, to obtain a supported ruthenium catalyst for 2,2-bipyridine, denoted as Cat-B.

[0096] 4) Performance test: Under standard reaction conditions, the pyridine conversion of Cat-B was significantly improved to 56.8%, the selectivity was 93.0%, and the yield was 52.8%.

[0097] Example 4: This embodiment describes the cycling, deactivation, and regeneration of a supported ruthenium catalyst for 2,2-bipyridine: 1) Cycling and Deactivation: The Cat-1 catalyst from Example 1 was recovered, washed three times with ethanol, and then directly used in the next identical reaction. After five cycles, the pyridine conversion rates were 51.2%, 49.8%, 47.5%, 44.1%, and 40.3%, respectively. After the fifth cycle, the activity decreased to 78.7% of the initial value, at which point it was considered a "deactivated catalyst".

[0098] 2) Regeneration: Take the above-mentioned deactivated catalyst and immerse it in 20 mL of 1 mol / L nitric acid solution, stirring at room temperature for 6 hours. Filter, wash with water until neutral, and dry. Subsequently, the obtained solid is completely reassembled and reduced according to steps 2.2 and 3 of Example 1 to obtain the regenerated catalyst, denoted as Cat-1R.

[0099] 3) Performance after regeneration: The pyridine conversion rate of Cat-1R was 49.5%, the yield was 47.0%, and the activity was restored to 96.7% of that of the fresh Cat-1 catalyst.

[0100] Comparative Example 1: This comparative example uses a conventional stepwise impregnation method to prepare a supported ruthenium catalyst for 2,2-bipyridine: 1.5 g of pretreated SBA-15 and 2.2 g of (3-triethoxysilylpropyl)-2,2′-bipyridine (same as in Example 1) were refluxed in 100 mL of anhydrous toluene at 110 °C for 24 hours to obtain the ligand grafting material. The obtained ligand grafting material was impregnated with RuCl3 ethanol solution (containing 0.12 g of RuCl3·3H2O) at room temperature for 12 hours, filtered, dried, and reduced under the same conditions as in Example 1 to obtain a supported ruthenium catalyst for 2,2-bipyridine, denoted as Ref-1 (Ru loading of 0.40 mmol / g). Its initial pyridine conversion was 35.6%, the yield was 31.4%, and the conversion decreased to 18.2% after three uses.

[0101] Comparative Example 2: This comparative example prepared a supported ruthenium catalyst for 2,2-bipyridine without Soxhlet extraction and purification: The preparation method for this comparative example is the same as that in Example 1, except that after the reaction in step 2.2, only conventional filtration and washing (washing three times each with DMF and methanol) were performed instead of Soxhlet extraction. A supported ruthenium catalyst for 2,2-bipyridine was obtained, denoted as Ref-2. Its initial conversion rate was 44.5%, and its cycling stability was significantly worse than that of Cat-1.

[0102] As can be seen from the above embodiments, the "metal-guided assembly" preparation method provided by this invention is key to preparing high-performance pyridine dehydrogenation coupling catalysts. The supported ruthenium catalyst (Cat-1) for 2,2-bipyridine prepared by this invention is significantly superior to the conventional method (Ref-1) in terms of activity, selectivity, and regenerability. Furthermore, the preparation method provided by this invention has high tunability; by changing the bridging structure (Cat-A) or introducing a co-catalyst metal (Cat-B), the performance of the supported ruthenium catalyst for 2,2-bipyridine can be further improved. Moreover, a rigorous purification process (Soxhlet extraction) is a necessary step to ensure the high performance of the supported ruthenium catalyst for 2,2-bipyridine.

[0103] The embodiments of the present invention have been described above; however, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the above embodiments of the present invention without inventive effort are within the protection scope of the present invention.

Claims

1. A method for preparing a supported ruthenium catalyst for 2,2-bipyridine, characterized in that, Includes the following steps: (1) The carrier is calcined to obtain a pretreated carrier; (2) The pretreated carrier is covalently grafted with a bissilane compound and a first organic solvent to obtain an intermediate compound; The intermediate compound includes a support and a bissilane compound bonded to silanol groups on the surface of the support. (3) The intermediate compound is mixed with a silane coupling agent with a terminally modified bipyridine group, ruthenium trichloride and a second organic solvent, and then subjected to metal-directed assembly, solid-liquid separation, washing, Soxhlet extraction and drying to obtain an active precursor; (4) The active precursor is reduced to obtain the supported ruthenium catalyst for 2,2-bipyridine.

2. The preparation method according to claim 1, characterized in that, The carrier is silicon dioxide; The silicon dioxide is ordered mesoporous silicon dioxide; The specific surface area of ​​the carrier is greater than 500 m². 2 / g.

3. The preparation method according to claim 1, characterized in that, The calcination is carried out in an air or oxygen atmosphere; The calcination process includes sequentially performing calcination by heating, calcination at a constant temperature, and calcination by cooling. The heating rate for the calcination is 1~5℃ / min; The constant temperature calcination temperature is 500~600℃, and the holding time is 4~6 hours; The cooling is natural cooling; The final temperature of the cooling process is below 80°C.

4. The preparation method according to claim 1, characterized in that, The bissilane compound is one or more of 1,4-bis(triethoxysilyl)benzene and bis(triethoxysilyl)ethane.

5. The preparation method according to claim 1, characterized in that, The silane coupling agent with a terminal modified with a bipyridine group is (3-triethoxysilylpropyl)-2,2′-bipyridine; The molar ratio of ruthenium trichloride to the silane coupling agent with a terminal bispyridine group is 0.8~1.2:

1.

6. The preparation method according to claim 1, characterized in that, The reduction is carried out in a reducing atmosphere; The reduction includes sequentially performed heating reduction and isothermal reduction; The heating rate for the reduction is 2~5℃ / min; The isothermal reduction temperature is 250~350℃, and the holding time is 1~3 hours.

7. The preparation method according to claim 1, characterized in that, The process after drying and before reduction also includes post-grafting metal exchange of the obtained product. The post-grafting metal exchange includes the following steps: mixing the active precursor, alcohol solvent and cobalt salt to carry out the post-grafting metal exchange reaction.

8. The supported ruthenium catalyst for 2,2-bipyridine obtained by the preparation method according to any one of claims 1 to 7.

9. The use of the supported ruthenium catalyst for 2,2'-bipyridine as described in claim 8 in the preparation of 2,2'-bipyridine.

10. The method for regenerating the supported ruthenium catalyst for 2,2-bipyridine according to claim 8, characterized in that, Includes the following steps: (A) The deactivated supported ruthenium catalyst for 2,2-bipyridine was impregnated in acid to obtain a regenerated intermediate compound; (B) The regenerated intermediate compound is mixed with a silane coupling agent with a terminally modified bipyridine group, ruthenium trichloride, and a second organic solvent, and then reduced after metal-directed assembly.

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