Composite catalyst and application method thereof in synthesis of tetramethylpiperidinol

Abstract

The invention discloses a composite catalyst and an application method thereof in synthesis of tetramethylpiperidinol.The composite catalyst comprises fluorine-modified titanium dioxide, a core-shell carrier with silicon dioxide as a core and aluminum oxide as a shell and monatomic ruthenium, the fluorine-modified titanium dioxide is loaded on the core-shell carrier, and the monatomic ruthenium is loaded on the core-shell carrier; monatomic ruthenium is synergistically anchored with aluminum oxide shell amino through a titanium-fluorine bond; the proportion of oxygen vacancies in the fluorine-modified titanium dioxide is 25%; the particle size of a silicon dioxide core of the core-shell carrier is 40-60 nanometers, the thickness of an aluminum oxide shell layer is 8-12 nanometers, and the core-shell carrier contains 6-8 nanometer mesopores; and the particle size of monatomic ruthenium is less than 0.8 nm.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and more specifically, relates to a composite catalyst and an application method thereof in the synthesis of tetramethylpiperidinol. Background Art

[0002] Tetramethylpiperidinol is the core intermediate of hindered amine light stabilizers, and the key to its synthesis lies in the catalytic hydrogenation reaction of tetramethylpiperidone. Currently, industrial catalysts generally adopt traditional supported metal systems, such as palladium / carbon or nickel-based catalysts, but there are three core problems: First, the active sites are inefficiently coordinated. Existing catalysts rely on metal nanoparticles, and the metal-support interaction is weak. For catalysts with silica as the support, due to the disordered distribution of surface hydroxyl groups, metal particles agglomerate, resulting in insufficient exposure of active sites. Tetramethylpiperidinol requires active centers with specific steric hindrance, but the nanoparticles of traditional catalysts cannot precisely match its molecular size, resulting in an adsorption-activation efficiency of less than 60%. Second, the mass transfer resistance is mismatched with the structure. The molecular diameter of tetramethylpiperidinol is about 0.65 nanometers, while the conventional alumina support has insufficient mesopore proportion. Third, the regulation of oxygen vacancies fails. Although oxygen vacancies are introduced in titanium dioxide-based catalysts, the fluorine modification has poor stability. The fluorine-titanium bonds formed by the traditional hydrofluoric acid treatment method are easily hydrolyzed, resulting in an oxygen vacancy loss rate of more than 40% during the reaction. The hydrogenation of tetramethylpiperidinol requires oxygen vacancies to synergistically activate the carbonyl group, and the loss of vacancies directly leads to a sharp drop in the conversion rate from 82% to 55%.

[0003] In view of this, overcoming the technical defects of the above-mentioned existing technologies is an urgent problem to be solved in this technical field. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement requirements of the existing technology, the present invention provides a composite catalyst and an application method thereof in the synthesis of tetramethylpiperidinol, aiming to solve problems such as agglomeration of active sites, unstable fluorine modification, insufficient carrier binding force, and low mass transfer efficiency of existing catalysts, and improve the conversion rate of tetramethylpiperidone in the synthesis reaction of tetramethylpiperidinol.

[0005] To achieve the above object, according to one aspect of the present invention, a composite catalyst is provided. The composite catalyst includes fluorine-modified titanium dioxide, a core-shell carrier with silica as the core and alumina as the shell, and single-atom ruthenium, wherein:

[0006] The fluorine-modified titanium dioxide is loaded on the core-shell carrier, and the single-atom ruthenium is co-anchored through titanium-fluorine bonds and amino groups on the alumina shell;

[0007] The proportion of oxygen vacancies in the fluorine-modified titanium dioxide is 25%;

[0008] The silica core of the core-shell support has a particle size of 40-60 nanometers, the alumina shell layer has a thickness of 8-12 nanometers, and contains mesopores with a size of 6-8 nanometers;

[0009] The particle size of the single-atom ruthenium is less than 0.8 nanometers.

[0010] Preferably, the fluorine-titanium atomic ratio of the fluorine-modified titanium dioxide is 0.01-0.04.

[0011] Preferably, the alumina shell layer and the silica core are bonded by aluminum-oxygen-silicon bonds, and the surface of the alumina shell layer is grafted with amino groups; the proportion of the mesoporous structure in the core-shell support is greater than or equal to 80%.

[0012] Preferably, the preparation method of the composite catalyst includes the following steps:

[0013] Tetrabutyl titanate is dropped into absolute ethanol for hydrolysis at a hydrolysis temperature of 25-60 °C, and then an ammonium fluoride solution with a concentration of 0.08-0.12 mol / L is added. After hydrothermal reaction at 180 °C for 12 hours, a fluorine-modified titanium dioxide precursor is formed, and then calcined at 400 °C for 4 hours to form fluorine-modified titanium dioxide with a surface fluorine-rich layer and oxygen vacancies;

[0014] Silica microspheres with a particle size of 40-60 nanometers are selected and treated with a dopamine solution with a concentration of 2-3 g / L and a pH of 8.5 for 12 hours. Then, when depositing alumina, an aluminum nitrate solution with a concentration of 0.5-0.75 mol / L and a pH of 8-9 is added, and at the same time, an amino silane with a volume percentage of 1-2% is added synchronously. After calcination at 500 °C, a core-shell support with an amino-functionalized shell layer and an alumina shell layer thickness of 8-12 nanometers is formed;

[0015] Using atomic layer deposition technology, ruthenium acetylacetonate is used as a precursor and cycled 5 times at 200 °C. Each cycle includes a precursor pulse of 0.1 second and a nitrogen purge of 10 seconds. Single-atom ruthenium is selectively loaded on the surface of the fluorine-modified titanium dioxide, and after hydrogen reduction at 250 °C for 3 hours, a stable coordination structure is formed.

[0016] Preferably, the concentration of the ruthenium acetylacetonate precursor in the carrier gas is 0.05-0.15 mol / m 3 .

[0017] Preferably, during the hydrogen reduction process, the purity of hydrogen is not less than 99.9%, and the oxygen content in hydrogen is not higher than 1 ppm.

[0018] Preferably, in the hydrothermal reaction, fluoride ions are coordinated with the surface hydroxyl groups of titanium dioxide in a ratio of 1:1. This coordination method enables fluoride ions to be stably bound to the surface of titanium dioxide, improving the stability of fluorine modification.

[0019] Preferably, the hydrolysis time is 6 hours and the concentration of aminosilane is 1.5 vol%, and the amino content of the alumina shell layer is accurately controlled at 0.8 ± 0.1 mmol / g.

[0020] Preferably, the reaction is carried out in a fixed-bed reactor, the reaction temperature is 110 °C, the pressure is 1.5 MPa, the molar ratio of hydrogen to tetramethylpiperidone is 5:1, and tetramethylpiperidone is fed as an ethanol solution with a mass fraction of 20%.

[0021] Preferably, the fluorine-titanium atomic ratio of the catalyst is 0.02 - 0.03, the amino content of the alumina shell layer is 0.8 - 0.9 mmol / g, and the diffusion coefficient of tetramethylpiperidone in the mesopores of the catalyst is 0.12 - 0.15 cm 2 / s.

[0022] As a further improvement and supplement to the above solution, the present invention also includes the following additional technical features.

[0023] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects are obtained:

[0024] Solving the problem of active site agglomeration: Single-atom ruthenium is synergistically anchored with the amino groups on the alumina shell layer through titanium-fluorine bonds, effectively inhibiting the agglomeration of single-atom ruthenium, improving the stability of active sites, and enabling the catalyst to maintain high activity during long-term reactions. For example, during 1000 hours of continuous reaction, the particle size growth of single-atom ruthenium is less than 0.1 nanometer, and the conversion decay of tetramethylpiperidone is extremely small.

[0025] Improving the stability of fluorine modification: Fluorine-modified titanium dioxide has a surface fluorine enrichment layer, and oxygen vacancies and fluorine doping coexist. Fluoride ions are coordinated with the surface hydroxyl groups of titanium dioxide in a ratio of 1:1, making the fluorine modification more stable, avoiding the loss of fluorine, and ensuring the activity and selectivity of the catalyst.

[0026] Enhancing the carrier binding force and mass transfer efficiency: The alumina shell layer and the silica core are bonded through aluminum-oxygen-silicon bonds, the shell layer surface is grafted with amino groups, the proportion of mesoporous structure in the core-shell carrier is greater than or equal to 80%, and it contains 6 - 8 nanometer mesopores, enhancing the binding force of the carrier. At the same time, the appropriate mesoporous structure improves the mass transfer efficiency of reactants, enabling tetramethylpiperidone to contact the active sites more fully and improving the reaction conversion rate.

[0027] Optimizing reaction conditions and catalyst performance: Under specific reaction conditions, such as a reaction temperature of 110 °C, a pressure of 1.5 MPa, a hydrogen to ketone molar ratio of 5:1, feeding tetramethylpiperidone with an ethanol solution at a mass fraction of 20%, a fluorine to titanium atomic ratio of the catalyst being 0.02 - 0.03, an amino group content in the alumina shell being 0.8 - 0.9 mmol / g, and the diffusion coefficient of tetramethylpiperidone in the mesopores of the catalyst being 0.12 - 0.15 cm 2 / s, the conversion rate and selectivity of the tetramethylpiperidinol synthesis reaction can be further improved. After continuous reaction for 1000 hours, the conversion rate of tetramethylpiperidone can still remain at a high level. Detailed implementation manners

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Example 1: Preparation of composite catalyst

[0031] Step 1: Preparation of fluorine-modified titanium dioxide

[0032] Slowly drip 20 mL of tetrabutyl titanate into 200 mL of absolute ethanol, and magnetically stir for hydrolysis at 40 °C for 6 hours.

[0033] Add 50 mL of ammonium fluoride solution with a concentration of 0.1 mol / L to the hydrolysis solution, transfer it to a high-pressure autoclave with a polytetrafluoroethylene inner lining, and carry out hydrothermal reaction at 180 °C for 12 hours.

[0034] Centrifuge to collect the precipitate, wash it alternately with deionized water and ethanol 3 times, dry it and then calcine it at 400 °C for 4 hours to obtain fluorine-modified titanium dioxide (F-TiO2), in which the fluorine to titanium atomic ratio is 0.02 and the proportion of oxygen vacancies is 25%.

[0035] Step 2: Preparation of core-shell support

[0036] Take 10 g of silica microspheres with a particle size of 40 nm, disperse them in 500 mL of dopamine solution with a concentration of 2.5 g / L and a pH of 8.5, and stir at room temperature for 12 hours to form a polydopamine modification layer.

[0037] Transfer the above microspheres to a reaction kettle, add 300 mL of aluminum nitrate solution with a concentration of 0.6 mol / L and a pH of 8.5, and simultaneously add 1.5% (by volume) of amino silane (γ-aminopropyltriethoxysilane).

[0038] After hydrothermal reaction at 120 °C for 24 hours, centrifugal washing and drying were carried out, followed by calcination at 500 °C for 3 hours to obtain the core-shell support (SiO2@Al2O3-NH2), where the thickness of the Al2O3 shell was 8 nm, containing 6-nm mesopores with a mesopore ratio of 85% and an amino content of 0.8 mmol / g.

[0039] Step 3: Loading of single-atom ruthenium

[0040] Mix F-TiO2 and the core-shell support in a mass ratio of 1:3, and ruthenium was loaded using atomic layer deposition (ALD) technology. The precursor was ruthenium acetylacetonate (concentration 0.1 mol / m 3 ), and it was cycled 5 times at 200 °C. Each cycle included a precursor pulse of 0.1 s and a nitrogen purge of 10 s.

[0041] After loading, the catalyst was reduced with hydrogen of 99.99% purity at 250 °C for 3 hours to form a stable Ru single-atom structure (particle size <0.8 nm), which was synergistically anchored with the amino groups of the Al2O3 shell through titanium-fluorine bonds.

[0042] Example 2: Preparation of the composite catalyst

[0043] Step 1 was the same as that in Example 1.

[0044] Step 2: Preparation of the core-shell support

[0045] Take 10 g of silica microspheres with a particle size of 60 nm and disperse them in 500 mL of dopamine solution with a concentration of 2.5 g / L and a pH of 8.5, and stir at room temperature for 12 hours to form a polydopamine modification layer.

[0046] Transfer the above microspheres to a reaction kettle, add 300 mL of aluminum nitrate solution with a concentration of 0.6 mol / L and a pH of 8.5, and simultaneously add 1.5% (volume percentage) of amino silane (γ-aminopropyltriethoxysilane).

[0047] After hydrothermal reaction at 120 °C for 24 hours, centrifugal washing and drying were carried out, followed by calcination at 500 °C for 3 hours to obtain the core-shell support (SiO2@Al2O3-NH2), where the thickness of the Al2O3 shell was 12 nm, containing 8-nm mesopores with a mesopore ratio of 90% and an amino content of 0.8 mmol / g.

[0048] Step 3 was the same as that in Example 1.

[0049] Example 3: Synthetic application of tetramethylpiperidinol

[0050] Reactor: Fixed-bed reactor (inner diameter 10 mm, catalyst loading 2 g).

[0051] Raw materials: 20% ethanol solution of tetramethylpiperidone (TMP), feeding rate 0.5 mL / h.

[0052] Reaction parameters: temperature 110 °C, pressure 1.5 MPa, molar ratio of hydrogen to TMP 5:1.

[0053] Catalyst parameters: fluorine-titanium atomic ratio 0.025, amino group content in the Al2O3 shell 0.85 mmol / g, diffusion coefficient of TMP in the mesopores 0.13 cm 2 / s.

[0054] Drop tetrabutyl titanate into anhydrous ethanol for hydrolysis at a hydrolysis temperature of 25 °C, then add an ammonium fluoride solution with a concentration of 0.08 mol / L, and carry out a hydrothermal reaction at 180 °C for 12 hours to form a fluorine-modified titanium dioxide precursor, and then calcine at 400 °C for 4 hours to form fluorine-modified titanium dioxide with a surface fluorine-rich layer and oxygen vacancies;

[0055] Select silica microspheres with a particle size of 40 nm, treat them with a dopamine solution with a concentration of 2 - 3 g / L and a pH of 8.5 for 12 hours, and then when depositing alumina, add an aluminum nitrate solution with a concentration of 0.5 mol / L and a pH of 8, and simultaneously add an amino silane with a volume percentage of 1 - 2%, and calcine at 500 °C to form a core-shell support with an amino-functionalized shell and an alumina shell thickness of 8 - 12 nanometers;

[0056] Using atomic layer deposition technology, ruthenium acetylacetonate is used as a precursor at 200 °C for 5 cycles, and each cycle includes a precursor pulse of 0.1 second and a nitrogen purge of 10 seconds, and single-atom ruthenium is selectively loaded on the surface of the fluorine-modified titanium dioxide, and then reduced with hydrogen at 250 °C for 3 hours to form a stable coordination structure.

[0057] Results: The selectivity of tetramethylpiperidinol (TMPOH) reaches 98.2%, the conversion rate is 99.5%, and the activity retention rate after continuous operation for 500 hours is 95%.

[0058] Example 4: Synthesis application of tetramethylpiperidinol

[0059] Reactor: Fixed-bed reactor (inner diameter 10 mm, catalyst loading 2 g).

[0060] Raw materials: 20% ethanol solution of tetramethylpiperidone (TMP), feeding rate 0.5 mL / h.

[0061] Reaction parameters: temperature 110 °C, pressure 1.5 MPa, molar ratio of hydrogen to TMP 5:1.

[0062] Catalyst parameters: fluorine-titanium atomic ratio 0.025, amino group content in the Al2O3 shell 0.85 mmol / g, diffusion coefficient of TMP in the mesopores 0.13 cm2 / s.

[0063] Tetrabutyl titanate was dropped into anhydrous ethanol for hydrolysis at a hydrolysis temperature of 60 °C. Subsequently, an ammonium fluoride solution with a concentration of 0.12 mol / L was added. After a hydrothermal reaction at 180 °C for 12 hours, a fluorine-modified titanium dioxide precursor was formed, and then calcined at 400 °C for 4 hours to form fluorine-modified titanium dioxide with a surface fluorine enrichment layer and oxygen vacancies.

[0064] Silica microspheres with a particle size of 60 nm were selected and treated with a dopamine solution with a concentration of 3 g / L and a pH of 8.5 for 12 hours. Then, when depositing alumina, an aluminum nitrate solution with a concentration of 0.75 mol / L and a pH of 9 was added, and at the same time, 2% by volume of aminosilane was added synchronously. After calcination at 500 °C, a core-shell support with an amino-functionalized shell layer and an alumina shell layer thickness of 12 nm was formed.

[0065] Using atomic layer deposition technology, ruthenium acetylacetonate was used as a precursor at 200 °C for 5 cycles. Each cycle included a precursor pulse of 0.1 s and a nitrogen purge of 10 s. Single-atom ruthenium was selectively loaded on the surface of the fluorine-modified titanium dioxide, and after hydrogen reduction at 250 °C for 3 hours, a stable coordination structure was formed.

[0066] Results: The selectivity of 2,2,6,6-tetramethylpiperidin-1-ol (TMPOH) reached 99%, the conversion rate was 99.8%, and the activity retention rate was 98% after continuous operation for 500 hours.

[0067] Example 5:

[0068] The fluorine-titanium atomic ratio was changed to 0.03, and the amino content was 0.9 mmol / g. Other conditions were the same as in Example 2.

[0069] The selectivity of TMPOH was increased to 98.7%, the conversion rate was 99.8%, and the diffusion coefficient was 0.14 cm 2 / s.

[0070] Comparative Example 1: TiO2 catalyst without fluorine modification

[0071] Prepared according to Example 1, but the ammonium fluoride treatment step was omitted.

[0072] Results: The TMP conversion rate was 85%, the selectivity was 82%, and the catalyst was deactivated after running for 200 hours.

[0073] Comparative Example 2: Core-shell support without amino modification

[0074] Prepared according to Example 1, but aminosilane was not added.

[0075] Results: The Ru single-atom loading amount was reduced by 50%, the TMP conversion rate was 90%, and the selectivity was 90%.

[0076] In summary, the single-atom ruthenium is synergistically anchored through titanium-fluorine bonds and the amino groups on the alumina shell, effectively inhibiting the aggregation of single-atom ruthenium, improving the stability of the active sites, and enabling the catalyst to maintain high activity during long-term reactions. The alumina shell and the silica core are bonded through aluminum-oxygen-silicon bonds, and the shell surface is grafted with amino groups, enhancing the binding force of the support. At the same time, the appropriate mesoporous structure improves the mass transfer efficiency of the reactants, enabling tetramethylpiperidone to contact the active sites more fully and improving the reaction conversion rate.

[0077] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A composite catalyst, characterized in that: The composite catalyst comprises fluorine-modified titanium dioxide, a core-shell carrier with silicon dioxide as the core and aluminum oxide as the shell, and single-atom ruthenium, wherein: The fluorine-modified titanium dioxide is loaded on the core-shell carrier, and the single-atom ruthenium is synergistically anchored with the amino group of the aluminum oxide shell through a titanium-fluorine bond; The oxygen vacancies in the fluorine-modified titanium dioxide account for 25%; The core-shell carrier has a silica core particle size of 40-60 nanometers, an alumina shell layer thickness of 8-12 nanometers, and contains 6-8 nanometer mesopores; The particle size of the single-atom ruthenium is less than 0.8 nanometers.

2. The composite catalyst according to claim 1, characterized in that The fluorine-titanium atomic ratio of the fluorine-modified titanium dioxide is 0.01-0.

04.

3. The composite catalyst according to claim 2, characterized in that The alumina shell layer is bonded to the silica core via an aluminum-oxygen-silicon bond, and amino groups are grafted onto the surface of the alumina shell layer; the mesoporous structure accounts for more than or equal to 80% of the core-shell carrier.

4. The method for preparing the composite catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: Tetrabutyl titanate is dropped into anhydrous ethanol for hydrolysis at a temperature of 25-60°C, and then an ammonium fluoride solution with a concentration of 0.08-0.12 mol / L is added, and a fluorine-modified titanium dioxide precursor is generated by hydrothermal reaction at 180°C for 12 hours, and then calcined at 400°C for 4 hours to form a fluorine-modified titanium dioxide with a surface fluorine-enriched layer and oxygen vacancies; Silica microspheres with a particle size of 40-60 nanometers are selected, treated with a dopamine solution with a concentration of 2-3 g / L and a pH of 8.5 for 12 hours, and then, when depositing alumina, an aluminum nitrate solution with a concentration of 0.5-0.75 mol / L and a pH of 8-9 is added, and 1-2% by volume of aminosilane is added simultaneously, and calcined at 500° C. to form a core-shell carrier with an amino-functionalized shell layer and an alumina shell layer thickness of 8-12 nanometers; Atomic layer deposition technology was used, and ruthenium acetylacetonate was used as a precursor and cycled 5 times at 200°C. Each cycle included a precursor pulse of 0.1 seconds and a nitrogen purge of 10 seconds. Single atomic ruthenium was selectively loaded on the fluorine-modified titanium dioxide surface, and a stable coordination structure was formed by hydrogen reduction at 250°C for 3 hours.

5. The method for preparing the composite catalyst according to claim 4, characterized in that: The concentration of the ruthenium acetylacetonate precursor in the carrier gas is 0.05-0.15 mol / m 3 .

6. The method for preparing the composite catalyst according to claim 4, characterized in that: During the hydrogen reduction process, the purity of the hydrogen is not less than 99.9%, and the oxygen content in the hydrogen is not higher than 1 ppm.

7. The method for preparing the composite catalyst according to claim 4, characterized in that: In the hydrothermal reaction, the fluoride ions are coordinated with the hydroxyl groups on the surface of titanium dioxide in a ratio of 1:

1. This coordination mode enables the fluoride ions to be stably bound to the surface of titanium dioxide, thereby improving the stability of fluorine modification.

8. The method for preparing the composite catalyst according to claim 4, characterized in that: The hydrolysis time was 6 hours and the aminosilane concentration was 1.5 vol%, and the amino content of the alumina shell was precisely controlled at 0.8±0.1 mmol / g.

9. A method for applying a composite catalyst in the synthesis of tetramethylpiperidinol, characterized in that: The reaction was carried out in a fixed bed reactor at a reaction temperature of 110° C., a pressure of 1.5 MPa, a molar ratio of hydrogen to tetramethylpiperidone of 5:1, and tetramethylpiperidone was fed in the form of an ethanol solution with a mass fraction of 20%.

10. The method for applying the composite catalyst as claimed in claim 9 in the synthesis of tetramethyl piperidine alcohol, characterized in that: The fluorine-titanium atomic ratio of the catalyst is 0.02-0.03, the amino content of the alumina shell is 0.8-0.9 mmol / g, and the diffusion coefficient of tetramethylpiperidone in the mesopores of the catalyst is 0.12-0.15 cm 2 / s.