Rhodium-silicon catalyst, process for its preparation and use

Abstract

This invention discloses a rhodium-silicon catalyst, its preparation method, and its application. The catalyst is a Rh / SiO2 catalyst, comprising a support, a silicon dioxide support, and an active component. The Rh species exist in one or more forms, namely Rh clusters or Rh nanoparticles formed by the aggregation of Rh clusters. Based on the total mass of the Rh / SiO2 catalyst, the loading of Rh species is 0.2-2.0 wt%; the average particle size of the Rh species is 0.7-2.0 nm. This invention uses a water-in-oil reverse microemulsion method to prepare the Rh / SiO2 catalyst in one step. By adjusting the loading of Rh, the average particle size of the Rh species can be controlled. When the Rh species in the catalyst of this invention exist in the form of Rh clusters with a particle size of 1.0 nm, its application in the heterogeneous catalytic hydroformylation of formaldehyde exhibits advantages such as high reactivity, high selectivity for ethanolaldehyde, high stability, and easy separation and recovery.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to a rhodium-silicon catalyst, its preparation method and application, and more specifically to a method for controlling the particle size of Rh species in the rhodium-silicon catalyst, as well as a method for improving the formaldehyde conversion rate, ethanol-aldehyde selectivity and stability of the formaldehyde hydroformylation catalyst in heterogeneous catalytic formaldehyde hydroformylation reaction. Background Technology

[0002] Ethylene glycol, the simplest polyol, is an extremely important platform compound used as a solvent, antifreeze, and coolant. It is also used to synthesize various high-value-added chemicals, such as polyester fibers and polyester resins. The production of polyester fibers accounts for over 90% of the apparent demand for ethylene glycol. In recent years, the global polyester industry has developed rapidly, and the substantial increase in polyester demand has led to a year-on-year increase in the demand for its upstream raw material, ethylene glycol. Global ethylene glycol production is mainly concentrated in North America, Asia, the Middle East, and Europe. However, due to the mismatch between supply and demand in different production areas and the deepening of global ethylene glycol trade, my country's ethylene glycol production capacity is limited, and a large portion still relies on resources from the Middle East and North America. Therefore, improving domestic ethylene glycol production processes and enhancing product quality is of great significance for developing low-cost, high-quality ethylene glycol and its downstream industries.

[0003] In 1948, DuPont (US2534018A) first proposed a process route for the direct synthesis of ethylene glycol from syngas, considered the simplest and most efficient method. From a green chemistry perspective, this process route conforms to the principle of atom economy and has advantages such as a short process flow, low equipment investment, wide availability of raw materials, and low production costs. Currently, the catalysts for the direct synthesis of ethylene glycol from syngas are mainly homogeneous Rh-based, Ru-based, and Co-based catalysts, among which rhodium-phosphine complex homogeneous catalysts exhibit the best catalytic effect. In 1974, Union Carbide (US3833634A) first reported a carbonyl rhodium complex catalyst that, under harsh conditions (230℃ and 172 MPa, CO / H2 = 1:1), achieved one-step synthesis of ethylene glycol from syngas and proposed that the formation of ethylene glycol is related to H2. x Rh(CO) y (L) z(x=0-1, y=1-3, z=1-3, x+y+z=3-5; L: ligand) species are closely related. In 1980, Keim et al. of RWTH Aachen University, Germany (J. Catal. 1980, 61(2), 359-365.) found that under the conditions of 230℃ and 200MPa, the Rh(CO)2acac catalyst exhibited better catalytic performance in the polar solvent N-methylpyrrolidone, with a selectivity of 44.4% for ethylene glycol in the liquid phase product, but in the non-polar solvent toluene, it mainly produced methanol. Keim et al. believed that Rh has excellent hydrogenation activity in polar solvents, and can catalyze the hydrogenation of formyl species to form hydroxymethyl species, thereby promoting carbonyl insertion to form the key intermediate of glycolaldehyde, which is then hydrogenated to form ethylene glycol. Although the direct method can achieve the one-step conversion of syngas into ethylene glycol, the required reaction conditions are extremely harsh, and the selectivity of ethylene glycol in the product is low. Therefore, achieving the direct synthesis of ethylene glycol from syngas under mild conditions is a major challenge.

[0004] The direct synthesis of ethylene glycol from syngas involves three consecutive intermediate steps: ① CO hydrogenation to formaldehyde; ② formaldehyde hydroformylation to glycolaldehyde; ③ glycolaldehyde hydrogenation to ethylene glycol. The intermediate step of formaldehyde hydroformylation to glycolaldehyde is considered crucial in determining the selectivity of ethylene glycol. Given the thermodynamically favorable nature of this step, researchers have focused extensively on the formaldehyde hydroformylation process, aiming to guide the construction of highly active catalyst centers in the direct synthesis route through efficient catalyst design and reaction mechanism research, thereby reducing reaction temperature and pressure and improving the selectivity and yield of ethylene glycol. Currently, the reported formaldehyde hydroformylation catalyst systems are similar to those of the direct synthesis method, mainly homogeneous carbonyl rhodium, ruthenium, and cobalt composite catalysts, among which Rh-based catalysts exhibit the best activity and have been the most widely studied. In 1982, Monsanto (EP0002908A1) reported that rhodium carbonyl complexes could achieve formaldehyde hydroformylation under relatively mild conditions. The following year (US4405814A), they further reported that adding a small amount of triethylamine (110°C and 28.5 MPa syngas pressure) to a homogeneous system composed of triphenylphosphine carbonyl rhodium chloride and N,N-dibutylformamide could improve the conversion rate of formaldehyde and the selectivity of glycolaldehyde. Although rhodium complexes can achieve the formaldehyde hydroformylation process, this reaction still requires harsh conditions, and the amount of noble metal Rh catalyst used is relatively large (≥4×10⁻⁶). -3 (mol / L), making it difficult to separate the catalyst from the product after the reaction.

[0005] In existing technologies, Rh-based catalysts typically employ an impregnation method to load Rh active components onto a support surface. This method has several drawbacks: 1. The resulting Rh-based catalyst support exhibits poor Rh dispersion, with Rh existing as aggregated nanoparticles of uneven size, ranging from a few nanometers to hundreds of nanometers. It is impossible to obtain Rh clusters at the single-atom or atomic level, and it is even more difficult to freely control the size of Rh clusters and the particle size of Rh species. 2. Due to the scarcity and high price of precious metal Rh, reducing the Rh loading to lower catalyst costs results in very low catalytic activity. Conversely, a high Rh loading not only increases costs but also makes the active components more prone to agglomeration into nanoparticles, further reducing catalytic activity. Therefore, the impregnation method for preparing Rh-based catalysts struggles to balance low Rh loading with good dispersion and high catalytic activity.

[0006] In addition, it is desirable to simultaneously improve the formaldehyde conversion rate, ethanol aldehyde selectivity, and catalyst stability in the heterogeneous catalytic formaldehyde hydroformylation reaction.

[0007] To address the above problems, this invention is proposed. Summary of the Invention

[0008] This invention aims to provide a rhodium-silicon catalyst and a method for controlling the particle size of Rh species in the rhodium-silicon catalyst. Using this method, Rh species can be obtained in one or more forms, such as Rh clusters of different particle sizes or Rh nanoparticles formed by the aggregation of Rh clusters, in an Rh / SiO2 catalyst. Furthermore, when the Rh species in the Rh / SiO2 catalyst of this invention exist in the form of Rh clusters with an average particle size of 1.0 nm, this catalyst, when used for heterogeneous catalytic hydroformylation of formaldehyde, exhibits mild reaction conditions, high reactivity, high selectivity for ethanolaldehyde, high stability, and easy separation and recovery, making it a potential industrial catalyst.

[0009] Furthermore, the method of this invention can yield atomically dispersed noble metal-based solid catalysts, enabling the transformation of many reactions from homogeneous catalysis to heterogeneous catalysis. Atomically dispersed noble metal-based solid catalysts retain the high activity of homogeneous catalysts while possessing the high stability and recyclability of heterogeneous catalysts. The Rh / SiO2 catalyst preparation method of this invention is simple and inexpensive, producing catalysts with uniform Rh species particle size, exhibiting high catalytic activity, ethanol aldehyde selectivity, and stability, making it easy to implement in industrial applications.

[0010] The present invention aims to provide a preparation scheme for a Rh / SiO2 catalyst for heterogeneous catalysis of formaldehyde hydroformylation. The preparation method has the advantages of simple operation, low cost and high reproducibility.

[0011] To achieve the objectives of this invention, the specific technical solution is as follows:

[0012] The first aspect of this invention provides a rhodium-silicon catalyst, which is a Rh / SiO2 catalyst comprising a support and an active component. The support is silicon dioxide, and the active component is an Rh species. The Rh species exists in one or more forms, namely Rh clusters or Rh nanoparticles formed by the aggregation of Rh clusters. Based on the total mass of the Rh / SiO2 catalyst, the loading of the Rh species is 0.2-2.0 wt%. The average particle size of the Rh species is 0.7-2.0 nm.

[0013] Preferably, the loading of the Rh species is 0.2-1.0 wt%; the average particle size of the Rh species is 0.7-1.1 nm. More preferably, the loading of the Rh species is 0.7 wt%, and the average particle size of the Rh species is 1.0 nm.

[0014] The first aspect of this invention provides a method for preparing Rh / SiO2 as described in the first aspect of this invention, comprising the following steps:

[0015] 1) Preparation of water-in-oil reverse microemulsion: The oil phase, water phase, surfactant, and co-surfactant are mixed in a certain proportion at a constant temperature to form a colorless and transparent water-in-oil reverse microemulsion.

[0016] 2) Preparation of rhodium precursor solution: Weigh the soluble rhodium precursor, dissolve it in a solvent, and sonicate to dissolve it to obtain a rhodium precursor solution;

[0017] 3) Mixing: The rhodium precursor solution from step 2) is added dropwise to the water-in-oil reverse microemulsion from step 1), and the mixture is stirred at a constant temperature to obtain a uniformly dispersed solution.

[0018] 4) Introduction of silicon precursor: Add the silicon precursor to the solution in step 3) and continue stirring at a constant temperature to obtain a well mixed solution;

[0019] 5) Adding a catalyst: Add the alkaline catalyst to the solution obtained in step 4), and keep stirring at a constant temperature to obtain a suspension;

[0020] 6) Demulsification: Add the demulsifier to the suspension obtained in step 5), and continue stirring at a constant temperature to obtain a flocculent mixture;

[0021] 7) Separation and washing: The flocculent mixture obtained in step 6) is washed multiple times to obtain a solid precipitate;

[0022] 8) Drying and crushing: The solid precipitate obtained in step 7) is dried and crushed to obtain catalyst precursor powder;

[0023] 9) Calcination: The catalyst precursor powder obtained in step 8) is calcined to obtain the Rh / SiO2 catalyst.

[0024] Preferably, the constant temperature mentioned in steps 1) and 3)-6) is 25-75°C. More preferably, the constant temperature for stirring in steps 1) and 3)-6) is selected as 25-45°C. The stirring times in steps 1) and 3)-6) are 0.5-1h, 0.5-2h, 1-5h, 6-24h, and 0.5-5h, respectively.

[0025] Preferably, the oil phase in step 1) is selected from one or more of cyclohexane, n-heptane, dodecane, hexadecane, and octadecane. More preferably, the oil phase in step 1) is selected from one or more of cyclohexane and n-heptane.

[0026] Preferably, the aqueous phase in step 1) is selected from one or more of ultrapure water, deionized water, pure water, and distilled water. More preferably, the aqueous phase in step 1) is selected from one or more of ultrapure water and deionized water.

[0027] Preferably, the surfactant in step 1) is selected from one or more of polyethylene glycol octylphenyl ether, nonylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, and lauroyl diethanolamine. More preferably, the surfactant in step 1) is selected from one or more of polyethylene glycol octylphenyl ether and nonylphenol polyoxyethylene ether.

[0028] Preferably, the co-surfactant in step 1) is selected from one or more of ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, n-hexanol, and 2-hexanol. More preferably, the co-surfactant in step 1) is selected from one or more of n-propanol, n-butanol, n-pentanol, and n-hexanol.

[0029] Preferably, the molar ratio of the oil phase, aqueous phase, surfactant, and co-surfactant in step 1) is 1:0.01-0.2:0.05-0.5:0.2-1.2. More preferably, the molar ratio of the oil phase, aqueous phase, surfactant, and co-surfactant in step 1) is 1:0.05-0.1:0.1-0.3:0.5-1.0.

[0030] Preferably, the rhodium precursor in step 2) is selected from one or more of rhodium acetylacetonate, rhodium acetylacetonate dicarbonyl, tetrarhodium dodecylcarbonyl, hexarhodium dodecylcarbonyl, hydrated rhodium chloride, rhodium chloride, rhodium iodide, rhodium nitrate, and sodium rhodium chloride. More preferably, the rhodium precursor in step 2) is selected from one or more of rhodium acetylacetonate dicarbonyl, hydrated rhodium chloride, rhodium chloride, and rhodium nitrate.

[0031] Preferably, the solvent used in step 2) is selected from one or more of ultrapure water, deionized water, anhydrous methanol, anhydrous ethanol, acetone, and toluene. The amount of solvent used is determined according to the amount of rhodium precursor used. In this invention, the amount of solvent used corresponding to 0.0026g of rhodium chloride hydrate is 0.5-2.0mL. More preferably, the solvent used in step 2) is selected from one or more of ultrapure water, anhydrous methanol, and acetone, and the amount used is 0.5-1.0mL.

[0032] Preferably, the silicon precursor in step 4) is selected from one or more of sodium silicate, tetramethylsilane, phenylsilane, methyldiphenylsilane, tetraethyl orthosilicate, and tetrabutyl orthosilicate. More preferably, the silicon precursor in step 4) is selected from one or more of sodium silicate, tetramethylsilane, tetraethyl orthosilicate, and tetrabutyl orthosilicate.

[0033] Preferably, the molar ratio of the silicon precursor in step 4) to the oil phase in step 1) is 0.02-0.2:1. More preferably, the molar ratio of the silicon precursor in step 4) to the oil phase in step 1) is 0.04-0.1:1.

[0034] Preferably, the alkaline catalyst in step 5) is selected from one or more of NaOH, NaHCO3, KOH, KHCO3, and NH3·H2O, the pH is adjusted to 8-14, and the stirring time is 12-48 h. More preferably, the alkaline catalyst in step 5) is selected from one or more of NaOH, NaHCO3, and NH3·H2O, the pH is selected to be 8-10, and the stirring time is selected to be 6-24 h.

[0035] Preferably, the demulsifier in step 6) is selected from one or more of anhydrous ethanol, acetone, and isopropanol. The amount of demulsifier used is determined according to the amount of suspension used in step 5). In this invention, the amount of demulsifier used is 5-20 mL, and the demulsification time is 0.5-5 h. More preferably, the demulsifier in step 6) is selected from one or more of anhydrous ethanol and acetone, the amount used is 5-10 mL, and the demulsification time is selected as 1-3 h.

[0036] Preferably, the separation method in step 7) is one or more of filtration, rotary evaporation, and centrifugation, and the washing solvent is one or more of deionized water, anhydrous methanol, and anhydrous ethanol, with 1-5 washing cycles. More preferably, the separation method in step 7) is centrifugation, the washing solvent is one or more of deionized water and anhydrous ethanol, and the washing cycles are 3-5.

[0037] Preferably, the drying temperature in step 8) is 50-150°C and the drying time is 4-24 hours. More preferably, the drying temperature in step 8) is 50-150°C and the drying time is 4-24 hours.

[0038] Preferably, the calcination temperature in step 9) is 200-600℃, the heating rate is 1-10℃ / min, and the calcination time is 4-10h. More preferably, the calcination temperature in step 9) is 400-600℃, the heating rate is 1-5℃ / min, and the calcination time is 4-6h.

[0039] A third aspect of the present invention provides an application of the rhodium-silicon catalyst described in the first aspect of the present invention, wherein the rhodium-silicon catalyst is a Rh / SiO2 catalyst, and the Rh / SiO2 catalyst is applied to the heterogeneous catalytic hydroformylation reaction of formaldehyde.

[0040] Specifically, the Rh / SiO2 catalyst is applied to the gas-liquid-solid heterogeneous catalytic hydroformylation reaction of formaldehyde. The reaction conditions are as follows: the reactor is a batch reactor; the raw materials are a mixture of paraformaldehyde, CO and H2 gas, with a CO to H2 molar ratio of 1:1; the ligand is an organophosphorus ligand, with a ligand to Rh molar ratio of 0-10; the reaction temperature is 50-150℃; the pressure is 1-10MPa; and the reaction time is 1-12h.

[0041] More preferably, the reaction conditions for the Rh / SiO2 catalyst in the gas-liquid-solid heterogeneous catalytic hydroformylation reaction are as follows: the reactor is a high-pressure batch reactor, and the Rh concentration is 5 × 10⁻⁶. -4 ~2×10 -3 The reaction system contains formaldehyde, a mixture of CO and H2, ligands, and solvents. The molar ratio of formaldehyde to Rh is 500-1500, the molar ratio of CO to H2 is 1:1, the ligand is an organophosphorus ligand, and the molar ratio of the ligand to Rh is 1-10. The solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, acetonitrile, and toluene. The reaction temperature is 75-135℃, the pressure is 5-11MPa, and the reaction time is 1-8h.

[0042] The fourth aspect of this invention provides a method for controlling the particle size of Rh species in the rhodium-silicon catalyst described in the first aspect of this invention. The Rh / SiO2 catalyst is prepared according to the preparation method described in the second aspect of this invention, and when the Rh loading is 0.2-1.0 wt%, including 0.2 wt% and excluding 1.0 wt%, the Rh species on the Rh / SiO2 catalyst exist in the form of Rh atomic clusters, and the average particle size of the Rh species is 0.7-1.1 nm.

[0043] When the Rh loading is 1.0-2.0 wt%, excluding 1.0 wt% and including 2.0 wt%, the Rh species on the Rh / SiO2 catalyst exist in the form of Rh atomic clusters and Rh nanoparticles, and the average particle size of the Rh species is 1.1-2.0 nm.

[0044] When the Rh loading is higher than 2.0 wt%, the Rh species on the Rh / SiO2 catalyst exist in the form of Rh nanoparticles with an average size greater than 2.0 nm.

[0045] Specifically, when the Rh loading is 0.2 wt%, the particle size range of the Rh species is 0.6-0.8 nm, and the average particle size is 0.7 nm; when the Rh loading is 0.7 wt%, the particle size range of the Rh species is 0.8-1.3 nm, and the average particle size is 1.0 nm; when the Rh loading is 1.0 wt%, the particle size range of the Rh species is 0.9-1.3 nm, and the average particle size is 1.1 nm; and when the Rh loading is 2.0 wt%, the particle size range of the Rh species is 1.3-3.3 nm, and the average particle size is 2.0 nm.

[0046] A fifth aspect of this invention provides a method for improving the formaldehyde conversion rate, ethanolaldehyde selectivity, and stability of the formaldehyde hydroformylation catalyst in a formaldehyde hydroformylation reaction. The method described in the fourth aspect of this invention controls the active component Rh species in the Rh / SiO2 catalyst to exist in the form of Rh clusters. Based on the total mass of the Rh / SiO2 catalyst, the loading of the Rh species is 0.2-1.0 wt%, including 0.2 wt% and including 1.0 wt%, and the average particle size of the Rh species is 0.7-1.1 nm. More preferably, the loading of the Rh species is 0.2-1.0 wt%, and the average particle size of the Rh species is 1.0 nm.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. This invention employs a water-in-oil reverse microemulsion method to prepare Rh / SiO2 catalysts. By controlling the loading of Rh species, the Rh species can be controlled to exist in one or more forms, such as Rh clusters of different particle sizes or Rh nanoparticles formed by the aggregation of Rh clusters, in the Rh / SiO2 catalyst. Furthermore, when the Rh species in the Rh / CeO2 catalyst of this invention exist in the form of Rh clusters with an average particle size of 1.0 nm, it can significantly improve the formaldehyde conversion rate, ethanolaldehyde selectivity, and the stability of the formaldehyde hydroformylation reaction catalyst. Compared with Rh / SiO2 catalysts prepared by the impregnation method, this invention truly achieves the effect of reducing the amount of precious metals used while ensuring catalytic activity. This invention utilizes the unique geometric structure and electronic effects of the Rh active component; Rh clusters can promote the hydroformylation reaction of formaldehyde, generating ethanolaldehyde with high selectivity.

[0049] 2. The preparation method of the Rh / SiO2 catalyst for heterogeneous catalytic hydroformylation of formaldehyde provided by the present invention is simple, reliable, easy to operate, highly reproducible, and suitable for large-scale production.

[0050] 4. The Rh / SiO2 catalyst for heterogeneous catalytic hydroformylation of formaldehyde provided by this invention is a solid catalyst. After the gas-liquid-solid heterogeneous catalytic hydroformylation reaction, the precious metal catalyst can be separated and recovered by simple centrifugation or filtration, which greatly reduces the reaction cost.

[0051] 5. The heterogeneous catalytic formaldehyde hydroformylation Rh / SiO2 catalyst provided by this invention uses SiO2 prepared by the water-in-oil reverse microemulsion method as a support, which can better disperse Rh inside the SiO2 microspheres, playing a confinement role and enhancing the interaction between Rh and the SiO2 support. At the same time, it modulates the Rh clusters to a suitable size, significantly improving the formaldehyde hydroformylation reaction performance. Under short reaction time, mild reaction temperature and pressure, the 0.7% Rh / SiO2 catalyst in which Rh exists in the form of atomic clusters with an average particle size of 1.0 nm exhibits relatively excellent catalytic activity, with a formaldehyde conversion rate of more than 25% and an ethanolaldehyde selectivity of more than 90%.

[0052] 6. Compared with traditional homogeneous catalysts for the heterogeneous catalytic hydroformylation of formaldehyde, the Rh / SiO2 catalyst provided by this invention can reduce the amount of precious metal Rh used, while exhibiting excellent cycle stability and easy separation and recovery after reaction. It has high economic value and market prospects, and is a potential industrial catalyst. Attached Figure Description

[0053] Figure 1 TEM and HAADF-STEM images of Rh / SiO2 catalysts with different Rh contents prepared by the water-in-oil reverse microemulsion method;

[0054] Figure 2 Statistical diagram of Rh species particle size of Rh / SiO2 catalysts with different Rh contents prepared by the water-in-oil reverse microemulsion method;

[0055] Figure 3 A comparison of the formaldehyde hydroformylation performance of Rh / SiO2 catalysts with different Rh contents prepared by the water-in-oil reverse microemulsion method;

[0056] Figure 4 Cyclic performance test results of the formaldehyde hydroformylation performance of the Rh / SiO2 catalyst prepared by the water-in-oil reverse microemulsion method;

[0057] Figure 5 TEM and HAADF-STEM images of the Rh / SiO2 catalyst prepared by the impregnation method;

[0058] Figure 6 Comparison of formaldehyde hydroformylation performance of Rh / SiO2 catalysts prepared by different methods;

[0059] Figure 7 Color comparison of Rh / SiO2 catalysts prepared by different methods after reaction. Detailed Implementation

[0060] The present invention will be described below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions and conditions described in the manual, or according to the manufacturer's recommendations. Unless otherwise specified, the general equipment, materials, reagents, etc., used are all commercially available. The raw materials required for catalyst synthesis in the following embodiments and comparative examples were all obtained commercially.

[0061] Examples 1-12 illustrate the preparation of Rh / SiO2 catalysts with different Rh contents.

[0062] Example 1

[0063] Measure 15.0 mL of cyclohexane, 3.6 mL of polyethylene glycol octylphenyl ether, 3.2 mL of n-hexanol, and 1.0 mL of ultrapure water using a pipette, add them to a 100 mL round-bottom flask, and stir at 30 °C for 30 min to obtain a colorless and transparent water-in-oil reverse microemulsion. Weigh 0.0026 g of rhodium chloride hydrate and dissolve it in 1 mL of ultrapure water by ultrasonication to obtain a uniformly dispersed solution. Slowly add the solution dropwise to the microemulsion and continue stirring for 30 min. Measure 1.87 mL of tetraethyl orthosilicate and add it to the microemulsion, and continue stirring for 3 h. 0.079 mL of NH3·H2O was slowly added dropwise to the microemulsion, and stirring was continued for 18 h. 10 mL of ethanol was added to break the emulsion. The mixture was centrifuged and washed three times with ethanol. It was dried at 110 °C for 12 h and ground into a 200-300 mesh powder. The powder was heated to 400 °C in a muffle furnace at a heating rate of 2 °C / min, held for 4 h, and then cooled to room temperature to obtain a 0.2% Rh / SiO2 catalyst.

[0064] Example 2

[0065] Except for weighing 0.009 g of rhodium chloride hydrate and measuring 1.86 mL of tetraethyl orthosilicate, the preparation method was exactly the same as in Example 1, and a 0.7% Rh / SiO2 catalyst was obtained.

[0066] Example 3

[0067] Except for weighing 0.013 g of rhodium chloride hydrate and measuring 1.85 mL of tetraethyl orthosilicate, the preparation method was exactly the same as in Example 1, and a 1.0% Rh / SiO2 catalyst was obtained.

[0068] Example 4

[0069] Except for weighing 0.026 g of rhodium chloride hydrate and measuring 1.83 mL of tetraethyl orthosilicate, the preparation method was exactly the same as in Example 1, and a 2.0% Rh / SiO2 catalyst was obtained.

[0070] Example 5

[0071] Except for replacing the method of ultrasonically dissolving 0.0026g of rhodium chloride hydrate in 1mL of ultrapure water with the method of ultrasonically dissolving 0.0025g of rhodium dicarbonyl acetylacetone in 1mL of acetone, the preparation method was exactly the same as in Example 1, and a 0.2% Rh / SiO2 catalyst was obtained.

[0072] Example 6

[0073] Except for replacing the method of ultrasonically dissolving 0.009g of rhodium chloride hydrate in 1mL of ultrapure water with ultrasonically dissolving 0.009g of rhodium dicarbonyl acetylacetone in 1mL of acetone, the preparation method was exactly the same as in Example 2, and a 0.7% Rh / SiO2 catalyst was obtained.

[0074] Example 7

[0075] Except for replacing the method of ultrasonically dissolving 0.013g of rhodium chloride hydrate in 1mL of ultrapure water with ultrasonically dissolving 0.013g of rhodium dicarbonyl acetylacetone in 1mL of acetone, the preparation method was exactly the same as in Example 3, and a 1.0% Rh / SiO2 catalyst was obtained.

[0076] Example 8

[0077] Except for replacing 0.026g of hydrated rhodium chloride with ultrasonic dissolution in 1mL of ultrapure water with 0.025g of dicarbonyl acetylacetone rhodium with ultrasonic dissolution in 1mL of acetone, the preparation method was exactly the same as in Example 4, and a 2.0% Rh / SiO2 catalyst was obtained.

[0078] Example 9

[0079] Except for replacing 1.87 mL of tetraethyl orthosilicate with 1.14 mL of tetramethylsilane, the preparation method was exactly the same as in Example 1, yielding a 0.2% Rh / SiO2 catalyst.

[0080] Example 10

[0081] Except for replacing 1.86 mL of tetraethyl orthosilicate with 1.14 mL of tetramethylsilane, the preparation method was exactly the same as in Example 2, yielding a 0.7% Rh / SiO2 catalyst.

[0082] Example 11

[0083] Except for replacing 1.85 mL of tetraethyl orthosilicate with 1.13 mL of tetramethylsilane, the preparation method was exactly the same as in Example 3, yielding a 1.0% Rh / SiO2 catalyst.

[0084] Example 12

[0085] Except for replacing 1.83 mL of tetraethyl orthosilicate with 1.12 mL of tetramethylsilane, the preparation method was exactly the same as in Example 4, yielding a 2.0% Rh / SiO2 catalyst.

[0086] Examples 13-16 show the preparation of comparative Rh / SiO2 catalysts via impregnation.

[0087] Example 13

[0088] 0.002 g of hydrated rhodium chloride was ultrasonically dissolved in 2 mL of ultrapure water. This solution was then added dropwise to 0.998 g of SiO2 support. After stirring with a glass rod, the solution was ultrasonically dried for 6 h to remove excess moisture. The dried solid was then dried in a forced-air drying oven at 110 °C for 12 h to obtain a dry solid. This solid was ground to 200-300 mesh and then placed in a muffle furnace. The temperature was increased to 400 °C at a rate of 2 °C / min and maintained for 4 h before being cooled to room temperature to obtain a 0.2% Rh / SiO2-impregnated catalyst.

[0089] Example 14

[0090] 0.018 g of hydrated rhodium chloride was ultrasonically dissolved in 2 mL of ultrapure water. This solution was then added dropwise to 0.993 g of SiO2 support. After stirring with a glass rod, the solution was ultrasonically dried for 6 h to remove excess moisture. The dried solid was then dried in a forced-air drying oven at 110 °C for 12 h to obtain a dry solid. This solid was ground to 200-300 mesh and then placed in a muffle furnace. The temperature was increased to 400 °C at a rate of 2 °C / min and maintained for 4 h before being cooled to room temperature to obtain a 0.7% Rh / SiO2-impregnated catalyst.

[0091] Example 15

[0092] 0.026 g of hydrated rhodium chloride was ultrasonically dissolved in 2 mL of ultrapure water. This solution was then added dropwise to 0.990 g of SiO2 support. After stirring with a glass rod until homogeneous, the solution was ultrasonically dried for 6 h to remove excess moisture. The dried solid was then dried in a forced-air drying oven at 110 °C for 12 h to obtain a dry solid. This solid was ground to 200-300 mesh and then placed in a muffle furnace. The temperature was increased to 400 °C at a rate of 2 °C / min and maintained for 4 h before being cooled to room temperature to obtain a 1.0% Rh / SiO2-impregnated catalyst.

[0093] Example 16

[0094] 0.052 g of hydrated rhodium chloride was ultrasonically dissolved in 2 mL of ultrapure water. The solution was then added dropwise to 0.980 g of SiO2 support. After stirring with a glass rod, the solution was ultrasonically dried for 6 h to remove excess moisture. The solution was then dried in a forced-air drying oven at 110 °C for 12 h to obtain a dry solid. The solid was ground to 200-300 mesh and then placed in a muffle furnace. The temperature was increased to 400 °C at a rate of 2 °C / min and held for 4 h before being cooled to room temperature to obtain a 2.0% Rh / SiO2-impregnated catalyst.

[0095] Comparative TEM, HAADF-STEM, and Rh species particle size distributions of the catalysts obtained in Examples 1-4 are shown in the attached figures. Figure 1 and attached Figure 2As shown, all Rh / SiO2 prepared by the water-in-oil reverse microemulsion method are uniformly sized nanospheres. On catalysts with Rh content of 0.2%-1.0%, Rh exists in the form of uniformly sized Rh atomic clusters with average particle sizes of 0.7, 1.0 and 1.1 nm, respectively. However, when the Rh content increases to 2.0%, Rh exists in both atomic cluster and nanoparticle forms, and the particle size distribution is uneven, with a particle size range of 1.3-3.3 nm and an average particle size of 2.0 nm.

[0096] The catalysts obtained in Examples 1-4 and 14 were used for the hydroformylation reaction of formaldehyde, and their catalytic activities were compared. The specific catalytic reaction methods are as follows:

[0097] 1) Weigh the catalyst. Add 0.002 molar amounts of Rh / SiO2 catalyst to 100 mL of quartz liner.

[0098] 2) Loading the reactor. Weigh paraformaldehyde as formaldehyde donor (molar ratio of formaldehyde to Rh is 1000-1500), organophosphorus ligand (molar ratio of ligand to Rh is 1-10), measure 20 mL of organic solvent, add it to 100 mL of quartz liner, and seal it in the stainless steel high-pressure reactor body.

[0099] 3) Pressurization. Introduce a CO / H2 mixture with a molar ratio of 1:1 at 3 MPa into the high-pressure reactor, then release the pressure. Repeat this process three times to purge the air from the reactor. After pressurizing to the reaction pressure of 5-11 MPa, perform a leak test. Once it is confirmed that there is no gas leakage, release the pressure to no more than 3 MPa above the reaction pressure.

[0100] 4) Catalyst performance test. Start the programmed temperature rise at a rate of 10℃ / min. After the temperature reaches the reaction temperature of 75-135℃, pressurize to the reaction pressure of 5-11MPa, start stirring, and start timing. After reacting for 1-8 hours, stop heating and stirring, remove the reactor, and allow it to cool naturally to room temperature.

[0101] 5) Product Analysis. An internal standard was added to the post-reaction solution, and analysis was performed using a Shimadzu 2014C GC gas chromatograph. The detectors were a thermal conductivity detector and a flame ionization detector (FID), with helium as the carrier gas. The FID column was a Porapak-T (1.0m × 3.2mm) packed column, and the FID column was a WondaCap FFAP (30m × 0.53mm × 1μm) capillary column. Data processing was performed using Labsolutions software, and the reactant and product concentrations were obtained based on the internal standard curve.

[0102] The catalytic performance of Rh / SiO2 catalysts with different Rh loadings was compared, and the test results are shown in the appendix. Figure 3Rh cluster catalysts of different particle sizes all exhibited formaldehyde hydroformylation activity. The 0.2% Rh / SiO2 catalyst with an average Rh cluster particle size of 0.7 nm showed low activity, with an ethanolaldehyde selectivity below 80%. Increasing the average Rh cluster particle size to 1.0 nm resulted in the 0.7% Rh / SiO2 catalyst exhibiting optimal catalytic activity, with a formaldehyde conversion exceeding 25% and an ethanolaldehyde selectivity exceeding 90%. Further increasing the Rh cluster size significantly reduced the catalytic activity; when Rh clusters aggregated to form non-uniform Rh nanoparticles, the activity decreased substantially. The activity test results demonstrate that by controlling the Rh content, the particle size of Rh species can be controlled, particularly the particle size distribution of Rh clusters. When the average Rh cluster particle size was 1.0 nm, the Rh / SiO2 catalyst exhibited the best formaldehyde hydroformylation activity and ethanolaldehyde selectivity.

[0103] To investigate the stability of the Rh / SiO2 catalyst prepared by the water-in-oil reverse microemulsion method in the heterogeneous catalytic hydroformylation reaction of formaldehyde, this invention subjected the reacted Rh / SiO2 catalyst to filtration and washing to separate the solid catalyst, and then conducted a cycle stability test. Except that the catalyst was the catalyst recovered after the reaction, the remaining steps were the same as the catalytic method described above. The cycle stability test results are attached. Figure 4 After four cycles of reaction, the selectivity of ethanolaldehyde in the Rh / SiO2 catalyst remained at approximately 90%. This result indicates that the Rh / SiO2 catalyst prepared by the water-in-oil reverse microemulsion method exhibits superior stability.

[0104] To investigate the effect of preparation methods on the catalytic performance of Rh / SiO2 catalysts in the hydroformylation of formaldehyde, this invention compares the structure and catalytic performance of two Rh / SiO2 catalysts prepared by the water-in-oil reverse microemulsion method and the impregnation method. Figure 1 The 0.7% Rh / SiO2 catalyst prepared by the water-in-oil reverse microemulsion method consists of uniformly dispersed nanospheres with uniform Rh cluster particle size and an average particle size of 1.0 nm. (See attached image) Figure 2 ). And attached Figure 5 The 0.7% Rh / SiO2 catalyst prepared by the impregnation method showed no specific morphology after high-temperature calcination, and the Rh species particles were large and unevenly distributed. (See attached image.) Figure 6 The chart comparing the catalytic performance of catalysts prepared by the two methods shows that the catalyst prepared by the water-in-oil reverse microemulsion method has significantly better catalytic performance than the catalyst prepared by the impregnation method. The former's selectivity for ethanol aldehydes exceeds 90%, which is much higher than that of the latter. (Attached) Figure 7The color of the solutions after the reaction of catalysts prepared by the two methods was compared. The solution prepared by the water-in-oil reverse microemulsion method was clear and transparent, while the solution prepared by the impregnation method was noticeably yellow, indicating significant leaching of Rh from the catalyst into the solution. These results suggest that the water-in-oil reverse microemulsion method is more suitable for preparing Rh / SiO2 catalysts with uniform morphology and structure, uniform Rh cluster size, high catalytic activity, and high stability.

[0105] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the formaldehyde conversion rate, ethanol-aldehyde selectivity, and catalyst stability in the heterogeneous catalytic hydroformylation reaction of rhodium-silicon catalysts, characterized in that, The catalyst is a Rh / SiO2 catalyst, comprising a support and an active component. The support is silica, and the active component is an Rh species, specifically an Rh cluster. Based on the total mass of the Rh / SiO2 catalyst, the loading of the Rh species is 0.7 wt%; the average particle size of the Rh species is 1.0 nm. The preparation method of the rhodium-silicon catalyst includes the following steps: 1) Preparation of water-in-oil reverse microemulsion: The oil phase, water phase, surfactant, and co-surfactant are mixed in a certain proportion at a constant temperature to form a colorless and transparent water-in-oil reverse microemulsion. 2) Preparation of rhodium precursor solution: Weigh the soluble rhodium precursor, dissolve it in a solvent, and sonicate to dissolve it to obtain a rhodium precursor solution; 3) Mixing: The rhodium precursor solution from step 2) is added dropwise to the water-in-oil reverse microemulsion from step 1), and the mixture is stirred at a constant temperature to obtain a uniformly dispersed solution. 4) Introduction of silicon precursor: Add the silicon precursor to the solution in step 3) and continue stirring at a constant temperature to obtain a well mixed solution; 5) Adding a catalyst: Add the alkaline catalyst to the solution obtained in step 4), and keep stirring at a constant temperature to obtain a suspension; 6) Demulsification: Add the demulsifier to the suspension obtained in step 5), and continue stirring at a constant temperature to obtain a flocculent mixture; 7) Separation and washing: The flocculent mixture obtained in step 6) is centrifuged and washed multiple times to obtain a solid precipitate; 8) Drying and crushing: The solid precipitate obtained in step 7) is dried and crushed to obtain catalyst precursor powder; 9) Calcination: The catalyst precursor powder obtained in step 8) is calcined to obtain the Rh / SiO2 catalyst.

2. The method according to claim 1, characterized in that, The oil phase mentioned in step 1) is selected from one or more of cyclohexane, n-heptane, dodecane, hexadecane, and octadecane; the aqueous phase mentioned in step 1) is selected from one or more of ultrapure water, deionized water, pure water, and distilled water; the surfactant mentioned in step 1) is selected from one or more of polyethylene glycol octylphenyl ether, nonylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, and lauroyl diethanolamine; the co-surfactant mentioned in step 1) is selected from one or more of ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, n-hexanol, and 2-hexanol; the molar ratio of the oil phase, aqueous phase, surfactant, and co-surfactant mentioned in step 1) is 1:0.01-0.2:0.05-0.5:0.2-1.2; The rhodium precursor mentioned in step 2) is selected from one or more of rhodium acetylacetone, rhodium dicarbonyl acetylacetone, tetrarhodium dodecylcarbonyl, hexarhodium dodecylcarbonyl, rhodium chloride, rhodium iodide, rhodium nitrate, and sodium rhodium chloride; the solvent in step 2) is selected from one or more of ultrapure water, deionized water, anhydrous methanol, anhydrous ethanol, acetone, and toluene.

3. The method according to claim 1, characterized in that, In steps 1) and 3)-6), the constant temperature is 25-75 °C; the stirring times in steps 1) and 3)-6) are 0.5-1 h, 0.5-2 h, 1-5 h, 6-24 h and 0.5-5 h, respectively.

4. The method according to claim 1, characterized in that, The silicon precursor mentioned in step 4) is selected from one or more of sodium silicate, tetramethylsilane, phenylsilane, methyldiphenylsilane, tetraethyl orthosilicate, and tetrabutyl orthosilicate; the molar ratio of the silicon precursor mentioned in step 4) to the oil phase in step 1) is 0.02-0.2:1; The alkaline catalyst mentioned in step 5) is selected from one or more of NaOH, NaHCO3, KOH, KHCO3, and NH3·H2O, and the pH is adjusted to 8-14, with continuous stirring time of 6-24 h; The demulsifier mentioned in step 6) is selected from one or more of anhydrous ethanol, acetone, and isopropanol.

5. The method according to claim 1, characterized in that, In step 7), the washing solvent is one or more of deionized water, anhydrous methanol, and anhydrous ethanol, and the number of washing cycles is 1-5. The drying method described in step 8) is forced air drying, with a drying temperature of 50-150 ℃ and a drying time of 4-24 h; the crushing method described in step 8) is grinding, grinding to a particle size of 200-300 mesh. In step 9), the calcination temperature is 200-600 ℃, the heating rate is 1-10 ℃ / min, and the calcination time is 4-10 h.

6. The method according to claim 1, characterized in that, The Rh / SiO2 catalyst described herein is applied to a gas-liquid-solid heterogeneous formaldehyde hydroformylation reaction. The reaction conditions are as follows: the reactor is a high-pressure reactor; the raw materials are a mixture of paraformaldehyde, CO, and H2 gas with a CO to H2 molar ratio of 1:1; the ligand is an organophosphorus ligand with a ligand to Rh molar ratio of 0-20; the reaction temperature is 50-150℃; the pressure is 1-11 MPa; and the reaction time is 1-12 h.

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