Preparation method and application of a bisphosphine ligand-modified rhodium-silicon catalyst

Abstract

This invention provides a method for preparing and applying a rhodium-silicon catalyst modified with bisphosphine ligands. The method involves first modifying the surface of a support with bisphosphine ligands, followed by impregnation and adsorption in a rhodium precursor solution to obtain a highly dispersed rhodium-based supported catalyst. This invention anchors rhodium through the coordination of bisphosphine ligands while simultaneously regulating its electronic structure, solving the problem of separation, recovery, and recycling of traditional homogeneous catalysts. It also achieves high dispersion of the active metal and high TOF of the ethanolaldehyde.

Description

Technical Field

[0001] This invention relates to the preparation and application of catalysts, specifically to a method for preparing a rhodium-silicon catalyst modified with bisphosphine ligands. The catalyst prepared by this method is applied in the field of formaldehyde hydroformylation to prepare ethanolaldehyde. Background Technology

[0002] Glycoaldehyde is an important chemical raw material widely used in the chemical, pharmaceutical, and food industries, possessing considerable market value. Its reaction with acrolein to produce ribose, a crucial molecule in the origin of life, is significant. Glycoaldehyde can also be hydrogenated to produce ethylene glycol, an important chemical raw material. In the food industry, glycoaldehyde serves as an effective browning agent, acting as an excellent browning promoter for food coloring, seasonings, and flavorings.

[0003] Formaldehyde hydroformylation is an important route for the production of glycolaldehyde and a crucial intermediate step in the direct synthesis of ethylene glycol from syngas. Currently reported catalysts for formaldehyde hydroformylation are mainly Co-based, Ru-based, and Rh-based homogeneous catalysts, with Rh catalysts being widely studied due to their superior activity. In 1977, Monsanto reported in patent EP0002908A that formaldehyde hydroformylation could be achieved under relatively mild conditions using bis(triphenylphosphine)-rhodium carbonyl chloride. In 1983, patent US4405814 reported that adding triethylamine to the RhCl(CO)(PPh3)2 catalytic system could effectively improve the reaction activity, achieving a glycolaldehyde yield as high as 86%. Although homogeneous reactions can achieve high glycolaldehyde yields and selectivity, the products are difficult to separate, and the precious metal catalysts are difficult to recover and recycle, which limits their industrial application.

[0004] The development of heterogeneous catalysts can effectively overcome the shortcomings of homogeneous reactions. Patent CN105618035A reports a supported catalyst for the hydroformylation of formaldehyde, in which Rh is loaded onto a SiO2 support via impregnation, solving the problem of catalyst separation. However, this catalyst exhibits low activity, with an ethanolaldehyde conversion rate significantly lower than that of homogeneous catalysts. In 2021, patent CN112337508A reported a Rh / N-SiO2 catalyst prepared via grafting, increasing the loading of rhodium at both the active center and the site, thus increasing the possibility of contact between the active center rhodium and the reactants, improving reaction activity, and achieving a maximum ethanolaldehyde yield of 59.1%. However, this catalyst exhibits poor stability.

[0005] As can be seen, existing Rh-based catalysts exhibit low activity and poor stability. Therefore, it is essential to develop formaldehyde hydroformylation catalysts with high activity and high stability.

[0006] To address the above problems, this invention is proposed. Summary of the Invention

[0007] The present invention aims to provide a highly active and stable rhodium-based catalyst for heterogeneous formaldehyde hydroformylation reaction.

[0008] The heterogeneous rhodium-based catalyst of this invention is prepared using porous silica as a support. The catalyst undergoes dehydration condensation between Si-OH and a silane coupling agent on the support, followed by further modification with a bisphosphine ligand, and finally forms a complex with an active metal. Its chemical formula is Rh / PNP-X, where the rhodium loading is 0.2-1.0 wt% based on the total mass of the Rh / PNP-X catalyst; X represents the support, which is one of amorphous SiO2, SBA-15, MCM-41, or HMS; and PNP represents the bisphosphine ligand bis[2-(diphenylphosphino)ethyl]ammonium.

[0009] This invention provides a method for preparing the catalyst described above, which is carried out according to the following steps:

[0010] (1) Under N2 protection, carrier X is added to an organic solvent to prepare a slurry with a solid content of 0.02-0.2 g / mL. Then, silane coupling agent is added dropwise according to the volume ratio of silane coupling agent to slurry of 0.02-0.2:1. The reaction is continued under N2 protection at 40-120℃ for 24-48 h. After filtration, the solid phase is washed with the above organic solvent, distilled water and ethanol respectively, and then dried under vacuum.

[0011] The carrier X is one or more of amorphous SiO2, SBA-15, MCM-41, and HMS, preferably amorphous SiO2.

[0012] The organic solvent is one of toluene, xylene, and ethanol, preferably toluene.

[0013] The silane coupling agent is one of chlorotriethoxysilane, trimethoxychlorosilane, (3-chloropropyl)trimethoxysilane, (3-chloropropyl)triethoxysilane, (chloromethyl)trimethoxysilane, and (chloromethyl)triethoxysilane, preferably (3-chloropropyl)triethoxysilane.

[0014] (2) Under N2 protection, the solid obtained in step (1) was added to an organic solvent to prepare a slurry with a solid content of 0.02-0.2 g / mL. Then, bisphosphine ligand bis[2-(diphenylphosphino)ethyl]ammonium hydrochloride (PNP) was added at a mass ratio of 1-4:1 between the bisphosphine ligand and the solid added in (1). Then, a deprotonating agent was added at a molar ratio of 1-5:1 between the deprotonating agent and the bisphosphine ligand. The mixture was stirred and the temperature was raised to 40-150℃ under N2 protection for 24-48 h before filtration. The solid phase was washed with dichloromethane and distilled water, and then dried at 100-120℃ overnight.

[0015] The organic solvent is one of toluene, xylene, and ethanol, preferably toluene.

[0016] The deprotonating agent is one of triethylamine, potassium carbonate, potassium bicarbonate, and sodium carbonate, preferably triethylamine.

[0017] (3) Prepare a rhodium solution with a concentration of 2.0-20.0 mmol / L by adding the rhodium precursor to an organic solvent, and dissolve it by sonication. The rhodium precursor is one of Rh(acac)(CO)2, RhCl3, HRh(PPh3)2Cl, Rh(PPh3)3Cl, and HRh(PPh3)3, preferably Rh(acac)(CO)2; wherein acac represents acetylacetone and PPh3 represents triphenylphosphine. The organic solvent is one of methanol, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, and acetylacetone, preferably ethanol.

[0018] (4) Add the PNP-X support prepared in step (2) to the rhodium solution in step (3) and stir for 5-48 h under N2 protection at 25 °C. Wash with the organic solvent, ethanol and deionized water in step (3) respectively, filter, and vacuum dry at 80-120 °C for 1-24 h to remove excess organic solvent to obtain the supported rhodium catalyst Rh / PNP-X for formaldehyde hydroformylation, wherein the rhodium loading is 0.2-1.0 wt%.

[0019] This invention provides an application of the above-mentioned catalyst, wherein the catalyst is an Rh / PNP-X catalyst, applied to a heterogeneous formaldehyde hydroformylation reaction;

[0020] Specifically, the Rh / PNP-X 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, the molar ratio of CO to H2 is 1:(0.5-2), the mass ratio of the added ligand triphenylphosphine to the catalyst is 0.5-25:1, the reaction temperature is 70-120℃, the pressure is 6-15MPa, and the reaction time is 1-5h.

[0021] The beneficial effects of this invention are as follows: By modifying the surface of the support, this invention increases the interaction between the metal and the support. The organic ligands influence the electronic structure of the central metal, which helps to lower the valence state of Rh and thus promotes the reaction. Furthermore, the Rh catalyst prepared from the organically grafted support prevents metal aggregation through ligand coordination, thereby improving the catalytic efficiency per unit Rh. Compared with existing technologies, the catalyst prepared by this invention, in addition to having the advantages of easy separation of solid catalysts from products and easy recovery and recycling of precious metals, significantly improves the catalytic efficiency per unit Rh, achieving 129.2 h⁻¹. -1 The high glycolaldehyde conversion frequency (TOF) Attached Figure Description

[0022] Figure 1 The infrared spectrum of the precursor prepared in Example 1.

[0023] Figure 2 Transmission electron microscopy (TEM) image of the Rh / PNP-SiO2 catalyst prepared in Example 1.

[0024] Figure 3 The graph shows a comparison of the activity of the Rh / PNP-SiO2 catalyst prepared in Example 1 with that of Comparative Examples 1 and 2. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in detail below, but the scope of protection of the present invention is not limited thereto.

[0026] The formaldehyde conversion rate, ethanol aldehyde selectivity, and TOF calculations in the embodiments of this application are as follows:

[0027] Conversion rate (formaldehyde) = (Mass of formaldehyde converted / Total mass of formaldehyde) × 100%

[0028] Selectivity (glycoaldehyde) = Amount of glycolaldehyde produced / Amount of formaldehyde converted × 100%

[0029] Yield (ethanolaldehyde) = Conversion (formaldehyde) × Selectivity (ethanolaldehyde)

[0030] TOF (glycoaldehyde) = Amount of glycolaldehyde produced / (Amount of rhodium in catalyst × Reaction time)

[0031] Example 1

[0032] Catalyst preparation:

[0033] The first aspect of this application provides a method for preparing a metal phosphide catalyst, comprising:

[0034] (1) Under N2 atmosphere, 2.0 g of amorphous SiO2 was added to 30 mL of toluene, followed by the dropwise addition of 4.0 mL of (3-chloropropyl)triethoxysilane. The reaction was carried out at 110 °C for 24 hours. After filtration, the solid phase was washed twice with toluene, and then twice each with ethanol and distilled water. The solid phase was dried in an oven at 100 °C for 24 hours to obtain surface-modified Cl-SiO2.

[0035] (2) Under N2 atmosphere, 3.82 g PNP, 1.00 g Cl-SiO2 and 1.64 g triethylamine were added to 30 mL of toluene, stirred, and reacted at 110 °C for 24 h under N2 atmosphere. Triethylamine was used as a deprotonating agent and also to capture HCl released during the reaction. The obtained solid was filtered, washed with dichloromethane and distilled water, and then dried at 100 °C overnight to obtain the bisphosphine ligand-modified support PNP-SiO2.

[0036] (3) Add 0.05g Rh(acac)(CO)2 to 40mL of ethanol and sonicate to disperse it evenly.

[0037] (4) The PNP-SiO2 support prepared in step (2) was added to the rhodium solution in step (3) and stirred for 24 h under N2 protection at 25 °C. The mixture was washed with alcohol and deionized water respectively, filtered, and dried under vacuum at 95 °C for 12 h to remove excess organic solvent, so as to obtain Rh / PNP-SiO2 catalyst with a rhodium loading of 0.54 wt%.

[0038] Catalyst evaluation:

[0039] The above catalyst was evaluated in a reaction apparatus for the hydroformylation of formaldehyde. First, paraformaldehyde (CH2O) was added to a 100 mL autoclave. n 1.97 g of formaldehyde, 0.785 g of triphenylphosphine, 25 mL of N,N-dimethylacetamide solvent, and 1.0 g of Rh / PNP-SiO2 catalyst were added. The reactor was purged three times with low-pressure nitrogen to remove air. Then, the reactor was purged three times with the raw material gas (CO:H2 molar ratio 1:1) to remove N2. The pressure was increased to 12 MPa, the temperature was raised to 95 °C, the stirring device was turned on, and the reaction was stopped after 3 hours, followed by natural cooling. Using isopropanol as an internal standard, the formaldehyde conversion rate and the selectivity of ethanolaldehyde, the main product of the formaldehyde hydroformylation reaction, were determined by gas-liquid chromatography. The results showed that the formaldehyde conversion rate was 31.8%, the ethanolaldehyde selectivity was 97.1%, and the time-of-flight (TOF) of the catalyst was 129.2 h⁻¹. -1 .

[0040] Example 2

[0041] Catalyst preparation:

[0042] (1) Under N2 atmosphere, 4.0 g of SBA-15 was added to 60 mL of toluene, followed by 4.0 mL of (3-chloropropyl)triethoxysilane. The reaction was carried out at 110 °C for 24 hours. The mixture was filtered, and the solid phase was washed twice with toluene, and then twice each with ethanol and distilled water. The solid phase was dried in an oven at 100 °C for 24 hours to obtain surface-modified Cl-SBA-15.

[0043] (2) Under a nitrogen atmosphere, 3.82 g PNP, 1.00 g Cl-SBA-15, and 1.64 g triethylamine were added to 30 mL of toluene, stirred, and reacted at 110 °C for 24 h. Triethylamine was used as a deprotonating agent and also to capture HCl released during the reaction. The obtained solid was filtered, washed with dichloromethane and distilled water, and then dried overnight at 100 °C to obtain the bisphosphine ligand-modified support PNP-SBA-15.

[0044] (3) Add 0.1g Rh(acac)(CO)2 to 40mL of ethanol and sonicate to disperse it evenly.

[0045] (4) The PNP-SBA-15 support prepared in step (2) was added to the rhodium solution in step (3) and stirred for 24 h under N2 protection at 25 °C. The mixture was washed with ethanol and deionized water respectively, filtered, and dried under vacuum at 95 °C for 12 h to remove excess organic solvent, so as to obtain the Rh / PNP-SBA-15 catalyst with a Rh loading of 0.41 wt%.

[0046] Catalyst evaluation:

[0047] The catalyst was evaluated according to the activity evaluation method in Example 1, and the results were as follows: formaldehyde conversion rate was 25.3%, ethanolaldehyde selectivity was 95.6%, and TOF was 76.5 h. -1 .

[0048] Example 3

[0049] Catalyst preparation:

[0050] (1) Under N2 atmosphere, 2.0 g of MCM-41 was added to 30 mL of toluene, followed by 4.0 mL of (3-chloropropyl)trimethoxysilane. The reaction was carried out at 110 °C for 24 hours. The mixture was filtered, and the solid phase was washed twice with toluene, and then twice each with ethanol and distilled water. The solid phase was dried in an oven at 80 °C for 12 hours to obtain surface-modified Cl-MCM-41.

[0051] (2) Under N2 atmosphere, 3.82 g PNP, 1.00 g Cl-MCM-41 and 1.64 g triethylamine were added to 30 mL toluene, stirred and reacted at 110 °C for 24 h. The obtained solid was filtered, washed with dichloromethane and distilled water, and then dried at 100 °C overnight to obtain the bisphosphine ligand modified support PNP-MCM-41.

[0052] (3) Add 0.1g Rh(acac)(CO)2 to 60mL of ethanol and sonicate to disperse it evenly.

[0053] (4) The PNP-MCM-41 support prepared in step (2) was added to the rhodium solution in step (3) and stirred for 24 h under N2 protection at 25 °C. The mixture was washed with ethanol and deionized water respectively, filtered, and dried under vacuum at 95 °C for 12 h to remove excess organic solvent, so as to obtain the Rh / PNP-MCM-41 catalyst with a Rh loading of 0.28 wt%.

[0054] Catalyst evaluation:

[0055] The catalyst was evaluated according to the activity evaluation method in Example 1, and the results were as follows: formaldehyde conversion rate was 23.5%, ethanolaldehyde selectivity was 96.2%, and TOF was 70.6 h. -1 .

[0056] Example 4

[0057] Catalyst preparation:

[0058] The method is the same as in Example 1, except that the (3-chloropropyl)triethoxysilane in step (1) is replaced with an equal volume of (chloromethyl)triethoxysilane to obtain the supported catalyst Rh / PNP-SiO2, with a Rh loading of 0.38 wt%. 。 .

[0059] Catalyst evaluation:

[0060] The catalyst was evaluated according to the activity evaluation method in Example 1, and the results were as follows: formaldehyde conversion rate was 29.4%, ethanolaldehyde selectivity was 95.1%, and TOF was 110.2 h. -1 .

[0061] Example 5

[0062] Catalyst preparation:

[0063] The method is the same as in Example 1, except that Rh(acac)(CO)2 in step (3) is replaced with an equimolar amount of RhCl3 to obtain the supported catalyst Rh / PNP-SiO2, with an Rh loading of 0.75wt%.

[0064] Catalyst evaluation:

[0065] The catalyst was evaluated according to the activity evaluation method in Example 1, and the results were as follows: formaldehyde conversion rate was 2%, ethanolaldehyde selectivity was 99.1%, and TOF was 8h. -1 .

[0066] Comparative Example 1

[0067] A comparison was made using a homogeneous catalyst, Rh(acac)(CO)2.

[0068] The activity evaluation method was the same as in Example 1, and the results were as follows: formaldehyde conversion rate was 41.3%, ethanolaldehyde selectivity was 98.4%, and TOF was 60.4 h. -1 .

[0069] Comparative Example 2

[0070] Application comparisons were conducted using Rh / SiO2 heterogeneous catalysts. The preparation method of the Rh / SiO2 heterogeneous catalyst is as follows:

[0071] (1) Add 0.1g Rh(acac)(CO)2 to 40mL of ethanol and sonicate it to disperse evenly to prepare a rhodium solution.

[0072] (2) Add 2g of amorphous SiO2 to the rhodium solution prepared in step (1). Stir at 30°C under N2 atmosphere for 24h. Filter the mixture and wash it three times with ethanol and deionized water. Dry the solid under vacuum at 95°C overnight to obtain the catalyst Rh / SiO2.

[0073] Catalyst evaluation:

[0074] The activity evaluation method was the same as in Example 1, and the results were as follows: formaldehyde conversion rate was 37.5%, ethanolaldehyde selectivity was 96.6%, and TOF was 79.0 h. -1 .

[0075] Table 1. Reaction conditions and results of Examples 1-5 and Comparative Examples

[0076] sample Formaldehyde conversion rate Glycoaldehyde selectivity <![CDATA[TOF(h -1 )]]> Example 1 31.8％ 97.1％ 129.2 Example 2 25.3％ 95.6％ 76.5 Example 3 23.5％ 96.2％ 70.6 Example 4 29.4％ 95.1％ 110.2 Example 5 2％ 99.1％ 8 Comparative Example 1 41.3％ 98.4％ 60.4 Comparative Example 2 37.5％ 96.6％ 79.0

[0077] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a rhodium-silicon catalyst modified with bisphosphine ligands, characterized in that, The rhodium-silicon catalyst is a Rh / PNP-X catalyst, comprising a support and an active component. The support is one of amorphous SiO2, SBA-15, MCM-41, and HMS, and the active component is an Rh species. Based on the total mass of the Rh / PNP-X catalyst, the loading of Rh element is 0.2-1.0 wt%. The preparation method steps are as follows: (1) Under N2 protection, carrier X was added to organic reagent to prepare a slurry with a solid content of 0.02-0.2 g / mL. Then, silane coupling agent was added dropwise according to the volume ratio of silane coupling agent to slurry of 0.02-0.2:

1. The temperature was raised to 40-120 °C and reacted for 24-48 h under N2 protection. After filtration, the solid phase was washed with the above organic solvent, distilled water and ethanol respectively, and then dried under vacuum. The organic solvent is one of toluene, xylene, and ethanol; The silane coupling agent is one of chlorotriethoxysilane, trimethoxychlorosilane, (3-chloropropyl)trimethoxysilane, (3-chloropropyl)triethoxysilane, (chloromethyl)trimethoxysilane, and (chloromethyl)triethoxysilane. (2) Under N2 protection, the solid obtained in step (1) is added to an organic solvent to prepare a slurry with a solid content of 0.02-0.2 g / mL. Then, bisphosphine ligand bis[2-(diphenylphosphino)ethyl]ammonium hydrochloride PNP is added at a mass ratio of 1-4:1 between the bisphosphine ligand and the solid added in (1). Then, deprotonating agent is added at a molar ratio of 1-5:1 between the deprotonating agent and the bisphosphine ligand. The mixture is stirred and the temperature is raised to 40-150 °C under N2 protection for 24-48 h. The mixture is then filtered. The solid phase is washed with dichloromethane and distilled water, and then dried at 100-120 °C overnight. The organic solvent is one of toluene, xylene, and ethanol; The deprotonating agent is one of triethylamine, potassium carbonate, potassium bicarbonate, and sodium carbonate; (3) Add the rhodium precursor to an organic reagent to prepare a rhodium solution with a concentration of 2.0-20.0 mmol / L, and sonicate it to dissolve; the rhodium precursor is one of Rh(acac)(CO)2, RhCl3, HRh(PPh3)2Cl, Rh(PPh3)3Cl, and HRh(PPh3)3; wherein acac represents acetylacetone and PPh3 represents triphenylphosphine; the organic solvent is one of methanol, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, and acetylacetone; (4) Add the PNP-X support prepared in step (2) to the rhodium solution in step (3), stir at 25 °C and under N2 protection for 5-48 h; wash with the organic solvent, ethanol and deionized water in step (3) respectively, filter, and vacuum dry at 80-120 °C for 1-24 h to remove excess organic solvent, and obtain the supported rhodium catalyst Rh / PNP-X for formaldehyde hydroformylation.

2. The catalyst prepared by the method according to claim 1.

3. The catalyst prepared by the method described in claim 1 is used for the gas-liquid-solid heterogeneous formaldehyde hydroformylation reaction. The reaction conditions are as follows: the reactor is a batch reactor; the raw materials are a mixture of paraformaldehyde, CO, and H2; the molar ratio of CO to H2 is 1:(0.5-2); the mass ratio of the added ligand triphenylphosphine to the catalyst is 0.5-25:1; the reaction temperature is 70-120 °C; the pressure is 6-15 MPa; and the reaction time is 1-5 h.

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