CN112808306A - Preparation method and application of metal oxygen cluster catalyst with stable organic acid - Google Patents
Preparation method and application of metal oxygen cluster catalyst with stable organic acid Download PDFInfo
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Abstract
The invention discloses a preparation method of a metal oxygen cluster catalyst with stable organic acid, which comprises the following steps: melting and roasting the metal oxide and potassium hydroxide at a molar ratio of 1 (8-12) at a high temperature, wherein the melting time is 2-8h and the temperature is 300-; dissolving a hydrated oxide and a cation precursor in ethanol, adding hydrogen peroxide, stirring and mixing, adding an organic acid for coordination, wherein the molar ratio of the hydrated oxide to the cation precursor to the organic acid is (0.5-2) to 1:1, the molar ratio of the hydrogen peroxide to the hydrated oxide is 12:1, and evaporating to dryness to obtain the metal oxygen cluster catalyst with stable organic acid. The metal oxygen cluster catalyst with stable organic acid has the advantages of simple preparation method, cheap and easily-obtained raw materials, high catalytic activity, good stability and recycling.
Description
Technical Field
The invention belongs to the technical field of green and clean catalysis, and particularly relates to a metal oxygen cluster catalyst which reduces the electron cloud density of a metal center after coordination of organic acid and has a stable structure, and the prepared metal oxygen cluster catalyst is applied to the reaction of selectively epoxidizing propylene and other olefins to prepare an epoxy compound.
Background
The epoxidation of olefins and alkenols plays an important role in industrial and synthetic chemistry. Epoxy compounds are important intermediates in the synthesis of fine chemicals, in particular for the manufacture of surfactants, polymers and epoxy resins. However, epoxidation reactions typically employ peroxy acids and hazardous organic solvents, which are expensive and environmentally hazardous. Hydrogen peroxide may be the best oxidant in addition to oxygen, both from an environmental and economic standpoint. Furthermore, it is sometimes better than oxygen because oxygen/organic mixtures sometimes spontaneously ignite and special ways must be taken to assess risk during the reaction.
In the epoxidation of propylene, the chlorohydrin process, the co-oxidation process (ethylbenzene co-oxidation process, cumene co-oxidation process, isobutane co-oxidation process) and the direct oxidation process (hydrogen peroxide direct oxidation process, oxygen direct oxidation process) are mainly used industrially at present. The chlorohydrin method has the defects of serious corrosion to equipment, serious environmental pollution of the generated calcium chloride-containing wastewater and the like, and is gradually eliminated, and the co-oxidation method has the defects of long process flow, various raw materials, high propylene purity requirement, high pressure for process operation, high equipment cost and high construction investment because alloy steel is adopted for equipment materials. The mutual restriction factors of the raw material source and the product sale are large, and in addition, the COD content of the sewage generated by the co-oxidation method is also high. Compared with the former two methods, only propylene oxide and water are generated in the production process of the direct oxidation method, the process flow is simple, the product yield is high, other co-products are not generated, basically no pollution is caused, the method belongs to an environment-friendly green chemical process, and the method is an important development direction of propylene epoxidation in the future. The current research results of the process for directly performing gas-phase epoxidation on propylene by using oxygen in the direct oxidation method are far from the industrial application, the research on the direct liquid-phase epoxidation of propylene by using hydrogen peroxide is more, and the related processes are gradually mature. Microporous titanium silicalite molecular sieves (TS-1) are widely used in propylene epoxidation reactions. However, since the pores in TS-1 are too small, the bulky olefin cannot easily contact the active sites in the pores, and thus the epoxidation activity for higher olefins is poor. In addition, these catalysts are susceptible to loss of active species under the reaction conditions. Meanwhile, homogeneous transition metal complexes are used as catalysts in olefin epoxidation. For example, homogeneous tungsten-containing complexes have higher catalytic activity than heterogeneous tungsten-based catalysts. In addition, the molybdenum complex also shows good catalytic activity and selectivity in olefin epoxidation reaction. These homogeneous catalysts suffer from common problems such as poor stability under catalytic oxidation conditions and difficulty in catalyst separation and recovery, which limits their use.
Organic-inorganic nanostructured materials are interesting systems with a wide variety of properties, which result from the intimate bonding of chemical bonds between inorganic and organic frameworks. As one of the nanostructured materials, metal oxide-based clusters have a wide and fascinating nature due to the variability of the constituent metals and structures, and, at the same time, have d0Transition metal (V) of railV,MoⅥ,WⅥ,NbⅤ,TaⅤEtc.) are potential oxygen donors in liquid phase oxidation reactions, they are receiving increasing attention.
Disclosure of Invention
The invention aims to provide a preparation method of a metal oxygen cluster catalyst with stable organic acid, and the prepared catalyst has the advantages of simple method, high catalytic activity and good stability.
It is another object of the present invention to provide a use of the organic acid-stable metal oxygen cluster catalyst prepared by the method in olefin epoxidation reactions.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the first aspect of the present invention provides a method for preparing an organic acid-stable metal-oxygen cluster catalyst, comprising the steps of:
melting and roasting the metal oxide and potassium hydroxide at a molar ratio of 1 (8-12) at a high temperature, wherein the melting time is 2-8h and the temperature is 300-;
dissolving a hydrated oxide and a cation precursor in ethanol, adding hydrogen peroxide, stirring and mixing, adding an organic acid for coordination, wherein the molar ratio of the hydrated oxide to the cation precursor to the organic acid is (0.5-2) to 1:1, the molar ratio of the hydrogen peroxide to the hydrated oxide is 12:1, and evaporating to dryness to obtain the metal oxygen cluster catalyst with stable organic acid.
The metal oxide is at least one of vanadium oxide, niobium oxide, tantalum oxide, tungsten oxide and molybdenum oxide.
The molar ratio of the metal oxide to the potassium hydroxide is 1: 10.
The melting time is 5h, and the temperature is 500-600 ℃.
The molar ratio of the hydrated oxide to the cationic precursor to the organic acid is 1:1: 1.
The cation precursor is selected from tetrabutylammonium hydroxide, choline hydroxide, guanidine carbonate and the like.
The organic acid is at least one of lactic acid, glycolic acid, tartaric acid, picolinic acid, pyrazine carboxylic acid, propionic acid and 3-hydracrylic acid.
The coordination time of adding the organic acid is 1-24 h.
The metal oxygen cluster catalyst with stable organic acid has the metal content of 15-25 wt% and the particle size of 2-3 nm.
In a second aspect, the invention provides the use of an organic acid-stable metal oxygen cluster catalyst prepared by the process in an olefin epoxidation reaction.
The olefin is C3 and C3 linear or branched chain olefin or cycloolefine, and is selected from propylene, cyclooctene, 1-octene, cis-2-octene, trans-2-octene, and cyclohexene.
The application of the organic acid stable metal oxygen cluster catalyst in olefin epoxidation reaction comprises the following steps:
dissolving a metal oxygen cluster catalyst with stable organic acid, olefin and toluene in methanol, adding hydrogen peroxide, heating for reaction, and completely reacting to obtain an epoxy compound; the molar ratio of the olefin to the organic acid-stable metal oxygen cluster catalyst is 100: 1; the concentration of the hydrogen peroxide is 20-50 wt%; the molar ratio of the hydrogen peroxide to the olefin is (0.8-2) to 1 (preferably 1: 1); the molar ratio of the toluene to the organic acid-stable metal oxygen cluster catalyst is (30-60): 1;
the alkene is selected from cyclooctene, 1-octene, cis-2-octene, trans-2-octene, cyclohexene;
or, the operation process of the propylene epoxidation reaction is as follows: dissolving a metal oxygen cluster catalyst with stable organic acid and toluene in methanol at room temperature, adding hydrogen peroxide, charging propylene with the pressure of 1.5MPa, heating for reaction, and completely reacting to obtain propylene oxide; the mol ratio of the propylene to the organic acid stable metal oxygen cluster catalyst is 3000: 1; the concentration of the hydrogen peroxide is 20-50 wt%; the molar ratio of the hydrogen peroxide to the propylene is 1: 3; the molar ratio of the toluene to the organic acid-stable metal oxygen cluster catalyst is (30-60): 1.
the concentration of the hydrogen peroxide is 30 percent.
The heating reaction is carried out at the temperature of 40-60 ℃ for 1-24 hours, and the temperature is preferably 40 ℃ or 50 ℃.
Due to the adoption of the technical scheme, the invention has the following advantages and beneficial effects:
the organic acid stable metal oxygen cluster catalyst has the advantages of simple preparation method, cheap and easily obtained raw materials, high catalytic activity, good stability, recycling and good catalyst stability, and compared with industrialized TS-1, the catalyst has the activity on low-carbon olefin and also has good activity on high-carbon olefin, such as cyclooctene, 1-octene and the like, and the TS-1 has poor activity on long-carbon olefin due to the pore channel, so the catalyst has a very good industrial application prospect.
The organic acid stable metal oxygen cluster catalyst is applied to the preparation of epoxide by olefin epoxidation, and the conversion rate of olefin is 99% at most and the selectivity of epoxide is 99% at most after reaction for 3 hours at 50 ℃.
Drawings
FIG. 1 is a high resolution TEM image of niobium oxide and organic acid-stable metal-oxygen cluster catalyst prepared in example 1.
FIG. 2 is an infrared spectrum of a niobium oxide and organic acid stabilized metal oxygen cluster catalyst prepared in example 1.
FIG. 3 is a thermogravimetric analysis of niobium oxide and organic acid-stabilized metal oxygen clusters prepared in example 1.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below in connection with preferred embodiments. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
The vanadium oxide used in the examples of the present invention was purchased from alatin chemical agents, ltd, 25g of analytical grade; niobium oxide was purchased from ai shou (Shanghai) chemical technology, Inc., 250g of analytical grade; the tantalum oxide is purchased from Shanghai Merlin Biotechnology, Inc., 250g of analytical reagent; the molybdenum oxide is purchased from Shanghai Merlin Biotechnology, Inc., and 500g of the molybdenum oxide is analytically pure; tungsten oxide Shanghai Michelin Biochemical technology, Inc., 250g of analytical grade; tetrabutylammonium hydroxide was purchased from alatin chemicals ltd, 500g of analytical grade; guanidine carbonate was purchased from alatin chemical, ltd, 500g of analytical grade; choline hydroxide was purchased from Shanghai Michelin Biochemical technology, Inc., 500mL of a 44 wt% aqueous solution; the lactic acid was purchased from Aladdin chemical reagent, Inc., 500mL of analytical grade; glycolic acid was purchased from Shanghai Tantake technologies, Inc. at 250g of analytical grade; tartaric acid was purchased from alatin chemicals, inc, 500g of analytical grade; picolinic acid was purchased from alatin chemicals, inc, 250g of analytical grade; pyrazine carboxylic acid was purchased from alatin chemicals, ltd, 100g of analytical grade; propionic acid was purchased from alatin chemical reagent, ltd, 500mL analytical grade; 3-Hydroxypropionic acid was purchased from Aladdin Chemicals, Inc., 5g of analytical grade; the potassium hydroxide is purchased from chemical reagents of national drug group, Inc., and 500g of the potassium hydroxide is analytically pure; acetic acid was purchased from Shanghai Tantake Technique, Inc., 500mL of analytical grade; cyclooctene was purchased from Shanghai Tantake technology, Inc., 25mL of analytical grade; cyclohexene was purchased from Shanghai Tantake Tech technologies, Inc. 100mL of analytical grade; 1-octene was purchased from Shanghai Tantake technologies, Inc., 500mL of analytical grade; cis 2-octene was purchased from Shanghai Tantake technologies, Inc., 25mL of analytical purity; trans 2-octene was purchased from Shanghai Tantake technologies, Inc. at 25mL analytical purity; 1, 5-cyclooctadiene was purchased from Shanghai Tantake Technology, Inc., 100mL of analytically pure; propylene was purchased from Shanghai spring rain specialty gases, Inc., 40L high purity gas.
The GC-MS model used in the embodiment of the invention is Agilent-6890GC-5973MS, and the chromatographic column model is HP-5MS, 30m multiplied by 0.25 mm.
Example 1
2.65g of niobium oxide (Nb)2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, the hydrated niobium oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (V, Ta, Mo and W) can be obtained by the same.
Mixing the hydrated niobium oxide (2.24g, 2.50mmol) and tetrabutylammonium hydroxide (0.65g, 2.50mmol) in 20mL of ethanol according to a molar ratio of 1:1, stirring, adding 30% hydrogen peroxide (11.00g, 30mmol), stirring for clarification, adding lactic acid (0.23g, 2.50mmol), stirring for 6h, and heating at 60 ℃ for drying to obtain a reddish brown viscous liquid, namely the organic acid stable metal oxygen cluster catalyst. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
The resulting catalyst can be confirmed by elemental analysis and infrared, e.g. [ TBA ]][LA]Stable niobium oxygen cluster Nb-OC @ [ TBA @][LA]The C, H, N element analyses were 42.8%, 7.2% and 2.6%, respectively, and the Nb content was 18.2% by ICP. Substantially in accordance with the amount added, while the structural characteristic peak of the corresponding functional group was also observed by infrared. For example, v (2874) and v (2965) on an infrared spectrum are C-H vibration peaks in organic acid, 1300--1Is the C-N vibration peak of 1646cm-1Is the carbonyl vibration peak in the organic acid coordinated with niobium, 885cm-1And 840cm-1Respectively, are the oscillation peaks of niobium-oxygen double bond (Nb ═ O) and niobium-oxygen niobium (Nb-O-Nb). These characterizations demonstrate that the niobium oxo cluster catalyst stabilized by organic acid was successfully synthesized.
Dissolving the prepared metal oxygen cluster catalyst (0.03g and 0.01mmol) and 0.05g of toluene in 5mL of methanol at room temperature, adding 1.1g of hydrogen peroxide (30 wt%), placing the reaction solution in a liner of a reaction kettle, placing the liner in the reaction kettle, sealing, slowly discharging a small amount of propylene after filling the reaction kettle, repeating for three times, filling 1.5MPa propylene (about 30mmol) into the reaction kettle, stirring for 12h at 40 ℃, stopping the reaction, immediately placing the reaction kettle in ice water for cooling, adding methanol into the reaction system for diluting after the reaction kettle is cooled to room temperature, performing qualitative and quantitative analysis on the diluted reaction solution by GC-MS (gas chromatography-mass spectrometry) (keeping the temperature at 50 ℃ for 2 min, then raising the temperature at 15 ℃/min to 220 ℃ for 2 min), wherein the yield of the propylene oxide relative to the hydrogen peroxide is 40%.
For the separation and recovery of the catalyst, manganese dioxide can be used for removing trace hydrogen peroxide possibly remaining in the reaction liquid, under the premise of ensuring that no hydrogen peroxide exists in the system, rotary evaporation is carried out for half an hour at the temperature of 60 ℃, and the solvent methanol, the added internal standard and the reaction generated water are removed. The last residue is the recycled catalyst which can be directly used for the next reaction, and the niobium-oxygen cluster catalyst is stable and can be recycled for more than 10 times without reducing the activity too much.
FIG. 1 is a high resolution TEM image of niobium oxide and organic acid-stable metal-oxygen cluster catalyst prepared in example 1. The four figures in the figure represent high resolution transmission electron microscopy images of different resolution times of commercial niobium oxide (a, b) and organic acid-stable niobium oxygen clusters (c, d), respectively, and illustrate that the organic acid-stable niobium oxygen clusters have much smaller particle size, are more dispersed and have more exposed active sites than commercial niobium oxide, which is also the reason why the catalyst can efficiently catalyze the epoxidation of propylene and other olefins.
FIG. 2 is an infrared spectrum of a niobium oxide and organic acid stabilized metal oxygen cluster catalyst prepared in example 1.
FIG. 3 is a thermogravimetric analysis of niobium oxide and organic acid-stabilized metal oxygen clusters prepared in example 1. It is clear from the figure that the niobium oxygen cluster with stable organic acid has good thermal stability, the weight is basically kept constant before 100 ℃, and the niobium oxygen cluster is not decomposed, which also indicates that the catalyst is very stable under the condition of removing the solvent by rotary evaporation at 60 ℃ after each reaction is finished, is convenient to separate and recover, and can be recycled for a plurality of times.
Example 2
2.65g of niobium oxide (Nb)2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, the hydrated niobium oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (V, Ta, Mo and W) can be obtained by the same.
Mixing and stirring the hydrated niobium oxide (2.24g and 2.50mol) and tetrabutylammonium hydroxide (0.65g and 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, adding hydrogen peroxide (11.00g and 30mol), stirring for clarification, adding lactic acid (0.23g and 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Cyclooctene (0.11g, 1mmol), the prepared metal oxygen cluster catalyst (0.03g, 0.01mmol) and toluene (0.05 g) are dissolved in methanol (2 mL), the solution is fully stirred and mixed in a reaction tube, hydrogen peroxide (30 wt%) 0.11g is added, the temperature is raised to 50 ℃ for reaction for 3 hours, after the reaction is finished, cyclohexane is used for multiple times of extraction, the collected cyclohexane phase is dried by anhydrous magnesium sulfate, the magnesium sulfate is removed by centrifugation, the obtained supernatant is subjected to qualitative and quantitative analysis by GC-MS (constant temperature of 150 ℃ for 5 minutes), the conversion rate of the cyclooctene is 99.9%, and the selectivity of epoxide is 99.9%.
The residual hydrogen peroxide in the reaction is removed by manganese dioxide in the extracted methanol solution, then the solvent is removed by rotary evaporation at 60 ℃, the residual catalyst can catalyze the next reaction, and the catalyst is easy to separate, recycle and reuse. Compared with the complex catalyst reported in the literature, the catalyst is easier to separate and recover and is more stable, and compared with commercial TS-1, the activity is better.
Example 3
2.65g of niobium oxide (Nb)2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, the hydrated niobium oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (V, Ta, Mo and W) can be obtained by the same.
Mixing and stirring the hydrated niobium oxide (2.24g and 2.50mol) and tetrabutylammonium hydroxide (0.65g and 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, adding hydrogen peroxide (11.00g and 30mol), stirring for clarification, adding lactic acid (0.23g and 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Dissolving 1-octene (0.11g, 1mmol), the prepared metal oxygen cluster catalyst (0.03g, 0.01mmol) and 0.05g of toluene in 2mL of methanol, fully stirring and mixing the solution in a reaction tube, adding 0.11g of hydrogen peroxide (30 wt%), heating to 50 ℃, reacting for 8 hours, extracting for multiple times by using cyclohexane after the reaction is finished, drying the collected cyclohexane phase by using anhydrous magnesium sulfate, centrifuging to remove the magnesium sulfate, and performing qualitative and quantitative analysis on the obtained supernatant by using GC-MS (constant temperature of 150 ℃ for 5 minutes), wherein the conversion rate of 1-octene is 40.5% and the selectivity of epoxide is 99.9%.
The residual hydrogen peroxide in the reaction is removed by manganese dioxide in the extracted methanol solution, then the solvent is removed by rotary evaporation at 60 ℃, the residual catalyst can catalyze the next reaction, and the catalyst is easy to separate, recycle and reuse.
Example 4
2.65g of niobium oxide (Nb)2O5) And 5.62g of potassium hydroxide (KOH) are placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, and the precipitate is dried for 0 hour at the temperature of 60 DEG C5h, finally obtaining hydrated niobium oxide with the water content of about 70 percent, and obtaining other hydrated metal oxides (V, Ta, Mo, W) by the same method.
Mixing and stirring the hydrated niobium oxide (2.24g and 2.50mol) and tetrabutylammonium hydroxide (0.65g and 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, adding hydrogen peroxide (11.00g and 30mol), stirring for clarification, adding lactic acid (0.23g and 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Dissolving cis-2-octene (0.11g, 1mmol), the prepared metal oxygen cluster catalyst (0.03g, 0.01mmol) and 0.05g of toluene in 2mL of methanol, fully stirring and mixing the solution in a reaction tube, adding 0.11g of hydrogen peroxide (30 wt%), heating to 50 ℃, reacting for 8 hours, extracting for multiple times by using cyclohexane after the reaction is finished, drying the collected cyclohexane phase by using anhydrous magnesium sulfate, centrifuging to remove the magnesium sulfate, and carrying out qualitative and quantitative analysis on the obtained supernatant by using GC-MS (constant temperature of 150 ℃ for 5 minutes), wherein the conversion rate of cis-2-octene is 66.5% and the selectivity of epoxide is 99.9%.
The residual hydrogen peroxide in the reaction is removed by manganese dioxide in the extracted methanol solution, then the solvent is removed by rotary evaporation at 60 ℃, the residual catalyst can catalyze the next reaction, and the catalyst is easy to separate, recycle and reuse.
Example 5
2.65g of niobium oxide (Nb)2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, the hydrated niobium oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (V, Ta, Mo and W) can be obtained by the same.
Mixing and stirring the hydrated niobium oxide (2.24g and 2.50mol) and tetrabutylammonium hydroxide (0.65g and 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, adding hydrogen peroxide (11.00g and 30mol), stirring for clarification, adding lactic acid (0.23g and 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Dissolving trans-2-octene (0.11g, 1mmol), the prepared metal oxygen cluster catalyst (0.03g, 0.01mmol) and 0.05g of toluene in 2mL of methanol, fully stirring and mixing the solution in a reaction tube, adding 0.11g of hydrogen peroxide (30 wt%), heating to 50 ℃, reacting for 8 hours, extracting for multiple times by using cyclohexane after the reaction is finished, drying the collected cyclohexane phase by using anhydrous magnesium sulfate, centrifuging to remove the magnesium sulfate, and carrying out qualitative and quantitative analysis on the obtained supernatant by using GC-MS (constant temperature of 150 ℃ for 5 minutes), wherein the conversion rate of trans-2-octene is 25.5% and the selectivity of epoxide is 99.9%.
The residual hydrogen peroxide in the reaction is removed by manganese dioxide in the extracted methanol solution, then the solvent is removed by rotary evaporation at 60 ℃, the residual catalyst can catalyze the next reaction, and the catalyst is easy to separate, recycle and reuse.
Example 6
2.65g of niobium oxide (Nb)2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, the hydrated niobium oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (V, Ta, Mo and W) can be obtained by the same.
Mixing and stirring the hydrated niobium oxide (2.24g and 2.50mol) and tetrabutylammonium hydroxide (0.65g and 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, adding hydrogen peroxide (11.00g and 30mol), stirring for clarification, adding lactic acid (0.23g and 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Cyclohexene (0.08g, 1mmol), the metal oxygen cluster catalyst (0.03g, 0.01mmol) prepared above and 0.05g toluene are dissolved in 2mL methanol, the solution is fully stirred and mixed in a reaction tube, 0.11g hydrogen peroxide (30 wt%) is added, the temperature is raised to 50 ℃ for reaction for 8h, after the reaction is finished, the cyclohexane is used for multiple times of extraction, the collected cyclohexane solution is dried by anhydrous magnesium sulfate, the magnesium sulfate is removed by centrifugation, the obtained supernatant is subjected to qualitative and quantitative analysis by GC-MS (maintaining at 50 ℃ for 3 minutes, raising the temperature at 20 ℃/min to 250 ℃) to ensure that the conversion rate of the cyclohexene is 88.9%, and the selectivity of the epoxide is 80.9%.
The residual hydrogen peroxide in the reaction is removed by manganese dioxide in the extracted methanol solution, then the solvent is removed by rotary evaporation at 60 ℃, the residual catalyst can catalyze the next reaction, and the catalyst is easy to separate, recycle and reuse.
Example 7
4.42g of tantalum oxide (Ta)2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, hydrated tantalum oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (V, Nb, Mo and W) can be obtained by the same method.
Mixing and stirring the hydrated tantalum oxide (3.67g and 2.50mol) and tetrabutylammonium hydroxide (0.65g and 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, adding hydrogen peroxide (11.00g and 30mol), stirring for clarification, adding lactic acid (0.23g and 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Dissolving the prepared metal oxygen cluster catalyst (0.03g, 0.01mmol) and 0.05g of toluene in 5mL of methanol, adding 1.1g of hydrogen peroxide (30 wt%), placing the reaction solution in a liner of a reaction kettle, placing the liner in the reaction kettle, sealing, slowly discharging a small amount of propylene after filling the reaction kettle, repeating for three times, filling 1.5MPa propylene (about 30mmol) into the reaction kettle, stirring for 12h at 40 ℃, stopping the reaction, immediately placing the reaction kettle in ice water for cooling, adding methanol into the reaction system for diluting after the reaction kettle is cooled to room temperature, carrying out qualitative and quantitative analysis on the diluted reaction solution by GC-MS (gas chromatography-mass spectrometry) (keeping the temperature at 50 ℃ for 2 min, then raising the temperature at 15 ℃/min to 220 ℃ for 2 min), wherein the yield of the propylene oxide relative to the hydrogen peroxide is 38%.
For the separation and recovery of the catalyst, manganese dioxide can be used for removing trace hydrogen peroxide possibly remaining in the reaction liquid, under the premise of ensuring that no hydrogen peroxide exists in the system, rotary evaporation is carried out for half an hour at the temperature of 60 ℃, and the solvent methanol, the added internal standard and the reaction generated water are removed. The last residue is the recycled catalyst which can be directly used for the next reaction, and the niobium-oxygen cluster catalyst is stable and can be recycled for more than 10 times without reducing the activity too much.
Example 8
1.82g of vanadium (V) oxide2O5) And 5.62g of potassium hydroxide (KOH) is placed in a mortar, the mixture is uniformly ground and then transferred to a nickel crucible, the mixture is roasted for 5 hours at the temperature of 550 ℃, water is added for dissolution and filtration after cooling to obtain a clear solution, then acetic acid is added for adjusting the pH value to about 5 to generate a large amount of white precipitate, the solution is subjected to suction filtration for 0.5 hour, the solution is dried for 0.5 hour at the temperature of 60 ℃, finally, hydrated vanadium oxide with the water content of about 70 percent is obtained, and other hydrated metal oxides (Ta, Nb, Mo and W) can be obtained by the same method.
Mixing the hydrated vanadium oxide (1.53g, 2.50mol) and tetrabutylammonium hydroxide (0.65g, 2.50mol) in 20mL of ethanol according to the molar ratio of 1:1, stirring, adding hydrogen peroxide (11.00g, 30mol), stirring for clarification, adding lactic acid (0.23g, 2.50mmol), stirring for 6h, heating at 60 ℃ and evaporating to dryness to obtain a reddish brown viscous liquid, namely the metal oxygen cluster catalyst with stable organic acid. The metal content of the obtained metal oxygen cluster catalyst with stable organic acid is 15-25 wt%, and the particle size is 2-3 nm.
Dissolving the prepared metal oxygen cluster catalyst (0.03g, 0.01mmol) and 0.05g of toluene in 5mL of methanol, adding 1.1g of hydrogen peroxide (30 wt%), placing the reaction solution in a liner of a reaction kettle, placing the liner in the reaction kettle, sealing, slowly discharging a small amount of propylene after filling the reaction kettle, repeating for three times, filling 1.5MPa propylene (about 30mmol) into the reaction kettle, stirring for 12h at 40 ℃, stopping the reaction, immediately placing the reaction kettle in ice water for cooling, adding methanol into the reaction system for diluting after the reaction kettle is cooled to room temperature, carrying out qualitative and quantitative analysis on the diluted reaction solution by GC-MS (gas chromatography-mass spectrometry) (keeping the temperature at 50 ℃ for 2 min, then raising the temperature at 15 ℃/min to 220 ℃ for 2 min), wherein the yield of the propylene oxide relative to the hydrogen peroxide is 35%.
For the separation and recovery of the catalyst, manganese dioxide can be used for removing trace hydrogen peroxide possibly remaining in the reaction liquid, rotary evaporation is carried out for half an hour at the temperature of 60 ℃ on the premise of ensuring that no hydrogen peroxide exists in the system, and the solvent methanol, the added internal standard and the water generated by the reaction are removed. The last residue is the recycled catalyst which can be directly used for the next reaction, and the niobium-oxygen cluster catalyst is stable and can be recycled for more than 10 times without reducing the activity too much.
The content of metal in the metal oxygen cluster catalyst with stable organic acid is detected by inductively coupled plasma emission spectroscopy (ICP), the content of niobium in the metal oxygen cluster catalyst with stable organic acid is 18.2 wt%, the recovery of the catalyst is very simple, the methanol solvent is removed by rotary evaporation at 60 ℃, and the content of niobium in the recovered catalyst is 17.9 wt%.
Comparing the particle size of commercial niobia with that of different organic acid-stable metal oxygen cluster catalysts by High Resolution Transmission Electron Microscopy (HRTEM), commercial niobia has a relatively large particle size (about 15-25nm) and is prone to agglomeration, but the organic acid-stable metal oxygen cluster catalyst has a particle size of only 2-3nm and is very dispersed and has few agglomeration phenomena, which is why the catalyst is highly active in olefin epoxidation.
Comparative example 1
The reaction residence time in the catalyst system is 2.63min, the reaction residence time in the TS-1 is 15-30min, the PO selectivity in the catalyst system after the reaction is 98.2%, the PO selectivity in the TS-1 is 98.7%, the total PO yield in the catalyst system is 89.8%, and the total PO yield in the TS-1 is 87.6%.
Compared with the prior art, the metal oxygen cluster catalyst is used for propylene epoxidation reaction in a microchannel reactor, has the advantages of mild condition, short retention time, high total PO yield and selectivity and the like, and has wide industrial application prospect.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A preparation method of a metal oxygen cluster catalyst with stable organic acid is characterized by comprising the following steps:
melting and roasting the metal oxide and potassium hydroxide at a molar ratio of 1 (8-12) at a high temperature, wherein the melting time is 2-8h and the temperature is 300-;
dissolving a hydrated oxide and a cation precursor in ethanol, adding hydrogen peroxide, stirring and mixing, adding an organic acid for coordination, wherein the molar ratio of the hydrated oxide to the cation precursor to the organic acid is (0.5-2) to 1:1, the molar ratio of the hydrogen peroxide to the hydrated oxide is 12:1, and evaporating to dryness to obtain the metal oxygen cluster catalyst with stable organic acid.
2. The method of claim 1, wherein the metal oxide is at least one of vanadium oxide, niobium oxide, tantalum oxide, tungsten oxide, and molybdenum oxide.
3. The method of claim 1, wherein the molar ratio of the metal oxide to the potassium hydroxide is 1: 10.
4. The method as claimed in claim 1, wherein the melting time is 5h and the temperature is 500-600 ℃.
5. The method of claim 1, wherein the hydrated oxide, the cationic precursor, and the organic acid are present in a molar ratio of 1:1: 1.
6. The method of claim 1, wherein the cation precursor is selected from tetrabutylammonium hydroxide, choline hydroxide, guanidine carbonate.
7. The method for producing an organic acid-stable metal oxide cluster catalyst according to claim 1, wherein the organic acid is at least one of lactic acid, glycolic acid, tartaric acid, picolinic acid, pyrazinecarboxylic acid, propionic acid, and 3-hydroxypropionic acid.
8. The method of claim 1, wherein the organic acid-stable metal oxide cluster catalyst is added for a period of 1-24 hours;
the metal oxygen cluster catalyst with stable organic acid has the metal content of 15-25 wt% and the particle size of 2-3 nm.
9. Use of an organic acid stable metal oxo cluster catalyst prepared by the process of any one of claims 1 to 8 in an olefin epoxidation reaction.
10. The use of the organic acid stable metal oxygen cluster catalyst in olefin epoxidation reaction according to claim 9, wherein the olefin is a linear or branched olefin or cyclic olefin having C3 and C3 or higher.
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