A composite metal single atom ozone catalytic oxidation catalyst and preparation method thereof

Abstract

The present invention discloses a composite metal single-atom ozone catalytic oxidation catalyst and a preparation method thereof. A nitrogen-containing ligand, an organic carbohydrate, and / or a silicon-containing template are dissolved in a water / alcohol organic solvent, mixed with a soluble metal salt solution, and prepared into a mixed solution of nitrogen-containing and silicon-containing single-atom precursors under the conditions of hydrothermal reaction and mechanical stirring; then dispersed and dissolved in a sufficient amount of solvent to form an impregnation liquid, and the carrier is completely immersed in the impregnation liquid; then a reducing agent is gradually added, and after the addition is completed, the mixture is impregnated and dried; then calcined in stages under an inert atmosphere, and then alkali leaching is performed to remove the silicon-based ligands, and finally a composite metal single-atom ozone catalytic oxidation catalyst is obtained. The present invention has a high loading amount and ozone catalytic activity, a large specific surface area, and a pleated sheet structure similar to graphene oxide, and has a highly efficient catalytic effect.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to a composite metal single-atom ozone catalytic oxidation catalyst and a preparation method thereof. Background Art

[0002] The research of single-atom catalysis technology in academia and industry has a history of nearly 20 years. The catalytic active sites formed by the bonding and coordination of single atoms of catalytic active components with heteroatoms achieve the maximum utilization of the atoms in the catalytic sites, often showing characteristics such as high activity, high selectivity and high stability. This technology is widely regarded in the field of heterogeneous catalysis as an effective way to effectively solve the current technical problems such as the high price of precious metal and rare earth metal catalysts, the low catalytic efficiency and selectivity of transition metal catalysts, and the poor uniformity of active sites compared with homogeneous catalysts, resulting in poor reaction controllability.

[0003] The active site of a single-atom catalyst does not refer to a single zero-valent metal atom center, but rather to the coordination structure formed by the single atom of the catalytically active component and other atoms on the ligand or carrier, which causes electron transfer and effectively catalyzes the reaction. Single-atom catalysis is different from nanocatalysis and sub-nanocatalysis. It only increases the contact area of ​​the active site with the reactants. When the particle dispersion reaches the single-atom size, it causes a sharp increase in surface free energy, quantum size effect, unsaturated coordination environment and metal-carrier interaction. These synergistic characteristics give the catalyst extremely high catalytic performance. Single-atom catalysts also have shortcomings. When metal particles are reduced to the single-atom level, the specific surface area increases sharply, resulting in a sharp increase in the metal surface free energy, and it is very easy to agglomerate and couple to form large clusters, which leads to reduced catalyst deactivation or reduced selectivity. Therefore, meeting the requirements of stability, high selectivity and high loading at the same time has become a technical problem that needs to be solved in the field of single-atom catalysts. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a composite metal single-atom ozone catalytic oxidation catalyst with high loading, high catalytic activity and high stability and a preparation method thereof.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is a method for preparing a composite metal single-atom ozone catalytic oxidation catalyst, characterized in that it comprises the following steps:

[0006] Step 1: dissolving a nitrogen-containing ligand, an organic carbohydrate, and / or a silicon-containing template in a water / alcohol organic solvent, and then mixing with a soluble metal salt solution to prepare a mixed solution of nitrogen-containing and silicon-containing single atom precursors under conditions of hydrothermal reaction and mechanical stirring;

[0007] Step 2, uniformly dispersing and dissolving the mixed solution of the precursors prepared in step 1 in a sufficient amount of solvent to prepare an impregnation solution, completely immersing the carrier in the impregnation solution, and ensuring sufficient mixing by a circulating water pump;

[0008] Step 3, gradually add the reducing agent to the impregnation solution of step 2, mix and impregnate for 3 to 12 hours, and then put it into a 60 to 110 ° C oven for drying to obtain a catalyst semi-finished product;

[0009] Step 4, calcining the semi-finished catalyst obtained in step 3 in stages under an inert atmosphere, the first calcination stage, i.e., the decomposition temperature of the nitrogen-containing ligand, and the second calcination stage, i.e., the decomposition temperature of the organic carbohydrate, to obtain a primary composite metal single atom ozone catalytic oxidation catalyst;

[0010] Step 5, subjecting the primary composite metal single atom ozone catalytic oxidation catalyst obtained in step 4 to alkaline leaching to remove silicon-based ligands, and finally obtaining a composite metal single atom ozone catalytic oxidation catalyst.

[0011] In a preferred technical solution, the soluble metal salt solution in step 1 is one or two of the hydrochlorides, nitrates, sulfates or acetates of Fe, Co, Ni, Cu, Mn, Pt, Pd and Ru.

[0012] In the above technical solution, although Pt is very expensive, its usage is small and its catalytic efficiency is generally higher under the condition of the same usage of transition metal ions, so Pt, Fe and Mn are preferred.

[0013] The preferred technical solution is that the nitrogen-containing ligand is dicyandiamide, melamine, urea, aminophosphoric acid resin, thiourea, ammonium fluoride, heme oxide, 2,4,6-triaminopyrimidine and a hydrophilic imidazole ionic liquid type ligand, including iodide, bromide, nitrate, methyl sulfate, methanesulfonate, trifluoromethanesulfonate, dimethyl phosphate and tetrafluoroborate of 1,3-dimethylimidazole, 1-vinyl-3-methylimidazole and 1-propyl-3-methylimidazole.

[0014] In the above technical scheme, dicyandiamide, melamine and 1,3-dimethylimidazole tetrafluoroborate are preferred, and melamine and methyl sulfate of 1-propyl-3-methylimidazole are more preferred.

[0015] In a preferred technical solution, the organic carbohydrates in step 1 are water-soluble organic carbohydrates, specifically including one or two of water-soluble lignin, water-soluble chitosan, glucose, sodium alginate, polyethylene glycol, water-soluble polyols, and isobutylene-maleic anhydride copolymer.

[0016] In the above technical solution, isobutylene-maleic anhydride copolymer or polyethylene glycol is preferred.

[0017] In a preferred technical solution, the silicon-containing template in step 1 specifically includes one of ethyl orthosilicate, N-n-butyl-3-aminopropyltrimethoxysilane or bis[3-(triethoxysilyl)propyl]amine (KH-A1171).

[0018] In the above technical solution, N-n-butyl-3-aminopropyltrimethoxysilane is preferred.

[0019] In a preferred technical solution, the alcohol organic solvent in step 1 is one of anhydrous ethanol, propanol, butanol and isopropanol.

[0020] In the above technical solution, isopropanol is preferred, and the volume ratio of water to alcohol is 5: 1 to 25: 1. The amount of solvent used is sufficient to dissolve all solid components, and the viscosity of the mixture should be suitable for stirring and subsequent hydrothermal reaction.

[0021] In a preferred technical solution, the mass ratio of the soluble metal salt, the organic carbohydrate, the nitrogen-containing ligand and the silicon-containing template in step one is (24-64): (1-4): (15-40): (5-15).

[0022] In the above technical solution, if the amount of metal salt exceeds a certain amount, some carbide and nitride particles will be generated. This may be because the metal atom loading exceeds the threshold and agglomerates to form multi-atom clusters, and the dispersed form of single atoms can no longer be maintained. High viscosity organic carbon will make the precursor difficult to stir, and the amount of solvent can be appropriately increased.

[0023] According to a preferred technical solution, the hydrothermal reaction in step 1 is carried out in a closed container equipped with a stirring paddle, the reaction conditions are 45-65°C, the reaction time is 2-12 hours, preferably 55°C.

[0024] In the above technical solution, a higher reaction temperature may cause premature carbonization of organic carbon, thereby affecting the subsequent impregnation step.

[0025] In a preferred technical solution, the reducing agent in step three is one of potassium borohydride, sodium borohydride, sodium thiosulfate, oxalic acid, and ascorbic acid, and the molar ratio of the reducing agent to the metal ion is (1 to 1.5):1.

[0026] The preferred technical solution is that the calcination temperature in the first stage is 550-650°C, the calcination insulation time is 2-8 hours, the calcination temperature in the second stage is 750-1000°C, the calcination time is 2-8 hours, and finally a primary composite metal single atom ozone catalytic oxidation catalyst is obtained.

[0027] In the above technical solution, in order to ensure the complete degradation and conversion of nitrogen-containing coordination, it is preferred that the first stage calcination is carried out at 600-650°C for 6 hours, and the second stage calcination is carried out at 850-1000°C for 2-4 hours.

[0028] The advantages of the present invention are:

[0029] 1. The catalyst prepared by the present invention has a high loading amount and ozone catalytic activity, a large specific surface area, and a wrinkled sheet structure similar to graphene oxide;

[0030] 2. In the present invention, nitrogen atoms play an anchoring role on metal atoms when they are doped into the lattice of graphite-like carbon materials, so that single metal atoms are evenly anchored in the graphene sheets through coordination with nitrogen to form a catalyst with multiple active sites;

[0031] 3. In the present invention, the silicon-containing template effectively improves the thermal stability of the catalyst calcination process and avoids the catalytic deactivation caused by sintering;

[0032] 4. In the present invention, the process of staged calcination ensures a high ratio of carrier coordination sites to single-atom catalysts and also improves sintering stability;

[0033] 5. The preparation method of the present invention has a simple process, and the raw materials and reagents are common, easily available and low in cost. It is simple and easy to operate and has good stability, and is suitable for large-scale production;

[0034] 6. The hydrothermal synthesis in the present invention has low requirements on the reactor, and the low temperature reaction conditions are also more energy-efficient;

[0035] 7. The inert atmosphere used in the calcination process of the present invention is relatively safe and easy to implement. The small amount of ammonia generated during the sintering process (from the decomposition of nitrogen-containing coordination) can be treated by simply setting up an ammonia absorption tower;

[0036] 8. In the present invention, the catalyst structure system constructed with the composite single atom of Cu / Mn as the center exhibits an ozone catalytic oxidation removal rate of organic pollutants, and is expected to be widely used in the field of advanced oxidation water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. The accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0038] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0039] Figure 1 This is a transmission electron microscope (TEM) morphology image of the composite metal single atom ozone catalytic oxidation catalyst of Example 1;

[0040] Figure 2 This is a sub-angstrom resolution dark field scanning transmission electron micrograph (HAADF-STEM) of the composite metal single atom ozone catalytic oxidation catalyst of Example 1;

[0041] Figure 3 This is a transmission electron microscope (TEM) morphology image of the composite metal single atom ozone catalytic oxidation catalyst of Example 2;

[0042] Figure 4 This is a sub-angstrom resolution dark field scanning transmission electron micrograph (HAADF-STEM) of the composite metal single atom ozone catalytic oxidation catalyst of Example 2;

[0043] Figure 5 This is a transmission electron microscope (TEM) morphology image of the composite metal single atom ozone catalytic oxidation catalyst of Example 3;

[0044] Figure 6 This is a sub-angstrom resolution dark field scanning transmission electron micrograph (HAADF-STEM) of the composite metal single atom ozone catalytic oxidation catalyst of Example 3;

[0045] Figure 7 It is a comparison chart of wastewater influent water quality indicators of Examples 1 to 3;

[0046] Figure 8 It is a comparison chart of the water quality indicators of wastewater produced by Examples 1 to 3;

[0047] Fig. 9 It is a comparison chart of the removal rate of organic pollutants before and after the wastewater reaction of Examples 1 to 3. DETAILED DESCRIPTION

[0048] The operating conditions of the ozone catalytic oxidation of wastewater in each embodiment of the present invention are specifically as follows: the dimensions of the columnar reaction container are 14 cm in diameter, 60 cm in height, the reaction chamber volume is 2.5 L, the filling volume of the catalyst bed is 1.8 L, the water inlet is 90% of the total volume of the reactor, the reaction mode is intermittent reaction, the ozone dosage is 5 g / h, and the reaction time is 2 to 8 h.

[0049] Embodiment 1:

[0050] The catalyst precursor is composed of a solution of 5g of ISOBAM104 (copolymer of isobutylene and maleic anhydride) with a solid content, 40g of dicyandiamide, 20g of ethyl orthosilicate, 30g of copper sulfate pentahydrate and 20g of ferric sulfate nonahydrate dissolved in 3L of a mixed solvent of deionized water / isopropanol (5:1), and reacted for 4h under sufficient stirring at a reaction temperature of 45°C. The prepared solution containing the precursor is added to an appropriate amount of deionized water and fully mixed under the action of a circulating water pump.

[0051] Add 1kg of 2-4cm activated carbon particles with an iodine value of not less than 500, and slowly add 60mL of 1mol / L sodium borohydride solution. After continuous mixing for 12 hours, filter to obtain solid catalyst particles, and transfer to a vacuum oven at 80°C to dry for 6 hours or until completely dry.

[0052] The completely dried catalyst semi-finished product is transferred into a tubular heating reactor protected by nitrogen atmosphere, calcined at 600°C for 4 hours in the first stage, calcined at 900°C for 2 hours in the second stage, cooled to below 150°C or close to room temperature under the protection of nitrogen atmosphere, taken out to obtain the finished composite metal single-atom ozone catalytic oxidation catalyst, and then transferred to 2M NaOH aqueous solution for alkaline leaching for 1 hour, filtered and washed until the washing liquid is neutral, and dried to obtain the finished composite metal single-atom ozone catalytic oxidation catalyst, such as Figures 1-2 shown.

[0053] The reaction time for ozone catalytic oxidation of wastewater from a Lancoke coking enterprise in Shaanxi using the composite metal single atom ozone catalytic oxidation catalyst is 2 hours.

[0054] Embodiment 2:

[0055] The catalyst precursor is composed of 6g of glucose aqueous solution, 40g of melamine, 30g of KH-A1171, 40g of copper sulfate pentahydrate and 20g of cobalt acetate pentahydrate dissolved in 2L of deionized water / isopropanol (2:1) mixed solvent, and reacted for 6h under fully stirring conditions at a reaction temperature of 55°C. The prepared solution containing the precursor is added to an appropriate amount of deionized water and fully mixed under the action of a circulating water pump.

[0056] Add 1 kg of columnar activated carbon with a diameter of 0.7 cm and a length of 2 to 4 cm, and slowly add 72 mL of 1 mol / L potassium borohydride solution. After continuous mixing for 12 hours, filter and obtain solid catalyst particles, transfer to a vacuum oven at 80°C and dry for 6 hours or until completely dry.

[0057] The completely dried catalyst was transferred into a tubular heating reactor protected by nitrogen atmosphere, calcined at 600°C for 4 hours in the first stage, calcined at 900°C for 4 hours in the second stage, cooled to below 150°C or close to room temperature under nitrogen atmosphere protection, taken out to obtain a primary composite metal single atom ozone catalytic oxidation catalyst, and then transferred to 2M NaOH aqueous solution for alkaline leaching for 2 hours, filtered and washed until the washing liquid was neutral, and dried to obtain a finished catalyst. Figures 3-4 shown.

[0058] The reaction time of using the composite metal single atom ozone catalytic oxidation catalyst to catalyze the ozone oxidation of high-concentration concentrated organic wastewater from a polyimide membrane in Wuxi is 8 hours.

[0059] Embodiment 3:

[0060] The composition of the catalyst precursor is: 10g of water-soluble lignin, 20g of 1,3-dimethylimidazolium bromide, 30g of N-n-butyl-3-aminopropyltrimethoxysilane, 20g of ferric sulfate nonahydrate and 40g of manganese chloride tetrahydrate are dissolved in 3L of deionized water / isopropanol (2:1) mixed solvent, and reacted for 4 hours under sufficient stirring conditions at a reaction temperature of 55°C.

[0061] Add the prepared solution containing the precursor into an appropriate amount of deionized water and mix thoroughly under the action of a circulating water pump.

[0062] Add 1 kg of γ-activated alumina balls with a diameter of 4 to 6 mm, and slowly add 80 mL of 1 mol / L sodium borohydride solution. After continuous mixing for 12 hours, filter and obtain the solid catalyst balls, transfer them to a vacuum oven at 80°C and dry them for 6 hours or until completely dry.

[0063] The completely dried catalyst was transferred into a tubular heating reactor protected by nitrogen atmosphere, calcined at 650°C for 4 hours in the first stage, calcined at 900°C for 4 hours in the second stage, cooled to below 150°C or close to room temperature under nitrogen atmosphere protection, and the finished composite metal single atom ozone catalytic oxidation catalyst was obtained. The catalyst was then transferred to 1M NaOH aqueous solution for alkaline leaching for 3 hours, filtered and washed until the washing liquid was neutral, and dried to obtain the finished catalyst. Figures 5-6 shown.

[0064] The reaction time for ozone catalytic oxidation of high-concentration organic wastewater from a petrochemical enterprise in Shandong using this composite metal single-atom ozone catalytic oxidation catalyst is 3 hours.

[0065] like Figures 7 to 9As shown, the wastewater inlet, water production and organic pollutant removal rates of the three embodiments are compared. It can be seen that the composite metal single-atom ozone catalytic oxidation catalyst of the present invention has a high removal rate of organic pollutants in wastewater and is a very efficient catalyst.

Claims

1. A method for preparing a composite metal single atom ozone catalytic oxidation catalyst, It is characterized in that The following steps are involved: Step 1: dissolving a nitrogen-containing ligand, an organic carbohydrate and a silicon-containing template in water and an alcohol organic solvent, and then mixing with a soluble metal salt solution to prepare a mixed solution of nitrogen-containing and silicon-containing single-atom precursors under the conditions of hydrothermal reaction and mechanical stirring, wherein the mass ratio of the soluble metal salt, the organic carbohydrate, the nitrogen-containing ligand and the silicon-containing template is (24-64): (1-4): (15-40): (5-15), and the soluble metal salt solution is a hydrochloride, nitrate, sulfate or acetate of two of Fe, Co, Ni, Cu, Mn, Pt, Pd and Ru; Step 2, uniformly dispersing and dissolving the mixed solution of the precursors prepared in step 1 in a sufficient amount of solvent to prepare an impregnation solution, completely immersing the carrier in the impregnation solution, and ensuring sufficient mixing by a circulating water pump; Step 3, gradually adding a reducing agent to the impregnation solution of step 2, wherein the reducing agent is one of potassium borohydride, sodium borohydride, sodium thiosulfate, oxalic acid, and ascorbic acid, and the molar ratio of the reducing agent to the metal ion is (1-1.5):

1. After the addition is completed, the mixture is mixed and impregnated for 4-12 hours, and then placed in an oven at 60-110° C. for drying to obtain a catalyst semi-finished product; Step 4, calcining the catalyst semi-finished product obtained in step 3 in stages under an inert atmosphere, the first calcination stage, i.e., the decomposition temperature of the nitrogen-containing ligand, the first stage calcination temperature is 550-650°C, the calcination holding time is 2-8 hours, the second calcination stage, i.e., the decomposition temperature of the organic carbohydrate, to obtain a primary composite metal single atom ozone catalytic oxidation catalyst, the second stage calcination temperature is 750-1000°C, and the calcination time is 2-8 hours; Step 5, subjecting the primary composite metal single atom ozone catalytic oxidation catalyst obtained in step 4 to alkaline leaching to remove silicon-based ligands, and finally obtaining a composite metal single atom ozone catalytic oxidation catalyst.

2. A method for preparing a composite metal single atom ozone catalytic oxidation catalyst according to claim 1, It is characterized in that The nitrogen-containing ligands are dicyandiamide, melamine, urea, aminophosphoric acid resin, thiourea, ammonium fluoride, heme oxide, 2,4,6-triaminopyrimidine and hydrophilic imidazole ionic liquid type ligands, including iodide, bromide, nitrate, methyl sulfate, methanesulfonate, trifluoromethanesulfonate, dimethyl phosphate or tetrafluoroborate of 1,3-dimethylimidazole, 1-vinyl-03-methylimidazole and 1-propyl-3-methylimidazole.

3. A method for preparing a composite metal single atom ozone catalytic oxidation catalyst according to claim 1, It is characterized in that The organic carbohydrates in step 1 are water-soluble organic carbohydrates, specifically including one or two of water-soluble lignin, water-soluble chitosan, glucose, sodium alginate, polyethylene glycol, water-soluble polyols, and isobutylene-maleic anhydride copolymer.

4. The method for preparing a composite metal single atom ozone catalytic oxidation catalyst according to claim 1, It is characterized in that The silicon-containing template in step 1 specifically includes one of ethyl orthosilicate, N-n-butyl-3-aminopropyltrimethoxysilane or bis[3-(triethoxysilyl)propyl]amine.

5. A method for preparing a composite metal single atom ozone catalytic oxidation catalyst according to claim 1, It is characterized in that The alcohol organic solvent in step 1 is one of anhydrous ethanol, propanol, butanol and isopropanol.

6. A composite metal single atom ozone catalytic oxidation catalyst, Features: The catalyst is prepared by the method for preparing a composite metal single-atom ozone catalytic oxidation catalyst according to any one of claims 1 to 5.

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