A chitin sponge-supported Pd-based nanocatalyst, its preparation method and application

Abstract

The present invention discloses a chitin sponge-supported Pd-based nanocatalyst, its preparation method and application, belonging to the technical fields of dechlorination reaction technology and new catalyst preparation technology. Chitin is dissolved in an alkali solution, compounded with a sponge and then heated to obtain a chitin sponge carrier rich in amino groups and with three-dimensional intertwined nanofibers; metal ions are adsorbed on it and reduced to metal nanoparticles. This catalyst is a macroscopic shaped material with elasticity and easy-to-control shape and size, with a metal loading of more than 18 wt.%, and the average particle size is about 3 nm; the metal nanoparticles can be uniformly and densely distributed on the chitin nanofibers and are not easily shed and lost; it has well-developed internal pores, which is conducive to mass transfer and the exposure of active sites; it can completely dechlorinate 1 mM of p-chlorophenol at a continuous flow rate of 6500 L·m⁻²·h⁻¹ at room temperature, and can operate for more than 500 h without deactivation at a flow rate of 65 L·m⁻²·h⁻¹.

Description

Technical Field

[0001] The present invention belongs to the technical fields of dechlorination reaction technology and novel catalyst preparation technology, and particularly relates to a Pd-based nanocatalyst supported on chitin sponge, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and does not necessarily constitute an admission or imply in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Chlorinated organic compounds are a type of commonly used chemical raw materials, intermediates, and organic solvents, which are widely used in industries such as petroleum, metallurgy, pharmaceuticals, and papermaking. They have the characteristics of high toxicity, stable chemical structure, difficult biodegradation, and easy bioaccumulation. The excessive use of chlorinated organic compounds has gradually increased their exposure in the ecological environment, posing a great threat to human health and the natural environment. Due to the strong C-Cl bonding (>327 kJ·mol -1 ) and strong biological toxicity of chlorinated organic compounds, conventional biochemical or physicochemical methods used in sewage treatment plants are difficult to achieve the complete degradation of chlorinated organic compounds. In recent years, a large number of studies have been devoted to developing hydrodechlorination strategies. Through catalytic reactions, the C-Cl bond is broken, and chlorinated organic compounds are converted into less toxic chemical substances, followed by subsequent conventional treatment. Among the existing catalysts, supported palladium (Pd)-based catalysts have much higher hydrogen dissociation and C-Cl bond breaking activities than Ni, Fe, and Cu-based catalysts, and are easier to recover than homogeneous catalysts, so they have received extensive attention. The carriers of these catalysts are usually activated carbon, silica, and foam metal, and the catalytic activity can be further improved by adding metal promoters such as magnesium, cobalt, copper, and bismuth.

[0004] The invention patent (CN 101298049 B) discloses a hydrodechlorination catalyst suitable for chlorinated organic pollutants in water. The foam metal carrier is cut into small pieces, degreased by washing in an organic solvent, the oxide layer is removed by ultrasonic treatment with dilute sulfuric acid solution, and then Pd is plated on the surface of the carrier by electroless plating to obtain a Pd / foam metal catalyst. Since the preparation process does not require high-temperature hydrogen reduction treatment, the catalyst formed has small particle size, high dispersion, and strong activity.

[0005] The invention patent (CN 103406150 B) discloses a metal Pd complex catalyst supported on a polyacrylic acid polymer and its preparation method. The metal complex is 5-acrylamido-1,10-phenanthroline. The preparation method includes five steps: nitration reaction, amination reaction, acylation reaction, polymer polymerization reaction, and preparation of the polymer-supported metal Pd complex catalyst. When the finally obtained catalyst is applied to the hydrodechlorination reaction of chloroaromatics, it can proceed at room temperature and under 0.1 MPa hydrogen, and the conversion rate is 90%.

[0006] The invention patent (CN 105457651 B) discloses a hydrodechlorination catalyst with Pd and Cu as the main catalysts and at least one of Mg, Ca, Ba, Co, Mo, Ni, Sm, Ce as the promoter, which is supported on activated carbon. The catalyst can be used for the catalytic hydrodechlorination of CFC-113 (1,1,2-trichloro-1,2,2-trifluoroethane) to prepare trifluorochloroethylene, with a conversion rate of up to 95% and a selectivity of 95%.

[0007] However, there are still some problems with traditional supported Pd-based catalysts when facing practical applications, mainly including the following points: (1) Short service life and easy deactivation: The main inducements for deactivation include the poisoning of the catalyst by Cl ions generated by dechlorination, the deposition and coverage of organic matter on the catalyst surface, the loss of active metal, and the agglomeration of catalytically active metal particles; (2) Slow dechlorination kinetics: The low solubility of hydrogen in water leads to low utilization rate of hydrogen atoms, slow reaction kinetics, and inability to meet the application scenarios under high concentration or high throughput; (3) Low loading of active metal: The catalytic activity of Pd is greatly affected by its particle size. The larger the particle size, the lower the activity. Therefore, in order to control the size of metal particles, the loading of Pd in existing supported Pd-based catalysts generally remains below 5 wt.%, resulting in a low density of active sites in the catalyst; (4) Low internal mass transfer efficiency of the catalyst: When facing the sewage treatment application system, the powder catalyst usually needs to be shaped by adding a binder or high-pressure pressing to improve its separation and recovery performance or reduce the bed layer resistance in the fixed bed system. However, the shaping process will greatly affect the internal mass transfer and the exposure of active sites of the material, thereby affecting the catalytic performance.

[0008] Therefore, how to develop a dechlorination catalyst with high catalytic performance, rich mass transfer channels, high loading of active metal, and durable service life remains the research focus in the related field. Summary of the Invention

[0009] To solve the deficiencies of the prior art, the object of the present invention is to provide a chitin sponge-supported Pd-based nanocatalyst, its preparation method and application. The chitin sponge-supported Pd-based nanocatalyst provided by the present invention can completely dechlorinate 1 mM of p-chlorophenol at room temperature with a flux of 6500 L·m -2 ·h -1 , and can operate for more than 500 hours without deactivation at a flux of 65 L·m -2 ·h -1 .

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] In the first aspect of the present invention, a preparation method of a chitin sponge-supported Pd-based nanocatalyst is provided, and the method includes the following steps:

[0012] (1) Provide a chitin sponge composite material, which is prepared by the following steps:

[0013] (1a) Disperse chitin into an alkaline aqueous solution, dissolve chitin by repeated freezing and thawing to obtain a chitin solution; then immerse the sponge in the obtained chitin solution, so that the sponge absorbs the chitin solution until saturation;

[0014] (1b) Heat-treat the sponge filled with the chitin solution obtained in step (1a) under sealing to obtain a self-assembled three-dimensional network of chitin nanofibers with a degree of deacetylation ≤ 60%, preferably ≤ 50%;

[0015] (1c) Wash the three-dimensional network of chitin nanofibers obtained in step (1b) to neutrality, and preferably dry it to obtain a chitin sponge composite material;

[0016] (2) Provide a solution containing Pd ions, immerse the chitin sponge composite material obtained in step (1) in the solution containing Pd ions, and after adsorption equilibrium, separate the chitin sponge from the solution;

[0017] (3) Reduce the metal ions in the chitin sponge obtained in step (2) to nano-metal particles,

[0018] Wash, and preferably dry it to obtain a chitin sponge-supported Pd-based nanocatalyst.

[0019] In a preferred embodiment of the present invention, in the aforementioned step (1a), the content of chitin in the chitin solution is 0.5-8 wt.%.

[0020] In one embodiment of the present invention, the base in the alkaline aqueous solution in the aforementioned step (1a) is selected from one or more of the following compounds: potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, urea, ammonia water, hexamethylenetetramine; preferably a mixture of potassium hydroxide and urea or a mixture of sodium hydroxide and urea, and the concentration of the base in the alkaline aqueous solution is preferably 3-25 wt.%.

[0021] In another preferred embodiment, the freezing temperature in step (1a) is -10°C to -80°C.

[0022] In another preferred embodiment of the present invention, the temperature of the heat treatment in step (1b) is 30-150°C, preferably 80-120°C; preferably, the holding time at the above temperature is 0.5-24 hours, more preferably 6-12 hours.

[0023] In one embodiment of the present invention, the solution containing Pd ions in step (2) can be prepared from any Pd-containing compound. The solution containing Pd ions preferably further contains other metal ions, including Pt, Au, Ag, Co, Ni, Fe, Mn, Mo, W, Cu, Ru, Rh, Os, Ir, etc. The molar ratio of Pd ions to other metal ions in the solution is preferably 50:1 to 1:50, more preferably 5:1 to 1:1; preferably, in the solution containing Pd ions, the total concentration of metal ions is 0.1-100 mM, preferably 1-50 mM, more preferably 5-15 mM.

[0024] In a preferred embodiment of the present invention, the reducing agent used to reduce the metal ions in step (3) is a substance with a redox potential lower than Pd 2+ / Pd in the Pd ion solution, preferably one or a combination of reducing agents such as sodium borohydride, ammonia borane, hydrazine hydrate, formic acid, hydrogen.

[0025] In a preferred embodiment of the present invention, the metal loading in the chitin sponge-supported Pd-based nanocatalyst obtained in step (3) is 0.1-50 wt.%, preferably 5-20 wt.%.

[0026] In a preferred embodiment of the present invention, drying is carried out after washing in steps (1c) and (3); preferably, the drying includes freeze-drying, supercritical drying, drying at normal pressure or vacuum drying; preferably freeze-drying.

[0027] The present invention also provides a chitin sponge-supported Pd-based nanocatalyst material, which can be prepared according to the above preparation method of the chitin sponge-supported Pd-based nanocatalyst;

[0028] Or, a catalyst containing the above-mentioned chitin sponge-supported Pd-based nanocatalyst material.

[0029] The chitin sponge-supported Pd-based nanocatalyst of the present invention is a macroscopic formed material with elasticity and easy-to-control shape and size. The metal loading can reach more than 18 wt.%, while the average particle size is only about 3 nm. Due to the strong affinity of the amino groups generated by partial deacetylation of chitin fibers (deacetylation rate ≤ 60%, preferably ≤ 50%) for metals, metal nanoparticles can be evenly, densely and firmly distributed on chitin nanofibers, and are not easily shed, lost and agglomerated and grown; moreover, chitin fibers are three-dimensionally intertwined into a three-dimensional network, generating developed pores, which is conducive to mass transfer and the exposure of active sites.

[0030] The inventors found that in the preparation method of the present invention, when the sponge is not used, chitin gel or chitin powder with similar chemical properties can be obtained, and then a chitin-supported Pd-based nanocatalyst can be prepared through a metal loading and reduction step.

[0031] The present invention also provides the application of the chitin sponge-supported Pd-based nanocatalyst in catalytic dechlorination reactions.

[0032] In some embodiments of the present invention, the above-mentioned chitin-supported Pd-based nanocatalyst is applied to the catalytic dechlorination reaction of chlorinated organic compounds.

[0033] Preferably, the dechlorination reaction is a batch reaction. The Pd-based nanocatalyst material prepared according to the present invention or a catalyst containing the catalyst material, chlorinated organic compounds, reducing agent, and preferably also a reaction medium and other materials are placed in a reactor for reaction; further preferably, heating or / and stirring are used to promote the reaction; or

[0034] Preferably, the dechlorination reaction is a continuous reaction. The chitin sponge-supported Pd-based nanocatalyst prepared according to the present invention or a catalyst containing the catalyst material is filled in a reactor to form a fixed bed, and materials containing chlorinated organic compounds, reducing agent, and preferably also a reaction medium and other materials are passed into the reactor to pass through the catalyst bed for catalytic reaction; further preferably, heating is used to increase the reaction rate.

[0035] Preferably, the chlorinated organic compounds include chlorinated aromatic compounds, chlorinated aliphatic compounds, chlorinated cyclic compounds, and organochlorine pesticides, etc.; further preferably, the chlorinated aromatic compounds include chlorobenzene, chlorobiphenyl, and chlorophenol, etc.; the chlorinated aliphatic compounds include chlorinated alkanes, chlorinated olefins, etc.; the chlorinated cyclic compounds include chlorocyclohexane; the organochlorine pesticides include triclosan (chemical name: 5-chloro-2-(2',4'-dichlorophenoxy)phenol, chemical formula: C 12H7Cl3O2), DDT (also known as dichlorodiphenyltrichloroethane, chemically named bis(p-chlorophenyl)trichloroethane, is an organochlorine insecticide with the chemical formula C 14 H9Cl5), hexachlorocyclohexane (chemically named hexachlorocyclohexane, is an organic compound with the chemical formula C6H6Cl6).

[0036] Preferably, the reducing agent includes one or more combinations of reducing agents such as sodium borohydride, ammonia borane, hydrazine hydrate, formic acid, and hydrogen.

[0037] The remarkable features and advantages of the present invention are as follows:

[0038] (1) In the Pd-based nanocatalyst supported by chitin sponge obtained in the present invention, the metal loading can be as high as more than 18 wt.%, and the average size of the metal nanoparticles is controlled at only about 3 nm. At the same time, high-density loading of the active metal and full exposure of the active sites are achieved. The second metal introduced into the Pd-based catalyst can optimize the distribution of Pd atoms on the support, the electron cloud density and distribution of the d orbitals through geometric effects and electronic effects, etc., optimize its adsorption and desorption capabilities for reaction substrates, intermediates, and products, and then change the electron density around the C-Cl bond through coordination, reduce the activation bond-breaking energy barrier, and thus effectively improve the hydrodechlorination reaction activity and anti-deactivation ability of the catalyst.

[0039] (2) The chitin nanofibers as the support are separated from each other and intertwined three-dimensionally to generate developed pores, which are beneficial to internal mass transfer and full exposure of catalytic sites; through partial deacetylation treatment (the degree of deacetylation is ≤60%, preferably ≤50%, and further preferably 5-30%), the nanofibers are endowed with rich amino groups, which are beneficial to the dispersion and anchoring of metals, and inhibit the loss and aggregation of metals during use.

[0040] (3) The support has the advantages of elasticity, low density, fast mass transfer, easy regulation of shape and size, etc. macroscopically. No additional shaping treatment is required, which is convenient for operation and use and for assembly; the support raw materials are cheap and easy to obtain, and the preparation method is simple and easy to scale up production.

[0041] (4) In addition to hydrogen, the catalyst can also use water-soluble compounds such as ammonia borane, hydrazine hydrate, and formic acid as reducing agents for the dechlorination reaction to improve the reaction efficiency.

[0042] (5) The catalytic dechlorination efficiency of the catalyst prepared in the present invention is significantly higher than that of existing catalysts. It can completely dechlorinate 1 mM of p-chlorophenol at a continuous flow rate of 6500 L·m -2 ·h -1 at room temperature, and can operate at a flow rate of 65 L·m -2 ·h -1 for more than 500 hours without deactivation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments and descriptions thereof of the invention are used to explain the invention and do not constitute an improper limitation to the invention.

[0044] Figure 1 Photograph of the chitin sponge-supported PdAu nanocatalyst prepared for Example 1;

[0045] Figure 2 SEM images of a) the original commercially available sponge and b) the original chitin;

[0046] Figure 3 SEM image of the chitin sponge-supported PdAu nanocatalyst prepared for Example 1;

[0047] Figure 4 TEM images and particle size distribution diagram of the chitin sponge-supported PdAu nanocatalyst prepared for Example 1, where a and b are TEM images at different magnifications, and c is the particle size distribution diagram;

[0048] Figure 5 TEM images and particle size distribution diagram of the chitin sponge-supported Pd nanocatalyst prepared for Example 2;

[0049] Figure 6 TEM images and particle size distribution diagram of the PdAu nanocatalyst supported on the non-deacetylated chitin sponge prepared for Comparative Example 1;

[0050] Figure 7 Kinetic experiments on the dechlorination of 4-chlorophenol (4-CP) catalyzed by different catalysts and the corresponding phenol yields (Example 4);

[0051] Figure 8 Experimental results of the application of the chitin sponge-supported PdAu nanocatalyst to the continuous-flow catalytic dechlorination of 4-CP (Example 5);

[0052] Figure 9 Kinetic experimental results of the catalytic dechlorination of 4-CP using hydrogen as a reducing agent (Example 7). DETAILED DESCRIPTION OF THE INVENTION

[0053] In the present invention, the sponge mentioned should be understood as a porous material with water absorption, which can be made of lignocellulose fibers or foamed material polymers, such as melamine sponge, polyurethane and other materials. The saturated absorption of the sponge in the present invention should be understood as that the sponge absorbs the chitin solution to reach equilibrium, that is, the amount of the chitin solution absorbed by the sponge no longer changes with the time of the sponge immersed in the chitin solution. The metal ions mentioned in the present invention should be understood as simple metal ions not combined with other electron donors, or complex ions complexed with electron donors. In the present invention, CF-MS is the abbreviation of chitin fiber-melamine sponge composite material.

[0054] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0055] In the present invention, the degree of deacetylation of chitin is determined by potentiometric titration.

[0056] The specific steps are as follows: Weigh a certain amount of chitin sample, adjust the pH to around 2.0 with 1 mol / L hydrochloric acid solution, stir magnetically while titrating, and then titrate with the calibrated 0.1 mol / L NaOH solution. The degree of deacetylation (DD) is calculated according to the following formula:

[0057]

[0058] Among them, C is the exact concentration of NaOH (mol / L), W is the exact mass of chitin (g), V1 is the volume of NaOH corresponding to the first inflection point (mL), V2 is the volume of NaOH corresponding to the second inflection point (mL), 0.016 represents the relative molecular mass of amino group (kg / mol), and the theoretical content of amino group in chitosan is 0.0994.

[0059] Example 1

[0060] Preparation of chitin sponge-supported PdAu nanoparticle catalyst (PdAu / CF-MS):

[0061] (1) Disperse 4 g of chitin powder into 96 g of an aqueous solution of NaOH and urea, where the mass ratio of NaOH / urea / water is 11:4:85; then place the turbid liquid in a -50 °C refrigerator and freeze it for 4 hours, and then thaw it at room temperature; repeat the above freezing and thawing 2-3 times until all the chitin is dissolved to obtain a transparent chitin solution.

[0062] (2) Cut the commercially available melamine sponge into pieces, immerse them in the above chitin solution, repeatedly press until saturated, transfer the sponge filled with chitin solution to a polytetrafluoroethylene liner, seal it, and place it in an oven for heat treatment at 100 °C for 12 hours to enable the self-assembly of chitin nanofibers into a three-dimensional network and simultaneously achieve partial deacetylation treatment; wash the obtained composite material repeatedly with water until neutral, and freeze-dry it to obtain a partially deacetylated chitin sponge composite material.

[0063] (3) Immerse 1.5 g of the chitin sponge composite material in 200 mL of an aqueous solution containing 5 mM K2PdCl4 and 5 mM HAuCl4, adsorb it on a rotary bed for 6 hours, and wash it 3 times with water to remove excess metal ions.

[0064] (4) Immerse the composite material adsorbed with metal in 200 mL of an aqueous solution of NaBH4 with a concentration of 0.1 M. After reacting for 3 hours, separate the solid and liquid, wash it 3 times with water, and freeze-dry it to obtain a PdAu nanoparticle catalyst supported on chitin sponge (PdAu / CF-MS).

[0065] As Figure 1 shown, the chitin sponge composite material prepared in the present invention is a macroscopic molding material with elasticity, low density, and easy control of shape and size. As Figure 2 and Figure 3 shown, chitin was originally closely packed before treatment. After dissolution-heating self-assembly, the nanofibers are separated from each other and intertwined into a three-dimensional network, filling the large pores of the sponge, and the pores in the material are very rich. As Figure 4 shown, the metal particles are distributed very densely and uniformly on the nanofibers, and the average size of the nanoparticles is 3.2 nm. The total loading of Pd and Au in this catalyst is 18.7 wt.%. It is very rare to control the particle size so small and uniform at such a high metal loading.

[0066] Example 2

[0067] Prepare a Pd nanoparticle catalyst supported on chitin sponge (Pd / CF-MS):

[0068] (1) Immerse 1.5 g of the chitin sponge composite material prepared in Example 1 in 200 mL of an aqueous solution containing 10 mM K2PdCl4, adsorb it on a rotary bed for 6 hours, and wash it 3 times with water to remove excess metal ions.

[0069] (2) Immerse the composite material adsorbed with metal in 200 mL of an aqueous solution of NaBH4 with a concentration of 0.1 M. After reacting for 3 hours, separate the solid and liquid, wash it 3 times with water, and freeze-dry it to obtain a Pd nanoparticle catalyst supported on chitin sponge (Pd / CF-MS).

[0070] As Figure 5 shown, the metal particles are very densely and evenly distributed on the nanofibers, and the average size of the nanoparticles is 3.7 nm. The Pd loading in this catalyst is 12.2 wt.%.

[0071] Example 3

[0072] Preparation of chitin powder-supported PdAu nanoparticles catalyst (PdAu / CF):

[0073] (1) Disperse 4 g of chitin powder into a mixed aqueous solution of 96 g of NaOH and urea, where the mass ratio of NaOH / urea / water is 11:4:85; then place the turbid liquid in a -50 °C refrigerator for 4 hours, and then thaw it at room temperature; repeat the above freezing and thawing 2-3 times until all the chitin is dissolved to obtain a transparent chitin solution.

[0074] (2) Pour the above chitin solution into a polytetrafluoroethylene liner, seal it, and heat-treat it in an oven at 100 °C for 12 hours to self-assemble the chitin nanofibers into a three-dimensional network and simultaneously achieve partial deacetylation treatment; wash the obtained composite material repeatedly with water until it is neutral, dry it, and grind it to obtain partially deacetylated chitin powder.

[0075] (3) Immerse 1.5 g of the obtained chitin powder in 200 mL of an aqueous solution containing 5 mM K2PdCl4 and 5 mM HAuCl4, adsorb on a rotary bed for 6 hours, and wash it 3 times with water to remove excess metal ions.

[0076] (4) Immerse the chitin impregnated with metal in 200 mL of an aqueous solution of 0.1 M NaBH4, after reacting for 3 hours, separate the solid and liquid, wash it 3 times with water, and dry it to obtain a chitin powder-supported PdAu nanoparticles catalyst (PdAu / CF).

[0077] Example 4

[0078] Catalytic dechlorination experiment of 4-chlorophenol (4-CP):

[0079] Add 50 mL of a pre-mixed aqueous solution containing 1 mM 4-CP and 2 mM formic acid-sodium formate to a 100 mL flask, and control the temperature of the system at 30 °C using a water bath. Add the PdAu / CF-MS catalyst prepared in Example 1 with a cumulative Pd dosage of 0.02 mmol to the solution, and stir magnetically (600 r / min). Take samples regularly, filter, and analyze the substrate and product concentrations using high-performance liquid chromatography.

[0080] Under similar reaction systems and conditions, replace the catalyst with the catalysts prepared in Example 2, Comparative Example 1, and Comparative Example 3, and investigate their catalytic performance.

[0081] As Figure 7 shown, in the absence of a reducing agent, the PdAu / CF-MS catalyst has no ability to remove 4-CP. This experiment can rule out the adsorption of the material and the reduction reaction of 4-CP by the metal itself. Pd / CF-MS has high activity for catalytic dechlorination and can achieve a dechlorination efficiency of ~100% for 1 mM 4-CP within 30 min. The dechlorination product is mainly phenol. After combining Au and Pd, the performance of the PdAu / CF-MS catalyst is better than that of the Pd / CF-MS catalyst, indicating that there is a synergistic effect between Pd and Au in the catalytic dechlorination reaction. The PdAu nanoparticle catalyst supported on the non-deacetylated chitin sponge prepared in Comparative Example 1 (PdAu / CF-MS non-deacetylated) showed poor catalytic performance. The dechlorination efficiency for 1 mM 4-CP was only 20% after 30 min of reaction and hardly changed during the 10-30 min period, indicating that the catalyst was almost deactivated. The above results fully demonstrate the beneficial effects of the PdAu / CF-MS catalyst designed in the present disclosure in terms of metal loading, particle size, internal mass transfer, etc., thereby improving the catalytic performance.

[0082] Example 5

[0083] PdAu / CF-MS continuous flow catalytic dechlorination experiment of 4-CP:

[0084] A cylindrical PdAu / CF-MS catalyst (Example 1) (diameter 16 mm, height 20 mm) was filled into a glass tube with an inner diameter of 14 mm, and both ends were sealed with nuts with conduits. A pre-mixed aqueous solution containing 1 mM 4-CP and 4 mM formic acid-sodium formate was pumped into the reaction tube by a peristaltic pump, and the solution passed through the catalyst bed for reaction. Samples were taken regularly, filtered, and the substrate and product concentrations were analyzed using high performance liquid chromatography.

[0085] The experimental results show that in the range of continuous flow rate of 0-6500 L·m -2 ·h -1 , the dechlorination efficiency of 4-CP can reach ~100%. Such a high treatment flux shows the excellent catalytic activity and internal mass transfer rate of the PdAu / CF-MS catalyst. As Figure 8 shown, when the continuous flow rate was fixed at 65 L·m -2 ·h -1 , the catalytic reaction system still maintained a dechlorination efficiency of ~100% for 4-CP after continuous operation for 500 hours, but only the product distribution gradually changed. Moreover, no metal loss was detected during the reaction. This result demonstrates the excellent catalytic stability of the PdAu / CF-MS catalyst.

[0086] Example 6

[0087] Dechlorination experiment of 2,4-dichlorophenol catalyzed by PdAu / CF-MS:

[0088] Add 50 mL of a pre-mixed aqueous solution containing 1 mM 2,4-dichlorobenzene and 4 mM formic acid-sodium formate into a 100 mL flask, and control the temperature of the system at 30 °C using a water bath. Add a PdAu / CF-MS catalyst with a cumulative Pd dosage of 0.02 mmol to the solution, and stir magnetically (600 r / min). Take samples regularly, filter, and analyze the substrate and product concentrations using high-performance liquid chromatography.

[0089] The experimental results show that PdAu / CF-MS can completely dechlorinate 2,4-dichlorophenol within 60 min and convert it into phenol.

[0090] Example 7

[0091] Catalytic dechlorination experiment of 4-CP using hydrogen as a reducing agent:

[0092] Add 50 mL of an aqueous solution containing 1 mM 4-CP into a 100 mL flask, seal it with a rubber stopper, and control the temperature of the system at 30 °C using a water bath. Add a PdAu / CF-MS catalyst with a cumulative Pd dosage of 0.02 mmol to the solution, and introduce a certain amount of hydrogen, and stir magnetically (600 r / min). Take samples regularly, filter, and analyze the substrate and product concentrations using high-performance liquid chromatography.

[0093] As Figure 9 shown, under the same reaction conditions, using hydrogen equivalent to formic acid as a reducing agent, the conversion rate of 4-CP is very low and almost negligible; even when using a continuous hydrogen flow and increasing the cumulative reducing agent dosage by 100 times, the dechlorination efficiency is still significantly lower than that of the experimental system using formic acid as a reducing agent. The above results indicate that under the catalysis of PdAu / CF-MS, the hydrogenation dechlorination reaction using formic acid as a reducing agent has higher reactivity than hydrogen. The reason for this phenomenon should be that the solubility of hydrogen in water is relatively low, resulting in slow reaction kinetics; while formic acid is easily soluble in water, and the active hydrogen generated on the catalyst surface can be directly used for the hydrogenation dechlorination reaction.

[0094] Comparative Example 1

[0095] Prepare a PdAu nanoparticle catalyst supported on chitin sponge without deacetylation (PdAu / CF-MS without deacetylation):

[0096] (1) Disperse 4 g of chitin powder into 96 g of an aqueous solution of NaOH and urea, where the mass ratio of NaOH / urea / water is 11:4:85; then place the turbid liquid in a refrigerator at -50 °C for 4 hours, and then thaw it at room temperature; repeat the above freezing and thawing 2 - 3 times until all the chitin is dissolved to obtain a transparent chitin solution;

[0097] (2) Cut commercially available melamine sponge into blocks and immerse them in the above chitin solution, repeatedly press until saturated, transfer the sponge filled with chitin solution to a polytetrafluoroethylene liner, and place it in a water bath at 50 °C for heat treatment for 30 min to allow the self-assembly of chitin nanofibers into a three-dimensional network without deacetylation reaction occurring; wash the obtained composite material repeatedly with water until neutral, and freeze-dry it to obtain an un-deacetylated chitin sponge composite material.

[0098] (3) Immerse 1.5 g of the obtained chitin sponge composite material in 200 mL of an aqueous solution containing 5 mM K2PdCl4 and 5 mM HAuCl4, adsorb on a rotary bed for 6 hours, and wash with water 3 times to wash away the excess metal ions.

[0099] (4) Immerse the composite material adsorbed with metal in 200 mL of an aqueous solution of 0.1 M NaBH4, after reacting for 3 hours, separate the solid and liquid, wash with water 3 times, and freeze-dry to obtain a PdAu nanoparticle catalyst supported on un-deacetylated chitin sponge (PdAu / CF-MS un-deacetylated).

[0100] As Figure 6 shown, the metal particles are sparsely and unevenly distributed on the un-deacetylated chitin nanofibers, and the average size of the nanoparticles is 14.2 nm. The total loading of Pd and Au in this catalyst is only 1.6 wt.%. Comparing with Example 1, it can be found that the partial deacetylation treatment of chitin has an important influence on the adsorption of metals and the dispersion of particles. The reason is that the deacetylation treatment can convert part of the acetyl groups on chitin into amino groups, and the latter has a stronger affinity for metals, which helps the anchoring of metals.

[0101] Comparative Example 2

[0102] Preparation of a chitin sponge-supported Au nanoparticle catalyst (Au / CF-MS):

[0103] (1) Immerse 1.5 g of the chitin sponge composite material prepared in Example 1 in 200 mL of an aqueous solution containing 10 mM HAuCl4, adsorb on a rotary bed for 6 hours, and wash with water 3 times to wash away the excess metal ions.

[0104] (2) The composite material adsorbed with metal was immersed in 200 mL of an aqueous solution of NaBH4 with a concentration of 0.1 M. After reacting for 3 hours, solid-liquid separation was carried out, and it was washed with water three times and freeze-dried to obtain a chitosan sponge-supported Au nanoparticle catalyst (Au / CF-MS).

[0105] After testing, this catalyst has no catalytic dechlorination performance for 4-CP. Combining with Example 4, it can be shown that Au is not an active metal, while Pd is an active metal. However, after combining Au and Pd, the performance of the catalyst is better than that of the single Pd catalyst. The above results verify the synergistic effect between Pd and Au in the catalytic dechlorination reaction.

[0106] Comparative Example 3

[0107] Catalytic 4-CP dechlorination experiment without adding a reducing agent:

[0108] 50 mL of an aqueous solution containing 1 mM 4-CP was added to a 100 mL flask, sealed with a rubber stopper, and the temperature of the system was controlled at 30 °C using a water bath. A PdAu / CF-MS catalyst with a cumulative Pd dosage of 0.02 mmol was added to the solution, and magnetic stirring (600 r / min) was carried out. Samples were taken regularly, filtered, and the substrate and product concentrations were analyzed using high-performance liquid chromatography.

[0109] As Figure 7 shown, without adding a reducing agent, the PdAu / CF-MS catalyst has no ability to remove 4-CP. This experiment can rule out the adsorption effect of the material and the reduction reaction of 4-CP by the metal itself.

[0110] Through the above description, the preparation method and application of the catalyst of the present invention have been clearly disclosed. However, those skilled in the art are well aware that some modifications can be made on the basis of the present invention. But as long as it does not depart from the spirit of the present invention, any modification made to the present invention should be within the scope of the present invention.

Claims

1. A preparation method of a chitin sponge-supported Pd-based nanocatalyst, the method comprising the following steps: (1) Provide a chitin sponge composite material, which is prepared by the following steps: (1a) Disperse chitin into alkaline aqueous solution 1, dissolve chitin by repeated freezing and thawing to obtain a chitin solution; subsequently immerse the sponge in the obtained chitin solution, so that the sponge absorbs the chitin solution to saturation; (1b) Heat-treat the sponge filled with the chitin solution obtained in step (1a) under sealing to obtain a self-assembled chitin nanofiber three-dimensional network with a degree of deacetylation ≤ 60%; (1c) Wash the chitin nanofiber three-dimensional network obtained in step (1b) with water until neutral to obtain a chitin sponge composite material; (2) Provide a solution containing Pd ions, immerse the chitin sponge composite material obtained in step (1) in the solution containing Pd ions, and after adsorption equilibrium, separate the chitin sponge from the solution; (3) Reduce the metal ions in the chitin sponge obtained in step (2) to nano-metal particles, wash to obtain a chitin sponge-supported Pd-based nanocatalyst.

2. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 1, characterized in that, (1b) Heat-treat the sponge filled with the chitin solution obtained in step (1a) under sealing to obtain a self-assembled chitin nanofiber three-dimensional network with a degree of deacetylation ≤ 50%.

3. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 1, characterized in that, (1c) Wash the chitin nanofiber three-dimensional network obtained in step (1b) with water until neutral, dry to obtain a chitin sponge composite material.

4. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 1, characterized in that, (3) Reduce the metal ions in the chitin sponge obtained in step (2) to nano-metal particles, wash, dry to obtain a chitin sponge-supported Pd-based nanocatalyst.

5. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 1, characterized in that, The content of chitin in the chitin solution described in step (1a) is 0.5 - 8 wt.%.

6. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to any one of claims 1-5, characterized in that, The base in the alkaline aqueous solution 1 described in step (1a) is selected from one or more of the following compounds: potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, urea, ammonia water, hexamethylenetetramine.

7. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 6, characterized in that, The base in the alkaline aqueous solution 1 described in step (1a) is a mixture of potassium hydroxide and urea or a mixture of sodium hydroxide and urea.

8. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 6, characterized in that, The concentration of the base in the alkaline aqueous solution 1 is 3 - 25 wt.%.

9. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to any one of claims 1-5, characterized in that, The temperature of the heat treatment described in step (1b) is 30 - 150 °C.

10. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 9, characterized in that, The temperature of the heat treatment described in step (1b) is 80 - 120 °C.

11. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 9, characterized in that, The holding time at a temperature of 30 - 150 °C is 0.5 - 24 hours.

12. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 11, characterized in that, The holding time at a temperature of 80 - 120 °C is 6 - 12 hours.

13. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to any one of claims 1-5, characterized in that, The solution containing Pd ions described in step (2) further contains other metal ions, including Pt, Au, Ag, Co, Ni, Fe, Mn, Mo, W, Cu, Ru, Rh, Os, Ir.

14. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 13, characterized in that, The molar ratio of Pd ions to other metal ions is 50:1 - 1:

50.

15. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 14, characterized in that, The molar ratio of Pd ions to other metal ions is 5:1 - 1:

1.

16. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 13, characterized in that, The total concentration of metal ions in the solution containing Pd ions is 0.1 - 100 mM.

17. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 16, characterized in that, The total concentration of metal ions in the solution containing Pd ions is 1 - 50 mM.

18. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 17, characterized in that, The total concentration of metal ions in the solution containing Pd ions is 5-15 mM.

19. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to any one of claims 1-5, characterized in that, In step (3), the reducing agent used to reduce the metal ions is a substance with a redox potential lower than Pd / Pd in the Pd ion solution. 2+ / Pd.

20. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 19, characterized in that, The reducing agent is one or a combination of more than one of sodium borohydride, ammonia borane, hydrazine hydrate, formic acid, and hydrogen.

21. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to any one of claims 1-5, characterized in that, In step (3), the metal loading in the chitin sponge-supported Pd-based nanocatalyst obtained is 0.1-50 wt.%.

22. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 21, characterized in that, In step (3), the metal loading in the chitin sponge-supported Pd-based nanocatalyst obtained is 5-20 wt.%.

23. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 3 or 4, characterized in that, In step (1c) or step (3), the drying includes freeze-drying, supercritical drying, drying at normal pressure, or vacuum drying.

24. The preparation method of the chitin sponge-supported Pd-based nanocatalyst according to claim 23, characterized in that, The drying is freeze-drying.

25. The chitin sponge-supported Pd-based nanocatalyst material prepared by the method according to any one of claims 1-24, or a catalyst containing the catalyst material.

26. The application of the chitin sponge-supported Pd-based nanocatalyst material according to claim 25, or a catalyst containing the catalyst material, in a catalytic dechlorination reaction.

27. The application according to claim 26, characterized in that, The dechlorination reaction is a batch reaction, and the Pd-based nanocatalyst material or a catalyst containing the catalyst material, a chlorinated organic compound, and a reducing agent are placed in a reactor.

28. The application according to claim 27, characterized in that, The Pd-based nanocatalyst material or a catalyst containing the catalyst material, a chlorinated organic compound, a reducing agent, and a reaction medium are placed in a reactor.

29. The application according to claim 27, wherein Heating or / and stirring are used to promote the reaction.

30. The application according to claim 26, characterized in that, The dechlorination reaction is a continuous reaction. The Pd-based nanocatalyst material or a catalyst containing the catalyst material is filled in a reactor to form a fixed bed, and a chlorinated organic compound and a reducing agent are introduced into the reactor to pass through the catalyst bed for catalytic reaction.

31. The application according to claim 30, characterized in that, A chlorinated organic compound, a reducing agent, and a reaction medium are introduced into the reactor.

32. The application according to claim 30, characterized in that, Heating is used to increase the reaction rate.

33. The application according to claim 27 or 30, characterized in that, wherein The chlorinated organic compound includes chlorinated aromatic compounds, chlorinated aliphatic compounds, chlorinated cyclic compounds, and organochlorine pesticides.

34. The application according to claim 33, wherein, The chlorinated aromatic compounds include chlorobenzene, chlorobiphenyl, and chlorophenol; the chlorinated aliphatic compounds include chlorinated alkanes and chlorinated alkenes; the chlorinated cyclic compounds include chlorocyclohexane; the organochlorine pesticides include triclosan, DDT, and hexachlorocyclohexane.

35. The application according to claim 27 or 30, characterized in that, The reducing agent includes one or a combination of more than one of sodium borohydride, ammonia borane, hydrazine hydrate, formic acid, and hydrogen.

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