A phosphorus-modified Pd-Fe bimetallic catalyst, its preparation method and its application

Abstract

This invention discloses a phosphorus-modified Pd-Fe bimetallic catalyst, its preparation method, and its application. SBA-15 mesoporous silica is used as a support, and diethyl phosphite is used as a phosphorus modifier to support the Pd-Fe bimetallic catalyst. The preparation process involves pretreatment with SBA-15 to activate the silanol groups, followed by transesterification of diethyl phosphite to form -Si-O-P(O)(OEt)- bonds for anchoring, and then calcination and reduction to generate P-O-Si bonds that coordinate with Pd-Fe. This catalyst utilizes the ordered mesopores of SBA-15 to promote TNT diffusion, and diethyl phosphite to regulate the electronic states and dispersion of Pd-Fe, achieving a waste TNT conversion rate ≥99.5%, a TAT selectivity ≥96%, and a conversion rate ≥98% after 15 cycles. This solves the problems of poor stability, low selectivity, and easy clogging of mesopores in existing catalysts, making it suitable for the harmless treatment of waste TNT.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of environmental protection and catalytic materials, specifically to a phosphorus-modified Pd-Fe bimetallic catalyst, its preparation method, and its application. Background Technology

[0002] The current waste TNT treatment industry faces the core pain point that "a single technology cannot meet the treatment needs of complex pollution systems." Specifically, this manifests as follows: biodegradation methods cannot stably treat ammunition dismantling waste containing metal fragments due to heavy metal sensitivity and low-temperature failure issues; advanced oxidation methods are difficult to handle the complex system of coexisting nitrotoluene isomers in TNT production wastewater due to excessive use of oxidants and byproduct toxicity issues; and single-metal catalytic hydrogenation methods are limited by catalyst poisoning, high-temperature and high-pressure requirements, and byproduct control challenges, making them unable to efficiently treat expired explosives containing 60-90% pure TNT.

[0003] To overcome the aforementioned technical bottlenecks, the industry has attempted to adopt bimetallic catalyst systems. However, traditional supports and phosphorus modifiers have significant technical defects: activated carbon supports suffer from disordered pores that hinder TNT molecule diffusion, while TiO2 supports suffer from insufficient active sites that lead to metal component loss. Although SBA-15 mesoporous silica has ordered mesopores that can accommodate TNT molecule diffusion, traditional phosphorus modifiers such as phosphoric acid have weak binding forces and are prone to loss, while triphenylphosphine benzene rings are large and prone to clogging mesopores. Existing phosphorus modifiers can only improve stability or selectivity in a single way and cannot simultaneously achieve the synergistic effect of "high dispersion of active components, precise control of electronic states, and resistance to impurity poisoning".

[0004] The industry generally believes that the bimetallic catalytic system combining SBA-15 mesoporous silica with phosphorus modifiers is theoretically feasible. However, traditional technologies suffer from a key problem: the lack of synergistic effect between the support, modifier, and active component. Weak binding between phosphoric acid and silanol groups leads to aqueous phase loss; triphenylphosphine blocks mesopores, reducing catalytic activity; and single-function modifiers cannot meet the diverse treatment needs of complex waste TNT systems. These technical deficiencies result in existing bimetallic catalysts still facing problems such as active component loss, difficulty in selectivity control, and insufficient resistance to poisoning in practical applications, hindering their industrial application. Summary of the Invention

[0005] Addressing the core problems of existing waste TNT catalytic hydrogenation technologies, namely "poor carrier pore compatibility, easy loss of modifiers, agglomeration of active components, and difficulty in balancing selectivity and stability," this invention provides a phosphorus-modified Pd-Fe bimetallic catalyst, its preparation method, and its application. It utilizes SBA-15 mesoporous silica to solve the problem of hindered TNT molecule diffusion and employs diethyl phosphite to address the weak binding force of the phosphorus modifier and mesopore blockage. Through the synergistic design of the carrier and modifier, this catalyst solves the problems of low catalytic efficiency, poor selectivity, and insufficient stability in existing waste TNT treatment technologies. It is suitable for treating various waste TNT systems, including ammunition dismantling waste, TNT production wastewater, and expired explosives.

[0006] The technical solution adopted in this invention is as follows:

[0007] A phosphorus-modified Pd-Fe bimetallic catalyst includes a support, a Pd-Fe bimetallic active component supported on the support, and a phosphorus modifier anchored to the surface of the support via an ester exchange reaction. The carrier is SBA-15 mesoporous silicon; The phosphorus modifier is diethyl phosphite. The diethyl phosphite forms a -Si-OP(O)(OEt)- bond with the silanol groups on the surface of SBA-15 mesoporous silicon through an ester exchange reaction. After calcination, it is converted into a -Si-OP- bond and coordinated with the Pd-Fe bimetallic compound.

[0008] Optionally, the SBA-15 mesoporous silicon has a pore size of 5–15 nm and a specific surface area of ​​600–1200 m². 2 / g, surface silanol density ≥2.5 mmol / g.

[0009] Optionally, in the Pd-Fe bimetallic active component, the loading of Pd and Fe is 2-5 wt% and 1-3 wt%, respectively, and the atomic ratio of Pd to Fe is 1:1-3. The average particle size of the Pd-Fe bimetal is 2–5 nm, and its dispersion in SBA-15 mesoporous silica is ≥90%.

[0010] Optionally, the diethyl phosphite has a loading of 0.5 to 2 wt% based on phosphorus.

[0011] The preparation method of the Pd-Fe bimetallic catalyst with phosphorus modifier according to any one of the present invention includes: Step 1: SBA-15 pretreatment: Place SBA-15 mesoporous silica in 0.5-1 mol / L hydrochloric acid, reflux at 80°C for 2 hours, wash with water until neutral, and dry at 100-120°C for 6-8 hours; Step 2: Bimetallic impregnation: Add the pretreated SBA-15 mesoporous silica to an ethanol-water solution containing Pd precursor and Fe precursor, with a volume ratio of ethanol-water solution of 1:4. Stir at 25-40℃ for 4-8 hours, while simultaneously performing ultrasonic-assisted dispersion with an ultrasonic power of 300-500 W and an ultrasonic time of 30-60 min. Step 3: Phosphorus modifier modification: Add an ethanol dilution of diethyl phosphite dropwise to the mixture in Step 2. The concentration of the ethanol dilution of diethyl phosphite is 5-10 wt%. Adjust the pH of the system to 4-5. Stir at 25-30℃ for 2-3 hours. Then, heat to 80-90℃ to evaporate the solvent to obtain a solid precursor. Step 4: Calcination and reduction: The solid precursor obtained in step 3 is first placed in a nitrogen atmosphere with a nitrogen flow rate of 70-90 mL / min and heated to 320-380℃ for calcination for 1.5-2.5 h. Then, the atmosphere is switched to hydrogen with a hydrogen flow rate of 50-70 mL / min and the temperature is raised to 480-520℃ for reduction for 1.5-3 h. The precursor is then allowed to cool naturally to room temperature to obtain the final product.

[0012] Optionally, in step 2, the Pd precursor is palladium chloride, and the Fe precursor is ferrous chloride. The total concentration of Pd and Fe precursors in the ethanol-water solution was 0.02–0.06 mol / L, and the solid-liquid ratio of SBA-15 mesoporous silica to the ethanol-water solution was 1:5–7 g / mL.

[0013] Optionally, in step 3, the molar ratio of diethyl phosphite to Pd-Fe bimetal is 0.3 to 0.6:1.

[0014] The application of the Pd-Fe bimetallic catalyst with any of the phosphorus modifiers described in this invention in the selective catalytic hydrogenation of waste TNT.

[0015] Optional, including: The waste TNT mentioned refers to ammunition dismantling waste, TNT production wastewater, or expired explosives. Among them, ammunition dismantling waste needs to be pre-crushed to a particle size of ≤1 mm, and TNT production wastewater needs to be filtered through a 0.22 μm filter membrane to remove suspended impurities. The system for the catalytic hydrogenation reaction is a water-ethanol mixture, wherein the volume ratio of water to ethanol is 7:3 to 9:1. The catalytic hydrogenation reaction conditions are: reaction temperature 40-70℃, hydrogen pressure 1-3 MPa, catalyst dosage of 8%-15% of the mass of waste TNT, and reaction time 2-4 h.

[0016] Optionally, after the catalytic hydrogenation reaction is completed, the Pd-Fe bimetallic catalyst with phosphorus modifier is recovered by centrifugation. The centrifugation speed is 3500-4500 rpm, and the centrifugation time is 10-20 min.

[0017] The advantages of this invention include: (1) Excellent catalytic performance: waste TNT conversion rate ≥99.5%, TAT selectivity ≥96%, which is 9.4 percentage points higher than that of traditional Pd / C catalysts and 3.8 percentage points higher in selectivity; (2) Outstanding stability: The conversion rate is still ≥98% after 15 cycles; (3) Strong resistance to toxicity: In Pb² + The conversion rate remains above 98% in a system with a concentration of 10 mg / L, thus solving the problem of impurity poisoning. (4) Green and economical process: The reaction temperature is reduced by 20-40℃ and the pressure is reduced by 1-3 MPa; (5) Wide range of applications: It is suitable for both solid and liquid systems, and is applicable to TNT concentrations ranging from 50 to 5000 mg / L. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart illustrating the preparation process of the phosphorus-modified Pd-Fe bimetallic catalyst of the present invention. Figure 2 This is a TEM image of the phosphorus-modified Pd-Fe bimetallic catalyst of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments.

[0020] This invention, based on the design concept of "synergistic effect of support-modifier-active component," proposes the following innovative ideas: It utilizes SBA-15 mesoporous silica to address the problem of TNT molecule diffusion obstruction; employs diethyl phosphite to solve the problems of weak binding force of phosphorus modifiers and mesoporous blockage; and designs a Pd-Fe bimetallic catalyst to address the problems of active component poisoning and insufficient selectivity. Ultimately, it achieves "high conversion rate, high selectivity, and long-term recyclability" for the harmless treatment of waste TNT, while also considering resource recovery. Specifically, it involves a Pd-Fe bimetallic catalyst using SBA-15 mesoporous silica as a support and diethyl phosphite as a phosphorus modifier, and its application in the selective catalytic hydrogenation harmless treatment or resource recovery of waste 2,4,6-trinitrotoluene (TNT). Through the synergistic design of the support and modifier, this catalyst solves the problems of low catalytic efficiency, poor selectivity, and insufficient stability in existing waste TNT treatment technologies, and is suitable for the treatment of various waste TNT systems, including ammunition dismantling waste, TNT production wastewater, and expired explosives.

[0021] The core design logic of this invention is "three-component synergistic optimization". The functions and mechanisms of each component are as follows: (1) The carrier is selected with a pore size of 5-15 nm, a specific surface area of ​​600-1200 m² / g, and a surface silanol density ≥2.5. (1) SBA-15 with mmol / g has ordered mesopores that can serve as diffusion channels for TNT and hydrogen. The silanol group serves as the anchoring point for diethyl phosphite, preventing the aggregation of active components. (2) The phosphorus modifier (diethyl phosphite) has a loading of 0.5-2wt% (preferably 1wt%) based on the element P. It forms a -Si-OP(O)(OEt)- bond with the silanol group of SBA-15 through an ester exchange reaction. After calcination, it is converted into a stable -Si-OP- bond, which not only anchors the Pd-Fe bimetal but also regulates the d-band center of Pd through electron transfer. The steric hindrance of the ethyl group can also prevent impurity ions from poisoning the active site. (3) Pd-Fe bimetallic active components: Pd loading 2-5wt%, Fe loading 1-3wt%, atomic ratio 1:1-3:1. Pd is the main active center, and Fe increases the electron density of Pd through d orbital electron transfer. The two work together to enhance the catalytic activity.

[0022] The phosphorus-modified Pd-Fe bimetallic catalyst of the present invention has the following core components by weight percentage (wt%): (1) Support: SBA-15 mesoporous silica (100 parts, pore size 5-15 nm, specific surface area 600-1200 m² / g); (2) Active components: Pd 2-5 wt%, Fe 1-3 wt% (Pd to Fe atomic ratio 1:1-3:1); (3) Phosphorus modifier: diethyl phosphite (0.5-2 wt% based on P, forming -Si-OP- bonds with SBA-15).

[0023] Combination Figure 1The phosphorus-modified Pd-Fe bimetallic catalyst of the present invention adopts a five-step preparation process of "pretreatment-impregnation-modification-calcination-reduction". The specific steps are as follows: (1) SBA-15 pretreatment: SBA-15 mesoporous silica is placed in 0.5-1 mol / L hydrochloric acid (solid-liquid ratio 1:10 g / mL), refluxed at 80°C for 2 hours, washed with water until neutral, and dried at 100-120°C for 6-8 hours to activate the surface silanol groups; (2) Bimetallic impregnation: Prepare an ethanol-water solution of PdCl2 and FeCl2 (ethanol:water = 1:4, volume ratio) with a total concentration of 0.02-0.06 mol / L; add the pretreated SBA-15 to the solution (solid-liquid ratio 1:5-7 g / mL), stir at 25-40°C for 4-8 hours, and simultaneously dispersed with ultrasonic assistance (power 300-500W, time 30-60 minutes). (3) Phosphorus modifier modification: Diethyl phosphite was diluted with ethanol to 5-10 wt%, and added dropwise to the system at a P to Pd-Fe molar ratio of 0.3-0.6:1. The pH was adjusted to 4-5, and the mixture was stirred at 25-30℃ for 2-3 h. The solvent was evaporated at 80-90℃ to obtain a solid precursor. (4) Calcination treatment: The precursor was placed in a nitrogen atmosphere (flow rate 70-90 mL / min) and calcined at 320-380℃ for 1.5-2.5 h to remove organic impurities and solidify PO-Si bonds. (5) Hydrogen reduction: The atmosphere was switched to hydrogen (flow rate 50-70 mL / min), and the mixture was reduced at 480-520℃ for 1.5-3 h. The mixture was then naturally cooled to room temperature to obtain the target catalyst.

[0024] The application of the phosphorus-modified Pd-Fe bimetallic catalyst of the present invention in the selective catalytic hydrogenation of waste TNT.

[0025] The catalyst of this invention is applicable to the selective catalytic hydrogenation of various waste TNT systems. The specific application steps are as follows: (1) Waste TNT pretreatment: Ammunition dismantling waste: crushed to a particle size ≤1mm to remove metal fragments; TNT production wastewater: filtered through a 0.22μm filter membrane to remove suspended impurities; expired explosives: crushed to a particle size ≤0.5 mm and mixed with water at a ratio of 1:10 to form a suspension.

[0026] (2) Catalytic hydrogenation reaction: In a high-pressure reactor, waste TNT, catalyst (8-15% of the TNT mass), and a water-ethanol mixed solvent (water:ethanol = 7:3-9:1, volume ratio) are added. After purging with nitrogen three times, hydrogen is introduced to 1-3 MPa, and the reaction is stirred at 40-70°C for 2-4 hours. After the reaction is completed, the mixture is cooled and centrifuged at 4000-4500 rpm for 10-20 minutes to separate the catalyst (which is washed with water, dried, and recycled) from the reaction solution (TNT is recovered or disposed of harmlessly).

[0027] Example 1: The raw material composition of this embodiment (based on actual usage): 10g of SBA-15 mesoporous silica (pore size 10nm±0.5nm, specific surface area 800±50m² / g, silanol density 2.8mmol / g); 0.502g of PdCl2 (analytical grade, Pd content 59.5%); FeCl2 0.305 g of 4H₂O (analytical grade, Fe content 28.0%); 0.401 g of diethyl phosphite (purity 99%); 100 mL of 0.8 mol / L hydrochloric acid; 30 mL of anhydrous ethanol; 40 mL of deionized water.

[0028] Preparation of this embodiment: Step 1: SBA-15 pretreatment Add 10g of SBA-15 to 100mL of 0.8mol / L hydrochloric acid, place in an 80℃ oil bath, and stir and reflux at 300r / min for 2 hours; take 5mL of washing solution every 30min to measure pH, and after the pH stabilizes to 7.0, transfer the mixture to a centrifuge tube, centrifuge at 4000rpm for 10 minutes, and discard the supernatant; repeat the washing-centrifugation operation with deionized water 5 times until the pH of the washing solution is 7; place the washed SBA-15 in a vacuum drying oven and dry at 110℃ and 0.09MPa for 7 hours to obtain the activated carrier.

[0029] Step 2: Bimetallic impregnation with 0.502g PdCl2 and 0.305g FeCl2 Add 4H2O to a mixed solvent of 10 mL anhydrous ethanol and 40 mL deionized water, and stir at 500 r / min for 20 min at 25 °C until completely dissolved; add the activated carrier prepared in step one, transfer to a 30 °C constant temperature water bath, and stir at 500 r / min for 6 h; simultaneously turn on the sonicator (power 400 W, frequency 40 kHz), sonicate for 10 min every 15 min, and sonicate for a total of 45 min to form a homogeneous suspension.

[0030] Step 3: Phosphorus Modification Take 0.401g of diethyl phosphite, dilute it to 8wt% with 20mL of anhydrous ethanol, and add it dropwise to the above suspension at a rate of 1 drop / second; adjust the pH of the system to 4.5±0.1 with 0.1mol / L hydrochloric acid, and stir at 300r / min for 3 hours at 25℃; transfer the mixture to a rotary evaporator, and evaporate the solvent at 85℃, 150rpm, and 0.08MPa to obtain a brownish-yellow solid precursor.

[0031] Step 4: Calcination and Reduction. The solid precursor was loaded into a quartz boat (filling height ≤ 5 mm) and placed in the center of a tube furnace. Nitrogen gas (purity 99.999%, flow rate 80 mL / min) was first purged for 30 minutes to remove air from the furnace. The temperature was increased to 350°C at a rate of 5°C / min and calcined for 2 hours. Then, hydrogen gas (purity 99.999%, flow rate 60 mL / min) was used to increase the temperature to 500°C at a rate of 8°C / min and reduced for 2 hours. The heating was turned off, and the hydrogen atmosphere was allowed to cool naturally to room temperature to obtain a black granular catalyst (labeled Cat-1).

[0032] Example 2: The raw material composition of this embodiment (based on actual usage): 10g of SBA-15 mesoporous silica (pore size 8nm±0.5nm, specific surface area 700±50m² / g); 0.401g of PdCl2; FeCl2 0.203 g of 4H₂O; 0.301 g of diethyl phosphite; 100 mL of 0.8 mol / L hydrochloric acid; 25 mL of anhydrous ethanol; 40 mL of deionized water. The preparation steps in this example are the same as in Example 1 (only the ultrasonic time was adjusted to 30 minutes, and the rotary evaporation temperature was adjusted to 80°C). (Marked as Cat-B) Example 3: The raw material composition of this embodiment (based on actual usage): 10g of SBA-15 mesoporous silica (pore size 12nm±0.5nm, specific surface area 900±50m² / g); 0.603g of PdCl2; FeCl2 0.406 g of 4H₂O; 0.502 g of diethyl phosphite; 100 mL of 0.8 mol / L hydrochloric acid; 35 mL of anhydrous ethanol; 40 mL of deionized water. The preparation steps in this example are the same as in Example 1 (only the calcination temperature was adjusted to 360℃ and the reduction temperature to 510℃). (Marked as Cat-C) Example 4: This embodiment refers to Example 1, except that "0.401g of diethyl phosphite" is replaced with "0.401g of 85wt% phosphoric acid", and the amounts of the remaining raw materials (10g of SBA-15 mesoporous silica, 0.502g of PdCl2, FeCl2) are the same. The catalyst (labeled Cat-2) was obtained by keeping the preparation steps and 0.305g of 4H2O completely unchanged.

[0033] Example 5: This embodiment refers to Example 1, except that the steps of "0.401g of diethyl phosphite" and "phosphorus modification" are omitted, and the remaining raw material amounts (10g of SBA-15 mesoporous silica, 0.502g of PdCl2, FeCl2) are the same. The catalyst (labeled Cat-3) was obtained by keeping the preparation steps completely unchanged (4H2O 0.305g, etc.) and other preparation steps completely unchanged.

[0034] Performance evaluation: (1) Catalytic activity test: TNT conversion rate and TAT selectivity: Take 10.00g of ammunition dismantling waste containing 30wt% TNT (crushed to 0.8-1.0mm), add it together with 0.120g of target catalyst and 200mL of water-ethanol mixed solvent (volume ratio 8:2, filtered through 0.22μm filter membrane) to 500mL high pressure reactor; after sealing, replace with 0.5MPa nitrogen three times, and purge with hydrogen to 2.0MPa; heat to 60℃ (heating rate 2℃ / min), stir at 500r / min for 3h; after the reaction is completed, cool to 25℃, take 5mL of reaction solution, centrifuge at 4500rpm for 15min, filter the supernatant through 0.22μm filter membrane, and determine the concentration by high performance liquid chromatography (C18 column, mobile phase methanol-water = 6:4, detection wavelength 254nm).

[0035] The test results show that Example 1 achieved a TNT conversion rate of 99.8% (residual concentration 0.08 mg / L), a TAT selectivity of 96.5%, and only 0.42% byproducts; the catalyst remained particulate after the reaction, without agglomeration. Example 4 (phosphoric acid replacing diethyl phosphite) had an initial conversion rate of only 95.0%, which decreased to 85.2% after 8 cycles; Example 5 (phosphorus-free modification) achieved a conversion rate of 92.5% and a TAT selectivity of 82.1% (with 8.5% azo byproducts), demonstrating that diethyl phosphite modification is crucial for improving catalytic activity and selectivity.

[0036] The catalysts obtained in Examples 2 and 3 (labeled Cat-1B and Cat-1C, respectively) were subjected to the same catalytic activity, selectivity, and cycle stability tests as in Example 1. The results are shown in Table 1. Table 1. Test results of catalytic activity, selectivity and cycle stability of the catalyst.

[0037] As shown in the table above, within the core parameter range of the claims of this invention (such as support pore size, metal loading, and phosphorus loading), the catalyst can consistently achieve high conversion rates (≥99.5%), high selectivity (≥96%), and excellent cycling stability (conversion rate ≥98% after 15 cycles). This contrasts sharply with the comparative examples (Examples 4 and 5), fully demonstrating that the technical effect of this invention is brought about by the specific technical combination of "SBA-15 support," "Pd-Fe bimetal," and "diethyl phosphite modification," and that this effect can be achieved throughout the claimed parameter range.

[0038] (2) Anti-toxicity test: Take 100 mL containing 200 mg / L TNT and Pb² + 0.024 g of the target catalyst was added to 10 mg / L of simulated wastewater and placed in a 250 mL high-pressure reactor. Hydrogen was introduced to 1.5 MPa, and the reactor was stirred at 400 r / min for 2 h at 50 °C. The TNT conversion rate was tested according to the above-mentioned "catalytic activity test" method. The results are shown in Table 2.

[0039] Table 2 Results of Anti-toxicity Tests

[0040] As shown in Table 1, Examples 1-3 were in the presence of Pb² + The system maintains a high conversion rate and exhibits significantly better resistance to poisoning than Examples 4 and 5 and commercially available Pd / C catalysts, demonstrating that the steric hindrance of diethyl phosphite can effectively prevent impurity ions from poisoning active sites, and this effect remains stable within the range of the claims parameters.

[0041] (3) TEM analysis: After cycling the catalyst of Example 1 15 times, 10 mg of the sample was dispersed in 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 minutes; one drop of the dispersion was dropped onto a copper grid, and after air drying, it was observed using a transmission electron microscope (accelerating voltage 200 kV). The TEM image of the catalyst is shown below. Figure 2 As shown, the results indicate that the average particle size of Pd-Fe particles in the catalyst is still 3.2 nm, with a dispersion of 92% and no obvious agglomeration; the SBA-15 mesoporous structure is intact and there is no clogging phenomenon, which verifies the structural stability of the catalyst.

[0042] (4) Performance Analysis: Through the above performance tests, the phosphorus-modified Pd-Fe bimetallic catalyst prepared in this invention has the following core advantages: High activity: The conversion rate of various waste TNT (solid waste, wastewater, expired explosives) is ≥99.5%, and the TAT selectivity is ≥96%; Strong stability: The conversion rate is still ≥98% after 15 cycles; Excellent resistance to poisoning: In Pb² content + Cu² + In systems with impurities, the conversion rate remains above 98%; the process is excellent: the reaction temperature is 40-70℃ and the pressure is 1-3MPa, no special equipment is required, and it is suitable for industrial scale-up.

[0043] This invention innovatively uses SBA-15 mesoporous silica as a support and introduces diethyl phosphite as a phosphorus modifier. Its ester group (-OEt) can undergo an exchange reaction with the silanol groups of SBA-15 to form a stable -Si-OP(O)(OEt)- bond. After calcination, the remaining PO-Si bond can strongly coordinate with the Pd-Fe bimetal, achieving synergistic anchoring of the "support-modifier-active component". This innovative design simultaneously solves three core problems: support compatibility, modifier stability, and active component dispersibility. This enables the catalyst to exhibit high activity, high selectivity, and strong resistance to poisoning in waste TNT treatment, breaking through the technical bottleneck of traditional technologies that cannot simultaneously achieve stability and selectivity. It provides a feasible technical solution for the green and efficient treatment of waste TNT.

[0044] The preferred embodiments described above in conjunction with the accompanying drawings are preferred but not intended to limit the invention. The various specific technical features described above can be combined in any suitable form without contradiction, and this invention will not elaborate on them one by one. Any simple modifications or alterations made by those skilled in the art, such as arbitrary combinations or equivalent substitutions, to the technical solutions without departing from the scope of the technical solutions do not affect the essence of the technical solutions and still fall within the protection scope of the technical solutions represented by the embodiments of this invention.

Claims

1. A Pd-Fe bimetallic catalyst with a phosphorus modifier, characterized in that, It includes a support, a Pd-Fe bimetallic active component loaded on the support, and a phosphorus modifier anchored to the surface of the support via an ester exchange reaction; The carrier is SBA-15 mesoporous silicon; The phosphorus modifier is diethyl phosphite. The diethyl phosphite forms a -Si-OP(O)(OEt)- bond with the silanol groups on the surface of SBA-15 mesoporous silicon through an ester exchange reaction. After calcination, it is converted into a -Si-OP- bond and coordinated with the Pd-Fe bimetallic compound.

2. The Pd-Fe bimetallic catalyst with phosphorus modifier according to claim 1, characterized in that, The SBA-15 mesoporous silicon has a pore size of 5–15 nm and a specific surface area of ​​600–1200 m². 2 / g, surface silanol density ≥2.5 mmol / g.

3. The Pd-Fe bimetallic catalyst with phosphorus modifier according to claim 1 or 2, characterized in that, In the Pd-Fe bimetallic active component, the loading of Pd and Fe is 2-5 wt% and 1-3 wt%, respectively, and the atomic ratio of Pd to Fe is 1:1-3. The average particle size of the Pd-Fe bimetal is 2–5 nm, and its dispersion in SBA-15 mesoporous silica is ≥90%.

4. The Pd-Fe bimetallic catalyst with phosphorus modifier according to claim 1 or 2, characterized in that, The diethyl phosphite described herein has a loading of 0.5 to 2 wt% based on phosphorus.

5. A method for preparing the Pd-Fe bimetallic catalyst with phosphorus modifier according to any one of claims 1-4, characterized in that, include: Step 1: SBA-15 pretreatment: Place SBA-15 mesoporous silica in 0.5-1 mol / L hydrochloric acid, reflux at 80°C for 2 hours, wash with water until neutral, and dry at 100-120°C for 6-8 hours; Step 2: Bimetallic impregnation: Add the pretreated SBA-15 mesoporous silica to an ethanol-water solution containing Pd precursor and Fe precursor, with a volume ratio of ethanol-water solution of 1:

4. Stir at 25-40℃ for 4-8 hours, while simultaneously performing ultrasonic-assisted dispersion with an ultrasonic power of 300-500 W and an ultrasonic time of 30-60 min. Step 3: Phosphorus modifier modification: Add an ethanol dilution of diethyl phosphite dropwise to the mixture in Step 2. The concentration of the ethanol dilution of diethyl phosphite is 5-10 wt%. Adjust the pH of the system to 4-5. Stir at 25-30℃ for 2-3 hours. Then, heat to 80-90℃ to evaporate the solvent to obtain a solid precursor. Step 4: Calcination and reduction: The solid precursor obtained in step 3 is first placed in a nitrogen atmosphere with a nitrogen flow rate of 70-90 mL / min and heated to 320-380℃ for calcination for 1.5-2.5 h. Then, the atmosphere is switched to hydrogen with a hydrogen flow rate of 50-70 mL / min and the temperature is raised to 480-520℃ for reduction for 1.5-3 h. The precursor is then allowed to cool naturally to room temperature to obtain the final product.

6. The method for preparing the Pd-Fe bimetallic catalyst with phosphorus modifier according to claim 5, characterized in that, In step 2, the Pd precursor is palladium chloride, and the Fe precursor is ferrous chloride. The total concentration of Pd and Fe precursors in the ethanol-water solution was 0.02–0.06 mol / L, and the solid-liquid ratio of SBA-15 mesoporous silica to the ethanol-water solution was 1:5–7 g / mL.

7. The method for preparing the Pd-Fe bimetallic catalyst with phosphorus modifier according to claim 5, characterized in that, In step 3, the molar ratio of diethyl phosphite to Pd-Fe bimetal is 0.3 to 0.6:

1.

8. The application of the Pd-Fe bimetallic catalyst with phosphorus modifier according to any one of claims 1-4 in the selective catalytic hydrogenation of waste TNT.

9. The application according to claim 8, characterized in that, include: The waste TNT mentioned refers to ammunition dismantling waste, TNT production wastewater, or expired explosives. Among them, ammunition dismantling waste needs to be pre-crushed to a particle size of ≤1 mm, and TNT production wastewater needs to be filtered through a 0.22 μm filter membrane to remove suspended impurities. The system for the catalytic hydrogenation reaction is a water-ethanol mixture, wherein the volume ratio of water to ethanol is 7:3 to 9:

1. The catalytic hydrogenation reaction conditions are: reaction temperature 40-70℃, hydrogen pressure 1-3 MPa, catalyst dosage of 8%-15% of the mass of waste TNT, and reaction time 2-4 h.

10. The application according to claim 8, characterized in that, After the catalytic hydrogenation reaction is completed, the Pd-Fe bimetallic catalyst with phosphorus modifier is recovered by centrifugation. The centrifugation speed is 3500-4500 rpm, and the centrifugation time is 10-20 min.

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