A method for low-temperature regeneration of VOCs honeycomb catalysts

Abstract

This invention discloses a method for low-temperature regeneration of VOCs honeycomb catalysts. Addressing the problems of active metal loss and difficulty in removing deep-seated carbon deposits during catalyst regeneration, this method involves pretreating the deactivated catalyst and then submerging it in a composite regeneration solution. Subsequently, it undergoes heating degradation, during which periodic micro-negative pressure pulsation is applied, and the carbon deposits from the deep pores are discharged through a pressure difference. After emptying the waste liquid, the catalyst is immersed in a tannic acid aqueous solution for cross-linking, constructing a three-dimensional polyphenol network membrane in situ within the pores to retain active metals. Finally, a programmed gradient temperature calcination process is performed to obtain the regenerated catalyst. This invention integrates chemical degradation, physical exfoliation under pressure, and polyphenol network confinement remodeling processes, effectively inhibiting metal component loss and aggregation while thoroughly removing mesoporous carbon deposits, thus restoring the catalyst's metal dispersion and overall activity.

Description

Technical Field

[0001] This invention relates to the field of catalyst regeneration technology, specifically a method for low-temperature regeneration of VOCs honeycomb catalysts. Background Technology

[0002] In catalytic combustion processes for volatile organic compounds (VOCs), honeycomb catalysts are typically used, with cordierite as the substrate, an alumina coating, and an active metal (such as a noble or transition metal) supported on the surface. As the catalyst's service life increases, incompletely combusted organic macromolecules in the reaction gas readily undergo condensation reactions on the catalyst surface and within the micropores, forming dense carbon deposits. These carbon deposits not only physically block gas mass transfer channels but also cover the catalytically active sites on the surface, leading to a significant increase in the catalyst's ignition temperature, a substantial decrease in overall catalytic efficiency, and eventual deactivation.

[0003] To restore the activity of deactivated catalysts, the main industrial methods currently employed are high-temperature heat treatment and conventional liquid-phase chemical cleaning. However, relying solely on high-temperature roasting to remove carbon deposits typically requires reaction temperatures above 500°C (i.e., traditional high-temperature regeneration methods). Under prolonged high-temperature, oxygen-rich environments, active metal particles on the catalyst surface are highly susceptible to thermal migration and secondary sintering and agglomeration, resulting in a sharp decrease in metal dispersion. This loss of active sites is irreversible. Simultaneously, the intense localized exothermic heating can easily cause cracking or even peeling of the substrate coating. To mitigate high-temperature damage, liquid-phase chemical immersion treatment is often used as a supplementary method. Existing chemical cleaning agents primarily rely on strong oxidants or acid / alkali solutions to degrade surface contaminants. In practice, conventional fluids, limited by high surface tension and capillary resistance in micropores, struggle to effectively penetrate and remove deep carbon deposits, leading to incomplete pore cleaning. Even more critically, the forceful destruction of carbon deposits using chemical agents often triggers the dissolution of active metal components, resulting in the loss of large amounts of precious or transition metal ions with the waste liquid.

[0004] These technological limitations make it difficult for existing regeneration methods to strike a balance between "thoroughly removing deep carbon deposits" and "protecting and reshaping active metal components." The regenerated catalyst often has a low performance recovery rate, making it difficult to meet the requirements of long-term recycling in industrial systems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for low-temperature regeneration of VOCs honeycomb catalysts, solving the problem that dense carbon deposits easily form deep within the pores of existing VOCs honeycomb catalysts after long-term service. Conventional cleaning and heat treatment are insufficient to remove these deep carbon deposits, and the regeneration process often easily leads to the loss and aggregation of active components such as precious metals or transition metals, ultimately resulting in an increase in catalyst ignition temperature and an irreversible decrease in overall catalytic activity.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for low-temperature regeneration of VOCs honeycomb catalysts, comprising the following steps: S1. Physically pretreat the deactivated VOCs honeycomb catalyst to remove loose free dust from the surface and pores. S2. Place the pretreated catalyst in the reactor, pump in the composite regeneration initial liquid to submerge the catalyst, and perform static soaking at normal pressure and set temperature. The composite regeneration initial liquid is used to inhibit the ineffective catalysis of surface active metals by coordination masking while oxidizing and degrading deep mesoporous carbon deposits, and to provide an adaptive acid-base phase transition buffer under thermodynamic activation. S3. The reactor is heated and kept at a constant temperature for degradation. During the constant temperature degradation, a periodic micro-negative pressure pulse treatment is applied inside the reactor. The carbon deposits in the deep micropores are actively stripped and pumped out through the pressure difference. S4. After draining the waste liquid in the reactor, the catalyst is initially dehydrated. Then, the catalyst is immersed in a tannic acid aqueous solution for static soaking and crosslinking to construct a three-dimensional polyphenol network membrane that retains active metals in situ in the pores. After draining the waste liquid, the catalyst is washed with water and dehydrated again. S5. The dehydrated catalyst is transferred into a drying oven for programmed gradient calcination, and then cooled in the oven to obtain the regenerated catalyst.

[0007] By employing the above technical solution, and utilizing an integrated process of chemical oxidative degradation, gas pressure physical stripping, and confined remodeling of the active metal polyphenol network, the effect of thoroughly removing deep mesoporous carbon deposits and fully restoring the dispersion of active metals is achieved. The specific reaction and mechanism of action are explained step-by-step as follows: Once the composite regenerated initial liquid is pumped into the reactor and permeates into the mesoporous network of the catalyst, the ethylene glycol butyl ether in the system will reduce the surface tension of the liquid phase, allowing the liquid to effectively enter the deep carbon deposition region.

[0008] Subsequently, during the system heating phase, a liquid-phase chemical reaction was initiated. Sodium persulfate undergoes bond breaking under heating conditions and generates sulfate radicals, as shown in the following reaction equation: S2O8 2- +ΔT→2SO4• - ; This free radical possesses strong oxidizing properties, directly attacking and breaking the carbon-carbon bonds of large carbon deposits, degrading them into water-soluble small organic molecules. Accompanying this oxidative degradation process, urea undergoes a hydrolysis reaction: CO(NH2)2 + H2O → 2NH3 + CO2; The generated ammonia gas dissolves in water to form a weakly alkaline environment, which can neutralize the acidic substances produced by the decomposition of persulfate, maintain acid-base balance, and prevent the alumina substrate from dissolving. At the same time, disodium ethylenediaminetetraacetate coordinates with the active metal ions on the catalyst surface to form steric hindrance, thereby inhibiting the ineffective decomposition of sodium persulfate catalyzed by the metal center.

[0009] During chemical degradation, a periodic micro-negative pressure pulsation treatment is superimposed. When the system is evacuated, the fluid inside the pores expands outward; during repressurization, fresh external reactants are pumped into the depths of the pores. This alternating pressure difference creates a physical pumping effect, forcibly expelling the degradation residues from the mesoporous network.

[0010] After the waste liquid is emptied and enters the cross-linking stage, the adjacent phenolic hydroxyl groups in the tannic acid structure undergo a multidentate chelation reaction with free or complexed active metal ions, forming a three-dimensional polyphenol network membrane through self-assembly and cross-linking within the micropores. This network anchors the metal ions within the physical grid, preventing them from being lost with the water during subsequent washing and centrifugation.

[0011] Finally, the three-dimensional polyphenol network membrane is pyrolyzed and carbonized through gradient heating, forming a nanoscale physically confined space. Within this space, metal clusters undergo in-situ deconstruction, dispersing into sub-nanometer or single-atom forms. As the carbon skeleton is completely burned out, the dispersed active metals are re-anchored to oxygen vacancies on the alumina surface, exposing more low-coordination reaction sites and effectively lowering the activation energy of the reaction.

[0012] Preferably, in step S1, the physical pretreatment is performed by using industrial compressed air with a pressure of 0.3MPa to 0.6MPa to reciprocate purging along the axial direction of the honeycomb channels for 3 to 5 minutes; in step S2, the temperature is set to 25°C to 35°C, and the static soaking time is 1.5h to 3.0h.

[0013] By employing the above technical solution and controlling specific air purging pressure and time, it is possible to remove floating dust from the pores while maintaining the structural integrity of the cordierite substrate, thus establishing initial channels for liquid-phase fluid penetration. Limiting the static immersion temperature and time ensures that the composite regenerated initial solution achieves complete wetting and penetration of the micropores without premature thermal decomposition.

[0014] Preferably, in step S3, the heating method is to raise the system to 70°C to 80°C at a rate of 0.5°C / min to 1.0°C / min, and maintain the constant temperature for degradation for 3.0h to 5.0h.

[0015] By adopting the above technical solution, setting a medium temperature range and a slow heating rate, the activation energy threshold of persulfate is matched, maintaining the stable release of sulfate free radicals, avoiding instantaneous large-scale gas production that could cause cracking of the substrate coating, and ensuring that the carbon macromolecules have sufficient chain-breaking degradation time.

[0016] Preferably, in step S3, the specific parameters of the periodic micro-negative pressure pulsation are as follows: the pulsation period is set to 10 min to 20 min. In each pulsation period, the absolute pressure inside the reactor is pumped down to 0.06 MPa to 0.08 MPa using a vacuum system for the first 3 min to 8 min, and then repressurized to 0.1 MPa and maintained for 7 min to 12 min. This cycle is repeated until the isothermal degradation ends.

[0017] By adopting the above technical solution, the limited pressure difference range and time period can overcome the capillary resistance of deep mesoporous fluids. During the pumping stage, impurities are carried outwards, and during the repressurization stage, a high-concentration oxidant solution is added, establishing a material exchange cycle inside and outside the micropores and solving the problem of degradation products remaining in the mesopores.

[0018] Preferably, the specific implementation method of step S4 is as follows: the treatment conditions for the initial dehydration and the second dehydration are: centrifugation at 300 rpm to 600 rpm for 3 min to 8 min; the mass fraction of the tannic acid aqueous solution is 0.3 wt% to 1.0 wt%, and the soaking conditions are static soaking at 20 ℃ to 30 ℃ under normal pressure for 10 min to 20 min; the water washing process is: washing with deionized water 2 to 3 times, each time for 10 min to 20 min.

[0019] By employing the above technical solution, centrifugation removes free waste liquid, reducing the impact of the preceding process on the concentration dilution of the tannic acid solution. By limiting the tannic acid concentration and static soaking parameters at room temperature, the polyphenol network membrane is ensured to have appropriate cross-linking density, which can both retain metal coordination compounds and avoid pore blockage. Deionized water washing is mainly used to remove uncross-linked small molecules and salt byproducts.

[0020] Preferably, in step S5, the specific implementation of the programmed gradient temperature calcination is as follows: First stage: the temperature is increased to 120℃ to 160℃ at a heating rate of 1.0℃ / min to 3.0℃ / min, and held at a constant temperature for 1.5h to 3.0h; Second stage: the temperature is increased to 220℃ to 280℃ at a heating rate of 1.0℃ / min to 3.0℃ / min, and held at a constant temperature for 2.0h to 4.0h.

[0021] By adopting the above technical solution, the first-stage temperature zone is used to remove free water and chemically bound water, thus solidifying the polyphenol metal framework structure. The second-stage temperature zone reaches the pyrolysis critical region of the polymer film, promoting a spatial confinement effect during the slow-release carbonization process, driving the metal atoms to redisperse, and avoiding secondary sintering and growth of metal grains caused by direct high-temperature calcination.

[0022] Preferably, the VOCs honeycomb catalyst is a transition metal honeycomb catalyst or a noble metal honeycomb catalyst with monolithic cordierite as the substrate and an alumina mesoporous coating on the surface. By adopting the above technical solution, the applicable substrate types of the method are clarified, and the established polyphenol crosslinking and temperature calcination parameters have stable metal anchoring and activity remodeling effects for both platinum-palladium and manganese-copper systems.

[0023] Secondly, the present invention provides a composite regeneration initial solution for the method described in the first aspect and a method for preparing the same, employing the following technical solution: A composite regeneration initial solution comprises the following components in weight percentage: ethylene glycol butyl ether 3.0% to 8.0%; disodium ethylenediaminetetraacetate 1.0% to 3.0%; urea 2.0% to 5.0%; sodium persulfate 5.0% to 10.0%; the balance being deionized water.

[0024] A method for preparing a composite regenerated initial solution includes the following steps: Add deionized water to a corrosion-resistant mixing vessel with a temperature controlled between 15°C and 25°C. While stirring, add ethylene glycol butyl ether, disodium ethylenediaminetetraacetate, and urea in sequence, stirring until completely dissolved to form a homogeneous mixture. Keep the system temperature below 30°C and continue stirring, then slowly add sodium persulfate until completely dissolved. Seal and store in a dark place for later use.

[0025] The components in the composite regenerated initial solution exhibit synergistic effects. Specifically, ethylene glycol butyl ether reduces the wetting angle at the liquid-solid interface, increasing the fluid's penetration into the catalyst pores. Disodium ethylenediaminetetraacetate specifically coordinates and masks exposed metal ions, reducing the ineffective consumption of sodium persulfate. Urea, upon heating, produces weakly alkaline ammonia gas, which reacts with the acid produced by the decomposition of sodium persulfate to form a dynamic buffer pair, preventing a sharp drop in the solution pH. Sodium persulfate, as the core component, provides active free radicals for the oxidation reaction.

[0026] In the preparation method, the solution temperature is strictly limited and the final addition sequence of sodium persulfate is controlled, which effectively prevents the spontaneous decomposition reaction of sodium persulfate caused by heat accumulation and ensures the chemical stability of the composite regenerated initial solution during room temperature storage and industrial pumping.

[0027] Preferably, the composite regeneration initial solution is composed of the following components by mass percentage: ethylene glycol butyl ether 5.0%; disodium ethylenediaminetetraacetate 2.0%; urea 3.5%; sodium persulfate 7.5%; and the balance being deionized water.

[0028] By adopting the above technical solution, the ratio defines the balance point of surface activity, metal masking amount and acid-base buffering amount, ensuring the penetration rate of deep channels while supplying sufficient oxide groups to completely break the carbon deposit structure.

[0029] This invention provides a method for low-temperature regeneration of VOCs honeycomb catalysts. It has the following beneficial effects: 1. This invention achieves thorough removal of deep-seated carbon deposits and synergistic protection of the catalyst substrate by using a composite regeneration solution comprising sodium persulfate, urea, disodium ethylenediaminetetraacetate (EDTA), and ethylene glycol butyl ether. ETA reduces the surface tension of the fluid, promoting its penetration into the mesopores, while heated sodium persulfate releases strong oxidizing free radicals that degrade large carbon molecules. During this reaction, heated urea generates weakly alkaline ammonia gas, neutralizing the acidity of the system and preventing the dissolution of the alumina support; simultaneously, disodium ethylenediaminetetraacetate coordinates with the surface metal to mask the reaction, preventing the ineffective consumption of persulfate by the metal catalyst, thus maintaining the structural stability of the catalyst while degrading carbon deposits.

[0030] 2. The isothermal oxidation degradation stage of this invention introduces periodic micro-negative pressure pulsation treatment, effectively solving the problem of easy retention of degradation products inside mesopores. In the alternating cycle of vacuuming and repressurization, the fluid inside the pores generates a physical pumping effect of expansion and contraction, overcoming the capillary resistance in deep micropores. This dynamic pressure difference change can forcibly strip and discharge the carbon residue and salt by-products after chain breakage, accelerate the mass transfer and exchange of high-concentration oxidant from the outside into the pores, and thus fully restore the effective specific surface area and pore flow rate of the catalyst.

[0031] 3. This invention employs a tannic acid crosslinking combined with a programmed gradient temperature calcination process to achieve in-situ confined remodeling of the active metal component. Tannic acid undergoes a multidentate chelation reaction with metal ions to generate a three-dimensional polyphenol network film, preventing the loss of free active metal during subsequent dehydration and washing steps. Subsequent gradient temperature calcination causes the polyphenol network to undergo slow-release carbonization, forming a nanoscale physical confinement space. This drives the deconstruction of the originally aggregated metal clusters, which are then re-anchored to the support surface in a highly dispersed form, increasing the effective catalytic active sites and reducing the ignition temperature of the regenerated catalyst. Attached Figure Description

[0032] Figure 1 Figure (a) shows the oxidation slow release and pH adaptive buffering mechanism test curves of the embodiments and comparative examples of the present invention. Figure (a) represents the change in the residual rate of persulfate during the degradation stage, with the solid line representing Example 1 and the dashed line representing Comparative Example 1. Figure (b) shows the change trajectory of the pH value of the system over time, with the solid line representing Example 1 and the dotted line representing the comparative example. Figure 2 This is a tracking diagram of the active metal loss behavior during the catalyst washing stage of this invention; Figure 3 Figure 1 shows the evaluation of the catalyst pore structure and carbon removal rate of the present invention. Figure 2(a) shows the comparison of the evolution of specific surface area of ​​different samples, and Figure 3(b) reflects the distribution trend of the synchronous evolution of total pore volume and micropore volume of the above samples. Figure 4 Figure 1 shows the test results of the retention rate and dispersion recovery of the active metal in the catalyst of the present invention. Figure 2(a) reflects the trajectory of the relative retention rate of platinum and palladium components in the sample at different treatment stages. The solid line represents the Pt component and the dashed line represents the Pd component. Figure 3(b) reveals the evolution law of the metal dispersion of the surface catalytic sites corresponding to the above states. Figure 5 The figure shows a comparison of the desalination completeness and inorganic impurity residue of the catalyst of the present invention. Figure (a) shows the difference in conductivity levels of the waste liquid discharged from Example 1, Comparative Example 1 and Comparative Example 3 at the end of the process water washing. Figure (b) uses a logarithmic vertical axis to systematically characterize the residual mass fraction of sodium ions in the deep layer inside the solid catalyst after regeneration in the fresh state, deactivated state and each treatment scheme. Figure 6 The above is an evaluation chart of the macroscopic mechanical strength recovery rate of the catalyst of the present invention. In the figure, (a) reflects the change of axial compressive strength of the specimen when subjected to compressive load along the direction of the honeycomb channel, and (b) reflects the distribution of radial compressive strength when subjected to pressure perpendicular to the channel wall. Figure 7 The graphs show the catalytic activity evaluation curves for the degradation of toluene VOCs by various catalyst samples of the present invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a method for low-temperature regeneration of VOCs honeycomb catalysts. The basic chemical reagents used in the examples and comparative examples are all commercially available conventional industrial-grade products, and the deionized water is conventionally self-made, which will not be described in detail here.

[0035] The following details the specific sources and initial baseline conditions of the feedstock (deactivated VOCs cell catalyst) used for this process validation: Example of raw material 1: Raw material name: Deactivated Pt-Pd / Al2O3 honeycomb catalyst; Standard specifications: monolithic cordierite substrate (pore density 200 cpsi), surface coated with γ-Al2O3 mesoporous coating, with platinum and palladium as the active metals; Characteristics of deactivation: The catalyst originated from a toluene waste gas catalytic oxidation unit of a chemical plant, which was deactivated and taken offline after 3 years of continuous industrial operation. The catalyst appeared dark gray-black, and the micropores were severely blocked by carbon deposits of tar and polycyclic aromatic hydrocarbon polymers. Initial characterization revealed slight Ostwald ripening (agglomeration) of the Pt-Pd nanoparticles on the surface.

[0036] Raw material example 2: Raw material name: Deactivated Mn-Cu / Al2O3 honeycomb catalyst; Standard specifications: monolithic cordierite substrate (pore density 400 cpsi), surface coated with γ-Al2O3 mesoporous coating, with manganese and copper as the active metals loaded; Characteristics of deactivation: Originating from VOCs treatment equipment in a printing and packaging plant, the equipment deactivated and was taken offline after 2.5 years of continuous industrial operation. A large amount of high-viscosity, high-molecular-weight oligomers, generated from incomplete combustion of resin-based organic solvents, adhered to the catalyst end face and pore inner walls, resulting in a high pore blockage rate and a significant decrease in intrinsic catalytic activity.

[0037] Preparation Example 1: This preparation example provides a method for preparing a composite regeneration initial solution for low-temperature regeneration of VOCs honeycomb catalysts, using optimal ratio parameters, and includes the following steps: Step 1: Add 82.0 kg of industrial deionized water to the corrosion-resistant mixing vessel equipped with a mechanical stirring device and a jacket cooling system, turn on the jacket circulating cooling water, and control the bottom liquid temperature at 20℃. Step 2: Turn on the stirrer (150 rpm) and slowly add 5.0 kg of ethylene glycol butyl ether (EGBE), 2.0 kg of disodium ethylenediaminetetraacetate (EDTA-2Na) and 3.5 kg of industrial urea into the vessel in sequence. Continue stirring for 20 minutes until the solid components are completely dissolved and a clear homogeneous mixture is formed. Step 3: While maintaining the system temperature below 25℃ and continuously stirring, slowly add 7.5 kg of sodium persulfate (Na2S2O8) to the system in batches, and continue stirring for 30 minutes until completely dissolved to obtain a composite regeneration initial solution with a component mass fraction of (5.0% EGBE + 2.0% EDTA-2Na + 3.5% urea + 7.5% Na2S2O8). Seal and protect from light for later use.

[0038] Preparation Example 2: This preparation example provides a method for preparing a composite regeneration initial solution for low-temperature regeneration of VOCs honeycomb catalysts, using the lower limit of the ratio parameters, including the following steps: Step 1: Add 89.0 kg of industrial deionized water to the corrosion-resistant mixing vessel equipped with a mechanical stirring device and a jacket cooling system, turn on the jacket circulating cooling water, and control the bottom liquid temperature at 15℃. Step 2: Turn on the stirrer and slowly add 3.0 kg of ethylene glycol butyl ether (EGBE), 1.0 kg of disodium ethylenediaminetetraacetate (EDTA-2Na), and 2.0 kg of industrial urea into the reactor in sequence, and continue stirring for 15 minutes until completely dissolved; Step 3: While maintaining the system temperature below 20℃ and continuously stirring, slowly add 5.0 kg of sodium persulfate (Na2S2O8) to the system and continue stirring for 20 minutes until completely dissolved to obtain a composite regeneration initial solution with a component mass fraction of (3.0% EGBE + 1.0% EDTA-2Na + 2.0% urea + 5.0% Na2S2O8). Seal and protect from light for later use.

[0039] Preparation Example 3: This preparation example provides a method for preparing a composite regeneration initial solution for low-temperature regeneration of VOCs honeycomb catalysts, using the upper limit of the ratio parameters, and includes the following steps: Step 1: Add 74.0 kg of industrial deionized water to the corrosion-resistant mixing vessel equipped with a mechanical stirring device and a jacket cooling system, turn on the jacket circulating cooling water, and strictly control the bottom liquid temperature at 25℃. Step 2: Turn on the stirrer and slowly add 8.0 kg of ethylene glycol butyl ether (EGBE), 3.0 kg of disodium ethylenediaminetetraacetate (EDTA-2Na), and 5.0 kg of industrial urea into the reactor in sequence, and continue stirring for 30 minutes until completely dissolved; Step 3: While maintaining the system temperature below 30℃ and continuously stirring, slowly and evenly add 10.0 kg of sodium persulfate (Na2S2O8) to the system. Control the addition rate to prevent excessive temperature rise due to local heat of dissolution. Continue stirring vigorously for 40 minutes until completely dissolved to obtain a composite regeneration initial solution with a component mass fraction of (8.0% EGBE + 3.0% EDTA-2Na + 5.0% urea + 10.0% Na2S2O8). Seal and protect from light for later use.

[0040] Example 1: This embodiment provides a method for low-temperature regeneration of VOCs honeycomb catalysts, employing an optimal combination of process parameters, including the following steps: Step 1: Take the deactivated Pt-Pd / Al2O3 honeycomb catalyst module described in Example 1 and use industrial compressed air at a pressure of 0.4MPa to reciprocate along the axial direction of the honeycomb channels for 4 minutes to remove loose free dust. Step 2: Place the pretreated catalyst in a jacketed reactor with a vacuum interface, and pump in the composite regenerated initial liquid prepared in Preparation Example 1, ensuring the liquid level is 5 cm above the top of the catalyst. Maintain atmospheric pressure, set the system temperature to 30°C, and allow it to soak statically for 2.0 h. Step 3: Turn on the jacket heating of the reactor and raise the system temperature to 75°C at a constant rate of 0.8°C / min, and maintain the constant temperature for 4.0 hours.

[0041] During the isothermal period, periodic micro-negative pressure pulsation is applied: the pulsation period is set to 15 minutes. In the first 5 minutes of each period, the absolute pressure is pumped down to 0.08 MPa using a vacuum pump. Then, the pressure is restored to 0.1 MPa by opening the pressure recovery valve and maintained for 10 minutes. This cycle is repeated until the isothermal period ends. Step 4: Drain the waste liquid in the reactor, transfer the catalyst into a centrifuge, and centrifuge at 400 rpm for 5 minutes to dry it.

[0042] The catalyst was then immersed in a 0.5 wt% tannic acid aqueous solution and statically soaked at 25°C and atmospheric pressure for 15 min. The tannic acid solution was drained, and deionized water was pumped in for two washes, each lasting 15 min. After washing, the catalyst was centrifuged again at 400 rpm for 5 min. Step 5: Transfer the dried catalyst into a programmed temperature drying oven and heat it to 150℃ at a rate of 2.0℃ / min, maintaining the temperature for 2.0h; then continue heating to 250℃ at a rate of 2.0℃ / min, maintaining the temperature for 3.0h. After heat treatment, allow the furnace to cool naturally to obtain the regenerated catalyst.

[0043] Example 2: This embodiment provides a method for low-temperature regeneration of VOCs honeycomb catalysts, using a combination of lower limit process parameters, including the following steps: Step 1: Take the deactivated Pt-Pd / Al2O3 honeycomb catalyst module described in Example 1 and use industrial compressed air at a pressure of 0.3MPa to reciprocate along the axial direction of the honeycomb channels for 5 minutes to remove loose free dust. Step 2: Place the pretreated catalyst in the reactor and pump in the composite regenerated initial solution prepared in Preparation Example 2. Maintain atmospheric pressure, set the system temperature to 25℃, and statically soak for 3.0 h; Step 3: Turn on the heating of the reactor jacket and raise the system temperature to 70°C at a rate of 0.5°C / min, and maintain the constant temperature for 5.0 hours.

[0044] During the constant temperature period, periodic micro-negative pressure pulsation is applied: the pulsation period is 20 minutes. In each cycle, the absolute pressure is drawn down to 0.08 MPa for the first 8 minutes, then restored to 0.1 MPa and maintained for 12 minutes, and the cycle is repeated. Step 4: Drain the waste liquid and centrifuge the catalyst at 300 rpm for 8 minutes. Immerse the catalyst in a 0.3 wt% tannic acid aqueous solution and statically soak it at 20°C for 20 minutes. Drain the tannic acid solution and wash it three times with deionized water, 20 minutes each time. After washing, centrifuge again at 300 rpm for 8 minutes. Step 5: Transfer the catalyst into a drying oven and heat it to 120℃ at a rate of 1.0℃ / min, maintaining the temperature for 3.0h; then heat it to 220℃ at a rate of 1.0℃ / min, maintaining the temperature for 4.0h. After heat treatment, cool it with the furnace to obtain the regenerated catalyst.

[0045] Example 3: This embodiment provides a method for low-temperature regeneration of VOCs honeycomb catalysts, employing an upper limit combination of process parameters, including the following steps: Step 1: Take the deactivated Pt-Pd / Al2O3 honeycomb catalyst module described in Example 1 and use industrial compressed air at a pressure of 0.6MPa to reciprocate along the axial direction of the honeycomb channels for 3 minutes to remove loose free dust. Step 2: Place the pretreated catalyst in the reactor and pump in the composite regenerated initial solution prepared in Preparation Example 3. Maintain atmospheric pressure, set the system temperature to 35℃, and statically soak for 1.5 hours; Step 3: Turn on the jacket heating of the reactor and heat the system to 80°C at a rate of 1.0°C / min, and maintain the constant temperature for 3.0 hours.

[0046] During the constant temperature period, periodic micro-negative pressure pulsation is applied: the pulsation period is 10 minutes, and the absolute pressure is drawn down to 0.06 MPa for the first 3 minutes of each period, then restored to 0.1 MPa and maintained for 7 minutes, and the cycle is repeated. Step 4: Drain the waste liquid and centrifuge the catalyst at 600 rpm for 3 minutes. Immerse the catalyst in a 1.0 wt% tannic acid aqueous solution and statically soak it at 30°C for 10 minutes.

[0047] Drain the tannic acid solution and wash twice with deionized water, 10 min each time. After washing, centrifuge again at 600 rpm for 3 min to remove excess water. Step 5: Transfer the catalyst into a drying oven and heat it to 160℃ at a rate of 3.0℃ / min, maintaining the temperature for 1.5 hours; then heat it to 280℃ at a rate of 3.0℃ / min, maintaining the temperature for 2.0 hours. After heat treatment, cool it with the furnace to obtain the regenerated catalyst.

[0048] Example 4: This embodiment provides a method for low-temperature regeneration of VOCs honeycomb catalysts to verify the universality of this process for transition metal catalyst systems, including the following steps: Step 1: Take the deactivated Mn-Cu / Al2O3 honeycomb catalyst module described in Example 2 and purge it along the axial direction of the honeycomb channels with industrial compressed air at a pressure of 0.4 MPa for 4 minutes. Step 2: Place the pretreated catalyst in the reactor and pump in the composite regenerated initial solution obtained in Preparation Example 1. Maintain atmospheric pressure, set the system temperature to 30℃, and statically soak for 2.0 h; Step 3: Increase the temperature to 75℃ at a rate of 0.8℃ / min and hold at that temperature for 4.0 hours. During the isothermal period, the pulsation cycle is set to 15 minutes (0.08 MPa for the first 5 minutes, and 0.1 MPa for the last 10 minutes), and repeat the cycle. Step 4: Drain the waste liquid and centrifuge at 400 rpm for 5 min. Immerse in a 0.5 wt% tannic acid aqueous solution under normal pressure for 15 min. Wash twice with deionized water for 15 min each time, and centrifuge again for 5 min after washing. Step 5: Increase the temperature to 150℃ at 2.0℃ / min and hold for 2.0h; continue to increase the temperature to 250℃ at 2.0℃ / min and hold for 3.0h. Cool with the furnace to obtain the regenerated catalyst.

[0049] Comparative Example 1: Compared with Example 1, the difference is that EDTA-2Na is not added to the composite regeneration initial solution (it is made up with an equal amount of deionized water), and everything else is the same.

[0050] Comparative Example 2: Compared with Example 1, the difference is that urea is not added to the composite regeneration initial solution (it is made up with an equal amount of deionized water), and everything else is the same.

[0051] Comparative Example 3: Compared with Example 1, the difference is that no periodic micro-negative pressure pulsation is applied in step three (the degradation process is maintained at 0.1MPa atmospheric pressure), and the rest are the same.

[0052] Comparative Example 4: Compared with Example 1, the difference is that in step four, after centrifugation, the tannic acid aqueous solution is not used for soaking, but deionized water is used directly for washing; the rest are the same.

[0053] Comparative Example 5: Compared to Example 1, this comparative example uses a conventional high-temperature heat treatment process for regeneration, including the following steps: Take the deactivated Pt-Pd / Al2O3 honeycomb catalyst module described in Example 1, and use industrial compressed air at a pressure of 0.4 MPa to reciprocate along the axial direction of the honeycomb channels for 4 minutes to remove loose free dust. Then, place it directly in a muffle furnace.

[0054] The temperature was increased to 500℃ in air at a heating rate of 5.0℃ / min, and then calcined at this temperature for 4.0 h. After heat treatment, the catalyst was naturally cooled in the furnace to obtain a regenerated catalyst, without the use of any chemical reagents for liquid-phase treatment.

[0055] Test Example 1: This test case examines the reaction solutions of Example 1, Comparative Example 1 (without EDTA-2Na), and Comparative Example 2 (without urea) during the heating and isothermal degradation stages.

[0056] The time when each system reaches a constant temperature of 75℃ during the prescribed heating process is recorded as time 0. Subsequently, in-situ sampling and online monitoring are carried out at five time points: 0.5h, 1.0h, 2.0h, 3.0h, and 4.0h.

[0057] For the persulfate consumption kinetics test, 2 mL of reaction solution was drawn from the side sampling port of the reactor each time and quickly injected into an ice-water mixture containing excess potassium iodide to quench the reaction. Starch indicator was then added, and iodometric titration was performed using a 0.1 mol / L sodium thiosulfate standard solution to calculate the residual S₂O₈ at each time point. 2- The absolute concentration is calculated and converted into a percentage of the initial concentration (residual rate).

[0058] To monitor the acid-base buffering process of the system, a composite glass electrode pH meter that can withstand an 80°C working environment is installed inside the reactor. This probe is directly connected to the host computer data acquisition system and records the real-time pH value of the reaction solution at the corresponding time points.

[0059] Table 1. Data on persulfate residue and pH value monitoring during the isothermal degradation phase of each reaction system.

[0060] Based on the data in Table 1 and the appendix Figure 1 In Example 1, the persulfate consumption rate during the initial stage of isothermal degradation was significantly lower than that in Comparative Example 1. In Comparative Example 1, where EDTA coordination masking was not introduced, the active metal remaining on the catalyst surface exhibited a strong catalytic decomposition effect, leading to increased S2O8 content in the system. 2-Within half an hour of heating to 75°C, the oxidant rapidly depleted to 43.6%. This rapid and disordered free radical burst directly exhausts the oxidant at the pore opening, severing the oxidation mass transfer chain into the depths of the micropores. In Example 1, after adding EDTA, the metal atoms were firmly encapsulated by the multidentate ligands. The steric hindrance effect, combined with the change in coordination field strength, effectively raised the activation energy barrier of persulfate at the metal interface. This mechanism promotes the activation of S2O8. 2- Instead, it follows a thermal activation pathway, maintaining a relatively constant decomposition slope throughout the 4-hour treatment cycle. This near-zero-order kinetic release ensures, at the engineering level, that the generation rate of high-potential sulfate radicals matches the capillary permeation rate of EGBE within narrow pores, thereby achieving continuous, layer-by-layer stripping of deep-pore carbon deposits.

[0061] In terms of pH evolution during the reaction process, Comparative Example 2 reveals the inherent thermodynamic instability defects of conventional wet oxidation processes. Without urea intervention, the decomposition of persulfate and the generation of short-chain fatty acids from the cracking of macromolecular organic matter rapidly increased the free proton concentration. The pH of the reaction solution dropped below 3.0 within one hour and irreversibly slipped into the strongly acidic range. This extreme acidic environment inevitably induced the proton dissociation of EDTA in its complexed state, leading to the large-scale dissolution and loss of previously masked active metals in ionic form. The pH trend of the system in Example 1 confirms the design intent of the phase change buffer. When oxidation-induced acid production caused the system pH to shift towards slightly acidic, the originally inert urea activated the acid-catalyzed hydrolysis pathway under thermodynamic drive at 75°C. The continuously released ammonia molecules from hydrolysis constructed an adaptive acid-base neutralization network in the liquid phase, robustly anchoring the macroscopic pH within a slightly acidic to neutral window of 6.4 to 6.8. By intervening in this feedback regulation mechanism, not only is the reverse thermodynamic channel for EDTA dissociation and precipitation completely blocked, but the carbon dioxide generation process in parallel with hydrolysis also provides a sufficient in-situ nucleation gas source for subsequent micro-negative pressure pulsating gas lift, proving that this scheme has a high degree of logical self-consistency in deep chemical environment control.

[0062] Test Example 2: The subjects of this test are Example 1 (introducing a tannic acid crosslinking network before water washing) and Comparative Example 4 (skipping the tannic acid treatment and directly entering the desalination water washing after degradation), aiming to track the liquid phase metal migration behavior induced by the regeneration operation.

[0063] After the catalyst degradation was completed and the initial liquid was removed by centrifugation, all free wastewater discharged during the two deionized water washing processes was collected quantitatively. Wastewater samples from different batches were transferred into polytetrafluoroethylene beakers and placed on a constant-temperature hot plate at 90°C to slowly evaporate and concentrate to one-tenth of the original volume in order to enrich the extremely low concentration of the analyte.

[0064] Add an appropriate amount of a mixture of high-purity nitric acid and hydrofluoric acid to the concentrated residue, and then place it in a microwave digester for digestion treatment to completely destroy the organic masking substances such as residual EDTA or tannic acid in the wastewater, ensuring that the metal ions are completely converted into the free state. Then, dilute to the standard volume with 2% dilute nitric acid.

[0065] The specific mass concentrations of Pt and Pd in ​​the constant-volume solution were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). By combining the original volume of the cleaning solution with the theoretical total mass of precious metals loaded on the spent catalyst, the absolute metal loss and cumulative loss rate for each washing cycle were calculated in reverse.

[0066] Table 2. Test data on metal concentration and cumulative loss rate of wastewater in each washing cycle of Example 1 and Comparative Example 4.

[0067] Based on the data in Table 2 and the appendix Figure 2 In Comparative Example 4, irreversible active phase collapse occurred during the conventional deionized water washing process. After only two washes with deionized water, the cumulative loss rates of Pt and Pd soared to 23.18% and 19.35%, respectively. In actual catalyst industrial regeneration scenarios, water washing is an essential operation to remove the high concentration of inorganic sodium salts remaining from the oxidation reaction. However, the EDTA macromolecular complex used to shield metal activity in the pre-degradation stage has extremely strong hydrophilicity, causing the noble metals attached to the support surface to transform into highly water-soluble coordination ions. Without targeted interfacial intervention, these valuable active nuclei, as revealed in Comparative Example 4, will be indiscriminately washed out of the pores along with the deionized water flow, rendering the regeneration product completely waste.

[0068] Example 1 successfully broke through this engineering deadlock by briefly introducing a low-concentration tannic acid aqueous solution after initial centrifugation, forcibly suppressing the metal loss rate under the same washing intensity to a trace level of less than 0.3%. A deeper investigation into the underlying interfacial chemical evolution revealed that the densely packed catechol functional groups on the tannic acid backbone have a much stronger thermodynamic affinity for transition and noble metals than EDTA at room temperature. When these groups penetrate the microporous liquid membrane, they instantly trigger a spontaneous ligand exchange reaction. This exchange does not remain at the single-molecule level; instead, multiple polyphenol ligands form high-density supramolecular crosslinks with free metal ions, directly assembling a hydrophobic three-dimensional metal-polyphenol network (MPN) polymer membrane in situ on the alumina mesoporous surface. This microscopic "filter" precisely anchors the catalytically active metal components, endowing them with extremely strong resistance to water erosion. The trace amounts of loss separated from the washing liquid suggest that free sulfate and sodium ions can easily penetrate the sub-nanometer pore size of the polyphenol network and be carried away by deionized water, while larger noble metal clusters, constrained by deep chemical bonds, are completely retained on the support substrate. Through in-situ construction of the polyphenol interface, complete removal of inorganic salt impurities and zero leakage of high-value catalytic cores are macroscopically achieved.

[0069] Test Example 3: Experiment Description and Data This test example selected fresh Pt-Pd / Al2O3 catalyst, the deactivated catalyst described in raw material example 1, the regenerated catalyst of example 1, the regenerated catalyst of comparative example 1 (without EDTA) and the regenerated catalyst of comparative example 3 (without micro-negative pressure pulsation) as the test objects.

[0070] A suitable amount of sample was mechanically extracted from the central area of ​​each group of honeycomb catalyst modules, placed in an agate mortar and ground manually, and then sieved through a standard test sieve of 80 to 100 mesh to collect powder test samples with uniform particle size distribution.

[0071] Weigh approximately 0.15g of the sieved sample and place it into a glass sample tube. Transfer the tube to the degassing station of the physical adsorption instrument and heat it in a high vacuum environment at 200℃ for 6 hours to completely remove the moisture and impurity gases adsorbed by physical adsorption.

[0072] The degassed sample tubes were transferred to the analysis station and subjected to high-purity nitrogen adsorption-desorption isotherm testing at liquid nitrogen temperature (-196℃).

[0073] After the test was completed, the specific surface area of ​​the sample was calculated using the Brunauer-Emmett-Teller multi-point method in the accompanying software, and the total pore volume and micropore volume of the sample were calculated using the Barrett-Joyner-Halenda model combined with desorption branch data.

[0074] Table 3. Evaluation data of specific surface area and multilevel pore volume of catalysts for each group.

[0075] Based on the data in Table 3 and the appendix Figure 3 The specific surface area and micropore volume of the deactivated catalyst showed a precipitous drop compared to its fresh state, which is consistent with the typical characteristic of deep blockage of mesoporous channels by high-molecular-weight aromatic hydrocarbon byproducts after long-term operation in industrial settings. In routine waste catalyst treatment practices, it is frequently observed that relying solely on conventional chemical reagents for static soaking often results in the reaction solution only remaining on the shallow surface of the honeycomb pores. Comparative Example 3, which omitted the micro-negative pressure pulsation operation and possessed a complete chemical formula, only barely recovered the measured specific surface area to 87.27 m². 2 / g, with a low total pore volume. Long-chain fragments generated during degradation mix with unreacted tar, forming a highly viscous flow-blocking layer within the micropores. The fluid resistance of the narrow capillary walls completely blocks the physical channels for the reaction waste liquid to diffuse outward, causing deep carbon deposits to remain intact within the carrier.

[0076] The pore parameters of Example 1 were restored to levels close to those of a fresh catalyst, demonstrating the disruptive effect of deep coupling between physical aerodynamics and chemical oxidation. In the degradation system, carbon dioxide molecules released from the thermal decomposition of urea nucleate extensively in the interstitial spaces of the carbon deposit layer, while alternating pressures of 0.08 MPa to 0.1 MPa externally forcefully apply periodic pressure differences. These micron- and nano-scale bubbles undergo dramatic volume expansion and contraction during the pressure drop and recovery cycles. What appears to be a macroscopically stable soaking process triggers a strong hydrodynamic aerodynamic micro-piston effect within the microscopic channels, actively pumping out the viscous fluid and degradation waste liquid that are trapped in the deep pore dead zones, thus creating mass transfer space for the high-concentration interface agent containing fresh persulfate ions to penetrate inward. The negative consequences of the lack of EDTA coordination in Comparative Example 1, which led to the ineffective consumption of the oxidant, were also confirmed here. As the free radicals rapidly exploded and were completely consumed after contacting the surface metal, the inward oxidation mass transfer chain broke, and the micropore volume only recovered to 0.025 cm³ / g. This confirmed that the air-conditioning-controlled oxidation scheme in the absence of a chemical reaction rate could not effectively open up the entire porous structure.

[0077] Test Example 4: The test cases included fresh Pt-Pd / Al2O3 catalyst, deactivated catalyst taken from an industrial site, regenerated catalyst prepared in Example 1, and regenerated catalyst of Comparative Example 4 in which the tannic acid soaking operation was omitted in the process flow.

[0078] To determine the total active metal retention rate, 0.25 g of a homogeneous sample, pulverized and passed through a 100-mesh sieve, was accurately weighed and placed in a polytetrafluoroethylene digestion vessel. Freshly prepared aqua regia solution was added, and a temperature-controlled digestion program at 180°C was performed in a microwave digester to ensure complete destruction of the cordierite and alumina matrix. After acid removal and volume adjustment, the sample was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) to obtain the absolute mass fractions of platinum and palladium. The mass retention rate was then calculated based on the values ​​from the fresh sample.

[0079] The metal dispersion was assessed using a multifunctional automated chemisorption analyzer to perform carbon monoxide pulse adsorption analysis. A trace sample, packed in a quartz U-tube, was placed in a 10% hydrogen / argon mixed gas stream and pretreated at 300°C for one hour. After the system was purged and cooled to room temperature, a metering loop was used to inject CO gas of a known concentration at fixed time intervals. A thermal conductivity detector (TCD) continuously tracked and recorded the peak area of ​​unadsorbed CO in the exhaust gas after each pulse until adsorption on the sample surface reached saturation. The dispersion of the surface-active metal was calculated based on the cumulative chemisorption and catalytic stoichiometry.

[0080] Table 4. Quantitative test results of active phase retention and dispersion state of catalysts under different treatment states

[0081] According to the data in Table 4, the deactivated catalyst did not show significant metal mass loss after long-term service, but its metal dispersion dropped sharply from 45.8% to 16.3%. The long-term high-temperature gas scouring combined with the incomplete combustion of volatile organic compounds in the industrial environment provided ample thermodynamic driving force for the migration and aggregation of noble metal atoms on the surface. The resulting coarse metal grains directly reduced the effective contact area of ​​the gas-solid reaction. In the regeneration and cleaning process lacking specific interface constraints, Comparative Example 4 revealed the inherent defects of conventional wet desalination processes. Although the EDTA macromolecules introduced during the degradation stage successfully protected the interior of the support, they endowed the active metal with extremely strong hydrophilic and easily soluble properties. Subsequent rinsing with large amounts of deionized water resulted in the complete loss of over 20% of the platinum-palladium phase with the cleaning waste liquid. Such loss of structural materials is considered unacceptable deterioration in industrial assessments.

[0082] Re-examining the test results of Example 1, while maintaining a mass retention rate close to 98%, the metal dispersion defied the trend and increased to 48.2%, achieving structural reorganization exceeding that of the original fresh sample. The tannic acid polyphenol network, which self-assembled in situ at the catalyst interface, not only acted as a physical filter to trap water-soluble metal complexes during the liquid-phase desalination stage, but also further triggered a key spatial confinement mechanism during the subsequent gradient heating stage. When the drying environment entered the range of 150°C to 250°C, the three-dimensional cross-linked organic polyphenol framework had not yet completely disintegrated. The microscopic pores deconstructed the originally aggregated large particles and forcibly confined them within narrow grid units. Thermal stress caused the aggregates to split, and under the three-dimensional encapsulation of the outer carbon skeleton, the disintegrated metal clusters lost the channels for long-range outward migration. As the temperature continued to rise, causing the confinement framework to slowly oxidize and remove, these forcibly dispersed sub-nanometer-sized metal clusters anchored nearby to the surface oxygen vacancies or defect sites of the alumina support. By utilizing the phase transition deconstruction process of organic networks, the secondary sintering of particles that is easily induced by conventional high-temperature calcination was successfully avoided, and the highly dispersed remodeling of the catalytic active core was achieved by using a confined pyrolysis mechanism.

[0083] Test Example 5: The test cases cover fresh Pt-Pd / Al2O3 catalysts, industrial deactivated catalysts, regenerated catalysts prepared in Example 1, and regenerated catalysts of Comparative Example 1 (lacking EDTA coordination protection) and Comparative Example 3 (lacking micro-negative pressure gas stripping) prepared due to the lack of specific protection or physical cleaning methods.

[0084] To monitor the liquid phase ions in the washing system, in the regeneration and desalination process of Example 1, Comparative Example 1 and Comparative Example 3, the waste liquid discharged after the last (second) deionized water washing was collected. After the liquid temperature was constant at 25°C, the endpoint conductivity was measured using a high-precision portable conductivity meter to preliminarily assess the completion of macroscopic water washing and desalination.

[0085] For the quantitative analysis of inorganic salts deeply embedded in solid-phase catalysts, samples from each group, after complete heat treatment and drying, were pulverized using an agate mortar and passed through a 100-mesh sieve. 1.00 g of powder was accurately weighed and dispersed in 50 mL of ultrapure water with a resistivity of 18.2 MΩ·cm. The solution was then continuously extracted for 120 minutes in a constant-temperature water bath ultrasonic oscillator at 90°C, forcibly stripping salt compounds adsorbed deep within the micropores through thermodynamic and ultrasonic cavitation effects.

[0086] The extracted suspension was separated in a high-speed centrifuge. The supernatant was filtered through a 0.22 μm aqueous microporous membrane and then injected into an ion chromatograph (IC). The sodium ion concentration in the extract was determined using a standard curve method. + The absolute concentration of sodium in the solid catalyst was calculated, and the residual sodium content (mg / kg) was calculated accordingly.

[0087] Table 5. Data on liquid phase conductivity and solid phase sodium ion residue distribution at the catalyst desalination washing endpoint.

[0088] Based on the data in Table 5 and the appendix Figure 5 The residual sodium in the solid phase of both fresh and deactivated catalysts was at extremely low levels. However, after the regeneration process involving high-concentration sodium persulfate reagent, the desalination effects of the samples showed significant divergence. The residual sodium ions in the solid phase of Comparative Example 1 and Comparative Example 3 soared to 1756.4 mg / kg and 843.8 mg / kg, respectively. In such a high-concentration alkali metal impurity environment, the acidic sites on the alumina support surface would be directly neutralized and poisoned, which is a fatal defect leading to loss of intrinsic activity in chemical catalysis evaluation. Tracing the microscopic physical mass transfer resistance, it can be found that Comparative Example 1 suffered from ineffective dissipation of the front-end oxidant due to the lack of EDTA protection, while Comparative Example 3 suffered from the retention of high-viscosity tar due to the lack of gas pressure pulse application. Both cases inevitably left a large number of ink bottle-shaped physical dead ends deep in the mesopores. The persulfate and its reduction decomposition products (sodium sulfate) that diffused into the depths of the pores were tightly sealed at the bottom of the pores by viscous organic residues or gas-liquid interfacial tension. In the subsequent deionized water washing stage, the cleaning fluid can only flow sideways along the large pores with the least resistance, and cannot form an effective concentration gradient to penetrate, so that the sodium salt accumulated in the micropores cannot be displaced outward.

[0089] In Example 1, the conductivity of the final washing solution had decreased to 21.3 μS / cm, near the level of desalinated pure water, and the residual sodium in the solid phase remained stable at 42.1 mg / kg, essentially returning to the background state of fresh catalyst. This result indirectly confirms the high engineering effectiveness of the micro-negative pressure pulsating exclusion mechanism constructed in the pre-degradation stage of this scheme. After the flow-blocking layer was forcibly stripped away by the alternating pneumatic micro-piston effect within the pores, the entire honeycomb pore network regained its unobstructed connectivity, allowing the washing water to deeply flush without hindrance. From a deeper perspective of interfacial chemoselectivity, although the aforementioned tests have confirmed that the polyphenol network assembled in situ with tannic acid successfully blocked the loss path of noble metal clusters, this network structure did not cause secondary obstacles to the mass transfer of sodium ions. This is because the supramolecular pore size between the polyphenol cross-linked frameworks is typically in the sub-nanometer to several nanometer range, while the kinetic diameter of hydrated sodium ions is only about 0.36 nanometers. Driven by the concentration gradient, these free, small-sized inorganic salts and sulfate ions can easily penetrate this hydrophobic polymer filter and diffuse into the macroscopic aqueous phase. Through the deep coupling of physical unblocking and the molecular sieve effect at the chemical interface, the long-standing engineering paradox of "adding salt for carbon removal, and adding salt inevitably leading to poisoning" in traditional wet regeneration processes has been successfully overcome.

[0090] Test Example 6: The test cases cover fresh Pt-Pd / Al2O3 honeycomb catalysts, deactivated catalysts after long-term service in industrial settings, low-temperature wet regeneration catalysts prepared in Example 1, and Comparative Example 5 regeneration catalysts treated with conventional 500°C air calcination process, in order to evaluate the physical damage to the mechanical properties of ceramic substrates caused by different cleaning methods.

[0091] Standard cubic test blocks measuring 50mm × 50mm × 50mm were cut from the inside of each batch of catalyst modules using a diamond wire cutter. The feed rate was kept constant during the cutting process. The blocks were ultrasonically cleaned and dried to ensure that the upper and lower stress-bearing ends of the test blocks were flat and parallel to each other, avoiding data distortion caused by eccentric pressure.

[0092] The prepared standard test blocks were transferred into an electric heating drying oven and degassed at a constant temperature of 110℃ for 4 hours to completely eliminate the plasticizing interference of ambient humidity on the strength of the porous ceramic skeleton. Then, they were transferred to a glass desiccator to cool naturally to room temperature for later use.

[0093] Mechanical strength testing is performed using a computer-controlled electronic universal testing machine. When testing axial compressive strength, pressure should be applied along the axis of the borehole, that is, the borehole direction of the specimen block should be aligned parallel to the loading axis; when testing radial compressive strength, pressure should be applied with the pressure axis perpendicular to the borehole axis.

[0094] The testing machine indenter is set to apply a compressive load downwards at a constant displacement rate of 1.0 mm / min. The system synchronously records the load-displacement curve through a built-in high-precision tension / compression sensor. When the specimen experiences macroscopic brittle fracture or a sudden drop in the curve, the peak failure load (N) is extracted and the compressive strength value (MPa) is calculated by combining it with the compressed cross-sectional area. Each group of samples is tested in parallel for 5 times, and the arithmetic mean is taken.

[0095] Table 6. Test data of axial and radial macroscopic compressive strength of honeycomb catalysts in various treatment states.

[0096] Based on the data in Table 6 and the appendix Figure 6The axial and radial strength of the deactivated catalyst showed an anomalous slight increase compared to the fresh state. In numerous on-site maintenance projects involving dust removal and denitrification equipment, it was frequently observed that the tar network formed by the condensation of high-molecular-weight aromatic volatiles within the cordierite ceramic channels acted like an adhesive, solidifying loose dust particles and the carrier skeleton into a unified whole. This physical clogging effect endowed the deactivated substrate with a pseudo-increase in stiffness. Comparative Example 5 revealed serious defects in the industrial applicability of traditional high-temperature calcination processes. After undergoing aerobic heat treatment at 500℃, although the carbon deposits were burned off, the macroscopic mechanical framework of the catalyst almost collapsed, with the radial strength retention rate sharply reduced to 45.0%. The catalyst's microstructure is composed of a cordierite ceramic substrate and an active alumina coating applied to its surface; the linear expansion coefficients of these two inorganic materials differ significantly. During the rapid heating and subsequent cooling cycles, significant thermal stress accumulated at the solid-solid interface, directly inducing the propagation of microcracks penetrating the honeycomb thin wall. These types of internal damage cannot be identified by the naked eye, often leading to large-scale pulverization and collapse of the regeneration components when they are being filled back into the reaction tower or subjected to the impact of high-pressure fan airflow.

[0097] The results of Example 1 demonstrate the absolute advantage of the low-temperature liquid-phase reaction system in maintaining structural integrity. The highest temperature point of the overall regeneration process was strictly locked at 250°C during the later stage of tannic acid confined pyrolysis, a temperature far below the critical threshold for cordierite ceramics to experience lattice distortion or destructive thermal stress. This was achieved by relying on S2O8... 2- Under mild conditions of 75℃, slow-release oxidation with free radicals, combined with micro-negative pressure pulsating pneumatic suction stripping, effectively dismantles the carbon deposit network through a synergistic combination of chemical degradation and physical fluid dynamics, avoiding severe interfacial thermal expansion conflicts. The measured axial and radial strength retention rates remained consistently above 95%, with minimal strength loss stemming solely from slight hydrodynamic erosion of the coated electrode surface during carbon removal. This approach replaces destructive thermal energy input with chemical and fluid coupling, overcoming the engineering bottleneck of mechanical life decay in spent VOCs catalysts and ensuring that the regenerated products meet the stringent requirements of industrial fixed-bed assembly and continuous erosion resistance.

[0098] Test Example 7: The samples evaluated in this test case include fresh Pt-Pd / Al2O3 honeycomb catalyst, untreated industrial deactivated catalyst, regenerated catalyst prepared in Example 1, and regenerated catalysts prepared by Comparative Example 4 (without tannic acid crosslinking protection during the water washing stage) and Comparative Example 5 (using conventional 500℃ high-temperature aerobic roasting for ash removal) using a process with intrinsic defects.

[0099] The experiment was conducted in a continuous flow fixed-bed microcatalytic evaluation device. Columnar catalyst units were cut from each group of honeycomb test blocks using a sampler, wrapped with quartz wool, and tightly packed into the isothermal section of a quartz tubular reactor with an inner diameter of 20 mm to ensure that no significant wall short-circuiting escape occurred when gas flowed through.

[0100] High-purity air was used as both the balance gas and the carrier gas. Toluene liquid was evaporated by bubbling and introduced into the mixer. The initial concentration of toluene in the reaction stream was stably controlled at 1000 ppm using a mass flow meter. The total gas flow rate was set to achieve a volume hourly space velocity (VHSV) of 20000 h⁻¹. -1 The level.

[0101] The evaluation process employed programmed temperature control, with the system recording data starting at 160℃ and setting temperature test nodes at 20℃ intervals. Each temperature point was held constant for 30 minutes to ensure the reaction system reached equilibrium between gas-solid adsorption and conversion.

[0102] A gas chromatograph equipped with a flame ionization detector (FID) was connected in parallel at both ends of the reactor's inlet and outlet pipelines to monitor changes in toluene concentration online. The catalytic degradation conversion rate of toluene at each temperature node was calculated by dividing the difference between the inlet and outlet toluene concentrations by the initial inlet concentration.

[0103] Table 7. Test data on the catalytic degradation conversion rate of toluene VOCs by each catalyst sample as a function of temperature.

[0104] Based on the data in Table 7 and the appendix Figure 7The deactivated catalyst exhibited extremely low toluene conversion rates across the entire temperature range. Even when the ambient temperature rose to 280℃, its degradation rate for the target pollutant barely reached 78.5%. Long-term accumulation of high-molecular-weight tar not only masked the catalytic sites on the support surface, but this deep carbon buildup also created a physical barrier to the diffusion and mass transfer of reactant gases into the mesopores. In routine evaluations of such expired samples in fixed-bed microreactors, it is frequently observed that the obstructed internal diffusion process severely limits the apparent reaction rate, leading to a macroscopic "activation shutdown." Comparative Example 4, due to the omission of tannic acid crosslinking protection, experienced the loss of the platinum-palladium active phase during the initial water washing stage. The curves showed a slight recovery in catalytic activity, but the critical characteristic temperature T50 for achieving 50% conversion lagged significantly to around 210℃. The irreversible reduction in the absolute number of metal atoms participating in the redox cycle at the surface directly lowered the upper limit of the overall bed degradation efficiency. Although Comparative Example 5, treated with conventional air roasting, forcibly burned off all the carbon deposits using high-temperature heat energy of 500℃, improving the physical connectivity of the porous material, the high temperature caused significant migration and agglomeration of the originally dispersed metal particles on the oxide layer surface. Grain growth resulted in a substantial reduction in the effective exposed area of ​​precious metals per unit mass, and its conversion rate during the ignition stage could never approach the specifications of the original sample.

[0105] The activity evolution trajectory presented in Example 1 macroscopically validates the effectiveness of all the previously constructed microscopic mechanisms. The ignition temperature T50 of this group of regenerated samples decreased to approximately 185°C, and even showed a slightly better conversion rate than the original fresh catalyst in the low-temperature range of 160°C to 200°C. The deep coupling of physical pneumatics and chemical oxidation completely dismantled the viscous degradation residues in the dead corners of the pores, reopening an unobstructed channel network for the deep penetration of gaseous toluene and oxygen molecules. The more crucial role occurred during the evolution of the polyphenol network. The three-dimensional organic framework assembled by tannins at room temperature retained all the metal phase during washing and desalting. As the temperature gradient slowly increased in the later stage, the polyphenol polymer film underwent pyrolysis and constructed a nanoscale physically confined structure. This three-dimensional network forced the metal clusters, which had already agglomerated to some extent during long-term service, to be deconstructed in situ. After the carbon skeleton was completely burned off, the metal clusters were redistributed in sub-nanometer or even single-atom form and firmly anchored on the oxygen vacancies on the alumina surface. The noble metal surface that undergoes reverse sintering exposes a higher proportion of low-coordination reaction sites, which significantly reduces the apparent activation energy of CH bond breaking in toluene molecules, thus establishing a comprehensive or even super-recovery of overall catalytic activity at the reaction engineering level. Furthermore, the deactivated Mn-Cu / Al2O3 transition metal catalyst system used in Example 4, tested with the same catalytic evaluation device, showed that its ignition temperature and VOCs complete conversion temperature were essentially restored to fresh state levels. This further confirms that the polyphenol network confinement reshaping and pneumatic negative pressure pulse synergistic strategy described in this invention is not only applicable to noble metal systems, but also has high engineering versatility for the low-temperature regeneration of non-noble metal (transition metal) catalysts that are easily lost during water washing.

[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of low temperature regenerative VOCs honeycomb catalyst characterized by, Includes the following steps: S1. Physically pretreat the deactivated VOCs honeycomb catalyst to remove loose free dust from the surface and pores. S2. Place the pretreated catalyst in a reactor, pump in the composite regeneration initial solution to submerge the catalyst, and perform static soaking at atmospheric pressure and a set temperature of 25℃~35℃. The composite regeneration initial solution is used to oxidize and degrade deep mesoporous carbon deposits while inhibiting ineffective catalysis by surface-active metals through coordination masking and providing adaptive acid-base buffering under thermodynamic activation. The composite regeneration initial solution consists of the following components by mass percentage: Ethylene glycol butyl ether: 3.0%–8.0%; Disodium ethylenediaminetetraacetate: 1.0%–3.0%; Urea: 2.0%–5.0%; Sodium persulfate: 5.0%–10.0%; The remainder is deionized water; S3. The reactor is heated and kept at a constant temperature of 70℃~80℃ for degradation. During the constant temperature degradation, periodic micro-negative pressure pulse treatment is applied inside the reactor. The carbon deposits in the deep micropores are actively peeled off and pumped out through the pressure difference. S4. After draining the waste liquid in the reactor, the catalyst is initially dehydrated. Then, the catalyst is immersed in a tannic acid aqueous solution for static soaking and crosslinking to construct a three-dimensional polyphenol network membrane that retains active metals in situ in the pores. After draining the waste liquid, the catalyst is washed with water and dehydrated again. S5. The dehydrated catalyst is transferred into a drying oven for programmed gradient calcination. The first stage is heated to 120℃~160℃, and the second stage is heated to 220℃~280℃. After cooling in the furnace, the regenerated catalyst is obtained.

2. The method of claim 1, wherein the temperature of the VOCs is between 100°C and 300°C. The composite regenerated initial solution is composed of the following components by mass percentage: Ethylene glycol butyl ether 5.0%; Disodium ethylenediaminetetraacetate 2.0%; Urea 3.5%; Sodium persulfate 7.5%; The remainder is deionized water.

3. The method of claim 1, wherein the temperature of the VOCs honeycomb catalyst is between 100°C and 300°C. The composite regenerated initial solution is prepared through the following steps: Add deionized water to a corrosion-resistant mixing tank with a temperature controlled at 15℃~25℃, and then add ethylene glycol butyl ether, disodium ethylenediaminetetraacetate and urea in sequence while stirring, and stir until completely dissolved. While maintaining the system temperature below 30°C and continuously stirring, slowly add sodium persulfate until it is completely dissolved.

4. The method for low-temperature regeneration of VOCs honeycomb catalyst according to claim 1, characterized in that, In step S1, the physical preprocessing is implemented as follows: Use industrial compressed air at a pressure of 0.3MPa to 0.6MPa to reciprocate along the axial direction of the honeycomb channel for 3 to 5 minutes. In step S2, the static soaking time is 1.5h to 3.0h.

5. The method for low-temperature regeneration of VOCs honeycomb catalyst according to claim 1, characterized in that, In step S3, the system is heated at a rate of 0.5℃ / min to 1.0℃ / min and kept at a constant temperature for degradation for 3.0h to 5.0h.

6. The method for low-temperature regeneration of VOCs honeycomb catalyst according to claim 1, characterized in that, In step S3, the specific parameters of the periodic micro-negative pressure pulsation are as follows: The pulsation cycle was set to 10 min to 20 min. In each pulsation cycle, the absolute pressure inside the reactor was evacuated to 0.06 MPa to 0.08 MPa using a vacuum system for the first 3 min to 8 min. Then the pressure was restored to 0.1 MPa and maintained for 7 min to 12 min. This cycle was repeated until the isothermal degradation was completed.

7. The method for low-temperature regeneration of VOCs honeycomb catalyst according to claim 1, characterized in that, The specific implementation method of step S4 is as follows: The initial and subsequent dehydration conditions were both: centrifugation at 300 rpm to 600 rpm for 3 to 8 minutes. The tannic acid aqueous solution has a mass fraction of 0.3wt% to 1.0wt%, and the soaking conditions are static soaking at normal pressure for 10 to 20 minutes at a temperature of 20℃ to 30℃. The water washing process is as follows: wash with deionized water 2 to 3 times, each time for 10 to 20 minutes.

8. The method for low-temperature regeneration of VOCs honeycomb catalyst according to claim 1, characterized in that, In step S5, the specific implementation method of the programmed gradient temperature rise calcination is as follows: First stage: Heating at a rate of 1.0℃ / min to 3.0℃ / min and held at a constant temperature for 1.5h to 3.0h; Second stage: Continue heating at a rate of 1.0℃ / min to 3.0℃ / min and maintain the temperature for 2.0h to 4.0h.

9. The method for low-temperature regeneration of VOCs honeycomb catalyst according to claim 1, characterized in that, The VOCs honeycomb catalyst is a transition metal honeycomb catalyst or a noble metal honeycomb catalyst with monolithic cordierite as the substrate and coated with an alumina mesoporous coating on the surface. The active metal supported on the catalyst includes a combination of platinum and palladium, or a combination of manganese and copper.

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