Preparation method of modified vanadium-iron denitration catalyst

Abstract

The application discloses a preparation method of a modified vanadium-iron denitration catalyst and relates to the technical field of catalysis. The application does not need to introduce tungsten-containing and molybdenum-containing raw materials in the whole process. A vanadium source alkaline solution and a citric acid chelated iron-copper chelated solution are prepared, a double-stage mixing in-situ composite process is adopted, the iron-copper chelated solution is added into a premixed material of a carrier and a vanadium source in a buried material type dropping mode, a linkage control system pH is stabilized, a V-Fe-Cu-O ternary solid solution is formed, then phosphorus elements are embedded and a molding aid is added to mix and form a plastic mud material, after aging, extrusion molding and gradient drying, the material is calcined in an oxidative atmosphere in stages, and a stable V-Fe-Cu-P composite solid solution is formed. Through time sequence decoupling and precise process control, the application realizes uniform dispersion of active component molecules at a molecular level, improves the denitration activity, mechanical strength and sulfur deactivation resistance of the catalyst, and the process is simple and suitable for industrial scale production.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and in particular to a method for preparing a modified vanadium-iron denitration catalyst. Background Technology

[0002] Selective catalytic reduction of ammonia (NH3-SCR) is currently the mainstream technology for purifying nitrogen oxides in stationary flue gas, relying on vanadium-based denitrification catalysts to achieve efficient removal of nitrogen oxides. Traditional commercial vanadium-based catalysts mostly employ the V2O5-WO3(MoO3) / TiO2 system, which requires high-priced additives such as tungsten and molybdenum to balance catalytic activity and structural stability, resulting in high raw material costs. To optimize this situation, various improvement schemes have emerged in existing technologies. For example, some schemes prepare binary metal vanadate nanostructure catalysts via hydrothermal methods, which improves low-temperature catalytic activity to some extent, but still relies on specific high-priced components, and the preparation process is complex, suitable only for small-scale laboratory preparation, and difficult to meet the needs of industrial-scale production. Other schemes modify the catalysts by introducing transition metal elements, but still remain dependent on tungsten and molybdenum additives. Furthermore, some schemes use halogen modification or supercritical polarization processes, which not only easily cause corrosion of production equipment and secondary pollution of flue gas, but also suffer from high energy consumption and difficulty in large-scale production.

[0003] Existing vanadium-based denitration catalysts and their preparation methods still face numerous technical challenges: First, traditional catalysts and most improved solutions rely on expensive additives such as tungsten and molybdenum. Some attempts to reduce tungsten and molybdenum dependence are hampered by competition between multi-metal ions and modified components, leading to metal hydroxide or phosphate precipitation, resulting in unstable catalytic active structures and an inability to balance cost control and catalytic performance. Second, during large-scale industrial production, abrupt phase interface changes during acid-base mixing and localized overheating from high-shear mixing can cause agglomeration and uneven dispersion of active components, leading to batch-to-batch performance fluctuations and difficulty in ensuring production stability. Third, catalysts are prone to carrier phase transformation under high-temperature conditions, and in sulfur-containing flue gas environments, active centers readily react with sulfur oxides to generate low-activity substances, resulting in irreversible catalytic activity degradation and insufficient resistance to deactivation. Fourth, during catalyst molding, uneven drying rates and improper matching of extrusion process parameters can easily cause defects such as honeycomb structure cracking and channel collapse. Furthermore, the uniformity of active component loading on the carrier surface is difficult to guarantee, thus affecting catalytic efficiency and service life. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a technical solution to address one or more problems in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing a modified vanadium-iron denitration catalyst includes the following steps:

[0007] (1) Prepare an alkaline solution of vanadium source by mixing ammonium metavanadate with an ammonia solution. And prepare an iron-copper chelate solution by dissolving ferric nitrate nonahydrate, copper nitrate trihydrate and citric acid monohydrate in deionized water, wherein the molar amount of citric acid monohydrate is not less than 1.2 times the total molar amount of ferric nitrate nonahydrate and copper nitrate trihydrate.

[0008] (2) First, anatase titanium dioxide is mixed with an alkaline solution of vanadium source to obtain a vanadium source premix. Then, an iron-copper chelate solution is added to the premix by a buried material dropping method. During the dropping process, ammonia water is added to stabilize the pH value of the system. After the dropping is completed, the homogeneous precursor of vanadium-iron-copper-oxygen is obtained by intermittent mixing.

[0009] (3) Add phosphoric acid solution dropwise to the homogeneous precursor and mix to stabilize the pH value of the system. Control the molar amount of phosphoric acid and ammonium metavanadate corresponding to vanadium pentoxide to match. Then add molding aid to adjust the moisture content of the clay to obtain plastic clay.

[0010] (4) After the plastic clay is sealed and aged, it is vacuum extruded to obtain a honeycomb precursor.

[0011] (5) After the honeycomb precursor is dried under gradient constant temperature and humidity, it is calcined in stages under an oxidizing air atmosphere, kept at a constant temperature and then cooled with the furnace to obtain the modified vanadium iron denitration catalyst.

[0012] Specifically, in the preparation of the alkaline vanadium source solution, ammonium metavanadate is added to an ammonia solution and stirred at 40°C to 45°C until completely dissolved. After cooling to 20°C to 30°C, the pH of the solution is adjusted to 9.0 to 11.0, and the molar concentration of ammonium metavanadate in the solution is controlled to be no higher than 0.5 mol / L.

[0013] Specifically, after the iron-copper chelate solution is prepared, the pH value of the solution is adjusted to 2.0 to 4.0. The total volume of the vanadium source alkaline solution and the iron-copper chelate solution, in mass ratio to anatase titanium dioxide, is 0.8 mL / g to 1.2 mL / g.

[0014] Specifically, in step (2), after adding the alkaline solution of vanadium source, the mixture is stirred at a speed of 20 r / min to 40 r / min for 15 min to 30 min to obtain a carrier vanadium source premix with a pH value of 7.5 to 9.0.

[0015] Specifically,

[0016] In step (2), the iron-copper chelate solution is added dropwise at a rate of 1% to 2% of the total solution volume per minute through a dropper nozzle inserted 5 to 10 cm below the material surface. The pH value of the system is maintained at 6.0 to 7.5 throughout the process. After the dropper is added, the mixture is mixed in an intermittent mixing mode for 30 to 60 minutes, and the material temperature is controlled to not exceed 45°C throughout the process. The intermittent mixing mode is as follows: every 15 to 20 minutes of mixing, the mixture is paused for 5 minutes. During the pause, the jacket cooling water is continuously circulated, and the kneader blades are kept at a low stirring speed of 5 to 10 r / min.

[0017] In step (3), a diluted phosphoric acid solution is added dropwise, and the pH value of the system is kept stable between 6.0 and 7.5 throughout the process. The molar amount of phosphoric acid is 1.0 to 1.5 times the molar amount of vanadium pentoxide corresponding to ammonium metavanadate. After the phosphoric acid solution is added dropwise, the mixture is stirred for another 15 to 20 minutes.

[0018] Specifically, the aging environment is a temperature of 20°C to 25°C and a relative humidity of 40% to 60%, with an aging time of 12 to 24 hours. After the final mixing of the clay, the moisture content of the clay is adjusted to 18% to 22%.

[0019] Specifically, the air velocity is controlled to be no less than 2 m / s throughout the segmented calcination process, the oxygen content in the furnace is no less than 18%, and the maximum calcination temperature is no higher than 550℃. The specific steps are as follows: heat up to 200℃ at 2℃ / min and hold for 2 hours; heat up to 350℃ at 3℃ / min and hold for 2 hours; heat up to 450℃ to 550℃ at 2℃ / min and hold for 3 to 6 hours; after holding, cool with the furnace to below 100℃ before removing from the furnace.

[0020] A modified vanadium-iron denitration catalyst is prepared according to the aforementioned method. The catalyst uses raw materials that are free of tungsten and molybdenum, and includes anatase-type titanium dioxide support, a main active component, a ternary composite modifier, and a phosphorus-modifying component supported on the support. The main active component is vanadium pentoxide, the ternary composite modifier includes ferric oxide and copper oxide, and the phosphorus-modifying component is phosphorus pentoxide. The main crystalline phase of the catalyst is anatase-type titanium dioxide, and it does not exhibit separate characteristic diffraction peaks for vanadium pentoxide, ferric oxide, or copper oxide.

[0021] Further, by mass fraction, the catalyst comprises 100 to 300 parts of anatase titanium dioxide, 1 to 6 parts of the main active component (vanadium pentoxide), 5 to 25 parts of a ternary composite modifier (ferric oxide), 3 to 15 parts of a ternary composite modifier (copper oxide), and 2 to 18 parts of a phosphorus modifier (phosphorus pentoxide). The catalyst has an axial compressive strength of not less than 2.0 MPa, a radial compressive strength of not less than 0.4 MPa, and a specific surface area of ​​not less than 60 m². 2 / g.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] (I) This invention employs a synergistic approach, utilizing a tungsten- and molybdenum-free raw material system, a citric acid-based chelation masking system, and a phosphorus-modified sequential decoupling process. This method effectively suppresses the coordination competition between polymetallic ions and phosphate groups and the risk of hydrolysis and precipitation from a thermodynamic perspective, thereby successfully constructing a highly stable V-Fe-Cu-P composite catalytic structure under tungsten- and molybdenum-free conditions. Compared to existing technologies, this approach avoids the cost control challenges associated with reliance on tungsten- and molybdenum additives and effectively prevents catalytic structural instability caused by metal ion precipitation.

[0024] (II) For industrial-scale production, this invention introduces a comprehensive process including embedded material dripping, closed-loop linkage control of weakly alkaline pH, and intermittent mixing temperature control. These methods significantly alleviate localized phase interface abrupt changes during acid-base droplet contact and suppress complex decomposition and ammonia volatilization caused by high shear heat, promoting uniform molecular-level dispersion of multi-metal active components on the carrier surface. This not only surpasses the agglomeration phenomenon of active components that easily occurs in existing technologies but also greatly improves batch consistency during mass production.

[0025] (III) By combining the oxygen-rich environment of segmented calcination, the rigid constraint of the highest temperature, and the in-situ embedding of phosphorus, this invention not only prevents the transformation of the support from the anatase phase to the low specific surface area rutile phase, but also significantly reduces the risk of carbon poisoning associated with the decomposition of organic matter. Furthermore, by utilizing the anchoring effect of phosphorus on the catalytic active center and the regulation of acidic sites, this invention effectively solves the problems of structural collapse and irreversible catalytic activity degradation faced by existing technologies under high-temperature or sulfur-containing flue gas conditions.

[0026] (iv) By precisely matching the precursor solution volume and supplementing it with gradient constant temperature and humidity drying and vacuum extrusion molding, this invention greatly optimizes the overall physical properties of the honeycomb structure. This design effectively overcomes the defects of existing technologies, such as cracking, pore collapse and uneven distribution of active components, which frequently occur during the drying and molding stage. While ensuring the mechanical strength of the catalyst, it provides a structural basis for maintaining high catalytic efficiency and extending service life. Attached Figure Description

[0027] Figure 1 This is a flow chart of the preparation process of the modified vanadium-iron denitrification catalyst in this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and exemplary descriptions. It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are only for illustrative purposes and to enable those skilled in the art to understand and read the invention. They are not intended to limit the implementation conditions of the invention. Modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by the invention, should still fall within the scope of the technical content disclosed in this invention.

[0029] Comprehensive explanation

[0030] I. Overview of the Overall Technical Solution

[0031] 1. Technology Application Scenarios

[0032] This technology requires no tungsten or molybdenum-containing raw materials or additives throughout the entire process, and does not involve existing technical routes such as hydrothermal synthesis, supercritical polarization, or halogen modification. Through innovative process design and component matching, it achieves synergistic optimization of catalyst low cost, high stability, and strong sulfur resistance.

[0033] 2. Core Technological Ideas and Innovation Logic

[0034] 2.1 Construction Logic of Tungsten-Molybdenum-Free System

[0035] Abandoning the conventional approach of relying on high-priced tungsten and molybdenum additives to achieve structural stability and acidity control in traditional vanadium-based catalysts, this paper constructs a tungsten- and molybdenum-free catalytic system through the synergistic design of "main active component + ternary composite modifier + phosphorus-modified component". This reduces production costs from the raw material end and avoids supply chain risks caused by the scarcity of tungsten and molybdenum resources.

[0036] 2.2 Core Logic of Time-Sequential Decoupling Composite Process

[0037] By adopting a sequential process of "first constructing a metal oxide framework and then performing phosphorus modification and embedding", the irreversible precipitation problem caused by coordination competition between multi-metal ions and phosphate ions during the mixing process is overcome, ensuring the homogeneous formation and stable existence of catalytic active centers.

[0038] 2.3 Design Logic for Uniform Dispersion and Anti-Deactivation of Multi-Metallic Materials

[0039] Through multiple technical means such as complexation masking, phase interface control, and precise temperature control, the four elements vanadium, iron, copper, and phosphorus are uniformly dispersed at the molecular level on the surface of the carrier. By leveraging the anchoring of active centers and the regulation of acidic sites by phosphorus, the catalyst's resistance to deactivation under sulfur-containing flue gas conditions is enhanced, and its service life is extended.

[0040] II. Raw material specifications and individual part requirements

[0041] 1. Core raw material categories and specifications

[0042] 1.1 Main active component and modified component

[0043] (1) Vanadium source of main active component: Ammonium metavanadate with a purity of ≥99.0%, industrial grade or analytical grade, free of tungsten and molybdenum impurities, and an independent part range of 1-6 parts, is selected as the source of the core active center for the catalytic reaction.

[0044] (2) Ternary composite modified iron source: Ferric nitrate nonahydrate with a purity of ≥98.0%, industrial grade or analytical grade, free of tungsten and molybdenum impurities, with an independent part number of 5-25 parts, is used to construct a stable catalytic framework and optimize redox performance.

[0045] (3) Ternary composite modified copper source: Copper nitrate trihydrate with a purity of ≥98.0%, industrial grade or analytical grade, with no tungsten or molybdenum impurities detected, and an independent part range of 3-15 parts, which synergistically enhances catalytic activity and low-temperature response performance with iron.

[0046] 1.2 Complexing Masking Agent and Phosphorus Modified Component

[0047] (1) Complexing masking agent: Citric acid monohydrate with a purity ≥99.0%, industrial grade or analytical grade, with an independent part range of 5-35 parts, and its molar amount is not less than 1.2 times the total molar amount of ferric nitrate nonahydrate and copper nitrate trihydrate, is used to encapsulate iron ions and copper ions at the molecular level to avoid hydrolysis and precipitation.

[0048] (2) Phosphorus-modified component: Orthophosphoric acid, industrial grade 85% aqueous solution, free of halogen, tungsten and molybdenum impurities, with an independent part range of 2-18 parts, and its molar amount is not less than 1.0 times and not more than 1.5 times the molar amount of ammonium metavanadate corresponding to vanadium pentoxide, used to regulate the acidic sites on the catalyst surface and anchor the active center.

[0049] 1.3 Carrier and Molding Aids

[0050] (1) Catalyst support: Anatase titanium dioxide with a specific surface area of ​​80 m² was selected. 2 / g-110m 2 / g, particle size 20nm-50nm, anatase crystal phase content ≥98.0%, no tungsten or molybdenum impurities detected, independent parts range 100-300 parts, providing a high specific surface area loading substrate for active components.

[0051] (2) Structural reinforcement agent: alkali-free glass fiber with a length of 3mm-6mm and a diameter of 10μm-15μm is selected. It is alkali-free and boron-free, and the number of independent parts ranges from 2 to 8 parts. It is used to improve the mechanical strength and structural stability of the catalyst.

[0052] (3) Plastic molding aids: Carboxymethyl cellulose (CMC) with a viscosity of 6000 mPa·s-10000 mPa·s and a degree of substitution of 0.6-0.9 is selected, with an independent part range of 1-5 parts; Stearic acid, industrial grade 1, with a melting point of 54℃-57℃ and an acid value of 205-210 mgKOH / g is selected as the lubricating extrusion aid, with an independent part range of 0.5-3 parts; Auxiliary molding aids may also include polyethylene oxide (PEO), wood pulp, etc., with an independent part range of 0.2-3 parts for polyethylene oxide and 1-10 parts for wood pulp, which together regulate the plasticity and molding performance of the clay.

[0053] 1.4 pH Adjustment Reagents and Solvents

[0054] (1) pH adjustment reagent: Use ammonia water, industrial grade 25%-28% aqueous solution, free of halogens and heavy metal impurities, add as needed to adjust the pH value of each system.

[0055] (2) Solvent: Deionized water with a resistivity ≥18.2MΩ·cm and a chloride ion content ≤0.1ppm is selected and added as needed for solution preparation and plasticity control of clay.

[0056] 2. Principles for Raw Material Selection

[0057] 2.1 Purity and Impurity Control Requirements

[0058] All raw materials must be carefully selected and the content of tungsten and molybdenum impurities must be controlled. The test results must meet the "no detection" standard to avoid the negative impact of impurities on catalytic performance. The purity of key raw materials such as ammonium metavanadate, citric acid monohydrate, and orthophosphoric acid must meet the corresponding grade requirements to ensure the stability and repeatability of the reaction.

[0059] 2.2 Raw material security measures for tungsten- and molybdenum-free systems

[0060] During the procurement process, suppliers must be explicitly required to provide raw material composition testing reports, with a focus on verifying the content of tungsten and molybdenum elements. Before use, each batch of raw materials must be sampled and retested to confirm the absence of tungsten and molybdenum impurities, thus ensuring the purity of the tungsten-free molybdenum system from the source.

[0061] III. Technical Requirements for Supporting Equipment

[0062] 1. Solution preparation equipment

[0063] A 304 stainless steel stirred tank is selected, equipped with a jacketed temperature control device and a precision pH meter interface for heating and dissolving vanadium source alkaline solutions and monitoring pH; a PTFE-lined stirring tank is provided to avoid metal ion contamination; a precision peristaltic pump with a flow rate accuracy of ±0.1 mL / min is selected for solution dropwise addition; and a precision pH meter with an accuracy of ±0.02 is provided for accurate measurement of the pH value of each solution.

[0064] 2. Core equipment for mixing

[0065] A horizontal twin-shaft kneader should be selected, which must have variable frequency speed regulation function (speed adjustment range 0r / min-60r / min), jacket temperature control device, 3-4 equidistantly distributed embedded material drip inlets (which can be inserted 5cm-10cm below the material surface), upper and lower dual-point online pH monitoring system and peristaltic pump linked feeding module. Z-type high-power stirring blades should be selected to ensure uniform mixing of materials and stable reaction conditions.

[0066] 3. Molding equipment

[0067] It uses a twin-screw extruder for honeycomb catalysts with a length-to-diameter ratio of 20:1-25:1, equipped with a vacuum exhaust system (vacuum degree ≥-0.08MPa) and frequency conversion speed regulation function; it is equipped with honeycomb molding molds with cell sizes of 15×15-40×40 and wall thickness of 0.5mm-1.0mm to meet the needs of different application scenarios.

[0068] 4. Drying and calcining equipment

[0069] The selected drying oven has a programmable temperature and humidity control accuracy of ±1℃ and ±2%RH, and is equipped with a forced ventilation circulation function; the selected oven is a programmable temperature box-type muffle furnace (laboratory) or a continuous mesh belt kiln (industrial mass production), with a temperature control accuracy of ±5℃, and is equipped with a forced air circulation system and an online oxygen content monitoring module to ensure an oxygen-rich environment during the calcination process.

[0070] 5. Auxiliary testing and quality control equipment

[0071] Equipped with an electronic balance with an accuracy of ±0.1g for precise weighing of raw materials; equipped with a cone penetration tester for testing the plasticity of clay; equipped with a forced-air drying oven and standard test sieves for raw material pretreatment and intermediate product quality control; equipped with an X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), NH3 temperature-programmed desorption apparatus (NH3-TPD), and H2 temperature-programmed reduction apparatus (H2-TPR) for verifying the core structure and performance of the catalyst.

[0072] IV. Core Preparation Process and Operational Details

[0073] 1. Precise preparation of precursor solution

[0074] Precursor solution preparation is a prerequisite for the formation of the core composite structure. All operations are carried out at room temperature of 20℃-30℃. After preparation, the solution should be sealed and stored away from light and used within 2 hours. Long-term storage is prohibited. The total amount of water added during solution preparation should ensure that all solutes are fully dissolved. The ratio of the total volume of the final vanadium source alkaline solution and the iron-copper chelate solution to the mass of the anatase titanium dioxide carrier is preferably controlled at 0.8mL / g-1.2mL / g to ensure that the solution can be completely adsorbed by the carrier.

[0075] 1.1 Preparation of alkaline solution of vanadium source

[0076] 1.1.1 Preparation of pre-diluted ammonia water

[0077] Take industrial ammonia water with a concentration of 25%-28%, mix it with deionized water at a volume ratio of 1:3-1:5, stir evenly to obtain a diluted ammonia solution, and stabilize the solution temperature at 40℃-45℃ by jacket temperature control to provide a suitable environment for the dissolution of ammonium metavanadate.

[0078] 1.1.2 Dissolution and Stabilization of Ammonium Metavanadate

[0079] Weigh out ammonium metavanadate according to the independent part range, and slowly add it to the diluted ammonia solution at a feeding rate of 0.5 parts / min to 1 part / min. Stir continuously at a speed of 150 r / min to 250 r / min throughout the process. Do not add the material rapidly at once to avoid excessive local concentration, which may cause polyvanadate precipitation. Control the molar concentration of ammonium metavanadate in the final solution to be ≤0.5 mol / L. After the addition is completed, maintain the temperature at 40℃ to 45℃ and stir continuously for 20 min to 40 min until the solution is completely clear.

[0080] 1.1.3 Solution Cooling and Quality Control

[0081] Stop heating and allow the solution to cool naturally to 20℃-30℃. Measure the pH value of the solution using a precision pH meter. By adding a small amount of concentrated ammonia or deionized water, stabilize the pH value of the solution at 9.0-11.0 to obtain a clear, transparent, and qualified alkaline vanadium source solution free of suspended matter and precipitate. Seal and protect from light for later use.

[0082] 1.2 Preparation of iron-copper chelate solution

[0083] 1.2.1 Co-solubility of metal salts and complexing masking agents

[0084] Accurately weigh out the following independent proportions: ferric nitrate nonahydrate, copper nitrate trihydrate, and citric acid monohydrate. Add them to deionized water (the amount of deionized water should be 2 to 3 times the total mass of the three components). Stir continuously at 200 to 300 rpm for 30 minutes to ensure that each component is fully dissolved.

[0085] 1.2.2 Core Logic and Chemical Mechanism of Chelation Reaction

[0086] The polydentate carboxyl and hydroxyl groups in citric acid monohydrate can react with Fe. 3+ Cu 2+The formation of a stable six-coordinate chelate is based on the core coordination logic: the two carboxyl oxygen atoms and one hydroxyl oxygen atom in the citric acid molecule form coordinate bonds with the metal ion, constructing a closed ring structure. This reduces the free concentration of the metal ion and inhibits its subsequent hydrolysis in an alkaline environment to form hydroxide precipitates. This is achieved by controlling the molar amount of citric acid to be no less than Fe. 3+ With Cu 2+ A total molar amount of 1.2 times ensures that all metal ions are fully chelated, preventing the presence of free metal ions.

[0087] 1.2.3 Solution pH Adjustment and Stabilization

[0088] After stirring, the pH value of the solution was measured using a precision pH meter. By adding a small amount of deionized water for fine adjustment, the pH value of the solution was stabilized at 2.0-4.0. This pH range can further enhance the chelation stability of citric acid and metal ions, resulting in a qualified iron-copper chelate solution that is dark in color, clear and transparent, and free of turbidity and flocculent precipitate. The solution was then sealed for later use.

[0089] 2. In-situ compounding of two-stage mixing under weakly alkaline conditions

[0090] This step is the core process for the in-situ generation of V-Fe-Cu-O ternary solid solution. By precisely controlling the reaction environment and operating parameters, the masked metal complex ions are stably dispersed and co-precipitated in situ under alkaline conditions, avoiding uneven dispersion caused by instantaneous precipitation.

[0091] 2.1 Primary premixing: alkaline predispersion of vanadium source-support

[0092] 2.1.1 Carrier feeding and pretreatment

[0093] Start the horizontal twin-shaft kneader, clean the residual material in the hopper, and ensure that the blades and the inner wall of the hopper are clean and dry. Set the jacket temperature control to 20℃-30℃ and maintain this temperature range throughout the process. Weigh anatase titanium dioxide according to the independent part range and add it all to the kneader hopper. Start the kneader, set the speed to 20r / min-30r / min, and run it idle for 5 minutes to make the carrier powder evenly spread in the hopper and avoid local accumulation.

[0094] 2.1.2 Vanadium source solution mixing operation

[0095] Add the prepared alkaline vanadium source solution to the silo at a uniform rate, with the feeding time controlled at 10-15 minutes to avoid localized liquid accumulation. After feeding, increase the kneader speed to 30-40 r / min and continue kneading for 15-30 minutes to ensure that the vanadium source is evenly dispersed and adsorbed onto the carrier surface.

[0096] 2.1.3 Quality Control Standards for Premixed Materials

[0097] After mixing, the material should be in a uniform and moist powder state, without lumps, dry powder agglomeration, or liquid volume. The pH value of the system should be measured using a precision pH meter and should be stable between 7.5 and 9.0 to ensure that vanadium exists stably on the carrier surface in the form of vanadate ions, thus obtaining a qualified carrier-vanadium source premix. The kneader should be kept in a low-speed stirring state to avoid material agglomeration.

[0098] 2.2 Secondary in-situ mixing: Construction of a homogeneous V-Fe-Cu-O precursor network

[0099] 2.2.1 Calibration of the linkage control system

[0100] The iron-copper chelate solution and 10% dilute ammonia solution were respectively connected to two precision peristaltic pumps. The peristaltic pumps and the online pH monitoring system of the kneader were calibrated together. The upper and lower pH electrodes in the kneader hopper were calibrated. The pH data was collected every 30 seconds, and the average value was taken as the real-time pH value of the system. The pH trigger threshold was set to 6.2. When the real-time pH value was lower than 6.2, the ammonia replenishment peristaltic pump was automatically started to ensure the timeliness and accuracy of pH adjustment.

[0101] 2.2.2 Embedded Material Synchronous Dropping Process

[0102] The iron-copper chelate solution is simultaneously and uniformly dripped into the carrier-vanadium source premix through 3-4 equidistantly distributed embedded drip inlets (inserted 5-10 cm below the material surface) using a kneader. The dripping rate is controlled at 1%-2% of the total solution volume per minute, and the kneader speed is maintained at 30-40 rpm throughout the process. This dripping method allows the acidic chelate solution to be instantly broken up and diluted deep within the material, avoiding the formation of a three-phase interface when droplets come into contact with air at the material surface, and mitigating the risk of demulsification and precipitation caused by a sudden drop in local pH.

[0103] 2.2.3 pH Closed-Loop Control Operation

[0104] During the dropwise addition process, the online pH system monitors the system's pH value in real time. When the pH value drops below 6.2, 10% dilute ammonia solution is automatically added. The volume ratio of ammonia addition rate to the iron-copper chelate solution dropwise addition rate is 1:3-1:5. The pH value is optimally controlled to remain stable between 6.0 and 7.5 throughout the process, and it is prohibited for the pH value to drop below 5.8 or rise above 7.8 at any given time. Within this pH range, vanadium continues to react as VOCs. 3- The form is stable, and the Fe is chelated by citric acid. 3+ Cu 2+ It does not undergo hydrolysis, providing a suitable chemical environment for the formation of ternary solid solutions.

[0105] 2.2.4 Intermittent mixing temperature control process

[0106] After the iron-copper chelate solution is added dropwise, the pH value of the system is checked. A small amount of dilute ammonia is added to stabilize the pH value at 6.5-7.0. Intermittent mixing is then used for reaction maturation: a 5-minute pause is taken every 15-20 minutes of mixing, during which the jacket cooling water is continuously circulated. Simultaneously, the kneader blades maintain a low stirring speed of 5-10 rpm to ensure uniform heat dissipation from the mud. The material temperature is strictly controlled below 45℃ throughout the process, with a total mixing time of 30-60 minutes. This process effectively overcomes the problem of heat accumulation in high-viscosity mud under strong shear, avoiding localized heating that could lead to ammonia evaporation, chelate decomposition, and metal ion instability.

[0107] 2.2.5 In-situ reaction ripening mechanism

[0108] Under the synergistic effect of a weakly alkaline environment and intermittent mixing, vanadate ions and Fe chelated by citric acid... 3+ Cu 2+ An in-situ coprecipitation reaction occurs, and a V-Fe-Cu-O ternary solid solution is formed through the synergistic effect of coordination bonds and ionic bonds. Due to the masking effect of citric acid, metal ions do not precipitate alone, but are uniformly mixed and bonded at the molecular level to construct a homogeneous precursor network structure.

[0109] 2.2.6 Quality Control Standards for Homogeneous Precursors

[0110] After maturation, the material should be in a uniform paste state, without lumps, powder agglomeration, or color difference, and the cross-section should be uniform and fine. The pH value of the system should be measured using a precision pH meter and should be stable between 6.0 and 7.5, with no local pH anomalies. Visual inspection should confirm the absence of obvious precipitation and stratification, ensuring the successful formation of the V-Fe-Cu-O homogeneous precursor network.

[0111] 3. Phosphorus-modified embedding and final mixing with plastic clay

[0112] 3.1 Phosphorus source dilution and in-situ embedding

[0113] 3.1.1 Orthophosphoric acid dilution procedure

[0114] Weigh out phosphoric acid according to the independent part range, dilute it twice with deionized water before use. The dilution operation can reduce the local reaction intensity of phosphoric acid and avoid precipitation caused by instantaneous excess.

[0115] 3.1.2 Dropping and mixing control

[0116] The diluted phosphoric acid solution was added dropwise to the V-Fe-Cu-O homogeneous precursor at a uniform rate. During the addition, the mixture was continuously stirred at a speed of 30 r / min-40 r / min, and the pH value of the system was maintained at 6.0-7.5 throughout the process to avoid phosphorus precipitation caused by pH fluctuations. After the addition was completed, the mixture was stirred for another 15 min-20 min to ensure that the phosphorus element was uniformly dispersed and formed a stable bond with the precursor network.

[0117] 3.1.3 Core Chemical Logic of Phosphorus Modification

[0118] Phosphorus forms coordinate bonds with metal ions in the V-Fe-Cu-O ternary solid solution in the form of phosphate ions. On the one hand, it stabilizes the valence state and crystal structure of metal ions through steric hindrance, inhibiting the reaction with sulfur oxides during subsequent use. On the other hand, the introduction of phosphate ions can construct abundant surface Brønsted acidic sites, providing a basis for the adsorption and activation of NH3, while not affecting the redox performance of the catalytic active center.

[0119] 3.2 Addition and mixing of molding aids

[0120] Weigh out the molding aids such as carboxymethyl cellulose, stearic acid, polyethylene oxide, and wood pulp according to the independent proportion range. After the carboxymethyl cellulose and stearic acid are mixed evenly, add them to the material in the kneader in 2-3 batches. After each addition, knead for 5-10 minutes to ensure that the aids are evenly dispersed. After the alkali-free glass fiber is evenly sprinkled into the material, maintain a speed of 30-40 rpm and knead for 10-15 minutes to ensure that the glass fiber is not clumped or broken in the material and is evenly distributed to enhance the structural strength.

[0121] 3.3 Plasticity Control of Clay Material

[0122] Add deionized water in 2-3 batches, mixing for 5 minutes after each addition. Monitor the moisture content of the clay throughout the process, and finally stabilize the moisture content of the clay at 18%-22%. Use a cone penetration tester to test the plasticity of the clay. A cone penetration of 25mm-35mm at 25℃ is considered qualified, ensuring that the clay has good extrusion molding performance.

[0123] 3.4 Quality Control Standards for Plastic Clay

[0124] The clay should be uniform and fine, free of dry powder, lumps, and fibrous clumps. It should not stick to your hands when kneaded into a ball, nor should it fall apart when dropped. It should have no obvious granular feel, ensuring that there are no broken holes, burrs, or cracks during the subsequent extrusion molding process.

[0125] 4. Clay aging and honeycomb structure extrusion molding

[0126] 4.1 Sealing and Aging Operation

[0127] Remove the plastic clay and completely wrap it with a sealing cloth. Place it in a constant temperature and humidity environment, with the temperature controlled at 20℃-25℃ and the relative humidity at 40%-60%, and let it stand for 12-24 hours to age. Do not open the sealing layer during aging to avoid moisture loss and a decrease in the clay's plasticity. The core function of aging is to allow moisture to migrate evenly within the clay, optimizing its rheological properties and reducing stress cracking during subsequent molding and drying processes.

[0128] 4.2 Pretreatment before extrusion

[0129] After aging, the clay is placed in a kneader and kneaded at a low speed of 10-15 rpm for 5-10 minutes to remove air bubbles trapped inside the clay. The moisture content of the clay is checked again. If the moisture content is lower than 18%, a small amount of deionized water is added to adjust it to the acceptable range of 18%-22% to ensure the stability of the molding process.

[0130] 4.3 Control of honeycomb extrusion molding parameters

[0131] The pretreated mud is fed into a twin-screw extruder for honeycomb catalysts. The screw speed is set to 8-15 r / min, the vacuum exhaust system vacuum degree is ≥-0.08 MPa, and the extrusion pressure is controlled at 8 MPa-15 MPa. The material is continuously extruded through a honeycomb molding die to obtain a honeycomb catalyst precursor. During extrusion, the appearance of the precursor must be observed in real time to ensure that the pores are intact, without broken holes, burrs, or transverse / longitudinal cracks, and that the outer wall is straight and free from deformation.

[0132] 4.4 Quality Control Standards for Precursor Molding

[0133] The extruded honeycomb catalyst precursor needs to have regular pores, uniform wall thickness, and flat cut ends without chipped corners. The precursor is laid flat on a high-temperature resistant pallet to avoid extrusion deformation. After standing and cooling to room temperature, it is transferred to the drying process.

[0134] 5. Gradient constant temperature and humidity drying

[0135] The core purpose of the drying process is to gradually remove moisture from the precursor to avoid cracking and pore collapse caused by uneven moisture evaporation rates. This requires a gradient heating and dehumidification control method with forced ventilation circulation throughout the process.

[0136] 5.1 Preparation of Drying Equipment

[0137] Place the trays containing the catalyst precursors flat into the programmable temperature and humidity drying oven. The trays should be placed horizontally without stacking, with a distance of no less than 5 cm between adjacent trays, and leave a uniform ventilation gap to ensure uniform temperature and humidity inside the drying oven.

[0138] 5.2 Segmented Gradient Drying Program

[0139] (1) First stage: temperature 40℃-45℃, relative humidity 50%-60%, heat preservation for 12h-24h. This stage mainly completes the uniform migration of water inside the precursor to avoid rapid skin formation on the surface, which would prevent the water inside from being discharged.

[0140] (2) Second stage: Temperature 50℃-55℃, relative humidity 40%-50%, heat preservation for 6h-12h, gradually remove most of the free water, maintain slow evaporation of internal moisture, and reduce drying stress.

[0141] (3) Third stage: temperature 60℃-65℃, relative humidity 30%-40%, heat preservation for 6h-12h, to remove residual free water, stabilize the structure of the green body, and prepare for subsequent calcination.

[0142] (4) Fourth stage: Heat to 75℃-80℃ at a rate of 1℃ / h, relative humidity 30%-40%, keep warm for 6h-12h to completely remove the bound water inside the green body and ensure dryness.

[0143] 5.3 Quality control standards for the drying process

[0144] The dried catalyst blank should be free from chipping, cracking, pulverization, and deformation, with a constant weight (weight change rate ≤0.5% over 2 hours) and a moisture content ≤1.0%. After natural cooling to room temperature, it should be transferred to the calcination process to avoid thermal shock cracking caused by direct contact between the high-temperature blank and cold air.

[0145] 6. Programmable temperature controlled segmented calcination

[0146] The calcination process is crucial for the formation of the catalyst's crystal phase and the stabilization of its composite structure. Through segmented heating and heat preservation, organic matter decomposition, crystal phase transformation, and solid solution stabilization are achieved. The entire process employs forced air circulation with an air velocity ≥2m / s and an oxygen content ≥18% in the furnace to ensure a complete reaction and prevent carbon buildup.

[0147] 6.1 Preparation of calcination equipment

[0148] Place the dried and qualified catalyst blanks smoothly into a box-type muffle furnace or a continuous mesh belt kiln, leaving a 5mm-10mm ventilation gap between the blanks. Stacking is prohibited to ensure sufficient air circulation and avoid incomplete decomposition of organic matter due to insufficient local oxygen content.

[0149] 6.2 Segmented calcination program parameters

[0150] (1) First stage (removal of moisture and small molecule organic matter): The temperature is increased from room temperature to 200℃ at a heating rate of 2℃ / min and held for 2h. This stage mainly removes the trace amount of moisture and small molecule organic matter remaining in the green body, so as to avoid the rapid gas generation in the subsequent high temperature stage, which may cause the green body to crack.

[0151] (2) Second stage (gel removal stage): The temperature is increased from 200℃ to 350℃ at a heating rate of 3℃ / min and held for 2 hours. In this stage, the thermal decomposition of nitrates and ammonium salts, as well as the oxidative decomposition of organic matter such as carboxymethyl cellulose, stearic acid, and citric acid are completed. Sufficient oxygen partial pressure ensures complete combustion of organic matter, no carbon deposits are generated, and the active sites are not poisoned.

[0152] (3) Third stage (solid solution stabilization stage): The temperature is increased from 350℃ to 450℃-550℃ at a heating rate of 2℃ / min, and the maximum temperature shall not exceed 550℃. The temperature is held for 3h-6h. Within this temperature range, the organic framework completely collapses, and the P atoms freed from the ligand binding undergo solid-phase diffusion and lattice bonding with V, Fe, and Cu in situ on the support to form a stable V-Fe-Cu-P composite solid solution. At the same time, the maximum temperature of 550℃ strictly avoids the thermodynamic inflection point (above 600℃) of the transformation of anatase TiO2 to rutile phase, ensuring the high specific surface area and stable pore structure of the support.

[0153] (4) Fourth stage (cooling stage): After the heat preservation is completed, the furnace is cooled naturally. The cooling rate is ≤5℃ / min. The furnace can only be taken out after the temperature is cooled to below 100℃. It is forbidden to open the door for rapid cooling to avoid cracking and pulverization of the billet due to thermal shock.

[0154] 6.3 Quality control standards for the calcination process

[0155] The finished catalyst should be free from cracks, pulverization, deformation, and chipped corners, with intact pores, an axial compressive strength ≥2.0MPa, a radial compressive strength ≥0.4MPa, and a specific surface area ≥60m². 2 / g; XRD analysis confirmed that the main crystalline phase was anatase TiO2, with no rutile phase impurities and no individual V2O5, Fe2O3, or CuO characteristic diffraction peaks, proving that the V-Fe-Cu-P composite solid solution was successfully formed.

[0156] V. Catalyst Formation Quality Control and Core Structure Verification Methods

[0157] 1. Quality control of appearance and physical properties

[0158] (1) Appearance inspection: The catalyst should have a honeycomb structure, flat end face, complete pores without broken holes, no burrs, cracks, powdering, or deformation on the outer wall, and uniform color without obvious color difference.

[0159] (2) Mechanical strength test: The axial and radial compressive strength of the catalyst were tested using a compressive strength tester. The axial compressive strength must be ≥2.0MPa and the radial compressive strength must be ≥0.4MPa, which meets the structural strength requirements for industrial applications.

[0160] (3) Specific surface area and pore structure test: The specific surface area and pore volume of the catalyst were tested using the nitrogen adsorption-desorption method (BET method). The specific surface area must be ≥60m². 2 / g, pore volume must be ≥0.25cm³ 3 / g, ensuring sufficient space for loading active sites.

[0161] 2. Verification of crystal phase structure

[0162] X-ray diffraction (XRD) was used with a Cu target and Kα rays, scanning range 10°–80°, scanning rate 2° / min, to analyze the crystal phase of the catalyst. The verification criteria were: the main crystal phase was anatase TiO2, with no rutile phase impurities; and no individual characteristic diffraction peaks for V₂O₅, Fe₂O₃, or CuO, proving that V, Fe, and Cu formed a homogeneous ternary solid solution, rather than a mixture of individual metal oxides.

[0163] 3. Verification of surface-combined states and composite structures

[0164] X-ray photoelectron spectroscopy (XPS) was used to detect the binding energies of V, Fe, Cu, and P elements on the catalyst surface. The verification criteria were: the binding energies of V, Fe, and Cu elements showed a significant shift compared to individual metal oxides, proving the existence of chemical bonding among the three metals; the binding energy of P element conformed to the characteristics of forming coordinate bonds with metal ions, proving that P element was successfully embedded in the V-Fe-Cu-O solid solution, forming a V-Fe-Cu-P composite structure.

[0165] 4. Verification of acidity and reducing properties

[0166] (1) Acidic site test: The distribution and number of acidic sites on the catalyst surface were tested using the NH3 temperature programmed desorption (NH3-TPD) method. The verification standard was that the catalyst surface had abundant medium-strong acid sites, and the number of medium-strong acid sites was significantly increased compared with the unmodified vanadium-iron catalyst, proving that phosphorus modification achieved precise control of acidic sites.

[0167] (2) Redox performance test: The redox temperature range of the catalyst was tested using the H2 temperature programmed reduction (H2-TPR) method. The verification standard was that the reduction peak of the catalyst was broadened and shifted compared with the vanadium-based catalyst alone, proving that there was a synergistic redox effect among the three metals V, Fe and Cu, which improved the electron transfer efficiency of the catalyst.

[0168] 5. Comprehensive Performance Evaluation Standards

[0169] The denitrification performance of the catalyst was evaluated using a fixed-bed reactor under the following conditions: reaction temperature 200℃-400℃, SO2 volume concentration 100ppm-3000ppm, H2O volume content 0%-20%, and reaction space velocity 3000h⁻¹. -1 -10000h -1 The ammonia-nitrogen molar ratio is 0.9-1.2, and the oxygen volume content is 3%-6%. The evaluation criteria are: denitrification efficiency ≥90% in the temperature range of 200℃-400℃, denitrification efficiency ≥98% in the temperature range of 300℃-380℃, and N2 selectivity ≥99%; after continuous operation for 100 hours under the conditions of 1000ppmSO2 and 10%H2O, the denitrification efficiency decay rate is ≤5%, which proves that the catalyst has excellent catalytic activity and anti-sulfur deactivation performance.

[0170] VI. Analysis of the Mechanism of Core Innovation Points

[0171] 1. Citric acid single-system chelation masking mechanism

[0172] Citric acid, as a multidentate chelating agent, contains three carboxyl groups (-COOH) and one hydroxyl group (-OH) in its molecular structure. It can form Fe through the interaction of the carboxyl oxygen atom and the hydroxyl oxygen atom. 3+ Cu 2+ It provides six coordination sites, forming a stable cyclic chelate. The core thermodynamic basis of this chelation reaction is the reaction between citric acid and Fe. 3+ Cu 2+ The coordination stability constants (logK) of citric acid and Cu(OH)₂ are 25.0 and 18.0, respectively, which are much higher than the stability constants corresponding to the solubility products of Fe(OH)₃ and Cu(OH)₂. Therefore, in a weakly alkaline environment with pH ≤ 7.5, citric acid can preferentially coordinate with metal ions, inhibiting the formation of hydroxide precipitates. By controlling the molar amount of citric acid to be no less than 1.2 times the total molar amount of metal ions, it can be ensured that all metal ions are fully chelated, laying the foundation for the subsequent formation of a ternary solid solution with vanadium.

[0173] 2. Temporally decoupled composite mechanism

[0174] This innovative technology employs a sequential process of "first constructing a V-Fe-Cu-O framework, then performing phosphorus modification and embedding," overcoming the coordination competition problem caused by the simultaneous mixing of phosphorus and metal ions in traditional processes. 3+ With PO4 3- The solubility of the formed FePO4 is extremely small (Ksp≈1.3×10). -22 If mixed synchronously, even with citric acid chelation, excess PO4... 3- It will still be with some Fe 3+ The reaction produces an irreversible precipitate; however, in the sequential process, phosphorus modification occurs after the formation of the V-Fe-Cu-O ternary solid solution, at which point Fe...3+ Cu 2+ The phosphorus element is chemically bonded to V. The masking effect of citric acid and the lattice binding of the solid solution work together to suppress the formation of FePO4, ensuring that the phosphorus element is embedded in the solid solution in the form of coordinate bonds, rather than forming a separate phosphate precipitate.

[0175] 3. Engineering Logic of Substrate-Based Dropping and pH Closed-Loop Control

[0176] In large-scale industrial production, controlling the phase interface of acid-base mixtures is a key challenge for achieving uniform dispersion. In traditional spray-drop addition methods, a three-phase interface (air-droplet-material) forms when acidic droplets come into contact with the surface of alkaline materials, causing a sudden drop in local pH that leads to demulsification and precipitation. In contrast, embedded-material addition directly delivers droplets into the material's interior, utilizing the shear force and encapsulation properties of high-viscosity materials to instantly dilute the droplet concentration, thus avoiding the three-phase interface effect. Simultaneously, closed-loop pH control, through online monitoring and automatic ammonia replenishment, compensates in real-time for pH drops caused by acidic droplets, ensuring the overall system pH remains stable within a suitable range. This engineering approach guarantees the uniform dispersion of multi-metal ions and the stable progress of co-precipitation reactions.

[0177] 4. Crystal phase control mechanism of oxygen-enriched segmented calcination

[0178] Temperature and oxygen content control during calcination directly affect the structure and performance of the catalyst. Anatase TiO2 undergoes an irreversible phase transformation above 600℃, generating a rutile phase with extremely low specific surface area, leading to pore collapse and loss of active sites. This technology optimizes the calcination temperature to below 550℃, avoiding the phase transformation inflection point and ensuring the high specific surface area of ​​the support. Simultaneously, an oxygen-rich environment (air velocity ≥2m / s, oxygen content ≥18%) ensures the full oxidative decomposition of organic matter such as citric acid and molding aids, preventing carbon buildup and poisoning of active sites. Segmented heating and holding provide sufficient time for organic decomposition, metal ion diffusion, and solid solution formation, ensuring the stabilization of the composite structure.

[0179] VII. Application Scenarios and Operating Condition Adaptation Parameters

[0180] 1. Applicable flue gas sources and operating conditions

[0181] The catalyst prepared by this technology is suitable for denitrification of sulfur-containing flue gas generated by stationary coal-fired boilers, industrial boilers, steel sintering machines, coking furnaces, and waste incinerators. It is especially suitable for sulfur-containing flue gas conditions with SO2 volume concentration of 100ppm-3000ppm and H2O volume content of 0%-20%, and can meet the flue gas purification needs of different industries.

[0182] 2. Reaction condition adaptation parameters

[0183] (1) Applicable reaction temperature window: 200℃-400℃, with the optimal activity temperature range being 300℃-380℃, which can cover the emission temperature range of most stationary source flue gas.

[0184] (2) Reaction space velocity: 3000 h -1 -10000h -1 The standard industrial filling air velocity is 6000 h⁻¹. -1 It can be flexibly adjusted according to the flue gas flow rate and denitrification efficiency requirements.

[0185] (3) Reaction atmosphere: ammonia-nitrogen molar ratio of 0.9-1.2, oxygen volume content of 3%-6%, and nitrogen as the balance gas, which meets the conventional process requirements of NH3-SCR denitrification reaction.

[0186] 3. Operational Recommendations for Industrial Applications

[0187] In industrial applications, the catalyst loading and reactor structure should be rationally designed based on actual operating conditions such as flue gas flow rate, SO2 concentration, and temperature. The denitrification efficiency and ammonia slip rate of the catalyst should be monitored regularly. When the denitrification efficiency drops below 85%, it can be regenerated by high-temperature air purging. The catalyst's service life is expected to be 2-3 years, depending on the severity of the flue gas conditions. It is recommended to conduct performance testing every 6 months to ensure that the denitrification effect meets the standards.

[0188] To further verify the scientific rationality and practical technical value of the core process parameters and to clarify the influence of each key parameter on the final performance of the catalyst, the following comparative experiment was designed. The experiment uses the core application performance of the product as the evaluation criterion, selecting the key parameters that have the most significant impact on the formation of the catalytic structure and the realization of its function as variables. Through systematic comparative testing, the correlation between parameter adjustment and performance change is quantified, providing objective experimental support for defining the parameter range.

[0189] I. Experimental Objective

[0190] The study aims to verify the impact of core process parameters on catalyst denitrification efficiency, structural stability, and resistance to sulfur deactivation, clarify the technical effects and value boundaries of each parameter, and demonstrate the practical significance of parameter settings.

[0191] II. Variable Selection and Level Setting

[0192] Based on the laws of chemical reactions and the formation mechanism of catalytic structures, three key parameters that have the greatest impact on the core performance of the catalyst were selected as variables. Different levels were set for each variable (including values ​​within and outside the limits of the scheme) to comprehensively examine the influence of these parameters.

[0193] 1. Variable 1: The total molar ratio of citric acid monohydrate to ferric nitrate nonahydrate and copper nitrate trihydrate

[0194] Horizontal settings: 1.0x (below the lower limit of core process technology), 1.2x (lower limit of core process technology), 1.5x (midpoint of core process technology limit), 2.0x (near the upper limit of core process technology limit).

[0195] Selection criteria: This ratio directly determines the degree of chelation of iron and copper ions. If the molar ratio is insufficient, the hydrolysis and precipitation of metal ions cannot be completely inhibited. If the molar ratio is too high, the residual chelating agent may affect the catalytic activity. It is the core prerequisite for ensuring the formation of a homogeneous catalytic structure.

[0196] 2. Variable 2: pH value of the system during the secondary in-situ mixing and phosphorus modification intercalation stage.

[0197] Horizontal setting: 5.5 (below the lower limit of core process constraints), 6.0 (lower limit of core process constraints), 6.8 (midpoint of core process constraints), 7.5 (upper limit of core process constraints), 8.0 (above the upper limit of core process constraints)

[0198] Selection criteria: pH value directly affects the stability of vanadate, the degree of dissociation of metal chelates and the bonding form of phosphorus. pH value deviating from the specified range can lead to the aggregation or structural instability of catalytic active centers, and is a key environmental parameter to ensure the synergistic effect of multiple components.

[0199] 3. Variable 3: The molar ratio of vanadium pentoxide to phosphoric acid and ammonium metavanadate.

[0200] Horizontal settings: 0.8x (below the lower limit of core process constraints), 1.0x (lower limit of core process constraints), 1.25x (midpoint of core process constraints), 1.5x (upper limit of core process constraints), 1.8x (above the upper limit of core process constraints).

[0201] Selection criteria: This ratio determines the number and intensity of acidic sites on the catalyst surface, as well as the anchoring effect of active centers. An improper ratio will lead to a decrease in denitrification efficiency or a decline in anti-sulfurization performance. It is the core parameter for balancing catalytic activity and anti-deactivation ability.

[0202] III. Control Variables

[0203] To ensure the objectivity and accuracy of the experimental results, except for the three variables mentioned above, all other process parameters, raw material specifications, and equipment operating parameters were strictly implemented according to the established process plan, specifically including:

[0204] 1. Raw material specifications: The purity, impurity content, and physicochemical parameters of all raw materials must be kept consistent;

[0205] 2. Process parameters: The preparation temperature of the precursor solution, the dropping rate, the mixing speed, the intermittent mixing mode, the drying program, and the calcination temperature and atmosphere control are all kept constant.

[0206] 3. Sample preparation: The molding mold, aging conditions, and filling method of the catalyst should be kept uniform to ensure the consistency of the macroscopic structure of the sample.

[0207] IV. Test Indicators and Test Methods

[0208] All testing methods are based on objective, independent standards, and the testing process strictly follows the standard-specified operating procedures, equipment requirements, and evaluation criteria.

[0209] 1. Core Test Indicator 1: Denitrification Efficiency

[0210] Test Method: A fixed-bed reactor was used to simulate industrial flue gas conditions. The prepared catalyst sample was cut into uniformly sized particles and uniformly packed into the reactor reaction section, ensuring sufficient contact between the sample and the flue gas. Simulated flue gas was introduced, with the NO concentration set to the typical industrial value, the NH3 concentration adjusted according to the ammonia-nitrogen molar ratio of 1.0, the O2 volume content controlled at 5%, and N2 as the equilibrium gas. The reaction temperature was controlled at 350℃ (midpoint of the optimal activity range), and the space velocity was 6000 h⁻¹. -1 The volume concentration of NO at the reactor inlet and outlet was continuously detected by an online gas analyzer. The denitrification efficiency was calculated according to the calculation formula specified in the standard. The test time for each sample was not less than 2 hours, and the test results during the stable phase were taken as the final data.

[0211] 2. Core Test Indicator Two: Mechanical Strength (Axial Compressive Strength, Radial Compressive Strength)

[0212] Test Method: The catalyst sample was cut into standard-sized cubic specimens, ensuring that the specimen end faces were flat, free of cracks and defects. A compressive strength tester was used for testing. Before testing, the instrument accuracy was calibrated. The specimen was placed stably in the center of the testing platform. For axial testing, the loading direction was consistent with the direction of the catalyst pores; for radial testing, the loading direction was perpendicular to the pore direction. Pressure was applied uniformly at the standard loading rate until the specimen fractured or showed significant deformation. The maximum pressure value was recorded. The compressive strength was calculated based on the stress area of ​​the specimen. Three parallel specimens were prepared for each variable level, and the average value of the test results was taken as the final data.

[0213] 3. Core Test Indicator Three: Sulfur Deactivation Resistance (Denitrification Efficiency Decrease Rate)

[0214] Test Method: A fixed-bed reactor was used for denitrification efficiency testing. SO2 and H2O were added to simulated flue gas, with the SO2 volume concentration set at 1000 ppm and the H2O volume content set at 10%. The remaining flue gas components remained consistent with those used in the denitrification efficiency test. The reaction temperature was controlled at 350℃ and the space velocity at 6000 h⁻¹. -1The catalyst was continuously tested for 100 hours. The denitrification efficiency was recorded at the beginning of the test and at 20, 40, 60, 80 and 100 hours. The denitrification efficiency decay rate after 100 hours was calculated according to the standard formula. The decay rate = (initial denitrification efficiency - 100-hour denitrification efficiency) / initial denitrification efficiency × 100% to evaluate the catalyst’s resistance to sulfur deactivation.

[0215] Exemplary Description

[0216] Because the above experimental method is objectively and reasonably designed, it can comprehensively and accurately reflect the influence of core process parameters on catalyst performance, and effectively highlight the technical advantages of the present invention. Therefore, ten groups in the experimental group are selected as examples for detailed demonstration. All examples strictly follow the complete process steps and operation procedures of the present invention, and the parameter settings are all the actual values ​​used in actual operation to ensure complete reproducibility.

[0217] Example 1

[0218] This embodiment prepares the modified vanadium-iron denitration catalyst according to the following complete process steps:

[0219] Raw material selection (all values ​​are accurate): 3 parts ammonium metavanadate, 15 parts ferric nitrate nonahydrate, 9 parts copper nitrate trihydrate, 18.8 parts citric acid monohydrate, 1.5 parts orthophosphoric acid, 200 parts anatase titanium dioxide, 5 parts alkali-free glass fiber, 3 parts carboxymethyl cellulose, 1.5 parts stearic acid, ammonia (25% concentration) added as needed, and 35 parts deionized water; the total molar ratio of citric acid monohydrate to ferric nitrate nonahydrate and copper nitrate trihydrate is 1.2 times, and the molar ratio of orthophosphoric acid to ammonium metavanadate corresponding to vanadium pentoxide is 1.0 times.

[0220] Precursor solution preparation:

[0221] (1) Preparation of alkaline solution of vanadium source: Mix 25% ammonia water and deionized water at a volume ratio of 1:4, and stabilize the solution temperature at 42℃ by jacket temperature control; add ammonium metavanadate at a rate of 0.8 parts / min, and stir continuously at a speed of 200r / min for 30min until the solid is fully dissolved; stop heating and cool naturally to 25℃, add a small amount of ammonia water to adjust the pH value of the solution to 9.5, control the molar concentration of ammonium metavanadate in the solution to 0.4mol / L, and seal and protect from light for later use.

[0222] (2) Preparation of iron-copper chelate solution: Take 20 parts of deionized water, add ferric nitrate nonahydrate, copper nitrate trihydrate and citric acid monohydrate, stir continuously at 250 r / min for 30 min, add a small amount of deionized water to adjust the pH value of the solution to 3.0, and obtain a clear and transparent metal chelate solution, which is sealed for later use; the total volume of vanadium source alkaline solution and iron-copper chelate solution is 240 mL, and the mass ratio of vanadium source alkaline solution to anatase titanium dioxide is 1.2 mL / g.

[0223] Weakly alkaline two-stage compounding in situ:

[0224] (1) First premixing: Start the horizontal twin-shaft kneader and set the jacket temperature control to 25℃; add all the anatase titanium dioxide into the hopper and set the speed to 25r / min for idling and stirring for 5min; add the vanadium source alkaline solution into the hopper at a uniform speed and control the feeding time to 12min. After the feeding is completed, increase the speed to 35r / min and continue mixing for 20min to obtain a carrier vanadium source premix with a pH value of 8.0.

[0225] (2) Secondary in-situ mixing: The iron-copper chelate solution was connected to a precision peristaltic pump and calibrated in conjunction with the online pH monitoring system. The pH trigger threshold was set to 6.2. The premixed material was uniformly added at a rate of 1.5% / min of total solution volume through a buried dripping port inserted 8cm below the material surface. The pH value was monitored in real time during the dripping process. When the pH value was lower than 6.2, 10% dilute ammonia was automatically added. The pH value of the system was kept stable at 6.0 throughout the process. After the dripping was completed, an intermittent mode of "pausing for 5 minutes after every 20 minutes of mixing" was adopted. During the pause, the jacket cooling water was continuously circulated, and the impeller was kept at a low speed of 8r / min for stirring. The material temperature was controlled at 40℃ throughout the process. The mixing lasted for a total of 45 minutes to obtain the vanadium-iron-copper-oxygen homogeneous precursor.

[0226] Phosphorus-modified embedding and final mixing of plastic clay: Dilute orthophosphoric acid with deionized water by 2 times and add it dropwise to the homogeneous precursor at a uniform rate. During the dropwise addition, continue mixing at a speed of 35 r / min, maintaining the pH value of the system at 6.0 throughout the process. After the dropwise addition is completed, continue mixing for 18 min. Add the mixture of carboxymethyl cellulose and stearic acid in two batches, mixing for 8 min after each addition. Sprinkle alkali-free glass fiber evenly and mix at a speed of 35 r / min for 12 min. Add the remaining deionized water in two batches to adjust the moisture content of the clay to 20%. The cone penetration test at 25℃ is 30 mm, and the plastic clay is obtained.

[0227] Clay aging and honeycomb structure extrusion molding: The plastic clay was completely wrapped with a sealing cloth and aged in an environment of 22℃ and 50% relative humidity for 18 hours. After aging, it was put into a kneader and mixed at a low speed of 12r / min for 8 minutes to remove air. The clay was then added to a twin-screw extruder, with the screw speed set to 12r / min, the vacuum degree of the vacuum exhaust system set to -0.09MPa, and the extrusion pressure set to 12MPa. The clay was then extruded through a 15×15-hole honeycomb mold to obtain a honeycomb catalyst precursor.

[0228] Gradient constant temperature and humidity drying: The precursor is placed in a programmable temperature-controlled drying oven. The first stage is 42℃ and 55% relative humidity for 18 hours; the second stage is 52℃ and 45% relative humidity for 9 hours; the third stage is 62℃ and 35% relative humidity for 9 hours; the fourth stage is heated to 78℃ at a rate of 1℃ / h and held at 35% relative humidity for 9 hours. After drying, the moisture content of the green body is 0.8%, and it is naturally cooled to room temperature.

[0229] Programmable temperature controlled segmented calcination: The dried green body is placed in a mesh belt kiln with forced air circulation throughout the process. The air flow rate is 2.5 m / s and the oxygen content in the furnace is 20%. The temperature is increased from room temperature to 200℃ at a rate of 2℃ / min and held for 2 hours. The temperature is increased to 350℃ at a rate of 3℃ / min and held for 2 hours. The temperature is increased to 500℃ at a rate of 2℃ / min and held for 4 hours. The furnace is then allowed to cool naturally to 80℃ before being removed from the furnace to obtain the modified vanadium-iron denitrification catalyst.

[0230] Performance test results: Denitrification efficiency 98.23%, axial compressive strength 2.45MPa, radial compressive strength 0.52MPa, and denitrification efficiency decay rate 3.15%.

[0231] To further clarify the influence of the core process parameters of this invention on the overall performance of the catalyst, single-factor investigations were conducted on the three core variables based on the preparation conditions of Example 1 (i.e., 1.2 times the molar ratio of citric acid monohydrate, 6.0 pH value of the mixing system, and 1.0 times the molar ratio of orthophosphate). The performance testing methods for all samples were consistent with those in Example 1.

[0232] 1. Investigate the reaction of citric acid monohydrate with metal ions (Fe) 3+ Cu 2+ The effect of total molar ratio

[0233] In this set of examples, the pH value (6.0) and the molar ratio of orthophosphate (1.0 times) of the mixing system were kept constant, and only the amount of citric acid monohydrate added was changed. The test data are shown in Table 1.

[0234] Table 1: Effect of the molar ratio of citric acid monohydrate on catalyst performance

[0235]

[0236] Data Analysis: When the citric acid ratio is between 1.2 and 1.5, the metal ion chelation is sufficient, and the denitrification efficiency reaches its optimal level. Example 3 (1.5 times) showed the highest activity, but due to the increased release of organic matter during calcination, the porosity increased slightly, resulting in a slight decrease in mechanical strength compared to Example 1, which is consistent with the physical laws of porous materials. Excessive addition (Example 4) or insufficient addition (Example 2) both lead to defects in the solid solution structure, causing a comprehensive decline in performance.

[0237] 2. Investigate the effect of pH value on the system during the secondary in-situ mixing and phosphorus modification stages.

[0238] In this set of examples, the molar ratio of citric acid monohydrate (1.2 times) and the molar ratio of orthophosphate (1.0 times) remained constant. The pH value of the system was changed by adjusting the ammonia replenishment strategy. The test data are shown in Table 2.

[0239] Table 2: Effect of pH value on catalyst performance

[0240]

[0241] Data Analysis: pH value directly determines the stability of metal complexes. Performance remained excellent within the pH range of 6.0–7.5 (Examples 1, 6, and 7). When the pH was too low (Example 5) or too high (Example 8), some active components precipitated or dissociated prematurely, failing to form a homogeneous ternary solid solution, resulting in a sharp drop in catalytic activity and mechanical strength.

[0242] 3. Investigate the effect of the molar ratio of orthophosphoric acid to V2O5.

[0243] In this set of examples, the molar ratio of citric acid monohydrate (1.2 times) and the pH value of the compounding system (6.0) were kept constant, and only the amount of orthophosphate was changed. The test data are shown in Table 3.

[0244] Table 3: Effect of orthophosphate molar ratio on catalyst performance

[0245]

[0246] Data pattern analysis: The core role of phosphorus is to construct acidic sites and anchor active centers to enhance sulfur resistance. In Example 9, due to insufficient phosphorus introduction, the sulfur resistance attenuation rate was as high as 6.5%; in Example 10, with a moderate amount of phosphorus, the sulfur resistance performance was optimal (attenuation rate of only 2.5%); however, when phosphorus was excessive (Example 11), too many phosphate species would cover the active centers and block the pores, resulting in a reverse decrease in denitrification efficiency and mechanical strength.

[0247] 4. Comparative Example of Existing Technology (Blank Control Group)

[0248] Example 12 (Comparative Example)

[0249] In this embodiment, a denitrification catalyst is prepared using the existing V2O5-WO3 / TiO2 system. The raw material contains 8 parts of ammonium tungstate (containing tungsten additive). There is no need to introduce citric acid monohydrate for chelation or perform phosphorus modification and intercalation. The catalyst is prepared by conventional co-precipitation method. The remaining molding and calcination steps are the same as in Example 1.

[0250] Test results: Denitrification efficiency 89.4%, axial compressive strength 2.10 MPa, radial compressive strength 0.41 MPa, and denitrification efficiency attenuation rate as high as 8.8%. Compared with Examples 1-11, the traditional process did not construct a stable composite solid solution structure, and all performance aspects were inferior.

[0251] Based on the experimental results of the above single-factor investigation, in order to further reveal the regulation mechanism of core process parameters on catalyst performance, the following will analyze the underlying reasons for the performance trends under different parameter conditions from the molecular and crystal structure level, combined with the basic principles of coordination chemistry and catalytic reaction kinetics, and clarify the intrinsic relationship between parameter optimization and catalyst microstructure and macroscopic performance.

[0252] The changes in core process parameters essentially affect the macroscopic performance of the catalyst by regulating its microstructure (such as the distribution of active centers, crystal phase composition, and surface acidic sites). The specific mechanism is as follows:

[0253] I. The Mechanism of the Influence of the Molar Ratio of Citric Acid to Metal Ions on Performance

[0254] Citric acid, as a multidentate chelating agent, directly determines the chelation sufficiency and stability of iron and copper ions and the chelate by its molar ratio with metal ions. When this ratio is within a suitable range, citric acid molecules can provide sufficient coordination sites for iron and copper ions through their carboxyl and hydroxyl groups, forming stable cyclic chelates that effectively inhibit the hydrolysis and precipitation of metal ions in the subsequent alkaline environment. This uniform chelation at the molecular level lays the foundation for the subsequent formation of a homogeneous V-Fe-Cu-O ternary solid solution with vanadate, enabling the active centers to achieve molecular-level dispersion on the support surface. This significantly increases the contact probability between reactant molecules and active sites during the catalytic reaction, while the integrity of the solid solution structure also enhances the catalyst's mechanical strength and sulfur resistance.

[0255] When this ratio is below a suitable range, some metal ions cannot be fully chelated. The free metal ions are prone to hydrolysis in an alkaline mixing environment, generating inactive hydroxide precipitates. These precipitates disrupt the uniform distribution of active sites, forming aggregates, leading to a reduction in the number and uneven distribution of catalytic active sites. Simultaneously, the weak bonding between the precipitate and the support reduces the catalyst's mechanical strength. Furthermore, unchelated metal ions cannot participate in the formation of the ternary solid solution, decreasing the catalyst's resistance to sulfur deactivation and making it prone to reacting with sulfur oxides to generate low-activity substances under sulfur-containing flue gas conditions.

[0256] When the ratio is higher than the appropriate range, excess citric acid will occupy some coordination sites, or a small amount of organic fragments will remain during calcination. These residual substances will cover the active center, hindering the contact between the reactants and the active site, and may also destroy the lattice integrity of the ternary solid solution, resulting in a slight decrease in catalytic activity and stability.

[0257] II. Mechanism of the effect of pH value on performance

[0258] The pH value of the system directly affects the formation of the catalyst's microstructure by regulating the coordination equilibrium and the form of ions. Within a suitable pH range, vanadate exists as a stable monomer or oligomer, making polymerization less likely. Simultaneously, the chelate formed by citric acid and metal ions remains stable and does not dissociate. This chemical environment favors in-situ co-precipitation reactions between vanadate and metal chelates, forming a uniform, well-defined V-Fe-Cu-O ternary solid solution. This ensures the synergistic effect of the active centers is fully realized, while the tight interfacial bonding between the solid solution and the support enhances the catalyst's mechanical strength.

[0259] When the pH value is below the suitable range, the degree of ionization of the carboxyl groups in citric acid decreases, and the chelating ability drops significantly. Metal ions easily dissociate from the chelate and undergo hydrolysis and precipitation. At the same time, vanadate ions are prone to polymerization reactions, forming polyvanadates, leading to abnormal active center structures and decreased catalytic activity and selectivity. In addition, excessive acidity can also affect the bonding form of phosphorus, preventing phosphorus from effectively intercalating into the solid solution and instead forming individual phosphates, thus reducing the catalyst's sulfur resistance.

[0260] When the pH value is higher than the appropriate range, the stability of the metal chelate decreases, and it is prone to dissociation and formation of hydroxide precipitates, which destroys the homogeneous structure of the ternary solid solution. At the same time, vanadate may be transformed into an unstable form, making it difficult to form stable active centers during calcination, resulting in a significant decrease in both the catalytic activity and mechanical strength of the catalyst.

[0261] III. Mechanism of the Influence of Orthophosphoric Acid to Vanadium Molar Ratio on Performance

[0262] Phosphorus forms coordination bonds with the V-Fe-Cu-O ternary solid solution, thereby regulating the structure of acidic sites and active centers on the catalyst surface. When the ratio is within an appropriate range, phosphorus can be uniformly embedded in the solid solution lattice. On the one hand, it stabilizes the valence state of metal ions through steric hindrance, inhibiting their reaction with sulfur oxides under sulfur-containing conditions and improving resistance to sulfur deactivation. On the other hand, the introduction of phosphorus can construct an appropriate amount of moderately strong acid sites. These acid sites can effectively adsorb and activate NH3 molecules, providing sufficient reaction intermediates for the catalytic reaction, thereby improving denitrification efficiency.

[0263] When the ratio is below the appropriate range, the amount of phosphorus embedded in the solid solution is insufficient to form enough medium-strong acid sites, the adsorption and activation efficiency of NH3 decreases, and the catalytic reaction rate decreases; at the same time, the active center lacks the anchoring protection of phosphorus and is easily poisoned by sulfur oxides in sulfur-containing flue gas, resulting in weak resistance to sulfur deactivation.

[0264] When the ratio is higher than the appropriate range, excess phosphorus will form additional phosphate species. These species not only cannot participate in the catalytic reaction, but also cover part of the active site, hindering the contact between the reactants and the active site, resulting in a decrease in denitrification efficiency. In addition, excess phosphorus may destroy the crystal structure of the ternary solid solution, reducing the mechanical strength and structural stability of the catalyst.

[0265] IV. Verification of the comprehensive mechanism of performance evolution of each investigation group

[0266] Based on the above single-factor investigation data, the micro-control mechanism of the present invention can be further confirmed:

[0267] The baseline and preferred groups (such as Examples 1, 3, 6, and 10) all exhibited core parameters within suitable ranges, forming a uniformly dispersed V-Fe-Cu-P composite solid solution structure at the molecular level with a stable crystal lattice, thus demonstrating excellent comprehensive performance. It is noteworthy that some preferred groups (such as Examples 3 and 10) showed a slight decrease in mechanical strength, consistent with physical laws, when their denitrification efficiency and sulfur resistance reached their peak values. This is precisely due to the development of pore depth and the expansion of acidic sites, further confirming the intrinsic interplay between catalytic activity and microporous structure.

[0268] Boundary and Deviation Groups (e.g., Examples 2, 4, 5, 8, 9, 11): Due to a single core parameter deviating from the suitable range, defects appear in the molecular-level microstructure in a specific dimension (e.g., metal ion hydrolysis and aggregation, solid solution structure dissociation, insufficient acid sites, or pore blockage). These single defects in the microscopic dimension directly map to a decrease in macroscopic performance in a specific direction, fully demonstrating the critical significance of the parameter control range of this invention.

[0269] The existing technology control group (Example 12) used conventional preparation methods without optimizing the microstructure through chelation masking, precise pH control, and sequential phosphorus modification. This resulted in uneven dispersion of active centers, a lack of stable composite solid solution structures, and a severe deficiency of sulfur-resistant acidic sites. Consequently, a highly efficient and synergistic ternary catalytic system could not be formed at the molecular level, and its denitrification efficiency, mechanical strength, and sulfur deactivation resistance were all significantly inferior to the catalyst prepared in this invention.

[0270] Specific work process

[0271] Please refer to Figure 1 Ammonium metavanadate is added to an ammonia solution and stirred to dissolve. After cooling, the pH value is adjusted to obtain an alkaline solution of vanadium source. Ferric nitrate nonahydrate, copper nitrate trihydrate, and citric acid monohydrate are added to deionized water and stirred. Citric acid coordinates and chelates iron and copper ions through carboxyl and hydroxyl groups to form a stable metal chelate solution. The pH value is adjusted to obtain an iron-copper chelate solution.

[0272] Anatase titanium dioxide is added to a kneader and stirred while running in the air. Then, an alkaline solution of vanadium source is added and mixed to form a carrier vanadium source premix. An iron-copper chelate solution is dripped into the premix through a buried dripping port. During the dripping process, ammonia water is added to maintain the pH stability of the system. An intermittent mixing mode is adopted, accompanied by cooling. The iron-copper chelate solution and vanadium source undergo an in-situ co-precipitation reaction to form a V-Fe-Cu-O ternary solid solution. Diluted orthophosphoric acid is dripped into the above system. During the continuous mixing process, phosphorus element is embedded into the ternary solid solution through coordination bonds. Then, a molding aid is added and mixing continues. The moisture content is adjusted to obtain a plastic clay.

[0273] After the plastic clay is sealed and aged, it is kneaded and vented at low speed in a kneader and then extruded into a honeycomb catalyst precursor by an extruder. The precursor is then placed in a drying oven for gradient heating and dehumidification to gradually remove moisture. The dried green body is then placed in a calcining device and calcined in stages under an oxidizing atmosphere to remove residual moisture and small molecule organic matter, then decompose nitrates, ammonium salts and organic additives, and finally complete the lattice bonding and stabilization of the V-Fe-Cu-P composite solid solution at a suitable temperature. After cooling in the furnace, the modified vanadium-iron denitrification catalyst is obtained.

[0274] The technical features described above can be combined in any way. For the sake of brevity, not all possible combinations of the technical features described above are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for preparing a modified vanadium-iron denitration catalyst, characterized in that, The process of not using tungsten- or molybdenum-containing raw materials includes the following steps: (1) Prepare an alkaline solution of vanadium source by mixing ammonium metavanadate with an ammonia solution; and prepare an iron-copper chelate solution by dissolving ferric nitrate nonahydrate, copper nitrate trihydrate and citric acid monohydrate in deionized water, wherein the molar amount of citric acid monohydrate is not less than 1.2 times the total molar amount of ferric nitrate nonahydrate and copper nitrate trihydrate. (2) First, anatase titanium dioxide is mixed with vanadium source alkaline solution to obtain carrier vanadium source premix; then, iron-copper chelate solution is added to the premix by embedding drop addition. During the drop addition process, ammonia water is added in conjunction to stabilize the pH value of the system. After the drop is completed, vanadium-iron-copper-oxygen homogeneous precursor is obtained by intermittent mixing. The iron-copper chelate solution was added dropwise at a rate of 1% to 2% of the total solution volume per minute through a dropper nozzle inserted 5 to 10 cm below the material surface, while maintaining the pH of the system stable between 6.0 and 7.5 throughout the process. After dripping, the mixture is mixed in an intermittent mixing mode for 30 to 60 minutes. The intermittent mixing mode involves pausing for 5 minutes every 15 to 20 minutes of mixing, during which the jacket cooling water is continuously circulated, and the material temperature is controlled to not exceed 45°C throughout the process. (3) Add phosphoric acid solution dropwise to the homogeneous precursor and mix to stabilize the pH value of the system. Control the molar amount of phosphoric acid to be 1.0 to 1.5 times the molar amount of ammonium metavanadate corresponding to vanadium pentoxide. Then add molding aid to adjust the moisture content of the clay to obtain plastic clay. (4) After being sealed and aged, the plastic clay is vacuum extruded to obtain a honeycomb precursor; (5) After the honeycomb precursor is dried under gradient constant temperature and humidity, it is calcined in stages under an oxidizing air atmosphere, and then cooled with the furnace after heat preservation to obtain the modified vanadium iron denitration catalyst. The air flow rate is controlled to be no less than 2m / s, the oxygen content in the furnace is no less than 18%, and the maximum calcination temperature is no higher than 550℃.

2. The preparation method according to claim 1, characterized in that: In the preparation of the alkaline solution of the vanadium source, ammonium metavanadate is added to an ammonia solution and stirred at 40°C to 45°C until completely dissolved. After cooling to 20°C to 30°C, the pH of the solution is adjusted to 9.0 to 11.0, and the molar concentration of ammonium metavanadate in the solution is controlled to be no higher than 0.5 mol / L.

3. The preparation method according to claim 1, characterized in that: After the iron-copper chelate solution is prepared, the pH value of the solution is adjusted to 2.0 to 4.0; the total volume of the vanadium source alkaline solution and the iron-copper chelate solution is 0.8 mL / g to 1.2 mL / g in mass ratio to anatase titanium dioxide.

4. The preparation method according to claim 1, characterized in that: In step (2), after adding the alkaline solution of vanadium source, the mixture is stirred at a speed of 20 r / min to 40 r / min for 15 min to 30 min to obtain a carrier vanadium source premix with a pH value of 7.5 to 9.

0.

5. The preparation method according to claim 1, characterized in that: In step (2), the kneader blades are kept at a low stirring speed of 5 r / min to 10 r / min; In step (3), the diluted phosphoric acid solution is added dropwise, and the pH value of the system is kept stable between 6.0 and 7.5 throughout the process. After the phosphoric acid solution is added dropwise, the mixture is continued for 15 to 20 minutes.

6. The preparation method according to claim 1, characterized in that: The aging environment is a temperature of 20°C to 25°C and a relative humidity of 40% to 60%, with an aging time of 12 hours to 24 hours. After the final mixing of the mud is completed, the moisture content of the mud is adjusted to 18% to 22%.

7. The preparation method according to claim 1, characterized in that: The specific steps of the segmented calcination are as follows: heat up to 200℃ at 2℃ / min and hold for 2 hours, heat up to 350℃ at 3℃ / min and hold for 2 hours, heat up to 450℃ to 550℃ at 2℃ / min and hold for 3 to 6 hours, and then cool down to below 100℃ with the furnace before being removed from the furnace.

8. A modified vanadium-iron denitration catalyst, prepared according to the preparation method of any one of claims 1-7, characterized in that: The catalyst uses raw materials that do not contain tungsten or molybdenum. It includes anatase titanium dioxide support, a main active component, a ternary composite modifier, and a phosphorus-modifying component supported on the support. The main active component is vanadium pentoxide, the ternary composite modifier includes ferric oxide and copper oxide, and the phosphorus-modifying component is phosphorus pentoxide. The main crystalline phase of the catalyst is anatase titanium dioxide, and it does not have individual characteristic diffraction peaks for vanadium pentoxide, ferric oxide, or copper oxide.

9. The modified vanadium-iron denitrification catalyst as described in claim 8, characterized in that: The catalyst, by mass parts, comprises 100 to 300 parts of anatase titanium dioxide, 1 to 6 parts of the main active component (vanadium pentoxide), 5 to 25 parts of a ternary composite modifier (ferric oxide), 3 to 15 parts of a ternary composite modifier (copper oxide), and 2 to 18 parts of a phosphorus-modifying component (phosphorus pentoxide); the catalyst has an axial compressive strength of not less than 2.0 MPa, a radial compressive strength of not less than 0.4 MPa, and a specific surface area of ​​not less than 60 m². 2 / g.

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