A method for preparing a low-temperature ammonia-free denitrification catalyst and its application

Abstract

This application provides a method for preparing a low-temperature ammonia-free denitrification catalyst and its application, relating to the field of catalyst technology. The method for preparing the low-temperature ammonia-free denitrification catalyst includes: using tartaric acid to complex a metal precursor, ultrasonically impregnating and loading it onto a composite support, and then obtaining the catalyst through stepwise calcination. The catalyst contains an active component, an anti-sulfur agent, MgO@CNTs, a titanium-germanium composite support, and a silicon-aluminum composite sol binder. The active component includes Mn₃O₄, Fe₂O₃, and CeO₂, and the anti-sulfur agent includes MoO₃ and Co₃O₄. This catalyst exhibits high-efficiency denitrification performance for industrial flue gas under low-temperature conditions of 80-150℃, achieving a NOx removal rate of 95.2% at 150℃ while demonstrating significant anti-sulfur performance.

Description

Technical Field

[0001] This application relates to the field of catalyst technology, and in particular to a method for preparing a low-temperature ammonia-free denitrification catalyst and its application. Background Technology

[0002] While current mainstream ammonia-based denitrification technology can achieve emission standards, it has created a more intractable secondary pollution chain—ammonium salt particles formed by ammonia escape not only corrode downstream equipment but also combine with acidic substances in the atmosphere to form difficult-to-monitor secondary pollutants. This stopgap approach forces companies into a dilemma: either bear the high safety risks of liquid ammonia storage and the ever-increasing cost of denitrification agents, or face environmental penalties due to excessive ammonia escape. The industry has attempted to control nitrogen oxide generation at the source through combustion optimization, but the frequent load fluctuations of gas-fired boilers make it difficult to maintain combustion stability. When the boiler is under low load, the local high-temperature zone caused by temperature field imbalance in conventional low-NOx burners will conversely increase the nitrogen oxide generation rate. This condition-dependent defect means that front-end control technology can never completely replace end-of-pipe treatment. While existing ammonia-free denitrification catalysts avoid the risk of ammonia pollution, their activity temperature window is fundamentally misaligned with the actual operating conditions of gas-fired boilers—when the flue gas temperature drops below 300℃, the catalytic activity exhibits a precipitous decline. The root cause lies in the severely insufficient activation capacity of traditional catalyst surface chemisorption sites for reactants under low-temperature conditions, and the fact that microporous structures are easily blocked by capillary condensation in water-containing flue gas. Even more challenging is the fact that existing technologies generally develop catalysts with their physical structure design separated from their chemical reaction pathways. For example, while impregnation methods can increase the surface acidic site density, they sacrifice mesopore connectivity; while template methods for preparing hierarchical pore structures optimize mass transfer efficiency, they lead to a decrease in the dispersion of active components. This mutual constraint between physical structure and chemical performance forms a difficult-to-break technological loop, resulting in a persistent trade-off between low-temperature activity and water / sulfur resistance. The market urgently needs a catalyst that can penetrate the "low-temperature activity forbidden zone," simultaneously meeting three contradictory requirements: maintaining structural stability in low-temperature, high-humidity environments; possessing precise molecular recognition capabilities under complex flue gas compositions; and achieving rapid activation response under frequent start-stop conditions. Existing patented technologies have proposed improving low-temperature activity through noble metal doping or rare earth modification. However, such solutions not only significantly increase material costs, but their improvement effect is often quickly offset in sulfur-containing flue gas. Other studies have attempted to compensate for insufficient activity by increasing the specific surface area of ​​the catalyst, but have ignored the limiting size effect of the microporous structure—when the pore size approaches the dynamic diameter of water molecules, the preferential adsorption of water molecules will completely block the reactant transport channels. This failure mechanism hidden at the microscale is easily overlooked in conventional testing, but directly leads to the collective failure of catalysts that perform well in the laboratory in engineering applications. A deep analysis of the industry pain points reveals that the real technological barrier lies in how to build a "three-in-one" synergistic system: creating new low-temperature activation pathways at the reaction principle level to overcome limitations; designing moisture-resistant and clog-resistant biomimetic mass transfer channels at the physical structure level; and constructing a multi-active-site relay catalytic network at the chemical composition level.This requires overturning the traditional catalyst development paradigm, integrating previously isolated optimizations of material science parameters, structural mechanical properties, and surface chemical processes into unified design variables. Only through the deep integration of reaction mechanism innovation and material genome reconstruction can low-temperature ammonia-free denitrification technology with engineering practical value be developed, fundamentally solving the environmental compliance dilemma faced by gas-fired boilers under variable load conditions.

[0003] In summary, there is an urgent need to develop a novel method for preparing low-temperature ammonia-free denitrification catalysts and their applications. Summary of the Invention

[0004] This application provides a method for preparing a low-temperature ammonia-free denitrification catalyst and its application, in order to solve the problems mentioned in the background art.

[0005] To address the aforementioned technical problems, this application discloses a method for preparing a low-temperature ammonia-free denitrification catalyst, comprising the following steps:

[0006] S1. Preparation of titanium-germanium composite carrier;

[0007] S2. Preparation of a carrier loaded with active components and anti-sulfur additives: The precursors of the active components and anti-sulfur additives are complexed with tartaric acid to obtain a metal tartaric acid complex solution. MgO@CNTs, titanium-germanium composite carriers and binders are immersed in the metal tartaric acid complex solution and ultrasonically dispersed.

[0008] S3. A low-temperature ammonia-free denitrification catalyst was prepared by drying and calcining.

[0009] Furthermore, the method for preparing the titanium-germanium composite support includes ball milling titanium dioxide and germanium dioxide for 120 min and then spray drying them in a spray drying tower to obtain the titanium-germanium composite support.

[0010] Furthermore, titanium dioxide and germanium dioxide were added to a ball mill jar at a ball-to-material ratio of 10:1 and ball-milled at 300 r / min for 120 min. The slurry after ball milling was fed into a spray drying tower with an inlet temperature of 200℃ and an outlet temperature of 90℃ to obtain a titanium-germanium composite carrier with a particle size of 5-10 μm.

[0011] Furthermore, Mn(NO3)2·4H2O, Fe(NO3)3·9H2O, Ce(NO3)3·6H2O, and (NH4)6Mo7O are added. 24 Dissolve 4H2O and Co(NO3)2·6H2O in deionized water, add tartaric acid in 1.5 times the total molar amount of metal ions, and stir at 500 r / min for 120 min at 60℃ to prepare a metal tartaric acid complex solution.

[0012] Furthermore, MgO@CNTs, titanium-germanium composite carrier and silicon-aluminum composite sol were immersed in a metal tartaric acid complex solution, and 2 parts of polyethylene oxide dispersant were added at 60°C and ultrasonically dispersed for 60 min. After standing for 12 h, a carrier loaded with active components and anti-sulfur additives was obtained.

[0013] Furthermore, the support loaded with active components and anti-sulfur additives was dried at 80°C for 12 hours, heated from 100°C to 300°C at a rate of 2°C / min, calcined at 300°C for 1 hour, heated from 300°C to 500°C at a rate of 5°C / min, and calcined at 500°C for 4 hours to obtain a low-temperature ammonia-free denitrification catalyst.

[0014] Furthermore, the preparation method of the MgO@CNTs includes: immersing 5 parts by weight of MWCNTs in 80 parts of HNO3, ultrasonically treating at 80°C for 2 hours, centrifuging and washing, and drying at 110°C for 12 hours to obtain pretreated MWCNTs; dissolving 1 part of Mg(NO3)2·6H2O in 10 parts of deionized water, adding 3 parts of EDTA, stirring and adding the pretreated MWCNTs at 60°C, vacuum shaking and impregnating at 40°C for 6 hours, drying at 60°C for 12 hours, and calcining at 550°C for 5 hours under N2 atmosphere at a rate of 2°C / min to obtain MgO@CNTs.

[0015] Furthermore, the low-temperature ammonia-free denitrification catalyst prepared by the above preparation method comprises, by weight, 25-30 parts of active component, 10-14 parts of anti-sulfur agent, 52-57 parts of composite carrier and 3-8 parts of binder.

[0016] Furthermore, the active components include manganese tetroxide, ferric oxide, and cerium dioxide; the antisulfur additives include molybdenum trioxide and cobalt tetroxide; the composite carrier includes MgO@CNTs and titanium-germanium composite carrier; and the binder is a silicon-aluminum composite sol.

[0017] This application discloses the application of a low-temperature ammonia-free denitrification catalyst prepared by the above-described method in industrial flue gas denitrification. The low-temperature ammonia-free denitrification catalyst is suitable for low-temperature environments of 80-150℃, with NOx concentration in flue gas ≤1000mg / m³ and SO2 ≤200ppm.

[0018] The mechanism of action of the above-mentioned raw material components is as follows: Firstly, the active component, as the core driving force for low-temperature ammonia-free denitrification, achieves efficient denitrification through electron transfer and surface acidity regulation of polymetallic oxides. Manganese tetroxide, with its abundant surface oxygen vacancies and variable valence states (Mn²⁺ / Mn³⁺ / Mn...),... 4⁺) directly activates nitrogen oxide molecules at low temperatures, promoting their dissociation into reactive nitrogen-oxygen intermediates. Ferric oxide enhances ammonia adsorption and activation by providing Lewis acidic sites, while its interfacial electron transfer with manganese further accelerates the redox cycle. The introduction of cerium dioxide significantly improves oxygen storage capacity through Ce³⁺ / Ce 4 The conversion buffers the oxygen concentration fluctuations in the reaction system, maintaining the catalyst's stability in an oxygen-deficient environment. These three components form a synergistic network of "manganese as the primary oxidation agent, iron providing acidity, and cerium regulating oxygen balance," achieving deep reduction of nitrogen oxides. Secondly, the anti-sulfur additive resists sulfur poisoning through a dual pathway of physical isolation and chemical conversion. Molybdenum trioxide preferentially reacts with sulfur dioxide in flue gas to generate thermally stable molybdenum sulfate, blocking the diffusion of sulfur to the active components; simultaneously, molybdenum species modify the acidity of the support surface, reducing the low-temperature deposition of ammonium bisulfate. Cobalt tetroxide, with its sulfur adsorption selectivity, converts gaseous sulfur dioxide into solid cobalt sulfide, and maintains the cleanliness of active sites through the regeneration cycle of lattice oxygen. Together, they form a "molybdenum capture - cobalt fixation" sulfur barrier layer, significantly delaying the activity decay caused by sulfur species coverage. Thirdly, the composite support improves the catalyst's mass transfer efficiency and active site dispersion through microstructural design and chemical modification. In MgO@CNTs, magnesium oxide nanoparticles are anchored to the surface of carbon nanotubes. Their alkaline sites neutralize acidic components in the flue gas, while the high conductivity of the carbon nanotubes promotes electron migration from the support to the active components, accelerating redox kinetics. The titanium-germanium composite support stabilizes the nano-dispersion of the active components through the strong metal-support interaction (SMSI effect) formed by the titanium-germanium heterolattice. Its mesoporous structure provides gas diffusion channels, shortening the path for reactants to reach the active sites. The "conductive framework-mesoporous confinement" structure of both optimizes the reaction microenvironment. Fourthly, the silicon-aluminum composite sol acts as a binder, forming a three-dimensional silicon-aluminum-oxygen network through the condensation reaction between colloidal particles. This network transforms into an inorganic ceramic binder phase during calcination, not only mechanically anchoring the active components to the support particles, but also forming Si-OM (M=Mn, Fe, Ce) covalent bonds with metal oxides on its surface with its silanol groups, enhancing interfacial bonding. At the same time, the nano-filling effect of the binder reduces catalyst pore blockage, maintaining high specific surface area and gas permeability.

[0019] The mechanism of action of the above preparation methods is as follows: The pretreatment of the support directly determines the loading efficiency of the active components. In the preparation of MgO@CNTs, the nitric acid acidification of carbon nanotubes generates carboxyl and hydroxyl groups, enhancing surface hydrophilicity and magnesium ion anchoring sites; the chelating effect of EDTA on magnesium ions delays hydrolysis and precipitation, ensuring monolayer dispersion of magnesium oxide on the carbon nanotube surface. Ball milling of the titanium-germanium support breaks the grain boundaries between titanium dioxide and germanium dioxide through mechanical alloying, forming a titanium-germanium solid solution, whose lattice strain induces more oxygen defects as nucleation sites for subsequent active components. The complexation of the metal precursor with tartaric acid is key to the uniformity of dispersion. The dicarboxyl groups of tartaric acid form five-membered ring chelates with metal ions (Mn²⁺, Fe³⁺, etc.), inhibiting particle agglomeration during calcination through steric hindrance. In the stepwise impregnation strategy, the silica-alumina sol first wets the support surface to form a hydroxylated layer, and the metal complex is then adsorbed onto the support surface through hydrogen bonding and electrostatic interactions, achieving molecular-level dispersion. The addition of polyethylene oxide prevents particle sedimentation through long-chain polymer entanglement, forming a stable suspension system. A step-by-step calcination process drives the directional generation of the active phase. In the low-temperature stage (100–300℃), physical water and tartaric acid decomposition products are mainly removed, avoiding carbon residue. In the medium-temperature stage (300–500℃), the slow heating promotes the stepwise decomposition of nitrates into oxides, while the magnesium-titanium-germanium support undergoes solid-phase diffusion with the active components, forming a mixed crystalline phase of Mn2O3-Fe2O3-CeO2. Cobalt tetroxide and molybdenum trioxide undergo crystal transformation at this temperature, and their spinel structure and the formation of layered cobalt molybdate further enhance sulfur resistance. The final multi-level porous structure of the catalyst originates from the thermally induced self-organization of the multi-components. The silica-alumina binder phase melts at 500℃ to form a glassy network, welding MgO@CNTs and the titanium-germanium support into a single unit; the active component particles grow epitaxially on the support surface, their size limited by the mesopore size of the support; and the cobalt and molybdenum oxides segregate at the grain boundaries, forming sulfur-resistant isolation bands. This "core-shell-isolation zone" micro-region distribution maximizes the exposure of active sites and inhibits sintering. In summary, this catalyst achieves denitrification under ammonia-free conditions via an "endogenous reduction" pathway: carbon monoxide in the flue gas is oxidized to carbon dioxide at the iron-manganese active sites, while the generated reactive oxygen species oxidize nitrogen oxides to nitrate intermediates; cerium dioxide promotes the decomposition of nitrates into nitrogen gas, forming a closed redox cycle. The anti-sulfur component preferentially adsorbs sulfur dioxide, blocking its contact with active sites and ensuring unobstructed reaction pathways.

[0020] Compared with the prior art, this application provides a method for preparing a low-temperature ammonia-free denitrification catalyst and its application, which has the following beneficial effects:

[0021] 1. This application uses manganese tetroxide as the main active component, combined with the oxygen storage capacity of cerium dioxide, to significantly broaden the low-temperature reaction window; the titanium-germanium composite carrier is formed with a high specific surface area structure through ball milling and spray drying, which enhances the dispersion of the active component; Mn3O4 is responsible for the initial activation of NO, Fe2O3 drives the reduction reaction, and CeO2 maintains the reaction stability. The three form a closed-loop catalytic network, and synergistically construct a low-temperature ammonia-free denitrification system of "manganese as the main oxidation - iron to provide acidity - cerium to regulate oxygen balance" to enhance efficiency;

[0022] 2. The denitrification process of this application does not require the addition of ammonia or other reducing agents, which solves the ammonia escape problem of traditional SCR technology, avoids ammonium salt blockage and equipment corrosion, and forms a redox cycle with ferric oxide and manganese tetroxide to directly catalyze the decomposition of NOx into N2; the tartaric acid complex impregnation process ensures the uniform loading of active components on the surface of the carrier and improves catalytic activity.

[0023] 3. The low-temperature ammonia-free denitrification catalyst prepared in this application still maintains high stability in sulfur-containing flue gas with SO2 ≤ 200 ppm. The sulfur-resistant additives molybdenum trioxide and cobalt tetroxide can inhibit sulfate formation. Molybdenum trioxide preferentially adsorbs SO2 and forms a reversible intermediate. Cobalt tetroxide inhibits SO3 formation through electron transfer. In addition, the basic sites of MgO in the MgO@CNTs support neutralize acidic sulfides and protect the active center.

[0024] 4. The carrier involved in this application synergistically enhances mechanical strength and catalyst lifespan. After calcination, the composite carriers MgO@CNTs and titanium-germanium composite carriers reduce the wear rate of the prepared low-temperature ammonia-free denitration catalyst and extend its lifespan. The CNTs network is fully utilized to improve the conductivity and toughness of the carrier. The titanium-germanium composite carrier is used to suppress the TiO2 phase transition through germanium doping. The OX@CMC type silicon-aluminum composite sol binder is used to enhance the overall physical structure of the low-temperature ammonia-free denitration catalyst.

[0025] 5. This application overcomes to a large extent the industry problem of difficulty in balancing activity, sulfur resistance and lifespan in low-temperature ammonia-free denitrification by optimizing the synergistic active components of Mn3O4 / Fe2O3 / CeO2, designing an anti-sulfur structure through electron transfer of MoO3 / Co3O4, functionalizing the carrier of MgO@CNTs with acid-base regulation, and preparing the process of tartaric acid complexation and step calcination. Attached Figure Description

[0026] Figure 1 This is a SEM image of the low-temperature ammonia-free denitrification catalyst prepared in Example 1 of this application;

[0027] Figure 2 This is a SEM image of the catalyst prepared in Comparative Example 1 of this application. Detailed Implementation

[0028] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0029] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit this application. They are merely used to distinguish components or operations described using the same technical terms and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions and features of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0030] Unless otherwise specified, the examples and comparative examples are parallel experiments with the same components, component content, preparation steps, and preparation parameters. The experimental methods in the following examples are conventional methods unless otherwise specified. Unless otherwise specified, the experimental materials used in the following examples are analytical reagents (AR) and were all purchased from commercial channels.

[0031] DL-tartaric acid was purchased from Sichuan Lvcheng Biotechnology Co., Ltd., CAS No.: 133-37-9, food grade; polyethylene oxide was Dow UCARFLOC 309; multi-walled carbon nanotubes (MWCNTs) were purchased from Zhejiang Yamei Nano, model: AM-C6-068-1, diameter 5-10 nm, purity 99.9%.

[0032] Example 1

[0033] This embodiment discloses a low-temperature ammonia-free denitrification catalyst, which comprises, by weight, 28 parts of active component, 12 parts of antisulfur additive, 55 parts of composite support and 5 parts of binder; the active component comprises 20 parts of manganese tetroxide, 5 parts of ferric oxide and 3 parts of cerium dioxide; the antisulfur additive comprises 8 parts of molybdenum trioxide and 4 parts of cobalt tetroxide; the composite support comprises 30 parts of MgO@CNTs and 25 parts of titanium-germanium composite support; the binder is a silicon-aluminum composite sol.

[0034] The preparation method of the MgO@CNTs includes: immersing 5 parts by weight of MWCNTs in 80 parts of HNO3, ultrasonically treating at 80℃ for 2 hours, centrifuging and washing until pH=7, and drying at 110℃ for 12 hours to obtain pretreated MWCNTs; dissolving 1 part of Mg(NO3)2·6H2O in 10 parts of deionized water, adding 3 parts of EDTA, stirring at 60℃ until completely dissolved, adding the pretreated MWCNTs, vacuum shaking and impregnating at 40℃ for 6 hours, drying at 60℃ for 12 hours, and calcining at 550℃ for 5 hours under N2 atmosphere at a rate of 2℃ / min to obtain MgO@CNTs.

[0035] The preparation method of the silicon-aluminum composite sol includes: mixing and stirring 10 parts by weight of OX@CMC-OS type and 10 parts by weight of OX@CMC-OAC type from Guozhuang New Material Technology (Jiangsu) Co., Ltd. at low speed at 40°C for 30 minutes to obtain silicon-aluminum composite sol.

[0036] A method for preparing a low-temperature ammonia-free denitrification catalyst includes the following steps:

[0037] S1. Preparation of titanium-germanium composite carrier: Titanium dioxide and germanium dioxide are added to a ball mill jar with a ball-to-material ratio of 10:1 and ball milled at 300 r / min for 120 min. The slurry after ball milling is fed into a spray drying tower with an inlet temperature of 200℃ and an outlet temperature of 90℃ to obtain a titanium-germanium composite carrier with a particle size of 5-10 μm.

[0038] S2. Preparation of supports for loaded active components and antisulfur additives: Mn(NO3)2·4H2O catalyst (equivalent to 20 parts of Mn3O4 catalyst), Fe(NO3)3·9H2O catalyst (equivalent to 5 parts of Fe2O3 catalyst), Ce(NO3)3·6H2O catalyst (equivalent to 3 parts of CeO2 catalyst), and (NH4)6Mo7O 24 ·4H2O (equivalent to 8 parts MoO3) and Co(NO3)2·6H2O (equivalent to 4 parts Co3O4) were dissolved in 500 mL of deionized water, and tartaric acid with a total molar amount of metal ions of 1.5 times was added. The mixture was stirred at 500 r / min for 120 min at 60 °C to prepare a metal tartaric acid complex solution. MgO@CNTs, titanium-germanium composite carrier and silicon-aluminum composite sol were immersed in the metal tartaric acid complex solution. 2 parts of polyethylene oxide dispersant were added at 60 °C and ultrasonically dispersed for 60 min. After standing for 12 h, a carrier loaded with active components and antisulfur additives was obtained.

[0039] S3. Preparation of low-temperature ammonia-free denitrification catalyst: Dry at 80℃ for 12h, heat from 100℃ to 300℃ at 2℃ / min, calcine at 300℃ for 1h; heat from 300℃ to 500℃ at 5℃ / min, calcine at 500℃ for 4h to obtain low-temperature ammonia-free denitrification catalyst.

[0040] The amount of hydrated precursor added during the preparation of the carriers supporting the active components and antisulfur additives is calculated based on the weight parts of the corresponding target oxides of the catalysts. Specifically, 20 parts of Mn3O4 catalyst are added with Mn(NO3)2·4H2O catalyst, 5 parts of Fe2O3 catalyst are added with Fe(NO3)3·9H2O catalyst, 3 parts of CeO2 catalyst are added with Ce(NO3)3·6H2O catalyst, and 8 parts of MoO3 are added with (NH4)6Mo7O. 24 Add 4H2O and Co(NO3)2·6H2O in 4 parts of Co3O4.

[0041] The low-temperature ammonia-free denitrification catalyst prepared in Example 1 was scanned using a scanning electron microscope, and the results are as follows: Figure 1 As shown in the image, the material is distributed in a granular structure. These particles are unevenly distributed and in contact with each other. There are obvious signs of interaction or tight surface bonding between them. This is because the silicon-aluminum composite sol used has strong adhesion, which enables the ultra-fine MgO@CNTs to be tightly bonded to the surface of the titanium-germanium composite carrier. The silicon-aluminum composite sol reacts with the hydroxyl groups on the surface of the components through silicon-oxygen-aluminum bonds and has strong temperature resistance. It is difficult to observe independent MgO@CNTs or titanium-germanium composite carriers at a large magnification.

[0042] Example 2

[0043] This embodiment discloses a low-temperature ammonia-free denitrification catalyst, which comprises, by weight, 25 parts of active component, 10 parts of antisulfur additive, 52 parts of composite carrier and 3 parts of binder; the active component comprises 19 parts of manganese tetroxide, 4 parts of ferric oxide and 2 parts of cerium dioxide; the antisulfur additive comprises 7 parts of molybdenum trioxide and 3 parts of cobalt tetroxide; the composite carrier comprises 28 parts of MgO@CNTs and 24 parts of titanium-germanium composite carrier; the binder is a silicon-aluminum composite sol, and other contents are consistent with those in Example 1.

[0044] Example 3

[0045] This embodiment discloses a low-temperature ammonia-free denitrification catalyst, which comprises, by weight, 30 parts of active component, 14 parts of antisulfur additive, 57 parts of composite support, and 8 parts of binder; the active component comprises 21 parts of manganese tetroxide, 6 parts of ferric oxide, and 3 parts of cerium dioxide; the antisulfur additive comprises 9 parts of molybdenum trioxide and 5 parts of cobalt tetroxide; the composite support comprises 32 parts of MgO@CNTs and 25 parts of titanium-germanium composite support; the binder is a silicon-aluminum composite sol, and the other contents are consistent with those in Example 1.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that the silica-alumina composite sol is replaced with an equal weight of PVA 3350 purchased from Sigma-Aldrich, otherwise the same.

[0048] The catalyst prepared in Comparative Example 1 was scanned using a scanning electron microscope, and the results are as follows: Figure 2 As shown in the image, it can be observed that MgO@CNTs and the titanium-germanium composite support are almost completely independent, with little interaction and low correlation between the substances.

[0049] Comparative Example 2

[0050] The difference from Example 1 is that it lacks an equal part by weight of MgO@CNTs, otherwise it is the same.

[0051] Comparative Example 3

[0052] The difference from Example 1 is that it lacks an equal weight of titanium-germanium composite carrier, but otherwise it is the same.

[0053] Application Example 1

[0054] The low-temperature ammonia-free denitrification catalyst prepared in Example 1 is specifically applied in industrial flue gas treatment in steel sintering machines, coke ovens, etc., where the flue gas temperature is 80-150℃, NOx concentration ≤1000mg / m³, and SO2 ≤200ppm. Specifically, the low-temperature ammonia-free denitrification catalyst is prepared as a 150×150×300mm honeycomb module and filled into the denitrification reactor at a space velocity of 20,000h⁻¹ without the need to add ammonia or other reducing agents.

[0055] Performance testing

[0056] 1. The denitrification efficiency performance of the examples and comparative examples was tested. A fixed-bed reactor was used, filled with catalyst particles, and the flue gas was simulated with NOx = 800 mg / m³ (NO is the main component), O2 = 5%, CO = 0.5% (to provide a reducing environment), N2 balance gas, and space velocity of 20,000 h⁻¹. The NOx concentration at the inlet and outlet was measured by a German M60x flue gas analyzer, and the conversion rate was calculated. The results are shown in Table 1.

[0057] Table 1

[0058] 80°C denitrification efficiency 100°C denitrification efficiency Denitrification efficiency at 150°C Example 1 68.5% 88.2% 95.2% Comparative Example 1 52.3% 75.4% 87.9% Comparative Example 2 42.1% 63.7% 82.5% Comparative Example 3 46.8% 70.2% 84.6%

[0059] As shown in Table 1, Example 1 achieved a denitrification rate of 95.2% at 150°C, significantly higher than the comparative example, demonstrating its optimal low-temperature activity. Comparative Example 1 exhibited the lowest low-temperature efficiency due to the decreased dispersion of the active components caused by weak carrier binding force.

[0060] 2. The sulfur resistance stability of the examples and comparative examples was tested. The flue gas was kept at a constant temperature of 150°C and 200 ppm SO2 was added. The denitrification efficiency was measured after one month of continuous operation. The results are shown in Table 2.

[0061] Table 2

[0062] Initial denitrification efficiency Efficiency after 1 month Example 1 95.2% 93.1% Comparative Example 1 87.9% 76.5% Comparative Example 2 82.5% 70.3% Comparative Example 3 84.6% 74.8%

[0063] As shown in Table 2, Example 1 exhibited a lower efficiency decay rate, which was attributed to the preferential adsorption mechanism of MoO3 / Co3O4 and the neutralizing effect of MgO@CNTs. Comparative Example 1 suffered structural collapse due to the poor acid resistance of the adhesive; Comparative Example 2 (lacking MgO@CNTs) lost its alkaline buffering capacity, and exhibited significant sulfur poisoning at manganese active sites.

[0064] 3. Mechanical strength test: Referring to ASTM D5757, the catalysts prepared in the examples and comparative examples were impacted in a pneumatic abrasion device at a gas velocity of 15 m / s for 30 minutes. The mass loss rate was calculated. The compressive strength of the honeycomb module (150×150×300 mm) prepared with the catalysts prepared in the examples and comparative examples was tested using the three-point bending method (Instron 5966).

[0065] Table 3

[0066] Wear rate (mass loss) Shear strength (MPa) Example 1 1.2% 43.5 Comparative Example 1 1.7% 38.6 Comparative Example 2 2.7% 32.8 Comparative Example 3 2.1% 35.2

[0067] As shown in Table 3, Example 1 exhibited the lowest wear rate and the highest shear strength, attributed to the strong adhesion of the silica-alumina sol and the tough support of MgO@CNTs. Comparative Example 1, due to the poor thermal stability of its organic binder, showed the weakest strength and wear resistance. In summary, Comparative Example 1, due to the PVA binder causing uneven dispersion and loose structure of the active components, easily led to overall performance degradation. Comparative Example 2, lacking MgO@CNTs, weakened electron conduction and sulfur resistance, resulting in decreased denitrification efficiency and accelerated sulfur poisoning. Comparative Example 3, due to the lack of a titanium-germanium support, caused the active components to sinter and aggregate, resulting in significant low-temperature activity loss. In contrast, the low-temperature ammonia-free denitrification catalyst prepared in Example 1, through the synergistic effect of its components, achieved high low-temperature activity, strong sulfur resistance, and excellent mechanical strength.

[0068] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. If such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for preparing a low-temperature ammonia-free denitrification catalyst, characterized in that, Includes the following steps: S1. Preparation of titanium-germanium composite carrier; S2. Preparation of a carrier loaded with active components and anti-sulfur additives: The precursors of the active components and anti-sulfur additives are complexed with tartaric acid to obtain a metal tartaric acid complex solution. The composite carrier and binder are immersed in the metal tartaric acid complex solution and ultrasonically dispersed. S3. A low-temperature ammonia-free denitrification catalyst was obtained by drying and calcining. The active components include manganese tetroxide, ferric oxide, and cerium dioxide; the antisulfur additives include molybdenum trioxide and cobalt tetroxide; the composite carrier includes MgO@CNTs and a titanium-germanium composite carrier; and the binder is a silicon-aluminum composite sol. The titanium-germanium composite carrier has a titanium-germanium heterostructure.

2. The preparation method according to claim 1, characterized in that, The method for preparing titanium-germanium composite carriers includes ball milling titanium dioxide and germanium dioxide for 120 min and then spray drying them in a spray drying tower to obtain titanium-germanium composite carriers.

3. The preparation method according to claim 2, characterized in that, Titanium dioxide and germanium dioxide were added to a ball mill jar with a ball-to-material ratio of 10:1 and ball-milled at 300 r / min for 120 min. The slurry after ball milling was fed into a spray drying tower with an inlet temperature of 200℃ and an outlet temperature of 90℃ to obtain a titanium-germanium composite carrier with a particle size of 5-10 μm.

4. The preparation method according to claim 1, characterized in that, Combine Mn(NO3)2·4H2O, Fe(NO3)3·9H2O, Ce(NO3)3·6H2O, (NH4)6Mo7O 24 Dissolve 4H2O and Co(NO3)2·6H2O in deionized water, add tartaric acid in 1.5 times the total molar amount of metal ions, and stir at 500 r / min for 120 min at 60℃ to prepare a metal tartaric acid complex solution.

5. The preparation method according to claim 1, characterized in that, MgO@CNTs, titanium-germanium composite carrier and silicon-aluminum composite sol were immersed in a metal tartaric acid complex solution, and 2 parts of polyethylene oxide dispersant were added at 60℃ and ultrasonically dispersed for 60 min. After standing for 12 h, a carrier loaded with active components and anti-sulfur additives was obtained.

6. The preparation method according to claim 1, characterized in that, The support loaded with active components and anti-sulfur additives was dried at 80℃ for 12h, heated from 100℃ to 300℃ at 2℃ / min, calcined at 300℃ for 1h, heated from 300℃ to 500℃ at 5℃ / min, and calcined at 500℃ for 4h to obtain a low-temperature ammonia-free denitrification catalyst.

7. The preparation method according to claim 1, characterized in that, The preparation method of the MgO@CNTs includes: immersing 5 parts by weight of MWCNTs in 80 parts of HNO3, ultrasonically treating at 80°C for 2 hours, centrifuging and washing, and drying at 110°C for 12 hours to obtain pretreated MWCNTs; dissolving 1 part of Mg(NO3)2·6H2O in 10 parts of deionized water, adding 3 parts of EDTA, stirring and adding the pretreated MWCNTs at 60°C, impregnating under vacuum at 40°C for 6 hours, drying at 60°C for 12 hours, and calcining at 550°C for 5 hours under N2 atmosphere at a rate of 2°C / min to obtain MgO@CNTs.

8. The preparation method according to claim 1, characterized in that, The low-temperature ammonia-free denitrification catalyst prepared by the above preparation method comprises, by weight, 25-30 parts of active component, 10-14 parts of anti-sulfur additive, 52-57 parts of composite carrier and 3-8 parts of binder.

9. The application of a low-temperature ammonia-free denitrification catalyst prepared by any one of claims 1-8 in industrial flue gas denitrification, characterized in that, The low-temperature ammonia-free denitrification catalyst is suitable for low-temperature environments of 80-150℃, with NOx concentration in flue gas ≤1000mg / m³ and SO2 ≤200ppm.

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