A method for preparing a catalyst for the oxidation of sulfur dioxide modified with rubidium salt

Abstract

This application provides a method for preparing a rubidium salt-modified sulfur dioxide oxidation catalyst, comprising the following steps: S1, providing diatomaceous earth, silica, sodium sulfate, a forming agent, vanadium pentoxide, caustic alkali, silicate, and rubidium sulfate; S2, adding vanadium pentoxide and rubidium sulfate to an aqueous solution of caustic alkali, whereby vanadium pentoxide dissolves under alkaline conditions to form a soluble vanadate or metavanadate complex system, followed by adding an aqueous sulfuric acid solution to adjust the pH value, ensuring the vanadate system remains stable in the solution, and then adding silicate to obtain a first solution; S3, mixing diatomaceous earth, silica, sodium sulfate, and the forming agent uniformly to obtain a dry base material, adding it to the first solution and mixing, then kneading, shaping, drying, and calcining to obtain the finished catalyst. This application can improve the activity of vanadium catalysts at low temperatures and enhance the catalyst strength.

Description

Technical Field

[0001] This application relates to the field of vanadium catalyst technology, specifically to a method for preparing a rubidium salt modified sulfur dioxide oxidation catalyst. Background Technology

[0002] Sulfuric acid is a strong inorganic acid that reacts with most metals. It is an important industrial raw material, often called the "mother of the chemical industry," and is used in the manufacture of fertilizers, pharmaceuticals, explosives, pigments, detergents, and batteries. It is also widely used in petroleum purification, metal smelting, and dye industries. Industrially, sulfuric acid production primarily uses the contact process, which mainly consists of three stages: roasting pyrite or burning sulfur to produce SO2; oxidizing SO2 to SO3 under vanadium catalyst; and absorbing SO3 with 98.3% concentrated H2SO4 to obtain fuming sulfuric acid, which is then adjusted to 98% concentration with dilute acid to obtain the final product.

[0003] Vanadium catalysts are comprehensive catalytic systems using diatomaceous earth as a support, vanadium pentoxide as the active component, and alkali metal sulfates as co-catalysts. Since the catalytic oxidation of sulfur dioxide to sulfur trioxide is an exothermic reaction, and the equilibrium constant decreases with increasing temperature, highly active, low-temperature catalysts are preferred to improve the overall conversion rate of sulfur dioxide.

[0004] In existing technologies, cesium hydroxide is typically added to enhance the activity of highly active low-temperature vanadium catalysts in the low-temperature range. However, cesium hydroxide is extremely corrosive and hygroscopic, requiring strict special protection and equipment during its preparation, storage, and feeding. This increases the complexity and hazard of the process, necessitating special neutralization and post-processing steps, and increasing economic investment. Furthermore, cesium is generally considered to have high biotoxicity, which is inconsistent with current green and environmentally friendly trends. Therefore, finding a material to replace cesium hydroxide is essential. Summary of the Invention

[0005] This application provides a method for preparing a rubidium salt modified sulfur dioxide oxidation catalyst. The catalyst is modified with rubidium sulfate and combined with silicate, so that the strength of the catalyst is significantly improved after calcination and the activity at low temperature is also significantly improved without rapid degradation.

[0006] In a first aspect, this application provides a method for preparing a rubidium salt-modified sulfur dioxide oxidation catalyst, comprising the following steps: S1. Provide 100 parts by weight of diatomaceous earth, 5-8 parts by weight of silica, 8-11 parts by weight of sodium sulfate, 4-8 parts by weight of forming agent, 10-15 parts by weight of vanadium pentoxide, 20-30 parts by weight of caustic alkali, 4-8 parts by weight of silicate, and 0.5-50 parts by weight of rubidium sulfate. S2. Vanadium pentoxide and rubidium sulfate are added to an aqueous solution of caustic alkali. Vanadium pentoxide dissolves under alkaline conditions to form a soluble vanadate or metavanadate complex system. Then, sulfuric acid aqueous solution is added to adjust the pH value so that the vanadate system exists stably in the solution. Silicate is then added to obtain the first solution. S3. Mix diatomaceous earth, fumed silica, sodium sulfate and forming agent evenly to obtain dry base material, add to the first solution and mix, then knead, shape, dry and calcine to obtain the catalyst product.

[0007] According to this application, the catalyst uses diatomaceous earth as the main carrier, providing a porous framework structure and basic mechanical strength; vanadium pentoxide is the main active component, providing the redox active centers required for sulfur dioxide oxidation; caustic alkali is used to dissolve and activate vanadium pentoxide, forming a uniformly dispersed vanadate system, and controlling the acid-base environment during the preparation process; rubidium sulfate, at high temperature, synergistically forms a low-melting-point vanadium sulfate active phase with vanadium pentoxide and sulfates in the system, significantly reducing the catalyst's ignition temperature and improving its low-temperature reactivity; sodium sulfate participates in the sulfate phase construction at calcination and reaction temperatures, while improving the plasticity and molding performance of the wet material; a molding agent is used to improve the molding operability and initial strength of the wet material; silica, as a high specific surface area silica phase, is used to refine the pore structure, improve the dispersibility of vanadium pentoxide, and undertake the process control function of catalyst appearance color; silicates are added during the solution preparation stage, and the silicates are transformed into a highly dispersed silicon-oxygen structural phase, playing an interfacial anchoring and spatial confinement role for the low-melting-point molten salt active phase, thereby ensuring the structural stability and mechanical strength of the catalyst.

[0008] Specifically, in this catalyst system, rubidium sulfate is introduced through the use of Rb. + A low-melting-point vanadium sulfate active phase is formed, significantly increasing the SO2 oxidation rate at low temperatures. Meanwhile, silicates, uniformly mixed with vanadium and rubidium, precipitate in situ during calcination, forming a highly dispersed silica-oxygen network. This network, unlike the porous framework provided by diatomaceous earth, interpenetrates and couples with the low-melting-point active phase. On one hand, it anchors and spatially confines the active phase, inhibiting its migration and aggregation at high temperatures, thus ensuring the long-term dispersion of the active phase and sustained low-temperature activity. On the other hand, by precisely controlling the silicate content, shrinkage stress during drying and calcination can be effectively adjusted, preventing macroscopic cracks in the catalyst and ensuring its complete particle morphology and excellent mechanical strength. Therefore, silicates are both a structural enhancer for the stable performance of the rubidium sulfate active phase and a key process factor for ensuring the complete formation and strength of the catalyst, ultimately achieving a simultaneous improvement in low-temperature activity and mechanical strength.

[0009] The preparation method involves adding vanadium pentoxide to a caustic alkaline aqueous solution, causing the vanadium pentoxide to dissolve under alkaline conditions and transform into a soluble vanadate system mainly composed of metavanadate and polyvanadate. Simultaneously, rubidium sulfate is introduced as a rubidium source, ensuring that rubidium ions are uniformly dispersed in the vanadate solution. This guarantees the formation of the rubidium precursor required for the low-melting-point vanadium sulfate active phase during subsequent acidification and calcination. Subsequently, sulfuric acid solution is slowly added to neutralize and adjust the system, maintaining the pH at 2-4. This acidic environment prevents vanadate precipitation. Silicate is added to this acidic vanadium-rubidium mixed solution under continuous stirring; that is, the silicate must be mixed with the vanadium and rubidium components during the solution stage, rather than being simply added to the dry base later. This is because silicates can generate highly active silica species in acidic vanadium and rubidium-containing environments, achieving uniform blending and mutual coupling with vanadium and rubidium ions at the molecular scale, forming a highly dispersed first solution containing vanadium, rubidium, and silicon components. If silicates are added later than when they are mixed with dry base materials, this molecular-level coupling derived from solution blending cannot be achieved. The silicon-oxygen network formed after calcination will be independent of the active phase and will be difficult to play an anchoring and reinforcing role on the active phase. Diatomaceous earth, silica, sodium sulfate, and a forming agent are pre-mixed to obtain a dry base material, which is then thoroughly mixed with the first solution to ensure that the active components and additives are uniformly loaded onto the surface and pores of the support. Subsequently, through kneading, shaping, drying, and calcination, vanadium oxide species and rubidium salts form a stable low-melting-point vanadium sulfate active phase on the support surface. Simultaneously, during calcination, silicates are transformed into a highly dispersed silica-oxygen structural phase—originating from silicate precursors blended at the molecular level in the solution stage. During calcination, these precursors precipitate in situ, forming a secondary silica-oxygen network that interpenetrates with the active phase. This network differs from the macroscopic porous framework provided by diatomaceous earth itself; it forms an interfacial coupling structure with the low-melting-point active phase at the nanoscale. This network, on the one hand, spatially confines and anchors the low-melting-point active phase, inhibiting the migration and aggregation of molten salt at high temperatures, thus ensuring the long-term dispersion of the active phase and the sustained performance of its low-temperature activity. On the other hand, by precisely controlling the silicate content, the shrinkage stress during the drying and calcination process can be effectively adjusted, ensuring that the catalyst possesses a complete particle morphology and excellent mechanical strength. Sodium sulfate participates in the construction of the sulfate phase and improves the plasticity of the dry base material, the forming agent ensures the workability and initial strength of the wet material, and silica independently undertakes the process functions of refining the pore structure, improving the dispersibility of active components and regulating the appearance color, ultimately resulting in a catalyst with high activity, low ignition temperature, high mechanical strength and long-term structural stability.

[0010] Compared with existing methods for preparing vanadium-based sulfur dioxide oxidation catalysts using cesium hydroxide as an additive, this application differs fundamentally in the form of additive introduction and the mechanism of active phase construction. In existing technologies, cesium hydroxide participates in the system as a strong base, requiring an in-situ conversion from hydroxide to sulfate during vanadium water preparation and subsequent acidification. This conversion process is significantly affected by the neutralization rate, local acid-base environment, and mass transfer conditions, easily leading to uneven distribution of cesium salts in the support and fluctuations in the composition of the active phase. In contrast, this application directly uses rubidium sulfate as the rubidium source, eliminating the need for anion conversion during preparation. Rubidium ions can be uniformly introduced into the vanadate system and directly participate in the construction of a stable low-melting-point vanadium-based sulfate active phase under calcination and reaction conditions, thereby significantly reducing the ignition temperature and improving the reactivity. Furthermore, this application introduces a silicate precursor into the vanadium salt system at the solution stage after pH adjustment, enabling it to be molecularly blended with vanadium and rubidium components. This results in the formation of a highly dispersed secondary silica-oxygen network in situ during calcination, which interpenetrates with the active phase. This network, together with the diatomite framework, constitutes a continuous three-dimensional structure. It not only effectively confines the low-melting-point molten salt active phase and anchors the interface, inhibiting the migration and aggregation of the active phase, but also ensures that no macroscopic cracks are generated in the catalyst during the drying and calcination process by precisely controlling the silicate content. This simultaneously achieves high activity, high mechanical strength, and high yield.

[0011] In some implementations, step S3 includes the following steps: S3-1. After mixing diatomaceous earth, fumed silica, sodium sulfate, and molding agent evenly, a dry base material is obtained. 50% of the first solution is then mixed with the dry base material to obtain a preliminary mixture. S3-2. Add the remaining 50% of the vanadium-containing first solution to the initial mixture and continue mixing. Then knead, shape, dry, and calcine to obtain the finished catalyst.

[0012] In some of the aforementioned methods, the active components are introduced and uniformly dispersed by adding the first solution to the dry base material in two stages. Specifically, diatomaceous earth, silica, sodium sulfate, and a forming agent are first mixed to form a dry base material, and 50% of the first solution is introduced for preliminary mixing. This allows vanadate, rubidium salt, and silicate to preferentially wet the carrier surface and pore structure, forming a uniform initial mixture. Subsequently, the remaining 50% of the vanadium-containing homogeneous solution is added to the initial mixture. During the continuous mixing process, the active components are further replenished, allowing the solution to gradually distribute and penetrate into the particles at the formed carrier-active component interface, thereby avoiding local enrichment or agglomeration caused by a single addition of liquid.

[0013] In some embodiments, a method for preparing a rubidium salt-modified sulfur dioxide oxidation catalyst includes the following steps: S1. Provide 100 parts by weight of diatomaceous earth, 5-8 parts by weight of silica, 8-11 parts by weight of sodium sulfate, 4-8 parts by weight of forming agent, 10-15 parts by weight of vanadium pentoxide, 20-30 parts by weight of caustic alkali, 4-8 parts by weight of silicate, and 0.5-50 parts by weight of rubidium sulfate. S2. Dissolve the caustic alkali in deionized water, add vanadium pentoxide and rubidium sulfate to the caustic alkali solution to dissolve, then add sulfuric acid solution to neutralize the pH to 2-6, and then add 4-8 parts of silicate to dissolve to obtain the first solution; S3-1. Mix diatomaceous earth, fumed silica, sodium sulfate and molding agent evenly to obtain dry base material. Take 50% of the first solution and stir and mix it with the dry base material for 3-5 minutes to obtain the initial mixture. S3-2. Add the remaining 50% of the first solution to the initial mixture and continue stirring and mixing for 3-5 minutes. Then knead and shape the mixture, dry it at 80-100℃ for 30-60 minutes, and then calcine it at 450-600℃ for 30-60 minutes to obtain the catalyst product.

[0014] The above methods specifically illustrate the reaction conditions and dosage ratios of each step in the preparation of rubidium salt-modified sulfur dioxide oxidation catalysts, under which rubidium salt-modified sulfur dioxide oxidation catalysts can be obtained.

[0015] In some embodiments, the mass concentration of the sulfuric acid aqueous solution is 50-60%.

[0016] In some of the methods mentioned above, the amount of water introduced into the entire system is more suitable for subsequent mixing and molding after adjusting the pH value of the sulfuric acid aqueous solution within this range to 2-6.

[0017] In some embodiments, the amount of rubidium sulfate used is 4 to 8 parts.

[0018] In some of the methods mentioned above, the amount of rubidium sulfate used within this range can balance the improvement of low-temperature activity and mechanical strength.

[0019] In some embodiments, the molding agent is any one of cellulose and methylcellulose, the caustic alkali is any one of sodium hydroxide and potassium hydroxide, and the silicate is any one of lithium silicate, sodium silicate, potassium silicate, and cesium silicate.

[0020] In some of the aforementioned methods, cellulose or methylcellulose molding agents, by regulating the viscosity of the wet material and the initial strength of the preform, not only ensure smooth catalyst molding but also contribute to the formation of a uniform, stable catalyst pore structure with high activity and good mechanical strength after calcination. Through strong basic coordination-complexation and acid-base reactions, sparingly soluble metal oxides are converted into soluble anionic salts, thereby achieving homogenization and dispersion. The alkali metal ions contained in the silicic acid used can partially enter the low-melting-point vanadium sulfate active phase, adjusting the lattice and electronic environment of the active phase, and lowering its formation and ignition temperatures. Meanwhile, considering industrial production costs, lithium silicate, sodium silicate, and potassium silicate should be given priority, as the preparation or purchase cost of cesium silicate is too high.

[0021] In some embodiments, the rubidium sulfate has a purity of ≥98%.

[0022] In some of the methods described above, rubidium sulfate within this purity range can ensure a sufficient supply of rubidium ions while reducing the introduction of impurities, thus ensuring that the performance of the catalyst is not affected.

[0023] In some embodiments, the specific surface area of ​​the silica is 160~200m². 2 / g.

[0024] In some of the aforementioned methods, when the specific surface area is within this range, silica can provide sufficient surface hydroxyl groups and a high external specific surface area, enabling vanadium pentoxide, rubidium salts, and silicate precursors to achieve uniform adsorption and dispersion during mixing and impregnation. This refines the size of the active phase and shortens the mass transfer path of the reactants, thereby improving the catalytic activity in the low-temperature range. At the same time, moderate pore volume and framework strength are beneficial for constructing a dense and continuous silicon-oxygen network structure together with diatomaceous earth and silicates, enhancing the interparticle bonding force and compressive strength. If the specific surface area is too low, the dispersion will be insufficient and the activity utilization rate will decrease; if it is too high, it will easily lead to excessive liquid absorption, loose structure, and decreased molding strength.

[0025] In some embodiments, the silica content of the diatomaceous earth is ≥85wt%.

[0026] In some of the above methods, using diatomaceous earth with a SiO2 content of more than 85 wt% can ensure that the support has high chemical inertness, high porosity and good thermal stability. This avoids the formation of inert secondary phases between impurities and vanadium active species, which would lead to deactivation. It also facilitates the uniform dispersion and stable loading of vanadium and rubidium salts, thereby ensuring the catalyst activity and service life.

[0027] In a second aspect, this application provides a rubidium salt modified sulfur dioxide oxidation catalyst, prepared according to any embodiment of the first aspect.

[0028] According to this application, a rubidium salt modified sulfur dioxide oxidation catalyst replaces cesium in the prior art with rubidium, which not only ensures the activity of the catalyst in the low-temperature stage, but also reduces the complexity and danger of the process. At the same time, by adding silicate in the solution stage, the low-temperature activity of the catalyst is further improved, ensuring the structural stability and mechanical strength of the catalyst.

[0029] Compared with the prior art, the beneficial effects of this application are at least as follows: This application introduces rubidium sulfate into a vanadium-based active system, enabling rubidium ions to synergistically construct a low-melting-point vanadium-based sulfate active phase with vanadium oxide species and sulfate. This significantly reduces the formation temperature and operating temperature range of the active phase, allowing the catalyst to achieve higher oxygen transfer capacity and reaction rate at lower temperatures. Consequently, it effectively reduces the ignition temperature of the catalyst and improves the activity of the sulfur dioxide oxidation reaction. This application introduces silicate components during solution preparation. The silicate is uniformly mixed with vanadium and rubidium species in the solution stage and precipitates in situ during calcination, forming a highly dispersed silicon-oxygen network. The low-melting-point active phase constructed from silicate and rubidium sulfate forms an interpenetrating, interfacially coupled composite structure: the active phase is uniformly loaded on the surface of this network and penetrates its structural gaps, while the network spatially confines and disperses the active phase. This "in-situ precipitation network" derived from solution blending exhibits far superior dispersion uniformity and contact interface with the active phase compared to the macroscopic framework provided by diatomaceous earth itself, thus more effectively inhibiting the migration and aggregation of the active phase and fully realizing the low-temperature activity potential of rubidium sulfate. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] Figure 1 This is a self-made activity evaluation device; Figure 2 A comparison of the appearance of the samples from Example 1 and Comparative Example 4; Figure 3 A comparison of the appearance of the samples from Example 1 and Comparative Example 7; Figure 4 The XPS full spectrum of the rubidium salt modified sulfur dioxide oxidation catalyst prepared in Example 1 of this application is shown below. Figure 5 This is the XPS 3d scan of the rubidium salt modified sulfur dioxide oxidation catalyst prepared in Example 1 of this application. Detailed Implementation

[0032] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0033] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0036] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be applied in accordance with the techniques or conditions described in the literature in the art or in accordance with... Please refer to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available standard products.

[0037] Diatomaceous earth: SiO2 content 86wt%; Silica: Specific surface area 189m² 2 / g; Sodium sulfate: 99.9% purity, 90 mesh particle size; Rubidium sulfate: purity 98.5%; Cellulose: Average degree of polymerization 1500.

[0038] Example 1 Catalyst preparation: Dissolve 25 parts of potassium hydroxide in 65 parts of deionized water. Add 12 parts of vanadium pentoxide and 6 parts of rubidium sulfate to the potassium hydroxide aqueous solution and stir until completely dissolved. Then add 50 wt% sulfuric acid aqueous solution to neutralize the pH value to 4. Add 6 parts of potassium silicate to dissolve and obtain the first solution. Mix 100 parts diatomaceous earth, 6 parts fumed silica, 10 parts sodium sulfate, and 6 parts cellulose evenly to obtain a dry base material. Take 50% of the first solution and stir and mix it with the dry base material for 5 minutes to obtain a preliminary mixture. Add the remaining 50% of the first solution to the initial mixture and continue stirring for 5 minutes to obtain the mixture. Add the mixture to a kneader at 90°C and knead under negative pressure for 5 minutes to obtain the wet material. The wet material is added to an extruder, extruded and then dried in a 90°C oven. Finally, it is calcined at 500°C for 45 minutes to obtain the catalyst product.

[0039] The XPS full spectrum and Rd 3d scan of the above rubidium salt modified sulfur dioxide oxidation catalyst are shown below. Figures 4-5 As shown, this indicates that rubidium is effectively loaded onto the catalyst.

[0040] Comparative Example 1 Catalyst preparation: It is largely the same as Example 1, except that rubidium sulfate is replaced with an equimolar amount of cesium hydroxide.

[0041] Comparative Example 2 Catalyst preparation: It is largely the same as Example 1, except that rubidium sulfate is replaced with an equimolar amount of potassium sulfate.

[0042] Comparative Example 3 Catalyst preparation: It is largely the same as Example 1, except that potassium silicate is replaced with an equal mass of silica sol.

[0043] Comparative Example 4 Catalyst preparation: It is largely the same as Example 1, except that potassium silicate is replaced with an equimolar amount of potassium sulfate.

[0044] Comparative Example 5 Catalyst preparation: It is largely the same as Example 1, except that potassium silicate is replaced with an equimolar amount of lithium silicate.

[0045] Comparative Example 6 Catalyst preparation: It is largely the same as Example 1, except that potassium silicate is replaced with an equimolar amount of sodium silicate.

[0046] Comparative Example 7 Catalyst preparation: Dissolve 25 parts of potassium hydroxide in 65 parts of deionized water, add 12 parts of vanadium pentoxide and 6 parts of rubidium sulfate to the potassium hydroxide aqueous solution and stir until completely dissolved, then add 50 wt% sulfuric acid aqueous solution to neutralize the pH to 4 to obtain the first solution; Mix 100 parts diatomaceous earth, 6 parts fumed silica, 10 parts sodium sulfate, 6 parts cellulose, and 6 parts potassium silicate evenly to obtain a dry base material. Take 50% of the first solution and stir and mix it with the dry base material for 5 minutes to obtain a preliminary mixture. Add the remaining 50% of the first solution to the initial mixture and continue stirring for 5 minutes to obtain the mixture. Add the mixture to a kneader at 90°C and knead under negative pressure for 5 minutes to obtain the wet material. The wet material is added to an extruder, extruded and then dried in a 90°C oven. Finally, it is calcined at 500°C for 45 minutes to obtain the catalyst product.

[0047] Test section Sample preparation: The catalysts obtained in Example 1 and Comparative Examples 1 to 5 were processed into particles with both ends ground flat and a length of 6 mm to 7 mm, with 40 particles per group.

[0048] Activity testing: Following the methods specified in the Chinese chemical industry standard "HG / T 2089-2014 Experimental Method for Activity of Catalysts for the Oxidation of Sulfur Dioxide to Sulfuric Acid", the catalysts prepared in Example 1 and Comparative Examples 1-5 were tested using a self-made activity evaluation device (the evaluation device described in "HG / T 2089-2014 Experimental Method for Activity of Catalysts for the Oxidation of Sulfur Dioxide to Sulfuric Acid", such as...). Figure 1 Activity testing was conducted on the reactor (as shown). The solid catalyst was loaded into the reactor, and after confirming there were no leaks, the switch was turned on to begin the experiment. The temperature was initially increased at a rate of 3°C per minute. After 60 minutes, dry air was introduced, with the space velocity controlled at approximately 3600 h⁻¹. -1 After another 45 minutes, high-purity sulfur dioxide was introduced, controlling the sulfur dioxide volume fraction to approximately 10%. The temperature was then increased to 600℃ at a rate of 3℃ per minute for 5 hours. After reaching the heat resistance time, the temperature was decreased to the activation temperature of 350℃ at a rate of 200℃ / h and stabilized for 1 hour. The concentrations of SO2 at the inlet and outlet were measured using iodometric titration at 350℃. Finally, the conversion rate (E) of SO2 at 350℃ was calculated using the following formula, where φ1 is the SO2 inlet volume fraction and φ2 is the SO2 outlet volume fraction. The experimental results are shown in Table 1.

[0049]

[0050] Strength test: Following the method specified in the Chinese chemical industry standard "HG / T2782 Determination of Crushing Resistance of Fertilizer Catalyst Particles", individual catalyst particles were taken, and their surface quality was visually inspected. Catalysts with cracks on their surface were directly deemed unqualified and did not require further testing. Catalysts without cracks were placed on an intelligent strength particle testing machine, the machine was turned on, and the pressure was gradually increased until the particles broke. Ten sets of tests were conducted for each technical scheme, and the average score was taken. The test results are shown in Table 1.

[0051] Table 1

[0052] Comparing Example 1 and Comparative Example 1, it can be seen that replacing rubidium sulfate with an equimolar amount of cesium hydroxide slightly decreases the low-temperature activity of the catalyst, while the decrease in compressive strength is very small. The comparative results show that rubidium sulfate, as a rubidium source, can directly introduce rubidium ions during the preparation process and uniformly disperse them in the vanadate system. After calcination, it forms a more uniformly distributed low-melting-point vanadium sulfate active phase, thus achieving slightly better low-temperature activity. Although cesium hydroxide can also provide alkali metal ions to construct the active phase, it needs to undergo an in-situ transformation from hydroxide to sulfate during the preparation process. This transformation process is greatly affected by the neutralization rate and the local acid-base environment, which easily results in a slightly less uniform distribution of cesium salts compared to the rubidium sulfate system, thus slightly reducing the activity.

[0053] Comparing Example 1 and Comparative Example 2, it is evident that replacing rubidium sulfate with an equimolar amount of potassium sulfate significantly reduced the catalyst's low-temperature activity, while the compressive strength remained relatively stable. This indicates that rubidium ions play an irreplaceable role in constructing the active phase of low-melting-point vanadium-based sulfates.

[0054] As shown in Example 1 and Comparative Example 3, replacing potassium silicate with an equal mass of silica sol significantly reduced the low-temperature activity and compressive strength of the catalyst, while no obvious cracks appeared. This comparative result indicates that the form of the silicon source has a decisive influence on the catalyst performance. Although the silica sol used in Comparative Example 3 can provide silicon dioxide and form a certain silicon-oxygen framework after calcination, maintaining the basic integrity of the particles and preventing cracks, it cannot deeply couple with the vanadium-rubidium system during preparation like potassium silicate. The silicon-oxygen network formed after calcination lacks effective interfacial interaction with the low-melting-point active phase, making it difficult to fully anchor and confine the active phase. This leads to migration and aggregation of the active phase, a reduction in active sites, and a decrease in low-temperature activity. At the same time, the silica sol experiences significant drying shrinkage, resulting in a less dense framework structure and a corresponding decrease in mechanical strength.

[0055] As can be seen from Example 1 and Comparative Example 4, replacing potassium silicate with an equimolar amount of potassium sulfate resulted in a decrease in the low-temperature activity of the catalyst, and as... Figure 2As shown, the catalyst exhibits obvious cracks and does not meet basic production standards, therefore mechanical strength testing is unnecessary. This comparative result demonstrates that potassium silicate plays an irreplaceable dual role in this invention—the silicon-oxygen network it transforms into serves both as an interfacial anchoring structure for the rubidium sulfate active phase and as a skeletal support for regulating drying and calcination shrinkage stress and ensuring the catalyst's intact formation.

[0056] As shown in Examples 1 and Comparative Examples 5-6, replacing potassium silicate with equimolar amounts of lithium silicate and sodium silicate did not significantly alter the mechanical strength of the catalyst, but resulted in varying degrees of decrease in low-temperature activity. This is because, although both lithium silicate and sodium silicate are soluble silicates that can be blended with the vanadium-rubidium system in solution and form a silicon-oxygen network after calcination, their cation types have a significant impact on catalyst activity. Lithium ions have a small radius and poor compatibility with the vanadium system, resulting in insufficient uniformity of the formed active phase. Sodium ions have better compatibility than lithium but still inferior to potassium, and their active phase composition is still less desirable than that of the potassium system.

[0057] As can be seen from Example 1 and Comparative Example 7, when the timing of adding potassium silicate is changed from the solution stage to the dry-based mixing stage, the low-temperature activity of the catalyst decreases significantly, and at the same time... Figure 3 As shown, microcracks appeared on the surface, which did not meet the basic production standards, so mechanical strength testing was not necessary. This comparative result indicates that potassium silicate must achieve molecular-level blending with the vanadium and rubidium system in the solution stage in order to form a coupled network that interpenetrates with the low-melting-point active phase after calcination. Only then can silicate anchor the active phase, inhibit its migration and agglomeration to ensure high activity, and uniformly regulate drying shrinkage stress to avoid crack formation and ensure high strength. However, simply physically mixing potassium silicate in Comparative Example 7 with the dry base material may have the same effect as raw materials such as diatomaceous earth and silica, failing to achieve interfacial coupling, resulting in insufficient anchoring of the active phase, uneven stress regulation, and overall deterioration of performance.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a rubidium salt-modified sulfur dioxide oxidation catalyst, characterized in that, Includes the following steps: S1. Provide 100 parts by weight of diatomaceous earth, 5-8 parts by weight of silica, 8-11 parts by weight of sodium sulfate, 4-8 parts by weight of forming agent, 10-15 parts by weight of vanadium pentoxide, 20-30 parts by weight of caustic alkali, 4-8 parts by weight of silicate, and 0.5-50 parts by weight of rubidium sulfate. S2. Vanadium pentoxide and rubidium sulfate are added to an aqueous solution of caustic alkali. Vanadium pentoxide dissolves under alkaline conditions to form a soluble vanadate or metavanadate complex system. Then, sulfuric acid aqueous solution is added to adjust the pH value so that the vanadate system exists stably in the solution. Silicate is then added to obtain the first solution. S3. Mix diatomaceous earth, fumed silica, sodium sulfate and forming agent evenly to obtain dry base material, add to the first solution and mix, then knead, shape, dry and calcine to obtain the finished catalyst.

2. The preparation method according to claim 1, characterized in that, S3 includes the following steps: S3-1. After mixing diatomaceous earth, fumed silica, sodium sulfate, and molding agent evenly, a dry base material is obtained. 50% of the first solution is then mixed with the dry base material to obtain a preliminary mixture. S3-2. Add the remaining 50% of the first solution to the initial mixture and continue mixing. Then knead, shape, dry, and calcine to obtain the finished catalyst.

3. The preparation method according to claim 2, characterized in that, Includes the following steps: S1. Provide 100 parts by weight of diatomaceous earth, 5-8 parts by weight of silica, 8-11 parts by weight of sodium sulfate, 4-8 parts by weight of forming agent, 10-15 parts by weight of vanadium pentoxide, 20-30 parts by weight of caustic alkali, 4-8 parts by weight of silicate, and 0.5-50 parts by weight of rubidium sulfate. S2. Dissolve the caustic alkali in deionized water, add vanadium pentoxide and rubidium sulfate to the caustic alkali solution to dissolve, then add sulfuric acid solution to neutralize the pH to 2-6, and then add 4-8 parts of silicate to dissolve to obtain the first solution; S3-1. Mix diatomaceous earth, fumed silica, sodium sulfate and molding agent evenly to obtain dry base material. Take 50% of the first solution and stir and mix it with the dry base material for 3-5 minutes to obtain the initial mixture. S3-2. Add the remaining 50% of the first solution to the initial mixture and continue stirring and mixing for 3-5 minutes. Then knead and shape the mixture, dry it at 80-100℃ for 30-60 minutes, and then calcine it at 450-600℃ for 30-60 minutes to obtain the catalyst product.

4. The preparation method according to claim 3, characterized in that, The mass concentration of the sulfuric acid aqueous solution is 50-60%.

5. The preparation method according to claim 1, characterized in that, The amount of rubidium sulfate used is 4 to 8 parts.

6. The preparation method according to claim 1, characterized in that, The molding agent is any one of cellulose and methylcellulose, the caustic alkali is any one of sodium hydroxide and potassium hydroxide, and the silicate is any one of lithium silicate, sodium silicate, potassium silicate, and cesium silicate.

7. The preparation method according to claim 1, characterized in that, The purity of the rubidium sulfate is ≥98%.

8. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the silica is 160~200 m². 2 / g.

9. The preparation method according to claim 1, characterized in that, The silica content of the diatomaceous earth is ≥85wt%.

10. A rubidium salt-modified sulfur dioxide oxidation catalyst, characterized in that, The preparation method according to any one of claims 1 to 9 is used.

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