Vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation as well as preparation method and application of vanadium-molybdenum composite catalyst

Abstract

The invention relates to the technical field of industrial catalysis and flue gas treatment, in particular to a vanadium-molybdenum composite catalyst for catalytically oxidizing SO2 into SO3 under a wet process condition as well as a preparation method and application of the vanadium-molybdenum composite catalyst. According to the catalyst, V2O5 and MoO3 are used as composite active components and are preferably loaded on a carrier subjected to hydrophobic modification, and by constructing a V-O-Mo bonded active phase structure and utilizing the electronic modulation effect and hydrophobic characteristic of MoO3 on V2O5, the activity, stability and poisoning resistance of the catalyst under the conditions of high humidity and low temperature are remarkably improved. The catalyst is especially suitable for efficient conversion and resource recovery of SO2 in industrial flue gas containing a large amount of water vapor.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalyst preparation and air pollution control technology, specifically relating to a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation, its preparation method, and its application. Background Technology

[0002] Sulfur dioxide (SO2) is one of the major air pollutants, primarily originating from the combustion of fossil fuels, non-ferrous metal smelting, and various chemical production processes. Catalytic oxidation of SO2 to sulfur trioxide (SO3) is not only a core process in the sulfuric acid industry but also a key technological route for achieving flue gas desulfurization and resource recovery of sulfur. Currently, the most widely used catalysts in industry are vanadium-based catalysts, consisting of vanadium pentoxide (V2O5) as the main active component, alkali metal sulfates such as potassium sulfate (K2SO4) as co-catalysts, and diatomaceous earth or special silica as the support.

[0003] However, these traditional vanadium-based catalysts are primarily designed and optimized for dry, high-temperature (typically operating temperature windows between 400℃ and 600℃) contact process sulfuric acid production. In modern industry, especially in flue gas treatment in non-electric industries such as glass, ceramics, steel sintering, and small coal-fired boilers, the generated flue gas exhibits the following significant characteristics: large fluctuations in SO2 concentration, low flue gas temperature (typically between 200℃ and 400℃), and a large amount of water vapor (volume content can reach 10%-20%, or even higher). These "wet" or "high-humidity" operating conditions pose a severe challenge to traditional vanadium catalysts, specifically in the following aspects: 1. Significantly insufficient low-temperature activity: Traditional catalysts have a high ignition temperature. In the low-temperature region below 400℃, their intrinsic catalytic activity is low, resulting in unsatisfactory SO2 conversion rate, which cannot meet the requirements of efficient desulfurization. 2. The water vapor poisoning effect is significant: High concentrations of water vapor compete with reactants SO2 and O2, as well as products SO3, for adsorption on the active sites of the catalyst. More importantly, water vapor rapidly combines with the generated SO3, forming a sulfuric acid (H2SO4) liquid film or acid mist on the catalyst surface and within the pores. This liquid film physically covers and blocks the active sites, hindering the diffusion and contact of reactant molecules, leading to a significant decrease in catalyst activity. 3. Increased deactivation due to sulfation: In a wet process, substances such as sulfuric acid or ammonium bisulfate formed are difficult to desorb from the catalyst surface and will undergo irreversible sulfation reactions with the active components or support, resulting in permanent deactivation of active sites. This may also cause pulverization of catalyst particles and an increase in pressure drop in the reaction bed, greatly shortening the catalyst's service life.

[0004] 4. Increased risk of equipment corrosion: Sulfuric acid generated at low temperatures is highly corrosive, posing a serious threat to subsequent heat exchangers, pipelines and other equipment.

[0005] Therefore, developing an SO2 oxidation catalyst that can maintain high activity, high stability, and long lifespan under low temperature and high humidity conditions is of great significance for broadening the application scope of flue gas desulfurization technology, improving the level of pollution control in non-power industries, and realizing the low-temperature and efficient recovery of sulfur resources. Summary of the Invention

[0006] The purpose of this invention is to provide a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation, the catalyst comprising: a composite oxide active phase consisting of V2O5 and MoO3 supported on a support surface to form a VO-Mo structural unit; wherein the atomic ratio of Mo to V in the composite oxide active phase is 0.1-1.0.

[0008] As a further improvement, the ratio of the number of Mo to V atoms in the active component is preferably 0.2-0.8, and most preferably 0.4-0.6.

[0009] The V2O5 and MoO3 are not simply physically mixed, but rather form a composite metal oxide active phase by forming VO-Mo chemical bonds during the preparation process. This composite structure is the key to generating a synergistic catalytic effect.

[0010] As a further improvement, the carrier is prepared by surface hydrophobic modification of a porous oxide with a modifier.

[0011] As a further improvement, the porous oxide is at least one of titanium dioxide, silicon dioxide, and aluminum oxide.

[0012] Preferably, the carrier is titanium dioxide.

[0013] As a further improvement, the modifier is at least one of silane coupling agents, zirconate coupling agents, and silazane; For better hydrophobic modification effect, preferably, the modifier is methyltriethoxysilane, a silane coupling agent.

[0014] This invention also provides a method for preparing a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation, characterized by comprising the following steps: a. Dissolve vanadium source and molybdenum source in a solvent containing a complexing agent to prepare a composite precursor solution containing vanadium source and molybdenum source; b. The carrier is impregnated in the composite precursor solution to obtain the impregnated material; c. Aging and drying treatment of the impregnated material; d. The solid dried in step c is calcined in air at 400-500℃ for 4-6 hours to obtain the catalyst.

[0015] As a further improvement, in step a, the vanadium source is at least one of ammonium metavanadate, ammonium vanadate, and vanadium oxalate, and the molybdenum source is at least one of ammonium molybdate, ammonium heptamolybdate, and molybdenum nitrate.

[0016] As a further improvement, the complexing agent in step a is at least one of oxalic acid, citric acid, and ammonium oxalate.

[0017] As a further improvement, the aging conditions in step c are: static aging at room temperature to 80°C for 1-24 hours; the drying conditions are: drying at 80-120°C for 4-12 hours.

[0018] Step d will cause the precursor to decompose and undergo a solid-phase reaction, ultimately forming a composite metal oxide active phase with VO-Mo bonds.

[0019] The present invention also provides the application of a vanadium-molybdenum composite catalyst for the oxidation of SO2 in wet flue gas in the catalytic oxidation of SO2 to SO3 under wet conditions, wherein the wet conditions are that the water vapor volume content in the reaction gas is not less than 5%.

[0020] As a further improvement, the reaction temperature of the catalytic oxidation is 250-400℃.

[0021] Preferably, the volume content of water vapor in the reaction gas is 5%-20%; the temperature range of the catalytic oxidation reaction is 300℃-380℃.

[0022] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a vanadium-molybdenum composite catalyst for wet SO2 oxidation of flue gas, its preparation method, and its application, resulting in a catalyst with the following effects: 1. Excellent Low-Temperature and High-Humidity Activity: The introduction of MoO3 significantly modulates the electronic activity of V2O5. Since Mo's electronegativity is typically lower than V's, it donates electrons to the V center, weakening the V=O bond energy. This weakened V=O bond is more easily reduced in the SO2 oxidation reaction and also more readily re-oxidized in the presence of gaseous oxygen, thus significantly reducing the activation energy of the entire catalytic cycle. This results in excellent oxidation activity of the catalyst even at low temperatures. Experiments show that the catalyst of this invention achieves an SO2 conversion rate of over 85% at 300℃ and 10% water vapor. 2. Significantly enhanced resistance to water vapor poisoning and stability: The MoO3 component itself has a certain hydrophobic tendency. When it forms a composite structure with V2O5, it helps to reduce the affinity and adsorption strength of the entire active surface for water molecules. At the same time, the use of a hydrophobically modified support can reduce the condensation and accumulation of water molecules and sulfuric acid liquid film in the catalyst channels from a macroscopic perspective, thereby effectively protecting the active sites from being covered. The stable active phase structure formed by VO-Mo bonding also inhibits the loss of active components and structural collapse in wet processing environments. 3. Excellent resistance to sulfation: By optimizing the surface acidic sites and electronic structure, the catalyst of this invention reduces its excessive adsorption of sulfate species, making it easier for the generated SO3 or H2SO4 to desorb and leave the active sites and enter the gas phase. This fundamentally alleviates the problem of permanent deactivation caused by the strong adsorption of sulfuric acid or sulfate, and enables the catalyst to maintain stable high performance during long-term operation. 4. Highly targeted and with broad application prospects: This catalyst is specifically designed to cope with high humidity and low temperature flue gas environments, perfectly filling the performance gap of traditional dry catalysts in this field. Its preparation method is mature, reliable, and easy to scale up for production. It has huge market potential and good industrial application prospects in the fields of flue gas treatment and sulfur resource recovery in non-power industries. Attached Figure Description

[0023] Figure 1 The graph shows the activity test results of the catalysts prepared in Example 1 and Comparative Examples 1-2. Figure 2 The graph shows the stability test results of the catalysts prepared in Example 1 and Comparative Example 1. Figure 3 The graph shows the activity test results of the catalysts prepared in Examples 1-2. Detailed Implementation

[0024] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0025] The preparation of hydrophobically modified titanium dioxide includes the following steps: Weigh 10g of commercial titanium dioxide and disperse it in 150mL of anhydrous toluene. Add 5% (by weight) of methyltriethoxysilane to the mixture and reflux at 110℃ for 6h. After the reaction is complete, filter the mixture and wash it several times with ethanol. Dry the mixture at 110℃ for 6h to obtain hydrophobically modified titanium dioxide.

[0026] Example 1 A method for preparing a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation includes the following steps: a. Weigh 0.267g of ammonium metavanadate (NH4VO3) and 0.201g of ammonium molybdate ((NH4)6Mo7O 24 Dissolve 4H2O in 5 mL of 5 wt% oxalic acid aqueous solution at 50 °C, and stir until completely clear to obtain a composite precursor solution; b. Impregnate 10g of hydrophobically modified titanium dioxide in a composite precursor solution to obtain the impregnated material; c. After impregnation, seal and let stand (age) the material at room temperature for 12 hours, and then dry it in an 80°C forced-air drying oven for 12 hours; d. The solid dried in step c was calcined in a muffle furnace at 450°C under static air for 5 hours to obtain the catalyst, denoted as Cat-1.

[0027] Example 2 A method for preparing a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation includes the following steps: a. Weigh out 0.267g of ammonium metavanadate (NH4VO3) and 0.080g of ammonium molybdate ((NH4)6Mo7O 24 Dissolve 4H2O in 5 mL of 5 wt% oxalic acid aqueous solution at 50 °C, and stir until completely clear to obtain a composite precursor solution; b. Impregnate 10g of hydrophobically modified titanium dioxide in a composite precursor solution to obtain the impregnated material; c. After impregnation, seal and let stand (age) the material at room temperature for 12 hours, and then dry it in an 80°C forced-air drying oven for 12 hours; d. The solid dried in step c was calcined in a muffle furnace at 450°C under static air for 5 hours to obtain the catalyst, denoted as Cat-2.

[0028] Comparative Example 1 The process is basically the same as in Example 1, except that in step a, "weighing 0.267g of ammonium metavanadate (NH4VO3) and 0.201g of ammonium molybdate ((NH4)6Mo7O3)" is used instead of the other two steps. 24 The phrase “·4H2O)” is changed to “weigh 0.267g ammonium metavanadate (NH4VO3)”. The phrase “immerse 10g of hydrophobically modified titanium dioxide in the composite precursor solution” in step b is changed to “immerse 10g of unmodified titanium dioxide in the composite precursor solution”. The resulting catalyst is denoted as Ref-1.

[0029] Comparative Example 2 The catalyst is basically the same as in Example 1, except that the step b, "immersing 10g of hydrophobically modified titanium dioxide in the composite precursor solution", is changed to "immersing 10g of unmodified titanium dioxide in the composite precursor solution". The resulting catalyst is referred to as Ref-2.

[0030] Performance testing: Catalyst evaluation was conducted on a fixed-bed microreactor with the following reaction gas composition: 5000 ppm SO2, 10% O2, 10% H2O (introduced via a saturator), N2 equilibrium, and a total gas space velocity of 30000 h⁻¹. -1 The gas was heated to the target temperature using a tubular furnace. After separating the liquid acid mist using a condensation method, the residual SO2 concentration in the tail gas was titrated using iodometric titration to calculate the conversion rate. The results of the activity test and stability test were also obtained.

[0031] The activity test results are shown in [link to test]. Figure 1 : The catalyst Cat-1 prepared in Example 1 exhibited the best low-temperature activity, with an SO2 conversion rate of 85% at 300°C and as high as 95% at 350°C. The catalyst Ref-1 prepared in Comparative Example 1 had the worst activity, with a conversion rate of only 68% at 350℃; The catalyst Ref-2 prepared in Comparative Example 2 has an activity between Cat-1 and Ref-1, with a conversion rate of 82% at 350°C, indicating that the introduction of Mo does indeed improve the activity. However, without the synergistic protection of the hydrophobic support, its performance is still inferior to Cat-1 of the present invention.

[0032] For stability test results, see Figure 2 : It can be operated continuously for 100 hours at 350℃ with 10% water vapor. The catalyst Cat-1 prepared in Example 1 exhibited extremely high stability, with the conversion rate decreasing only from 95% to 94% after 100 hours; The conversion rate of catalyst Ref-1 prepared in Comparative Example 1 dropped rapidly from the initial 68% to 55%, showing obvious hydrothermal deactivation.

[0033] The above results demonstrate that the present invention successfully prepared an SO2 oxidation catalyst with high activity and high stability under wet and low-temperature conditions by using V2O5 and MoO3 as composite active components and hydrophobically modified porous oxides as a support. This catalyst is suitable for the efficient conversion and resource recovery of SO2 in industrial flue gas containing a large amount of water vapor.

[0034] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation, characterized in that, The catalyst comprises: a composite oxide active phase consisting of V2O5 and MoO3 supported on the surface of a support, forming a VO-Mo structural unit; wherein the ratio of the number of Mo to V atoms in the composite oxide active phase is 0.1-1.

0.

2. The vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation according to claim 1, characterized in that, The carrier is prepared by surface hydrophobic modification of porous oxide with a modifier.

3. The vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation according to claim 1, characterized in that, The porous oxide is at least one of titanium dioxide, silicon dioxide, and aluminum oxide.

4. The vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation according to claim 3, characterized in that, The modifier is at least one of silane coupling agents, zirconate coupling agents, and silazane.

5. The vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation according to claim 4, characterized in that, The modifier is methyltriethoxysilane.

6. A method for preparing a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation as described in any one of claims 1-5, characterized in that, Includes the following steps: a. Dissolve vanadium source and molybdenum source in a solvent containing a complexing agent to prepare a composite precursor solution containing vanadium source and molybdenum source; b. The carrier is impregnated in the composite precursor solution to obtain the impregnated material; c. Aging and drying treatment of the impregnated material; d. The solid dried in step c is calcined in air at 400-500℃ for 4-6 hours to obtain the catalyst.

7. The method for preparing a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation according to claim 6, characterized in that, In step a, the vanadium source is at least one of ammonium metavanadate, ammonium vanadate, and vanadium oxalate, and the molybdenum source is at least one of ammonium molybdate, ammonium heptamolybdate, and molybdenum nitrate.

8. The method for preparing a vanadium-molybdenum composite catalyst for wet flue gas SO2 oxidation according to claim 6, characterized in that, In step a, the complexing agent is at least one of oxalic acid, citric acid, and ammonium oxalate.

9. The application of the vanadium-molybdenum composite catalyst for the wet oxidation of SO2 in flue gas as described in any one of claims 1-5 in the wet oxidation of SO2 to SO3, characterized in that: The wet process conditions are that the water vapor volume content in the reaction gas is not less than 5%.

10. The application according to claim 9, characterized in that, The reaction temperature for the catalytic oxidation is 250-400℃.

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