Vanadium isomorph substituted phosphomolybdic acid low-temperature denitration catalyst and preparation method thereof

Abstract

The invention discloses a vanadium isomorphic substituted phosphomolybdic acid low-temperature denitration catalyst and a preparation method thereof. The preparation method of the catalyst comprises the following steps: dissolving MoO3 in distilled water, heating to 100 DEG C, then adding 85% H3PO4, and slowly adding a H2O2 solution of V2O5 into the mixed solution; stirring and refluxing the mixed solution at 100 DEG C for 6 hours; and cooling, filtering to remove insoluble substances, and drying the filtrate in a vacuum drying oven at 85 DEG C to obtain a product PMoVn (n represents the number of V-substituted Mo atoms in a Keggin structure). The preparation method comprises the following steps: adding a certain amount of PMoVn and TiO2 into distilled water, stirring for 1 hour at room temperature, drying in a water bath at 85 DEG C, and further drying for 3 hours at 105 DEG C; and finally, calcining the solid at 350 DEG C for 3 hours to obtain the V isomorphic substituted phosphomolybdic acid catalyst PMoVn / TiO2. The catalyst prepared by the preparation method disclosed by the invention has relatively high low-temperature denitration activity and relatively strong SO2 resistance.

Description

Technical Field

[0001] The present invention relates to the field of denitration catalysts, and particularly to a vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst and a preparation method thereof. Background Art

[0002] Non-electric industrial flue gas typified by steel industry flue gas is an important NO x emission source. Nitrogen oxides (NO x ) are typical air pollutants. Their emissions can not only cause environmental problems such as greenhouse effect, photochemical smog, acid rain and ozone depletion, but also pose potential hazards to human health. NH3-SCR is currently the most mature and effective method for removing NO x . The key to this method is to develop highly efficient catalysts. Commercial V2O5-WO3(MoO3) / TiO2 catalysts exhibit excellent catalytic performance in the working temperature range of 300-400 °C and have achieved remarkable results in treating nitrogen oxide waste gas from coal-fired power plants. However, the temperature of non-electric industrial flue gas such as steel is relatively low, generally about 180-240 °C, and contains a large amount of SO2. In this temperature range, traditional metal oxide catalysts are easily deactivated by SO2 and cannot provide sufficient performance. For this reason, the process mode of "pre-desulfurization + temperature-raising flue gas denitration" is usually adopted in engineering, but the investment and operation costs are high. Therefore, there is an urgent need to develop SCR catalysts with excellent denitration efficiency and good anti-sulfide / water vapor performance under low-temperature conditions.

[0003] Heteropoly acid (HPA) is a class of environmentally friendly catalysts with unique structures. Due to their strong acidity and redox properties, they have attracted extensive attention in the fields of heterogeneous and homogeneous catalysis. Among many structural types of HPA, most of those used in catalytic applications are Keggin heteropoly acids (Keggin HPA) because they have stronger acidity, higher thermal stability and are easier to obtain, and have good application potential in the NH3 selective catalytic reduction (NH3-SCR) reaction. However, the activity of heteropoly acid alone as a denitration catalyst is relatively low, and its denitration activity is often improved by metal doping or it is used as an additive to modify low-temperature denitration catalysts.

[0004] The invention patent application with the publication number CN109794300A discloses a copper-doped phosphomolybdic acid low-temperature denitration catalyst. Copper nitrate is added to the phosphomolybdic acid solution and mixed evenly, and then the copper-modified phosphomolybdic acid catalyst is prepared by evaporation to dryness and calcination. The Cu doping improves the denitration activity of the phosphomolybdic acid catalyst, but SO2 in the flue gas will cause the catalyst activity to decline. When 400 ppm SO2 and 8 vol.% water vapor are introduced into the flue gas, the denitration efficiency of the catalyst drops to 51.5% within 3 hours at 200 °C. The invention patent application with the publication number CN109794272A discloses a vanadium-modified phosphomolybdic acid low-temperature denitration catalyst and a preparation method thereof. V2O5 is added to the phosphomolybdic acid solution, and then the vanadium-modified phosphomolybdic acid catalyst is prepared by evaporation to dryness and calcination. The activity test results show that the denitration rate of the catalyst is the highest at 71.5% at 150 °C, and the denitration rate of the catalyst is higher than 98% at 200-300 °C. When the reaction temperature is controlled at 200 °C and 200 ppm SO2 and 4 vol.% water vapor are introduced into the flue gas, the denitration rate of the catalyst drops to 85% within 3 hours. With vanadium-modified phosphomolybdic acid, the main components of the active components are a mixture of V2O5 and phosphomolybdic acid. V2O5 can promote the oxidation of SO2 to SO3, and then form ammonium sulfate deposition, and V2O5 itself can react with SO2 and be sulfated. The short-term sulfur resistance is okay, but it cannot operate stably for a long time.

[0005] The invention patent application with the publication number CN116328783A discloses a preparation method of a highly stable SCR denitration catalyst. Phosphomolybdic acid HPMo and Cu(NO3)2 (the decomposition temperature of Cu(NO3)2 is 170 °C) are dissolved into the liquid phase, mixed, dried, and then calcined. The obtained active components mainly contain HPMo and CuO. The denitration activity of pure HPMo is not high. This invention uses Cu to modify phosphomolybdic acid to improve the catalyst activity, but whether CuO can react with SO2 to form CuSO4 and deactivate in low-temperature sulfur-containing flue gas. Therefore, the sulfur resistance of this invention is not strong.

[0006] In summary, using transition metal modification can improve the denitration activity of heteropolyacid catalysts. However, at present, the transition metal modification of heteropolyacids generally adopts a direct mixing method. The components of the catalyst contain two substances, heteropolyacid and transition metal oxide. The transition metal is not bonded to the heteropolyacid by chemical bonds. Transition metal oxides are amphoteric oxides and can react with SO2 in the flue gas to form sulfates. When the operation time is relatively long, the catalyst will be deactivated. Therefore, developing a heteropolyacid low-temperature denitration catalyst with high denitration activity and strong sulfur resistance, prolonging the service life of the catalyst, and reducing the denitration operation cost have important theoretical significance and engineering value. Summary of the Invention

[0007] The object of the present invention is to improve the catalytic activity of the low-temperature denitration catalyst, and at the same time enhance the performance of the catalyst in resisting SO2 and water vapor poisoning under low-temperature conditions, and provide a vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst for selective catalytic reduction denitration and a preparation method thereof. Adopting the technical solution of the present invention can ensure that the catalyst efficiently removes NO in low-temperature sulfur-containing flue gas. x 。

[0008] To achieve the above object and other related objects, the technical solution provided by the present invention is: a vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst, characterized in that: using anatase TiO2 as a carrier, and using vanadium isomorphously substituted Keggin-type phosphomolybdic acid as an active component, and the mass percentage of the active component in the total weight of the catalyst is 5-50%.

[0009] The preferred technical solution is: the vanadium / molybdenum molar ratio is 1:6-1:1; the phosphorus / molybdenum molar ratio is 1:11-1:8.

[0010] To achieve the above object and other related objects, the technical solution provided by the present invention is: a preparation method of the vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst as described in claim 1 or 2, comprising the following steps:

[0011] Step 1: Preparation of the active component PMoVn

[0012] Dissolve V2O5 in H2O2, stir evenly to obtain a mixed solution;

[0013] Add MoO3 to distilled water and heat, then add H3PO4;

[0014] Add the mixed solution and stir and reflux; then filter, and after drying the filtrate, obtain PMoVn, where n represents the number of vanadium atoms substituting molybdenum atoms in the Keggin structure;

[0015] Step 2: Preparation of the catalyst PMoVn / TiO2

[0016] Add TiO2 and PMoVn to distilled water, stir evenly to obtain a mixed slurry;

[0017] The mixed slurry is dried in a water bath at 85°C, and then dried at 105°C for 3 h, and ground to obtain a powder;

[0018] The powder is calcined to finally obtain the catalyst a% PMoVn / TiO2, where a represents the active component loading.

[0019] The preferred technical solution is: in step 1, the heating temperature of the mixture of MoO3 and distilled water is 100°C, the mass concentration of H3PO4 is 85%; the reflux temperature is 90-110°C, and the reflux time is 6 h.

[0020] The preferred technical solution is as follows: in step 2, the calcination temperature of the powder is 300-500 °C, and the calcination time is 1-5 h.

[0021] Due to the application of the above technical solution, the advantages of the present invention compared with the prior art are as follows:

[0022] 1. In the present invention, the transition metal V replaces the Mo atom in Keggin-type structure HPMo in the form of isomorphous substitution, which enhances the surface acidity and redox performance of the catalyst, and promotes the adsorption and activation of reactants NO x and NH3. PMoVn / TiO2 has high low-temperature denitrification activity. SO2 is mainly physically adsorbed unstably on the surface of PMoVn / TiO2, and the catalyst shows strong sulfur resistance. The present invention provides a technical basis for the industrial application of phosphomolybdic acid catalyst in low-temperature denitrification.

[0023] 2. The preparation method of the present invention is simple, the raw materials are widely available, and the cost is low.

[0024] At present, the active components of commercial low-temperature denitrification catalysts are mainly transition metal oxides (V2O5-WO3, V2O5-MoO3, etc.), which are suitable for low-sulfur or sulfur-free working conditions. In engineering, the process mode of pre-desulfurization plus temperature-rising flue gas denitrification is usually adopted, with high operating costs, which does not conform to the development trend of pollution reduction and carbon emission reduction. The vanadium isomorphous substitution phosphomolybdic acid low-temperature denitrification catalyst described in the present invention has high low-temperature denitrification activity and strong sulfur resistance. When the reaction temperature is 180 °C, the denitrification efficiency is about 91%, and when the temperature is 210 °C, the denitrification efficiency can reach 100%. In addition, the vanadium isomorphous substitution phosphomolybdic acid catalyst has strong sulfur and water resistance. Under the flue gas conditions where the reaction temperature is higher than 180 °C, it can operate without desulfurization pretreatment and heating of the flue gas, greatly reducing the denitrification operation cost. Brief Description of the Drawings

[0025] Figure 1 Sulfur resistance of the catalyst.

[0026] Figure 2 Water resistance of the catalyst.

[0027] Figure 3 Sulfur and water resistance of the catalyst. Detailed Embodiments

[0028] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this embodiment.

[0029] Please refer to Figures 1-3It should be noted that the structures, proportions, sizes, etc. shown in the drawings of this specification are only used to match the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size. The following examples are provided to better understand the present invention, rather than to limit the present invention. The experimental materials used in the following examples are all obtained from regular biochemical reagent stores unless otherwise specified.

[0030] Concept of the present invention: A vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst and its preparation method. Dissolve MoO3 in distilled water and heat it, then add H3PO4 with a concentration of 85%, and slowly add an H2O2 solution of V2O5 to the mixed solution. Heat and stir the mixed solution under reflux. After cooling, filter to remove the insoluble substances, and dry the filtrate in a vacuum drying oven at 85°C to obtain the product PMoVn (where n represents the number of V atoms substituting Mo atoms in the Keggin structure). Using PMoVn as the active component and TiO2 as the carrier, add a certain amount of PMoVn and TiO2 to distilled water, stir and mix evenly, and then carry out drying and calcination in sequence to finally obtain the V isomorphously substituted phosphomolybdic acid catalyst PMoVn / TiO2.

[0031] The scientific principle of the present invention is as follows:

[0032] Keggin-type heteropolyacid HPMo has strong surface acidity and thermal stability, and its own redox ability is not strong. In the field of low-temperature denitration, its super acidity is mainly used as an additive. The present invention uses the heteropolyacid HPMo that is not easily sulfated as the active component, and uses the transition metal V to substitute the Mo atom in the Keggin-type structure HPMo in an isomorphous substitution manner. The catalyst PMoVn / TiO2 has stronger surface acidity than HPMo / TiO2, and the adsorption energy of PMoV3-V sites for NH3 and NO is also significantly improved, promoting the adsorption and activation of reactants. At the same time, the vanadium isomorphous (V isomorphous) substitution also increases the surface adsorbed oxygen content of the catalyst (by more than 50%), regulates the redox ability of the catalyst, promotes the decomposition of nitrate species intermediate products on the catalyst surface, and improves the low-temperature denitration activity of the catalyst.

[0033] SO2 is physically adsorbed on the Lewis acid sites of HPMo surface and forms stable chemisorption on the Brønsted acid sites. However, the adsorption of SO2 on PMoV3 after V substitution mainly shows unstable physical adsorption. Therefore, SO2 will not be catalytically oxidized to SO3, which can inhibit the formation of ammonium sulfate. At the same time, the active component of the catalyst PMoV3 / TiO2 is heteropolyacid without metal oxide components, so it will not react with SO2 and be sulfated in low-temperature sulfur-containing flue gas. In addition, in-situ infrared analysis shows that the presence of SO2 limits the NH3-SCR reaction on the surface of HPMo / TiO2, but SO2 does not change the NH3-SCR reaction path on the PMoV3 / TiO2 catalyst. The PMoV3 / TiO2 catalyst has strong sulfur resistance.

[0034] In addition, the adsorption capacity of the PMoV3 cluster after V substitution for H2O is much lower than that of the HPMo cluster, showing strong water resistance.

[0035] Example 1

[0036] (1) Preparation of active component

[0037] 5 g of MoO3 was added to 30 ml of distilled water and mixed evenly. After heating the mixture to 100 °C, 0.2 ml of 85% phosphoric acid was added and stirred evenly. Then, it was stirred and refluxed at 100 °C for 6 h, cooled and filtered to remove insoluble substances, and then the filtrate was dried in a vacuum drying oven at 85 °C to obtain the active component HPMo. Among them, the molar ratio of P to Mo is 1:12.

[0038] (2) Preparation of catalyst

[0039] 1 g of HPMo and 1.5 g of TiO2 were added to 30 ml of distilled water and stirred at room temperature for 1 h to mix evenly. Then, it was dried in a water bath at 85 °C and further dried at 105 °C for 3 h. The obtained solid was calcined at 350 °C for 3 h to obtain the catalyst 40% HPMo / TiO2 with an active component loading of 40%.

[0040] Example 2

[0041] (1) Preparation of active component

[0042] Add 5 g of MoO3 to 30 ml of distilled water and mix evenly. After heating the mixture to 100 °C, add 0.2 ml of phosphoric acid with a concentration of 85%, and stir evenly to obtain Solution A. Dissolve 0.29 g of V2O5 in 10 ml of hydrogen peroxide H2O2 to obtain Solution B. Slowly add Solution B to Solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV1 with 1 V atom substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:11, and the molar ratio of V to Mo is 1:11.

[0043] (2) Preparation of catalyst

[0044] Add 1 g of PMoV1 and 1.5 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 h. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 40% PMoV1 / TiO2 with an active component loading of 40%.

[0045] Example 3

[0046] (1) Preparation of active component

[0047] Add 5 g of MoO3 to 30 ml of distilled water and mix evenly. After heating the mixture to 100 °C, add 0.2 ml of phosphoric acid with a concentration of 85%, and stir evenly to obtain Solution A. Dissolve 0.63 g of V2O5 in 22 ml of hydrogen peroxide H2O2 to obtain Solution B. Slowly add Solution B to Solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV2 with 2 V atoms substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:10, and the molar ratio of V to Mo is 2:10.

[0048] (2) Preparation of catalyst

[0049] Add 1 g of PMoV2 and 1.5 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 h. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 40% PMoV2 / TiO2 with an active component loading of 40%.

[0050] Example 4

[0051] (1) Preparation of active component

[0052] Add 5 g of MoO3 to 30 ml of distilled water and mix evenly. After heating the mixture to 100 °C, add 0.2 ml of phosphoric acid with a concentration of 85%, and stir evenly. Denote it as solution A. Dissolve 1.05 g of V2O5 in 37 ml of hydrogen peroxide H2O2, and denote it as solution B. Slowly add solution B to solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV3 with 3 V atoms substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:9, and the molar ratio of V to Mo is 3:9.

[0053] (2) Preparation of catalyst

[0054] Add 1 g of PMoV3 and 1.5 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 hours. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 40% PMoV3 / TiO2 with an active component loading of 40%.

[0055] Example 5

[0056] (1) Preparation of active component

[0057] Add 5 g of MoO3 to 30 ml of distilled water and mix evenly. After heating the mixture to 100 °C, add 0.2 ml of phosphoric acid with a concentration of 85%, and stir evenly. Denote it as solution A. Dissolve 1.58 g of V2O5 in 55 ml of hydrogen peroxide H2O2, and denote it as solution B. Slowly add solution B to solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV4 with 4 V atoms substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:8, and the molar ratio of V to Mo is 4:8.

[0058] (2) Preparation of catalyst

[0059] Add 1 g of PMoV4 and 1.5 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 hours. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 40% PMoV4 / TiO2 with an active component loading of 40%.

[0060] Example 6

[0061] (1) Preparation of active component

[0062] Add 5 g of MoO3 to 30 ml of distilled water and mix well. Heat the mixture to 100 °C, then add 0.2 ml of 85% phosphoric acid and stir evenly. Denote it as solution A. Dissolve 1.05 g of V2O5 in 37 ml of hydrogen peroxide (H2O2), and denote it as solution B. Slowly add solution B to solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV3 where 3 V atoms substitute phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:9, and the molar ratio of V to Mo is 3:9.

[0063] (2) Preparation of catalyst

[0064] Add 0.5 g of PMoV3 and 2.0 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 h. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 20% PMoV3 / TiO2 with an active component loading of 20%.

[0065] Example 7

[0066] (1) Preparation of active component

[0067] Add 5 g of MoO3 to 30 ml of distilled water and mix well. Heat the mixture to 100 °C, then add 0.2 ml of 85% phosphoric acid and stir evenly. Denote it as solution A. Dissolve 1.05 g of V2O5 in 37 ml of hydrogen peroxide (H2O2), and denote it as solution B. Slowly add solution B to solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV3 where 3 V atoms substitute phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:9, and the molar ratio of V to Mo is 3:9.

[0068] (2) Preparation of catalyst

[0069] Add 0.6 g of PMoV3 and 1.4 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 h. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 30% PMoV3 / TiO2 with an active component loading of 30%.

[0070] Example 8

[0071] (1) Preparation of active component

[0072] Add 5 g of MoO3 to 30 ml of distilled water and mix evenly. After heating the mixture to 100 °C, add 0.2 ml of phosphoric acid with a concentration of 85%, and stir evenly to obtain Solution A. Dissolve 1.05 g of V2O5 in 37 ml of hydrogen peroxide H2O2 to obtain Solution B. Slowly add Solution B to Solution A, stir and reflux at 100 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV3 with 3 V atoms substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:9, and the molar ratio of V to Mo is 3:9.

[0073] (2) Preparation of catalyst

[0074] Add 1.0 g of PMoV3 and 1.0 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 h. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 50% PMoV3 / TiO2 with an active component loading of 50%.

[0075] Example 9

[0076] (1) Preparation of active component

[0077] Add 5 g of MoO3 to 30 ml of distilled water and mix evenly. After heating the mixture to 100 °C, add 0.2 ml of phosphoric acid with a concentration of 85%, and stir evenly to obtain Solution A. Dissolve 1.05 g of V2O5 in 37 ml of hydrogen peroxide H2O2 to obtain Solution B. Slowly add Solution B to Solution A, stir and reflux at 90 °C for 6 h, cool and filter to remove insoluble substances. Dry the filtrate in a vacuum drying oven at 85 °C to obtain the active component PMoV3 with 3 V atoms substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:9, and the molar ratio of V to Mo is 3:9.

[0078] (2) Preparation of catalyst

[0079] Add 1 g of PMoV3 and 1.5 g of TiO2 to 30 ml of distilled water, stir at room temperature for 1 h to mix evenly. Then, dry in a water bath at 85 °C and further dry at 105 °C for 3 h. Calcinate the obtained solid at 350 °C for 3 h to obtain the catalyst 40% PMoV3 / TiO2 with an active component loading of 40%.

[0080] Example 10

[0081] (1) Preparation of active component

[0082] 5 g of MoO3 was added to 30 ml of distilled water and mixed evenly. After heating the mixture to 100 °C, 0.2 ml of phosphoric acid with a concentration of 85% was added and stirred evenly, denoted as solution A. 1.05 g of V2O5 was dissolved in 37 ml of hydrogen peroxide H2O2, denoted as solution B. Solution B was slowly added to solution A, and stirred and refluxed at 110 °C for 6 h, then cooled and filtered to remove insoluble substances. The filtrate was dried in a vacuum drying oven at 85 °C to obtain the active component PMoV3 with 3V atoms substituting phosphomolybdic acid. Among them, the molar ratio of P to Mo is 1:9, and the molar ratio of V to Mo is 3:9.

[0083] (2) Preparation of catalyst

[0084] 1 g of PMoV3 and 1.5 g of TiO2 were added to 30 ml of distilled water and stirred at room temperature for 1 h to mix evenly. Then, it was dried in a water bath at 85 °C and further dried at 105 °C for 3 h. The obtained solid was calcined at 350 °C for 3 h to obtain the catalyst 40% PMoV3 / TiO2 with an active component loading of 40%.

[0085] Performance testing of the catalyst

[0086] 1. Performance test one

[0087] The catalysts in Examples 1 - 10 were respectively tableted and sieved to obtain catalyst particles with a particle size of 40 - 60 mesh. 0.15 g of catalyst particles was weighed and placed in a fixed-bed denitration reactor (the inner diameter of the reaction tube is 8 mm) to test its denitration performance. The simulated flue gas consists of 500 ppm NO, 500 ppm NH3, and 8 vol% O2, with N2 as the balance gas. The total gas flow rate was maintained at 100 mL / min, and the gas hourly space velocity (GHSV) was approximately 40000 h -1 . The test temperature range was set between 120 and 300 °C, and each reaction temperature was stabilized for 40 minutes. A flue gas analyzer was used to measure the gas concentrations at the inlet and outlet. The NO conversion rate and N2 selectivity were calculated using the following formulas:

[0088]

[0089] The results are listed in Table 1.

[0090] Table 1: Denitration activity of the catalysts in Examples 1 - 10 of catalyst preparation

[0091]

[0092] As can be seen from the denitrification activity test of the catalysts in Table 1, when there is no SO2 and H2O in the flue gas, Example 4 shows good denitrification activity at 150 °C. Example 4 is the catalyst under the optimal preparation conditions, and its denitrification activity reaches 81.5% at 150 °C and remains above 98% in the temperature range of 180 °C to 300 °C.

[0093] The N2 selectivity test results of the catalysts in Examples 1-10 are shown in Table 2.

[0094] Table 2: Denitrification activity of the catalysts prepared in Examples 1-10 of the catalyst

[0095]

[0096]

[0097] As can be seen from Table 2, in the temperature range of 120-270 °C, the N2 selectivity of the catalysts in Examples 1-10 is 100%; when the reaction temperature is 300 °C, the N2 selectivity of the catalysts in Examples 1, 2, 3, 4, 6, 7, 8, 9, and 10 is 100%. The N2 selectivity of the catalyst in Example 5 decreases slightly, but it also reaches 99.3%.

[0098] 2. Performance Test II

[0099] The sulfur and water resistance of the HPMo / TiO2 catalyst and 3V-substituted PMoV3 / TiO2 in Example 4 with the best denitrification activity were compared and tested. The catalysts were respectively tableted and sieved to obtain catalyst particles with a particle size of 40-60 mesh. Weigh 0.15 g of catalyst particles and place them in a fixed-bed denitrification reactor (the inner diameter of the reaction tube is 8 mm) to test their denitrification performance. The simulated flue gas consists of 500 ppm NO, 500 ppm NH3, 8 vol% O2, 0-200 ppm SO2, and 0-6 vol% H2O, with N2 as the balance gas. The total gas flow rate is maintained at 100 mL / min, and the gas hourly space velocity (GHSV) is about 40000 h -1 . The test temperature range is set at 200 °C, and a flue gas analyzer is used to measure the gas concentrations at the inlet and outlet. The results are as Figures 1 to 3 shown.

[0100] From Figure 1It can be seen that after introducing 200 ppm SO2, the denitration rate of the HPMo / TiO2 catalyst decreased rapidly and stabilized at about 43%; after cutting off SO2 for 10 h, the denitration rate of the HPMo / TiO2 catalyst increased to some extent, but it could not reach the level before introducing SO2. The isomorphous substitution of 3V significantly improved the sulfur resistance of the HPMo / TiO2 catalyst, and the denitration activity of the catalyst did not decrease after introducing 200 ppm SO2. This is because the isomorphous substitution of V regulated the redox property and surface acidity of HPMo, inhibited the adsorption and catalytic oxidation of SO2, and thus inhibited the formation of ammonium sulfate salt.

[0101] From Figure 2 it can be seen that after introducing 6 vol.% water vapor, the denitration activity of the HPMo / TiO2 catalyst decreased rapidly to about 23%; after cutting off the water vapor, the denitration activity of the HPMo / TiO2 catalyst was completely restored. The water vapor mainly reduced the denitration activity of the HPMo / TiO2 catalyst through physical competitive adsorption. Under the condition of introducing 6 vol.% water vapor, the denitration efficiency of the PMoV3 / TiO2 catalyst was hardly affected, showing excellent water resistance.

[0102] From Figure 3 it can be seen that when simultaneously introducing 200 ppm SO2 and 6 vol.% H2O into the flue gas, the NO removal rate of the HPMo catalyst decreased from 52% to 23% within 7 h. After cutting off SO2 and H2O for 1 h, the NO removal rate only recovered to 30%. The NO removal rate of the PMoV3 / TiO2 catalyst decreased from 100% to 95% within 7 h. After cutting off SO2 and H2O, the NO removal rate almost recovered to 100%. When simultaneously introducing SO2 and H2O, SO2 and H2O molecules were adsorbed on the surface of the PMoV3 / TiO2 catalyst in small amounts through synergistic action, resulting in a slight decrease in the catalyst activity. The above results show that compared with PMo / TiO2, the introduction of V effectively improved the tolerance to H2O and SO2.

[0103] The present invention replaces Mo atoms in phosphomolybdic acid with vanadium atoms in an isomorphous substitution manner, thereby enhancing the surface acidity of the catalyst. The adsorption energies of PMoV3-V sites for NH3 and NO are also significantly improved, promoting the adsorption and activation of reactants. At the same time, the isomorphous substitution of V also increases the surface adsorbed oxygen content of the catalyst (by more than 50%), regulates the redox ability of the catalyst, promotes the decomposition of nitrate species intermediate products on the catalyst surface, and improves the low-temperature denitration activity of the catalyst. SO2 is physically adsorbed on the L acid sites of the HPMo surface and forms a stable chemical adsorption on the B acid sites. However, the adsorption of SO2 on PMoV3 after V substitution mainly shows unstable physical adsorption. Therefore, SO2 will not be catalytically oxidized to SO3, and the formation of ammonium sulfate can be inhibited. At the same time, the active component of the catalyst PMoV 3 / The active component of TiO2 is heteropolyacid without metal oxide components, and it will not react with SO2 and be sulfated in low-temperature flue gas containing sulfur. In addition, combined with in-situ infrared analysis, it can be seen that the presence of SO2 limits the NH3-SCR reaction on the surface of HPMo / TiO2, but SO2 does not change the NH3-SCR reaction path on the PMoV3 / TiO2 catalyst. The PMoV3 / TiO2 catalyst has strong sulfur resistance.

[0104] The above are only preferred embodiments for explaining the present invention, and are not intended to limit the present invention in any form. Therefore, any modification or change to the present invention made under the same inventive spirit should still be included in the scope intended to be protected by the present invention.

Claims

1. A low-temperature denitration catalyst of vanadium isomorphously substituted phosphomolybdic acid, characterized in that: Using anatase TiO2 as the carrier and vanadium isomorphously substituted Keggin-type phosphomolybdic acid as the active component, and the mass percentage of the active component in the total weight of the catalyst is 5-50%.

2. The vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst according to claim 1, wherein: The vanadium / molybdenum molar ratio is 1:6-1:1; the phosphorus / molybdenum molar ratio is 1:11-1:

8.

3. A preparation method of the vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst as described in claim 1 or 2, characterized in that: It includes the following steps: Step 1: Preparation of the active component PMoVn Dissolve V2O5 in H2O2 and stir evenly to obtain a mixed solution; Add MoO3 to distilled water and heat, then add H3PO4; Add the mixed solution and stir under reflux; then filter, and after drying the filtrate, obtain PMoVn, where n represents the number of vanadium atoms substituting molybdenum atoms in the Keggin structure; Step 2: Preparation of the catalyst PMoVn / TiO2 Add TiO2 and PMoVn to distilled water and stir evenly to obtain a mixed slurry; The mixed slurry is dried in a water bath at 85 °C, then dried at 105 °C for 3 h, and ground to obtain a powder; The powder is calcined to finally obtain the catalyst a% PMoVn / TiO2, where a represents the active component loading.

4. The preparation method of the vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst according to claim 3, characterized in that: In Step 1, the heating temperature of the mixture of MoO3 and distilled water is 100 °C, the mass concentration of H3PO4 is 85%; the reflux temperature is 90-110 °C, and the reflux time is 6 h.

5. The preparation method of the vanadium isomorphously substituted phosphomolybdic acid low-temperature denitration catalyst according to claim 3, characterized in that: In Step 2, the calcination temperature of the powder is 350 °C, and the calcination time is 3 h.

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