Zirconium vanadate catalyst with oxygen vacancies and preparation method and application thereof

Abstract

The present invention relates to the technical field of catalysts, and discloses a zirconium vanadate catalyst with oxygen vacancies, a preparation method thereof, and an application thereof, wherein vanadium and zirconium in the zirconium vanadate catalyst are in an amorphous form and are uniformly dispersed in the catalyst; in the ESR image of the zirconium vanadate catalyst, the diffraction peak intensity is 8634.91au-44721.07au. The zirconium vanadate catalyst of the present invention has suitable oxygen vacancies, which not only ensures the structural stability of the zirconium vanadate catalyst, but also improves the catalyst activity of the zirconium vanadate catalyst.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a zirconium vanadate catalyst with oxygen vacancies and a preparation method and application thereof. Background Art

[0002] Excessive NOx emissions not only directly harm human health, but may also cause a series of environmental problems, including ozone depletion, acid rain, haze, photochemical smog, and greenhouse gas emissions. The main sources of NOx include exhaust from mobile sources (such as diesel ships and motor vehicles) and exhaust from stationary sources (such as power plants, industrial furnaces, and chemical plants). These nitrogen oxides exist in the form of NO, NO2, N2O, and their derivatives, of which about 95% exist in the form of NO. In order to cope with increasingly stringent nitrogen oxide emission standards, common NOx post-combustion reduction technologies include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). So far, it is internationally recognized that selective catalytic reduction is the most effective NOx removal technology. Its technology is efficient, stable, and has a wide range of applications, and can reduce NOx emissions by more than 90%.

[0003] Catalysts play a vital role in the selective catalytic reduction (SCR) process, and their main task is to efficiently and selectively remove nitrogen oxides from exhaust gas. SCR catalysts mainly include precious metal catalysts, transition metal oxide catalysts, and transition metal ion-exchanged zeolite catalysts. Among these catalysts, metal oxide catalysts are widely used in SCR applications due to their excellent catalytic activity, high stability, good controllability, and low cost. Although commercial V2O5-WO3 / TiO2 catalysts perform well, they still have some inherent defects in practical use, such as a narrow operating temperature window, limited high temperature tolerance, low N2 selectivity, and NH3 overoxidation at high temperatures. Therefore, researchers are exploring other new SCR catalysts to more effectively remove NOx under various operating conditions.

[0004] Oxygen vacancy (OV) is a common lattice defect in metal oxides, usually formed by the detachment of oxygen atoms from the lattice. Oxygen vacancies play a vital role in the catalytic process. They change the electronic and geometric properties of the catalyst by adjusting the defect structure, thereby improving its reactivity. In the NH3-SCR process, oxygen vacancies have received extensive attention due to their unique structural characteristics. On the one hand, oxygen vacancies can serve as adsorption and activation sites for reactants, promote the adsorption of reactants at high temperatures, and improve the high-temperature activity of the catalyst; on the other hand, oxygen vacancies can also optimize the redox characteristics of the catalyst, thereby improving the low-temperature activity. In addition, oxygen vacancies can effectively reduce the negative impact of sulfur dioxide on the active sites of the catalyst, and play an important balancing role in the stability and activity of the catalyst.

[0005] Oxygen vacancies come from the lack of oxygen in the catalyst crystal structure. For different types of catalysts, the oxygen vacancies that can be formed are limited. Although the increase of oxygen vacancies can improve the catalytic performance of the catalyst, when there are too many oxygen vacancies, the stability of the catalyst crystal structure will decrease, which will cause the catalyst to degenerate or deactivate. Therefore, for different types of catalysts, the oxygen vacancy content should be adapted to their structural types.

[0006] Therefore, combined with the above content about oxygen vacancies, further research is conducted on the oxygen vacancy content that can be matched by the zirconium vanadate catalyst, so as to enhance the redox property and acidity of the catalyst surface and further improve the low-temperature activity of the catalyst. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a zirconium vanadate catalyst with oxygen vacancies and a preparation method and application thereof. The zirconium vanadate catalyst of the present invention has suitable oxygen vacancies, which not only ensures the structural stability of the zirconium vanadate catalyst, but also improves the catalytic activity of the zirconium vanadate catalyst.

[0008] The invention provides a zirconium vanadate catalyst with oxygen vacancies, wherein vanadium and zirconium in the zirconium vanadate catalyst are in an amorphous state and are uniformly dispersed in the catalyst; in an ESR image of the zirconium vanadate catalyst, a diffraction peak intensity is 8634.91au-44721.07au.

[0009] The present invention also provides a method for preparing the zirconium vanadate catalyst, which comprises:

[0010] A solution containing a vanadium source is added dropwise to a solution containing a zirconium source to obtain a mixed solution, the pH value of the mixed solution is adjusted, a hydrothermal reaction is carried out, the solution is cooled, filtered, washed, dried, calcined once, a reducing atmosphere is introduced, calcined twice, and a reducing atmosphere is introduced again to obtain a zirconium vanadate catalyst having oxygen vacancies.

[0011] Furthermore, the vanadium source includes ammonium metavanadate (NH4VO3).

[0012] Furthermore, the zirconium source includes one or more of zirconium nitrate and zirconium oxynitrate.

[0013] Furthermore, in the mixed solution, the molar ratio of the vanadium source to the zirconium source is 1:1, calculated based on the vanadium ions in the vanadium source and the zirconium ions in the zirconium source.

[0014] Furthermore, in the solution containing the vanadium source, the concentration of the vanadium source in the solution is 0.065 mol / L in terms of vanadium ions.

[0015] Furthermore, in the solution containing the zirconium source, the concentration of the zirconium source in the solution is 0.065 mol / L, calculated as zirconium ions.

[0016] Furthermore, the pH value of the mixed solution was adjusted to 9 using aqueous ammonia.

[0017] Furthermore, the concentration of the ammonia water is 1 mol / L.

[0018] Furthermore, after the pH value of the mixed solution is adjusted to 9 by using ammonia water, stirring may be performed for a stirring time of 0.9h-1.1h.

[0019] In the present invention, stirring is beneficial to the sufficient precipitation of the precipitate of the reaction of the vanadium source and the zirconium source. Those skilled in the art can adjust the stirring time and stirring speed according to the actual situation, so as to facilitate the complete precipitation of the precipitate.

[0020] Furthermore, the temperature of the hydrothermal reaction is 170° C.-190° C., and the time of the hydrothermal reaction is 11 h-13 h.

[0021] Furthermore, the cooling to room temperature is 25°C-30°C.

[0022] Furthermore, in the specific step of washing, the product is washed with distilled water and anhydrous ethanol in sequence until the pH value of the product is 7, and the washing is completed.

[0023] Furthermore, the drying temperature is 70° C.-90° C., and the drying time is 11 h-13 h.

[0024] Furthermore, the temperature of the first calcination is 440°C-460°C, and the time of the first calcination is 3.5h-4.5h.

[0025] Furthermore, the speed of reaching the temperature of the primary calcination is 5.5°C / min-6.5°C / min.

[0026] Furthermore, after the first calcination, the product needs to be purged in nitrogen.

[0027] Furthermore, after purging in nitrogen, a reducing atmosphere and nitrogen are introduced simultaneously.

[0028] Furthermore, the reducing atmosphere includes ammonia, and the amount of ammonia introduced is 100ppm-500ppm.

[0029] Furthermore, the temperature of the secondary calcination is 440° C.-460° C., and the time of the secondary calcination is 3.5 h-4.5 h.

[0030] Furthermore, the speed of reaching the temperature of the secondary calcination is 5.5°C / min-6.5°C / min.

[0031] Furthermore, the specific method of introducing the reducing atmosphere again includes: introducing the reducing atmosphere until the product is cooled to room temperature.

[0032] Furthermore, after the product was cooled to room temperature, nitrogen was introduced.

[0033] Furthermore, the method for preparing the solution containing the vanadium source comprises:

[0034] Dissolve the vanadium source in deionized water in a water bath.

[0035] Furthermore, the temperature of the water bath is 75°C-85°C, and the water bath time is 25min-35min.

[0036] Those skilled in the art should understand that, in order to evenly disperse the vanadium source in deionized water, stirring may be performed while conducting a water bath to promote the dispersion of the vanadium source.

[0037] Furthermore, the method for preparing the solution containing a zirconium source comprises:

[0038] Dissolve the zirconium source in deionized water and stir.

[0039] Those skilled in the art should understand that stirring can be used to promote the dissolution of the solvent, and the stirring time can be adjusted by those skilled in the art according to actual conditions as long as the purpose of dissolving the zirconium source is achieved.

[0040] The present invention also provides the use of the zirconium vanadate catalyst with oxygen vacancies in denitration at a temperature below 230°C.

[0041] The embodiments of the present invention have the following technical effects:

[0042] 1. The present invention proposes a method for regulating the oxygen vacancy concentration on the catalyst surface, and prepares catalysts with different oxygen vacancy concentrations by chemical reduction, which significantly improves the low-temperature activity of the catalyst and the feasibility of performance regulation.

[0043] 2. This product has excellent low-temperature SCR catalytic performance, and the NO conversion rate in the range of 200-400°C reaches more than 80%, which is suitable for a variety of low-temperature catalytic scenarios. The presence of oxygen vacancies and Zr ions can promote the catalyst reaction system. The redox cycle increases the surface active oxygen species and improves the low-temperature activity of the catalyst.

[0044] 3. This product reveals the optimization strategy of oxygen vacancy concentration on catalytic activity, discovers and verifies the best catalytic activity of catalysts with moderate oxygen vacancy concentration in low-temperature SCR reaction, and clarifies the limiting mechanism of high or low concentration oxygen vacancies on catalytic performance. It reveals the "two-sided" mechanism of oxygen vacancies on the generation and conversion of reactive oxygen species (ROS), which promotes the generation of H2O2 and •OH at low concentrations and inhibits their generation due to strong adsorption at high concentrations, providing new theoretical guidance for catalyst design.

[0045] 4. The present invention discloses for the first time the oxygen vacancy content of the zirconium vanadate catalyst that is suitably formed, thereby improving the catalytic activity of the catalyst while ensuring the stability of the zirconium vanadate catalyst structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 is an ESR diagram provided by the embodiments of the present invention and the comparative examples, wherein Figure 1 a is the ESR diagram of Example 1 to Example 3, Figure 1 (b) is the ESR graph of Comparative Example 1 to Comparative Example 3.

[0048] Figure 2 is the XPS test result of the embodiment of the present invention and the comparative example, wherein Figure 2 a is the O1s spectrum of the embodiment and the comparative example, Figure 2 b is the V 2p spectrum of the embodiment and the comparative example, Figure 2 c is the Zr 3d spectrum of the embodiment and comparative example.

[0049] Figure 3 It is the NH3-TPD characterization results of the embodiments and comparative examples.

[0050] Figure 4 It is the H2-TPD characterization result of embodiment and comparative example.

[0051] Figure 5 It is the test result of NO conversion rate of the embodiment and the comparative example.

[0052] Figure 6 These are the N2 selectivity test results of the embodiment and the comparative example.

[0053] Figure 7 It is the N2 selectivity test result of comparative example. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0055] In a first aspect, some embodiments of the present invention provide a zirconium vanadate catalyst having oxygen vacancies, wherein vanadium and zirconium in the zirconium vanadate catalyst are in an amorphous form and are uniformly dispersed in the catalyst; in the ESR image of the zirconium vanadate catalyst, the diffraction peak intensity is 8634.91au-44721.07au.

[0056] In a second aspect, some embodiments of the present invention also provide a method for preparing the zirconium vanadate catalyst, the preparation method comprising:

[0057] A solution containing a vanadium source is added dropwise to a solution containing a zirconium source to obtain a mixed solution, the pH value of the mixed solution is adjusted, a hydrothermal reaction is carried out, the solution is cooled, filtered, washed, dried, calcined once, a reducing atmosphere is introduced, calcined twice, and a reducing atmosphere is introduced again to obtain a zirconium vanadate catalyst having oxygen vacancies.

[0058] In some embodiments, the vanadium source includes ammonium metavanadate (NH4VO3).

[0059] In some embodiments, the zirconium source includes one or more of zirconium nitrate and zirconium oxynitrate.

[0060] In some embodiments, the molar ratio of the vanadium source to the zirconium source in the mixed solution is 1:1, calculated based on the vanadium ions in the vanadium source and the zirconium ions in the zirconium source.

[0061] In some embodiments, in the solution containing the vanadium source, the concentration of the vanadium source in the solution is 0.065 mol / L in terms of vanadium ions.

[0062] In some embodiments, in the solution containing the zirconium source, the concentration of the zirconium source in the solution is 0.065 mol / L, calculated as zirconium ions.

[0063] In some embodiments, the pH value of the mixed solution is adjusted to 9 using aqueous ammonia.

[0064] In some embodiments, the concentration of the ammonia water is 1 mol / L.

[0065] In some embodiments, after the pH value of the mixed solution is adjusted to 9 by using ammonia water, stirring may be performed for a time of 0.9 h to 1.1 h.

[0066] In some embodiments, the temperature of the hydrothermal reaction is 170° C.-190° C., and the time of the hydrothermal reaction is 11 h-13 h.

[0067] In some embodiments, the cooling to room temperature is 25°C-30°C.

[0068] In some embodiments, the specific step of washing is to wash the product with distilled water and anhydrous ethanol in sequence until the pH value of the product reaches 7, and the washing is completed.

[0069] In some embodiments, the drying temperature is 70° C.-90° C., and the drying time is 11 h-13 h.

[0070] In some embodiments, the primary calcination temperature is 440° C.-460° C., and the primary calcination time is 3.5 h-4.5 h.

[0071] In some embodiments, the speed of reaching the primary calcination temperature is 5.5° C. / min-6.5° C. / min.

[0072] In some embodiments, after a calcination, the product needs to be purged in nitrogen.

[0073] In the present invention, the introduction of nitrogen can remove other gas molecules on the catalyst surface, thereby facilitating the formation of oxygen vacancies.

[0074] In some embodiments, after purging in nitrogen, a reducing atmosphere and nitrogen are introduced simultaneously.

[0075] In the present invention, nitrogen is introduced at the same time as the reducing atmosphere to serve as a balance gas for the reaction environment, and the amount of nitrogen introduced can be adjusted according to actual conditions.

[0076] In some embodiments, the reducing atmosphere includes ammonia gas, and the amount of ammonia gas introduced is 100 ppm-500 ppm.

[0077] In some embodiments, the secondary calcination temperature is 440° C.-460° C., and the secondary calcination time is 3.5 h-4.5 h.

[0078] In some embodiments, the speed of reaching the secondary calcination temperature is 5.5° C. / min-6.5° C. / min.

[0079] In some embodiments, the specific method of introducing the reducing atmosphere again includes: introducing the reducing atmosphere until the product is cooled to room temperature.

[0080] In some embodiments, after the product is cooled to room temperature, nitrogen is introduced.

[0081] In some embodiments, the method for preparing the solution containing the vanadium source comprises:

[0082] Dissolve the vanadium source in deionized water in a water bath.

[0083] In some embodiments, the temperature of the water bath is 75° C.-85° C., and the water bath time is 25 min-35 min.

[0084] In some embodiments, the method for preparing the solution containing a zirconium source comprises:

[0085] Dissolve the zirconium source in deionized water and stir.

[0086] In a third aspect, some embodiments of the present invention also provide the use of the zirconium vanadate catalyst having oxygen vacancies in denitration at a temperature below 230°C.

[0087] The following is described in conjunction with specific embodiments:

[0088] Embodiment 1:

[0089] (1) Dissolve 2.5759 g Zr(NO3)2·5H2O in 25 mL deionized water and stir vigorously for 30 min to obtain solution A.

[0090] (2) At the same time, 0.70164 g of NH4VO3 was dissolved in 25 mL of deionized water, heated to 80 °C in a water bath, and stirred vigorously for 30 min to obtain solution B. The molar ratio of Zr ions to V ions was 1:1.

[0091] (3) Stir solution A and solution B until they are completely dissolved, then slowly pour solution B into solution A and continue stirring for 1 hour to obtain solution C.

[0092] (4) Prepare 1 mol / L ammonia solution, titrate solution C to pH = 9, and stir vigorously for 1 h.

[0093] (5) The resulting mixture was placed in a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180 °C for 12 h.

[0094] (6) After the reactor was cooled to 25°C, the slurry was filtered and washed with distilled water and ethanol several times until the pH value was 7.

[0095] (7) The obtained filter cake was then placed in an oven and dried at 80°C for 12 h. The dried sample was placed in a muffle furnace and calcined at 450°C for 4 h at a rate of 6°C / min to obtain a zirconium vanadate catalyst.

[0096] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0097] (9) Then, 200 ppm ammonia gas was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 450°C at a rate of 6°C / min for 4 h.

[0098] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0099] Embodiment 2:

[0100] The catalyst preparation steps of Example 2 are the same as (1) to (7) of Example 1.

[0101] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0102] (9) Then, 100 ppm ammonia gas was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 450°C at a rate of 6°C / min for 4 h.

[0103] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0104] Embodiment 3:

[0105] The catalyst preparation steps of Example 3 are the same as (1) to (7) of Example 1.

[0106] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0107] (9) Then, 500 ppm ammonia gas was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 450°C at a rate of 6°C / min for 4 h.

[0108] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0109] Comparative Example 1:

[0110] The catalyst preparation steps of Comparative Example 1 are the same as (1) to (7) of Example 1.

[0111] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0112] (9) Then, 200 ppm C3H8 was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 450°C at a rate of 6°C / min for 4 h.

[0113] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0114] Comparative Example 2:

[0115] The catalyst preparation steps of Comparative Example 2 are the same as (1) to (7) of Example 1.

[0116] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0117] (9) Then, 100 ppm C3H8 was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 450°C at a rate of 6°C / min for 4 h.

[0118] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0119] Comparative Example 3:

[0120] The catalyst preparation steps of Comparative Example 3 are the same as (1) to (7) of Example 1.

[0121] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0122] (9) Then, 500 ppm C3H8 was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 450°C at a rate of 6°C / min for 4 h.

[0123] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0124] Comparative Example 4:

[0125] The preparation steps of the catalyst of Comparative Example 4 are the same as those of Example 1 (1) to (7).

[0126] Comparative Example 5:

[0127] The catalyst preparation steps of Comparative Example 5 are the same as (1) to (7) of Example 1.

[0128] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0129] (9) Then, 500 ppm ammonia was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 200 °C at a rate of 6 °C / min for 4 h.

[0130] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0131] Comparative Example 6:

[0132] The catalyst preparation steps of Comparative Example 6 are the same as (1) to (7) of Example 1.

[0133] (8) The zirconium vanadate catalyst powder is placed in a N2 atmosphere for purging to remove other gas molecules on the catalyst surface.

[0134] (9) Then, 500 ppm ammonia was introduced, and N2 was also introduced into the environment, and the calcination was maintained at 600 °C at a rate of 6 °C / min for 4 h.

[0135] (10) Finally, the catalyst was cooled to room temperature in the same reducing atmosphere and purged with N2 gas to obtain a zirconium vanadate catalyst with oxygen vacancies on the surface.

[0136] Comparative Example 7:

[0137] (1) Dissolve 2.5759 g Zr(NO3)2·5H2O in 25 mL deionized water and stir vigorously for 30 min to obtain solution A.

[0138] (2) At the same time, 1.40328 g of NH4VO3 was dissolved in 50 mL of deionized water, heated to 80°C in a water bath, and stirred vigorously for 30 min to obtain solution B. The molar ratio of Zr ions to V ions was 1:2.

[0139] The catalyst preparation steps (3) to (10) of Comparative Example 7 are the same as those of Example 1.

[0140] The catalysts obtained from the examples and comparative examples were tested:

[0141] (1) ESR test of catalyst: Electron Spin Resonance Spectrometer (ESR) can qualitatively and quantitatively detect the unpaired electrons contained in atoms or molecules of a substance and explore the structural characteristics of its surrounding environment. The ESR instrument is BRUKER Magnettech ESR 5000, with a modulation of 0.2mT, a microwave power of 10mW, and 10.0dB.

[0142] (2) XPS test of catalyst: X-ray photoelectron spectroscopy (XPS) is usually used to detect the element valence and content of catalysts. This paper uses the Thermofisher ESCALAB Xi+ model for detection. And XPS PEAK software is used for peak fitting.

[0143] (3) NH3-SCR performance test of the catalyst: The catalyst was tested for denitrification activity in a fixed bed reactor. The test conditions adopted were: the reaction mixer contained NO (500ppm), NH3 (500ppm), O2 (10%), N2 was used as the balance gas, and the reaction space velocity was 50,000 h -1 The test temperature range is 130-430℃, and the dwell time is 60min every 50℃.

[0144] The calculation formula of NO removal rate is as follows:

[0145] ;

[0146] The calculation formula of N2 selectivity is as follows:

[0147] .

[0148] Results and Analysis:

[0149] Table 1 Oxygen vacancy concentration in Examples 1-3

[0150]

[0151] Table 2 The proportion of surface chemically adsorbed oxygen in Examples 1-3 and Comparative Examples 1-4

[0152]

[0153] Through the method of the present invention, oxygen vacancies are successfully formed on the surface of the zirconium vanadate catalyst. The formation of oxygen vacancies is mainly due to the loss of oxygen atoms in the crystal structure of the catalyst, thereby forming oxygen vacancies. Although oxygen vacancies promote the growth of surface active oxygen (such as OOH and OH, etc.), thereby improving the redox ability of the catalyst, but when the oxygen vacancy concentration is too high, too much oxygen vacancies may not only inhibit the generation of active oxygen through strong adsorption of oxygen species, but also cause the catalyst structure to be unstable. Therefore, different types of catalysts and the type of catalyst limit the oxygen vacancy content that can be formed. Even for the same type of catalyst, due to the different composition or ratio of elements in the catalyst, the formed catalyst will also have differences. Therefore, for the zirconium vanadate catalyst of the present invention, the oxygen vacancies on the catalyst surface are successfully regulated by the method of the present invention, so that the zirconium vanadate catalyst of the present invention can improve its redox ability on the basis of structural stability.

[0154] It should be understood by those skilled in the art that there are various methods for forming oxygen vacancies, and a common method is to use a reducing atmosphere. However, studies have found that when the catalyst selects different reducing gases to react, the final catalyst effect is different. By comparing Examples 1 to 3 of the present invention with Comparative Examples 1 to 3, it can be found in Table 2 that the active oxygen O α As the concentration of reducing gas NH3 / C3H8 increases, the surface active oxygen O α The proportion gradually increases, but due to different reducing gases, even if the amount of reducing gas introduced is the same, the oxygen vacancy content formed is different. It is further found that when the catalyst selects an inappropriate reducing gas, it may also cause a decrease in certain properties of the catalyst, such as selectivity. Figure 6 and Figure 7 The comparison shows that the selectivity of Examples 1 to 3 for N2 is the same as that of Comparative Example 4, while the selectivity of Comparative Examples 1 to 3 for N2 is lower than that of Comparative Example 4. It is speculated that this may be because the treatment of C3H8 as a reducing gas may cause the active sites on the catalyst surface to be occupied, thereby affecting the adsorption and activation of the reactant molecules in the NH3-SCR reaction. Therefore, for the zirconium vanadate catalyst of the present invention, it is further preferred that the reducing gas is ammonia.

[0155] On this basis, further research is conducted on the zirconium vanadate catalyst of the present invention. In the zirconium vanadate catalyst of the present invention, vanadium and zirconium exist in an amorphous form, so that the active sites in the catalyst are evenly dispersed, which can reduce the occurrence of local deactivation of the catalyst. In the present invention, it is ensured that vanadium and zirconium still exist in an amorphous form in the zirconium vanadate catalyst, and oxygen vacancies can be formed. Therefore, both the reducing gas and the reaction temperature are key conditions. When the reaction temperature is low, the zirconium vanadate catalyst lattice is not fully activated at high temperature, so the oxygen vacancies are not fully generated; and when calcined under high temperature conditions, it may not only cause the structure of ZrVOx itself to collapse, thereby reducing the catalytic activity, but also cause the crystal form of the catalyst to change from an amorphous to a crystalline structure. Therefore, based on the purpose of the present invention and the reaction conditions, when the reducing gas is selected as ammonia, the reaction temperature is further limited to 440°C-460°C. This temperature ensures that the crystal form of the zirconium vanadate catalyst will not change, and ammonia can also react at this temperature. By Figure 5 It was verified that the NO conversion rates of Examples 1 to 3 of the present invention at a temperature below 230°C were significantly better than those of Comparative Examples 1 and 5 to 7. In summary, the zirconium vanadate catalyst of the present invention needs to use nitrogen and the reaction temperature is 440°C-460°C.

[0156] exist Figure 5 It is further verified that even for the same type of zirconium vanadate catalysts, due to the differences in the ratios of elements in the zirconium vanadate catalysts, even if the method of the present invention is used, the catalytic performance of the catalyst obtained in Comparative Example 7 will not only not be improved, but will also be significantly reduced.

[0157] like Figure 1 (a) shows that the oxygen vacancy concentration on the catalyst surface is significantly increased after NH3 treatment. Among them, the catalyst treated with 500ppm NH3 has the strongest oxygen vacancy signal, followed by 200ppm and 100ppm NH3 treatment. This shows that the H and N atoms in NH3 can capture the O atoms in ZrVOx, thereby synthesizing a vanadate catalyst rich in oxygen vacancies. And by adjusting the concentration of reducing gas NH3, oxygen vacancies in different concentration ranges can be constructed on the catalyst surface. Similarly, if Figure 1 (b) The ESR image after treatment with reducing gas C3H8 also shows the same trend.

[0158] The quantitative results of oxygen vacancies on the catalyst surface are shown in Table 1. Reducing gas treatment can significantly enhance the concentration of oxygen vacancies on the catalyst surface, which is beneficial to the adsorption of NO and captures O2 in the air to form surface active oxygen, thereby activating the adsorbed reaction molecules and promoting the key intermediates. Similarly, the presence of oxygen vacancies is conducive to the adsorption of active substances NH3, promoting the activation and generation of key intermediates , accelerating the reaction process, following the Eley-Rideal or Langmuir-Hinshelwood mechanism.

[0159] exist Figure 2 According to the O 1s spectrum, as the concentration of reducing gas NH3 increases, the surface active oxygen O α The proportion is gradually increasing. 5+ With V 4+ Coexistence indicates the existence of circulation, which is beneficial to the NH3-SCR reaction. As the concentration of NH3 in the reducing gas increases, V 4+ The ratio increases, which indicates that there are some V 5+ is reduced. There is V in the system 5+ -OV-V 4+ (OV stands for oxygen vacancy) structure, which is more conducive to the generation of oxygen defects on the catalyst surface. This conclusion is consistent with the ESR results.

[0160] According to the NH3-TPD characterization results, Figure 3 It can be seen that after the treatment with low concentration reducing gas NH3, the amount of NH3 released by the catalyst has increased significantly, proving that the formation of oxygen vacancies will enhance the acidity of the catalyst surface. The peak at 100-300℃ has increased significantly after the treatment with low concentration reducing gas, which is due to the formation of surface defects promoting and Therefore, the generated V-OH groups act as Acid sites mainly play a role in the medium and low temperature range, which is beneficial to promoting the low-temperature catalytic activity of the catalyst.

[0161] exist Figure 4 According to the H2-TPR characterization results, the reduction peak of the zirconium vanadate catalyst appears between 500-550℃, which is mainly attributed to the V 5+reduction. And after treatment with low-concentration reducing gas NH3, the H2 consumption of the catalyst increased, indicating that its oxygen storage capacity was enhanced, and there were more reducible substances on the surface of the sample, which enhanced the redox property of the catalyst itself. In addition, the reduction peak after the reducing gas treatment shifted to the low temperature zone, which indicated that its low-temperature redox property was enhanced. However, as the concentration of oxygen vacancies on the surface of the ZrVOx catalyst further increased, the H2 consumption showed a downward trend. This shows that oxygen vacancies have a "two-sided nature" and the generation of surface active oxygen is highly dependent on the concentration of oxygen vacancies. Increasing the concentration of oxygen vacancies is an effective way to accelerate internal and interfacial charge transfer, but too many oxygen vacancies will promote the poor conversion and removal of ROS due to strong interactions, thereby leading to a decrease in redox property. Therefore, the surface of the ZrVOx catalyst treated with 500ppm reducing gas has an excessively high concentration of oxygen vacancies, which is not conducive to the circulation of surface oxygen. Therefore, it is further preferred that the amount of ammonia introduced is 200ppm.

[0162] The NH3-SCR performance test results of the catalysts of Examples 1 to 3 are as follows: Figure 5 As shown in the figure, the low-temperature catalytic activity of the zirconium vanadate catalyst treated with NH3 reducing gas has been improved. Among them, the NO conversion rate at 180℃ increased from 70% to 96%, and at 200℃ it increased from 92% to 97%, with excellent low-temperature catalytic activity. As the NH3 treatment concentration increases, the oxygen vacancy concentration gradually increases, and its catalytic activity decreases compared with the catalyst treated with 200ppm NH3, and the activity in the high-temperature zone decreases significantly. This may be because an appropriate amount of oxygen vacancies helps to promote the redox properties of the reaction and improve the catalytic activity. Excessive oxygen vacancies will make the catalyst too oxidizing, which is not conducive to the SCR reaction process.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a zirconium vanadate catalyst having oxygen vacancies, characterized in that: The preparation method comprises: adding a solution containing a vanadium source dropwise into a solution containing a zirconium source to obtain a mixed solution, adjusting the pH value of the mixed solution, performing a hydrothermal reaction, cooling, filtering, washing, drying, calcining once, introducing a reducing atmosphere, calcining twice, introducing a reducing atmosphere again, and obtaining a zirconium vanadate catalyst having oxygen vacancies; In the mixed solution, the molar ratio of the vanadium source to the zirconium source is 1:1, based on the vanadium ions in the vanadium source and the zirconium ions in the zirconium source. In the solution containing the vanadium source, the concentration of the vanadium source in the solution is 0.065 mol / L in terms of vanadium ions; In the solution containing the zirconium source, the concentration of the zirconium source in the solution is 0.065 mol / L in terms of zirconium ions; After the first calcination, the product needs to be purged in nitrogen; After purging in nitrogen, a reducing atmosphere and nitrogen are introduced simultaneously; The reducing atmosphere includes ammonia gas, and the amount of ammonia gas introduced is 100ppm-500ppm.

2. The method for preparing the zirconium vanadate catalyst according to claim 1, characterized in that: The pH value of the mixed solution was adjusted to 9 using ammonia water; the concentration of the ammonia water was 1 mol / L.

3. The method for preparing the zirconium vanadate catalyst according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 170° C.-190° C., and the time of the hydrothermal reaction is 11 h-13 h.

4. The method for preparing the zirconium vanadate catalyst according to claim 1, characterized in that: The drying temperature is 70°C-90°C, and the drying time is 11h-13h; The primary calcination temperature is 440°C-460°C, and the primary calcination time is 3.5h-4.5h; The speed of reaching the temperature of the primary calcination is 5.5°C / min-6.5°C / min.

5. The method for preparing the zirconium vanadate catalyst according to claim 1, characterized in that: The secondary calcination temperature is 440°C-460°C, and the secondary calcination time is 3.5h-4.5h; The speed of reaching the temperature of the secondary calcination is 5.5°C / min-6.5°C / min.

6. The zirconium vanadate catalyst having oxygen vacancies obtained by the preparation method according to any one of claims 1 to 5, characterized in that: The vanadium and zirconium in the zirconium vanadate catalyst are in an amorphous state and are uniformly dispersed in the catalyst; in the ESR image of the zirconium vanadate catalyst, the diffraction peak intensity is 8634.91au-44721.07au.

7. Use of the zirconium vanadate catalyst having oxygen vacancies obtained by the preparation method according to any one of claims 1 to 5 in denitration at a temperature below 230°C.

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