Low space velocity scr catalyst and method for making same

Abstract

This invention discloses a low-space-velocity (SCR) catalyst and its preparation method. The catalyst includes a coating and a support layer. The coating comprises a coating material consisting of a mixture of tungsten-doped (5%) anatase nano-titanium dioxide, titanium dioxide, and SSZ-13 molecular sieve, with a content of 56.1 wt% to 75.6 wt% of the total loading. The method includes the following steps: preparing a support layer solution and a coating material; preparing a catalyst slurry; drying a catalyst support with a support layer solution; coating the catalyst support with the catalyst slurry; and calcining and drying to obtain the catalyst. This invention improves the coating uniformity and efficiency by coating the support layer solution and the catalyst slurry, thereby improving the NO content of the catalyst under low space velocity conditions. x Conversion efficiency.

Description

Technical Field

[0001] This invention relates to the field of industrial exhaust gas purification and treatment technology, specifically a method for preparing a low space velocity SCR catalyst. Background Technology

[0002] Selective catalytic reduction (SCR) is an environmentally friendly technology widely used in industrial flue gas denitrification. This technology, also known as SCR catalytic reduction, selectively reduces nitrogen oxides (NOx) in flue gas into non-toxic, non-polluting nitrogen (N2) and water (H2O) using a reducing agent (such as ammonia, urea, or ammonia water) under the action of a catalyst. The SCR catalyst is the core of SCR technology, and its structure and performance directly affect the denitrification effect. The type, structure, and surface area of ​​the catalyst have a significant impact on the NOx removal efficiency. The construction cost of the SCR catalyst accounts for more than 20% of the cost of flue gas denitrification projects, and the operating cost accounts for more than 30%. The most commonly used catalysts are the V2O5-WO3(MoO3) / TiO2 series, where TiO2 is the main carrier, V2O5 is the main active ingredient, and WO3 and MoO3 are antioxidant and anti-poisoning auxiliary components. Catalyst types can be divided into plate, honeycomb, and corrugated plate types.

[0003] In-depth research into catalyst production technology and molding processes is a crucial aspect of the future development of SCR technology. Meanwhile, with increasingly stringent environmental regulations, the SCR catalyst industry will enter a period of stable demand. However, since existing domestic production capacity is still lower than market size, ensuring improved catalytic performance while increasing production capacity remains a pressing issue. Summary of the Invention

[0004] The purpose of this invention is to overcome the limitations of existing technologies in the application of NO at low airspeed conditions. x To address the low conversion efficiency, a low-space-velocity SCR catalyst and its preparation method are provided. The method improves coating uniformity and efficiency by coating the support layer solution and catalyst slurry, thereby increasing the NO conversion efficiency under low space velocity conditions. x Conversion efficiency.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] A low space velocity SCR catalyst includes a coating and a support layer, wherein,

[0007] The coating comprises:

[0008] The coating material is a mixture of anatase nano-titanium dioxide (5% tungsten doped), titanium dioxide, and SSZ-13 molecular sieve, with a content ranging from 56.1 wt% to 75.6 wt% of the total loading.

[0009] The active component is a mixture of V2O5 and transition metal oxides, wherein the V2O5 content is 3.0wt%~7.0wt% of the total loading, and the precursor is vanadium salt; the transition metal oxide content is 6.8wt%~15.3wt% of the total loading, and the precursor is transition metal salt.

[0010] The binder, silica, with silica sol as the precursor, comprises 4.2 wt% to 9.0 wt% of the total loading.

[0011] The support layer includes SSZ-13 molecular sieve, and the support layer accounts for 10.0wt%~15.0wt% of the total loading.

[0012] Furthermore, the support layer comprises SSZ-13 molecular sieve and alumina, wherein the SSZ-13 molecular sieve accounts for 90.0wt%~100.0wt% and the alumina layer accounts for 0.0wt%~10.0wt%;

[0013] In the coating material, the proportion of anatase nano-titanium dioxide with 5% tungsten doping is 0.0wt%~40.0wt%, the proportion of titanium dioxide is 50.0wt%~90.0wt%, and the proportion of SSZ-13 molecular sieve is 0.0wt%~10.0wt%.

[0014] In this invention, anatase nano-titanium dioxide with a tungsten content of 5% is used. Because WO3 is pre-distributed on the material surface, the dispersion is more uniform. After mixing the titanium dioxide material, a second layer of WO3 is dispersed, creating a thickness variation of WO3 on the surface of the mixed material. This increases the acidic sites inside and on the surface of the mixed material, promoting the formation of V-O-W on the surface and increasing Vo. 5+ The proportion of zirconium is increased to improve performance in the low-temperature range and broaden the active range of the catalyst. The addition of zirconium inhibits the polymerization of V2O5 at high temperatures, improves the thermal stability of the catalyst, and increases the oxygen vacancy on the surface of the coating material, thereby enhancing its resistance to SO2 and H2O in practical applications.

[0015] The support layer composed of SSZ-13 molecular sieve benefits from the increased specific surface area brought about by its eight-membered ring channel and three-dimensional intersecting channel crystal structure, which increases the coating's affinity for NO. X The increased contact area enhances catalyst efficiency; and the unique dendritic structure formed between the catalyst support and the coating affects the airflow direction through the inner surface of the catalyst, slowing down the flow rate and improving catalytic performance.

[0016] Vanadium metal ions and transition metal ions are preferentially added as active components under acidic liquid phase conditions. Combined with coating materials mixed in proportion, the active components are uniformly dispersed on the surface and pores of the coating material in the liquid phase environment, providing more adhesion sites for the active components, increasing the contact area between the active material and the reactants, and improving the catalyst performance.

[0017] A method for preparing a low space velocity SCR catalyst includes the following steps:

[0018] Preparation of the support layer solution and coating material;

[0019] Mix and dissolve vanadium salts with transition metal salts to prepare a catalyst slurry;

[0020] Prepare a catalyst support, coat the catalyst support with a support layer solution, and dry the catalyst support with the support layer solution.

[0021] After drying the catalyst support with the support layer solution, the catalyst slurry is coated onto the catalyst support, and the catalyst support with the catalyst slurry is dried.

[0022] A low space velocity SCR catalyst was obtained by calcining and drying the catalyst support containing the catalyst slurry.

[0023] Furthermore, spreading the support layer solution includes the following steps:

[0024] Place the catalyst support horizontally with the pores facing upwards;

[0025] The support layer solution is evenly spread on the end face of the channel, and the catalyst carrier is shaken until the support layer solution flows into the channel of the catalyst carrier.

[0026] The catalyst support with the support layer solution is dried.

[0027] Furthermore, spreading the catalyst slurry includes the following steps:

[0028] Place the catalyst support horizontally with the pores facing upwards;

[0029] The support layer solution is evenly spread on the end face of the channel, and the catalyst carrier is shaken until the support layer solution flows into the channel of the catalyst carrier.

[0030] The catalyst support containing the catalyst slurry is dried.

[0031] Furthermore, the preparation of the support layer solution includes the following steps:

[0032] A support layer mixture was obtained by mixing SSZ-13 molecular sieve, alumina, and glacial acetic acid in a certain mass ratio.

[0033] SSZ-13 molecular sieve content: 86wt%~92wt%, alumina content: 0wt%~7wt%, glacial acetic acid content: 0wt%~7wt%;

[0034] The support layer mixture was mechanically ball-milled for 0.1 h to 0.5 h.

[0035] Prepare a support layer solution.

[0036] Furthermore, the preparation of the coating material includes the following steps:

[0037] A coating mixture was prepared by mixing anatase nano-titanium dioxide (5% tungsten doping), titanium dioxide, and SSZ-13 molecular sieve in a specific mass ratio. The anatase nano-titanium dioxide (5% tungsten doping) comprised 0.0 wt% to 40.0 wt% of the total material, the titanium dioxide comprised 50.0 wt% to 90.0 wt% of the total material, and the SSZ-13 molecular sieve comprised 0.0 wt% to 10.0 wt% of the total material.

[0038] The coating mixture was mechanically ball-milled for 0.1 h to 0.5 h.

[0039] It is made into a coating material.

[0040] Furthermore, the preparation of the catalyst slurry includes the following steps:

[0041] The vanadium salt and transition metal salt are mixed and dissolved, stirred for 0.5 h to 1 h, mixed evenly, and the pH is adjusted to 3 to 6.

[0042] Add additives, heat to 60℃~90℃, keep warm for 0.5h~1h, then add coating materials and additives, heat to 60℃~90℃, keep stirring and keep warm for 1h~3h, after the warming is completed, cool the solution to room temperature;

[0043] Add a binder, adjust the pH to 6-8, and stir for 3-5 hours to prepare a catalyst slurry.

[0044] The catalyst loading is 150 g / L to 260 g / L.

[0045] Furthermore, the additive includes one or any combination of two or more substances such as ethylene glycol, glucose, sodium borohydride, ascorbic acid, and citric acid, and its content is 1 to 3 times that of V2O5.

[0046] The auxiliary agent includes one or a combination of any two or more substances selected from hydrochloric acid, nitric acid, acetic acid, oxalic acid, ethylenediamine, and ethanolamine, and its content is 0.207 to 0.345 times that of V2O5.

[0047] The binder is silica sol, accounting for 4.2 wt% to 9.0 wt% of the total loading.

[0048] Furthermore, when calcining and drying the catalyst support containing the catalyst slurry, the drying temperature is 110℃~150℃, the drying time is 0.5h~2h, the calcination temperature is 450℃~550℃, and the calcination time is 1h~3h.

[0049] The addition of SSZ-13 molecular sieve to coating materials, with its high specific surface area and acidity, provides more surface Brønsted (B) and Lewis (L) acid sites, increasing vanadium ion exchange capacity. Simultaneously, the higher acidity helps inhibit the adsorption of SO2 by the active component, improving the catalyst's sulfur resistance. The good hydrothermal stability of the molecular sieve also extends the catalyst's long-term service life in industrial applications. Furthermore, the modification of SSZ-13 molecular sieve produces more polymerized VOCs. X and low-priced VO X Improve low-temperature activity;

[0050] The addition of SiO2 maintains a long-term, effective, and tight bond between the catalyst coating material and the catalyst support, extending the catalyst's lifespan and reducing operating costs.

[0051] In summary, the present invention has the following advantages compared with the prior art:

[0052] This invention uses anatase nano-titanium dioxide with a tungsten content of 5%. Because WO3 is pre-distributed on the material surface, the dispersion is more uniform. After mixing the titanium dioxide material, a second layer of WO3 is dispersed, creating a difference in the thickness of the WO3 distribution on the surface of the mixed material. This increases the acidic sites inside and on the surface of the mixed material, promoting the formation of V-O-W on the surface and increasing Vo. 5+ The proportion of zirconium is increased to improve performance in the low-temperature range and broaden the active range of the catalyst. The addition of zirconium inhibits the polymerization of V2O5 at high temperatures, improves the thermal stability of the catalyst, and increases the oxygen vacancy on the surface of the coating material, thereby enhancing its resistance to SO2 and H2O in practical applications. Attached Figure Description

[0053] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0054] Figure 1 This is a diagram showing the fresh performance of the catalyst of this invention;

[0055] Figure 2 This is a diagram showing the aging performance of the catalyst of this invention. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0057] In this invention, the catalyst carrier is made of cordierite honeycomb ceramic with a honeycomb mesh size of 46. Cylindrical dimensions: radius: 25.4mm~550mm, height: 25.4mm~200mm; Square dimensions: length: 100mm~1000mm, width: 100mm~1000mm, height: 50mm~300mm.

[0058] Example 1:

[0059] Preparation of the support layer solution: SSZ-13 molecular sieve, alumina and glacial acetic acid were mixed in a mass ratio of 92:4:4 and mechanically ball-milled for 0.1h~0.5h to prepare the support layer solution.

[0060] Preparation of coating material: 5% tungsten-doped anatase nano-anatase nano-titanium dioxide, titanium dioxide and SSZ-13 molecular sieve are mixed at a designed mass ratio of 4:5:1 and then ball-milled for 0.5h~1h to obtain the coating material.

[0061] Preparation of the active component precursor solution: Platinum salt was added at 3.7% of the total carrier loading, zirconium salt at 3.7% of the total loading, and tungsten salt at 6.7% of the total loading. The mixture was dissolved and stirred for 0.5 h, and the pH was adjusted to 4.0. Citric acid was added at a mass ratio of 1.28 times that of V2O5, and ethanolamine was added at a mass ratio of 0.29 times that of V2O5. After stirring evenly, the solution was heated to 80℃ and kept stirred for 3 h to prepare the active component precursor solution.

[0062] Preparation of catalyst slurry: The prepared coating material was added, accounting for 53.6% of the total catalyst loading. After the heat preservation period, the mixture was cooled to room temperature, and then 7.5% of the total loading of silica sol was added. The pH was adjusted to 6.5, and the mixture was stirred for 1 hour to prepare the catalyst slurry.

[0063] Catalyst preparation: A φ25.4*25.4mm / 46-mesh ceramic support was selected. The support layer solution was uniformly spread on the surface of the pores inside the support using vacuum negative pressure. After completion, the catalyst was dried at 110℃ for 0.5h and weighed to ensure that the residual material was 0.65g. The catalyst slurry was uniformly spread on the surface of the pores inside the support again using vacuum negative pressure. After completion, the catalyst was dried at 110℃ for 0.5h and weighed to ensure that the residual material was 1.98g. Then, the coated catalyst was calcined at 500℃ for 1h to ensure that the total residual dry weight was 2.63g.

[0064] Example 2: In this example, the catalyst preparation process is the same as in Example 1, except that the mass ratio of anatase nano-anatase nano-titanium dioxide with 5% tungsten doping, anatase nano-titanium dioxide and SSZ-13 molecular sieve is 1:8:1.

[0065] Example 3: In this example, the catalyst preparation process is the same as in Example 1, except that the mass ratio of anatase nano-anatase nano-titanium dioxide with 5% tungsten doping, anatase nano-titanium dioxide and SSZ-13 molecular sieve is 4:6:0.

[0066] Example 4: In this example, the catalyst preparation process is the same as in Example 1, except that the mass ratio of anatase nano-anatase nano-titanium dioxide with 5% tungsten doping, anatase nano-titanium dioxide and SSZ-13 molecular sieve is 0:90:1.

[0067] Example 5: In this example, the catalyst preparation process is the same as in Example 1, except that the mass ratio of anatase nano-anatase nano-titanium dioxide with 5% tungsten doping, anatase nano-titanium dioxide and SSZ-13 molecular sieve is 0:1:0.

[0068] Examples 1 and 2-5 use the same transition metal and binder, but differ in the proportions of anatase nano-anatase nano-titanium dioxide, titanium dioxide, and SSZ-13 molecular sieve with a tungsten content of 5%. The purpose is to compare the differences in the fresh performance and aging performance of catalysts with different proportions in the mixture.

[0069] Example 6: In this example, the catalyst preparation process is the same as in Example 1, except that tungsten salt and zirconium salt are not added, and only vanadium salt is used.

[0070] Example 7: In this example, the catalyst preparation process is the same as in Example 1, except that zirconium salt is not added, and only vanadium salt and tungsten salt are used.

[0071] Example 8: In this example, the catalyst preparation process is the same as in Example 1, except that the zirconium salt is replaced with cobalt salt, the proportion remains the same, only the type is changed.

[0072] Example 9: In this example, the preparation process of the catalyst is the same as in Example 1, except that the ammonium salt is replaced with cobalt salt, zirconium is replaced with cerium salt, and cerium acetate is replaced with cerium salt, with the proportions remaining the same, only the types are changed.

[0073] In Examples 1 and 6-9, the titanium oxide mixtures contained titanium monoxide, anatase nano-titanium dioxide, and titanium trioxide in the same proportions, but with different transition metal types. The purpose was to compare the differences in freshness and aging performance of catalysts with different transition metal types.

[0074] By comparing the freshness and aging performance test results of Examples 1 and 2-5, as follows: Figure 1 , Figure 2 As shown, the results indicate that:

[0075] Example 1 shows a 5%-10% improvement in fresh performance and a 5%-15% improvement in aging performance compared to the comparative example. This is attributed to the proportional mixing of the three active components, which allows for uniform dispersion of the active components on the surface and within the pores of the coating material in a liquid phase environment. This provides more adhesion sites for the active components, increases the contact area between the active material and the reactants, and improves catalyst performance. The tungsten doping, combined with the additional tungsten, increases the acidic sites on the interior and surface, forming V-O-W on the TiO2 surface and enhancing Vo. 5+ The proportion of zirconium is increased to improve performance in the low-temperature range and broaden the active range of the catalyst. The addition of zirconium inhibits the polymerization of V2O5 at high temperatures, improves the thermal stability of the catalyst, and increases the surface vacancy sites of the coating material, thereby enhancing its resistance to H2O in practical applications. At the same time, the addition of SSZ-13 molecular sieve, with its high specific surface area and acidity, provides more surface Brønsted acid sites and Lewis acid sites for the coating material, increasing the vanadium ion exchange capacity and improving the catalyst performance. The good hydrothermal stability of the molecular sieve also improves the long-term service life of the catalyst in industrial applications.

[0076] By comparing the freshness and aging performance test results of Examples 1 and 6-9, as follows: Figure 1 , Figure 2 As shown, the results indicate that:

[0077] The vanadium-tungsten-zirconium composite oxide formed after calcination effectively inhibits platinum displacement and agglomeration, maintaining the high dispersibility, stable particle size and electronic state of vanadium; the appropriate ratio of vanadium, tungsten and zirconium fully utilizes the performance of the oxide, enhances the interaction between active components, improves its own stability, and achieves a long service life of the catalyst.

[0078] The catalyst performance testing methods are as follows:

[0079] The concentration of exhaust gas before and after passing through the catalyst was measured using a chromatograph to determine the ignition temperature and conversion efficiency temperature. The catalyst was then aged under a conditioned atmosphere, and tests were conducted under the same atmosphere to determine the ignition temperature and conversion efficiency after aging. The test boundaries are as follows:

[0080]

[0081] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low space velocity SCR catalyst, characterized in that, Includes a coating and a support layer, wherein, The coating comprises: The coating material is a mixture of anatase nano-titanium dioxide (5% tungsten doped), titanium dioxide, and SSZ-13 molecular sieve, with a content ranging from 56.1 wt% to 75.6 wt% of the total loading. The active component is a mixture of V2O5 and transition metal oxides, wherein the V2O5 content is 3.0wt%~7.0wt% of the total loading, and the precursor is vanadium salt; the transition metal oxide content is 6.8wt%~15.3wt% of the total loading, and the precursor is transition metal salt; the transition metal salt is platinum salt, zirconium salt, and tungsten salt. The binder, silica, with silica sol as the precursor, comprises 4.2 wt% to 9.0 wt% of the total loading. The support layer includes SSZ-13 molecular sieve, and the support layer accounts for 10.0wt%~15.0wt% of the total loading.

2. The low space velocity SCR catalyst according to claim 1, characterized in that, The support layer comprises SSZ-13 molecular sieve and alumina, with SSZ-13 molecular sieve accounting for 90.0wt%~100.0wt% and alumina layer accounting for 0.0wt%~10.0wt%. In the coating material, the proportion of anatase nano-titanium dioxide with 5% tungsten doping is 0.0wt%~40.0wt%, the proportion of titanium dioxide is 50.0wt%~90.0wt%, and the proportion of SSZ-13 molecular sieve is 0.0wt%~10.0wt%.

3. A method for preparing a low space velocity SCR catalyst, characterized in that, Includes the following steps: Preparation of the support layer solution and coating material; Mix and dissolve vanadium salts with transition metal salts to prepare a catalyst slurry; Prepare a catalyst support, coat the catalyst support with a support layer solution, and dry the catalyst support with the support layer solution. After drying the catalyst support with the support layer solution, the catalyst slurry is coated onto the catalyst support, and the catalyst support with the catalyst slurry is dried. The catalyst support containing the catalyst slurry after calcination and drying yields a low space velocity SCR catalyst as described in claim 1 or 2.

4. The method for preparing a low space velocity SCR catalyst according to claim 3, characterized in that, Spreading the support layer solution includes the following steps: The catalyst support is evenly spread with the support layer solution, and the catalyst support is shaken until the support layer solution flows into the pores of the catalyst support. A negative or positive pressure airflow is applied to the catalyst support until the support layer solution is uniformly spread within the pores of the catalyst support. The catalyst support with the support layer solution is dried.

5. The method for preparing a low space velocity SCR catalyst according to claim 3, characterized in that, Spreading the catalyst slurry includes the following steps: The catalyst support is evenly spread with the support layer solution, and the catalyst support is shaken until the support layer solution flows into the pores of the catalyst support. A negative or positive pressure airflow is applied to the catalyst support until the support layer solution is uniformly spread within the pores of the catalyst support. The catalyst support containing the catalyst slurry is dried.

6. The method for preparing a low space velocity SCR catalyst according to claim 3, characterized in that, The preparation of the support layer solution includes the following steps: A support layer mixture was obtained by mixing SSZ-13 molecular sieve, alumina and glacial acetic acid in a certain mass ratio. The support layer mixture was mechanically ball-milled for 0.1 h to 0.5 h. Prepare a support layer solution.

7. The method for preparing a low space velocity SCR catalyst according to claim 3, characterized in that, The preparation of the coating material includes the following steps: A coating mixture was prepared by mixing anatase nano-titanium dioxide (5% tungsten doping), titanium dioxide, and SSZ-13 molecular sieve in a specific mass ratio. The anatase nano-titanium dioxide (5% tungsten doping) comprised 0.0 wt% to 40.0 wt% of the total material, the titanium dioxide comprised 50.0 wt% to 90.0 wt% of the total material, and the SSZ-13 molecular sieve comprised 0.0 wt% to 10.0 wt% of the total material. The coating mixture was mechanically ball-milled for 0.1 h to 0.5 h. It is made into a coating material.

8. The method for preparing a low space velocity SCR catalyst according to claim 3, characterized in that, The preparation of the catalyst slurry includes the following steps: The vanadium salt and transition metal salt are mixed and dissolved, stirred for 0.5 h to 1 h, mixed evenly, and the pH is adjusted to 3 to 6. Add additives, heat to 60℃~90℃, keep warm for 0.5h~1h, then add coating materials and additives, heat to 60℃~90℃, keep stirring and keep warm for 1h~3h, after the warming is completed, cool the solution to room temperature; Add a binder, adjust the pH to 6-8, and stir for 3-5 hours to prepare a catalyst slurry.

9. The method for preparing a low space velocity SCR catalyst according to claim 8, characterized in that, The additives include one or any combination of two or more substances such as ethylene glycol, glucose, sodium borohydride, ascorbic acid, and citric acid, and their content is 1 to 3 times that of V2O5. The auxiliary agent includes one or a combination of any two or more substances selected from hydrochloric acid, nitric acid, acetic acid, oxalic acid, ethylenediamine, and ethanolamine, and its content is 0.207 to 0.345 times that of V2O5. The binder is silica sol, accounting for 4.2wt% to 9.0wt% of the total load.

10. The method for preparing a low space velocity SCR catalyst according to claim 3, characterized in that, When calcining and drying the catalyst support containing the catalyst slurry, the drying temperature is 110℃~150℃, the drying time is 0.5h~2h, the calcination temperature is 450℃~550℃, and the calcination time is 1h~3h.

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