A low-temperature denitration catalyst resistant to SO2 poisoning and its preparation method

Abstract

This invention discloses a low-temperature denitrification catalyst resistant to SO2 poisoning and its preparation method. Water, an alkali source, a silicon source, an aluminum source, a copper source, and a template agent are added to a polytetrafluoroethylene (PTFE) liner, mixed thoroughly, and aged at 30–80°C. The mixture is then transferred to an oven and crystallized at 120–180°C for 1–9 days. The product is filtered, washed, dried, and calcined to obtain FeCu-SSZ-13 molecular sieve. The surface of the FeCu-SSZ-13 molecular sieve is functionalized, and then hydrazine hydrate, nitrate, and chloride are added. The mixture is stirred and reacted in a water bath to obtain a free radical site-FeCu-SSZ-13 molecular sieve denitrification catalyst. The catalyst prepared by this invention can convert SO2, which is harmful to the NH3-SCR reaction, into a component beneficial to low-temperature denitrification. This not only hinders the reaction of SO2 with the denitrification active center and NH3, avoiding poisoning and deactivation of FeCu-SSZ-13, but also allows SO2 to promote the low-temperature denitrification reaction. The catalyst of this invention has a simple synthesis process, low cost, and strong sulfur resistance, and is expected to achieve long-term commercial application of heteroatom molecular sieve-based denitrification catalysts.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation and waste gas treatment, and specifically relates to a low-temperature denitrification catalyst resistant to SO2 poisoning and its preparation method. Background Technology

[0002] Nitrogen oxides (NO) x NO is one of the main air pollutants. x NO emissions not only contribute to acid rain and harm the environment, but also enter the lungs, causing bronchial diseases or emphysema, seriously damaging health. Therefore, reducing NO emissions is crucial. x Emissions have become one of the most urgent and important tasks in the prevention and control of air pollution.

[0003] Selective catalytic reduction of ammonia (NH3-SCR) is currently the most widely used flue gas denitrification technology globally, and its core lies in the denitrification catalyst. Among existing denitrification catalysts, such as V2O5-WO3 / TiO2, they can effectively meet the needs of medium- and high-temperature flue gas denitrification scenarios. Furthermore, heteroatom molecular sieve-based catalysts exhibit good denitrification capabilities for low-temperature flue gas (<250 ℃) from non-power industries such as steel, cement, chemicals, and glass. However, heteroatom molecular sieve-based catalysts are highly susceptible to SO2 during low-temperature flue gas denitrification, leading to the loss of redox capabilities at their metal active sites and the formation of ammonium sulfate that clogs their pores. This hinders the contact between NH3 and NO and the catalytic active centers, resulting in SO2 poisoning and deactivation of the heteroatom molecular sieve-based denitrification catalyst. This is a key reason why heteroatom molecular sieve-based denitrification catalysts cannot be widely commercially applied in low-temperature denitrification. Therefore, improving the sulfur resistance of heteroatom molecular sieve-based denitrification catalysts is currently a focus of widespread attention.

[0004] In recent years, to enhance the sulfur resistance of heteroatom molecular sieve-based denitration catalysts, numerous methods for improving their sulfur resistance have been extensively studied. The most effective method is to introduce sacrificial agents (such as Ce, Fe, and Zn) onto the surface of the catalyst, allowing them to preferentially react with SO2 and thus preventing the active sites of the catalyst from contacting SO2, thereby improving the sulfur resistance of the catalyst. However, the introduced sacrificial system can be completely consumed by SO2, failing to meet the requirements for long-term commercial applications. Therefore, the SO2 poisoning problem of heteroatom molecular sieve-based denitration catalysts has not yet been effectively solved. Therefore, developing a heteroatom molecular sieve-based catalyst capable of converting SO2 into a catalyst that promotes low-temperature denitration reactions is of great practical significance and industrial value for achieving its long-term commercial application. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature denitrification catalyst resistant to SO2 poisoning and its preparation method. A free radical generation system is introduced onto the surface of the heteroatom molecular sieve-based catalyst, enabling it to convert sulfur dioxide, which is detrimental to the NH3-SCR reaction, into a favorable component that promotes the reaction, thereby improving the sulfur resistance of the heteroatom molecular sieve-based catalyst in the low-temperature NH3-SCR reaction.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a low-temperature denitration catalyst resistant to SO2 poisoning includes the following steps:

[0008] 1) Deionized water, alkali source, silicon source, aluminum source, copper source and template agent were added sequentially to 100 mL of polytetrafluoroethylene liner, mixed evenly, aged at 30~80℃ for several hours, and then transferred to constant temperature oven for crystallization at 120~180℃ for 1~9 days. After crystallization, the solid product was filtered, washed and dried, and finally calcined at 500~700℃ for 1~6 h to obtain Cu-SSZ-13 molecular sieve.

[0009] 2) Constructing a free radical generation system on the surface of Cu-SSZ-13 molecular sieve: First, the surface of Cu-SSZ-13 molecular sieve is functionalized, and then hydrazine hydrate, nitrate and chloride are added in sequence. The mixture is stirred in a water bath and the solid product is collected to obtain the free radical site-Cu-SSZ-13 molecular sieve denitration catalyst.

[0010] Furthermore, the addition amount of each reaction raw material is controlled so that the molar ratio range is: 1 SiO2: 0.01~0.2 Al2O3: 0.1~2 Na2O: 100~500 H2O: 0.05-0.2 Cu: 0.01-0.3 template agent: 0.01~0.1 nitrate: 0.01~0.2 chloride: 0.1-2 hydrazine hydrate.

[0011] Further, the alkali source is sodium hydroxide; the silicon source is one or a mixture of several of kaolin, silica sol, sodium metasilicate, and sodium aluminosilicate; the aluminum source is one or a mixture of several of kaolin, rettore, sodium metasilicate, and aluminum chloride; the copper source is one or a mixture of several of copper nitrate, copper chloride, and copper sulfate; and the template agent is one or a mixture of several of adamantane, tetraethylenepentamine, tetrapropylammonium hydroxide, and ethylenediamine.

[0012] Furthermore, the nitrate is one or a mixture of zinc nitrate, zirconium nitrate, manganese nitrate, tantalum nitrate, and silver nitrate; the chloride is one or a mixture of boron chloride, lithium chloride, magnesium chloride, potassium chloride, zinc chloride, and calcium chloride.

[0013] Furthermore, the treatment reagents used for the surface functionalization treatment of Cu-SSZ-13 molecular sieves are one or a mixture of several of cetyl ammonium bromide, hexamethylenetetrammonium, ethanol, and copper polyvinylpyrrolidone.

[0014] Furthermore, the method for surface functionalization of Cu-SSZ-13 molecular sieve is as follows: Cu-SSZ-13 molecular sieve powder is ultrasonically dispersed in ethanol or water / ethanol mixture, then a treatment reagent is added, and the mixture is continuously stirred at 55~65 ℃ for 5.5~6.5 h.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. This invention constructs a free radical generation system on the surface of Cu-SSZ-13 molecular sieve by adding hydrazine hydrate, nitrate, and chloride. This system can convert SO2, which is detrimental to denitration reactions, into sulfate species beneficial to low-temperature denitration. These sulfate species promote the formation of denitration reaction intermediates on the surface of the Cu-SSZ-13 molecular sieve catalyst, thereby improving the low-temperature denitration efficiency of the catalyst. This method pioneers a new strategy for improving the sulfur resistance of heteroatom molecular sieve-based denitration catalysts. Compared with existing technologies, this invention is completely different from existing design concepts and can effectively overcome the problem of insufficient sulfur resistance in the long-term commercial application of heteroatom molecular sieve-based denitration catalysts, enabling their widespread commercial application.

[0017] 2. Compared with existing denitrification catalyst sulfur-resistant technologies, the free radical site-Cu-SSZ-13 molecular sieve denitrification catalyst prepared by this method can transfer SO2 molecules out of the NH3-SCR reaction system at the molecular level. SO2 does not form sulfate and ammonium salts with the denitrification active center, free radical site and ammonia. At the same time, SO2 molecules synergistically promote the low-temperature denitrification reaction of Cu-SSZ-13 molecular sieve catalyst during the transfer process.

[0018] 3. The radical site-Cu-SSZ-13 molecular sieve denitrification catalyst prepared by this method has excellent N2 selectivity and low-temperature sulfur resistance. At 125~300 ℃, the N2 selectivity is higher than 99% and the NO conversion rate is higher than 95%. In addition, the catalyst also has good hydrothermal stability. Attached Figure Description

[0019] Figure 1 The XRD patterns are of the products prepared in Examples 1-7 of this invention.

[0020] Figure 2 The diagram shows the low-temperature sulfur-resistant denitrification activity of the products prepared in Examples 1-7 of this invention. Implementation

[0021] The present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention. Example 1

[0022] Preparation method of FeCu-SSZ-13 molecular sieve

[0023] 60 mL of deionized water, 3.1 g of NaOH, 4.3 g of silica sol, 1.8 g of rettoiter, 0.85 g of copper sulfate, and 3.5 g of ethylenediamine were added sequentially to a 100 mL polytetrafluoroethylene liner. The mixture was stirred evenly at room temperature and then aged at 60 °C for 12 h. After aging, the mixture was transferred to a constant temperature oven and crystallized at 180 °C for 3 days. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 500 °C for 3 h to obtain FeCu-SSZ-13 molecular sieve. Example 2

[0024] Preparation method of free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst

[0025] In a 100 mL polytetrafluoroethylene liner, 60 mL of deionized water, 3.1 g of NaOH, 4.3 g of silica sol, 1.8 g of tartaric acid, 0.85 g of copper sulfate, and 3.5 g of ethylenediamine were added sequentially. The mixture was thoroughly mixed at room temperature and then aged at 60 °C for 12 h. After aging, the mixture was transferred to a constant temperature oven at 180 °C for crystallization for 3 days. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 500 °C for 3 h to obtain FeCu-SSZ-13 molecular sieve. 1.5 g of FeCu-SSZ-13 molecular sieve powder was weighed and placed in a round-bottom flask. Then, 350 mL of ethanol / water (v / v=5) was added, and the mixture was sonicated for 30 min. Then, 2 g of hexadecylammonium bromide and 0.35 g of hexamethylenetetrammonium were added sequentially, and the mixture was stirred continuously at 60 °C for 6 h. Subsequently, 8 mL of hydrazine hydrate, 0.35 g of tungsten nitrate and 0.03 g of magnesium chloride were added, and the mixture was stirred for 10 h. After filtration and drying, the free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst was obtained. Example 3

[0026] Preparation method of free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst

[0027] In a 100 mL polytetrafluoroethylene liner, 60 mL of deionized water, 3.1 g of NaOH, 4.3 g of silica sol, 1.8 g of tartaric acid, 0.85 g of copper sulfate, and 3.5 g of ethylenediamine were added sequentially. The mixture was thoroughly mixed at room temperature and then aged at 60 °C for 12 h. After aging, the mixture was transferred to a constant temperature oven at 180 °C for 3 days to crystallize. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 500 °C for 3 h to obtain FeCu-SSZ-13 molecular sieve. 1.5 g of FeCu-SSZ-13 molecular sieve powder was weighed and placed in a round-bottom flask. 450 mL of ethanol / water (v / v=5) was added, and the mixture was sonicated for 30 min. Then, 2.5 g of cetylammonium bromide and 0.36 g of hexamethylenetetrammonium were added sequentially, and the mixture was stirred continuously at 60 °C for 6 h. Subsequently, 10 mL of hydrazine hydrate, 0.35 g of tungsten nitrate, 0.25 g of manganese nitrate, 0.03 g of magnesium chloride and 0.02 g of nickel chloride were added, and the mixture was stirred continuously for 10 h. After filtration and drying, the free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst was obtained. Example 4

[0028] Preparation method of Cu-SSZ-13 molecular sieve denitration catalyst with free radical sites

[0029] In a 100 mL polytetrafluoroethylene (PTFE) liner, 50 mL of deionized water, 2 g of NaOH, 6 g of silica sol, 1 g of sodium aluminate, 1 g of copper nitrate, and 3 g of tetraethylenepentamine were added sequentially. The mixture was thoroughly mixed at room temperature and then aged at 40 °C for 6 h. After aging, the mixture was transferred to a constant temperature oven at 160 °C for crystallization for 4 days. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 600 °C for 5 h to obtain Cu-SSZ-13 molecular sieve. 2 g of Cu-SSZ-13 molecular sieve powder was weighed and placed in a round-bottom flask. 350 mL of ethanol / water (v / v=5) was added, and the mixture was sonicated for 30 min. Then, 1 g of hexadecylammonium bromide and 0.3 g of hexamethylenetetrammonium were added sequentially, and the mixture was stirred continuously at 80 °C for 3 h. Subsequently, 5 mL of hydrazine hydrate, 0.15 g of zinc nitrate and 0.05 g of lithium chloride were added, and the mixture was stirred for 10 h. After filtration and drying, the free radical site-Cu-SSZ-13 molecular sieve denitration catalyst was obtained. Example 5

[0030] Preparation method of Cu-SSZ-13 molecular sieve denitration catalyst with free radical sites

[0031] In a 100 mL polytetrafluoroethylene (PTFE) liner, 50 mL of deionized water, 2 g of NaOH, 6 g of silica sol, 1 g of sodium aluminate, 1 g of copper nitrate, and 3 g of tetraethylenepentamine were added sequentially. The mixture was thoroughly mixed at room temperature and then aged at 40 °C for 6 h. After aging, the mixture was transferred to a constant temperature oven at 160 °C for crystallization for 4 days. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 600 °C for 5 h to obtain Cu-SSZ-13 molecular sieve. 2 g of Cu-SSZ-13 molecular sieve powder was weighed and placed in a round-bottom flask. 375 mL of ethanol / water (v / v=5) was added, and the mixture was sonicated for 30 min. Then, 1.2 g of hexadecylammonium bromide and 0.31 g of hexamethylenetetrammonium were added sequentially, and the mixture was stirred continuously at 80 °C for 3 h. Subsequently, 12 mL of hydrazine hydrate, 0.15 g of zinc nitrate, 0.33 g of silver nitrate, 0.05 g of lithium chloride and 0.03 g of nickel chloride were added, and the mixture was stirred for 12 h. After filtration and drying, the free radical site-Cu-SSZ-13 molecular sieve denitration catalyst was obtained. Example 6

[0032] Preparation method of free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst

[0033] 45 mL of deionized water, 4 g of NaOH, 10 g of kaolin, 3 g of sodium aluminate, 0.95 g of copper chloride, and 15 g of adamantane were added sequentially to a 100 mL polytetrafluoroethylene liner. The mixture was thoroughly mixed at room temperature and then aged at 70 °C for 12 h. After aging, the mixture was transferred to a constant temperature oven at 170 °C for crystallization for 3 days. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 500 °C for 3 h to obtain FeCu-SSZ-13 molecular sieve. 1.8 g of FeCu-SSZ-13 molecular sieve powder was weighed and placed in a round-bottom flask. 350 mL of ethanol / water (v / v=5) was added, and the mixture was sonicated for 30 min. Then, 2.3 g of hexadecylammonium bromide and 0.41 g of hexamethylenetetrammonium were added sequentially, and the mixture was stirred continuously at 70 °C for 5 h. Subsequently, 6 mL of hydrazine hydrate, 0.25 g of manganese nitrate and 0.06 g of zinc chloride were added, and the mixture was stirred for 10 h. After filtration and drying, the free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst was obtained. Example 7

[0034] Preparation method of free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst

[0035] 45 mL of deionized water, 4 g of NaOH, 10 g of kaolin, 3 g of sodium aluminate, 0.95 g of copper chloride, and 15 g of adamantane were added sequentially to a 100 mL polytetrafluoroethylene liner. The mixture was thoroughly mixed at room temperature and then aged at 70 °C for 12 h. After aging, the mixture was transferred to a constant temperature oven at 170 °C for crystallization for 3 days. After crystallization, the solid product was filtered, washed, and dried. Finally, it was calcined at 500 °C for 3 h to obtain FeCu-SSZ-13 molecular sieve. 1.8 g of FeCu-SSZ-13 molecular sieve powder was weighed and placed in a round-bottom flask. 320 mL of ethanol / water (v / v=5) was added, and the mixture was sonicated for 30 min. Then, 1.3 g of hexadecylammonium bromide and 0.21 g of hexamethylenetetrammonium were added sequentially, and the mixture was stirred continuously at 70 °C for 5 h. Subsequently, 12 mL of hydrazine hydrate, 0.25 g of manganese nitrate, 0.28 g of zirconium nitrate, 0.08 g of calcium chloride and 0.06 g of zinc chloride were added, and the mixture was stirred continuously for 8 h. After filtration and drying, the free radical site-FeCu-SSZ-13 molecular sieve denitration catalyst was obtained.

[0036] Test Example 1

[0037] XRD testing of Cu-SSZ-13 molecular sieve denitration catalyst with free radical sites

[0038] The catalysts prepared in Examples 1-7 were subjected to XRD tests using a D / max Ultima IV diffractometer (Rigaku). The test results are as follows: Figure 1 As shown, the XRD characteristic diffraction peaks of the catalysts prepared in Examples 1-7 are consistent with those of the standard PDF#34-0137 card, indicating that the free radical site-Cu-SSZ-13 molecular sieve denitration catalyst can be successfully prepared by the method of the present invention.

[0039] Test Example 2

[0040] Evaluation of the low-temperature sulfur resistance and denitrification performance of Cu-SSZ-13 molecular sieve catalyst with free radical sites

[0041] The catalysts prepared in Examples 1-7 were evaluated for their sulfur resistance and denitrification activity in a fixed-bed reactor. The NO content at the outlet of the fixed-bed reactor was detected using Thermo Fisher IGS Gas. The catalyst particle size was 20-40 mesh, the reaction temperature was 125-300 °C, the reaction mixture consisted of SO2, NO, NH3, O2 and equilibrium gas N2, and the gas flow rate was 400 mL / min. Figure 2The figures show the low-temperature sulfur denitrification performance test results of the catalysts prepared in Examples 1-7. As can be seen from the figures, after 150 h of testing, the denitrification performance of the catalyst prepared in Example 1 was only 33%, while the denitrification performance of the catalysts prepared in Examples 2-7 remained above 80%, with the catalyst prepared in Example 3 exhibiting the highest denitrification activity. These results indicate that the free radical generation system loaded on Cu-SSZ-13 molecular sieve can convert SO2 into beneficial components that promote low-temperature denitrification.

Claims

1. A method for preparing a low-temperature denitration catalyst resistant to SO2 poisoning, characterized in that, Includes the following steps: 1) Add water, alkali source, silicon source, aluminum source, copper source and template agent to the polytetrafluoroethylene liner, mix evenly, age at 30~80℃ for several hours, then transfer to constant temperature oven, crystallize at 120~180℃ for 1~9 days, after crystallization, filter, wash and dry the solid product, and finally calcine to obtain Cu-SSZ-13 molecular sieve; 2) The surface of Cu-SSZ-13 molecular sieve is functionalized by using one or two of cetylammonium bromide and hexamethylenetetrammonium as treatment reagents. Then, hydrazine hydrate, nitrate and chloride are added in sequence. The resulting mixture is stirred and reacted in a water bath. The solid product is collected to obtain the free radical site-Cu-SSZ-13 molecular sieve denitration catalyst. The nitrate is one or a mixture of zinc nitrate, zirconium nitrate, manganese nitrate, and silver nitrate; the chloride is one or a mixture of lithium chloride, magnesium chloride, potassium chloride, zinc chloride, and calcium chloride.

2. The method for preparing a low-temperature denitrification catalyst resistant to SO2 poisoning according to claim 1, characterized in that, The addition amount of each reaction raw material is controlled so that the molar ratio is: 1 SiO2: 0.01~0.2 Al2O3: 0.1~2 Na2O: 100~500 H2O: 0.05-0.2 Cu: 0.01-0.3 template agent: 0.01~0.1 nitrate: 0.01~0.2 chloride: 0.1-2 hydrazine hydrate.

3. The method for preparing a low-temperature denitrification catalyst resistant to SO2 poisoning according to claim 1, characterized in that, The alkali source is sodium hydroxide; the silicon source is one or a mixture of several of kaolin, silica sol, sodium metasilicate, and sodium aluminosilicate; the aluminum source is one or a mixture of several of kaolin, rettore, sodium metasilicate, and aluminum chloride; the copper source is one or a mixture of several of copper nitrate, copper chloride, and copper sulfate; and the template agent is one or a mixture of several of adamantane, tetraethylenepentamine, tetrapropylammonium hydroxide, and ethylenediamine.

4. The method for preparing a low-temperature denitrification catalyst resistant to SO2 poisoning according to claim 1, characterized in that... Step 1) The roasting temperature is 500~700 ℃ and the time is 1~6 h.

5. The method for preparing a low-temperature denitrification catalyst resistant to SO2 poisoning according to claim 4, characterized in that, The surface functionalization treatment method of Cu-SSZ-13 molecular sieve is as follows: Cu-SSZ-13 molecular sieve powder is ultrasonically dispersed into ethanol or water / ethanol mixture, then treatment reagent is added, and the mixture is continuously stirred at 55~65 ℃ for 5.5~6.5 h.

6. The radical site-Cu-SSZ-13 molecular sieve denitration catalyst obtained by the preparation method according to any one of claims 1 to 5.

Images