Preparation method of water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancy construction

Abstract

The application discloses a preparation method of a water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancy construction. FeCu-SSZ-13 molecular sieves are added into an alkaline solution for alkaline treatment, the obtained product is reacted with a metal oxide precursor solution to introduce metal ions, and finally, a metal oxide / FeCu-SSZ-13 molecular sieve catalyst is obtained through steps such as calcination. The strong interface interaction between the metal oxide and the FeCu-SSZ-13 induces the generation of abundant oxygen vacancies in the metal oxide component, and these oxygen vacancies can effectively mediate the dissociation of H2O molecules to generate hydroxyl and radicals, thereby promoting the formation of key intermediates HONO and NH4NO2 in the low-temperature NH3-SCR reaction, and significantly enhancing the NH3-SCR reaction activity of the catalyst under the condition of containing water, and solving the problems of catalyst activity inhibition and deactivation caused by water molecule competitive adsorption at low temperature. The application provides a new mechanism of a two-way synergistic catalyst for realizing "water promoting reaction" through the construction of oxygen vacancies, and effectively solves the core problem of catalyst easy deactivation under the condition of low temperature and high humidity.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve preparation technology, and specifically relates to a method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction. Background Technology

[0002] Nitrogen oxides (NO) x Nitrogen monoxide (NO) and nitrogen dioxide (NO2), primarily composed of these two pollutants, are among the major air pollutants facing society today, posing a serious threat to natural ecosystems and human health. Ammonia selective catalytic reduction (NH3-SCR) technology is currently recognized as the most effective method for controlling NO. x The most effective solution to emissions lies in the development of high-performance catalysts. Cu-based chalcogenide (Cu-CHA) catalysts are considered to be a new generation of NH3-SCR catalysts with great application potential due to their excellent hydrothermal stability and high activity over a wide temperature window.

[0003] However, the durability of these high-performance catalysts faces severe challenges when applied in real-world scenarios. Whether from mobile sources (such as diesel engine exhaust during cold starts) or stationary sources (such as steel sintering machines and gas-fired boiler flue gas), their emission conditions generally exhibit two main characteristics: low exhaust temperatures (often below 180°C) and high water vapor content (volume fraction exceeding 15%). This harsh environment of low temperature and high humidity causes Cu-CHA catalysts to suffer significant "water poisoning" deactivation, which has become a key bottleneck restricting their large-scale commercial application. Essentially, the poisoning effect of water molecules on Cu-CHA catalysts is a complex physicochemical process, primarily achieved through interference with two key active sites. On one hand, water molecules engage in strong competitive adsorption and coordination with catalytic active sites, especially Cu sites responsible for low-temperature reactions. Water molecules preferentially occupy active sites and inhibit the valence state cycle of copper ions, leading to a significant decrease in catalyst activity at low temperatures. On the other hand, H2O reacts with the molecular sieve... The acid sites are bound, occupying the adsorption and activation sites of NH3 and inhibiting the protonation process of NH3.

[0004] Many researchers are currently working to solve this problem, but their efforts are primarily focused on joint research into water and sulfur resistance. For example, Chinese patent application CN120771899A discloses the preparation and application of a Fe-Mn / NbOPO4 catalyst for improving the water and sulfur resistance of the NH3-SCR reaction. After synthesizing the NbOPO4 support via a hydrothermal method, the Fe-Mn / NbOPO4 catalyst was prepared by loading the Fe and Mn active components onto the support using a wet impregnation method. Within a temperature range of 75–297℃, this catalyst exhibits NO... xThe conversion rate reached over 90%, and the reaction activity showed almost no significant decrease in water and sulfur resistance tests at 5 vol% H2O and 100 ppm SO2. Although this method improved the sulfur and water resistance of the molecular sieve catalyst, the H2O content evaluated for denitrification was only 5 vol%, which is far from the actual industrial application. Chinese patent application CN120618481A discloses a manganese-iron-based NH3-SCR denitrification catalyst, its preparation method, and its application. The manganese-iron-based NH3-SCR denitrification catalyst, obtained by reacting Mn salt, Fe salt, and Pr salt, exhibits good sulfur and water resistance and superior low-temperature catalytic activity in flue gas denitrification containing 10 vol% H2O. Although this method improves the low-temperature sulfur and water resistance of the molecular sieve catalyst to some extent, the low H2O content makes it unsuitable for high-humidity application scenarios. Therefore, in the face of the primary and universal problem of water poisoning at low temperatures that restricts the rapid activity of catalysts, the ultimate breakthrough in "water resistance" performance, and how to design and prepare SCR catalysts that have both high activity and excellent water resistance at low temperatures, is the core challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] Under low temperature and high humidity conditions, H2O occupies the active sites of Cu in the NH3-SCR reaction, preventing the formation of reaction intermediates and thus hindering the oxidation half-cycle; H2O and The protons at the acid sites combine to form H3O + Blocking the NH3 protonation pathway thereby inhibiting NH4 + The generation of oxygen vacancies suppresses the problem of low-temperature NH3-SCR. This invention provides a method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancies. The catalyst is a metal oxide / FeCu-SSZ-13 molecular sieve catalyst based on oxygen vacancy-mediated H2O dissociation.

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

[0007] A method for preparing a water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancies includes the following steps:

[0008] 1) Disperse FeCu-SSZ-13 molecular sieve into water or water / ethanol mixture, then add alkaline solution, stir at 65-75℃ for 1-1.2h to complete the alkaline treatment of FeCu-SSZ-13 molecular sieve, filter and dry the resulting product;

[0009] 2) Add a metal oxide precursor solution containing Mo to the dried product. 3+ Pd 2+ Mn 3+ , At least one metal ion in the sample is stirred evenly and then transferred to a reaction vessel lined with polytetrafluoroethylene. The mixture is then subjected to hydrothermal reaction at 80–150 °C for 3–5 h. The resulting product is then filtered, dried, and calcined to obtain a metal oxide / FeCu-SSZ-13 molecular sieve catalyst.

[0010] The alkaline solution mentioned in step 1) is at least one of NaOH, KOH, and CsOH.

[0011] The metal oxide precursor solution mentioned in step 2) is derived from chlorides, nitrates, sulfates, etc., containing metal ions.

[0012] In step 2), the mass ratio of metal ions to FeCu-SSZ-13 molecular sieve in the metal oxide precursor solution is 0.01 to 0.1:1.

[0013] The roasting described in step 2) is carried out at 500-650℃ for 2-6 hours.

[0014] The preparation method of FeCu-SSZ-13 molecular sieve in step 1) is as follows: the silicon source, aluminum source, sodium hydroxide, water and template agent are mixed evenly and aged at 28-32℃ for 3-4 hours. Then, the mixture is placed in a reaction vessel lined with polytetrafluoroethylene and crystallized at 120-180℃ for 1-7 days. The resulting crystallized product is washed and dried to obtain FeCu-SSZ-13 molecular sieve.

[0015] The amounts of silicon source, aluminum source, sodium hydroxide, water, and template agent are fed in the following molar ratio: SiO2:Al2O3:NaOH:H2O:template agent = 1:0.01~0.12:0.1~1:100:0.05~0.15. The silicon source is at least one of diatomaceous earth, sodium metasilicate, silica sol, and sodium aluminosilicate. The aluminum source is at least one of rettore, kaolin, and aluminum nitrate. The template agent is at least one of ethylenediamine, copper sulfate, copper nitrate, and tetraethylenepentamine.

[0016] This invention employs the above-mentioned technical solution to achieve a novel dual-pathway synergistic catalytic mechanism of "water-driven reaction" by constructing oxygen vacancies, effectively solving the core problem of catalyst deactivation under low-temperature and high-humidity conditions. Compared with existing technologies, the beneficial effects of this invention are as follows:

[0017] 1. The metal oxide / FeCu-SSZ-13 molecular sieve catalyst synthesized in this invention successfully achieves stable loading of metal oxides and exhibits excellent water resistance under low-temperature conditions. Even after long-term operation in a high-water-content atmosphere, the denitrification activity of the catalyst can be rapidly recovered and remain stable after the water supply is stopped, indicating that the metal oxide component effectively inhibits the occupation of active sites by water molecules and successfully solves the problem of catalyst deactivation under low-temperature and high-humidity conditions.

[0018] 2. EPR characterization confirmed that a rich interfacial structure was formed between the metal oxide and the support, inducing the generation of numerous oxygen vacancies. These oxygen vacancies, acting as activation centers for water molecules, can convert "toxic" H₂O into hydroxyl groups and protons (H₂O) that are beneficial for denitrification reactions. + The -OH group combines with NO in the low-temperature NH3-SCR reaction to form the key intermediate HONO, while H... + Effectively enhanced The acidity of the acid sites accelerates the formation of NH4NO2 active species, thereby significantly improving the reaction kinetics under low-temperature conditions. Therefore, the interfacial interaction between the metal oxide and the FeCu-SSZ-13 catalyst effectively establishes the H2O decomposition and conversion, ensuring the low-temperature, high-efficiency, and water-resistant denitrification of the molecular sieve catalyst.

[0019] 3. The catalyst of this invention possesses both excellent thermal stability and N2 selectivity. The directional conversion mechanism of water molecules mediated by the large number of oxygen vacancies generated in the metal oxide not only eliminates the water vapor inhibition effect but also significantly improves the reaction efficiency by promoting the HONO pathway. This synergistic effect increases the denitrification efficiency of the catalyst from the initial 55.6% to 74.7% within the 165°C range, while the N2 selectivity remains above 95%, achieving a breakthrough improvement in denitrification performance under low temperature and high humidity conditions. Attached Figure Description

[0020] Figure 1 The images shown are XRD patterns of the products of Embodiment 1 and Comparative Example 1 of the present invention.

[0021] Figure 2 The low-temperature water-resistant denitrification activity diagrams are for the products of Example 1 and Comparative Examples 1 and 2 of this invention.

[0022] Figure 3 This is a N2 selectivity diagram of the products of Embodiment 1 and Comparative Examples 1 and 2 of the present invention.

[0023] Figure 4 The EPR diagrams are for the products of Embodiment 1 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0024] Example 1

[0025] A method for preparing a water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancies includes the following steps:

[0026] (1) Dissolve 6.8g Na2SiO3, 1.8g rettore, 2.2g NaOH, 3.2g ethylenediamine and 1.5g copper nitrate in 100mL deionized water and age at 30℃ for 3h. Then transfer to a stainless steel reactor lined with polytetrafluoroethylene and crystallize at 160℃ for 3 days. After washing and drying, FeCu-SSZ-13 molecular sieve is obtained.

[0027] (2) Weigh 1g of FeCu-SSZ-13 molecular sieve and ultrasonically disperse it into 300mL of water / ethanol (v / v=1) mixture. Then add 0.1g of sodium hydroxide and stir continuously at 70℃ for 1h. Filter the resulting solid product and dry it.

[0028] (3) Add 10 ml of metal oxide precursor solution prepared with 0.08 g of tungsten hexachloride to the above-mentioned dried solid product, stir continuously for 30 min, transfer to a stainless steel reactor lined with polytetrafluoroethylene, and hydrothermally react at 80 °C for 4 h. Finally, filter, dry, and calcine at 550 °C for 6 h to obtain WO3 / FeCu-SSZ-13 molecular sieve catalyst.

[0029] Example 2

[0030] A method for preparing a water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancies includes the following steps:

[0031] (1) Dissolve 6g of diatomaceous earth, 1.2g of aluminum nitrate, 1.8g of NaOH, 2.6g of ethylenediamine and 1.4g of copper sulfate in 100mL of deionized water and age at 30℃ for 4h. Then transfer to a stainless steel reactor lined with polytetrafluoroethylene and crystallize at 160℃ for 3 days. After washing and drying, FeCu-SSZ-13 molecular sieve is obtained.

[0032] (2) Weigh 1g of FeCu-SSZ-13 molecular sieve and ultrasonically disperse it into 350mL of water / ethanol (v / v=1) mixture. Then add 0.1g of potassium hydroxide and stir continuously at 70℃ for 1h. Filter the resulting solid product and dry it.

[0033] (3) Add 10 ml of metal oxide precursor solution prepared with 0.08 g of manganese nitrate to the above-mentioned dried solid product, stir continuously for 30 min, transfer to a stainless steel reactor lined with polytetrafluoroethylene, crystallize at 80 °C for 4 h, and finally filter, dry, and calcine at 550 °C for 6 h to obtain Mn2O3 / FeCu-SSZ-13 molecular sieve catalyst.

[0034] Example 3

[0035] A method for preparing a water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancies includes the following steps:

[0036] (1) Dissolve 6.5g sodium aluminosilicate, 0.8g rettort, 1.6g NaOH, 2.5g tetraethylenepentamine and 1g copper nitrate in 100mL deionized water and age at 30℃ for 3h. Then transfer to a stainless steel reactor lined with polytetrafluoroethylene and crystallize at 160℃ for 3 days. After washing and drying, FeCu-SSZ-13 molecular sieve is obtained.

[0037] (2) Weigh 1g of FeCu-SSZ-13 molecular sieve and ultrasonically disperse it in 350mL of water. Then add 0.1g of sodium hydroxide and stir continuously at 70℃ for 1h. Filter the resulting solid product and dry it.

[0038] (3) Add 10 ml of metal oxide precursor solution prepared with 0.08 g palladium chloride to the above-mentioned dried solid product, stir continuously for 30 min, transfer to a stainless steel reactor lined with polytetrafluoroethylene, crystallize at 80 °C for 4 h, and finally filter, dry, and calcine at 550 °C for 6 h to obtain PdO / FeCu-SSZ-13 molecular sieve catalyst.

[0039] Example 4

[0040] A method for preparing a water-resistant low-temperature denitration molecular sieve catalyst based on oxygen vacancies includes the following steps:

[0041] (1) Dissolve 5.3g silica sol, 1.5g aluminum chloride, 2g NaOH, 3.7g ethylenediamine and 2g copper nitrate in 100mL deionized water, age at 30℃ for 3h, then transfer to a stainless steel reactor lined with polytetrafluoroethylene, crystallize at 160℃ for 3 days, and obtain FeCu-SSZ-13 molecular sieve after washing and drying the crystallized product.

[0042] (2) Weigh 1g of FeCu-SSZ-13 molecular sieve and ultrasonically disperse it into 400mL of water / ethanol (v / v=1) mixture. Then add 0.05g of sodium hydroxide and 0.05g of potassium hydroxide. Stir continuously at 70℃ for 1h. Filter the resulting solid product and dry it.

[0043] (3) Add 10 ml of metal oxide precursor solution prepared with 0.06 g ammonium molybdate to the above-mentioned dried solid product, stir continuously for 30 min, transfer to a stainless steel reactor lined with polytetrafluoroethylene, crystallize at 80 °C for 4 h, and finally filter, dry, and calcine at 550 °C for 6 h to obtain MoO2 / FeCu-SSZ-13 molecular sieve catalyst.

[0044] Comparative Example 1 (FeCu-SSZ-13)

[0045] Compared with Example 1, Comparative Example 1 did not perform surface functionalization treatment on the FeCu-SSZ-13 molecular sieve, nor did it add any metal oxides; all other steps were the same as in Example 1. Specifically, 6.8 g Na₂SiO₃, 1.8 g Ratox, 2.2 g NaOH, 3.2 g ethylenediamine, and 1.5 g copper nitrate were dissolved in 100 mL of deionized water and aged at 30 °C for 3 h. The resulting product was then transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 160 °C for 3 days. After washing, drying, and calcining at 550 °C for 6 h, the FeCu-SSZ-13 molecular sieve was obtained.

[0046] Comparative Example 2 (Metal Oxides)

[0047] Compared to Example 1, Comparative Example 2 did not add FeCu-SSZ-13 molecular sieve, and the reaction sample in Example 1 was directly scaled up by 5 times. Specifically, 0.5 g of sodium hydroxide was added to a 300 mL water / ethanol (v / v = 1) mixture, and the mixture was stirred continuously at 70 °C for 1 h. Then, 10 mL of a metal oxide precursor solution prepared with 0.4 g of tungsten hexachloride was added, and the mixture was stirred continuously for another 30 min. The mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene and hydrothermally reacted at 80 °C for 4 h. Finally, the mixture was filtered, dried, and calcined at 550 °C for 6 h to obtain the metal oxide catalyst.

[0048] XRD characterization of modified catalysts

[0049] X-ray powder diffraction (XRD) of all catalysts was performed on a D / max Ultima IV X-ray diffractometer manufactured by Rigaku Corporation of Japan. Figure 1 The XRD results are for the catalysts prepared in Example 1 (metal oxide / FeCu-SSZ-13) and Comparative Example 1 (FeCu-SSZ-13). By comparison with the standard SSZ-13 standard card (PDF#34-0137), the topological configuration of CHA can be clearly observed in Example 1 and Comparative Example 1.

[0050] Denitrification performance testing and N2 selectivity of modified catalyst

[0051] The catalysts prepared in Example 1 (metal oxide / FeCu-SSZ-13), Comparative Example 1 (FeCu-SSZ-13), and Comparative Example 2 (metal oxide) were subjected to low-temperature water-resistant denitrification activity tests in a fixed-bed reactor. The catalyst dosage was 0.4 g, and the reaction mixture contained 20 vol% H2O and NO. x The reaction mixture consisted of 500 ppm NH3 (500 ppm) and 5 vol% O2, with N2 as the equilibrium gas. The reaction temperature was 165 °C and the reaction space velocity was 60,000 h⁻¹. -1 .

[0052] like Figure 2 As shown, under H2O-free conditions at 165℃, both the metal oxide / FeCu-SSZ-13 and FeCu-SSZ-13 exhibited excellent initial activity in the first 2 hours, with NO conversion rates remaining stable above 93.5%. However, when 20 vol% H2O was introduced into the reaction system, their performance showed significant differences: the NO conversion rate of FeCu-SSZ-13 dropped sharply from 93.5% to 55.6% within 1 hour after water inlet, and continued to decrease slowly over the next 20 hours, showing obvious hydrothermal sensitivity. In stark contrast, the metal oxide / FeCu-SSZ-13 exhibited superior water resistance: under the same conditions, its NO conversion rate only decreased slightly to 74.7% and remained stable throughout the 20-hour reaction process. After the water inlet was stopped, the NO conversion rate of the metal oxide / FeCu-SSZ-13 rapidly recovered to above 94.6%, demonstrating its highly efficient regeneration capability of active sites after water vapor removal. It is noteworthy that the pure metal oxide showed no activity for NO conversion throughout the entire reaction process, ruling out the possibility of it contributing solely to the reactivity. This further confirms the core role of the metal oxide in enhancing the water resistance of FeCu-SSZ-13 through interface engineering. Furthermore, from... Figure 3 As can be seen, during the NH3-SCR reaction at 165℃ and 20 vol% H2O, the metal oxide / FeCu-SSZ-13 also exhibits excellent N2 selectivity (>99.1%).

[0053] Catalyst EPR test

[0054] Electron paramagnetic resonance (EPR) spectra were measured using a Bruker A300 instrument (Germany). Figure 4 EPR test results were obtained for the catalysts prepared in Example 1 (metal oxide / FeCu-SSZ-13), Comparative Example 1 (FeCu-SSZ-13), and Comparative Example 2 (metal oxide). The results clearly show that the EPR signal intensity of the metal oxide / FeCu-SSZ-13 catalyst at g = 2.003 is significantly higher than that of the pure metal oxide and FeCu-SSZ-13, indicating a significant increase in surface oxygen vacancy concentration. This data fully confirms the strong interfacial interaction between the metal oxide and FeCu-SSZ-13, inducing a directional transfer of electrons from FeCu-SSZ-13 to the metal oxide, thereby constructing a rich oxygen vacancy structure on the metal oxide surface.

[0055] These high-concentration oxygen vacancies play a crucial role in the low-temperature NH3-SCR reaction: these active sites can convert inhibitory water molecules into active species that promote denitrification, such as hydroxyl (-OH) and protons (H+). +Specifically, the hydroxyl group (-OH) formed by the dissociation of H2O at the oxygen vacancy combines with NO in the reaction system to generate the key intermediate HONO, while simultaneously producing protons (H2O). + Enhanced Acidity, together with other factors, accelerates the formation and transformation of active species in NH4NO2, thereby effectively mitigating the inhibitory effect of water vapor on catalytic activity.

Claims

1. A method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction, characterized in that, Includes the following steps: 1) Disperse FeCu-SSZ-13 molecular sieve in water or water / ethanol mixture, then add alkaline solution, stir at 65~75℃ for 1~1.2h to complete the alkaline treatment of FeCu-SSZ-13 molecular sieve, filter and dry the resulting product; 2) Add a metal oxide precursor solution containing Mo to the dried product. 3+ Pd 2+ Mn 3+ W 6⁺ At least one metal ion in the sample is stirred evenly and then transferred to a polytetrafluoroethylene-lined reactor. The mixture is then subjected to hydrothermal reaction at 80-150 °C for 3-5 h. The resulting product is filtered, dried, and calcined to obtain a metal oxide / FeCu-SSZ-13 molecular sieve catalyst.

2. The method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction according to claim 1, characterized in that, The alkaline solution mentioned in step 1) is at least one of NaOH, KOH, and CsOH.

3. The method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction according to claim 1, characterized in that, Step 2) The metal oxide precursor solution is derived from chlorides, nitrates, and sulfates containing metal ions.

4. The method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction according to claim 1, characterized in that, In step 2), the mass ratio of metal ions to FeCu-SSZ-13 molecular sieve in the metal oxide precursor solution is 0.01~0.1:

1.

5. The method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction according to claim 1, characterized in that, Step 2) describes roasting at 500-650 ℃ for 2-6 h.

6. The method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction according to claim 1, characterized in that, The preparation method of FeCu-SSZ-13 molecular sieve in step 1) is as follows: the silicon source, aluminum source, sodium hydroxide, water and template agent are mixed evenly and aged at 28~32 ℃ for 3~4 h. Then, it is placed in a reaction vessel with polytetrafluoroethylene lining and crystallized at 120~180 ℃ for 1~7 days. The obtained crystallized product is washed and dried to obtain FeCu-SSZ-13 molecular sieve.

7. The method for preparing a water-resistant low-temperature denitrification molecular sieve catalyst based on oxygen vacancy construction according to claim 6, characterized in that, The amounts of silicon source, aluminum source, sodium hydroxide, water, and template agent are fed in the following molar ratio: SiO2:Al2O3:NaOH:H2O:template agent = 1:0.01~0.12:0.1~1:100:0.05~0.

15. The silicon source is at least one of diatomaceous earth, sodium metasilicate, silica sol, and sodium aluminosilicate. The aluminum source is at least one of rettore, kaolin, and aluminum nitrate. The template agent is at least one of ethylenediamine, copper sulfate, copper nitrate, and tetraethylenepentamine.

8. The metal oxide / FeCu-SSZ-13 molecular sieve catalyst obtained by the preparation method according to any one of claims 1 to 7.

9. The application of the metal oxide / FeCu-SSZ-13 molecular sieve catalyst as described in claim 8 in the NH3-SCR reaction under aqueous conditions.

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