A NO x Preparation method and application of CO synergistic removal catalyst

Abstract

The application discloses a kind of NO x And CO synergistic removal catalyst preparation method and its application belong to nitrogen oxide catalytic reduction technical field.The catalyst includes high silica-alumina ratio molecular sieve carrier and Ir-based bimetallic cluster.Ir-based bimetallic cluster is confined by high silica-alumina ratio molecular sieve carrier, and the surface hydroxyl site of high silica-alumina ratio molecular sieve carrier is preoccupied by additive, to realize the ordered combination of Ir ion and additive ion.Meanwhile, under the action of liquid phase reducing agent, the charge density of active site is improved.The catalyst solves the problem of CO catalytic reduction NO x Catalyst active site regulation difficulty, stability is insufficient and so on, also simplify traditional preparation process, shorten preparation period, reduce cost.The prepared catalyst has excellent catalytic activity, is suitable for efficient removal of nitrogen oxides in complex flue gas environment, has broad industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of nitrogen oxide catalytic reduction technology, and more specifically relates to a NO... x Preparation method and application of CO synergistic removal catalyst. Background Technology

[0002] Nitrogen oxides (NO) x Air pollution originates widely from stationary sources such as vehicle exhaust, steel metallurgy, and power generation, and its emissions have become a global air pollution problem. x Air pollution not only causes serious environmental problems such as acid rain and photochemical smog, but also poses long-term harm to the human respiratory system and ecosystems. Therefore, developing efficient and environmentally friendly denitrification technologies is of great significance for air pollution control. Currently, the mainstream denitrification technology is NH3 selective catalytic reduction (NH3-SCR), which uses ammonia as a reducing agent. However, it suffers from problems such as ammonia escape, inconvenient storage and transportation, and potential secondary pollution. In contrast, CO selective catalytic reduction of NO... x CO-SCR technology is receiving increasing attention because it can directly utilize the CO already present in industrial flue gas as a reducing agent, which not only simplifies the system process but also helps to synergistically remove multiple pollutants.

[0003] A key challenge facing CO-SCR catalytic systems is that industrial flue gas typically contains around 14–17% O2. The competitive adsorption and preferential reaction of O2 inhibits the reduction reaction between CO and NO, leading to decreased catalyst activity. Simultaneously, SO2, often present in flue gas, readily adsorbs strongly onto active sites or forms sulfate deposits, resulting in catalyst deactivation. Among numerous metal catalysts, Ir-based catalysts exhibit excellent CO-SCR activity under oxygen-enriched conditions due to their superior oxygen resistance.

[0004] However, existing Ir-based CO-SCR catalysts still face several bottlenecks. On the one hand, Ir, as a precious metal, is scarce and expensive, limiting its large-scale application. On the other hand, traditional preparation methods easily lead to Ir existing in an unstable metallic state on the support surface, rapidly forming an oxidized state under oxygen-containing atmosphere, causing catalyst deactivation. Therefore, improving the stability of metallic Ir species has become a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a NO xThis invention presents a method for preparing and applying a catalyst for the synergistic removal of CO, addressing the problems of existing technologies. The invention employs a high silica-to-alumina ratio molecular sieve support to confine Ir-based bimetallic clusters. By pre-occupying hydroxyl sites on the surface of the high silica-to-alumina ratio molecular sieve support with an additive, the ordered combination of Ir ions and additive ions is achieved. Simultaneously, the charge density of the active sites is increased under the action of a liquid-phase reducing agent. The preparation method proposed in this invention is simple to operate, significantly shortening the catalyst preparation cycle and avoiding processes such as multi-step pH adjustment and multi-step calcination in a reducing atmosphere. In the obtained catalyst, the active component is in a stable metallic state, and NO is removed under an oxygen-containing atmosphere. x It has a significant effect in synergistic removal of CO.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of this invention: provides a NO x A catalyst for the synergistic removal of CO is provided, wherein the catalyst comprises a high silica-to-alumina ratio molecular sieve support and an Ir-based bimetallic cluster; the molar ratio of Si to Al in the high silica-to-alumina ratio molecular sieve support is 5–80:1; the Ir-based bimetallic cluster comprises Ir ions and promoter ions; the promoter ions comprise one or more of In ions, Sn ions, and Bi ions.

[0008] Furthermore, the Ir-based bimetallic cluster is NO. x The active sites of the catalyst are removed in synergy with CO.

[0009] Furthermore, the NO x The catalyst for CO removal has abundant aluminum hydroxyl, silanol, and silanol-bridged hydroxyl sites.

[0010] Preferably, the high silica-to-alumina ratio molecular sieve carrier includes a ZSM type molecular sieve with a cross-channel structure, a SAPO molecular sieve with a cross-channel structure, a Beta molecular sieve with a cross-channel structure, an X type molecular sieve with a supercage structure, a Y type molecular sieve with a supercage structure, or an MCM type molecular sieve with a supercage structure, and preferably a Beta molecular sieve with a cross-channel structure.

[0011] Preferably, in the Ir-based bimetallic cluster, the loading of Ir element is 0.1–2 wt.%, and the loading of auxiliary element is 0.1–20 wt.%.

[0012] The second technical solution of the present invention: providing the above-mentioned NO x The preparation method of the catalyst for synergistic CO removal includes the following steps:

[0013] A silicon source, an aluminum source, an alkali, a template agent, and water are mixed to obtain a molecular sieve precursor solution; the molecular sieve precursor solution is subjected to a hydrothermal crystallization reaction to obtain a molecular sieve support.

[0014] Citric acid, the metal precursor of the additive, the molecular sieve support, and the solvent are mixed and then subjected to rotary evaporation, drying, and calcination to obtain a molecular sieve-supported metal catalyst with additives.

[0015] The metal precursor of Ir, the liquid-phase reducing agent, the molecular sieve-supported auxiliary metal catalyst, and water were mixed and then subjected to rotary evaporation, drying, and calcination to obtain the NO. x A catalyst for synergistic CO removal.

[0016] Preferably, the silicon source comprises one or more of water glass, tetraethyl orthosilicate, fumed silica, silica sol, and amorphous SiO2 powder; the aluminum source comprises one or more of sodium aluminate, boehmite, amorphous aluminum hydroxide powder, and aluminum isopropoxide; the alkali comprises NaOH and / or KOH; the template agent comprises one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, and tetrapropylammonium hydroxide; the solvent comprises water and / or ethanol; and the liquid-phase reducing agent comprises urea and / or sodium borohydride.

[0017] Preferably, the hydrothermal crystallization reaction is carried out at a temperature of 80–180°C for a time of 24–96 hours.

[0018] Preferably, the metal precursor of Ir is an aqueous solution of an Ir salt; the solute in the aqueous solution of the Ir salt includes one or more of iridium nitrate, iridium acetate, and chloroiridium acid; the metal precursor of the auxiliary agent is an aqueous solution of an auxiliary agent metal salt, which includes one or more of nitrate, acetate, and chlorate; the molar ratio of the metal precursor of the auxiliary agent to citric acid is 1 to 6:1; and the molar ratio of the metal precursor of Ir to the liquid-phase reducing agent is 1:1.5 to 3.

[0019] Preferably, the calcination temperature is 400–600°C, the time is 4–8 h, and the heating rate is 1–10°C / min.

[0020] This invention uses a thorough mixture of auxiliary precursors (In, Sn, and Bi), citric acid, and solvents (water and / or ethanol), which are then added to a molecular sieve support. Citric acid, as a tricarboxylic acid ligand, forms stable multidentate chelates with the auxiliary metal ions, significantly enhancing the solubility and spatial distribution uniformity of the auxiliary metal ions. It maximizes the occupation of aluminum hydroxyl, silanol, and silicoaluminobridged hydroxyl sites on the molecular sieve surface, preventing the aggregation of auxiliary metal ions. Simultaneously, citric acid also has a certain ability to regulate the surface structure of the molecular sieve support and can be used as an acid for acid treatment, modifying and expanding the pores in the molecular sieve, increasing the specific surface area available for metal loading. Finally, an Ir metal precursor, a liquid-phase reducing agent (urea and / or sodium borohydride), and water are thoroughly mixed and then added to the molecular sieve-supported auxiliary metal catalyst. Under the action of urea and / or sodium borohydride, Ir ions grow orderly at the auxiliary ion sites, forming specific crystal faces. Simultaneously, the charge density around the Ir-based bimetallic clusters increases, forming a stable metallic state.

[0021] The third technical solution of the present invention: providing the above-mentioned NO x The application of a CO-co-catalyst for the selective reduction of nitrogen oxides by carbon monoxide in stationary flue gas and / or mobile exhaust gas, wherein the nitrogen oxides in the stationary flue gas and / or mobile exhaust gas include NO; the stationary flue gas and / or mobile exhaust gas also include CO, O2 and SO2; the volume ratio of CO to NO in the stationary flue gas and / or mobile exhaust gas is >10:1; and the volume concentration of O2 is >15%.

[0022] Preferably, the catalytic selective reduction of nitrogen oxides by carbon monoxide in stationary source flue gas and / or mobile source exhaust gas is a CO-SCR reaction.

[0023] This invention provides a catalyst for the selective catalytic reduction of nitrogen oxides (NOx), employing an impregnation method assisted by citric acid and a liquid-phase reducing agent to achieve ordered loading and charge stability of Ir ions within a molecular sieve. This method avoids the precipitation of metal precursors under alkaline conditions and simultaneously promotes the ordered binding of bimetallic ions within the molecular sieve channels, providing valence states and stability for the bimetallic cluster active sites. This method not only solves the problems of difficult active site control, poor oxygen and sulfur resistance, and insufficient stability in existing catalysts, but also simplifies the traditional preparation process, shortens the preparation cycle, and reduces costs. The prepared catalyst exhibits excellent catalytic activity, is suitable for the efficient removal of NOx in complex flue gas environments, and has broad industrial application prospects.

[0024] This invention introduces p-block indium (In) and iridium (Ir) to synergistically construct a bimetallic catalytic site. In, with its large atomic radius and low electronegativity, promotes pd orbital coupling, alters the d-band center position of Ir, and effectively modulates the electronic structure of Ir, thereby optimizing its adsorption strength for key intermediates, reducing energy barriers in the reaction pathway, and accelerating the occurrence of critical reaction steps. Furthermore, Ir itself exhibits excellent antioxidant properties and low-temperature catalytic activity in the CO-SCR reaction; the synergistic doping of In further improves its stability and reaction selectivity, effectively enhancing the catalyst's reactivity and sustained performance under complex flue gas conditions.

[0025] To achieve the ordered aggregation and charge stability of In and Ir metal species within molecular sieves, this invention employs an impregnation method assisted by citric acid and a liquid-phase reducing agent for catalyst preparation. Citric acid, as a weak organic acid, not only forms stable chelate complexes with promoter metal ions, preventing precipitation side reactions under alkaline conditions, but also induces a slow-release process of promoter metal ions on the surface of the molecular sieve pores, thereby enhancing metal migration and entry capabilities and improving the dispersion of promoter metal ions within the molecular sieve. Furthermore, under the action of urea and / or sodium borohydride, Ir ions grow orderly at promoter ion sites, forming specific crystal faces, while the charge density around the Ir-based bimetallic clusters increases, forming a stable metallic state. Compared to traditional pH-adjusting processes, the method described in this invention is simple to operate, environmentally friendly, optimizes metal utilization efficiency, and provides a feasible route for constructing high-performance catalytic materials for CO-SCR reactions.

[0026] The present invention discloses the following technical effects:

[0027] (1) The NO designed in this invention x The catalyst for CO removal works in synergy with the use of a high silica-to-alumina ratio molecular sieve as a support, which limits the number of hydroxyl groups used for anchoring active metals. By pre-occupying hydroxyl sites on the surface of the high silica-to-alumina ratio molecular sieve support with auxiliary metal ions, the orderly combination of Ir ions and auxiliary ions is achieved.

[0028] (2) This invention employs an impregnation method using citric acid and a liquid-phase reducing agent to prepare the catalyst. Citric acid can form chelates with metal ions, avoiding precipitation side reactions under alkaline conditions and improving the dispersion of the auxiliary metal ions within the molecular sieve. Under the action of urea and / or sodium borohydride, Ir ions grow orderly at the auxiliary ion sites, forming specific crystal faces. Simultaneously, the charge density around the Ir-based bimetallic clusters increases, forming a stable metallic state. This method is simple, environmentally friendly, and suitable for large-scale preparation. The resulting catalyst exhibits good thermal stability and reaction selectivity, contributing to the realization of NO x It can efficiently remove pollutants and avoid secondary pollution. Attached Figure Description

[0029] Figure 1 NO obtained in Example 1 x TEM and EDS-mapping images of the catalyst for CO synergistic removal, where a is the TEM image and b is the EDS-mapping image. Detailed Implementation

[0030] This invention provides a NO x A catalyst for the synergistic removal of CO is provided, wherein the catalyst comprises a high silica-to-alumina ratio molecular sieve support and an Ir-based bimetallic cluster; the molar ratio of Si to Al in the high silica-to-alumina ratio molecular sieve support is 5–80:1; the Ir-based bimetallic cluster comprises Ir ions and promoter ions; the promoter ions comprise one or more of In ions, Sn ions, and Bi ions.

[0031] In this invention, the Ir-based bimetallic cluster is NO. x The active sites of the catalyst are removed in synergy with CO.

[0032] In this invention, the NO x The catalyst for CO removal has abundant aluminum hydroxyl, silanol, and silanol-bridged hydroxyl sites.

[0033] In this invention, the high silica-to-alumina ratio molecular sieve support includes ZSM type molecular sieve with cross-channel structure, SAPO molecular sieve with cross-channel structure, Beta molecular sieve with cross-channel structure, X type molecular sieve with supercage structure, Y type molecular sieve with supercage structure, MCM type molecular sieve with supercage structure, etc., preferably Beta molecular sieve with cross-channel structure.

[0034] In this invention, the loading of Ir element in the Ir-based bimetallic cluster is 0.1–2 wt.%, and the loading of auxiliary element is 0.1–20 wt.%.

[0035] The present invention also provides the above-mentioned NO x The preparation method of the catalyst for synergistic CO removal includes the following steps:

[0036] A silicon source, an aluminum source, an alkali, a template agent, and water are mixed to obtain a molecular sieve precursor solution; the molecular sieve precursor solution is subjected to a hydrothermal crystallization reaction to obtain a molecular sieve support.

[0037] Citric acid, the metal precursor of the additive, the molecular sieve support, and the solvent are mixed and then subjected to rotary evaporation, drying, and calcination to obtain a molecular sieve-supported metal catalyst.

[0038] The metal precursor of Ir, the liquid-phase reducing agent, the molecular sieve-supported auxiliary metal catalyst, and water were mixed and then subjected to rotary evaporation, drying, and calcination to obtain the NO. x A catalyst for synergistic removal of CO.

[0039] In this invention, the silicon source includes one or more of water glass, tetraethyl orthosilicate, fumed silica, silica sol, and amorphous SiO2 powder; the aluminum source includes one or more of sodium aluminate, boehmite, amorphous aluminum hydroxide powder, and aluminum isopropoxide; the alkali includes NaOH and / or KOH; the template agent includes one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, and tetrapropylammonium hydroxide; the solvent includes water and / or ethanol; and the liquid-phase reducing agent includes urea and / or sodium borohydride.

[0040] In this invention, the specific steps of mixing the silicon source, aluminum source, alkali, template agent and water include: stirring and mixing the silicon source, template agent, alkali and half of the water to obtain a first mixture; stirring and mixing the aluminum source with the other half of the water to obtain a second mixture; and mixing the first mixture and the second mixture to obtain the molecular sieve precursor solution.

[0041] The mixing time is preferably 0.5 to 4 hours, more preferably 0.5 hours, 1 hour or 4 hours, and more preferably 1 hour.

[0042] In this invention, the temperature of the hydrothermal crystallization reaction is preferably 80-180°C, more preferably 80°C, 90°C, 100°C, 150°C or 200°C, and even more preferably 180°C; the time is preferably 24-96h, more preferably 12h, 24h, 48h, 72h or 96h, and even more preferably 96h.

[0043] In this invention, the hydrothermal crystallization reaction is followed by centrifugal washing and drying steps;

[0044] The centrifugal washing is preferably performed 3 to 5 times at room temperature, using water as the reagent; the duration of each centrifugal washing is preferably 5 to 20 minutes, more preferably 5 minutes, 10 minutes, 15 minutes or 20 minutes, and more preferably 10 minutes; the rotation speed of each centrifugal washing is preferably 4000 to 10000 rpm, more preferably 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm or 10000 rpm, and more preferably 4000 rpm.

[0045] During the centrifugal washing process, excess alkali and other impurities are washed away, and the pH value of the precipitate after centrifugal washing is 7-10.

[0046] The drying is carried out in an air atmosphere, and the drying temperature is preferably 80-120°C, more preferably 80°C, 90°C, 100°C, 110°C or 120°C, and even more preferably 100°C.

[0047] In this invention, the metal precursor of Ir is an aqueous solution of Ir salt; the solute in the aqueous solution of Ir salt includes one or more of iridium nitrate, iridium acetate, and chloroiridium acid; the metal precursor of the auxiliary agent is an aqueous solution of an auxiliary agent metal salt, which includes one or more of nitrate, acetate, and chlorate; the molar ratio of the metal precursor of the auxiliary agent to citric acid is 1 to 6:1, more preferably 3:1; the molar ratio of the metal precursor of Ir to the liquid-phase reducing agent is 1:1.5 to 3, more preferably 1:1.5.

[0048] In this invention, the aqueous solution of the Ir salt is prepared by mixing Ir salt and water at 20–80°C for 0.1–4 h; the aqueous solution of the In salt is prepared by mixing In salt and water at 20–80°C for 0.1–4 h.

[0049] The mixing temperature is further preferably 20°C, 30°C, 40°C, 50°C or 80°C, more preferably 50°C; the mixing time is further preferably 0.5h, 1h, 2h or 4h, more preferably 0.5h.

[0050] In this invention, the mixing temperature of citric acid, In metal precursor, molecular sieve support and solvent is preferably 20-90°C, more preferably 20°C, 30°C, 40°C, 50°C or 90°C, and even more preferably 80°C; the mixing time is preferably 1-8h, more preferably 1h, 2h, 4h or 8h, and even more preferably 4h.

[0051] In this invention, the calcination is carried out in an air atmosphere; the calcination temperature is preferably 400-600℃, more preferably 400℃, 450℃, 500℃, 550℃ or 600℃, and more preferably 550℃; the calcination time is preferably 4-8h, more preferably 4h, 5h, 6h, 7h or 8h, and more preferably 6h; the heating rate is preferably 1-10℃ / min, more preferably 1℃ / min, 2℃ / min, 5℃ / min or 10℃ / min, and more preferably 2℃ / min.

[0052] In this invention, the process before calcination includes centrifugal washing and drying steps; the parameters for centrifugal washing and drying are the same as those for centrifugal washing and drying in the molecular sieve carrier preparation process.

[0053] In this invention, the parameters for rotary evaporation, drying, and calcination of the Ir metal precursor, liquid-phase reducing agent, molecular sieve supported metal catalyst, and water are the same as those used in the preparation of the molecular sieve support and the molecular sieve supported metal catalyst.

[0054] The present invention also provides the above-mentioned NO x The application of a CO-co-catalyst for the selective reduction of nitrogen oxides by carbon monoxide in stationary flue gas and / or mobile exhaust gas, wherein the nitrogen oxides in the stationary flue gas and / or mobile exhaust gas include NO, wherein the NO x The catalyst for CO synergistic removal selectively catalyzes the reduction of NO in nitrogen oxides; the stationary source flue gas and / or mobile source tail gas also include CO, O2 and SO2; the volume ratio of CO to NO in the stationary source flue gas and / or mobile source tail gas is >10:1; and the volume concentration of O2 is >15%.

[0055] In this invention, the selective reduction of nitrogen oxides by carbon monoxide in stationary source flue gas and / or mobile source tail gas is the CO-SCR reaction.

[0056] In this invention, the concentration of NO in the stationary source flue gas and / or mobile source exhaust gas is preferably 50 to 500 ppm, more preferably 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 400 ppm or 500 ppm, and more preferably 400 ppm.

[0057] In this invention, the concentration of CO in the stationary source flue gas and / or mobile source exhaust gas is preferably 400 to 20,000 ppm, more preferably 400 ppm, 5,000 ppm, 6,000 ppm, 7,000 ppm, 8,000 ppm, 9,000 ppm, 10,000 ppm or 20,000 ppm, and even more preferably 8,000 ppm.

[0058] In this invention, the concentration of O2 in the stationary source flue gas and / or mobile source exhaust gas is 0 to 20 vol.%, and is not 0; the concentration of SO2 in the stationary source flue gas or mobile source exhaust gas is 0 to 400 ppm, and is not 0.

[0059] Further, the concentration of O2 in the stationary source flue gas and / or mobile source exhaust gas is preferably 1 vol.%, 2 vol.%, 3 vol.%, 4 vol.%, 5 vol.%, 15 vol.%, or 20 vol.%, more preferably 15 vol.%; the concentration of SO2 in the stationary source flue gas and / or mobile source exhaust gas is preferably 50 ppm, 100 ppm, 200 ppm, 300 ppm, or 400 ppm, more preferably 200 ppm.

[0060] In this invention, the NO x The reaction temperature for the selective reduction of nitrogen oxides by carbon monoxide in stationary source flue gas and / or mobile source tail gas catalyzed by the CO synergistic removal catalyst is preferably 100-500℃, more preferably 250℃, 275℃ or 300℃.

[0061] In this invention, before the selective reduction of nitrogen oxides by carbon monoxide in stationary source flue gas and / or mobile source tail gas by the NOx and CO synergistic removal catalyst (i.e., before the CO-SCR reaction), the process further includes pretreatment of the catalyst, specifically: removing the NOx and CO from the flue gas. x The catalyst for CO removal is pretreated at 200°C in an H2 / N2 mixed atmosphere for 30–240 min. The proportion of hydrogen in the H2 / N2 mixed atmosphere is preferably 1–10 vol.%, more preferably 1 vol.%, 2 vol.%, 3 vol.%, 4 vol.%, 5 vol.%, or 10 vol.%, and more preferably 5 vol.%.

[0062] In this invention, the pretreatment time is preferably 30 min, 60 min, 120 min, 180 min or 240 min, and more preferably 120 min.

[0063] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0064] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0065] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0066] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0067] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0068] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0069] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of the present invention are commercially available products, and the source of commercially available products does not affect the technical effect of the present invention.

[0070] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0071] Example 1

[0072] This embodiment provides a NO x The preparation steps for the catalyst for synergistic CO removal are as follows:

[0073] S1. Dissolve 1g of iridium acetate (with an Ir content of 50wt.%) in water to prepare 100mL of iridium acetate solution (Ir concentration of 5g / L), which serves as the first metal precursor solution.

[0074] S2. 10.42 g of TEOS (tetraethyl orthosilicate) and 9.25 g of 25% TEAOH (tetraethylammonium hydroxide) were mixed, and 7.5 mL of H2O was added. The mixture was stirred at 50 °C for 1 h to obtain the first mixture. 0.20 g of NaAlO2, 0.31 g of NaOH, and 3 mL of H2O were mixed and stirred at 50 °C for 1 h to obtain the second mixture. The first and second mixtures were transferred to a polytetrafluoroethylene liner and stirred at 50 °C for 1 h. Then, the mixture was placed in an autoclave and crystallized at 180 °C for 96 h. After the hydrothermal reaction was completed, the molecular sieve was centrifuged at 4000 rpm for 20 min and washed multiple times until pH = 7. Then, it was dried in air at 100 °C for 12 h to obtain Beta molecular sieve carrier powder.

[0075] S3. Prepare a 0.5 mol / L solution of citric acid, weigh 0.143 g of indium nitrate, take the citric acid solution according to the molar ratio of indium nitrate to citric acid of 3:1, mix it with Beta molecular sieve support powder and indium nitrate, heat in a water bath at 80℃ and stir for 4 h to obtain the catalyst solution.

[0076] S4. The catalyst solution was centrifuged at 4000 rpm for 20 min and washed multiple times until pH=7. Then it was dried in air at 100℃ for 12 h and calcined at 550℃ for 6 h at a heating rate of 2℃ / min. The resulting product was ground into powder to obtain the molecular sieve supported auxiliary metal catalyst.

[0077] S5. Weigh 2.94 mL of iridium acetate solution. Take urea according to the molar ratio of iridium acetate to urea of ​​1:1.5. Mix it with molecular sieve-supported auxiliary metal catalyst and iridium acetate solution. Heat in a water bath at 80°C and stir for 4 h to obtain catalyst solution.

[0078] S6. The catalyst solution was centrifuged at 4000 rpm for 20 min, and washed multiple times until pH = 7. It was then dried in air at 100℃ for 12 h, calcined at 550℃ at a heating rate of 2℃ / min for 6 h, and the resulting product was ground into powder to obtain NO. x A catalyst for synergistic removal of CO.

[0079] Figure 1 NO obtained in Example 1 x TEM and EDS-mapping images of the catalyst for CO synergistic removal, where a is the TEM image and b is the EDS-mapping image.

[0080] Example 2

[0081] The difference from Example 1 is that urea was replaced with sodium borohydride in the catalyst preparation process.

[0082] Example 3

[0083] The difference compared to Example 1 is that the preparation process of S2 is as follows:

[0084] 5.3 g of TPABr (templating agent), 0.6 g of NaOH, and 20 g of silica sol were added to 16 mL of H2O and mixed and stirred at 50 °C for 1 h to obtain the first mixture. 0.327 g of NaAlO2, 0.286 g of NaOH, and 20 mL of H2O were mixed and stirred at 50 °C for 1 h to obtain the second mixture. The first and second mixtures were transferred to a polytetrafluoroethylene liner and mixed and stirred at 50 °C for 3 h. Then, the mixture was placed in an autoclave and crystallized at 170 °C for 32 h. After the hydrothermal reaction, the molecular sieve was centrifuged at 4000 rpm for 20 min and washed multiple times until pH = 7. It was then dried in air at 100 °C for 12 h and heated at a rate of 1 °C / min to 550 °C for 6 h to obtain ZSM-5 molecular sieve carrier powder.

[0085] Comparative Example 1

[0086] The difference compared to Example 1 is that the addition of In salt was omitted during the preparation of the catalyst.

[0087] Comparative Example 2

[0088] The difference compared to Example 1 is that the addition of Ir salt was omitted during the preparation of the catalyst.

[0089] Comparative Example 3

[0090] The difference compared to Example 1 is that the addition of citric acid was omitted during the preparation of the catalyst.

[0091] Comparative Example 4

[0092] The difference compared to Example 1 is that the addition of a liquid-phase reducing agent was omitted during the preparation of the catalyst.

[0093] Effect verification:

[0094] 1. Performance testing of CO-SCR catalysts with different metal active components:

[0095] Take 0.200g of the catalysts prepared in Examples 1-3 and Comparative Examples 1-4, and conduct experiments respectively, as follows:

[0096] The catalyst was placed in a stationary reactor with NO concentration of 400 ppm, CO concentration of 8000 ppm, O2 concentration of 15 vol.%, SO2 concentration of 100 ppm, N2 as the balance gas, and a space velocity of 10000 h⁻¹. -1 The conversion rate of nitrogen oxides of the catalyst at different reaction temperatures (reaction time of 1 h) and at different reaction times (reaction temperature of 250 °C) was tested, and the results are shown in Table 1 and Table 2.

[0097] Before formal performance testing, all catalysts were pretreated. The pretreatment steps were as follows:

[0098] The catalyst was pretreated at 400℃ in a 5 vol.% H2 gas stream (N2 as the balance gas) for 30 min to improve its catalytic activity. Tables 1 and 2 show the nitrogen oxides (NOx)... x Conversion rate (μ) NO x The calculation method is shown in Equation 1-1. The real-time changes in the specific gas concentration during the experiment were determined by Bruker Tensor II infrared spectroscopy. The product of complete catalytic reduction is N2.

[0099]

[0100] Table 1

[0101]

[0102] Table 1 shows the conversion rates of nitrogen oxides by the catalysts prepared in Examples 1-3 and Comparative Examples 1-4 at different temperatures under conditions of 15 vol.% O2 concentration and 100 ppm SO2 concentration. It can be seen that Examples 1-3 exhibit superior catalytic activity at 225-300℃, and Example 2 shows slightly higher activity than Example 1, indicating that sodium borohydride is more effective as a liquid-phase reducing agent than urea. Example 1 shows slightly higher activity than Example 3, indicating that using a Beta-type molecular sieve as a support is more effective than using a ZSM-5-type molecular sieve. The peak activity (250℃) of Comparative Example 1 decreased by approximately 40-50% compared to Examples 1-3, while the peak activity of Comparative Example 2 decreased by approximately 70% compared to Examples 1-3, indicating a significant synergistic effect between the Ir and In bimetals, which can promote the adsorption and conversion of nitrogen oxides. Meanwhile, the performance of the In-based CO-SCR catalyst is very limited, with Ir being the main active site. The activity peak (250°C) of Comparative Example 3 decreased by approximately 40% compared to Example 1, but was slightly higher than that of Comparative Example 1, indicating that the synergistic effect between the Ir and In bimetals is more significant than the particle size effect of the Ir monometal. The activity peak (250°C) of Comparative Example 4 decreased by approximately 50% compared to Example 1, indicating that the liquid-phase reducing agent can increase the valence state of the bimetallic clusters, thereby increasing the activity peak.

[0103] 2. Stability Test:

[0104] Table 2

[0105]

[0106] Table 2 shows the conversion rates of nitrogen oxides by the catalysts prepared in Examples 1-3 and Comparative Examples 1-4 at different reaction times under conditions of 15 vol.% O2 concentration and 100 ppm SO2 concentration. It can be seen that Examples 1-3 maintained good stability within 13 hours. The activity of Comparative Example 1 began to decrease after 5 hours, indicating that the Ir active sites underwent irreversible changes under the influence of oxygen. Comparative Example 2 maintained good stability within 13 hours, but its activity was relatively low, indicating that the In active sites have a certain degree of oxygen resistance. Comparative Example 3 maintained good stability within 13 hours, indicating that the dispersibility of the bimetallic clusters mainly affects the catalytic activity and has a relatively small impact on stability. The activity of Comparative Example 4 began to decrease after 1 hour, indicating that the liquid-phase reducing agent plays a decisive role in the stability of the bimetallic clusters under high oxygen conditions.

[0107] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0108] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A type of NO x A catalyst for the synergistic removal of CO, characterized in that, The catalyst is composed of a high silica-to-alumina ratio molecular sieve support and Ir-based bimetallic clusters; the molar ratio of Si to Al in the high silica-to-alumina ratio molecular sieve support is 5~80:1; the Ir-based bimetallic clusters include Ir ions and promoter ions; the promoter ions are In ions; The high silica-to-alumina ratio molecular sieve support is a Beta molecular sieve with a cross-channel structure. The NO x The preparation method of the catalyst for synergistic CO removal includes the following steps: A silicon source, an aluminum source, an alkali, a template agent, and water are mixed to obtain a molecular sieve precursor solution; the molecular sieve precursor solution is subjected to a hydrothermal crystallization reaction to obtain a molecular sieve support. Citric acid, the metal precursor of the additive, the molecular sieve support, and the solvent are mixed and then subjected to rotary evaporation, drying, and calcination to obtain a molecular sieve-supported metal catalyst with additives. The metal precursor of Ir, the liquid-phase reducing agent, the molecular sieve-supported auxiliary metal catalyst, and water were mixed and then subjected to rotary evaporation, drying, and calcination to obtain the NO. x Co-existing catalyst for CO removal; The temperature of the hydrothermal crystallization reaction is 80~180℃.

2. The NO according to claim 1 x The method for preparing a catalyst for the synergistic removal of CO is characterized by, Includes the following steps: A silicon source, an aluminum source, an alkali, a template agent, and water are mixed to obtain a molecular sieve precursor solution; the molecular sieve precursor solution is subjected to a hydrothermal crystallization reaction to obtain a molecular sieve support. Citric acid, the metal precursor of the additive, the molecular sieve support, and the solvent are mixed and then subjected to rotary evaporation, drying, and calcination to obtain a molecular sieve-supported metal catalyst with additives. The metal precursor of Ir, the liquid-phase reducing agent, the molecular sieve-supported auxiliary metal catalyst, and water were mixed and then subjected to rotary evaporation, drying, and calcination to obtain the NO. x Co-existing catalyst for CO removal; The temperature of the hydrothermal crystallization reaction is 80~180℃.

3. The preparation method according to claim 2, characterized in that, The silicon source includes one or more of water glass, tetraethyl orthosilicate, silica sol, and amorphous SiO2 powder; the aluminum source includes one or more of sodium aluminate, boehmite, amorphous aluminum hydroxide powder, and aluminum isopropoxide; the alkali includes NaOH and / or KOH.

4. The preparation method according to claim 2, characterized in that, The template agent includes one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, and tetrapropylammonium hydroxide; the solvent includes water and / or ethanol; and the liquid-phase reducing agent includes urea and / or sodium borohydride.

5. The preparation method according to claim 2, characterized in that, The hydrothermal crystallization reaction takes 24 to 96 hours.

6. The preparation method according to claim 2, characterized in that, The metal precursor of Ir is an aqueous solution of Ir salt; the solute of the aqueous solution of Ir salt includes one or more of iridium nitrate, iridium acetate, and chloroiridium acid; the metal precursor of the auxiliary agent is an aqueous solution of the auxiliary agent metal salt, which includes one or more of nitrate, acetate, and chlorate.

7. The preparation method according to claim 2, characterized in that, The molar ratio of the metal precursor to citric acid in the auxiliary agent is 1~6:1; the molar ratio of the metal precursor to the liquid phase reducing agent of Ir is 1:1.5~3.

8. The preparation method according to claim 2, characterized in that, The calcination temperature was 400~600℃, the time was 4~8h, and the heating rate was 1~10℃ / min.

9. The NO according to claim 1 x The application of a CO-co-catalyst for the selective reduction of nitrogen oxides by carbon monoxide in stationary flue gas and / or mobile exhaust gas is characterized by, The nitrogen oxides in the stationary source flue gas and / or mobile source exhaust gas include NO; the stationary source flue gas and / or mobile source exhaust gas also include CO, O2 and SO2; the volume ratio of CO to NO in the stationary source flue gas and / or mobile source exhaust gas is >10:1; and the volume concentration of O2 is >15%.

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