In-coated H-Beta / Fe3O4 catalyst, preparation method thereof and application of In-coated H-Beta / Fe3O4 catalyst in methane selective catalytic reduction of nitric oxide

Abstract

The invention relates to an In (at) H-Beta / Fe3O4 catalyst, a preparation method thereof and application of the In (at) H-Beta / Fe3O4 catalyst in methane selective catalytic reduction of nitric oxide, and the preparation method comprises the following steps: firstly, carrying out ion exchange reaction on an H-Beta molecular sieve and an indium precursor solution, and calcining to obtain an In (at) H-Beta precursor; and mixing the In-coated H-Beta precursor with the Fe3O4 dispersion liquid, and calcining to obtain the In-coated H-Beta composite material. Compared with the prior art, the method has the advantages that molecular sieve confinement loading of indium species and surface modification synergy of the iron oxide nanoparticles are realized by adopting a hierarchical loading strategy, and the obtained catalyst shows excellent activity and water-resistant stability in CH4-SCR reaction, and has adjustable metal dispersity and strong metal-carrier interaction; a new scheme is provided for the development of a catalyst for efficiently resisting water poisoning, and the catalyst has a remarkable industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of energy and low-carbon environmental protection technology, and relates to an In@H-Beta / Fe3O4 catalyst, its preparation method, and its application in the selective catalytic reduction of nitrogen oxides by methane. Background Technology

[0002] With the rapid development of global industrialization, nitrogen oxides (NOx) have become increasingly important. x NOx emissions are a significant environmental issue. Current NOx removal methods primarily employ selective catalytic reduction (SCR), which reacts NOx with reducing agents such as NH3 to form N2 and H2O. Similarly, methane (CH4), a major component of natural gas, is considered a highly promising NOx reducing agent due to its abundant reserves (global proven reserves of approximately 196 trillion cubic meters) and low cost (about 1 / 5 that of NH3). SCR technology using CH4 as a reducing agent (CH4-SCR) can simultaneously eliminate NOx... x Compared to unburned CH4, it also avoids the secondary pollution problem of NH3, thus achieving both environmental and economic benefits.

[0003] In recent years, zeolite-based catalysts have shown significant advantages in the CH4-SCR field due to their tunable acidic sites (synergistic effects of Brønsted and Lewis acids) and unique pore confinement effects. For example, In@H-Beta zeolites anchor In species within the pores via ion exchange to form InO. + The active site can achieve more than 80% NO at 550℃. x Conversion rate. However, the performance of such catalysts deteriorates significantly under aqueous conditions: H2O molecules preferentially occupy Brønsted acid sites, blocking the protonation pathway of NO; ​​simultaneously, H2O reacts with InO... + The reaction generates In(OH)3, leading to the coverage of active sites and an activity decay of over 40% within 72 hours. Studies have shown that introducing transition metal oxides (such as Fe, Co, Ni, and Mn) to construct bifunctional active centers can effectively improve the water resistance and stability of the catalyst. Among these, Fe3O4, due to its unique Fe... 2+ / Fe 3+ Its redox pairs and hydrophobic surface properties enable it to inhibit H2O adsorption and stabilize active sites, making it a key material for improving the performance of In-based catalysts.

[0004] However, the existing oxide loading methods (such as mechanical mixing or single impregnation) still have the following drawbacks: (1) Oxide particles are prone to agglomeration, which can block molecular sieve channels and reduce mass transfer efficiency; (2) There is a lack of strong interaction between oxides and In species, and the interfacial bonding is unstable, resulting in limited improvement in water resistance; (3) The acid sites are unevenly distributed and cannot synergistically promote the dissociation of CH4 and NO. x activation.

[0005] Existing technology CN202310143044.9 discloses an In / HBeta@CeO2 catalyst, its preparation method, and its application. The preparation method includes: ultrasonically dispersing HBeta powder in a solvent; sequentially adding a surface stabilizer, a Ce source, a structure-directing agent, and a pore-forming agent while stirring; then refluxing and stirring at 60°C for 2 hours; followed by centrifugation, washing, drying, and calcination at 500°C for 3 hours to obtain HBeta@CeO2; adding the obtained HBeta@CeO2 to an In source solution; stirring at 80°C for 8 hours; filtering, washing, drying, and calcining at 500°C for 3 hours to obtain the product In / HBeta@CeO2. This technical solution introduces an appropriate amount of CeO2 into the catalyst while maintaining the integrity of the In / HBeta structure, reducing the poisoning effects of H2O and SO2, while allowing reactants to enter and exit, maintaining the stability of active sites, and improving denitrification efficiency.

[0006] Although this approach improves the stability of the catalyst to some extent, in-depth analysis reveals the following drawbacks and shortcomings: 1. Complex and costly preparation process: The existing technology uses a "self-assembly method" to construct the core-shell structure. Its preparation process (step S1) requires the simultaneous addition of multiple organic additives such as surface stabilizer (PVP), structure directing agent (HMTA), and pore-forming agent (CTAB). This not only makes the process lengthy and the conditions demanding, but also significantly increases production costs and the difficulty of subsequent treatments (such as washing and calcination to remove organic matter), which is not conducive to large-scale industrial production.

[0007] 2. Risk of pore blockage and mass transfer resistance: This existing technology first constructs an H-Beta@CeO2 core-shell structure, and then introduces In through impregnation or ion exchange. This "coating first, then loading In" strategy has inherent drawbacks: (1) Blockage risk: The self-assembled CeO2 shell may partially block the pores of the H-Beta molecular sieve, reducing the specific surface area and pore volume of the catalyst (as shown in Table 2 of its specification, the specific surface area of ​​the best sample IB@Ce-2 is 528 m²). 2 / g decreased to 440 m 2 / g), which will hinder the reactants (CH4, NO) xThe diffusion of the catalyst into its internal active sites limits its intrinsic activity.

[0008] (2) Low mass transfer efficiency: The In precursor needs to pass through the pre-formed CeO2 shell to enter the interior of the H-Beta molecular sieve for exchange. This process is inefficient and may lead to the enrichment of In species in the shell or near the surface, rather than their uniform distribution at the optimal active sites within the molecular sieve channels, thus affecting the active sites (InO2). + ) utilization rate.

[0009] 3. Limited synergistic catalytic effect, mechanism focuses on physical protection: The core mechanism of this existing technology is to use the CeO2 shell as a physical barrier to isolate the internal In active sites from poisoning by water and sulfur through sacrificial sites. Although CeO2 itself has oxygen storage and redox capabilities, this physically isolated structural design does not fully utilize the electronic and chemical synergistic effects between CeO2 and In species. The active center (InO2) + The active species and the promoter (CeO2) are spatially separated, lacking strong interfacial interactions to stabilize the active species or participate in the catalytic cycle together, which limits further improvement in catalytic performance.

[0010] 4. Incomplete inhibition of water molecules: CeO2 itself has a certain degree of hydrophilicity. Although the physical shell it forms can reduce direct contact with SO2, its ability to competitively inhibit the adsorption of water molecules is limited. In a high-temperature steam environment, water molecules can still penetrate the porous shell and interact with the Brønsted acid sites and InO inside. + The active site effect leads to a decrease in catalyst activity. Summary of the Invention

[0011] The purpose of this invention is to provide an In@H-Beta / Fe3O4 catalyst, its preparation method, and its application in the selective catalytic reduction of nitrogen oxides (NOx) of methane (CH4-SCR), addressing the problems of low-temperature activation difficulties, high-temperature activity decay, and poor water resistance inherent in traditional CH4-SCR catalysts. This invention constructs a Fe-O-In interfacial bond structure through an ion exchange-impregnation composite process, synergistically optimizing the Brønsted / Lewis acidic sites, significantly improving the catalyst's water resistance and stability. Experiments show that this catalyst, under complex flue gas conditions containing 5% H2O, exhibits improved NOx resistance. x With a conversion rate of ≥85%, N2 selectivity of ≥85%, and activity decay of ≤10% after 100 hours, it has excellent potential for industrial applications.

[0012] The objective of this invention can be achieved through the following technical solutions: A first aspect of the present invention provides an In@H-Beta / Fe3O4 catalyst, comprising an H-Beta molecular sieve support, and indium and Fe3O4 supported on the H-Beta molecular sieve support; The indium loading is 1.0~20.0 wt%; The Fe3O4 loading is 1.0~30.0 wt%, preferably 2.0~20.0 wt%.

[0013] In some specific embodiments, the average particle size of the Fe3O4 is 30 nm.

[0014] A second aspect of the present invention provides a method for preparing the In@H-Beta / Fe3O4 catalyst as described above, comprising: S1: H-Beta molecular sieve is reacted with indium precursor solution by ion exchange reaction and calcined to obtain In@H-Beta precursor; S2: The In@H-Beta precursor was mixed with Fe3O4 dispersion and calcined to obtain the desired product.

[0015] In some specific embodiments, the preparation method of the In@H-Beta / Fe3O4 catalyst includes: S1: Ion exchange method: H-Beta molecular sieve is subjected to ion exchange reaction with indium precursor solution, and after washing, drying and calcination, In@H-Beta precursor is obtained; S2: Impregnation method: The In@H-Beta precursor obtained in step S1 is mixed with the Fe3O4 precursor dispersion, concentrated by rotary evaporation, dried and calcined to obtain the In@H-Beta / Fe3O4 catalyst.

[0016] This invention employs a hierarchical loading strategy to achieve synergistic effects between molecular sieve-confined loading of indium species and surface modification of iron oxide nanoparticles. The resulting catalyst exhibits excellent activity and water resistance in the CH4-SCR reaction, while also possessing tunable metal dispersion and strong metal-support interaction. This provides a new approach for the development of highly efficient water-poisoning resistant catalysts and has significant industrial application value.

[0017] Specifically, the beneficial effects of the present invention are reflected in: 1. Interface engineering enhances water resistance: The Fe-O-In bonded structure anchors In species, inhibiting their hydroxylation and deactivation; the hydrophobic surface of Fe3O4 nanoparticles (~30 nm in diameter) reduces H2O adsorption; under conditions containing 5~15 vol% H2O, the catalyst's NO content is reduced. xConversion rate ≥85%, N2 selectivity ≥85%. Superior to In@H-Beta / NiO (51.2%, 43.5%) and In@H-Beta / MnO2 (62.4%, 54.9%) under the same conditions.

[0018] 2. Dynamic oxygen cycle mechanism: Oxygen vacancies on the Fe3O4 surface activate O2 to generate O2. - Species, accelerating the NO→NO2→NO3 transition - The In@H-Beta / Fe3O4 catalyst exhibits excellent long-term stability and safety performance, with a lifespan of 250~350h and an activity decay of ≤5% (including 5~15 vol% H2O) after 100 hours. It can be reused 15 times at 550℃ without significant decrease in catalytic performance, and has good economic applicability and industrial application value.

[0019] In some specific embodiments, in step S1, the indium precursor is at least one of indium nitrate, indium chloride, indium oxide, or indium sulfate.

[0020] In some specific embodiments, the indium concentration in the indium precursor solution is 0.01~0.05 mol / L.

[0021] In some specific embodiments, in step S1, the feeding ratio of the H-Beta molecular sieve to the indium precursor is (0.7~1.6) g:(0.6~1.4) mmol.

[0022] In some specific embodiments, in step S1, the reaction temperature in the ion exchange reaction is 50~90℃ (preferably 60~80℃), and the reaction time is 1~5 h.

[0023] In some specific embodiments, in step S1, the calcination temperature is 550~650℃, the calcination time is 2.5~4.5 h, and the calcination atmosphere is air.

[0024] In some specific embodiments, in step S2, the mass ratio of the In@H-Beta precursor to Fe3O4 is (0.6~2.0):(0.05~0.2).

[0025] In some specific embodiments, in step S2, the temperature of the rotary evaporation is 75~105°C.

[0026] In some specific embodiments, in step S2, the calcination temperature is 450~700℃, the calcination time is 2~4.5 h, and the calcination atmosphere is at least one of air, nitrogen or argon.

[0027] In some specific embodiments, in step S2, the drying temperature is 70~120℃.

[0028] A third aspect of the invention provides an application of the In@H-Beta / Fe3O4 catalyst as described above, including using the catalyst for the selective catalytic reduction of nitrogen oxides by methane.

[0029] In some specific embodiments, the methane selective catalytic reduction denitration reaction includes at least one of the following conditions: A: NO x The concentration is 50~500 ppm; the preferred concentration is 60~230 ppm. B: CH4 concentration is 50~500 ppm; preferred concentration is 30~240 ppm; C: O2 content is 3~10 vol% D: H2O content ≤ 25 vol%; preferred content ≤ 15 vol% E: The reaction temperature is 300~700℃; preferably 350~600℃; F: Volumetric space velocity is 20,000~100,000 h -1 ; G: Operating pressure is atmospheric pressure ~ 3 MPa; H: Used for denitrification treatment of exhaust gas from natural gas vehicles, flue gas from gas-fired boilers, or exhaust gas from diesel engines.

[0030] This invention proposes a novel In@H-Beta / Fe3O4 molecular sieve catalyst and its preparation method. A Fe-O-In interfacial bonding structure is constructed through an ion exchange-impregnation composite process, synergistically optimizing the distribution of acidic sites and pore mass transfer efficiency, thus overcoming the activity and water resistance bottlenecks of CH4-SCR catalysts. Specifically, the innovation of this invention is reflected in the following three aspects: Interface engineering enhances water resistance: In species are anchored by Fe-O-In bonding, inhibiting their hydroxylation and deactivation; the hydrophobic surface of Fe3O4 nanoparticles can reduce the physical / chemical adsorption of H2O molecules at active sites.

[0031] Dual acid site synergistic catalysis: Increased Brønsted acid site density leads to NO production via protonation of NO. + Intermediate; Lewis acid site (InO) + This reduces the activation energy of CH4 and promotes the generation of CH3· free radicals.

[0032] Dynamic oxygen cycle mechanism: Efficient activation of O2 generation by oxygen vacancies on Fe3O4 surface - Species, accelerating the NO→NO2→NO3 transition -It transforms and maintains oxygen supply stability through skeletal oxygen migration pathways.

[0033] Experiments show that the catalyst of this invention, under conditions containing 5% H2O, reduces NO... x With a conversion rate ≥80%, N2 selectivity ≥80%, and activity decay ≤5% after 100 hours, it represents a significant performance improvement over traditional In@H-Beta catalysts. Its excellent water resistance provides a reliable solution for denitrification treatment in high-humidity environments such as natural gas vehicle exhaust and gas-fired boilers, making it of significant industrial application value.

[0034] To address the shortcomings and deficiencies of existing technologies, this invention proposes an In@H-Beta / Fe3O4 catalyst prepared by graded loading, which achieves significant performance improvements through innovations in structural design and component selection.

[0035] Compared with the prior art, the present invention has the following characteristics: First, in view of the problem that its preparation process is complex and costly, the present invention adopts a simple and efficient graded loading process.

[0036] Existing self-assembly methods require various organic additives such as PVP, HMTA, and CTAB, resulting in cumbersome processes and high costs. This invention, however, combines a mature, stable, and low-cost ion exchange method with an impregnation method. First, indium species are precisely anchored within the molecular sieve pores through ion exchange. Then, Fe3O4 nanoparticles are modified onto the outer surface of the molecular sieve using an impregnation method. This method eliminates the need for any complex organic additives, greatly simplifying the production process, reducing raw material and processing costs, and possessing excellent potential for industrial scale-up.

[0037] Secondly, in response to the risks of channel blockage and mass transfer resistance, this invention ensures unobstructed mass transfer channels by reversing the load sequence.

[0038] The existing strategy of first coating and then loading In inevitably leads to the pre-formed CeO2 shell blocking part of the molecular sieve pores, hindering the subsequent entry of In species and the diffusion of reactants. The pre-confinement, post-modification strategy designed in this invention fundamentally solves this problem. We first ensure that the active In species enter the internal channels of the H-Beta molecular sieve efficiently and uniformly, forming highly dispersed active centers. The subsequently loaded Fe3O4 only modifies the outer surface of the molecular sieve, without affecting the internal pore structure. This design ensures the efficient entry of reactants (CH4, NO...) into the molecular sieve pores. x InO can quickly and without hindrance reach the interior. + This allows for the maximization of active site utilization and optimal catalytic reaction kinetics.

[0039] Third, to address the problem of limited synergistic catalytic effect, this invention constructs a Fe-O-In catalytic interface with stronger chemical synergistic effect.

[0040] In existing technologies, the CeO2 shell primarily functions as a physical barrier, spatially separated from the internal In active sites and lacking tight electronic and chemical interactions. This invention goes beyond simple physical protection. By tightly loading Fe3O4 nanoparticles onto the In@H-Beta surface, we construct a strongly interacting Fe-O-In interface. At this interface, Fe3O4 is no longer a passive protective layer but an active co-catalyst. Its unique Fe... 2+ / Fe 3+ Redox couples can efficiently activate oxygen in the gas phase, accelerating the key conversion step from NO to NO2, and can also convert NO to InO through the interface. + The site provides dynamic reactive oxygen species, which work synergistically with the In site to create a more efficient and faster catalytic cycle.

[0041] Fourth, to address the problem of incomplete suppression of water molecules, this invention selects Fe3O4, which has excellent hydrophobicity, as the protective component.

[0042] The CeO2 used in existing technologies is essentially a hydrophilic material. While its porous shell can block some substances, it still easily adsorbs water vapor, leading to water molecule penetration and poisoning of the internal active sites. This invention cleverly utilizes the excellent hydrophobic properties of Fe3O4. Fe3O4 nanoparticles supported on the catalyst surface form a microscopic hydrophobic interface that actively repels water molecules in the gas phase, preventing water adsorption and aggregation on the catalyst surface at the source. This results in a catalyst with superior resistance to water poisoning compared to CeO2 core-shell catalysts, maintaining long-term stable catalytic activity under high water content conditions. Attached Figure Description

[0043] Figure 1 This is a comparative graph showing the conversion rates of In@H-Beta / Fe3O4 prepared in Example 1, In@H-Beta prepared in Comparative Example 1, In@H-Beta / NiO prepared in Comparative Example 2, and In@H-Beta / MnO2 prepared in Comparative Example 3 in the selective catalytic reduction of nitrogen oxides by methane.

[0044] Figure 2 This is a graph evaluating the CH4-SCR activity of the H-Beta / Fe3O4 catalyst (without In).

[0045] Figure 3The diagram shows the N2 selectivity of the In@H-Beta / Fe3O4 catalyst (Example 1) in the CH4-SCR reaction. Dry represents the CH4-SCR reaction under anhydrous conditions, and Wet represents the CH4-SCR reaction under 5% H2O conditions.

[0046] Figure 4 The conversion rate of nitrogen oxides in the CH4-SCR reaction of In@H-Beta / Fe3O4 prepared in Example 2 under conditions of 5%, 10%, 15%, 20%, and 25% water vapor is given.

[0047] Figure 5 The conversion rate of nitrogen oxides in the CH4-SCR reaction of In@H-Beta prepared in Comparative Example 1 is shown as 5% water vapor.

[0048] Figure 6 The graph shows the activity recovery evaluation of the In@H-Beta / Fe3O4 (Example 1) catalyst under 5% steam "on / off" cycling conditions. Detailed Implementation

[0049] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0050] The following are more detailed implementation examples, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0051] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0052] H-Beta powder is the NKF-6 product of Nankai University Catalyst Factory.

[0053] Example 1 An In@H-Beta / Fe3O4 catalyst, the preparation method of which includes the following steps: S1: First, 0.96 g of H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred at 350 r / min for 10 minutes and sonicated for 5 minutes. Then, 31 mL of 0.03 mol / L indium nitrate solution was added, and the solution was magnetically stirred at 350 r / min for 3 hours at 85 °C. Next, the solution was filtered and washed with distilled water until pH ~7. The product was dried in an oven at 105 °C for 10 hours. Finally, it was calcined in air at 600 °C for 3 hours to obtain the In@H-Beta molecular sieve catalyst product. S2: Fe3O4 was loaded onto the In@H-Beta surface obtained in step S1. 1 g of In@H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 5 minutes and sonicated for 2 minutes. Then, 0.2 g of Fe3O4 powder was added, and the mixture was stirred at 350 r / min for 3 hours before rotary evaporation. The product was dried in an oven at 105 °C for 20 hours. Finally, calcination was performed at 600 °C under a nitrogen atmosphere for 2 hours to obtain the In@H-Beta / Fe3O4 molecular sieve catalyst, with an In loading of 11.12 wt% and a Fe3O4 loading of 20 wt%.

[0054] Example 2 An In@H-Beta / Fe3O4 catalyst, the preparation method of which includes the following steps: S1: First, 0.85 g of H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 10 minutes and sonicated for 5 minutes. Then, 15 mL of 0.06 mol / L indium acetate solution was added, and the solution was magnetically stirred at 85 °C for 3 hours. Next, the dispersion was filtered and washed with distilled water until pH ~7. The product was dried in an oven at 105 °C for 10 hours. Finally, it was calcined at 600 °C under a nitrogen atmosphere for 3 hours to obtain the In@H-Beta molecular sieve catalyst product. S2: Fe3O4 was loaded onto the In@H-Beta surface obtained in step S1. 0.9 g of In@H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 5 minutes and sonicated for 2 minutes. Then, 0.18 g of Fe3O4 powder was added, and the mixture was stirred for 3 hours before rotary evaporation. The product was dried in an oven at 105 °C for 20 hours. Finally, it was calcined at 600 °C under an argon atmosphere for 2 hours to obtain the In@H-Beta / Fe3O4 molecular sieve catalyst, with an In loading of 12.16 wt% and a Fe3O4 loading of 18 wt%.

[0055] Example 3 An In@H-Beta / Fe3O4 catalyst, the preparation method of which includes the following steps: S1: First, 0.54 g of H-Beta powder was dispersed in 25 mL of deionized water. The mixture was stirred for 8 minutes and sonicated for 3 minutes. Then, 22 mL of 0.015 mol / L indium sulfate solution was added, and the solution was magnetically stirred at 65 °C for 2 hours. Next, the dispersion was filtered and washed with distilled water until pH ~7. The product was dried in an oven at 105 °C for 6 hours. Finally, it was calcined in air at 600 °C for 4 hours to obtain the In@H-Beta molecular sieve catalyst product. S2: Fe3O4 was loaded onto the In@H-Beta surface obtained in step S1. 0.4 g of In@H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 5 minutes and sonicated for 2 minutes. Then, 0.08 g of Fe3O4 powder was added, and the mixture was stirred for 2 hours before rotary evaporation. The product was dried in an oven at 85 °C for 20 hours. Finally, calcination was carried out at 650 °C in air for 3 hours to obtain the In@H-Beta / Fe3O4 molecular sieve catalyst, with an In loading of 14.03 wt% and a Fe3O4 loading of 20 wt%.

[0056] Comparative Example 1 An In@H-Beta catalyst, the preparation method of which includes the following steps: First, 0.96 g of H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred at 350 r / min for 10 minutes and sonicated for 5 minutes. Then, 31 mL of 0.03 mol / L indium nitrate solution was added, and the solution was magnetically stirred at 350 r / min for 3 hours at 85 °C. Next, the solution was filtered and washed with distilled water until the pH reached ~7. The product was dried in an oven at 105 °C for 10 hours. Finally, it was calcined in air at 600 °C for 3 hours to obtain the In@H-Beta molecular sieve catalyst product.

[0057] Comparative Example 2 An In@H-Beta / NiO catalyst, the preparation method of which includes the following steps: S1: First, 0.96 g of H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred at 350 r / min for 10 minutes and sonicated for 5 minutes. Then, 31 mL of 0.03 mol / L indium nitrate solution was added, and the solution was magnetically stirred at 350 r / min for 3 hours at 85 °C. Next, the solution was filtered and washed with distilled water until pH ~7. The product was dried in an oven at 105 °C for 10 hours. Finally, it was calcined in air at 600 °C for 3 hours to obtain the In@H-Beta molecular sieve catalyst product. S2: NiO supported on the In@H-Beta surface obtained in step S1. 1 g of In@H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 5 minutes and sonicated for 2 minutes. Then, 0.2 g of NiO powder was added, and the mixture was stirred at 350 r / min for 3 hours before rotary evaporation. The product was dried in an oven at 105 °C for 20 hours. Finally, it was calcined at 600 °C under a nitrogen atmosphere for 2 hours to obtain the In@H-Beta / NiO molecular sieve catalyst.

[0058] Comparative Example 3 An In@H-Beta / MnO2 catalyst, the preparation method of which includes the following steps: S1: First, 0.96 g of H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred at 350 r / min for 10 minutes and sonicated for 5 minutes. Then, 31 mL of 0.03 mol / L indium nitrate solution was added, and the solution was magnetically stirred at 350 r / min for 3 hours at 85 °C. Next, the solution was filtered and washed with distilled water until pH ~7. The product was dried in an oven at 105 °C for 10 hours. Finally, it was calcined in air at 600 °C for 3 hours to obtain the In@H-Beta molecular sieve catalyst product. S2: MnO2 was loaded onto the In@H-Beta surface obtained in step S1. 1 g of In@H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 5 minutes and sonicated for 2 minutes. Then, 0.2 g of MnO2 powder was added, and the mixture was stirred at 350 r / min for 3 hours before rotary evaporation. The product was dried in an oven at 105 °C for 20 hours. Finally, the product was calcined at 600 °C under a nitrogen atmosphere for 2 hours to obtain the In@H-Beta / MnO2 molecular sieve catalyst.

[0059] Comparative Example 4 An In@H-Beta / CeO2 catalyst, the preparation method of which includes the following steps: S1: First, 0.96 g of H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred at 350 r / min for 10 minutes and sonicated for 5 minutes. Then, 31 mL of 0.03 mol / L indium nitrate solution was added, and the solution was magnetically stirred at 350 r / min for 3 hours at 85 °C. Next, the solution was filtered and washed with distilled water until pH ~7. The product was dried in an oven at 105 °C for 10 hours. Finally, it was calcined in air at 600 °C for 3 hours to obtain the In@H-Beta molecular sieve catalyst product. S2: CeO2 was loaded onto the In@H-Beta surface obtained in step S1. 1 g of In@H-Beta powder was dispersed in 45 mL of deionized water. The mixture was stirred for 5 minutes and sonicated for 2 minutes. Then, 0.2 g of CeO2 powder was added, and the mixture was stirred at 350 r / min for 3 hours before rotary evaporation. The product was dried in an oven at 105 °C for 20 hours. Finally, the product was calcined at 600 °C under a nitrogen atmosphere for 2 hours to obtain the In@H-Beta / CeO2 molecular sieve catalyst.

[0060] Comparative Example 5 (Fe3O4 was loaded first, then In was loaded) An In@H-Beta / Fe3O4 catalyst, the preparation method of which includes the following steps: S1: First, weigh 0.96 g of H-Beta powder and disperse it in 45 mL of deionized water. Stir at 350 r / min for 5 minutes, then sonicate for 2 minutes to ensure uniform dispersion. Next, add 0.2 g of Fe3O4 powder to the suspension and continue stirring at 350 r / min for 3 hours. After stirring, remove the solvent using a rotary evaporator to obtain a solid product. Place the product in an oven and dry at 105 °C for 20 hours. Finally, calcine the dried sample at 600 °C in a nitrogen atmosphere for 2 hours, and cool to obtain the H-Beta / Fe3O4 precursor.

[0061] S2: Weigh 1 g of the Fe3O4 / H-Beta precursor prepared in the above steps and disperse it in 45 mL of deionized water. Stir at 350 r / min for 10 minutes, then sonicate for 5 minutes. Subsequently, add 31 mL of 0.03 mol / L indium nitrate solution, and magnetically stir the mixture at 350 r / min at 85 °C for 3 hours. After the reaction is complete, filter the mixture and wash the filter cake repeatedly with distilled water until the pH of the washing effluent is approximately 7. Dry the washed product in an oven at 105 °C for 10 hours. Finally, calcine the dried sample in air at 600 °C for 3 hours, and after cooling, obtain the final product In@H-Beta / Fe3O4.

[0062] Comparative Example 6: H-Beta / Fe3O4 First, 0.96 g of H-Beta powder was weighed and dispersed in 45 mL of deionized water. The mixture was stirred at 350 r / min for 5 minutes, followed by ultrasonic treatment for 2 minutes to ensure uniform dispersion. Then, 0.2 g of Fe3O4 powder was added to the suspension, and stirring was continued at 350 r / min for 3 hours. After stirring, the solvent was removed using a rotary evaporator to obtain a solid product. This product was then placed in an oven and dried at 105 °C for 20 hours. Finally, the dried sample was calcined at 600 °C in a nitrogen atmosphere for 2 hours, and after cooling, the H-Beta / Fe3O4 precursor was obtained.

[0063] Application Examples In this embodiment, the catalysts prepared in Example 1 and Comparative Examples 1-6 are used for the selective catalytic reduction denitration reaction of methane. The specific steps are as follows: The CH4-SCR catalytic activity was evaluated in a fixed-bed quartz reactor (6 mm inner diameter). 100 mg of catalyst sample (40-60 mesh) was weighed and placed in the middle of the reactor, with quartz wool filling both ends of the catalyst bed for fixation. Before testing, the catalyst was pretreated in a N2 atmosphere (100 mL / min flow rate) at 300 °C for 1 hour to remove physically adsorbed moisture and impurities.

[0064] After pretreatment, the reactor was cooled to the initial reaction temperature of 350℃, and the activity test was conducted using simulated flue gas. The standard anhydrous (dry) reaction atmosphere consisted of 100 ppm NO, 100 ppm CH4, 5 vol% O2, with N2 as the balance gas, a total flow rate of 300 mL / min, and a corresponding volumetric hourly space velocity (GHSV) of 90,000 h⁻¹. -1 The activity test temperature range was 350℃ to 650℃, and data were collected after each temperature point had been stabilized for 30 minutes.

[0065] During the water resistance test, a certain concentration of water vapor is additionally introduced into the standard atmosphere. The water vapor is generated by a high-pressure constant-flow pump injecting liquid water into a heated mixer; the concentration is adjustable. The test has two modes: Continuous water resistance test: At 550℃, water vapor of a specific volume concentration (e.g., 5%, 10%, 15%, 20%, 25%) is introduced into the reaction atmosphere, and NO is continuously monitored. x Changes in conversion rate.

[0066] Steam cycle test: At 550℃, multiple cycles of "60 minutes of water flow - 30 minutes of water stoppage" were conducted to evaluate the recoverability of catalyst activity.

[0067] The composition of the reactor outlet gas was monitored online in real time using a Fourier transform infrared spectrometer (FTIR spectrometer). x The conversion rate of CH4 is calculated based on the inlet and outlet concentrations.

[0068] Appendix Figure 1 The NO content of the In@H-Beta / Fe3O4 catalyst prepared according to this invention (Example 1), the unmodified In@H-Beta catalyst (Comparative Example 1), and catalysts supported on other transition metal oxides (NiO, MnO2, corresponding to Comparative Examples 2 and 3, respectively) under anhydrous conditions is demonstrated. x Conversion rate comparison.

[0069] As can be seen from the figure: In@H-Beta / Fe3O4 exhibits the best activity: The In@H-Beta / Fe3O4 catalyst prepared in Example 1 showed the highest NO activity across the entire temperature range of 350-650℃.x Conversion rate. Its activity window (NO). x The widest temperature range for NO conversion (>80%) is at 550℃. x The conversion rate is close to 100%, which is significantly better than all other catalysts.

[0070] Effects of other metal oxides: Although loading NiO and MnO2 can also improve the low-temperature activity of In@H-Beta catalysts to some extent, the improvement in high-temperature performance is limited, and the overall activity is far inferior to that of Fe3O4 modified catalysts.

[0071] Synergistic enhancement effect of Fe3O4: Comparative Example 1's In@H-Beta catalyst at 550℃ NO x The conversion rate was approximately 87%, while the activity reached almost 100% after the addition of Fe3O4 (Example 1), indicating that the introduction of Fe3O4 was not merely a simple physical additive process, but rather produced a strong synergistic catalytic effect with In@H-Beta. This synergistic effect may originate from the Fe3O4... 2+ / Fe 3+ The redox couple promoted the conversion of NO to NO2 and stabilized InO through Fe-O-In interface interactions. + The active sites together accelerate the catalytic cycle.

[0072] Appendix Figure 2 This is a CH4-SCR activity evaluation graph for the H-Beta / Fe3O4 catalyst (without In). As shown in the graph, the catalyst with only Fe3O4 loading exhibits almost no NO production throughout the entire test temperature range. x The conversion activity indicates that Fe3O4 itself is not the active center for the CH4-SCR reaction. This result strongly demonstrates that the Fe3O4 in this invention significantly enhances catalytic performance through a synergistic effect with In species confined within the molecular sieve, rather than acting as a catalyst itself.

[0073] Appendix Figure 3 This is a graph showing the N2 selectivity of the In@H-Beta / Fe3O4 catalyst of this invention in the CH4-SCR reaction. The results indicate that the catalyst maintains over 85% N2 selectivity throughout the entire active temperature window (450-650℃), demonstrating excellent N2 selectivity for NO. x Its ability to efficiently and directionally reduce N2 to harmless N2 effectively avoids the generation of byproducts such as N2O.

[0074] Appendix Figure 4 With appendix Figure 5 A direct comparison of the water resistance properties of the catalysts before and after Fe3O4 modification was presented. (Attached) Figure 5The results showed that the unmodified In@H-Beta catalyst (Comparative Example 1) exhibited reduced NO after the introduction of 5 vol% water vapor. x The conversion rate dropped sharply from nearly 90% to about 40%, and the activity decreased by more than 50%, exhibiting extremely poor water resistance. This is mainly because water molecules react with NO. x Competitive adsorption occurs at the Brønsted acid sites of the molecular sieve, leading to the active site InO. + Irreversible hydroxylation occurs (InO) + + 2H2O →In(OH)3 + H + This deactivates the catalyst.

[0075] In comparison, attached Figure 4 The In@H-Beta / Fe3O4 catalyst of the present invention (Example 1) exhibits excellent performance at different water vapor concentrations: Excellent resistance to water poisoning: Under the same conditions of 5% water vapor introduction, the NO content of the In@H-Beta / Fe3O4 catalyst is significantly reduced. x The conversion rate only decreased from nearly 100% to 85%, and the activity retention rate was much higher than that of the unmodified catalyst.

[0076] Tolerance to high concentrations of water vapor: As the water vapor concentration gradually increases from 5% to 15%, NO... x Although the conversion rate decreased, it still remained above 60%, demonstrating its application potential in harsh, high-humidity environments. Even at an extreme water vapor concentration of 25%, it maintained a certain level of catalytic activity.

[0077] Appendix Figure 6 This is a graph showing the activity recovery evaluation of the In@H-Beta / Fe3O4 catalyst of the present invention under the "on / off" steam circulation conditions.

[0078] The experiment was conducted at 550°C, and the catalyst's water resistance was evaluated by repeatedly cycling through the process of "introducing 5% H2O for 60 minutes and stopping water flow for 30 minutes." As shown in the figure, each time water vapor was introduced, the NO conversion rate of the catalyst temporarily decreased from nearly 100% to approximately 83%, but its activity quickly recovered to the initial level once the water flow was stopped. After multiple cycles, the catalyst's activity did not show significant decline, demonstrating that the catalyst of this invention has strong resistance to water poisoning and excellent self-recovery characteristics.

[0079] In summary, this invention first prepares an In@H-Beta molecular sieve catalyst with In loaded in the pores by ion exchange method; then, it prepares an In@H-Beta / Fe3O4 catalyst by impregnating the In@H-Beta molecular sieve with Fe3O4.

[0080] The catalyst of this invention optimizes the distribution of acidic sites and improves mass transfer efficiency by confining In species within the pores of H-Beta molecular sieves, while a hydrophobic interface layer is formed on the surface of Fe3O4 nanoparticles. Fe-O-In interfacial bonding inhibits In hydroxylation deactivation, and Brønsted acid sites promote the protonation of NO to NO. + InO inside the channel + As Lewis acid sites, Fe3O4 lowers the activation energy of CH4 to generate CH3· radicals. Surface Fe3O4 reduces water adsorption through hydrophobic effects, and its oxygen vacancies efficiently activate O2 to generate O2. - Species drive the NO→NO2→NO3 transition. - Chain conversion, combined with dynamic migration of skeletal oxygen to maintain oxygen cycle stability, synergistically enhances catalytic activity and water resistance.

[0081] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An In@H-Beta / Fe3O4 catalyst, characterized in that, The catalyst comprises an H-Beta molecular sieve support, and indium and Fe3O4 supported on the H-Beta molecular sieve support; The indium loading is 1.0~20.0 wt%, and the Fe3O4 loading is 1.0~20.0 wt%.

2. A method for preparing the In@H-Beta / Fe3O4 catalyst as described in claim 1, characterized in that, include: S1: H-Beta molecular sieve is reacted with indium precursor solution by ion exchange reaction and calcined to obtain In@H-Beta precursor; S2: The In@H-Beta precursor was mixed with Fe3O4 dispersion and calcined to obtain the desired product.

3. The method for preparing the In@H-Beta / Fe3O4 catalyst according to claim 2, characterized in that, In step S1, the indium precursor is at least one of indium nitrate, indium chloride, indium oxide, or indium sulfate.

4. The method for preparing the In@H-Beta / Fe3O4 catalyst according to claim 2, characterized in that, In step S1, the feeding ratio of the H-Beta molecular sieve to the indium precursor is (0.7~1.6) g:(0.6~1.4) mmol.

5. The method for preparing the In@H-Beta / Fe3O4 catalyst according to claim 2, characterized in that, In step S1, the ion exchange reaction is carried out at a temperature of 50-90°C for 1-5 hours.

6. The method for preparing the In@H-Beta / Fe3O4 catalyst according to claim 2, characterized in that, In step S1, the calcination temperature is 550~650℃, the calcination time is 2.5~4.5 h, and the calcination atmosphere is air.

7. The method for preparing the In@H-Beta / Fe3O4 catalyst according to claim 2, characterized in that, In step S2, the mass ratio of the In@H-Beta precursor to Fe3O4 is (0.6~2.0):(0.05~0.2).

8. The method for preparing the In@H-Beta / Fe3O4 catalyst according to claim 2, characterized in that, In step S2, the calcination temperature is 450~700℃, the calcination time is 2~4.5 h, and the calcination atmosphere is at least one of air, nitrogen or argon.

9. The application of the In@H-Beta / Fe3O4 catalyst as described in claim 1, characterized in that, The catalyst is used for the selective catalytic reduction of nitrogen oxides by methane.

10. The application of the In@H-Beta / Fe3O4 catalyst according to claim 9, characterized in that, The methane selective catalytic reduction denitration reaction includes at least one of the following conditions: A: NO x Concentration ranges from 50 to 500 ppm; B: CH4 concentration is 50~500 ppm; C: O2 content is 3~10 vol% D: H2O content ≤ 25 vol% E: The reaction temperature is 300~700℃; F: Volumetric space velocity is 20,000~100,000 h -1 ; G: Operating pressure is atmospheric pressure ~ 3 MPa; H: Used for denitrification treatment of exhaust gas from natural gas vehicles, flue gas from gas-fired boilers, or exhaust gas from diesel engines.

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