Packaging of noble metal mof-based catalysts, methods of making and use

Abstract

The application relates to the technical field of MOF-based catalysts, in particular to a noble metal MOF-based catalyst, a preparation method and application. The catalyst is prepared by the method. The method comprises the following steps: preparing a noble metal-ligand chelation solution; adding manganese salt, a second organic ligand, a second organic solvent and water into the noble metal-ligand chelation solution in sequence, adjusting the pH value to 3-5 after stirring and dissolving, and obtaining a precursor suspension; cooling the precursor suspension to room temperature after a crystallization reaction; then, performing suction filtration, and performing first washing treatment on the obtained solid until the washing liquid is colorless and transparent; performing first vacuum drying treatment on the obtained solid, and obtaining a precursor powder; and performing reduction treatment, second washing treatment and second vacuum drying treatment on the precursor powder in sequence, and obtaining the catalyst. The application is the application of the catalyst in adsorptive catalytic oxidation of formaldehyde, and the conversion rate of formaldehyde can be greater than or equal to 95% at room temperature.

Description

Technical Field

[0001] This invention relates to the field of MOF-based catalyst technology, and in particular to an encapsulated noble metal MOF-based catalyst, its preparation method, and its application. Background Technology

[0002] Formaldehyde, a common volatile toxic pollutant, is widely found in indoor decoration materials, industrial production, and automotive interiors. Long-term exposure can seriously harm the human respiratory and immune systems, and also adversely affect the ecological environment. Therefore, developing efficient and stable formaldehyde purification technologies is of significant practical importance and market demand.

[0003] Room-temperature catalytic oxidation, which can directly convert formaldehyde into non-toxic and harmless carbon dioxide and water at room temperature without additional energy consumption and secondary pollution, has become a research hotspot in the field of formaldehyde purification. The core of room-temperature catalytic oxidation of formaldehyde lies in catalyst design. Noble metals such as Pd and Pt are widely used in formaldehyde purification due to their excellent catalytic activity. Currently, the preparation of most noble metal catalysts uses traditional inorganic supports such as alumina, silica, and activated carbon. Noble metal nanoparticles are loaded onto the surface or pores of the support through impregnation or precipitation methods to construct supported noble metal catalysts. However, these traditional supports have inherent structural defects, leading to numerous bottlenecks in practical applications and severely limiting their catalytic performance and lifespan.

[0004] For example, alumina supports have a relatively limited specific surface area and irregular pore structure with a wide pore size distribution, lacking effective spatial confinement sites. Noble metal nanoparticles, due to their extremely high surface energy, easily migrate and aggregate on the alumina support surface during preparation, forming large particles. Furthermore, during the catalytic reaction, the aggregation of noble metal particles is more pronounced due to the influence of the reaction atmosphere and temperature fluctuations, directly leading to a significant decrease in the specific surface area of ​​the noble metal, a sharp reduction in the number of active sites, and a significant decrease in the efficiency of catalytic formaldehyde oxidation. Simultaneously, the interaction between the alumina support and the noble metal nanoparticles is weak, achieving only simple physical loading and failing to effectively anchor the noble metal particles. This makes it easy for the noble metal to detach and be lost during the reaction, causing catalyst deactivation. In addition, traditional supports such as alumina lack specific adsorption and screening functions for formaldehyde, allowing other impurities in the reaction system to be directly adsorbed onto the surface of the noble metal active sites on the traditional support, forming stable adsorbed species that cover the active sites, leading to noble metal poisoning and loss of catalytic activity.

[0005] Compared to traditional supports, metal-organic frameworks (MOFs) offer advantages such as large specific surface area, tunable and regular pore structure, and flexible framework composition. They can optimize the dispersion of noble metals through mechanisms like pore confinement and strong interactions, providing a new technological path to address the aforementioned problems. Therefore, it is necessary to provide an encapsulated noble metal MOF-based catalyst, its preparation method, and its application to address the problems of noble metal nanoparticle (i.e., active component) agglomeration due to the lack of effective spatial confinement sites in traditional alumina supports; the weak interaction between traditional alumina supports and noble metal nanoparticles leading to easy detachment of noble metal nanoparticles; and the lack of specific adsorption and screening functions for formaldehyde in traditional alumina supports, resulting in the active sites of noble metals being covered by adsorbed impurities, leading to catalyst deactivation. Summary of the Invention

[0006] The purpose of this invention is to provide an encapsulated noble metal MOF-based catalyst, its preparation method, and its application. The specific technical solution is as follows: In a first aspect, the present invention provides a method for preparing an encapsulated noble metal MOF-based catalyst, comprising: Step S1: Prepare a noble metal-ligand chelate solution; A noble metal salt is added to a first organic solvent, and hydrochloric acid is added dropwise to aid dissolution. After stirring and dissolving, the first organic ligand is added, and stirring is continued to dissolve, thus preparing a noble metal-ligand chelate solution. The molar ratio of the noble metal salt, the hydrochloric acid, the first organic solvent, and the first organic ligand is 1:(100~200):(500~800):1; Step S2: Prepare encapsulated noble metal MOF-based catalyst; Manganese salt, a second organic ligand, a second organic solvent, and water are added sequentially to the noble metal-ligand chelate solution. After stirring and dissolving, the pH value is adjusted to 3-5 to obtain a precursor suspension. The molar ratio of the manganese salt, the second organic ligand, the second organic solvent, and the water is (1~1.5):1:(20~50):(120~150). The precursor suspension was subjected to a crystallization reaction and then cooled to room temperature. Subsequently, it was filtered, and the solid obtained by filtration was subjected to a first washing treatment until the washing liquid was colorless and transparent. The solid obtained by filtration was subjected to a first vacuum drying treatment to obtain precursor powder. The precursor powder was subjected to reduction treatment, second washing treatment, and second vacuum drying treatment in sequence to obtain the encapsulated noble metal MOF-based catalyst.

[0007] Optionally, the precious metal salt includes a platinum salt or a palladium salt; the platinum salt includes platinum chloride; the palladium salt includes palladium chloride; and the manganese salt includes manganese nitrate or manganese acetate.

[0008] Optionally, the volume ratio of the second organic solvent to the first organic solvent is 2 to 8:1; the first organic solvent includes N,N-dimethylformamide; the second organic solvent includes N,N-dimethylformamide.

[0009] Optionally, the molar ratio of the second organic ligand to the first organic ligand is 2 to 20:1; the first organic ligand includes terephthalic acid; the second organic ligand includes terephthalic acid.

[0010] Optionally, the crystallization reaction is carried out at a temperature of 120~150℃ and for a reaction time of 24~48h.

[0011] Optionally, the reduction atmosphere used in the reduction process includes hydrogen and an inert carrier gas, and the volume ratio of hydrogen to the inert carrier gas is 1:(2~6); the reduction temperature used in the reduction process is 200~300℃, and the reduction time is 2~4h.

[0012] Optionally, the first vacuum drying process uses a drying temperature of 60~120℃ and a drying time of 6~15h.

[0013] Optionally, the second vacuum drying process uses a drying temperature of 60~120℃ and a drying time of 6~15h.

[0014] In a second aspect, the present invention provides an encapsulated noble metal MOF-based catalyst, which is prepared by the aforementioned method for preparing encapsulated noble metal MOF-based catalysts.

[0015] In a third aspect, the present invention provides the application of the encapsulated noble metal MOF-based catalyst in the adsorption and catalytic oxidation of formaldehyde, characterized in that the encapsulated noble metal MOF-based catalyst has a formaldehyde conversion rate of greater than or equal to 95% at room temperature.

[0016] The application of the technical solution of the present invention has at least the following beneficial effects: (1) The present invention provides a method for preparing a noble metal MOF-based catalyst, wherein manganese salt, a second organic ligand, a second organic solvent, and water are added sequentially in step S2. After treatment in step S2, a flexible channel with adjustable pore size of 0.7~1.3 nm and a pore size of not less than 1100 nm can be prepared. 2A MOF-based support with a high specific surface area of ​​ / g; this MOF-based support ensures uniform dispersion of noble metal nanoparticles and confines and anchors them within the pores of the MOF-based support, thus solving the problems of easy aggregation and detachment of noble metal nanoparticles; the MOF-based support has tunable flexible channels of 0.7~1.3nm, which not only confines noble metal nanoparticles but also specifically adsorbs formaldehyde, preventing other large-volume impurities from entering, thereby improving the problem of active sites of noble metal nanoparticles being easily covered by impurities and deactivated. In addition, this MOF-based support can also improve the stability of encapsulated noble metal MOF-based catalysts. The specific principle is as follows: Regarding the formation of tunable flexible channels and high specific surface area, the MOF-based support prepared in this invention contains Mn-O coordination chains. These chains, together with a first organic ligand and a second organic ligand, form a reversible hinged framework that enables a reversible breathing effect between the narrow-pore and wide-pore phases, thereby forming a large number of tunable flexible channels of 0.7–1.3 nm. Because the MOF-based support contains a large number of tunable flexible channels of 0.7–1.3 nm, it possesses a high specific surface area, facilitating the uniform dispersion and loading of noble metal nanoparticles within the pores of the MOF-based support.

[0017] The function of adjustable flexible channels: 1) It can form flexible encapsulation and confinement of encapsulated noble metal nanoparticles, as well as multiple strong interactions, thereby inhibiting their migration, aggregation, and detachment. Specifically, the MOF-based support has a one-dimensional, uniform, and regular nanoporous structure. Noble metal ions enter the interior of the MOF-based support nanopores through a stirring and dissolution process, and after reduction treatment, noble metal nanoparticles are generated in situ. Because the nanopore size is fixed and uniformly distributed, the noble metal nanoparticles can only grow inside the nanopores and cannot migrate or aggregate at will, thus achieving precise confinement. Furthermore, there are multiple strong interactions between the MOF-based support and the noble metal nanoparticles, which firmly fix the noble metal nanoparticles inside the nanopores. The first strong interaction is coordination. The MOF-based support framework contains a large number of unsaturated Mn sites and oxygen donor coordination sites, which can form MO coordination bonds (i.e., noble metal-oxygen coordination bonds) with the atoms of the noble metal nanoparticles. This coordination interaction is much stronger than the physical adsorption or weak electrostatic interaction of traditional alumina supports, making it difficult for the noble metal to detach or migrate. The second strong interaction is the electron interaction, and Mn has a variable valence state (Mn 2+ / Mn 3+ The MOF-based support can transfer electrons with noble metals, forming electronic interactions and interfacial chemical bonds, further enhancing the anchoring strength of noble metal nanoparticles. The third strong interaction is the nanopore encapsulation effect. The flexible pores of the MOF-based support can encapsulate noble metal nanoparticles, forming a spatial locking effect, which can inhibit the migration and aggregation of noble metal nanoparticles even under reaction conditions.

[0018] 2) The adjustable flexible channels can adaptively match the size of formaldehyde molecules, achieving efficient and selective adsorption and transport of formaldehyde. At the same time, they automatically reject larger impurities, forming a natural molecular sieving function, which improves the problem that the active sites of noble metal nanoparticles are easily covered by impurities and deactivated.

[0019] In improving the stability of encapsulated noble metal MOF-based catalysts, on the one hand, the MOF-based support contains high-strength MnO coordination bonds, which can form a one-dimensional continuous rigid backbone, making the MOF-based support framework dense and robust, and not prone to hydrolysis and collapse in aqueous environments. Furthermore, the high-strength Mn-O coordination bonds construct a one-dimensional continuous rigid backbone with high chemical bond energy, making it resistant not only to hydrolysis but also to oxidation. On the other hand, the tunable flexible channels can exhibit a breathing effect in aqueous environments, allowing for adaptive contraction and structural self-protection, reducing the damage to internal coordination bonds by water molecules. In addition, the tunable flexible channels of the MOF-based support can form flexible encapsulation and confinement of the encapsulated noble metal nanoparticles, as well as multiple strong interactions, thereby inhibiting their migration, aggregation, and detachment. Furthermore, the presence of hydrophobic benzene ring structures in the MOF-based support framework reduces the hydrophilicity of the catalyst, further enhancing its hydrothermal stability. Therefore, this MOF-based support can also improve the stability of encapsulated noble metal MOF-based catalysts, enabling the catalysts to operate stably for extended periods in high humidity, ambient temperature, and indoor environments.

[0020] (2) The method for preparing a noble metal MOF-based catalyst provided by the present invention uses a low noble metal loading, which has the advantage of controllable cost; in addition, the method is simple in steps, the parameters are easy to control, and it is convenient for large-scale production.

[0021] (3) The encapsulated noble metal MOF-based catalyst prepared in this invention exhibits high catalytic degradation activity for formaldehyde, achieving a formaldehyde conversion rate of greater than or equal to 95% at room temperature. The specific catalytic degradation principle is as follows: The MOF-based support has a large number of tunable flexible channels of 0.7~1.3 nm, which can adaptively match the formaldehyde molecule size to achieve efficient and selective adsorption and transport of formaldehyde; Mn in the nanopores of the MOF-based support can preferentially activate formaldehyde to obtain activated H2COO. Noble metal nanoparticles in MOF-based carrier nanopores can activate H2COO Decomposed into HCOO - It further decomposes into CO2 and water.

[0022] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 The image shows the morphology of the distribution of noble metal nanoparticles inside the pores of the encapsulated noble metal MOF-based catalyst prepared in Example 1 (the white dots in the red circles represent noble metal nanoparticles). Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: A method for preparing an encapsulated noble metal MOF-based catalyst includes: Step S1: Prepare a noble metal-ligand chelate solution; 0.0337 g of PtCl4 was added to 5 mL of N,N-dimethylformamide, and 0.5 mL of hydrochloric acid was added dropwise to aid dissolution. After stirring and dissolving, 0.0166 g of the first organic ligand, terephthalic acid, was added, and the mixture was further stirred magnetically (at a speed of 300 r / min) to dissolve, thus preparing a noble metal-ligand chelate solution. The molar ratio of PtCl4, hydrochloric acid, N,N-dimethylformamide, and terephthalic acid was 0.0001:0.0162:0.0646:0.0001.

[0027] Step S2: Prepare encapsulated noble metal MOF-based catalyst; 0.295 g Mn(NO3)2·4H2O, 0.166 g terephthalic acid (the second organic ligand), 25 mL N,N-dimethylformamide, and 25 mL water were added sequentially to the noble metal-ligand chelate solution prepared in step S1. After dissolving by magnetic stirring (specifically at a speed of 400 r / min), the pH was adjusted to 3.5 using an acetate-sodium acetate buffer solution to obtain a homogeneous light brown precursor suspension. The molar ratio of Mn(NO3)2·4H2O, terephthalic acid, 25 mL N,N-dimethylformamide, and water was 0.01175:0.01:0.3229:1.3877. The molar ratio of terephthalic acid (the second organic ligand added in step S2) to terephthalic acid (the first organic ligand added in step S1) was 10:1.

[0028] The precursor suspension was transferred to a container lined with polytetrafluoroethylene (PTFE). After removing air bubbles, it was placed in a stainless steel hydrothermal reactor, the lid was tightened, and the reactor was placed in an electrically heated constant-temperature drying oven. The reactor was crystallized at 130°C for 36 hours, and then naturally cooled to room temperature (specifically 25±5°C; all room temperature readings in this text refer to this temperature). Subsequently, the solid was obtained by vacuum filtration. The solid was washed three times with anhydrous ethanol, and then twice with deionized water until the washing liquid was colorless and transparent. The light brown solid obtained by vacuum filtration was transferred to a petri dish and placed in a vacuum drying oven for the first vacuum drying treatment at 80°C for 12 hours, yielding the precursor powder.

[0029] The precursor powder was subjected to reduction treatment, a second washing treatment, and a second vacuum drying treatment in sequence to obtain an encapsulated noble metal MOF-based catalyst. The reduction treatment used a reduction atmosphere consisting of hydrogen and an inert carrier gas (specifically Ar gas), with a hydrogen to inert carrier gas volume ratio of 1:4; the reduction temperature was 250℃, and the reduction time was 3h.

[0030] The specific operation of the reduction treatment is as follows: The precursor powder is spread evenly in a quartz boat of a tube furnace (thickness ≤ 2 mm); the quartz boat is pushed into the constant temperature zone of the tube furnace, the gas path is connected, and Ar gas is first introduced (flow rate 40 mL / min) to purge the air in the tube furnace for 30 min; then, the Ar gas is switched to a reducing atmosphere (hydrogen volume ratio 20%, total flow rate 40 mL / min), and after the gas path is stable, the temperature is increased to 250℃ at a heating rate of 5℃ / min and reduced at a constant temperature for 3 h; after the reduction is completed, the heating device is turned off, and the hydrogen / Ar gas mixture is kept purging to allow the powder after reduction treatment to cool naturally to room temperature; after cooling, the gas path is turned off, the quartz boat is taken out, and a gray-black solid powder is obtained.

[0031] The second washing process involved washing the aforementioned gray-black solid powder once with anhydrous ethanol and then with deionized water. The second vacuum drying process involved placing the washed gray-black solid powder into a vacuum drying oven and drying it at 80°C for 12 hours, thus obtaining the encapsulated noble metal MOF-based catalyst prepared in Example 1.

[0032] Example 2: Unlike Example 1, the noble metal salt is palladium chloride.

[0033] Example 3: Unlike Example 1, in step S2, the amount of the second organic ligand terephthalic acid added is 0.0332 g, and the molar ratio of the second organic ligand terephthalic acid added in step S2 to the first organic ligand terephthalic acid added in step S1 is 2:1.

[0034] Example 4: Unlike Example 1, in step S2, the amount of the second organic ligand terephthalic acid added is 0.332 g, and the molar ratio of the second organic ligand terephthalic acid added in step S2 to the first organic ligand terephthalic acid added in step S1 is 20:1.

[0035] Example 5: Unlike Example 1, the reduction treatment used a reduction temperature of 200°C.

[0036] Example 6: Unlike Example 1, the reduction treatment used a reduction temperature of 300°C.

[0037] Example 7: Unlike Example 1, the reduction process used a reduction time of 2 hours.

[0038] Example 8: Unlike Example 1, the reduction process used a reduction time of 4 hours.

[0039] Comparative Example 1: A catalyst with alumina as a support and platinum (Pt) loaded on it was prepared using a conventional impregnation-reduction method, wherein the Pt loading was the same as in Example 1. The specific preparation method is as follows: Preparation of Pt impregnation solution: Take a 100mL single-necked flask, add 0.0337g PtCl4, add 1~2 drops of concentrated hydrochloric acid to aid dissolution, then add 5mL DMF and 20mL deionized water, and stir magnetically at 300r / min until PtCl4 is completely dissolved to obtain the impregnation solution, and let it stand for later use.

[0040] Pt impregnation loading: 0.872 g of γ-alumina support was added to the above impregnation solution, and the mixture was magnetically stirred at 400 r / min for 24 h at room temperature to ensure Pt impregnation. 4+ The solution is fully adsorbed onto the surface of the alumina carrier to obtain an impregnated suspension.

[0041] Post-processing of the carrier: The above suspension was transferred to a Buchner funnel and filtered under vacuum. The sample was washed three times with anhydrous ethanol and then twice with deionized water until the washings were colorless and transparent. The solid obtained by filtration was transferred to a petri dish and placed in a vacuum drying oven at 60°C for 12 hours to obtain Pt. 4+ / Al2O3 precursor powder; Pt 4+ The Al2O3 precursor powder was reduced to a Pt / Al2O3 catalyst, and the reduction method was the same as in Example 1.

[0042] Comparative Example 2: Comparative Example 2 directly used MIL-53 (Mn) as a catalyst, and the specific preparation method is as follows: 0.295 g Mn(NO3)2·4H2O, 0.166 g terephthalic acid, 25 mL N,N-dimethylformamide, and 25 mL water were added sequentially. After dissolving by magnetic stirring (specifically at a speed of 400 r / min), the pH was adjusted to 3.5 using an acetate-sodium acetate buffer solution to obtain a homogeneous precursor suspension. The molar ratio of Mn(NO3)2·4H2O, terephthalic acid, N,N-dimethylformamide, and water was 0.01175:0.01:0.3229:1.3877.

[0043] The subsequent crystallization reaction, washing and drying to obtain precursor powder, and the steps of reducing, washing and vacuum drying the precursor powder to obtain the catalyst are the same as in Example 1.

[0044] Comparative Example 3: Unlike Example 1, in step S2, Mn(NO3)2·4H2O is replaced with Al(NO3)3·9H2O. The specific steps are as follows: Step S1 is the same as in Example 1.

[0045] Step S2: Prepare encapsulated noble metal MOF-based catalyst; 0.441 g Al(NO3)3·9H2O, 0.166 g terephthalic acid, 25 mL N,N-dimethylformamide and 25 mL water were added sequentially to the noble metal-ligand chelate solution. After dissolving by magnetic stirring (specific speed 400 r / min), the pH was adjusted to 3.5 using an acetate-sodium acetate buffer solution to obtain a homogeneous light brown precursor suspension. The molar ratio of Al(NO3)3·9H2O, terephthalic acid, N,N-dimethylformamide and water is 0.01175:0.01:0.3229:1.3877.

[0046] The remaining steps are the same as in Example 1.

[0047] Comparative Example 4: Unlike Example 1, in step S2, the second organic ligand terephthalic acid added is 0.0166 g, and the molar ratio of terephthalic acid added in step S2 to that added in step S1 is 1:1.

[0048] Comparative Example 5: Unlike Example 1, in step S2, the amount of the second organic ligand, terephthalic acid, added is 0.498 g, and the molar ratio of the terephthalic acid added in step S2 to that added in step S1 is 30:1.

[0049] Comparative Example 6: Unlike Example 1, the reduction treatment used in step S2 is replaced by ascorbic acid liquid-phase reduction treatment. The specific reduction treatment method is as follows: Take 0.2g of the precursor powder prepared in Example 1, disperse it in a mixed solvent of 20mL deionized water and 10mL anhydrous ethanol, and ultrasonically disperse it for 15min to obtain a uniform suspension. The suspension was placed on a magnetic stirrer, and 0.0558 g of ascorbic acid was slowly added while stirring at room temperature. After the addition was complete, the temperature was raised to 60°C and stirred at a constant temperature for 3 hours to complete the Pt process. 2+ The reduction reaction; After the reduction reaction is complete, turn off the heating and continue stirring until the suspension cools naturally to room temperature.

[0050] In Comparative Example 6, the above suspension was subjected to solid-liquid separation by vacuum filtration. Subsequently, the separated solid was washed. Specifically, it was washed three times with deionized water and twice with anhydrous ethanol until the washing liquid was colorless and transparent. The gray-black solid obtained by vacuum filtration after washing was transferred to a petri dish, placed in a vacuum drying oven, and vacuum dried at 60°C for 12 h to obtain the MOF-based supported Pt catalyst prepared by ascorbic acid reduction.

[0051] Samples of the catalysts prepared in Examples 1-8 and Comparative Examples 1-6 were taken for catalytic oxidation performance testing and average pore size testing. The test results are shown in Table 1. The test methods are as follows: 1) Catalyst pretreatment: Take 0.1g of catalyst sample and place it in the middle of a quartz reaction tube. Use nitrogen (purity 99.99%) as the carrier gas and set the flow rate to 50mL / min. Proceed to 120℃ and hold for 2h to remove adsorbed water and impurities on the catalyst surface. Then, let it cool naturally to 35℃ and hold for 30min.

[0052] 2) Reaction system setup: A fixed-bed reactor was used for catalytic performance testing. The reaction gas was prepared by mixing formaldehyde standard gas (concentration 1000ppm), oxygen (purity 99.99%), and nitrogen in a volume ratio of 1:10:89. The total flow rate was controlled at 100mL / min to ensure a gas hourly space velocity (GHSV) of 60000mL·g. -1 ·h -1 They are connected to the reaction tube to form a closed-loop system.

[0053] 3) Reaction process control: Maintain a constant temperature of 35℃ and atmospheric pressure in the reaction system. Start timing after the reaction begins. The first 30 minutes are the system stabilization period, during which no data is collected. After stabilization, product gas samples are collected every 15 minutes using an Agilent 7890B gas chromatograph (equipped with a flame ionization detector). Five sets of data are collected continuously, with each set analyzed three times and the average value is taken to ensure data reliability.

[0054] 4) Post-experiment treatment: After the test, the formaldehyde standard gas was turned off, and nitrogen gas was continued to purge the reaction tube for 30 minutes. After cooling to room temperature, the catalyst was removed, and the experimental phenomena and instrument parameters were recorded.

[0055] 5) The formaldehyde conversion rate (i.e., X) is calculated based on the change in formaldehyde concentration before and after the reaction, using the following formula: X = [(C0- C t ) / C0]×100%; In the formula: C0 is the initial concentration (ppm) of formaldehyde in the reaction gas, determined by calibration with formaldehyde standard gas; C t The measured concentration (ppm) of formaldehyde in the product gas after the reaction is the average value of multiple measurements by gas chromatograph. The formaldehyde conversion result is retained to two significant figures, reflecting the catalytic oxidation ability of the catalyst for formaldehyde at 25℃.

[0056] Average pore size testing method: The pore size distribution of the sample was analyzed using a nitrogen adsorption-desorption surface area analyzer (model ASAP 2460) from Micron Technology. Sample preparation procedure: 0.1g of sample was pre-degassed under vacuum at 423K for 12h, and then the nitrogen adsorption-desorption curve of the sample was obtained at 77K. The pore size of the sample was calculated using the BJH model.

[0057] Table 1. Test results of catalytic oxidation ability of formaldehyde

[0058] From the data in Table 1, we know that: Compared to Comparative Examples 1-6, the catalysts prepared in Examples 1-8 of this invention not only possess tunable flexible channels of 0.8-1.3 nm, but also exhibit high catalytic conversion rates for formaldehyde. The specific principle is as follows: The catalyst MOF-based support prepared in Examples 1-8 of this invention contains Mn-O coordination chains. These chains, along with the first and second organic ligands, form a reversible hinged framework that enables a reversible breathing effect between the narrow-pore and wide-pore phases, thereby forming numerous tunable flexible channels of 0.8-1.3 nm. These tunable flexible channels can flexibly encapsulate and confine the encapsulated noble metal nanoparticles, as well as facilitate multiple strong interactions, ensuring that the noble metal nanoparticles are uniformly dispersed and loaded within the MOF-based support channels (see...). Figure 1 On the one hand, it inhibits the migration, aggregation, and shedding of formaldehyde; on the other hand, it can adaptively match the size of formaldehyde molecules to achieve efficient and selective adsorption and transport of formaldehyde, while automatically rejecting larger impurities, forming a natural molecular sieving function; in addition, Mn in the nanopores of the MOF-based support can preferentially activate formaldehyde to obtain activated H2COO. Noble metal nanoparticles in MOF-based carrier nanopores can activate H2COO Decomposed into HCOO - It is further decomposed into CO2 and water, achieving a formaldehyde conversion rate of greater than or equal to 95.3%.

[0059] Comparing Example 1 and Comparative Example 1, it was found that the average pore size of the catalyst prepared by the conventional impregnation-reduction method in Comparative Example 1, using alumina as a support and loaded with platinum (Pt), was significantly increased to 5.2 nm, while the formaldehyde conversion rate of this catalyst significantly decreased to 30.4%. The reasons are as follows: Comparative Example 1 uses alumina as a support, which has an irregular pore structure and a wide pore size distribution, resulting in a significantly increased average pore size of 5.2 nm. However, this significantly increased average pore size does not allow for the confinement of the noble metal Pt. Furthermore, the interaction between the alumina support and the noble metal nanoparticles is weak, only achieving simple physical loading and failing to effectively anchor the noble metal particles. This makes the noble metal prone to detachment and loss during the reaction, causing catalyst deactivation and resulting in a significant decrease in the formaldehyde conversion rate to 30.4%.

[0060] Comparing Example 1 and Comparative Example 2, it is evident that Comparative Example 2, which directly uses MIL-53(Mn) as a catalyst, exhibits a suitable average pore size, but its formaldehyde conversion rate significantly decreases to 68.6%. The reason is as follows: Comparative Example 2, which directly uses MIL-53(Mn) as a catalyst, is essentially equivalent to the MOF-based support in Example 1. While the nanopores of the MOF-based support can adaptively match the formaldehyde molecule size, achieving highly efficient and selective adsorption and transport of formaldehyde, the Mn within its nanopores can only activate formaldehyde, yielding activated H2COO. Lacking precious metal active components, it cannot completely decompose formaldehyde, resulting in a significant decrease in the formaldehyde conversion rate.

[0061] Comparing Example 1 and Comparative Example 3, it is evident that in Comparative Example 3, replacing Mn(NO3)2·4H2O with Al(NO3)3·9H2O in step S2 resulted in a catalyst with a suitable average pore size, but the formaldehyde conversion rate significantly decreased to 74.2%. The reason is as follows: the activation ability of Al in the MOF-based support for formaldehyde is significantly weaker than that of Mn. Therefore, the Al-containing MOF-based support yields activated H2COO. The reduction leads to the decomposition of precious metal nanoparticles into HCOO. - This reduction leads to a significant decrease in the conversion rate of formaldehyde.

[0062] Comparing Example 1 and Comparative Examples 4-5, it is evident that the molar ratio of the second organic ligand to the first organic ligand used in Comparative Example 4 was too low, and the molar ratio of the second organic ligand to the first organic ligand used in Comparative Example 5 was too high. Although the prepared catalysts all had suitable average pore sizes, their formaldehyde conversion rates were significantly reduced. The reasons are as follows: Comparative Example 4 used too little second organic ligand, resulting in a reduction in the MOF-based support synthesized in step S2. However, the noble metal-ligand chelation solution provided in step S1 remained unchanged, leading to an increase in the noble metal nanoparticles loaded on the MOF-based support. This increased the likelihood of aggregation, resulting in a significant decrease in the formaldehyde conversion rate, which was lower than that of Comparative Example 5. Comparative Example 5 used too much second organic ligand, increasing the MOF-based support synthesized in step S2. However, the noble metal-ligand chelation solution provided in step S1 remained unchanged, resulting in an unchanged noble metal nanoparticle content on the MOF-based support. This reduced the catalytic activity per unit area of ​​the MOF-based support, leading to a decrease in the formaldehyde conversion rate.

[0063] Comparing Example 1 and Comparative Example 6, it is evident that although the catalyst prepared by ascorbic acid liquid-phase reduction in Comparative Example 6 has a suitable average pore size, its formaldehyde conversion rate significantly decreased to 85.4%. The reasons are as follows: Example 1 employed a high-temperature reduction using a hydrogen-argon mixture, which generates active hydrogen, resulting in a stronger thermodynamic driving force for reduction. This allows for the complete reduction of high-valence precious metal oxides without organic carbon impurities. In contrast, Comparative Example 6 used only a mild liquid-phase reduction, with lower reduction capacity and completeness compared to Example 1. Consequently, the resulting catalyst exhibited lower catalytic activity than that of Example 1, leading to a significant decrease in formaldehyde conversion rate.

[0064] The catalyst prepared in Example 1 was sampled and subjected to 100-hour stability tests in high humidity, room temperature, and indoor environments, respectively. The test results are shown in Table 2. The test methods are as follows: (1) Stability test in high humidity environment (relative humidity 80%~85%) for 100h 1) Catalyst pretreatment: Take 0.1g of catalyst sample and place it in the middle of a quartz reaction tube. Use nitrogen (purity 99.99%) as the carrier gas and set the flow rate to 50mL / min. Proceed to 120℃ and hold for 2h to remove adsorbed water and impurities on the catalyst surface. Then, let it cool naturally to 35℃ and hold for 30min.

[0065] 2) Reaction system setup: A fixed-bed reactor was used for catalytic performance testing. The reaction gas was prepared by mixing formaldehyde standard gas (concentration 1000ppm), oxygen (purity 99.99%), and nitrogen in a volume ratio of 1:10:89. The total flow rate was controlled at 100mL / min to ensure a gas hourly space velocity (GHSV) of 60000mL·g. -1 ·h -1 The system is connected to the reaction tube to form a closed-loop system. At the same time, before the reaction gas enters the reaction tube, the relative humidity of the system is controlled at 80%~85% by a humidity generator. After stabilizing for 30 minutes, the system is connected to the closed-loop system to ensure the stability of the high humidity environment.

[0066] 3) Reaction process control: Maintain a constant temperature of 35℃, atmospheric pressure, and relative humidity of 80%~85% in the reaction system. Start timing after the reaction begins. The first 30 minutes are the system stabilization period, during which no data is collected. After stabilization, start timing for a 100-hour stability test. During the test, product gas samples are collected every hour using an Agilent 7890B gas chromatograph (equipped with a flame ionization detector). Three sets of data are collected every 5 hours, and the average value is taken. After the 100-hour test, an additional five sets of data are collected for final verification to ensure data reliability. During the test, humidity changes are monitored in real time, and the humidity generator parameters are adjusted in a timely manner to maintain a stable high-humidity environment.

[0067] 4) Post-experiment treatment: After the 100h stability test, the formaldehyde standard gas and humidity generator were turned off, and nitrogen gas was continued to purge the reaction tube for 30 minutes. After cooling to room temperature, the catalyst was taken out and the changes in the appearance of the catalyst, the humidity fluctuations during the experiment and the instrument parameters were recorded.

[0068] 5) The formaldehyde conversion rate (i.e., X) is calculated based on the change in formaldehyde concentration before and after the reaction, using the following formula: X = [(C0 - C t ) / C0]×100%; In the formula: C0 is the initial concentration (ppm) of formaldehyde in the reaction gas, determined by calibration with formaldehyde standard gas; C t The measured concentration (ppm) of formaldehyde in the product gas after the reaction is the average value of multiple measurements by the gas chromatograph. The formaldehyde conversion rate is retained to two significant figures. The conversion rate at different time points and the final conversion rate are recorded during the 100-hour test to reflect the catalytic oxidation stability of the catalyst for formaldehyde within 100 hours under high humidity (80%~85%) and 35℃ conditions.

[0069] (2) Stability test at room temperature (25±2℃) for 100 hours 1) Catalyst pretreatment: Take 0.1g of catalyst sample and place it in the middle of a quartz reaction tube. Use nitrogen (99.99% purity) as the carrier gas and set the flow rate to 50mL / min. Proceed to 120℃ and hold for 2h to remove adsorbed water and impurities on the catalyst surface. Then, allow it to cool naturally to 25℃ and hold for 30min to ensure that the catalyst reaches the room temperature test state.

[0070] 2) Reaction system setup: A fixed-bed reactor was used for catalytic performance testing. The reaction gas was prepared by mixing formaldehyde standard gas (concentration 1000ppm), oxygen (purity 99.99%), and nitrogen in a volume ratio of 1:10:89. The total flow rate was controlled at 100mL / min to ensure a gas hourly space velocity (GHSV) of 60000mL·g. -1 ·h -1 The system is connected to the reaction tube to form a closed loop system, and the system environment is maintained at room temperature (25℃±2℃) without additional temperature and humidity control.

[0071] 3) Reaction process control: Maintain a constant temperature of 25±2℃ and atmospheric pressure in the reaction system. Start timing after the reaction begins. The first 30 minutes are the system stabilization period, during which no data is collected. After stabilization, start a 100-hour stability test. During the test, product gas samples are collected every hour using an Agilent 7890B gas chromatograph (equipped with a flame ionization detector). Three sets of data are collected every 5 hours, and the average value is taken. After the 100-hour test, an additional five sets of data are collected for final verification to ensure data reliability. The system temperature is monitored in real time during the test to ensure that temperature fluctuations are within ±2℃.

[0072] 4) Post-experiment treatment: After the 100h stability test, the formaldehyde standard gas was turned off, and nitrogen was continued to purge the reaction tube for 30 minutes. After cooling to room temperature, the catalyst was taken out and the appearance changes of the catalyst, the temperature fluctuations during the experiment and the instrument parameters were recorded.

[0073] 5) The formaldehyde conversion rate (i.e., X) is calculated based on the change in formaldehyde concentration before and after the reaction, using the following formula: X = [(C0 - C t ) / C0]×100%; In the formula: C0 is the initial concentration (ppm) of formaldehyde in the reaction gas, determined by calibration with formaldehyde standard gas; C t The measured concentration (ppm) of formaldehyde in the product gas after the reaction is the average value of multiple measurements by gas chromatograph. The formaldehyde conversion result is retained to two significant figures. The conversion rate at different time points and the final conversion rate are recorded during the 100-hour test to reflect the catalytic oxidation stability of the catalyst for formaldehyde within 100 hours under normal temperature (25℃±2℃) and normal pressure conditions.

[0074] (3) Indoor environment (temperature 25±5℃, relative humidity 40%~60%) 100h stability test 1) Catalyst pretreatment: Take 0.1g of catalyst sample and place it in the middle of a quartz reaction tube. Use nitrogen (purity 99.99%) as the carrier gas and set the flow rate to 50mL / min. Proceed to 120℃ and hold for 2h to remove adsorbed water and impurities on the catalyst surface. Then, allow it to cool naturally to the room temperature (25±5℃) and hold for 30min to allow the catalyst to adapt to the room environment conditions.

[0075] 2) Reaction system setup: A fixed-bed reactor was used for catalytic performance testing. The reaction gas was prepared by mixing formaldehyde standard gas (concentration 1000ppm), oxygen (purity 99.99%), and nitrogen in a volume ratio of 1:10:89. The total flow rate was controlled at 100mL / min to ensure a gas hourly space velocity (GHSV) of 60000mL·g. -1 ·h -1 The reaction tube is connected to form a closed-loop system; the reaction device is placed in a normal indoor environment with an ambient temperature of 25±5℃ and a relative humidity of 40%~60%, without additional temperature and humidity control, only real-time monitoring of environmental parameters.

[0076] 3) Reaction process control: The reaction system pressure was maintained at atmospheric pressure, and the temperature (25±5℃) and relative humidity (40%~60%) were maintained naturally with the indoor environment. Timing was started after the reaction began, and no data was collected during the first 30 minutes, which was the system stabilization period. After stabilization, a 100-hour stability test was started. During the test, product gas samples were collected every hour using an Agilent 7890B gas chromatograph (equipped with a flame ionization detector). Three sets of data were collected every 5 hours, and the average value was taken. After the 100-hour test, an additional 5 sets of data were collected for final verification to ensure data reliability. During the test, the indoor temperature and humidity were recorded every 2 hours, and the fluctuation of environmental parameters was recorded.

[0077] 4) Post-experiment treatment: After the 100-hour stability test, the formaldehyde standard gas was turned off, and nitrogen was continued to purge the reaction tube for 30 minutes. After cooling to the room temperature, the catalyst was taken out and the changes in the appearance of the catalyst, the fluctuations in indoor temperature and humidity during the experiment and the instrument parameters were recorded.

[0078] 5) The formaldehyde conversion rate (i.e., X) is calculated based on the change in formaldehyde concentration before and after the reaction, using the following formula: X = [(C0 - C t ) / C0]×100%; In the formula: C0 is the initial concentration (ppm) of formaldehyde in the reaction gas, determined by calibration with formaldehyde standard gas; C t The measured concentration (ppm) of formaldehyde in the product gas after the reaction was taken as the average value of multiple measurements by gas chromatograph. The formaldehyde conversion rate was retained to two significant figures. The conversion rate and the final conversion rate at different time points during the 100-hour test were recorded. Combined with indoor temperature and humidity fluctuation data, the catalyst's catalytic oxidation stability of formaldehyde within 100 hours under normal indoor conditions (25±5℃, relative humidity 40%~60%) was reflected.

[0079] Table 2 Stability Test Results

[0080] From the data in Table 2, we know that: The catalyst prepared in Example 1 exhibits excellent stability and can operate stably for extended periods under high humidity, ambient temperature, and indoor environments. The specific principles are as follows: Firstly, the MOF-based support contains high-strength MnO coordination bonds, forming a one-dimensional continuous rigid backbone. This results in a dense and robust MOF-based support framework that is resistant to hydrolysis and collapse in aqueous environments. Furthermore, the high-strength Mn-O coordination bonds construct a one-dimensional continuous rigid backbone with high chemical bond energy, making it resistant not only to hydrolysis but also to oxidation. Secondly, the tunable flexible channels exhibit a breathing effect that allows for adaptive contraction in aqueous environments, forming a self-protective structure and reducing the damage to internal coordination bonds by water molecules. Additionally, the tunable flexible channels of the MOF-based support can flexibly encapsulate and confine the encapsulated noble metal nanoparticles, as well as through multiple strong interactions, thereby inhibiting their migration, aggregation, and detachment. Thirdly, the presence of hydrophobic benzene ring structures in the MOF-based support framework reduces the catalyst's hydrophilicity, further enhancing its hydrothermal stability.

[0081] The above description is only a preferred embodiment of the present invention and does not limit the scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A method for preparing an encapsulated noble metal MOF-based catalyst, characterized in that, include: Step S1: Prepare a noble metal-ligand chelate solution; A noble metal salt is added to a first organic solvent, and hydrochloric acid is added dropwise to aid dissolution. After stirring and dissolving, the first organic ligand is added, and stirring is continued to dissolve, thus preparing a noble metal-ligand chelate solution. The molar ratio of the noble metal salt, the hydrochloric acid, the first organic solvent, and the first organic ligand is 1:(100~200):(500~800):1; Step S2: Prepare encapsulated noble metal MOF-based catalyst; Manganese salt, a second organic ligand, a second organic solvent, and water are added sequentially to the noble metal-ligand chelate solution. After stirring and dissolving, the pH value is adjusted to 3-5 to obtain a precursor suspension. The molar ratio of the manganese salt, the second organic ligand, the second organic solvent, and the water is (1~1.5):1:(20~50):(120~150). The precursor suspension was subjected to a crystallization reaction and then cooled to room temperature. Subsequently, it was filtered, and the solid obtained by filtration was subjected to a first washing treatment until the washing liquid was colorless and transparent. The solid obtained by filtration was subjected to a first vacuum drying treatment to obtain precursor powder. The precursor powder was subjected to reduction treatment, second washing treatment, and second vacuum drying treatment in sequence to obtain the encapsulated noble metal MOF-based catalyst.

2. The preparation method of the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The precious metal salt includes platinum salt or palladium salt; the platinum salt includes platinum chloride; the palladium salt includes palladium chloride; the manganese salt includes manganese nitrate or manganese acetate.

3. The preparation method of the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The volume ratio of the second organic solvent to the first organic solvent is 2~8:1; the first organic solvent includes N,N-dimethylformamide; the second organic solvent includes N,N-dimethylformamide.

4. The preparation method of the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The molar ratio of the second organic ligand to the first organic ligand is 2~20:1; the first organic ligand includes terephthalic acid; the second organic ligand includes terephthalic acid.

5. The method for preparing the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The crystallization reaction is carried out at a temperature of 120~150℃ for a time of 24~48h.

6. The method for preparing the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The reduction atmosphere used in the reduction process includes hydrogen and an inert carrier gas, and the volume ratio of hydrogen to the inert carrier gas is 1:(2~6); the reduction temperature used in the reduction process is 200~300℃, and the reduction time is 2~4h.

7. The method for preparing the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The first vacuum drying process uses a drying temperature of 60~120℃ and a drying time of 6~15h.

8. The method for preparing the encapsulated noble metal MOF-based catalyst as described in claim 1, characterized in that, The second vacuum drying process uses a drying temperature of 60~120℃ and a drying time of 6~15h.

9. A type of encapsulated noble metal MOF-based catalyst, characterized in that, The catalyst was prepared using the method described in any one of claims 1 to 8 for encapsulating noble metal MOF-based catalysts.

10. The application of the encapsulated noble metal MOF-based catalyst as described in claim 9 in the adsorption and catalytic oxidation of formaldehyde, characterized in that, The encapsulated noble metal MOF-based catalyst has a formaldehyde conversion rate of greater than or equal to 95% at room temperature.

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