Nano-island structured ruthenium-based vocs catalyst and preparation method thereof

Abstract

This invention relates to the field of catalyst technology, and in particular to a ruthenium-based VOCs catalyst with a nano-island structure and its preparation method. The preparation method includes the following steps: Step 1, dissolving a cerium source and a precipitant in a solvent and mixing them thoroughly, then adding hydrogen peroxide and a modifier for aging; washing the aged product and dispersing it fully in water to obtain an aqueous dispersion; Step 2, adding a Ru source solution to the aqueous dispersion and stirring, followed by aging to obtain a mixed solution; adding the mixed solution to a Ti source solution and stirring, filtering, and drying and calcining the resulting solid to obtain the ruthenium-based VOCs catalyst with a nano-island structure. This invention successfully constructs a stable "single-atom nano-island" active structure, simultaneously improving the catalyst's activity and stability. This catalyst exhibits excellent durability, providing a reliable catalyst design scheme for the efficient purification of industrial VOCs.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a ruthenium-based VOCs catalyst with a nano-island structure and its preparation method. Background Technology

[0002] Volatile organic compounds (VOCs) are common and complex organic pollutants found in both indoor and outdoor air. Low-carbon alkanes (such as propane and methane) are typical VOC components emitted from fossil fuel combustion and industrial processes. They are not only key precursors to PM2.5 and ozone, but also structurally stable with high CH bond energies, making them difficult to catalyze and oxidize efficiently, thus posing a significant challenge to current VOCs control efforts.

[0003] Currently, VOCs treatment technologies can be divided into source control and end-of-pipe treatment. End-of-pipe treatment technologies are crucial in practical applications. Catalytic oxidation technology, which can completely convert VOCs into CO2 and H2O at relatively low temperatures under the action of a catalyst, is considered one of the most promising end-of-pipe treatment technologies. The core competitiveness of this technology lies in developing high-performance catalysts that can efficiently activate oxygen and deeply oxidize VOCs under mild conditions. Currently, the most widely used are noble metal (Pt, Pd, Ru, etc.) supported catalysts. However, noble metal nanoparticles in traditional catalysts are prone to sintering and detachment under harsh reaction conditions, leading to decreased activity; at the same time, high loading of noble metals results in high costs, further limiting their large-scale application. Summary of the Invention

[0004] Based on the above, this invention provides a ruthenium-based VOCs catalyst (Ru / CeO2@TiO2) with a "single-atom nanoisland" (SANI) structure and its preparation method. This invention selectively loads atomic-level Ru species onto CeO2 nanoislands, effectively inhibiting the migration and aggregation of active components, enhancing molecular oxygen activation, improving the catalytic oxidation performance of low-carbon alkanes (represented by propane), and strengthening the catalyst's stability.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is a method for preparing a ruthenium-based VOCs catalyst with a nano-island structure, comprising the following steps:

[0007] Step 1: Dissolve the cerium source and precipitant in a solvent and mix well. Add hydrogen peroxide and a modifier and age the mixture. Wash the aged product and then fully disperse it in water to obtain an aqueous dispersion.

[0008] Step 2: Add the Ru source solution to the aqueous dispersion and stir, then age to obtain a mixed solution; add the mixed solution to the Ti source solution and stir, filter, and dry and calcine the resulting solid to obtain a nano-island structured ruthenium-based VOCs catalyst.

[0009] The aqueous dispersion of the present invention is a CeO2 nanoparticle aqueous dispersion, wherein the particle size of the CeO2 nanoparticle is 3~4 nm.

[0010] In a preferred embodiment of the present invention, in step 1, the cerium source is Ce(NO3)3·6H2O; the precipitant is ammonia; the solvent is methanol; and the modifier is citric acid.

[0011] In a preferred embodiment of the present invention, in step 1, the ratio of the amount of cerium source to precipitant, solvent, hydrogen peroxide, modifier and water is 3-10g∶2-6mL∶20-100mL∶0.5-2mL∶0.3-1g∶5-80mL.

[0012] In this invention, if the proportion of precipitant is greater than that described above or the proportion of modifier is less than that described above, the prepared cerium nanoparticles may become larger, thereby reducing the catalytic oxidation and stability effects.

[0013] In step 1, the mixing method is stirring, and the stirring time is 1~10 minutes. This invention does not impose a special limitation on the stirring speed, and adopts the stirring speed commonly used by those skilled in the art.

[0014] In a preferred embodiment of the present invention, in step 1, the aging conditions are set as follows: standing at room temperature for 0.5 to 2 hours.

[0015] In step 1, the aged product is washed with deionized water.

[0016] In a preferred embodiment of the present invention, in step 2, the Ru source solution has a concentration of 6.5 × 10⁻⁶. -4 The solution contained 1.3 × 10⁻⁶ g / mL Ru(NO)(NO₃)₃ in water; the Ti source solution had a concentration of 1.3 × 10⁻⁶ g / mL. -2 A TiO2 solution with a concentration of g / mL, using water as the solvent.

[0017] In a preferred embodiment of the present invention, in step 2, the volume ratio of Ru source solution to aqueous dispersion and Ti source solution is 10-30:20-40:40-60.

[0018] In a preferred embodiment of the present invention, in step 2, the stirring time before and after aging is 1 to 6 hours independently; the aging conditions are set as follows: standing at room temperature for 0.2 to 1 hour.

[0019] In a preferred embodiment of the present invention, in step 2, the drying conditions are set as follows: drying at 60~120℃ for 6~12h; the calcination conditions are set as follows: heating to 400~500℃ at a heating rate of 1~5℃ / min and holding for 2~4h.

[0020] The second technical solution of the present invention is a ruthenium-based VOCs catalyst with a nano-island structure prepared by the above-mentioned preparation method.

[0021] This invention employs a two-step sequential impregnation method to prepare a Ru / CeO2@TiO2 catalyst with a "single-atom nanoisland" (SANI) structure (i.e., a ruthenium-based VOCs catalyst with a nanoisland structure).

[0022] The third technical solution of this invention is the application of the above-mentioned nano-island structure ruthenium-based VOCs catalyst in the catalytic oxidation of low-carbon alkanes.

[0023] In some embodiments of the present invention, the low-carbon alkane is methane, ethane, or propane.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention successfully constructed a stable "single-atom nanoisland" active structure, simultaneously improving the activity and stability of the catalyst. Through a unique preparation method, this invention disperses and stably anchors Ru at the atomic level onto the surface of CeO2 nanoparticles. Utilizing the strong metal-support interaction between the two, the migration and aggregation of single atoms under high-temperature reaction conditions are effectively suppressed, overcoming the bottleneck problem of poor stability in traditional single-atom catalysts.

[0026] 2. This invention establishes a highly efficient Ru4d–O2p–Ce4f orbital coupling mechanism, significantly improving the activation efficiency of molecular oxygen. Experimental characterization and theoretical calculations jointly confirm that this nanoisland structure induces a strong hybridization effect among the Ru, O, and Ce atomic orbitals. This unique electronic structure enhances the electron-donating capacity of the active sites, greatly promoting the adsorption, dissociation, and activation kinetics of oxygen molecules, which is the essential reason for its highly efficient catalysis.

[0027] 3. The catalyst of this invention exhibits excellent low-temperature activity and versatility in the catalytic oxidation of low-carbon alkanes such as propane. This catalyst not only demonstrates excellent low-temperature catalytic activity for propane (apparent activation energy as low as 58.53 kJ / mol), but also exhibits superior oxidation performance for other recalcitrant low-carbon alkanes such as methane and ethane, reflecting its broad application potential.

[0028] 4. This invention achieves a shift in the dominant reaction mechanism from the MvK pathway to the LH pathway, thereby improving reaction efficiency. Mechanistic studies show that the catalyst's superior oxygen activation and transport capabilities mean that the reaction no longer relies solely on the consumption of slowly generated lattice oxygen (MvK mechanism), but instead shifts to the LH mechanism, where more reactive surface-adsorbed oxygen directly participates in the reaction. This significantly increases the reaction rate and avoids the accumulation of intermediate products.

[0029] 5. The catalyst of this invention possesses both excellent long-term stability and industrial application potential. Under near-real-world operating conditions, after multiple cycles and long-term continuous testing, the catalyst retains over 95% of its catalytic activity, demonstrating excellent durability and providing a reliable catalyst design solution for the efficient purification of industrial VOCs. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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 these drawings without creative effort.

[0031] Figure 1 The XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1 are shown below.

[0032] Figure 2 TEM images of the catalysts prepared in Example 1 and Comparative Example 1; where a) to c) are the catalysts prepared in Example 1, and d) to f) are the catalysts prepared in Comparative Example 1;

[0033] Figure 3 The catalytic oxidation activity curves of the catalysts prepared in Example 1 and Comparative Example 1 for propane are shown.

[0034] Figure 4 The reaction kinetics fitting and apparent activation energy of the catalysts prepared in Example 1 and Comparative Example 1;

[0035] Figure 5 The catalytic oxidation activities of the catalysts prepared in Example 1 and Comparative Example 1 on propane (a) and on methane (b) and ethane (c) at different mass hourly space velocities are shown.

[0036] Figure 6 The stability test of the catalyst prepared in Example 1 after five catalytic cycles (a) and at T 90 and T 50 Long-term stability test at temperature for 24 hours (b). Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0043] The raw material information involved in the embodiments of the present invention is shown in Table 1:

[0044] Table 1 Raw Material Information

[0045]

[0046] The instrument information involved in this invention is shown in Table 2:

[0047] Table 2 Instrument Information

[0048]

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] A method for preparing a ruthenium-based VOCs catalyst (Ru / CeO2@TiO2) with a "single-atom nanoisland" (SANI) structure, comprising the following steps:

[0052] (1) Using Ce(NO3)3·6H2O as the cerium source, ammonia as the precipitant, and citric acid as the modifier and sensitizer, a precipitation method was adopted for synthesis. Specifically, 5g of Ce(NO3)3·6H2O and 4mL of ammonia were dissolved in 20mL of methanol, stirred for 5 minutes, and then 1mL of hydrogen peroxide and 0.6g of citric acid were added to the solution, followed by aging for 0.5 hours. After aging, the product was washed and redispersed in 50mL of water to obtain an aqueous dispersion of CeO2 nanoparticles with a particle size of approximately 3nm.

[0053] (2) Add 20 mL of Ru(NO)(NO3)3 solution (concentration 6.5 × 10⁻⁶) -4 (g / mL, water as solvent) was added dropwise to 30 mL of the CeO2 nanoparticle aqueous dispersion obtained in step 1, and the mixture was stirred continuously for 6 hours, followed by standing and aging for 1 hour. Then, the aged mixture was added dropwise to 50 mL of TiO2 solution (concentration 1.3 × 10⁻⁶ g / mL, water as solvent), and the mixture was stirred continuously for 6 hours, followed by standing and aging for 1 hour. -2 The solution was prepared in water (g / mL) and stirred continuously for 6 hours. Finally, the resulting solution was filtered, the solid product was collected, and dried at 80°C for 6 hours. The dried sample was then placed in a muffle furnace and heated at 5°C / min. -1 The temperature was programmed to rise to 400℃ and calcined at this temperature for 3 hours to obtain the target catalyst Ru / CeO2@TiO2.

[0054] Comparative Example 1

[0055] The Ru / CeO2 / TiO2 catalyst was prepared by a one-step mixed impregnation method, and the steps are as follows:

[0056] (1) Same as step (1) in Example 1.

[0057] (2) Add 20 mL of Ru(NO)(NO3)3 solution (concentration 6.5 × 10⁻⁶) -4 (g / mL, solvent: water) was directly added dropwise to a 30 mL aqueous dispersion of CeO2 nanoparticles and a 50 mL TiO2 solution (concentration 1.3 × 10⁻⁶ g / mL, with water as the solvent). -2 In a mixture of g / mL (water as solvent), the mixture was stirred for 6 hours, then filtered. The solid product was collected and dried at 80°C for 6 hours. The dried sample was then placed in a muffle furnace and heated at 5°C / min.-1 The temperature was programmed to rise to 400℃ and calcined at this temperature for 3 hours to obtain the Ru / CeO2 / TiO2 catalyst.

[0058] Comparative Example 2

[0059] Add 20 mL of Ru(NO)(NO3)3 solution (concentration 6.5 × 10⁻⁶) -4 (g / mL, solvent: water) was directly added dropwise to 50 mL of TiO2 solution (concentration 1.3 × 10 g / mL). -2 The sample was stirred in a solution of g / mL (water as solvent) for 6 hours, then filtered. The solid product was collected and dried at 80°C for 6 hours. The dried sample was then placed in a muffle furnace and heated at 5°C / min. -1 The temperature was programmed to rise to 400°C and calcined at this temperature for 3 hours to obtain the Ru / TiO2 catalyst.

[0060] Performance testing:

[0061] Reactor loading: In each test, accurately weigh 100 mg of 40-60 mesh catalyst and load it into the isothermal zone of the quartz tube reactor.

[0062] Reactant gas composition: The total flow rate of the feed gas is fixed at 50 mL·min. -1 It consists of 2500 ppm C3H8 (represented by propane) and 20 vol% O2, and uses high-purity N2 as the balance gas.

[0063] Reaction space velocity: Under these conditions, the mass hourly space velocity (WHSV) of the reaction is 3,000 mL·gcat. -1 ·h -1 To examine its potential for practical applications, some tests were also conducted at higher space velocities (such as 60,000 and 120,000 mL·gcat). -1 ·h -1 (This will be carried out under)

[0064] Product analysis: The concentration of the reactor outlet gas was analyzed and recorded in real time using an online gas chromatograph (GC-2014C) equipped with a flame ionization detector (FID).

[0065] Activity testing procedure: Catalyst activity is evaluated through a programmed temperature rise reaction. The propane conversion rate as a function of temperature is shown in the figure below. Figure 3 As shown. The conversion rate is calculated from the propane concentrations at the inlet and outlet. The low-temperature activity of the catalyst is determined by the temperatures at which the conversion reaches 50% and 90% (i.e., T). 50 , T 90 To measure and compare.

[0066] Stability testing: The stability of the catalyst is determined by its T...90 Continuous reaction testing for up to 24 hours was conducted near the temperature. Figure 6 (b) and multiple temperature cycling tests ( Figure 6 Use a)) to evaluate.

[0067] The catalysts prepared in Example 1 and Comparative Example 1 were characterized by XRD and HRTEM:

[0068] Figure 1 The XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1 are shown below. Figure 1 It can be seen that both Ru / CeO2@TiO2 and Ru / CeO2 / TiO2 exhibit typical TiO2 anatase phase and cubic fluorite CeO2 diffraction peaks. No metallic Ru or crystalline RuO was detected in any of the CeO2-containing samples. X The diffraction peaks are likely due to the low Ru loading and its highly dispersed state. This indicates that the catalyst is mainly composed of TiO2 and CeO2, with Ru having no obvious peak shape in XRD due to its extremely low loading.

[0069] Figure 2 TEM images of the catalysts prepared in Example 1 and Comparative Example 1; Figure 2 In sections a) to c), the presence of TiO2, CeO2, and Ru in the catalyst can be clearly observed. The TiO2 particles are approximately 20 nm long, the CeO2 particles are approximately 3 nm in diameter, and the Ru exists as single atoms on the CeO2 particles. Figure 2 Figures a) to b) show that the CeO2 nanoparticles in the Ru / CeO2@TiO2 catalyst prepared in Example 1 have a uniform particle size of approximately 3 nm. Figure 2 In the HAADF-STEM image (c), atomically dispersed Ru species can be identified, and their signals highly overlap with those of the CeO2 region. However, no obvious Ru atom distribution was detected on the TiO2 support, indicating that Ru species preferentially anchor to CeO2 nanoparticles, successfully constructing a "nano-island" type composite structure. In the Ru / CeO2 / TiO2 catalyst prepared in Comparative Example 1, Figure 2 Figures d) to f) show that Ru atoms are mainly distributed on the TiO2 surface and exhibit an aggregated state, forming clusters.

[0070] Figure 3 The catalytic oxidation activity curves of the catalysts prepared for Example 1 and Comparative Example 1 for propane show that Example 1 has extremely high catalytic oxidation activity for propane and is superior to Comparative Example 1. That is, Ru / CeO2@TiO2 has the best low-temperature catalytic activity.

[0071] Figure 4 The reaction kinetics and apparent activation energy of the catalysts prepared in Example 1 and Comparative Example 1 are fitted by [the relevant data]. Figure 4 It can be seen that the catalyst prepared in Example 1 has a low Ea value (58.53 kJ / mol), indicating that it has a very high activation energy, which is more conducive to the reaction.

[0072] Figure 5 The catalytic oxidation activities of the catalysts prepared for Example 1 and Comparative Example 1 on propane at different mass hourly space velocities, and the catalytic oxidation activities of the catalysts prepared for Example 1 and Comparative Example 1 on methane and ethane, show that Ru / CeO2@TiO2 maintains high activity even at high hourly space velocities and has extremely strong universality. Figure 6 Stability tests of catalysts prepared in Example 1 and Comparative Example 1 after five catalytic cycles and at T 90 and T 50 24-hour long-term stability test at temperature, by Figure 6 It can be seen that the catalyst prepared in Example 1 has a near-T... 90 and T 50 The 24-hour long-term stability test at the temperature showed that its activity retention rate exceeded 95%, indicating that it has excellent durability.

[0073] Table 3 Comparison of catalytic performance of catalysts prepared in Example 1 and Comparative Example 1

[0074]

[0075] As can be seen from the comparison between Example 1 and Comparative Example 1 in Table 3, Ru / CeO2@TiO2 exhibits the best low-temperature catalytic activity in this invention, with its T 50 and T 90All were significantly lower than the Ru / CeO2 / TiO2 catalyst prepared in Comparative Example 1. The activity order of the catalysts was: Ru / CeO2@TiO2 > Ru / CeO2 / TiO2. This activity trend fully demonstrates the unique advantages of the nano-island structure. The superior performance of Ru / CeO2@TiO2 does not stem from a single component, but rather from its successfully constructed "single-atom nano-island" structure and the Ru4d–O2p–Ce4f orbital coupling effect induced by it. This unique electronic structure greatly promotes the activation of molecular oxygen, thereby significantly improving the catalytic oxidation efficiency of propane. In contrast, the Ru / CeO2 / TiO2 prepared by the physical mixing method has relatively low activity due to the lack of such a precise interfacial structure and strong electronic interactions; while the catalyst with a single support has the worst performance due to the easy aggregation of active sites or insufficient oxygen activation ability. In summary, the Ru / CeO2@TiO2 catalyst with a "single-atom nanoisland" (SANI) structure provided by this invention not only exhibits excellent low-temperature activity and stability far exceeding that of conventional single-atom catalysts in the catalytic oxidation of propane, but also demonstrates good versatility for other recalcitrant low-carbon alkanes such as methane and ethane, indicating its enormous application potential in the practical industrial VOCs purification field.

[0076] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a ruthenium-based VOCs catalyst with a nano-island structure, characterized in that, Includes the following steps: Step 1: Dissolve the cerium source and precipitant in a solvent and mix well. Add hydrogen peroxide and a modifier and age the mixture. Wash the aged product and then fully disperse it in water to obtain an aqueous dispersion. Step 2: Add Ru source solution to aqueous dispersion and stir, then age to obtain mixed solution; add mixed solution to Ti source solution and stir, filter, and dry and calcine the obtained solid to obtain nano-island structured ruthenium-based VOCs catalyst; In step 1, the cerium source is Ce(NO3)3·6H2O; the precipitant is ammonia; the solvent is methanol; and the modifier is citric acid. In step 1, the ratio of cerium source to precipitant, solvent, hydrogen peroxide, modifier and water is 3-10g: 2-6mL: 20-100mL: 0.5-2mL: 0.3-1g: 5-80mL; In step 1, the aging conditions are set as follows: stand at room temperature for 0.5~2 hours; In step 2, the Ru source solution was a Ru(NO)(NO3)3solution with a concentration of 6.5 x 10 -4 g / mL, and the solvent was water; the Ti source solution was a TiO2solution with a concentration of 1.3 x 10 -2 g / mL, and the solvent was water. In step 2, the volume ratio of Ru source solution to aqueous dispersion and Ti source solution is 10-30:20-40:40-60; In step 2, the aging conditions are set as follows: stand at room temperature for 0.2~1 hours; In step 2, the calcination conditions are set as follows: the temperature is increased to 400-500℃ at a heating rate of 1-5℃ / min and held for 2-4 hours.

2. The preparation method according to claim 1, characterized in that, In step 2, the stirring time before and after aging is 1 to 6 hours independently.

3. The preparation method according to claim 1, characterized in that, In step 2, the drying conditions are set as follows: 60~120℃ for 6~12 hours.

4. A ruthenium-based VOCs catalyst with a nano-island structure prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the ruthenium-based VOCs catalyst with nano-island structure as described in claim 4 in the catalytic oxidation of low-carbon alkanes.

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