A lanthanum aluminate supported palladium monatomic catalyst for catalyzing oxidation of VOCs and a preparation method thereof

Abstract

The application discloses a lanthanum aluminate supported palladium monatomic catalyst for catalyzing VOCs oxidation and a preparation method thereof, and belongs to the field of catalytic chemistry and environmental chemistry. The preparation method is as follows: a palladium salt, La2O3 and gamma-Al2O3 are fully mixed by using a high-energy ball milling method, and then the mixture is treated by high-temperature calcination to obtain a Pd1 / LaAlO3-Al2O3 monatomic catalyst. The catalyst shows good catalytic activity for toluene oxidation and has excellent thermal stability. The catalyst has a good application prospect in the field of atmospheric pollution control.

Description

Technical Field

[0001] This invention relates to a highly efficient lanthanum aluminate-supported palladium single-atom catalyst for the oxidation of VOCs and its preparation method. The catalyst exhibits excellent catalytic activity for toluene oxidation. It belongs to the fields of catalytic chemistry and environmental chemistry. Background Technology

[0002] Volatile organic compounds (VOCs) have attracted widespread attention as a prevalent class of pollutants. VOCs mainly originate from industries such as organic chemicals, petrochemicals, packaging and printing, and surface coating. VOCs have a significant impact on human health, being important precursors to secondary pollutants such as respirable particulate matter (PM2.5) and ozone (O3), thus contributing to atmospheric environmental problems such as haze and photochemical smog. Most VOCs are toxic, directly harming human health and even causing death. Among various methods for treating VOCs, catalytic oxidation is considered one of the most effective elimination methods due to its low energy consumption, high efficiency, and low secondary pollution. The key to this method is the development of catalysts with good low-temperature oxidation activity, high-temperature stability, and low cost. Common catalysts include noble metal catalysts and non-noble metal catalysts. Pd-based catalysts are widely used and possess excellent hydrothermal stability. By rationally designing experiments to prepare low-loading, highly dispersed Pd-based single-atom catalysts for efficient catalytic oxidation of VOCs, the wider industrial application of noble metal catalysts can be realized. γ-Al₂O₃ is widely used as a catalyst support due to its high specific surface area, uniform pore structure, good thermal stability, and suitable surface acidity / basicity. Its general formula is ABO₃. 3±δ Perovskite-type metal oxides possess more stable crystal structures and superior thermal stability compared to single transition metal oxides. Their unique self-regenerating properties help suppress the aggregation and growth of the active phase on the catalyst surface, maintaining good thermal stability. Incorporating noble metals into perovskite crystals has a significant advantage in suppressing the thermal sintering of noble metals. In the present and future, with rapid societal development, environmental pollution issues are receiving increasing attention. Single-atom catalyst synthesis strategies typically rely on wet chemical methods, which generate waste liquids through the extensive use of solvents, causing secondary pollution. Wet chemical routes, such as initial wet impregnation and strong electrostatic adsorption methods, are common in laboratory-scale catalyst synthesis. These methods are time-consuming and complex, hindering scalability. Furthermore, single-atom catalysts prepared using these methods generally exhibit poor thermal stability. Therefore, the large-scale synthesis of single-atom catalysts with excellent thermal stability remains a challenge. Traditional methods for preparing ABO... 3±δTraditional methods for preparing perovskite metal oxide catalysts, such as sol-gel and co-precipitation methods, require solvents or surfactants, which can lead to secondary pollution. This method, however, involves simple ball milling followed by mechanochemical activation and calcination to stabilize the single-atom catalyst. This process generates no waste liquid and causes no secondary pollution, making it a highly efficient, convenient, versatile, and environmentally friendly solvent-free method. In this invention, noble metal precursors and perovskite metal oxide precursors (La₂O₃ and γ-Al₂O₃) are subjected to high-energy ball milling followed by calcination to successfully prepare a Pd₁ / LaAlO₃-Al₂O₃ catalyst. This catalyst can efficiently catalyze the elimination of toluene. After aging at 800℃ for 10 hours, its catalytic performance remains stable for up to 50 hours, exhibiting excellent thermal stability. Furthermore, compared to palladium nanoparticle catalysts supported on lanthanum aluminate prepared by traditional impregnation methods, the single-atom catalyst with a lower noble metal loading exhibits higher catalytic activity. Moreover, the catalyst maintains high catalytic activity after a 50-hour thermal stability test.

[0003] To our knowledge, no literature or patents have reported on the direct preparation of palladium single-atom catalysts on LaAlO3 (a composite material of LaAlO3 and Al2O3) using ball milling combined with high-temperature calcination, nor on their performance in toluene oxidation. This invention discloses a controllable preparation method for Pd1 / LaAlO3-Al2O3 single-atom catalysts. Studies have shown that the Pd1 / LaAlO3-Al2O3 single-atom catalyst exhibits excellent catalytic activity and thermal stability for toluene oxidation, while simultaneously reducing the amount of precious metals required. Summary of the Invention

[0004] The purpose of this invention is to prepare Pd1 / LaAlO3-Al2O3 single-atom catalysts using a green, solvent-free ball milling method for the efficient and stable catalytic oxidation of toluene, reducing the amount of precious metals required and meeting the needs of large-scale industrial applications of precious metal catalysts.

[0005] A method for preparing a highly efficient Pd1 / LaAlO3-Al2O3 supported palladium single-atom catalyst for VOCs oxidation, the present invention specifically includes the following steps:

[0006] First, palladium nitrate dihydrate powder was weighed and dissolved in deionized water to prepare a palladium nitrate aqueous solution. La₂O₃ powder was added and stirred for 5 hours. The mixture was then rotary evaporated and dried in an oven, preferably at 80°C for 2 hours. The resulting dried product was ball-milled with γ-Al₂O₃ for 5 hours, and then transferred to a muffle furnace for calcination in air. The temperature was increased to 850°C at a rate of 5°C / min and held for 5 hours to obtain a Pd₁ / LaAlO₃-Al₂O₃ single-atom catalyst. The catalyst obtained in this invention is preferably used for the efficient catalysis of VOCs, particularly toluene.

[0007] The molar ratio of lanthanum to aluminum is 20-200:210. The loading of Pd is 0.5wt%-1.0wt%.

[0008] Catalyst performance evaluation:

[0009] Toluene was selected as the probe molecule for evaluating the performance of the catalyst. The gas mixture consisted of 1000 ppm toluene + 20 vol% O2 + N2 (equilibrium gas) with a space velocity of 20,000 mL / (g·h). The reaction temperatures required to achieve 50% toluene conversion and 90% conversion on the Pd1 / LaAlO3-Al2O3 single-atom catalyst were determined (T0). 50％ and T 90％ The temperatures were 191℃ and 207℃, respectively. The Pd1 / LaAlO3-Al2O3 single-atom catalyst exhibited excellent catalytic activity. After aging at 800℃ for 10 hours, the catalyst still maintained 85% of its high-efficiency catalytic activity after a long-term stability test of 50 hours.

[0010] The microstructure of the Pd1 / LaAlO3-Al2O3 samples was explored using high-resolution HADDF-STEM and energy-dispersive X-ray spectroscopy (EDX). It was clearly observed that palladium atoms were well dispersed as single atoms on the LaAlO3 surface. In-situ CO–DRIFTS patterns of Pd1 / LaAlO3-Al2O3 also confirmed the presence of single Pd atoms.

[0011] The catalyst preparation process of this invention is simple and can be used to prepare high-efficiency noble metal single-atom catalysts for the oxidation of VOCs on a large scale. It exhibits good low-temperature catalytic activity for toluene, has a long catalyst lifetime, and has good application prospects in the field of air pollution control. Attached Figure Description

[0012] Figure 1 The image shows the XRD pattern of the prepared catalyst.

[0013] Figure 2 The HAADF-STEM image and EDX elemental spectrum of the Pd1 / LaAlO3-Al2O3 single-atom catalyst are shown.

[0014] (a), (b), (c), and (d) are HAADF-STEM images of the Pd1 / LaAlO3-Al2O3 single-atom catalyst, and (e) is a mapping image of Al, O, La, and Pd.

[0015] Figure 3 This is an in-situ CO–DRIFTS diagram of the Pd1 / LaAlO3-Al2O3 single-atom catalyst.

[0016] Figure 4The figures show the activity curves of the prepared Pd1 / LaAlO3-Al2O3 single-atom catalyst and the comparative Pd / Al2O3 catalyst for the catalytic oxidation of toluene. The reaction conditions were: 1000 ppm toluene + 20 vol% O2 + N2 (equilibrium gas), and a space velocity of 20,000 mL / (g·h).

[0017] Figure 5 The image shows the thermal stability test results of the Pd1 / LaAlO3-Al2O3 single-atom catalyst after aging for the catalytic oxidation of toluene. Detailed Implementation

[0018] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments, and the various catalyst materials obtained by the present invention are described with reference to the accompanying drawings.

[0019] Example 1

[0020] (1) Preparation of Pd1 / LaAlO3-Al2O3 catalyst:

[0021] The palladium:lanthanum:aluminum molar ratio was 1:20:208. 0.10 g of palladium nitrate dihydrate (Pd(NO3)2·2H2O) powder was dissolved in 20 mL of deionized water in a beaker to prepare a palladium nitrate aqueous solution. Then, 1.22 g of lanthanum oxide powder was added and stirred for 5 h. The mixture was then rotary evaporated and dried in an oven at 120 °C for 30 min. The dried product was ball-milled with 3.98 g of γ-Al2O3 for 5 h, and then transferred to a muffle furnace for calcination in air atmosphere. The temperature was increased to 850 °C at a rate of 5 °C / min and held for 5 h to obtain a Pd1 / LaAlO3-Al2O3 single-atom catalyst. The Pd loading was approximately 0.75 wt%.

[0022] (2)Pd NPs Preparation of LaAlO3 catalyst:

[0023] Weigh 5.037 g of lanthanum nitrate hexahydrate and 4.364 g of aluminum nitrate nonahydrate and dissolve them in 100 mL of deionized water in a beaker. While stirring at 40 °C, add ammonia solution dropwise to adjust the pH to 9-10. After stirring for 2 h, heat the suspension to 70 °C and age for 20 h. Dry the precipitate in an oven, grind it into powder, and calcine it in a muffle furnace at 850 °C for 6 h to obtain lanthanum aluminate composite metal oxide powder. Weigh 0.0175 g of palladium nitrate dihydrate powder and dissolve it in 5 mL of deionized water in a round-bottom flask. Add 4.2 mL of 2 g / L PVA and stir for 0.5 h. Add 0.01244 g of sodium borohydride to prepare a 2 g / L sodium borohydride solution in an ice-water bath and stir for 0.5 h. After adding 1g of lanthanum aluminate powder and stirring for 5 hours, the sample was filtered five times with ethanol and deionized water, respectively. After filtration, the sample was dried in an oven and then calcined in a muffle furnace at 400℃ for 6 hours to obtain Pd. NPs / LaAlO3, with Pd NPs / LaAlO3 represents the catalyst.

[0024] (3) The Pd1 / LaAlO3-Al2O3 single-atom catalyst was used for the catalytic oxidation of toluene. 50 mg of catalyst (particle size 40–60 mesh) was weighed and loaded into a quartz fixed-bed reactor. A toluene reaction gas with a concentration of 1000 ppm was introduced into the fixed-bed reactor. The reaction gas composition was 1000 ppm toluene, 20 vol% O2, and N2 (equilibrium gas). The total gas flow rate was 16.7 mL / min, and the space velocity (SV) was 20,000 mL / (gh). The Te of the toluene conversion rate catalyzed by the Pd1 / LaAlO3-Al2O3 single-atom catalyst was measured. 50％ and T 90％ The temperatures were 191℃ and 207℃, respectively.

[0025] (4) After aging the Pd1 / LaAlO3-Al2O3 single-atom catalyst in a muffle furnace at 800℃ for 10h, the activity thermal stability test was carried out at 200℃. During the activity test of up to 50h, the performance was not significantly weakened compared with the fresh sample and the catalyst was stable.

Claims

1. A method for preparing a highly efficient Pd1 / LaAlO3-Al2O3 supported palladium single-atom catalyst for VOCs oxidation, characterized in that, Specifically, the following steps are included: First, palladium nitrate dihydrate powder was weighed and dissolved in deionized water to prepare an aqueous solution of palladium nitrate. La2O3 powder was added and stirred for 5 h. The mixture was then rotary evaporated and dried in an oven at 80 °C for 2 h. The resulting dried product was ball-milled with γ-Al2O3 for 5 h and then transferred to a muffle furnace for calcination in air atmosphere. The temperature was raised to 850 °C at a heating rate of 5 °C / min and held for 5 h to obtain a Pd1 / LaAlO3-Al2O3 single-atom catalyst.

2. The method according to claim 1, characterized in that, The molar ratio of lanthanum to aluminum is 20-200:

210.

3. The method according to claim 1, characterized in that, The Pd loading is 0.5wt%-1.0wt%.

4. The Pd1 / LaAlO3-Al2O3 supported palladium single-atom catalyst prepared according to the method of any one of claims 1-3.

5. The application of the Pd1 / LaAlO3-Al2O3 supported palladium single-atom catalyst prepared according to any one of claims 1-3, characterized in that, Used for the catalytic oxidation of VOCs.

6. The application according to claim 5, characterized in that, Used for the catalytic oxidation of toluene.

7. The application according to claim 6, characterized in that, A catalyst with a particle size of 40–60 mesh was weighed and loaded into a quartz fixed-bed reactor. A toluene reactant gas with a concentration of 1000 ppm was introduced into the reactor. The reactant gas composition consisted of 1000 ppm toluene, 20 vol% O2, and N2 as a balance gas. The total gas flow rate was 16.7 mL / min, and the space velocity (SV) was 20,000 mL / g∙h. The Te of the toluene conversion catalyzed by the Pd1 / LaAlO3 single-atom catalyst was measured. 50% and T 90% The temperatures were 191℃ and 207℃, respectively.

8. According to the application described in claim 6, after aging the catalyst with a particle size of 40–60 mesh in a muffle furnace at 800°C for 10 h, it is loaded into a quartz fixed-bed reactor. Toluene reaction gas with a concentration of 1000 ppm is introduced into the fixed-bed reactor. The reaction gas composition is 1000 ppm toluene, 20 vol% O2, and N2 as a balance gas. The total gas flow rate is 16.7 mL / min, and the space velocity is 20,000 mL / g∙h. The active thermal stability test is carried out at 200°C. After a long-term stability test of 50 h, the catalyst still retains 85% of the high-efficiency catalytic activity.

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