A method for preparing a platinum-based lanthanum cobaltate catalyst for NO oxidation

Abstract

A method for preparing platinum-based lanthanum cobalt oxide catalysts for NO oxidation is disclosed, belonging to the fields of catalytic chemistry and environmental chemistry. PtMn bimetallic nanoparticles are supported on a lanthanum cobalt oxide support, and PtMn / LaCoO3-air + steam and PtMn / LaCoO3-nitrogen + steam catalysts are obtained after hydrothermal treatment. The preparation method is as follows: Platinum acetylacetone and manganese decacarbonyl are simultaneously reduced using an oil-phase reduction method to form PtMn bimetallic nanoparticles. The PtMn nanoparticles are then loaded onto the lanthanum cobalt oxide support using an impregnation method. The loaded catalyst is placed in a tube furnace and calcined at 650℃ for 8 hours in an air or nitrogen atmosphere containing H2O to form a catalyst. The obtained catalyst contains a richer content of active oxygen species and exhibits good catalytic activity for NO oxidation under low-temperature conditions, showing promising application prospects in the field of motor vehicle exhaust pollution control.

Description

Technical Field

[0001] This invention relates to a hydrothermal pretreatment method for a lanthanum cobalt oxide-supported PtMn bimetallic particle catalyst and its preparation method. Specifically, it involves preparing PtMn bimetallic particles using an oil-phase reduction method, loading the PtMn bimetallic particles onto a lanthanum cobalt oxide (LaCoO3) support using an impregnation method, pretreating the synthesized perovskite metal oxide-supported noble metal catalyst using hydrothermal technology, and calcining the catalyst in an air atmosphere containing 10 vol% H2O and a nitrogen atmosphere containing 10 vol% H2O to form the catalyst. The catalyst treated by this technology exhibits good low-temperature activity for the catalytic oxidation of NO and belongs to the fields of catalytic chemistry and environmental chemistry. Background Technology

[0002] With social development, environmental protection requirements are placing stricter demands on the automotive exhaust purification industry. In recent years, mobile source pollution emissions have become a major contributor to NOx emissions in large and medium-sized cities. x The main sources of pollution. How to effectively control NOx from mobile sources such as motor vehicles. x Improving emissions and mitigating complex regional air pollution is one of the most pressing environmental issues that needs to be addressed. Currently, NOx emissions from diesel vehicle exhaust... x Purification technologies mainly include in-engine purification technology and external purification technology, with external purification being the primary focus. Diesel vehicle external purification NO. x Control technologies mainly include three types: direct catalytic decomposition, nitrogen oxide storage reduction, and selective catalytic reduction. In all the mainstream catalytic reactions involving nitrogen oxide control mentioned above, the catalytic oxidation of NO is a crucial step. In ammonia selective catalytic reduction (NH3-SCR), a suitable NO to NO2 content ratio in the gas mixture is needed to accelerate NO removal. Simultaneously, NO oxidation also helps eliminate carbon deposits in diesel vehicle exhaust treatment devices. Therefore, promoting the low-temperature oxidation reaction of NO is a key aspect of NO control in diesel vehicles. x Important issues in control technology.

[0003] Noble metal Pt exhibits good catalytic oxidation activity and stability for NO. However, the performance of noble metal catalysts varies significantly depending on the support used. Studies have shown that multiple factors, including the type of support and the size of the noble metal particles, can influence the low-temperature activity of Pt-based catalysts.

[0004] Heterogeneous catalytic reactions occur on the surface of solid catalysts. Porous materials (especially ordered mesoporous and ordered macroporous materials) possess well-developed pore structures and high specific surface areas, which facilitate the diffusion, adsorption, and activation of reactant molecules, as well as the adsorption and diffusion of product molecules, thus exhibiting superior catalytic performance. Perovskite metal oxides have been widely used as catalysts and catalyst supports due to their excellent redox capabilities, oxygen storage and release capabilities, and resistance to sintering. Numerous studies have shown that perovskite materials possess excellent catalytic thermal stability because the lattice defects in perovskites facilitate the oxidation (MA) of reactant molecules. (J. Chen, et al., Chem. Rev., 2001, 101: 1981-2018). Chen et al. (J. Chen, et al., Appl. Catal. B, 2013, 134-135: 251-257) prepared lanthanide perovskites with different B-site elements using the sol-gel method and compared their applications in NO catalysis. LaCoO3 exhibited the best activity, revealing the relationship between active oxygen content and NO catalytic oxidation activity. Different pretreatment conditions can alter the electronic structure of noble metal catalysts and the activity of oxygen species on the catalyst support surface.

[0005] To the best of our knowledge, there are currently no literature or patent reports on the preparation of PtMn / LaCoO3-air + steam and PtMn / LaCoO3-nitrogen + steam catalysts by combining hydrothermal pretreatment in air or nitrogen atmospheres and their application in the field of NO catalytic oxidation. Summary of the Invention

[0006] The present invention relates to the preparation of PtMn bimetallic nanoparticles using an oil-phase reduction method, the loading of PtMn bimetallic nanoparticles onto a lanthanum cobalt oxide support using an impregnation method, and the subsequent calcination in 10 vol% H2O and air atmosphere to form a PtMn / LaCoO3-air + steam catalyst; and calcination in 10 vol% H2O and nitrogen atmosphere to form a PtMn / LaCoO3-nitrogen + steam catalyst. The Pt loading in the above catalysts is 0.5 wt%-1.0 wt%.

[0007] The preparation of PtMn nanoparticles using an oil-phase reduction method and their loading onto a lanthanum cobalt oxide support using an impregnation method mainly includes the following steps:

[0008] (1) Preparation of PtMn nanoparticles by oil phase reduction method: Pt and Mn were added in a molar ratio of 1:1; platinum acetylacetone, dibenzyl ether, oleylamine and oleic acid were weighed and stirred at room temperature for 1 h under nitrogen protection, and this was recorded as solution A; decacarbonyl dimanganese was added to oleylamine and stirred at room temperature to dissolve, and this was recorded as solution B; solution A was heated to 170℃ in nitrogen atmosphere and held for 10 min, at which time solution B was quickly injected into solution A, heated to 265℃ in nitrogen atmosphere and held for 1 h, cooled to room temperature in nitrogen atmosphere, and separated by centrifugation with ethanol and cyclohexane to obtain uniform PtMn bimetallic nanocrystals, and the prepared nanoparticles were dispersed in cyclohexane for storage;

[0009] (2) Calculate the amount of solution containing PtMn bimetallic nanocrystals required according to a certain loading amount, add a certain amount of lanthanum cobalt oxide support to the cyclohexane solution containing bimetallic nanocrystals; stir and impregnate for 8 hours, and centrifuge to obtain the loaded catalyst.

[0010] (3) The obtained loaded catalyst was subjected to hydrothermal treatment to obtain PtMn / LaCoO3-air + steam catalyst and PtMn / LaCoO3-nitrogen + steam catalyst, respectively. The specific steps are as follows:

[0011] The obtained loaded catalyst was loaded into a ceramic boat and placed in a tube furnace for calcination. The temperature was increased from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 hours. Air containing 10 vol% H2O was introduced throughout the calcination process. After cooling, 1 wt% PtMn / LaCoO3-air + steam catalyst was obtained.

[0012] Alternatively, the temperature can be increased from room temperature to 650℃ at a rate of 5℃ / min and maintained at that temperature for 8 hours. Nitrogen gas containing 10 vol% H2O is introduced throughout the calcination process, and the temperature is lowered to obtain a 1 wt% PtMn / LaCoO3-nitrogen + steam catalyst.

[0013] The catalyst obtained in this invention, when applied to the catalytic oxidation of NO, particularly for the oxidation of NO in diesel vehicle exhaust, exhibits excellent low-temperature catalytic activity. Under reaction conditions of 0.5 vol% NO + 10 vol% O2 + 89.5 vol% N2 and a space velocity of 100,000 mL / (gh), the conversion rate of NO oxidation by the PtMn / LaCoO3-air + steam catalyst at 250°C is 55%, and the conversion rate of NO oxidation by the PtMn / LaCoO3-nitrogen + steam catalyst at 250°C is 70%.

[0014] This invention features controllable morphology of nanocatalysts and a simple preparation process.

[0015] The PtMn / LaCoO3-air + steam catalyst and PtMn / LaCoO3-nitrogen + steam catalyst obtained by the present invention after appropriate water vapor treatment of the loaded catalyst both have the characteristics of high content of surface active oxygen species and good low-temperature catalytic activity, and have good application prospects in the field of catalytic oxidation.

[0016] Using a D8 ADVANCE X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and a Thermo Fisher 42i NO-NO2-NO x The crystal structure of the catalyst and the ratio of adsorbed oxygen to lattice oxygen in the surface active oxygen species were determined by instruments such as analyzers. ads / O latt The results showed that all samples prepared by the method of the present invention had good crystallinity. The adsorbed oxygen content in the active oxygen species on the catalyst surface increased significantly after hydrothermal treatment. The low-temperature catalytic activity of the hydrothermally treated catalyst for NO oxidation was significantly improved compared with that of the air-calcined catalyst under different atmospheres. Attached Figure Description

[0017] Figure 1 The XRD patterns of the prepared PtMn / LaCoO3, PtMn / LaCoO3-air + steam and PtMn / LaCoO3-nitrogen + steam catalysts are shown.

[0018] Figure 2 O1s XPS spectra of the prepared PtMn / LaCoO3, PtMn / LaCoO3-air + steam and PtMn / LaCoO3-nitrogen + steam catalysts;

[0019] Figure 3 The activity curves of the prepared PtMn / LaCoO3, PtMn / LaCoO3-air + steam, and PtMn / LaCoO3-nitrogen + steam for the catalytic oxidation of NO are shown. Detailed Implementation

[0020] To further illustrate the present invention, the following detailed description is provided with reference to embodiments, but the invention is not limited to the following embodiments.

[0021] Example 1

[0022] The platinum and manganese were added in a 1:1 molar ratio. Platinum acetylacetonate, dibenzyl ether, oleylamine, and oleic acid were weighed and stirred at room temperature for 1 hour under nitrogen protection; this solution is denoted as solution A. Decacarbonyl dimanganese was added to oleylamine and dissolved by stirring at room temperature; this solution is denoted as solution B. Solution A was heated to 170°C under a nitrogen atmosphere and held for 10 minutes. Solution B was then rapidly injected into solution A, and the temperature was raised to 265°C under a nitrogen atmosphere and held for 1 hour. The temperature was then lowered to room temperature under a nitrogen atmosphere, and the mixture was centrifuged with ethanol and cyclohexane to obtain uniformly sized PtMn bimetallic nanocrystals. The prepared nanoparticles were dispersed in cyclohexane for storage.

[0023] 30 mmol of La(NO3)3·6H2O and Co(NO3)3 were dissolved in a mixture of 3 mL of ethylene glycol and 5 mL of anhydrous methanol. The mixture was stirred at room temperature until fully dissolved. A certain amount of anhydrous methanol was added to bring the total metal concentration to 2 mol / L, and the mixture was stirred at room temperature for another 1 h. 4 g of polymethyl methacrylate hard template was weighed and added to the above solution for about 4 h. After that, the sample was filtered using a Buchner funnel to remove the remaining solution and dried at room temperature for 48 h. The dried sample was then placed in a tube furnace and heated under a nitrogen atmosphere (50 mL / L). The temperature was increased from room temperature to 300℃ at a rate of 1℃ / min and held at that temperature for 3h. Then the temperature was reduced to room temperature, and the temperature was increased to 650℃ at a rate of 1℃ / min in air atmosphere (50mL / min) and held at that temperature for 4h to obtain lanthanum cobalt oxide support. The amount of PtMn bimetallic solution required was calculated according to the loading of 1wt%, and a certain amount of lanthanum cobalt oxide support was added to a measured amount of cyclohexane solution containing bimetallic nanocrystals. The mixture was stirred and impregnated for 8h, and centrifuged to obtain the supported catalyst.

[0024] The obtained supported catalyst was loaded into a ceramic boat and placed in a tube furnace. Air containing 10 vol% H2O was introduced for calcination. The temperature was increased from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 hours. After cooling, a 1 wt% PtMn / LaCoO3-air + steam catalyst was obtained.

[0025] Under reaction conditions with a gas composition of 0.5 vol% NO, 10 vol% O2, 89.5 vol% N2 and a space velocity of 100,000 mL / (gh), the catalyst achieved a NO oxidation conversion rate of 55% at 250 °C.

[0026] Example 2

[0027] The platinum and manganese were added in a 1:1 molar ratio. Platinum acetylacetonate, dibenzyl ether, oleylamine, and oleic acid were weighed and stirred at room temperature for 1 hour under nitrogen protection; this solution is denoted as solution A. Decacarbonyl dimanganese was added to oleylamine and dissolved by stirring at room temperature; this solution is denoted as solution B. Solution A was heated to 170°C under a nitrogen atmosphere and held for 10 minutes. Solution B was then rapidly injected into solution A, and the temperature was raised to 265°C under a nitrogen atmosphere and held for 1 hour. The temperature was then lowered to room temperature under a nitrogen atmosphere, and the mixture was centrifuged with ethanol and cyclohexane to obtain uniformly sized PtMn bimetallic nanocrystals. The prepared nanoparticles were dispersed in cyclohexane for storage.

[0028] 30 mmol of La(NO3)3·6H2O and Co(NO3)3 were dissolved in a mixture of 3 mL of ethylene glycol and 5 mL of anhydrous methanol. The mixture was stirred at room temperature until fully dissolved. A certain amount of anhydrous methanol was added to bring the total metal concentration to 2 mol / L, and stirring was continued at room temperature for 1 h. A certain amount of polymethyl methacrylate hard template was weighed and added to the above solution for about 4 h. After that, the sample was filtered using a Buchner funnel to remove the remaining solution and dried at room temperature for 48 h. The dried sample was then placed in a tube furnace and heated in a nitrogen atmosphere (50 mL / L). The temperature was increased from room temperature to 300℃ at a rate of 1℃ / min and held at that temperature for 3h. Then the temperature was reduced to room temperature, and the temperature was increased to 650℃ at a rate of 1℃ / min in air atmosphere (50mL / min) and held at that temperature for 4h to obtain lanthanum cobalt oxide support. The amount of PtMn bimetallic solution required was calculated according to the loading of 1wt%, and a certain amount of lanthanum cobalt oxide support was added to a measured amount of cyclohexane solution containing bimetallic nanocrystals. The mixture was stirred and impregnated for 8h, and centrifuged to obtain the supported catalyst.

[0029] The obtained supported catalyst was loaded into a ceramic boat and placed in a tube furnace. Nitrogen gas containing 10 vol% H2O was introduced for calcination. The temperature was increased from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 hours. After cooling, a 1 wt% PtMn / LaCoO3-nitrogen + steam catalyst was obtained.

[0030] Under reaction conditions with a gas composition of 0.5 vol% NO, 10 vol% O2, 89.5 vol% N2 and a space velocity of 100,000 mL / (gh), the catalyst achieved a NO oxidation conversion rate of 70% at 250 °C.

Claims

1. A method for preparing a lanthanum platinum-based cobalt oxide catalyst, characterized in that, Includes the following steps: (1) Preparation of PtMn nanoparticles by oil phase reduction method: Pt and Mn were added in a molar ratio of 1:1; platinum acetylacetone, dibenzyl ether, oleylamine and oleic acid were weighed and stirred at room temperature for 1 h under nitrogen protection, and this was recorded as solution A; decacarbonyl dimanganese was added to oleylamine and stirred at room temperature to dissolve, and this was recorded as solution B; solution A was heated to 170℃ in nitrogen atmosphere and held for 10 min, at which time solution B was quickly injected into solution A, heated to 265℃ in nitrogen atmosphere and held for 1 h, cooled to room temperature in nitrogen atmosphere, and separated by centrifugation with ethanol and cyclohexane to obtain uniform PtMn bimetallic nanocrystals; the prepared nanoparticles were dispersed in organic solvents such as cyclohexane for storage; (2) Calculate the amount of solution containing PtMn bimetallic nanocrystals required according to a certain loading amount, add a certain amount of lanthanum cobalt oxide support to a cyclohexane solution containing bimetallic nanocrystals; stir and impregnate, and centrifuge to obtain the loaded catalyst; (3) The obtained loaded catalyst was subjected to hydrothermal treatment to obtain PtMn / LaCoO3-air + steam catalyst and PtMn / LaCoO3-nitrogen + steam catalyst, respectively; the specific steps are as follows: The obtained loaded catalyst was loaded into a ceramic boat and placed in a tube furnace for calcination. The temperature was increased from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 h. Air containing 10 vol% H2O was introduced throughout the calcination process. After cooling, 1 wt% PtMn / LaCoO3-air + steam catalyst was obtained. Alternatively, the temperature can be increased from room temperature to 650℃ at a rate of 5℃ / min and maintained at that temperature for 8 h. Nitrogen gas containing 10 vol% H2O is introduced throughout the calcination process, and the temperature is lowered to obtain a 1 wt% PtMn / LaCoO3-nitrogen + steam catalyst.

2. The catalyst prepared according to the method of claim 1, characterized in that, The sample surface is rich in adsorbed reactive oxygen species.

3. The application of the catalyst prepared according to the method of claim 1, characterized in that, It is used in the catalytic oxidation of NO.

4. The application according to claim 3, characterized in that, Used for NO oxidation in diesel vehicle exhaust.

5. The application according to claim 3, characterized in that, The conversion rate of NO oxidation by PtMn / LaCoO3-air + steam catalyst at 250℃ is 55%, and the conversion rate of NO oxidation by PtMn / LaCoO3-nitrogen + steam catalyst at 250℃ is 70%.

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