Preparation method of platinum-based lanthanum cobaltate catalyst for NO oxidation

Abstract

The invention discloses a preparation method of a platinum-based lanthanum cobaltate catalyst for NO oxidation, and belongs to the field of catalytic chemistry and environmental chemistry. The preparation method comprises the following steps: loading PtMn bimetallic nanoparticles on a lanthanum cobaltate carrier, and treating by a hydrothermal technology to obtain a PtMn / LaCoO3-air and steam catalyst and a PtMn / LaCoO3-nitrogen and steam catalyst. The preparation method comprises the following steps: simultaneously reducing platinum acetylacetonate and dimanganese decacarbonyl by adopting an oil phase reduction method to form PtMn bimetallic nanoparticles, and loading the PtMn nanoparticles on the lanthanum cobaltate carrier by adopting an impregnation method. The loaded catalyst is placed in a tubular furnace and roasted for 8 h at the temperature of 650 DEG C in the atmosphere of H2O-containing air or nitrogen, the catalyst is formed, and the obtained catalyst contains richer active oxygen species, shows good catalytic activity on NO oxidation under the low-temperature condition and has good application prospects in the field of motor vehicle tail gas pollution control.

Description

Technical Field

[0001] The present invention relates to a lanthanum cobalt oxide-loaded PtMn bimetallic particle catalyst pretreated by hydrothermal technology and a preparation method thereof, and specifically relates to a method for preparing PtMn bimetallic particles by adopting an oil phase reduction method, loading the PtMn bimetallic particles on a lanthanum cobalt oxide (LaCoO3) carrier by adopting an impregnation method, pretreating the synthesized perovskite metal oxide-loaded noble metal catalyst by adopting a hydrothermal technology, and calcining in an air atmosphere containing 10 vol% H2O and in a nitrogen atmosphere containing 10 vol% H2O to form a catalyst. The catalyst treated by this technology has good low-temperature activity for NO catalytic oxidation, and belongs to the fields of catalytic chemistry and environmental chemistry. Background Art

[0002] With the development of society, environmental protection requirements have put forward more stringent requirements on the automobile exhaust purification industry. In recent years, mobile source pollution emissions have become the main source of NO in the air of large and medium-sized cities. x The main source of pollution. How to effectively control NO from mobile sources x Emissions and mitigation of complex regional air pollution are one of the environmental issues that need to be addressed urgently. x Purification technologies mainly include in-engine purification technology and out-engine purification technology, among which out-engine purification is the main one. x The control technologies mainly include direct catalytic decomposition, nitrogen oxide storage reduction and selective catalytic reduction. In the above mainstream catalytic reactions involving nitrogen oxide control, the catalytic oxidation process of NO is an important link. In the ammonia selective catalytic reduction technology (NH3-SCR), a suitable ratio of NO to NO2 content is required in the mixed gas to accelerate the removal of NO. At the same time, the oxidation of NO is also beneficial to the elimination of carbon deposits in the diesel vehicle exhaust treatment device. Therefore, how to promote the low-temperature oxidation reaction of NO is a key issue in diesel vehicle NO x Important issues in control technology.

[0003] The precious metal Pt has good NO catalytic oxidation activity and stability. The effects of precious metal catalysts on different carriers vary significantly. Studies have found that various factors such as carrier type and precious metal particle size can affect 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) have a developed pore structure and a high specific surface area, which is conducive to the diffusion, adsorption and activation of reactant molecules and the adsorption and diffusion of product molecules, and thus have better catalytic performance. Perovskite-type metal oxides have been widely used in catalysts and catalyst carriers due to their good redox ability, oxygen storage and release capacity, and anti-sintering ability. A large number of research results show that perovskite-type materials have excellent catalytic thermal stability. This is because the lattice defects in perovskites are conducive to the oxidation of reactant molecules (MA 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 by sol-gel method and used them for NO catalytic reaction for comparison. LaCoO3 showed the best activity and revealed the relationship between active oxygen content and NO catalytic oxidation activity. Different pretreatment conditions can change the electronic structure of noble metal catalysts and the activity of oxygen species on the surface of catalyst carriers.

[0005] To the best of our knowledge, there is no literature or patent reporting on the method of preparing PtMn / LaCoO3-air+steam and PtMn / LaCoO3-nitrogen+steam catalysts by combining hydrothermal pretreatment in air or nitrogen atmosphere and using them in the field of NO catalytic oxidation research. Summary of the invention

[0006] The present invention is to prepare PtMn bimetallic nanoparticles by oil phase reduction method, load PtMn bimetallic nanoparticles on lanthanum cobalt oxide carrier by impregnation method, and calcine in 10 vol% H2O, air atmosphere to form PtMn / LaCoO3-air+steam catalyst; calcine in 10 vol% H2O, nitrogen atmosphere to form PtMn / LaCoO3-nitrogen+steam catalyst. The Pt loading in the above catalyst is 0.5wt%-1.0wt%.

[0007] The PtMn nanoparticles are prepared by an oil phase reduction method and loaded on a lanthanum cobalt oxide carrier by an impregnation method, which mainly includes the following steps:

[0008] (1) Preparation of PtMn nanoparticles by oil phase reduction method: Add materials according to the molar ratio of metal Pt and Mn of 1:1; weigh platinum acetylacetonate, dibenzyl ether, oleylamine and oleic acid, stir at room temperature for 1 hour under nitrogen protection, and record it as solution A; add dimanganese decacarbonyl to oleylamine, stir and dissolve at room temperature, and record it as solution B; heat solution A to 170°C in a nitrogen atmosphere and keep it for 10 minutes, then quickly inject solution B into solution A, heat to 265°C in a nitrogen atmosphere and keep it for 1 hour, cool to room temperature in a nitrogen atmosphere, and centrifuge with ethanol and cyclohexane to obtain PtMn bimetallic nanocrystals of uniform size, and disperse the prepared nanoparticles in cyclohexane for storage;

[0009] (2) The required amount of solution containing PtMn bimetallic nanocrystals is calculated according to a certain loading amount, and a certain amount of lanthanum cobaltate carrier is added to the cyclohexane solution containing bimetallic nanocrystals; the solution is stirred and immersed for 8 hours, and the loaded catalyst is obtained by centrifugation.

[0010] (3) The obtained supported catalyst is 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 loaded catalyst was placed in a porcelain boat and calcined in a tube furnace at a rate of 5°C / min from room temperature to 650°C and maintained at this temperature for 8 hours. During the calcination process, air containing 10 vol% H2O was introduced and the temperature was lowered to obtain a 1wt% PtMn / LaCoO3-air+steam catalyst.

[0012] Alternatively, the temperature was raised from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 hours. Nitrogen containing 10 vol% H2O was introduced throughout the calcination process, and the temperature was lowered to obtain a 1wt% PtMn / LaCoO3-nitrogen+steam catalyst.

[0013] The catalyst obtained by the present invention is applied to NO catalytic oxidation, especially to NO oxidation of diesel vehicle exhaust gas, and shows excellent low-temperature catalytic activity. Under the reaction conditions of reaction gas composition of 0.5 vol% NO+10 vol% O2+89.5 vol% N2 and space velocity of 100000 mL / (gh), the conversion rate of NO oxidation by PtMn / LaCoO3-air+steam catalyst at 250°C is 55%, and the conversion rate of NO oxidation by PtMn / LaCoO3-nitrogen+steam catalyst at 250°C is 70%.

[0014] The invention has the characteristics of controllable nano catalyst morphology, simple preparation process and the like.

[0015] The PtMn / LaCoO3-air+steam catalyst and PtMn / LaCoO3-nitrogen+steam catalyst obtained by appropriately treating the loaded catalyst with water vapor in the present invention 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] The X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and the Thermo Fisher 42i NO-NO2-NO x The crystal structure of the catalyst, the ratio of adsorbed oxygen to lattice oxygen in the surface active oxygen species (O ads / O latt ) and catalytic oxidation activity for NO. The results show that each sample prepared by the method of the present invention has good crystallinity, the adsorbed oxygen content in the active oxygen species on the catalyst surface after hydrothermal treatment is significantly increased, and the low-temperature catalytic activity of NO oxidation of the catalyst after hydrothermal treatment in different atmospheres is significantly improved compared with the catalyst calcined in air. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD spectra of the prepared PtMn / LaCoO3, PtMn / LaCoO3-air+steam and PtMn / LaCoO3-nitrogen+steam catalysts;

[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 catalytic oxidation of NO. DETAILED DESCRIPTION

[0020] In order to further illustrate the present invention, the following embodiments are described in detail, but the present invention is not limited to the following embodiments.

[0021] Example 1

[0022] The molar ratio of metal platinum to manganese was 1:1. Platinum acetylacetonate, dibenzyl ether, oleylamine and oleic acid were weighed and stirred at room temperature for 1 hour under nitrogen protection, which was recorded as solution A; dimanganese decacarbonyl was added to oleylamine and stirred and dissolved at room temperature, which was recorded as solution B; solution A was heated to 170°C in a nitrogen atmosphere and kept for 10 minutes, at which time solution B was quickly injected into solution A, heated to 265°C in a nitrogen atmosphere and kept for 1 hour, cooled to room temperature in a nitrogen atmosphere, and centrifuged with ethanol and cyclohexane to obtain PtMn bimetallic nanocrystals of uniform size, and the prepared nanoparticles were dispersed in cyclohexane for storage.

[0023] 30mmol La(NO3)3·6H2O and Co(NO3)3 were dissolved in a mixture of 3mL ethylene glycol and 5mL anhydrous methanol, stirred at room temperature until fully dissolved, a certain amount of anhydrous methanol was added to make the total metal concentration 2mol / L, and stirring was continued at room temperature for 1h; 4g of polymethyl methacrylate hard template was weighed and added to the above solution and immersed for about 4h, then filtered with a Buchner funnel to remove the remaining solution, and dried at room temperature for 48h; the dried sample was placed in a tube furnace and heated in a nitrogen atmosphere (50mL / min) at a rate of 1°C / min from room temperature to 300°C and keep at this temperature for 3h, then cool to room temperature, switch to air atmosphere (50mL / min) and heat to 650°C at a rate of 1°C / min and keep at this temperature for 4h to obtain a lanthanum cobaltate carrier; calculate the required amount of PtMn bimetallic solution according to 1wt% loading, add a certain amount of lanthanum cobaltate carrier to the measured cyclohexane solution containing bimetallic nanocrystals; stir and immerse for 8h, and centrifuge to obtain a supported catalyst.

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

[0025] Under the reaction conditions of reaction gas composition of 0.5 vol% NO, 10 vol% O2, 89.5 vol% N2 and space velocity of 100000 mL / (gh), the conversion rate of NO oxidation by the catalyst at 250°C was 55%.

[0026] Example 2

[0027] The molar ratio of metal platinum to manganese was 1:1. Platinum acetylacetonate, dibenzyl ether, oleylamine and oleic acid were weighed and stirred at room temperature for 1 hour under nitrogen protection, which was recorded as solution A; dimanganese decacarbonyl was added to oleylamine and stirred and dissolved at room temperature, which was recorded as solution B; solution A was heated to 170°C in a nitrogen atmosphere and kept for 10 minutes, at which time solution B was quickly injected into solution A, heated to 265°C in a nitrogen atmosphere and kept for 1 hour, cooled to room temperature in a nitrogen atmosphere, and centrifuged with ethanol and cyclohexane to obtain PtMn bimetallic nanocrystals of uniform size, and the prepared nanoparticles were dispersed in cyclohexane for storage.

[0028] 30mmol La(NO3)3·6H2O and Co(NO3)3 were dissolved in a mixture of 3mL ethylene glycol and 5mL anhydrous methanol, stirred at room temperature until fully dissolved, a certain amount of anhydrous methanol was added to make the total metal concentration 2mol / L, and stirring was continued at room temperature for 1h; a certain amount of polymethyl methacrylate hard template was weighed and added to the above solution and immersed for about 4h, then filtered with a Buchner funnel to remove the remaining solution, and dried at room temperature for 48h; the dried sample was placed in a tube furnace and heated in a nitrogen atmosphere (50mL / min) at a rate of 1°C / min from room temperature to 300°C and keep at this temperature for 3h, then cool to room temperature, switch to air atmosphere (50mL / min) and heat to 650°C at a rate of 1°C / min and keep at this temperature for 4h to obtain a lanthanum cobaltate carrier; calculate the required amount of PtMn bimetallic solution according to 1wt% loading, add a certain amount of lanthanum cobaltate carrier to the measured cyclohexane solution containing bimetallic nanocrystals; stir and immerse for 8h, and centrifuge to obtain a supported catalyst.

[0029] The obtained supported catalyst was loaded into a porcelain boat and placed in a tubular furnace. Nitrogen containing 10 vol% H2O was introduced for calcination. The temperature was raised from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 hours. The temperature was then cooled to obtain a 1wt% PtMn / LaCoO3-nitrogen+steam catalyst.

[0030] Under the reaction conditions of reaction gas composition of 0.5 vol% NO, 10 vol% O2, 89.5 vol% N2 and space velocity of 100000 mL / (gh), the conversion rate of NO oxidation by the catalyst at 250°C was 70%.

Claims

1. A method for preparing a platinum-based lanthanum cobaltate catalyst, characterized in that: The following steps are involved: (1) Preparation of PtMn nanoparticles by oil phase reduction method: Add materials according to the molar ratio of metal Pt and Mn of 1:1; weigh platinum acetylacetonate, dibenzyl ether, oleylamine and oleic acid, stir at room temperature for 1 hour under nitrogen protection, and record it as solution A; add dimanganese decacarbonyl to oleylamine, stir and dissolve at room temperature, and record it as solution B; heat solution A to 170°C in a nitrogen atmosphere and keep it for 10 minutes, then quickly inject solution B into solution A, heat to 265°C in a nitrogen atmosphere and keep it for 1 hour, cool to room temperature in a nitrogen atmosphere, and centrifuge with ethanol and cyclohexane to obtain PtMn bimetallic nanocrystals of uniform size, and disperse the prepared nanoparticles in an organic solvent such as cyclohexane for storage; (2) calculating the amount of solution containing PtMn bimetallic nanocrystals required according to a certain loading amount, adding a certain amount of lanthanum cobaltate carrier to the cyclohexane solution containing bimetallic nanocrystals; stirring and impregnating, and centrifuging to obtain a loaded catalyst; (3) The obtained supported catalyst is 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 loaded catalyst was placed in a porcelain boat and calcined in a tube furnace at a rate of 5°C / min from room temperature to 650°C and maintained at this temperature for 8 hours. During the calcination process, air containing 10 vol% H2O was introduced and the temperature was lowered to obtain a 1wt% PtMn / LaCoO3-air+steam catalyst. Alternatively, the temperature was raised from room temperature to 650°C at a rate of 5°C / min and maintained at this temperature for 8 hours. Nitrogen containing 10 vol% H2O was introduced throughout the calcination process, and the temperature was lowered to obtain a 1wt% PtMn / LaCoO3-nitrogen+steam catalyst.

2. The method according to claim 1, characterized in that The active oxygen adsorbed on the sample surface is rich.

3. The catalyst prepared according to the method of claim 1 or 2.

4. Use of the catalyst prepared by the method according to claim 1 or 2, in catalytic oxidation of NO, especially in oxidation of NO in diesel exhaust.

5. The use according to claim 4, wherein 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%.

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