Preparation method of catalyst with low noble metal content and application of catalyst in argon oxygen removal

Abstract

The invention discloses a preparation method of a catalyst with low noble metal content and application of the catalyst in argon oxygen removal. The catalyst can still meet the precision requirement of argon oxygen removal when the content of precious metal is lower than 0.1 wt%, a steady-state high-temperature environment is not needed in the preparation process, the catalyst is not modified by adding auxiliaries, and the precious metal component has the advantage of being easy to recycle and regenerate. The catalyst provided by the invention is a noble metal supported catalyst, noble metal is platinum group metal and a noble metal precursor supported on the surface of the composite oxide, and the activity of the catalyst is remarkably improved after being treated by one or a sequential combination process of Joule heat or plasma irradiation and other unsteady-state high-temperature method steps, so that the content of low noble metal in the catalyst is reduced; the method has high industrial application value.

Description

Technical Field

[0001] The invention relates to the field of argon deoxygenation catalysts, and particularly relates to a preparation method of a catalyst with low noble metal content and application of the catalyst in argon deoxygenation. Background Art

[0002] Argon is a common rare gas. Because of its stable chemical and physical properties, argon usually acts as a protective gas in industry. Argon is needed as a protective gas in aircraft manufacturing, shipbuilding, atomic industry, etc. In recent years, with the rapid development of the solar photovoltaic power generation industry, high-purity argon (purity> 99.999%) has become an indispensable purification and protective gas in the preparation of monocrystalline silicon and polycrystalline silicon, resulting in a shortage of high-purity argon. However, the content of argon in the air is extremely low (only 0.93%). It is usually separated and extracted as a by-product from the air separation oxygen production process. The production cost is high, and the production capacity is limited. The purification and recovery technology is expensive and energy-intensive. Therefore, it is very necessary to develop low-cost and low-energy argon purification methods for the development of the photovoltaic industry.

[0003] Commonly used deoxygenation methods are divided into physical and chemical methods. Physical methods use the porous properties of materials to physically adsorb oxygen to reduce the oxygen content, but the preparation process of adsorption materials is relatively complicated, resulting in high production costs, high energy consumption during production, and low deoxygenation accuracy, which is not conducive to large-scale industrial production. Chemical methods use catalytic reactions or chemical adsorption to achieve the purpose. Catalytic methods have the characteristics of easy separation, long life and reusability, low energy consumption and cost. Catalytic methods are often used for large-scale deoxygenation in industry.

[0004] Catalysts with precious metals as active components have significant advantages in deoxygenation. Their function is to catalyze the reaction of CO with oxygen (O2) to produce harmless carbon dioxide (CO2). Precious metal catalysts have the advantages of maximized atomic utilization, unique electronic structure and adjustable coordination environment. At the same time, they have high catalytic activity, high selectivity and good anti-poisoning ability, and can effectively remove CO under low temperature conditions. Among them, single-atom dispersed platinum group catalysts have shown extremely excellent deoxygenation performance in various studies. Platinum group metals, mainly considered to be rhodium, ruthenium, platinum, palladium and other elements, are used as catalysts in automotive catalytic converters. Platinum group metal catalysts have been considered to be one of the most important functional materials in the fields of catalysis, fuel cells, energy storage, air pollution control, etc. However, during the reaction, platinum group metals tend to sinter into large agglomerates, which is the main factor leading to the deactivation of catalytic performance. For this reason, researchers have adopted various strategies to reduce the risk of sintering deactivation, including reducing the loading of active metal components, adding additives, and using defect vacancies or holes in the support material to extend the life of the catalyst. However, most catalysts still have problems such as easy deactivation due to moisture, high cost, poor stability, weak anti-poisoning ability, and poor availability. In addition, due to the high cost and scarcity of precious metals, the production cost is greatly increased. From an economic point of view, the industry needs catalysts with lower metal loadings to achieve higher activity while reducing production costs.

[0005] Therefore, the development of a deoxygenation catalyst with low noble metal content, high activity and reusability is an urgent need of the current argon purification industry and an important part of promoting the development of the photovoltaic industry. The deoxygenation catalyst of the present invention is a noble metal-supported catalyst, in which the noble metal is a platinum group metal, supported on the surface of a composite oxide as a noble metal precursor, and processed by a non-steady-state high-temperature method such as a Joule heat or plasma irradiation or a sequential combination process, aiming to reduce the noble metal content of the catalyst while reducing the energy consumption of the production process by changing the preparation means and achieving the purpose of regulating the catalyst microstructure. Experimental verification shows that the activity of the catalyst prepared by this method is significantly improved and relatively stable. Summary of the invention

[0006] Aiming at the technical problems of the existing noble metal argon deoxygenation catalysts, such as the excessively high noble metal loading and the increase in production cost caused by the addition of auxiliary agents, the poor low-temperature activity and high-temperature stability, and the high-temperature environment required for the preparation process, which lead to large energy consumption in the production process and low utilization rate of active components, the present invention provides a method for preparing a catalyst with low noble metal content and its application in argon deoxygenation, wherein the noble metal is a platinum group metal, and is loaded on the surface of a composite oxide as a noble metal precursor, and is treated by a non-steady-state high-temperature method such as Joule heat or plasma irradiation or a combination of both in sequence, in order to reduce the noble metal content of the catalyst while reducing the energy consumption of the production process by changing the preparation means and achieving the purpose of regulating the microstructure of the catalyst. Experimental verification shows that the activity of the catalyst prepared by this method is significantly improved and relatively stable, and the deactivated catalyst has the characteristics of easy recycling and sustainable utilization.

[0007] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: A method for preparing a catalyst with a low noble metal content, wherein the catalyst uses a composite metal oxide as a carrier, a platinum group metal as an active center loaded on the carrier surface, the active component is at least one of Pt, Pb, Os, Ir, Ru, and Rh, and the mass ratio of the active component to the total amount of the catalyst is less than 0.1%. The preparation method adopts an impregnation method to prepare the catalyst, and then controls the surface structure by Joule heat and plasma irradiation, and specifically comprises the following steps: S1. Add water to the platinum group metal precursor and stir by ultrasonic for 3-7 minutes to obtain a uniform mixed solution, and adjust the pH to 6-8; S2. Under stirring, adding a composite metal oxide to the mixture, the mass ratio of the platinum group metal precursor to the composite metal oxide is 0.003-0.19: 2-3, and drying after impregnation; S3. The dried solid is subjected to Joule heat treatment at a temperature of 700-1200°C, a treatment time of 0.3-0.8s, and a number of cycles of 4-8 times; S4. Plasma treatment in an inert atmosphere for 5-15 minutes.

[0008] Furthermore, the platinum group metal precursor is at least one of platinum ammonium nitrate, palladium acetylacetonate, palladium acetate, chloroplatinic acid or platinum ammonium nitrate.

[0009] Furthermore, the composite metal oxide is at least one of SiO2, Al2O3, and CeO2.

[0010] Furthermore, the mass of the active component accounts for 0.02%-0.09% of the total mass of the catalyst.

[0011] Furthermore, in S2, the immersion temperature is 80-110°C, and the immersion time is 4-6 hours.

[0012] Furthermore, in S4, the atmosphere of the plasma treatment is argon, helium or nitrogen.

[0013] Furthermore, in S4, the power of the plasma treatment is 150-300 W, and the gas flow rate is 20-50 ml / min.

[0014] The catalyst with low precious metal content obtained by the above preparation method is used in the argon deoxygenation reaction, and has the advantages of high low-temperature activity, strong high-temperature stability and reduced production cost. At the same time, a preparation method of a catalyst with low precious metal content is also provided, which reduces the energy consumption of the production process by changing the preparation means and regulates the microstructure of the catalyst.

[0015] The beneficial effects of the present invention are: The preparation method of the present invention changes the traditional preparation method of direct reduction after impregnation, and instead regulates the surface structure of the catalyst under a non-steady-state high-temperature environment such as Joule heat and plasma irradiation, so that the obtained catalyst has a lower noble metal content while still having higher low-temperature activity and high-temperature stability. This not only reduces the use of noble metals, but also makes the deactivated catalyst easy to recycle and sustainably utilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of the catalyst obtained in the present invention, Figure 1 It can be seen that nanoparticles and single atoms of active components exist simultaneously in the catalyst, and a certain number of oxygen vacancies exist on the catalyst surface after plasma treatment and non-steady-state high-temperature treatment.

[0017] Figure 2 TEM spectra of the catalyst obtained in the comparative example (a) and the 0.1wt.% Pt / CeO2 obtained in Example 1 (b).

[0018] Figure 3 DRIFTS spectra of the catalyst obtained in the comparative example (a) and the 0.1wt.% Pt / CeO2 obtained in Example 1 (b).

[0019] Figure 4 A comparison of oxygen vacancies in the catalysts. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below with reference to specific embodiments, but the present invention is not limited thereto. Example 1

[0021] Preparation of 0.1wt.% Pt / CeO2 Argon Deoxygenation Catalyst (1) Add 0.008 g of chloroplatinic acid hexahydrate, a platinum metal precursor, to water and stir for 5 min to obtain a uniform mixed solution, and adjust the pH to about 7; (2) Add 3 g of composite metal oxide CeO2 to the mixed solution under stirring, immerse at 100°C for 5 hours, and then dry; (3) The dried solid was subjected to Joule heat treatment at a temperature of 800°C, a treatment time of 0.4 s, and a number of cycles of 6 times; (4) Under argon atmosphere, the power was controlled to 200 W, the argon flow rate was 30 ml / min, and the plasma treatment was performed for 10 min to obtain a 0.1 wt.% Pt / CeO2 argon deoxygenation catalyst. Example 2

[0022] Preparation of 0.2wt.% Pb / CeO2 Argon Deoxygenation Catalyst (1) Add 0.016 g of chloroplatinic acid hexahydrate, a platinum metal precursor, to water and stir for 5 min to obtain a uniform mixed solution, and adjust the pH to about 7; (2) Add 3 g of composite metal oxide CeO2 to the mixed solution under stirring, immerse at 100°C for 5 hours, and then dry; (3) The dried solid was subjected to Joule heat treatment at a temperature of 800°C, a treatment time of 0.4 s, and a number of cycles of 6 times; (4) Under argon atmosphere, the power was controlled to 200 W, the argon flow rate was 30 ml / min, and the plasma treatment was performed for 10 min to obtain a 0.2 wt.% Pt / CeO2 argon deoxygenation catalyst. Example 3

[0023] Preparation of PtPd / CeO2 Catalyst for Deoxygenation in Argon Gas (1) Add 0.008 g of chloroplatinic acid hexahydrate, a platinum metal precursor, to water and stir for 5 min to obtain a uniform mixed solution, and adjust the pH to about 7; (2) Add 3 g of composite metal oxide CeO2 to the mixed solution under stirring, immerse at 100°C for 5 hours, and then dry; (3) Take another 0.0574 g of palladium acetylacetonate and mix with 50 g of acetone, stir, and ultrasonicate for 5 min to obtain a uniform palladium acetylacetonate solution; (4) 17.3492 g of the above-mentioned palladium acetylacetonate solution was added to the solid obtained in step (2) under stirring, and the mixture was immersed at 100° C. for 5 hours, and then dried; (5) The dried solid was subjected to Joule heat treatment at a temperature of 800°C, a treatment time of 0.4 s, and a number of cycles of 6 times; (6) Under argon atmosphere, the power was controlled to 200 W, the argon flow rate was 30 ml / min, and the plasma treatment was performed for 10 min to obtain a PbPt / CeO2 argon deoxygenation catalyst. Example 4

[0024] Preparation of Pt / Al2O3 Catalyst for Deoxygenation in Argon Gas (1) Add 0.08045 g of chloroplatinic acid hexahydrate, a platinum metal precursor, to water and stir to form a uniform mixed solution, and adjust the pH to about 7; (2) Add 3 g of composite metal oxide Al2O3 to the mixed solution under stirring, immerse at 100°C for 5 hours, and then dry; (3) The dried solid was subjected to Joule heat treatment at a temperature of 800°C, a treatment time of 0.4 s, and a number of cycles of 6 times; (4) Under argon atmosphere, the power was controlled to 200 W, the argon flow rate was 30 ml / min, and the plasma treatment was performed for 10 min to obtain a Pt / Al2O3 argon deoxygenation catalyst. Comparative Example

[0025] Different from the non-steady-state high-temperature treatment in Example 1, a conventional steady-state calcination treatment is adopted, and the specific steps are as follows: (1) Add 0.008 g of chloroplatinic acid hexahydrate, a platinum metal precursor, to water and stir for 5 min to obtain a uniform mixed solution, and adjust the pH to about 7; (2) Add 3 g of composite metal oxide CeO2 to the mixed solution under stirring, immerse at 100°C for 5 hours, and then dry; (3) The dried solid was calcined at a temperature of 800° C. for 8 hours to obtain a steady-state treated catalyst.

[0026] The performance test of the catalysts obtained in the above examples and comparative examples was carried out in a fixed bed reactor, and the specific steps are as follows: 0.3 g of catalyst was filled in a reaction tube, both ends were filled with quartz sand to maintain the bed height, quartz wool was added to isolate the quartz sand and the catalyst, and a fixed bed reactor was assembled; A carbon monoxide and oxygen mixed gas is introduced into the reaction tube for reaction, and the product obtained by the reaction is connected to a gas chromatograph through a pipeline for online analysis; Reaction conditions: introduce argon, carbon monoxide and oxygen mixed gas (the volume ratio of carbon monoxide to oxygen is 1:2) at a flow rate of 30-40 ml / min, the initial temperature is 20°C, and each 20°C is a detection point until the carbon monoxide is completely oxidized to carbon dioxide.

[0027] Figure 2TEM spectra of the catalyst obtained in the comparative example and the 0.1wt.% Pt / CeO2 obtained in Example 1. The distribution state of the active components on the carrier can be more intuitively observed through TEM. Figure 2 (a) shows that only the lattice fringes of CeO2 are observed under high magnification photography, and there are no obvious Pt particles on the carrier surface, proving that in the catalyst obtained in the comparative example, the Pt particles are dispersed in the form of single atoms on the carrier surface. Figure 2 (b) shows that particles can be clearly seen on the catalyst surface under high magnification photography, proving that after treatment, the Pt on the surface of the catalyst obtained in Example 1 is reduced to larger metal platinum particles.

[0028] The adsorption and oxidation behaviors of CO on the catalyst surface can reveal the differences in the active sites on the surface and their CO adsorption capacity. Figure 3 is the DRIFTS spectrum of the catalyst. Figure 3 It can be seen that compared with the catalyst obtained in the comparative example, the catalyst obtained in Example 1 produces new metallic active sites, has a high CO adsorption capacity, and has a weaker adsorption capacity, so that it can show better catalytic activity during the reaction. The generation of new active sites solves the problem of competitive adsorption of CO and O2 on the catalyst surface, thereby significantly improving the performance of the catalyst.

[0029] The defect concentration on the catalyst surface can be detected by Raman spectroscopy. Figure 4 The oxygen vacancy concentration statistics of the above-mentioned embodiments and comparative examples are shown in Figure 2. By comparison, it can be seen that the method of the present invention can produce a certain number of holes on the catalyst surface. Among them, the surface defect concentration of Example 1 is the largest, proving that the defect concentration is an effective factor in improving the activity of the catalyst.

Claims

1. A method for preparing a catalyst with low noble metal content, characterized in that: The catalyst uses a composite metal oxide as a carrier, a platinum group metal as an active center loaded on the carrier surface, the active component is at least one of Pt, Pb, Os, Ir, Ru, and Rh, and the mass ratio of the active component to the total amount of the catalyst is less than 0.1%. The preparation method comprises the following steps: S1. Add water to the platinum group metal precursor and stir by ultrasonic for 3-7 minutes to obtain a uniform mixed solution, and adjust the pH to 6-8; S2. Under stirring, the mixed solution was added with a composite metal oxide, the mass ratio of the platinum group metal precursor to the composite metal oxide was 0.003-0.19: 2-3, and then dried after impregnation; S3. The dried solid is subjected to Joule heat treatment at a temperature of 700-1200°C, a treatment time of 0.3-0.8s, and a number of cycles of 4-8 times; S4. Plasma treatment in an inert atmosphere for 5-15 minutes.

2. The method for preparing a catalyst with low noble metal content according to claim 1, characterized in that: The platinum group metal precursor is at least one of platinum ammonium nitrate, palladium acetylacetonate, palladium acetate, chloroplatinic acid or platinum ammonium nitrate.

3. The method for preparing a catalyst with low noble metal content according to claim 1, characterized in that: The composite metal oxide is at least one of SiO2, Al2O3, and CeO2.

4. The method for preparing a catalyst with low noble metal content according to claim 1, characterized in that: The mass of active components accounts for 0.02-0.09% of the total mass of the catalyst.

5. The method for preparing a catalyst with low noble metal content according to claim 1, characterized in that: In S2, the immersion temperature is 80-110° C., and the immersion time is 4-6 hours.

6. The method for preparing a catalyst with low noble metal content according to claim 1, characterized in that: In S4, the atmosphere of the plasma treatment is argon, helium or nitrogen.

7. The method for preparing a catalyst with low noble metal content according to claim 1, characterized in that: In S4, the power of plasma treatment is 150-300W, and the gas flow rate is 20-50ml / min.

8. Use of the catalyst with low noble metal content obtained by the preparation method according to any one of claims 1 to 7 in argon deoxygenation reaction.

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