Method for preparing nano-catalyst by dielectric barrier discharge low-temperature plasma and application of nano-catalyst

Abstract

The invention discloses a method for preparing a nano-catalyst by dielectric barrier discharge low-temperature plasma and application. The preparation method comprises the following steps: (1) preparing hydroxyapatite; (2) dipping in a transition metal salt solution: placing the hydroxyapatite obtained in the step (1) in the transition metal salt solution, and drying to obtain a precursor I; (3) dipping in a noble metal salt solution: placing the precursor I obtained in the step (2) in the noble metal salt solution, and drying to obtain a precursor II; and (3) preparation of the catalyst: carrying out dielectric barrier discharge low-temperature plasma treatment on the precursor II to obtain a catalyst finished product. The particle size of the prepared catalyst is nanoscale, the obtained catalyst is small in particle size and good in dispersity, and the toluene catalytic oxidation activity is higher than that of a catalyst obtained through a traditional thermal preparation method.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method and application of preparing nano catalysts using dielectric barrier discharge low-temperature plasma. Background Art

[0002] Toluene, as a volatile pollutant, is highly destructive to the environment due to its volatility and difficulty in degradation. Toluene participates in atmospheric photochemical reactions and can produce precursors that cause haze and photochemical smog. It is also easily accumulated in organisms and has extremely strong carcinogenic, teratogenic, and mutagenic effects. Therefore, its removal is extremely important. Currently, catalytic combustion technology is the most common removal technology, which has the advantages of many treatment objects, high efficiency, and simple process. However, since coke accumulation or catalyst poisoning will form during the removal process, the focus of the development and application of catalytic combustion technology is mainly on the research and development and preparation of catalysts. Designing and manufacturing an excellent catalyst is essential for the removal of volatile pollutants.

[0003] At present, this catalyst is mainly prepared by the traditional pyrolysis method, and the precursor is calcined or reduced to obtain the catalyst. For example, Chinese patent CN110681382A discloses a MOF-cobalt-based metal oxide catalyst for catalytic oxidation of toluene, using imidazole-4,5-dicarboxylic acid and cobalt acetate tetrahydrate as raw materials, adding 2-propylene diamine solution, and obtaining pure red octahedral crystals after solvent thermal reaction, and then drying and calcining at 250°C and 350°C in air for 1 hour to obtain the catalyst. Chinese patent CN116212889A discloses a Cu-MnO 2 The catalyst is prepared by a one-step solvothermal method by reacting a certain molar amount of Cu(NO 3 ) 2 ·3H 2 O doping into KMnO 4 With (NH 4 ) 2 C 2 O 4 ·H 2 O, then ethylene glycol solvent is added to mix evenly to form a Cu-Mn precursor, and then the Cu-Mn precursor is transferred into a high-pressure reactor to react at a certain temperature, and finally calcined at a high temperature to obtain different Cu-MnO 2 Catalyst powder. The above catalyst preparation methods all adopt the method of calcining or reducing the precursor to obtain the catalyst, but the process may cause problems such as sintering and agglomeration of metal particles, and the processing time is relatively long. Summary of the invention

[0004] The purpose of the present invention is to provide a method and application of preparing nanocatalysts by dielectric barrier discharge low temperature plasma, so as to solve the problem of metal particle sintering and agglomeration in the above-mentioned method of calcining or reducing a precursor to obtain a catalyst. The present invention prepares a loaded noble metal nanocatalyst by dielectric barrier discharge low temperature plasma technology, which can obtain a nanocatalyst with good dispersion, small particle size, high low temperature catalytic activity, good catalytic stability in a short time, can be carried out at normal temperature and pressure, and is suitable for scale-up and industrial production.

[0005] To achieve the above object, the present invention provides a method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma in a first aspect, comprising the following steps: (1) Preparation of hydroxyapatite (2) Immersion in transition metal salt solution The hydroxyapatite obtained in step (1) is placed in a transition metal salt solution and dried to obtain a precursor 1; (3) Impregnation with precious metal salt solution Placing the precursor 1 obtained in step (2) in a noble metal salt solution and drying to obtain the precursor 2; (3) Preparation of catalyst The precursor 2 is subjected to dielectric barrier discharge low-temperature plasma treatment to obtain a finished catalyst product.

[0006] Preferably, in step (1), the preparation process of hydroxyapatite is: Soluble calcium salt and soluble phosphate salt are dissolved in deionized water or ethanol, stirred for reaction for 2 to 3 hours, aged for 1.5 to 3 hours, and a precipitated product is obtained; the precipitated product is washed to neutrality, dried, and then calcined at 400 to 700 °C to obtain hydroxyapatite with a lamellar stacking structure.

[0007] Preferably, in step (1), the soluble calcium salt is one or both of calcium hydroxide and calcium nitrate, and the soluble phosphate salt is one or both of diammonium hydrogen phosphate and phosphorus pentoxide.

[0008] Preferably, in step (1), the molar ratio of calcium ions in the soluble calcium salt to phosphorus ions in the soluble phosphorus salt is 1.6-1.7:1.

[0009] Preferably, in step (2), the transition metal salt solution is a cobalt nitrate solution, and the cobalt content of the precursor is 3-15%.

[0010] Preferably, in step (3), the noble metal salt solution is a silver nitrate solution, and the silver content in the second precursor is 0.5-5%.

[0011] Preferably, in step (4), the specific process of dielectric barrier discharge low temperature plasma treatment is: Precursor 2 is placed in an open quartz boat, and the quartz boat is placed between two electrodes in a dielectric barrier discharge low-temperature plasma treatment device, a working gas is introduced, and dielectric barrier discharge low-temperature plasma treatment is performed under the condition of additional input power to obtain a catalyst.

[0012] Preferably, in step (4), the input power is 80-200 W, the working gas is at least one of hydrogen, air, argon and oxygen, and the processing time is 5-30 min.

[0013] The second aspect of the present invention provides a nanocatalyst prepared by the above method.

[0014] The third aspect of the present invention provides an application of a nanocatalyst, which is an application of the nanocatalyst in synergistic catalytic removal of toluene.

[0015] Therefore, the method and application of preparing nanocatalysts by using the above-mentioned dielectric barrier discharge low-temperature plasma has the following beneficial effects: (1) The preparation process of the present invention does not require calcination. The Ag precursor on the carrier can be quickly reduced at room temperature and pressure to obtain an Ag / Co / HAP catalyst with small particle size and good dispersibility. It is a universal noble metal nanocatalyst for toluene oxidation reaction.

[0016] (2) Since low-temperature plasma itself is rich in a large number of active groups and high-energy electrons and has a strong reducing ability, the present invention can use it in conjunction with a catalyst to remove toluene. This method can be operated at room temperature and pressure, requires low energy consumption, is low in cost, and has wide applicability.

[0017] (3) The preparation method of the present invention has the characteristics of low temperature, controllability, simplicity and high efficiency. The prepared catalyst has a nanometer-scale particle size, small particle size and good dispersibility, and its catalytic activity is higher than that of the catalyst obtained by the traditional thermal preparation method.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the XRD pattern of HAP prepared in Example 1; Figure 2 is the N of HAP prepared in Example 1 2 Isothermal adsorption-desorption curves; Figure 3 XRD patterns of the catalysts prepared in Examples 2-3 and Comparative Example 1; Figure 4 N is the N of the catalysts prepared in Comparative Example 1 and Example 2. 2 Isothermal adsorption-desorption curves; Figure 5 This is a SEM image of the HAP prepared in Example 1; Figure 6 TEM image of the catalyst prepared in Example 2; Figure 7 The test results of the thermal catalytic oxidation reaction of toluene using the catalysts of Comparative Example 1 and Examples 2-3 are as follows; Figure 8 The test results of the catalyst low temperature plasma synergistic catalytic oxidation of toluene in Comparative Example 1 and Examples 2-3; Fig. 9 This is the structural diagram of the homemade single dielectric barrier discharge reactor. DETAILED DESCRIPTION

[0020] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and a specific operation process, but the present invention is not limited to this embodiment.

[0021] Example 1 A method for preparing a hydroxyapatite carrier comprises the following steps: At room temperature, 3.7045 g of Ca(OH) 2 Dissolve in 40 mL of deionized water to obtain a soluble calcium salt solution. Add 3.962 g of (NH 4 ) 2 HPO 4 Dissolve in 50 mL of deionized water to obtain a soluble phosphate solution, slowly add the soluble phosphate solution to the soluble calcium salt solution, stir vigorously, react for 3 h, age for another 2 h before filtering, and then wash the product thoroughly with deionized water until the pH value of the filtrate reaches neutral. The precipitate is dried at 100 ° C overnight, and then calcined at 600 ° C in air for 2 h to obtain hydroxyapatite with a lamellar stacking structure, labeled as HAP.

[0022] Example 2 A 3%Ag / 5%Co / HAP-H 2 The method for preparing a catalyst comprises the following steps: The hydroxyapatite prepared in Example 1 was used as the carrier, and a sequential equal volume impregnation method was adopted to first impregnate 5% Co(NO 3 ) 2 The solution was allowed to stand for 4 h and dried in an oven at 60 °C to obtain the precursor 1. Then, 3% AgNO 3 The solution was dried to obtain precursor 2.

[0023] Take 0.3 g of the second precursor sample and put it into the plasma reactor, using a mixture of hydrogen and argon as the working gas (total gas flow rate 40 ml•min -1 , the ratio of hydrogen to argon was 5:95), atmospheric pressure dielectric barrier discharge cold plasma was used for reduction, the discharge input power was adjusted to 160 W, the reduction time was 10 min, and 3%Ag / 5%Co / HAP-H was obtained. 2 Catalyst products.

[0024] Example 3 A method for preparing a 3%Ag / 5%Co / HAP-Ar catalyst comprises the following steps: The hydroxyapatite prepared in Example 1 was used as the carrier, and a sequential equal volume impregnation method was adopted to first impregnate 5% Co(NO 3 ) 2 The solution was allowed to stand for 4 h and dried in an oven at 60 °C to obtain the precursor 1. Then, 3% AgNO 3 The solution was dried to obtain precursor 2.

[0025] Take 0.3 g of the two precursor samples and put them into the plasma reactor, using pure Ar as the working gas (total gas flow rate 40 ml•min -1 ), atmospheric pressure dielectric barrier discharge cold plasma was used for reduction, the discharge input power was adjusted to 160 W, the reduction time was 10 min, and 3%Ag / 5%Co / HAP-Ar catalyst product was obtained.

[0026] Comparative Example 1 A method for preparing a 3%Ag / 5%Co / HAP catalyst comprises the following steps: The hydroxyapatite prepared in Example 1 was used as the carrier, and a two-step equal volume impregnation method was adopted. First, 5% Co(NO 3 ) 2 The solution was allowed to stand for 4 h and dried in an oven at 60 °C to obtain the precursor 1. Then, 3% AgNO 3 The solution was dried to obtain precursor 2, and then 5% H 2 / Ar was calcined at 300 ℃ for 2 h to obtain 3%Ag / 5%Co / HAP catalyst prepared by traditional impregnation method.

[0027] Comparative Example 2 A method for preparing a 3%Ag / 15%Co / HAP catalyst comprises the following steps: The hydroxyapatite prepared in Example 1 was used as the carrier. A two-step equal volume impregnation method was used. First, 15% Co(NO 3 ) 2The solution was allowed to stand for 4 h and dried in an oven at 60 °C to obtain a precursor 1, which was placed in a muffle furnace and calcined in air at 500 °C for 4 h to obtain a catalyst 15% Co / HAP.

[0028] On the base, 3% AgNO was impregnated with equal volume 3 The solution was allowed to stand and dried, and then placed in a tube furnace with 5% H 2 / Ar was calcined at 300 °C for 2 h to obtain the catalyst 3%Ag / 15%Co / HAP.

[0029] Test Example 1 Characterization of the catalysts prepared in the examples and comparative examples Figure 1 The XRD pattern of HAP prepared in Example 1 is as follows: Figure 1 As shown, the hydroxyapatite prepared in Example 1 has an obvious HAP characteristic peak (JCPDS 09-0432), indicating that the hydroxyapatite has been successfully prepared.

[0030] Figure 2 is the N of HAP prepared in Example 1 2 Isothermal adsorption-desorption curves. It can be seen from Table 1 that the specific surface area of ​​hydroxyapatite prepared in Example 1 is 80.7 m 2 / g.

[0031] Figure 3 The XRD patterns of the catalysts prepared in Examples 2-3 and Comparative Example 1 are as follows: Figure 3 As shown, they all have obvious HAP characteristic peaks.

[0032] Figure 4 N is the N of the catalysts prepared in Comparative Example 1 and Example 2. 2 Isothermal adsorption-desorption curves. From Table 1, it can be seen that the specific surface area of ​​the catalyst prepared in Comparative Example 1 is 52.4 m 2 / g, the specific surface area of ​​the catalyst prepared in Example 2 is 53.0 m 2 / g.

[0033]

[0034] Figure 5 is the SEM picture of Example 1, from Figure 5 It can be seen that the HAP sample prepared in Example 1 is a lamellar stacking structure with a size of about 10-100 nm; Figure 6 This is the TEM image of Example 2. In Example 2, nano-Ag is evenly dispersed, and the size of the Ag nanoparticles is about 2.4 nm.

[0035] Test Example 2 The catalysts of the examples and comparative examples were subjected to catalytic oxidation of toluene.

[0036] (1) Thermal catalytic oxidation reaction of toluene The toluene thermal oxidation reaction test was carried out in a fixed bed microreactor (quartz tube inner diameter 10 mm). The catalyst dosage was 100 mg, and the toluene thermal oxidation performance was studied. The reaction temperature was controlled by program temperature rise, and the reaction gas was toluene (10 ml•min -1 ), O 2 (25 ml•min -1 ) and N 2 (95 ml•min -1 ), the total reaction flow rate was 130 ml•min -1 , air velocity is 78000 ml•h -1 •g cat -1 The gas phase components were quantitatively analyzed by an online gas chromatograph (Agilent GC-7890B) equipped with TCD and FID detectors.

[0037] (2) Co-catalytic oxidation reaction of toluene in low-temperature plasma At room temperature and atmospheric pressure, a single dielectric barrier discharge reactor (such as Fig. 9 ) was used to oxidize toluene in a reactor. The single dielectric barrier discharge reactor consisted of a quartz tube (8 mm inner diameter × 1 mm thickness), a stainless steel rod (3 mm diameter) as a high-voltage electrode axially inserted into the quartz tube, and a stainless steel wire mesh as a ground electrode wrapped around the outside of the quartz tube. About 0.1 g of catalyst particles were loaded into the discharge region between the ground electrode wire mesh and the high-voltage electrode rod, and the energy required for the experiment was provided by a CTP-2000K plasma experimental device. The reaction gas, space velocity, and quantitative analysis device were consistent with the thermal oxidation reaction of toluene.

[0038] The catalysts in Comparative Example 1 and Examples 2-3 were used for the thermal catalytic oxidation reaction of toluene. The test results of the thermal catalytic oxidation of toluene are as follows: Figure 7 As shown, compared with Comparative Example 1, the toluene conversion rate of the catalyst of Example 2 at 270°C is 100%, followed by Example 3, whose conversion rate at 280°C is 97.9%. This shows that the catalyst prepared by dielectric barrier discharge low-temperature plasma treatment in the present invention has a good catalytic oxidation removal effect of toluene at low temperature.

[0039] The catalysts in Comparative Example 1 and Examples 2-3 were used for low-temperature plasma synergistic catalytic oxidation reaction. The test results of plasma synergistic catalytic oxidation of toluene are shown in FIG. Figure 8As shown, compared with Comparative Example 1, the toluene conversion rate of Example 2 is 88% when the input power is 10 W, and the toluene conversion rate is 100% when the input power is 13 W; followed by Example 3, where the toluene conversion rate is 81% when the input power is 10 W, and the toluene conversion rate is 99% when the input power is 13 W. This shows that the catalyst prepared by dielectric barrier discharge low-temperature plasma treatment in the present invention has a good toluene catalytic oxidation removal effect at low temperature.

[0040] Therefore, the present invention adopts the method and application of preparing nanocatalysts using dielectric barrier discharge low-temperature plasma of the above structure. The nanocatalyst obtained by the preparation method solves the shortcomings of sintering and agglomeration of metal particles when synthesizing catalysts under traditional thermal preparation conditions. The process can be synthesized in one step without introducing the risk of new impurities and pollutants. This preparation method has the advantages of simple process route, strong universality, and fast synthesis speed.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma, characterized in that: The following steps are involved: (1) Preparation of hydroxyapatite (2) Immersion in transition metal salt solution The hydroxyapatite obtained in step (1) is placed in a transition metal salt solution and dried to obtain a precursor 1; (3) Impregnation with precious metal salt solution Placing the precursor 1 obtained in step (2) in a noble metal salt solution and drying to obtain the precursor 2; (3) Preparation of catalyst The precursor 2 is subjected to dielectric barrier discharge low-temperature plasma treatment to obtain a finished catalyst product.

2. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 1, characterized in that: In step (1), the preparation process of hydroxyapatite is: Soluble calcium salt and soluble phosphate salt are dissolved in deionized water or ethanol, stirred for reaction for 2 to 3 hours, and aged for 1.5 to 3 hours to obtain a precipitated product; the precipitated product is washed to neutrality, dried, and then calcined at 400 to 700 °C to obtain hydroxyapatite with a lamellar stacking structure.

3. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 2, characterized in that: In step (1), the soluble calcium salt is one or both of calcium hydroxide and calcium nitrate, and the soluble phosphate salt is one or both of diammonium hydrogen phosphate and phosphorus pentoxide.

4. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 3, characterized in that: In step (1), the molar ratio of calcium ions in the soluble calcium salt to phosphorus ions in the soluble phosphorus salt is 1.6-1.7:

1.

5. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 1, characterized in that: In step (2), the transition metal salt solution is a cobalt nitrate solution, and the cobalt content of the precursor is 3-15%.

6. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 1, characterized in that: In step (3), the noble metal salt solution is a silver nitrate solution, and the silver content in the second precursor is 0.5-5%.

7. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 1, characterized in that: In step (4), the specific process of dielectric barrier discharge low temperature plasma treatment is as follows: Precursor 2 is placed in an open quartz boat, and the quartz boat is placed between two electrodes in a dielectric barrier discharge low-temperature plasma treatment device, a working gas is introduced, and dielectric barrier discharge low-temperature plasma treatment is performed under the condition of additional input power to obtain a catalyst.

8. The method for preparing nanocatalysts by dielectric barrier discharge low-temperature plasma according to claim 7, characterized in that: In step (4), the input power is 80-200 W, the working gas is at least one of hydrogen, air, argon and oxygen, and the processing time is 5-30 min.

9. A nanocatalyst, characterized in that: The method is prepared by any one of claims 1 to 8.

10. The use of a nanocatalyst according to claim 9, characterized in that: Application of nanocatalysts in synergistic catalytic removal of toluene.

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