Plasma-assisted zeolite catalyst preparation method and application thereof

Abstract

The invention belongs to the technical field of methane dry reforming catalysts, and particularly relates to a method for plasma-assisted preparation of a zeolite catalyst and application thereof. The preparation method comprises the following specific preparation steps: mixing attapulgite stone powder with an acid solution, and carrying out hydrothermal treatment to obtain treated attapulgite stone powder; dissolving the treated attapulgite stone powder and tetrapropylammonium hydroxide in an alkali solution, carrying out hydrothermal treatment, and calcining to obtain attapulgite-based zeolite; the preparation method comprises the following steps: dissolving attapulgite-based zeolite and tetrapropylammonium hydroxide in deionized water to prepare a mixed solution; adding the nickel ethylenediamine complex solution and the molybdenum ethylenediamine complex solution into the mixed solution, and carrying out hydrothermal treatment to obtain a NiMo-ADM precursor; the precursor is calcined after being subjected to DBD plasma treatment, and the zeolite catalyst is prepared. The method has the characteristics of simple process and low cost, the non-noble metal catalyst with high activity and stability is prepared through a simple synthesis mode, and efficient methane dry reforming is realized.

Description

Technical Field

[0001] The invention belongs to the field of methane dry reforming catalysts, and particularly relates to a plasma-assisted preparation method of a zeolite catalyst and application thereof. Background Art

[0002] The methane dry reforming reaction simultaneously utilizes two abundant greenhouse gases (CO2 and CH4) to generate synthesis gas, thereby producing clean energy and other important chemicals. Although the catalyst will coke and sinter during the reaction, it is currently the most economical and efficient method to achieve CH4 conversion. Methane steam reforming is a mature methane hydrogen production process, which includes many parallel or series reactions, and the concentration of H2 in the product is high. However, the system is complex, and excessively high reaction temperatures will reduce the service life of the tubular furnace and increase energy consumption. The methane partial oxidation reforming reaction is a raw material for the direct synthesis of methanol and important industrial processes of Fischer-Tropsch synthesis. Compared with steam reforming, it has low energy consumption and low production and operation costs, but it may cause explosions due to the CH4 / O2 mixture, which is highly dangerous. In addition, the existence of reaction hotspots will also lead to sintering of the active center of the catalyst, which cannot be industrialized. The autothermal reforming process combines steam reforming and partial oxidation. It is an advanced method for preparing synthesis gas. It has low energy demand, but low hydrogen production rate, which increases the reaction limit of water-oxygen feed ratio. Therefore, among the several methods of methane conversion, methane dry reforming is the most green, energy-saving and safe conversion reaction, and has broader application prospects.

[0003] Dielectric barrier discharge plasma is used in the preparation of Ni-based catalysts due to its high electron energy and low system temperature. The bombardment of high-energy electrons in dielectric barrier discharge plasma can achieve rapid nucleation of nanoparticles, while the low system temperature can inhibit the rapid growth of crystals. A large number of studies have shown that dielectric barrier discharge plasma technology can regulate the size and electronic structure of catalyst particles, increase the number of unsaturated sites on their surfaces, promote preferential exposure of some crystal planes and surface atoms, and strengthen the interaction between metal and support. In addition, high-energy electrons bombard the surface interface to induce Auger rearrangement, causing surface oxygen to detach from the lattice in the form of O+, thereby generating oxygen vacancy defects. All of the above effects can promote the catalyst to form a special structure and improve activity, especially anti-carbon deposition and anti-sintering performance, thereby improving stability.

[0004] Ni-based catalysts are widely used in methane-carbon dioxide reforming reactions due to their high catalytic activity and low cost. However, Ni-based catalysts are prone to sintering of active components at high temperatures, resulting in carbon deposition, which significantly reduces their catalytic performance. A large number of studies have shown that introducing another metal into a Ni-based monometallic catalyst to form a bimetallic catalyst can easily change the surface properties of the catalyst, thereby obtaining better catalytic performance. This phenomenon is also known as the synergistic effect.

[0005] Therefore, it is of great significance to use plasma technology to assist the preparation of a new nickel-based zeolite catalyst. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for the hot spots and difficult problems of Ni-based catalysts in view of the deficiencies of the prior art, give full play to the advantages of both calcination and plasma technologies, introduce plasma into the combustion process, and use plasma technology to assist in the preparation of a Ni-based catalyst with the addition of a second metal.

[0007] In order to solve the above technical problems, the present invention discloses a method for plasma-assisted preparation of zeolite catalysts, the specific steps of which are:

[0008] S1. The attapulgite powder is mixed with an acid solution and subjected to hydrothermal treatment to obtain treated attapulgite powder;

[0009] S2. The treated attapulgite powder and tetrapropylammonium hydroxide were dissolved in an alkaline solution, hydrothermally treated and then calcined to obtain an attapulgite-based zeolite;

[0010] S3. The attapulgite-based zeolite and tetrapropylammonium hydroxide were dissolved in deionized water to obtain a mixed solution; and then the nickel ethylenediamine complex solution and the molybdenum ethylenediamine complex solution were added to the mixed solution, and after hydrothermal treatment, a NiMo-ADM precursor was obtained;

[0011] S4. The NiMo-ADM precursor is treated with DBD plasma and then calcined to prepare the zeolite catalyst.

[0012] Wherein, in S1, the mass volume ratio of the attapulgite powder to the acid solution is 1:(5-8);

[0013] Preferably, in S1, the acid solution is a hydrochloric acid solution with a concentration of 3.5 mol / L; the conditions of the hydrothermal treatment are 180° C., 24 h, and the hydrothermal autoclave is filled to 70%.

[0014] Wherein, in S2, the mass volume ratio of the treated attapulgite powder, tetrapropylammonium hydroxide and alkaline solution is 1:1:(3-5); the specific conditions of the calcination are to increase the temperature to 500-600°C at a heating rate of 4°C / min and keep warm for 5h;

[0015] Preferably, in S2, the alkaline solution is a sodium hydroxide solution with a concentration of 0.01 mol / L; the conditions of the hydrothermal treatment are 180° C., 24 h, and the hydrothermal autoclave is filled to 70%.

[0016] Wherein, in S3, the volume ratio of the nickel ethylenediamine complex solution, the molybdenum ethylenediamine complex solution and the mixed solution is 1:1:(3-5);

[0017] Preferably, the nickel ethylenediamine complex solution is prepared by dissolving nickel salt and ethylenediamine in deionized water; wherein the mass volume ratio of the nickel salt, ethylenediamine and deionized water is 1:(0.4-0.5):(7-8);

[0018] Preferably, the molybdenum ethylenediamine complex solution is prepared by dissolving a molybdenum salt and ethylenediamine in deionized water; wherein the mass volume ratio of the molybdenum salt, ethylenediamine and deionized water is 1:(1-1.5):(18-22);

[0019] More preferably, the nickel salt is nickel nitrate hexahydrate, and the molybdenum salt is ammonium molybdate tetrahydrate;

[0020] More preferably, in S3, the hydrothermal reaction conditions are 180° C., 64 h, and the hydrothermal reactor is filled to 70%.

[0021] Among them, in S3, the mass volume ratio of the attapulgite-based zeolite, tetrapropylammonium hydroxide and deionized water is 1:(3-5):(8-12).

[0022] Among them, in S4, the specific conditions of the DBD plasma treatment are: discharge power 180-220W, discharge time 25-35min; the specific conditions of the calcination are heating to 500-600°C at a heating rate of 4°C / min and keeping warm for 6h.

[0023] Specifically, in some embodiments of the present invention, a zeolite catalyst is prepared by the above-mentioned plasma-assisted method for preparing a zeolite catalyst, and the zeolite catalyst is added to a quartz reactor and experiments are carried out in a U-shaped tube furnace. The catalyst performance is evaluated by online gas chromatography analysis, which proves that the zeolite catalyst can stably convert methane and carbon dioxide, and proves the application prospect of the zeolite catalyst in the field of preparing synthesis gas by methane dry reforming.

[0024] Beneficial effects: 1. The preparation process of the Ni7Mo1-ADM-P catalyst of the present invention has the characteristics of simple method and low cost. Through a simple synthesis method, a non-precious metal catalyst with high activity and stability is prepared to achieve efficient methane dry reforming;

[0025] 2. The Ni7Mo1-ADM-P catalyst prepared by the present invention has a short induction period and can achieve stable conversion within 4 hours;

[0026] 3. The Ni7Mo1-ADM-P catalyst prepared by the present invention operates stably for 100 hours under high temperature conditions without any signs of deactivation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0028] Figure 1 N2 adsorption-desorption isotherms of the catalysts prepared in Example 1 of the present invention and Comparative Examples 1-2;

[0029] Figure 2 This is a stability evaluation diagram of the catalysts prepared in Example 1 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0030] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0031] Example 1: Preparation of Ni7Mo1-ADM-P

[0032] (1) 10 g of attapulgite powder was dissolved in 60 mL of HCl solution (3.5 mol / L) to prepare solution A, and the solution was hydrothermally treated at 180° C. with a hydrothermal autoclave filled to 70% for 24 h, and the solution was filtered and dried to obtain the treated attapulgite powder;

[0033] (2) 5 g of tetrapropylammonium hydroxide and 5 g of treated attapulgite powder were dissolved in 20 mL of NaOH solution (0.01 mol / L) to obtain solution B, which was hydrothermally treated at 180° C. with the hydrothermal autoclave filled to 70% for 24 h, filtered, dried, and heated to 550° C. at a heating rate of 4° C. / min, and kept warm for 5 h to obtain attapulgite-based zeolite;

[0034] (3) Under the condition of stirring in a constant temperature water bath at 35°C, 2 g of attapulgite-based zeolite and 7.29 g of tetrapropylammonium hydroxide were added to 20 ml of deionized water and stirred for 6 h to obtain solution 1. 0.69 g of Ni(NO3)2·6H2O and 0.3195 ml of ethylenediamine were added to 5 ml of deionized water to obtain solution 2. 0.25 g of (NH4)6Mo7 O 24 4H2O and 0.3ml ethylenediamine were added to 5ml deionized water to obtain solution 3. Solution 2 and solution 3 were added dropwise to solution 1 under stirring in a water bath at room temperature, stirred for 2h, hydrothermally treated at 180℃ with the hydrothermal autoclave filled to 70% for 64h, filtered and dried to obtain NiMo-ADM precursor.

[0035] (4) The NiMo-ADM precursor was treated with DBD plasma at a discharge voltage of 200 V, a discharge current of 1 A, a discharge power of 200 W, and a discharge time of 30 min. The treated precursor was heated to 550°C at a heating rate of 4°C / min and kept at this temperature for 6 h to obtain Ni7Mo1-ADM-P.

[0036] Comparative Example 1: Preparation of Ni7-ADM-O Catalyst

[0037] The difference from Example 1 is that in step (3), only Ni(NO3)2·6H2O and ethylenediamine are added to form a complex. In step (4), the precursor is not subjected to DBD plasma treatment but directly calcined, and the calcination conditions are the same as those in Example 1.

[0038] Comparative Example 2: Preparation of Ni7Mo1-ADM-O catalyst

[0039] The difference from Example 1 is that in step (4), the precursor is not subjected to DBD plasma treatment but is directly calcined, and the calcination conditions are the same as those in Example 1.

[0040] Evaluation of catalyst structure performance of Example 1 and Comparative Examples 1-2:

[0041] Figure 1 The N2 adsorption-desorption isotherms of the catalysts prepared in Example 1 and Comparative Examples 1-2 are shown in FIG. Figure 1 It can be seen that the N2 adsorption-desorption curves of all samples are a combination of type I and type IV isotherms, accompanied by h4 type hysteresis loops, which indicates that all zeolite encapsulated catalysts have a composite channel structure, including ordered micropores and mesopores formed by zeolite layer stacking. The specific surface area, total pore volume and pore size of Example 1 and Comparative Examples 1-2 are shown in Table 1. The data in Table 1 are obtained by BET. The ADM catalyst is a porous material, S BET The values ​​are all greater than 300m 2 Compared with Comparative Example 2, the specific surface area of ​​Example 1 treated with plasma is significantly increased, which indicates that plasma promotes the formation of zeolite layer stacking mesopores.

[0042] Table 1 Catalyst structural parameters

[0043]

[0044] Evaluation of catalytic performance of catalysts in Example 1 and Comparative Examples 1-2:

[0045] 0.1 g of the catalyst prepared in Example 1 and Comparative Examples 1-2 were weighed and added to a quartz reactor, and the experiment was carried out in a U-shaped tube furnace. The temperature was raised to 750°C under a nitrogen atmosphere (flow rate of 50 mL / min) at a heating rate of 10°C / min, and a CH4 / CO2 synthesis gas (1:1) flow rate of 50 mL / min and a gas hourly space velocity of 60000 mL h -1 ·g -1 cat The catalyst performance was evaluated by online gas chromatography for 100 h.

[0046] Figure 2 The stability evaluation diagram of the catalysts prepared in Example 1 and Comparative Examples 1-2 applied to methane dry reforming is shown in FIG. Figure 2 It can be seen that Ni7Mo1-ADM-P has a high catalytic activity. After 4 hours of reaction, the reaction efficiency reaches the highest and remains stable, and can remain stable within 100 hours. The CH4 conversion rate, CO2 conversion rate and H2 / CO of the stabilized comparative example 1 are 80%, 76% and 0.92 respectively. The CH4 conversion rate, CO2 conversion rate and H2 / CO of the stabilized comparative example 2 are 91%, 89% and 0.95 respectively. The CH4 conversion rate, CO2 conversion rate and H2 / CO of the stabilized example 1 are 93%, 91% and 0.97 respectively.

[0047] The present invention provides a method for plasma-assisted preparation of zeolite catalyst and its application. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for plasma-assisted preparation of zeolite catalysts, characterized in that: The specific steps are: S1. The attapulgite powder is mixed with an acid solution and subjected to hydrothermal treatment to obtain treated attapulgite powder; S2. The treated attapulgite powder and tetrapropylammonium hydroxide were dissolved in an alkaline solution, hydrothermally treated and then calcined to obtain an attapulgite-based zeolite; S3. The attapulgite-based zeolite and tetrapropylammonium hydroxide were dissolved in deionized water to obtain a mixed solution; and then the nickel ethylenediamine complex solution and the molybdenum ethylenediamine complex solution were added to the mixed solution, and after hydrothermal treatment, a NiMo-ADM precursor was obtained; S4. The NiMo-ADM precursor is treated with DBD plasma and then calcined to prepare the zeolite catalyst.

2. The method according to claim 1, characterized in that In S1, the mass volume ratio of the attapulgite powder to the acid solution is 1:(5-8).

3. The method according to claim 1, characterized in that: In S2, the mass volume ratio of the treated attapulgite powder, tetrapropylammonium hydroxide and alkaline solution is 1:1:(3-5); the specific conditions of the calcination are to increase the temperature to 500-600°C at a heating rate of 4°C / min and keep warm for 5h.

4. The method according to claim 1, characterized in that In S3, the volume ratio of the nickel ethylenediamine complex solution, the molybdenum ethylenediamine complex solution and the mixed solution is 1:1:(3-5).

5. The method according to claim 4, characterized in that The nickel ethylenediamine complex solution is prepared by dissolving nickel salt and ethylenediamine in deionized water; wherein the mass volume ratio of the nickel salt, ethylenediamine and deionized water is 1:(0.4-0.5):(7-8).

6. The method according to claim 4, characterized in that The molybdenum ethylenediamine complex solution is prepared by dissolving a molybdenum salt and ethylenediamine in deionized water; wherein the mass volume ratio of the molybdenum salt, ethylenediamine and deionized water is 1:(1-1.5):(18-22).

7. The method according to claim 1, characterized in that In S3, the mass volume ratio of the attapulgite-based zeolite, tetrapropylammonium hydroxide and deionized water is 1:(3-5):(8-12).

8. The method according to claim 1, characterized in that In S4, the specific conditions of the DBD plasma treatment are: discharge power 180-220W, discharge time 25-35min; the specific conditions of the calcination are heating to 500-600°C at a heating rate of 4°C / min and keeping the temperature for 6h.

9. The zeolite catalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the zeolite catalyst according to claim 9 in the field of preparing synthesis gas by dry reforming of methane.

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