CN115364890B - Supported methane thermocatalytic cracking catalyst and preparation method and application thereof - Google Patents

Abstract

The invention relates to the technical field of thermal catalytic cracking catalysts, and discloses a supported methane thermal catalytic cracking catalyst and its preparation method and application. The method includes: S1, mixing the active metal component with water to obtain an impregnation liquid; S2, contacting the carrier with the impregnation liquid, and the conditions of the contact reaction at least meet: the temperature is 22-28°C and the time is 2-8h, obtain the intermediate; S3, dry and roast the intermediate to obtain the supported methane thermal catalytic cracking catalyst; wherein, in S2, the carrier is IM-5 molecular sieve. The catalyst provided by the invention has good stability, and the by-product after the catalyst is used in the thermal catalytic cracking reaction of methane is nanocarbon with high economic value.

Description

A supported methane thermal catalytic cracking catalyst and its preparation method and application

Technical field

The invention relates to the technical field of thermal catalytic cracking catalysts, and in particular to a supported methane thermal catalytic cracking catalyst and its preparation method and application.

Background technique

As one of the main energy sources, fossil fuel reserves are increasingly depleted. At the same time, the environmental problems caused by the emission of large amounts of greenhouse gases from fossil fuel combustion have made renewable and clean energy the focus of attention. Among them, hydrogen is a clean, renewable green energy carrier.

Steam methane reforming (SMR) is currently one of the most commonly used methods for large-scale hydrogen production. Despite decades of commercial optimization, the strong endothermic reactions in SMR still lead to excessive energy consumption and cost.

In addition, the separation of product _H2 and _COx in SMR, as well as the additional carbon tax caused by the large amount _{of COx} generated during the SMR process, will further increase production costs. In the large-scale SMR (LS-SRM) process, approximately 10 kilograms of CO ₂ are produced for every 1 kilogram of hydrogen produced, and the proportion of CO ₂ increases as the scale of the process decreases.

Hydrogen is an important raw material in the hydrogenation reaction of heavy oil. Moreover, the hydrogenation reaction requires very high purity of hydrogen. CO with a concentration of only 10 ppm is fatal to precious metal catalysts, so CO needs to be removed from the hydrogen as completely as possible. , but its cost is quite expensive.

However, catalytic decomposition of methane (CDM) can produce CO _{x-free hydrogen at a lower cost by avoiding the formation of CO x .} Catalytic decomposition of methane: CH ₄ (g) → C (s) + 2H ₂ (g), ΔH0 _298K = +75.6KJ/mol. Through a simple endothermic reaction, methane is decomposed to generate hydrogen and carbon nanomaterials. Therefore, the decomposition process is an environmentally friendly reaction process, which has attracted the research and attention of many domestic and foreign scholars. In terms of hydrogen production, from an economic point of view, the methane catalytic decomposition process is better than the steam reforming process; from a technical point of view, the methane catalytic decomposition process is also better than the photocatalytic decomposition of water. Furthermore, the methane catalytic decomposition process is easily scalable to produce multi-walled nanotubes with high mechanical strength and crystallinity. This multi-walled carbon nanotube material has been widely used due to its excellent electrical, mechanical and chemical properties, thereby bringing higher additional economic value to the methane catalytic decomposition process. The study of catalysts used in the methane catalytic decomposition process is of great significance for optimizing the process.

CN110683511A discloses a chemical chain circulation method of methane cracking hydrogen production coupled with CO ₂ reduction. This method combines the methane catalytic cracking hydrogen production reaction and the CO ₂ reduction reaction, and regenerates the catalyst after the methane cracking hydrogen production reaction, which improves the efficiency Carbon dioxide conversion and carbon monoxide selectivity.

CN110721691A discloses a new catalyst material of _{NixFe3 -x} - _{Ca2FeyAl2 - yO5} , its preparation and _application in _methane hydrogen production, through _{Ca2FeyAl2 - yO5} Loading Ni _x Fe _3-x nanoparticles and achieving high dispersion of active metal particles allows the catalyst to maintain high catalytic activity and stability during methane cracking and hydrogen production, achieving high methane conversion rate and continuous high-efficiency production of high-concentration hydrogen. , and at the same time obtain nanocarbon with low graphitization degree.

In addition, the catalysts used in CDM usually support transition metals (nickel, iron and cobalt) on various oxides or mixed oxide supports, such as MgO, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , MgO-Al ₂ O ₃ , TiO ₂ , SiO ₂ -Al ₂ O ₃ , CeO ₂ -ZrO ₂ , zeolite and mesoporous structure silicon carrier, etc.

Although there are many studies on methane cracking hydrogen production catalysts, carbon is generated when using these catalysts for cracking, which covers the reaction active sites, causing rapid deactivation of the catalyst. Moreover, the carbon generated by cracking is usually amorphous carbon, and its utilization value is not high.

Contents of the invention

The purpose of the present invention is to overcome the defects of poor stability of catalysts in the prior art and low utilization value of by-products in applications.

In order to achieve the above objects, a first aspect of the present invention provides a method for preparing a supported methane thermal catalytic cracking catalyst, which method includes:

S1, mix the active metal component and water to obtain an impregnating solution;

S2, contact the carrier with the impregnation liquid, and the conditions of the contact reaction at least meet: temperature is 22-28°C, time is 2-8h, and the intermediate is obtained;

S3, dry and roast the intermediate to obtain the supported methane thermal catalytic cracking catalyst;

Wherein, in S2, the carrier is IM-5 molecular sieve;

In S3, the drying temperature is 100-200°C and the drying time is 2-20h; the roasting temperature is 400-550°C and the roasting time is 2-10h.

A second aspect of the present invention provides a supported methane thermal catalytic cracking catalyst prepared by the method described in the first aspect.

A third aspect of the present invention provides the use of the supported methane thermal catalytic cracking catalyst described in the second aspect for producing hydrogen and carbon nanotubes in a methane thermal catalytic cracking reaction.

The method provided by the invention has the advantages of simple preparation process, low cost, short preparation cycle and good catalyst stability; at the same time, the catalyst has a high carbon production rate when used in the thermal catalytic cracking reaction of methane, and the by-product nanocarbons are of high utilization value. of carbon nanotubes.

Description of the drawings

Figure 1 shows the methane conversion rate of different catalysts as a function of time.

Figure 2 is a scanning electron microscope photo of the solid phase generated after the methane cracking hydrogen production reaction with different catalysts.

Figure 3 shows the adsorption and desorption isotherms of catalyst NFZI-1 and Comparative Example 1.

Figure 4 shows the pore size distribution curves of catalyst NFZI-1 and Comparative Example 1.

Figure 5 shows the adsorption and desorption isotherms of catalyst NFZI-2 and Comparative Example 2.

Figure 6 shows the pore size distribution curves of catalyst NFZI-2 and Comparative Example 2.

Figure 7 shows the weight loss percentage of the solid phase generated after the methane cracking hydrogen production reaction with different catalysts as a function of temperature.

Figure 8 shows the weight loss rate percentage of the solid phase generated after the methane cracking hydrogen production reaction with different catalysts as a function of temperature.

Figure 9 shows the Raman spectrum curves of different catalyst carbon products.

Detailed ways

The endpoints of ranges and any values disclosed herein are not limited to the precise range or value, but these ranges or values are to be understood to include values approaching such ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges. These values The scope shall be deemed to be specifically disclosed herein.

It should be noted that in various aspects of the present invention, for the same components or terms in various aspects, the present invention is only described once in one aspect without repeated description. Those skilled in the art should not understand it as Limitations of Invention.

As mentioned above, the first aspect of the present invention provides a method for preparing a supported methane thermal catalytic cracking catalyst, which method includes:

S1, mix the active metal component and water to obtain an impregnating solution;

S2, contact the carrier with the impregnation liquid, and the conditions of the contact reaction at least meet: temperature is 22-28°C, time is 2-8h, and the intermediate is obtained;

S3, dry and roast the intermediate to obtain the supported methane thermal catalytic cracking catalyst;

Wherein, in S2, the carrier is IM-5 molecular sieve;

In S3, the drying temperature is 100-200°C and the drying time is 2-20h; the roasting temperature is 400-550°C and the roasting time is 2-10h.

Preferably, in S1, the water is deionized water.

It should be noted that in S1, the present invention has no specific requirements on the mixing process and conditions. It is only necessary to mix the active metal component and water to a uniformity known to those in the art.

Preferably, in S1, the active metal component contains a main active metal component and an auxiliary active metal component; in the active metal component, the main active metal component contains the element Ni; in In the active metal component, the auxiliary active metal component contains element Fe and element Zn.

Preferably, in the active metal component, the main active metal component is at least one of nickel nitrate, basic nickel carbonate, and nickel sulfate.

Preferably, in the active metal component, the auxiliary active metal component is at least one selected from the group consisting of iron nitrate, iron sulfate, and ferrous sulfate and at least one selected from the group consisting of zinc nitrate, zinc sulfate, and zinc acetate. A combination.

Preferably, the active metal components are iron nitrate and zinc nitrate, and the dosage mass ratio of iron nitrate and zinc nitrate is 1:0.5-1.5.

Preferably, in S1, the mass ratio of the active metal component to the water is 1:1-10.

Preferably, in the active metal component, the mass ratio of the main active metal component to the auxiliary active metal component is 0.1-10:1.

Preferably, in S2, the mass ratio of the active metal component to the IM-5 molecular sieve is 1:0.9-10.

Preferably, in S2, the molar ratio of Si element to Al element in the IM-5 molecular sieve is 30-55:1. The inventor found that under this preferred situation, the prepared supported supported methane thermal catalytic cracking catalyst has better stability.

It should be noted that the present invention has no specific requirements on the source of the IM-5 molecular sieve. It can be a commercially available product or can be prepared by methods known in the art. Hereinafter, an exemplary method for preparing IM-5 molecular sieve is provided. Methods:

(1) Dissolve NaOH and NaAlO ₂ in water, stir continuously for 30-60 minutes under 60-90°C water bath conditions to prepare a mixed solution;

(2) Under stirring conditions, add the 1,5-bis(N-methylpyrrolidine)pentane bromide salt (MPPBr ₂ ) aqueous solution dropwise into the mixed solution, and stir continuously for 1-2 hours under 60-90°C water bath conditions;

(3) Under vigorous stirring conditions, add SiO ₂ dropwise to the mixture, stir continuously for 2-3 hours under 60-90°C water bath conditions, and mix to form a gel mixture;

(4) Transfer the gel mixture into the crystallization kettle, and under the crystallization reaction conditions of 160-180°C, the dynamic crystallization will hydrothermal crystallize the colloid or solid-liquid mixture for 7-10 days to synthesize IM-5 molecular sieve.

Wherein, the stirring rate is 250-350rpm, the vigorous stirring rate is 380-500rpm, the 1,5-bis(N-methylpyrrolidine)pentane bromide salt (MPPBr ₂ ) aqueous solution, NaAlO ₂ , the molar ratio of NaBr, NaOH, SiO ₂ and H ₂ O is 1:1-2:0.5-1:2-4:5-7:240-260.

Preferably, in S3, the drying temperature is 120-150°C and the drying time is 4-10h; the roasting temperature is 450-550°C and the roasting time is 4-6h.

Preferably, the calcination is performed in an air atmosphere.

The method provided by the invention can obtain a methane thermal catalytic cracking catalyst with high reactivity and stability without using dispersant, template agent or surfactant.

As mentioned above, the second aspect of the present invention provides a supported methane thermal catalytic cracking catalyst prepared by the method described in the first aspect.

A third aspect of the present invention provides the use of the supported methane thermal catalytic cracking catalyst described in the second aspect for producing hydrogen and carbon nanotubes in a methane thermal catalytic cracking reaction.

Preferably, in the application, the conditions for the methane thermal catalytic cracking reaction at least meet: the reaction temperature is 500-800°C, the pressure is 0-0.13MPa, the reactor is a tubular reactor, and the reaction raw material is methane.

It should be noted that in the application of the above catalyst, the present invention has no special restrictions on the number and connection mode of reactors for the methane thermal catalytic cracking reaction. It can be carried out in one reactor, or in multiple parallel or series reactions. performed in the device.

In the present invention, there are no special restrictions on other conditions and processes of the methane thermal catalytic cracking reaction, and those skilled in the art can use known technical means to carry out the reaction. In order to reflect the performance of the catalyst provided by the present invention, a preferred specific reaction mode is provided below, which should not be understood by those skilled in the art as a limitation of the present invention.

The supported methane thermal catalytic cracking catalyst provided by the present invention is pressed into tablets using a tablet press, and then sieved to produce catalyst particles of 0.42-0.63 mm. 0.05-0.8g of catalyst particles are filled into a tubular reactor with an inner diameter of 10 mm, and the tubular reactor is installed vertically in the heating furnace. The reaction tube is heated to 500-600°C under an N ₂ atmosphere of 40-80 mL/min, with a heating rate of 10°C/min. After stabilizing at 500-600°C for 10-30 minutes, the flow of N ₂ is stopped. Then, a H ₂ atmosphere of 10-50 mL/min was introduced to carry out the catalyst reduction reaction for 1-3 hours. After the reaction was completed, the H ₂ was stopped and switched to a N ₂ atmosphere purge of 40-80 mL/min. The heating rate was 10°C. /min to raise the temperature to 650-800°C, and then turn off N ₂ after stabilizing at 650-800°C for 10-30 minutes. Switch to a mixture of CH ₄ of 5-50 mL/min and N ₂ of 1-20 mL/min to carry out methane catalytic cracking and hydrogen production reaction. Among them, the above-mentioned methane thermal catalytic cracking reaction is carried out under a pressure of 0.1013MPa.

It should be noted that the catalyst reduction reaction in the above-mentioned thermal catalytic cracking reaction of methane can be performed in a 100% _H2 atmosphere or in a mixed atmosphere of _H2 and _N2 . Among them, under mixed atmosphere conditions, H ₂ accounts for 50%-100% of the total flow rate of the mixed atmosphere, and the space velocity of the mixed atmosphere is 2-6L/(h·gcat).

Similarly, the methane cracking hydrogen production reaction in the above-mentioned thermal catalytic cracking reaction of methane can be carried out under a 100% CH ₄ atmosphere, or under a mixed atmosphere of inert gases such as CH ₄ and N ₂ (or Ar). Wherein, under the mixed atmosphere conditions, CH ₄ accounts for 50%-100% of the total flow rate of the mixed atmosphere, and the space velocity of the mixed atmosphere is 1-4L/(h·gcat).

The inventor found that when the supported methane thermal catalytic cracking catalyst provided by the present invention is used in the methane thermal catalytic cracking reaction, the hydrogen selectivity can reach 100%, and the carbon production is relatively high, among which the carbon products have high economic value. in the form of carbon nanotubes.

The method for preparing a catalyst provided by the invention can obtain a catalyst with higher reactivity and stability without using dispersant, template agent or surfactant.

The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials used are all common commercial products.

IM-5 molecular sieve I: The molar ratio of Si element to Al element is 50:1;

Pseudo-boehmite: purchased from Hejin Juhua Aluminum Co., Ltd., brand: industrial grade (JHN-03), γ-Al ₂ O ₃ content ≥ 97wt%;

ZSM-5 molecular sieve: purchased from Tianjin Nankai Molecular Sieve Co., Ltd., brand name: NKF-5-25FXH, the molar ratio of Si element to Al element is 50:1.

In the present invention, unless otherwise specified, the normal temperature or room temperature involved in the following examples is 25±3°C.

Determination of the active metal content of the supported methane cracking hydrogen production catalyst prepared in the following example: analysis using X-ray fluorescence spectrometer elemental quantitative analysis method;

Thermogravimetric analysis: Use thermogravimetric analysis characterization curve TGA analysis method.

Tablet press: model SZT-15T laboratory manual tablet press, purchased from Tianjin Zhongtuo Technology Development Co., Ltd.

Preparation of γ-Al ₂ O ₃ :

10g of pseudo-boehmite is roasted at high temperature at 600°C for 5 hours to obtain γ-Al ₂ O ₃ .

Preparation of IM-5 molecular sieve I:

(1) Dissolve NaOH and NaAlO ₂ in water, stir continuously for 50 minutes under 70°C water bath conditions to prepare a mixed solution;

(2) Under stirring conditions, add the 1,5-bis(N-methylpyrrolidine)pentane bromide salt (MPPBr ₂ ) aqueous solution dropwise into the mixture, and stir continuously for 1.5 hours under 70°C water bath conditions;

(3) Under vigorous stirring conditions, add SiO ₂ dropwise into the mixture, stir continuously for 2.5 hours in a 70°C water bath, and mix to form a gel mixture;

(4) Transfer the gel mixture into the crystallization kettle, and under the crystallization reaction conditions of 170°C, dynamic crystallization will hydrothermal crystallize the colloid or solid-liquid mixture for 8 days to synthesize IM-5 molecular sieve.

Wherein, the stirring rate is 200rpm, the vigorous stirring rate is 400rpm, 1,5-bis(N-methylpyrrolidine)pentane bromide (MPPBr ₂ ), NaAlO ₂ , NaBr, NaOH, SiO ₂ The molar ratio of H ₂ O is 1:1.7:0.6:3.1:6:240.

Preparation Example 1

Preparing a supported methane cracking hydrogen production catalyst NFZI-1, the method includes:

S1, dissolve 2.212g nickel nitrate, 0.287g iron nitrate and 0.208g zinc nitrate in 6g deionized water, mix and set aside;

S2, weigh 5g of IM-5 molecular sieve I and place it in a crucible, add the impregnating liquid obtained in S1 into the crucible to completely infiltrate the molecular sieve for contact reaction, and obtain an intermediate;

Among them, the temperature of the contact reaction is 25°C and the time is 4 hours;

S3, place the intermediate to dry in an oven, and roast it in a muffle furnace under an air atmosphere to obtain a supported hydrogenation catalyst, which is recorded as NFZI-1;

Among them, the drying temperature is 120℃ and the time is 10h; the roasting temperature is 450℃ and the time is 5h;

The active metal content in NFZI-1 is determined as follows: based on the total weight of the catalyst and calculated as elements, Ni: 10wt%, Fe: 1wt%, and Zn: 1wt%.

Preparation Example 2

Preparing a supported methane cracking hydrogen production catalyst NFZI-2, the method includes:

S1, dissolve 2.433g nickel nitrate, 1.581g iron nitrate and 1.142g zinc nitrate in 6g deionized water, mix and set aside;

S2, weigh 5g of IM-5 molecular sieve I and place it in a crucible, add the impregnating liquid obtained in S1 into the crucible to completely infiltrate the molecular sieve for contact reaction, and obtain an intermediate;

Among them, the temperature of the contact reaction is 23°C and the time is 6 hours;

S3, place the intermediate to dry in an oven, and roast it in a muffle furnace in an air atmosphere to obtain a supported hydrogenation catalyst, which is recorded as NFZI-2;

Among them, the drying temperature is 100℃ and the time is 12h; the roasting temperature is 450℃ and the time is 5h;

The active metal content in NFZI-2 is determined as follows: based on the total weight of the catalyst and calculated in terms of elements, Ni: 10wt%, Fe: 5wt%, and Zn: 5wt%.

Comparative example 1

This comparative example was carried out using a method and dosage similar to Preparation Example 1, except that the carrier used was γ-Al ₂ O ₃ and the dosage was 5 g. The obtained supported hydrogenation catalyst was recorded as Comparative Example 1.

The active metal content in the catalyst comparative example 1 was determined as follows: based on the total weight of the catalyst and calculated as elements, Ni: 10wt%, Fe: 1wt%, and Zn: 1wt%.

Comparative example 2

This comparative example was carried out using a method and dosage similar to Preparation Example 2, except that the carrier used was 5 g of ZSM-5 molecular sieve, and the supported hydrogenation catalyst obtained was recorded as Comparative Example 2.

The active metal content in the catalyst comparative example 2 was determined as follows: based on the total weight of the catalyst and calculated as elements, Ni: 10wt%, Fe: 5wt%, and Zn: 5wt%.

Test example 1

This test example is used to illustrate the low-temperature nitrogen physical adsorption desorption (BET) characterization of NFZI-1, NFZI-2, catalyst comparative example 1 and catalyst comparative example 2.

Figures 3 and 5 show the adsorption and desorption isotherms of the above catalysts. It can be seen from the hysteresis loop of the isotherms that NFZI-1 and NFZI-2 are typical microporous materials, while Comparative Examples 1 and 2 2 is not.

Figures 4 and 6 show the pore size distribution curves of the above catalysts. It can be seen from the pore size distribution curves that compared with catalysts Comparative Example 1 and Comparative Example 2, NFZI-1 and NFZI-2 have larger pore structures. This facilitates diffusion of reactants and products in the catalyst.

The specific surface area (S _BET ) and pore volume (V _total ) data of the above catalysts are shown in Table 1.

For the prepared catalysts, the specific surface area and pore volume of NFZI-1 and NFZI-2 are both larger and higher than those of catalysts Comparative Examples 1 and 2, which can better improve the catalytic reaction performance of the catalysts.

Table 1

project NFZI-1 NFZI-2 Comparative example 1 Comparative example 2 S _BET (m ² /g) 316 276 252 233 V _total (cm ³ /g) 0.440 0.366 0.385 0.358

The following test examples are used to illustrate the application of the above catalysts in the catalytic cracking of methane to produce hydrogen, including the following methods:

The supported hydrogenation catalyst obtained in the above preparation examples and comparative examples was pressed into tablets using a tablet press, and sieved to produce catalyst particles of 0.425 mm. Weigh 0.2g of catalyst particles and fill them in a tubular reactor with an inner diameter of 10 mm. The tubular reactor is installed vertically in the heating furnace of the reaction device. The reaction tube was heated to 550°C under an N ₂ atmosphere of 60 mL/min at a heating rate of 10°C/min. After stabilizing for 20 minutes, the N ₂ was turned off. Reduce by introducing 20mL/min _H2 atmosphere for 2h. After the reduction, turn off _H2 , switch to 60mL/min _N2 atmosphere, and heat up to 670℃ at a heating rate of 10℃/min. After stabilizing for 20min, turn off _N2 . Switch between 12.5 mL/min CH ₄ and 5 mL/min N ₂ mixed gas to carry out the methane catalytic cracking hydrogen production reaction.

The obtained methane conversion rate and hydrogen generation rate change curves with time are shown in Figure 1.

Among them, methane conversion rate:

Carbon production rate: Y _C (%) = M _C /M _cat ×100%;

Hydrogen production rate:

Methane feed amount: molCH ₄ , in, mol;

Amount of product methane: molCH ₄ , out, mol;

Catalyst carbon deposit mass: _MC , g;

Catalyst mass: M _cat , g;

Amount of product hydrogen: molH ₂ , out, mol;

Methane conversion rate:

Carbon production rate: Y _c (%);

Hydrogen production rate: mol/gcat.

After NFZI-1, NFZI-2, Catalyst Comparative Example 1 and Catalyst Comparative Example 2 were applied to the methane catalytic cracking hydrogen production reaction, the generated solid phases were numbered G1, G2, DG1, and DG2 respectively.

Test example 2

This test example is used to illustrate the carbon production rate of the above catalyst used in the methane catalytic cracking hydrogen production reaction. See Table 2 for details.

Table 2

project NFZI-1 NFZI-2 Comparative example 1 Comparative example 2 Carbon production rate% 469 1095 70 221

It can be seen from the above data that the reaction stability of different catalysts varies greatly. The stability of the catalyst prepared with IM-5 as the carrier is better. Increasing the metal loading can improve the stability of the catalyst.

In the application of methane catalytic cracking hydrogen production reaction, the carbon production rate of using NFZI-1 and NFZI-2 is significantly higher than that of using catalysts Comparative Examples 1 and 2. Among them, using NFZI-2 has the highest carbon production rate and can Reaching 1095%.

Test example 3

This test example is used to illustrate the scanning electron microscopy and thermogravimetric characterization of G1, G2, DG1, and DG2.

The scanning electron micrographs of G1, G2, DG1, and DG2 are shown in Figure 2. That is, Figure 2 shows the surfaces of catalysts NFZI-1 and NFZI-2 prepared with IM-5 molecular sieve as a carrier in the methane catalytic cracking hydrogen production reaction. The generated carbon products are all carbon nanotubes, and the carbon nanotubes are longer; while the surface of the catalyst Comparative Example 1 prepared using γ-Al ₂ O ₃ as a carrier has fewer carbon nanotubes and contains more spherical products; Although there are a large number of carbon nanotubes on the surface of the catalyst Comparative Example 2 prepared with ZSM-5 as a carrier, the carbon nanotubes produced are relatively curled.

The thermogravimetric analysis characterization curve TGA analysis method was used to analyze the thermogravimetric characterization of G1, G2, DG1, and DG2. The results are shown in Figures 7 and 8, thereby obtaining the thermal stability and content of the carbon nanotubes.

It can be seen from Figure 7, Figure 8 and Table 2 that the weight loss and weight loss rate of G1, G2, DG1, and DG2 are consistent with the carbon production rate of the catalyst.

In addition, since amorphous carbon begins to burn below 200°C, in the thermogravimetric analysis of G1, G2, DG1, and DG2, the weight loss below 200°C is due to the combustion of disordered carbon (i.e., amorphous carbon) existing on the surface; The weight loss at 400-700°C is due to the combustion of carbon nanotubes (ordered carbon).

Therefore, in Figures 7 and 8, the thermogravimetric characterization of G1 and G2 both present one-step weight loss curves at 400-700°C, indicating that their carbon products are all the same type of carbon nanotubes. Both DG1 and DG2 present two-step weight loss curves, indicating the presence of two forms of carbon. G1, G2, DG1, and DG2 all show different weight loss percentages within 400-700°C, respectively: G1 is 56.95%, G2 is 74.67%, DG1 is 24.57%, and DG2 is 5.16%. The larger weight loss percentage means The content of carbon nanotubes is relatively high.

It can be seen that the carbon products in G1 and G2 are all the same type of carbon nanotubes.

Test example 4

This test example uses Raman spectroscopy to study the crystallinity, purity and graphitization degree of multi-walled carbon nanotubes deposited on the catalyst after the catalytic cracking of methane to produce hydrogen. The results are shown in Figure 9.

Two strong Raman bands were detected in the Raman spectrum, which are characteristic of carbon nanomaterials. The center of the strips are 1336cm ^-1 and 1570cm ^-1 respectively, and are marked as D band and G band respectively. D band represents disordered carbon or amorphous carbon, and G band represents ordered carbon or crystalline carbon. I _D /I _G explains the degree of graphitization and crystallinity of carbon nanotubes. The lowest I _D /I _G value indicates that the carbon nanotube has the highest degree of graphitization and crystallinity. According to the thermogravimetric analysis results, the catalysts prepared using γ-Al ₂ O ₃ and ZSM-5 as carriers both contain amorphous carbon, and the presence of amorphous carbon leads to an increase in I _D / _IG . At the same time, as the production of carbon nanotubes on the catalyst increases, the I _D / _IG of the generated carbon nanotubes increases, and the degree of crystallization of the carbon nanotubes decreases.

The above results show that the catalyst prepared with IM-5 molecular sieve as the carrier has better stability and is easier to form high-quality carbon nanotubes.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, many simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the disclosed content of the present invention. All belong to the protection scope of the present invention.

Claims (4)

1. A method for preparing a supported methane thermal catalytic cracking catalyst, characterized in that the method includes: S1, mix the active metal component with water to obtain an impregnating liquid; in S1, the active metal component contains a main active metal component and a co-active metal component; the main active metal component contains the element Ni ; The auxiliary active metal component contains element Fe and element Zn; the dosage mass ratio of the main active metal component and the auxiliary active metal component is 0.1-10:1; S2, contact the carrier with the impregnation liquid, and the conditions of the contact reaction at least meet: temperature is 22-28°C, time is 2-8h, and the intermediate is obtained; S3, dry and roast the intermediate to obtain the supported methane thermal catalytic cracking catalyst; Wherein, in S2, the carrier is IM-5 molecular sieve, and the molar ratio of Si element to Al element in the IM-5 molecular sieve is 30-55:1; In S3, the drying temperature is 100-200°C and the drying time is 2-20h; the roasting temperature is 400-550°C and the roasting time is 2-10h; The main active metal component, the auxiliary active metal component, the IM-5 molecular sieve and water are used in an amount such that the content of element Ni in the supported methane thermal catalytic cracking catalyst prepared in S3 is 10wt%, The content of element Fe is 5wt%, and the content of element Zn is 5wt%. 2. The method according to claim 1, wherein the main active metal component is at least one of nickel nitrate, basic nickel carbonate, and nickel sulfate; and/or The active metal component is a combination of at least one selected from iron nitrate, iron sulfate, and ferrous sulfate and at least one selected from zinc nitrate, zinc sulfate, and zinc acetate. 3. The supported methane thermal catalytic cracking catalyst obtained by the method of claim 1 or 2. 4. Application of the supported methane thermal catalytic cracking catalyst according to claim 3 to produce hydrogen and carbon nanotubes in the methane thermal catalytic cracking reaction.