A method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs

Abstract

The present invention belongs to the field of gas treatment and relates to a method for producing carbon nanotubes by catalytically cracking VOCs at low temperatures. The method uses TiO2 as a carrier, loads metal Ni, introduces alkaline MgO to control the acidity of the TiO2, and strengthens the metal Ni for fixation to obtain a special catalyst. The catalyst adsorbs the carbon source after VOC cracking onto its surface at low temperatures. After the reaction, carbon atoms and byproducts are generated. The carbon atoms then deposit on the catalyst surface and reach a saturated state, ultimately precipitating to form CNTs. The method controls the residence time of the carbon source on the catalyst surface and optimizes the metal Ni loading to improve the morphological properties of the carbon nanotubes. A certain amount of CO is introduced to assist in the catalytic reduction of amorphous carbon deposition on the catalyst surface. The CNTs formed on the catalyst surface are then stripped using methods such as an online ultrasonic-assisted system.

Description

Technical Field

[0001] The present invention belongs to the field of gas treatment, and in particular relates to a method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs using a multifunctional low-temperature nickel-based titanium dioxide catalyst. Background Art

[0002] Volatile organic compounds (VOCs) are organic compounds with high saturated vapor pressures (greater than 13.33 Pa) under standard conditions, low boiling points, small molecular weights, and easy volatility at room temperature. Although numerous methods are currently available for VOC pollution control, most involve adsorption, combustion, and biological methods, resulting in high costs and low degradation efficiency. Furthermore, emerging technologies, such as plasma technology, photocatalytic oxidation, and membrane separation, also suffer from high energy consumption, low catalyst efficiency, and susceptibility to deactivation, as well as high investment costs. Chemical vapor deposition (CVD) is a technique that can effectively convert VOCs into high-value-added products (such as carbon nanotubes and other nanocarbon products). However, due to high temperatures, catalyst surfaces are prone to agglomeration, leading to rapid deactivation. Furthermore, the resulting nanocarbon products have low conversion rates and are of limited purity. They are often doped with metals and amorphous carbon, requiring further purification and increasing investment costs. Therefore, there is an urgent need to develop efficient catalytic systems that can be used at low temperatures to promote the production of nanocarbon products.

[0003] Titanium dioxide is an inorganic compound. Due to its large specific surface area, abundant surface active sites, excellent thermal stability and chemical inertness, it is often used as a catalyst carrier. At the same time, TiO2 is non-toxic, inexpensive and easy to prepare on a large scale, which meets the requirements of green chemistry. It has been widely used in industrial waste gas treatment. Its high efficiency and economy provide feasibility for the resource utilization of VOCs. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to address the deficiencies of the existing technology and provide a method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs using a multifunctional low-temperature nickel-based titanium dioxide catalyst, thereby solving the problems of high-temperature energy consumption requirements, catalyst deactivation, low product purity, and amorphous carbon deposition in the existing technology, and providing a new approach for the low-cost, high-performance preparation of CNTs.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for producing carbon nanotubes by catalytically cracking VOCs at low temperatures, wherein TiO2 is used as a carrier, metal Ni is loaded, and MgO is introduced to load and fix the metal Ni to obtain a multifunctional low-temperature nickel-based titanium dioxide catalyst; VOCs are catalytically cracked at low temperatures under the action of the above catalyst to produce carbon nanotubes.

[0007] Preferably, the loading amount of the metal Ni is 1%-10% of the total mass of the catalyst.

[0008] Preferably, the amount of MgO added is 0.5%-5% of the total mass of the catalyst. The introduction of alkaline MgO regulates the acidity of TiO2 and strengthens the loading and fixation of metal Ni.

[0009] Furthermore, the multifunctional low-temperature nickel-based titanium dioxide catalyst of the present invention is prepared specifically by the following steps:

[0010] a. Mix TiO2 and MgO to form a composite carrier;

[0011] b. The composite support is immersed in a nickel salt solution by an impregnation method. After sufficient impregnation, the composite support is taken out, dried and calcined to obtain the composite support.

[0012] Preferably, in step a, the TiO2 and MgO are mixed by mechanical stirring for 1-5 hours.

[0013] Preferably, in step b, the nickel salt solution is an aqueous solution of nickel nitrate with a concentration of 0.1-1 mol / L.

[0014] Preferably, in step b, the drying temperature is 60-120° C., and the drying time is 6-12 hours; the roasting temperature is 300-600° C., and the roasting time is 2-5 hours.

[0015] Preferably, a certain amount of catalyst is added to the reactor, and a certain amount of VOCs and CO is introduced at a temperature range of 200-400°C. The residence time and flow rate are controlled. After a period of reaction, the CNTs are peeled off and collected using an online ultrasonic-assisted system. The reaction is continued to achieve continuous production of high-purity CNTs.

[0016] Furthermore, the specific steps include:

[0017] S1. VOCs are introduced into a reactor and cracked in the presence of a multifunctional low-temperature nickel-based titanium dioxide catalyst;

[0018] S2, controlling the residence time of the carbon source on the catalyst surface to 10-60 minutes;

[0019] S3, introduce CO, control the volume ratio of VOCs to CO to be 4:1-2:1, and the flow rate to be 10-100 ml / min;

[0020] S4. Peeling off the CNTs formed on the catalyst surface.

[0021] Preferably, the VOCs are aromatic hydrocarbon compounds, including but not limited to at least one of benzene, toluene, and xylene;

[0022] Preferably, the CNTs are peeled off from the catalyst surface using an online ultrasound-assisted system with an ultrasound frequency of 20-100 kHz and an ultrasound power of 100-500 W.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The catalyst of the present invention uses TiO2 as the carbon source adsorption center, and its large specific surface area ensures contact space between the carbon source and the active components of the catalyst. In the temperature range of 200-400℃, the carbon source after VOCs cracking is adsorbed onto the catalyst and reacts to generate carbon atoms and byproducts (such as H2, H2O, etc.). The carbon atoms are then deposited on the catalyst surface and reach a saturated state, and finally precipitate to form CNTs. The morphology and properties of the CNTs are improved by controlling the residence time of the carbon source on the catalyst surface and optimizing the metal Ni loading. At the same time, a certain amount of CO is introduced and its flow rate is controlled to assist in reducing the amorphous carbon deposition on the catalyst surface. The CNTs formed on the catalyst surface are peeled off by methods such as an online ultrasonic-assisted system. The introduction of MgO fixes the metal Ni on the catalyst surface, avoiding metal-mixed CNTs and effectively improving the purity of the CNTs. Finally, by controlling the CO inflow flow rate and flow rate, not only the purity of the CNTs is further improved, but also the high activity of the catalyst is maintained.

[0025] (2) The present invention uses TiO2 as a catalyst carrier. The surface acid sites can adsorb and enrich carbon sources, while helping to maintain the structural stability of the catalyst and having a certain degree of anti-poisoning ability. The introduction of MgO regulates the surface acid sites of the TiO2 carrier, which is conducive to lowering the catalytic cracking temperature of VOCs. At the same time, it fixes the metal Ni in the catalyst, not only improving the purity of CNTs, but also maintaining the catalytic activity of the catalyst and extending its service life. The introduction of CO not only effectively reduces the deposition of amorphous carbon on the catalyst surface, but also the generated CO can be reused.

[0026] (3) The present invention realizes the resource utilization treatment of VOCs, reduces the pressure of treating VOCs in the large-scale production process of factories, reduces the adverse impact on the environment, and at the same time generates CNTs with high added value, which has certain economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] Figure 1 This is a diagram of the reaction apparatus.

[0029] Figure 2Graph showing the purity of CNTs prepared in various embodiments and comparative examples.

[0030] Figure 3 Graph showing the carbon source conversion rates of various embodiments and comparative examples. DETAILED DESCRIPTION

[0031] The present invention can be better understood with reference to the following examples.

[0032] like Figure 1 As shown, this is a diagram of the reactor device for producing carbon nanotubes by low-temperature catalytic cracking of VOCs according to the present invention. A VOCs inlet 1 is provided on one side of the reactor, and a CO inlet 2 is provided on the other side, which are respectively used to inject VOCs and CO into the reactor. An online ultrasonic auxiliary system 5 composed of a YM-ZDY003 ultrasonic vibrator is provided inside the reactor, and a catalyst addition channel 6 is provided in the online ultrasonic auxiliary system 5, which is used to add the multifunctional low-temperature nickel-based titanium dioxide catalyst of the present invention into the reactor. An exhaust port 3 is provided at the top of the reactor, and a discharge port 4 is provided at the bottom. During the specific preparation, a certain amount of catalyst is added to the reactor, and a certain amount of VOCs and CO are introduced at a temperature range of 200-400°C, and the residence time and flow rate are controlled. After a period of reaction is completed, the CNTs are peeled off through the online ultrasonic auxiliary system and collected, and the reaction is continued to achieve continuous production of high-purity CNTs.

[0033] Comparative Example 1

[0034] In this comparative example, the specific preparation method of the catalyst is as follows:

[0035] (1) Weigh 10 g of TiO2 as a carrier.

[0036] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0037] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0038] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0039] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0040] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0041] (6) Introduce CO, control the volume ratio of VOCs to CO to be 2:1, and the flow rate to be 50 ml / min.

[0042] (7) The CNTs formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0043] The carbon nanotubes were collected and their purity was tested.

[0044] Comparative Example 2

[0045] In this comparative example, the specific preparation method of the catalyst is as follows:

[0046] (1) TiO2 and MgO were mixed in a mass ratio of 20:1 and mechanically stirred for 3 hours to form a solid mixture.

[0047] (2) Add the solid mixture in step (1) to 200 ml of distilled water and stir thoroughly for 6 hours.

[0048] (3) The stirred liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a catalyst.

[0049] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0050] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0051] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0052] (6) Introduce CO, control the volume ratio of VOCs to CO to be 2:1, and the flow rate to be 50 ml / min.

[0053] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0054] The carbon nanotubes were collected and their purity was tested.

[0055] Comparative Example 3

[0056] In this comparative example, the specific preparation method of the multifunctional low-temperature conversion Ni-based TiO2 catalyst is as follows:

[0057] (1) TiO2 and MgO were mixed in a mass ratio of 20:1 and mechanically stirred for 3 hours to form a carrier.

[0058] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0059] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0060] The obtained catalyst is applied to the resource recovery of VOCs to prepare TiO2:

[0061] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0062] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0063] (6) The CNTs formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0064] The carbon nanotubes were collected and their purity was tested.

[0065] Example 1

[0066] In this embodiment, the specific preparation method of the multifunctional low-temperature conversion Ni-based TiO2 catalyst is as follows:

[0067] (1) TiO2 and MgO were mixed in a mass ratio of 20:1 and mechanically stirred for 3 hours to form a carrier.

[0068] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0069] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0070] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0071] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0072] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0073] (6) Introduce CO, control the volume ratio of VOCs to CO to be 2:1, and the flow rate to be 50 ml / min.

[0074] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0075] The carbon nanotubes were collected and their purity was tested.

[0076] Example 2

[0077] In this embodiment, the specific preparation method of the multifunctional low-temperature conversion Ni-based TiO2 catalyst is as follows:

[0078] (1) TiO2 and MgO were mixed in a mass ratio of 25:1 and mechanically stirred for 3 hours to form a carrier.

[0079] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0080] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0081] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0082] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0083] (5) The residence time of benzene on the catalyst surface is controlled to be 30 minutes.

[0084] (6) Introduce CO, control the volume ratio of VOCs to CO to be 2:1, and the flow rate to be 50 ml / min.

[0085] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0086] The carbon nanotubes were collected and their purity was tested.

[0087] Example 3

[0088] In this embodiment, the specific preparation method of the multifunctional low-temperature conversion Ni-based TiO2 catalyst is as follows:

[0089] (1) TiO2 and MgO were mixed in a mass ratio of 30:1 and mechanically stirred for 3 hours to form a carrier.

[0090] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0091] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0092] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0093] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0094] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0095] (6) Introduce CO, control the volume ratio of VOCs to CO to be 2:1, and the flow rate to be 50 ml / min.

[0096] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0097] The carbon nanotubes were collected and their purity was tested.

[0098] Example 4

[0099] In this embodiment, the specific preparation method of the multifunctional low-temperature conversion Ni-based titanium dioxide catalyst is as follows:

[0100] (1) TiO2 and MgO were mixed in a mass ratio of 25:1 and mechanically stirred for 3 hours to form a carrier.

[0101] (2) Prepare a 1.0 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the nickel loading is 10% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0102] (3) The impregnated liquid was dried at 80 °C for 12 h and then calcined in a muffle furnace at 400 °C for 3 h to obtain a multifunctional low-temperature conversion Ni-based titanium dioxide catalyst.

[0103] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0104] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 200°C after adding a catalyst.

[0105] (5) The residence time of benzene on the catalyst surface is controlled to be 30 minutes.

[0106] (6) Introduce CO, control the volume ratio of VOCs to CO to 2:1, and control the flow rate of CO to 50 ml / min.

[0107] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0108] The carbon nanotubes were collected and their purity was tested.

[0109] Example 5

[0110] In this embodiment, the specific preparation method of the multifunctional low-temperature conversion Ni-based TiO2 catalyst is as follows:

[0111] (1) TiO2 and MgO were mixed in a mass ratio of 20:1 and mechanically stirred for 3 hours to form a carrier.

[0112] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0113] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0114] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0115] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0116] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0117] (6) Introduce CO, control the volume ratio of VOCs to CO to 3:1, and control the flow rate of CO to 50 ml / min.

[0118] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0119] The carbon nanotubes were collected and their purity was tested.

[0120] Example 6

[0121] In this embodiment, the specific preparation method of the multifunctional low-temperature conversion Ni-based TiO2 catalyst is as follows:

[0122] (1) TiO2 and MgO were mixed in a mass ratio of 20:1 and mechanically stirred for 3 hours to form a carrier.

[0123] (2) Prepare a 0.5 mol / L nickel nitrate aqueous solution, add the support prepared in step (1) into the solution by impregnation so that the Ni loading is 5% of the total mass of the catalyst, and stir thoroughly for 6 hours.

[0124] (3) The impregnated liquid was dried at 80°C for 12 hours and then calcined in a muffle furnace at 400°C for 3 hours to obtain a multifunctional low-temperature conversion Ni-based TiO2 catalyst.

[0125] The obtained catalyst was applied to the resource recovery of VOCs to prepare CNTs:

[0126] (4) Aromatic hydrocarbon compounds such as benzene, toluene, and xylene are introduced into the reactor as VOCs, and a cracking reaction is carried out at 300°C after adding a catalyst.

[0127] (5) Control the residence time of VOCs on the catalyst surface to 30 minutes.

[0128] (6) Introduce CO, control the volume ratio of VOCs to CO to 4:1, and control the flow rate of CO to 50 ml / min.

[0129] (7) The carbon nanotubes formed on the catalyst surface were stripped using an online ultrasonic-assisted system (ultrasonic frequency of 50 kHz and ultrasonic power of 300 W).

[0130] The carbon nanotubes were collected and their purity was tested.

[0131] Figure 2 The purity graphs of CNTs under different control examples and examples are given. It can be seen that: by comparing control example 1 and example 1, it can be seen that the addition of MgO during the catalyst preparation process can effectively improve the purity of CNTs. It is speculated that this is because MgO has a fixing effect on the metal Ni on the surface of the catalyst, preventing the metal from falling into the CNTs at high temperatures; by comparing control example 2 and example 1, it can be seen that the presence of metal Ni can effectively convert the carbon source into CNTs, thereby increasing the stability of the catalyst; by comparing control example 3 and example 1, it can be seen that the introduction of a certain amount of CO can effectively improve the purity of CNTs. This is because CO can remove amorphous carbon on the catalyst surface during the reaction and prevent it from falling into the CNTs.

[0132] Figure 3 The carbon source conversion rate diagrams for the control example and the embodiment are given. It can be seen that when the mass ratio of TiO2 and MgO is 20:1, the concentration of the nickel nitrate aqueous solution is 0.5 mol / L, and the volume ratio of VOCs to CO is 2:1, the carbon source conversion rate reaches a maximum of 52%, indicating that the addition of MgO, the loading of metallic Ni, and the introduction of an appropriate amount of CO can effectively improve the carbon source conversion rate, thereby increasing the yield of CNTs.

[0133] The present invention provides a method and approach for producing carbon nanotubes by low-temperature catalytic cracking of VOCs. While there are numerous methods and approaches for implementing this technical solution, the aforementioned are merely preferred embodiments of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs, characterized in that: TiO2 is used as a carrier to load metal Ni, and MgO is introduced to fix the metal Ni to obtain a multifunctional low-temperature nickel-based titanium dioxide catalyst; VOCs are catalytically cracked at low temperature under the action of the above catalyst to produce carbon nanotubes; The loading amount of the metal Ni is 1%-10% of the total mass of the catalyst; The amount of MgO added is 0.5%-5% of the total mass of the catalyst; The catalyst is prepared by the following steps: a. Mix TiO2 and MgO to form a composite carrier; b. Impregnating the composite support in a nickel salt solution by an impregnation method, taking it out after sufficient impregnation, drying it, and calcining it to obtain; In the temperature range of 200-400°C, the carbon source after cracking VOCs is adsorbed onto the surface of the multifunctional low-temperature nickel-based titanium dioxide catalyst and catalytically reacts to generate carbon nanotubes (CNTs); The specific steps of producing carbon nanotubes by low-temperature catalytic cracking of VOCs include: S1. VOCs are introduced into a reactor and cracked in the presence of a multifunctional low-temperature nickel-based titanium dioxide catalyst; S2, controlling the residence time of the carbon source on the catalyst surface to 10-60 minutes; S3, introduce CO, control the volume ratio of VOCs to CO to be 4:1-2:1, and the flow rate to be 10-100 ml / min; S4. Stripping the carbon nanotubes (CNTs) formed on the catalyst surface.

2. The method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs according to claim 1, characterized in that: In step a, the TiO2 and MgO are mixed by mechanical stirring for 1-5 hours.

3. The method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs according to claim 1, characterized in that: In step b, the nickel salt solution is an aqueous solution of nickel nitrate with a concentration of 0.1-1 mol / L.

4. The method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs according to claim 1, characterized in that: In step b, the drying temperature is 60-120° C., and the drying time is 6-12 hours; the roasting temperature is 300-600° C., and the roasting time is 2-5 hours.

5. The method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs according to claim 1, characterized in that: After the reaction is completed, the carbon nanotubes (CNTs) are peeled off using an online ultrasound-assisted system.

6. The method for producing carbon nanotubes by low-temperature catalytic cracking of VOCs according to claim 1, characterized in that: The VOCs are aromatic hydrocarbon compounds, including at least one of benzene, toluene, and xylene; The carbon nanotubes (CNTs) are peeled off from the catalyst surface using an online ultrasonic-assisted system, with an ultrasonic frequency of 20-100 kHz and an ultrasonic power of 100-500 W.

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