A protected catalyst and preparation method thereof

Abstract

This application discloses a protected catalyst and its preparation method, which relates to the field of protected catalysts and includes the following steps: mixing aluminum hydroxide, nickel-loaded carbon nanotubes, a nickel salt, and a solvent, extruding and molding the mixture, and then calcining at high temperature; the nickel-loaded carbon nanotubes are obtained by subjecting carbon nanotubes to plasma modification to obtain plasma-modified carbon nanotubes, and then loading nickel onto the plasma-modified carbon nanotubes. This application utilizes plasma-treated carbon nanotubes to partially load nickel, and then mixes and extrudes the aluminum hydroxide, nickel-loaded carbon nanotubes, and nickel salt, followed by calcination. This method improves the bonding between the carrier and the nickel active ingredient, increases the specific surface area of ​​the protected catalyst, and, when used in conjunction with the main catalyst, improves the overall catalytic efficiency and stability.

Description

Technical Field

[0001] The present application relates to the field of protected catalysts, and in particular to a protected catalyst and a preparation method thereof. Background Art

[0002] Protective catalysts are often used in the second-stage reformer for converting gaseous hydrocarbons to protect the main catalyst and catalyze the reaction between gaseous hydrocarbons and water to convert them into carbon dioxide and hydrogen. At the same time, they have good applications in both recycling gaseous hydrocarbons in production tail gas and producing hydrogen.

[0003] Currently, a protective catalyst consists of a carrier and an active metal component. Alumina is commonly used as the carrier, and nickel and rare earth elements are the active metal components. The active metal components are loaded onto the carrier through impregnation or mixed extrusion. In the secondary reformer, to enhance the protective effect of the protective catalyst on the main catalyst, the specific surface area of ​​the protective catalyst is controlled to be smaller than that of the main catalyst to prevent airflow erosion.

[0004] However, the use of mixed extrusion will cause the specific surface area of ​​the protected catalyst to decrease under external pressure. If the specific surface area is too low, the catalytic effect of the protected catalyst itself will be weakened. The content of active metal components loaded by impregnation is limited, and the bonding effect between the active metal components and the carrier is weak, which makes the active metal components easy to sinter and agglomerate, reducing the active sites and reducing the catalytic effect of the protected catalyst itself. If the specific surface area of ​​the protected catalyst is too high, the ability to resist airflow erosion will be reduced, resulting in a worse protection effect on the main catalyst. Summary of the Invention

[0005] In view of the deficiencies of the above-mentioned related technologies, the purpose of this application is to provide a protected catalyst and a preparation method thereof, by using plasma-treated carbon nanotubes to load part of the nickel, and then mixing aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salts and extruding them and then calcining them. On the one hand, the combination effect of the carrier and the nickel active component is improved, and on the other hand, the specific surface area of ​​the protected catalyst is controlled to an appropriate size, and when used in combination with the main catalyst, the overall catalytic efficiency and catalytic stability are improved.

[0006] In the first aspect, the present application provides a method for preparing a protected catalyst using the following technical solution:

[0007] A method for preparing a protective catalyst comprises the following steps: mixing aluminum hydroxide, nickel-loaded carbon nanotubes, nickel salt and a solvent, extruding and molding the mixture, and then calcining at high temperature; wherein the nickel-loaded carbon nanotubes are obtained by subjecting carbon nanotubes to plasma modification to obtain plasma-modified carbon nanotubes, and loading nickel elements on the plasma-modified carbon nanotubes.

[0008] Preferably, the plasma modification comprises the following steps: subjecting the carbon nanotubes to an alkali treatment, and then subjecting the carbon nanotubes to an oxidizing gas ionized plasma atmosphere to obtain plasma-modified carbon nanotubes.

[0009] Preferably, the oxidizing gas comprises oxygen.

[0010] Preferably, the gas flow rate of the plasma modification is 6-9 mL / min, the ionization voltage is 90-110 V, and the treatment time is 15-25 min.

[0011] Preferably, the gas flow rate of the plasma modification is 8 mL / min, the ionization voltage is 100 V, and the treatment time is 20 min.

[0012] Preferably, the loading of nickel elements on the plasma-modified carbon nanotubes comprises the following steps: uniformly mixing the plasma-modified carbon nanotubes, nickel chloride and water, and then evaporating and calcining the mixture to obtain nickel-loaded carbon nanotubes.

[0013] Preferably, the weight ratio of the plasma-modified carbon nanotubes to the nickel chloride is 50:5-9.

[0014] Preferably, the weight ratio of the plasma-modified carbon nanotubes to the nickel chloride is 50:7.

[0015] Preferably, the calcination temperature is 300-330° C. and the calcination time is 2-4 hours.

[0016] Preferably, the calcination temperature is 320° C. and the calcination time is 3 hours.

[0017] Preferably, the weight ratio of the aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salt is 20:3-7:0.4-1.2.

[0018] Preferably, the weight ratio of the aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salt is 10:2.5:0.4.

[0019] Preferably, the high-temperature calcination is carried out at a temperature of 950-1000° C. and for a time of 4.5-6 hours.

[0020] Preferably, the high-temperature calcination temperature is 980° C. and the time is 5 hours.

[0021] Preferably, the nickel salt includes one or more of nickel chloride, nickel nitrate, nickel sulfate and nickel carbonate.

[0022] Preferably, the nickel salt is nickel carbonate.

[0023] On the other hand, the present application provides a technical solution for protecting a catalyst using the following method:

[0024] A protected catalyst is prepared by the above-mentioned preparation method of the protected catalyst.

[0025] In summary, this application includes at least one of the following beneficial technical effects:

[0026] 1. By using plasma-treated carbon nanotubes to partially load nickel, and then mixing aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salts for extrusion and calcination, firstly, the tubular structure of nickel-loaded carbon nanotubes has a strong carrying capacity. The protected catalyst obtained after extrusion and calcination not only improves the carrying strength of the protected catalyst, but also improves the ability of the protected catalyst to resist airflow scouring, thereby protecting the main catalyst. It also appropriately increases the specific surface area of ​​the protected catalyst on the basis of mixed extrusion, thereby improving the catalytic efficiency. Secondly, it improves the binding effect between the carrier and the active metal nickel, and minimizes the negative effect of reduced catalytic efficiency caused by the reduction of active sites due to the agglomeration of active metals. Under the combined effect, it is beneficial to improve the protection effect of the main catalyst and improve the overall catalytic efficiency and catalytic stability when the main catalyst and the protective catalyst are used together;

[0027] 2. This application treats carbon nanotubes with an alkali and then with an oxygen plasma. This not only increases the specific surface area of ​​the carbon nanotubes, but also forms oxygen-containing groups such as carboxyl groups on the surface of the carbon nanotubes, which are beneficial for the binding of the active metal component nickel ions. The combined effect increases the loading content and adhesion of the active metal component nickel on the carbon nanotubes, thereby increasing the content and stability of the active metal component nickel in the protected catalyst.

[0028] 3. The nickel-loaded carbon nanotubes in the present application also act as a pore expander in the protective catalyst. When aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salts are mixed and extruded, it is beneficial to appropriately increase the overall specific surface area of ​​the protective catalyst. At the same time, the active metal nickel and nickel salts loaded on the carbon nanotubes are calcined at high temperature, and the active metal components exist simultaneously in the carbon nanotubes and alumina structures, respectively, thereby improving the uniformity and stability of the distribution of the active metal component nickel in the protective catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a comparison of the conversion rate-time curves of methane conversion in Example 1 and Example 8 in combination with the main catalyst;

[0030] Figure 2 This is a comparison chart of the conversion rate-time curves of methane conversion in Examples 1-5 in combination with the main catalyst. DETAILED DESCRIPTION

[0031] The present application is described in further detail below in conjunction with Examples. The following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. In the following examples, if specific conditions are not specified, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The methods used are conventional methods well known in the art unless otherwise specified, and the consumables and reagents used are commercially available unless otherwise specified. Unless otherwise indicated, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention.

[0032] The raw materials used in the examples and comparative examples can all be obtained commercially.

[0033] Example 1

[0034] Example 1 of the present application provides a protected catalyst, which is prepared by the following steps:

[0035] (1) 3.2 g of potassium hydroxide and 0.8 g of carbon nanotubes were added to 16 mL of ultrapure water and stirred thoroughly, then placed in a constant temperature oil bath at 120 °C for evaporation. The remaining solid was transferred to a tubular furnace and heated to 800 °C at a heating rate of 30 °C / min under an argon atmosphere. The temperature was maintained constant and calcined for 1 h. Finally, the calcined product was added to ultrapure water and neutralized by adding 1 mol / L hydrochloric acid dropwise. The product was repeatedly rinsed with ultrapure water until it became neutral, then dried and ground to obtain alkali-treated carbon nanotubes. The alkali-treated carbon nanotubes were placed in a DBD discharge reactor, and oxygen was introduced at a flow rate of 8 mL / min. The output voltage was controlled to be 100 V and the treatment time was 20 min. During the reaction, the alkali-treated carbon nanotubes were stirred evenly three times to obtain plasma-modified carbon nanotubes.

[0036] (2) 5 g of plasma-modified carbon nanotubes, 100 mL of ammonia water (1 mol / L), and 7 mL of nickel chloride solution (0.1 g / mL) were mixed and stirred for 10 h. The mixture was then evaporated in a 60°C constant temperature oil bath for 5 h. The mixture was then dried in an oven at 80°C to obtain a mixed powder. The mixed powder was placed in a tube furnace and calcined at 320°C for 3 h under an argon atmosphere to obtain nickel-loaded carbon nanotubes.

[0037] (3) 10 g of aluminum hydroxide, 2.5 g of nickel-loaded carbon nanotubes, 0.4 g of nickel carbonate and 1 mL of acetic acid solution (4 wt%) were mixed and extruded into a cylindrical mixture, dried at 100 °C for 2 h, and then calcined at 980 °C for 5 h to obtain a protected catalyst.

[0038] In this embodiment, the carbon nanotubes are multi-walled carbon nanotubes with a length of 0.5-2 μm and a diameter of 30-50 nm.

[0039] Example 2

[0040] Example 2 of the present application provides a protected catalyst. The difference between Example 2 and Example 1 is that the nickel-loaded carbon nanotubes used in step (3) of Example 2 are 1.5 g and the nickel carbonate is 0.6 g.

[0041] Example 3

[0042] Example 3 of the present application provides a protected catalyst. The difference between Example 3 and Example 1 is that the nickel-loaded carbon nanotubes used in step (3) of Example 3 are 3.5 g and the nickel carbonate is 0.2 g.

[0043] Example 4

[0044] Example 4 of the present application provides a protected catalyst. The difference between Example 4 and Example 1 is that the nickel chloride solution used in step (2) of Example 4 is 5 mL.

[0045] Example 5

[0046] Example 5 of the present application provides a protected catalyst. The difference between Example 5 and Example 1 is that the nickel chloride solution used in step (2) of Example 5 is 9 mL.

[0047] Example 6

[0048] Example 6 of the present application provides a protective catalyst. The difference between Example 6 and Example 1 is that when plasma treatment is performed in step (1) of Example 6, the treatment time is 25 minutes.

[0049] Example 7

[0050] Example 7 of the present application provides a protective catalyst. The difference between Example 7 and Example 1 is that when plasma treatment is performed in step (1) of Example 7, the treatment time is 15 minutes.

[0051] Example 8

[0052] Example 8 of the present application provides a protected catalyst. The difference between Example 8 and Example 1 is that in step (1) of Example 8, the carbon nanotubes are not subjected to alkali treatment. The carbon nanotubes are placed in a DBD discharge reactor, oxygen is introduced at a flow rate of 8 mL / min, the output voltage is controlled to 100 V, the treatment time is 20 min, and the carbon nanotubes are stirred evenly three times during the reaction to obtain plasma-modified carbon nanotubes.

[0053] Comparative Example 1

[0054] Comparative Example 1 provides a protected catalyst, which is prepared by the following steps: 10 g of aluminum hydroxide, 0.4 g of nickel carbonate and 10 mL of acetic acid solution (4w%) are mixed and extruded into a cylindrical mixture, dried at 100°C for 2 h, and then calcined at 980°C for 5 h to obtain a protected catalyst.

[0055] Comparative Example 2

[0056] Comparative Example 2 provides a protected catalyst, which is prepared by the following steps: 10 g of aluminum hydroxide, 2.5 g of carbon nanotubes, 0.4 g of nickel carbonate and 10 mL of acetic acid solution (4 w %) are mixed and extruded into a cylindrical mixture, dried at 100 ° C for 2 h, and then calcined at 980 ° C for 5 h to obtain a protected catalyst.

[0057] Comparative Example 3

[0058] Comparative Example 3 provides a protected catalyst. The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, only the carbon nanotubes are treated in step (1), and the loading of active metal nickel in step (2) is not performed, and the obtained plasma-modified carbon nanotubes replace the nickel-loaded carbon nanotubes in step (3).

[0059] Comparative Example 4

[0060] Comparative Example 4 provides a protective catalyst. The difference between Comparative Example 4 and Example 1 is that in step (1) of Comparative Example 4, argon is used instead of oxygen for plasma treatment.

[0061] Comparative Example 5

[0062] Comparative Example 5 provides a protective catalyst. The difference between Comparative Example 5 and Example 1 is that in step (1) of Comparative Example 5, hydrogen is used instead of oxygen for plasma treatment.

[0063] Test and Inspection

[0064] (1) Specific surface areas (m2) of the protected catalysts obtained in Examples 1-8 and Comparative Examples 1-5 were measured respectively. 2 / g) and pore volume (cm 3 / g), as shown in Table 1 below.

[0065] Table 1:

[0066] Data Source <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Example 1 534.7 0.76 Example 2 513.4 0.74 Example 3 543.3 0.78 Example 4 526.9 0.74 Example 5 531.5 0.75 Example 6 528.1 0.73 Example 7 521.8 0.76 Example 8 506.6 0.71 Comparative Example 1 317.9 0.48 Comparative Example 2 486.2 0.65 Comparative Example 3 493.5 0.67 Comparative Example 4 508.4 0.71 Comparative Example 5 505.7 0.70

[0067] (2) The protective catalysts of Examples 1-8 and Comparative Examples 1-5 were mixed with the main catalyst HZ204 type protective catalyst (Hubei Huihuang Technology Co., Ltd., with a specific surface area of ​​573.5 m 2 / g) is used in the top of the methane secondary reformer, with a pressure of 3.2MPa, a controlled temperature of 850-960℃, and a space velocity of 3000h -1 , react for 20h. Detect the conversion rate of methane, wherein the conversion rate-time change curve comparison diagram of Example 1 and Example 8 is as follows Figure 1 As shown, the comparison diagram of the conversion rate-time change curve of comparative examples 1-5 is as follows Figure 2 After the reaction was completed, the specific surface areas (m 2 / g), as shown in Table 2 below.

[0068] Table 2:

[0069] Data Source <![CDATA[Specific surface area of the protective catalyst (m 2 / g)]]> <![CDATA[Specific surface area of the main catalyst (m 2 / g)]]> Example 1 533.1 569.8 Example 2 511.5 567.5 Example 3 541.2 566.3 Example 4 525.1 567.8 Example 5 529.6 567.1 Example 6 525.7 566.7 Example 7 519.4 565.6 Example 8 503.2 561.4 Comparative Example 1 261.3 497.9 Comparative Example 2 452.6 522.4 Comparative Example 3 467.9 534.5 Comparative Example 4 489.4 541.7 Comparative Example 5 483.3 543.8

[0070] Result Analysis

[0071] The following combination Figure 1-2 , the data results in Table 1 and Table 2 are used to explain this application in detail.

[0072] Reference Figure 1 and Figure 2When Example 1, Example 8, and Comparative Examples 1-5 were used in conjunction with the main catalyst to convert methane, as the reaction time increased, the methane conversion rate in the system using Comparative Examples 1-5 as the protective catalyst decreased significantly, and the decrease rate reached 3.7-5.9% in 200h, while the methane conversion rate in the system using Example 1 and Example 8 as the protective catalyst decreased by only 0.9-1.2%, and the decrease in conversion rate was less than one-third of the decrease in conversion rate in the comparative example system. This shows that the protective catalysts of Examples 1-8 of the present application are beneficial to improving the catalytic stability of the reaction system when used in conjunction with the main catalyst. The analysis is that, on the one hand, the addition of nickel-loaded carbon nanotubes improves the uniformity of the dispersion of the metal active component in the protective catalyst. At the same time, the nickel-loaded carbon nanotubes are treated with alkali during the preparation process to remove amorphous carbon and impurities, thereby increasing their specific surface area. The oxygen plasma treatment forms oxygen-containing functional groups on the surface of the carbon nanotubes, which enhances the interaction between the metal active component nickel and the carbon nanotubes. Under the combined effect, the binding effect of the carbon nanotubes and the metal active component nickel is improved in terms of binding strength and binding range. On the other hand, the nickel-loaded carbon nanotubes not only play a role in expanding the pores, but also play a structural reinforcement role in protecting the catalyst, improving the ability to resist airflow scour during the reaction process, thereby protecting the main catalyst. Under this combined effect, the loss of active sites caused by the agglomeration of active metal components in the reaction system is reduced, the service life of the main catalyst is extended, and the catalytic stability is improved. The decrease in the conversion rate of the system when Example 1 is combined with the main catalyst is lower than the decrease in the conversion rate of the system when Example 8 is combined with the main catalyst, indicating that the alkali treatment of the carbon nanotubes followed by the oxygen plasma treatment is beneficial to further improve the catalytic stability of the reaction system.

[0073] With reference to Table 1 and Table 2, it can be seen that the specific surface area of ​​the protection catalyst of Example 1-8 is slightly smaller than the specific surface area of ​​the main catalyst used in conjunction with it, which is beneficial to maintaining the stability of the specific surface area of ​​the protection catalyst and protecting the main catalyst under high temperature conditions. At the same time, the specific surface area of ​​the protection catalyst is improved compared to that of the protection catalyst of Comparative Example 1-5, thereby improving the catalytic efficiency of the protection catalyst itself. The specific surface area decrease after the main catalyst of Example 1-8 is converted into methane is much lower than the specific surface area decrease after the main catalyst of Comparative Example 1-5 is converted into methane. Moreover, the specific surface area decrease ratio of the main catalyst matched with Example 1-8 is only 0.41%-1.58%, which is much lower than the specific surface area decrease ratio of the main catalyst matched with Comparative Example 1-5, which is 3.52%-7.39%. This shows that Example 1-8, when used in conjunction with the main catalyst, is beneficial to maintaining the stability of the main catalyst specific surface area, extending the life of the main catalyst, and improving catalytic efficiency. Moreover, the change in specific surface area of ​​the protected catalyst of Example 1-8 is smaller than the change in specific surface area of ​​the protected catalyst of Comparative Example 1-5, and the degree of carbon deposition of the protected catalyst of Example 1-8 is low. The protected catalyst of Example 1-8 of the present application is also beneficial in reducing the degree of carbon deposition of itself and the main catalyst.

[0074] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing a protected catalyst, characterized in that: The following steps are involved: Aluminum hydroxide, nickel-loaded carbon nanotubes, nickel salt and solvent are mixed and extruded, and then calcined at high temperature; the nickel-loaded carbon nanotubes are obtained by subjecting carbon nanotubes to plasma modification to obtain plasma-modified carbon nanotubes, and loading nickel elements on the plasma-modified carbon nanotubes; The plasma modification comprises the following steps: subjecting the carbon nanotubes to an alkali treatment, and then placing the carbon nanotubes in a plasma atmosphere obtained by ionizing an oxidizing gas to obtain plasma-modified carbon nanotubes.

2. The method for preparing a protected catalyst according to claim 1, wherein: The gas flow rate of the plasma modification is 6-9 mL / min, the ionization voltage is 90-110 V, and the treatment time is 15-25 min.

3. The method for preparing a protected catalyst according to claim 1, wherein: The method of loading nickel elements on plasma-modified carbon nanotubes comprises the following steps: uniformly mixing plasma-modified carbon nanotubes, nickel chloride and water, and then evaporating and calcining to obtain nickel-loaded carbon nanotubes.

4. The method for preparing a protected catalyst according to claim 3, wherein: The weight ratio of the plasma-modified carbon nanotubes to the nickel chloride is 50:5-9.

5. The method for preparing a protected catalyst according to claim 3, wherein: The calcination temperature is 300-330° C. and the calcination time is 2-4 hours.

6. The method for preparing a protected catalyst according to claim 1, wherein: The weight ratio of the aluminum hydroxide, nickel-loaded carbon nanotubes and nickel salt is 20:3-7:0.4-1.

2.

7. The method for preparing a protected catalyst according to claim 1, wherein: The high temperature calcination temperature condition is 950-1000° C. and the time is 4.5-6 hours.

8. The method for preparing a protected catalyst according to claim 1, characterized in that: The nickel salt includes one or more of nickel chloride, nickel nitrate, nickel sulfate and nickel carbonate.

9. A protected catalyst, characterized in that: The catalyst is prepared by the method for preparing a protected catalyst according to any one of claims 1 to 8.

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