A silica-supported nickel-based catalyst, its preparation method and application

Abstract

The present invention provides a silica-supported nickel-based catalyst, its preparation method and application. The silica-supported nickel-based catalyst includes hydrophilic fumed silica with a specific surface area of 300-500 m2 / g; nickel particles distributed on the surface of the hydrophilic fumed silica; the size of the nickel particles is 3-5 nm. In the present invention, the precursor salt of Ni is added to deionized water and dissolved with the assistance of ultrasonic dispersion. The above solution is added to the silica solid in portions, and stirred until a silica gel is formed. After drying the gel, it is reduced. The catalyst preparation method provided by the present invention obtains Ni particles with a relatively small particle size, and the preparation method is simple and easy to scale up. The catalyst prepared by this method is applied to the dry reforming reaction of methane and carbon dioxide, and shows very stable catalytic performance under the reaction conditions of high space velocity (100-300 L / gcat / h).

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a silica-supported nickel-based catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the gradual strengthening of people's understanding of the greenhouse effect, the capture and utilization of the two main greenhouse gases, methane and carbon dioxide, have attracted increasing attention. Among them, directly converting the two greenhouse gases, carbon dioxide and methane, into syngas through the methane dry reforming process at high temperature is an effective and economical method, which has received great attention. Compared with the methane steam reforming reaction, the ratio of H2 and CO in the syngas obtained from the methane carbon dioxide dry reforming reaction is close to 1, and it can be used as the feed gas for Fischer-Tropsch synthesis of long-chain olefins.

[0003] Currently, the catalysts for catalyzing the methane dry reforming reaction are mainly divided into two types, noble metal-based, such as Rh and Ru, and non-noble metal-based catalysts, such as Ni. Noble metal catalysts have high reaction activity, but due to their high cost, they are not conducive to large-scale promotion and use, and face the problems of carbon deposition and metal sintering leading to catalyst deactivation. Although non-noble metal-based catalysts also face problems such as carbon deposition and sintering, due to their low price, they still have good prospects in the industrial application of the methane dry reforming reaction. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a silica-supported nickel-based catalyst, a preparation method thereof, and an application thereof, and the catalyst has good anti-sintering property, high activity and high stability.

[0005] The present invention provides a silica-supported nickel-based catalyst, including hydrophilic fumed silica with a specific surface area of 300-500 m 2 / g;

[0006] Nickel particles distributed on the surface of the hydrophilic fumed silica; the size of the nickel particles is 3-5 nm.

[0007] In the present invention, the nickel particles account for 0.5-10% of the mass of the silica-supported nickel-based catalyst loaded with the hydrophilic fumed silica.

[0008] The present invention provides a preparation method of the silica-supported nickel-based catalyst according to the above technical solution, including the following steps:

[0009] Mix a nickel precursor salt and water, and dissolve it with ultrasonic assistance to obtain a mixed solution;

[0010] Add the mixed solution to solid hydrophilic fumed silica in portions, and stir while adding until a gel is formed;

[0011] The gel is dried at 60-100 °C to obtain a silica-supported nickel-based catalyst.

[0012] The method provided by the present invention is simple, low in cost and easy to realize industrialization.

[0013] In the present invention, a precursor salt of nickel and water are mixed and dissolved with ultrasonic assistance to obtain a mixed solution. In the present invention, the precursor salt of nickel is selected from nickel nitrate or nickel chloride.

[0014] After obtaining the mixed solution, the present invention adds the mixed solution to solid hydrophilic fumed silica in portions while stirring until a gel is formed. In the present invention, the silica is hydrophilic silica. The mixed solution is added to the solid hydrophilic fumed silica in 1-5 portions.

[0015] In the present invention, the mass ratio of the hydrophilic fumed silica, water and the precursor salt of nickel is 1:1-4:0.005-0.1.

[0016] The gel is dried at 60-100 °C to obtain a silica-supported nickel-based catalyst.

[0017] In a specific embodiment, the gel is dried at 80 °C; the drying time is 10-15 h; in a specific embodiment, drying overnight is sufficient.

[0018] The present invention provides a method for preparing syngas, comprising the following steps:

[0019] The raw material gas is subjected to dry reforming reaction in the presence of the silica-supported nickel-based catalyst described in the above technical solution to obtain syngas;

[0020] The raw material gas comprises methane, carbon dioxide and nitrogen with a volume ratio of 2:2:1.

[0021] In the present invention, before the silica-supported nickel-based catalyst catalyzes the dry reforming reaction, it is first reduced at 780-820 °C for 100-140 min; in a specific embodiment, it is first reduced at 800 °C for 60 min.

[0022] In the present invention, the temperature of the dry reforming reaction is 750 °C; the flow rate of the raw material gas is 50-150 sccm; the mass of the silica-supported nickel-based catalyst is 9-30 mg.

[0023] The evaluation process of the reaction performance of the catalyst in the present invention is as follows:

[0024] It was heated to 800 °C at a rate of 10 °C / min in H2 with a flow rate of 40 mL / min and reduced at atmospheric pressure for 1 h. The temperature was changed to 750 °C, and a certain flow rate of CH4 / CO2 / N2 (volume fraction 2 / 2 / 1) was introduced for continuous reaction at atmospheric pressure. Among them, N2 was used as an internal standard gas to calculate the conversion rates of CH4 and CO2. The products were analyzed online at atmospheric pressure after passing through a cold trap and analyzed by a gas chromatograph equipped with a TCD. The chromatographic conditions were a 5A molecular sieve packed column and a capillary packed column (50 m).

[0025] The present invention provides a silica-supported nickel-based catalyst, including hydrophilic fumed silica with a specific surface area of 300 - 500 m 2 / g; nickel particles distributed on the surface of the hydrophilic fumed silica; the size of the nickel particles is 3 - 5 nm. After the above nickel-based catalyst is reduced at 800 °C for 1 h, the size of the nickel particles is 3 - 5 nm, and no nickel particles with larger sizes appear, showing good anti-sintering performance. In addition, this catalyst has high activity and high stability under high space velocity conditions (200 - 300 L / g cat / h) in the dry reforming of methane reaction. Description of the Drawings

[0026] Figure 1 Performance of the Ni / SiO2 catalyst prepared in Examples 1 - 3 of the present invention in the dry reforming of methane reaction;

[0027] Figure 2 Electron micrograph of the Ni / SiO2 catalyst prepared in Example 1 of the present invention after being reduced in hydrogen at 800 °C for 1 h. Detailed Description of the Invention

[0028] In order to further illustrate the present invention, the following examples are used to describe in detail a silica-supported nickel-based catalyst provided by the present invention, its preparation method and application, but they cannot be understood as limiting the protection scope of the present invention.

[0029] The specific surface area of the silica used in the following cases is 300 - 500 m 2 / g.

[0030] Example 1

[0031] 74.4 mg of Ni(NO3)2·6H2O was weighed and added to 1 mL of deionized water, and ultrasonic assistance was used for dissolution to obtain an aqueous nickel nitrate solution. 500 mg of hydrophilic fumed silica was weighed, and the obtained aqueous nickel nitrate solution was added to the hydrophilic fumed silica in 4 portions, while adding and stirring until a gel was formed. After the above gel was air-dried overnight, it was transferred to an oven at 80 °C and dried overnight to obtain a silica-supported nickel-based catalyst.

[0032] Take 30 mg of the above catalyst and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm, and the corresponding space velocity is 100 L / g cat / h. The specific evaluation results are shown in Figure 1 .

[0033] Example 2

[0034] Take 30 mg of the catalyst prepared in Example 1 and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 100 sccm, and the corresponding space velocity is 200 L / g cat / h. The specific evaluation results are shown in Figure 1 .

[0035] Example 3

[0036] Take 30 mg of the catalyst prepared in Example 1 and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 150 sccm, and the corresponding space velocity is 300 L / g cat / h. The specific evaluation results are shown in Figure 1 .

[0037] It can be seen from Figure 1 that when the space velocity of the catalytic reaction gradually increases from 100 L / g cat / h to 300 L / g cat / h, the conversion rate of methane and the hydrogen-carbon ratio decrease accordingly. However, even at a space velocity of 300 L / g cat / h, Example 3 still shows very stable catalytic performance, and the methane conversion rate and the hydrogen-carbon ratio even show an upward trend. The above results prove that the prepared catalyst still has high activity and stability even under relatively large space velocity conditions.

[0038] Example 4

[0039] Take 9 mg of the catalyst prepared in Example 1 and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm. The specific results are shown in Table 1.

[0040] Example 5

[0041] Weigh 12.4 mg of Ni(NO3)2·6H2O and add it to 1 mL of deionized water. Dissolve it with ultrasonic assistance to obtain an aqueous nickel nitrate solution. Weigh 500 mg of hydrophilic fumed silica, and add the obtained aqueous nickel nitrate solution to the hydrophilic fumed silica in 4 portions while stirring until a gel is formed. After air-drying the above gel overnight, transfer it to an oven at 80 °C and dry it overnight to obtain a silica-supported nickel-based catalyst.

[0042] Take out 54 mg of the catalyst and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm. The specific results are shown in Table 1.

[0043] Example 6

[0044] Weigh 248 mg of Ni(NO3)2·6H2O and add it to 1 mL of deionized water. Dissolve it with ultrasonic assistance to obtain an aqueous nickel nitrate solution. Weigh 500 mg of hydrophilic fumed silica, and add the obtained aqueous nickel nitrate solution to the hydrophilic fumed silica in 4 portions while stirring until a gel is formed. After air-drying the above gel overnight, transfer it to an oven at 80 °C and dry it overnight to obtain a silica-supported nickel-based catalyst.

[0045] Take out 2.7 mg of the catalyst and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm. The specific results are shown in Table 1.

[0046] Comparative Example 1

[0047] Weigh 74.4 mg of Ni(NO3)2·6H2O and add it to 1 mL of ethanol. Dissolve it with ultrasonic assistance to obtain an ethanol solution of nickel nitrate. Weigh 500 mg of hydrophobic fumed silica, and add the obtained ethanol solution of nickel nitrate to the hydrophobic fumed silica in 4 portions while stirring until a gel is formed. After air-drying the above gel overnight, transfer it to an oven at 80 °C and dry it overnight.

[0048] Take out 30 mg of the catalyst and place it in a fixed-bed reactor. After reducing it at 800 °C in hydrogen for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm. The specific results are shown in Table 2.

[0049] Comparative Example 2

[0050] Take 30 mg of the catalyst and place it in a fixed-bed reactor. After reducing it in hydrogen at 800 °C for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 100 sccm. The specific results are shown in Table 2.

[0051] Comparative Example 3

[0052] Weigh 60.8 mg of NiCl2·6H2O and add it to 1 mL of deionized water. Dissolve it with ultrasonic assistance to obtain an aqueous nickel nitrate solution. Weigh 500 mg of hydrophilic fumed silica, and add the obtained aqueous nickel chloride solution to the hydrophilic fumed silica in 4 portions. Stir while adding until a gel is formed. After drying the above gel overnight, transfer it to an oven at 80 °C and dry it overnight.

[0053] Take 9 mg of the catalyst and place it in a fixed-bed reactor. After reducing it in hydrogen at 800 °C for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm. The specific results are shown in Table 1.

[0054] Comparative Example 4

[0055] Take out a part of the catalyst prepared in Example 5 and calcine the catalyst at 550 °C for 3 h.

[0056] Take 54 mg of the catalyst and place it in a fixed-bed reactor. After reducing it in hydrogen at 800 °C for 1 h, evaluate the performance of the dry reforming of methane. Evaluation conditions: reaction temperature is 750 °C, reaction gas flow rate is 50 sccm. The specific results are shown in Table 3.

[0057] Table 1 Catalyst performance evaluation results of Examples 4-6 and Comparative Example 3

[0058]

[0059] Table 2 Catalyst performance evaluation results of Examples 1-2 and Comparative Examples 1-2

[0060]

[0061] Table 3 Catalyst catalytic performance evaluation results of Example 5 and Comparative Example 4

[0062]

[0063] As can be seen from Table 1, by only changing the variable of the Ni loading amount, the stability of the catalyst shows obvious differences. When the Ni loading amount is the lowest (0.5 wt%), and at the same time the mass of the added catalyst is the highest, the catalyst shows the best stability. When the Ni loading amount is the highest, 10 wt%, and the amount of the added catalyst is the least, both the catalytic activity and stability of the catalyst are the worst.

[0064] As can be seen from Table 2, under the same reaction conditions, the activities and stabilities of the nickel catalysts supported on hydrophobic silica in Comparative Examples 1-2 are worse than those of the catalysts of hydrophilic silica in Examples 1-2.

[0065] As can be seen from Table 3, the activity of the catalyst after calcination decreases, which may be due to the growth of Ni particles during the calcination process and the reduction of exposed active sites.

[0066] As can be seen from the above examples, the catalyst of the present invention is prepared by an impregnation method without adding other additives. The method is simple and easy to industrialize. The active metal in the catalyst prepared by this method is highly dispersed and has high activity and high stability under high space velocity conditions (200-300 L / g cat / h) in the dry reforming of methane.

[0067] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing syngas, comprising the following steps: Carrying out dry reforming reaction on the raw material gas in the presence of a silica-supported nickel-based catalyst to obtain syngas; The raw material gas comprises methane, carbon dioxide and nitrogen with a volume ratio of 2:2:1; Before the silica-supported nickel-based catalyst catalyzes the dry reforming reaction, it is first reduced at 780-820 °C for 40-80 min; The temperature of the dry reforming reaction is 750 °C; the flow rate of the raw material gas is 50-150 sccm; The preparation method of the silica-supported nickel-based catalyst consists of the following steps: Mixing a nickel precursor salt and water, and ultrasonically assisting dissolution to obtain a mixed solution; the mass ratio of hydrophilic fumed silica, water and nickel precursor salt is 1:1-4:0.005-0.1; the nickel precursor salt is selected from nickel nitrate; Adding the mixed solution to the solid hydrophilic fumed silica in 4-5 times, stirring while adding until a gel is formed; Drying the gel at 60-100 °C for 10-15 h to obtain the silica-supported nickel-based catalyst; The silica-supported nickel-based catalyst includes hydrophilic fumed silica with a specific surface area of 300 to 500 m 2 / g; Nickel particles distributed on the surface of the hydrophilic fumed silica; the size of the nickel particles is 3-5 nm; The nickel particles account for 0.5-3% of the mass of the silica-supported nickel-based catalyst.

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