A method for preparing an ultrathin sheet nickel silicate catalyst by a wet ball milling method

Abstract

The present invention discloses a method for preparing an ultrathin sheet nickel silicate catalyst by a wet ball milling method, belonging to the technical field of inorganic nanomaterial preparation. In the present invention, a certain proportion of soluble nickel salt (nickel source), silicon oxide material (silicon source), as well as a certain amount of fluorine-containing etching agent and alkaline substance are added to a ball milling tank. By adjusting parameters such as ball milling process parameters and ball-to-material ratio, an ultrathin sheet nickel silicate catalyst with high dispersion and stable structure is synthesized at room temperature. Compared with the catalysts prepared by traditional hydrothermal method and ammonia evaporation method, the preparation method of the present invention is green and environmentally friendly, the preparation conditions are mild, the preparation period is shorter, and the catalyst has better catalytic activity.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic nanomaterial preparation, and specifically relates to a method for preparing an ultrathin layered nickel silicate catalyst by a wet ball milling method. Background Art

[0002] Nickel silicate has been widely used in many technical fields such as catalysis, batteries, optoelectronic materials, and energy storage due to its advantages of regular and ordered lamellar structure, high specific surface area, and excellent surface and interface confinement effects. Currently, the methods for preparing nickel silicate mainly include hydrothermal method, ammonia evaporation method, and neutral hydrolysis precipitation method. Among them, when preparing nickel silicate by the traditional hydrothermal method, there are often disadvantages such as high hydrothermal reaction temperature (>150 °C) and long hydrothermal time (>16 h) (CN 111017940 A). Below these harsh hydrothermal conditions, it is difficult to synthesize nickel silicate catalyst by the hydrothermal method. Therefore, the improved hydrothermal method can reduce the requirements of reaction conditions, but still needs to be realized under hydrothermal conditions above 100 °C and longer than 12 h (CN 113600247 A). On the other hand, although the preparation conditions of the ammonia evaporation method (80 °C) are much milder than those of the hydrothermal method, the volatilization of ammonia will cause certain health hazards and environmental impacts on operators. In addition, the addition amount of ammonia water needs to be strictly controlled. If too much ammonia water is added, the alkalinity is too strong and the silica material is damaged too much, and the pore structure is seriously damaged; if too little ammonia water is added, nickel hydroxide will be generated instead of the target substance, nickel silicate. Therefore, the process of preparing nickel silicate by the ammonia evaporation method is cumbersome and has certain safety hazards. On the other hand, nickel silicate prepared by the hydrothermal method and the ammonia evaporation method has a common disadvantage: the prepared nickel silicate sheets are relatively thick (>30 nm), resulting in a low metal utilization rate of the catalyst. Similar to the ammonia evaporation method, the neutral hydrolysis precipitation method (Chemical Engineering Journal 313 (2017) 759–768) also needs to synthesize nickel silicate at a temperature of 80 °C. In addition, this method needs to strictly control the pH of the solution within the range of 7-7.5 during the synthesis process, and still needs to stir vigorously for 18 hours after precipitation. Therefore, this method is still cumbersome and the whole process takes too long. In addition, based on the layered structure of nickel silicate, the thickness of nickel silicate has a certain influence on the utilization rate of metal Ni. Generally, if the layer thickness decreases, Ni atoms will be completely exposed and participate in the reaction. Therefore, it is necessary to study how to obtain nickel silicate nanosheets with a lower thickness at a higher Ni content. Summary of the Invention

[0003] In order to overcome the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing an ultrathin layered nickel silicate catalyst by a wet ball milling method, which solves the problems of high reaction temperature and long reaction time in the synthesis of layered nickel silicate by the existing hydrothermal method. The wet ball milling method has mild conditions (room temperature, atmospheric pressure), is green and environmentally friendly without pollution, has a shorter preparation period (only two hours), and can prepare an ultrathin layered nickel silicate catalyst with higher catalytic performance.

[0004] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A method for preparing an ultrathin layered nickel silicate catalyst by a wet ball milling method, adding a water-soluble nickel salt, a fluorine-containing etching agent and an alkaline substance to deionized water, then adding a silica material, transferring it to a ball milling tank, and ball milling at room temperature and atmospheric pressure. After the ball milling is completed, the ball-material mixture is washed, centrifuged, dried, and calcined to obtain ultrathin layered nickel silicate.

[0006] Specifically, the ball milling speed is 200 - 400 revolutions per minute, the ball milling time is 2 - 10 hours, and the ball-to-material ratio is 10:1 - 20:1. Preferably, the ball milling speed is 400 revolutions per minute and the ball milling time is 6 hours.

[0007] Specifically, the ball-material mixture is washed, centrifuged, dried, and calcined in an air atmosphere at 400 - 600 °C for 2 - 6 hours to obtain layered nickel silicate.

[0008] Specifically, 8 - 16 mmol of a water-soluble nickel salt, 110 - 130 mmol of a fluorine-containing etching agent and 65 - 85 mol of an alkaline substance are added to 13 - 23 mL of deionized water, and then 30 - 50 mmol of a silica material is added.

[0009] In order to better achieve the exfoliation effect, formamide can also be added during the ball milling process, and the addition amount of formamide is 90 - 110 mmol.

[0010] Furthermore, the water-soluble nickel salt includes but is not limited to one or a mixture of more than one of nickel nitrate, nickel chloride, nickel acetylacetonate, nickel acetate or their hydrates.

[0011] Furthermore, the fluorine-containing etching agent includes but is not limited to one or a mixture of more than one of fluosilicic acid, fluoroboric acid, nonafluoropentanoic acid, ammonium fluoride; the alkaline substance includes but is not limited to one or a mixture of more than one of hexamethylenetetramine, formamide, ammonium carbonate, urea.

[0012] Furthermore, the silica material is a material containing silica, and can be one of artificial synthetic mesoporous silica materials, biomass-based silica, and other commercially available amorphous silica.

[0013] The ultrathin layered nickel silicate catalyst prepared by the wet ball milling method is used for CO 2 methanation, CO methanation reaction, CO 2 -CH 4 dry reforming to synthesize syngas, and the preparation of carbon nanotubes.

[0014] It should be noted that although the ball milling method is carried out under room temperature conditions, during the high-speed rotation of the ball mill, a very high temperature and pressure are generated at the moment of friction between the grinding balls, and the formation of layered nickel silicate occurs under such instantaneously generated high temperature and high pressure conditions. In addition, the ball milling method is an effective method for exfoliating layered materials. The mechanical force generated by the friction between the grinding balls forces the lamellae to slide relative to each other, thereby breaking the interlayer force and finally obtaining ultrathin layered nickel silicate.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with the reported methods for preparing layered nickel silicate, the preparation conditions of this invention are milder: layered nickel silicate can be synthesized at room temperature and atmospheric pressure; (2) Compared with other methods, the preparation period is shorter: only 2 hours, in sharp contrast to the hydrothermal time of up to 24 hours for the hydrothermal method; (3) The obtained sample has a small thickness and high activity: this method uses the simple ball milling method to prepare layered nickel silicate and also utilizes the ball milling method to exfoliate relatively thick layered nickel silicate sheets to obtain ultrathin layered nickel silicate, greatly improving the metal utilization rate and catalytic performance; (4) The preparation process is more environmentally friendly and there is no waste gas: compared with the ammonia evaporation method and the neutral hydrolysis precipitation method, this method does not produce 3 this toxic and harmful gas; (5) The product has high crystallinity: compared with the ammonia evaporation method and the neutral hydrolysis precipitation method, the sample prepared by this method has higher crystallinity; (6) The preparation is simple, no precision instruments are required, and it is easy to mass-produce: compared with the precision instrument hydrothermal autoclave (expensive and low synthesis efficiency) used in the hydrothermal method, this method only requires a ball mill to mass-produce on a large scale.

[0016] Table 1 shows the conditions required for different preparation methods of layered nickel silicate.

[0017] Brief Description of the Drawings

[0018] Figure 1 XRD pattern of NiPs-BM-400-6 obtained in Example 1.

[0019] Figure 2 SEM image of NiPs-BM-400-6 obtained in Example 1.

[0020] Figure 3 TEM image of the layered nickel silicate obtained by reducing NiPs-BM-400-6 obtained in Example 1 with hydrogen.

[0021] Figure 4 The NiPs-BM-400-6 prepared in Example 1, the NiPs-DA prepared in Comparative Example 1, and the NiPs-HT prepared in Comparative Example 2 were used for CO 2 methanation in terms of carbon dioxide conversion (a), methane selectivity (b), and methane yield (c).

[0022] Figure 5 The NiPs-BM-400-6 prepared in Example 1 and the NiPs-BM-400-6-F prepared in Example 2 were used for CO 2 methanation in terms of carbon dioxide conversion (a), methane selectivity (b), and methane yield (c).

[0023] Figure 6 The ultrathin nickel silicate prepared with different ball milling times in Example 1 was used for CO 2 methanation in terms of carbon dioxide conversion (a), methane selectivity (b), and methane yield (c).

[0024] Figure 7 The ultrathin nickel silicate prepared with different ball milling speeds in Example 1 was used for CO 2 methanation in terms of carbon dioxide conversion (a), methane selectivity (b), and methane yield (c).

[0025] Figure 8 The AFM images of the NiPs-BM-400-6 obtained in Example 1 and the NiPs-HT prepared in Comparative Example 2. Detailed implementation manners

[0026] The technical solution of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0027] Example 1

[0028] 12 mmol of nickel nitrate, 118.9 mmol of ammonium fluoride, and 75 mmol of urea were weighed and dissolved in 18 mL of deionized water. 40 mmol of silica was stirred evenly and dispersed in the above solution, and then transferred to a ball milling jar. 180 g of ZrO 2 balls were added and ball milled at a certain speed for a certain time. Finally, it was washed with deionized water, centrifuged, dried at 60 °C, and finally calcined in an air atmosphere at 400 °C for 2 hours to obtain ultrathin nickel silicate, denoted as NiPs-BM-ball milling speed-ball milling time. During the experiment, the ball milling speeds were 200, 400, and 600 revolutions per minute respectively, and the ball milling times were 2, 6, and 10 hours respectively.

[0029] Figure 1XRD pattern of NiPs-BM-400-6 obtained in Example 1, and the result proves that the sample is nickel phyllosilicate.

[0030] Figure 2 SEM image of NiPs-BM-400-6 obtained in Example 1. The SEM image shows that flaky substances are attached to the nanoblock, which is a typical morphology of nickel phyllosilicate.

[0031] Figure 3 TEM image of nickel phyllosilicate after hydrogen reduction of NiPs-BM-400-6 obtained in Example 1, showing that the nickel particle size after reduction of nickel phyllosilicate is very small and highly dispersed.

[0032] Example 2

[0033] Weigh 12 mmol of nickel nitrate, 118.9 mmol of ammonium fluoride, 75 mmol of urea and 99.7 mmol of formamide and dissolve them in 18 mL of deionized water. Stir 40 mmol of silica evenly and disperse it in the above solution, then transfer it to a ball milling tank, add 180 g of ZrO 2 balls, and ball mill for 6 hours at a condition of 400 revolutions per minute. Finally, wash with deionized water, centrifuge, dry at 60 °C, and finally calcine in an air atmosphere at 400 °C for 2 hours to obtain ultrathin nickel phyllosilicate, denoted as NiPs-BM-400-6-F.

[0034] Example 3

[0035] Weigh 8 mmol of nickel nitrate, 110 mmol of ammonium fluoride and 65 mmol of urea and dissolve them in 13 mL of deionized water. Stir 30 mmol of silica evenly and disperse it in the above solution, then transfer it to a ball milling tank, add 180 g of ZrO 2 balls, and ball mill for 6 hours at a condition of 400 revolutions per minute. Finally, wash with deionized water, centrifuge, dry at 60 °C, and finally calcine in an air atmosphere at 400 °C for 2 hours to obtain ultrathin nickel phyllosilicate.

[0036] Example 4

[0037] Weigh 16 mmol of nickel nitrate, 130 mmol of ammonium fluoride and 85 mmol of urea and dissolve them in 23 mL of deionized water. Stir 50 mmol of silica evenly and disperse it in the above solution, then transfer it to a ball milling tank, add 180 g of ZrO 2 balls, and ball mill for 6 hours at a condition of 400 revolutions per minute. Finally, wash with deionized water, centrifuge, dry at 60 °C, and finally calcine in an air atmosphere at 400 °C for 2 hours to obtain ultrathin nickel phyllosilicate.

[0038] Comparative Example 1 (Double Accelerator Hydrothermal Method)

[0039] Weigh 12 mmol of nickel nitrate, 118.9 mmol of ammonium fluoride and 75 mmol of urea and dissolve them in 50 mL of deionized water. Stir 40 mmol of silica evenly and disperse it in the above solution, then transfer it to an autoclave and carry out hydrothermal reaction at 120 °C for 12 h. Finally, wash with deionized water, centrifuge, dry at 60 °C, and finally calcine in an air atmosphere at 400 °C for 2 h to obtain nickel phyllosilicate, denoted as NiPs-DA.

[0040] Comparative Example 2 (Traditional Hydrothermal Method)

[0041] Weigh 12 mmol of nickel nitrate and dissolve it in 50 mL of deionized water. Stir 40 mmol of silica evenly and disperse it in the above solution, then transfer it to an autoclave and carry out hydrothermal reaction at 200 °C for 24 h. Finally, wash with deionized water, centrifuge, dry at 60 °C, and finally calcine in an air atmosphere at 400 °C for 2 h to obtain nickel phyllosilicate, denoted as NiPs-HT.

[0042] Catalyst performance evaluation

[0043] The nickel phyllosilicates prepared in Example 1, 2 and Comparative Example 1 were used as catalysts for CO 2 methanation. The specific process was as follows: Mix 5.0 g of quartz sand (20 - 40 mesh) and 0.1 g of reduced catalyst (20 - 40 mesh), and place them in the quartz tube of a fixed-bed reactor. Then, first heat the fixed-bed to 400 °C in a pure H 2 atmosphere (100 mL / min) and reduce for 30 min (reduce the NiO oxidized by air), and then cool to the starting reaction temperature (300 °C) in a H 2 flow. Then introduce the reaction gas into the reactor and investigate the catalytic activity of the catalyst within 300 - 550 °C. During the test process, the space velocity was 60,000 mL / h·g, and the inlet and outlet gases were analyzed online by Micro GC 7820. Two chromatographic columns were equipped with two TCD detectors. The concentrations of H 2 , N 2 , CH 4 and CO in the gas products were detected by the TCD detector with a molecular sieve column, while the concentration of CO 2 was analyzed by another TCD with a Plot Q column.

[0044] From Figure 4 it can be seen that the carbon dioxide conversion rate, methane selectivity and methane yield of NiPs-BM-400-6 are all higher than those of NiPs-DA and NiPs-HT prepared under the same conditions.

[0045] From Figure 5It can be understood that formamide can improve the catalytic activity of the catalyst to a certain extent.

[0046] From Figure 6 and 7 It can be understood that the preferred ball milling time is 6 hours and the ball milling speed is 400 rpm.

[0047] From Figure 8 It can be understood that the thickness of nickel metasilicate obtained from NiPs-BM-400-6 is less than that of NiPs-HT. In addition, based on the ICP detection of the product, the Ni content in NiPs-BM-400-6 is 23.86 wt%, the Ni content in NiPs-DA is 21.74 wt%, and the Ni content in NiPs-HT is 6.97 wt%. The Ni content in NiPs-BM-400-6 is higher than that in NiPs-DA and NiPs-HT. Since its nanosheets are thinner, more Ni species exist on the surface rather than in the bulk phase. The Ni atoms on the surface are more likely to contact and participate in the reaction with the reactants, further improving the utilization rate of the metal and thus promoting the progress of the reaction.

[0048] The catalytic performance of Example 1 and Comparative Examples 1 and 2 was tested, and the CO methanation reaction was selected as the model reaction. 0.1 g of the catalyst with a particle size of 20 - 40 mesh was loaded into a quartz reaction tube. After reduction with hydrogen at 700 °C, the reaction feed gas H 2 :CO:N 2 (volume flow rate ratio of 3:1:1) was introduced for the reaction. The reaction pressure was atmospheric pressure, the mass space velocity was 60000 mL / h·g, and the reaction temperature was 400 °C.

[0049] Table 2 shows the CO conversion rate and CH 4 yield of the catalysts in Example 1 and Comparative Examples 1 and 2 in the CO methanation reaction.

[0050] Serial Number CO Conversion Rate (%) <![CDATA[CH 4 Selectivity (%)]]> <![CDATA[CH 4 Yield (%)]]> Example 1 88 93 82 Comparative Example 1 76 85 65 Comparative Example 2 80 87 70

[0051] The catalytic performance of Example 1 and Comparative Examples 1 and 2 was tested, and CO 2 -CH 4 dry reforming to syngas reaction was selected as the model reaction. 0.1 g of the catalyst with a particle size of 20 - 40 mesh was loaded into a quartz reaction tube. After reduction with hydrogen at 700 °C, the reaction feed gas CO 2 :CO 2 :N 2 (volume flow rate ratio of 3:3:14) was introduced for the reaction. The reaction pressure was atmospheric pressure, the mass space velocity was 60000 mL / h·g, and the reaction temperature was 700 °C.

[0052] Table 3 shows the CO 2 -CH4 CO in the dry reforming syngas reaction 2 conversion rate, CH 4 conversion rate H 2 / CO ratio.

[0053] Serial Number <![CDATA[CO 2 Conversion rate (%)]]> <![CDATA[CH 4 Conversion rate (%)]]> <![CDATA[H 2 / CO ratio]]> Example 1 68 85 1.6 Comparative Example 1 52 71 1.6 Comparative Example 2 56 75 1.6

[0054] Catalytic performance tests were carried out on Example 1 and Comparative Examples 1 and 2, and the carbon nanotube growth reaction was selected as the model reaction. The growth of carbon nanotubes was carried out using an atmospheric pressure CVD apparatus. 1 g of the catalyst powder prepared above and reduced under hydrogen at 700 °C was placed in the CVD reaction furnace. After sealing both ends, 500 sccm of argon was introduced to discharge the air, and then 300 sccm of CO gas was introduced. The growth of carbon nanotubes was carried out at 900 °C for 30 minutes. After the growth was completed, the introduction of CO gas was stopped. After the temperature was lowered to room temperature under an argon atmosphere, the sample was taken out.

[0055] Table 4 shows the mass of carbon nanotubes produced by the catalysts in Example 1 and Comparative Examples 1 and 2 in the carbon nanotube growth reaction.

Claims

1. A method for preparing an ultrathin sheet nickel silicate catalyst by a wet ball milling method, characterized in that, a water-soluble nickel salt, a fluorine-containing etching agent and an alkaline substance are added to deionized water, then a silica material is added, and the mixture is transferred to a ball milling tank and ball milled at normal temperature and pressure. After the ball milling is completed, the ball-material mixture is washed, centrifuged, dried and calcined to obtain ultrathin sheet nickel silicate.

2. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 1, characterized in that, the ball milling speed is 200 - 400 revolutions per minute, the ball milling time is 2 - 10 hours, and the ball-to-material ratio is 10:1 - 20:

1.

3. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 1, characterized in that, the ball milling speed is 400 revolutions per minute and the ball milling time is 6 hours.

4. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 1, characterized in that, the ball-material mixture is washed, centrifuged and dried, and then calcined in an air atmosphere at 400 - 600 °C for 2 - 6 hours to obtain nickel silicate sheets.

5. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 1, characterized in that, 8 - 16 mmol of a water-soluble nickel salt, 110 - 130 mmol of a fluorine-containing etching agent and 65 - 85 mol of an alkaline substance are added to 13 - 23 mL of deionized water, and then 30 - 50 mmol of a silica material is added.

6. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 5, characterized in that, 90 - 110 mmol of formamide is added during the ball milling process.

7. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 5, characterized in that, the water-soluble nickel salt is one or a mixture of more than one of nickel nitrate, nickel chloride, nickel acetylacetonate, nickel acetate or their hydrates.

8. The method for preparing an ultrathin sheet nickel silicate catalyst by the wet ball milling method according to claim 1, characterized in that, the fluorine-containing etching agent is one or a mixture of more than one of fluosilicic acid, fluoroboric acid, nonafluoropentanoic acid, ammonium fluoride; the alkaline substance is one or a mixture of more than one of hexamethylenetetramine, formamide, ammonium carbonate, urea.

9. The ultrathin sheet nickel silicate catalyst prepared by the method according to any one of claims 1 - 8.

10. The ultrathin nickel silicate catalyst prepared according to claim 9 is used for CO 2 methanation, CO methanation reaction, CO 2 -CH 4 dry reforming to produce syngas, and the preparation of carbon nanotubes.

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