A method for synthesizing layered nickel silicate by using oleylamine assisted impregnation method and application thereof in preparation of nickel-based catalyst

Abstract

The application belongs to the field of layered nickel silicate synthesis, and discloses a method for synthesizing layered nickel silicate by using an oleylamine assisted impregnation method and application of the method in preparation of a high-activity and high-stability nickel-based catalyst. The preparation method of the nickel-based catalyst comprises the following steps: uniformly mixing nickel nitrate hexahydrate and oleylamine in water, then adding silica gel for impregnation, stirring to form a paste, drying in an oven, and then heating and calcining under air condition to obtain layered nickel silicate; and then reducing by hydrogen to obtain a high-activity and high-stability nickel-based catalyst. The oleylamine assisted impregnation method is used for synthesizing layered nickel silicate, which is used as a precursor for synthesizing high-dispersion and high-stability layered nickel silicate (silicon dioxide) supported nickel nanoparticles, and the nickel nanoparticles have high activity and long service life for high-temperature methane dry reforming reaction.

Description

Technical Field

[0001] This invention belongs to the field of layered nickel silicate synthesis, and specifically relates to a method for synthesizing layered nickel silicate using oleylamine-assisted impregnation and its application in the preparation of highly active and stable nickel-based catalysts. Background Technology

[0002] Layered nickel silicate, as a precursor formed by the reaction of nickel salts or oxides with mesoporous silica, can be decomposed into highly dispersed nickel nanoparticles with strong binding force to silica, exhibiting excellent catalytic performance in high-temperature industrial catalysis. Hydrothermal methods (MVSivaiah, S. Petit, J. Barrault, C. Batiot-Dupeyrat, S. Valange, Catal. Today, 2010, 157, 397.) and precipitation methods (HCLiu, H. Wang, JHShen, Y. Sun, ZMLiu, Appl. Catal. A: Gen., 2008, 337, 138.) have been used to prepare layered nickel silicate. However, the hydrothermal method requires washing after hydrothermal treatment to remove impurity ions, making the process cumbersome and resulting in significant waste discharge. The precipitation method requires multiple mixing steps and generates substantial waste liquid. Furthermore, the impregnation method, despite being relatively simple, has rarely been reported for the preparation of layered nickel silicate. Summary of the Invention

[0003] To overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for synthesizing layered nickel silicate using an oleylamine-assisted impregnation method. Compared to existing hydrothermal, deposition, and impregnation methods, this method is simpler, easier to operate, produces less waste liquid, and has the potential for large-scale industrialization.

[0004] Another objective of this invention is to provide a method for preparing a highly active and stable nickel-based catalyst.

[0005] Another object of the present invention is to provide the application of the above-mentioned highly active and stable nickel-based catalyst.

[0006] The objective of this invention is achieved through the following solution:

[0007] A method for synthesizing layered nickel silicate using an oleylamine-assisted impregnation method includes the following steps:

[0008] Nickel nitrate hexahydrate and oleylamine are mixed evenly in water, then silica gel is added for impregnation. After stirring, a paste is formed, which is then dried in an oven and calcined under air conditions to obtain layered nickel silicate.

[0009] A method for preparing a highly active and stable nickel-based catalyst, comprising the following steps:

[0010] Nickel nitrate hexahydrate and oleylamine are mixed evenly in water, and then silica gel is added for impregnation. After stirring, a paste is formed, which is then dried in an oven and calcined under air conditions to obtain layered nickel silicate. After reduction with hydrogen (pure hydrogen atmosphere), a highly active and stable nickel-based catalyst is obtained.

[0011] The molar ratio of nickel nitrate hexahydrate to oleylamine is 1:1 to 1:4, preferably 1:4;

[0012] The amounts of nickel nitrate hexahydrate and water used are such that 9 mL of water is used for every 1.3 g of nickel nitrate hexahydrate.

[0013] The amount of silica gel used is such that 5g of silica gel is used for every 1.3g of nickel nitrate hexahydrate.

[0014] The stirring time is less than 1 minute;

[0015] The drying process refers to drying at 60–80°C for 8–16 hours; the particle size of the powder formed after drying is less than 5 nm.

[0016] The heating and calcination mentioned refers to heating at 600-800℃ for 2-6 hours, preferably calcining at 700℃ for 4 hours.

[0017] The hydrogen reduction temperature is 600-800℃, the hydrogen reduction time is 1-3h, and the hydrogen flow rate is 20-40mL / min.

[0018] Preferably, the hydrogen reduction temperature is 700℃, the hydrogen reduction time is 2h, and the hydrogen flow rate is 30mL / min.

[0019] A highly active and stable nickel-based catalyst prepared by the above method, wherein the highly active and stable nickel-based catalyst is nickel nanoparticles supported on layered nickel silicate and silicon dioxide.

[0020] The application of the aforementioned highly active and stable nickel-based catalysts in the dry reforming reaction of methane.

[0021] The application of the highly active and stable nickel-based catalyst in the dry reforming reaction of methane specifically includes the following steps: fixing the catalyst in a reactor with quartz wool, and incubating at 700℃ and 72000 ml / h. -1 g -1 The gas hourly space velocity of the gas is introduced into the reaction gas CO2 and CH4 and the carrier gas N2 to obtain the products hydrogen and carbon monoxide; wherein the flow ratio of the reaction gas CO2 and CH4 and the carrier gas N2 is 1:1:1.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] The oleylamine-assisted impregnation method was used to synthesize layered nickel silicate, which was then used as a precursor for the synthesis of highly dispersed and stable layered nickel silicate (silica) supported nickel nanoparticles. It exhibited high activity and long lifespan for high-temperature methane dry reforming reactions.

[0024] Compared with existing technologies, this invention is the first to use oleylamine as an auxiliary agent in the impregnation method. The process is simple, easy to operate, and produces less waste liquid, making it potential for large-scale industrial application. Furthermore, the nickel-based catalyst synthesized by this method has been used for the first time in the dry reforming of methane, achieving excellent results. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of layered nickel silicate and highly active, highly stable nickel-based catalyst using the oleylamine-assisted impregnation method of this invention.

[0026] Figure 2 This is an SEM image of the product obtained after calcination at 700℃ in Example 1.

[0027] Figure 3 The diagram is a temperature-progression-reduction (TPR) diagram, where (i) represents Comparative Example 1 and (ii) represents Example 1.

[0028] Figure 4 The figure shows EXAFS data, where (i) represents Comparative Example 1, (ii) represents Example 1, and (iii) represents pure nickel oxide.

[0029] Figure 5 This is a transmission electron microscope image of hydrogen reduction at 700℃ in Example 2.

[0030] Figure 6 The diagram shows the methane dry reforming reaction activity of the products in Example 2 and Comparative Example 2.

[0031] Figure 7 This is a transmission electron microscope image taken 100 hours after the catalyst reaction in Example 2.

[0032] Figure 8 This is a temperature-programmed reduction diagram after 100 hours of catalytic reaction using the catalyst in Example 2. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments used that do not specify the manufacturer are all commercially available conventional products. In the embodiments, nickel oxide is nanoparticles with a particle size of less than 10 nm. In the embodiments, silica gel is purchased from Kanto Chemical Co., Ltd., with a particle size of 40-60 micrometers, a specific surface area of ​​753 square meters / gram, and an average pore size of 7.5 nanometers.

[0034] Example 1: Preparation of layered nickel silicate

[0035] First, nickel nitrate hexahydrate (1.3 g) and oleylamine (molar ratio 1:4) were ultrasonically mixed in 9 ml of deionized water (2-3 minutes). Then, 5 g of silica gel was added for equal volume impregnation. After short-term stirring (less than 1 minute), a paste was formed. The paste was then placed in a 60°C oven and dried overnight for 12 hours to form a powder. After that, it was calcined in air at 700°C for 4 hours.

[0036] The SEM image of the product obtained after calcination at 700℃ in Example 1 is shown below. Figure 2 As shown, needle-like structures are generally a hallmark of layered silicates, therefore from Figure 2 As can be seen from this, we have successfully obtained layered nickel silicate.

[0037] Example 2: Preparation of highly active and stable nickel-based catalysts

[0038] First, nickel nitrate hexahydrate (1.3 g) and oleylamine (molar ratio 1:4) were ultrasonically mixed in 9 ml of deionized water (2-3 minutes). Then, 5 g of silica gel was added for equal-volume impregnation. After short-term stirring (less than 1 minute), a paste was formed, which was then dried overnight in a 60°C oven for 12 hours to obtain a powder. Subsequently, it was calcined in air at 700°C for 4 hours. Finally, it was reduced with pure hydrogen at 700°C for 2 hours to obtain a highly active and stable nickel-based catalyst.

[0039] Comparative Example 1: Layered Nickel Silicate Prepared with Oil-Free Amine

[0040] First, nickel nitrate hexahydrate (1.3 g) was ultrasonically mixed in 9 ml of deionized water (2-3 minutes). Then, 5 g of silica gel was added for equal volume impregnation. After short-term stirring (less than 1 minute), a paste was formed. The paste was then dried in a 60°C oven for 12 hours to become powder. After that, it was calcined in air at 700°C for 4 hours.

[0041] Comparative Example 2: Highly Active and Stable Nickel-Based Catalysts Prepared with Oil-Free Amines

[0042] First, nickel nitrate hexahydrate (1.3 g) was ultrasonically mixed in 9 ml of deionized water (2-3 minutes). Then, 5 g of silica gel was added for equal-volume impregnation. After short-term stirring (less than 1 minute), a paste was formed, which was then dried in a 60°C oven for 12 hours to obtain powder. Subsequently, it was calcined in air at 700°C for 4 hours. Finally, it was reduced with pure hydrogen at 700°C for 2 hours to obtain a highly active and stable nickel-based catalyst.

[0043] Figure 3 The diagram shows a temperature-programmed reduction (TPR) plot, where (i) represents Comparative Example 1 and (ii) represents Example 1. The reducing gas was a 5% hydrogen / nitrogen mixture at a flow rate of 60 mL / min. The reduction process involved heating from room temperature to 900°C at a rate of 10°C / min. Generally, for silicates, reduction temperatures above 600°C, especially above 700°C, indicate the formation of layered silicates. As can be seen from the plot, the corresponding layered silicates were formed in Example 1.

[0044] Figure 4 The figures are EXAFS data, where (i) represents Comparative Example 1, (ii) represents Example 1, and (iii) represents pure nickel oxide. Compared to un-oleylamine and commercially available nickel oxide, the oleylamine-assisted synthesized sample has a longer Ni-Ni bond length (overlapping with Ni-Si) (see...). Furthermore, it is known that Ni-Si is longer than Ni-Ni, indicating that the addition of oleylamine helps to form more Ni-Si, which in turn promotes the metal-carrier interaction and improves the stability of nickel particles.

[0045] Figure 5 The image shows a transmission electron microscope (TEM) image of the nickel nanoparticles after hydrogen reduction at 700°C in Example 2. As can be seen from the image, highly dispersed nickel nanoparticles (less than 5 nm) are visible after hydrogen reduction at 700°C, surrounded by needle-like structures (layered nickel silicate). This structure is beneficial to the stability of nickel.

[0046] Application Examples

[0047] 0.05 g of the highly active and stable nickel-based catalyst prepared in Example 2 or Comparative Example 2 was fixed on both sides in a reactor tube with an inner diameter of 4 mm using quartz wool. The reactants (CO2 and CH4) were fed for a reforming reaction (N2 as the carrier gas). The reaction was carried out at 72000 ml / h. -1 g -1 The gas hourly space velocity (GHSV) was determined. Nitrogen was used as an internal standard (the amount of this pure substance was used as a standard to compare the content of the analyte). The gas flow rate was N2∶CO2∶CH4 (1:1:1), and the total flow rate of the reactant gas and carrier gas was 60 ml / min.

[0048] Figure 6The graph shows the activity of the products from Example 2 and Comparative Example 2 in the dry reforming reaction of methane, where silane-nickel-oleylamine represents the product from Example 2, and silane-nickel represents the product from Comparative Example 2. As can be seen from the graph, the sample synthesized with oleylamine assistance exhibits higher activity and stability when applied to the dry reforming reaction of methane.

[0049] Figure 7 This is a transmission electron microscope (TEM) image of the catalyst in Example 2 after 100 hours of catalytic reaction. No carbon buildup was observed after the reaction, and the metal particle size did not significantly increase; a small amount of needle-like layered nickel silicate remained, demonstrating the high activity and stability of the nickel-based catalyst.

[0050] Figure 8 The graph shows the temperature-programmed reduction after 100 hours of catalytic reaction in Example 2. The reducing gas was a 5% hydrogen / nitrogen mixture at a flow rate of 60 mL / min. The reduction process involved heating from room temperature to 900°C at a rate of 10°C / min. As can be seen from the graph, the reduction temperature remained high after the reaction, indicating the continued presence of layered nickel silicate and a strong nickel-silicon interaction, highlighting the stability of the nickel catalyst of this invention.

[0051] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for synthesizing layered nickel silicate using an oleylamine-assisted impregnation method, characterized in that... Includes the following steps: Nickel nitrate hexahydrate and oleylamine are mixed evenly in water, then silica gel is added for impregnation. After stirring, a paste is formed, which is then dried in an oven and calcined under air conditions to obtain layered nickel silicate. The molar ratio of nickel nitrate hexahydrate to oleylamine is 1:1 to 1:4; The amounts of nickel nitrate hexahydrate and water used are such that 9 mL of water is used for every 1.3 g of nickel nitrate hexahydrate. The amount of silica gel used is as follows: 5g of silica gel is used for every 1.3g of nickel nitrate hexahydrate; the heating and calcination refers to heating at 600~800℃ for 2~6h.

2. The method for synthesizing layered nickel silicate using the oleylamine-assisted impregnation method according to claim 1, characterized in that: The heating and calcination mentioned refers to calcination at 700℃ for 4 hours.

3. A method for preparing a nickel-based catalyst using an oleylamine-assisted impregnation method, characterized in that... Includes the following steps: The layered nickel silicate prepared according to claim 1 is reduced with hydrogen to obtain a nickel-based catalyst.

4. The method for preparing nickel-based catalysts using the oleylamine-assisted impregnation method according to claim 3, characterized in that: The hydrogen reduction temperature is 600-800℃, the hydrogen reduction time is 1-3h, and the hydrogen flow rate is 20-40mL / min.

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