A hydrophobic substance-doped carbon-coated nickel catalyst, a preparation method and application thereof

Abstract

This invention discloses a hydrophobic-doped carbon-coated nickel catalyst, its preparation method, and its application. The aim is to provide a catalyst that can effectively improve the hydrophobic properties of pure nickel-based catalysts and promote the further coupling of lower alcohols to higher alcohols. This catalyst exhibits excellent catalytic efficiency, high reactivity, high ethanol conversion rate, and good selectivity for C8+ higher alcohols in the one-step synthesis of higher alcohols from aqueous ethanol. The technical solution is as follows: Ni@MA and hydrophobic SiC are added to a ball mill jar at a mass ratio of 1:0.5~2 and ball-milled for 1-8 hours at 300 rpm to obtain the hydrophobic-doped carbon-coated nickel catalyst Ni@MA-SiC; further, the hydrophobic-doped carbon-coated nickel catalyst Ni@MA-SiC is obtained; the hydrophobic-doped carbon-coated nickel catalyst, alkali, ethanol, and water form a reaction system, which is reacted for 12 hours under a hydrogen atmosphere, an initial pressure of 0.1 MPa, and 230℃ to obtain higher alcohols; this invention belongs to the field of synthetic technology.

Description

Technical Field

[0001] This invention relates to a catalyst, specifically a carbon-coated nickel catalyst doped with hydrophobic substances. The invention also relates to the preparation method and application of the catalyst, belonging to the field of synthesis technology. Background Technology

[0002] Biomass, as an abundant renewable carbon source, boasts significant advantages such as wide availability and carbon neutrality. Its efficient conversion and utilization have become a crucial pathway to alleviate the energy crisis and environmental pressures. Bio-based ethanol, as an important byproduct of biomass conversion, has demonstrated enormous potential in the energy sector. In recent years, global bioethanol production has steadily increased, its production technology has matured, and costs have gradually decreased. However, currently, bioethanol is mainly used in the fuel ethanol sector. Direct use as fuel presents challenges such as low energy density and high corrosivity, limiting its wider application.

[0003] Converting bioethanol into high-value-added chemicals through specific chemical reactions is a key strategy for expanding its application areas and enhancing the utilization value of biomass resources. Among these, aqueous-phase coupling reactions of ethanol, especially the Guerbet reaction, can directionally synthesize higher alcohols. Higher alcohols have high cetane numbers, resulting in excellent combustion performance and providing more powerful engines. Simultaneously, they exhibit good compatibility with conventional diesel fuel and can be used directly as diesel additives, effectively improving diesel quality and reducing particulate matter and nitrogen oxides in exhaust emissions. Furthermore, higher alcohols are important intermediates in fine chemicals, with wide applications in surfactants, lubricants, plasticizers, and other fields, and market demand continues to grow.

[0004] However, in practical applications of aqueous-phase coupling reactions of ethanol, the presence of water molecules is unavoidable. Water molecules readily adsorb onto the catalyst surface, occupying active sites and causing catalyst "poisoning," thus significantly reducing catalyst activity. Furthermore, when an oil-water two-phase reaction occurs in the later stages of the reaction, water molecules adhering to the catalyst surface prevent contact between the catalyst and reactants in the oil phase, reducing the selectivity of higher alcohols.

[0005] Therefore, it is particularly necessary to develop a catalyst that can effectively improve the hydrophobic properties of pure nickel-based catalysts and promote the further coupling of lower alcohols to higher alcohols. Summary of the Invention

[0006] To address the aforementioned shortcomings, the present invention aims to provide a catalyst that can effectively improve the hydrophobic properties of simple nickel-based catalysts and promote the further coupling of lower alcohols to higher alcohols.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned catalyst.

[0008] Another objective of this invention is to provide the application of the above-mentioned catalyst in the one-step synthesis of higher alcohols from aqueous ethanol. This catalyst has excellent catalytic efficiency, high reactivity, high ethanol conversion rate, and good selectivity for C8+ higher alcohols.

[0009] Therefore, the first technical solution provided by this invention is as follows:

[0010] A method for preparing a hydrophobic material-doped carbon-coated nickel catalyst involves adding Ni@MA and hydrophobic SiC at a mass ratio of 1:0.5~2 into a ball mill jar and ball milling for 1-8 hours at a speed of 300 rpm to obtain the hydrophobic material-doped carbon-coated nickel catalyst Ni@MA-SiC.

[0011] Furthermore, in the above-mentioned method for preparing the hydrophobic material-doped carbon-coated nickel catalyst, the mass ratio of Ni@MA to hydrophobic SiC is 1:0.5~2.

[0012] Furthermore, in the above-mentioned method for preparing the hydrophobic material-doped carbon-coated nickel catalyst, the Ni@MA is prepared through the following steps:

[0013] S1. Add malic acid and nickel nitrate hexahydrate to deionized water at a molar ratio of 2:0.5-1.5, stir until clear, and obtain a mixed solution;

[0014] S2. Dry the mixed solution obtained in step S1 to obtain a gel-like precursor;

[0015] S3. The precursor obtained in step S2 is placed in an inert gas atmosphere and subjected to a controlled high-temperature self-reduction carbonization reaction at 500-600℃ for 1-3 hours to passivate and obtain a carbon-coated nickel Ni@MA catalyst.

[0016] Furthermore, in the above-mentioned method for preparing the hydrophobic material-doped carbon-coated nickel catalyst, the malic acid and nickel nitrate hexahydrate mentioned in step S1 are in a molar ratio of 2:1.

[0017] The drying process described in step S2 involves drying at 80°C for 12 hours.

[0018] Furthermore, in the preparation method of the above-mentioned hydrophobic material-doped carbon-coated nickel catalyst, step S3 involves a controlled high-temperature self-reduction carbonization reaction at 550°C for 2 hours, followed by passivation with an oxygen-argon mixture for 1 hour to obtain the carbon-coated nickel Ni@MA catalyst.

[0019] Furthermore, in the above-mentioned method for preparing the hydrophobic material-doped carbon-coated nickel catalyst, the hydrophobic SiC is prepared through the following steps:

[0020] S1. Pretreatment is performed by calcining SiC in air at 800℃ for 2 hours;

[0021] S2. Disperse the pretreated SiC in an ultrasonic solvent and sonicate for 1 hour to obtain solution A;

[0022] S3. Add hexadecyltrimethoxysilane dropwise to the solvent while stirring to obtain solution B;

[0023] S4. Add solution B to solution A at room temperature and stir for 24 hours;

[0024] S5. Wash and separate with anhydrous ethanol, and dry at 80℃ for 6-12 hours to obtain hydrophobic SiC;

[0025] The mass ratio of SiC to hexadecyltrimethoxysilane is 1:0.25~4.

[0026] Furthermore, in the above-mentioned method for preparing the hydrophobic material-doped carbon-coated nickel catalyst, the solvents in steps S2 and S3 are anhydrous ethanol or toluene.

[0027] The second aspect of the present invention is to provide a hydrophobic material-doped carbon-coated nickel catalyst, which is prepared by the method described in the first aspect.

[0028] The third aspect of this invention is to provide the application of a hydrophobic material-doped carbon-coated nickel catalyst in the aqueous coupling of ethanol to synthesize higher alcohols.

[0029] A method for the aqueous-ethanol coupling synthesis of higher alcohols involves a reaction system consisting of a hydrophobic material-doped carbon-coated nickel catalyst, an alkali, ethanol, and water, as described in the second scheme, coupled under hydrogen atmosphere, initial pressure of 0.1 MPa, and 230°C for 12 hours to obtain higher alcohols.

[0030] The alkali is sodium hydroxide;

[0031] The mass ratio of the hydrophobic material-doped carbon-coated nickel catalyst, alkali, ethanol, and water is 0.1-0.2:0.75-0.1:5:5.

[0032] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0033] 1. The technical solution provided by this invention synthesizes a hydrophobic material-doped carbon-coated nickel catalyst by ball milling prepared carbon-coated nickel and hydrophobically modified SiC. By ball milling the hydrophobic SiC and carbon-coated nickel catalyst, the catalyst surface has good hydrophobic properties, which reduces the phenomenon of catalyst internal pore blockage caused by dehydration due to aldol condensation reaction and water molecules in the reaction raw materials during the reaction process, and avoids the catalyst "poisoning" phenomenon caused by water molecules occupying active sites, thereby maintaining the high activity of the catalyst.

[0034] 2. The catalyst preparation method of the present invention is relatively simple to operate, and the raw materials and equipment used are common and easy to obtain; in the preparation process, the conditions of each step are easy to control, which is conducive to large-scale production and industrial application.

[0035] 3. The technical solution provided by this invention applies various prepared hydrophobic catalysts to the one-step synthesis of higher alcohols from aqueous ethanol, exhibiting excellent catalytic efficiency, high reactivity, high ethanol conversion rate, and increased selectivity for C8+ higher alcohols. Attached Figure Description

[0036] Figure 1 This is a contact angle test chart for commercially available SiC.

[0037] Figure 2 This is a contact angle test diagram of hydrophobic SiC provided in this application.

[0038] Figure 3 The Ni1-SiC provided in Example 1 of this application 0.5 TEM image (200nm).

[0039] Figure 4 The Ni1-SiC provided in Example 1 of this application 0.5 TEM image (100nm).

[0040] Figure 5 This is a contact angle test diagram of Ni0.5-SiC in Example 1 of this application. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that, unless otherwise specified in the examples, the conditions should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0043] The commercially available SiC provided in this application was purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0044] Example 1

[0045] This embodiment provides a hydrophobic material-doped carbon-coated nickel catalyst, which is prepared by the following method:

[0046] 0.6 g of Ni@MA and 0.3 g of hydrophobic SiC were added to a ball mill jar and ball-milled at 300 rpm for 8 hours. The resulting catalyst was denoted as Ni1-SiC. 0.5 .

[0047] Example 2

[0048] This embodiment provides a hydrophobic material-doped carbon-coated nickel catalyst, which is prepared by the following method:

[0049] 0.6g of Ni@MA and 0.6g of hydrophobic SiC were added to a ball mill jar and ball milled at a speed of 300 rpm for 8 hours. The resulting catalyst was denoted as Ni1-SiC1.

[0050] Example 3

[0051] This embodiment provides a hydrophobic material-doped carbon-coated nickel catalyst, which is prepared by the following method:

[0052] 0.6g of Ni@MA and 1.2g of hydrophobic SiC were added to a ball mill jar and ball-milled at a speed of 300 rpm for 8 hours. The resulting catalyst was denoted as Ni1-SiC2.

[0053] The Ni@MA described in Examples 1-3 was prepared by the following steps:

[0054] 1) Take 5.4g of malic acid and 5.82g of nickel nitrate hexahydrate, add them to 50ml of deionized water and stir for 2 hours until clear; transfer the solution to a crucible and dry at 80℃ for 12 hours to make it into a gel-like precursor.

[0055] 2) The precursor was placed in an inert gas atmosphere and subjected to a controlled high-temperature self-reduction carbonization reaction at 550°C for 2 hours, followed by passivation with an oxygen-argon mixture for 1 hour to obtain a carbon-coated nickel Ni@MA catalyst.

[0056] The SiC described in Examples 1-3 is prepared by the following steps:

[0057] 1) Disperse 1g of SiC ultrasonically in 20mL of anhydrous toluene; while stirring, add 1.5g of hexadecyltrimethoxysilane dropwise to 20mL of anhydrous toluene;

[0058] 2) At room temperature, the two solutions from step 1) are slowly mixed while stirring, and then magnetically stirred for 24 hours. The solid obtained above is washed and centrifuged multiple times with anhydrous ethanol, and then dried at 80°C for 6 hours to obtain hydrophobic SiC.

[0059] Comparative Example 1

[0060] This comparative example provides a nickel-based catalyst, Ni@MA prepared in Examples 1-3.

[0061] Comparative Example 2

[0062] This comparative example provides a nickel-based catalyst, obtained by uniformly mixing 0.6 g of Ni@MA and 0.3 g of hydrophobic SiC. The resulting catalyst is denoted as Ni1-SiC. 0.5 -D1.

[0063] To verify the hydrophobicity of the catalyst provided in this application, the applicant tested commercial SiC and the hydrophobic SiC described in this application. The test results are as follows: Figure 1 and Figure 2 As shown, through Figure 1 and Figure 2 It is known that commercial SiC is not hydrophobic, while SiC modified with hexadecyltrimethoxysilane is hydrophobic. Through... Figure 3 and Figure 4 It can be seen that the Ni1-SiC0.5 catalyst has a relatively uniform particle distribution, and the carbon-coated nickel and hydrophobic SiC exhibit a good bonding state. Figure 5 It can be seen that the catalyst Ni0.5-SiC also has good hydrophobicity.

[0064] To verify the catalytic performance of the hydrophobic material-doped carbon-coated nickel catalyst provided in this application, the following describes its application in the aqueous coupling of ethanol to higher alcohols.

[0065] Application Example 1

[0066] Application Example 1 provides a method for the aqueous coupling of ethanol to synthesize higher alcohols. 0.1 g of the catalyst prepared in Example 1, 0.88 g of sodium hydroxide, 5 g of ethanol, and 5 g of water are added to a high-pressure reactor. The reaction is carried out at an initial pressure of 0.1 MPa and a temperature of 230°C for 12 h. After the reaction is completed, the reactor is cooled to room temperature, and then the gaseous and liquid products are collected. The liquid product is centrifuged, and the oil phase, aqueous phase, and catalyst solid phase are collected separately. The oil and aqueous phases are then analyzed by gas chromatography.

[0067] The formulas for calculating the selectivity of C4OH, C6OH, and C8+OH are as follows:

[0068]

[0069]

[0070]

[0071]

[0072] Application Example 2

[0073] This application example provides a method for the aqueous-phase coupling of ethanol to synthesize higher alcohols. The preparation and detection methods are basically the same as in Example 1, except that an equal amount of the catalyst Ni1-SiCl prepared in Example 2 is used instead of the catalyst Ni1-SiC prepared in Example 1. 0.5 .

[0074] Application Example 3

[0075] This application example provides a method for the aqueous-phase coupling of ethanol to synthesize higher alcohols. The preparation and detection methods are basically the same as in Example 1, except that an equal amount of the catalyst Ni1-SiC2 prepared in Example 3 is used instead of the catalyst Ni1-SiC2 prepared in Example 1. 0.5 .

[0076] Comparative Application Example 1

[0077] Comparative Application Example 1 provides a method for the aqueous-phase coupling of ethanol to synthesize higher alcohols. The preparation and detection methods are basically the same as in Example 1, except that an equal amount of the catalyst Ni@MA prepared in Example 1 is used instead of the catalyst Ni1-SiC prepared in Example 1. 0.5 .

[0078] Comparative Application Example 2

[0079] Comparative Application Example 1 provides a method for the aqueous coupling of ethanol to synthesize higher alcohols. Its preparation and detection methods are basically the same as in Example 1, the difference being the use of an equal amount of Ni1-SiC catalyst prepared in Comparative Example 2. 0.5 -D1 replaces the Ni1-SiC catalyst prepared in Example 1 0.5 .

[0080] The calculation results are shown in Table 1.

[0081] project catalyst Ethanol conversion rate % [C4OH selectivity] <![CDATA[Selectivity of C6OH (%)]]> <![CDATA[C 8+ OH selectivity % Application Example 1 <![CDATA[The catalyst Ni1-SiC prepared in Example 1 0.5 > 88.05 18.69 27.29 53.80 Application Example 2 <![CDATA[The catalyst Ni1 - SiC1 prepared in Example 2]]> 81.59 24.33 27.57 45.55 Application Example 3 <![CDATA[The catalyst Ni1-SiC2 prepared in Example 3]]> 76.54 27.10 28.46 44.15 Comparative Application Example 1 The catalyst Ni@MA prepared in Comparative Example 1 61.96% 33.62 26.93 37.25 Comparative Application Example 2 <![CDATA[Catalyst Ni1-SiC prepared in Comparative Example 1 0.5 -D1]]> 70.76 30.18 31.07 38.75

[0082] As shown in Table 1, the hydrophobic-doped carbon-coated nickel catalysts prepared using the method of this invention in Application Examples 1-3 achieved ethanol conversion rates of 88.05%, 81.59%, and 76.54%, respectively. In contrast, the Ni@MA catalyst prepared using the conventional method in Application Example 1 only achieved an ethanol conversion rate of 61.96%. This demonstrates that combining carbon-coated nickel and hydrophobically modified SiC through ball milling can significantly improve the catalyst's ethanol conversion capability.

[0083] Regarding the selectivity for C8+ higher alcohols, Application Examples 1-3 showed selectivity of 53.80%, 45.55%, and 44.15%, respectively, all higher than the 37.25% and 38.75% in the comparative application examples. This indicates that the hydrophobic material-doped carbon-coated nickel catalyst of the present invention can more effectively promote the coupling of lower alcohols to higher alcohols, thereby increasing the proportion of the target product, C8+ higher alcohols, formed.

[0084] Meanwhile, as the proportion of hydrophobic SiC in the catalyst increased, the ethanol conversion rate decreased, but the selectivity for C4OH and C6OH increased. This may be because excessive hydrophobic SiC altered the surface structure and active site distribution of the catalyst to some extent. However, even with the decrease in ethanol conversion, the selectivity for C8+ higher alcohols remained at a high level, indicating that the catalyst of this invention has a good overall promoting effect on the synthesis of higher alcohols.

[0085] In summary, the hydrophobic-doped carbon-coated nickel catalyst and its preparation method provided by this invention have significant advantages in the reaction of ethanol-water coupling to synthesize higher alcohols. It not only improves the activity and stability of the catalyst, but also enhances the selectivity for higher alcohols, providing an efficient and feasible method for the synthesis of higher alcohols, and has broad prospects for industrial application.

Claims

1. A method for preparing a carbon-coated nickel catalyst doped with hydrophobic substances, characterized in that, Ni@MA and hydrophobic SiC were added to a ball mill jar at a mass ratio of 1:0.5~2 and ball milled for 1-8 hours to obtain a carbon-coated nickel catalyst Ni@MA-SiC doped with hydrophobic material.

2. The method for preparing the hydrophobic material-doped carbon-coated nickel catalyst according to claim 1, characterized in that, The mass ratio of Ni@MA to hydrophobic SiC is 1:0.5~2.

3. The method for preparing the hydrophobic-doped carbon-coated nickel catalyst according to claim 1, characterized in that, The Ni@MA is prepared by the following steps: S1. Add malic acid and nickel nitrate hexahydrate to deionized water at a molar ratio of 2:0.5-1.5, stir until clear, and obtain a mixed solution; S2. Dry the mixed solution obtained in step S1 to obtain a gel-like precursor; S3. The precursor obtained in step S2 is placed in an inert gas atmosphere and subjected to a controlled high-temperature self-reduction carbonization reaction at 500-600℃ for 1-3 hours to passivate and obtain a carbon-coated nickel Ni@MA catalyst.

4. The method for preparing the hydrophobic material-doped carbon-coated nickel catalyst according to claim 1, characterized in that, The malic acid and nickel nitrate hexahydrate mentioned in step S1 are in a molar ratio of 2:1; The drying process described in step S2 involves drying at 80°C for 12 hours.

5. The method for preparing the hydrophobic-doped carbon-coated nickel catalyst according to claim 1, characterized in that, Step S3 involves a controlled high-temperature self-reducing carbonization reaction at 550°C for 2 hours, followed by passivation with an oxygen-argon mixture for 1 hour to obtain a carbon-coated nickel Ni@MA catalyst.

6. The method for preparing a carbon-coated nickel catalyst doped with hydrophobic materials according to claim 1 or 2, characterized in that, The hydrophobic SiC is prepared by the following steps: S1. Pretreatment is performed by calcining SiC in air at 800℃ for 2 hours; S2. Disperse the pretreated SiC in an ultrasonic solvent and sonicate for 1 hour to obtain solution A; S3. Add hexadecyltrimethoxysilane dropwise to the solvent while stirring to obtain solution B; S4. Add solution B to solution A at room temperature and stir for 24 hours; S5. Wash and separate with anhydrous ethanol, and dry at 80℃ for 6-12 hours to obtain hydrophobic SiC; The mass ratio of SiC to hexadecyltrimethoxysilane is 1:0.25~4.

7. The hydrophobic material-doped carbon-coated nickel catalyst according to claim 5, characterized in that, The solvents used in steps S2 and S3 are anhydrous ethanol or toluene.

8. A carbon-coated nickel catalyst doped with a hydrophobic substance, characterized in that, Prepared using the method described in any one of claims 1-7.

9. The application of the hydrophobic material-doped carbon-coated nickel catalyst of claim 8 in the aqueous coupling of ethanol to synthesize higher alcohols.

10. A method for synthesizing higher alcohols by aqueous coupling of ethanol, characterized in that, A reaction system consisting of a carbon-coated nickel catalyst doped with hydrophobic material as described in claim 8, an alkali, ethanol, and water was coupled and reacted for 12 hours under a hydrogen atmosphere, an initial pressure of 0.1 MPa, and a temperature of 230°C to obtain a higher alcohol. The alkali is sodium hydroxide; The mass ratio of the hydrophobic material-doped carbon-coated nickel catalyst, alkali, ethanol, and water is 0.1-0.2:0.75-0.1:5:5.

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