A Ni-Bi bimetallic catalyst and its application in catalyzing the one-step synthesis of high-carbon alcohols from ethanol

Abstract

The present invention belongs to the technical field of organic synthesis, and in particular to a Ni-Bi bimetallic catalyst and its catalytic one-step synthesis of higher alcohols from ethanol. In order to develop a catalyst capable of improving the yield of C6+ higher alcohols, the present invention provides a Ni-Bi bimetallic catalyst and a preparation method thereof, wherein NiBi is alloyed by introducing bismuth atoms, so that the arrangement of atoms on the nickel surface is reconstructed, the metal Ni electronic environment is regulated, and then the catalytic performance of the catalyst Ni active center is regulated, so that the Ni-Bi bimetallic catalyst has high load, low particle size, and high directional reaction activity for higher alcohols, and is applied in the reaction of catalytic one-step synthesis of higher alcohols from ethanol, showing excellent catalytic efficiency, high reaction activity and high selectivity for high-value C6+ higher alcohol products. In addition, the present invention is simple to prepare, low in cost, and more conducive to its production application.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a Ni-Bi bimetallic catalyst and an application thereof in catalyzing the one-step synthesis of higher carbon alcohols from ethanol. Background Art

[0002] As a renewable energy source, the effective conversion and utilization of biomass resources is of great significance to ensuring energy security and low-carbonization of energy structure, and can also alleviate the pressure of today's energy shortage to a certain extent. Among them, bioethanol is the world's largest biomass, but it still has problems such as low calorific value, easy water absorption and low added value. In contrast, C6+ high-carbon alcohols have the advantages of high energy density, low corrosiveness and low water absorption, and are one of the ideal substitutes for diesel blended fuels. At the same time, C6+ high-carbon alcohols can efficiently obtain isomeric hydrocarbon components of sustainable aviation fuels through one-step hydrodeoxygenation. In addition, in the field of chemicals, C6+ high-carbon alcohols are also important fine chemical raw materials, and have important uses and high added value in the fields of plasticizers, surfactants, pharmaceutical intermediates, food additives, etc. It can be seen that the development of efficient synthesis technology of C6+ high-carbon alcohols has important application prospects.

[0003] Studies have shown that through the principle of alcohol condensation reaction, bioethanol can be directly reconstructed through water phase coupling to generate high value-added C4+ high-carbon alcohol products. Among them, transition metal Ni-based catalysts have excellent dehydrogenation performance and are cheaper than rare precious metals such as Pd and Ru, so they are widely developed for ethanol upgrading to synthesize C4+ high-carbon alcohols. However, limited by the strong metallicity of Ni catalysts, they still have the following problems in the synthesis of C4+ high-carbon alcohols: (1) The yield of high-carbon alcohol products is not high, especially the selectivity of high-value-added C6+ high-carbon alcohol products is not high, and the main product in most catalytic systems is still butanol; (2) The strong CC bond breaking ability of transition metals leads to a large number of gaseous by-products such as CH4, CO, and CO2 in the reaction products, which reduces the economic efficiency of carbon atoms in the conversion process. At the same time, Fe, Co, Sn and other metals have been used to dope and regulate highly active metals such as Ni and Pd, and applied to the ethanol coupling reaction system. Although the selectivity of C6+ high-carbon alcohol products can be improved compared with single metal Ni-based catalysts, there are still problems such as expensive catalyst preparation, relatively harsh reaction conditions, and limited improvement in the selectivity of C6+ high-carbon alcohol products. Therefore, it is necessary to further develop catalysts with better catalytic activity based on Ni-based catalysts to increase the yield of C6+ high-carbon alcohols and reduce the production of by-products. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the present invention proposes a Ni-Bi bimetallic catalyst, which controls the stoichiometric ratio of nickel and bismuth, introduces bismuth atoms to construct NiBi alloying, promotes the reconstruction of the surface atomic arrangement of the Ni active center, and regulates the electronic environment of the metal Ni, so that the catalyst exhibits excellent catalytic activity for the directional synthesis of C6+ high-carbon alcohols by ethanol-water phase coupling at a relatively low temperature.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a method for preparing a Ni-Bi bimetallic catalyst, comprising the following steps:

[0007] S1. Dissolve a nickel salt, a bismuth salt and a carbon source precursor in a solvent, stir to form a complex to obtain a homogeneous solution, and then dry to obtain a nickel-bismuth bimetallic catalyst gel precursor; the Ni / Bi molar ratio of the nickel salt and the bismuth salt is 1:(0.05-5), and the total molar ratio of Ni+Bi in the nickel salt and the bismuth salt to the molar ratio of carbon atoms in the carbon source precursor is 1:(1-4);

[0008] S2. The nickel-bismuth bimetallic catalyst gel precursor of S1 is placed in an inert gas atmosphere and subjected to a controlled high-temperature self-reduction carbonization reaction at 400-700° C. for 2-4 hours to obtain a Ni-Bi bimetallic catalyst.

[0009] Relative to rare noble metals such as Pd and Ru, transition metal Ni is abundant in production and has good catalytic performance in many typical reactions, so Ni-based non-noble metal catalysts can well replace noble metal catalysts, reduce catalyst costs, and improve economic benefits. Meanwhile, although Ni-based metal catalysts have excellent catalytic activity for alcohol dehydrogenation and hydrogenation reactions, the selectivity of by-products is too high due to the strong CC bond breaking ability of Ni-based monometallic catalysts. For this reason, the present invention constructs NiBi alloying by introducing bismuth atoms, and by controlling the stoichiometric matching ratio of nickel and bismuth, the surface atomic arrangement of Ni active center is reconstructed, the electronic environment of metal Ni is regulated, and the introduction of bismuth atoms can also effectively inhibit Ni from sintering and agglomerating under high loading conditions. Therefore, by controlling the molar ratio of metal Ni to Bi, a suitable Ni-Bi bimetallic catalyst is provided, which can have the advantages of high loading, low particle size, excellent catalytic efficiency, high reactivity, etc.

[0010] Furthermore, the nickel salt includes nickel nitrate, nickel chloride, nickel acetate, nickel hydroxide, preferably nickel nitrate.

[0011] Furthermore, the bismuth salt includes bismuth nitrate, bismuth citrate, and bismuth hydroxide, preferably bismuth nitrate.

[0012] Furthermore, the molar ratio of Ni / Bi in the nickel salt and the bismuth salt is 1:(1-3).

[0013] Furthermore, the carbon source precursor is an organic compound containing C, H, and O that can complex with nickel and bismuth metal ions, preferably citric acid, and the total molar ratio of Ni+Bi in the nickel salt and bismuth salt to the molar ratio of carbon atoms in the carbon source precursor is 1:2.5.

[0014] Furthermore, the temperature of the controlled high temperature self-reduction carbonization reaction is 500-600°C, and the reaction time is 2-4 hours, more preferably 500°C for 3 hours.

[0015] Furthermore, the heating rate of the controlled high temperature self-reduction carbonization reaction is 1-10°C / min. When the heating rate is controlled within this range, the average particle size of the catalyst is smaller and more uniform, and more preferably 2-5°C / min.

[0016] The second aspect of the present invention provides a Ni-Bi bimetallic catalyst prepared by the preparation method described in the first aspect.

[0017] The metal loading of the Ni-Bi bimetallic catalyst prepared by the present invention is 30-85wt%, more preferably 60-80wt%; the average particle size is less than 10nm, more preferably 3nm-9nm.

[0018] The third aspect of the present invention provides the use of the Ni-Bi bimetallic catalyst described in the second aspect in the aqueous phase catalytic synthesis of higher carbon alcohols from ethanol.

[0019] The reaction of ethanol aqueous phase catalytic synthesis of higher carbon alcohols follows the Guerbet reaction principle, and the reaction can generally be summarized as: (1) metal active center catalyzes ethanol dehydrogenation; (2) base / acid catalyzes aldehyde condensation of aldehyde intermediates after alcohol dehydrogenation; (3) after the high carbon chain is formed by the aldol condensation, the metal active center catalyzes its hydrogenation to finally obtain the desired high carbon alcohol product.

[0020] The fourth aspect of the present invention provides a method for catalyzing ethanol to synthesize high-carbon alcohols in one step, specifically: the Ni-Bi bimetallic catalyst described in the second aspect is combined with a base, ethanol, and water to form a reaction system, the initial pressure is set to 0.1-1MPa, and the reaction is carried out at 140-200°C for 10-20h to synthesize high-carbon alcohols.

[0021] The Ni-Bi bimetallic catalyst synthesized by the method of the present invention is applied to the one-step catalytic synthesis of higher carbon alcohols from ethanol, and the selectivity of C6+ higher carbon alcohol products can exceed 70%.

[0022] Furthermore, the added amount of the Ni-Bi bimetallic catalyst is not less than 1 g per 100 g of ethanol.

[0023] Furthermore, the molar ratio of ethanol to water is 5:1 to 1:5, preferably 2:5; the molar ratio of ethanol to alkali is 1:5 to 1:15, preferably 1:5. More preferably, the mass ratio of Ni-Bi bimetallic catalyst: alkali: small molecule alcohol: water is 0.3:0.87:5:5.

[0024] Furthermore, the alkali in the reaction system may be sodium hydroxide or potassium hydroxide.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention discloses a Ni-Bi bimetallic catalyst and a preparation method thereof. First, a nickel salt, a bismuth salt and a carbon source precursor are dissolved in a solvent, a homogeneous solution is obtained after stirring to form a complex, and then a nickel-bismuth bimetallic catalyst gel precursor is obtained by drying, and then the nickel-bismuth bimetallic catalyst gel precursor is placed in an inert gas atmosphere for a controlled high-temperature self-reduction carbonization reaction to obtain a catalyst. The present invention alloys NiBi by introducing bismuth atoms, thereby reconstructing the atomic arrangement on the nickel surface, regulating the electronic environment of the metal Ni, and then regulating the catalytic performance of the catalyst Ni active center, so that the Ni-Bi bimetallic catalyst has the characteristics of high load, low particle size, and high directional reaction activity for high-carbon alcohols, and is applied to the reaction of catalyzing ethanol to synthesize higher alcohols in one step, showing excellent catalytic efficiency, high reaction activity and high selectivity for high-value C6+ high-carbon alcohol products. In addition, the present invention is simple to prepare, low in cost, and more conducive to its production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 TEM image of the Ni-Bi bimetallic catalyst obtained when the molar ratio of nickel salt to bismuth salt is 1:2, the molar ratio of total metal salt to citric acid is 1:2.5, and the calcination temperature is 500°C;

[0028] Figure 2 The XRD pattern of the Ni-Bi bimetallic catalyst obtained when the molar ratio of nickel salt to bismuth salt is 1:2, the molar ratio of total metal salt to citric acid is 1:2.5, and the calcination temperature is 500°C;

[0029] Figure 3 The particle size distribution diagram of the Ni-Bi bimetallic catalyst obtained when the molar ratio of nickel salt to bismuth salt is 1:2, the molar ratio of total metal salt to citric acid is 1:2.5, and the calcination temperature is 500°C. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0032] Example 1 Preparation method of Ni-Bi bimetallic catalyst

[0033] The specific preparation method comprises the following steps:

[0034] (1) According to Table 1, citric acid, nickel salt, and bismuth salt were weighed according to a certain molar ratio (molar ratio of nickel salt to bismuth salt, molar ratio of total metal salt to citric acid), and the citric acid, nickel salt, and bismuth salt were dissolved in 50 ml of 0.2 M nitric acid solution in turn to obtain solutions with concentrations of 1 M, 0.13 M, and 0.27 M, respectively, of citric acid, nickel salt, and bismuth salt, and the solution was magnetically stirred at a speed of 500 rpm at room temperature for 30 min to obtain a homogeneous solution, and the obtained homogeneous solution was placed on an 80° C. heating plate and stirred at a speed of 500 rpm for 18 h, and then transferred to an oven at 80° C. and dried for 12 h to obtain a Ni-Bi bimetallic catalyst precursor.

[0035] (2) According to Table 1, the Ni-Bi bimetallic catalyst precursor was placed in a tubular furnace, heated to a certain calcination temperature at a heating rate of 5°C / min under a nitrogen atmosphere, and calcined at this temperature for 3 h to obtain a Ni-Bi bimetallic catalyst.

[0036] (3) The transmission electron microscope (TEM) observation of the Ni-Bi bimetallic catalyst of group 1 shows that the catalyst has the characteristics of high loading and good dispersion. X-ray diffraction (XRD) observation shows that after the introduction of Bi metal, the diffraction peaks of Ni and Bi are relatively weak, indicating that after the introduction of bismuth atoms to construct NiBi alloying, a disordered amorphous structure is partially formed. Particle size distribution analysis shows that the catalyst has the characteristics of low particle size, with a particle size range of 3.5nm to 9.5nm and an average particle size of less than 10nm. In addition, similar TEM and XRD results were observed for the catalysts of groups 2-14, and they have similar particle size distributions. However, due to the molar ratio of nickel salt to bismuth salt being too high or too low, or no Bi metal being introduced, or the calcination temperature being too high or too low, the TEM and XRD results of groups 15-19 show that the catalyst has poor dispersion, no or less amorphous structure, and a large particle size with uneven distribution.

[0037] Table 1 Preparation parameters of Ni-Bi bimetallic catalysts

[0038]

[0039]

[0040] Example 2 Performance Test of Ni-Bi Bimetallic Catalyst

[0041] The catalyst prepared in Example 1 was applied to the reaction system of synthesizing higher alcohols from ethanol and water phase, and the reaction conditions were: 0.3g catalyst, 0.87g sodium hydroxide, 5g ethanol, 5g water, initial pressure of 0.1MPa, and reaction at 180°C for 12h. After the reaction, the reactor was cooled to room temperature, and then the gas phase and liquid phase products were collected. The liquid phase product was centrifuged and filtered to obtain a liquid phase and a catalyst solid phase. The liquid phase product was centrifuged and allowed to stand for 10min to accelerate spontaneous phase separation to obtain an organic phase and an aqueous phase. After the liquid phase product was centrifuged and separated, it was detected and analyzed by gas chromatography. The main product of the organic phase was C6+ higher alcohol. The catalytic activity results of the product obtained in Example 1 are shown in Table 2 below.

[0042] in,

[0043]

[0044]

[0045]

[0046] From the data in Table 2, it can be seen that when the molar ratio of nickel to bismuth is 1:(1-3) and calcined at 500°C for 3h, the ethanol conversion rate, alcohol product yield and high-carbon alcohol product selectivity are relatively high, especially when the molar ratio of nickel to bismuth is 1:2, the catalytic reaction can have an ethanol conversion rate of 76.2% and a high-carbon alcohol product selectivity of 72C%. When the calcination temperature is reduced to 400°C or increased to 600°C, the ethanol conversion rate is low and the selectivity of C6+ products is reduced. For example, in groups 15-16, when the molar ratio of nickel nitrate to bismuth nitrate is too high or too low, the ethanol conversion rate is low and the carbon yield of alcohol products is also low; and in groups 18-19, the calcination temperature is too high or too low, which also has a significant effect on the ethanol conversion rate and the carbon yield of alcohol products. In addition, in group 17, due to the lack of the introduction of Bi metal, the carbon yield of alcohol products is also very low.

[0047] Table 2 Catalytic performance test results of Ni-Bi bimetallic catalysts

[0048] Group Ethanol conversion rate (%) Yield of alcohol products (C%) C6+ product selectivity (C%) Group 1 76.2 44.2 72.26 Group 2 64.1 28.4 60.68 Group 3 67.3 29.5 61.56 Group 4 72.1 35.1 60.22 Group 5 72.3 37.4 68.70 Group 6 73.7 41.9 70.11 Group 7 63.5 37.6 58.71 Group 8 52.4 22.0 46.99 Group 9 70.6 38.3 61.55 Group 10 69.6 37.0 66.21 Group 11 60.3 26.7 55.83 Group 12 66.1 27.8 53.62 Group 13 63.8 30.4 62.73 Group 14 74.1 41.0 66.57 Group 15 33.5 18.8 40.49 Group 16 62.2 28.5 60.15 Group 17 60.4 30.8 54.30 Group 18 40.9 10.4 43.28 Group 19 52.8 23.5 50.71

[0049] In summary, the Ni-Bi bimetallic catalyst synthesized by the method of the present invention is applied in the reaction of catalyzing the one-step synthesis of higher alcohols from ethanol, and exhibits excellent catalytic efficiency, high reaction activity and high selectivity for high-value C6+ higher-carbon alcohol products, and the C6+ product selectivity can exceed 70%. In addition, the present invention is simple to prepare and low in cost, which is more conducive to its production and application.

[0050] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for catalyzing ethanol to synthesize higher alcohols in one step, characterized in that: A Ni-Bi bimetallic catalyst is combined with a base, ethanol and water to form a reaction system, and the reaction is carried out at 140-200°C for 10-20h to synthesize high carbon alcohols; The preparation method of the Ni-Bi bimetallic catalyst comprises the following steps: S1. Dissolve a nickel salt, a bismuth salt and a carbon source precursor in a solvent, wherein the carbon source precursor is selected from citric acid, and stir to form a complex to obtain a homogeneous solution, which is then dried to obtain a nickel-bismuth bimetallic catalyst gel precursor; the Ni / Bi molar ratio of the nickel salt and the bismuth salt is 1:(0.05-5), and the total molar ratio of Ni+Bi in the nickel salt and the bismuth salt to the molar ratio of carbon atoms in the carbon source precursor is 1:(1-4); S2. The nickel-bismuth bimetallic catalyst gel precursor of S1 is placed in an inert gas atmosphere and subjected to a controlled high-temperature self-reduction carbonization reaction at 400-700° C. for 2-4 hours to obtain a Ni-Bi bimetallic catalyst.

2. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The nickel salts include nickel nitrate, nickel chloride, nickel acetate and nickel hydroxide.

3. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The bismuth salts include bismuth nitrate, bismuth citrate and bismuth hydroxide.

4. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The molar ratio of Ni / Bi in the nickel salt and the bismuth salt is 1:(1-3).

5. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The total molar ratio of Ni+Bi in the nickel salt and bismuth salt to the molar ratio of carbon atoms in the carbon source precursor is 1:2.

5.

6. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The temperature of the controlled high temperature self-reduction carbonization reaction is 500-600° C. and the time is 2-4 hours.

7. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The heating rate of the controlled high-temperature self-reduction carbonization reaction is 1-10°C / min.

8. The method for catalyzing ethanol to synthesize higher alcohols in one step according to claim 1, characterized in that: The added amount of the Ni-Bi bimetallic catalyst is not less than 1 g per 100 g of ethanol.

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