EMBEDDED HYDROTHERMAL-RESISTANT NiSn-CS NANO-CATALYST AND PREPARATION METHOD THEREFOR AND APPLICATION THEREOF

Abstract

The present invention discloses an embedded hydrothermal-resistant NiSnCS nano-catalyst and a preparation method therefor and use thereof. The method includes the following steps: firstly dissolving a Ni salt, a Sn salt and chitosan to form a sol solution; and then removing a solvent from the sol solution to obtain a gel, and subjecting the gel to carbonization treatment to obtain the embedded hydrothermal-resistant NiSnCS nano-catalyst; wherein temperature of the carbonization treatment is 400 C. to 600 C., and duration of the carbonization treatment is 1 to 4 hours. The embedded hydrothermal-resistant NiSnCS nano-catalyst prepared by the present invention significantly improves the dispersion of NiSn catalytic active sites and the stability of the structure and activity in hydrothermal environments. When used for the synthesis of higher alcohols from lower alcohols, the catalyst demonstrates excellent catalytic efficiency and hydrothermal resistance, as well as easy separation and recycling, low pollution, and excellent recycling performance.

Claims

1. A preparation method for an embedded hydrothermal-resistant NiSnCS nano-catalyst, characterized in that, the preparation method comprises the following steps: S1, dissolving a Ni salt, a Sn salt and chitosan (C.sub.6H.sub.11NO.sub.4).sub.n to form a sol solution, wherein a molar ratio of a mixture of the Ni salt and the Sn salt to the chitosan is 1:(1-1.5), and the chitosan has a Mw of 700-250000; and S2, removing a solvent from the sol solution in S1 to obtain a gel, and subjecting the gel to carbonization treatment in an inert atmosphere to obtain the embedded hydrothermal-resistant NiSnCS nano-catalyst; wherein temperature of the carbonization treatment is 400 C. to 600 C., and duration of the carbonization treatment is 2 hours.

2. The preparation method for the embedded hydrothermal-resistant NiSnCS nano-catalyst according to claim 1, wherein the chitosan of S1 has a Mw of 100000-150000.

3. The preparation method for the embedded hydrothermal-resistant NiSnCS nano-catalyst according to claim 1, wherein a molar ratio of the Ni salt to the Sn salt in S1 is 1:(0.03-0.24).

4. The preparation method for the embedded hydrothermal-resistant NiSnCS nano-catalyst according to claim 1, wherein the temperature of the carbonization treatment is 500 C., and the duration of the carbonization treatment is 2 hours.

5. A catalyst prepared by the preparation method for the embedded hydrothermal-resistant NiSnCS nano-catalyst according to claim 1.

6. Application of the embedded hydrothermal-resistant NiSnCS nano-catalyst according to claim 5 in catalyzing synthesis of higher alcohols from lower alcohols.

7. The application of the embedded hydrothermal-resistant NiSnCS nano-catalyst in catalyzing synthesis of higher alcohols from lower alcohols according to claim 6, wherein a mass ratio of the NiSnCS nano-catalyst to an inorganic base to a lower alcohol to water is 1:(1-4):(10-43):(10-43), a catalysis temperature is 200 C.-270 C., and a pressure is 0.1-2 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a SEM image of an embedded hydrothermal-resistant NiSnCS nano-catalyst in Example 4 of the present invention;

[0030] FIG. 2 is a TEM image of the embedded hydrothermal-resistant NiSnCS nano-catalyst in Example 4 of the present invention at different magnifications;

[0031] FIG. 3 is a TEM image of the embedded hydrothermal-resistant NiSnCS nano-catalyst in Example 4 of the present invention after 5 cycles;

[0032] FIG. 4 is a TEM image of a NiSn nano-catalyst in Comparative Example 3 of the present invention;

[0033] FIG. 5 is a TEM image of an embedded hydrothermal-resistant NiSnCS nano-catalyst in Example 6 of the present invention;

[0034] FIG. 6 is a TEM image of an embedded hydrothermal-resistant NiSnCS nano-catalyst in Comparative Example 2 of the present invention;

[0035] FIG. 7 is a XRD diagram of embedded hydrothermal-resistant NiSnCS nano-catalysts in Examples 1 to 5 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The present invention will be further described in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventional purchased raw materials and reagents.

Example 1

[0037] A preparation method for an embedded hydrothermal-resistant NiSnCS nano-catalyst included the following steps: [0038] S1, certain amounts of Ni(NO.sub.3).sub.2.Math.6H.sub.2O, SnCl.sub.4.Math.5H.sub.2O and chitosan (Mw: 700-1000) were simultaneously added to an acetic acid aqueous solution, and stirred to form a homogenous sol, where a mass ratio of Ni(NO.sub.3).sub.2.Math.6H.sub.2O to SnCl.sub.4.Math.5H.sub.2O to chitosan to acetic acid to water was 1.84:0.055:1:0.63:50, i.e. a molar ratio of a metal precursor (a mixture of the Ni salt and the Sn salt) to chitosan monomer was 1:1; and [0039] S2, the sol obtained in S1 was transferred to a 50 C. drying oven for drying for 48 hours to obtain a NiSnCS nano-catalyst precursor, and then the nano-catalyst precursor was subjected to carbonization treatment at 500 C. in N2 atmosphere for 2 hours to obtain the embedded hydrothermal-resistant NiSnCS nano-catalyst.

Example 2

[0040] A preparation method for an embedded hydrothermal-resistant NiSnCS nano-catalyst included the following steps: [0041] S1, certain amounts of Ni(NO.sub.3).sub.2.Math.6H.sub.2O, SnCl.sub.4.Math.5H.sub.2O and chitosan (Mw: 50000) were simultaneously added to an acetic acid aqueous solution, and stirred to form a homogenous sol, where a mass ratio of Ni(NO.sub.3).sub.2.Math.6H.sub.2O to SnCl.sub.4.Math.5H.sub.2O to chitosan to acetic acid to water was 1.84:0.66:1:0.63:50, i.e. a molar ratio of a metal precursor (a mixture of the Ni salt and the Sn salt) to chitosan monomer was 1:1; and [0042] S2, the sol obtained in S1 was transferred to a 50 C. drying oven for drying for 48 hours to obtain a NiSnCS nano-catalyst precursor, and then the nano-catalyst precursor was subjected to carbonization treatment at 500 C. in N2 atmosphere for 2 hours to obtain the embedded hydrothermal-resistant NiSnCS nano-catalyst.

Example 3

[0043] A preparation method for an embedded hydrothermal-resistant NiSnCS nano-catalyst included the following steps: [0044] S1, certain amounts of Ni(NO.sub.3).sub.2.Math.6H.sub.2O, SnCl.sub.4.Math.5H.sub.2O and chitosan (Mw: 100000) were simultaneously added to an acetic acid aqueous solution, and stirred to form a homogenous sol, where a mass ratio of Ni(NO.sub.3).sub.2.Math.6H.sub.2O to SnCl.sub.4.Math.5H.sub.2O to chitosan to acetic acid to water was 1.84:0.11:1:0.63:50, i.e. a molar ratio of a metal precursor (a mixture of the Ni salt and the Sn salt) to chitosan monomer was 1:1; and [0045] S2, the sol obtained in S1 was transferred to a 50 C. drying oven for drying for 48 hours to obtain a NiSnCS nano-catalyst precursor, and then the nano-catalyst precursor was subjected to carbonization treatment at 500 C. in N2 atmosphere for 2 hours to obtain the embedded hydrothermal-resistant NiSnCS nano-catalyst.

Examples 4 to 5

[0046] In Example 4, the chitosan of S1 has a Mw of 150000, and others were the same as those in Example 3.

[0047] In Example 5, the chitosan of S1 has a Mw of 250000, and others were the same as those in Example 3.

Examples 6 to 7

[0048] In Example 6, temperature of the carbonization treatment in S2 was 400 C., and others were the same as those in Example 4.

[0049] In Example 7, temperature of the carbonization treatment in S2 was 600 C., and others were the same as those in Example 4.

Examples 8 to 9

[0050] In Example 8, duration of the carbonization treatment in S2 was 1 hour, and others were the same as those in Example 4.

[0051] In Example 9, duration of the carbonization treatment in S2 was 4 hours, and others were the same as those in Example 4.

Examples 10 to 12

[0052] In Example 10, a molar ratio of the mixture of Ni salt and Sn salt to chitosan was 1:1.5 in S1, and others were the same as those in Example 4.

[0053] In Example 11, a molar ratio of the mixture of Ni salt and Sn salt to chitosan was 1:2 in S1, and others were the same as those in Example 4.

[0054] In Example 12, a molar ratio of the mixture of Ni salt and Sn salt to chitosan was 1:0.2 in S1, and others were the same as those in Example 4.

Comparative Examples 1 to 2

[0055] In Comparative Example 1, temperature of the carbonization treatment in S2 was 300 C., and others were the same as those in Example 4.

[0056] In Comparative Example 2, temperature of the carbonization treatment in S2 was 700 C., and others were the same as those in Example 4.

Comparative Example 3

[0057] A preparation method for a NiSn nano-catalyst included the following steps: [0058] S1, certain amounts of Ni(NO.sub.3).sub.2.Math.6H.sub.2O and SnCl.sub.4.Math.5H.sub.2O were simultaneously added to an acetic acid aqueous solution, and stirred to form a uniform solution, where a mass ratio of Ni(NO.sub.3).sub.2.Math.6H.sub.2O to SnCl.sub.4.Math.5H.sub.2O to acetic acid to water was 1.84:0.11:0.63:50; and [0059] S2, the uniform solution obtained in S1 was transferred to a 50 C. drying oven for drying for 48 hours to obtain a NiSn nano-catalyst precursor, and then the nano-catalyst precursor was subjected to carbonization treatment at 500 C. in N2 atmosphere for 2 hours to obtain the NiSn nano-catalyst.

TABLE-US-00001 TABLE 1 Summary of respective examples and comparative examples Molar Temper- ratio of ature Duration Molar mixture of of ratio of Ni salt car- car- of Ni and Sn bonization bonization salt to salt to Number Mw treatment treatment Sn salt chitosan Example 1 700- 500 C. 2 h 1:0.03 1:1 1000 Example 2 50000 500 C. 2 h 1:0.24 1:1 Example 3 100000 500 C. 2 h 1:0.06 1:1 Example 4 150000 500 C. 2 h 1:0.06 1:1 Example 5 250000 500 C. 2 h 1:0.06 1:1 Example 6 150000 400 C. 2 h 1:0.06 1:1 Example 7 150000 600 C. 2 h 1:0.06 1:1 Example 8 150000 500 C. 1 h 1:0.06 1:1 Example 9 150000 500 C. 4 h 1:0.06 1:1 Example 10 150000 500 C. 2 h 1:0.06 1:1.5 Example 11 150000 500 C. 2 h 1:0.06 1:2 Example 12 150000 500 C. 2 h 1:0.06 1:0.2 Comparative 150000 300 C. 2 h 1:0.06 1:1 Example 1 Comparative 150000 700 C. 2 h 1:0.06 1:1 Example 2 Comparative / 500 C. 2 h 1:0.06 / Example 3

Result Test

(1) SEM and TEM Tests

[0060] FIG. 1 and FIG. 2 are the SEM image and TEM images at different magnifications of the NiSnCS nano-catalyst in Example 4, respectively. From the SEM image, it can be seen that the prepared catalyst has an embedded structure, with carbon-wrapped NiSn nanoparticles embedded in a thin layer of carbon, with small particle diameter and good dispersion. FIG. 3 shows the TEM image of the product obtained in Example 4 after 5 cycles of catalysis. Compared with the structure before the reaction (FIG. 2), it can be seen that the catalyst structure is stable. FIG. 4 shows the TEM image of the product obtained from Comparative Example 3, which shows that the NiSn nanoparticles are relatively large and severely agglomerated. FIG. 5 shows the TEM image of the product obtained in Example 6, where the NiSn nanoparticles in the catalyst are larger and the carbon layer is thicker. FIG. 6 shows the TEM image of the product obtained from Comparative Example 2, wherein the NiSn nanoparticles in the catalyst have a larger particle size and are prone to aggregation, resulting in poor dispersion, and low reaction activity.

(2) XRD Test

[0061] The XRD diagram of the products obtained in Examples 1-5 of the present invention are shown in FIG. 7. As the molecular weight of chitosan increases, the characteristic diffraction peaks of metal Ni and NiSnCS gradually increase. NiSnCS plays a decisive role in the catalytic process, indicating that chitosan as a carbon source in the carbon shell layer is beneficial for achieving the stability of the metal sites. However, as the molecular weight of chitosan continues to increase, the crystal phases of metal Ni and NiSnCS gradually weaken.

(3) Catalysis Performance Test of Catalyst

[0062] The test method is as follows: the products obtained from Examples 1 to 12 and Comparative Examples 1 to 3, with a homogeneous base (NaOH), synergistically catalyzed the carbon-carbon coupling reaction of ethanol to form higher fuel alcohols in a 70 mL steel magnetic stirring reactor. The mass ratio of catalyst to NaOH to ethanol to water was 1:3:33:33, the reaction temperature was 230 C., the initial pressure was 0.1 MPa, and the reaction duration was 12 hours. After the reaction was completed, the reactor was cooled to room temperature, and then centrifugation and filtration were carried out to obtain liquid and catalyst solid phases. The gas and liquid phase products were collected, and the liquid phase product was centrifuged and left to stand to accelerate spontaneous phase separation and obtain organic and aqueous phases. The liquid phase product was separated by centrifugation and analyzed by gas chromatography. The main product in the organic phase is C4+ higher alcohols. The catalyst prepared in Example 4 was taken for repeating the synergistic catalysis, with homogeneous base (NaOH), of the carbon-carbon coupling reaction of ethanol to form higher in the magnetic stirring reactor, under the same conditions as above. This process was repeated four times.

TABLE-US-00002 TABLE 2 Catalytic activity results of the products obtained in respective examples and comparative examples Ethanol Yield of Selectivity conversion higher of higher rate alcohol alcohol Number (C-mol %) (C-mol %) (%) Example 1 60.5 37.2 92.3 Example 2 61.3 38.6 91.8 Example 3 69.0 38.2 94.7 Example 4 68.7 39.7 98.7 Example 5 66.1 41.5 94.2 Example 6 68.4 38.2 93.8 Example 7 63.9 38.5 94.6 Example 8 55.4 32.3 83.8 Example 9 52.9 31.6 82.1 Example 10 66.3 40.5 93.9 Example 11 58.8 35.4 88.2 Example 12 53.2 33.7 85.9 Comparative 28.2 11.3 76.7 Example 1 Comparative 8.7 4.5 96.7 Example 2 Comparative 28.2 11.3 76.7 Example 3

[0063] From Examples 1-5, it can be seen that during the preparation process, as the molecular weight of chitosan increases, the catalytic effect of the prepared catalyst for synthesizing higher alcohols shows an increasing trend followed by a decreasing trend. This may be related to the thickness of the carbon shell layer wrapped around the surface of NiSn nanoparticles. Appropriate carbon shell thickness is beneficial for protecting the metal core of the catalyst, enhancing its catalytic stability in hydrothermal reaction environment, and thus improving the conversion rate of ethanol and the selectivity of liquid-phase generation. As the molecular weight of chitosan continues to increase, the thickness of the carbon shell layer also increases, which is not conducive to the material transfer between the aqueous phase and the metal active core of the catalyst in the reaction, resulting in a decrease in the conversion rate of ethanol.

[0064] From Example 4, Examples 6-7, and Comparative Examples 1-2, it can be seen that a too low carbonization temperature can lead to insufficient carbonization of chitosan and incomplete exposure of metal active sites; while a too high carbonization temperature may easily cause the metal particles to aggregate and grow, thereby affecting the catalytic activity of the catalyst. Among them, the embedded hydrothermal-resistant NiSnCS nano-catalyst prepared at a carbonization temperature of 500 C. has better catalytic activity.

[0065] From Examples 4 and 8-9, it can be seen that a short carbonization duration can lead to insufficient carbonization of chitosan, incomplete reduction of metal ions, and a decrease in metal active sites; while a too long carbonization duration can damage the structure of the carbon layer and cause metal particles to aggregate and grow, thereby affecting the catalytic activity of the catalyst. Among them, the embedded hydrothermal-resistant NiSnCS nano-catalyst prepared with a carbonization duration of 2 hours has better catalytic activity.

[0066] From Examples 4 and 10-12, it can be seen that the molar ratio of the mixture of Ni salt and Sn salt to chitosan is too small, so that the metal active sites on the catalyst are too less and the catalyst performance is poor; while the molar ratio of the mixture of Ni salt and Sn salt to chitosan is too high, and chitosan cannot fully reduce metal ions, as well as NiSn nanoparticles cannot be fully embedded into the carbon layer, thereby reducing the activity of the catalyst. Among them, the embedded hydrothermal-resistant NiSnCS nano-catalyst prepared with a molar ratio of a mixture of Ni salt and Sn salt to chitosan being 1:1 has better catalytic activity.

[0067] The catalysts prepared by the present invention exhibit excellent performance in catalyzing the synthesis of C4+ higher alcohols from ethanol, with the highest ethanol conversion rate reaching 66.3% and the C4+ higher alcohol selectivity reaching 85.1%.

TABLE-US-00003 TABLE 3 The 1.sup.st, 3.sup.rd, and 5.sup.th Catalytic activity results of the catalyst prepared in Example 4 Ethanol Yield of Selectivity conversion higher of higher rate alcohol alcohol Number (C-mol %) (C-mol %) (%) The 1.sup.st time 66.3 39.7 95.5 The 3.sup.rd time 65.9 38.4 95.2 The 5.sup.th time 65.7 36.5 94.8

[0068] The catalytic activity results of the catalyst prepared in Example 4 in catalyzing the synthesis of C4+ higher alcohols from ethanol are shown in Table 3. From the data in the table, it can be seen that its catalytic performance is stable. Even after the fifth cycle of catalysis, the ethanol conversion rate is still as high as 65.7%, and the C4+ higher alcohol selectivity reaches 94.8%. 5 Obviously, the above embodiments of the present invention are only examples provided to clearly illustrate the present invention, and are not limitations on the embodiments of the present invention. For ordinary technical personnel in the art, other forms of changes or modifications can be made based on the above description. It is not necessary and impossible to exhaustively list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.