Nickel-based catalyst as well as preparation method and application thereof

Abstract

The invention discloses a nickel-based catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalyst synthesis. The nickel-based catalyst is prepared by an equivalent-volume impregnation method, a mechanochemical method and a deposition-precipitation method, the operation is simple, the cost is low, and the used raw materials are few; the method for regulating and controlling the selectivity of the prepared nickel-based catalyst to C4 olefin is simple and easy to implement, and the waterproof performance is good. According to the nickel-based catalyst, niobium oxide is used as a carrier, nickel is loaded on the niobium oxide carrier to catalyze heterogeneous ethylene oligomerization reaction, no co-catalyst is needed, the dispersity of loaded metal is effectively increased, carbon deposition and blockage are not prone to occurring in the reaction process, and the catalytic stability of the nickel-based catalyst for catalyzing the ethylene oligomerization reaction is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst synthesis, and particularly relates to a nickel-based catalyst, a preparation method thereof and an application thereof. Background Art

[0002] In modern chemical industry, a large amount of linear 1-butene and linear 2-butene are required, and their main utilization methods are to polymerize into chemical products such as high-carbon number polymers and antioxidants. Linear α-olefins (LAOs) have also been an important high-end chemical raw material in the chemical industry, mainly including 1-butene, 1-hexene, 1-octene, etc., and are widely used in ethylene copolymer monomers (C4-6), LLDPE copolymer monomers (C6, C8), and plasticizer alcohols (C8-10). At present, the main production method of α-olefins is ethylene oligomerization, and the ethylene in this method comes from naphtha cracking or ethane cracking, and the energy consumption of its production raw material ethylene is relatively large. At present, nickel-based catalysts have been proven to have good effects in the production of 1-butene. As a 2-olefin which is an isomer of 1-butene, it has important applications in the polymerization industry and the olefin disproportionation field. Therefore, developing a method for selectively regulating the carbon four olefins in ethylene oligomerization has high research value in modern chemical industry. Chinese Patent with publication number CN107159278A uses a ferric sulfate and nickel sulfate type supported catalyst (the carrier is alumina with a macroporous structure) to oligomerize butene, and realizes the effective dimerization of butene under the process conditions of 165~215 °C and 1.2~6.0 MPa. Chinese Patent with publication number CN118878390A uses a boron element modified nickel-based catalyst to oligomerize propylene and n-butene raw materials, and the product is separated to obtain products with carbon number from six to ten, and directly realizes the oligomerization reaction of mixed olefin feed under specific process conditions. Chinese Patent with publication number CN119406456A uses a catalytic system of a carbon chromium-based catalyst, an organic boron assistant and an aluminum-containing activator to realize the selective oligomerization of ethylene, which has high catalytic activity, good repeatability and stable operation. However, it requires the participation of an organic boron assistant and an aluminum-containing activator, and the catalyst recovery is difficult and the preparation method is cumbersome.

[0003] For the preparation of carbon four olefins by ethylene oligomerization, the related technologies use molecular sieves to support active metals, but the durability of the catalyst is poor, and it is easy to form carbon deposits, and there is also a lack of relevant methods for regulating the carbon four olefin products. Therefore, it is of great significance to develop a method for selectively regulating the carbon four products in ethylene oligomerization. Summary of the Invention

[0004] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, the abstract of the specification and the title of the invention of the present application to avoid obscuring the purpose of this part, the abstract of the specification and the title of the invention, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0005] In view of the above problems and / or problems existing in the prior art, the present invention is proposed.

[0006] One object of the present invention is to provide a method for preparing a nickel-based catalyst. The prepared nickel-based catalyst is used as a catalyst to catalyze the oligomerization of ethylene into C4 olefins, showing high selectivity controllability and stability.

[0007] To solve the above technical problems, the present invention provides the following technical solution: A method for preparing a nickel-based catalyst, comprising,

[0008] Using ordinary niobium oxide as a catalyst support and a nickel salt solution as a precursor for loading metals, under the condition that water is used as a solvent, the incipient wetness impregnation method or the deposition precipitation method is used to load metallic nickel on the niobium oxide support to obtain a catalyst precursor;

[0009] Performing heat treatment on the catalyst precursor to obtain the nickel-based catalyst;

[0010] Wherein, the nickel-based catalyst is a niobium oxide support and active metallic nickel attached to the niobium oxide support, and the content of nickel in the nickel-based catalyst is 3-6 wt%, more preferably 3 wt%.

[0011] As a preferred embodiment of the method for preparing the nickel-based catalyst of the present invention, wherein: the particle size of the nickel-based catalyst is 20-60 mesh, more preferably 20-40 mesh.

[0012] The present invention uses ordinary niobium oxide as a catalyst support, which provides good conditions for the high dispersion of active metallic nickel on the support, increases the dispersion of the loaded metal, is not easily carbon-deposited and blocked during the reaction, and improves the catalytic stability of the nickel-based catalyst. In addition, the nickel-based catalyst prepared by the present invention is a heterogeneous catalyst, having better stability and a larger specific surface area, and is more easily recovered compared with homogeneous oligomerization catalysts.

[0013] As a preferred embodiment of the method for preparing the nickel-based catalyst of the present invention, wherein: the purity of the ordinary niobium oxide is 99.9%;

[0014] The nickel salt solution is a nickel nitrate solution or a nickel sulfate solution, and the molar concentration of nickel in the nickel salt solution is 0.1-0.4 mol / L, more preferably 0.1 mol / L.

[0015] In the present invention, the nickel salt solution is preferably a nitrate or a sulfate, more preferably a hydrated nitrate or a hydrated sulfate, and specifically preferably nickel nitrate hexahydrate or nickel sulfate hexahydrate. In the present invention, during the calcination of the catalyst, sulfate radicals cannot be completely removed by calcination and are enriched on the surface of the catalyst. Compared with nitrates, the acidity of the catalyst will increase when sulfates are used. In the present invention, the preparation method of the nickel salt solution preferably includes: dissolving nickel nitrate hexahydrate or nickel sulfate hexahydrate in water and performing ultrasonic treatment to obtain the nickel salt solution. In the present invention, the water is preferably deionized water. In the present invention, the frequency of the ultrasonic treatment is preferably 50 Hz, and the time is preferably 10 min.

[0016] In the present invention, the incipient wetness impregnation method can uniformly disperse nickel, an active metal, onto the niobium oxide support, improving the atomic utilization rate. The catalyst prepared by the deposition precipitation method has a better dispersion degree of the active metal and higher activity compared to the catalyst prepared by the mechanochemical method.

[0017] As a preferred embodiment of the preparation method of the nickel-based catalyst of the present invention, in the incipient wetness impregnation method: the nickel salt solution is dropped into the niobium oxide support and continuously stirred. The rotational speed of the rotor stirring is preferably 200 - 800 r / min, specifically preferably 450 r / min; the time for single impregnation is preferably 2 - 10 h, specifically preferably 8 h; then it is placed in an oven for drying. The drying temperature is preferably 60 - 120 °C, specifically preferably 100 °C, and the drying time is preferably 8 - 12 h, specifically preferably 10 h, to obtain a catalyst precursor.

[0018] As a preferred embodiment of the preparation method of the nickel-based catalyst of the present invention, in the deposition precipitation method: the niobium oxide support is dispersed in water, then the nickel salt solution is dropped, and it is continuously stirred at a speed of 200 - 800 r / min, specifically preferably 450 r / min; then a precipitant is slowly dropped, and the mixture is heated and stirred to obtain a mixed solution. After the mixed solution is filtered and washed until neutral, it is placed in an oven for drying. The drying temperature is preferably 60 - 120 °C, specifically preferably 100 °C, and the drying time is preferably 8 - 12 h, specifically preferably 10 h, to obtain a catalyst precursor.

[0019] As a preferred embodiment of the preparation method of the nickel-based catalyst of the present invention, the precipitant includes ammonia water or urea.

[0020] After the deposition is completed, the present invention performs heat treatment on the catalyst precursor to obtain the nickel-based catalyst.

[0021] As a preferred embodiment of the preparation method of the nickel-based catalyst of the present invention, wherein: for the heat treatment, the dried catalyst precursor is ground and calcined in a muffle furnace; the atmosphere for the heat treatment is preferably air or nitrogen, more preferably air; the temperature is preferably 200-800 °C, specifically preferably 400 °C, 500 °C or 600 °C; the heating rate for heating to the temperature of the heat treatment is preferably 0.5-5 °C / min, specifically preferably 2 °C / min; the time is preferably 4-6 h, more preferably 4 h.

[0022] Another object of the present invention is to provide a nickel-based catalyst obtained by the preparation method as described above.

[0023] Another object of the present invention is to provide a method for regulating the selectivity of ethylene oligomerization to C4 olefins, including,

[0024] Ethylene undergoes an oligomerization reaction on a fixed-bed reactor under the action of a nickel-based catalyst to obtain the C4 olefins;

[0025] The nickel-based catalyst is the nickel-based catalyst as described above.

[0026] As a preferred embodiment of the method for regulating the selectivity of ethylene oligomerization to C4 olefins of the present invention, wherein: the nickel-based catalyst is pretreated with nitrogen, the pretreatment temperature is 300 °C, and the pretreatment time is 2-8 h;

[0027] The temperature of the ethylene oligomerization reaction is preferably 130-330 °C, preferably 130-260 °C, and specifically can be 130 °C, 200 °C, 250 °C, 300 °C; the pressure is preferably 1-3 MPa, and specifically can be 1 MPa, 2 MPa, 2.5 MPa or 3 MPa;

[0028] The weight hourly space velocity of the ethylene feed is 3-10 h -1 , specifically can be 7.5 h -1 .

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The preparation method provided by the present invention prepares a nickel-based catalyst by the incipient wetness impregnation method or the deposition precipitation method, which is simple and efficient in operation, uses less raw materials, and has low cost; the present invention uses niobium oxide as a carrier, which can effectively load and disperse the active metal nickel, and is not prone to a large amount of carbon deposition during the oligomerization reaction, and is not easily blocked during the reaction, and improves the catalytic stability of the nickel-based catalyst in the ethylene oligomerization reaction compared with the molecular sieve-supported nickel-based catalyst.

[0031] In the present invention, the nickel-based catalyst prepared by the above technical solution is used as a catalyst to catalyze the oligomerization of ethylene into C4 olefins, showing high selectivity controllability and stability. The oligomerization reaction of the present invention is carried out in a fixed-bed reactor, which can realize continuous production and is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0033] Figure 1 XRD pattern of the catalyst prepared in Example 5 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail in conjunction with the embodiments of the specification.

[0035] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar promotions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0036] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that mutually excludes other embodiments.

[0037] Unless otherwise specified, the raw materials used in the embodiments are all commercially purchased.

[0038] Example 1

[0039] Dissolve 0.297 g of Ni(NO3)3·6H2O in 5 mL of deionized water, and continuously sonicate it in an ultrasonic bath at 50 Hz for 10 min to obtain a metal salt solution with a nickel nitrate concentration of 0.1 mol / L. Weigh 2 g of niobium oxide support, slowly add the nickel nitrate salt solution to the niobium oxide support, and continuously stir at a speed of 450 r / min for 8 h. Then place it in an oven for drying, with a drying temperature of 100 °C and a drying duration of 10 h. After drying, grind the catalyst, place it in a muffle furnace for calcination, with the heat treatment atmosphere being air, the calcination temperature set at 400 °C, the calcination time set at 4 h, and the heating rate set at 2 °C / min. After calcination, grind it in a mortar, and then perform tabletting and screening to screen it to a particle size of 20 - 40 mesh to obtain the nickel-based catalyst, which is named Ni / Nb2O5-im.

[0040] Subsequently, dilute it with quartz sand and place it in a fixed-bed reactor. The catalyst bed is fixed in the isothermal section of the reactor using quartz wool. The catalyst is pretreated with nitrogen, with the pretreatment temperature set at 300 °C, the pretreatment time set at 2 h, and the heating rate of 2 °C / min. Its weight hourly space velocity is 7.5 h -1 。

[0041] The obtained series of nickel-based catalysts are used for the oligomerization reaction of ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 1. The ethylene conversion rate and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 1.

[0042] Table 1 Reaction conditions and test results of the series of catalysts obtained in Example 1

[0043]

[0044] It can be seen from Table 1 that when the temperature is 130 °C and the pressure is 3 MPa, the selectivity of 1-butene is the highest.

[0045] Example 2

[0046] Dissolve 0.268 g of NiSO4·6H2O in 5 mL of deionized water, and continuously ultrasonicate it in an ultrasonic bath at 50 Hz for 10 min to obtain a metal salt solution with a nickel sulfate concentration of 0.1 mol / L. Weigh 2 g of niobium oxide support, slowly drop the nickel nitrate salt solution into the niobium oxide support, and continuously stir at a rotation speed of 450 r / min for 8 h. Then place it in an oven for drying, with a drying temperature of 100 °C and a drying duration of 10 h. After drying, grind the catalyst, place it in a muffle furnace for calcination, with the heat treatment atmosphere being air, the calcination temperature set at 400 °C, the calcination time set at 4 h, and the heating rate set at 2 °C / min. After calcination, place it in a mortar for grinding, and then perform tablet screening to screen it to a particle size of 20 - 40 mesh to obtain the nickel-based catalyst, which is named NiSO4 / Nb2O5-im.

[0047] Subsequently, dilute it with quartz sand and place it in a fixed-bed reactor. The catalyst bed is fixed in the isothermal section of the reactor using quartz wool. The catalyst is pretreated with nitrogen, with the pretreatment temperature set at 300 °C, the pretreatment time set at 2 h, and the heating rate of 2 °C / min. Its weight hourly space velocity is 7.5 h -1 。

[0048] The obtained series of nickel-based catalysts are subjected to an oligomerization reaction of ethylene to produce C4 olefins under the conditions (pressure, temperature) shown in Table 2. The ethylene conversion rate and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 2.

[0049] Table 2 Reaction conditions and test results of the series of catalysts obtained in Example 2

[0050]

[0051] It can be seen from Table 2 that the selectivity of 2-butene on the niobium oxide support loaded with nickel sulfate is higher than that in Example 1.

[0052] Example 3

[0053] Weigh 0.268 g of NiSO4·6H2O and 2 g of niobium oxide support, place them together in a mortar, carefully grind them for 0.5 h, and then place the catalyst precursor in a muffle furnace for calcination. The calcination atmosphere is air, the calcination temperatures are 400 °C, 500 °C, and 600 °C, the heating rate is 2 °C / min. After calcination, nickel-based catalysts are obtained, named NiSO4 / Nb2O5-me-400, NiSO4 / Nb2O5-me-500, and NiSO4 / Nb2O5-me-600.

[0054] Subsequently, it was diluted with quartz sand and placed in a fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen. The pretreatment temperature was set at 300 °C, the pretreatment time was set at 2 h, the heating rate was 2 °C / min, and the weight hourly space velocity was 7.5 h -1 .

[0055] The obtained series of nickel-based catalysts were subjected to oligomerization reaction of ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 3. The ethylene conversion rate and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 3

[0056] Table 3 Reaction conditions and test results of the series of catalysts obtained in Example 3

[0057]

[0058] It can be seen from Table 3 that as the calcination temperature increases, the ethylene conversion rate gradually decreases

[0059] Example 4

[0060] Disperse 2 g of niobium oxide support in 30 ml of deionized water; place it in an ultrasonic bath and continuously ultrasonicate for 10 min at 50 Hz to disperse it. Subsequently, weigh 0.297 g of Ni(NO3)3·6H2O and dissolve it in 5 mL of deionized water, and continuously ultrasonicate in the ultrasonic bath for 10 min at 50 Hz to obtain a metal salt solution with a nickel nitrate concentration of 0.1 mol / L. Slowly drop the metal salt solution into the niobium oxide support and deionized water, and continuously stir at a rotation speed of 450 r / min. Subsequently, slowly drop the precipitant ammonia water and then heat and stir to obtain a mixed solution. The heating temperature is 70 °C. Filter and wash the mixed solution until it is neutral, and then place it in an oven for drying. The drying temperature is set at 100 °C, and the drying time is set at 10 h to obtain a catalyst precursor. After drying, grind the catalyst, place it in a muffle furnace for calcination. The heat treatment atmosphere is air, the calcination temperature is set at 400 °C, the calcination time is set at 4 h, and the heating rate is set at 2 °C / min. After calcination, place it in a mortar for grinding, and then perform tabletting and screening to screen it to a particle size of 20 - 40 mesh to obtain the nickel-based catalyst, and name the catalyst Ni / Nb2O5-NH4OH

[0061] Subsequently, it was diluted with quartz sand and placed in a fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen. The pretreatment temperature was set at 300 °C, the pretreatment time was set at 2 h, the heating rate was 2 °C / min, and the weight hourly space velocity was 7.5 h -1 .

[0062] The obtained series of nickel-based catalysts were subjected to oligomerization reaction of ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 4. The ethylene conversion rate and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 4.

[0063] Table 4 Reaction conditions and test results of the series of catalysts obtained in Example 4

[0064]

[0065] It can be seen from Table 4 that the conversion rate of the catalyst prepared in Example 4 is higher than that of the previous examples.

[0066] Example 5

[0067] Disperse 2 g of niobium oxide support in 30 ml of deionized water; place it in an ultrasonic bath and continuously ultrasonic for 10 min at 50 Hz to disperse it. Then weigh 0.297 g of Ni(NO3)3·6H2O and dissolve it in 5 mL of deionized water, and continuously ultrasonic for 10 min at 50 Hz in the ultrasonic bath to obtain a metal salt solution with a nickel nitrate concentration of 0.1 mol / L. Slowly drop the metal salt solution into the niobium oxide support and deionized water, and continuously stir at a speed of 450 r / min. Then slowly drop the precipitant urea and heat and stir to obtain a mixed solution. The heating temperature is 70 °C. Filter and wash the mixed solution until it is neutral, then place it in an oven for drying. The drying temperature is set at 100 °C and the drying time is set at 10 h to obtain a catalyst precursor. After drying, grind the catalyst, place it in a muffle furnace for calcination. The heat treatment atmosphere is air, the calcination temperature is set at 400 °C, the calcination time is set at 4 h, and the heating rate is set at 2 °C / min. After calcination, grind it in a mortar, and then perform tablet screening to screen it to a particle size of 20-40 mesh to obtain the nickel-based catalyst, and name the catalyst Ni / Nb2O5-urea.

[0068] The XRD pattern of this catalyst is as Figure 1 shown. The XRD pattern shows diffraction peaks of the typical Nb2O5 phase (JCPDS #30-0873), and does not show NiO diffraction peaks, indicating that nickel is well dispersed on the support.

[0069] Subsequently, dilute it with quartz sand and place it in a fixed-bed reactor. The catalyst bed is fixed in the isothermal section of the reactor with quartz wool. The catalyst is pretreated with nitrogen. The pretreatment temperature is set at 300 °C, the pretreatment time is set at 2 h, and the heating rate is 2 °C / min. Its weight hourly space velocity is 7.5 h -1 .

[0070] The obtained series of nickel-based catalysts were used to oligomerize ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 5. The ethylene conversion rate and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 5.

[0071] Table 5 Reaction conditions and test results of the series of catalysts obtained in Example 5

[0072]

[0073] Example 6

[0074] Disperse 2 g of niobium oxide support in 30 ml of deionized water; place it in an ultrasonic bath and continuously ultrasonicate for 10 min at 50 Hz to disperse it. Subsequently, weigh 0.297 g of Ni(NO3)3·6H2O and dissolve it in 5 mL of deionized water, and continuously ultrasonicate in the ultrasonic bath for 10 min at 50 Hz to obtain a metal salt solution with a nickel nitrate concentration of 0.1 mol / L. Slowly add the metal salt solution to the niobium oxide support and deionized water, and continuously stir at a speed of 450 r / min. Then slowly add the precipitant urea and heat and stir to obtain a mixed solution. The heating temperature is 70 °C. Filter and wash the mixed solution until it is neutral, then place it in an oven for drying. The drying temperature is set at 100 °C, and the drying time is set at 10 h to obtain a catalyst precursor. After drying, grind the catalyst, place it in a muffle furnace for calcination. The heat treatment atmosphere is air, the calcination temperature is set at 400 °C, the calcination time is set at 4 h, and the heating rate is set at 2 °C / min. After calcination, a nickel-based catalyst is obtained. Name the catalyst Ni / Nb2O5-urea, place it in a mortar for grinding, and then perform tabletting and screening, and screen it to particle sizes of 20-40 mesh, 40-60 mesh, and 100 mesh respectively.

[0075] Subsequently, dilute it with quartz sand and place it in a fixed-bed reactor. The catalyst bed is fixed in the constant-temperature section of the reactor with quartz wool. The catalyst is pretreated with nitrogen. The pretreatment temperature is set at 300 °C, the pretreatment time is set at 2 h, and the heating rate is 2 °C / min. Its weight hourly space velocity is 7.5 h -1 。

[0076] The obtained series of nickel-based catalysts were used to oligomerize ethylene to C4 olefins at the particle sizes shown in Table 6, with a pressure of 2 MPa and a temperature of 130 °C. The ethylene conversion rate and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 6.

[0077] Table 6 Reaction conditions and test results of the series of catalysts obtained in Example 6

[0078]

[0079] In summary, when nickel sulfate is used as the metal salt solution, the selectivity of 2-butene in the ethylene oligomerization to produce C4 olefins is increased. While when nickel nitrate is used as the metal salt solution, the selectivity of 1-butene is increased. Using urea as the precipitant in the deposition precipitation method can improve the activity of the catalyst under the same conditions.

[0080] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A preparation method of a nickel-based catalyst, characterized in that: Comprising, Using ordinary niobium oxide as a catalyst support and nickel salt solution as a precursor for supported metal, under the condition that water is used as a solvent, the metal nickel is loaded on the niobium oxide support by the incipient wetness impregnation method or the deposition-precipitation method to obtain a catalyst precursor; Performing heat treatment on the catalyst precursor to obtain the nickel-based catalyst; Wherein, the nickel-based catalyst is a niobium oxide support and active metal nickel attached to the niobium oxide support, and the content of nickel in the nickel-based catalyst is 3-6 wt%.

2. The preparation method of the nickel-based catalyst according to claim 1, characterized in that: The purity of the ordinary niobium oxide is 99.9%; The nickel salt solution is nickel nitrate solution or nickel sulfate solution, and the molar concentration of nickel in the nickel salt solution is 0.1-0.4 mol / L.

3. The preparation method of the nickel-based catalyst according to claim 1, characterized in that: The particle size of the nickel-based catalyst is 20-60 mesh.

4. The preparation method of the nickel-based catalyst according to any one of claims 1 to 3, characterized in that: For the incipient wetness impregnation method, the nickel salt solution is dropped into the niobium oxide support and continuously stirred, the stirring speed is 200-800 r / min, the single impregnation time is 2-10 h, and then it is placed in an oven for drying, the drying temperature is 60-120 °C, and the drying time is 8-12 h to obtain a catalyst precursor.

5. The preparation method of the nickel-based catalyst according to any one of claims 1 to 3, characterized in that: For the deposition-precipitation method, the niobium oxide support is dispersed in water, then the nickel salt solution is dropped, and it is continuously stirred at a speed of 200-800 r / min, then a precipitant is dropped, and the mixture is heated and stirred to obtain a mixed solution. The mixed solution is filtered and washed to neutrality and then placed in an oven for drying, the drying temperature is 60-120 °C, and the drying time is 8-12 h to obtain a catalyst precursor.

6. The preparation method of the nickel-based catalyst according to claim 5, characterized in that: The precipitant includes ammonia water or urea.

7. The preparation method of the nickel-based catalyst according to claim 1, characterized in that: For the heat treatment, the dried catalyst precursor is ground and calcined in a muffle furnace. The atmosphere for heat treatment is air or nitrogen, the temperature is 200-800 °C, the heating rate to the heat treatment temperature is 0.5-5 °C / min, and the time is 4-6 h.

8. The nickel-based catalyst obtained by the preparation method according to any one of claims 1-7.

9. A method for regulating the selectivity of ethylene oligomerization to C4 olefins, characterized in that: Comprising, Ethylene undergoes an oligomerization reaction on a fixed-bed reactor under the action of the nickel-based catalyst to obtain the C4 olefin; The nickel-based catalyst is the nickel-based catalyst according to claim 8.

10. The method for regulating the selectivity of ethylene oligomerization to C4 olefins according to claim 9, characterized in that: The nickel-based catalyst is pretreated with nitrogen, the pretreatment temperature is 300 °C, the pretreatment time is 2-8 h, the temperature of the oligomerization reaction is 130-330 °C, and the pressure is 1-3 MPa; The weight hourly space velocity of the ethylene feed is 3 to 10 h -1 .

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