A niobium oxide supported nickel-based catalyst, its preparation method and use

Abstract

The application discloses a niobium oxide supported nickel-based catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a niobium source and a molybdenum source, adopting a coprecipitation method, adding a precipitator to adjust the pH to 9-11, and then performing washing, drying and calcination to obtain a Mo-doped niobium oxide carrier, wherein the molar ratio of the niobium source to the molybdenum source is 1:0.01-1:1; and the Mo-doped niobium oxide carrier is placed in an atomic layer deposition reaction cavity, nickel precursors and reaction gas are alternately pulsed and deposited, and after several deposition cycles, the niobium oxide supported nickel-based catalyst is obtained. The Mo element is introduced into the niobium oxide carrier in different proportions to perform doping modification, the acid property of the catalyst is adjusted, and the process condition is adjusted to enrich the trimer or tetramer product, so that the industrial application flexibility and economic value of the catalyst are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a niobium oxide supported nickel-based catalyst, its preparation method, and its application. Background Technology

[0002] Propylene oligomerization is an important type of olefin-value-adding conversion process that transforms propylene monomers into olefin products with higher carbon numbers (such as C6, C9, C10, C2 ... 12 + Olefins have wide applications in fine chemicals, fuel additives, surfactants, and lubricating oil intermediates. Besides dimerization products, propylene oligomerization also generates trimers, tetramers, and other oligomers. Therefore, designing suitable catalysts to regulate the product selectivity of propylene oligomerization is of significant research importance and application value.

[0003] Currently, heterogeneous catalysts used for propylene oligomerization mainly include solid phosphoric acid catalysts (SPA), molecular sieve catalysts, and supported nickel-based catalysts. Solid phosphoric acid catalysts are among the earliest industrially used catalysts, but they suffer from drawbacks such as low selectivity for higher oligomers, poor mechanical strength, easy sludge formation and agglomeration, and difficulty in regeneration. Molecular sieve catalysts (such as H-ZSM-5) have been extensively studied due to their regular pore structure and tunable acidity; however, their acidity control methods are limited, making it difficult to maintain high selectivity for products with specific degrees of polymerization while achieving high conversion rates.

[0004] In recent years, nickel-based heterogeneous catalysts have been considered highly efficient solid catalysts for propylene dimerization and oligomerization. Among them, niobium oxide (Nb₂O₅), as a novel solid acid support material, has attracted attention due to its unique surface acidity (possessing both Brønsted and Lewis acid sites) and strong metal-support interactions. There are existing reports on the use of nickel supported on niobium oxide for propylene oligomerization.

[0005] Chinese patent CN114054050B discloses a Ni-based solid acid catalyst for the dimerization of propylene to C6 olefins, its preparation method, and its application. The catalyst consists of a solid acid support and an active metal component, nickel, supported thereon, and catalyzes the oligomerization of high-pressure liquid propylene in a fixed-bed reactor. In this patent, the NiSO4 / Nb2O5 catalyst, under conditions of 50℃ and 3.0 MPa, achieves a propylene conversion of 92.3%, a dimerization selectivity of 88.2%, and a dimerization yield of 81.4%. Furthermore, Ling et al. demonstrated that the synergistic effect between NiSO4 and Nb2O5 can be adjusted by controlling the calcination temperature at 70℃, 2.5 MPa, and a liquid hourly space velocity of 3 h⁻¹. -1Under the given conditions, the NiSO4 / Nb2O5 catalyst calcined at 400℃ exhibited the highest propylene conversion (approximately 89%) and C6 product selectivity (75%).

[0006] However, existing Ni / Nb2O5 catalyst systems mainly focus on the dimerization of propylene, pursuing high selectivity for C6 products, but not for trimers (C9) and tetramers (C6). 12 + First, the selectivity is low. Second, the surface acidity and number of acid sites on pure niobium oxide supports are limited. Niobium oxide exhibits low acidity after calcination at 500℃. The lack of systematic methods for controlling the acidity of the support makes it difficult to fully utilize the synergistic catalytic effect between the nickel active component and the acidic sites on the support. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] One objective of this invention is to provide a method for preparing a niobium oxide-supported nickel-based catalyst, which involves doping and modifying the niobium oxide support by introducing different proportions of Mo, and enriching trimers (C9) or tetramers (C6) by adjusting the catalyst acidity and process conditions. 12 + This significantly enhances the industrial application flexibility and economic value of catalysts.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a niobium oxide-supported nickel-based catalyst, comprising, Niobium source and molybdenum source are mixed and co-precipitated. A precipitant is added to adjust the pH to 9-11. After washing, drying and calcination, Mo-doped niobium oxide support is obtained. The molar ratio of niobium source to molybdenum source is 1:0.01-1:1. The Mo-doped niobium oxide support was placed in an atomic layer deposition reaction chamber, and alternating pulse deposition was performed using a nickel precursor and a reaction gas. After several deposition cycles, the niobium oxide-supported nickel-based catalyst was obtained.

[0011] In a preferred embodiment of the preparation method of the niobium oxide supported nickel-based catalyst of the present invention, the niobium source is selected from at least one of ammonium oxalate niobate, niobium pentachloride, and niobium ethoxide; the molybdenum source is ammonium molybdate; and the precipitant is selected from at least one of ammonia, urea, ammonium carbonate, and ammonium bicarbonate.

[0012] In a preferred embodiment of the preparation method of the niobium oxide supported nickel-based catalyst of the present invention, the calcination temperature is 400~700℃.

[0013] In a preferred embodiment of the preparation method of the niobium oxide supported nickel-based catalyst of the present invention, the molar ratio of the niobium source to the molybdenum source is 1:0.05 to 1:0.5.

[0014] In a preferred embodiment of the preparation method of the niobium oxide supported nickel-based catalyst of the present invention, the nickel precursor of the atomic layer deposition is selected from at least one of nickel dicene, bis(methylcyclopentadienyl)nickel, Ni(thd)2, and Ni(dmamb)2; and the reaction gas is oxygen or ozone.

[0015] As a preferred embodiment of the preparation method of the niobium oxide supported nickel-based catalyst of the present invention, each deposition cycle of the atomic layer deposition includes: a nickel precursor vapor pulse for 0.5-10 s, followed by exposure for 10-60 s, and inert gas purging for 10-90 s; a reactant gas pulse for 0.5-10 s, followed by exposure for 10-60 s, and inert gas purging for 10-90 s.

[0016] In a preferred embodiment of the preparation method of the niobium oxide supported nickel-based catalyst of the present invention, the reaction chamber temperature of the atomic layer deposition is 150~350℃, and the deposition cycle is 10~300 times.

[0017] In a preferred embodiment of the preparation method of the niobium oxide-supported nickel-based catalyst of the present invention, the loading amount of Ni in the niobium oxide-supported nickel-based catalyst is 1~15wt%.

[0018] Another object of the present invention is to provide a niobium oxide-supported nickel-based catalyst prepared by the above-described preparation method, wherein the catalyst comprises a Mo-doped modified niobium oxide support and a NiO active component supported thereon.

[0019] As a preferred embodiment of the niobium oxide supported nickel-based catalyst of the present invention, wherein the Mo / Nb molar ratio in the catalyst is 0.01~1:1.

[0020] As a preferred embodiment of the niobium oxide-supported nickel-based catalyst of the present invention, wherein the Mo / Nb molar ratio in the catalyst is 0.05~0.3.

[0021] Another object of the present invention is to provide the application of the niobium oxide-supported nickel-based catalyst as described above in the oligomerization reaction of propylene, wherein the catalyst is loaded into a fixed-bed reactor, propylene feedstock is introduced, and the reaction is carried out at a reaction temperature of 50-100°C, a reaction pressure of 2.0-4.0 MPa, and a liquid hourly space velocity of 1-10 h⁻¹.-1 Propylene oligomerization reaction was carried out under the following conditions.

[0022] As a preferred embodiment of the application of the niobium oxide-supported nickel-based catalyst of the present invention in the propylene oligomerization reaction, wherein the reaction temperature of the propylene oligomerization reaction is 70~100℃ and the liquid hourly space velocity is 2~6h. -1 .

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention enhances the acidity of the niobium oxide support through Mo doping, resulting in a synergistic catalytic effect with the highly dispersed nickel active component precisely loaded by ALD, significantly improving the conversion rate of propylene. By controlling the Mo doping amount and combining it with ALD technology for precise control of the dispersion of the nickel active component, highly selective enrichment of products with specific degrees of polymerization can be achieved. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0025] Figure 1 The images show the XRD characterization of the A-1 and A-4 catalysts obtained in Example 1 of this invention. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0029] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0030] Example 1

[0031] (1) Preparation of Mo-doped niobium oxide support

[0032] Five mixed solutions of ammonium niobate oxalate (Nb source) and ammonium molybdate (Mo source) were prepared, with Nb:Mo molar ratios controlled at 1:0, 1:0.05, 1:0.1, 1:0.2, and 1:0.3, respectively. Each mixed solution was heated to 70°C and stirred until completely dissolved. Under vigorous stirring, ammonia (25 wt%) was added dropwise to adjust the pH to 9.0, and the reaction was continued for 8 h. The reaction product was washed with deionized water, filtered, and dried at 80°C for 12 h to obtain a powder. The obtained powder was calcined in air at a heating rate of 10°C / min to 500°C for 6 h. After cooling, niobium oxide supports with different Mo doping amounts were obtained, denoted as NbO. x (Pure Nb2O5), Mo 0.05 NbO x Mo 0.1 NbO x Mo 0.2 NbO x and Mo 0.3 NbO x .

[0033] (2) Atomic layer deposition (ALD) loading of nickel active components

[0034] Each of the above-mentioned supports was placed in an atomic layer deposition reaction chamber, and the reaction chamber was evacuated to a pressure of 2 Torr. Nickel-cerocenium (Ni(Cp)2) was used as the nickel precursor and heated to 150 °C to vaporize it; O2 was used as the reaction gas. The reaction chamber temperature was 250 °C.

[0035] Each ALD deposition cycle consisted of: a 3-second pulse of nickel-ceramic vapor followed by 30 seconds of exposure; nitrogen purging for 45 seconds; a 3-second pulse of O2 followed by 30 seconds of exposure; and nitrogen purging for 45 seconds. This deposition cycle was repeated 100 times to obtain a series of NiO-supported catalysts, designated A-1 (Mo / Nb=0), A-2 (Mo / Nb=0.05), A-3 (Mo / Nb=0.1), A-4 (Mo / Nb=0.2), and A-5 (Mo / Nb=0.3).

[0036] The XRD characterization of the A-1 and A-4 catalysts obtained in Example 1 of this invention is as follows: Figure 1 As shown in Table 1, the actual Ni loading in each catalyst was determined by ICP-OES.

[0037] Table 1 Elemental content of each catalyst in Example 1

[0038] The catalyst was loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 80 °C, a pressure of 3.0 MPa, and a liquid hourly space velocity of 6 h⁻¹. -1 Propylene oligomerization was carried out under certain conditions, and the results are shown in Table 2.

[0039] Table 2 Propylene oligomerization performance of each catalyst in Example 1

[0040] As shown in Table 2, as the Mo / Nb molar ratio increases from 0 to 0.3, the propylene conversion rate first increases and then decreases, reaching its highest level (85.1%) when Mo / Nb = 0.2. The C6 selectivity gradually decreases from 85.3% to 20.5%, while the C9 selectivity increases from 11.5% to 53.7%. 12 + The selectivity gradually increased from 3.2% to 25.8%, indicating that the degree of polymerization of propylene oligomers can be increased by adjusting the Mo / Nb ratio.

[0041] Example 2

[0042] (1) Preparation of Mo-doped niobium oxide support

[0043] Ammonium niobate oxalate and ammonium molybdate were uniformly dispersed in deionized water at a molar ratio of Nb:Mo = 1:0.2, and heated to 70 °C with stirring until completely dissolved. Under vigorous stirring, ammonia (25 wt%) was added dropwise to adjust the pH of the system to 8.0, 9.0, 10.0, and 11.0, respectively, and the reaction was continued with stirring for 8 h. The reaction product was washed with deionized water, filtered, and dried at 80 °C for 12 h to obtain a powder. The obtained powder was calcined in air at a heating rate of 10 °C / min to 500 °C for 6 h, and after cooling, Mo-doped niobium oxide supports prepared under different pH conditions were obtained.

[0044] (2) Atomic layer deposition (ALD) loading of nickel active components

[0045] Nickel was loaded with the same ALD parameters and number of cycles as in step (2) of Example 1 to obtain a series of catalysts, which are designated as B-1 (pH=8.0), B-2 (pH=9.0), B-3 (pH=10.0) and B-4 (pH=11.0).

[0046] ICP-OES analysis showed that the Ni loading in each catalyst was 3.4–3.6 wt%.

[0047] Table 3 Elemental content of each catalyst in Example 2

[0048] The catalyst was loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 80 °C, a pressure of 3.0 MPa, and a liquid hourly space velocity of 6 h⁻¹. -1 Propylene oligomerization was carried out under certain conditions, and the results are shown in Table 4.

[0049] Table 4. Propylene oligomerization performance of various catalysts in Example 2

[0050] As shown in Table 4, the propylene conversion rate was the highest (85.1%) when pH=9.0, and the C6 selectivity was 50.2%. Too low a pH (8.0) or too high a pH (11.0) both led to a decrease in conversion rate. This is because pH affects the hydrolysis and condensation behavior of Mo and Nb during coprecipitation, which in turn affects the uniformity of Mo doping in niobium oxide and the surface acidity.

[0051] Example 3

[0052] (1) Preparation of Mo-doped niobium oxide support

[0053] Ammonium niobate oxalate and ammonium molybdate were uniformly dispersed in deionized water at a molar ratio of Nb:Mo = 1:0.2, and heated to 70 °C with stirring until completely dissolved. Under vigorous stirring, ammonia water (25 wt%) was added dropwise to adjust the pH of the system to 9.0, and the reaction was continued with stirring for 8 h. The reaction product was washed with deionized water, filtered, and dried at 80 °C for 12 h to obtain a powder. The obtained powder was calcined in air at a heating rate of 10 °C / min to 400 °C, 500 °C, 600 °C, and 700 °C for 6 h, respectively. After cooling, Mo-doped niobium oxide supports calcined at different temperatures were obtained.

[0054] (2) Atomic layer deposition (ALD) loading of nickel active components

[0055] Nickel was loaded according to the same ALD parameters and number of cycles as in step (2) of Example 1, and a series of catalysts were obtained, which were denoted as C-1 (400℃), C-2 (500℃), C-3 (600℃) and C-4 (700℃).

[0056] The catalyst was loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 80 °C, a pressure of 3.0 MPa, and a liquid hourly space velocity of 6 h⁻¹. -1 Propylene oligomerization was carried out under certain conditions, and the results are shown in Table 5.

[0057] Table 5 Propylene oligomerization performance of various catalysts in Example 3

[0058] Table 5 shows that calcination temperature has a significant impact on catalyst performance. The highest propylene conversion (85.1%) was achieved at a calcination temperature of 500℃. At excessively low calcination temperatures (400℃), the interaction between Mo and Nb was insufficient, resulting in inadequate formation of acidic sites and a predominance of C6 olefins. Conversely, excessively high calcination temperatures (700℃) may lead to a reduction in acidic sites on the support, significantly decreasing the conversion rate and resulting in a predominance of C6 olefins as the product.

[0059] Example 4

[0060] (1) Preparation of Mo-doped niobium oxide support

[0061] Ammonium niobate oxalate and ammonium molybdate were uniformly dispersed in deionized water at a molar ratio of Nb:Mo = 1:0.2, and heated to 70°C with stirring until completely dissolved. Under vigorous stirring, ammonia water (25 wt%) was added dropwise to adjust the pH of the system to 9.0, and the reaction was continued for 8 h. The reaction product was washed with deionized water, filtered, and dried at 80°C for 12 h to obtain a powder. The obtained powder was calcined in air at a heating rate of 10°C / min to 500°C for 6 h, and after cooling, Mo-doped niobium oxide support (Mo) was obtained. 0.2 NbO x ).

[0062] (2) Atomic layer deposition (ALD) loading of nickel active components

[0063] The above Mo 0.2 NbO x The support was placed in the atomic layer deposition reaction chamber, and ALD deposition cycles of 50, 100, 150 and 200 were performed according to the same ALD parameters as in step (2) of Example 1, respectively, to obtain a series of catalysts, which were denoted as D-1 (50 times), D-2 (100 times), D-3 (150 times) and D-4 (200 times).

[0064] The Ni loading in each catalyst was determined by ICP-OES and is shown in Table 6.

[0065] Table 6 Elemental content of each catalyst in Example 4

[0066] The catalyst was loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 80 °C, a pressure of 3.0 MPa, and a liquid hourly space velocity of 6 h⁻¹. -1 Propylene oligomerization was carried out under certain conditions, and the results are shown in Table 7.

[0067] Table 7 Propylene oligomerization performance of various catalysts in Example 4

[0068] As shown in Table 7, with the increase in the number of ALD cycles from 50 to 200 and the increase in Ni loading from 1.7 wt% to 6.8 wt%, the propylene conversion rate first increased and then stabilized. The conversion rate reached its highest point (86.3%) when the number of ALD cycles reached 150 (Ni loading approximately 5.2 wt%), and remained essentially unchanged (86.0%) when the number of cycles increased further to 200. The C6 selectivity gradually decreased with increasing Ni loading (from 58.3% to 40.1%), while the C9 and C6 selectivity remained relatively stable. 12 + The selectivity gradually increased (from 28.6% and 13.1% to 38.6% and 21.3%, respectively). This indicates that the Ni loading can be precisely controlled by adjusting the number of ALD cycles, thereby affecting the catalytic performance.

[0069] Example 5

[0070] The A-4 catalyst (Mo / Nb=0.2, ALD 100 times) from Example 1 was selected to evaluate the propylene oligomerization reaction under different reaction conditions.

[0071] (1) Different reaction temperatures

[0072] At a reaction pressure of 3.0 MPa and a liquid hourly space velocity of 6 h⁻¹ -1 Under the specified conditions, the effect of reaction temperature on catalytic performance was investigated, and the results are shown in Table 8.

[0073] Table 8. Propylene oligomerization properties at different reaction temperatures in Example 5

[0074] 'a' indicates that the product contains C6, C9, and C6. 12 + In addition, there are small amounts of other pyrolysis byproducts.

[0075] As shown in Table 8, as the reaction temperature increases from 70℃ to 100℃, the propylene conversion rate significantly increases (from 78.5% to 90.5%), while the C6 selectivity decreases significantly (from 56.7% to 39.9%), and the C9 and C6 selectivity also decrease. 12 + The selectivity increased significantly (from 28.0% and 15.3% to 38.5% and 20.7%, respectively). This indicates that increasing the temperature significantly promoted chain growth in the oligomerization reaction, shifting the product distribution from dimers to trimers and tetramers, and also significantly improving the reactivity. However, other pyrolysis byproducts were present when the reaction temperature reached 100℃.

[0076] (2) Different reaction pressures

[0077] The reaction temperature was 80℃ and the liquid hourly space velocity was 6 h⁻¹.-1 Under the given conditions, the effect of reaction pressure on catalytic performance was investigated, and the results are shown in Table 9.

[0078] Table 9 Propylene oligomerization performance under reaction pressure in Example 5

[0079] As shown in Table 9, with the reaction pressure increasing from 2.0 MPa to 4.0 MPa, the propylene conversion rate significantly increased (from 76.2% to 87.8%), while the C6 selectivity significantly decreased (from 57.5% to 44.8%). The C9 and C6 selectivity also decreased. 12 + The selectivity increased significantly (from 28.6% and 13.9% to 36.0% and 19.2%, respectively). This is because the increased pressure increased the reactant concentration, which favored shifting the oligomerization equilibrium towards the product side, and also promoted the further conversion of the dimerization product.

[0080] (3) Different liquid hourly space velocities (LHSV)

[0081] The effect of liquid hourly space velocity on catalytic performance was investigated under the conditions of reaction temperature 80 ℃ and reaction pressure 3.0 MPa. The results are shown in Table 10.

[0082] Table 10 Propylene oligomerization performance at different liquid hourly space velocities in Example 5

[0083] As shown in Table 10, as the liquid hourly space velocity increases from 2 h... -1 Rise to 8 h -1 The propylene conversion rate gradually decreased (from 90.5% to 82.3%), while the C6 selectivity gradually increased (from 43.9% to 52.8%), and the C9 and C6 selectivity decreased. 12 + Selectivity gradually decreased (from 36.4% and 19.7% to 30.5% and 16.7%, respectively). This is because the lower liquid hourly space velocity results in a longer residence time, leading to higher conversion and more trimer and tetramer products.

[0084] Comparative Example 1

[0085] (1) Preparation of Mo-doped niobium oxide support

[0086] Mo was prepared using the same method as step (1) in Example 1. 0.1 NbO x Mo 0.2 NbO x and Mo 0.3 NbO x Carrier.

[0087] (2) Impregnation method for loading nickel active components

[0088] Nickel loading was achieved using the initial wet impregnation method: nickel nitrate was dissolved in deionized water to prepare a 0.1 mol / L nickel nitrate aqueous solution. The above-mentioned Mo... 0.1 NbO x Mo 0.2 NbO x and Mo 0.3 NbO x The support was added to an aqueous nickel nitrate solution and impregnated with stirring at room temperature for 8 hours. After impregnation, it was dried at 100°C for 12 hours, and then calcined at 500°C for 4 hours in air at a heating rate of 5°C / min to obtain Ni / Mo. 0.1 NbO x Ni / Mo 0.2 NbO x and Ni / Mo 0.3 NbO x Catalysts, designated E-1, E-2, and E-3.

[0089] Comparative Example 2

[0090] (1) Preparation of pure niobium oxide support

[0091] Ammonium niobate oxalate was uniformly dispersed in deionized water and heated to 70°C with stirring until completely dissolved. Under vigorous stirring, ammonia (25 wt%) was added dropwise to adjust the pH to 9.0, and the reaction was continued for 8 h. The reaction product was washed with deionized water, filtered, and dried at 80°C for 12 h to obtain a powder. The obtained powder was calcined in air at a heating rate of 10°C / min to 500°C for 6 h, and after cooling, pure niobium oxide support (NbO) was obtained. x ).

[0092] (2) Impregnation method for loading nickel active components

[0093] Ni / NbO was prepared according to step (2) of Comparative Example 1. x Catalyst, denoted as E-4.

[0094] ICP-OES analysis showed that the Ni loading in the E-4 catalyst was 3.5 wt%, and the Nb content was 66.8 wt%.

[0095] Catalysts E-1, E-2, E-3, and E-4 were loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 80 °C, a pressure of 3.0 MPa, and a liquid hourly space velocity of 6 h⁻¹. -1 Propylene oligomerization was carried out under certain conditions, and the results are shown in Table 11.

[0096] Table 11 Propylene oligomerization performance of each catalyst in the examples and comparative examples

[0097] 'a' indicates that the products of E-4, excluding C6, C9, and C6, contain C6, C9, and C6. 12 + In addition, there are small amounts of other pyrolysis byproducts.

[0098] As shown in Table 11, compared with the comparative example, the propylene conversion rate of Example A-4 (Mo doping + ALD method) of the present invention (85.1%) is significantly higher than that of the impregnated Mo-doped sample E-2 (65.3%) and the impregnated undoped sample E-4 (58.2%), and C9 and C 12 + The selectivity (32.8% and 17.0%) was higher than that of the undoped sample E-4 (5.2% and 1.0%), and also higher than that of the Mo-doped sample E-2 (29.3% and 16.2%), indicating that Mo doping and the ALD method have a significant synergistic enhancement effect, and neither can be dispensed with. When using the impregnation method, the interaction between Ni and Mo is weak, and even adjusting the Mo / Nb ratio has little effect on improving the degree of polymerization.

[0099] Comparative Example 3

[0100] Following the method in step (1) of Example 1, the Mo source was replaced with ferric nitrate nonahydrate, and the Nb:Fe molar ratio was controlled to be 1:0.1 and 1:0.2, respectively, to obtain niobium oxide supports with different Fe doping amounts, denoted as Fe 0.1 NbO x Fe 0.2 NbO x Using the same method, the Mo source was replaced with copper nitrate trihydrate, and the Nb:Cu molar ratio was controlled to be 1:0.1 and 1:0.2, respectively, to obtain niobium oxide supports with different Cu doping amounts, denoted as Cu. 0.1 NbO x Cu 0.2 NbO x .

[0101] Following the method in step (2) of Example 1, the above-mentioned supports were loaded with nickel active components using atomic layer deposition (ALD) to obtain Ni / Fe 0.1 NbO x Ni / Fe 0.2 NbO x Ni / Cu 0.1 NbO x Ni / Cu 0.2 NbO x The catalysts are designated as F-1, F-2, F-3, and F-4, respectively.

[0102] Catalysts F-1, F-2, F-3, and F-4 were loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 80 °C, a pressure of 3.0 MPa, and a liquid hourly space velocity of 6 h⁻¹. -1 Propylene oligomerization was carried out under certain conditions, and the results are shown in Table 12.

[0103] Table 12 Propylene oligomerization performance of each catalyst in Comparative Example 3

[0104] 'a' indicates that the products of F-1, F-2, F-3, and F-4, excluding C6, C9, and C4, are... 12 + In addition, there are other pyrolysis byproducts.

[0105] As can be seen from Table 12, the doping of Fe and Cu is more effective in regulating activity, and less effective in regulating selectivity.

[0106] The elemental content of the catalysts prepared in the above embodiments and comparative examples was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). Before testing, the catalyst samples were microwave-digested to prepare the test solution. The accurate Ni content in the sample was calculated by comparing the emission spectral intensities of the sample solution with those of standard solutions of Ni, Nb, and Mo.

[0107] The phase structures of the catalysts prepared in the above embodiments and comparative examples were characterized using powder XRD, employing a MinFlex 600 diffractometer equipped with a Cu Kα radiation source. Before testing, the samples were ground into powder and placed on the sample stage. During the test, the step size was set to 0.02, the scan rate to 10° / min, and the scan range to 5°–70°.

[0108] The catalyst reaction products prepared in the above embodiments and comparative examples were analyzed online by gas chromatography and quantified by external standard method.

[0109] Propylene conversion and product selectivity are calculated using the following formulas: Propylene conversion rate = (mass of propylene in feed - mass of propylene in product) / mass of propylene in feed × 100%; C6 selectivity = (Mass of C6 olefins in the product / Mass of total product) × 100%; C9 selectivity = (Mass of C9 olefins in the product / Mass of total product) × 100%; C 12 + Selectivity = C in the product 12 + Olefin mass / Total product mass × 100%.

[0110] In summary, this invention, through a synergistic strategy of Mo-doped niobium oxide support and precisely loaded NiO active component using ALD, achieves for the first time the directional control of the degree of polymerization of propylene oligomerization products. Catalytic performance evaluation shows that as the Mo / Nb ratio increases from 0 to 0.3, the propylene conversion initially increases and then decreases, indicating that the directional switching of products between dimers, trimers, and tetramers can be achieved by adjusting the Mo / Nb ratio. The conversion rate of the ALD method sample is significantly higher than that of the impregnation method sample, demonstrating the significant advantage of the ALD method in improving the performance of the active component. This invention combines the advantages of high activity, tunable product composition, and controllable preparation process, providing a novel technical solution for the preparation of propylene oligomerization catalysts.

[0111] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a niobium oxide-supported nickel-based catalyst, characterized in that: include, Niobium source and molybdenum source are mixed and co-precipitated. A precipitant is added to adjust the pH to 9-11. After washing, drying and calcination, Mo-doped niobium oxide support is obtained. The molar ratio of niobium source to molybdenum source is 1:0.01-1:

1. The Mo-doped niobium oxide support was placed in an atomic layer deposition reaction chamber, and alternating pulse deposition was performed using a nickel precursor and a reaction gas. After several deposition cycles, the niobium oxide-supported nickel-based catalyst was obtained.

2. The method for preparing the niobium oxide-supported nickel-based catalyst as described in claim 1, characterized in that: The niobium source is selected from at least one of ammonium oxalate niobate, niobium pentachloride, and niobium ethoxide; the molybdenum source is ammonium molybdate; the molar ratio of the niobium source to the molybdenum source is 1:0.05 to 1:0.

5. The precipitant is selected from at least one of ammonia, urea, ammonium carbonate, and ammonium bicarbonate. The roasting temperature is 400~700℃.

3. The method for preparing the niobium oxide-supported nickel-based catalyst as described in claim 1, characterized in that: The nickel precursor for atomic layer deposition is selected from at least one of nickel dicene, bis(methylcyclopentadienyl)nickel, Ni(thd)2, and Ni(dmamb)2; the reaction gas is oxygen or ozone.

4. The method for preparing the niobium oxide-supported nickel-based catalyst as described in claim 3, characterized in that: Each deposition cycle of the atomic layer deposition includes: a pulse of nickel precursor vapor for 0.5-10 s, followed by exposure for 10-60 s and purging with inert gas for 10-90 s; a pulse of reactive gas for 0.5-10 s, followed by exposure for 10-60 s and purging with inert gas for 10-90 s.

5. The method for preparing the niobium oxide-supported nickel-based catalyst as described in claim 4, characterized in that: The reaction chamber temperature for atomic layer deposition is 150~350℃, and the deposition cycle is 10~300 times.

6. A niobium oxide-supported nickel-based catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The catalyst comprises a Mo-doped modified niobium oxide support and a NiO active component supported thereon, wherein the Ni loading in the catalyst is 1~15 wt%.

7. The niobium oxide-supported nickel-based catalyst according to claim 6, characterized in that, The molar ratio of Mo to Nb in the catalyst is 0.01 to 1:

1.

8. The niobium oxide-supported nickel-based catalyst according to claim 6, characterized in that, The molar ratio of Mo to Nb in the catalyst is 0.05 to 0.

3.

9. The application of the niobium oxide-supported nickel-based catalyst according to any one of claims 6 to 8 in the propylene oligomerization reaction, characterized in that, The catalyst was loaded into a fixed-bed reactor, and propylene feedstock was introduced. The reaction was carried out at a temperature of 50-100°C, a pressure of 2.0-4.0 MPa, and a liquid hourly space velocity of 1-10 h⁻¹. -1 Propylene oligomerization reaction was carried out under the following conditions.

10. The application according to claim 9, characterized in that, The reaction temperature for the propylene oligomerization reaction is 70~100℃, and the liquid hourly space velocity is 2~6h. -1 .

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