A novel composite catalyst for olefin dimerization and a preparation method thereof

Abstract

The present application relates to the technical field of composite catalyst preparation, and particularly relates to a novel composite catalyst for olefin dimerization and a preparation method thereof, which comprises the following components: nickel naphthenate, Raney cobalt, triethylaluminum and tricyclohexylphosphine, and the molar ratio of the components of Raney cobalt, triethylaluminum and tricyclohexylphosphine is: Co / Ni of Raney cobalt is 0.10-5.00; Al / (Ni+Co) of triethylaluminum is 1.00-20.00; and P / Ni of tricyclohexylphosphine is 0.50-3.00, with the molar amount of nickel in the nickel naphthenate as the reference Ni=1.00. The present application forms a kind of heteronuclear Ni-Co bimetallic cluster active center with unique electronic structure and coordination geometry; by implementing pre-complexing operation of the nickel naphthenate, Raney cobalt, tricyclohexylphosphine and triethylaluminum in a strictly controlled temperature window and moisture environment, it is ensured that the Ni-Co bimetallic heteronuclear cluster active species can be fully generated and reach stable chemical composition and structure configuration before the start of the catalytic reaction.

Description

Technical Field

[0001] This invention relates to the field of composite catalyst preparation technology, and in particular to a novel composite catalyst for olefin dimerization and its preparation method. Background Technology

[0002] Dimerization of low-carbon olefins (ethylene, propylene, butene, etc.) is an important pathway to obtain high-value-added C4-C8 olefins. The products are widely used as basic raw materials for high-value downstream products such as fuel additives, plasticizers, fine chemical intermediates, and polymer comonomers. From a catalytic chemistry perspective, the core challenge of olefin dimerization lies in the precise control of selectivity—dimers with high branching selectivity (i.e., high regioselectivity) not only possess superior physicochemical properties.

[0003] Supported nickel catalysts offer advantages such as separability, regeneration, and relatively simple post-processing. However, their catalytic activity and selectivity are generally inferior to homogeneous systems. Furthermore, the limited mass and heat transfer within solid catalyst particles often necessitates higher operating temperatures (80°C to 150°C), resulting in lower selectivity for target branched products (60% to 80%) and significant energy consumption. Existing nickel / phosphine homogeneous catalytic systems still suffer from several significant technical limitations:

[0004] For the widely used single-phosphine coordination nickel catalytic system, although PCy3 can effectively increase the proportion of branched products, its excessive steric hindrance can partially shield the active center, reducing the reaction rate of substrate coordination and insertion, thus causing a decrease in catalytic activity. The catalytic turnover frequency is only about 15,000 h, which is much lower than that of the system using smaller phosphine ligands, and the sacrifice of catalytic efficiency is unavoidable.

[0005] Existing industrialized nickel-based homogeneous catalytic systems use nickel as the sole active metal center. Its inherent electronic structure and coordination geometry determine that there is a strict Sabatier-type activity-selectivity trade-off upper limit for catalytic activity and selectivity. It is difficult to achieve a breakthrough improvement by simply adjusting the ligands or co-catalysts. Using pre-designed ligand frameworks with complex structures and high preparation costs to anchor nickel and cobalt centers separately results in complicated synthesis steps and low overall yield of the complexes, which seriously restricts their transformation from laboratory to industrial scale.

[0006] Currently, it is mainly used as a catalyst for the selective hydrogenation of unsaturated compounds in organic synthesis, and also for specific reactions such as Pauson-Khand cyclization. However, when coupling the unique porous framework structure of Raney cobalt with a homogeneous nickel coordination catalytic system to construct a synergistic Ni-Co bimetallic composite catalytic system, conventional moisture control strategies commonly used in existing technologies, such as online dehydration of adsorbents and solvent pre-drying, are difficult to stably and reliably meet the stringent requirements of ultra-low water content for highly active dimerization catalytic systems, resulting in poor performance reproducibility between batches of catalyst preparation. Summary of the Invention

[0007] The purpose of this invention is to address the problem of simultaneously achieving high branch selectivity, mild reaction conditions, and simplified post-processing, and to propose a novel composite catalyst for olefin dimerization and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A novel composite catalyst for olefin dimerization comprises the following components: nickel naphthenate, Raney cobalt, triethylaluminum, and tricyclohexylphosphine, wherein the molar amount of nickel in the nickel naphthenate is Ni≡1.00:

[0010] The molar ratios of Raney cobalt, triethylaluminum, and tricyclohexylphosphine are as follows:

[0011] Raney cobalt has a Co / Ni ratio of 0.10-5.00;

[0012] The Al / (Ni+Co) ratio of triethylaluminum is 1.00-20.00.

[0013] The P / Ni ratio of tricyclohexylphosphine is 0.50-3.00.

[0014] Preferably, the molar ratio of Raney cobalt, triethylaluminum, and tricyclohexylphosphine is:

[0015] Raney cobalt has a Co / Ni ratio of 0.20-1.00;

[0016] The Al / (Ni+Co) ratio of triethylaluminum is 5.00-12.00.

[0017] The P / Ni ratio of tricyclohexylphosphine is 0.80-1.50.

[0018] Preferably, the molar ratio of Raney cobalt, triethylaluminum, and tricyclohexylphosphine is:

[0019] Raney cobalt has a Co / Ni ratio of 0.20-1.00;

[0020] The Al / (Ni+Co) ratio of triethylaluminum is 5.00-12.00.

[0021] The P / Ni ratio of tricyclohexylphosphine is 0.80-1.50.

[0022] Preferably, the Raney cobalt is prepared by selective aluminum dissolution activation of a cobalt-aluminum alloy with alkaline solution, wherein the mass content of cobalt is not less than 85% and the mass content of residual aluminum is 5% to 15%; the particle size D50 of the Raney cobalt is 5μm to 50μm and the BET specific surface area is 20m² / g to 100m² / g.

[0023] Preferably, the triethylaluminum is provided in the form of a toluene solution with a mass concentration of 10% to 25%.

[0024] Preferably, the tricyclohexylphosphine has a Tolamn cone angle of 170° and is provided in pure form or as a toluene solution.

[0025] A method for preparing a novel composite catalyst for olefin dimerization includes the following steps:

[0026] Step S1, Raney cobalt pretreatment, refers to washing and replacing the Raney cobalt multiple times with anhydrous toluene under an inert atmosphere to remove residual moisture from the Raney cobalt;

[0027] Step S2, Moisture detection, refers to the moisture content of the solvent obtained in the last washing operation during step S1, Raney cobalt pretreatment, and the moisture content is controlled to not exceed 100 ppm.

[0028] Step S3, pre-complexation reaction, refers to the process of adding Raney cobalt, nickel naphthenate, tricyclohexylphosphine, and toluene solvent sequentially to a reactor under an inert atmosphere after Raney cobalt pretreatment in step S1 and moisture detection in step S2. After stirring evenly, a toluene solution of triethylaluminum is added, and the pre-complexation reaction is carried out at a temperature of 0 to 50°C for 1 to 5 hours. The components Raney cobalt, triethylaluminum, and tricyclohexylphosphine are calculated based on the amount of nickel in nickel naphthenate (Ni≡1.00), with Co / Ni=0.10-5.00, P / Ni=0.50-3.00, and Al / (Ni+Co)=1.00-20.00.

[0029] Step S4, catalyst suspension, refers to the mixture obtained after step S3, the pre-complexation reaction, which is a suspension-type composite catalyst used for olefin dimerization catalysis.

[0030] Preferably, in step S3, the temperature of the pre-complexation reaction is 10 to 30°C, and the time is 2 to 4 hours.

[0031] Preferably, in step S2, the moisture content control standard for moisture detection is no more than 50 ppm.

[0032] Preferably, in step S1, the water content of anhydrous toluene in the Raney cobalt pretreatment is less than 20 ppm;

[0033] In step S3, the number of Reynolds stirring in the reactor during the pre-complexation reaction is on the order of 1,000 to 10,000 to ensure that the Raney cobalt particles are in a uniformly suspended fluidized state.

[0034] Preferably, in step S3, the molar ratio of each component in the pre-complexation reaction is: Co / Ni = 0.20-1.00, Al / (Ni+Co) = 5.00-12.00, P / Ni = 0.80-1.50.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. This invention creatively extends the application of porous framework Raney cobalt, a material primarily used as a hydrogenation catalyst to a Ziegler-Natta type homogeneous coordination dimerization catalytic system. After the introduction of Raney cobalt, a large amount of unsaturated coordinated Co exposed on the porous framework walls... 0 The active sites can selectively interact with some homogeneous Ni active complexes in the pre-complexation stage through metal-support (framework) atomic-level chemical interactions, forming a type of heteronuclear Ni-Co bimetallic cluster active center with unique electronic structure and coordination geometry. The formation of this novel active structure is a unique feature that conventional homogeneous nickel catalytic systems do not possess at all.

[0037] 2. This invention uses Co as a post-transition metal, whose inherent d-orbital energy levels and coordination preferences differ significantly from those of Ni. When Co is used on the surface of the Raney cobalt framework... 0 When atoms of Ni(II) undergo heteronuclear clustering under the regulation of PCy3 ligands, the two metal centers are bridged by phosphine ligands or directly bonded to metal, resulting in a significant delocalization redistribution effect of electron density. This enriches the electron density of the Ni center to a certain extent and enhances the electrophilicity of the Co center. On the one hand, it strengthens the σ-electron-donating coordination ability of the Ni center to the π bond of olefins, thus appropriately improving the catalytic activity. On the other hand, it further amplifies the kinetic advantage of the β-H elimination step relative to chain growth, which is conducive to the selective formation of dimers. The olefin isomerization function inherent in the heteronuclear Co center and the chain growth function of the Ni center achieve spatial separation and functional complementarity, forming a precise synergistic mechanism of nickel-catalyzed chain growth and cobalt-catalyzed isomerization.

[0038] 3. This invention performs a pre-complexation operation on nickel naphthenate, Raney cobalt, tricyclohexylphosphine, and triethylaluminum in a strictly controlled temperature window and moisture environment. This ensures that the active species of the Ni-Co bimetallic heteronuclear cluster are fully generated and reach a stable chemical composition and structural configuration before the catalytic reaction begins, thereby improving the structural uniformity and batch reproducibility of the catalyst active center.

[0039] 4. This invention uses bio-derived propanol / butanol as the starting material for the reaction. Under the action of a novel composite catalyst, C6-C8 mixed olefins are dimerized and further hydrogenated to obtain C6-C8 straight-chain or branched alkanes. Attached Figure Description

[0040] Figure 1 This is a schematic flowchart illustrating a method for preparing a novel composite catalyst for olefin dimerization proposed in this invention.

[0041] Figure 2 and Figure 3 This is a schematic diagram of the synthesis reaction equation for propanol / isobutanol. Detailed Implementation

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0043] Reference Figures 1-3 A novel composite catalyst for olefin dimerization comprises the following components: nickel naphthenate, Raney cobalt, triethylaluminum, and tricyclohexylphosphine.

[0044] It should be noted that:

[0045] Nickel naphthenate, as a nickel source precursor, provides Ni(II) ions required for the catalytic dimerization of olefins. The naphthenate ligands possess moderate coordination ability, resulting in good solubility of nickel in aromatic solvents such as toluene, providing favorable conditions for the in-situ generation of homogeneous catalytic active species. Simultaneously, the coordination strength of the naphthenate is neither too strong to hinder subsequent reduction and alkylation reactions of Ni centers by alkylaluminum, nor too weak to cause instability, hydrolysis, or precipitation deactivation of Ni(II) ions in solution. Therefore, it has become the most classic and widely used nickel precursor form in Ziegler-Natta type olefin dimerization catalytic systems. The mass fraction of nickel in nickel naphthenate is 8%-15% (metallic).

[0046] Raney cobalt is a key innovative component that fundamentally distinguishes it from existing technologies. This material is prepared by selectively dissolving most of the aluminum component from a cobalt-aluminum alloy using an alkaline solution (an aqueous solution of NaOH or KOH, typically 10 wt% to 30 wt%). The remaining trace amounts of skeletal aluminum (existing in zero- or low-valence oxide states, with a residual aluminum content of 3%–12%) may provide potential Lewis acid sites. The resulting Raney cobalt possesses a high specific surface area and a three-dimensionally interconnected porous framework structure. The cobalt content in Raney cobalt is not less than 85% by mass (based on total metal content), and the residual aluminum content is 3% to 12% by mass. Its particle size is designed to ensure uniform dispersion in the liquid-phase catalytic system and an acceptable sedimentation rate.

[0047] Further explanation:

[0048] Raney cobalt plays the following multi-level synergistic catalytic role in the catalytic system:

[0049] First, the bimetallic atomic-level synergistic effect: during the pre-complexation stage, the Co on the Raney cobalt surface... 0 Atom-level chemical interactions occur between the atoms and the homogeneous Ni complex (actually active species are Ni(0)-PCy3 or Ni(I)-PCy3 species) that have been in situ reduced and alkylated by triethylaluminum, forming heteronuclear Ni-Co bimetallic cluster-type active centers. The Co center (with high d-orbital electron density and strong reverse π-feedback capability) undergoes partial electron transfer to the Ni center, appropriately regulating the electron density of Ni and enhancing its σ-electron-donating coordination activation capability for olefin π bonds. Simultaneously, the inherent olefin isomerization catalytic function of the Co center itself (through reversible β-H elimination / reinsertion cycles, driving the alkyl metal intermediate to thermodynamically favorable positions in the branching direction for isomerization) is preserved and utilized. The spatial proximity and complementary electronic regulation of the two metal centers, Ni and Co, enable the two fundamental steps—chain growth and skeletal isomerization—that compete for catalytic activity in single-metal systems to achieve spatial separation and functional synergy, overcoming the activity-selectivity tradeoff set by the Sabatier principle for single-metal catalysts.

[0050] Second, the porous framework characteristic of Raney cobalt provides a unique confined microenvironment for olefin coordination and C-C coupling reactions near the nickel active site. The size-constrained effect of the micropores reduces the effective reaction volume around the active site, inhibiting the continuous insertion of multiple monomer molecules (i.e., limiting the formation of trimers, tetramers, and higher-order oligomers). This makes the β-H elimination / chain transfer step kinetically more dominant than the continuous chain growth step, thus expanding the carbon number distribution of the product spectrum from broadly distributed oligomers (C6, C9, C4, C5, C6, C6, C9 ... 12 And higher hydrocarbon mixtures) narrowed down to dimers (C6 or C8) as the dominant products;

[0051] Third, residual Lewis acid aids catalysis: Residual aluminum components in the Raney cobalt framework that are not completely dissolved by alkali exist in the form of highly dispersed zero-valent aluminum or low-valent aluminum oxide (AlOx, x<1.5) on the surface or subsurface layer of the cobalt framework. These residual aluminum sites act as weak Lewis acid sites, which can activate the C=C double bond of olefins through polarization, promote the coordination of olefins to the active metal center and the subsequent insertion step, and indirectly increase the overall conversion frequency of the catalytic reaction;

[0052] Fourth, enhanced stability: A high specific surface area Raney cobalt porous framework is introduced into the homogeneous catalytic system, allowing some active nickel complexes to interact with the Co on the framework surface. 0 The chemical anchoring of atoms is fixed to the solid surface, reducing the bimolecular deactivation association rate between active species in the homogeneous solution and extending the effective lifespan of the catalyst under reaction conditions.

[0053] Triethylaluminum, as a classic co-catalyst in Ziegler-Natta catalytic systems, simultaneously performs the following multiple activation functions:

[0054] ① Reduce Ni(II) precursors to catalytically active low-valence Ni(0) or Ni(I) species;

[0055] ② Alkylation of the active nickel center forms Ni-C σ bonds (i.e., Ni-ethyl species), which are the starting active species for the catalytic cycle;

[0056] ③ As an irreversible sacrificial scavenger of the system, it preferentially reacts with residual moisture, dissolved oxygen and other impurities containing active protons in the system to protect the main catalytic active center from poisoning to the greatest extent.

[0057] ④ Establish a reversible chain transfer equilibrium with Ni-H species at the active Ni center, regulate the molecular weight distribution of the product olefin through chain transfer reaction, and avoid excessive accumulation of high molecular weight products.

[0058] By using halogen-free triethylaluminum, the long-term electrochemical corrosion risk of halogens on stainless steel reaction equipment and the inner walls of distillation columns can be fundamentally avoided, as well as product quality problems caused by excessive halogen residues in the final dimerization product. Triethylaluminum is provided in the form of toluene solution with a mass concentration of 10%-25%.

[0059] in:

[0060] Raney cobalt refers to a porous framework catalytic material with metallic cobalt as the main component, obtained by selectively dissolving most of the aluminum component in an aqueous solution of alkali metal hydroxide (usually NaOH or KOH) under temperature-controlled conditions from a cobalt-aluminum alloy (cobalt mass fraction is usually 40% to 60%). Its BET specific surface area is generally in the range of 20 m² / g to 100 m² / g, and the pore size distribution has a bimodal or multimodal characteristic.

[0061] Nickel naphthenate refers to the naphthenate of nickel(II), in which the naphthenic acid portion is usually derived from a mixture of naphthenic acids in petroleum refining fractions. The number of cycloalkyl carbons n is mainly between 8 and 12, and the mass fraction of nickel is 8% to 15% on a metallic basis.

[0062] It is important to note that:

[0063] Compared with some existing technologies using halogenated alkyl aluminum (such as diethylaluminum monochloroEt2AlCl, ethylaluminum dichloroEtAlCl2, or ethylaluminum sesquichlorideEt3Al2Cl3, etc.), triethylaluminum has the significant advantage of being free of halide ions. This completely avoids the risk of long-term electrochemical corrosion of stainless steel reaction equipment and distillation column inner walls caused by the introduction of halogens, as well as product quality and application safety issues caused by excessive halogen residues in the final dimerization product.

[0064] Tricyclohexylphosphine (PCy3) acts as a key ligand that regulates both steric and electronic effects. PCy3 possesses the following outstanding physicochemical properties: the three cyclohexyl substituents are arranged in a near-C3v symmetrical pyramidal pattern around the central phosphorus atom, with a calculated Tolamn cone angle of approximately 170°, making it one of the most electron-donating and sterically hindered monodentate tertiary phosphine ligands known to date. The irreplaceable role of PCy3 in nickel-catalyzed olefin dimerization is mainly reflected in:

[0065] First, its large steric hindrance effect creates a crowded coordination environment around the active center. This environment is kinetically advantageous for the β-H elimination reaction (which requires a large reaction space for the β-hydrogen atom to approach and transfer to the metal center) over the further coordination insertion (chain growth) of the olefin. This promotes the dissociation and release of the dimer from the metal center in the form of an olefin, rather than further reaction with subsequent monomers to form trimers or higher oligomers.

[0066] Secondly, its strong σ-electron-donating ability increases the electron density of the active Ni center, enhances the d-π back-bonding of the Ni center to the π* antibonding orbitals of the olefin, weakens the C=C double bond order of the coordinated olefin, and activates the subsequent C-C coupling step. It is precisely because of the above-mentioned dual characteristics of large steric hindrance and strong electron donation of PCy3 that the product regioselectivity of the nickel catalytic system containing PCy3 in the propylene dimerization reaction is highly directed towards 2,3-dimethylbutene.

[0067] Based on the molar amount of nickel in nickel naphthenate (Ni≡1.00), the molar ratios of Raney cobalt, triethylaluminum, and tricyclohexylphosphine are as follows:

[0068] Raney cobalt has a Co / Ni ratio of 0.10-5.00;

[0069] The Al / (Ni+Co) ratio of triethylaluminum is 1.00-20.00.

[0070] The P / Ni ratio of tricyclohexylphosphine is 0.50-3.00.

[0071] It is worth noting that, through the reinforcing effect of the Ni-Co bimetallic synergy, the P / Ni molar ratio can be reduced to below 1.0 (i.e., 0.50-0.99), significantly saving the material cost of expensive PCy3 phosphine ligands.

[0072] Preparation Examples 1-7: Preparation of Composite Catalysts

[0073] The composite catalyst was prepared according to the proportions in Table 1. The amount of nickel naphthenate was taken as 1 (molar basis), and the amounts of other components were expressed as molar ratios. The specific steps are as follows:

[0074] Under nitrogen protection, 5g of commercially available wet Raney cobalt (cobalt content ≥90%, D50=25μm) was washed three times with 30mL of anhydrous toluene (water content <20ppm), stirring for 15min each time, followed by standing and decantation of the supernatant. After the final wash, the supernatant was measured for moisture content using a Karl Fischer coulometric micromoisture analyzer, confirming it to be ≤50ppm.

[0075] Under nitrogen protection, Raney cobalt, nickel naphthenate (toluene solution, nickel content 8%), and tricyclohexylphosphine (PCy3, purity >98%) were added sequentially to a 250 mL autoclave containing 50 mL of anhydrous toluene, according to the proportions in Table 1, and stirred for 10 min. Subsequently, a toluene solution of triethylaluminum (concentration 15%) was added dropwise at a slow rate. The pre-complexation temperature was controlled at 25 °C, and the reaction was carried out with stirring (Reynolds number approximately 5000) for 3 h to obtain a dark-colored catalyst suspension.

[0076] Table 1 Catalyst components and molar ratios in Preparation Examples 1-7

[0077]

[0078] It is worth noting that:

[0079] The molar ratio refers to the ratio between the mass of the target element (or compound) in each component and the mass of nickel in nickel naphthenate.

[0080] Take another portion of the catalyst suspension that has undergone pre-complexation according to the above steps, and perform... 31 In-situ P¹H NMR analysis revealed a characteristic peak at δ 12.3 ppm belonging to free PCy3, and a broad peak at δ -5.8 ppm belonging to the Et3Al-PCy3 adduct, with an integral area ratio of approximately 1:1.5–1:3 (depending on the actual Al / P ratio). After the addition of propylene, the intensity of the free PCy3 peak fluctuated slightly with the reaction progress but remained constant, confirming the effective supply of phosphine ligands throughout the catalytic cycle.

[0081] Examples 1-9: Applications of olefin dimerization

[0082] The catalyst suspension obtained in the above preparation example was applied to the olefin dimerization reaction. Specific procedures: Under nitrogen protection, a 250 mL autoclave containing 1 g (based on the total nickel + cobalt metal content) of catalyst suspension was cooled to -10 °C, and 100 g of olefin feedstock (see Table 2) was slowly introduced. After the feedstock introduction was complete, the temperature was gradually raised to room temperature (25 °C), and the reaction was carried out under sealed stirring for 20 h. After depressurization, the reaction solution was hydrolyzed with 5 mL of saturated NaHCO3 solution, the solid was removed by filtration, and the mixture was allowed to stand for separation. The organic phase was then subjected to atmospheric pressure distillation to obtain the dimerized olefin product, which was further hydrogenated (Pd / Al2O3, 0.5 MPa H2, 50 °C) to obtain saturated alkanes. The results are shown in Table 3.

[0083] Table 2 Conditions of Examples 1-9

[0084]

[0085] Comparative Examples 1-3

[0086] Using propylene as a raw material and employing the catalyst composition of Preparation Example 1, the effects of varying catalyst dosage and reaction temperature on the reaction were investigated. The conditions and results are shown in Table 3.

[0087] The molar ratios of Raney cobalt, triethylaluminum, and tricyclohexylphosphine are as follows:

[0088] Raney cobalt has a Co / Ni ratio of 0.20-1.00;

[0089] The Al / (Ni+Co) ratio of triethylaluminum is 5.00-12.00.

[0090] The P / Ni ratio of tricyclohexylphosphine is 0.80-1.50.

[0091] Table 3. Reaction results of Examples 1-9 and Comparative Examples 1-3

[0092]

[0093] It can be known that:

[0094] Comparing Example 1 and Example 2, it can be seen that the introduction of Raney cobalt (Example 1) significantly improved the branch selectivity from 80% to 90% while maintaining the yield;

[0095] Example 3 shows that although excess Co (Co / Ni=1.0) further improves the branching selectivity (92%), the dimerization yield decreases due to the increase in non-selective oligomerization side reactions.

[0096] Example 4 shows that excess triethylaluminum (Al / (Ni+Co)=20) will cause excessive polymerization and reduce the target yield;

[0097] Example 6 shows that for isobutylene, which is easily polymerizable, a branch selectivity of up to 98% can be obtained by using a lower Co / Ni molar ratio (0.10) and Al / (Ni+Co) molar ratio (5.00);

[0098] Comparative Example 1 shows that while lowering the pre-complexation and reaction initiation temperature to -40°C slightly improves the branched selectivity to 92% and increases the yield to 88%, the required cryogenic conditions significantly increase refrigeration energy consumption and operating costs. Overall, the economic efficiency is inferior to Example 1, which operates under mild conditions from -10°C to room temperature. This comparison also demonstrates the technical advantage of this invention, which achieves high selectivity without relying on extreme low temperatures through the synergistic catalytic effect of Raney cobalt.

[0099] Comparative Example 3 shows that when the catalyst dosage is increased to 11% (based on total metals relative to the olefin feedstock), the excessively high concentration of active sites leads to a significant increase in higher oligomers such as trimers and tetramers. The yield of the dimer target product drops to 60%, the purity drops to 90%, and the product distribution becomes significantly more complex. Therefore, the catalyst dosage should be controlled below 10%, preferably 1%-8%.

[0100] Raney cobalt is prepared by selective aluminum dissolution activation of cobalt-aluminum alloy with alkaline solution, wherein the mass content of cobalt element is not less than 85% and the mass content of residual aluminum element is 3% to 12%; more preferably, the mass content of cobalt element is not less than 90% and the mass content of residual aluminum element is 3% to 10%.

[0101] A comparison of Examples 8-9 with Example 1 shows that in the presence of Raney cobalt (Co / Ni = 0.30-0.50), the P / Ni molar ratio can be reduced to 0.50-0.80, while the branch selectivity remains at 87%-89%, significantly better than Example 2 without Raney cobalt (P / Ni = 1.00, selectivity only 80%). This fully verifies the partial substitution and reinforcement function of the Ni-Co bimetallic synergistic effect on the expensive PCy3 phosphine ligand, providing experimental evidence for a substantial reduction in ligand usage in industrial applications.

[0102] Triethylaluminum is provided as a toluene solution with a mass concentration of 10% to 25%.

[0103] Tricyclohexylphosphine has a Tolamn cone angle of 170° and is supplied in pure form or as a toluene solution.

[0104] Regarding the catalytic performance of this composite catalyst:

[0105] Significantly improved selectivity of branched olefins: Under optimal ratio and process conditions, the selectivity of branched olefins can reach over 90%, which is more than 10 percentage points higher than the control catalyst without Raney cobalt, significantly improving the single-pass yield of high-value branched products.

[0106] Effective reduction in ligand costs: Through the reinforcing effect of the Ni-Co bimetallic synergy, the P / Ni molar ratio can be reduced to 0.50 to 1.50. Compared with the traditional system that requires P / Ni ≥ 2, this can significantly save the material cost of expensive PCy3 phosphine ligands, thereby reducing the economic operating costs of the entire industrial production process.

[0107] The reaction conditions remain mild: the catalytic reaction can operate efficiently under mild conditions close to ambient temperature (10 to 35°C) and normal or low pressure (0.05 to 1.00 MPa), without the need for heating to high temperatures or using expensive high-pressure reaction equipment. It has low energy consumption and relatively relaxed requirements for equipment.

[0108] Excellent product purity: After simple hydrolysis termination reaction, liquid-liquid phase separation and atmospheric pressure distillation purification, the purity of the dimer olefin product can be stably reached above 99%, which can meet the stringent requirements of downstream high value-added chemical synthesis for raw material purity.

[0109] It is important to note that the reaction between triethylaluminum and tricyclohexylphosphine is not an equimolar irreversible consumption reaction, but rather the formation of a reversible Lewis acid-base adduct (R3Al←PR3). The formation constant of this adduct is approximately 10. 2 -10 3 M -1 On the order of magnitude, a dynamic dissociation equilibrium exists in solution as follows: AlEt3+ PCy3⇌Et3Al-PCy3

[0110] Experiments show that even under conditions with an Al / P molar ratio as high as 40, a detectable concentration of free PCy3 still exists in the system (characteristic resonance signals can be observed at δ 10-15 ppm via 31P NMR spectroscopy). This portion of free phosphine ligands is sufficient to coordinate with the nickel center to form the (Ni-PCy3)-Et active complex. The formation of the triethylaluminum-phosphine adduct actually acts as a 'buffer reservoir' for phosphine ligands, releasing PCy3 on demand during the catalytic cycle, which is beneficial for maintaining the stability of the effective phosphine concentration around the active center.

[0111] It needs to be clarified that when the molar amount of nickel in nickel naphthenate is based on Ni ≡ 1.00, and the molar ratio of each component is within the stated range, the molar excess of triethylaluminum relative to tricyclohexylphosphine does not constitute a sufficient condition for the irreversible consumption and inactivation of phosphine ligands. A reversible Lewis acid-base adduct is formed between triethylaluminum and tricyclohexylphosphine, and its dissociation equilibrium ensures that the concentration of free phosphine ligands required for catalytic activity is consistently maintained. Based on the 'buffer reservoir' effect of this adduct, the effective phosphine ligand concentration around the nickel active site is significantly smoothed out by fluctuations in the Al / P ratio. This is the intrinsic chemical reason why this catalyst system can stably exert its catalytic performance within a wide sizing window.

[0112] It should be noted that the specific models and specifications of nickel naphthenate, Raney cobalt, triethylaluminum, and tricyclohexylphosphine need to be selected and determined based on the actual specifications of the device. The specific selection calculation method adopts the existing technology in this field, so it will not be elaborated here.

[0113] Analysis of the composite catalyst reveals the following effects:

[0114] High branched selectivity: By forming Ni-Co heteronuclear bimetallic clusters, the branched olefin selectivity can reach more than 90% under optimal conditions, which is more than 10 percentage points higher than the control system without Raney cobalt.

[0115] High dimer selectivity: Utilizing the spatial confinement effect of Raney cobalt, side reactions such as trimerization and tetramerization are effectively suppressed, and the selectivity of dimer products reaches 70-90%.

[0116] The reaction conditions are mild: it can operate efficiently at near ambient temperature (10-35℃) and normal or low pressure (0.05-1.0MPa), with low energy consumption and relaxed equipment requirements.

[0117] High product purity: After simple hydrolysis, phase separation and atmospheric distillation, the purity of the dimerolefin product is stably above 99%.

[0118] Significantly reduced ligand costs: Thanks to the synergistic reinforcement of bimetals, the P / Ni molar ratio can be reduced to 0.5-1.5, greatly saving the amount of expensive PCy3 required.

[0119] Improved process safety and reproducibility: By strictly controlling moisture levels (≤100ppm) and using temperature-time controlled pre-complexation steps, the utilization rate and production safety of alkylaluminum are ensured from the source, and the common problem of large batch-to-batch fluctuations in catalyst performance is solved.

[0120] The functional principle of this invention can be explained through the following operational methods:

[0121] Step S1, Raney cobalt pretreatment, refers to the repeated washing and replacement of Raney cobalt with anhydrous toluene under an inert atmosphere to remove residual moisture. Specifically, under an inert atmosphere that strictly excludes air and moisture (usually using high-purity nitrogen or argon with a purity of not less than 99.999% or not less than 99.99% as the protective gas, which needs to be further purified by molecular sieve / copper-based deoxygenation catalyst before use), commercially available wet Raney cobalt (using water or lower fatty alcohol as the protective solvent to prevent the active hydrogen adsorbed on the surface from oxidizing and spontaneously combusting upon contact with air) is repeatedly soaked, washed, and replaced with fully dehydrated and deoxygenated anhydrous toluene (with a water content of less than 20 ppm) to remove residual moisture adhering to the porous framework of Raney cobalt.

[0122] Step S2, moisture detection, refers to the moisture content of the solvent obtained from the final washing operation in Step S1, the Raney cobalt pretreatment, which must be controlled to not exceed 100 ppm. Specifically, after completing the final washing operation, a small amount of supernatant is taken from the system, and its moisture content is accurately measured using a Karl Fischer coulometric micro-moisture analyzer. The moisture content is strictly controlled to not exceed 100 ppm (by mass), with a further preferred target of not exceeding 50 ppm. Only after the moisture content is confirmed to meet the above limit can the next pre-complexation operation proceed. If the moisture content exceeds the specified limit, the washing and displacement operation in Step S1 should be repeated until the moisture content meets the standard.

[0123] Further explanation is needed:

[0124] Strict control of the moisture content in the Raney cobalt introduction system is one of the key quality control steps in the entire catalyst preparation process. The strict control of moisture provides dual protection for catalyst performance and safety on two levels:

[0125] Firstly, the reaction of triethylaluminum with water exhibits extremely high reactivity (the standard Gibbs free energy change ΔG° for the hydrolysis of the C2H5-Al ​​bond is highly negative, indicating that the reaction equilibrium tends towards complete hydrolysis), and the reaction equation is as follows:

[0126] Al(C2H5)3+H2O→Al(C2H5)2OH+C2H6↑

[0127] Furthermore, the hydrolysis reaction itself is a strongly exothermic process (the enthalpy ΔH of the reaction is approximately -250 kJ / mol). Even if there are only trace amounts of water remaining in the system, it may cause local hot spots and uncontrollable temperature rises due to the concentrated hydrolysis of alkyl aluminum during large-scale production, posing a significant safety hazard.

[0128] Secondly, the alkylaluminum hydrolysis products (ethylaluminum hydroxide and its condensation products) do not have the ability to activate the precursor of the main catalyst. Instead, due to their Lewis acidity, they will non-selectively compete with nickel centers or phosphine ligands for coordination, interfering with the normal formation of the target Ni-Co heteronuclear cluster active species in the pre-complexation step, resulting in a significant decrease in catalyst activity and selectivity.

[0129] Therefore, a moisture content of ≤100ppm is a rigid process parameter boundary and an important distinguishing feature from the relatively extensive catalyst preparation operations in existing technologies.

[0130] Step S3, pre-complexation reaction, refers to the process of adding Raney cobalt, nickel naphthenate, tricyclohexylphosphine, and toluene solvent sequentially to a reactor under an inert atmosphere after Raney cobalt pretreatment in step S1 and moisture detection in step S2. After stirring evenly, a toluene solution of triethylaluminum is added, and the pre-complexation reaction is carried out at a temperature of 0 to 50°C for 1 to 5 hours. The components Raney cobalt, triethylaluminum, and tricyclohexylphosphine are calculated based on the amount of nickel in nickel naphthenate (Ni≡1.00), with Co / Ni=0.10-5.00, P / Ni=0.50-3.00, and Al / (Ni+Co)=1.00-20.00. Specifically, under a continuously purging inert protective atmosphere, Raney cobalt solid (pretreated in step S1 with Raney cobalt pretreatment and step S2 with strict moisture detection) is sequentially added to a thoroughly dried glass or 316L stainless steel reactor, along with a toluene solution of commercially available nickel naphthenate, pure tricyclohexylphosphine or a toluene solution, and additional anhydrous toluene solvent (the total solvent amount is based on ensuring sufficient contact between all components in the system and the subsequently added olefins). A mechanical or magnetic stirrer is started to thoroughly mix the solid and liquid components. The stirring speed is generally adjusted based on the Reynolds number, with uniform mixing as the lower limit, depending on the reactor volume and stirring method. Subsequently, a toluene solution containing triethylaluminum (the mass concentration of triethylaluminum is approximately 10% to 25%; commercially available products need to be recalibrated under an inert atmosphere before use) is added dropwise to the mixture at a controlled, slow rate using a constant-pressure dropping funnel or a micro-injection pump.

[0131] To further emphasize:

[0132] The moment the triethylaluminum solution begins to be added dropwise marks the official start of the pre-complexation chemical reaction.

[0133] Triethylaluminum undergoes a rapid reduction reaction with nickel naphthenate in solution (i.e., Ni(II) → Ni(0) or Ni(I)), accompanied by a gradual change in solution color from the characteristic green of nickel naphthenate to dark brown to near black (indicating the formation of low-valence Ni species).

[0134] The generated active low-valent Ni complex then coordinates with the free PCy3 in the solution to reach equilibrium, generating a homogeneous (Ni-PCy3)-Et active complex monomer fragment;

[0135] Under continuous stirring and contact conditions, the homogeneous (Ni-PCy3)-Et complex gradually migrates and diffuses to the surface of the Raney cobalt porous framework suspended in the solvent, interacting with the unsaturated Co exposed on the framework walls. 0 Atomic-level metal-metal interactions and coordination reconstruction occur at atomic sites, ultimately assembling to form the active center of a Ni-Co heteronuclear bimetallic cluster with a defined structure.

[0136] Please note:

[0137] The operating parameters for the pre-complexation reaction are as follows:

[0138] Reaction temperature: 0 to 50°C, more preferably 10 to 30°C;

[0139] Reaction time: 1 to 5 hours, more preferably 2 to 4 hours;

[0140] Stirring rate: moderate, with the principle of ensuring that the solid Raney cobalt particles are in a uniform suspended fluidized state without settling.

[0141] Pre-complexation is a necessary pretreatment step for the full generation of catalytic active centers and the attainment of stable configurations; it is by no means an optional auxiliary operation. If pre-complexation is insufficient (e.g., reaction temperature too low, time too short), only a small portion of the total nickel content will actually enter the catalytic dimerization cycle, resulting in low catalytic conversion efficiency. Conversely, if pre-complexation is excessive (temperature too high, time too long), excess triethylaluminum will undergo an irreversible over-reduction side reaction with the already formed Ni-Co active species, generating inactive nickel black (metallic Ni). 0 The degradation of free PCy3 ligands (as nanoparticle aggregates) by alkylation also leads to irreversible loss of activity. Another important reason for strictly controlling the pre-complexation temperature range is to ensure operational safety: triethylaluminum begins to undergo significant self-decomposition at temperatures above approximately 60°C (releasing ethylene and generating diethylaluminum hydride via the β-H elimination pathway), which not only wastes the co-catalyst but also may cause abnormal pressure increases within the reactor due to the released ethylene gas.

[0142] In some implementation methods:

[0143] Pre-complexation refers to the process of thoroughly mixing and contacting the catalyst components (nickel naphthenate, Raney cobalt, tricyclohexylphosphine, and a toluene solution of triethylaluminum) under specified temperature and time conditions before the start of the catalytic reaction to generate active species in situ.

[0144] Under strictly controlled pre-complexation conditions, triethylaluminum first reduces Ni(II) species in nickel naphthenate to Ni(I) or Ni(0) via a single-electron transfer or two-electron reduction pathway, and then ethylates them to form a catalytically active Ni-Et intermediate.

[0145] At the same time, tricyclohexylphosphine, due to its large steric cone angle, selectively coordinates at the nickel center to form a sterically hindered and electron-rich (Ni-PCy3)-Et active complex fragment.

[0146] During continuous stirring and contact, the homogeneous (Ni-PCy3)-Et active complex fragments are gradually adsorbed and anchored to the surface Co of the Raney cobalt porous framework.0 At the site, atomic-level reconstruction forms a unique Ni-Co bimetallic heteronuclear cluster, in which direct metal-metal bonding (d) may exist between Ni and Co. 9 -d 10 Interaction or d 10 -d 10 (Through metal-philic interactions) or indirect coupling via bridging PCy3 ligands. This heteronuclear bimetallic cluster is the actual active center for catalyzing olefin dimerization.

[0147] Step S4, catalyst suspension, refers to the mixture obtained after the pre-complexation reaction in step S3, which is a suspension-type composite catalyst for olefin dimerization catalysis. Specifically, in step S3, after the pre-complexation reaction reaches the specified time, stirring is stopped, and the system is allowed to cool naturally or be kept warm to a predetermined temperature (usually between ambient temperature and 30°C). The resulting dark-colored mixture containing solid Raney cobalt particles and homogeneous nickel complex is a catalyst suspension that can be directly used for subsequent olefin dimerization catalysis.

[0148] The suspension consists of the following phases: a continuous liquid phase is anhydrous toluene solvent that has been thoroughly dehydrated and deoxygenated, containing dissolved free (Ni-PCy3)-Et homogeneous active complexes, incompletely consumed triethylaluminum (existing in solution equilibrium as monomers and dimers) as a sacrificial impurity remover, and free PCy3 ligands (in dynamic chemical equilibrium with nickel centers through coordination / decoupling); the dispersed solid phase consists of Raney cobalt particles suspended in the solvent, with Ni-Co heteronuclear bimetallic cluster active centers anchored on their porous framework surface. Under continuous inert protective atmosphere and strict sealing conditions, this catalyst suspension can maintain its original complete catalytic activity for a relatively long period (at least one week) without significant activity decay, which provides practical operational convenience for catalyst pre-preparation and short-term storage in industrial batch production.

[0149] It is important to note that:

[0150] In the catalytic dimerization cycle, the olefin molecule is first coordinated and activated by the active center of the Ni-Co heteronuclear cluster (where the Lewis acidity of the Co center promotes the polarization orientation of the olefin), and then undergoes chain growth by 1,2-insertion into the Ni-Et bond to generate Ni-alkyl intermediates;

[0151] In this intermediate stage, the adjacent Co center plays its isomerization catalytic role, catalyzing the rearrangement isomerization of Ni-alkyl intermediates along the carbon skeleton through a reversible β-H elimination / reinsertion step, causing the alkyl chain to thermodynamically migrate towards the more stable branched isomer.

[0152] Finally, through the β-H elimination step, the dimerene product dissociates from the metal center and is released into the solution, while the regenerated Ni-H active species enter the next catalytic cycle.

[0153] In conventional homogeneous nickel systems, isomerization and chain growth occur at the same active site, competing for the active site. In contrast, in heteronuclear bimetallic systems, Ni and Co centers each share the functions of chain growth and isomerization, allowing them to proceed in parallel. This fundamentally overcomes the contradiction that isomerization inevitably leads to activity loss in single-metallic-center systems, achieving a synergistic improvement in catalytic activity and branched selectivity at a higher level.

[0154] Step S3, the temperature of the pre-complexation reaction is 10 to 30°C, and the time is 2 to 4 hours.

[0155] In step S2, the moisture content control standard for moisture detection is no more than 50 ppm.

[0156] Step S1: The water content of anhydrous toluene in the Raney cobalt pretreatment is less than 20 ppm;

[0157] In step S3, the Reynolds number of the stirring in the reactor during the pre-complexation reaction is on the order of 1,000 to 10,000 to ensure that the Raney cobalt particles are in a uniformly suspended fluidized state.

[0158] Within the aforementioned general framework of molar ratios, there exists a more preferred ratio range (particularly effective when propylene is used as a substrate). Specifically, in step S3, the molar ratios of the components in the pre-complexation reaction are: Co / Ni = 0.20-1.00, Al / (Ni+Co) = 5.00-12.00, and P / Ni = 0.80-1.50.

[0159] It is worth noting that reducing the P / Ni molar ratio to below 1.0 (i.e., P / Ni = 0.50 to 0.99) is one of the significant advantages compared to existing technologies. Employing single-phosphine coordination (with a P / Ni ratio slightly higher than the stoichiometric ratio to push the equilibrium towards coordination) is sufficient to achieve excellent catalytic activity and branched selectivity, fundamentally reducing the amount of expensive PCy3 phosphine ligands used per batch and providing a crucial institutional guarantee for the economic optimization of the entire catalytic process cost.

[0160] Regarding the preparation process:

[0161] Compared to the conventional approach of using catalysts for dimerization reactions immediately after each component is mixed separately or in a single step, this pre-complexation preparation step, which involves strict control over moisture detection standards and temperature-time windows, has the following substantial differences:

[0162] In step S2, a clear moisture detection and control point is set in the moisture detection: the moisture content is detected and controlled before the Raney cobalt is introduced into the system by Karl Fischer method to ensure that the residual moisture does not exceed 100 ppm, so as to ensure the effective utilization rate of triethylaluminum in the subsequent pre-complexation step (reducing side reaction consumption) and production safety from the source.

[0163] In step S3, a temperature- and time-controlled pre-complexation operation is implemented in the pre-complexation reaction: the four components are fully pre-complexed for 1 to 5 hours within a temperature window of 0 to 50°C, so that the active center of the Ni-Co heteronuclear bimetallic cluster is fully generated and reaches a stable configuration before the catalytic reaction is started. This fundamentally improves the structural uniformity of the active species of the catalyst and the batch-to-batch performance reproducibility, solving the prominent common problem of large batch-to-batch fluctuations in catalyst performance in the prior art.

[0164] To verify the formation of the active center of the Ni-Co heteronuclear bimetallic cluster and its unique catalytic performance relative to physical mixtures, the following control experiment was conducted:

[0165] Control Experiment A: The conditions of Preparation Example 1 were followed, but without Raney cobalt; instead, a homogeneous cobalt salt (cobalt naphthenate, 8% Co content) with an equal molar amount of cobalt was used, with all other conditions remaining the same. When applied to propylene dimerization, the branching selectivity was only 72%, significantly lower than the 90% of Example 1, indicating that the Co2+ homogeneous species do not possess the Raney cobalt skeleton Co. 0 The unique synergistic catalytic function of atoms.

[0166] Control Experiment B: The Raney cobalt in Preparation Example 1 was replaced with conventional cobalt powder (purity ≥99.5%, D50 = 25 μm) with similar specific surface area and particle size, and pre-complexation and dimerization reactions were carried out under the same conditions. The results showed that the branch selectivity was only 78%, further confirming the porous framework structure and surface Co of the Raney cobalt. 0 An unsaturated coordination environment of atoms is a necessary condition for realizing atomic-level synergistic catalysis of Ni-Co.

[0167] The aforementioned control experiment ruled out the possibility that 'the general presence of cobalt can produce a synergistic effect,' thus reinforcing the technological contribution and irreplaceability of Raney cobalt as a key innovative component.

[0168] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A novel composite catalyst for olefin dimerization, characterized in that, It includes the following components: nickel naphthenate, Raney cobalt, triethylaluminum, and tricyclohexylphosphine, with Ni ≡ 1.00 based on the molar amount of nickel in nickel naphthenate: The molar ratios of Raney cobalt, triethylaluminum, and tricyclohexylphosphine are as follows: Raney cobalt has a Co / Ni ratio of 0.10-5.00; The Al / (Ni+Co) ratio of triethylaluminum is 1.00-20.

00. The P / Ni ratio of tricyclohexylphosphine is 0.50-3.

00.

2. The novel composite catalyst for olefin dimerization according to claim 1, characterized in that, The molar ratio of Raney cobalt, triethylaluminum, and tricyclohexylphosphine is as follows: Raney cobalt has a Co / Ni ratio of 0.20-1.00; The Al / (Ni+Co) ratio of triethylaluminum is 5.00-12.

00. The P / Ni ratio of tricyclohexylphosphine is 0.80-1.

50.

3. The novel composite catalyst for olefin dimerization according to claim 2, characterized in that, The Raney cobalt is prepared by selective aluminum dissolution activation of a cobalt-aluminum alloy with alkaline solution, wherein the mass content of cobalt is not less than 85% and the mass content of residual aluminum is 5% to 15%; the particle size D50 of the Raney cobalt is 5μm to 50μm and the BET specific surface area is 20m² / g to 100m² / g.

4. A novel composite catalyst for olefin dimerization according to claim 3, characterized in that, The triethylaluminum is provided in the form of a toluene solution with a mass concentration of 10% to 25%.

5. A novel composite catalyst for olefin dimerization according to claim 4, characterized in that, The tricyclohexylphosphine has a Tolan cone angle of 170° and is provided in pure form or as a toluene solution.

6. A method for preparing a novel composite catalyst for olefin dimerization as described in claim 5, characterized in that, The preparation method includes the following steps: Step S1, Raney cobalt pretreatment, refers to washing and replacing the Raney cobalt multiple times with anhydrous toluene under an inert atmosphere to remove residual moisture from the Raney cobalt; Step S2, Moisture detection, refers to the moisture content of the solvent obtained in the last washing operation during step S1, Raney cobalt pretreatment, and the moisture content is controlled to not exceed 100 ppm. Step S3, pre-complexation reaction, refers to the process of adding Raney cobalt, nickel naphthenate, tricyclohexylphosphine, and toluene solvent sequentially to a reactor under an inert atmosphere after Raney cobalt pretreatment in step S1 and moisture detection in step S2. After stirring evenly, a toluene solution of triethylaluminum is added, and the pre-complexation reaction is carried out at a temperature of 0 to 50°C for 1 to 5 hours. The components Raney cobalt, triethylaluminum, and tricyclohexylphosphine are calculated based on the amount of nickel in nickel naphthenate (Ni≡1.00), with Co / Ni=0.10-5.00, P / Ni=0.50-3.00, and Al / (Ni+Co)=1.00-20.

00. Step S4, catalyst suspension, refers to the mixture obtained after step S3, the pre-complexation reaction, which is a suspension-type composite catalyst used for olefin dimerization catalysis.

7. The method for preparing a novel composite catalyst for olefin dimerization according to claim 6, characterized in that, In step S3, the temperature of the pre-complexation reaction is 10 to 30°C, and the time is 2 to 4 hours.

8. The method for preparing a novel composite catalyst for olefin dimerization according to claim 7, characterized in that, In step S2, the moisture content control standard for moisture detection is no more than 50 ppm.

9. A method for preparing a novel composite catalyst for olefin dimerization according to claim 8, characterized in that, In step S1, the water content of anhydrous toluene in the Raney cobalt pretreatment is less than 20 ppm. In step S3, the number of Reynolds stirring in the reactor during the pre-complexation reaction is on the order of 1,000 to 10,000 to ensure that the Raney cobalt particles are in a uniformly suspended fluidized state.

10. A method for preparing a novel composite catalyst for olefin dimerization according to claim 9, characterized in that, In step S3, the molar ratio of each component in the pre-complexation reaction is: Co / Ni = 0.20-1.00, Al / (Ni+Co) = 5.00-12.00, P / Ni = 0.80-1.50.

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