Ethylene Oligomerization Research Articles

Design of bi-functional Ni-zeolites for ethylene oligomerization: Controlling Ni speciation and zeolite properties by one-pot and post-synthetic Ni incorporation

The design of diverse Ni-zeolites has been performed attempting to control different physico-chemical properties of the zeolite supports as well as the Ni speciation to study their influence on the industrially relevant ethylene oligomerization reaction. In this sense, Ni-containing medium-pore MFI and large-pore BEA zeolites have been synthesized with different particle sizes, Si/Al molar ratios and following different Ni-incorporation strategies (one-pot versus post-synthesis). Characterization techniques reveal the preferential presence of cationic Ni2+ and NiO nanoclusters inside the zeolitic pores when Ni has been incorporated by post-synthesis impregnation or one-pot approaches, respectively. The presence of Ni2+ species, rather than other factors, mainly governs olefin oligomerization under near-ambient pressures, guiding preferentially towards C4-C6 olefins as main products. Crystal size, acidity and/or Ni incorporation methodology, on the other hand, play key roles under high-pressure reaction conditions, resulting in the formation of heavier olefins, especially in zeolites containing less cationic nickel, larger proportion of NiO clusters and higher Brønsted acid site density.

Unveiling meta-Alkyloxy/-Silyloxy-Substituted N-Aryl PNP Ligands for Efficient Cr-Catalyzed Ethylene Tetramerization.

Novel N-aryl-functionalized PNP ligands (1-4) bearing m-alkyloxy/-silyloxy substituents were prepared and evaluated for chromium-catalyzed ethylene oligomerization using MMAO-3A as an activator. The selected Cr/PNP system under optimized condition exhibited high 1-octene-selective (up to 70 wt %) ethylene tetramerization at a remarkable rate (over 3000 kg gCr-1 h-1). More importantly, the undesirable polyethylene selectivity was restricted to a minimum level of ∼1-2 wt % for pre-catalysts derived with ligands 1 and 2. Employing chlorobenzene as a reaction medium yielded best productivity in conjunction to the total α-olefin (1-C6 + 1-C8) selectivity (∼88 wt %). N-aryl PNP ligands (3 and 4) incorporating m-silyloxy substituents in the phenyl ring exhibited relatively poorer tetramerization performance while yielding higher PE fraction as compared to their m-alkyloxy derivatives. A detailed molecular structure of the best-performing pre-catalyst 1-Cr was established by single-crystal X-ray diffraction analysis. The stability of 1/Cr-based catalyst system was investigated for a reaction time of up to 2 h under optimized condition.

Li Plating Regulation on Fast‐Charging Graphite Anodes by a Triglyme‐LiNO3 Synergistic Electrolyte Additive

AbstractGraphite anodes are prone to dangerous Li plating during fast charging, but the difficulty to identify the rate‐limiting step has made a challenging to eliminate Li plating thoroughly. Thus, the inherent thinking on inhibiting Li plating needs to be compromised. Herein, an elastic solid electrolyte interphase (SEI) with uniform Li‐ion flux is constructed on graphite anode by introducing a triglyme (G3)‐LiNO3 synergistic additive (GLN) to commercial carbonate electrolyte, for realizing a dendrite‐free and highly‐reversible Li plating under high rates. The cross‐linked oligomeric ether and Li3N particles derived from the GLN greatly improve the stability of the SEI before and after Li plating and facilitate the uniform Li deposition. When 51 % of lithiation capacity is contributed from Li plating, the graphite anode in the electrolyte with 5 vol.% GLN achieved an average 99.6 % Li plating reversibility over 100 cycles. In addition, the 1.2‐Ah LiFePO4 | graphite pouch cell with GLN‐added electrolyte stably operated over 150 cycles at 3 C, firmly demonstrating the promise of GLN in commercial Li‐ion batteries for fast‐charging applications.

Li Plating Regulation on Fast-Charging Graphite Anodes by a Triglyme-LiNO3 Synergistic Electrolyte Additive.

Graphite anodes are prone to dangerous Li plating during fast charging, but the difficulty to identify the rate-limiting step has made a challenging to eliminate Li plating thoroughly. Thus, the inherent thinking on inhibiting Li plating needs to be compromised. Herein, an elastic solid electrolyte interphase (SEI) with uniform Li-ion flux is constructed on graphite anode by introducing a triglyme (G3)-LiNO3 synergistic additive (GLN) to commercial carbonate electrolyte, for realizing a dendrite-free and highly-reversible Li plating under high rates. The cross-linked oligomeric ether and Li3N particles derived from the GLN greatly improve the stability of the SEI before and after Li plating and facilitate the uniform Li deposition. When 51% of lithiation capacity is contributed from Li plating, the graphite anode in the electrolyte with 5 vol.% GLN achieved an average 99.6% Li plating reversibility over 100 cycles. In addition, the 1.2-Ah LiFePO4 | graphite pouch cell with GLN-added electrolyte stably operated over 150 cycles at 3 C, firmly demonstrating the promise of GLN in commercial Li-ion batteries for fast-charging applications.

Chromium-Based Complexes Bearing Aminophosphine and Phosphine-Imine-Pyrryl Ligands for Selective Ethylene Tri/Tetramerization.

A series of Cr-based complexes 6-10 bearing aminophosphine (P,N) ligands Ph2P-L-NH2 [L = CH2CH2 (1), L = CH2CH2CH2 (2), and L = C6H4CH2 (3)] and phosphine-imine-pyrryl (P,N,N) ligands 2-(Ph2P-L-N=CH)C4H3NH [L = CH2CH2CH2 (4) and L = C6H4CH2 (5)] were prepared, and their catalytic properties were examined for ethylene tri/tetramerization. X-ray crystallographic analysis of complex 8 indicated the κ2-P,N bidentate coordination mode at the Cr(III) center and the distorted octahedral geometry of monomeric P,N-CrCl3. Upon activation by methylaluminoxane (MAO), complexes 7-8 bearing P,N (PC3N backbone) ligands 2-3 showed good catalytic reactivity for ethylene tri/tetramerization. On the other hand, complex 6 bearing the P,N (PC2N backbone) ligand 1 was found active for non-selective ethylene oligomerization, while complexes 9-10 bearing P,N,N ligands 4-5 only produced polymerization products. In particular, the high catalytic activity of 458.2 kg/(g·Cr·h), excellent selectivity of 90.9% (1-hexene and 1-octene combined), and extremely low PE content of 0.1% were obtained with complex 7 in toluene at 45 °C and 45 bar. These results suggest that rational control of P,N and P,N,N ligand backbones, including a carbon spacer and rigidity of a carbon bridge, can lead to the high-performance catalyst for the ethylene tri/tetramerization process.

Preparation of branched oligoethylene and polar functionalized oligoethylene using unsymmetrical arylamine based cationic Ni(II) and Pd(II) iminopyridyl catalysts

In this contribution, three unsymmetrical arylamine based pyridine-imine ligands and the corresponding nickel and palladium complexes were prepared and used for ethylene oligomerization. The nickel complexes are highly active (level of 106 g·mol−1·h−1) in catalyzing ethylene oligomerization to produce highly branched (66–89/1000C) oligoethylenes (1.4–3.2 kg/mol). The corresponding palladium complexes presented moderate catalytic activities (level of 104 g·mol−1·h−1) and low molecular weight (0.4–0.6 kg/mol) oligoethylenes with high branching densities (103–126/1000C) were yielded in ethylene oligomerization. Moreover, high incorporation ratio (6.86–14.16 mol%) ester functionalized oligoethylenes with low molecular weights (ca. 0.4 kg/mol) were yielded with these palladium complexes in ethylene–methyl acrylate co-oligomerization. Methyl branching comprises the majority of all the branching for the oligoethylenes yielded by nickel complexes and branching of C3+ comprises the majority with palladium ones. Hyperbranched architecture was identified for all the produced oligoethylenes and ester functionalized oligoethylenes. Most interestingly, compared with the reported pyridine-imine catalysts with fully substituted benzothiophenes, the partially benzothiophene substituted ones exhibited significantly higher activity and yielded much higher molecular weight oligoethylenes.

Mechanism insight into ethylene oligomerization on zeolite K-LTA surface: A DFT and kMC study

The regeneration gas used in the K-LTA zeolite dryer of the MTO plant is planning to be changed from high purity nitrogen to the top gas of the demethanizer tower with high ethylene content, which is helpful to energy saving and emission reduction. However, there is a risk of ethylene oligomerization and carbon deposition when the regeneration gas passes through the K-LTA zeolite. The reaction mechanism of ethylene oligomerization on the K-LTA zeolite surface must be clarified. DFT calculations showed that ethylene could be physically adsorbed on Si–OH, Al–OH, the incomplete α- and β-cage on [100]-D4R-e surface. Butoxide forms through ethylene dimerization by stepwise and concerted mechanisms first. Then the reaction of ethylene and butoxide to n-hexyloxide leads to the continued growth of the carbon chain. The oligomerization reaction barriers of rate-determining steps are between 1.65∼1.75 eV, which is more difficult to occur than other zeolites. The ethylene oligomerization reaction can be divided into stepwise polymerization path, concerted polymerization path and concerted butene path. kMC simulation found that the dominant reaction paths are different under different temperatures. When the regeneration temperature reaches 473 K, trace n-butene is generated. At 513 K, ethylene oligommerization occurs and carbon deposition is formed. The results put forward higher requirements for strictly controlling the temperature of the dryer to ensure the excellent performance of K-LTA zeolite.

Alkylaluminum/Urea Hybrid Cocatalysts and Their Use in Iron‐Catalyzed Oligomerization of Ethylene

AbstractThe bis(imino)pyridyl iron‐based ethylene oligomerization catalysts have the advantages of mild reaction conditions, high activity and high selectivity to linear α‐olefins. However, barriers, such as high polymer content in the product mixture and large methylaluminoxane (MAO) dosage, are still limitations for the development of these systems at the industrial scale. In this study, new cocatalysts are prepared by the reaction of alkylaluminums with urea and its derivatives, and successfully used to activate iron‐based catalysts. It is found that the type and molar ratio of alkylaluminum and urea have significant influence on the performance of the cocatalysts. The activity of the preferred triisobutylaluminum/urea activated systems reaches more than 3.0 × 108 g (mol‐Fe)−1 h−1, and the polymer content can be controlled to be less than 2 wt.%. Notably, the catalytic system exhibits good high temperature stability, the activity can still reach 1.0 × 108 g (mol‐Fe)−1 h−1 even at 120 °C. Further 1H NMR studies show that alkylaluminum can react with the NH moieties of urea, forming complex alkylaluminum clusters, even aluminoxane‐like structures. This study offers a promising family of cocatalysts, making it possible to simultaneously improve their performance and reduce their cost.

Syntheses and Catalytic Behavior of Dendritic Macrocyclic Schiff‐Base Nickel (II) Complexes in Ethylene Oligomerization

AbstractThe functionalized dendrimers play an important role in catalytic application. A dendritic Schiff base macrocyclic compound was designed and synthesized with the 1.0 generation dendrimer polyamidoamine (1.0G PAMAM) and terephthalaldehyde for ethylene oligomerization. The role of solvent in the synthesized process of dendritic macrocyclic Schiff base ligand was studied. Surprisingly, intermolecular or intramolecular cyclization occurred and formed bicyclic Schiff base ligand (Ligand 1) and polycyclic Schiff base ligand (Ligand 2). And their corresponding nickel complexes (Catalyst 1 and Catalyst 2) were also synthesized with NiCl2(DME) as material to be used for ethylene oligomerization. The effects of the reaction parameters and the chemical structure of the ligand on the catalytic behavior were investigated with methyl‐aluminoxane (MAO) as cocatalyst, and Catalyst 1 and Catalyst 2 displayed the high catalytic activity and the high selectivity for low‐carbon olefin in ethylene oligomerization. Catalyst 2 based on Ligand 2 had a higher catalytic activity of 9.12×104 g (mol Ni h)−1 in ethylene oligomerization because of large dendritic ring in the ligand for ethylene diffusion and mass transfer. Moreover, two synthesized nickel complexes based on dendritic macrocyclic Schiff base ligand had a higher catalytic activity compared with the corresponding dendritic salicylaldehydeimine nickel (II) catalyst.

Preparation of nickel catalysts bearing Schiff base macrocycles and their performance in ethylene oligomerization

Preparation of nickel catalysts bearing Schiff base macrocycles and their performance in ethylene oligomerization

Ethylene oligomerization over mesoporous FeNi-BTC catalysts: Effect of the textural properties of the catalyst on the reaction performance

Mesoporous FeNi-1,3,5-benzenetricarboxylates (FeNi-BTCs) with different Fe/Ni ratios were prepared, and their catalytic activities in ethylene oligomerization were evaluated. The textural properties of the bimetallic FeNi-BTC were considerably affected by the Fe/Ni ratio, exhibiting a volcano relationship, with the maximum specific surface area, pore volume, and diameter observed at Fe/Ni = 10/90. The enhanced textural properties of the FeNi-BTC catalyst resulted in accelerated ethylene oligomerization and an increased C6–C8 oligomer selectivity. Using the Fe10Ni90-BTC catalyst, the rate of ethylene consumption and C6–C8 oligomer selectivity reached as high as 2823 g C2H4/g Ni h and 49%, which were approximately four- and two-fold higher than those of Ni-BTC, respectively. The remarkable reaction performance of the Fe10Ni90-BTC catalyst could be rationalized in terms of its well-defined mesoporous structure, which could decrease the mass transfer resistance and thereby facilitate intrapore ethylene diffusion during ethylene oligomerization. These results clearly demonstrate the potential of the FeNi-BTC catalyst in promoting ethylene oligomerization with a high activity and selectivity towards C6∼C8 oligomers. In the catalyst recycling study, whereas the catalytic activity decreased due to the partial deformation of the FeNi-BTC catalyst with repeated recycling, the selectivity towards C6+ oligomers gradually increased.

Nanoparticle forming polyelectrolyte complexes derived from well-defined block copolymers

Polymers can be used in nanoparticle associated formulations to encapsulate cytotoxic drugs (e.g., paclitaxel). Polyelectrolyte complexes (PECs) that form drug associated colloids also have potential to form particulate associated formulations. We used RAFT polymerisation to prepare small families of narrow molecular weight distributed (i) methacrylate block co-polymers comprised of oligomeric ethylene glycol, poly(ethylene glycol) methyl ether methacrylate (PEGMA), and dimethyl amino pendent chains, 2-(dimethylamino) ethyl methacrylate (DMAEMA), and (ii) poly(methacrylic acid), PMAA. These polymers were examined for their ability to form PECs capable of drug encapsulation. Optimal control in RAFT polymerisation was confirmed by the linear increase of molecular weight and the narrow dispersity of the polymers (<1.2) as determined by 1H nuclear magnetic resonance and gel permeation chromatography. Dynamic light scattering and transmission electron microscopy showed formation of well-defined monodispersed nanoparticles with a hydrodynamic diameter of 25 ± 3 nm upon self-assembly of poly(PEGMA0.23-b-DMAEMA0.77)99 and PMAA75. These PECs are highly haemocompatible. Thin film hydration was used to encapsulate two hydrophobic drugs, paclitaxel and carmofur, into spherical nanoparticles. The results show that carmofur was encapsulated markedly more effectively than paclitaxel (72 vs 1.5%).

Synthesis, characterization and ethylene oligomerization of MIL-125(Ti)-NH2 grafted salicylaldehyde nickel complexes

Metal-organic framework MIL-125(Ti)-NH2 was prepared and coordinated with salicylaldehyde and NiCl2·6H2O to create a heterogeneous catalyst for ethylene polymerization. The structure of the products was characterized by a variety of physical methods, such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma mass spectrometry (ICP-MS), and nitrogen adsorption-desorption. The catalytic performance of MIL-125(Ti)-NH2-Sal-Ni was also investigated. The results showed that the reaction temperature, Al/Ni molar ratio, and ethylene pressure influenced on the catalytic activity and product selectivity. Under optimal reaction conditions, the catalytic activity of MIL-125(Ti)-NH2-Sal-Ni for ethylene oligomerization could reach 5.90 × 104 g·(mol Ni·h)−1 using cyclohexane as the solvent and MAO as the co-catalyst; the main products were C4 and C6. In addition, MIL-125(Ti)-NH2-Sal-Ni had good catalytic stability and recycling, which could be reused at least twice without significant loss of activity. Moreover, based on the evaluation of catalytic performance, the catalytic ethylene oligomerization mechanism of MIL-125(Ti)-NH2-Sal-Ni was also deduced.

Modulating Quantum Interference Between Destructive and Constructive States in Double N‐Substituted Single Molecule Junctions (Adv. Electron. Mater. 2/2023)

Quantum Interferences In article number 2201024, Xiangfeng Shao, Colin J. Lambert, Hao-Li Zhang, and co-workers present the significant modulation effect of double N-substitution on quantum interference (QI) in meta-phenylene ethylene oligomer molecular devices, reveal how two N-atoms synergistically modulate the molecular conductance between destructive QI and constructive QI states. The findings of this work pave a path toward utilization of heterocyclic aromatic hydrocarbons in molecular electronics.

Computer-assisted design of asymmetric PNP ligands for ethylene tri-/tetramerization: A combined DFT and artificial neural network approach

The combination of computational and experimental sciences accelerates the design and development of molecular catalysts. A general strategy for developing ethylene oligomerization catalysts is still lacking. Consequently, herein, we proposed a widely applicable strategy for designing ethylene oligomerization catalysts. We combined density functional theory (DFT) and an artificial neural network (ANN) to establish a relation between catalyst structure and performance. The structure optimization and electronic calculation of a series of asymmetric PNP/Cr active species were conducted using DFT, and the steric and electronic descriptors were extracted to establish datasets. The catalyst prediction model was constructed using ANN and the leave-one-out cross-validation (LOOCV) method was used to verify the generalization ability of the models. The optimized ANN-based models used to predict 1-hexene and 1-octene selectivity exhibited high R2 values, which indicates satisfactory prediction accuracy of the models. We designed new PNP ligands and successfully predicted the ethylene oligomerization performance of PNP/Cr precatalysts using ANN-based models, which were verified through experiments. In addition, we found that the steric properties more significantly affect the performance of precatalysts than the electronic properties.

The second coordination sphere effect of benzothiophene groups enhances chain transfer in ethylene (co)oligomerization

The second coordination sphere effect of benzothiophene groups could facilitate the chain transfer in iminopyridyl Ni(ii)/Pd(ii)-catalyzed ethylene (co)oligomerization, in contrast to the phenomenon observed in the corresponding α-diimine system.

Unravelling the chain growth mechanism in Cr/NNN-catalysed ethylene oligomerization

Density functional theory (DFT) methods were employed to explore the inherent chain growth mechanism targeting a special and controversial Cr/NNN ethylene oligomerization system.

Исследование новых макропористых катализаторов в процессе алкилирования фенола олигомерами этилена

The features of phenol alkylation by higher alpha-olefins in order to obtain mono-substituted alkylphenols (o-AF and p-AF) using commercial industrial samples of sulfocationites: Hydrolite ZG CD552, ND-102 and the line of catalysts Purolite CT275DR/4503, CT275DR/4883, CT151DR, CT169DR, which belong to macroporous and are in different price categories. A feature of these cationites is a particularly strong matrix of regularly cross-linked divinylbenzene styrene copolymer. The structure of the granules combines the increased rigidity of the polymer mesh with a highly developed surface of the pores for exchange, which provides a large concentration of available exchange groups and high diffusion permeability of the granules. A comparative analysis of the catalytic activity of alkylation catalysts was carried out, which showed that, despite the high activity of all the studied catalysts in the reaction of alkylation of phenol with ethylene oligomers (OE) of the C16-C18 fraction, most of the studied catalysts showed low thermal stability and showed a tendency to rapid mechanical destruction. During the research, optimal technological parameters for each catalyst were established, including temperature and molar ratio of reagents, providing maximum yields of the target monoalkylphenol at the level of 97-98 %.

Palladium-catalyzed polar solvent empowered synthesis of hyper-branched ethylene oligomers and their applications

Neutral palladium complexes derived from naphthoxy imine ligands produce highly branched ethylene oligomers in polar solvents, which upon functionalization serve as compatibilizers between LLDPE and Nylon-6.

Heterogenization of molecular catalysts within porous solids: the case of Ni-catalyzed ethylene oligomerization from zeolites to metal-organic frameworks.

The last decade has seen a tremendous expansion of the field of heterogenized molecular catalysis, especially with the growing interest in metal-organic frameworks and related porous hybrid solids. With successful achievements in the transfer from molecular homogeneous catalysis to heterogenized processes come the necessary discussions on methodologies used and a critical assessment on the advantages of heterogenizing molecular catalysis. Here we use the example of nickel-catalyzed ethylene oligomerization, a reaction of both fundamental and applied interest, to review heterogenization methodologies of well-defined molecular catalysts within porous solids while addressing the biases in the comparison between original molecular systems and heterogenized counterparts.