Dual roles of trifluoroborate in nickel-catalyzed ethylene polymerization: Electronic perturbation and anchoring for heterogenization

Brookhart-type α-diimine nickel and palladium catalysts have been extensively studied over the past several decades; however, the heterogenization of these metal complexes has received much less attention. In this contribution, we installed a trifluoroborate potassium substituent on an α-diimine framework. The ionic nature of trifluoroborate potassium endowed the α-diimine nickel complex with a strong affinity for the SiO₂ support, while its electron-donating nature enhanced the catalyst stability and polyethylene molecular weight. In the presence of only 100 equiv. of Et₂AlCl cocatalyst, the SiO₂-supported catalyst demonstrated significantly better performance than its homogeneous analog during ethylene polymerization, with extremely high activity (1.42–6.53 × 10⁷ g mol⁻¹ h⁻¹) and high thermal stability. The heterogeneous system led to the formation of high-molecular-weight polyethylenes (M_n 142,500–732,800 g/mol), narrow polydispersities (2.18–3.00), tunable branching densities (21–64 per 1000 carbon atoms), and great mechanical properties. Moreover, the efficient copolymerization of ethylene with comonomers such as methyl 10-undecenoate, 6-chloro-1-hexene or 5-hexenylacetate was achieved. These superior properties enabled by the trifluoroborate potassium moiety may inspire its applications in other polymerization catalyst systems.     

Selective ethylene trimerization with a cyclopentadienyl-arene titanatrane catalyst

Cyclopentadienyl-arene titanatrane catalysts activated by methylaluminoxane (MAO) cocatalysts were studied for the trimerization of ethylene. The introduction of electron-rich multidentate ligands to the catalysts?? active sites resulted in good productivity and selectivity for ethylene trimerization. Various amounts of MAO were tested, and methods of its introduction to the system were varied. It has been shown that pre-alkylation of the catalyst with MAO increases the productivity of ethylene trimerization. The effects of reaction temperature and pressure on 1-hexene productivity and selectivity were also studied. The rate of ethylene conversion was approximately first order with respect to ethylene concentration. 1-Hexene was produced under moderate conditions, allowing energy savings to be gained through lower temperature reactions.     

Effect of inorganic oxide supports on the activity of chromium‐based catalysts in ethylene trimerization

Novel heterogeneous catalysts were prepared using immobilization of bis(2‐decylsulfanylethyl)amine–CrCl₃ (Cr‐SNS‐D) on various supports, namely commercial TiO₂, Al₂O₃ and magnetic Fe₃O₄@SiO₂ nanoparticles, to yield solid catalysts denoted as support@Cr‐SNS‐D. The structure of the catalysts was confirmed on the basis of spectroscopic analyses, N₂ adsorption–desorption and inductively coupled plasma (ICP) analysis. The surface areas of Al₂O₃@Cr‐SNS‐D, Fe₃O₄@SiO₂@Cr‐SNS‐D and TiO₂@Cr‐SNS‐D catalysts were determined to be 70, 23 and 41 m² g^?1, respectively. A decrease in surface area from that of the supports clearly establishes accurate immobilization of Cr‐SNS‐D catalyst on the surface of the parent carriers. The loading of Cr was determined to be 0.02, 0.16 and 0.11 mmol g^?1 for Cr‐SNS‐D supported on TiO₂, Al₂O₃ and Fe₃O₄@SiO₂, respectively, using ICP analysis. After preparation and full characterization of the catalysts, ethylene trimerization reaction was accomplished in 40 ml of dry toluene, at 80°C and 25 bar ethylene pressure and in the presence of methylaluminoxane (Al/Cr = 700) within 30 min. The supported chromium catalysts were found to be efficient and selective for the ethylene trimerization reaction. The highest activity (74 650 g_1‐hexene g_Cr^?1 h^?1), as well as no polyethylene formation during reaction processes, was observed when TiO₂ was used as the catalyst support.     

Polymer-supported Ziegler–Natta catalysts. II. Ethylene homo- and copolymerization with TiCl4/MgR2/poly(ethylene-co-acrylic acid) catalyst

A novel polymer-supported titanium-based catalyst shows high activity and nondecaying kinetic profiles for ethylene polymerization. The presence of 1-hexene comonomer drastically increases the catalyst activity, exhibiting a similarity to the MgCl₂-supported catalysts. However, the nondecaying kinetic profiles of copolymerization distinguish this catalyst from the latter. Infrared analysis indicates that the transition metals were immobilized on the polymer support via functional groups. The effects of polymerization conditions on catalyst activity have been assessed. Characterization of the resulting polymer product by means of ¹³C-NMR, DSC, and SEM demonstrates a branch-free structure with high melting point, high crystallinity, and high molecular weight for the ethylene homopolymer. The reactivity ratios of ethylene-1-hexene copolymerization are evaluated from ¹³C-NMR analysis data. © 1994 John Wiley & Sons, Inc.     

新型均相铬系催化剂的制备与催化乙烯齐聚

合成了3种新型的N取代基中含有O/N杂原子的1,3,5-三氮杂环己烷[NNN]型配体,利用氢核磁共振谱(1H NMR)、碳核磁共振谱(13C NMR)及电子轰击质谱(EI-MS)等方法对其进行表征.将[NNN]型配体与Cr(Ⅲ)络合制备相应的均相铬催化剂,采用电喷雾质谱(ESI-MS)及元素分析分别对其进行表征.以甲基烷氧铝(MAO)为助催化剂,考察了反应温度、反应压力及铝铬摩尔比等因素对催化乙烯齐聚催化性能的影响.研究结果表明,在以甲苯为溶剂,反应温度50℃,反应压力0.8 MPa,铝铬摩尔比为500∶1,Cr浓度为2.0×10-4mol/L的反应条件下,取代基为3-二甲氨基丙基的均相铬催化剂的催化活性能够达到15.71×105g/(mol Cr·h),对1-己烯和1-辛烯的选择性达到91.02%,而取代基为3-乙氧基丙基的均相铬催化剂的催化活性比较低,为11.54×105g/(mol Cr·h),但对1-己烯和1-辛烯的选择性较高,达到93.05%.     

Copolymerization of ethylene and 1-hexene with TiCl4/MgCl2 catalysts modified by 2,6-diisopropylphenol

A supported TiCl4/MgCl2 catalyst without internal electron donor (O-cat) was prepared firstly. Then it was modified by 2,6-diisopropylphenol to make a novel modified catalyst (M-cat). These two catalysts were used to catalyze ethylene/1-hexene copolymerization and 1-hexene homopolymerization. The influence of cocatalyst and hydrogen on the catalytic behavior of these two catalysts was investigated. In ethylene/1-hexene copolymerization, the introduction of 2,6-iPr2C6H3O-groups did not deactivate the supported TiCl4/MgCl2 catalyst. Although the 1-hexene incorporation in ethylene/1-hexene copolymer prepared by M-cat was lower than that prepared by O-cat, the composition distribution of the former was narrower than that of the latter. Methylaluminoxane (MAO) was a more effective activator for M-cat than triisobutyl-aluminium (TIBA). MAO led to higher yield and more uniform chain structure. In 1-hexene homopolymerization, the presence of 2,6-iPr2C6H3O-groups lowered the propagation rate constants. Two types of active centers with a chemically bonded 2,6-iPr2C6H3O-group were proposed to explain the observed phenomena in M-cat.     

Temperature dependence of the microstructure of 1-butyl-3-methylimidazolium tetrafluoroborate in aqueous solution

Many applications of ionic liquids (ILs) are closely related with their microstructure in mixtures. For example, morphology and pore size of the MCM-41 prepared in aqueous ILs are greatly dependent on the aggregation behavior of the ILs in water. Therefore, the study on the microstructure of ILs in aqueous solutions is of great importance. In this work, ¹H NMR, dynamic light scattering and attenuated total reflection infrared spectroscopy have been used to investigate the temperature effect on the structures of aqueous 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]) solutions. It was shown that the size of the IL aggregates becomes larger with decreasing temperature. When the system temperature is below the upper critical solution temperature (UCST) of the binary mixture at about 4 °C, the aggregate size of the IL is larger than 1000 nm. Additionally, the two-dimensional IR results reveal that at low IL concentrations, H₂O can interact with [BF₄]⁻ prior to the CH groups of the imidazolium ring, whereas cation and anion of the IL tend to form aggregate at high IL concentrations. With the decrease of temperature, the interactions between cation and anion of the IL become stronger, but those between the IL and water become weaker, thereby resulting in the growth of the aggregate of cation with anion of the IL. This result may give a reasonable explanation for the origin of the UCST behavior of aqueous [C₄mim][BF₄] solution.     

Copolymerization of ethylene α-olefin using MgCl2-ethanol adduct catalysts

The effects of the type and concentration of comonomers 1-hexene and 1-octene in the copolymerization of ethylene were investigated using pre polymerized Ziegler-Natta (catalyst a) and without pre polymerized (catalyst b) catalysts in the presence of hydrogen as a chain transfer agent. The properties of produced polymers were characterized by a set of techniques: (SEM), (EDX), (DSC), (GPC). TIBA and DEAC were used as co catalysts. The results of microscopic and SEM images showed the morphology and structure of catalysts (a) and (b) and the obtained spherical polymers. In the presence of 1-hexene, activity of catalyst (a) was at its maximum. The comonomer 1-octene at 32 mmol presented its activity (1.7 × 10³ g polymer/(g cat.h)) and after that, the activities decreased. Copolymerization of ethylene and 1-hexene by catalyst (b) showed higher activity (1.6 × 10³ g polymer/ polymer/(g cat.h)) at 40 mmol concentration of 1-hexene in comparison to catalyst (a).     

First Cr(III)-SNS complexes and their use as highly efficient catalysts for the trimerization of ethylene to 1-hexene

Cr(III) complexes of tridentate SNS ligands have been prepared and evaluated as catalysts for ethylene trimerization, with several giving very high activity and excellent selectivity toward 1-hexene when activated with methylaluminoxane. The new complexes illustrate the potential of sulfur-based ligands on early transition metals for catalysis.     

Catalytic vapor-phase oxidation of 2,2,2-trifluoroethanol

The synthesis of trifluoroacetaldehyde by vapor-phase oxidation of 2,2,2-trifluoroethanol using supported vanadium catalysts was studied. Significant differences were observed in the reaction outcomes resulting from different types of catalysts. The ZrO₂- and Al₂O₃-supported catalyst demonstrated both high catalytic activity and selectivity. The addition of co-catalysts such as MoO₃ or SnO₂ improved catalytic performance (Selectivity: up to 91%; S.T.Y.: >200 g L⁻¹ h⁻¹). The experimental results on catalyst lifetime showed a marked decrease in the activity of the Al₂O₃-supported catalyst within tens of hours, while the ZrO₂-supported catalyst showed little, if any, performance alterations for 2000 h.     

Synthesis of Ti(OH)OF ⋅ 0.66 H2O in Imidazolium-based Ionic Liquids

The influence of the cation of imidazolium-derived ionic liquids (ILs) on a low-temperature solution-based synthesis of hexagonal tungsten bronze (HTB) type Ti(OH)OF ⋅ 0.66 H₂O and bronze-type TiO₂(B) is investigated. The IL (C_xmim BF₄) acts as solvent and also as reaction partner with respect to the decomposition of [BF₄]⁻, releasing F⁻. In the present study, the chain length of the alkyl chain side groups attached to the imidazolium ring was varied (C₂mim BF₄ to C₁₀mim BF₄), and the obtained solids were analyzed by Powder X-Ray diffraction (PXRD) followed by Rietveld refinement. As a main finding these analyses indicate a transformation of Ti(OH)OF ⋅ 0.66 H₂O into TiO₂(B), and upon prolonged reaction time finally also into anatase TiO₂. Rietveld analysis suggests that when using ILs with longer alkyl chains, the conversion of Ti(OH)OF ⋅ 0.66 H₂O is slower compared to syntheses performed with smaller alkyl chains. Hence, Ti(OH)OF ⋅ 0.66 H₂O appears to be metastable and is stabilized by long-chain ILs serving as surfactant attached to the crystallites’ surface. In this view, the ILs shield the nanoparticles and thus slow down the conversion into the more stable compounds. This confirms previous findings that ILs act as both, solvent and reaction medium in this reaction, thus enabling the synthesis of peculiar Ti-oxides.     

Cyclodextrin-supported Co(OH)2 Clusters as Electrocatalysts for Efficient and Selective H2O2 Synthesis

Co-based material catalysts have shown attractive application prospects in the 2 e⁻ oxygen reduction reaction (ORR). However, for the industrial synthesis of H₂O₂, there is still lack of Co-based catalysts with high production yield rate. Here, novel cyclodextrin-supported Co(OH)₂ cluster catalysts were prepared via a mild and facile method. The catalyst exhibited remarkable H₂O₂ selectivity (94.2 % ~ 98.2 %), good stability (99 % activity retention after 35 h), and ultra-high H₂O₂ production yield rate (5.58 mol g_catalyst⁻¹ h⁻¹ in the H-type electrolytic cell), demonstrating its promising industrial application potential. Density functional theory (DFT) reveals that the cyclodextrin-mediated Co(OH)₂ electronic structure optimizes the adsorption of OOH* intermediates and significantly enhances the activation energy barrier for dissociation, leading to the high reactivity and selectivity for the 2 e⁻ ORR. This work offers a valuable and practical strategy to design Co-based electrocatalysts for H₂O₂ production.     

烷基咪唑离子液体对脂肪酶催化酯水解反应活性的影响

考察了1-烷基-3-甲基咪唑类离子液体对柱状假丝酵母脂肪酶(CRL)催化橄榄油水解反应活性的影响,利用电导法确定了磷酸盐缓冲液中Br^-,Cl^-,[BF₄]^-系列咪唑离子液体的临界胶束浓度(CMC)和[PF₆]^-系列咪唑离子液体的溶解度.结果显示,离子液体的阴、阳离子对酶活性的影响规律与离子液体的Kosmotropicity性质无明显关联,但与离子液体在体系中的含量密切相关,在最适离子液体含量时,酶活性达到最高;阳离子[C_nMIM]⁺中的n越大,可促进酶活性的离子液体适宜含量越低;Br^-,[BF₄]^-系列离子液体的浓度超过CMC时则抑制酶活;阴离子对酶活性的最大促进作用顺序为Br^->Cl^->[BF₄]^->[PF₆]^-.离子液体对酶活性的影响随体系pH和温度的不同而改变,在最适离子液体浓度时的最适pH均为7.000.在pH 7.000,30 ^oC以及[C₈MIM]Br离子液体浓度为47.6 mmol/L的最佳条件下,最高相对酶活力和比活力分别达到1734%和54.4 U/mg protein.     

Boosting Selective Oxidation of Ethylene to Ethylene Glycol Assisted by In situ Generated H2O2 from O2 Electroreduction

Ethylene glycol is a useful organic compound and chemical intermediate for manufacturing various commodity chemicals of industrial importance. Nevertheless, the production of ethylene glycol in a green and safe manner is still a long-standing challenge. Here, we established an integrated, efficient pathway for oxidizing ethylene into ethylene glycol. Mesoporous carbon catalyst produces H₂O₂, and titanium silicalite-1 catalyst would subsequently oxidize ethylene into ethylene glycol with the in situ generated H₂O₂. This tandem route presents a remarkable activity, i.e., 86 % H₂O₂ conversion with 99 % ethylene glycol selectivity and 51.48 mmol g_ecat⁻¹ h⁻¹ production rate at 0.4 V vs. reversible hydrogen electrode. Apart from generated H₂O₂ as an oxidant, there exists ⋅OOH intermediate which could omit the step of absorbing and dissociating H₂O₂ over titanium silicalite-1, showing faster reaction kinetics compared to the ex situ one. This work not only provides a new idea for yielding ethylene glycol but also demonstrates the superior of in situ generated H₂O₂ in tandem route.     

Highly Active Hydrogen-rich Photothermal Reverse Water Gas Shift Reaction on Ni/LaInO3 Perovskite Catalysts with Near-unity Selectivity

Photo-assisted reverse water gas shift (RWGS) reaction is regarded green and promising in controlling the reaction gas ratio in Fischer Tropsch synthesis. But it is inclined to produce more byproducts in high H₂ concentration condition. Herein, LaInO₃ loaded with Ni-nanoparticles (Ni NPs) was designed to obtain an efficient photothermal RWGS reaction rate, where LaInO₃ was enriched with oxygen vacancies to roundly adsorbing CO₂ and the strong interaction with Ni NPs endowed the catalysts with powerful H₂ activity. The optimized catalyst performed a large CO yield rate (1314 mmol g_Ni⁻¹ h⁻¹) and ≈100 % selectivity. In situ characterizations demonstrated a COOH* pathway of the reaction and photoinduced charge transfer process for reducing the RWGS reaction active energy. Our work provides valuable insights on the construction of catalysts concerning products selectivity and photoelectronic activating mechanism on CO₂ hydrogenation.     

Catalytic Trimerization of Ethylene with Highly Active Half-sandwich Titanium Complexes Bearing Pendant p-Fluorophenyl Groups

Two new complexes[η~5-C_5H_4CMe_2-(p-fluorophenyl)]TiCl_3(1)and[μ~5-C_5H_4C(cyclo-C_5H_(10))-(p-fluoro-phenyl)]TiCl_3(2)were synthesized and characterized.Their activities and selectivities for trimerization of ethylenewere investigated.The introduction of fluorine atom greatly weakened the arene coordination,but this disadvanta-geous factor can be eliminated by introduction of a bulky substituent,such as cyclo-C_5H_(10),to the bridging carbonlinked to the Cp ring.The combinative effect of the fluorine substitute and the bridging unit can make complex 2 asa highly active and selective catalyst for ethylene trimerization.Its productivity and selectivity for 1-hexene canreach 1024.0 kg·mol~(-1)·h(-1) and 99.3% respectively.     

Synergistic Effects of the ZnCl2-SiCl4 Modified TiCl4 /MgCl2 /THF Catalytic System on Ethylene/1-Hexene and Ethylene/1-Octene Copolymerizations简

The copolymerizations of ethylene with 1-hexene or 1-octene by using TiCl4 /MgCl2 /THF catalysts modified with different metal halide additives(ZnCl2, SiCl4, and the combined ZnCl2-SiCl4) were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnCl2-SiCl4 revealed the highest activities for both ethylene/1-hexene and ethylene/1-octene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements, the characteristic C―O―C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiCl4 /MgCl2 /THF catalytic system leading to an increase in activities as well as comonomer insertion(as proven by13C-NMR). However, Lewis acidmodifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst, it was found that polymers with ZnCl2 and/or SiCl4 modification exhibited a slight decrease in melting temperature, crystallinity and density. It is suggested that these results were obtained based on the different amount of α-olefins insertion, regardless of the types of Lewis acids and comonomer.     

Wurtzite CuGaS2 with an In-Situ-Formed CuO Layer Photocatalyzes CO2 Conversion to Ethylene with High Selectivity

We present surface reconstruction-induced C−C coupling whereby CO₂ is converted into ethylene. The wurtzite phase of CuGaS_2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO₂ to ethylene (C₂H₄). Upon illumination, the catalyst efficiently converts CO₂ to C₂H₄ with 75.1 % selectivity (92.7 % selectivity in terms of R_electron) and a 20.6 μmol g⁻¹ h⁻¹ evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu²⁺, with the assistance of existing Cu⁺, functioning as an anchor for the generated *CO and thereby facilitating C−C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO₂ reduction reaction pathway to selective formation of ethylene.     

Optimization of ethylene trimerization using catalysts based on TiCl3/half‐sandwich ligands

Catalytic trimerization of ethylene using three titanium‐based complexes [η⁵‐C₉H₆C(R)thienyl]TiCl₃ with various types of bridges (R = cyclo‐C₅H₁₀ ( C1 ), cyclo‐C₄H₈ ( C2 ) and (CH₃)₂ ( C3 )) has been successfully optimized and compared. First of all, three benzofulvene precursors, C₉H₆C(R), were synthesized. Then the corresponding indenyl‐based ligands were obtained via the reaction of the precursors with thienyllithium. The final titanium‐based catalysts display a distorted tetrahedral geometry, as expected for Ti(IV), with the ligand coordinated with a hemilabile behaviour. The structures of the compounds were confirmed on the basis of various analyses. The effect of catalyst concentration, ethylene pressure, reaction temperature and nature of the bridge as the significant factor affecting coordination and orientation of thienyl group relative to the metal centre on 1‐hexene (1‐C₆) productivity and selectivity was investigated. Results revealed that the bulky bridge groups such as cyclo‐C₅H₁₀ and cyclo‐C₄H₈ are appropriate for ethylene trimerization due to the closer coordination of sulfur atom with Ti, especially in cationic state, and catalyst C2 with cyclo‐C₄H₈ bridge exhibits moderate productivity equal to 785 kg 1‐C₆ (mol Ti)^?1 h^?1. According to the results, ethylene at a pressure of 10 bar, 50°C and 1.5 μmol of catalyst were selected as the best conditions for obtaining 1‐C₆ with high productivity and selectivity. The presence of indenyl enhances the thermal stability of the catalysts and preserves their activity in higher temperatures such as 50 and 80°C.     

Solar-Driven CO2 Conversion via Optimized Photothermal Catalysis in a Lotus Pod Structure

Photothermal CO₂ reduction is one of the most promising routes to efficiently utilize solar energy for fuel production at high rates. However, this reaction is currently limited by underdeveloped catalysts with low photothermal conversion efficiency, insufficient exposure of active sites, low active material loading, and high material cost. Herein, we report a potassium-modified carbon-supported cobalt (K⁺−Co−C) catalyst mimicking the structure of a lotus pod that addresses these challenges. As a result of the designed lotus-pod structure which features an efficient photothermal C substrate with hierarchical pores, an intimate Co/C interface with covalent bonding, and exposed Co catalytic sites with optimized CO binding strength, the K⁺−Co−C catalyst shows a record-high photothermal CO₂ hydrogenation rate of 758 mmol g_cat⁻¹ h⁻¹ (2871 mmol g_Co⁻¹ h⁻¹) with a 99.8 % selectivity for CO, three orders of magnitude higher than typical photochemical CO₂ reduction reactions. We further demonstrate with this catalyst effective CO₂ conversion under natural sunlight one hour before sunset during the winter season, putting forward an important step towards practical solar fuel production.