Catalysts For Oligomerization Research Articles

Nickel and molybdenum containing mesoporous catalysts for ethylene oligomerization and metathesis

Ethylene is converted into propylene by one-pot cascade reactions over catalysts prepared using a commercial mesoporous non-ordered silica as a support.

Sulfated alumina aerogel-based superacid catalysts for 1-hexene oligomerization

Al2O3 aerogel samples were synthesized by supercritical drying in two different media: isopropanol and methyl tert-butyl ether. After sulfation in a SO2Cl2 vapor, the aerogel acquired superacid properties (–12.4 ≤ H0 ≤–11.99) and efficiently catalyzed 1-hexene oligomerization and dimerization.

Regeneration of Refinery Gas Treatment Superacid Catalysts by SCF Solvent Extraction

The mechanisms of the process of extractive regeneration of oligomerization catalysts based on pillared clays in supercritical carbon dioxide (SCF-CO 3 ) in pure state and with addition of chlorine compounds (CCl 4 or C 2 H 4 Cl 2 ) are studied. The catalyst efficiency in the oligomerization process after regeneration with various SCF solvents is compared. The carburized and regenerated catalysts are studied by thermal analysis methods. Chlorine-containing additives are found to be effective in the regeneration process.

Ethylene oligomerization studies by nickel(ii) complexes chelated by (amino)pyridine ligands: experimental and density functional theory studies

Reductions of imine compounds 2-methoxy-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L1), 2-methoxy-N-((pyridin-2-yl)methylene)ethanamine (L2), N,N-diethyl-N-((pyridin-2-yl)methylene)ethane-1,2-diamine (L3) and 2-((pyridin-2-yl)methyleneamino)ethanol (L4) using NABH4 produced their corresponding amine analogues N-(2-methoxyethyl)-1-(pyridin-2-yl)ethanamine (L1a), 2-methoxy-N-((pyridin-2-yl)methyl)-ethanamine (L2a), N,N-diethyl-N-((pyridin-2-yl)methyl)ethane-1,2-diamine (L3a) and 2-((pyridin-2-yl)methylamino)ethanol (L4a) in good yields. Reactions of the (amino)pyridine ligands L1a–L4a with [NiBr2(DME)] afforded nickel(II) complexes, [NiBr2(L1a)2] (1), [NiBr2(L2a)2] (2), [NiBr2(L3a)2] (3) and [NiBr2(L4a)2] (4), respectively in quantitative yields. Molecular structures of complexes 2 and 4 confirmed the formation of the bis(chelated)nickel(II) complexes. Activation of complexes 1–4 with either EtAlCl2 or methylaluminoxane (MAO), produced active ethylene oligomerization catalysts to afford mostly ethylene dimers (C4), in addition to trimmers (C6) and tetramers (C8). Density functional theory studies provided valuable insight into the reactivity trends and influence of complex structure on the ethylene oligomerization reactions.

2-Benzoimidazol-8-alkylquinolinylnickel(II) complexes as efficient catalysts for ethylene oligomerization and vinyl polymerization of norbornene

A series of nickel complexes LNiCl2 (C1–C16), where L represents 2-benzoimidazol-8-alkylquinoline and its derivatives, were prepared as potential catalysts for the oligomerization of ethylene. The molecular structure of a representative complex C2·CH3CH2OH was determined by single-crystal X-ray diffraction. Upon treatment with diethylaluminium chloride (Et2AlCl), all nickel complex pre-catalysts exhibited good activities in the oligomerization of ethylene. Furthermore, in the presence of methylaluminoxane (MAO), the nickel pre-catalysts were suitable for vinyl polymerization of norbornene.

Discovery and Development of Pyridine-bis(imine) and Related Catalysts for Olefin Polymerization and Oligomerization.

For over 40 years following the polyolefin catalyst discoveries of Hogan and Banks (Phillips) and Ziegler (Max Planck Institute), chemists traversed the periodic table searching for new transition metal and lanthanide-based olefin polymerization systems. Remarkably, none of these "hits" employed iron, that is, until three groups independently reported iron catalysts for olefin polymerization in the late 1990's. The history surrounding the discovery of these catalysts was only the beginning of their uniqueness, as the ensuing years have proven these systems remarkable in several regards. Of primary importance are the pyridine-bis(imine) ligands (herein referred to as PDI), which produced iron catalysts that are among the world's most active for ethylene polymerization, demonstrated "staying power" despite over 15 years of ligand improvement efforts, and generated highly active polymerization systems with cobalt, chromium, and vanadium. Although many ligands have been employed in iron-catalyzed polymerization, the PDI family has thus far provided the most information about iron's capabilities and tendencies. For example, iron systems tend to be highly selective for ethylene over higher olefins, making them strong candidates for producing highly crystalline polyethylene, or highly linear α-olefins. Iron PDI polymerizes propylene with 2,1-regiochemistry via a predominantly isotactic, chain end control mechanism. Because the first insertion proceeds via 1,2-regiochemistry, iron (and cobalt) PDI systems can be tailored to make highly linear dimers of α-olefins by "head-to-head" coupling, resulting from a switch in regiochemistry after the first insertion. Finally, PDI ligands, while not being surpassed in activity, have inspired the development of related ligand families and complexes, such as pendant donor diimines (PDD), which are also highly efficient at producing linear α-olefins. This Account will detail a variety of oligomerization and polymerization results achieved with PDI and PDD catalysts. Our studies on ligand modification are discussed, but numerous ligands have been synthesized by others. Computational approaches, identification of catalyst active sites, noninnocent ligand studies, commercialization efforts, and other outstanding research are only briefly mentioned, at most. The reader is directed to review articles where appropriate, in order to address the cursory treatment of these areas.

Ni-exchanged AlSBA-15 mesoporous materials as outstanding catalysts for ethylene oligomerization

Ni-exchanged mesoporous materials with SBA-15 topology were prepared by post-synthesis alumination of SBA-15 silica with sodium aluminate at room temperature, followed by ion exchange with nickel. Exploration of various parameters resulted in a simple preparation method for catalysts with perfect pore system and aluminium tetrahedrally coordinated in the silica framework for Si/Al > 6. These properties were proved by using appropriate characterisation techniques, including powder X-ray diffraction, N2 sorption, TEM, and 27Al MAS NMR. Ni-AlSBA-15 exhibited outstanding catalytic properties in the oligomerization reaction of ethylene performed at 150 ∘C and 3.5 MPa. Activity up to 175 g of oligomers per gram of catalyst per hour was the highest reported to date with Ni-based solid catalysts.

α-Phosphanyl amino acids: synthesis, structure and properties of alkyl and heterocyclic N-substituted diphenylphosphanylglycines

N-Alkyl and N-heterocyclic substituted diphenylphosphanylglycines 1a–j were synthesized by a convenient one-pot, three-component reaction of diphenylphosphane, the corresponding primary amine and glyoxylic acid hydrate in diethyl ether. Phosphanylglycolates 2 and phosphoniobis(glycolates) 3 were detected as intermediates. In the case of steric hindrance or low basicity of the amine only 2 or mixtures of 2 and 1 are formed. Reactivity studies of selected phosphanylglycines showed facile decarboxylation and hydrolysis, oxidation and formation of coordination compounds with BH3 or W(CO)5. N-Alkyl derivatives (tert-butyl, n-hexyl, benzhydryl) with moderate steric hindrance reacted with Ni(COD)2 in THF or toluene in the presence of ethylene with heating under pressure to yield highly active oligomerization catalysts, and converting the ethylene to liquid and low-molecular-weight solid ethylene oligomers (MNMR 500–1250 g/mol) with high selectivity for linear α-olefins. Smaller N-alkyl or N-heterocyclic amino substituents at the phosphanyl acetic skeleton interfere with the ethylene conversion and deactivate the catalyst. The structures of the compounds were elucidated by solution NMR and single crystal XRD studies.

Mesoporous mordenites obtained by desilication: Mechanistic considerations and evaluation in catalytic oligomerization of pentene

Desilication of mordenite crystals previously enriched in silica by dealumination has been investigated in order to better understand the process of mesopore formation. Pentene oligomerization in the liquid phase in the presence of an alkane solvent has been used to evaluate the catalytic activity of the desilicated zeolite. Relevant physico-chemical characteristics such as texture, porosity, acidity and composition of zeolite samples desilicated at 80 °C in NaOH solutions at different base concentrations were analyzed quantitatively. The generation of mesoporosity is due to the hydrolysis and dissolution of the surface of the crystals, probably initiated by the formation of etch pits at low coordination atoms, followed by surface roughening, formation and growth of internal mesopores, fragmentation and, ultimately, by a complete dissolution of the crystal. Such a process which is similar to the one involved in the chemical weathering of rocks, results in a severe loss of crystalline material and of the strong acidity associated to it. The oligomerization catalyst prepared from desilicated mesoporous mordenite proved highly stable and selective for the production of C15–C30 oligomers from pentene.

Heterogeneous oligomerization of ethylene over highly active and stable Ni-AlSBA-15 mesoporous catalysts

Ni-AlSBA-15 oligomerization catalysts (2.6wt% Ni, Si/Al=7) were prepared by post-synthesis alumination of SBA-15 silica with sodium aluminate, followed by ion exchange with nickel. Characterization techniques, including powder X-ray diffraction, N2 sorption, TEM, 27Al, and 29Si MAS NMR proved the perfect pore system of the SBA-15 materials, with aluminum tetrahedrally mainly coordinated in the silica framework. Ni-AlSBA-15 exhibited outstanding catalytic behavior in the oligomerization reaction of ethylene. At 150°C and 3.5MPa, in both batch and flow mode, the catalyst was highly active (up to 175g of oligomers per gram of catalyst per hour), selective (C4, C6, C8, and C10 olefins, no cracking products), and stable (high conversion during 80h on stream). These performances were superior than those exhibited by other Ni-based heterogeneous catalysts, without using alkylaluminum cocatalysts. A mechanistic pathway involving metallacyclic intermediates is supported by the experimental results.

Comparative study of new chromium-based catalysts for the selective tri- and tetramerization of ethylene

Small changes in ligand structure and conditions make a chromium ethylene oligomerization catalyst to switch from 1-hexene to 1-octene selectivity.

Modified mesoporous catalysts based on Al-HMS and Al-MCF for the oligomerization of α-olefins

High-performance decene-1 oligomerization catalysts based on mesoporous Al-HMS and Al-MCF aluminosilicates modified with an F-4SF sulfonated perfluorinated copolymer have been synthesized. Under batch conditions with a conversion of 90% and in a flow system with a conversion of 83%, these catalysts provide the formation of an oligomerization product with viscosity properties characteristic of poly-α-olefins, the precursors of poly-α-olefin oils.

Solid phosphoric acid catalyst for propene oligomerization: Effect of silicon phosphate composition

Solid phosphoric acid catalysts have been industrially used for propene oligomerization to improve the gasoline quality. However, solid phosphoric acid catalysts will lose their mechanical strength in the presence of water which is used to hydrolyze silicon phosphates to produce free phosphoric acids for maintaining the catalytic activity. In this case, to harmonize the catalyst lifetime and activity of solid phosphoric acid catalysts, the properties of silicon phosphate were investigated to achieve the maximum catalytic performance. A solid phosphoric acid catalyst was prepared with kieselguhr and concentrated phosphoric acid. Trace water was used to promote the release of active components from silicon phosphates during the reaction. Free phosphoric acid content, as a vital property of a solid phosphoric acid catalyst, was measured by ammonia temperature-programmed desorption. The crystal phase composition of silicon phosphates in a solid phosphoric acid catalyst was analyzed by X-ray diffraction. The catalytic performance was evaluated in a fixed bed under the conditions of 210°C and 4MPa. A solid phosphoric acid catalyst with relative content of 51% Si5O(PO4)6 and 49% SiP2O7 showed the best performance in improving catalytic activity and lifetime, and the conversion of propene was above 99% for nearly 70h.

Understanding the role of aluminum-based activators in single site iron catalysts for ethylene oligomerization

In a combined experimental and theoretical study, the activation process of a single site ethylene oligomerization catalyst with aluminum-based activators has been studied. The results put forward a plausible deactivation reaction path of the catalyst for trimethylaluminum, while for methylaluminoxane and a novel phenoxyaluminum-based activator, the experimental catalyst’s activity correlates with the energy barrier for the ethylene insertion.

Neutral nickel ethylene oligo- and polymerization catalysts: towards computational catalyst prediction and design.

DFT calculations have been used to elucidate the chain termination mechanisms for neutral nickel ethylene oligo- and polymerization catalysts and to rationalize the kind of oligomers and polymers produced by each catalyst. The catalysts studied are the (κ(2)-O,O)-coordinated (1,1,1,5,5,5-hexafluoro-2,4-acetylacetonato)nickel catalyst I, the (κ(2)-P,O)-coordinated SHOP-type nickel catalyst II, the (κ(2)-N,O)-coordinated anilinotropone and salicylaldiminato nickel catalysts III and IV, respectively, and the (κ(2)-P,N)-coordinated phosphinosulfonamide nickel catalyst V. Numerous termination pathways involving β-H elimination and β-H transfer steps have been investigated, and the most probable routes identified. Despite the complexity and multitude of the possible termination pathways, the information most critical to chain termination is contained in only few transition states. In addition, by consideration of the propagation pathway, we have been able to estimate chain lengths and discriminate between oligo- and polymerization catalysts. In agreement with experiment, we found the Gibbs free energy difference between the overall barrier for the most facile propagation and termination pathways to be close to 0 kcal mol(-1) for the ethylene oligomerization catalysts I and V, whereas values of at least 7 kcal mol(-1) in favor of propagation were determined for the polymerization catalysts III and IV. Because of the shared intermediates between the termination and branching pathways, we have been able to identify the preferred cis/trans regiochemistry of β-H elimination and show that a pronounced difference in σ donation of the two bridgehead atoms of the bidentate ligand can suppress hydride formation and thus branching. The degree of rationalization obtained here from a handful of key intermediates and transition states is promising for the use of computational methods in the screening and prediction of new catalysts of the title class.

Benzazaphospholine-2-carboxylic acids: Synthesis, structure and properties of heterocyclic phosphanyl amino acids

1,3-Dialkyl-1,3-benzazaphospholine-2-carboxylic acids 2a,b can be conveniently prepared by metalation and alkylation of N-methyl- and N-neopentyl-o-phosphanylaniline in liquid ammonia and cyclocondensation of the resulting N,P-disecondary phosphanylanilines 1a,b with glyoxylic acid hydrate (GAH) in ether. The primary neopentylphosphanylaniline reacts with two equivalents of GAH and forms a phosphanylbis(amino acid) 3 with toluidine. α-Branched P-substituents induce strongly preferred formation of trans-diastereoisomers with R,R- and S,S-configuration at P and C2, as shown by a crystal structure analysis of 2a, whereas a P-neopentyl (P-Np) group gives rise to trans/cis-diastereoisomeric mixtures. The trans-configuration exhibits the P lone-pair in cis-position to the COOH group, suitable for formation of five-membered chelate rings, as in diphenylphosphanylacetate nickel catalysts for ethylene oligomerization. Screening of 2a,b/Ni(COD)2 solutions in THF by a batch procedure indeed showed formation of catalysts for conversion of ethylene to linear oligomers and waxy low-molecular weight polymers. The conversion depends strongly on the size of the N-alkyl group, being slow and limited for the N-Me catalyst 2a/Ni and much faster and more complete for the N-Np-substituted catalysts 2b/Ni and 2c/Ni (N-Np, P-tBu). Comparison of 2b/Ni with 2c/Ni shows that the more bulky P-substituent further increases the catalyst activity.

Effect of chemical composition and method of preparation on the physicochemical properties of the NiO/B2O3-Al2O3 system and its catalytic activity in ethylene oligomerization

The effect the chemical composition of a support, the content of nickel, and the method of its binding has on the physicochemical and catalytic properties of the NiO/B2O3-Al2O3 system is studied. The boron oxide content in the support is varied from 2 to 30 wt %, while the nickel concentration is 0.59–3.18 wt %. The catalyst samples are studied via X-ray diffraction analysis, temperature-programmed desorption of ammonia, IR spectroscopy (including that of adsorbed CO), and UV-VIS diffuse reflectance spectroscopy. Tests of the catalysts in ethylene oligomerization are conducted in a fixed-bed flow reactor at a temperature of 200°C, a pressure of 1 MPa, and a space velocity of ethylene of 0.5 h−1. The feedstock is an ethylene-methane gas mixture containing 30 wt % of ethylene. It is suggested that the activity of the NiO/B2O3-Al2O3 system in ethylene oligomerization can be attributed to the formation of octahedral Ni2+ cations environed by borate anions on the surface of the system. The most active catalysts contain 2–3 wt % Ni and 10–20 wt % B2O3 in the supports. The method of preparation (adsorption binding or impregnation) has little effect on the state of nickel in the NiO/B2O3-Al2O3 system samples and their catalytic properties. The prepared catalysts are characterized by the ease of preparation, availability, and a low cost of the initial materials, as compared to known catalysts.

FI Catalysts for Olefin Oligomerization and Polymerization: Production of Useful Olefin-Based Materials by Unique Catalysis

This contribution highlights the uniqueness of FI catalysts (phenoxy-imine ligated group 4 metal complexes) for olefin coordination insertion catalysis. FI catalysts possess characteristic structural and electronic features that are different from those of group 4 metallocene catalysts. These special features in turn initiate versatile catalytic properties that result in useful olefin-based materials some of which have already been commercialized.

A broadly applicable and practical oligomeric (salen)Co catalyst for enantioselective epoxide ring-opening reactions

The (salen)Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available precursors. This catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen)Co catalysts in a wide variety of enantioselective epoxide ring-opening reactions. The application of catalyst 4a is illustrated in the kinetic resolution of terminal epoxides by nucleophilic ring-opening with water, phenols, and primary alcohols; the desymmetrization of meso epoxides by addition of water and carbamates; and the desymmetrization of oxetanes by intramolecular ring opening with alcohols and phenols. The favorable solubility properties of complex 4a under the catalytic conditions facilitated mechanistic studies, allowing elucidation of the basis for the beneficial effect of oligomerization. Finally, a catalyst selection guide is provided to delineate the specific advantages of oligomeric catalyst 4a relative to (salen)Co monomer 1 for each reaction class.

Active Sites of a NiSO4/γ-Al2O3 Catalyst for the Oligomerization of Isobutene

Structural characterization, the mechanism of catalytic activity generation and the nature of active sites of a NiSO4/γ-Al2O3 catalyst for isobutene oligomerization were studied by temperature programmed reduction (TPR), X-ray diffraction (XRD), diffuse reflectance infrared fourier transformed (DRIFTS) and X-ray photoelectron spectroscopy (XPS) techniques. The TPR measurements together with the XRD data indicated that calcination of the catalyst at 500 °C did not form either nickel oxide or nickel aluminate. The presence of only one type of surface nickel species formed by the incorporation of nickel ions into the surface vacant sites of γ-alumina lattice was indicated by XPS with Ar+ ions sputtering and TPR measurements. XPS analysis of the calcined catalyst suggested that the oxidation state of nickel ions in the calcined catalyst was (+2) and after calcination the nickel ions were coordinated to relatively more basic ligands. The surface acid centers of the catalyst were found to be only Lewis type. SO4 2− ions were found to be present as a chelating bidentate ligand and enhanced the acidity of metal ( $$ {\text{Al}}^{3 + } $$ and/or $$ {\text{Ni}}^{2 + } $$ ) Lewis acid centers. The results suggested that the combined effects of the presence of the bidentate SO4 2− ligand and dehydroxylation generate coordinatively unsaturated $$ {\text{Ni}}^{2 + } $$ that interact with isobutene during the oligomerization reaction. The formation of lower-valent nickel ions ( $$ {\text{Ni}}^{x + } ,x\; \le\; 1 $$ ) was demonstrated by in situ DRIFTS using CO as a probe molecule and by XPS measurements. Formation of a binuclear bridging carbonyl complex, $$ [{\text{Ni}}({\text{CO}})^{ + } ]_{2} $$ suggested that some lower-valent nickel species were formed via in situ reduction by isobutene. Analysis of Ni 2p photolines indicated the appearance of a new lower-valent nickel species ( $$ {\text{Ni}}^{x + } ,x \;\le\; 1 $$ ) during the course of isobutene oligomerization. Hence it is plausible that lower-valent nickel species might act as the active center for the oligomerization reaction, while the SO4 2− ions enhance the acidity of the Lewis acid sites on the surface and assist in the adsorption of reactant molecules on the surface.