Heterogeneous Catalyst Systems Research Articles

ChemInform Abstract: Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel—Crafts Alkylation of Indole.

AbstractEither enantiomeric alkylated indole (III) can be selectively obtained in the presence of a copper catalyst derived from dihydroxylated brucine.

Theoretical study of heterogeneous Ziegler-Natta catalysts: A comparison between TiCl3 catalysts and MgCl2 supported catalysts by using paired interacting orbitals (PIO) analysis

Two types of industrial heterogeneous Ziegler-Natta propylene polymerization catalysts, TiCl3 type and MgCl2 supported TiCl4 type, were examined by paired interacting orbitals (PIO) analysis proposed by Fujimoto et al.. The ligand located trans to propylene was found to obstruct the insertion but was essential for the stereospecific insertion of propylene. The ligand located trans to the alkyl group of the active site was found to be necessary for activating the alkyl-Ti bond. The regioselectivity and stereoselectivity of the iso-specific polymerization site on the heterogeneous Ziegler-Natta catalyst system were confirmed. The polymerization activity of MgCl2 supported TiCl4 catalyst was larger than that of the TiCl3 catalyst.

Removing Organic Nitrogen Compounds From Middle Distillate Fuels with a Catalyst Used as a Filtering Media

Fuel storage instability reactions of middle distillate fuel continue to be of great interest to the Department of Defense. Unlike civilian fuel, military fuel typically remains in storage tanks for one or more years. As fuel is removed from these tanks, the tanks are subsequently filled with more recently purchased fuel. In many cases, the mixed fuel is not compatible, resulting in chemical sediment and sludge formation. This fuel incompatibility can result in chemical degradation reactions that form solids that will plug nozzles and filters and render the entire contents of the storage tank unusable. Previous research has shown that polar organic nitrogen functional groups are involved in fuel instability reactions. These organo-nitrogen compounds are difficult and expensive to completely remove during the refining process; hence, this investigation involved the removal of these compounds employing three heterogeneous catalyst systems and combinations of these systems as filtering media. An unstable fuel was treated separately with Sc2O3, Cu/Sc2O3, fullerene (F), a 1:1 ratio of Sc2O3:(F), and a 1:1 ratio of Cu/Sc2O3:(F). The composition of the filtrates after filtering with the different catalytic systems was analyzed by combined gas chromatography/mass spectrometry (GC/MS). The results of this study showed that after treating the fuel with the catalyst systems, the organic nitrogen compounds detected in the extract were 0.29% carbazoles, 18.2% indoles, and 1.0% for both pyrroles and tetrahydroquinolines, and neither pyridines nor quinolines were detected. This investigation showed that scandium oxide, which is a recycled catalyst, is capable of removing organic nitrogen compounds from fuels.

Immobilized Chromium Catalyst System for Selective Ethene Trimerization to 1‐Hexene with a PNPNH Ligand

Tie me catalyst down, support: A selective homogeneous chromium-based ethene trimerization catalyst is heterogenized by immobilization on a functionalized polymer support. The immobilized catalyst displays good selectivity towards 1-hexene, and retains high activity for long times on-stream, combining advantages of homogeneous and heterogeneous catalyst systems.

ChemInform Abstract: Metathesis of Functionalized Acyclic Olefins

Abstract The metathesis of functionally substituted olefins, i.e olefins containing one or more heteroatoms, affords interesting prospects in the synthesis of valuable organic products. Since the first report on the successful metathesis of certain functional olefins, viz. longchain fatty acid esters, much research has been done into the possibilities of this reaction. It appears that many types of functionalized olefins undergo metathesis in the presence of a suitable catalyst. Despite the fact that many metathesis catalysts are inactive, interesting results have been obtained in the past with two catalyst systems, viz. the homogeneous system WCl6-Sn(CH3)4 and the heterogeneous system Re2O7/Al2O3-Sn(CH3)4. The scope of the reaction of functionalized olefins has been studied for a number of groups. The functional groups suited for metathesis include -COOR, -OCOR, -COR, -OR, -CN, -OSiR3, -Cl etc. Unsaturated carboxylic acids and alcohols can be metathesized by introducing a protecting group, e.g. a trimethylsilyl group. New homogeneous catalyst systems developed in recent years are nearly all based on tungsten compounds. Generally, however, the heterogeneous rhenium-based catalyst system turns out to be more attractive. The catalyst is active even at room temperature and can be recovered easily. In addition it is active towards certain compounds, especially allyl compounds, that are inactive with the tungsten catalysts. An important development was the access to the metathesis of unsaturated nitriles. Here, the system Re2O7/Al2O3-SnR4 in particular gives good results. Higher activities than those observed for the Re2O7/ Al2O3 catalysts can be achieved using modified rhenium catalysts. Thus, noteworthy results were obtained when a third metal oxide was incorporated and when a different support was used, e.g. silica-alumina. These developments are the subject of further study at the present time and will lead to catalysts with activities of practical interest.

Solution Electrospinning of Polyolefins: The Effect of Comonomers in Propylene/α‐Olefin Copolymers

AbstractTwo propylene copolymers with similar comonomer content and molecular weight were electrospun from solution. The 1‐octene and 1‐decene copolymers yielded ribbon‐like fibers. Isotactic poly(propylene) prepared by both heterogeneous and homogeneous catalyst systems could not be electrospun from the same solvent system used for the copolymers. The presence of the higher 1‐alkene comonomers in small amounts (about 1 mol‐%) not only affects the crystallinity of the polymer compared to the homopolymer, but appears to influence the solubility as well. The combined effect of lowering crystallinity and increasing solubility indicates that the use of higher 1‐alkene comonomers in low amounts could be a route to prepare poly(propylene) based electrospun fibers.magnified image

Reducing ATRP Catalyst Concentration in Batch, Semibatch and Continuous Reactors

AbstractAn overview of solution ATRPs carried out in batch, semibatch and continuous tubular and stirred‐tank reactor systems is presented. Initial work using a heterogeneous catalyst system with copper to polymer chain ratios of close to unity demonstrated the versatility of ATRP in producing homopolymer and copolymer at reasonable rates with good MW control and narrow polydispersity. The significant drawbacks of low catalyst solubility and high copper levels are now being addressed through use of the ARGET ATRP chemistry. Nearly colorless acrylate and methacrylate polymers have been produced with copper catalyst levels below 50 ppm (relative to monomer), with excellent control of MW obtained both in batch and continuous systems.magnified image

Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel–Crafts Alkylation of Indole

Heterogeneous chiral catalysts have attracted considerable attention from a wide range of scientific disciplines because of their fundamental and practical importance. Recent efforts have focused on the development of more efficient and practical immobilization methods for homogeneous chiral catalysts, and notable success has been achieved by using covalent tethering strategies in asymmetric reactions. Although different conformational preferences between homogeneous and heterogeneous systems are possible, successful orthogonal enantioselectivity using heterogeneous systems—that is, orthogonal to that observed with homogeneous systems—has not yet been achieved. Herein we describe the first example of such selectivity. Our rationale was based on the premise that solid supports, such as zeolites and silicates, would immobilize homogeneous chiral metal complexes, which are generated from rigid multifunctional brucine-derived ligands 1, through electrostatic interactions. This mode is believed to provide a facile mechanism for inducing conformational changes with immobilized chiral complexes.

Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel–Crafts Alkylation of Indole

Orthogonal Enantioselectivity Approaches Using Homogeneous and Heterogeneous Catalyst Systems: Friedel–Crafts Alkylation of Indole

Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis

AbstractA fully heterogeneous and highly efficient dual catalyst system for alkane metathesis (AM) has been developed. The system is comprised of an alumina‐supported iridium pincer catalyst for alkane dehydrogenation/olefin hydrogenation and a second heterogeneous olefin metathesis catalyst. The iridium catalysts bear basic functional groups on the aromatic backbone of the pincer ligand and are strongly adsorbed on Lewis acid sites on alumina. The heterogeneous systems exhibit higher lifetimes and productivities relative to the corresponding homogeneous systems as catalyst/catalyst interactions and bimolecular decomposition reactions are inhibited. Additionally, using a “two‐pot” device, the supported Ir catalysts and metathesis catalysts can be physically separated and run at different temperatures. This system with isolated catalysts shows very high turnover numbers and is selective for the formation of high molecular weight alkanes.

Fe(HSO4)3 and Fe(HSO4)3/DMSO as Efficient, Heterogeneous, and Reusable Catalyst Systems for the Oxidative Coupling of Thiols

Fe(HSO4)3 has been used as a heterogeneous, efficient, and recyclable catalyst in ethanol for the selective oxidation of thiols to their corresponding disulfides. The same results were obtained under identical conditions using catalytic amounts of Fe(HSO4)3 in the presence of DMSO. Different types of aliphatic, aromatic, and heteroaromatic thiols have been used in the reaction, and in all cases the products were obtained in good to excellent yields.

Heterogenized copper catalysts for the amination of arylhalide: Synthesis, characterization and catalytic applications

This research investigated the synthesis, characterization and catalytic activity of heterogenized copper complexes for the selective amination of aryl halides. Amination reactions using homogeneous copper catalyst systems are not generally selective and it is also difficult to recover the catalyst from the homogeneous system for recycling. To overcome these difficulties, our efforts were directed towards the development of cheaper heterogeneous catalyst systems, which can be easily recovered and recycled. Heterogenized analogs of the homogenous Cu complexes were prepared using two methods: (a) encapsulation of copper complexes in zeolite-Y and (b) tethering of copper complexes on various supports like zeolite-Y, silica, charcoal, or clay. The encapsulated and tethered copper catalysts on zeolite-Y were characterized using EPR, Diffused reflectance UV–vis, XRD, IAS, ICPES, SEM, and TEM. The results confirmed that the copper complexes were truly heterogenized in zeolite-Y support. Encapsulated and tethered copper complexes were tested for amination of aryl iodide. The effects of various reaction parameters were examined using tethered Cu(Phen)(PPh 3)Br-PTA-Y catalyst to determine optimum conditions. A recycle study of encapsulated and tethered Cu catalyst was carried out to test their robustness for possible commercial exploitation.

Comparison of imidazolium and pyridinium ionic liquids as the media for biphasic ethylene polymerization in the presence of titanocene catalyst

Tetrachloroaluminate ionic liquids having 1-n-octyl-3-methylpyridinium [C 8 -β-mpy] + [AlCl 4 ] ― or 1-n-octyl-4-methylpyridinium cation [C 8 -γ-mpy] + [AlCl 4 ] ― , respectively, were investigated in the biphasic ionic liquid/hexane mode ethylene polymerization as media of bis(cyclopentadienyl)titanium(IV)dichloride (Cp 2 TiCl 2 ) titanocene catalyst activated by AlEtCl 2 alkylaluminum compound. The results were compared to those obtained with using 1-n-octyl-3-methylimidazolium tetrachloroaluminate ionic liquid ([C 8 -mim] + [AlCl 4 ] ― ). It was found that the pyridinium ionic liquids enable to obtain better polyethylene (PE) yields in total than the imidazolium ionic liquids. The best results were obtained using [C 8 -γ-mpy] + [AlCl 4 ] ― , in which the alkyl substituents were in para (γ) positions at the pyridinium cation. The considerable amount of PE formed in the ionic liquid phase, largely contaminated, was observed at higher activator/catalyst (Al/Ti) molar ratio. It results from the mass transfer limitation through the phases. This obstacle disappears at lower activator/catalyst molar ratio and polyethylene produced is easily transported into the hexane phase. The effects of Al/Ti ratio and polymeryzation time on the total PE yield were also studied. PE obtained in the biphasic ionic liquid/hexane mode reveals molecular characteristics similar to polyethylenes produced in the presence of both homogeneous (low molecular weight) or heterogeneous (broad molecular weight distribution) metallocene catalyst systems. Additionally, it shows some unique features, such as high crystallinity degree and bulk density. .

Zr–Zeolite Beta: A New Heterogeneous Catalyst System for the Highly Selective Cascade Transformation of Citral to (±)‐Menthol

The transformation of citral to menthols involves hydrogenation steps as well as cyclisation of the intermediate, citronellal. The ability of Zr-zeolite beta to catalyse the cyclisation with high diastereoselectivity to (+/-)-isopulegol is the critical step in this cascade transformation. Bifunctional catalysts containing nickel or rhodium supported on Zr-zeolite beta gave menthols in yields of 87-89% and an excellent diastereoselectivity of 94% for the desired (+/-)-menthol. Dual catalyst systems of Zr-zeolite beta and nano-dispersed Ni on an MCM-41 support were equally effective and have the added advantage that the rates of the acid- and hydrogenation-catalysed steps can be independently varied. By applying a pressure ramp of 0.2-2 MPa, the yield of menthols could be increased to 95%, with 94% diastereoselectivity for (+/-)-menthol. The low initial pressure minimises the rates of competing hydrogenation reactions to byproducts such as citronellol and 3,7-dimethyloctanol.

The multi-step reactions for the synthesis of C 8 aldehydes and alcohol from propene in a single pot using an eco-friendly multi-functional catalyst system: Kinetic performance for parametric optimization

Kinetics of multi-step reactions including hydroformylation, aldol condensation and hydrogenation was carried out in a single pot for optimization of the reaction parameters for the synthesis of C 8 aldehydes and alcohol from propene using an eco-friendly multi-functional heterogeneous catalyst system [HF/HT] where [HF] = rhodium complex, HRh(CO)(PPh 3) 3 and [HT] = hydrotalcite, Mg 1− x Al x (OH 2) x+ (CO 3 2−) x/ n · mH 2O. The catalyst [HF/HT] was synthesized by impregnation of [HF] onto the surface of [HT]. In the typical catalytic experiments conducted in a 100 mL high pressure reactor under the employed reaction conditions: propene = 10 atm, CO = 5 atm, H 2 = 15 atm, [HF/HT] = 700 mg, HT/HF ratio = 7, Mg/Al molar ratio of [HT] = 3.5, aldol temperature = 250 °C, reaction time = 12 h, agitation speed = 1000 rpm, and in 50 mL toluene as a solvent, 68.4 × 10 −3 M of 2-ethylhexanol with 18% selectivity was achieved. The rates of reactions were determined by analyzing the amounts of products formed at different time using gas chromatography. Kinetics of the various reactions were performed in detail by investigating the effect of reaction parameters such as Mg/Al molar ratio of [HT] at aldol temperature 150 and 250 °C, amount of [HT] and [HF] complex, aldol temperature, partial pressure of CO and H 2 on the rates of formation of products namely, 2-ethylhexanol, 2-ethylhexanal, 2-ethylhexenal, butanals and butanols. The rates of reactions were found to be influenced by all these studied parameters. On increasing these parameters, the rates of formation of the products and their further conversions in single pot were favored.

ChemInform Abstract: Simple and Mild Procedures for Synthesis of Benzimidazole Derivatives Using Heterogeneous Catalyst Systems.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Comparison of Syndiotactic Polystyrene Morphology Obtained Via Heterogeneous and Homogeneous Polymerization with Metallocene Catalyst

AbstractSummary: Supported catalyst system for the slurry phase polymerization of styrene in toluene was prepared by the immobilization of 2‐methylindenyltrichlorotitanium(2‐MeIndTiCl3) on silica and activation of this catalyst was performed by methylaluminoxane(MAO) in polymerization media. Homogeneous polymerization of styrene with 2‐methylindenyltrichlorotitanium activated by MAO was performed in toluene. The morphology of obtained syndiotactic polystyrene (sPS) via heterogeneous and homhgeneous catalyst system was compared. Polymerization of styrene by homogeneous catalyst lead to formation of gel and resultant polymers presented a compact and dense texture while the global gelation do not occur with silica supported catalyst at different Ti/SiO2 mol ratios and sPS was obtained as separated particles. Unlike to the homogeneous catalyst, obtained polymers showed a porous texture. Highly porous texture of sPS was obtained with Ti/SiO2 = 0.5% mol ratio.

Three‐dimensional shapes and spatial distributions of Pt and PtCr catalyst nanoparticles on carbon black

High-angle annular dark-field scanning transmission electron microscopy tomography is applied to the study of Pt and PtCr nanoparticles supported on carbon black, which are used as heterogeneous catalysts in the electrodes of proton exchange membrane fuel cells. By using electron tomography, the three-dimensional architecture of the heterogeneous catalyst system can be determined, providing high-spatial-resolution information about the shapes, faceting and crystallographies of 5-20 nm single and multiply twinned catalyst particles, as well as their positions with respect to the carbon support. Approaches that can be used to provide improved information about the distribution and orientation of the particles on their support are proposed and discussed. Our results show that electron tomography provides important information that is complementary to high-resolution lattice imaging. Both techniques are required to understand fully the nature and role of the surfaces of faceted catalyst particles.

An Interface between the Universal Force Field and the Effective Fragment Potential Method

In order to properly describe reactions in heterogeneous catalyst systems, the reactants, solvent, and bulk effects of the surface must be taken into account. Embedded-cluster QM (quantum mechanics)/MM (molecular mechanics) methods can treat reactions on surfaces (the gas-surface interface), and the effective fragment potential method (EFP) can accurately treat the solvent effects on reactions (the gas-liquid interface). In order to create a QM/MM/EFP hybrid method for treatment of heterogeneous catalytic systems in the presence of a solvent (the liquid-surface interface), an EFP-MM interaction potential has been developed. Example calculations on small clusters of silica and water have been carried out.

Simple and mild procedures for synthesis of benzimidazole derivatives using heterogeneous catalyst systems

Abstractmagnified imageTsOH/graphite and N,N‐dimethylaniline/graphite were found to be catalyst systems for condensation reaction of o‐phenylendiamine with different aldehydes to form benzimidazole derivatives under mild and simple conditions. The graphite was easily recovered by a simple extraction and could be reused without decrease of activity in the presence of fresh TsOH and N,N‐dimethylaniline.