High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH₄)₂PtCl₆ and Ru(OH)₃) on the carbon support before metal reduction; the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method, even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst. Based on XPS measurements, the high activity of this catalyst was found to originate from both metallic Ru (Ru⁰) and hydrous ruthenium oxides (RuO_xH_y) species on the catalyst surface. However, RuO_xH_y was found to be more active than metallic Ru. In addition, the anhydrous ruthenium oxide (RuO₂) species on the catalyst surface was found to be less active.     

Influence of the synthesis conditions on the structural and thermal properties of poly(l‐lactide)‐b‐poly(ethylene glycol)‐b‐poly(l‐lactide)

The poly(l ‐lactide)‐b‐poly(ethylene glycol)‐b‐poly(l ‐lactide) block copolymers (PLLA‐b‐PEG‐b‐PLLA) were synthesized in a toluene solution by the ring‐opening polymerization of 3,6‐dimethyl‐1,4‐dioxan‐2,5‐dione (LLA) with PEG as a macroinitiator or by transterification from the homopolymers [polylactide and PEG]. Two polymerization conditions were adopted: method A, which used an equimolar catalyst/initiator molar ratio (1–5 wt %), and method B, which used a catalyst content commonly reported in the literature (<0.05 wt %). Method A was more efficient in producing copolymers with a higher yield and monomer conversion, whereas method B resulted in a mixture of the copolymer and homopolymers. The copolymers achieved high molar masses and even presenting similar global compositions, the molar mass distribution and thermal properties depends on the polymerization method. For instance, the suppression of the PEG block crystallization was more noticeable for copolymer A. An experimental design was used to qualify the influence of the catalyst and homopolymer amounts on the transreactions. The catalyst concentration was shown to be the most important factor. Therefore, the effectiveness of method A to produce copolymers was partly due to the transreactions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40419.     

Crosslinking of poly(vinyl alcohol) using dianhydrides as hardeners

The crosslinking reaction of poly(vinyl alcohol) (PVA) with 3,3′,4,4′-tetracarboxybenzophenone dianhydride, pyromellitic carboxylic acid anhydride, and Epiclon B-4400 as hardeners was studied either in solution or by differential scanning calorimetry. A catalyst agent had to be used in all cases. Depending on the concentration of hardener and catalyst, differences are observed. T_g values increase with the ratio of hardener and catalyst, while activation energies decrease with the amount of catalyst but little changes can be seen when different dianhydride amounts are used. The thermal properties of the final products were unaltered by the hardener used. The decomposition temperature is initiated at a similar temperature in linear and crosslinked PVA, but while uncured PVA undergoes a complete degradation in one step, crosslinked PVA degrades in several steps. © 1996 John Wiley & Sons, Inc.     

Statistical optimization of process variables in batch alkylation of p-cresol with tert-butyl alcohol using ionic liquid catalyst by response surface methodology

Alkylation of p-cresol with tert-butyl alcohol was studied using ionic liquid catalyst prepared from N-(1,4-sulfonic acid) butyl triethylammonium hydrogen sulfate. An experimental design using response surface methodology (RSM) is used to optimize the process parameters in this batch alkylation to minimize rigorous experimental procedures and conserve the catalyst. The parameters, namely, temperature, reactant mole ratio, catalyst (IL) to p-cresol mole ratio and time of reaction on the conversion of p-cresol and yield of 2-tert-butyl-p-cresol (TBC) were optimized using Box–Behnken design. Low temperature, low p-cresol to alcohol ratio and low catalyst (IL) to p-cresol ratio in a batch reactor were found to maximize conversion of p-cresol and yield of TBC.     

Preparation of polypropylene‐based nanocomposites using nanosized MCM‐41 as support and in situ polymerization

MCM‐41 nanoparticles were used for preparing nanocomposites through the in situ polymerization of propylene. The performance of the catalytic system and the final properties of the materials obtained are highly dependent on the methodology used for impregnation of the catalyst onto the support particles, and therefore an optimization study for the impregnation methodology of the catalyst (Me₂Si(Ind)₂ZrCl₂) was carried out. Two different methodologies were used; the results in terms of catalytic activity and polymer molecular masses indicated that the most promising one involved the pre‐activation of the catalyst with the cocatalyst, methylaluminoxane, followed by impregnation onto the MCM‐41 nanoparticles. Thus, an optimized route for the preparation of polypropylene nanocomposites achieving significant improvements in catalyst activity was developed. The nanocomposite materials were characterized by GPC, TGA and DSC. The dispersion state and the size of the nanoparticles incorporated in the polypropylene matrix were investigated by transmission electron microcopy. Additionally, this methodology allows simultaneous control of the desired amount of support and the concentration of catalyst to be used in the in situ polymerization. © 2015 Society of Chemical Industry     

Recovery of Wilkinson’s Catalyst from Hydrogenated Nitrile Butadiene Rubber Latex Nanoparticles

Three different chelating ligands were used to separate Wilkinson’s catalyst from HNBR nanoparticles in latices. N,N,N′,N′,N′′-pentamethyldiethylenetriamine was found to be very effective in removing the catalyst. HNBR particle size and the extraction temperature on catalyst removal were investigated. The mechanism involved in the separation process was elucidated. This study promotes the possible commercialization of the green latex direct hydrogenation technique.

     

Ethylene polymerization with hybrid nickel diimine/Cp2TiCl2 catalyst: a new method to prepare blends of linear and branched polyethylene

Blends of linear polyethylene (LPE) and branched polyethylene (BPE) display very good mechanic properties that can be beneficial for various applications such as shear thinning and melt elasticity. LPE, BPE and amorphous polyethylene can be produced using nickel diimine (DMN) catalyst under various polymerization conditions, while LPE can be obtained using metallocene catalyst. Thus, LPE/BPE blends can be achieved by in situ polymerization using a hybrid DMN/metallocene catalyst. A novel hybrid catalyst made of DMN and Cp₂TiCl₂ was designed and used for ethylene polymerization. A synergistic effect of the two active sites in the hybrid DMN/metallocene catalyst was observed. Blends of linear and low branched polyethylene were synthesized when polymerization was conducted at low temperature (0 °C), while blends of linear and highly branched polyethylene were obtained at high temperature (50 °C). However, the miscibility of the polymers obtained at 50 °C was dramatically reduced as compared to those obtained at 0 °C. Mesoporous particles (MCM‐41) consisting of aluminosilicate with cylindrical pores were used to support the hybrid catalyst, in which MCM‐41 provides sufficient nanoscale pores to facilitate the polymerization in well‐controlled confined spaces. Blends of LPE and BPE were synthesized by in situ polymerization without adding comonomer and characterized. The miscibility of the polymer blends can be improved by supporting the hybrid catalyst on MCM‐41. Copyright © 2009 Society of Chemical Industry     

Ethylene polymerization using fluorinated FI Zr-based catalyst

A fluorinated FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′-flouroanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. It was revealed that ortho-F-substituted phenyl ring on the N electronically plays a key role in the suppression of chain transfer reactions especially β-hydride transfer which resulted in an increase in the molecular weight of the obtained polymer and moderation of the catalyst activity as well. Methylaluminoxane (MAO) and triisobuthylaluminum (TIBA) were used as a cocatalyst and a scavenger, respectively. The catalyst showed the maximum activity at about [Al]:[Zr] = 32000:1 M ratio and further addition of MAO did not affect the activity of the catalyst. Ortho-F not only impressed the activity, but also reduced the [Al]:[Zr] molar ratio needed to reach the highest activity in comparison with the similar non-fluorinated FI catalysts. The highest activity of the prepared catalyst was obtained at 35 °C. At the monomer pressure of 3 bars polyethylene was obtained with the viscosity average molecular weight (M _v) of 1.3 × 10⁶ indicating the dramatic effect of ortho-F substitution on the polymerization mechanism. The polymerization was carried out using different amounts of hydrogen. Neither the activity of the catalyst nor the viscosity average molecular weight (M _v) of the obtained polymer was sensitive to the hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst.     

Easy separation and reutilization of the Jacobsen's catalyst in olefin oxidation

A new method for recycling the Jacobsen's catalyst used for the catalytic oxidation of R-(+)-limonene and cis-ethyl cinnamate at room temperature by in situ generated dimethyldioxirane (DMD) as oxidizing agent is presented. Neither the immobilization of the catalyst to the solid support nor modification of its chemical structure is involved in this method. Therefore, the excellent catalytic properties of the Jacobsen's catalyst could be retained. Limonene diepoxide was the main product of the oxidation of R-(+)-limonene, whereas a single epoxide with good enanantioselectivity (78% ee) was obtained in the asymmetric oxidation of cis-ethyl cinnamate. On the other hand, R-(+)-limonene showed to be more reactive than cis-ethyl cinnamate. In both cases, the catalyst was recovered and recycled without appreciable loss of its initial catalytic activity.     

Oxidation of hydroquinone to p‐benzoquinone catalyzed by Cu(II) supported on chitosan flakes

Copper (sorbed on chitosan flakes) was used as a catalyst for the oxidation of hydroquinone, with dioxygen (from air) and hydrogen peroxide as oxidizing agents. The supported catalyst was very efficient at oxidizing hydroquinone into p‐benzoquinone. With hydrogen peroxide at pH 5.8, drastic oxidizing conditions led to the formation of subproducts. With a short contact time, together with the use of a low hydrogen peroxide concentration and a small amount of the catalyst, the formation of subproducts could be minimized. The influence of the catalyst/substrate and hydrogen peroxide/substrate ratios was investigated to determine optimum experimental conditions for a high initial oxidation rate and a high production of p‐benzoquinone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3034–3043, 2006     

Study of TATP: Influence of Reaction Conditions on Product Composition

The influence of reaction conditions (temperature, catalyst type, catalyst concentration – represented as molar ratio catalyst/acetone n_c/n_a) on the composition of the product formed from the reaction of acetone and hydrogen peroxide (30%) under acid catalysis was studied. 3,3,6,6,9,9‐Hexamethyl‐1,2,4,5,7,8‐hexoxonane (TATP) was found to be the major product when the content of the catalyst in the reaction mixture is low (n_c/n_a ≤ 0.5). A single side product (peak 10.2) in an amount ranging from 1.5 to 8% of the total peak area was present in all the prepared samples. Three other side products were found when catalyzing by hydrochloric and nitric acids. Temperature and catalyst type did not have a significant influence on the composition of the product at low catalyst concentration. Increasing the catalyst concentration led to the formation of 3,3,6,6‐tetramethyl‐1,2,4,5‐tetroxane (DADP) either as a co‐product of TATP or as an exclusive product depending on the concentration of the catalyst.     

12-tungstophosphoric and 12-tungstosilicicacid supported onto hydrous zirconia for liquid phase tert-butylation of m-cresol

Supported 12-tungstophosphoricacid (12-TPA) and 12-tunstosilicicacid (12-TSA) were used as heterogeneous catalysts for liquid-phase tert-butylation of m-cresol, an industrial important reaction. Alkylation reactions have been carried out with supported 12-TPA by varying different parameters such as % loading of 12-tungstophosphoricacid onto support, mole ratio of alcohol to m-cresol, reaction temperature, amount of the catalyst, reaction time and calcination temperature to optimize the conditions. To see the effect of the acidity on the reaction, the same reaction was studied over supported 12-TSA. Both the catalysts give 100% selectivity for o-isomer with different % conversion. The difference in catalyst performance of both the catalyst was correlated with the value of total acidity as well as Bronsted acidity.     

Alkoxysilane modification of a Ti‐based catalyst system for ethylene dimerization: A step forward in enhancing productivity and selectivity

Alkoxysilanes were used as novel enhancing agents in the Ti‐based catalyst for the highly selective ethylene dimerization to butene‐1. The dimerization of ethylene was carried out using the homogeneous Ti(OBu)₄/THF/TEA/alkoxysilane catalyst system, where Ti(OBu)₄, THF (tetrahydrofuran), TEA (triethylaluminum), and alkoxysilane were used as catalyst, additive, activator, and modifier, respectively. The nature and concentration of alkoxysilanes on the dimerization rate, catalyst yield, by‐products production, and selectivity to butene‐1 were investigated in detail. It was found that the performance of alkoxysilanes assisted with the class of the Ti‐based catalyst system, developed in this work, has been furthered by high productivity and selectivity with respect to the bare catalyst system. It proved that alkoxysilanes could play an excellent improving role in the selective ethylene dimerization process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44615.     

Modelling the kinetics of fast catalytic cracking reactions

Instantaneous kinetic constants and gasoline selectivities have been determined for catalytic cracking of n-hexadecane. The pulse technique was used in order to model the sequential build-up of coke which occurs on cracking catalyst within a riser transport-line reactor. The total amount of hydrocarbon injected per unit weight of catalyst was between 0 and 10. The mathematical model used to analyze the data was based on the unsteady state mass balance of the microcatalytic reactor with the assumption of plug flow. Results suggest a fast deactivation process during the run with fresh catalyst, while regenerated catalyst showed a slower deactivation. The catalyst regenerated three times evidenced a low apparent activation energy when temperature was increased from 500°C to 550°C.     

Copolymerization of ethylene–propylene using high‐activity bi‐supported Ziegler–Natta TiCl4 catalyst

Heterogeneous Ziegler–Natta TiCl₄ catalyst using MgCl₂ and SiO₂ as supports was prepared under controlled conditions. Mg(OEt)₂ was used as a starting material and was expected to convert to active MgCl₂ during catalyst preparation. Due to the high surface area and good morphological control, SiO₂ was chosen as well. Slurry copolymerization of ethylene and propylene (EPM) was carried out in dry n‐heptane by using the catalyst system SiO₂/MgCl₂/TiCl₄/EB/TiBA or TEA/MPT/H₂ at temperatures of 40–70°C, different molar ratios of alkyl aluminum : MPT : Ti, hydrogen concentrations, and relative and total monomers pressure. Titanium content of the catalyst was 2.96% and surface area of the catalyst was 78 m²/g. Triisobutyl aluminum (TiBA) and triethyl aluminum (TEA) were used as cocatalysts, while ethyl benzoate (EB) and methyl p‐toluate (MPT) were used as internal and external donors, respectively. H₂ was used as a chain‐transfer agent. Good‐quality ethylene propylene rubber (EPR) of rubber was obtained at the ratio of [TiBA] : [MPT] : [Ti] = 320 : 16 : 1 and polymerization temperature was 60°C. When TiBA was used as a cocatalyst, a higher and more rubberlike copolymer was obtained. For both of the cocatalysts, an optimum ratio of Al/Ti was obtained relative to the catalyst productivity. Ethylene content of the copolymer obtained increased with increasing TiBA concentration, while inverse results were obtained by using TEA. Addition of H₂ increased the reactivity of the catalyst. The highest product was obtained when 150 mL H₂/L solvent was used. Increasing temperature from 40 to 70°C decreased the productivity of the catalyst, while irregular behavior was observed on ethylene content. Relative pressure of P_P/P_E = 1.4 : 1 and total pressure of 1 atm was the best condition for the copolymerization. Polymers with ethylene contents of 25–84% were obtained. Increasing ethylene content of EPR decreased T_g of the polymer obtained to a limiting value. Viscosity‐average molecular weight (M_v) decreased with increasing temperature and TiBA and H₂ concentration. However, increasing the polymerization time increased the M_v. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2597–2605, 2004     

In situ synthesis of SAPO-34 crystals grown onto α-Al2O3 sphere supports as the catalyst for the fluidized bed conversion of dimethyl ether to olefins

SAPO-34 is an excellent catalyst for the conversion of dimethyl ether (DME) to olefins, but because conventionally synthesized SAPO-34 crystals are too small to be used directly in a fluidized bed, they have to be used as, and have the disadvantages of, a spray-dried catalyst. In this study, SAPO-34 crystals were synthesized in situ to grow on the surface of small α-Al₂O₃ spheres to produce a zeolite catalyst for a fluidized bed reactor. The influences of the composition of the crystal gel and surface structure of the support were investigated. The catalytic performance of the zeolite crystals grown on the support (surface zeolite) for the conversion of DME to olefins was investigated in a fixed bed microreactor and a fluidized bed reactor. The experiments showed that these surface SAPO-34 crystals gave the same activity and product selectivity as conventionally synthesized free SAPO-34 crystals and a higher reaction rate (normalized to the weight of SAPO-34) than the spray-dried catalyst. In situ synthesis is a simple and effective way to produce a SAPO-34 catalyst for a fluidized bed reactor.     

Microemulsion Systems with Rhodium Tris(3-sulfophenyl)phosphine Trisodium Salt Complex for Product Isolation and Catalyst Recycling in the Hydrogenation of Dimethyl Itaconate

Microemulsion systems with the nonionic surfactant p-tert-octylphenoxy polyethoxyethanol (OP9.5EO), the anionic surfactant dioctyl sulfosuccinate sodium salt (DOSS) and the narrow range nonionic surfactant alkyl polyethylene glycol ether (C10EO5) were used as solvent systems in the catalytic hydrogenation of dimethyl itaconate (DMI) catalysed by the water soluble catalyst complex Rh-TPPTS in order to achieve product isolation and catalyst recycling. The DOSS systems, which are more sensitive to the substrate and catalyst addition allowed for the hydrogenation to proceed with an initial hydrogenation rate about three times higher than with the nonionic surfactants, when the surfactant concentration was 15 wt%. Systems with 3 wt% surfactant were used in order to accomplish catalyst recycling. With a biphasic DOSS mixture a turnover number (TON) of 1,200 mol of DMI hydrogenated per mol of catalyst (Rh) was obtained in 3 consecutive runs. A three-phase system for the OP9.5EO mixture allowed the catalyst to be recycled 3 times and a TON of 1,500 in 4 runs was obtained. A TON of 800 in 2 runs was obtained using a three-phase C10EO5 mixture.     

Effects of the Competition between Grafting Reaction and Decomposition on the Miscibility and Rheological Behaviors of PS/POE Blends in the Presence of AlCl3

For increasing the compatibility of polystyrene (PS) and polyolefin elastomer (POE) blends, a Lewis acid catalyst, aluminium chloride (AlCl₃), was adopted to initiate the Friedel-Crafts alkylation reaction and induce the formation of PS-graft-POE copolymer. The dynamic mechanical and rheological tests were used to study the effects of catalyst content on the miscibility and rheological behaviors. The results showed that the viscosity increased and the MFI decreased with the increase of the catalyst content. However, when the catalyst content was overmuch, the viscosity decreased and the MFI increased. The variety of miscibility and rheological behaviors of PS/POE blends was the results of the competition between in situ graft reaction and decomposition of blending compounds.     

Catalytic behavior of palladium in the hydrogenation of edible oils

Palladium supported on alumina was used to hydrogenate soybean and canola oil. Previous literature reports indicated that palladium forms moretrans isomers than nickel. At 750 psig, 50 ppm palladium, and at 70 C, only 9.4%trans were formed when canola oil was hydrogenated to IV 74. In general, high pressure and low temperature favored lowtrans formation with no appreciable loss in catalyst activity. The effect of pressure, temperature and catalyst concentration on reaction rate,trans formation and selectivity is presented. A survey of various catalyst supports is discussed. Apparent activation energies of 6.3 to 8.9 kcal/mol were obtained; they are in good agreement with values reported in the literature.     

Optimization of the chemoenzymatic epoxidation of soybean oil

The lipase Candida antarctica (Novozyme 435) immobilized on acrylic resin was used as an unconventional catalyst for in situ epoxidation of soybean oil. The reactions were carried out in toluene. The peracid used for converting TG double bonds to oxirane groups was formed by reaction of FFA and hydrogen peroxide. The reaction conditions were optimized by varying the lipase concentration, solvent concentration, molar ratio of hydrogen peroxide to double bond, oleic acid concentration, and reaction temperature. The kinetic study showed that 100% conversion of double bonds to epoxides can be obtained after 4 h. The addition of free acids was not required for the reaction to proceed to conversions exceeding 80%, presumably owing to generation of FFA by hydrolysis of soybean oil. The enzyme catalyst was found to deteriorate after repeated runs.