Aqueous Catalyst Research Articles

Hydroformylation of 2,5‐norbornadiene in organic/aqueous two‐phase system and acceleration by cationic surfactants

The organic/aqueous biphasic hydroformylation of 2,5‐norbornadiene (NBD) was investigated for the first time using HRh(CO)(TPPTS)3 (TPPTS: trisodium salt of tri(m‐sulphonylphenyl)phosphine) as the catalyst precursor. A comparison was made of homogeneous and biphasic systems. The optimum reaction parameters are discussed and the reaction mechanism is presented. In order to ensure the process attained high activity under moderate conditions, the effect of various cationic surfactants was tested in the biphasic hydroformylation of NBD. The results indicated that the hydroformylation of NBD in the biphasic system exhibited high activity and high selectivity to dialdehyde products under mild conditions. The addition of cationic surfactants markedly accelerated the reaction. A single long‐chain surfactant seemed to exert a greater impact on the hydroformylation of NBD than a double long‐chain surfactant. Moreover, the recycling of aqueous solution containing catalyst with or without surfactant was investigated. In the absence of the surfactant, the aqueous catalyst could be recycled six times without a significant decrease in activity and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.

Rhodium-Catalyzed Hydroformylation of Long-Chain Olefins in Aqueous Multiphase Systems in a Continuously Operated Miniplant

We investigate aqueous multiphase systems for catalytic gas/liquid reactions, namely, the rhodium-catalyzed hydroformylation of the long-chain olefin 1-dodecene. The multiphase system was formulated from 1-dodecene, water, and a nonionic surfactant, which increases the solubility between the two nonmiscible liquid phases. On the basis of these systems, we present in this paper a transfer of lab experiments (semibatch) to a successful operation of a miniplant in continuous mode. Under optimized conditions, the reaction showed turnover frequencies of ∼200 h–1 and high selectivity of 98:2 to the desired linear aldehyde. The miniplant was operated continuously for a total of 130 h. The control of the phase separation and catalyst recycling for product isolation for a long time period appeared to be challenging. Nevertheless, the separation was kept stable for over 24 h. The organic components in the product phase amounted to desired values between 95 and 99 wt %. The desired 99.99% of the catalyst remained in the aqueous catalyst phase.

Hydroaminomethylation of the Renewable Limonene with Ammonia in an Aqueous Biphasic Solvent System

AbstractWith the hydroaminomethylation of the natural compound limonene with ammonia an atom‐economic method for the synthesis of primary amines is described. This tandem reaction allows the direct conversion of the unfunctionalized monoterpene to a valuable amine product. For the first time, ammonia served as substrate to result in a maximum primary amine yield of 25 %. To overcome unwanted side reactions, a biphasic solvent system was used, consisting of an aqueous catalyst phase and an organic product phase. As catalyst the water‐soluble transition metal complex [Rh(cod)Cl]2/triphenylphosphine trisulfonate was chosen. In combination with the surfactant hexadecyltrimethylammonium chloride it provided a good phase interaction and the possibility for easy phase separation after the reaction.

Fabrication of elastic composite hydrogels using surface‐modified cellulose nanofiber as a multifunctional crosslinker

ABSTRACTWe fabricate composite hydrogels using surface‐modified cellulose nanofiber (CNF) and N‐isopropylacrylamide (NIPAm) as a multifunctional crosslinker and monomer, respectively. We expect to produce unique network structures that lead to elastomeric properties rarely reported for CNF‐based materials. The modification of CNF is performed to introduce polymerizable vinyl groups onto the surface of CNF via condensation between the surface hydroxyl groups and 3‐(trimethoxysilyl)propylmethacrylate. The modification and morphology of the surface‐modified CNF (mCNF) are confirmed by FTIR, solid‐state NMR, and FE‐SEM, respectively. We conduct in situ radical polymerization under various conditions using mixtures of the mCNF aqueous suspension, NIPAm monomer, radical initiator, and catalyst. The mechanical properties of the obtained hydrogels (water content = 90 wt %) are evaluated. The gels can be elastically stretched to more than 700 times their original lengths and exhibit an apparent shape recovery with a small permanent deformation (∼1/5 of the applied deformation under the gravity field). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42906.

Construction and Self-Assembly of Single-Chain Polymer Nanoparticles via Coordination Association and Electrostatic Repulsion in Water.

Simultaneous coordination-association and electrostatic-repulsion interactions play critical roles in the construction and stabilization of enzymatic function metal centers in water media. These interactions are promising for construction and self-assembly of artificial aqueous polymer single-chain nanoparticles (SCNPs). Herein, the construction and self-assembly of dative-bonded aqueous SCNPs are reported via simultaneous coordination-association and electrostatic-repulsion interactions within single chains of histamine-based hydrophilic block copolymer. The electrostatic-repulsion interactions are tunable through adjusting the imidazolium/imidazole ratio in response to pH, and in situ Cu(II)-coordination leads to the intramolecular association and single-chain collapse in acidic water. SCNPs are stabilized by the electrostatic repulsion of dative-bonded block and steric shielding of nonionic water-soluble block, and have a huge specific surface area of function metal centers accessible to substrates in acidic water. Moreover, SCNPs can assemble into micelles, networks, and large particles programmably in response to the solution pH. These unique media-sensitive phase-transformation behaviors provide a general, facile, and versatile platform for the fabrication of enzyme-inspired smart aqueous catalysts.

Tuning preparation conditions towards optimized separation performance of thermally polymerized organo-silica monolithic columns in capillary liquid chromatography

Tuning of preparation conditions, such as variations in the amount of a porogen, concentration of an aqueous acid catalyst, and adjustment in polymerization temperature and time, towards optimized chromatographic performance of thermally polymerized monolithic capillaries prepared from 3-(methacryloyloxy)propyltrimethoxysilane has been carried out. Performance of capillary columns in reversed-phase liquid chromatography was assessed utilizing various sets of solutes. Results describing hydrophobicity, steric selectivity, and extent of hydrogen bonding enabled comparison of performance of hybrid monolithic columns prepared under thermal (TSG) and photopolymerized (PSG) conditions. Reduced amounts of porogen in the polymerization mixture, and prolonged reaction times were necessary for the preparation of monolithic columns with enhanced retention and column efficiency that reached to 111,000 plates/m for alkylbenzenes with shorter alkyl chains. Both increased concentration of catalyst and higher temperature resulted in faster polymerization but inevitably in insufficient time for pore formation. Thermally polymerized monoliths produced surfaces, which were slightly more hydrophobic (a methylene selectivity of 1.28±0.002 TSG vs 1.20±0.002 PSG), with reduced number of residual silanols (a caffeine/phenol selectivity of 0.13±0.001 TSG vs 0.17±0.003 PSG). However, steric selectivity of 1.70±0.01 was the same for both types of columns. The batch-to-batch repeatability was better using thermal initiation compared to monolithic columns prepared under photopolymerized conditions. RSD for retention factor of benzene was 3.7% for TSG capillaries (n=42) vs. 6.6% for PSG capillaries (n=18). A similar trend was observed for columns prepared within the same batch.

ChemInform Abstract: Multiphase Reaction Media Involving Water and Carbon Dioxide for Selective Hydrogenation

AbstractReview: 43 refs.

Sulfinato iron(III) complex for electrocatalytic proton reduction.

We report the first example of a sulfinato Fe(III) complex acting as a highly active electrocatalyst for proton reduction. The sulfinate binds to the metal through oxygen, resulting in a seven-membered chelate ring that is likely hemilabile during catalysis. Proton reduction occurs at -1.57 V versus Fc/Fc(+) in CH3CN with an ic/ip = 13 in CH3CN (kobs = 3300 s(-1)) and an overpotential of 800 mV. The catalysis is first order with respect to [catalyst] and second order with respect to [trifluoracetic acid]. An 11% increase in catalytic activity is observed in the presence of water, suggesting that sulfinate moieties are viable functional groups for aqueous proton reduction catalysts.

Suzuki–Miyaura reactions promoted by a PdCl2/sulfonate‐tagged phenanthroline precatalyst in water

This work reports Suzuki–Miyaura cross‐coupling reactions of arylboronic acid with aryl halide or aryl dibromide mediated by PdCl2 (0.05 mol%) and sodium 4‐(1H‐imidazo[4,5‐f][1,10]phenanthrolin‐1‐yl)butane‐1‐sulfonate (0.05 mol%) at 100 °C in water. The corresponding cross‐coupling products were obtained in good to excellent yields. The catalytic system was recovered from the organic products by extraction with ether and the residual aqueous catalyst phase showed high activity after reuse of at least four cycles. Copyright © 2014 John Wiley & Sons, Ltd.

Silica-supported PtSn Catalysts Obtained Through Surface Organometallic Chemistry on Metals Techniques Using a Hydrosoluble Organotin Promoter. Application to the Selective Hydrogenation of α, β-Unsaturated Aldehydes and Ketones

Abstract: In this paper we propose the preparation of a PtSn bimetallic catalyst through techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M) using water as solvent. The system, PtSn0.2 ac , was employed in the chemoselective liquid-phase hydrogenation of acetophenone, cinnamaldehyde and benzaldehyde. The results were com-pared with those obtained with a PtSn catalyst also prepared via SOMC/M, but using a conventional paraffinic solvent. The aqueous medium-prepared catalyst resulted to be as active in and selective to the desired product (unsaturated alco-hols) as that obtained from n- heptane. This catalyst has the advantage of being prepared in a solvent compatible with the environment, without losing the superior characteristics of SOMC/M-based systems. Keywords: PtSn catalysts, SOMC/M, Hydrosoluble organotin promoter, Acetophenone, Cinnamaldehyde, Chemoselective hydrogenation. INTRODUCTION The reduction of α,β-unsaturated aldehydes and ketones leads to the production of alcohols used as intermediates in the production of compounds of interest in fine chemistry [1,2]. The catalytic hydrogenation of unsaturated carbonyl compounds is relatively simple with respect to the C=C bond, due to the well-known fact that its hydrogenation is thermodynamically favored. However, the desired product from these reactions is generally the unsaturated alcohol. Due to this fact, th e design of catalysts having the ability of inhibiting t he hydrogenation of the C=C bond and/or favor-ing the hydrogenation of the C=O group remains an issue of permanent interest. Most reports found in the tliterature for the hydrogenation of unsaturated carbonyl tcompounds are based on catalysts involving metals of 8, 9, 10 or 11 groups (mostly of the Pt group), modified with a more electroposi-tive metal, generating a bimetallic system [2, 3]. The second metal may exist as adatom, forming an alloy, partially oxi-dized or in ionic state. The difference in electronegativity between the two metals may favor the polarization of the carbonyl bond causing high selectivities to unsaturated alco-hols. In some systems, bimetallic geometric effects caused by the presence of the second metal have also been observed [2]. Thus, the addition of a second metal may lead to varia-tions in the activity and/or selectivity of the catalytic system, either through electronic interactions with the first metal or by modifying the architecture of the active site.

Economical and efficient aqueous reductions of high melting-point imines and nitroarenes to amines: promotion effects of granular PTFE

The reductions of high melting-point imines and nitroarenes to amines in aqueous media using Zn powder, granular PTFE (polytetrafluoroethylene), catalytic Aliquat 336 and NH4Cl or 5% NaOH at room temperature have been achieved. A major advantage of this procedure is that the cost of the catalyst is only 1/7200 of that of a previously reported nitroaromatic aqueous reduction catalyst. Altogether 13 imines and 11 nitroarenes were reduced to the corresponding amines with excellent yields. The effects of the amount of granular PTFE, and solubilities and melting points of the substrates, and melting points of the products on the reaction rates are discussed. For the first time, the relationship between the aqueous reaction rates and melting points of the products was investigated, which leads to a conclusion that lower melting-point products form faster than higher melting-point ones in the aqueous reductions. The Aliquat 336, granular PTFE and water are all recyclable.

Pd-tetrahydrosalan-type complexes as catalysts for sonogashira couplings in water: efficient greening of the procedure.

New sulfonated tetrahydrosalen-type ligands and their water-soluble palladium(II) complexes have been synthesized. The palladium(II) complexes catalyze the Sonogashira coupling (23 examples) of various aryl halides (including chloroarenes) with terminal alkynes, with good to excellent conversions under mild conditions (80°C, air, no Cu(I) cocatalyst) in aqueous-organic mixtures and turnover frequencies of up to 2790 h(-1) . Under optimized reaction conditions to minimize environmental contamination, diphenylacetylenes can be isolated in 76-98% yield. The aqueous catalyst solution can be recycled four times with decreasing activity; however, yields between 93 and 98% can still be achieved with extended reaction times. Several water-insoluble products can be isolated in excellent yield by simple filtration and purification by washing with water; this method is used, for the first time, for this type of C-C coupling procedure.

Optimization of photocatalytic decolorization of C.I. Basic Blue 41 in semi‐pilot scale prototype solar photoreactor

AbstractBACKGROUNDThe photocatalytic decolorization of C.I. Basic blue (BB41) in aqueous catalyst suspensions of titanium dioxide (TiO2), Degussa P25, was carried out in a semi‐pilot scale prototype solar photoreactor equipped with compound parabolic collectors (CPCs). The experiments on the solar reactor were performed with and without collectors. Response surface methodology (RSM) was applied to assess individual and interactive effects of the four main independent parameters (initial dye concentration, TiO2concentration, flow rate and initial pH) on the decolorization efficiency, the central composite design (CCD) was used for optimization of UV/TiO2 process.RESULTSThe presence of the collectors has increased the rate of decolorization of 50% for an initial dye concentration of 40 mg L−1 and after 80 kJ L−1 of visible energy accumulated. Predicted values of decolorization efficiency according to RSM were in close agreement with the experimental values (R2 = 0.9626, Adj‐R2 = 0.9252). Optimization results showed that maximum decolorization efficiency was achieved at the optimum conditions catalyst concentration 0.577 g L−1, initial dye concentration 17.933 mg L−1, flow rate 1446.8 L h−1 and initial pH 4.6 for 60 kJ L−1 of VIS energy accumulated.CONCLUSIONThe photocatalytic decolorization of a textile dye, C.I. Basic Blue 41, in a tubular solar prototype photoreactor was optimized. Response surface methodology based on the central composite design has been shown to be a powerful tool in the development of any photocatalytic process due to its impact on the economy and practicability of the process. © 2014 Society of Chemical Industry

Multiphase reaction media involving water and carbon dioxide for selective hydrogenation

The features of multiphase reaction media using water (bulk water, supported thin aqueous phase) and dense phase carbon dioxide are reviewed for selective hydrogenation of carbonyl, nitro, and cyano compounds. The interface of aqueous and organic phases is important in determining the rate of hydrogenation and the product selectivity. For supported aqueous phase catalysts, the interface between the thin aqueous film and a support material (for example, porous silica gel) has also an influential impact. The pressurization of a liquid reaction mixture (organic and/or aqueous phases) with carbon dioxide shows interesting positive effects on the reaction rate, the product selectivity, and the deactivation of a conventional supported metal catalyst. In some cases the use of both water and dense phase carbon dioxide serves as an effective reaction medium. In other words, these green solvents may act as reaction promoters. Possible roles of their actions are discussed.

Synthesis of VO2 Nanopowders. Part I. Sol–Gel Processing of Vanadium Alkoxide Precursor Within Inverse Micelles

Hydrolysis and condensation of VO(Oi–Pr)3 within inverse micelles containing aqueous ammonia catalyst is conducted under different reaction conditions as a synthesis strategy for preparing VO2 nanoparticles having average diameter <100 nm. Sol–gel processing of VO(Oi–Pr)3 to form VxOy gel particles is controlled by varying NH3(aq) concentration and using oleic acid or acetic acid pre-treatments. Isolated VxOy gel nanoparticles are reduced to VO2 nanoparticles by thermal annealing, although annealing conditions must be optimized for each batch of gel particles. VO2 nanoparticles of average diameters 24 or 70 nm prepared by this method show an expected hysteretic semiconductor-to-metal phase transition near 68 °C.

Epoxidation of Alkenes with Aqueous Hydrogen Peroxide and Quaternary Ammonium Bicarbonate Catalysts

A range of solid and liquid catalysts containing bicarbonate anions were synthesised and tested for the epoxidation of alkenes with aqueous hydrogen peroxide. The combination of bicarbonate anions and quaternary ammonium cations opens up for new catalytic systems that can help to overcome challenges with catalyst separation and reuse.

A single catalyst of aqueous CoIII for deodorization of mixture odor gases: A development and reaction pathway study at electro-scrubbing process

A constant generation of aqueous CoIII active catalyst and its utility on various odor gases deodorization at electro-scrubbing process is the primary investigation. The CoIII activation and regeneration for continuous use is established by electrochemical undivided cell in H2SO4 medium. The generated aqueous CoIII is then applied to simultaneous deodorization of simulated odor gases, namely, ammonia, trimethylamine, hydrogen sulfide, methyl mercaptan, and acetaldehyde, for municipal waste treatment plant emissions. The electro-scrubbing process results indicated that deodorization is almost complete at a low gas flow rate of 30Lmin−1. FTIR and pH studies demonstrated that amine compounds are removed via complex formation with H2SO4 and CoIII. In the case of sulfur compounds, deodorization of methyl mercaptan and hydrogen sulfide are removed by the CoIII-MEO (CoIII-mediated electrocatalytic oxidation) process via the formation of acetic acid as intermediate and SO42− as a product. Also, acetaldehyde deodorization results obtained by pH, total acidity and CO2 analyses evidence the process follow CoIII-MEO. The constant generation of aqueous active CoIII and an electro-scrubbing process offers promise as a means of removing odorous waste gases from gaseous emissions.

The degradation of phenol in water solution by TiO2 photocatalysis in a helical reactor

Heterogeneous photocatalysis is an advanced oxidation process (AOP) which has been widely studied by numerous researchers in the world and is used to degrade or remove a wide range of pollutants in water and air. The photocatalytic oxidation and mineralization of phenol in aqueous catalyst suspensions of titanium dioxide (TiO2) Degussa P25 (80% anatase, 20% rutile) has been carried out in a helical reactor. The photodegradation was investigated using two kinds of high pressure mercury irradiation lamps one emitting at 254 nm (15 Watts) and the other emitting at 365 nm (400 Watts). The effects of the recirculation flow, source of withdrawal, initial phenol concentration, amount of catalyst, suspension pH and light intensity on photodegradation of phenol were investigated. These parameters were studied to find the optimal conditions for a complete and fast oxidation of this organic compound. Kinetic experiments were performed at 32 oC over a range of phenol concentrations from 2.5 to 25 mg l-1, a range of TiO2 concentrations from 0.1 to 1 g l1, a range of suspensions pH from 3 to 9. The helical reactor was operated under a continuous flow-mode. Results showed that photodegradation is an effective method for the removal of phenol from wastewaters. The efficiency of the process depends strongly on the experimental conditions. The amount of catalyst, UV irradiation time, pH and light intensity were important parameters in the degradation process. The rate constants for the different parameters (TiO2, phenol concentration) were evaluated. Kinetic studies showed that titanium dioxide photocatalyst P25 was very active in phenol degradation; we observed that 99% of pollutant was degraded after 6 hours of UV irradiation; furthermore, we observed that phenol degradation was more effective under acidic conditions than alkaline. The kinetics were described by the Langmuir- Hinshelwood (L-H) kinetic model. An overall pseudo-first order kinetic constant has been calculated for phenol conversion and values obtained in acidic pH are higher than those calculated for basic pH media.

A supported aqueous phase catalyst coating in micro flow Mizoroki–Heck reaction

The application of a supported aqueous phase catalyst (SAPC) coating was investigated for the Mizoroki–Heck reaction in micro flow and favorably compared to the use of an SAPC in a batch system. In batch, an 83% yield was observed after 4h at 180°C with a catalyst loading of 0.4mol%, while in flow a residence time of 2.9min provided a 21% yield with only 0.01mol% catalyst loading. In batch the SAPC could be re-used twice without any significant loss in yield, but further re-use was prevented due to problematic accumulation of an ammonium salt. In the micro flow system, this problem could be overcome by adding water to the product flow prior to cooling, allowing even more effective use of the catalyst.

A hierarchical Co-Fe LDH rope-like nanostructure: facile preparation from hexagonal lyotropic liquid crystals and intrinsic oxidase-like catalytic activity.

Hierarchical rope-like structures based on Co-Fe layered double hydroxide (LDH) nanosheets were synthesized by the coprecipitation method from a hexagonal lyotropic liquid crystal (LLC) nanoreactor, and were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TG) and inductively coupled plasma (ICP) analyses. It was found that the rope-like LDH structures were composed of LDH nanosheets with a lateral size of about 200-400 nm and an average thickness of 4.47 nm in the form of face-to-edge interactions. The length and the diameter of the rope-like assemblies were about 3-6 μm and 150-300 nm, respectively, and their aspect ratio was as high as 20. Interestingly, the LDH rope-like assemblies were ordered to form an array with the oriented directions parallel to each other. A formation mechanism for the hierarchical LDH structures in the LLC media was proposed. In addition, the catalytic activity of the hierarchical rope-like LDH assemblies for the oxidation reaction of the typical horseradish peroxidase (HRP) substrate, 3,3',5,5'-tetramethylbenzidine (TMB), was examined, and results revealed that they had a higher oxidase-like catalytic activity towards the oxidization of TMB by dissolved oxygen. We expect that the hierarchical rope-like LDHs can offer the potential applications in aqueous redox catalysts, biosensors, medical diagnostics and so on.