Preparation of nanoparticulate metal catalysts in porous supports using an ionic liquid route; hydrogenation and C-C coupling

Aerogels containing palladium metal nanoparticles were prepared using an ionic liquid route and tested for activity towards hydrogenation and Heck C-C coupling reactions. (C) 2003 Elsevier B.V. All rights reserved.

The effect of the addition of sodium compounds in the liquid-phase hydrodechlorination of chlorobenzene over palladium catalysts

The hydrodechlorination of chlorobenzene over supported palladium catalysts has been studied. The palladium catalysts: deactivate as the reaction proceeds due to the HCl formed as by-product. The effect of the addition of sodium compounds has been analysed for the neutralisation of HCl. When NaOH was added to the reaction mixture, no beneficial effect was observed due to the detrimental effect of the alkaline medium on the textural and metallic properties of the catalysts. Doping the support with NaOH prior to impregnation with the metal precursor leads (after calcination and reduction) to catalysts with better activity and tolerance to deactivation, especially those obtained when using PdCl2 as the metal precursor. Low metal dispersion and the capture of chloride by forming NaCl are the: main factors contributing to the: improved catalytic properties. Finally, doping the catalysts with NaOH or NaNO3, after reduction of the metal precursor leads to a moderate increase in initial activity and final conversion, although NaOH impregnation also gave rise to support corrosion and metal dispersion modification. (C) 2001 Elsevier Science B.V, All rights reserved.

Liquid phase behavior of ionic liquids with alcohols: Experimental studies and modeling

Ionic liquids (ILs) have been suggested as potential

Continuous flow hydroformylation using supported ionic liquid phase catalysts with carbon dioxide as a carrier.

A supported ionic liquid phase (SILP) catalyst prepared from [PrMIM][Ph2P(3-C6H4SO3)] (PrMIM = 1-propyl-3-methylimidazolium), [Rh(CO)(2)(acac)] (acacH = 2,4-pentanedione) [OctMIM]NTf2 (OctMIM = 1-n-octyl-3-methylimidazolium, Tf = CF3SO2) and microporous silica has been used for the continuous flow hydroformylation of 1-octene in the presence of compressed CO2. Statistical experimental design was used to show that the reaction rate is neither much affected by the film thickness (IL loading) nor by the syngas: substrate ratio. However, a factor-dependent interaction between the syngas: substrate ratio and film thickness on the reaction rate was revealed. Increasing the substrate flow led to increased reaction rates but lower overall yields. One of the most important parameters proved to be the phase behaviour of the mobile phase, which was studied by varying the reaction pressure. At low CO2 pressures or when N-2 was used instead of CO2 rates were low because of poor gas diffusion to the catalytic sites in the SILP. Furthermore, leaching of IL and Rh was high because the substrate is liquid and the IL had been designed to dissolve in it. As the CO2 pressure was increased, the reaction rate increased and the IL and Rh leaching were reduced, because an expanded liquid phase developed. Due to its lower viscosity the expanded liquid allows better transport of gases to the catalyst and is a poorer solvent for the IL and the catalyst because of its reduced polarity. Above 100 bar (close to the transition to a single phase at 106 bar), the rate of reaction dropped again with increasing pressure because the flowing phase becomes a better and better solvent for the alkene, reducing its partitioning into the IL film. Under optimised conditions, the catalyst was shown to be stable over at least 40 h of continuous catalysis with a steady state turnover frequency (TOF, mol product (mol Rh)(-1)) of 500 h(-1) at low Rh leaching (0.2 ppm). The selectivity of the catalyst was not much affected by the variation of process parameters. The linear: branched (1:b) ratios were ca. 3, similar to that obtained using the very same catalyst in conventional organic solvents.

Dependence of the kinetics of liquid-phase photocatalyzed reactions on oxygen concentration and light intensity

The initial kinetics of the oxidation of 4-chlorophenol, 4-CP, photocatalyzed by titania films and aqueous dispersions were studied as a function of oxygen partial pressure, P-O2, and incident light intensity, I. The reaction conditions were such that the kinetics were independent of [4-CP] but strongly dependent on PO2-a situation that allowed investigation of the less-often studied kinetics of oxygen reduction. The observed kinetics fit a pseudo-steady-state model in which the oxygen is Langmuir-adsorbed on the titania photocatalyst particles before being reduced by photogenerated electrons. The maximum rate of photocatalysis depends directly on I-beta, where, beta = 1 for films and 0.7 for dispersions of titania, indicating that the kinetics are dominated by the surface reactions of the photogenerated electrons and holes for the films and by direct recombination for the powder dispersions. Using the pseudo-first-order model, for both titania films and dispersions, the apparent Langmuir adsorption constant, K-LH, derived from a Langmuir-Hinshelwood analysis of the kinetics, appears to be largely independent of incident light intensity, unlike KLH for 4-CP Consequently, similar values are obtained for the Langmuir adsorption constant, K-ads, extracted from a pseudosteady-state analysis of the kinetics for oxygen on TiO2 dispersions and films in aqueous solution (i.e., ca. 0.0265 +/- 0.005 kPa(-1)), and for both films and dispersions, oxygen appears to be weakly adsorbed on TiO2 compared with 4-CP, at a rate that would take many minutes to reach equilibrium. The value of Kads for oxygen on titania particles dispersed in solution is ca. 4.7 times lower than that reported for the dark Langmuir adsorption isotherm; possible causes for this difference are discussed. (c) 2006 Elsevier Inc. All rights reserved.

Kinetics of liquid phase semiconductor photoassisted reactions: Supporting observations for a pseudo-steady-state model

The kinetics of liquid phase semiconductor photocatalytic and photoassisted reactions are an area of some debate, reignited recently by an article by Ollis(1) in which he proposed a simple pseudo- steady- state model to interpret the Langmuir- Hinshelwood type kinetics, commonly observed in such systems. In the current article, support for this model, over other models, is provided by a reinterpretation of the results of a study, reported initially in 1999,2 of the photoassisted mineralization of 4- chlorophenol, 4-CP, by titania films and dispersions as a function of incident light intensity, I. On the basis of this model, these results indicate that 4- CP is adsorbed more strongly on P25 TiO2 when it is in a dispersed, rather than a film form, due to a higher rate constant for adsorption, k(1). In addition, the kinetics of 4- CP removal appear to depend on I-beta where, beta = 1 or 0.6 for when the TiO2 is in a film or a dispersed form, respectively. These findings are discussed both in terms of the pseudo- steady- state model and other popular kinetic models.

An efficient recyclable peroxometalate-based polymer-immobilised ionic liquid phase (PIILP) catalyst for hydrogen peroxide-mediated oxidation

A linear cation-decorated polymeric support with tuneable surface properties and microstructure has been prepared by ring-opening metathesis polymerisation (ROMP) of a pyrrolidinium-functionalised norbornene-based monomer with cyclooctene. The derived peroxophosphotungstate-based polymer-immobilised ionic liquid phase (PIILP) catalyst is an efficient and recyclable system for the epoxidation of allylic alcohols and alkenes, with only a minor reduction in performance on successive cycles.

Solvent effects in the hydrogenation of 2-butanone

In liquid-phase reaction systems, the role of the solvent is often limited to the simple requirement of dissolving and/or diluting substrates. However, the correct choice, either pure or mixed, can significantly influence both reaction rate and selectivity. For multi-phase heterogeneously catalysed reactions observed variations may be due to changes in mass transfer rates, reaction mechanism, reaction kinetics, adsorption properties and combinations thereof. The liquid-phase hydrogenation of 2-butanone to 2-butanol over a Ru/SiO catalyst, for example, shows such complex rate behaviour when varying water/isopropyl alcohol (IPA) solvent ratios. In this paper, we outline a strategy which combines measured rate data with physical property measurements and molecular simulation in order to gain a more fundamental understanding of mixed solvent effects for this heterogeneously catalysed reaction. By combining these techniques, the observed complex behaviour of rate against water fraction is shown to be a combination of both mass transfer and chemical effects. © 2012 Elsevier Inc. All rights reserved.

An efficient Cu(II)-bis(oxazoline)-based polymer immobilised ionic liquid phase catalyst for asymmetric carbon–carbon bond formation

The asymmetric Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene and the Mukaiyama-aldol reaction between methylpyruvate and 1-phenyl-1-trimethylsilyloxyethene have been catalysed by heterogeneous copper(II)-bis(oxazoline)-based polymer immobilised ionic liquid phase (PIILP) systems generated from a range of linear and cross linked ionic polymers. In both reactions selectivity and ee were strongly influenced by the choice of polymer. A comparison of the performance of a range of Cu(II)-bis(oxazoline)-PIILP catalyst systems against analogous supported ionic liquid phase (SILP) heterogeneous catalysts as well as their homogeneous counterparts has been undertaken and their relative merits evaluated.

Optimised extraction of heterocyclic aromatic amines from blood using hollow fibre membrane liquid-phase microextraction and triple quadrupole mass spectrometry

Heterocyclic aromatic amines (HCA) are carcinogenic mutagens formed during cooking of proteinaceous foods, particularly meat. To assist in the ongoing search for biomarkers of HCA exposure in blood, a method is described for the extraction from human plasma of the most abundant HCAs: 2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx) (and its isomer 7,8-DiMeIQx), using Hollow Fibre Membrane Liquid-Phase Microextraction. This technique employs 2.5 cm lengths of porous polypropylene fibres impregnated with organic solvent to facilitate simultaneous extraction from an alkaline aqueous sample into a low volume acidic acceptor phase. This low cost protocol is extensively optimised for fibre length, extraction time, sample pH and volume. Detection is by UPLC-MS/MS using positive mode electrospray ionisation with a 3.4 min runtime, with optimum peak shape, sensitivity and baseline separation being achieved at pH 9.5. To our knowledge this is the first description of HCA chromatography under alkaline conditions. Application of fixed ion ratio tolerances for confirmation of analyte identity is discussed. Assay precision is between 4.5 and 8.8% while lower limits of detection between 2 and 5 pg/mL are below the concentrations postulated for acid-labile HCA-protein adducts in blood.

Use of Short Time-on-Stream Attenuated Total Internal Reflection Infrared Spectroscopy To Probe Changes in Adsorption Geometry for Determination of Selectivity in the Hydrogenation of Citral

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A new experimental procedure based on attenuated total reflection infrared spectroscopy has been developed to investigate surface species under liquid phase reaction conditions. The technique has been tested by investigating the enhanced selectivity in the hydrogenation of α,β-unsaturated aldehyde citral over a 5% Pt/SiO2 catalyst toward unsaturated alcohols geraniol/nerol, which occurs when citronellal is added to the reaction. The change in selectivity is proposed to be the result of a change in the citral adsorption mode in the presence of citronellal. Short time on stream attenuated total internal reflection infrared spectroscopy has allowed identification of the adsorption modes of citral. With no citronellal, citral adsorbs through both the C═C and C═O groups; however, in the presence of citronellal, citral adsorption occurs through the C═O group only, which is proposed to be the cause of the altered reaction selectivity.

Enhancing Liquid-Phase Olefin-Paraffin Separations Using Novel Silver-Based Ionic Liquids

This paper describes the extraction of C5-C8 linear α-olefins from olefin/paraffin mixtures of the same carbon number using silver(I)/N,N-dimethylbenzamide bis(trifluoromethylsulfonyl)imide ([Ag(DMBA)₂][Tf₂N]) or silver(I)/propylamine bis(trifluoromethylsulfonyl)imide ([Ag(PrNH₂)₂][Tf₂N]) as the extracting agent. The separation performance of the system increased with increasing chain length. [Ag(DMBA)₂][Tf₂N] appeared to outperform [Ag(PrNH₂)₂][Tf₂N] in terms of both selectivity and distribution coefficient. The [Ag(DMBA)₂][Tf₂N] system was successfully modeled using the universal quasi-chemical activity coefficient (UNIQUAC) model. These results support the potential future development of amine/amide-based ligands for producing soluble silver complexes useful for the separation of olefins from paraffins.

Investigation of the solid-liquid phase transition of carbon at 150 GPa with spectrally resolved X-ray scattering

We have resolved the solid-liquid phase transition of carbon at pressures around 150GPa. High-pressure samples of different temperatures were created by laser-driven shock compression of graphite and varying the initial density from 1.30g/cm³ to 2.25g/cm³. In this way, temperatures from 5700K to 14,500K could be achieved for relatively constant pressure according to hydrodynamic simulations. From measuring the elastic X-ray scattering intensity of vanadium K-alpha radiation at 4.95keVat a scattering angle of 126°, which is very sensitive to the solid-liquid transition, we can determine whether the sample had transitioned to the fluid phase. We find that samples of initial density 1.3g/cm³ and 1.85g/cm³ are liquid in the compressed states, whereas samples close to the ideal graphite crystal density of 2.25g/cm³ remain solid, probably in a diamond-like state.

Acrolein hydrogenation on Pt(211) and Au(211) surfaces:a density functional theory study

Partial hydrogenation of acrolein, the simplest alpha, beta-unsaturated aldehyde, is not only a model system to understand the selectivity in heterogeneous catalysis, but also technologically an important reaction. In this work, the reaction on Pt(211) and Au(211) surfaces is thoroughly investigated using density functional theory calculations. The formation routes of three partial hydrogenation products, namely propenol, propanal and enol, on both metals are studied. It is found that the pathway to produce enol is kinetically favoured on Pt while on Au the route of forming propenol is preferred. Our calculations also show that the propanal formation follows an indirect pathway on Pt(211). An energy decomposition method to analyze the barrier is utilized to understand the selectivities at Pt(211) and Au(211), which reveals that the interaction energies between the reactants involved in the transition states play a key role in determining the selectivity difference.

Efficient and selective hydrogen peroxide-mediated oxidation of sulfides in batch and segmented and continuous flow using a peroxometalate-based polymer immobilised ionic liquid phase catalyst

The peroxometalate-based polymer immobilized ionic liquid phase catalyst [PO4{WO(O-2)(2)}(4)]@PIILP has been prepared by anion exchange of ring opening metathesis-derived pyrrolidinium-decorated norbornene/ cyclooctene copolymer and shown to be a remarkably efficient system for the selective oxidation of sulfides under mild conditions. A cartridge packed with a mixture of [PO4{WO(O-2)(2)}(4)]@PIILP and silica operated as a segmented or continuous flow process and gave good conversions and high selectivity for either sulfoxide (92% in methanol at 96% conversion for a residence time of 4 min) or sulfone (96% in acetonitrile at 96% conversion for a residence time of 15 min). The immobilized catalyst remained active for 8 h under continuous flow operation with a stable activity/selectivity profile that allowed 6.5 g of reactant to be processed (TON = 46 428) while a single catalyst cartridge could be used for the consecutive oxidation of multiple substrates giving activity-selectivity profiles that matched those obtained with fresh catalyst.