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fff; International audience; For the Suzuki–Miyaura C–C coupling, it is well accepted that the active catalytic species in the liquid phase are leached from the solid palladium precursor. This was demonstrated for shaped solid Pd precursors which allows fixed-bed applications in flow chemistry. Yet, many interesting solid Pd precursors, including supported nanoparticles (NPs), are available as finely divided powders that cannot be used in fixed-bed reactors because of the too high pressure drop generated. In this work, open cell foam materials (OCF) are used as supports for Pd/C, Siliacat-Pd(0) and Pd(II)-DPP catalysts powders and Pd(0) NPs. The coupling of 4-iodoacetophenone with phenylboronic acid is used as a model reaction to evaluate the activity of leached species. Some experiments with other aryl halides are also reported. It is shown that all the catalytic foams are able to leach active species and that trace amounts in the range 30–300 ppb of Pd in solution are sufficient to carry out the reaction while maintaining a low pressure drop.

The transition from batch catalytic processes to continuous flow processes requires highly active and stable catalysts that still need to be developed. The preparation and characterization of catalysts where palladium single atoms and nanoparticles are simultaneously present on carbon nanotubes were recently reported by us. These catalysts are considerably more active than commercial or previously described catalysts for the liquid phase hydrogenation of terpenes. Herein is shown that under solvent-free conditions, squalene (SQE) could be converted into squalane (SQA,98 %) using only 300 ppm of Pd in less than 1.4 h at 20 bar H

International audience; We recently reported (R. Castro Contreras, B. Guicheret, B. F. Machado, C. Rivera-Cárcamo, M. A. Curiel Alvarez, B. Valdez Salas, M. Ruttert, T. Placke, A. Favre Réguillon, L. Vanoye, C. de Bellefon, R. Philippe and P. Serp, J. Catal., 2019, 372, 226–244) that a structure/activity correlation exists in Pd/C catalysts for myrcene hydrogenation, which integrates the Pd dispersion, and the surface concentration of oxygen groups and defects of the support. Here, through a combined experimental–theoretical study, we provide an explanation of the influence of these three structural characteristics of Pd/C catalysts for alkene hydrogenation. Highly dispersed Pd nanoparticles (PdNP) are necessary to activate dihydrogen. A high concentration of surface defects on the support is necessary to stabilize Pd single atoms (PdSA), which coexist with PdNP on Pd/C catalysts. A high concentration of oxygenated surface groups is also necessary on the support to allow hydrogen spillover. We demonstrate that such a combination allows cooperative catalysis to operate between PdNP and PdSA that involves the formation of PdSA–H species, which are much more active than PdNP–H for alkene hydrogenation but also isomerization. Importantly, we also report an efficient method to control the ratio between PdSA and PdNP in Pd/C catalysts of similar loadings and show that the control of this ratio allows the development of a new generation of stable and highly active catalysts integrating the ultra-rational use of precious metals in short supply. Indeed, for myrcene hydrogenation, activity variations of several orders of magnitude were measured as a function of the value of this ratio.

A kinetic study concerning the self-metathesis of methyl oleate and methyl elaidate was performed, using a variety of NHC-ruthenium pre-catalysts, bearing either mesityl groups or di-isopropyl-phenyl groups on the NHC ligand and various trans ligands with respect to the NHC unit. We showed that the system can be satisfactorily described using one initiation constant per pre-catalyst and four propagation constants that, conversely, do not depend on the pre-catalyst. The difference of reactivity with oleate (Z) and elaidate (E) can be fully explained by the propagation parameters; the studied pre-catalysts initiate with the same rate starting from the Z or the E olefin. The ranking of the propagation parameters is driven by the thermodynamic equilibrium. The transformation rates of Z and E isomers is only driven by these propagation constants and nothing differentiates the initiation step.

This article presents an experimental kinetic study of the Suzuki&ndash, Miyaura reaction of 4-iodoacetophenone with phenylboronic acid catalyzed by the Herrmann&ndash, Beller palladacycle. This catalyst, together with the solvent (ethanol) and the base (sodium methylate), were chosen to ensure catalyst stability and reactants solubility all along the reaction. Based on the study of initial reaction rates, a quasi-first-order was found for 4-iodoacetophenone with a first-order dependence on the initial concentration of palladium. A zero-order was found for the base and the phenylboronic acid. The oxidative addition step of the mechanism was thus considered as the rate determining step. A global rate law was derived and validated quantitatively. A global activation energy, with an average value of ca. 63 kJ/mol was determined.

An extractive-reaction process for the synthesis of HMF from fructose was implemented in microreactor. Experimental conditions were 10 wt.% fructose in water, MIBK as extracting solvent and HCl as catalyst in a temperature window of 120–160 °C, a MIBK/H2O ratio 1 to 9 and an HCl concentration of 0.25–2 M. The dehydration of fructose to HMF is achieved in less than 40s with a total HMF yield higher than 90% at 150 °C. Aqueous and organic phase spontaneously separate at the outlet of the reactor and HMF is obtained in MIBK with a yield of 80% and a purity of 92%.

An improved method for the oxidation of benzylic and aliphatic alcohols using concentrated bleach (1.6 M NaOCl) using 2-step continuous flow microreactors is reported herein. Enhancement of the reaction rate was obtained by on-line pH adjustment. In the first step, the pH of the bleach was precisely decreased to pH 8.5 using CO2. Such pH is a compromise between oxidative properties, chemical stability and unwanted precipitation. The aqueous bleach solution was subsequently used for the oxidation of benzyl alcohols in EtOAc using catalytic amounts of TBAB (n-Bu4N+Br−) in a segmented flow microreactor. The total conversion of benzyl alcohols was obtained in less than 1 min using 2 eq. of NaOCl at r.t. without any metal catalysts. Selective benzyl alcohol oxidation (>98%) was demonstrated on primary and secondary alcohols. For aliphatic alcohols, 0.1 mol% TEMPO was used as a co-catalyst in synergy with TBAB and a total conversion with high selectivity (>98%) was achieved in less than 2 min.

The organocatalyzed aerobic oxidation of aldehydes to acids was reproduced from the original report. In- and ex-situ analysis of the reaction mixture as the function of time reveals that, unlike the claim in the publication, the aerobic oxidation of aromatic and aliphatic aldehydes leads predominantly to the formation of peracids. The latter are transformed into the corresponding carboxylic acids during the workup procedure. The buildup of peracids in solution poses safety problems that should not be overlooked. This finding has also an influence on the way new catalysts are investigated to improve this reaction as well as on aerobic aldehyde-mediated co-oxidation.

International audience; The influence of the carbon support characteristics on Pd loading, dispersion and activity in Pd/C catalysts has been analyzed. Several carbon nanomaterials, including multi-walled CNTs, nitrogen-doped CNTs, sulfur-doped CNTs, large- and small-diameter nanofibers, few-layer graphene, and a fibrous carbon have been produced, functionalized, defunctionalized and characterized using several techniques (e.g., nitrogen adsorption, Raman spectroscopy, XPS, TGA, and elemental analysis). These supports present different surface chemistry, arising from different features (defect concentration, inter-defect distances, long-range order, and orientation of the graphene layers) and specific surface areas. The most relevant parameters were obtained by characterization of the materials by Raman, XPS, nitrogen adsorption, and XRD. Twenty-four palladium catalysts with the same nominal loading (2%w/w) were prepared by wet impregnation using an acetone solution of Pd nitrate. These 24 catalysts were characterized by ICP, XRD, XPS and TEM. The final Pd loading varied between 1 and 2%w/w and the Pd particle size ranged from 1.5 to 3.3 nm, depending on the nature of the support. The parameters influencing both Pd loading and dispersion are discussed, and their very high activity for the myrcene complete hydrogenation are reported.

The continuous selective aerobic oxidation of benzyl alcohol in flow was developed using an immobilized Ru0 catalyst. After optimization of the reaction conditions, the stability and productivity of the equipment were examined over time using tert-amyl alcohol as solvent, and no deactivation occurred. A cumulative TON close to 15 000 was obtained with a constant activity (TOF = 4 min−1). A semi-empirical kinetic rate expression was proposed.

International audience; (C.d.B.); Tel.: +33-4-72-43-1755 (V.M.) † These authors contributed equally to this work. Abstract: A critical review of conclusions about the putative heterogeneous mechanism in the Suzuki-Miyaura coupling by supported Pd solids is reported. In the first section, the turnover frequencies (TOF) of 20 well-established homogeneous catalysts are shown to be in the range 200 to 1,000,000,000 h −1. The evidences used to prove a heterogeneous mechanism are discussed and another interpretation is proposed, hypothesizing that only the leached species are responsible for the catalytic reaction, even at ppb levels. Considering more than 40 published catalytic systems for which liquid phase Pd content have been reported, activities have been computed based on leached Pd concentrations and are shown to be in the range TOF 150 to 70,000,000 h −1. Such values are compatible with those found for the well-established homogeneous catalysts which questions the validity of the conclusions raised by many papers about the heterogeneous (solid) nature of Suzuki-Miyaura catalysis. Last, a tentative methodology is proposed which involves the rational use of well-known tests (hot-filtration test, mercury test.. .) to help to discriminate between homogeneous and heterogeneous mechanisms.

The Mukaiyama epoxidation was studied using a segmented flow reactor. Full conversion of cis-cyclooctene (0.67 M) with high selectivity (>99%) towards cyclooctene oxide was reached in 5 minutes using 2-ethylhexanal (2 M) as a sacrificial co-reductant, 100 ppm of Mn(II) as catalyst and 5 bar of oxygen. To gain further insights into the Mukaiyama reaction we have investigated the influence of the cis-cyclooctene/2-ethylhexanal ratio and cis-cyclooctene concentration. It was shown that after an induction period during which time aldehyde was oxidised faster than the alkene, the theoretical stoichiometry of the Mukaiyama reaction (1 mole of epoxide per mole of oxidised aldehyde) was observed. Then, different metal catalysts and catalyst loading were evaluated. The best results were obtained with Mn(II). We can suspect that the differences in productivity described in the literature for Mukaiyama epoxidation reaction could be explained by oxygen mass transfer resistance rather than catalytic efficiency. Surprisingly the selectivity of 2-ethylhexanal oxidation toward 2-ethylhexanoic acid was not improved by the co-oxidation of cis-cyclooctene. These results raised questions regarding the activated oxygen specie(s) responsible for the epoxidation and the exact mechanism of this reaction.

International audience; The homogeneous vs heterogeneous contributions when using solid catalysts for the Suzuki-Miyaura coupling is still disputed. Leaching is often observed and quantified albeit with unclear conclusions about contributions of the leached species and of the solid catalyst to the global catalytic activity. In this work, a new flow reactor design to discriminate both contributions is proposed. With the help of a simple reactor model, it has been possible to conclude that the coupling of 4-iodoacetophenone with phenylboronic acid proceeded with the leached homogeneous species only, whatever the solid Pd/silica used, whereas chloro-derivatives behaves differently. This reactor is simple to build and could be of general use to reveal actual heterogeneous vs homogeneous catalysis for many reactions. Keywords Suzuki-Miyaura · Heterogeneous · Leaching · Palladium The knowledge of the reaction location is of prime importance both to design efficient industrial processes and to understand the underlying fundamental mechanisms. For example, many catalytic processes are operated with heterogeneous (solid) catalysts for easier separation and downstream treatments thus to lower operating costs. However, when the fluid phase is a liquid, it appears that the knowledge of the reaction location is not straightforward. Indeed, active catalytic species may leach from the solid, which is then a simple catalyst precursor, and solubilizes in the liquid phase in which it catalyzes the reaction. Several papers including recent reviews have analyzed such situations for many different type of catalytic processes.[1,2] One must realize that the design of a catalytic reactor is largely based on the assumption of the reaction location simply because the reaction time, i.e. the contact time between the

International audience; The electrochemical in situ regeneration of spent Pd/C/foam catalysts was investigated using a modified Mahoney-Robinson reactor (RM). The same reactor was used for reaction and regeneration experiments with and without removal/weighing of the catalyst between each measurement. The feasibility of the electrochemical regeneration was assessed by monitoring the catalyst activity versus cumulative turnover number (TON). The results showed that the catalyst activity was fully recovered after regeneration and that the catalyst had the same deactivation rate after several reaction/regeneration cycles. The influence of the foam pretreatment step and of the pH electrolyte solution on the catalyst loss was also studied. A basic pretreatment of the foam before the catalyst coating led to a significant improvement of the catalyst adherence on the foam.

Continuous-flow technology with channel dimension in the millimeter region found widespread applications in numerous applications. The epoxidation of methyl oleate with molecular oxygen using an aldehyde as sacrificial reductant (Mukaiyama reaction) was implemented in a segmented flow microreactor. The effect of aldehyde structure and aldehyde/methyl oleate molar ratio on the conversion to epoxides was studied. Total conversion of methyl oleate (0.67 M in heptane) with a selectivity higher than 99% and a cis/trans ratio ∼75/25 was reach in less than 4 min, at room temperature, using three equivalents of 2-ethylhexanal, 100 ppm of Mn(II) as catalyst and five bar of oxygen. Practical applications: As the result of the small reactor volumes, very high surface-to-volume ratio and high heat exchange efficiency compared to classical batch reactors, the overall safety of oxidation processes is significantly improved using continuous-flow technology. Microreactors also provide better mass transfer, and thus, improve the productivity of the aerobic epoxidation of methyl oleate using aldehyde as sacrificial reductant while maintaining the high selectivity of the process. (i) Epoxidation of methyl oleate with molecular oxygen is performed safely using continuous-flow technology. (ii) Total conversion is obtained in 4 min at r.t. using 100 ppm of Mn(II) and a sacrificial reductant. (iii) The selectivity and cis/trans ratio are comparable to batch.

International audience; Aldol-condensation of furfural with acetone catalysed by activated dolomite was investigated at temperatures from 306 to 413 K. The process of activation by calcination and hydration produced catalytically active calcium and magnesium hydroxides with improved surface area and surface basicity. The aldolcondensation mechanism began with a deprotonation of acetone forming a carbanion intermediate by hydroxyl ions, which then reacted with the carbonyl group of furfural to form a water soluble C-8 monomer (4-(furan-2-yl)-4-hydroxybutan-2-one). This C-8 monomer readily dehydrated to form selectively alpha,beta-unsaturated ketone (4-(2-furyl)-3-buten-2-one), which in turn, reacted with furfural forming a C-13 dimer (1,4-pentadien-3-one,1,5-di-2-furanyl). Compared with conventional sodium hydroxide catalyst, activated dolomite was less selective towards lumped C-8 monomers and C-13 dimers owing to carbon losses and deactivation, particularly at high temperatures. Activated dolomite was more selective to C-13 dimer owing to higher adsorption enthalpy of C-8 monomer compared with acetone competitor. Activated dolomite is therefore a promising catalyst to produce C-13 dimers which can be transformed upon hydrogenation and deep hydrodeoxygenation in high-quality diesel fuels. The first-order kinetic model with respect to furfural and acetone fitted well with actual experimental results with an average normalised standard deviation of 6.2%. (C) 2013 Elsevier B.V. All rights reserved.

International audience; Commercially available H-Y (Faujasite) and H-ZSM5 zeolites with various SiO2/Al2O3 ratio (from 5 to 280) were used as acid catalyst for vapour phase methanol dehydration in mild condition (T\textless250 degrees C; P\textless5 bar). All tested catalysts were giving very high selectivity while conversion was highly dependent on both acid content and surface hydrophobicity expressed as Weitkamp hydrophobicity index (HI index). For H-Y and H-ZSM5 zeolites, a correlation was found between catalysts productivity expressed in kg of DME per hour per concentration of acid sites and HI index. Such results could rise to the design of more efficient catalyst for gas-phase DME synthesis from methanol.

The catalytic hydrogenation of three pro-chiral substrates methyl Z-α-acetamidocinnamate (MAC), methyl 2-acetamidoacrylate (M-Acrylate) and ethyl 4-methyl-3-acetamido-2-propanoate (E-EMAP) with rhodium precursors complexed with chiral diphosphines is reported at 1–30 bar hydrogen pressure. A library of 56 chiral diphosphines, including 23 BINAP derivatives, 7 JOSIPHOS, 5 BIPHEP, 3 DUPHOS derivatives, and 18 other ligands, was used. While it was generally accepted that high hydrogen pressure would result in lower ees, it is now demonstrated on a statistical basis that an equivalent distribution between beneficial and detrimental pressure effects on ee prevails and that the hydrogen pressure effect on enantioslectivity is not an isolated phenomenon since more than 33% of the reaction systems studied are strongly affected. In some case, the enantioselectivity can be improved up to 97% just by applying a higher hydrogen pressure. Extension of these conclusions to other non-chiral reagents is proposed.

A continuous-flow microreactor is applied for the selective aerobic neat oxidation of 2-ethylhexanal. Under 7.5 bar of O2 and 10 ppm of Mn(II) as catalyst, a production of up to 130 g/h of 2-ethylhexanoic acid can be obtained with a PFA tubing of 7 m (O 1.65 mm, reactor volume ca. 15 mL). The synergistic use of alkali metal salts and Mn(II) as catalyst improve the selectivity up to 94% under those conditions. We show that the productivity of this simple tube microreactor is limited by the thermal management.

Colloidal suspensions of monodisperse platinum nanoparticles of 2 nm diameter have been used to catalyze the hydrosilylation of 1-octene with a polymethylhydrosiloxane. The nanoparticles were found to be as efficient as Karstedt's complex, showing that colloid formation from homogeneous species during hydrosilylation reactions is not necessarily a deactivation pathway. These results also reactivated the debate on whether Karstedt's complex was truly homogeneous or colloidal during catalysis.

Aerobic oxidation using a combination of copper salts and 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) represent useful tools for organic synthesis and several closely related catalyst systems have been reported. To gain further insights, these catalytic systems were evaluated in a gas–liquid segmented flow device. The improvement of oxygen mass transfer has a significant influence on the turnover-limiting step. Hence, an improved catalytic system using copper(II) as copper source was implemented in a microreactor for the safe and efficient oxidation of primary alcohol.

The methylchlorodisilanes MeCl 2 SiSiCl 2 Me, MeCl 2 SiSiClMe 2 and MeCl 2 SiSiMe 3 disproportionate in the presence of nucleophilic catalysts into the methylchlorosilanes MeSiCl 3 , Me 2 SiCl 2 , Me 3 SiCl and the polysilanes Si n Me n Cl n +2 , Si n Me n +1 Cl n +1 and Si n Me n +2 Cl n ( n =3–5). Qualitative kinetic studies of the disproportionation reveal that the catalytic activities of the nucleophiles are ranked according to: phosphine oxides (OPnBu 3 , OP(NMe 2 ) 3 )>chlorides (nBu 4 NCl, nBu 4 PCl)>phosphines (PnBu 3 , PiPr 3 , PMe 2 Ph, P(NMe 2 ) 3 , PCy 3 , PPh 3 )>phosphites (P(OPh) 3 ). For the PR 3 compounds, a correlation is observed between the π acceptor character the activity for the disproportionation, the lower π acceptor the nucleophile, the higher the rate. A two step mechanism is proposed which involves the formation of an intermediate followed by condensation with the substrate disilane to afford the polysilanes. Investigation of the reaction of the intermediate with hydrogen as a test reaction provides evidences for the condensation step to be rate limiting in the disproportionation. That result, combined with the fact that poor π acceptor nucleophiles (phosphine oxides, chlorides and trialkylphosphines) are more active disproportionation catalysts, supports the description of the intermediate as a stabilised silylene.

A high throughput test which is based on a micromachined mixer for molecular gas-liquid reactions was evaluated for the kinetic investigation of the asymmetric hydrogenation of methyl Z-(α)-acetamidocinamate with a rhodium/(S,S-BDPPTS) catalyst in an aqueous phase. Up to 214 tests were performed in a short time and with an average inventory of Rh/test as low as 14 μg. Comparisons with traditional batch experiments are provided.

A centrifugal partition chromatograph (CPC) was used as a liquid–liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid–liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented.

Analysis of the literature on α-methylstyrene (AMS) hydrogenation reveals very large variations in the reported reaction rates. The presence of traces of water and mass-transfer limitations make reproducible intrinsic kinetic determination difficult. Under anhydrous conditions, the intrinsic kinetic law was, nevertheless, determined under a wide range of operating conditions: 0.5−100 wt % AMS, 0.1−0.6 MPa, 273−320 K, with an activation energy of 38.7 ± 1.5 kJ·mol-1.

A safe, straightforward, and atom economic approach for the oxidation of aliphatic aldehydes to the corresponding carboxylic acids within a continuous flow reactor is reported. Typically, the reaction is performed at room temperature using 5 bar of oxygen in PFA tubing and does require neither additional catalysts nor radical initiators except for those already contained in the starting materials. In some cases, a catalytic amount of a Mn(II) catalyst is added. Such a flow process may prove to be a valuable alternative to traditionally catalyzed aerobic processes.

The aerobic oxidation of aldehyde was investigated using a continuous flow microreactor under 5 bar of oxygen at room temperature. High-throughput screening of experimental conditions resulted in the development of an improved protocol. The synergistic use of a large range of salts and Mn(II) catalyst was found to be a very efficient catalytic system for selective aldehyde oxidation. Indeed for short residence time (i.e. 6 min.), a quantitative conversion of 2-ethylhexanal was obtained with a selectivity toward carboxylic acid of 98%.

Kinetic data acquisition and screening of transition metal complexes for homogeneous liquid phase catalysis calls for numerous testing in multiphase G/L, L/L and G/L/L systems. It is shown first, with an example in asymmetric hydrogenation, why detailed kinetics must be performed. Then, new reactors leading to fast experimental techniques are proposed. A liquid–liquid centrifugal partition chromatography is evaluated for determining rate constants and partition isotherms by combining frontal analysis and elution chromatography, the catalyst being maintained in a stationary aqueous phase. Two microreactors offering short residence time have also been tested and compared with a fast test reaction ( t R ca. 5–20 s). The combination of reacting pulses, carrier liquids and micromixer is proposed as a general high throughput tool for the investigation of G/L, L/L and G/L/L catalytic systems in a fast sequential way.

The isomerization of allylic alcohols to carbonyl compounds catalysed by water soluble transition metal complexes of Rh, Ru and Pd in a water/n-heptane biphasic system is reported. The substrates investigated are secondary or primary alcohols bearing the C C bond in the terminal or inner position. Conversions into carbonyl compounds were quantitative except for geraniol (44 % yield in citronelal). Activities up to 2 500 h−1 and turnover numbers of more than 2 600 are reported. The differences in the observed reactivity within a family of C4–C8 homologous allylic alcohols is only related to thermodynamic parameters such as the solubility and L/L partition dictated by the hydrocarbon chain and not by their intrinsic reactivity. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS

Detoxification of water containing chlorinated aromatic compounds is performed in a single fixed bed using a periodic sequence of three steps: transient adsorption, catalytic hydrogenation, and thermal regeneration. The solid is both the adsorbent (activated carbon) and the catalyst (2.6% ruthenium loading). For chlorophenols, the end products are cyclohexanol and sodium chloride diluted in less than 2% of the amount of processed water. Adsorption is the critical step. The whole breakthrough curve is easily modeled. Conversely, the model fails to describe the early beginning which governs the purity of the effluent. The reaction step is performed under mild conditions (T < 353 K, P < 0.4 MPa) and is governed by the transient desorption of the pollutant, the catalytic reaction, and the mass-transfer processes. Thermal regeneration under hydrogen flow restores the adsorbent capacity and catalytic activity.

AbstractThe Trost–Tsuji C–C coupling between ethyl cinnamyl carbonate and ethyl acetoacetate catalysed by a water soluble Pd/TPPTS catalyst (TPPTS=triphenylphosphine trisulphonate, sodium salt) and possible side reactions have been investigated in several biphasic media at 60–80°C. The use of the ionic liquid 1-butyl-3-methylimidazolium chloride as the catalytic layer brings definitive advantages over an aqueous catalytic phase: Palladium chloride may be used as the catalyst precursor, the solubility of the organic reagents is much higher which leads to faster reaction rates, the formation of cinnamyl alcohol is suppressed and common organic layers such as alkanes can be used with no noticeable catalyst deactivation. The yields in the C–C product up to 90% with TOF numbers of 23 h−1 may, thus, be achieved.

Catalytic hydrodechlorination and hydrodearomatisation of 13 different mono-, di-, tri-, tetra- and pentachlorophenols were carried out simultaneously under mild reaction conditions (298–353 K, 0.3–0.5 MPa). Experimental conditions suitable for complete conversion of the pollutants into nontoxic cyclohexanol and sodium chloride were first determined using a commercial Ru/C catalyst. A new supported ruthenium catalyst was then designed that possesses a carbonaceous support suitable to concentrate chlorophenol through adsorption. Using parachlorophenol as a model molecule, the influence of the base concentration in solution and the kinetics of the reaction under chemical regime were studied. A p-chlorophenol→phenol→cyclohexanol consecutive kinetic scheme was considered that drove to numerous possible kinetic models. A dynamic simulation software was used both for helping in model discrimination and for kinetic parameter estimation. The estimated activation energy values amount to ca. 45.0±2.7 and 33.2±2.4 kJ mol−1 for the hydrodechloration and the hydrodearomatisation steps, respectively.

The biphasic catalytic reduction of the C–C double bond of dimethylitaconate with a water soluble rhodium/triphenylphosphinetrisulphonated sodium salt (TPPTS) complex is investigated. Kinetic studies in a well-mixed batch reactor provide kinetics parameters and an activation energy of 71 kJ mol−1 but cannot discriminate between a first order or a complex kinetic model within the range of substrate concentration where the approximation of linear liquid/liquid partition is respected. Catalytic tests in the centrifugal partition chromatograph (CPC) reactor under steady-state operations in chemical regime and plug flow mode allow discriminating the kinetic models, the complex kinetic rate law being preferred.

Non-linear kinetics in asymmetric catalytic reactions may lead to non-linear enantioselectivity. In the H-transfer asymmetric reduction of arylketones with isopropanol/acetone catalyzed by a rhodium diamine complex, this has been quantified and used in order to achieve a significant increase in enantiomeric excess upon addition of reagents as simple as acetone. The question of the generalization of such a non-linear kinetic approach of enantioselective catalytic processes is also addressed.

New methods and reactors for the kinetic investigation of homogeneous catalysis are described. These are oriented towards the minimisation of the amount of catalyst required for testing new catalytic reactions, kinetics determination and/or catalyst selection. The use of the centrifugal partition chromatograph (CPC) as a chromatographic catalytic reactor for steady-state and transient kinetics is reported. Examples are given which involve monophasic and biphasic reductions. The former is the enantioselective reduction of acetophenone to 2-phenylethanol by isopropanol catalysed by a Rh/chiral diamine system. The biphasic reductions are: (i) the reduction of benzaldehyde into benzylic alcohol catalysed with a Ru/TPPTS complex and (ii) the reduction of dimethylitaconate into dimethylmethylsuccinate catalysed with a Rh/TPPTS complex, both reductions taking place in cyclohexane/water mixtures with sodium formate as the hydrogen transfer reagent. Finally, for first order reactions, analytical solutions are found which demonstrate that kinetic parameters can be readily obtained by using the CPC as a chromatographic reactor in the transient (pulse) mode.

A centrifugal partition chromatograph (CPC) is used as a liquid-liquid reactor for the catalytic reduction of benzaldehyde to benzylic alcohol. The catalyst is a water-soluble ruthenium complex with triphenylphosphinetrisulfonated, sodium salt (TPPTS) as a ligand. Kinetic study in a well-mixed batch reactor reveals that the reaction is of first order with respect to the substrate. Hydrodynamics and mass transfer in the CPC have been studied. Residence-time distribution analysis evidences the plug-flow pattern of the CPC. Comparison of the characteristic reaction time with the mass transfer time shows that the chemistry is the actual limiting process. Finally, catalytic tests in the CPC reactor confirm the kinetic data obtained in the batch reactor. The CPC is thus found to be a very effective continuous plug-flow liquid-liquid catalytic reactor.

A safe, straightforward, and atom economic approach for the oxidation of aliphatic aldehydes to the corresponding carboxylic acids within a continuous flow reactor is reported. Typically, the reaction is performed at room temperature using 5 bar of oxygen in PFA tubing and does require neither additional catalysts nor radical initiators except for those already contained in the starting materials. In some cases, a catalytic amount of a Mn(II) catalyst is added. Such a flow process may prove to be a valuable alternative to traditionally catalyzed aerobic processes.

International audience; A G-L-S "slurry Taylor" flow is investigated for the three-phase catalytic hydrogenation of 3-methyl-1-pentyn-3-ol in a capillary reactor. A system to continuously feed a homogeneous liquid-solid suspension without flow fluctuation is designed and validated allowing delivery of a stable and controlled gas-liquid-solid "slurry Taylor" flow. The catalyst particles are transported as a suspension by means of internal vortices occurring in the liquid slugs of the segmented flow. This original contact mode involving a solid catalyst in a continuous milli-reactor is evaluated by performing the fast catalytic hydrogenation of 3-methyl-1-pentyn-3-ol on a palladium catalyst supported on silica. The results obtained for this contactor show an excellent repeatability and are compared with those obtained in a laboratory stirred tank vessel under semi-batch conditions. Conditions to achieve reaction limited regime have been identified for both reactors demonstrating the good mass transfer performances of the "slurry Taylor" flow. An alternative way to monitor the reaction progress through simple image analysis of the H-2 bubble shrinkage is also studied and discussed. This technique allowed a conversion profile to be established over the corresponding residence time comparable with the results obtained in the laboratory-scale batch reactor and the final GC measurements.

The deactivation and regeneration of Pd/carbon coated support catalysts, used during nitrobenzene hydrogenation, were studied. Three methods have been tested: electrochemical treatment, chemical oxidation and oxygen plasma treatment. The regenerated catalysts were characterized by physisorption of nitrogen (BET method) and were compared with the activities of fresh catalysts. It was found that the electrochemical treatment allows the complete regeneration of the catalyst, without any modification of textural properties. Simple chemical oxidation did not allow the activity recovery of Pd catalysts and led to modification of the textural properties of carbon. Finally, the catalyst may be regenerated also by plasma method, albeit with some increase of the pore diameter.

The purpose of these comments is to express some concern regarding the choice of the test reaction used to characterize the activity of some nanoporous aluminosilicate catalysts produced using an evaporation-induced self-assembly approach described in the recent Catal. Sci. Technol. paper of A. E. Graham et al. [2012, 2, 2258–2263].

The hydroformylation of olefins (oxo synthesis) is the most important process for the production of higher aldehydes (>C4). The liquid phase oxidation of the latter to carboxylic acids by molecular oxygen or air has been known for more than 150 years and is an industrially important process. However, in the recent literature, several different oxidizing reagents and catalytic processes have been reported for this oxidation but most of them have limitations as they use environmentally unacceptable reagents or unnecessarily sophisticated conditions. Herein, we re-evaluated the air oxidation of aldehydes. We show that under mild conditions (air or oxygen and non-optimized stirring), reactions are transfer limited and thus catalyst has no effect on reaction rate. Using efficient stirring (self-suction turbine), uncatalysed air oxidation of 0.8 M aldehyde is possible in 50 min at room temperature whereas less than 10 min was necessary with 10 ppm Mn(II). Thus, recommendations for avoiding common pitfalls that may rise during the evaluation of new catalysts are made.

Many three-phase catalytic reactions are limited by gas-liquid mass transfer. Previous works have found the transfer rate to be increased by the presence of fine catalyst particles. Most of the studies concerned active carbon particles in aqueous media. This paper intends to point out and to explain this effect in the case of catalytic hydrogenation of adiponitrile over Raney nickel particles. The experiments based on pressure variation due to the hydrogen absorption in a stirred batch reactor point out clearly an increase of k1a at an optimum catalyst loading. This positive effect is reduced at high stirring speed and turns back to a small negative effect when using inert particles. The enhancement of gas-liquid mass transfer by particles is maximum when a layer of water is physisorbed at the catalyst surface. The water located at the solid surface could induce a better adhesion of the particles to the bubble. The total gas-liquid mass transfer could be enhanced when using particles with high hydrogen adsorption capability, by a “shuttle” or a “bridge” effect. The solid particles act as hydrogen carriers. These assumptions have been further supported by original experiments involving the same equipment and measurements with a simultaneous reaction. A model which takes into account particles adhesion at the interface has been set up and is in good agreement with the experiments.

The catalytic hydrogenation of adiponitrile into hexamethylenediamine (HMD) under mild conditions (20 bar H2, 120 to 180°C) using monometallic Ni, Co and Ru and bimetallic NiCr, NiTi, NiCo and CoFe Ziegler-type catalysts is reported. It is found that water exerts a strong negative influence on the selectivity to the primary amine HMD whereas it has a spectacular beneficial effect on the catalyst activity, especially for Ni based catalysts. Adding a second metal (Cr, Ti) as a dopant for nickel has a beneficial effect on the selectivity in HMD but results in lower activities. The ratio Ni/M (M Cr, Ti) does not appear to be a key parameter in these systems as the doping effect on the HMD selectivity already appears at low dopant loading (atom.-%: 3% for Cr, 10% for Ti) and is constant up to 60%. The temperature has an influence on the HMD selectivity: the NiCr and NiTi catalysts show a peculiar behaviour, maintaining a high selectivity level (ca. 90%) over all the temperature range. This is not the case for the Co based catalysts.

The metalloligated mixed-metal cluster [PdPtCo2(CO)7(μ-dppm)2] (2) (dppm = μ-Ph2PCH2PPh2) possesses numerous potential reaction centers (e.g., metal(s), metal-metal bonds, CO, and dppm ligands) and this has previously led to an investigation of the site selectivity of reactions with nucleophiles. The exocyclic CO(CO)4 fragment was substituted with a chloride ligand and the resulting chiral, triangular cluster PdPtCoCl(CO)3(μ-dppm)2 (4) has been structurally characterized. The Pd-Co and Pt-Co edges of this almost equilateral triangle are bridged by a dppm ligand, and two of the three carbonyls borne by the Co atom are semi-triply bridging above and below the plane of the metals. The “Co(CO)3P” fragment behaves as an anionic 4-electron donor organometallic bridging group toward thed9-d9 Pd(I)-Pt(I) unit. Crystal data for4, monoclinic space groupP21/n with Z=4 in a unit cell of dimensionsa=12.291(3),b=19.321(4),c=23.680(5) A,β=100.05(2)°. The structure has been solved from diffractometer data by Patterson, Fourier methods and refined by full-matrix least squares on the basis of 3512 observed reflections (l>3σ) toR(F) andRw(F) values of 0.059 and 0.061.

International audience; The catalytic system prepared from [Rh(COD)(2)]BF4 and (R,R)-Me-BPE provides a spectacular detrimental hydrogen pressure effect on ee from 94% down to 56% in the hydrogenation of methylacrylate, whereas it has a strong beneficial effect on the hydrogenation of E-emap (from 42% up to 72%). The kinetic parameters have been determined for both systems and have helped to identify the most enantioselective controlling steps (MECS). Accordingly, further explanations for the structure-ee and hydrogen pressure relationship are proposed. (c) 2012 Elsevier B.V. All rights reserved.