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Abstract  

Ferrisilicates of MFI structure (HZSM-5) with Si/Fe ratios of 27.5, 35 and 67 have been studied by in situ Mössbauer spectroscopy, and the results are correlated with studies on catalytic conversions of toluene. Various species of iron ions are identified from 300 K spectra recorded after combinations of evacuation and reduction at 570 and 670 K, respectively. The roles of identified species are suggested in catalytic processes.

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Abstract  

Profiles of temperature programmed reduction (TPR) of V2O5 under H2 have been studied through water analysis. This new approach enhances the sensitivity of the method. The influence of experimental parameters on the temperature corresponding to the maximum reduction rate,T m, has been studied. The hydrogen concentration and heating rate are the two major factors that influenceT m. In our method, the amount of solid and the flow rate are also important factors in monitoring of profile distortions attributed to water condensation at the outlet of the reactor. An approach of the mechanism of reduction of V2O5 has been carried out. The best kinetic model which describes the reduction rocess is the Avrami-Erofeev tridimensional nucleation model.

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Abstract  

The acid properties of the Ca/NaY zeolite were investigated by means ofn-butylamine desorption and thermal decomposition, using both thermogravimetry (TG) and differential scanning calorimetry (DSC). The total acidity of the zeolite was calculated from the TG data, while DSC was used with the Borchardt-Daniels kinetic model to determine the relative acid strength of the catalyst, given in J per acid site. The enthalpies of these processes are proportional to the acid site strength in each specific temperature range.

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Journal of Flow Chemistry
Authors:
Eloïc Colombo
,
Philippe Ratel
,
Laurent Mounier
, and
Fabrice Guillier

Abstract

A series of substituted indole-2-carboxylic acid ethyl esters and aza-indole analogs have been prepared using continuous-flow hydrogenation. The identification of some key parameters using a design of experiments (DoE)-based approach allowed efficient optimization of each synthesis. The scale-up study for the multigram preparation of one model indole substrate showed the importance of working at steady state with the H-Cube pparatus. A new useful method for the easy preparation of substituted indoles in various quantities is presented.

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The aldol condensation of methyl acetate with formaldehyde to form methyl acrylate was studied in a continuous-flow reactor using a series of supported cesium basic catalysts with commercially available materials (ZSM-5, SiO2, and γ-Al2O3) as carriers prepared by vacuum impregnation. The catalysts were characterized by N2 adsorption-desorption, Fourier transform-infrared (FT-IR), X-ray diffraction (XRD), and temperature-programmed desorption of ammonia and carbon dioxide (NH3/CO2-TPD). The obtained results indicated that the selectivity of methyl acrylate was mainly influenced by the properties of supports. The formation of acetone is approximately proportional to the acidity of supports. The basicity of the catalysts was favorable to the formation of methyl acrylate according to the results of CO2-TPD. The hydrolysis of methyl acetate was inhibited over Cs-HT-SiO2 prepared by SiO2 after hydrothermal treatment. Furthermore, SiO2 with the large mesoporous volume is superior to other supports, which shows the best catalytic activity for the aldol condensation reaction. On the other hand, the catalytic performance of zeolite basic catalysts was strongly influenced by the effect of reactant diffusion. Internal diffusion resulted in the increase of conversion of methyl acetate with increasing specific surface area, while the conversion of methyl acetate decreased with increasing the weight hourly space velocity (WHSV) due to the external diffusion.

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Dendrimer-encapsulated Au/Ag alloy nanoparticles (Au/Ag DENs) were covalently attached to a monolayer-functionalized inner surface of glass microreactors. The influence of the bimetallic alloy structure and of the different metal ratios was investigated for the reduction of 4-nitrophenol using NaBH4. TheAu/Ag—dendrimer nanocomposite with a 1:1 Au/Ag metal ratio showed the highest activity as compared to othermetal ratios and to pure Ag and Au. The dendrimer template exerted a stabilizing effect for six consecutive days of use with almost no decrease in conversion. This strategy enables the screening and investigation of a variety of bimetallic nanocatalysts in continuous-flow microreactors.

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An integrated process including continuous-flow syntheses directly coupled to product isolation via continuous crystallization is presented. For the synthesis part, Ce0.495Sn0.495Pd0.01O2—δ was used as heterogeneous catalyst in a custom-made packed-bed reactor (the so-called “Plug and Play” reactor) for continuous Suzuki—Miyaura crosscouplings of various para- and ortho-substituted bromoarenes with phenylboronic acid using environmentally friendly aqueous ethanolic mixtures as reaction solvents. The reactions were stable for up to 30 h without any detectable catalyst deactivation. The desired biaryl products were obtained in gram scale with good to excellent yields and high selectivity. For three methyl-, ketyl-, and nitrile-functionalized biphenyl products, isolation was done using water as antisolvent in an integrated crystallization process as continuous downstream protocol. The desired products could be isolated with high purity and with yields of up to 95% for the overall process.

Open access
Journal of Flow Chemistry
Authors:
József Madarász
,
Gergely Farkas
,
Szabolcs Balogh
,
Áron Szöllősy
,
József Kovács
,
Ferenc Darvas
,
László Ürge
, and
József Bakos

Abstract

Highly active immobilized hydrogenation catalytic systems were used in the H-Cube™ hydrogenation reactor. “In situ” produced [Rh(COD)((S)-MonoPhos)2]BF4 complex was immobilized on commercially available Al2O3 and mesoporous Al2O3 by means of phosphotungstic acid (PTA), respectively. The optimum reaction conditions were determined and studied at different temperature, pressure, and flow rate values. Furthermore, the effect of the substrate concentration, microstructure of the support, and the stability of the complex were investigated. A continuous-flow reaction system using a stationary-phase catalyst for the asymmetric hydrogenation of methyl acetamidoacrylate was developed and run continuously for 12 h with >99% conversion and 96–97% enantioselectivity.

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Abstract  

Polyacrylic hydrogels were14C- and3H-labeled in three main steps. In the first one, the monomer as sodium salt was14C-labeled at the carboxyl group via the carbonation of vinylmagnesium bromide and [1-14C]acrylic acid was obtained, followed by labeling with tritium via isotopic exchange in heterogeneous catalysis. The monomer was purified and its radiochemical purity was analyzed using TLC. In the last step, the hydrogel was obtained through radiopolymerization of the doubly labeled monomer using a60Co source. The oligomers and unpolymerized monomers were eliminated from the hydrogel by swelling in water followed by dehydration with methanol.

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Abstract  

Fundamentals and fields of application of time- and temperature-resolved diffraction methods are presented. X-ray diffraction and neutron diffraction will be considered. Dynamic diffraction methods are increasingly applied in different fields like solid state reactions, heterogeneous catalysis and biological sciences. New methods like synchrotron radiation and position-sensitive detectors permit a considerable expansion of potential research areas. The dynamic diffraction methods are compared with the classical thermoanalytical methods thermogravimetry and DSC.

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