Search results for "catalyst"

Novel supported substituted prolinamide as recyclable catalyst for asymmetric aldol reaction

2010

Improving the onset potential and Tafel slope determination of earth-abundant water oxidation electrocatalysts

2021

To date, a plethora of electrocatalysts for the Oxygen Evolution Reaction (OER) have been proposed. For evaluating their electrocatalytic behavior the determination of the onset potential in each studied electrolyte is a key parameter. Nevertheless, this evaluation becomes particularly problematic for first- transition metal catalysts as well as by the use of electroactive collectors ( e.g. Ni foams) whose redox peaks overlap the onset potential. A usual solution to detect the onset potential requires the availabil- ity of in-situ mass spectrometric determination of the generated oxygen. In this work, we present fast and easier available cyclic voltammetry and coulovoltammetric responses to…

Linear, tripodal, macrocyclic: Ligand geometry and ORR activity of supported Pd(II) complexes

2021

Abstract The novel ligand H3L designed to spontaneously adsorb onto MWCNT via electron-deficient pyrimidine residues and bind metal cations is used to prepare an oxygen reduction reaction (ORR) cathode catalyst based on supported Pd(II) complexes. Herein we report the synthesis of the ligand, its solution behaviour (protonation constants, binding constants for the test cation Cu(II), UV evidence of Cu(II) and Pd(II) complexes formation) and ORR performances together with XPS and STEM characterization. Tripodal nature of the H3L ligand frame it in-between previously studied macrocyclic and linear open chain ligands, allowing to draw meaningful comparisons.

Benzyl alcohol to benzaldehyde oxidation on MnOx clusters: Unraveling atomistic features

2021

Abstract The catalytic oxidation of benzyl alcohol with O 2 is a promising option for the production of benzaldehyde, from both environmental and economical viewpoints. In particular, highly dispersed MnO x systems feature good activity and selectivity in a wide range of temperatures, although deactivation phenomena by over-oxidation and/or poisoning of active sites are generally recorded. On this account, a density functional theory study was performed on cluster-sized catalyst models, namely Mn 4 O 8 and over-oxygenated Mn 4 O 9 fragments, to predict the reactivity pattern of MnO x catalysts in the selective aerobic oxidation of benzyl alcohol. Several pathways concur to determine the who…

Electrocatalytic carboxylation of chloroacetonitrile at a silver cathode for the synthesis of cyanoacetic acid

2008

Abstract The electrocatalytic carboxylation of chloroacetonitrile to cyanoacetic acid performed at silver cathodes was investigated both theoretically and experimentally. Silver exhibits powerful electrocatalytic activities towards the reduction of chloroacetonitrile. In CO 2 -saturated CH 3 CN, reduction of NCCH 2 Cl occurs at potentials that are about 0.7 V more positive than those observed at glassy carbon and gives cyanoacetic acid in good yields. Theoretical considerations on the effect of operative parameters on the performances of the process were confirmed by electrocarboxylation experiments performed in undivided cells equipped with sacrificial anodes both in a bench-scale electroc…

From CO2 to dimethyl carbonate with dialkyldimethoxystannanes: the key role of monomeric species.

2011

International audience; The formation of dimethyl carbonate (DMC) from CO(2) and methanol with the dimer [n-Bu(2)Sn(OCH(3))(2)](2) was investigated by experimental kinetics in support of DFT calculations. Under the reaction conditions (357-423 K, 10-20 MPa), identical initial rates are observed with three different reacting mixtures, CO(2)/toluene, supercritical CO(2), and CO(2)/methanol, and are consistent with the formation of monomeric di-n-butyltin(iv) species. An intramolecular mechanism is, therefore, proposed with an Arrhenius activation energy amounting to 104 ± 10 kJ mol(-1) for DMC synthesis. DFT calculations on the [(CH(3))(2)Sn(OCH(3))(2)](2)/CO(2) system show that the exothermi…

Trapping AsPh3 via reaction with NiS/γ-Al2O3 in the presence of H2: Reaction mechanism and kinetics

2021

International audience; Removal of As from petroleum feedstocks is an important process which can be realized using As trapping mass containing supported nickel sulfide. In order to understand the mechanism of the trapping we studied the reaction of AsPh3 with NiS/γ-Al2O3 in the presence of H2 in a batch reactor in toluene solution at 230 °C. This reaction results in formation of NiAs, benzene and H2S. Also, the intermediate species, thiophenol and diphenylsulfide, were observed. Despite formation of NiAs layer in the course of reaction, the rate of AsPh3 decomposition is not affected by the solid state diffusion up to ∼ 50 % of nickel conversion. The rate determining step in these conditio…

Electroreduction of aliphatic chlorides at silver cathodes in water

2010

The effect of water on the reduction of aliphatic chlorides at silver cathodes was investigated by cyclovoltammetric experiments in acetonitrile, water and their mixture and focused electrolyses in water solutions. The addition of water to acetonitrile gives rise to the formation of new peaks and/or the displacement of pre-existent peaks at dramatically less negative potentials. In a water medium, silver shows a very large electrocatalytic effect towards the reduction of chlorinated aliphatic compounds belonging to the classes of chloromethanes, chloroethanes and chloroethenes, dramatically higher than that observed in aprotic solvents such as dimethylformamide (DMF) or acetonitrile (ACN). …

Coadsorption of NRR and HER Intermediates Determines the Performance of Ru-N4 toward Electrocatalytic N2 Reduction

2021

Efficiency of the electrochemical N2 reduction reaction (NRR) to ammonia is seriously limited by the competing hydrogen evolution reaction (HER) but our current atomic-scale insight on the factors controlling HER/NRR competition are unknown. Herein we unveil the elementary mechanism, thermodynamics, and kinetics determining the HER/NRR selectivity on the state-of-the-art NRR electrocatalyst, Ru-N4 using constant potential density functional theory calculations (DFT). The calculations show that NRR and HER intermediates coadsorb on the catalyst where HER is greatly suppressed by the NRR intermediates. The first reaction step leading to either *NNH or *H determines the selectivity towards NRR…

Ru(bpy)2Cl2: A catalyst able to shift the course of the photorearrangement in the Boulton-Katritzky reaction

2015

The Boulton-Katritzky reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a-e) in the presence of catalytic amounts of Ru(bpY)(2)Cl-2. We have observed the unexpected formation of the 1-aryl-5-…