Search results for " Catalysis"

Front Cover Picture: SBA‐15/POSS‐Imidazolium Hybrid as Catalytic Nanoreactor: the role of the Support in the Stabilization of Palladium Species for C…

2019

Cobalt−NHC Catalyzed C(sp2)−C(sp3) and C(sp2)−C(sp2) Kumada Cross‐Coupling of Aryl Tosylates with Alkyl and Aryl Grignard Reagents

2021

The first cobalt‐catalyzed cross‐coupling of aryl tosylates with alkyl and aryl Grignard reagents is reported. The catalytic system uses CoF3 and NHCs (NHC=N‐heterocyclic carbene) as ancillary ligands. The reaction proceeds via highly selective C−O bond functionalization, leading to the corresponding products in up to 98 % yield. The employment of alkyl Grignard reagents allows to achieve a rare C(sp2)−C(sp3) cross‐coupling of C−O electrophiles, circumventing isomerization and β‐hydride elimination problems. The use of aryl Grignards leads to the formation of biaryls. The C−O cross‐coupling sets the stage for a sequential cross‐coupling by exploiting the orthogonal selectivity of the cataly…

In situ polymerization of soil organic matter by oxidative biomimetic catalysis

2017

Abstract Background Agricultural practices that enhance organic matter content in soil can play a central role in sequestering soil organic carbon (SOC) and reducing greenhouse gases emissions. Methods We used a water-soluble iron-porphyrin to catalyze directly in situ oxidative polymerization of soil organic matter in the presence of H2O2 oxidant, with the aim to enhance OC stabilization, and, consequently, reduce CO2 emissions from soil. The occurred SOC stabilization was assessed by monitoring soil aggregate stability, OC distribution in water-soluble aggregates, soil respiration, and extraction yields of humic and fulvic acids. Results Soil treatment with H2O2 and iron-porphyrin increas…

Theoretical Study of Primary Reaction of Pseudozyma antarctica Lipase B as the Starting Point To Understand Its Promiscuity

2014

Pseudozyma antarctica lipase B (PALB) is a serine hydrolase that catalyzes the hydrolysis of carboxylic acid esters in aqueous medium but it has also shown catalytic activity for a plethora of reactions. This promiscuous activity has found widespread applications. In the present paper, the primary reaction of PALB, its native hydrolytic activity, has been studied using hybrid quantum mechanical/molecular mechanical (QM/MM) potentials. Free energy surfaces, obtained from QM/MM Molecular Dynamics (MD) simulations, show that the reaction takes place by means of a multi-step mechanism where the first step, the activation of the carbonyl group of the substrate and the nucleophilic attack of Ser1…

QM/MM Determination of Kinetic Isotope Effects for COMT-Catalyzed Methyl Transfer Does Not Support Compression Hypothesis

2004

Secondary alpha-D3 kinetic isotope effects calculated by the hybrid AM1/TIP3P/CHARMM method for the reaction of S-adenosylmethionine with catecholate anion in aqueous solution and catalyzed by rat liver catechol O-methyltransferase at 298 K are 0.94 and 0.85, respectively, in good accord with experiment. The large inverse effect for the enzymatic reaction is not due to compression but arises from significant increases in the stretching and bending force constants involving the isotopically substituted atoms of the transferring methyl group as between the reactant complex and the transition structure, larger than for the reaction in water.

Covalently Supported Ionic Liquid Phases: An Advanced Class of Recyclable Catalytic Systems

2016

In this review, the most recent advances in the synthesis and catalytic applications of covalently supported ionic liquid (IL) phases will be discussed. This class of recyclable catalytic materials is based on the covalent attachment of several types of ammonium salts, usually imidazolium, but also thiazolium, triazolium, and pyrrolidinium salts, on the surface of different supports, for example, silica, periodic mesoporous organosilica, polystyrene, magnetic-based materials, carbon nanotubes (NTs), halloysite NTs, polyhedral oligomeric silsesquioxane (POSS), and fullerenes. Moreover, poly(ionic liquid) materials, in which the IL-based structure also acts as a support, will be considered. T…

Linking Electrostatic Effects and Protein Motions in Enzymatic Catalysis. A Theoretical Analysis of Catechol O-Methyltransferase

2014

The role of protein motions in enzymatic catalysis is the subject of a hot scientific debate. We here propose the use of an explicit solvent coordinate to analyze the impact of environmental motions during the reaction process. The example analyzed here is the reaction catalyzed by catechol O-methyltransferase, a methyl transfer reaction from S-adenosylmethionine (SAM) to the nucleophilic oxygen atom of catecholate. This reaction proceeds from a charged reactant to a neutral product, and then a large electrostatic coupling with the environment could be expected. By means of a two-dimensional free energy surface, we show that a large fraction of the environmental motions needed to attain the…

Influence of barium and cerium oxides on alumina supported Pd catalysts for hydrocarbon combustion

2002

Abstract The effects of baria and ceria additions to alumina-supported palladium catalysts have been investigated. Two series of binary Al 2 O 3 –BaO and ternary oxides Al 2 O 3 –CeO 2 –BaO were prepared using a sol–gel method and then characterized, after high-temperature treatments, by XRD, BET, TG, TEM and EDXS analyses. The influence of baria and ceria on the thermal stability and morphology of the supports was examined. A baria content of 12 wt.% appears the most effective for alumina stabilization. Palladium catalysts were prepared by impregnation method using Pd(NH 3 ) 4 (NO 3 ) 2 and were characterized by XRD and TEM. The catalysts showed high activity in the total oxidation of meth…

Screening of ceria-based catalysts for internal methane reforming in low temperature SOFC

2010

Gaudillere, Cyril Vernoux, Philippe Mirodatos, Claude Caboche, Gilles Farrusseng, David 6th World Congress on Oxidation Catalysis (6WCOC) JUL 05-10, 2009 Lille, FRANCE; International audience; Ceria-based catalysts have been assessed for internal methane reforming at low temperature (400-600 C) in Solid Oxide Fuel Cell (SOFC) A combinatorial library of 15 metal (Cu Pt Ni) supported ceria was prepared using wet impregnation method The ceria-based oxides are undoped or doped with metal transition (Zr) or by rare earth (Gd or Pr) The effect of the metal the dopant and the surface area on the catalytic performances was investigated in high-throughput manner using a 16-parallel reactor The catal…

The catalytic performance of mesoporous cerium oxides prepared through a nanocasting route for the total oxidation of naphthalene

2010

Cerium oxides have been prepared by nanocasting of a mesoporous siliceous KIT-6. Through this synthesis method a partially ordered mesoporous structure, as demonstrated by several characterization techniques (N2 adsorption, XRD and HRTEM) has been obtained. Accordingly, very high surface areas have been achieved (up to 163 m2/g), despite using high calcination temperatures (550 °C). We have demonstrated that the aging temperature of the siliceous template is of outstanding importance, as this parameter is directly responsible for both the pore size and the surface area of the catalysts. In addition, whilst a low preparation temperature (40 °C) makes the further removal of the silica templat…