Meunier F.C.,National Engineering School of Caen
Angewandte Chemie - International Edition | Year: 2011
The shape of things to come: The preparation and combination of nanoparticles of copper and zinc oxide with controlled morphology opens new avenues in the understanding of metal-support interactions and may help resolving the intricacy of methanol synthesis during the hydrogenation of CO2. The improved selectivity to methanol formation observed with some of the morphology combinations suggests that the reverse water-gas-shift side-reaction to give CO could be dramatically minimized (see scheme). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Meunier F.C.,National Engineering School of Caen
Chemical Society Reviews | Year: 2010
This tutorial review discusses some of the current designs of reaction cells used for operando spectroscopy (X-ray absorption, UV-vis, Raman, transmission FTIR and DRIFTS) and the relation to the apparent reaction kinetics. Beam effects, the control of the catalyst bed temperature and bed by-pass are some of the potential problems that may lead to flawed activity measurements. Finally, four examples are given in which a good agreement was obtained between the activity of a powdered catalyst measured in a conventional reactor and in a spectroscopic cell. It is proposed that such comparison between reactors should become a standard procedure, to ensure the correctness of the data collected over typically non-ideal spectroscopic reaction cells. © 2010 The Royal Society of Chemistry.
Fernandez C.,National Engineering School of Caen |
Pruski M.,Iowa State University
Topics in Current Chemistry | Year: 2012
Solid-state nuclear magnetic resonance (NMR) of quadrupolar nuclei has recently undergone remarkable development of capabilities for obtaining structural and dynamic information at the molecular level. This review summarizes the key achievements attained during the last couple of decades in solid-state NMR of both integer spin and half-integer spin quadrupolar nuclei. We provide a concise description of the first- and second-order quadrupolar interactions, and their effect on the static and magic angle spinning (MAS) spectra. Methods are explained for efficient excitation of single- and multiple-quantum coherences, and acquisition of spectra under low- and high-resolution conditions. Most of all, we present a coherent, comparative description of the high-resolution methods for half-integer quadrupolar nuclei, including double rotation (DOR), dynamic angle spinning (DAS), multiple-quantum magic angle spinning (MQMAS), and satellite transition magic angle spinning (STMAS). Also highlighted are methods for processing and analysis of the spectra. Finally, we review methods for probing the heteronuclear and homonuclear correlations between the quadrupolar nuclei and their quadrupolar or spin-1/2 neighbors. © 2011 Springer-Verlag Berlin Heidelberg.
Valtchev V.,National Engineering School of Caen |
Tosheva L.,Manchester Metropolitan University
Chemical Reviews | Year: 2013
The steady interest in nanosized porous solids is due to the potential of these materials to offer sustainable solutions to global issues such as increasing energy demands and at the same time more rigorous environmental standards for industrial pollutants, depletion of resources, and health improvement. Considering the accumulated number of publications dedicated to porous nanoparticles and their somewhat limited outreach in cross-disciplinary fields, the aim of this review is to provide an overview of recent developments in the area of synthesis and applications of the different groups of porous nanomaterials. The classical definition of a zeolite is a crystalline aluminosilicate built of oxygen-linked tetrahedral silicon and aluminum atoms that form a three-dimensional microporous structure comprising channels and voids occupied by alkali or alkali-earth cations and water molecules.
Gaillard S.,University of St. Andrews |
Gaillard S.,National Engineering School of Caen |
Cazin C.S.J.,University of St. Andrews |
Nolan S.P.,University of St. Andrews
Accounts of Chemical Research | Year: 2012
Environmental concerns have and will continue to have a significant role in determining how chemistry is carried out. Chemists will be challenged to develop new, efficient synthetic processes that have the fewest possible steps leading to a target molecule, the goal being to decrease the amount of waste generated and reduce energy use. Along this path, chemists will need to develop highly selective reactions with atom-economical pathways producing nontoxic byproduct. In this context, C-H bond activation and functionalization is an extremely attractive method. Indeed, for most organic transformations, the presence of a reactive functionality is required. In Total Synthesis, the "protection and deprotection" approach with such reactive groups limits the overall yield of the synthesis, involves the generation of significant chemical waste, costs energy, and in the end is not as green as one would hope. In turn, if a C-H bond functionalization were possible, instead of the use of a prefunctionalized version of the said C-H bond, the number of steps in a synthesis would obviously be reduced. In this case, the C-H bond can be viewed as a dormant functional group that can be activated when necessary during the synthetic strategy. One issue increasing the challenge of such a desired reaction is selectivity. The cleavage of a C-H bond (bond dissociation requires between 85 and 105 kcal/mol) necessitates a high-energy species, which could quickly become a drawback for the control of chemo-, regio-, and stereoselectivity. Transition metal catalysts are useful reagents for surmounting this problem; they can decrease the kinetic barrier of the reaction yet retain control over selectivity. Transition metal complexes also offer important versatility in having distinct pathways that can lead to activation of the C-H bond. An oxidative addition of the metal in the C-H bond, and a base-assisted metal-carbon bond formation in which the base can be coordinated (or not) to the metal complexes are possible. These different C-H bond activation modes provide chemists with several synthetic options. In this Account, we discuss recent discoveries involving the versatile NHC-gold(I) and NHC-copper(I) hydroxide complexes (where NHC is N-heterocyclic carbene) showing interesting BrØnsted basic properties for C-H bond activation or C-H bond functionalization purposes. The simple and easy synthesis of these two complexes involves their halide-bearing relatives reacting with simple alkali metal hydroxides. These complexes can react cleanly with organic compounds bearing protons with compatible pKa values, producing only water as byproduct. It is a very simple protocol indeed and may be sold as a C-H bond activation, although the less flashy "metalation reaction" also accurately describes the process. The synthesis of these complexes has led us to develop new organometallic chemistry and catalysis involving C-H bond activation (metalation) and subsequent C-H bond functionalization. We further highlight applications with these reactions, in areas such as photoluminescence and biological activities of NHC-gold(I) and NHC-copper(I) complexes. © 2011 American Chemical Society.