Search results for " Catalysis"
showing 10 items of 585 documents
Dual Hydrogen Bond - Enamine Catalysis Enables a Direct Enantioselective Three-Component Domino Reaction
2011
A dual system, composed of an enantioselective enamine catalyst and a multiple-hydrogen-bond catalyst achieves the three-component enantioselective aldehyde—nitroalkene—aldehyde domino reaction using either two similar or two different aldehydes.
Stabilized Ru[(H2O)(6)](3+) in Confined Spaces (MOFs and Zeolites) Catalyzes the lmination of Primary Alcohols under Atmospheric Conditions with Wide…
2018
[EN] Imines are ubiquitous intermediates in organic synthesis, and the metal-mediated imination of alcohols is one of the most direct and simple methods for their synthesis. However, reported protocols lack compatibility with many other functional groups since basic supports/media, pure oxygen atmospheres, and/or released hydrogen gas are required during reaction. Here we show that, in contrast to previous metal-catalyzed methods, hexa-aqueous Ru(III) catalyzes the imination of primary alcohols with very wide functional group tolerance, at slightly acid pH and under low oxygen atmospheres. The inorganic metal complex can be supported and stabilized, integrally, within either faujasite-type …
NO reduction by CO in the presence of water over gold supported catalysts on CeO2-Al2O3 mixed support, prepared by mechanochemical activation
2007
Abstract The reduction of NO by CO was studied on gold catalysts supported on ceria-alumina, prepared by mechanochemical activation. The samples were characterized by means of XRD, TPR, XPS and Raman spectroscopy. The influence of water in the feed on the catalytic activity was evaluated as well. It was established that the addition of hydrogen and water improves NO reduction activity by CO. The role of water was connected to the hydrogen production by WGS. The role of oxygen vacancies created in ceria structure in the presence of alumina was also discussed. The 100% selectivity to N2 at about 200 8C was kept in all cases of catalytic measurements, making the studied gold catalysts promisin…
Preparation in mild conditions of photocatalytically active nanostructured TiO2 rutile
2006
Abstract Nano structured TiO 2 rutile samples were prepared in mild conditions by hydrolysis of TiCl 4 in different solutions. The powders revealed a fair photoactivity for the photoeatalytic degradation of 4-nitrophenol. The influence of preparation procedure, pH and presence of Cl − and N 3 − anions on the physicochemical features and photocatalytic activity of the powders was investigated.
Stereoselective Hydrosilylation of Enals and Enones Catalysed by Palladium Nanoparticles
2011
A highly versatile and efficient hydrosilylation method by palladium nanoparticle catalysis allows the direct and chemoselective synthesis of 1) enolsilanes of high isomeric purity, 2) saturated aldehydes or ketones, or 3) the corresponding saturated acetals from α,β-unsaturated aldehydes or ketones. The choice of the product is determined by simply switching the solvent from THF to mixtures of THF/water or THF/alcohol.
Synthesis, reactivity, crystal structures and catalytic activity of new chelating bisimidazolium-carbene complexes of Rh
2003
A series of new bridging, chelating and pincer N-heterocyclic carbenes of RhI and RhIII have been obtained under mild conditions. The compounds have been fully characterised and their crystal structures determined. The chelate-pincer coordination of the ligands means that the stability of these compounds is significantly greater than other carbene complexes of Rh. The compounds have been tested in catalytic reactions such as hydrogen transfer from alcohols to ketones, and hydrosilylation of terminal olefins and alkynes; they show a high activity for both processes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Zn,Al hydrotalcites calcined at different temperatures: Preparation, characterization and photocatalytic activity in gas–solid regime
2011
Abstract Layered double hydroxides (LDH) containing zinc and aluminium within the brucite-like layers and carbonate as the interlayer anion have been used as precursors for the preparation of mixed metal oxides by calcination. Zinc oxide and the ZnAl 2 O 4 spinel were formed with different degree of crystallinity depending of two parameters, i.e., the Zn 2+ /Al 3+ molar ratio and the calcination temperature (500–800 °C) of the LDH precursor. A pure spinel phase was obtained to remove ZnO upon a basic post-treatment in NaOH solution of the samples calcined at 800 °C. All the samples were tested for the photodegradation of 2-propanol in gas–solid regime. All the samples resulted active as het…
The Pyridyl Functional Groups Guide the Formation of Pd Nanoparticles Inside A Porous Poly(4-Vinyl-Pyridine)
2015
The reactivity of palladium acetate inside a poly(4-vinylpyridine-co-divinylbenzene) polymer is strongly influenced by the establishment of interaction between the Pd precursor and the pyridyl functional group in the polymer. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and simultaneous X-ray absorption near edge structure (XANES) and small angle X-ray scattering (SAXS) techniques have been applied to monitor the reactivity of palladium acetate in the presence of H-2 and CO as a function of temperature. H-2 reduces palladium acetate to Pd nanoparticles and acetic acid. The pyridyl groups in the polymer play a vital role both in stabilizing the formed acetic acid, thu…
Accelerated dinuclear palladium catalyst identification through unsupervised machine learning.
2021
Although machine learning bears enormous potential to accelerate developments in homogeneous catalysis, the frequent need for extensive experimental data can be a bottleneck for implementation. Here, we report an unsupervised machine learning workflow that uses only five experimental data points. It makes use of generalized parameter databases that are complemented with problem-specific in silico data acquisition and clustering. We showcase the power of this strategy for the challenging problem of speciation of palladium (Pd) catalysts, for which a mechanistic rationale is currently lacking. From a total space of 348 ligands, the algorithm predicted, and we experimentally verified, a number…
Straight Access to Indoles from Anilines and Ethylene Glycol by Heterogeneous Acceptorless Dehydrogenative Condensation.
2017
The development of original strategies for the preparation of indole derivatives is a major goal in drug design. Herein, we report the first straight access to indoles from anilines and ethylene glycol by heterogeneous catalysis, based on an acceptorless dehydrogenative condensation, under noninert conditions. In order to achieve high selectivity, a combination of Pt/Al2O3 and ZnO have been found to slowly dehydrogenate ethylene glycol generating, after condensation with the amine and tautomeric equilibrium, the corresponding pyrrole-ring unsubstituted indoles.