Search results for "hydrogenation"
showing 10 items of 155 documents
Selective Oxidation of n-Butane and Butenes over Vanadium-Containing Catalysts
2000
Abstract The oxidative dehydrogenation (OXDH) of n-butane, 1-butene, and trans-2-butene on different vanadia catalysts has been compared. MgO, alumina, and Mg–Al mixed oxides with Mg/(Al+Mg) ratios of 0.25 and 0.75 were used as supports. The catalytic data indicate that the higher the acid character of catalysts the lower is both the selectivity to C4-olefins from n-butane and the selectivity to butadiene from both 1-butene or trans-2-butene. Thus, OXDH reactions are mainly observed from n-butane and butenes on basic catalysts. The different catalytic performance of both types of catalysts is a consequence of the isomerization of olefins on acid sites, which appears to be a competitive reac…
Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation
2013
Hyperpolarization has found many applications in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, its usage is still limited to the observation of relatively fast processes because of its short lifetimes. This issue can be circumvented by storing the hyperpolarization in a slowly relaxing singlet state. Symmetrical molecules hyperpolarized by Parahydrogen Induced Hyperpolarization (PHIP) provide a straightforward access to hyperpolarized singlet states because the initial parahydrogen singlet state is preserved at almost any magnetic field strength. In these systems, which show a remarkably long 1H singlet state lifetime of several minutes, the conversion of t…
Fractal-like Hierarchical CuO Nano/Microstructures for Large-Surface-to-Volume-Ratio Dip Catalysts
2022
Dip catalysts are attracting interest in both academia and industry for catalyzing important chemical reactions. These provide excellent stability, better recoverability, recyclability, and easy scale-up. Using the unique microstructures of leaf skeletons, we present a fractal-like hierarchical surface that can be used as a versatile and efficient dip catalyst. Copper oxide microcactuses with nanoscalar features were fabricated onto the Bauhinia racemosa leaf skeletons via a combination of physical vapor deposition, electroplating, and chemical oxidation methods. The coated leaf skeletons have a very high surface area, and the three-dimensional (3D) morphology allows the reactants to encoun…
Insights into the catalytic production of hydrogen from propane in the presence of oxygen: Cooperative presence of vanadium and gold catalysts
2015
7 figures.-- © 2015. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Evolution of the optimal catalytic systems for the oxidative dehydrogenation of ethane: The role of adsorption in the catalytic performance
2022
Three samples that correspond to the evolution of optimal catalytic systems for the oxidative dehydrogenation of ethane have been synthesized and compared in terms of catalytic behavior and adsorption properties: (i) vanadium oxide supported on alumina, (ii) Sn-promoted NiO, and (iii) multicomponent MoVTeNbO with the M1 structure. The main difference in catalytic performance lies in the extent of the overoxidation of the ethylene formed, following the order VOx/Al2O3 > NiSnOx > MoVTeNb-M1. Accordingly, the selectivity to ethylene at medium and high ethane conversion follows the order MoVTeNb-M1 > NiSnOx > VOx/Al2O3. These results are confirmed by the relative reaction rates observed for the…
Effect of silver deposits on the photocatalytic activity of titanium dioxide samples for the dehydrogenation or oxidation of 2-propanol
1991
Abstract Until now, the effect of the deposition of metal particles onto a powdered semiconductor oxide on its photocatalytic activity has been determined for group VIII transition metals only. In this study, AGTiO2 samples were prepared by photodeposition, characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) and tested, under band-gap illumination, using the oxidation of 2-propanol (neat liquid phase or mixed with water) in the absence or presence of molecular oxygen. The silver deposits were found to be metallic both before and after use, but the size of the particles and their distribution on the support were markedly influenced by the type …
Redox and Catalytic Properties of Promoted NiO Catalysts for the Oxidative Dehydrogenation of Ethane
2017
[EN] NiO and metal-promoted NiO catalysts (M-NiO, with a M/(M+Ni) atomic ratio of 0.08, with M = Nb, Sn, or La) have been prepared, tested in the oxidative dehydrogenation (ODH) of ethane, and characterized by means of XRD, TPR, HRTEM, Raman, XPS, and in situ XAS (using H-2/He, air or C2H6/He mixtures). The selectivity to ethylene during the ODH of ethane decreases according to the following trend: Nb NiO Sn NiO > La NiO > NiO, whereas the catalyst reducibility (determined by both TPR and XAS using H-2/He mixtures) shows the opposite trend. However, different reducibility and catalytic behavior in the absence of oxygen (ethane/He mixtures) have been observed, especially when comparing Nb- a…
Modular P-Chirogenic Aminophosphane-Phosphinite Ligands for Rh-Catalyzed Asymmetric Hydrogenation: A New Model for Prediction of Enantioselectivity
2007
An original series of P-chirogenic aminophosphane-phosphinite (AMPP) ligands has been synthesized from (+)- or(–)-ephedrine in 23 to 61 % overall yields by a versatile three-step methodology. The AMPP ligands, bearing either one or two P-chirogenic centers, were used in the form of rhodium complexes for the catalyzed hydrogenation of α-acetamidocinnamate as a test reaction. Notably, even with AMPP ligands all derived from (+)-ephedrine, variation of the substituent on a P-center allowed the phenylalanine derivatives to be obtained in either (S) or (R) absolute configurations, with ee values ranging from 99 % (S) to 88 % (R). The asymmetric induction was analyzed with the aid of X-ray struct…
Computational study of metal-free N-doped carbon networks as hydrogenation catalysts
2015
The future development and assesment of an industry more environmental friendly will include the use of metal-free catalysts. Most of the reported metal-free catalysts are homogeneous and often their recycle is difficult; therefore, develop and investigate them is of interest both theoretical and experimental. Recently, N-doped nanotubes and graphene sheets, were synthesized [1,2], and it was demonstrated that the incorporation, within these carbon structures, of nitrogen atoms causes a greater electron mobility and introduces more active sites for catalytic reactions. This investigation is aimed at elucidating the main features of the hydrogen fragmentation over these carbon frameworks. Se…
Cyclodextrines confinantes : synthèse, propriétés complexantes et utilisation en catalyse asymétrique
2014
This manuscript is concerned with the design of novel catalytic systems derived from metallocyclodextrins. The first part describes new ways of functionalising the cyclodextrin primary face regioselectively for accessing inherently chiral P,P’ chelators. These heterodentate ligands gavequantitatively cis-chelate complexes with various d8 cations. Their rhodium(I) complexes were assessed in the asymmetric hydrogenation and hydroformylation of prochiral olefins. Thecoordination and catalytic properties of two phosphines derived from a- and b-cyclodextrin are also reported. With their phosphorus lone pair pointing toward the CD core, these confining ligands force the coordinated metal centre t…