Jean Sommer

Conversion of butane over the solid superacid ZrO2/SO42− in the presence of hydrogen

The conversion of n-butane to isobutane on the solid superacid ZrO2/SO42− has been studied in a microflow reactor in a helium/hydrogen stream at constant hydrocarbon pressure under kinetic-controlled conditions. The effect of the partial pressure of hydrogen indicates a dual role for this component, namely that it is an inhibitor at high partial pressure, but is essential for maintaining the catalyst activity. The presence of platinum to maintain the catalyst activity is not necessary if the hydrogen pressure is high enough.

Copper(I) Zeolites as Heterogeneous and Ligand‐Free Catalysts: [3+2] Cycloaddition of Azomethine Imines

Copper(I)-exchanged zeolites were used as heterogeneous ligand-free catalysts for [3+2] cycloaddition of azomethine ylides, which allows versatile, efficient, and highly regioselective synthesis of pyrazolone derivatives. These cheap and easy-to-prepare catalysts exhibit wide scope and compatibility with functional groups. They are very simple to use, easy to remove (by simple filtration), and recyclable (up to six times without loss of activity).

Conversion of butane over the solid superacid ZrO sub 2 /SO sub 4 sub 2 minus in the presence of hydrogen

The conversion of n-butane to isobutane on the solid superacid ZrO2/SO42− has been studied in a microflow reactor in a helium/hydrogen stream at constant hydrocarbon pressure under kinetic-controlled conditions. The effect of the partial pressure of hydrogen indicates a dual role for this component, namely that it is an inhibitor at high partial pressure, but is essential for maintaining the catalyst activity. The presence of platinum to maintain the catalyst activity is not necessary if the hydrogen pressure is high enough.

Quantitative Determination of Brönsted Acid Sites on Zeolites: A New Approach Towards the Chemical Composition of Zeolites

An original quantitative method based on H/D exchange between H2O/D2O molecules and the OH groups of different zeolites has been developed for the titration of the Brönsted acid sites present on the solid surface. The measured Brönsted acid sites density appears to be in good agreement with the theoretical amount estimated by the Si/Al ratio. In contrary to classical methods, this non-destructive anhydride method titrates the whole quantity of Brönsted acid sites of zeolites.

Activation of small alkanes on strong solid acids : mechanistic approaches

Abstract Various mechanistic aspects of small-alkane transformations on strong solid acids or superacids are developed in light of recent experiments involving isotope distribution patterns in 13C-labelled alkanes and protium/deuterium exchange between alkanes and D2O-exchanged catalysts. In comparison with experiments using liquid superacids, similarities and differences in hydrocarbon chemistry between the two types of catalysts are discussed as well as the initial steps leading to catalyst deactivation.

Fluoroanions and cations in the HF–SbF5 superacid system. A 19F and 1H NMR study

The ionic composition of the HF–SbF5 superacid system has been investigated by 1H and 19F high field NMR. The anionic distribution over the whole composition range could be directly calculated from the 19F NMR spectra. The cationic distribution was then estimated on the basis of charge balance. When the concentration of SbF5 in HF was higher than 20 mol%, increasing amounts of nonassociated SbF5 appeared. This change in composition can be linked to the change in reactivity of the superacid system in the activation process of small alkanes.

The H/D exchange reaction occurring at low temperature between small alkanes and D2O exchanged solid acids. III. The role of alkenes and carbenium ions as reaction intermediates

Abstract The intermolecular protium-deuterium exchange occurring between isobutane and D 2 O-exchanged acidic catalysts, such as sulfated zirconia and H-Beta zeolite, has been studied in the low temperature range: 20–200°C. The induction period, which is apparent at 100°C and below, is suppressed when small amounts of isobutene are added to isobutane. The results are discussed with respect to the formation of alkene intermediates from alkanes at low temperature on an acidic catalyst.

Alkane Activation over Acidic Zeolites: The First Step

The heterogeneous acid-catalyzed activation step of alkanes leading to the reaction intermediates (carbocationic or alkoxy species) was up to now the matter of a longstanding controversy. Gas chromatography and online mass spectroscopy measurements show that H(2) and methane are formed over H-zeolites, whereas HD and CH(3)D are formed over D-zeolites as the primary products in the reaction with isobutane. These results indicate that sigma-bond protolysis by strong acid sites is the first step for hydrocarbon activation on these catalysts at mild temperatures (473 K), in analogy to the activation path occurring in liquid superacid media.

ScIII-Doped Zeolites as New Heterogeneous Catalysts: Mukaiyama Aldol Reaction

Sc(III)-doped solids based on zeolite materials have been investigated for the first time as catalysts in organic synthesis. Sc(III)-USY zeolite proved to be a novel and very efficient heterogeneous catalyst for the Mukaiyama aldol reaction. This easy-to-prepare catalyst exhibited wide scope and compatibility with functional groups and is very simple to use, easy to remove (by simple filtration), and is recyclable (up to three times without loss of activity).

Formation of Carboxylic Acids from Small Alkanes in Zeolite H‐ZSM‐5

The activation of propane and isobutane in acidic zeolite H-ZSM-5 in the presence of both CO and H2O has been studied by in situ solid-state NMR and GC analysis. Evidence was provided for the conversion of propane to isobutyric acid at 373-473 K by cleavage of the C-C bond; methane and ethane are also produced. Isobutane is transformed into pivalic acid with simultaneous production of hydrogen. The low conversion (1-2%) at this temperature was rationalized by the existence of a small number of sites that are capable of generating carbenium ions which are trapped by CO at this temperature. A formate species was observed when CO and H2O were present on H-ZSM-5. This species disappeared in the presence of the alkane. At 573 K, the generation of large amounts of CO2 indicates a much higher conversion of the alkanes into carboxylic acids which, however, decompose under the reaction conditions.