Valérie Meille

Gas–liquid and gas–liquid–solid catalysis in a mesh microreactor

A microstructured mesh contactor that can offer residence time of more than minutes is used for gas-liquid-solid hydrogenations and gas-liquid asymmetric hydrogenations. Applications for catalyst/chiral inductor screening and for kinetic data acquisition are demonstrated.

Hydrodesulfurization of 4-methyl-dibenzothiophene: a detailed mechanistic study

A mechanism for the transformation of alkyl-dibenzothiophenes by hydrodesulfurization (HDS) on a NiMo catalyst is proposed. 4-Methyl-dibenzothiophene (4-MDBT) (1) has been chosen as a model for this study because this non-symmetrical molecule leads to the formation of a great variety of intermediates. Thanks to the synthesis of these compounds, a detailed study of the reaction course by the observation of the relative concentrations of intermediate products was realized. The results are consistent with adsorption of the molecules via the aromatic system, parallel to the catalyst surface, as proposed previously. The formation of a dihydrogenated intermediate is followed by successive hydrogenation or elimination steps. The rates of these reactions are dependent on the location of the methyl substituent and hence on the generated sterical hindrance. The relative amount observed in each compound is in total accordance with this mechanistic proposal.

A new route towards deep desulfurization: selective charge transfer complex formation

An alternative to the classical hydrodesulfurization process is proposed, based on the formation and subsequent removal of insoluble charge-transfer complexes between suitable π-acceptors and alkylated dibenzothiophenes.

A solid iridium catalyst for diastereoselective hydrogenation

An Ir(NHC) supported catalyst is used in the selective hydrogenation of terpinen-4-ol to cis p-menthan-4-ol. Its activity, selectivity and stability are compared to those of a homogeneous homologue [IrCl(COD)MesImPr] and to a commercial Pd/C. The solid Ir catalyst is much more selective than the Pd catalyst (92 vs. 42 % at 80 °C) but also more active, more selective and more stable than the iridium complex in solution. For the first time, a supported catalyst shows an enhanced activity with respect to a complex in a diastereoselective hydrogenation reaction.