Antoine Demortier

On the understanding of the reduction of sulfur (S8) in dimethylformamide (DMF)

Abstract We have re-examined, using cyclic voltammetry, the electrochemical reduction of sulfur in DMF. The main purpose of this work is the determination of the electrochemical mechanism of this reduction and the identification of the opening step of the ring S8. We propose the following electrochemical mechanism which neglects the weak disproportionation of S82−: S 8 c + e − ⇄ S 8 c - ( E c ) S 8 c - ⇄ S 8 1 - ( K 1 ) S 8 1 - + e − ⇄ S 8 1 2 - ( E 1 ) a n d E 1 > E c S 8 c - + S 8 1 - ⇄ S 8 c + S 8 1 2 - ( K 2 = exp ⁡ [ ( F / R T ) ( E 1 − E c ) ] ) This mechanism (ECE) takes into account the ring character (c) of sulfur in the solution and the linear character (1) of the S82− polysulfide. It has been simulated and adjusted to the experimental data in a wide range of temperatures (233 to 313 K) and scan rates (50 to 2000mV s−1). We shall discuss the choice of this mechanism and the results.

Infrared evidence for the formation of an intermediate compound during the synthesis of zeolite Na–A from metakaolin

Abstract Quantitative Infrared spectroscopy has been used to study the first step of the hydrothermal formation of zeolite Na–A from metakaolin. It is shown that metakaolin reacts with aqueous NaOH solutions, at room temperature, to give an amorphous solid, characterised by its IR spectrum. This compound, that has the same overall composition as zeolite Na–A must be regarded as the precursor of zeolite. At 60°C, the IR spectra show that the precursor is first synthesised and that zeolite Na–A is formed only when metakaolin has been totally transformed. The formation of the precursor corresponds to the induction period observed by several authors when X-ray diffraction is used to follow the synthesis.