Alfonso Sáez

Electrosynthesis of L-Cysteine on a Dispersed Pb/Carbon Black Electrode

The electrosynthesis of L-cysteine (RSH) in aqueous medium has been investigated using Pb particles dispersed on carbon as a cathode for L-cystine electroreduction. Pb particles were synthesized in a water-in-oil microemulsion and later dispersed on carbon Vulcan XC-72. The electrochemical characterization of the Pb/C catalyst was carried out by cyclic voltammetry and scanning electrochemical microscopy (SECM). In particular, an approach of the substrate generation/tip collection mode of the SECM has been used for imaging the RSH generation. Different 20 wt % Pb/C-supported cathodes have been fabricated and morphologically characterized. These cathodes were tested for RSH electrosynthesis and compared with a conventional bulk Pb cathode. After a 100% theoretical charge, our three-dimensional 20 wt % Pb/C cathode exhibits a 30% higher RSH yield and current efficiency than the other cathodes. This performance improvement is related to the increase in the available geometric area of this electrode. We demonstrate the feasibility of using Pb/C particles as a catalyst in a type of cathode for RSH electrosynthesis. Moreover, our Pb/C electrodes show a broad scope because they can be applied to other electrosyntheses of valuable organic compounds where bulk Pb is the conventional cathode at present.

An alternative to hydrogenation processes. Electrocatalytic hydrogenation of benzophenone

The electrocatalytic hydrogenation of benzophenone was performed at room temperature and atmospheric pressure using a polymer electrolyte membrane electrochemical reactor (PEMER). Palladium (Pd) nanoparticles were synthesised and supported on a carbonaceous matrix (Pd/C) with a 28 wt % of Pd with respect to carbon material. Pd/C was characterised by transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Cathodes were prepared using Pd electrocatalytic loadings (LPd) of 0.2 and 0.02 mg cm−2. The anode consisted of hydrogen gas diffusion for the electrooxidation of hydrogen gas, and a 117 Nafion exchange membrane acted as a cationic polymer electrolyte membrane. Benzophenone solution was electrochemically hydrogenated in EtOH/water (90/10 v/v) plus 0.1 M H2SO4. Current densities of 10, 15 and 20 mA cm−2 were analysed for the preparative electrochemical hydrogenation of benzophenone and such results led to the highest fractional conversion (XR) of around 30% and a selectivity over 90% for the synthesis of diphenylmethanol upon the lowest current density. With regards to an increase by ten times the Pd electrocatalytic loading the electrocatalytic hydrogenation led neither to an increase in fractional conversion nor to a change in selectivity.