Etude de l’effet de support sur l’activité Catalytique de nanoparticules d’Or.

Abstract

This thesis is devoted to the study of the support effect on the catalytic activity of gold nanoparticles. The precursor of the catalyst supports used is a Bentonite-type clay from the Maghnia (Algeria). It has been modified in different ways: purification (Na-B) without further treatment, activation by an acid (H-B) and bridging by transition metals such as aluminum (Al-B) and iron (Fe-B). These treatments improve the redox properties and increase Lewis and Brønsted acidity. These materials were used as supports for gold nanoparticles: Au/Na-B, Au/Al-B, Au/Fe-B and Au/H-B. They were then characterized by several spectroscopic, electronic and physicochemical methods (UV-vis RD, FTIR, DRX, SEM, MET, BET and measurement of acidity of solids using a probe molecule followed by FTIR,). The catalytic performances of the supports alone and the gold deposited over the different materials were evaluated in the oxidation reaction of cyclohexene by hydrogen peroxide in the liquid phase without solvent in the order to developpe a one-pot synthesis of adipic acid. The characterization results showed that the size and distribution of gold particles depends strongly on the support treatment Na-B, Al-B Fe-B and H-B. The study also showed that the optimization of the various gold deposition parameters (pH, nature of the precipitating agent, mode of heat treatment) makes it possible to control the average size of the particles and in particular the obtaining of nanoparticles of 'Gold. In addition, the acidity measurements of the Au/support catalysts made it possible to establish the order of the strength of acid sites as follow: 1%Au/Al- ˃1% u/H ˃1% u/Na-B. The results of the catalytic tests show that gold had a beneficial effect on the activity of the different bentonites. Moreover, excellent selectivities in adipic acid were obtained particularly with the 1% Au/H-B catalyst where a selectivity of 75% was reached with a conversion of 100%.