Synthesis of Gold Nanoparticles Catalysts Supported On Nanostructured Silica

Details

Supervisors

Hermans, Sophie

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité approfondie

Abstract

The interest in the valorization of biomass has increased significantly over the last few decades. In particular, lactose, produced in large quantities by the cheese industry, is very little or not at all valorized. Indeed, there are few direct applications due to its low potential as a sweetener and the intolerance of a large part of the population to this compound. On the other hand, several products derived from lactose have concrete applications, including lactobionic acid. Lactobionic acid is derived from the oxidation of lactose and is of interest to the pharmaceutical, cosmetic, chemical and food industries. Thus, in this study, the synthesis of materials based on gold (known for its oxidizing power) allowing to catalyze this oxidation reaction was undertaken. Three morphologies of silica supports such as full spheres, hollow spheres and hollow nanofibers were synthesized and characterized. Except for the nanofibers, SEM/TEM proved that these materials were obtained with the desired morphology. Then, gold was deposited on the solid silica spheres via various methods to obtain a wide range of particle sizes (from 9-12 to 34 nm). Wet impregnations resulted in 9-12 nm particles, wet impregnation followed by ammonia wash resulted in 34 nm particles and the colloidal method resulted in 11 nm particles. In addition, Au/h-BN catalysts were also prepared to evaluate the effect of the support. In parallel to these syntheses, a new HPLC method was developed in order to separate and correctly quantify the lactose from the lactobionic acid and also to be able to identify the different by-products obtained during the reaction. The catalytic performance of all these Au/support catalysts was evaluated. Compared to solid silica spheres, h-BN was found to be the most suitable support for this reaction. Indeed, a very small amount of lactobionic acid was produced using the Au/SiO2 catalysts, despite the use of gold particles of various sizes and the modification of the reaction conditions (catalyst mass and temperature). However, the majority product, obtained selectively (≥ 80%), was identified as lactulose, derived from the isomerization of lactose in basic media. This product also has pharmaceutical applications which makes it a product of interest and opens future perspectives to this work.