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ABSTRACT

 

Over the past decade, carbon materials have attracted a great deal of attention in a wide range of applications of technological importance. Thus in catalysis, a growing interest has emerged for the synthesis by nano-replication technique, owing to the attractive characteristics of the resulting materials, i.e. high surface areas, narrow pore size distributions, controlled pore shapes and volumes. Generally, its principle involves the preparation of the silica template and filling of the silica pores with an appropriate carbon precursor followed by its carbonization and removal of the silica framework.

The aim of the project CYCLOMAT lies within this framework and deals with the synthesis by nano-replication of metal carbon catalysts, in which metallic nanoparticles of gold or platinum will be embedded onto the surface of ordered mesoporous carbons. Two metals retain our attention, i.e. gold and platinum. Our project is based on the systematic use of cyclodextrins as promoting agents. Cyclodextrins are water soluble cyclic oligosaccharides formed of n glucopyranose units exhibiting a hydrophobic internal cavity that can host a large variety of molecules and a hydrophilic exterior surface thanks to the presence of a large number of hydroxyl groups. In the present case, the cyclodextrins are used with a threefold purpose: i) as carbon sources to stabilize the carbon architecture ii) as metal complexing agents (in the form of host-guest complexes or supramolecular adducts) to stabilize the metal precursors and iii) as polyhydroxylated molecules favoring the dispersions of the cyclodextrin-metal complexes on the silica walls.

Figure 1

This strategy is developed with the aim of developing a new generation of tolerant and robust catalysts with a minimum of agglomeration and metal leaching. Through this self-assembly approach, it is also expected that, during catalysis, the chemical transformations occur in confined media (pore), where the restricted molecular organization can lead to higher reactivities. To validate our concept, we have chosen to study the catalytic oxidation of 5-hydroxy-2-methylfurfural (HMF) in aqueous medium phase as the model reaction. This reaction constitutes a strategic challenge to replace key petroleum-based building blocks, by opening an access to the formation of 2,5-furandicarboxylic acid, which is a potential substitute of terephthalic acid and may be used as polymer precursor. In parallel, the synthesis and characterization of control carbon-based catalysts prepared by nanoparticles deposition and by conventional methods are also realized for comparison. The performances of these control catalysts are studied in the same reaction to evaluate the true effectiveness of the nano-replicated catalysts synthesized from cyclodextrins.

Finally, the topics developed during this three-year program fits with the P2N “Nanotechnology and Nanosystems 2011 (axe thématique 1: synthèse et fabrication de nanomatériaux et chimie en milieu confiné). To reach our objectives, we gather the scientific skills of two well known laboratories: 1) the UCCS-Artois, which brings their background in the supramolecular and cyclodextrin chemistry and synthesis of nano-replicated materials and 2) the IRCELYON specialized in the design of heterogeneous catalytic processes in water.

 

 

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