Microwave assisted syntheses of stable solvent based colloidal sols of tailored ceria nanoparticles
Olivier Poncelet*, Julien Jouhannaud*, Denis Chaumont**
*CEA Liten DTNM/L2T , 17 rue des Martyrs F-38054 Grenoble Cedex9, France
**Institut Carnot Bourgogne (ICB), UMR5209 CNRS, Facult� des Sciences Mirande, Universit� de Bourgogne, 9 Av. Alain Savary, BP 47870, F-21078 Dijon Cedex
The pressure of environmental laws in many advanced countries becoming more restricting year after year, it is asked to automobile companies to strongly control the carburant consumption of cars that they put on the market and also to eliminate toxic chemicals coming from exhaust emission gases. This is particularly true for diesel oil which is particularly efficient in terms of carburant consumption but known to release toxic chemicals in exhaust gases. Among the materials able to solve these concerns, ceria (CeO2) is a choice catalyst because it can work in two different ways first as an oxygen store by release of oxygen in the presence of reductives gases (CnHn and CO), and also by removing oxygen by interaction with oxidising species (NOx), leaving finally in exhaust gases H2O, CO2 and N2.
To be efficient ceria has to be used under nanoparticle form directly added in the diesel oil. The surface developed by the nanoparticles due to their small size positively influence the catalytic properties (both oxidation and reduction step) in terms of kinetic, so the ignition delay time for nanosized particles in the combustion chamber of diesel motors fits well with the high performance diesel motor characteristics. The true challenge is to be able to prepare stable solvent based sols of crystalline ceria nanoparticles which could be used without plugging the injection nozzles. We present various synthetic ways to produce ceria nanoparticles in water followed by their surface modification allowing stable colloidal sols in organic medium to be designed. We emphasize more particularly the microwave assisted synthesis which by enhancing nucleation of the nanosized particles versus growth of nanoparticles allows very narrow sized distribution of nanoparticles to be obtained. Moreover in terms of synthetic processes, microwave assisted syntheses allow to strongly reduced the synthetic time without compromise in terms of cristallinity (TEM and XRD). Surface modifications of the nanoparticles have been monitored by FT-IR, FT-Raman, while their sizes have been monitored by DLS (differential light scattering) from water to solvents suspension proving the efficiency of ether carboxylic acids as surface modifiers. Finally we will show preliminary results on the microwave assisted syntheses of mixed oxides materials (CeZrOx) and the way to design organic based sols of nanoparticles.