Synthesis and catalytic application of ceria nanoparticles and ceria-SiC composites
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1217-Y09-07
Synthesis and catalytic application of ceria nanoparticles and ceria-SiC composites Christian Schrage1, Emanuel Kockrick2 and Stefan Kaskel1 1 Dresden University of Technology, Mommsenstraße 6, Dresden, 01062, Dresden. 2 Institut de recherches sur la catalyse et l’enviroment de lyon, 2 avenue Albert Einstein, 69626 Villeurbanne cedex, France. ABSTRACT The synthesis of ceria nanoparticles using an inverse microemulsion technique and precipitation method was investigated. Ceria nanoparticles were synthesized by adding diluted ammonia to a microemulsion consisting of n-heptane, Marlophen NP5 and cerium nitrate. The micelle and particle size were adjustable in the range of 5-12nm by varying the molar ratio of water to surfactant and analyzed by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM). After isolation through precipitation, the nanoparticles were subsequently treated at 100-600 °C. The catalytic activity of particles annealed at 400 and 600 °C were tested in soot combustion reactions and characterized by temperature-programmed oxidation (TPO) indicating a size-dependant activity. To prevent the nanoparticles from aggregation, the microemulsion technique was adopted to integrate the nanoparticles homogeneously into a mesoporous SiC matrix through the use of a preceramic polymer. The obtained composite material was also tested in soot combustion reactions. INTRODUCTION Nanostructured inorganic particles are promising systems as oxidation catalysts due to the high surface to volume ratio. Especially, systems containing nanoscaled ceria are very attractive three-way catalysts for soot combustion reactions and were reported by several groups [1,2]. The reason for the catalytic effect is oxygen donation of ceria caused by partial reduction of Ce4+ to Ce3+ on the surface of catalyst particles [3]. Several methods were developed for the preparation of ceria nanoparticles, such as chemical vapor deposition routes [4], flame spray pyrolysis [5], precipitation synthesis [6,7] and template-assisted techniques in ordered mesoporous silica [8,9]. Also various microemulsion techniques were developed for the synthesis of nanoscaled ceria [10,11]. The challenge for the preparation of highly active nanoscale catalysts is a high dispersion and the accessibility of active centers on a support. In the following, we describe, one the one hand, the direct preparation of ceria nanoparticles using a microemulsion-precipitation technique to evaluate size dependency on the catalytic activity. One the other hand, the nanoparticles were integrated into a mesoporous SiC ceramic using a carbosilane precursor as a compound of the microemulsion. A microemulsion is a ternary, thermodynamic stable system consisting of a non-polar oil phase, a surfactant and a polar phase forming nanoscaled aqueous phases, dispersed in a continuous oil phase [12, 13]. The micelle size can be precisely defined by the molar water to surfactant ratio (RW-value). Inside these
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