• PDF / 509,274 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 65 Downloads / 211 Views

DOWNLOAD

REPORT

---

lame spray pyrolysis (FSP) has been used to synthesize high-surface-area ceria from cerium acetate in acetic acid solution. With the addition of an iso-octane/2-butanol mixture to that solution, homogeneous CeO2 nanoparticles were obtained. The specific surface area of the powders ranged from 240 to 101 m2/g by controlling the oxygen dispersion and liquid precursor flow rates through the flame. Furthermore, for production rates from 2 to 10 g/h a constant average primary particle size could be obtained at selected process parameters. The ceria showed high crystallinity and primary particles with a stepped surface. The powder exhibited good thermal stability and conserved up to 40% of its initial specific surface area when calcinated for 2 h at 900 °C. This shows the potential of FSP made ceria for high-temperature applications as in three-way catalysts or fuel cells.

I. INTRODUCTION

Ceria-based materials play a key role as an active component in the three-way catalyst for automotive exhaust gas treatment. Therefore, they have been extensively studied for their catalytic as well as special electronic and structural properties leading to a wealth of scientific contributions.1 One of the main goals is to lower the temperature required for oxygen diffusion through the material, which would lead to higher efficiency at lower temperatures.2 Therefore, ceria with enhanced textural and thermal properties and particularly with high specific surface area is sought. Various wet-chemical preparation methods have been used for its synthesis such as precipitation,3,4 hydrothermal synthesis,5,6 microemulsions,7,8 and surfactantassisted precipitation9 to name just a few. In most of the studies, powders with specific surface areas less than 100 m2/g were made. The relative loss of surface area at temperatures as low as 1000 K is a general drawback of those methods.10 This decrease in total surface area can be reduced by doping with transition metals like zirconium.11 Recently mesoporous ceria of high specific surface area (200 m 2 /g) with improved resistance to sintering (40 m2/g at 1173 K) was made by a surfactantassisted precipitation.9 The improvement was mainly attributed to the structural arrangement and morphology. Gas-phase (aerosol) technology provides an alternative route for the synthesis of high-surface-area ceria at high temperatures as it has been used to make a variety

a)

http://journals.cambridge.org

II. EXPERIMENTAL

The experimental apparatus of FSP is described in detail by Ma¨dler et al.20 According to this, the spray flame itself forms the reaction zone consisting of small evaporating and subsequently burning droplets which often leads to gas-phase synthesis of the desired product.

Address all correspondence to this author. e-mail: [email protected]

1356

of oxide nanoparticles.12 Spray pyrolysis of an aqueous solution of cerium nitrate at 400 °C resulted in hollow spheres with variable size and inhomogeneous surface with particle diameters between 100 and 2000 nm.13 Suzuki et al.14 prepared poly