Synthesis of ceria-zirconia mixed oxide via sol-gel process and its applications

Abstract

Ceria-based material is widely used in automotive pollution control because it is an excellent oxygen buffer. Enhancement of its thermal stability can be achieved by introducing zirconia by many synthesis methods. Sol-gel is a versatile technique that allows high-surface-area material to be produced. The aim of the research is to synthesize high-surface-area ceria-zirconia mixed oxides by sol-gel at ambient temperature with the aim of improving the catalytic activity and suitability for environmental applications. It was found that the surface area increases with increasing ceria content, up to 90 mol%, and surface stability is enhanced with increasing zirconia content, up to 40 mol%. The CO oxidation activity was found to be related to its composition. The cubic phase mixed oxides could be reduced easier than the tetragonal phase. The highest surface area (205.6 m²/g) was achieved with Ce:Zr equal to 6:4 with aging for 10 days. Aging time has a significant effect on the texture and structure of the mixed oxides. Heat treatment affects the pore structure. The mixed oxides show good compositional homogeneity and thermal stability. Copper was added to the mixed oxides via the surfactant-aided sol-gel process. Three different CuO species-(a) highly dispersed CuO, (b) copper ion in the solid solution, and (c) bulk CuO species-were produced during the synthesis process. The highly dispersed CuO species is the active phase for CO oxidation. The introduction of 20% Ce₀.₆Zr₀.₄O₂ mixed oxides into alumina causes optimized stability, with an acceptable specific surface area at high temperature.