A surface science approach to understanding emission control catalyst deactivation due to sulfation of ceria-zirconia mixed-metal oxides.

摘要

Cerium and zirconium oxides are materials that have unique catalytic properties and are finding many applications in industrial catalysis. Particularly, the great advances attained in the past 30 years in curbing the amount of gaseous pollutants released can be attributed to the development of catalysts employing such materials. However, oxides of sulfur are known poisons of many catalytic systems and are encountered in many commercial applications.;In this investigation, polycrystalline ceria-zirconia solid solutions of various molar ratios were synthesized. High resolution x-ray photoemission spectra were obtained and examined to reveal the surface species that form on these metal oxides after exposure to sulfur dioxide under various conditions. The model catalysts are exposed to sulfur dioxide using an in-situ high-pressure reaction cell. A reliable sample platen heater was designed to allow the observation of any temperature dependency up to 673 K. The results of this study demonstrate the formation of sulfate and sulfite adsorbed sulfur species. Temperature and compositional dependencies are also displayed, with higher temperatures and ceria mole fractions displaying a larger propensity for the formation of surface sulfur species.