Materials Science and Chemistry

Biography

Biography: Alain Demourgues

Abstract

In the last 20 years, intense efforts deal with the environmental impact decrease of the automotive exhaust gases. Highly severe regulations led to the design of new materials for CO, unburned hydrocarbons oxidation and for the NOx reduction from industrial sources, especially from diesel automotive engines. Diesel oxidation catalysts (DOC) have then been developed to oxidize CO, hydrocarbons and NO, in order to reach the NO₂/NOx ratios suitable for the downstream system of selective catalytic reduction (SCR) of NOx by ammonia. Therefore, rare-earth oxides (REO) involving mixed valence states such as Ce⁴⁺/Ce³⁺, Pr⁴⁺/Pr³⁺ and Tb⁴⁺/Tb³⁺ exhibit the best acid, basic and redox properties (with high oxygen availability and mobility) to fulfill the requirements of enhanced catalysts. Considering that Tb₄O₇ is too expensive for extended industrial applications, the objective is to finely tune the composition, structure, texture, oxygen mobility and storage of Ce/Pr/Zr based oxides to design effective and robust catalysts for DOC and SCR. Recent studies have evidenced that a fine tuning of some chemical CeO₂-ZrO₂-Pr₆O₁₁ compositions can stabilize Pr⁴⁺/Pr³⁺ rates associated with oxygen vacancies leading to high OSC, oxygen mobility, thermal stability up to 1400ºC and surface areas varying between 80 and 40 m²/g at 700ºC. Moreover, preliminary catalytic results for DOC application revealed outstanding properties without any PGM (platinum group metal). Neutron and X-ray diffraction analysis during the redox cycle reveal the occurrence of oxygen vacancies ordering depending on the Pr⁴⁺/Pr³⁺ and Ce⁴⁺/Ce³⁺ atomic ratios determined by magnetic measurements and XANES analysis.