Résumé
Automotive catalytic converters are composed of a stainless steel casing incorporating a metallic or ceramic honeycomb structure impregnated with a slurry containing the catalyst precursors (washcoat). The catalyst precursors are generally composed of (Ce,Zr)O2 mixed oxides as oxygen storage promoters on which fine noble metal particles (Pt, Pd, Rh; or PGM for platinum group metals) are previously dispersed.[1] Due to their versatile applications and the more stringent gas emission legislation, PGM demand is continuously increasing in opposition to the related weakening natural resources. The reprocessing of PGM from spent catalysts is thus gaining more interest and can be currently performed through hydro- or pyrometallurgical processes involving drastic conditions and concentrated reactants. Although efficient, such methods are known to be energy and time consuming, not environmentally friendly, and highly corrosive towards equipment. Selective ceria-based oxide dissolution can represent a promising alternative for the recycling of catalytic converters; such a route could allow the soft release of PGM from the honeycomb matrix and their subsequent recovery by simple separation methods such as centrifugation or filtration. To the best of our knowledge, CeO2 dissolution has been poorly described in the literature. It is a highly refractive material towards dissolution and its proton-promoted dissolution is not thermodynamically favourable (ΔrG°= 40 kJ.mol-1). However, in agreement with the high redox potential for Ce(IV)/Ce(III) couple (1.4 V/SHE), reductive dissolution ofceria can be considered.