Evaluation of sol-gel methods for the synthesis of doped-ceria environmental catalysis systems - Part II. Catalytic activity and resistance to thermal aging

Nanophase calcia-doped-ceria-based washcoats with the molar composition (CeO)(0.25)(CaO)(0.02)(Al2O3)(0.73)/(Pd, Rh), deposited on ceramic honeycombs via sol-gel methods were evaluated with respect to catalytic activity for hydrocarbons conversion and thermal aging. With the proper synthesis and deposition route, such systems were tailor-made with a meso-porous structure similar to that of commercial catalysts and with significant resistance to pore collapse and surface area loss upon thermal aging. All the prepared nanophase systems exhibited low light-off temperatures (in the range 500-550 K) achieved with half the amount of washcoat and half the amount of noble metals compared to currently available commercial catalysts. The performance of these systems was found to depend strongly on the deposition method (directly from the sol or from suspensions of sol-gel derived powders), on the type of precursor used for preparing the starting sols (metallo-organic or inorganic) and on the method used to insert the noble metal(s) in/on the washcoat. The performance and thermal stability of some of these systems makes them excellent candidates for three-way automotive catalysis, with a very low quantity of noble metals. (C) 2001 Elsevier Science B.V. All rights reserved.