Use of CeO2-based oxides in the three-way catalysis

Automotive catalytic converters: current status and some perspectives

The utilization of ceria in industrial catalysis

Some recent results on metal/support interaction effects in NM/CeO2 (NM: noble metal) catalysts

Nanostructured CeO2–ZrO2 mixed oxides have attracted great interest in the past 10 years, in particular as redox or oxygen storage promoters in the three-way catalysts. However, it has now became clear that both the chemistry of the simple oxides and the complex metal–CeO2-based oxide interactions can play a critical role in developing novel and highly active materials for a number of processes, ranging from catalysts for H2 production from fuels up to ceramic materials and solid state conductors for fuel cells. Despite the apparent simplicity of these systems, extreme variability of their chemical and textural properties has been observed. An attempt is made here to rationalise the various factors and the inter-connections to the structure, the texture, and the effects of the nanometre scale, which all contribute to the properties of these materials.

Nanostructured CeO2–ZrO2 mixed oxides

The influence of a reducing atmosphere on the thermal stability of CeO2 was studied on a high surface area ceria sample (115 m2 g−1) treated 2 h under hydrogen or carbon monoxide at various temperatures between 673 and 1123 K. Comparative experiments were done under air or vacuum, and also in presence of water or carbon dioxide in order to estimate the relative importance of the reduction products. An important decrease of the specific surface area was observed between 850 and 1000 K under air, vacuum, carbon monoxide or water pressure, the residual BET area being below 10 m2 g−1 at 1100 K. Under hydrogen, the same loss of surface was obtained at ca. 150 K lower temperatures. In all cases, the first step was the elimination of the microporosity followed by the growth of the crystallites. The peculiar influence of hydrogen was related to the high concentration of lattice oxygen vacancies created during the reduction of the bulk. In the case of carbon monoxide atmosphere which also reduces the sample, the carbonate species formed during the reduction are eliminated from the bulk at higher temperatures, which explain the better resistance to sintering compared to hydrogen. This was confirmed by a treatment under carbon dioxide atmosphere which was found to preserve the specific surface area better because of the stabilization of the carbonate species on the ceria.

G. Blanchard

Papers

Thermal stability of a high surface area ceria under reducing atmosphere