Biology and the Environment

Since the 1980s, catalytic antipollution systems for petrol-fuelled vehicles have considerably reduced emissions of CO, NO _x , and unburnt hydrocarbons. They use precious metals as catalyst on a hybrid support made from alumina and a mixture of cerium oxide and zirconium oxide, sometimes doped. Cerium oxide is a key element in these systems, thanks to its triple role as redox agent (maintaining the stoichiometry of the mixture of gases to be processed and hence the efficiency of the precious metal), dispersing and stabilising agent for the nanoparticles of precious metal, and thermal stabiliser for the alumina. However, these systems could only be developed with the help of nanoscale textured powders, able to conserve very high specific surface areas at high temperatures, and hence maintain constant and adequate reactivity over the lifetime of the catalyst (several tens of thousands of kilometers).