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Rare-earth manganites have a great potential for environmental applications based on their chemical and physical properties. The use of rare-earth manganites as catalysts for environmentally essential reactions was reviewed. Artificial neural networks were used to assess the catalytic activity in oxidation reactions. Relative catalytic activities of the catalysts were further discussed. We concluded that cerium manganite is the most practicable catalyst for technological purposes.

Preparation and Anion Exchange Properties of Zirconia. -Hydrous zirconia samples are prepared by gel precipitation from aqueous solutions of ZrOCl2·8 H2O or ZrO(NO3)2·xH2O at either non steady state pH ranging from 0.5 to 12 or at constant pH. At a constant pH of 10 the zirconyl chloride precursor yields zirconia samples with specific surface areas exceeding 300 m2/g. Upon calcination the specific surface area decreases progressively and the amorphous material crystallizes in the tetragonal phase. Amorphous zirconia exhibits an anion exchange capacity of 0.25 meq/g which decreases by 65% when the material becomes tetragonal. Monoclinic zirconia has almost no exchange capacity. -(TICHIT, D.; EL ALAMI, D.; FIGUERAS, F.; Appl.