Abstract: Cerium/zirconium mixed oxides (optionally including yttrium values), comprising solid solutions thereof, having contents of zirconium of up to 60 atom % and having thermally stable, very high specific surface areas at least greater than 80 m.sup.2 /g, preferably at least 100 m.sup.2 /g and more preferably at least 150 m.sup.2 /g, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such Ce.sub.x Zr.sub.1-x O.sub.2 particulates are conveniently prepared by thermally treating an aqueous solution of soluble compounds of cerium and zirconium (and optionally yttrium), e.g. the nitrates thereof, present in the desired stoichiometric amounts, and thence recovering and, if appropriate, calcining the reaction product thus formed.

Abstract: Ceric oxide (ceria) particulates exhibiting a particularly small crystallite size, well suited for catalyst/catalyst carrier applications, include a specific surface-stabilizing amount of silicon values (preferably less than 1% by weight thereof, expressed as SiO.sub.2) and have a specific surface of at least 40 m.sup.2 /g after calcination at 800.degree. C. for 6 hours and of at least 20 m.sup.2 /g after calcination at 1,000.degree. C. for 6 hours; such CeO.sub.2 particulates are advantageously prepared by (a) suspending certain ceric hydroxides in a basic aqueous reaction medium containing a silicon compound, (b) autoclaving the resulting suspension, (c) cooling and depressurizing such medium of reaction, (d) separating a ceric hydroxide therefrom, and (e) calcining the ceric hydroxide thus separated.

Abstract: Porous alumina-based compositions having high specific surface areas, well adopted for catalyst applications and prepared by precipitation/hydrothermal treatment/calcination technique, comprise an alumina matrix having from 10% to 50% by weight of at least one rare earth or alkaline earth metal second element dispersed therein, having a pore volume, corresponding to pores of a diameter less than 100 nm, ranging from 1.2 cm.sup.3 /g, at least 80% of which corresponding to pores having a diameter ranging from 10 nm to 100 nm, after heat treatment at a temperature of 350.degree. C. and having a pore volume, also corresponding to pores of a diameter less than 100 nm, ranging from 0.6 cm.sup.3 /g to 1.5 cm.sup.3 /g, at least 90% of which corresponding to pores having a diameter ranging from 20 nm to 100 nm, after heat treatment at a temperature of 1,200.degree. C. for four hours.

Abstract: Unique compositions based on at least one crystalline rare earth sesquisulfide, well suited for the coloration of a wide variety of substrates, e.g., cosmetics, plastics, paints and rubbers, contain a dopant amount of at least one alkali/alkaline earth metal, at least a fraction of which being included within the crystal lattice of such at least one rare earth sesquisulfide.

Abstract: Thermally stable ceric oxide-based compositions, well suited as catalysts/catalyst supports for a wide variety of reactions, notably for the catalytic conversion of exhaust gases emanating from internal combustion engines, comprise particulates of immixture of a major amount of ceric oxide with at least one other metal oxide of magnesium, gallium, boron, scandium, or mixture thereof, and having a specific surface greater than 10 m.sup.2 /g after calcination at 800.degree. C.