Abstract: Colloidal dispersions of finely divided particulates, well suited for the production of catalysts for the catalytic conversion of exhaust gases emanating from internal combustion engines, notably vehicular exhaust gases, comprise at least one rare earth compound and, optionally, at least one compound of at least one other element selected from among those of groups IVa, VIIa, VIII, Ib, IIb, IIIb and IVb of the Periodic Table, said particulates being at least 50% dispersible in water.

Abstract: The invention concerns a procedure for preparation of a precursor of a mixed cerium and zirconium oxide-based composition, characterized by the following steps:a liquid mixture is prepared containing cerium and zirconium compounds;the preceding mixture is placed in contact with carbonate or bicarbonate, thus forming a reactive medium exhibiting a neutral or basic pH during the reaction;the precipitate obtained is collected.A mixed cerium and zirconium oxide-based composition is obtained by calcining this precursor. This composition is characterized by the fact that it has a total pore volume of at least 0.6 cm.sup.3 /g, and that at least 40%, and more particularly at least 50%, of the total pore volume is composed of pores having a diameter of at most 1 .mu.m.

Abstract: Thermally stable/highly reducible catalyst compositions, well suited for the catalytic conversion of exhaust gases emanating from internal combustion engines notably vehicular exhaust gases, comprise alumina, the oxides of cerium praseodymium and zirconium, and, optionally, at least one other oxide of bismuth, of a rare earth, or of an element of group VIII of the Periodic Table, and exhibit a stabilized hydrogen-absorption capacity up to a temperature of at least 1,000.degree. C.

Abstract: Zirconium/cerium mixed oxides (optionally including thermally stabilizing dopant values), comprising solid solutions thereof, having contents of zirconium of up to 99% by weight, and having high specific surface areas, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such ZrO.sub.2 /CeO.sub.2 mixed oxides are conveniently prepared by (i) intimately admixing a zirconium sol with a cerium sol, the ratio r of the mean diameter r.sub.l of the particles of the zirconium sol to the diameter r.sub.2 of the particles of the cerium sol being at least 5, (ii) adding a precipitating amount of a base thereto, (iii) recovering the precipitate thus formed, and (iv) calcining the recovered precipitate.

Abstract: Zirconium/cerium mixed oxides (optionally including thermally stabilizing dopant values), comprising solid solutions thereof, having contents of zirconium of up to 99% by weight, and having high specific surface areas, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such ZrO.sub.2 /CeO.sub.2 mixed oxides are conveniently prepared by (i) intimately admixing a zirconium sol with a cerium sol, the ratio r of the mean diameter r.sub.1 of the particles of the zirconium sol to the diameter r.sub.2 of the particles of the cerium sol being at least 5, (ii) adding a precipitating amount of a base thereto, (iii) recovering the precipitate thus formed, and (iv) calcining the recovered precipitate.

Abstract: Zirconium/cerium mixed oxides (optionally including thermally stabilizing dopant values), comprising solid solutions thereof, having contents of zirconium of up to 99% by weight, and having high specific surface areas, are well suited as catalysts and/or catalyst supports, notably for the treatment/conversion of vehicular exhaust gases; such ZrO.sub.2 /CeO.sub.2 mixed oxides are conveniently prepared by (i) intimately admixing a zirconium sol with a cerium sol, the ratio r of the mean diameter r.sub.1 of the particles of the zirconium sol to the diameter r.sub.2 of the particles of the cerium sol being at least 5, (ii) spray drying the admixture thus obtained, and (iii) calcining the dried material.