A ceria-zirconia-based composite oxide including a composite oxide containing ceria and zirconia, wherein the ceria-zirconia-based composite oxide contains at least one member selected from the group consisting of praseodymium, lanthanum, and yttrium in an amount of 0.5 to 5.0 mol % relative to a total amount of the cations contained in the ceria-zirconia-based composite oxide, where the ratio of the content of both cerium and the at least one member selected from the group consisting of praseodymium, lanthanum, and yttrium in the ceria-zirconia-based composite oxide to the content of zirconium therein ([cerium and the at least one member selected from the group consisting of praseodymium, lanthanum, and yttrium]:[zirconium]) is in the range of 43:57 to 48:52 by mole ratio.

An catalyst for purifying exhaust gas comprising an OCS material that has sufficient heat resistance and achieves a favorable balance between the oxygen storage volume and the oxygen absorption/release rate includes an catalyst for purifying exhaust, which has a substrate and a catalyst coating layer formed on the substrate, wherein the catalyst coating layer comprises a ceria-zirconia-based composite oxide having a pyrochlore structure in an amount of 5 to 100 g/L based on the volume of the substrate, the ceria-zirconia-based composite oxide has a secondary particle size (D50) of 3 m to 7 m, and the ceria-zirconia-based composite oxide optionally contains praseodymium.

A core-shell oxide material comprises: a core which comprises a ceria-zirconia based solid solution powder having at least one ordered phase of a pyrochlore phase and a phase; and a shell which comprises an alumina based oxide disposed on at least a portion of a surface of the core.

A satisfactory oxygen storage material and a method for producing it are provided. The oxygen storage material comprises zirconia particles with a ceria-zirconia complex oxide supported on the zirconia particles. The ceria-zirconia complex oxide includes a pyrochlore phase and has a mean crystallite diameter of 10 nm to 22.9 nm.

Provided is an exhaust-gas-purification catalyst carrier that contains a ceria-zirconia complex oxide having a pyrochlore phase and a novel exhaust-gas-purification catalyst carrier that exhibit excellent OSC performance at any temperature region of a low temperature (around 400 C.) and a high temperature (around 800 C.). Proposed is the exhaust-gas-purification catalyst carrier containing a ceria-zirconia complex oxide which has a pyrochlore phase and is 7.0 m.sup.2/g or more in specific surface area and in the range of 100 to 700 in crystallite size.

A production method comprising: adding a hydroxycarboxylic acid to an aqueous solution containing a Ce salt, a Zr salt, an Al salt, and at least one selected from a La salt, an Mg salt, and a Ca salt, to produce a gel, heating the gel to obtain a solid product by decomposition of the salts, firing the solid product to obtain a fired product containing a ceria-zirconia-based regular array phase precursor and an aluminate-based composite oxide precursor, performing a reducing heat treatment of the fired product to obtain a first composite having mutually dispersed therein a pyrochlore phase and an aluminate-based composite oxide, and performing an oxidizing heat treatment of the first composite to obtain a second composite in which at least part of the pyrochlore phase is transformed into a phase; and an oxygen storage material having mutually dispersed therein the composite oxide and the regular array phase.

Disclosed is a hydrocarbon gas reforming supported catalyst, and methods for its use, that includes a catalytic material capable of catalyzing the production of a gaseous mixture comprising hydrogen and carbon monoxide from a hydrocarbon gas, and a support material comprising an alkaline earth metal/metal oxide compound having a structure of D-E, wherein D is a M.sub.1 or M.sub.1M.sub.2, M.sub.1 and M.sub.2 each individually being an alkaline earth metal selected from the group consisting of Mg, Ca, Ba, and Sr, E is a metal oxide selected from the group consisting of Al.sub.2O.sub.4, SiO.sub.2, ZrO.sub.2, TiO.sub.2, and CeO.sub.2, wherein the catalytic material is attached to the support material.

Provided is a cerium-zirconium-based composite oxide having an excellent OSC, high catalytic activity, and excellent heat resistance, and also provided is a method for producing the same. The cerium-zirconium-based composite oxide comprises cerium, zirconium, and a third element other than these elements. The third element is (a) a transition metal element or (b) at least one or more elements selected from the group consisting of rare earth elements and alkaline earth metal elements. After a heat treatment at 1,000 C. to 1,100 C. for 3 hours, (1) the composite oxide has a crystal structure containing a pyrochlore phase, (2) a value of {I111/(I111+I222)}100 is 1 or more, and (3) the composite oxide has an oxygen storage capacity at 600 C. of 0.05 mmol/g or more, and an oxygen storage capacity at 750 C. of 0.3 mmol/g or more.

This oxygen storage material has a chemical composition represented by Ce.sub.1-xZr.sub.xO.sub.2- (0.45x0.65, 0), has a peak attributed to a cubic pyrochlore-like structure ( phase) near 14.5 in an XRD pattern, and has a specific surface area of 3 [m.sup.2/g] or more.

The present disclosure provides an oxygen storage/release material that has achieved both the improved oxygen storage/release capacity at low temperature and heat tolerance, which comprises a ceria-zirconia-based composite oxide, wherein the ceria-zirconia-based composite oxide further comprises praseodymium (Pr) or neodymium (Nd), and has, in at least a part thereof, at least one ordered phase of phase and a pyrochlore phase, a proportion of primary particles having particle diameters of 0.4 m to 1.5 m is 40% to 100% on a particle number basis, and, when heated for 5 hours in the air at 1,100 C., I(14/29) value is 0.015 or more and I(28/29) value is 0.08 or less. The present disclosure also relates to a method for producing such oxygen storage/release material.