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Mixed oxides of cerium oxide and zirconium oxides having a high oxygen storage and high oxygen release rate are disclosed. The mixed oxides are made of polycrystalline particles of cerium oxide and zirconium oxide having a controlled domain structure on the subcrystalline level wherein adjacent doma

Mixed oxides of cerium oxide and zirconium oxides having a high oxygen storage and high oxygen release rate are disclosed. The mixed oxides are made of polycrystalline particles of cerium oxide and zirconium oxide having a controlled domain structure on the subcrystalline level wherein adjacent domains within a single crystallite have a different ratio of zirconium and cerium. The mixed oxides are prepared by a co-precipitation technique using mixed salt solutions of cerium and zirconium having a solid content of at least 23%, based on an oxide basis.

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Mixed oxides of cerium oxide and zirconium oxides having a high oxygen storage and high oxygen release rate are disclosed. The mixed oxides are made of polycrystalline particles of cerium oxide and zirconium oxide having a controlled domain structure on the subcrystalline level wherein adjacent doma

Mixed oxides of cerium oxide and zirconium oxides having a high oxygen storage and high oxygen release rate are disclosed. The mixed oxides are made of polycrystalline particles of cerium oxide and zirconium oxide having a controlled domain structure on the subcrystalline level wherein adjacent domains within a single crystallite have a different ratio of zirconium and cerium. The mixed oxides are prepared by a co-precipitation technique using mixed salt solutions of cerium and zirconium having a solid content of at least 23%, based on an oxide basis. to obtain the composite; preparing a dispersed precursor slurry of the modified alumina silica composite, and a rare earth exchanged USY zeolite (REUSY) containing at least one rare earth oxide present in an amount ranging from 3.8 to 4.0 wt %, and optionally kaolin clay; spray drying the slurry to obtain spherical particles; and subjecting the spherical particles to calcination. 2. The process according to claim 1, wherein the rare earth exchanged USY zeolite in the catalyst is present in an amount which ranges from 5 to 35 wt %. 3. The process according to claim 1, wherein the kaolin clay is present in an amount which ranges up to 60 wt % based on the total weight of the catalyst. 4. The process according to claim 1, wherein the modified alumina-silica composite is present in an amount ranging from 10-40 wt % based on total weight of the catalyst. 5. The process according to claim 4, wherein the modified alumina-silica composite has a silica to alumina ratio ranging from 0.1:1 to 10:1. 6. The process according to claim 4, wherein the acid is selected from the group consisting of an organic acid, a mineral acid, and mixtures thereof. 7. The process according to claim 4, wherein the aging of the acidified alumina occurs at a temperature ranging from 35-40° C. 8. A process for preparation of a hydrocarbon conversion catalyst for use in a Fluid Catalyst Cracking (FCC) unit, consisting essentially of the steps of: preparing a modified alumina-silica composite by reacting alumina with an acid to provide an acidified alumina, aging the acidified alumina for from 0.25 to 60 hours, and adding a silica source to obtain the composite; preparing a dispersed precursor slurry in water consisting essentially of the modified alumina silica composite and a rare earth exchanged USY zeolite (REUSY) containing at least one rare earth oxide present in an amount ranging from 3.8 to 4.0 wt %, and optionally kaolin clay; spray drying the slurry to obtain spherical particles; and subjecting the spherical particles to calcination to prepare the hydrocarbon conversion catalyst for use in a Fluid Catalyst Cracking (FCC) unit. 9. The process according to claim 8, wherein the rare earth exchanged USY zeolite in the catalyst is present in an amount which ranges from 5 to 35 wt %. 10. The process according to claim 8, wherein the kaolin clay is present in an amount which ranges up to 60 wt % based on the total weight of the catalyst. 11. The process according to claim 8, wherein the modified alumina-silica composite is present in an amount ranging from 10-40 wt % based on total weight of the catalyst. 12. The process according to claim 11, wherein the modified alumina-silica composite has a silica to alumina ratio ranging from 0.1:1 to 10:1. 13. The process according to claim 11, wherein the acid is selected from the group consisting of an organic acid, a mineral acid, and mixtures thereof. 14. The process according to claim 11, wherein the aging of the acidified alumina occurs at a temperature ranging from 35-40° C. 15. A process for preparation of a hydrocarbon conversion catalyst for use in a Fluid Catalyst Cracking (FCC) unit, consisting of the steps of: preparing a modified alumina-silica composite by reacting alumina with an acid to provide an acidified alumina, aging the acidified alumina for from 0.25 to 60 hours, and adding a silica source to obtain the composite; preparing a dispersed precursor slurry consisting essentially of the modified alumina silica composite and a rare earth exchanged USY zeolite (REUSY) containing at least one rare earth oxide present in an amount ranging from 3.8 to 4.0 wt %, and optionally kaolin clay; spray drying the slurry to obtain spherical particles; and subjecting the spherical particles to calcination to prepare the hydrocarbon conversion catalyst for use in a Fluid Catalyst Cracking (FCC) unit. 16. The process according to claim 15, wherein the rare earth exchanged USY zeolite in the catal yst is present in an amount which ranges from 5 to 35 wt %. 17. The process according to claim 15, wherein the kaolin clay is present in an amount which ranges up to 60 wt % based on the total weight of the catalyst. 18. The process according to claim 15, wherein the modified alumina-silica composite is present in an amount ranging from 10-40 wt % based on total weight of the catalyst. 19. The process according to claim 18, wherein the modified alumina-silica composite has a silica to alumina ratio ranging from 0.1:1 to 10:1. 20. The process according to claim 18, wherein the acid is selected from the group consisting of an organic acid, a mineral acid, and mixtures thereof. 21. 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