Silica microspheres, method of improving attrition resistance
AssigneeE. I. Du Pont de Nemours and Company
InventorJo-Ann T. Schwartz
Life of this patent
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Abstract
High-strength, non-agglomerated uniform porous microspheres of silica produced by spray drying a mixture comprising a colloidal silica sol and an additive selected from ammonium citrate or urea; an attrition resistant catalytic composite consisting essentially of metal crystallites such as palladium, platinum-palladium on said silica microsphere and method for preparing the same; and an improved process for making hydrogen peroxide from the direct combination of hydrogen and oxygen in the presence of said attrition resistant catalytic composite.
Claims17
A process for preparing high-strength, non-agglomerated porous uniform silica microspheres which comprises the steps of:
- (a) mixing an aqueous sol of colloidal silica particles, having a diameter in the range of 5 to 100 nm, with an effective amount of a soluble additive selected from the group consisting of from ammonium citrate and urea to inhibit premature formation of an impervious crust.
- (b) spray drying the mixture to form a powder consisting of microspherical silica particles, said particles comprising a conglomerate of the original colloidal silica particles and said additive;
- and
- (c) calcining the spray dried powder to remove volatile components and to sinter the colloidal silica particles within the microspheres without fusing the microspheres into agglomerates.
A process for producing an attrition resistant catalytic composite consisting essentially of fine metal crystallites dispersed throughout high strength, non-agglomerated porous silica microspheres which comprises the steps of:
- (a) preparing an aqueous solution of a metal salt or metal salts;
- (b) dissolving an additive selected from ammonium citrate or urea;
- (c) adding an aqueous sol of colloidal silica particles, having a diameter in the range of 5 to 100 nanometers;
- (d) spray drying the mixture to form a powder consisting of microspherical silica particles, said particles comprising a conglomerate of the original silica particles with metal salts and ammonium citrate or urea distributed throughout;
- and
- (e) calcining to remove volatile components and to sinter the colloidal silica particles within the microspheres without fusing the microspheres into agglomerates.
In a process for preparing silica particles wherein an aqueous sol of colloidal silica is spray dried, the improvement comprising the step of:
- spray drying said aqueous sol of colloidal silica in the presence of an effective amount of a soluble additive selected from ammonium citrate or urea to inhibit premature formation of an impervious crust during spray drying, resulting in high strength, non-agglomerated, spherical silica microspheres more resistant to attrition.
Dependencies are inferred from the claim text.