Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-06-27
2001-10-23
Langel, Wayne (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S302000, C502S303000, C502S308000, C502S313000, C502S325000, C502S326000, C502S327000, C502S333000, C502S334000, C502S339000, C502S340000, C502S341000, C502S344000, C502S349000, C502S439000, C502S527120, C501S105000, C501S152000
Reexamination Certificate
active
06306794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite oxide, a composite oxide carrier and a composite oxide catalyst.
2. Description of the Related Arts
In the case where three-way catalysts for reducing exhaust gases are exposed to a high temperature atmosphere, the oxygen storage capacity (hereinafter will be merely called OSC) achieved by ceria therein decreases. This is caused by sintering of active catalytic elements such as platinum (Pt) or palladium (Pd), and a promoter such as ceria, oxidation of the active catalytic metals, dissolution of rhodium (Rh)to a catalyst carrier, or the like. Furthermore, in the case where catalysts have low OSC, the active catalytic metals tend to be exposed to a changing atmosphere and consequently, the deterioration (coagulation and dissolution) of the active catalytic metals (platinum, palladium and rhodium) may be unfavorably accelerated.
Japanese patent application laid-open No. Hei 4-4043 discloses an oxide carrier in which alumina (Al
2
O
3
), ceria (CeO
2
) and zirconia (ZrO
2
) are co-precipitated to disperse zirconia between the other elements to solve the above problem. And Japanese patent application laid-open No. Hei 7-300315 discloses an oxide carrier in which cerium and zirconium ions are precipitated by adding electrified particles of alumina thereto. However, by using the co-precipitation method and mixing ratio disclosed herein, the dispersing characteristics of the component elements were not so enhanced as to improve OSC and the ratio of purification.
Japanese patent application laid-open No. Hei 7-315840 discloses an aluminum oxide-cerium oxide-zirconium oxide containing compound carrier which is formed by mixing a precipitate obtained from a solution containing a cerium salt and a zirconium salt with alumina powder. However, by the method disclosed therein, composite oxide carriers of which component elements exhibit high dispersing characteristics, cannot be manufactured.
Furthermore, carriers prepared by impregnating alumina powder with a solution containing a cerium salt and a zirconium salt exhibit high dispersing characteristics of a cerium oxide and a zirconium oxide, but the composite (solid solution) of the cerium oxide and the zirconium oxide is insufficient.
Another catalyst including a carrier obtained from a mixture of active alumina powder and ceria-zirconia composite oxide powder, which adsorbes and carries noble metals, has been also known. The catalyst thus arranged was, however, insufficient in OSC at low temperatures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a composite oxide, a composite oxide carrier in which component elements disperse with high homogeneity, and more particularly a composite oxide catalyst crystallites of oxides of cerium and/or zirconium and secondary particles thereof, of which the sizes are decreased to a predetermined value or less, to enhance the heat resistance thereof as a composite oxide and a catalyst carrier, and a composite oxide-containing catalyst in which the particle growth of an active catalytic metal and solid solution thereof into a carrier are restrained even at elevated temperatures to exhibit an excellent hest resistance.
In the case where a basic solution is added to a solution of salts of component elements gradually, the component element which is easy to precipitate at a low pH value, such as zirconium hydroxide, first precipitates due to the difference in pH value at which the component elements precipitate, thereby forming coagulated bodies, each being composed of a single component element, and then, the remaining component elements precipitate to form another coagulated bodies and consequently, objective high dispersing characteristics of component elements cannot be obtained. This results in insufficient preparation of a composite (solid solution) even after fired.
To overcome this problem, the present inventors have studied intensively, and as a result, completed the present invention.
A composite oxide manufactured by the method comprising the steps of forming a precursor of oxides from an aqueous solution of salts of a plurality of elements within several seconds, and then firing the precursor.
A composite oxide manufactured by the method comprising the steps of forming a precursor of oxides from high concentration salts of a plurality of elements, and then firing the precursor.
A composite oxide carrier manufactured by the method comprising the steps of forming a precursor of oxides composed of a plurality of elements by mixing a solution of salts of the plurality of elements of at least one of cerium (Ce) or zirconium (Zr), and aluminum (Al), with an alkaline solution by use of high speed mixing means, and then firing the precursor.
A composite oxide catalyst manufactured by the method comprising the steps of forming precursors of oxides of a plurality of elements and a catalyst metal by mixing a solution including salts of a plurality of elements of at least two of cerium, zirconium and aluminum and a salt of a catalyst metal with an alkaline solution by use of high speed mixing means, and by precipitating the precursors from the mixed solution, and firing the precipitated precursors.
The composite oxide carrier and composite oxide catalyst in accordance with the present invention are respectively composed of a composite oxide in which at least one of cerium and zirconium, and aluminium, each defining the carrier, disperse with extremely high homogeneity. With this structure, the heat resistance of the carrier is improved and consequently, enlargement of particles of the composite oxide defining the carrier, and sintering of adjacent particles of the composite oxide can be restrained, whereby the catalyst using the composite oxide carrier in accordance with the present invention is excellent in heat resistance.
With the present invention, the carrier is not limited to a general catalyst carrier. The carrier may be interpreted to indicate general formed bodies. For example, the carrier with the present invention can be also used as materials for sensors and electrodes, optical materials, semiconductor materials and structure materials. Furthermore, the carrier can be used for a three-way catalyst, NOx catalyst or oxidation catalyst or a part thereof, and a promoter.
The composite oxide carrier and composite oxide catalyst in accordance with the present invention has characteristics resulted from the manufacturing method thereof. Namely, the composite oxide carrier and composite oxide catalyst in accordance with the present invention are characterized by the composite oxide manufactured by the method including the precursor forming step and firing step. The composite oxide-containing catalyst is obtained by preparing a composite of catalytic components simultaneously with the formation of the precursor of composite oxide in the step of forming the precursor of the composite oxide. The composite oxide carrier and composite oxide catalyst in accordance with the present invention are identical to each other in the point that the precursor of composite oxide is formed.
Hereinafter, the composite oxide carrier in accordance with the present invention will be first explained.
To manufacture the composite oxide carrier in accordance with the present invention, in the spep of forming a precursor, a solution of salts of a pluraltiy of elements including at least one of cerium and zirconium, and aluminium, which define the composite oxide, is first mixed with an alkaline solution with the use of high speed mixing means to form a precursor of oxide composed of the plurality of elements. The elements defining the carrier may include at least one of alkaline metal elements, alkali earth metal elements such as barium, transition metal elements such as yttrium, platinum, rhodium, palladium and iron, and rare earth metal elements such as lanthanum other than cerium, zirconium and aluminum.
The transition metal elements denote metals of Groups 1B, 2B, 3A, 4A, 5A, 6A, 7A and 8 of the
Sobukawa Hideo
Suzuki Tadashi
Kabushiki Kaisha Toyota Chuo Kenkyusho
Langel Wayne
Nguyen Cam N.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Composite oxide, composite oxide carrier and catalyst does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite oxide, composite oxide carrier and catalyst, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite oxide, composite oxide carrier and catalyst will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2598560