Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1999-09-29
2001-10-23
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
Reexamination Certificate
active
06306360
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a spinel powder and a spinel slurry. More particularly, it relates to an MgAl
2
O
4
spinel powder which is excellent in catalytic activity, in particular, NO
x
-reduction performance and a slurry containing this powder which can form a coating layer scarcely peeling off and being free from cracking and which can be easily applied onto a catalytic base material, for example, a honeycomb construction to form a catalyst having excellent catalytic activity, in particular, NO
x
-reduction performance.
BACKGROUND OF THE INVENTION
Spinels have been produced by adjusting the pH of an acidic aqueous solution of a mixture of a water-soluble magnesium salt and a water-soluble aluminum salt with an alkali to form a precipitate of hydroxides and then heating the precipitate to thereby synthesize a spinel, i.e., the coprecipitation method.
As an example of the above-described coprecipitation method, JP-A-59-232915 discloses “a method for synthesizing a spinel by adjusting the pH of an aqueous solution of a mixture of a water-soluble magnesium salt and a water-soluble aluminum salt with an alkali in the presence of alcohol to form a precipitate and then drying and calcining this precipitate to thereby synthesize a spinel” (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
In this method, the coprecipitation is performed by adjusting the pH in the presence of an alcohol so as to give a spinel powder in the form of fine grains having a low cohesiveness and a low crystallinity.
The “water-soluble magnesium salt” and the “water-soluble aluminum salt” employed here as the starting materials include chlorides, sulfates and nitrates of magnesium or aluminum, and acetate, carbonate and oxalate of magnesium, etc. It is disclosed that chlorides are preferably employed therefor, since they are available in a highly pure state and compounds contaminating the hydroxide precipitate can be easily washed away in this case.
As techniques for producing catalysts, on the other hand, it is known to form a catalytic layer on the surface of a catalytic base material, for example, a honeycomb construction by preparing a slurry containing a noble metal and a powdery support such as a spinel powder and an alumina powder, and applying this slurry onto the catalytic base material (see, JP-A-3-131343, JP-A-7-328454, JP-A-10-99698).
Recently, exhaust controls become more and more strict. With an increase in the regulation level, it has been required to achieve an enhanced catalytic activity. Although the spinel powder obtained by the above-described coprecipitation method has a low cohesiveness, a low crystallinity and a high purity, a catalyst with the use of this spinel powder as a support cannot achieve a satisfactory catalytic activity, thus failing to satisfy the above requirement.
When a slurry containing a catalytic support is applied onto a catalytic base material in the catalyst-producing technique as described above, it is required that the slurry can be easily applied on and form a catalytic layer scarcely peeling off and being free from cracking.
SUMMARY OF THE INVENTION
The present invention has been completed to satisfy the above requirements.
The first object of the present invention is to provide an MgAl
2
O
4
spinel powder which makes it possible, when employed as a catalytic support, to give a catalyst being excellent in catalytic activity, in particular, NO
x
-reduction performance when used as an NO
x
storage-reduction catalyst support.
The second object of the present invention is to provide a slurry containing the above-described spinel powder which can form a coating layer scarcely peeling off and being free from cracking and which can be easily applied onto a catalytic base material such as a honeycomb construction to form a catalyst having excellent catalytic activity, in particular, NO
x
-reduction performance achieved when used as a storage-reduction catalyst support.
As a result of eager studies, the present inventors have found the above first object of the present invention can be achieved by the following.
(1) A spinel powder represented by a chemical formula MgAl
2
O
4
, wherein the spinel powder has a specific surface area of 40 m
2
/g or more, and the average diameter of the spinel powder ranges from 3 to 20 &mgr;m.
(2) A spinel powder represented by a chemical formula MgAl
2
O
4
, produced by the process of drying a mixture solution containing a water-soluble organic substance having a boiling point of 120° C. or above, converting the dried substance into a complex oxide by heating and then milling, wherein the spinel powder has a specific surface area of 55 m
2
/g or more and an average diameter of from 3 to 20 &mgr;m.
(3) A spinel powder represented by a chemical formula MgAl
2
O
4
, produced by the process of drying a solution containing an aluminum salt of a water-soluble carboxylic acid and a magnesium salt of a water-soluble carboxylic acid and converting the dried substance into a complex oxide by heating, wherein the spinel powder has a specific surface area of 55 m
2
/g or more and an average diameter of from 3 to 20 &mgr;m.
(4) A spinel powder comprising MgAl
2
O
4
as a main component produced by the process of mechanically mixing and milling a mixture of hydroxides for producing a spinel powder to convert into a complex hydroxide, heating a mixture composition of the obtained complex hydroxide and an unconverted hydroxide to convert into a complex oxide, wherein the spinel powder has a specific surface area of 42 m
2
/g or more and an average diameter of from 3 to 20 &mgr;m.
Further, the present inventors have found the above second object of the present invention can be achieved by a slurry comprising the above spinel powder.
REFERENCES:
patent: 3702882 (1972-11-01), Rettew et al.
patent: 4081408 (1978-03-01), Fischer, et al.
patent: 4274981 (1981-06-01), Suzuki et al.
patent: 4474745 (1984-10-01), Ritter, II
patent: 4495304 (1985-01-01), Yoo et al.
patent: 4542112 (1985-09-01), Matsui et al.
patent: 1 811 144 (1969-07-01), None
patent: 42 27 720 (1993-04-01), None
patent: 0 110 490 (1984-06-01), None
patent: 0 110 704 (1984-06-01), None
patent: 0 512 843 (1992-11-01), None
patent: 1 282 307 (1972-07-01), None
patent: 1 296 049 (1972-11-01), None
patent: 59-232915 (1984-12-01), None
R. J. Bratton, Ceramic Bulletin, vol. 48, No. 12, pp. 759 to 762, “Coprecipitates Yielding MgA12O4Spinel Powders”, 1969.
G. Gusmano, et al., Jounal of the European Ceramic Society, vol. 7, No. 1, pp. 31 to 39, “The Mechanism of MgA12O4Spinel Formation From the Thermal Decomposition of Coprecipitated Hydroxides”, Jan. 1, 1991.
Derwent Publications, AN 1986-161655, XP-002135217, SU 1 196 334, Dec. 7, 1985.
A. Mazzoni, et al., Chemical Abstracts, vol. 117, No. 16, Oct. 19, 1992, AN 117: 156011, XP-002135216 “Preparation of Spinel Powders (MgAl20) at Low Temperature by Mechanical Activation of Hydroxide Mixtures”, 1991.
K. Waldner, et al., Chemistry of Materials, vol. 8, No. 12, pp. 2850-2857, “Synthesis of a Double Alkoxide Precursor to Spinel (MgA12O4) Directly From (A1(OH)3, MgO, and Treiethanolamine and Its Pyrolytic Transformation to Spinel,” 1996.
Y. Suyama, et al., Cermics International, vol. 8, No. 1, pp. 17-21, “Characterization and Sintering of Mg-A1 Spinel Prepared by Spray-Pyrolysis Technique,” 1982.
Derwent Abstracts, AN 1985-041018, JP 59-232915, Dec. 27, 1984.
Suda Akihiko
Sugiura Masahiro
Yamamoto Toshio
Griffin Steven P.
Ildebrando Christina
Kabushiki Kaisha Toyota Chuo Kenkyusho
LandOfFree
Spinel powder and spinel slurry does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spinel powder and spinel slurry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spinel powder and spinel slurry will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2579488