Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1985-12-23
1987-09-08
Shine, W. J.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502525, 338 34, B01J 2310, B01J 2358, B01J 2378
Patent
active
046924299
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
This invention relates to a composition applicable as a catalyst used by being exposed to combustion exhaust gas for rendering noxious gaseous components therein harmless by a redox (reduction-oxidation) reaction and also applicable as sensors for detecting the stoichiometric air/fuel ratio by measuring a large change in electric resistance.
BACKGROUND ART
Noxious substances such as CO, HC (hydrocarbons) and NO.sub.x are contained in exhaust gas, and catalysts have been used for cleaning such exhaust gas by changing said noxious substances into harmless materials such as CO.sub.2, H.sub.2 O and N.sub.2 through a redox reaction. The catalysts used for this purpose included two types: (1) those using noble metals such as Pt or Pd group metals and (2) those using oxides of transition metals such as Mn, Cu, Ce, etc. Noble metal catalysts are called three-way conversion catalyst and capable of simultaneously eliminating both reductive noxious gases such as CO and HC and oxidative noxious gas such as NO.sub.x. It is known, however, that these noble metal catalysts sinter and become aggregated and lose their catalytic activity when they are exposed to a high temperature. On the other hand, oxide catalysts are used only for eliminating reductive noxious gases.
As to the sensors for detecting the stoichiometic ratio of combustion, there have been known the type in which platinum electrodes are set on both sides of the partition wall of stabilized zirconia solid electrolyte, one of said electrodes being exposed to an atmosphere where the partial pressure of oxygen is constant, such as air, while the other electrode being exposed to exhaust gas, thus forming an oxygen concentration cell, and a sudden change of its electromotive force is utilized for detecting the stoichiometric ratio, and the type in which a sudden change in electric resistance of a metal oxide such as SnO.sub.2, TiO.sub.2, MgCr.sub.2 O.sub.4, etc., is utilized. At an air/fuel ratio close to the stoichiometric ratio, the fuel is not perfectly burned and both reductive gases such as CO and HC and oxidative gases such as O.sub.2 and NO.sub.x coexist in the exhaust gas, so that there occurs no sudden change of electromotive force or electric resistance from the area of stoichiometric ratio of combustion unless said both types of gases are reacted with each other through the medium of a catalyst. In the systems utilizing the electromotive force of concentration cell, Pt of the electrode on the outside, which contacts with exhaust gas, performs said catalytic action, but in the systems utilizing the electric resistance of the metal oxide, almost no such catalytic action is occurred, so that it was necessary to add a noble metal to the metal oxide.
Recently, attempts have been made to use perovskite type metal oxides for exhaust gas cleaning catalysts or gas sensors, and the present inventors have also filed a patent application featuring the use of a material Sr.sub.(1+x)/2 La.sub.(1-x)/2 Co.sub.1-x MeO).sub.3-.delta. (Me:Fe, Mn, Cr or V.delta.: loss of oxygen) (U.S. Pat. Nos. 4,314,996 and 4,485,191). This material exhibits a mixed conductivity of electrons and O.sup.2- ions, and the invention of this patent application clarified the relation of such mixed conductivity to the catalytic performance or sensor characteristics and provided a composition with an optimal ratio of components for obtaining the desired characteristics. It is known that generally the oxygen content in a metal oxide varies according to the partial pressure of oxygen in the gas atmosphere, resulting in a change of electric resistance of the metal oxide, and this principle is already applied in various gas sensors. Said material, however, has a quite characteristic property that it can stably maintain the same crystal structure regardless of any voluminous release or takeup of oxygen. In this material, O.sup.2- ionic migration (electric conduction) occurs through the deletion of oxygen ions in the crystal lattice, and under high temperature like in exhaust gas, such
REFERENCES:
patent: 4044601 (1977-08-01), Sakurai et al.
patent: 4357426 (1982-11-01), Murata et al.
Sekido Satoshi
Tachibana Hirokazu
Yamamura Yasuharu
Research Association of Electric Conductive Inorganic Compounds
Shine W. J.
LandOfFree
Catalyst composition and multi-functional sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst composition and multi-functional sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst composition and multi-functional sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2158325