Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-05-26
2001-05-08
Wood, Elizabeth D. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S302000, C502S303000, C502S304000, C502S325000, C502S328000, C502S330000, C502S332000, C502S333000, C502S339000, C502S232000, C502S240000, C502S243000, C502S245000, C502S262000, C502S527240, C560S206000, C560S207000, C560S208000, C560S218000, C560S261000
Reexamination Certificate
active
06228800
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to a metal-supported article in which a palladium-containing metal component is supported on a carrier, a process for producing the above metal-supported article and a catalyst for chemical reaction composed of the above metal-supported article.
2. Background Art
Palladium or a palladium metal compound has been widely used as a catalyst in industry for many years.
The term “palladium metal compound” used herein is meant to include palladium intermetallic compounds in which the lattice of palladium is replaced with diverse metal and palladium alloys wherein the palladium and diverse metal form a solid solution.
Palladium has been used alone as a catalyst; however, in general, palladium is used in the form of a dispersion on a carrier because palladium is expensive and in view of the purpose of realizing a high reactivity. In chemical industry processes, a palladium-supported catalyst has been widely used in various reactions such as oxidation reactions, reduction reactions, hydrogenation reactions and the like and in catalysts for purging an automobile exhaust or the like. Palladium is supported on various carriers depending upon the reaction characteristics and uses. With a catalyst in which a noble metal component is uniformly supported even in the interior of the carrier, the diffusion of reactants and reaction product can be prevented by the resistance of fine pores in the interior of the carrier. In this case, it follows that the catalyst components supported in the interior of the carrier are not effectively utilized. Moreover, in some kinds of reactions, some types of reactors and the like, the catalyst components supported on the particle surface of a carrier are deactivated because their active sites are covered as a result of adsorption of reaction by-products, accumulation of poisoned substances and the like, or the carrier particles are cut by abrasion due to collision of the carrier particles with one another or with wall surfaces or the like. As a result, the active components of the catalyst are lost, and the catalyst is deactivated. Therefore, for the purpose of prolonging the life of the catalyst while maintaining its reaction activity, it has been proposed for a long time that the active components of the catalyst be supported slightly inside the carrier surface without being distributed on the outer surface of the carrier. As the catalyst preparation method as mentioned above, there has been known an impregnation method, an ion-exchange method, a chemical reaction method (for example, soluble palladium is insolubilized by reaction and deposited on a carrier) or the like.
An example in which the distribution of a palladium component on a carrier has been changed is reported in the Journal of Chemical Society of Japan (4), pp. 261-268 (1990). It is reported therein that when spherical alumina having a particle diameter of 3 mm (3,000 &mgr;m) is used as a carrier and palladium dissolved in hydrochloric acid is allowed to be adsorbed thereon by ion exchange, the palladium distribution and the amount of palladium supported are varied with adsorption time, for example, after one minute, after 25 minutes, after one hour, after 12 hours and after 20 hours, and the adsorption reaches approximately equilibrium in about one hour. However, even when the adsorption time is one minute, substantially no palladium is distributed from the outer surface of the carrier to a depth of about 300 &mgr;m and palladium is distributed in the form of a belt in a width of about 150 &mgr;m from the said about 300-&mgr;m depth in the direction of the carrier interior. Furthermore, the amount of palladium supported is increased with the lapse of time and palladium is uniformly distributed throughout the carrier after at least one hour. In said publication, there is no statement of a case of within one minute; however, when it is taken into consideration that after one minute, substantially no palladium is present in the area from the outer surface to a depth of about 300 &mgr;m of carrier and palladium is distributed in the form of a belt in a width of about 150 &mgr;m from said 300-&mgr;m depth in the direction of the carrier interior, it is actually difficult to control the distribution by this method so that the palladium is allowed to be substantially present within the very narrow range from the outer surface to a depth of 100 &mgr;m of carrier. Also, an example of the preparation of a catalyst in which silica gel is used as a carrier and palladium ions and ammonium ions are allowed to coexist is known, but in this case, palladium is uniformly supported in the carrier particles.
No palladium-supported article in which palladium is present only in the very narrow range from the outer surface to a depth of 100 &mgr;m in the carrier has been known.
DISCLOSURE OF INVENTION
This invention aims at providing a supported article in which the distribution of palladium in a carrier is controlled and Pd is allowed to be selectively present in a specific range in order to effectively utilize the noble metal Pd supported on a carrier. This invention also provides a highly active palladium-supported article by allowing palladium to be present in the vicinity of the surface of a carrier but not to be present in the interior of the carrier. In addition, this invention is directed to a noble metal-supported composition having a long catalyst life by further providing a layer in which no palladium is present as the outermost layer when accumulation of substances which would poison the catalyst and the loss of the active components due to abrasion may be encountered.
The present inventors have conducted research on supported catalysts and the reaction characteristics thereof based on many reaction examples. In many cases in which expensive noble metal components such as palladium and the like are used as the catalyst components, it is essential to support the catalyst components on a carrier. The present inventors have found that it is effective to support palladium in such a way that the reactants can react instantly. That is to say, when the diffusion rate of the reactants in the fine pores of the carrier affects the reaction rate, the inventors have found that it is effective to provide a catalyst wherein the distribution of a noble metal component, such as palladium or the like is as close as possible to the outer surface of the carrier, and no noble metal component is present in the center portion of the carrier where the influence of the diffusion is great. In addition, in a palladium-containing metal-supported article effective for heavy oil reformation, reactions is which the accumulation of poisoned substances takes place such as in a combustion catalyst or the like or in the case in which abrasion of catalyst particles is possible as in a fluidized bed, a bubble column, a stirring type reactor or the like, the inventors have found that the durability of the catalyst can be greatly improved without causing a reduction of reaction activity by supporting a noble metal component wherein a thin layer free from palladium is used as the outermost layer with the catalyst particle. If the durability can be improved without reducing the reaction activity, the catalyst life could be greatly prolonged and the economics could be improved. Heretofore, no technique for obtaining a metal-supported article in which a noble metal component is distributed in a very thin layer of less than 100 microns or technique for obtaining a metal-supported article which has a very thin layer substantially free from palladium-containing metal on the surface without reducing the reaction activity and wherein the palladium is supported in the surface layer having a thickness of less than 100 microns but is not present in the interior have bee known in the art.
Thus, the present invention is directed to a method for precisely controlling the vicinity of the surface of a carrier for palladium- or a palladium metal compound-supported catalyst.
The invention comprises the foll
Okamoto Hiroshige
Yamaguchi Tatsuo
Yamamatsu Setsuo
Asahi Kasei Kogyo Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Wood Elizabeth D.
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