Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1994-09-19
1996-12-10
Pal, Asok
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502326, 502332, 502334, 502339, B01J 2340, B01J 2342, B01J 2356
Patent
active
055830870
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for impregnating a catalyst support with platinum. The invention also relates to a method for the preparation of a catalyst and to a catalyst prepared by this method.
DESCRIPTION OF THE PRIOR ART
The catalyst has a carrier structure to the surface of which there has been applied a washcoat of a support material. The support used is typically alumina, silica, titanium dioxide, zeolite, or mixtures of these. Additives, such as cerium compounds, improving the thermal durability of the support are additionally used in the support. The support has a large specific surface and it constitutes the surface to which the catalytically active agent is affixed. Noble metals such as platinum, rhodium and palladium are generally used as the catalytically active agent. The purpose of platinum is to catalyze in particular the oxidation of carbon monoxide and hydrocarbons to carbon dioxide. Typically the amount of platinum used in a three-way catalyst per catalyst volume is 0.9-3 g/l.
The noble metal is added to the support by impregnation. The catalyst is dipped or immersed in a solution which contains noble metals. The noble metals will adhere to the surface of the support. After the impregnation the catalyst is first dried at room temperature and thereafter the catalyst is activated, for example by heating in a reducing atmosphere.
Two methods are generally used in noble metal impregnation. These methods are wet impregnation and chemisorption. In wet impregnation a completed honeycomb is dipped in a noble metal solution, whereupon the liquid is absorbed automatically into the honeycomb. Wet impregnation is characterized by a short impregnation period and a high noble-metal concentration in the solutions. Wet impregnation is based on the adsorption of the solution. The result is in this case often an uneven distribution of the noble metals on the surface of the support. In addition, the noble metal is present in the form of large particles, in which case the interface between the gas and the noble metal remains small, i.e. a poor dispersion is obtained. In impregnation based on chemisorption, electric forces are exploited for affixing the noble metal complex to the surface. Chemisorption is characterized by a long impregnation period and a low noble-metal concentration in the solutions. The impregnation is based on the noble metal compounds being chemically bonded to the surface. In this case the noble metal is present on the surface of the support in the form of small particles which are evenly distributed over the surface. Thereby a large interface between the gas and the noble metal is obtained, i.e. the dispersion is high.
In the solution used for the impregnation, platinum has a valence of either 2 or 4. Pt.sup.II compounds include Pt.sup.II (NH.sub.3).sub.4 Cl.sub.2 and Pt.sup.II (NH.sub.3).sub.4 (OH).sub.2. Respectively, Pt.sup.IV compounds which have been used for impregnation include hexachloroplatinic(IV) acid H.sub.2 Pt.sup.IV Cl.sub.6, and its potassium salt and ammonium salt.
In the working example of FI publication 900516, an aqueous solution was used which contained hexachloroplatinic(IV) acid and rhodium chloride. A catalyst structure which had been coated with a support layer and had thereafter been activated was immersed in this solution. Thereafter it was dried, and the precipitated noble metal salts were reduced by heating in a hydrogen flow.
Lay-open print DE 23 39 513 discloses a method of preparing a catalyst in which a solution containing, for example, Pt.sup.II (NH.sub.3).sub.4 (OH).sub.2 was added to a powder containing alumina and ceria. The solution, which had a volume of 151 ml, contained platinum 2.75 g. Thereafter the powder was dried.
If the platinum solution used for impregnation is prepared by using Pt.sup.II (NH.sub.3).sub.4 Cl.sub.2, chlorides are formed in the solution because in solution form the compound becomes ionized the solution. If the above-mentioned solution is used for wet impregnation in metallic catalysts, the chl
REFERENCES:
patent: 4082699 (1978-04-01), Petrow et al.
patent: 4837193 (1989-06-01), Akizuki et al.
Irzinski E. D.
Kemira Oy
Pal Asok
LandOfFree
Method for impregnating catalyst support with platinum does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for impregnating catalyst support with platinum, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for impregnating catalyst support with platinum will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-424065