Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Making catalytic electrode – process only
Patent
1991-08-08
1994-03-15
Kalafut, Stephen
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Making catalytic electrode, process only
429 44, H01M 488
Patent
active
052945804
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the preparation of a high capacity noble metal alloyed catalyst without the use of a noble metal precursor.
BACKGROUND OF THE INVENTION
Noble metal alloy catalyst preparation has typically consisted of first preparing or more commonly, purchasing, a noble metal precursor. The precursor was formed by precipitating a noble metal from solution onto a support, reducing the precipitated noble metal to the metal form with a reducing agent, such as formaldehyde. The precursor was the dispersed in a solution of alloying metals and the solvent was boiled away to disperse the alloying metals onto the precursor. Finally, the precursor with the alloying metals was heated in a calciner to alloy the metals.
Noble metal alloy catalysts have been produced without the use of a precursor. These catalysts were produced by precipitating a noble metal compound and alloying metals from solution and using a reducing agent to reduce the noble metal. The solution was then dried and calcined to alloy the metals.
Although this process required less steps, no precursor was formed and all the metals were deposited in one process, it also produced an environmentally harmful waste product. The liquid solution which contained a reducing agent such as formaldehyde had to be disposed of.
However, it was believed that the reducing agent was essential in attaining a high activity catalyst. The reducing agent seemed to precondition the support and/or the noble metal allowing high activity catalysts to be produced. Without the use of the reducing agent, the alloy metal loadings were low and inconsistent, and the catalyst had a low activity.
Additionally, there was a fear that if the noble metal was not reduced to its metal form prior to calcination, the noble metal surface area would be significantly reduced due to sintering, again lowering the resulting catalytic activity.
Therefore, what is needed in this art is an improved method of catalyst production which consistently and predictably produces high performance catalysts through simple, environmentally sound processes.
DISCLOSURE OF THE INVENTION
According to the present invention, noble metal alloy catalysts are produced by reducing the catalytic activity of the noble metal precipitate. A support and noble metal compound are intimately contacted in a liquid. The noble metal is precipitated onto the support. The catalytic activity of the noble metal is adjusted and at least one alloying metal is dissolved in the liquid. The alloying metal is precipitated onto the support. The supported noble metal and alloying metal precipitates are then calcined to reduce and alloy the metals.
BEST MODE FOR CARRYING OUT THE INVENTION
It is a common belief that in order to attain a high surface area noble metal alloyed catalyst, such as an alloyed platinum catalyst, a noble metal precursor must be used. However, it has been discovered that a high performance catalyst can be obtained in a single step process.
The present invention teaches a method of producing high performance noble metal alloy catalysts without a noble metal precursor by reducing the catalytic activity of the noble metal once it has been precipitated onto a support.
The process consists of dispersing a high surface area support into a liquid. High surface area supports with surface areas greater than about 50 m2/g are preferred, and with surface areas greater than about 80 m2/g especially preferred. Such supports could be those found to be useful in the preparation of catalysts for use in fuel cells, and would be known to those skilled in this art. Various types of supports, such as silica and alumina among others, can be utilized with this process, with carbon base supports preferred since they provide the necessary reducing environment during calcination. Some such carbon based supports available commercially include: acetylene-black produced by Gulf Oil Corporation, Pittsburgh, Pa., and VULCAN.RTM. XC-72 oil furnace black produced by Cabot Corporation, Boston, Mass. These carbon
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Patent Abstracts of Japan, vol. 13, No. 169 (C-587) (3517) Apr., 1989, For Kokai 63-319052, 63-319051.
Curbelo Pamela J.
International Fuel Cells Corporation
Kalafut Stephen
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