Catalysts for the preparation of an alkenyl carboxylate from an olefin, a carboxylic acid and oxygen are known in the art. Such catalysts are based on a Group 8 metal as a catalytically active metallic species on a carrier. In preferred embodiments the metallic species further comprise a Group 1b metal. The preparation of the catalysts is well documented.
For example, the process for preparing the catalyst of U.S. Pat. No. 4,048,096 comprises the steps of introducing a Group 8 metal compound onto a carrier and converting the Group 8 metal compound on the carrier into metallic species. The conversion of the Group 8 metal compound may be accomplished in a liquid phase reaction, whereby a reducing agent such as hydrazine or formaldehyde is added to liquid which comprises the Group 8 metal/carrier composition. Alternatively, the conversion of the Group 8 metal compound may be accomplished in a gas phase reaction, whereby a reducing agent such as hydrogen or ethylene is reacted with the Group 8 metal/carrier composition.
The process for preparing the catalyst as disclosed in U.S. Pat. No. 4,048,096 is not without problems. Complete conversion of the Group 8 metal compound on the carrier into metallic species requires typically the presence of a large excess of the reducing agent. This is in particular the case in the liquid phase reaction, and more in particular when the reducing agent has a tendency to decompose under the prevailing reaction conditions, so that a portion of it becomes ineffective in the reduction. After the reduction, any unconverted reducing agent needs to be handled and discarded in an appropriate manner, which may be particularly cumbersome in association with the liquid phase reaction or when the reducing agent is a noxious chemical, such as hydrazine. Further, there is undesirably a loss of the Group 8 metal or Group 8 metal compound occurring during the preparation, which leads to a reduced yield of the Group 8 metal on the catalyst and to increased costs. This is in particular the case when a gas phase reaction is applied.
USPTO Backgrounds
USPTO Backgrounds