A process for preparing a catalyst by (a) selecting a carrier which is a silica based carrier which has been subjected to a series of washings with one or more aqueous liquids consisting of aqueous liquids which have a pH of least 3, when measured at 20.degree. C., or which is a silica based carrier which is formed from materials one or more of which have been subjected to this series of washings, (b) precipitating a Group 8 metal compound onto the carrier, (c) converting the precipitated Group 8 metal compound into metallic species, and (d) subjecting the Group 8 metal/carrier composition to a purification treatment, before or after step (c); a catalyst which is obtainable by this process; and a process for preparing an alkenyl carboxylate by reacting a mixture comprising an olefin, a carboxylic acid and oxygen in the presence of the catalyst.