The preparation of copper on silica catalysts by the ion exchange method has been found to yield ion-exchanged copper and small copper crystallites (diameter 1.4 - 2 nm). The importance of the copper crystallites depend mainly on the concentration and amount of impregnating solution trapped in the filter cake and the acidity and amount of the wash solution. Catalytic activity for the hydrolysis of acrylonitrile is found to depend on copper surface area. Fast deactivation during the early stages of reaction may depend on copper crystallite size. Slower deactivation as a result of copper oxidation is possible unless the solutions are deoxygenated.