Gold and palladium catalysts were successfully applied in aerobic D-lactose oxidation. Comparison between these catalysts revealed, that gold catalysts are more active and selective for the production of the first reaction product, lactobionic acid, while Pd can be of importance when the product of second consecutive reaction, 2-keto-lactobionic acid is aimed at. The electrochemical catalyst potential response was measured in situ applied for characterization of processes on the catalyst surfaces. Several reaction parameters were varied to study possibilities to predict catalyst deactivation from the measured catalyst potential. (c) 2007 Elsevier B.V. All rights reserved.