Pd/h-BN catalysts were synthesized, which are active and selective in the oxidation of lactose to lactobionic acid. Several parameters in the preparation of Pd/h-BN catalysts were varied such as the impregnation solvent, the Pd precursor, the palladium loading, the activation method, in order to study their influence on the structural characteristics of the materials obtained. The effect of the Pd particle sizes on the catalytic performances in lactose oxidation was particularly investigated. It was shown that the most active catalysts in the oxidation of lactose have a particle size distribution comprised between 3 and 15 nm. The determining factor which influences badly the activity is the proportion of metallic particles inferior to 3 nm at the surface of the support. If the latter is above 10%, it has a negative effect on the lactose conversion. (C) 2013 Elsevier B.V. All rights reserved.