The hydrogenation of aromatic acids and other substituted phenyls has been studied for two palladium-based catalysts; one supported on carbon nanofibres (CNFs) and the other on a steam-activated carbon. The reactions were conducted in both aqueous solution and aprotic organic solvents. The major product over both catalysts was the same irrespective of the substrate indicating that support characteristics and Pd dispersion play at most only a minor role in defining the reaction pathway. The key factor in determining the major reaction product resulting from either preferential hydrogenation of the aromatic ring, or reaction of the external functional group, was the extent to which the external group interacted with water molecules which acted in some cases to protect the external function from interaction with the metal surface and induced selective reduction of the aromatic ring. (C) 2009 Elsevier Inc. All rights reserved.