The effect of sodium promoter on the catalytic hydrogenation of biphenol (BP) was investigated. Several reaction products were identified and the change in their distribution with time was analyzed to find the reaction mechanism. Different amount of sodium salt was impregnated on Pd/C to observe its effect on the composing reactions of BP hydrogenation. The existence of sodium metal decreased the C=C bond hydrogenation, but accelerated the C=O bond hydrogenation resulting in the increase of the yield to bicyclohexyl-4,4'-diol (BRD). The promotional effect of Na on the supported palladium on carbon catalysts were explained by electronic and geometric factors. (c) 2005 Elsevier B.V. All rights reserved.