Guaiacol hydrogenation in an aqueous medium in the presence of a palladium catalyst supported on a mesoporous dendrimer-containing polymer and the effect of addition of sulfuric acid to the catalyst system have been studied. It has been found that the main hydrogenation product is 2-methoxycyclohexanol. After the addition of sulfuric acid to the catalyst system, the reaction mechanism significantly changes and cyclohexanol becomes the main hydrogenation product.