Mo-catalysed hydrogenation processes of four coals, ranked between lignite B and high volatile bituminous coals, are studied. Ammonium heptamolybdate was used as a catalyst precursor. Hydrogenations were carried out at 300, 350 and 400 o C at a hydrogen pressure of 10 MPa, with reaction times ranging from 5 to 30 min. The maximum rate of the process, related to the textural characteristics of the coal, was calculated from the relationship between the conversion time and the reaction time. The results indicate that at 300 o C the catalyst is not active and the reaction mainly depends on the efficiency of the mass transfer process and thus on the coal macropore volume. At higher temperatures, however, the process takes place catalytically and in this case the catalytic activity is influenced by the coal surface.