Catalytic hydrogenolysis of the C-O bond of diphenyl ether (a lignin model compound) was investigated as a function of hydrogen pressure in scCO(2) medium in the presence of water. Using commercially available Rh/C catalyst, the C-O bond cleavage of diphenyl ether mainly results phenolic monomer at 80 degrees C. Hydrogen pressure is one of the key parameters because (i) C-O bond cleavage and the hydrogenation of aromatic rings are two competitive reactions; very sensitive to hydrogen pressure and (ii) hydrogen has complete solubility in scCO(2). Therefore, a critical control of hydrogen pressure was essential to reach the targeted cleavage of the C-O bond when the reaction was conducted in scCO(2) medium under pressurized condition. Depending on the hydrogen pressure, a significant change in the ratio of monocyclic:bicyclic products from 91:9 (0.2 MPa) to 58:42 (2 MPa) was revealed in the shortest reaction time of 5 min. Thus, low hydrogen pressure was the effective choice for the scission of the C-O bond, whereas higher hydrogen pressure hydrogenate the aromatic ring due to the higher coverage of hydrogen on the catalytic surface. Amount of the catalyst (catalyst:substrate ratio) displayed a subtle effect on the breakage of the C-O bond. A threshold ratio of 1:5 was preferred under the present reaction condition as the increased amount hampered the substrate:water ratio and hydrogenation of the aromatic ring occurred. In addition, as the change in temperature is associated with the change in the physical properties of scCO(2), hence, the effect on the transformation of DPE was complicated and difficult to explain. Furthermore, different organic solvents as neat, along with CO2 and with water also has substantial impact on the rapture of C-O bond. The obtained results from the solvent studies again proved that scCO(2) along with water was the best choice for C-O bond breakage and water is the driving force to mediate the reaction. In addition, a combination catalyst (Ni+Rh) was also tested for the same reaction under the similar working condition. Preliminary results suggested a synergistic effect in terms of the selectivity of monocyclic compounds. (C) 2016 Elsevier B.V. All rights reserved.