The hydro-process is performed in hydrogen providing solvents activated by the catalysts of Co–Mo, Ni–Mo and their oxides or loaded on Al2O3 under pressurized conditions of hydrogen and/or CO. Oxygen is removed as H2O and CO2
, and then the energy density is elevated. Pindoria [21,22] hydrotreated the volatiles from fast pyrolysis of eucalyptus in a two stage reactor. Hydro-cracking without catalysts was operated in the first stage, and catalytic hydrotreatment was operative in the second stage with lower temperature and the same pressure compared with that in the first stage. The analysis indicated that the deactivation of the catalyst did not result from carbon deposition. Instead, the embodiments of volatile components blocked the activated sites in the zeolite catalyst. This hydro-process produced much water and complicated the bio-oil with many impurities.