Comparison of Ni Based and Rh Based Catalyst Performance in the Oxidative Steam Reforming of Raw Bio-Oil

The effect of O₂ content in the oxidative steam reforming (OSR) of raw bio-oil has been studied, and the kinetic behavior, particularly deactivation, has been compared between two catalysts (Ni/La₂O₃-αAl₂O₃ and Rh/CeO₂-ZrO₂). The experiments have been carried out in an apparatus with two steps in series: (1) thermal treatment (at 500°C, for the controlled deposition of pyrolytic lignin) and (2) catalytic in-line reforming in a fluidized bed. The reaction conditions have been as follows: oxygen/carbon ratio (O/C), 0, 0.17, 0.34, and 0.67; 700°C; steam/carbon ratio (S/C), 6; space time, 0.3 g_catalysth/g_bio-oil (for Ni/La₂O₃-αAl₂O₃) and 0.15 g_catalysth/g_bio-oil (for Rh/CeO₂-ZrO₂); time on stream, 4 h. The content and morphology of the coke deposited on the catalysts has been determined by temperature-programmed oxidation (TPO), and the deterioration of the metallic properties of the catalysts by temperature-programmed reduction (TPR) and X-ray diffraction (XRD). The results (bio-oil conversion, product yield and their evolution with time on stream) show that for Rh/CeO₂-ZrO₂ catalyst the decrease in coke deposition as O/C ratio is increased involves attenuation of catalyst deactivation. Consequently, this catalyst is stable after 24 h operation for high O/C ratios, thus keeping constant the activity for reforming reactions and the WGS reaction, with a high yield of H₂ and low yields of CO, CH₄, and hydrocarbons. However, for the Ni/La₂O₃-αAl₂O₃ catalyst of lower activity than the Rh/CeO₂-ZrO₂, the decrease in coke content as O/C ratio is increased does not involve a noticeable attenuation in catalyst deactivation, which is due to Ni sintering.