Comparison of Ni based and Rh based catalysts performance in the oxidative steam reforming of raw bio-oil

Abstract

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 catalyst (Ni/La2O3-αAl2O3 and Rh/CeO2-ZrO2). The experiments have been carried out in an equipment with two steps in series: 1) thermal treatment (at 500 ºC, 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 ºC; steam/carbon ratio (S/C), 6; space time, 0.3 gcatalysth/gbio-oil (for Ni/La2O3-αAl2O3) and 0.15 gcatalysth/gbio-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, products 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.