Stability of a Rh/CeO2–ZrO2 Catalyst in the Oxidative Steam Reforming of Raw Bio-oil

Abstract

The oxidative steam reforming (OSR) of raw bio-oil (obtained by fast pyrolysis of pine sawdust) has been studied on a Rh/CeO2-ZrO2 catalyst under a wide range of operating conditions (600-750 ºC; steam to carbon molar ratio (S/C), 3-9; oxygen to carbon molar ratio (O/C), 0.34; space time, 0.15-0.6 gcatalysth/gbio-oil) in order to delimit the suitable conditions for high and stable H2 production. The runs were conducted in a two-step system provided with a thermal step (at 500 ºC) for bio-oil vaporization and pyrolytic lignin retention, followed by an on-line catalytic reforming step in a fluidized bed reactor. The spent catalyst was characterized by Temperature Programmed Oxidation (TPO), Temperature Programmed Reduction (TPR) and Transmission Electron Microscopy (TEM) in order to ascertain the causes of deactivation and the effect of the reaction conditions on these causes. The evolution with time on stream (TOS) of both bio-oil oxygenates conversion and yields of reaction products shows different periods and catalyst states, with two sharp changes associated with different catalyst deactivation causes: i) change in the states of Rh species and aging of the support (with fast dynamics) and ii) coke deposition (at low temperature) or Rh sintering (at high temperature, with slow dynamics).