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 °C; steam-to-carbon molar ratio, 3-9; oxygen-to-carbon molar ratio, 0.34; space time, 0.15-0.6 g_catalyst h/g_bio-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 °C) for bio-oil vaporization and pyrolytic lignin retention, followed by an online catalytic reforming step in a fluidized bed reactor. The spent catalyst was characterized by temperature-programmed oxidation, temperature-programmed reduction, and transmission electron microscopy in order to ascertain the causes of deactivation and the effect of the reaction conditions on these causes. The evolution with time on stream 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).