Steam Reforming of Toluene Over Pt/Ce _x Zr_1−x O₂/Al₂O₃ Catalysts

Steam reforming of toluene was investigated over Pt/Ce _x Zr_1−x O₂/Al₂O₃ catalysts with different ceria and zirconia content (x = 0.25, 0.50, 0.75, and 1.00). Toluene was used as model molecule representative of tar produced in biomass gasification. The main reactions over Pt/Ce _x Zr_1−x O₂/Al₂O₃ catalysts are the steam reforming of toluene and the water–gas shift. The dealkylation of toluene to benzene and methane takes place only at the beginning of the reaction. Toluene conversion significantly decreases during the reaction for all catalysts excepted for Pt/CeO₂/Al₂O₃ catalyst. Catalyst deactivation was attributed to carbon deposition as revealed by Raman spectroscopy. A clear relationship is observed between the acidity of the catalyst and the amount of carbon formed over Pt/Ce _x Zr_1−x O₂/Al₂O₃ catalysts. Decreasing the Ce/Zr ratio increased the density of acid sites as well as the amount of carbon formed. This result suggests that the main route for carbon deposition proceeds by the oligomerization of toluene molecule on the acid sites of the support. Pt/CeO₂/Al₂O₃ catalyst was quite stable during steam reforming of toluene without carbon deposition. For this catalyst, ceria covered the acid sites of alumina and did not introduce significant Lewis acid sites.