Methanol to Hydrocarbons: Enhanced Aromatic Formation Using Composite Group 13 Oxide/H-ZSM-5 Catalysts

The conversion of methanol to hydrocarbons using composite catalysts comprising physical mixtures of the zeolite H-ZSM-5 with group 13 oxides (-Al₂O₃, -Ga₂O₃, In₂O₃, Tl₂O₃) is reported and discussed. The addition of -Ga₂O₃ at 400 °C gives a marked enhancement in the yield of C₈ and C₉ aromatic compounds, whereas the addition of -Al₂O₃ has no effect and both the In₂O₃/H-ZSM-5 and Tl₂O₃/H-ZSM-5 are inactive. At 300 °C, a marked enhancement in the yield of aromatic hydrocarbons is observed for -Ga₂O₃ and In₂O₃, and a less marked enhancement is observed with Tl₂O₃ and -Al₂O₃. In particular, the addition of In₂O₃ to H-ZSM-5 as a simple physical mixture gives a significant enhancement in catalyst activity at 300 °C. The effect of the Si:Al atomic ratio of H-ZSM-5 is also investigated for the -Ga₂O₃/H-ZSM-5 composite catalysts and the enhancement in aromatic yield is observed with all the ratios investigated but the optimal -Ga₂O₃/H-ZSM-5 ratio is dependent upon the Si:Al ratio. Pretreatment or co-feeding of hydrogen decreases the yield of the aromatic products. The results are explained in terms of an active site formed by the interaction between the oxide and the zeolite.