The Conversion of methanol to hydrocarbons over Ga₂O₅-HZSM-5 and Ga₂O₅-WO₃ catalysts

The conversion of methanol over physical mixtures of Ga2O3 and H-ZSM-5 or WO3/gamma-Al2O3 is reported. The addition of Ga2O3 to H-ZSM-5 markedly increases the selectivity to aromatic hydrocarbon at the expense Of C-2-C-4 alkenes, without affecting the overall conversion. This effect is obtained at temperatures greater than or equal to400degreesC, and the maximum effect is observed at 1:1 mixtures of Ga2O3 and H-ZSM-5. Experiments using separate beds of Ga2O3 and H-ZSM-5 with different configurations do not reveal any significant effect. In addition, upon removal of Ga2O3 from the Ga2O3/H-ZSM-5 physical mixture the normal catalytic performance of the zeolite is observed. Ga2O3 is also shown to significantly enhance the catalytic activity of a WO3/gamma-Al2O3 catalyst when it is incorporated as a physical mixture. The results are explained in terms of a new active site that is formed at the point of contact between Ga2O3 and H-ZSM-5 or WO3/gamma-Al2O3 particles. In the case of H-ZSM-5/beta-Ga2O3, this site catalyzes the formation of aromatic products from C-2-C-5 alkenes, whereas for WO3/gamma-Al2O3:beta-Ga2O3 the new site catalyzes the formation of methane. (C) 2002 Elsevier Science.