In situ NMR studies of the conversion of methanol into gasoline on aluminosilicate and gallosilicate offretites

The conversion of CH3OH by the hydrogen forms of three offretites with different contents of framework Al and Ga has been monitored by C-13 NMR with magic-angle spinning. At 150 degrees C methanal is dehydrated to dimethyl ether. Na hydrocarbons are produced below 300 degrees C, and the equilibrium product distribution is achieved only at 370 degrees C. The distribution of both the intermediates and the final products is different for each of the three catalysts. Thus, branched long-chain hydrocarbons form in the intracrystalline space of Ga-offretite but not in Al,Ga- and Al-offretites. More methane is formed over the aluminum-containing samples, ca. 3.2% in Al-offretite and ca. 3.7% in Al,Ga-offretite, than in Ga-offretite (ca. 2.0%). No appreciable amount of aromatic species is detected at any temperature. We believe that the methanol-to-gasoline process over Al,Ga-offretites is bifunctional and involves Bronsted acid sites as well as extraframework Ga species.