Eric Gerard Derouane

Molecular Shape-Selective Catalysis by Zeolites

Zeolites are three-dimensional framework aluminosilicates presenting a large intracrystalline free volume which consists of cavities and/or pores. Building-in catalytically active sites within such structures is the essence of molecular shape-selective catalysis. These active sites can pertain to the zeolite framework itself: Bronsted acidic sites are associated to the presence of framework aluminum atoms; they can be converted into Lewis acidic sites by dehydroxylation. Catalytic centers can also be metals or their ions which can be introduced into the zeolite framework by a variety of techniques, ion-exchange being most commonly used.

Conversion of Methanol to Gasoline over Zeolite Catalysts I. Reaction Mechanisms

The conversion of methanol into hydrocarbons occurs over a large variety of acidic catalysts. These can be non-zeolitic compounds such as phosphoric acid, heteropolyacids, and silica-aluminas (1–5) or more commonly zeolites (6–11). The use of zeolite ZSM-5 as acid catalyst (8,12–25) is particularly attractive as it offers a new and viable route for the direct production of high-grade gasoline from methanol synthesized from coal or natural gas resources. Zeolite-based ZSM-5 catalysts are the key to Mobil’s Methanol-to-Gasoline (MTG) process for which a commercial plant is presently being built in New Zealand. The MTG process has unique advantages: (a) Hydrocarbons are produced in a rather narrow compositional range; little methane and no hydrocarbons larger than C11 are formed. (b) A high conversion of methanol can be combined with a high selectivity for aromatics and isoparaffins of high octane value. (c) ZSM-5 based catalysts are characterized by a very low aging rate.