title: Cooperativity between Al Sites Promotes Hydrogen Transfer and Carbon-Carbon Bond Formation upon Dimethyl Ether Activation on Alumina.
abstract: The methanol-to-olefin (MTO) process allows the conversion of methanol/dimethyl ether into olefins on acidic zeolites via the so-called hydrocarbon pool mechanism. However, the site and mechanism of formation of the first carbon-carbon bond are still a matter of debate. Here, we show that the Lewis acidic Al sites on the 110 facet of γ-Al2O3 can readily activate dimethyl ether to yield CH4, alkenes, and surface formate species according to spectroscopic studies combined with a computational approach. The carbon-carbon forming step as well as the formation of methane and surface formate involves a transient oxonium ion intermediate, generated by a hydrogen transfer between surface methoxy species and coordinated methanol on adjacent Al sites. These results indicate that extra framework Al centers in acidic zeolites, which are associated with alumina, can play a key role in the formation of the first carbon-carbon bond, the initiation step of the industrial MTO process.
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland.
authors.forename: Aleix
authors.initials: A
authors.lastname: Comas-Vives
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland.
authors.forename: Maxence
authors.initials: M
authors.lastname: Valla
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, CH-8093 Zürich, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Copéret
authors.affiliation: CNRS, Institut de Chimie de Lyon, École Normale Supérieure de Lyon, Université de Lyon , 46 allée d'Italie, F-69364 Lyon Cedex 07, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Sautet