from first principles PP-I-1

OP-III-20Reactivity of Methoxy Species in the Methanolto Olefin Reactions over H-ZSM-5Yamazaki H., Imai H., Yokoi T., Kondo J.N., Tatsumi T.Chemical Resources Laboratory, Tokyo Institute of Technology4259-R1-9 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japanttatsumi@cat.res.titech.ac.jpThe worldwide demand for ethene and propene, building blocks for the synthetic chemicals,has increased steadily in the last decade because of the growing demand for polymerproducts. The methanol to olefins (MTO) process is a promising industrial route [1]. Variousdiscussions have been made on the mechanism of the MTO reaction; one of the maindiscussions is devoted to the structure of hydrocarbons formed in zeolite channels, so-called“hydrocarbon pool (HCP)” [2, 3]. On the other hand, less research and discussion have beencarried out on the initial C-C bond formation from the starting C 1 compound, methanol [1, 3].MTO reactions start with the activation of methanol. The formation of methoxy species onzeolite upon exposure to methanol can be observed by infrared (IR) spectroscopy. Hungeret al. have recently been energetically studying the reactivity of methoxy species and claimedthat methoxy groups are active species [4]. Here we closely investigated the reactivity ofmethoxy species on H-ZSM-5 by IR spectroscopy using isotopes [5]. The methoxy groupswere supposed to migrate in the form of methyl cations in a similar manner to the motion ofprotons of acidic OH groups. However, we have found that the methyl carbenium cationmechanism is not applicable. The presence of carbene-like intermediate is the most likely; thisreaction probably proceeds in a concerted manner.We have also found that the reaction of methoxy species with DME is faster than that withethane or methanol. Methoxy species react with DME directly to form propene. Furthermore,it is implied that the initial hydrocarbon product in the MTO reaction is propene. Detailedinvestigations into the mechanism of the initial reactions are now in progress.References:[1] Stöcker, M., Zeolites and Catalysis; Synthesis, Reactions and Applications. Vol. 2., (Ed., J. Cejka,A. Corma, and S. Zones), pp. 687-711, Wiley-VCH, Weinheim, 2010.[2] M. Bjørgen, F. Joensen, K.-P. Lillerud, U. Olsbye, S. Svelle, Catal. Today 142, 90 (2009).[3] D. M. McCann, D. Lesthaeghe, P. W. Kletnieks, D. R. Guenther, M. J. Hayman,V. Van Speybroeck, M. Waroquier, J. F. Haw, Angew. Chem. Int. Ed. 47, 5179 (2008[4] W. Wang, M. Hunger, Acc. Chem. Res. 41, 8, 895 (2008).[5] H. Yamazaki, H. Shima, H. Imai, T. Yokoi, T. Tatsumi, J. N. Kondo, Angew. Chem. Int. Ed., 50,1853(2011).64