Mechanistic Investigation on 1,5- to 2,6-Dimethylnaphthalene Isomerization Catalyzed by Acidic β Zeolite: ONIOM Study with an M06-L Functional

• DOI: 10.1021/jp904098t
• Publication Date: 2009-08-17T16:19:39Z
• Authors: Chawanwit Kumsapaya; Karan Bobuatong; Pipat Khongpracha; Yuthana Tantirung...; Jumras Limtrakul
• Keywords: 02 engineering and technology; 0210 nano-technology

The isomerization of 1,5- to 2,6-dimethylnaphthalene (DMN) over β zeolite has been investigated by applying a newly developed density functional named M06-L, incorporated into the ONIOM scheme: M06-L/6-31G(d,p):UFF. Two consecutive reaction mechanisms over the extended zeolite framework have been carefully examined: the 1,5- to 1,6-DMN isomerization followed by the 1,6- to 2,6-DMN isomerization. Both catalytic processes take place via the same mechanism. The isomerization process starts from the protonation of the DMN step, creating the naphthalynic carbocation. Subsequently, the intramolecular methyl shift occurs from the α-position to the adjacent β-position of the naphthalynic carbocation. In the final step, the anionic zeolite framework takes a proton away from the naphthalynic carbocation, yielding a desired 1,6-DMN or 2,6-DMN molecule. The methyl migrations are the rate-determining steps and require activation barriers of 25.69 and 21.05 kcal/mol for the 1,5- to 1,6-DMN and 1,6- to 2,6-DMN processes...