Theoretical studies of IM-12 zeolite for acidic catalysts

We theoretically investigate the properties of the IM-12 to address a catalyst for acidic conversion reaction of larger organic molecules. The acidic characteristics of the IM-12 are investigated by density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Based on quantum mechanical (QM) calculation results, we find that the zeolite with Al element prefers the tetrahedral (T) sites, T4 and T6, when replacing Si in IM-12 framework. Isomorphously substituted IM-12 on the T4 and T6 sites by B, Al, and Ga is studied, respectively. Both of the sites give the Brönsted acidity order: B–IM-12 < Ga–IM-12 < Al–IM-12, which is the same as other zeolites. The calculated NH3 adsorption energies are compared with the calculated and experimental results of H–[Al]MOR [M. Elanany, D.P. Vercauteren, M. Koyama, M. Kubo, P. Selvam, E. Broclawik, A. Miyamoto, J. Mol. Catal. A 243 (2006) 1; C. Lee, D.J. Parrillo, R.J. Gorte, W.E. Farneth, J. Am. Chem. Soc. 118 (1996) 3262]. Molecular dynamics (MD) results show that IM-12 zeolite allows the large molecules such as diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) to diffuse faster than those in MOR zeolite and IM-12 may have significant selectivity for TIPB over DIPB. We conclude that the IM-12 with Al impurity would be a good candidate for large organic molecule acidic conversion reaction.