Structures and Reaction Mechanisms of Propene Oxide Isomerization on H-ZSM-5:  An ONIOM Study

Abstract

The isomerization mechanisms of propene oxide over H-ZSM-5 zeolite have been investigated via the utilization of 5T and 46T cluster models calculated by the B3LYP/6-31G(d,p) and the ONIOM(B3LYP/6-31G(d,p):UFF) methods, respectively. The reactions are considered to proceed through a stepwise mechanism: (1) the epoxide ring protonation, and concurrently the ring-opening, and (2) the 1,2-hydride shift forming the adsorbed carbonyl compound. Because of the asymmetric structure of propene oxide, two different C-O bonds (more or less substituted carbon atom sides) can be broken leading to two different types of products, propanal and propanone. The ring-opening step of these mechanisms is found to be the rate-determining step with an activation barrier of 38.5 kcal/mol for the propanal and of 42.4 kcal/mol for the propanone. Therefore, the propanal is predicted to be the main product for this reaction.

The adsorption of saturated and unsaturated hydrocarbons on nanostructured zeolites (H-MOR and H-FAU): An ONIOM study

“…The 120T extended framework connecting the quantum region was treated with the universal force field (UFF) [35] to represent the van der Waals contributions from the interactions of adsorbed molecules with the zeolite pore structures. This force field has been previously reported to provide a good description of the short-range van der Waals interactions between the sorbate molecules and the zeolitic wall [32][33][34]. The models of 120 tetrahedral Si atoms of MOR and FAU were obtained from their crystal structures [36,37].…”

“…We employ the ONIOM method that takes advantage of the density functional theory, for the accurate treatment of the interactions of adsorbed molecules with the acid site of zeolite, and the universal force field (UFF) to account for the van der Waals interaction due to the confinement of the zeolite framework which has been found to be important for the adsorption and reaction in microporous zeolites [29][30][31][32][33][34]. Moreover, the single point energy calculations at the MP2 level of theory and the basis set superposition errors (BSSE) corrections are carried out to refine the interaction energy.…”

A theoretical study of cis–trans isomerisation in H-ZSM5: probing the impact of cluster size and zeolite framework on energetics and structure

“…The 46 tetrahedra (nT) ONIOM model used here has been successfully applied to ZSM-5 on a number of previous occasions [7,[19][20][21]. The 46T representation was cut from the cross section of the straight channel and zigzag channel and the dangling bonds were saturated with hydrogen atoms as described elsewhere [7] (Fig.…”

Zeolite-catalyzed Isomerization of 1-Hexene to trans-2-Hexene: An ONIOM Study

“…33,35 Hybrid methods, especially, the Our-own-N-layered Integrated molecular Orbital + molecular Mechanics (ONIOM) methods, 36,37 were found to be appropriate in describing the acidic site of the zeolite surface and yielding reasonable estimates of the system energetics, yet they are capable of reasonable simplification for the computation of the complex zeolite-guest molecule system in which numerical and computation capacities are highly demanding. On account of the above consideration, in this work we constructed a 54T cluster model to represent the local structures of H-ZSM-5 zeolite, with the effects of the zeolite framework being implicitly included in subsequent calculations (see Fig.…”