Structures and Reaction Mechanisms of Cumene Formation via Benzene Alkylation with Propylene in a Newly Synthesized ITQ-24 Zeolite: An Embedded ONIOM Study

Elucidation of the mechanism and structure–reactivity relationship in zeolite catalyzed alkylation of benzene with propylene

The intrinsic mechanism and structure–reactivity relationship were systemically elucidated using the alkylation of benzene with propylene as a model reaction based on the periodic DFT calculations.

Insight into the stereoselectivity of TS-1 in epoxidation ofcis/trans-2-hexene: a computational study

The mechanism of the stereoselectivity forcis/trans-2-hexene epoxidation in TS-1 zeolite was studied using density functional theory and the ONIOM scheme.

Density functional theory studies on the skeletal isomerization of 1-butene catalyzed by HZSM-23 and HZSM-48 zeolites

This work reveals the topological effect of zeolites on both enthalpy and entropy of skeletal isomerization of 1-butene.

Adsorption and decarbonylation of furfural over H-ZSM-5 zeolite: a DFT study

The biomass-derived furfural adsorption and decarbonylation to furan over H-ZSM-5 (see picture) have been unraveled by means of density functional calculations with the M06-2X functional.

Recent advances of pore system construction in zeolite-catalyzed chemical industry processes

The kaleidoscopic applications of zeolite catalysts (zeo-catalysts) in petrochemical processes has been considered as one of the major accomplishments in recent decades. About twenty types of zeolite have been industrially applied so far, and their versatile porous architectures have contributed their most essential features to affect the catalytic efficiency. This review depicts the evolution of pore models in zeolite catalysts accompanied by the increase in industrial and environmental demands. The indispensable roles of modulating pore models are outlined for zeo-catalysts for the enhancement of their catalytic performances in various industrial processes. The zeolites and related industrial processes discussed range from the uni-modal micropore system of zeolite Y (12-ring micropore, 12-R) in fluid catalytic cracking (FCC), zeolite ZSM-5 (10-R) in xylene isomerization and SAPO-34 (8-R) in olefin production to the multi-modal micropore system of MCM-22 (10-R and 12-R pocket) in aromatic alkylation and the hierarchical pores in FCC and catalytic cracking of C4 olefins. The rational construction of pore models, especially hierarchical features, is highlighted with a careful classification from an industrial perspective accompanied by a detailed analysis of the theoretical mechanisms.

Layer selection effect on solid state 13C and 15N chemical shifts calculation using ONIOM approach

Solid state (13)C and (15)N chemical shifts of uracil and imidazole have been calculated using a 2-layer ONIOM approach at 32 levels of theory. The effect of electron correlation between two layers has been investigated by choosing two different kinds of layer selection. Factorial design has been applied as a multivariate technique to analyze the effect of wave function and layer selection on solid state (13)C and (15)N chemical shifts calculations. PBEPBE/6-311+G(d,p) was recommended as an optimally selected level of theory for high layer in both models. It is illustrated that considering the electron correlation of two layers of ONIOM models is important factor to calculate solid state (15)N chemical shifts. The agreement between the calculated and experimental values of solid state (13)C and (15)N chemical shifts using ONIOM (PBEPBE/6-311+G(d,p):AM1) for both uracil and imidazole confirmed the reliability of the selected wave functions and layer selection.

EFFECT OF HIGH-LEVEL LAYER SELECTION IN ONIOM ON Na+ ADSORPTION IN ZSM-5 ZEOLITE

Here we present a systematical investigation on the effect of high-level layer selection in our own N-layered integrated molecular orbital + molecular mechanics (ONIOM) method. We used the adsorption of Na+ in the M7 site of ZSM-5 as an instructive example. We embedded n tetrahedral sites (nT= 7, 19, 22, 33) for high-level layer into a low-level layer represented by 75T (denoted as nT@75T). Our calculations showed that 7T@75T behaved poorly in both structure optimization and interaction energy calculation. Hence only including the first coordination circle of the ion (i.e. 7T), as commonly used in literature, is not sufficiently good. However, for n ≥ 19, both structure optimization and interaction energy calculation by ONIOM are in good agreement with the full 75T model calculation. Such a reliable ONIOM calculation needs only 1/10 to 1/5 computational time for each self-consistent field (SCF) iteration as compared to the full 75T model calculation, highlighting its pivotal role in zeolite simulation.

ONIOM study of isomerization reactions of aromatic hydrocarbons in acidic mordenite zeolite

Two different mechanisms: Shift 1,2-isomerization and isomerization via the disproportionation reaction are investigated for aromatic hydrocarbons over acidic mordenite zeolite by using our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) scheme. The picture shows a schematic energy profile for the isomerization of toluene catalyzed by acidic mordenite.The geometrical structures and energies of isomerization reactions of aromatic hydrocarbons catalyzed by the 128T cluster model of acidic mordenite zeolite are studied by using our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) scheme. The aromatic hydrocarbons investigated are toluene, xylenes, and trimethylbenzenes. Two proposed intramolecular reaction mechanisms, that is, shift 1,2-isomerization and isomerization via the disproportionation reaction, are studied and discussed in detail. Both of the mechanisms firstly proceed by protonation of aromatic hydrocarbons to form the aromatic-based carbenium ions. Attempts to determine the prevailing reaction mechanism of the isomerization are evaluated. In most cases, the isomerization reactivity sequence is: trimethylbenzenes>xylenes>toluene. The conclusions obtained using the ONIOM scheme agree with the available periodic DFT and experimental results on acidic mordenite zeolite.