Theoretical Chemistry of Zeolite Reactivity

Abstract

IntroductionNowadays, advances in chemical theory rely to a significant extent on computations. Novel theoretical concepts arising directly from experiments usually require further investigations using computational modeling. This is necessary to develop a conclusive molecular-level picture of the observed phenomenon. As a result, computational methods are nowadays widely and extensively applied in the chemical, physical, biomedical, and engineering sciences. They are used in assisting the interpretation of experimental data and increasingly in predicting the properties and behavior of matter at the atomic level.Computational simulation techniques can be divided into two very broad categories. The first is based on the use of interatomic potentials (force fields). These methods are usually empirical and do not consider explicitly any electron in the system. The system of interest is described with functions (normally analytical), which expresses its energy as a function of nuclear coordinates. These are then used to calculate structures and energies by means of minimization methods, to calculate ensemble averages using Monte Carlo simulations, or to model dynamic processes via molecular dynamics simulations using classical Newton's law of motion. The current capabilities and challenges for the corresponding computational methods have been recently reviewed in excellent papers by Woodley and Catlow [1] and by Smit and Maesen [2, 3].The second category includes quantum chemical methods based on the calculation of the electronic structure of the system. Such methods are particularly important for processes that depend on bond breaking or making, which include, of course, catalytic reactions. Hartree Fock (HF), Density Functional Theory (DFT), and post-HF ab initio approaches have been used in modeling zeolites, although DFT methods have predominated in recent applications.This chapter focuses on illustrating the power and capabilities of modern quantum chemical techniques, and aims at highlighting the key areas and challenges

Stability and reactivity of active sites for direct benzene oxidation to phenol in Fe/ZSM-5: A comprehensive periodic DFT study

“…The vdW interaction between these subunits represents the vdW stabilization of the confined hydrocarbon species. Previous studies have shown that the addition of the empirical corrections to the results obtained at the PBE level results in both thermodynamic and kinetic parameters that are very close to those obtained at the higher ab initio level [88]. a-and b-sites represent a six-membered ring (6MR) in the straight channel and a deformed 6MR at the intersection of straight and sinusoidal channels, respectively [89].…”

Improving the selectivity to C4 products in the aldol condensation of acetaldehyde in ethanol over faujasite zeolites

“…This could result in possible confinement effects. Pidko and van Santen [65] have emphasized that in low-silica zeolites, where the density of exchangeable cations is high, the intrazeolite arrangement of cations plays a crucial role in activity and selectivity since these ions can undergo multiple noncovalent interactions with the reactants, resembling the active sites encountered in enzymes. Such interactions are present even with small molecules such as N 2 O 4 [66].…”

Engineering of Transition Metal Catalysts Confined in Zeolites

“…Modern computational methodologies provide practical tools to address the structural problem of zeolite catalysis at the molecular level. 231 , 232 Quantum chemical calculations, including semi-empirical methods, ab initio methods, and density functional theory (DFT), have made significant contributions to elucidate the molecular nature of active sites in zeolite catalysts. DFT calculations are currently considered as the most efficient methods due to a good balance between computational speed and accuracy.…”

“…The conventional preparation methods of zeolite-based transition metal catalysts usually give a variety of different intrazeolite species, which makes it very challenging to unambiguously identify the active sites solely by experiential characterization techniques. Modern computational methodologies provide practical tools to address the structural problem of zeolite catalysis at the molecular level. , Quantum chemical calculations, including semi-empirical methods, ab initio methods, and density functional theory (DFT), have made significant contributions to elucidate the molecular nature of active sites in zeolite catalysts. DFT calculations are currently considered as the most efficient methods due to a good balance between computational speed and accuracy.…”