Advances in theory and their application within the field of zeolite chemistry

Abstract

Zeolites are versatile and fascinating materials which are vital for a wide range of industries, due to their unique structural and chemical properties, which are the basis of applications in gas separation, ion exchange and catalysis. Given their economic impact, there is a powerful incentive for smart design of new materials with enhanced functionalities to obtain the best material for a given application. Over the last decades, theoretical modeling has matured to a level that model guided design has become within reach. Major hurdles have been overcome to reach this point and almost all contemporary methods in computational materials chemistry are actively used in the field of modeling zeolite chemistry and applications. Integration of complementary modeling approaches is necessary to obtain reliable predictions and rationalizations from theory. A close synergy between experimentalists and theoreticians has led to a deep understanding of the complexity of the system at hand, but also allowed the identification of shortcomings in current theoretical approaches. Inspired by the importance of zeolite characterization which can now be performed at the single atom and single molecule level from experiment, computational spectroscopy has grown in importance in the last decade. In this review most of the currently available modeling tools are introduced and illustrated on the most challenging problems in zeolite science. Directions for future model developments will be given.

Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

“…However, for large chemical systems, such as those encountered in heterogeneous catalysis, where adequate models typically include several hundred atoms, the “chemical accuracy” (4 kJ mol −1 for the energy barriers, one order of magnitude for the pre‐exponential factors) required for useful predictions is not attained. The exponential scaling with the system size of both the electronic structure methods (potential energy surface) and the nuclear motion problem (vibrational partition function) limits the applicable method to density functional theory (DFT) for the potential energy surface and the harmonic approximation for the vibrations 4, 5, 6, 7, 8. Depending on the functional, energy barriers may be in error by 10–20 kJ mol −1 , and the harmonic approximation is most problematic for low‐frequency modes, which are known to make the largest contribution to the partition functions 9…”

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

“…1 These materials have a three-dimensional periodic framework that consists of nanometersized channels and cages providing high porosity and large surface area. At present 218 distinct framework types are described, 2 of which only a small fraction is widely used as industrial material.…”

“…These topologies have 8-rings as their largest windows. Two compositions are considered as a starting point: (1) pure SiO 2 and (2) pure AlPO 4 structures. These pure materials (without acid sites) are listed in Table I: (1) SSZ-39, SSZ-13, and SSZ-16, and (2) AlPO-18, AlPO-34, and AlPO-56.…”

Effect of Feedstock and Catalyst Impurities on the Methanol‐to‐Olefin Reaction over H‐SAPO‐34

“…According to this mechanism, methanol reacts onto a pool of organic intermediates to yield a wide range of hydrocarbons 16. Active species in the HCP are poly‐methyl‐substituted benzeniums,17 and deactivation is likely caused primarily by coke deposition 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29…”

“…The formation of the hydrocarbon pool has been a source of significant debate by researchers and the literature is imbued with diverse and often conflicting theories resulting from a wide array of experimental analytical approaches 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39. The formation of the initial C−C bond during the induction period is at the base of this debate 2a–2c, 34.…”