The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

Abstract

Zeolites have a broad spectrum of applications as robust microporous catalysts for various chemical transformations. The reactivity of zeolite catalysts can be tailored by introducing heteroatoms either into the framework or at the extraframework positions that gives rise to the formation of versatile Brønsted acid, Lewis acid and redox‐active catalytic sites. Understanding the nature and catalytic role of such sites is crucial for guiding the design of new and improved zeolite‐based catalysts. This work presents an overview of recent computational studies devoted to unravelling the molecular level details of catalytic transformations inside the zeolite pores. The role of modern computational chemistry in addressing the structural problem in zeolite catalysis, understanding reaction mechanisms and establishing structure‐activity relations is discussed. Special attention is devoted to such mechanistic phenomena as active site cooperativity, multifunctional catalysis as well as confinement‐induced and multisite reactivity commonly encountered in zeolite catalysis.

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

“…Density functional theory (DFT) calculations are increasingly employed to gain insight into the reactivity of zeolites [16][17][18][19][20][21], for methanol dehydration [22][23][24][25] as well as subsequent steps in the MTO process involving the reaction of olefins and aromatics [26][27][28][29][30][31][32][33][34]. Kinetic models were developed to study initiation, step-wise methylation via surface methoxy species (SMS), concerted methylation, cracking and deactivation through coking revealing many features of the process [35][36][37][38][39].…”

Steering polymer growth by molding nanochannels: 1,5-hexadiene polymerization in high silica mordenite

“…Cu-or Ni-mordenites. [56,57] Also, the presence of Brønsted acid sites [58][59][60][61][62][63][64][65] could strongly affect the formation of a polymer inside the zeolite cavities: in particular, acid zeolites themselves can induce a polymerization reaction without the need of using high pressure and/or transition metals as catalysts. [46] Overall, despite such a long-standing interest, the field of polymer/zeolite nanocomposites remains underexplored and yet underexploited.…”

Small Crown-Ether Complexes as Molecular Models for Dihydrogen Adsorption in Undercoordinated Extraframework Cations in Zeolites

“…Much of this progress has been achieved by combining experiments with reliable theoretical calculations, which have been possible only due to the substantial growth in both computational power and innovative methodologies we have seen since the turn of the century. [6][7][8] Zeolites are porous silicates where framework Al substitutes some of the tetrahedral (Si) sites. This creates a negative framework charge that is compensated by positive counter ions, which are relatively flexible in their movement and are often strongly undercoordinated.…”