An Active Alkali-Exchanged Faujasite Catalyst for p-Xylene Production via the One-Pot Diels–Alder Cycloaddition/Dehydration Reaction of 2,5-Dimethylfuran with Ethylene

Abstract

The one-pot Diels–Alder cycloaddition (DAC)/dehydration (D) tandem reaction between 2,5-dimethylfuran and ethylene is a potent pathway toward biomass-derived p-xylene. In this work, we present a cheap and active low-silica potassium-exchanged faujasite (KY, Si/Al = 2.6) catalyst. Catalyst optimization was guided by a computational study of the DAC/D reaction mechanism over different alkali-exchanged faujasites using periodic density functional theory calculations complemented by microkinetic modeling. Two types of faujasite models were compared, i.e., a high-silica alkali-exchanged faujasite model representing isolated active cation sites and a low-silica alkali-exchanged faujasite in which the reaction involves several cations in the proximity. The mechanistic study points to a significant synergetic cooperative effect of the ensemble of cations in the faujasite supercage on the DAC/D reaction. Alignment of the reactants by their interactions with the cationic sites and stabilization of reaction intermediates contribute to the high catalytic performance. Experiments confirmed the prediction that KY is the most active catalyst among low-silica alkali-exchanged faujasites. This work is an example of how the catalytic reactivity of zeolites depends on multiple interactions between the zeolite and reagents.

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

“…DACD is considered as an important step in a perspective chemocatalytic technology for the production of aromatic products from renewable cellulosic biomass feedstock . The conversion of dimethylfuran with ethylene over different alkali‐exchanged Y zeolites has been studied in detail by periodic DFT calculations complemented with electronic structure analysis, microkinetic modelling and catalytic tests using a range of alkali‐exchanged FAU‐type zeolites . The study demonstrated the crucial role of the synergetic effect of the ensemble of cations in the FAU supercage on the DACD reaction.…”

The influence of spatial limits on the modeling chemical reactivity: The example of CO2 hydration in MeX zeolites (Me = K, Rb, Cs)

“…At first we started the ciNEB computations of CO 2 hydration reaction for the MeX cells with optimized fractional coordinates but the lattice constants being fixed to that calculated for NaX, thus overestimating slightly the experimental volumes for KX, RbX, and CsX (Table , dot‐dot‐dashed line in Figure ). This approach corresponds to the hypothesis of nearly constant cell parameters for all of them . Respective data for initial geometries (REA) before the reaction are given in the upper row of Table .…”

“…Current computational facilities allow modeling of complex chemical reactions in zeolites. They involve sufficiently large zeolite cells such as MeX or MeY with reagents larger than H 2 O and CO 2 such as 2,5‐dimethylfuran and ethylene . Often, the variations of the cell sizes are neglected while calculating chemical reactions using ciNEB.…”

“…Dramatic variations in the MTO process were observed due to a minor difference of 0.3 Å in the pore diameters between the HZSM‐12 and HZSM‐22 zeolites . The simulation of reactions between large cations and large molecules in confined media is rapidly expanding due to widely distributed software operating with atomic orbitals and plane waves . The recent analysis of the confinement effects on the processes in zeolites was performed mainly with respect to the ONIOM two‐layer approaches .…”

“…Later, this approach was transformed within the framework of ONIOM method . The development of computational facilities made possible the approach with periodic boundary conditions (PBCs), in which the problem of a change of internal space between different cationic forms was neglected, for example, because of apparently large porous space, such as in alkali MeFAU forms . The possibility of various methods to accurately calculate the reaction barrier in the pores and parallel cationic diffusion, which is very probable for heavy alkali cations, is different.…”