Multi‐site Cooperativity in Alkali‐Metal‐Exchanged Faujasites for the Production of Biomass‐Derived Aromatics

Abstract

The catalytic Diels–Alder cycloaddition–dehydration (DACD) reaction of furanics with ethylene is a promising route to bio‐derived aromatics. The reaction can be catalyzed by alkali‐metal‐exchanged faujasites. Herein, the results of periodic DFT calculations based on accurate structural models of alkali‐metal‐exchanged zeolites are presented, revealing the fundamental roles that confinement and the nature of the exchangeable cations in zeolite micropores have in the performance of faujasite‐based catalysts in the DACd reaction. Special attention is devoted to analyzing the effect of functional substituents on furanic substrates (furan, 2,5‐dimethylfuran, 2,5‐furandicarboxylic acid) on the catalyst behavior. It is demonstrated that the conventional reactivity theories of the Diels–Alder chemistry based on simplistic single‐site Lewis acidity and substituent effects do not apply if catalytic processes in the multiple‐site confined environment of zeolite nanopores are considered. The nature and cooperativity of the interactions between the multiple exchangeable cations and the substrates determine the reaction energetics of the elementary steps involved in the DACD process.

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

“…The computational analysis of the DACD conversion of substituted furans by alkali‐Y zeolites revealed only a minor role of the Lewis acidity of the reactive sites on the catalytic activity, which is to a large extend determined by the geometrical constraints imposed by the size of the cations and the reactants . It was demonstrated that the presence of electron‐donor or acceptor substituents on the furan ring does not have a direct effect on the DACD reactivity.…”

Electrical Double Layer as a Model of Interaction between Cellulose and Solid Acid Catalysts of Hydrolysis

“…A considerable portion of this biomass is represented by cellulose. This polymer can be hydrolyzed into soluble sugars, and the latter can be used as a feedstock for producing a multitude of chemicals: fuels like bioethanol or biobutanol, biodegradable polymer precursors like levulinic acid, platform chemicals (5‐hydroxymethyl furfural), etc . Catalysis of cellulose hydrolysis by strong mineral acids is well known and efficient, but isolation of the catalyst from the reaction products is complicated .…”

“…This polymer can be hydrolyzed into soluble sugars, and the latter can be used as a feedstock for producing a multitude of chemicals: fuels like bioethanol or biobutanol, biodegradable polymer precursors like levulinic acid, platform chemicals (5-hydroxymethyl furfural), etc. [3][4][5][6] Catalysis of cellulose hydrolysis by strong mineral acids is well known and efficient, but isolation of the catalyst from the reaction products is complicated. [7] Enzyme-catalyzed hydrolysis is slow, but the products are suitable for bioprocessing since they are free of acids or byproducts from acidinduced sugar conversion, which are harmful to microorganisms.…”

“…The electric charge of the dissociated acid groups or protonated glucose links is non-localized and uniformly distributed across the corresponding surface. 6. The protons that are not associated with either of the surfaces are distributed in the interplanar space according to the Poisson-Boltzmann equation (more on this below), forming a diffuse electrical layer.…”

“…This value will be important for calculating the overall electrostatic potential energy in the system. 6. Use the algorithm Steps 3-5 to calculate W cellðjÞ ; j ¼ 1; .…”