Influence of Confinement on Barriers for Alkoxide Formation in Acidic Zeolites

Abstract

The influence of the confinement imposed by eight different zeotypes on the formation of the alkoxides of 13 primary alcohols is studied using dispersion corrected density functional theory calculations with the PBE-D3 functional. Adsorption energies of the alcohols are computed along with barriers for formation of the alkoxides, which is the first step of the stepwise dehydration mechanism. We find that variations in the adsorption and transition state energies are largely governed by van der Waals interactions between substrates and the zeolite framework. Trends between different reactants, on the other hand, are largely due to the size of the molecules, which can be described quantitatively by the number of atoms constituting them. We find that the stabilization of adsorbates is largest for frameworks that are neither too small, leading to repulsive interaction, nor too spacious leading only to weak interaction.

Theoretical investigation of the olefin cycle in H-SSZ-13 for the ethanol-to-olefins process using ab initio calculations and kinetic modeling

“…69 Although our calculations were performed for H-SSZ-13 and not H-ZSM-5, we have observed previously that significant differences in activation barriers are typically transferable to other zeolite frameworks. 63,70…”

“…69 Although our calculations were performed for H-SSZ-13 and not H-ZSM-5, we have observed previously that significant differences in activation barriers are typically transferable to other zeolite frameworks. 63,70 An analysis of the kinetics shows that the largest contributions come from reactions no. 2, 4, 7, 11, 17, 22 and 23 (see ESI †).…”

“…Since vdW interaction generally depends on the specific fitting of the adsorbate and the microporous structure, different zeolites can be expected to differ in their vdW interactions with adsorbates, although on average, interaction increases with the size of the adsorbate. 63,70 3 Summary and conclusions…”

Molecular Views on Mechanisms of Brønsted Acid-Catalyzed Reactions in Zeolites

“…Whereas some computational studies consider the E1 mechanism only, passing through alkoxide intermediates and carbenium-like transition states, 618,655,656 other DFT comparative investigations suggest that the E2 mechanism is favored in the case of 2-propanol dehydration into propene in H-ZSM-5. 657,658 A E2 mechanism was also computed on pseudobridging silanols of amorphous silica−alumina, depicting an activation enthalpy fully compatible with experiments.…”

Machine Learning Prediction of Transition-State Energies in Small-Pore Zeolites Combining Acidity and Topology Descriptors

“…While it remains a great challenge due to the intricate topology structures and nonbonding interactions between guest and host moieties . Several attempts have been reported to unveil the effect of framework topology of zeolites on catalytic activity from the perspective of van der Waals (vdW) dispersion interactions. − In the case of the screening of large sets of zeolite candidates, it would be more attractive if the interested parameters could be directly predicted from readily accessible acidity and topology descriptors . However, the direct prediction of TS energies using both simple acidity and topology descriptors across different zeolite topologies is yet to be reported.…”