Toward the Mechanism of o-Xylene Isomerization in Selected Zeolites of Different Si/Al Ratios and Channel Sizes-Experiment Corroborated by Periodic DFT plus D Simulations

The present work comprises the characterization of zeolite properties in the view of their usability as catalysts in the isomerization of xylenes and ethanol-to-hydrocarbon (ETH) process. Therefore, the intermediate products of these reactions have been proposed as the 5- and 7-membered hydrocarbon ring structures. The quantum chemical calculations were carried out at the periodic DFT GGA + D level of theory to optimize the structures of zeolites and xylenes and the protonated forms of the latter. The isomerization and the ETH processes have similar intermediate products; their identification is not, however, possible spectroscopically; hence, the quantum chemical calculations deemed necessary. The calculations include thermal effects-the entropic contributions were calculated via the classic, harmonic vibrational analysis, and the Gibbs free energies were calculated at T = 298 K, the temperature at which the spectra of gaseous and adsorbed species were recorded. Based on the analysis of the contributions to the adsorption energy of the hydrocarbon 5- and 7-membered ring structures and having verified the results via comparison of the calculated IR spectra to the experimental ones, the most probable intermediate products were proposed.

Automated summary

This study characterizes the properties of zeolites for their use as catalysts in xylene isomerization and ethanol-to-hydrocarbon processes. Quantum chemical calculations were used to optimize structures and identify probable intermediate products, as spectroscopic identification was not possible. Thermal effects and Gibbs free energies were also considered in the analysis of the hydrocarbon ring structures to propose the most likely intermediate products.