Interaction of aromatics with Brönsted sites in zeolites: Demarcation line between regions of stable existence of H-complexes and ion pairs for various types of bases

Abstract

Interaction of naphthalene, cr and hexamethylbenzene with OH groups of SiO2, HNaY and H-ZSM-5 zeolites was studied by type of base appears to have its particular correlation of(PA -PA ) and the shift of Avon band in H-complexes. It has been found that if (PA* -PA U) is less than $5+5 kcal/mol, the formation of ion pairs is thermodynamically more favorable than that of H-complexes for all types of organic compounds.

Hydrogen Bond vs Proton Transfer in HZSM5 Zeolite. A Theoretical Study

“…The limitations of the 5T model are more dramatic when the proton affinity of the probe molecule lies in the 204-220 kcal mol -1 range because both minima (HB and IP) are obtained with similar stabilities, whereas the largest clusters provides the IP complex to clearly be the ground-state structure, in agreement with experiments. 21,34,35 The adsorption energies obtained with the 7T:63T cluster are in the range of the most accurate computed values and only somewhat underestimated with respect to calorimetric measurements. Moreover, it has been shown in a previous study 50 that similar ONIOM combinations lead to almost identical results to full periodic DFT calculations in the adsorption of H 2 O and NH 3 in HCHA.…”

Electrophilic aromatic substitution over zeolites generates Wheland-type reaction intermediates

“…2a). The observed bands at ~295, 334 and 415 nm are attributed to neutral alkylated benzenes, carbenium ions with alkyl side chain carbocation and aromatic ring protonation, respectively, whereas the band at 596 nm presumably develops due to the existence of π-complexes between the zeolite and aromatic species (vide infra for NMR results) [31][32][33][34][35][36][37][38][39] . The on-line MS data reveal the existence of diethyl ether, lower olefins (ethylene and propylene) and ethylbenzene ( Fig.…”

“…3, Supplementary Figs. 3-6 and Supplementary Methods II) [31][32][33][34][35][36][37][38] . Figure 3a-d reflects a redshift of the absorption maxima of a σ-complex (Wheland species), either upon ethylation of the zeolite or in the presence of an electron-donating group attached to the aromatic ring.…”

An ONIOM investigation of reaction mechanisms of propylene glycol dehydration over H-ZSM-5 and H-MOR catalysts

“…As zeolite catalysts as solid acid catalysts have been widely studied for the dehydration of alcohols [13][14][15][16], they have been employed for dehydration of propylene glycol to propanal. Zeolites were widely studied for their acidic properties of Brønsted acid sites [17,18] using several techniques [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Brønsted and Lewis acid sites in H-ZSM-5 and H-MOR catalysts were studied by means of 1 H and 27 Al doublequantum magic-angle spinning (DQ-MAS) NMR spectroscopy [34].…”