Theoretical study of the aluminum distribution effects on the double proton transfer mechanisms upon adsorption of 4,4'-bipyridine on H-ZSM-5.
The aluminum distribution effects on the adsorption of 4,4'-bipyridine (44BPY) in the straight channel of H-ZSM-5 simulated by two ten-membered ring clusters (2-10T) have been investigated by DFT methods. The energetic and structural properties of the complexes formed upon interaction of 44BPY with the zeolite Brønsted acid sites for six different aluminum distributions were determined by B3LYP/6-31+G* calculations. Dispersion energies were estimated by performing single point calculations at the MP2 and M06-2X levels. Interaction energies were corrected for basis set superposition error (BSSE). The minimum energy pathways of the double proton transfer from H-ZSM-5 to 44BPY were characterized. Two mechanisms are proposed: a concerted mechanism in which both protons are simultaneously transferred giving the bidentate ion pair complex (44BPYH₂²⁺/2-10T²⁻) and a consecutive mechanism in which one proton is transferred directly leading to the monodentate ion pair complex (44BPYH⁺/2-10T⁻), whereas the second proton can be transferred according to Al distribution. The formation of monodentate or bidentate complexes strongly depends on the Al distribution.
Laboratoire de Modélisation Moléculaire, Institut de Chimie, Université des Sciences et de Technologie, LTMM-USTHB, BP 32 Dar El Beida, Alger, Algérie.
Yamina
Y
Akacem
Martine
M
Castellà-Ventura
Emile
E
Kassab
D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D011522:Protons; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D013499:Surface Properties; D017641:Zeolites / Q000737:chemistry*
D011522:Protons; D011725:Pyridines; C570564:ZSM-5 zeolite; D017641:Zeolites; D000535:Aluminum; C034306:4,4'-bipyridyl