An efficient approach to explore the adsorption of benzene and phenol on nanostructured catalysts: a DFT analysis

Abstract

Adsorption of benzene and phenol on the 8T cluster model of ZSM-5 and Al-ZSM-5 catalysts, defined as ((H)₃SiO)₃–Si–O–Si–(OSi(H)₃)₃ and ((H)₃SiO)₃–Si–O(H)–Al–(OSi(H)₃)₃ structures, respectively, has been investigated comparatively using B3LYP, M06-2X, and wB97XD functionals employing the 6-311++G** standard basis set. Geometric parameters predict one and two types of hydrogen bonding in the guest-ZSM-5 and guest-Al-ZSM-5 complexes, respectively. Variations of adsorption energy, isotropic chemical shifts, δ_iso, of ¹H, ¹⁷O, ²⁷Al, and ²⁹Si atoms contributing in the hydrogen bonding as well as quadrupole coupling constant, C_Q, and asymmetry parameter, η_Q, of ²H, ¹⁷O, and ²⁷Al atoms have been well correlated with the strength of the hydrogen bonds. Atom in molecules (AIM) calculations showed a covalent nature for the hydrogen bonds in the phenol⋯Al-ZSM-5 adsorption complex. Furthermore, based on AIM, NQR and NMR, the C–H⋯O and O–H⋯π hydrogen bonds have been confirmed in the benzene adsorbate zeolite, which may highlight a crucial feature of the adsorption of benzene molecules inside the pores of zeolites. The differences in the adsorption behavior between benzene and phenol on the ZSM-5 and Al-ZSM-5 are attributed to the differences in the strength of the hydrogen bonding interactions. Finally, Al-ZSM-5 appears to be an efficient adsorbent for phenol and benzene.