A DFT exploration of the adsorption of benzene and phenol on the industrial nanostructruredcatayst (ZSM-5)

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 6-311++G** standard basis set. Geometric parameters predict oneand two types of hydrogen bondings in the guest-ZSM-5 and guest-Al-ZSM-5 complexes, respectively. Variations of adsorption energy have been well correlated with the strength of hydrogen bonds.ΔEads, of benzene and phenol on the zeolites was considered as the energy difference between the absorbed complex system and the total energy of separated fragments as follows:ΔEads= Ecomplex- (Ebenzene/phenol +Ezeolite) Where Ecomplex represents the single-point energy of the optimized adsorption complex while Ezeolite and Ebenzene/phenol are the single-point energies of the optimized bare zeolite, separate benzene or phenol, respectively. According to obtained data, the deformation energy is moreprominent for Al-ZSM-5...Phenol adsorption complex compared to other adsorption complexesthat can be due to the stronger hydrogen bonding in Al-ZSM-5...Phenol. Atom in Molecules (AIM) and Natural Bonding Orbital (NBO) calculationsshowed a covalent nature for hydrogenbonds in the phenol…Al-ZSM-5 adsorption complex.It is worth mentioning that the energycalculation with different analysis obey the similar trend from hydrogen bonding strength standpoint.The differences in the adsorption behaviorbetween benzene and phenol on the ZSM-5 and Al-ZSM-5 are attributed to the differences in the strength of hydrogen bonding interactions.

Keywords:

ZSM-5 , adsorption energy , DFT