Reaction mechanism of benzene alkylation with propylene catalyzed by HZSM-5 zeolite and H-Beta zeolite

Abstract In this work, two possible alkylation mechanisms (i.e., consecutive and associative mechanisms) of benzene and propylene to produce cumene were investigated by the density functional theory (DFT) using the B3LYP functional of the Gaussian 09 package with the 8 T model of HZSM-5 zeolite. The results showed that the main alkylation mechanism of benzene and propylene on HZSM-5 zeolite is the associative mechanism, which has a lower energy barrier than the consecutive mechanism. Moreover, two kinds of zeolites (i.e., HZSM-5 and H-Beta) for benzene alkylation with propylene to produce cumene are compared. For the associative mechanism, the activation energy (99 kJ/mol) on HZSM-5 is lower than that on H-Beta (106 kJ/mol). For the consecutive mechanism, in the protonation step, the activation energy of H-Beta is 66 kJ/mol, while the activation energy of HZSM-5 is 59 kJ/mol, which is due to HZSM-5 having stronger acidity to readily furnish Ha acidic protons. In the alkylation step, HZSM-5 has a lower energy barrier (229 kJ/mol) than H-Beta (294 kJ/mol). Thus, benzene alkylation with propylene is easier to carry out on HZSM-5 zeolite than on H-Beta zeolite.