Modification of chemical vapor-phase deposition and coking resistance over HZSM-5 catalysts for toluene disproportionation

Abstract To achieve higher catalytic activity of toluene disproportionation and improve the p-xylene selectivity and stability of coking resistance on HZSM-5 catalysts, tetrabutyl titanate, ethyl orthosilicate and diethyl phosphite were used for chemical gas-phase deposition modification on HZSM-5 catalysts. The properties of acid sites on catalysts were characterized by infrared spectroscopy (IR) and temperature-programmed desorption of pyridine (TPD), respectively. The experimental results showed that the type of acid sites and density of weaker acid sites over HZSM-5 zeolites deposited by oxides containing Ti, Si and P in chemical vapor coating did not change while the density of stronger acid sites decreased, in which acid intensity on HZSM-5 zeolite deposited by oxides containing P enhanced obviously. Using HZSM-5 zeolites modified as catalysts of toluene disproportionation, HZSM-5 catalysts deposited by oxides containing Si and P can greatly improve both catalytic activity and coking resistance on catalysts.