Effects of silylation on Ga/HZSM-5 for improved propane dehydroaromatization

Dehydroaromatization of propane to high value-added aromatics, especially benzene, toluene and xylene (BTX), has attracted widespread attention. Many works have been done to improve the catalytic performance of gallium loaded HZSM-5 catalysts. However, there were few reports focused on reducing the cracked by-products, such as methane and ethylene, derived from propane cracking reaction on external Bronsted acidic sites of zeolite. Herein, chemical liquid deposition (CLD) method was adopted to passivate the external strong Bronsted acid of Ga/HZSM-5, aiming to increase the most value-added BTX production by suppressing the undesired propane cracking reaction. The content of deposited SiO2 on the external surface of zeolite was tunable by varying the amount of liquid deposition reagent and duration time of CLD process. The results showed that an appropriate content of SiO2 on external surface of catalyst was beneficial to disable the external strong Bronsted acid sites. Due to depressing the undesired propane cracking reaction, BTX selectivity of 55% with propane conversion of 49% was achieved on Ga/Z5-4Si catalyst, higher than those of Ga/HZSM-5. Otherwise, prolonging the duration time of CLD process narrowed the micropore mouth size of zeolite, which could enhance the shape selective effect of Ga/ZSM-5 to increase the proportion of para-xylene in total xylene products.

Automated summary

Passivating the external strong Bronsted acid sites of gallium loaded HZSM-5 catalyst using chemical liquid deposition (CLD) method can increase the BTX production and suppress the undesired propane cracking reaction. An appropriate content of SiO2 on the external surface of the catalyst is beneficial, and prolonging the duration time of the CLD process can enhance the shape selective effect.