Enhancing catalytic performance for waste plastic upgrading: Simultaneous regulation of pore structure and acid sites in Ga-doped desilicated HZSM-5 catalysts

Though catalytic pyrolysis through HZSM-5 has shown great potential to convert waste plastics, it is urgent to modify the catalyst to improve its catalytic performance due to the low liquid product yields and inferior selectivity to high value-added monocyclic aromatic hydrocarbons (MAHs). During the study, two main modification methods, desilication via alkali treatment and Ga metal doping, were applied on HZSM-5 to reach simultaneous regulation of pore structure and acid site. It showed that selectivity to MAHs rose from 45.37 % to 58.45 % and 59.54 %, respectively, when 0.1 M and 0.4 M NaOH solutions were used for desilication. After Ga metal doping, selectivity to MAHs further increased to 67.43 % and 67.16 %, respectively, at A 0.1 M 5 %Ga/ZSM-5 and A 0.4 M 5 %Ga/ZSM-5, with selectivity to value-added benzene, toluene, ethylbenzene and xylene (BTEX) rising to 50.86 % and 46.45 % correspondingly. After three times of recycling, the catalyst still remained active with selectivity to MAHs staying above 65 %.