Pyrolysis of Yulin coal over ZSM-22 supported catalysts for upgrading coal tar in fixed bed reactor

•Coal pyrolysis tar was upgraded over ZSM-22-supported catalysts.•The addition of 5% catalysts could improve tar yield and quality.•ZSM-22-supported catalysts improved aliphatics, arenes and phenols.•CoOX/ZSM-22 was found to be more effective in producing aliphatics and arenes.

In the present study, catalytic pyrolysis of Yulin coal (YLC) using ZSM-22-supported catalysts was performed in a fixed-bed reactor and the resulting liquid products were determined with gas chromatography/mass spectrometer (GC/MS). The zeolite ZSM-22 and ZSM-22-supported CoOX, MoO3 and CoOX-MoO3 catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), scanning electron microscope-energy dispersive X-ray spectrometry (SEM-EDS) and temperature-programmed desorption of NH3 (NH3-TPD). The results showed that ZSM-22 and its metal oxides/ZSM-22 (MOs/ZSM-22) catalysts result in a higher tar yield, whereas lower char yield is produced. More importantly, the yield and distribution of tar could be controlled by tuning the type of acid sites of the catalysts. All catalysts significantly selectively improved the relative contents of aliphatics, arenes and phenols, whereas inhibited those of alcohols and nitrogen-containing compounds. Among those catalysts, MoO3/ZSM-22 was found to be more effective in producing phenols, and CoOX/ZSM-22 showed better performance in upgrading tar quality in terms of high selectivity for aliphatics (49.50%) and arenes (21.01%), while CoOX-MoO3/ZSM-22 favored to produce kerosene (13.75%).