Pyrolysis of Huang Tu Miao coal over faujasite zeolite and supported transition metal catalysts

Catalyst surface modification with supported metals is an efficient way of controlling coal pyrolysis and enhancing the production of high value-added chemicals. In this work, zeolite NaX and CoOx-, MoOx-, and CoOx–MoOx-supported NaX catalysts were prepared and characterized by transmission electron microscopy, scanning electron microscopy-energy dispersive spectroscopy, X-ray diffraction, and Brunauer–Emmett–Teller analysis. Huang Tu Miao (HTM) coal, a typical long flame coal in Western China, was selected as the testing material. The pyrolysis of HTM coal was conducted in 5% H2/N2 atmosphere, and the volatiles were examined by thermogravimetric (TG) Fourier-transform infrared (FTIR) spectroscopy. The addition of zeolite NaX significantly enhanced the production of CO, CH4, and aromatic and aliphatic hydrocarbons, and dramatically reduced the generation of CO2. These results are in contrast to the transition metal oxide-supported HZSM-5 in our previous report. In addition, the pyrolysis product profiles, expressed by FTIR absorbance, were similar for the HTM-NaX and HTM-HZSM-5 mixtures but different for the HTM-transition-metal-incorporated zeolite NaX and HZSM-5 mixtures. This result may imply differences in pyrolysis mechanism. Catalyst composition, pore size, and acidity may play key roles in pyrolysis. The pyrolysis kinetics of HTM coal was determined by the single reaction, first-order model. The lowest activation energy of the secondary degasification stage was observed in CoOx–MoOx/NaX.

► Catalytic pyrolysis of HTM coal was conducted over NaX and MOx/NaX catalysts.
► Catalyst composition, pore size and acidity may play key roles in the pyrolysis.
► The lowest activation energy of 2nd degasication was observed on CoOx–MoOx/NaX.
► The pyrolysis mechanism may be different for the HTM-NaX and HTM-HZSM-5 mixtures.