XPS study on transformation of N- and S-functional groups during pyrolysis of high sulfur New Zealand coal

X-ray photoelectron spectroscopy (XPS) was used to investigate the nitrogen and sulfur functional forms present in New Zealand coal (NXL) and its pyrolysis char prepared under argon atmosphere at 8 different temperatures between 300 and 1 000℃. The N 1s spectra obtained were curve-resolved into 4 peaks: pyridinic-N (398.8±0.4 eV), pyrrolic-N (400.2±0.3 eV), quaternary-N (401.4±0.3 eV) and nitrogen oxides (402.9±0.5 eV); and S 2p peaks into 6 peaks: pyrite (162.5±0.3 eV), sulphidic (163.3±0.4 eV), thiophenic (164.1±0.2 eV), sulfoxide (166.0±0.5 eV), sulfones (168.0±0.5 eV) and sulfate (169.5±0.5 eV). The results show that nitrogen present in coal in pyrrolic forms is converted into pyridinic functionalities upon heat treatment and nitrogen oxides disappeared above 900℃. The major organic sulfur form in NXL is thiophene and its content is over 50%. Pyrite is decomposed completely into troilite at 600℃.