In Situ Raman Spectroscopy Study on Catalytic Pyrolysis of a Bituminous Coal

How different catalysts would affect the evolution of char structure with increasing temperature during the pyrolysis of coal is fundamentally important for the clean utilization of coal. In this study, we applied in situ Raman spectroscopy and a fixed-bed reactor to characterize the evolution of char structure and product gas formation behavior. The results showed that the formation curves of the main gases presented two stages and the catalyst enhanced the pyrolysis significantly. The Raman spectra were fitted with a combination of four Lorentzian bands (D1, D2, D4, G) and one Gaussian band (D3) in the first-order region. Spectral parameters, such as band position, full widths at half-maximum (FWHM), and band area ratio, were used to characterize char structure. The D1 and G band FWHM and band area ratios ID1/IG, ID3/IG, and ID4/IG increased with increasing temperature, while the D1 and G band positions and IG/IAll decreased, indicating a decrease in the ordering of the char structure. The addition of catalyst led to a lower degree of char structural order. Thermogravimetric analysis was also used to measure the reactivity of char derived from pyrolysis, and the results showed a good correlation between reactivity indexes and IG/IAll.