## 1 Introduction  
Raman spectroscopy has been used to study carbonaceous materials since the 1970s [1]. As a unique type of spectroscopy, Raman spectroscopy has many advantages in coal structure analysis over other techniques [2]. Raman spectroscopy can provide fast, simple, repeatable, and lossless qualitative and quantitative analysis of defects, and has been widely used in the coal chemical industry. Raman spectroscopy can be used to analyze the structure of coal and the quality of organic matter in order to characterize the catalysts in the coal chemical process and to detect heavy fraction leaching [3]. [PERSON] et al. [4] have studied the identification of minerals in coals, one of the principal areas of the field, and identified calcite, pyrite, and dolomite by using a micro-Raman spectrometer. [PERSON] and [PERSON] [5] and [PERSON] and [PERSON] [6] have published the first Raman spectrum of coal and reported G (1575-1620 cm\({}^{-1}\)) and D-bands (1355-1380 cm\({}^{-1}\)). [PERSON] and [PERSON] have suggested that the 1575 cm\({}^{-1}\) band can be assigned to the graphite E\({}_{\rm 2g}\) mode with D\({}^{4}\)\({}_{\rm 6h}\) crystal symmetry, that the band at 1370 cm\({}^{-1}\) can be assigned to the A\({}_{\rm 1g}\) mode, and that the ratio I\({}_{\rm D}\)/I\({}_{\rm G}\) relates to the average graphite domain dimension. La. [PERSON] and [PERSON] have debated the origin of the band at 1580 cm\({}^{-1}\) by investigating IR absorption and the Raman scattering of very finely ground graphite (C-C bonds broken), coal, and carbon black. They have suggested that the band at 1350 cm\({}^{-1}\) most likely arises from graphitic structures, and not from aromatic or conjugated carbonyls, as had been suggestedearlier. [PERSON] and [PERSON] [7] have found that the width of the D-band for chars originates from various ranks of coals and decreases with increasing heat treatment temperature (from 240 cm\({}^{-1}\) at 500 \({}^{\circ}\)C, with La = 2 nm, to 40 cm\({}^{-1}\) at 1900 \({}^{\circ}\)C, with La = 7 nm). On the other hand, [PERSON] and [PERSON] [8] have found that the G+D\({}^{\prime}\) band of different coals decreases with increasing coal rank, although they did not observe a trend (the D\({}^{\prime}\) peak located around 1620 cm\({}^{-1}\) is due to irregular carbon and often appears with the G peaks). [PERSON] [9] has postulated a simple qualitative analysis in order to distinguish carbonaceous materials with low, medium, and high structural organization by analyzing 15 samples that included graphite, coke, coal and anthracite. He has found that the width of the D band relates to the degree of its disorder, but that neither the D nor the G bands can explain the degree of this disorder. After analyzing chars generated from the pyrolysis and gasification of Australian brown coal by Raman spectroscopy, [PERSON] et al. [10] have identified 10 characteristic bands that they believe are attributable to the highly disordered carbon structure of coal [11]. [PERSON] [12] has studied the relationship between the microstructure and the combustion reactivity of coal char by Raman spectroscopy [13]. Recently, much research has been carried out on the application of Raman spectroscopy to coal. Raman spectroscopy has been applied to rapidly determine organic matter maturity and value the chemical structure and thermal maturity of vitrinite [14; 15]. The relationship between coal structures and combustion characteristics has been investigated by micro-Raman spectroscopy, which can provide a new approach to rapidly predicting the coal properties by observing the reasonable correlations between the Raman spectral parameters and V\({}^{\text{daf}}\)[2]. In addition, Raman spectroscopy has been used to distinguish components of graphitized coals and quantitatively evaluate vitrinite reflectance in shale [16; 17]. An in-situ study at high temperature [18] can provide valuable information concerning structural evolution for fundamental research on coal pyrolysis.