*2.1. Elemental and Industrial Analysis Tests*

The elemental and industrial analysis tests were carried out by SX2-2.5-10 apparatus of Beijing Zhongxing weiye and Thermo Scientific Flash 2000 apparatus based on Chinese national standards GB/T212-2008 and GB/T476-2008. The experimental results are shown in Table 1.


**Table 1.** The results of elemental and industrial analysis tests.

#### *2.2. Experimental Protocol*

The gas coal samples were taken from the Huainan mining area in Anhui Province. The samples were crushed and sieved into 60–80 mesh particles before the experiments. The information on each carbon atom, the structural parameters of microcrystals, and the occurrence modes of C, O, N, and S atoms in the samples was obtained by 13C-NMR, XPS, and XRD tests. The macromolecular model of coal was constructed and optimized by the Materia Studio (MS) software. The specific process is shown in Figure 1.

**Figure 1.** Gas coal macromolecular modeling flow chart.

(1) 13C-NMR spectroscopy (13C-NMR)

The carbon atoms information was obtained using the Bruker400m solid-state NMR ( 13C-NMR) instrument. The experiment used high-resolution solid-state nuclear magnetic resonance spectroscopy. The MAS spin rate was 10 kHz, the recovery time was 4 s, and the pulse width was 4.5 μs. The pre-scan delay was 6.5 μs, and the scanning number was 3000.

(2) X-ray diffraction (XRD)

The microstructure parameters of coal were obtained using the German Bruker D8 Advance X-ray diffractometer (XRD) with Cu target radiation. The specified parameters were as follows: the counting time was 19.2 sec/step, the step size was 0.02034◦, the scan range was 5◦–80◦, the voltage was 40 kV, and the current was 40 mA.

(3) X-ray photoelectron spectroscopy (XPS)

The occurrence modes of C, O, N, and S atoms were obtained using the X-ray photoelectron spectrometer from Thermo Fisher Scientific, and the parameters were as follows: the monochromatic was Al Ka, the energy was 1486.6 eV, the angle of electron emission was 45◦, the beam spot was 500 μm, the number of scans was 5, and the charge correction was corrected using carbon C1s = 284.8 eV.

#### **3. Results and Discussions**

*3.1. The Analysis of the Elemental Normalization and the Atomic Ratio*

The content of elements, types, and the atomic percent were determined by proximate and ultimate analysis. The contents of oxygen in Table 1 were calculated by deducting the moisture and ash. The ultimate analysis was normalized to calculate the atomic ratio of each atom. The results are shown in Table 2. Based on the atomic ratios, if the number of C atoms in coal is n, the molecular formula of coal can be expressed as CnH0.828nO0.05nN0.017nS0.001n.

**Table 2.** The results of the elemental normalization and the atomic ratio.

