*3.3. XRD Test Results and Analyses*

To obtain the microcrystalline structure parameters of samples, the XRD test results were fitted by using the Jade software, and the results are reported in Figure 3. The characteristic peaks of 002 and 100 were located at 24.879◦ and 43.254◦, respectively. According to the calculation method in the literature [38,39] and combined with the calculation results in Figure 3, the parameters including La (the mean diameter of aromatic ring lamellar in a stacked cluster), Lc (the effective stacking height of aromatic ring layers along the vertical direction of aromatic core), d002 (the layer spacing of aromatic ring lamellar), and Nave (the effective stacking layer number of aromatic ring layers) were calculated, and the La, Lc, and d002 were 11.77, 6.62, and 3.575 nm, respectively. The calculated microcrystalline structure parameters provided effective data for the subsequent construction of the coal macromolecular structure model and the stacking mode of each aromatic layer in the model.

**Figure 3.** XRD spectrum of gas coal.

#### *3.4. XPS Test Results and Analyses*

The modes of occurrence of C, O, N, and S atoms in coal were performed by the XPS test to infer the connection patterns of aromatic rings. The result of XPS test is presented in Figure 4a. The spectrum was fitted by the Avantage software, and the fitting results are shown in Figure 4b–d. According to the results of the ultimate analysis, the content of S was only 0.18%, which was not enough for one S atom. Thus, it was not considered in the molecular structure. The molecular formula of gas coal was expressed as CnH0.828nO0.05nN0.017n.

The results of C fitted spectra are shown in Figure 4b. There were four peak positions in the C split peak spectrum, which indicated that the carbon in coal mainly existed in four forms. The centers of the four peaks were 284.45 eV, 284.8 eV, 285.18 eV, and 290.06 eV. These different peaks were assigned to C−C, C−H, C−O, and C=O, respectively. Among them, the content ratio of C−C, C−H, C−O, and C=O was 0.56:0.29:0.11:0.05.

The results of O fitted spectra are shown in Figure 4c. From Figure 4c, ether oxygen bond (C−O), carbonyl (C=O), and carboxyl (COOH) existed in the oxygen spectrogram. The proportions of oxygen were 52%, 46.0%, and 2%, respectively. The centers of the three peaks were 531.3 eV, 532.35 eV, and 535.41 eV. Therefore, the content ratio between C−O, C=O, and COOH was 0.26:0.23:0.01.

The results of N fitted spectra are shown in Figure 4d. The P1 peak (Pyridinic nitrogen N-6) located at 399.3 eV was the largest, accounting for 51.86%. The second was the P2 peak (Pyridinic nitrogen N-5) located at 400.02 eV, accounting for 25.93%. The P3 peak at 401.65 eV belonged to quaternary nitrogen, accounting for 17.27%. The P4 peak with the smallest proportion at 404.5 eV belonged to nitrogen oxide, accounting for 4.94%, which was formed by the oxidation of pyridine nitrogen and pyrrole nitrogen in air.

**Figure 4.** Peaking fitting spectra of gas coal X-ray photoelectron spectroscopy: (**a**) XPS detection spectrum, (**b**) C split-peak fitting spectra, (**c**) O split-peak fitting spectra, (**d**) N split-peak fitting spectra.

#### *3.5. Construction of the Molecular Structure Model of Gas Coal*
