# An Experimental Study of Glycerol Carbonate Synthesis over g-C\({}_{3}\)N\({}_{4}\) Catalysts
## 3 Results and Discussions
### Catalyst Characterization
The hysteresis loop observed at a high relative pressure (P/P\({}_{0}\)) of 0.5-1.0, categorized as type H\({}_{3}\), suggests the presence of slit-shaped pores associated with plate-like particles [59]. This characteristic is consistent with the layered morphology also observed in the SEM analysis. Similar results have been reported in previous studies [32; 40; 53]. Additionally, variations in N\({}_{2}\) adsorption volumes indicated differences in surface area among the samples. Table 1 summarizes the surface area, pore volume, and pore width of the synthesized catalysts. A decrease in the specific surface area was observed for PSCN compared to CN, from 10.85 to 10.10 m\({}^{2}\)/g, with an even further reduction to 9.19 m\({}^{2}\)/g in the case of MgPSCN, which is consistent with previous studies [26; 28; 40]. In contrast, LiPSCN exhibited a significant increase in surface area, reaching 17.32 m\({}^{2}\)/g. The comparable specific surface area of these samples did not have a significant impact on their catalytic activity. Furthermore, a substantial increase in pore width was observed, approximately 6-fold for both PSCN and LiPSCN compared to CN, while MgPSCN showed an increase of approximately 3-fold. The thermal stabilities of CN, PSCN, MgPSCN, and LiPSCN samples were assessed using thermogravimetric analysis (TGA) under a nitrogen (N\({}_{2}\)) atmosphere, as shown in Figure 6. An initial weight loss of 5%, 6.1%, 7.4%, and 6.5% was observed for CN, PSCN, MgPSCN, and LiPSCN, respectively, up to 200 \({}^{\circ}\)C. This weight loss is attributed to the evaporation of water molecules adsorbed physically and chemically, along with the removal of hydroxyl groups [60; 61]. In the temperature range of 200-400 \({}^{\circ}\)C, CN exhibited a minor weight loss of approximately 1%. However, doping with sulfur and phosphorus in PSCN led to an increased weight loss of around 3%, which can be explained by the lower thermal stability of the P-O-C bond compared to the C-C bond, thus reducing the initial decomposition temperature [62]. For MgPSCN and LiPSCN, the weight loss in this temperature range increased to 3.5% and 8%, respectively. This is likely due to the  
Figure 5: Adsorption–desorption isotherms and pore volume distribution for CN, PSCN, MgPSCN, and LiPSCN. enhanced thermal conductivity of metals and their oxides, facilitating more uniform heat transfer and promoting the catalytic decomposition of PSCN in this range [62]. The effect is particularly pronounced in LiPSCN between 400 and 600 \({}^{\circ}\)C, where a significant weight loss of 23.6% was recorded, compared to 15.2% for MgPSCN and 14.5% for PSCN in the same temperature range. Therefore, based on the previous results, PSCN and MgPSCN are considered to be more thermally stable than LiPSCN. The FTIR spectrum of the catalysts, particularly for the CN catalyst shown in Figure 7, exhibits broad peaks observed near 3000-3600 cm\({}^{-1}\), corresponding to N-H stretching vibrations. The peaks in the range of 1200-1650 cm\({}^{-1}\) are associated with the aromatic heterocyclic C-N rings. The peak at 800 cm\({}^{-1}\) is attributed to the breathing mode of triazine rings. These findings confirm the structural integrity of g-C\({}_{3}\)N\({}_{4}\), consistent with previously reported results [40; 52]. For PSCN, MgPSCN, and LiPSCN the reduced intensity of the C-N and N-H vibrational peaks indicate structural distortions caused by the incorporation of phosphorus and sulfur additives. Additionally, the slight shifts in the characteristic peaks reflect strong interactions between the active materials and the g-C\({}_{3}\)N\({}_{4}\) framework. These results are similar to those of previous studies [50], which found that the addition of phosphorus and sulfur altered the electronic properties and enhanced the Lewis basicity. A notable observation for MgPSCN is the further decrease in peak intensity compared to PSCN, indicating stronger structural distortions attributed to Mg-N coordination.