## 3 Results and Discussions
### Chemical Characterization of Pyrolytic Oil
#### 3.3.3 GC-MS  
The presence of a catalyst in the pyrolysis process of plastic waste improved the quality of the products obtained due to the multitude of reactions that occur during the pyrolytic process. In general, introducing a catalyst in this process can increase the concentration of aromatic compounds [42]. Figure S3 (in Supplementary Materials) shows the chromatograms and simulated distillation curves from the PE samples' thermal and catalytic in situ pyrolysis. In all samples, the pyrolytic oil was comprised of a complex mixture of organic compounds, resulting in the appearance of several peaks in the GC-MS chromatogram. The oil obtained from the residual PE without a catalyst was characterized in previous works. Many of the components present in this oil were 1-alkenes and n-alkanes in C\({}_{7}\)-C\({}_{32}\)[12, 35]. In the presence of the catalysts, the concentration of total paraffinic compounds decreased between 13 and 68 percent. The distribution of the number of carbons decreased while increasing the total content of aromatic compounds from 13.4 to 67.8%. The carbon chains are practically the same as those obtained without catalyst, approximately C\({}_{7}\) to C\({}_{28}\). Figure 4 shows the distribution of the hydrocarbon type presented in the liquid fraction according to designations ASTM D2425, D2786, D2789 and ASTM D3239 (detailed information is shown in Table S1 in Supplementary Materials). Figure 3: FTIR spectra of the pyrolytic oil samples from thermal and in situ catalytic pyrolysis: (**a**) Without catalyst; (**b**) HY; (**c**) HBEA and (**d**) HUSY. Similar results were obtained by [PERSON] and [PERSON] [43], who studied the catalytic pyrolysis of PE waste with zeolites HY and ZSM-5. Similar results were also found by [PERSON] et al. [44], who found that the thermal degradation of PE yielded compounds ranging in carbon number from C\({}_{1}\) to C\({}_{27}\) and higher. In contrast, the catalytic cracking of PE gave products with lower carbon numbers (from C\({}_{1}\) to C\({}_{17}\)). [PERSON] et al. [45] studied the catalytic degradation of HDPE on different zeolites obtaining a range of hydrocarbons C\({}_{3}\)-C\({}_{15}\). These authors studied the zeolite HY with a Si/Al molar ratio of 2.5, zeolite \(\beta\) (HBEA) with a Si/Al molar ratio of 25, similar to those used in this work, although they also worked with other catalysts such as ZSM-5 and moderite. HY zeolites and HBEA zeolite produced a higher amount of alkanes, with fewer alkenes and aromatics and very small amounts of cycloalkanes and cycloalkenes. In comparison, modernite and ZSM-5 gave a higher amount of olefins. Most alkanes were isoparaffins, having a high octane number, which produced a high-quality fuel. [PERSON] et al. [46] studied the catalytic pyrolysis of virgin LDPE with kaolin as a catalyst. The authors obtained a distribution of C\({}_{9}\)-C\({}_{25}\) hydrocarbons, mainly alkanes and alkenes. [PERSON] et al. [41] studied the thermal and catalytic pyrolysis of a mixture of plastic waste (PE, PP and PET). The authors found that the use of zeolites produces a decrease in the heavy oil fraction and wax formation. Additionally, HUSY had the best results in the total monoaromatic yield, and HZSM5 promoted the production of gases. Figure 5 shows the liquid products yield of the pyrolytic oil samples from thermal and in situ catalytic pyrolysis. The retention times of the representative carbon compounds of each oil show that there are valuable cuts in the range of heavy naphtha (C\({}_{6}\)-C\({}_{10}\)), kerosene (C\({}_{9}\)-C\({}_{15}\)) and diesel (C\({}_{13}\)-C\({}_{18}\)) [27]. Their proportion increased according to the bimodal distribution of the pore area of the catalyst used [47]. HBEA produced the largest amount of transportation fuels due to its smallest microporous surface area and the largest mesoporous surface area. The former reduced the formation of gases from the light fraction, and the latter increased the cracking of heavy fractions.