Lighter tars are largely useful in chemical industries but their quantity is quite little. Catalytic cracking is applied to improve the yield of light tars during pyrolysis. Consequently, in situ upgrading technique through a MoS₂ catalyst has been explored in this research work. MoS₂ catalyst is useful for the conversion of high energy cost into low energy cost. The variations in coal pyrolysis tar without and with catalyst were determined. Meanwhile, the obtained tar was analyzed using simulated distillation gas chromatograph and Elemental Analyzer. Consequently, the catalyst reduced the pitch contents and increased the fraction of light tar from 50 to 60 wt.% in coal pyrolysis tar. MoS₂ catalyst increased the liquid yield from 18 to 33 (wt.%, db) and decreased gas yield from 27 to 12 (wt.%, db) compared to coal without catalyst. Moreover, it increased H content and hydrogen-to-carbon ratio by 7.9 and 3.3%, respectively, and reduced the contents of nitrogen, sulphur, and oxygen elements by 8.1%, 15.2%, and 23.9%, respectively, in their produced tars compared to coal without catalyst.

Nonmetallic ionic liquids (ILs) exhibit unique advantages in catalyzing poly (ethylene terephthalate) (PET) glycolysis, but usually require longer reaction times. We found that exposure to UV radiation can accelerate the glycolysis reaction and significantly reduce the reaction time. In this work, we synthesized five nonmetallic dibasic ILs, and their glycolysis catalytic activity was investigated. 1,8-diazabicyclo [5,4,0] undec-7-ene imidazole ([HDBU]Im) exhibited better catalytic performance. Meanwhile, UV radiation is used as a reinforcement method to improve the PET glycolysis efficiency. Under optimal conditions (5 g PET, 20 g ethylene glycol (EG), 0.25 g [HDBU]Im, 10,000 µW·cm⁻² UV radiation reacted for 90 min at 185 °C), the PET conversion and BHET yield were 100% and 88.9%, respectively. Based on the UV-visible spectrum, it was found that UV radiation can activate the C=O in PET. Hence, the incorporation of UV radiation can considerably diminish the activation energy of the reaction, shortening the reaction time of PET degradation. Finally, a possible reaction mechanism of [HDBU]Im-catalyzed PET glycolysis under UV radiation was proposed.

Catalytic effects in fast pyrolysis of low-rank coal and coal tar conversion were investigated in a two-stage fixed-bed reactor over HZSM-5 zeolite and Mg/HZSM-5. Mg/HZSM-5 caused the lower total tar yield and the higher non-condensable gas yield but the fraction of light tar (boiling point below 360°C) increased to allow a slightly higher total yield of light tar. It also exhibited good catalytic activity and increased the species of light tar than HZSM-5 zeolite. The light tar fraction was increased from 45 to 74.6 wt% than without catalyst (66%) at the pyrolysis temperature of 600°C. Ex-situ catalytic fast pyrolysis over Mg/HZSM-5 also lowered the contents of element N and S in the resulting coal tars by 29% and 15% respectively. The corresponding increase in the content of element H and molar ratio of H to C of the resulting coal tars was reported as 17% and 13% respectively. The addition of Mg into HZSM-5 increased the ability of the catalyst for inhibiting coke deposition.

Compared with conventional pyrolysis, steam-assisted pyrolysis of polyethylene terephthalate (PET) can effectively eliminate char and upgrade terephthalic acid (TPA). However, during steam-assisted pyrolysis of PET, the degree of cracking still varies greatly, and while some of the product is excessively cracked to gas, the other part is still insufficiently cracked. In addition, these two types of products seriously affect the yield and purity of TPA. To further enhance the TPA, an attempt was made to reduce these impurities simultaneously by synergistic catalysis among the different components of the metal–acid catalyst. Through a series of experiments, Pt@Hzsm-5 was screened as the optimal catalyst. In the catalytic steam-assisted pyrolysis of PET, the optimum reaction temperature decreased to 400 °C, the calculated yield of TPA increased to 98.23 wt%, and the purity increased to 92.2%. The Pt@Hzsm-5 could be recycled three times with no significant decrease in the obtained yield of TPA. The catalytic mechanism of the Pt@Hzsm-5 was investigated through the analysis of the products and isotope tracing experiments. The Pt catalyzed the hydrogen transfer reaction between the water molecules and PET molecules, which inhibited the excessive cracking of TPA by improving the hydrogen transfer efficiency, reduced the generation of gaseous products, and improved the calculated yield of TPA. In contrast, the Hzsm-5 catalyzed the reaction of monovinyl ester cracking to TPA, effectively reducing the impurities in the solid product, increasing the olefin yield, and improving the purity of TPA. This discovery not only clarifies the synergistic catalytic effect of the Pt@Hzsm-5 in the steam-assisted pyrolysis of the PET reaction but also lays the foundation for further screening of other inexpensive metal–acid catalysts. This is of great significance to realize the industrial application of TPA preparation by PET pyrolysis.

With the increasing amount of plastic waste and the decreasing fossil energy, catalytic pyrolysis has become a promising technology for the production of fuels and chemicals from plastic waste. Polyethylene terephthalate (PET), a widely used plastic derived from non-renewable petroleum resources, is ubiquitous in daily life. However, the vast majority of PET is discarded within a year of use and is notoriously resistant to natural degradation, leading to significant environmental accumulation and pollution. This widespread waste and the inability to effectively recycle PET contribute to severe environmental pollution and resource depletion. In light of global trends toward sustainable development, circular economy principles, and pollution prevention, the development of efficient, sustainable, and environmentally friendly methods for processing waste PET has become an urgent priority. Among the potential solutions, catalytic pyrolysis has gained increasing attention as an effective strategy for recovering valuable chemical feedstocks from waste plastics. In this paper, we propose a novel strategy for catalytic pyrolysis of PET in a hydrogen (H₂) atmosphere to produce high-value-added chemical products, such as terephthalic acid (TPA), benzoic acid, and olefins. To this end, a NiMo catalyst is designed and investigated for its performance in PET catalytic pyrolysis. The paper aims to explore the structure-activity relationship between the NiMo catalyst and PET, assess the influence of various reaction conditions on the catalytic pyrolysis process, and elucidate the reaction mechanism for the formation of TPA. In particular, the high value conversion of waste poly(ethylene terephthalate) (PET) to aromatic products rich in terephthalic acid (TPA) is successfully achieved by pyrolysis using NiMo bimetallic catalysts in H₂. The catalytic performance of NiMo/Al₂O₃ and NiMo/ZSM-5 for pyrolysis of PET in a H₂ atmosphere at different temperatures (350–550℃) was investigated. In addition, NiMo catalysts with different Ni contents (Mo: 25wt%, Ni: 1wt%–10wt%) were prepared for the pyrolysis of PET in a H₂ atmosphere to evaluate the effect of Ni on the catalytic reaction. The experimental results show that the performance of NiMo catalyst is far superior to that of Ni or Mo catalyst. When NiMo/Al₂O₃ (Ni-5wt%) is used at 450℃, the highest aromatic compound yield of 62.6wt% is obtained and the TPA content reached 65.1%. Meanwhile, for the target product TPA, the catalytic performance of NiMo/ZSM-5 is slightly lower than NiMo/Al₂O₃. The excellent catalytic performance of the NiMo catalyst is due to a combination of effects. The characterization results show that active centers of the NiMo catalyst are dominated by MoO₂ and Ni. The promotion effect of Ni on the catalytic reaction is not only due to its own excellent hydrogenation performance, but also limits the agglomeration growth of MoO₂ particles, promotes the dispersion of MoO₂, lowers the activation temperature of the catalyst to increase the active sites, improves the thermal stability of the catalyst, and enriches the acidic sites of the catalyst. In addition, the mechanism of PET catalytic pyrolysis in a H₂ atmosphere was elucidated by in situ-GC. The main pathway for the conversion of PET to TPA is the transfer of H_β and the cleavage of alkoxy groups to generate carboxylic acids and vinyl esters, followed by the hydrocracking of vinyl esters into carboxyl groups and alkenes. This work provides valuable insights into the potential for improving the sustainability and efficiency of waste PET recycling, addressing both environmental concerns and resource management challenges.