Thermogravimetric kinetic study of low-rank coal pyrolysis over Fe–TiO2 and Fe–HZSM-5 catalysts: Activation energy and reaction mechanism analysis

Low-rank coal (LRC) is an abundant energy resource, but restricted by high moisture content, high volatile matter, and low calorific value. Therefore, in this study, the influence of the physicochemical properties of LRC and Fe–TiO 2 and Fe–HZSM-5 catalysts on pyrolysis kinetics, as well as the activation energy (E a ) and reaction mechanisms under both conventional and microwave-induced heating are systematically studied. The non-isothermal thermogravimetric analysis was performed based on the Coats–Redfern integral kinetic model to evaluate key kinetic parameters. Full characterization of the catalysts in terms of composition, dielectric properties, surface acidity, as well as specific surface area (S BET ) and pore structure was conducted to understand structure–reactivity relationships. Functional group variations during pyrolysis were also investigated by FTIR. The data showed that traditional catalytic pyrolysis had apparent E a (59.7–71.5 kJ/mol), and that second-order kinetics for Fe–TiO 2 and first-order kinetics for Fe–HZSM-5 were deduced. Distinct from catalytic pyrolysis, microwave catalytic pyrolysis (MCP) significantly reduced the E a to ∼6.0–6.2 kJ/mol and promoted a more uniform first-order reaction pathway. As one of the studied catalysts, Fe–HZSM-5 had a combined Brønsted–Lewis acidity and hierarchical pore structure favorable for reactions such as favorable for dehydration, deoxygenation, and aromatizations. In contrast, Fe–TiO 2 predominantly promoted thermal cracking and redox-activated pathways. These results further justified that MCP, especially with Fe–HZSM-5, was an energy-efficient, selective, and sustainable process for enhancing LRC conversion and improving the production of value-added products.