Formation mechanism of hydrogen production from catalytic pyrolysis of waste tires: A ReaxFF molecular dynamics and experimental study

The mechanism for the formation of gaseous products, especially hydrogen, from the catalytic pyrolysis of waste tires by using Ni-based catalysts has been studied. The catalytic pyrolysis of the three essential components of waste tires such as natural rubber (NR), styrene-butadiene rubber (SBR), and cis-polybutadiene rubber (BR) was simulated and the pyrolysis fracture of the molecular chain was investigated. This work aims to provide a deeper understanding of the reaction thermodynamics and kinetics for the formation mechanisms of gaseous products, primarily hydrogen. Microwave-assisted catalytic pyrolysis of the waste tires over Ni-based catalysts was carried out and used to assent to the simulation results. The study revealed that with the incorporation of 10 wt% Ni/ZSM-5 catalyst, the relative content of H₂ from the catalytic pyrolysis of waste tires can be significantly improved by about 41.3 % in comparison to the same measurement done in the absence of the catalyst. Kinetic and thermodynamic simulations for the catalytic pyrolysis of waste tires were also performed and the corresponding energy barriers and Gibbs free energy changes were calculated. Accordingly, the optimal reaction path for the hydrogen production was determined by comparing and analyzing the values of those parameters. It was confirmed that the addition of Ni, ZSM-5, and Ni/ZSM-5 catalysts promote the hydrogen production reaction pathways. Among those catalysts, the simulation result verified that Ni/ZSM-5 brings a pronounced hydrogen production capacity, which was consistent with the experimental findings.