Catalytic Decomposition of Toluene over Fe₂O₃ Nanocluster During Chemical Looping Gasification (CLG): ReaxFF MD Approach

Chemical looping gasification (CLG) is an effective technology for efficient utilization of coal, biomass and other fuels. In this work, the detailed mechanism of catalytic decomposition during CLG for toluene, a tar model compound, was studied by using reactive force field molecular dynamics (ReaxFF MD) method. Results show that toluene hardly decomposes at temperature lower than 2000 K. Improving temperature could significantly improve decomposition efficiency but also enhances the polymerization to produce PAHs and soot precursor, with largest molecule weight of 2175 (C₁₇₇H₅₁, 3000 K, 400 ps). Fe₂O₃ nanocluster, as oxygen carrier, could improve the decomposition efficiency of toluene and reduce the decomposition temperature. At 2000 K and 200 ps, the catalytic conversion of toluene reaches 60%. A large amount of H₂, CO, C₂H₂ and other small molecular gases are generated during the catalytic decomposition of toluene. At 3000 K, the yield of H₂, CO and C₂H₂ reached 132 %mole, 117 %mole and 40 %mole of toluene, respectively. Meanwhile, polymerization reactions are largely inhibited by Fe₂O₃ nanocluster and the largest molecule is C₂₀H₉O, the weight of which is much lower than soot precursor in thermal decomposition. Kinetic results show that the activated energy of catalytic decomposition is about 74 kJ/mole, which is much lower than thermal decomposition (382 kJ/mole). Detailed reaction mechanism reveals that lattice oxygen on Fe₂O₃ nanocluster act as the active sites, which enhance the decomposition of toluene.