Mechanistic insights into FeO and Fe2O3 catalytic cracking of toluene: a molecular dynamics study

The mechanistic differences in the high-temperature catalytic cracking reactions of ferrous oxide (FeO) and ferric oxide (Fe 2 O 3 ) on toluene (C 7 H 8 ; a model for biomass tar) were investigated using a reactive force-field molecular dynamics simulation (ReaxFF-MD) method. The results showed that FeO adsorbs H atoms to form HFe radicals mainly through Fe active sites (Fe 2+ ), promoting dehydrogenation and C-C bond breaking, maintaining activity through the redox cycling reaction of HFeO ⇌ Fe + HO–. The FeO system exhibited the highest hydrogen-producing efficiency, with a hydrogen recovery rate 10.0% greater than that of the pure pyrolysis system. The Fe 2 O 3 system inhibited H adsorption due to the surface Fe–O–Fe structure. The hydrogen recovery rate was 7.22% greater than those of the pure pyrolysis system and its strong oxidative properties resulted in H 2 O and CO generation. The Fe 2 O 3 -catalyzed system exhibited stronger oxidation ability, further increasing the proportion of C 1– C 4 small molecule products and reducing the C 12+ coke precursor generation. The results revealed the distinct pathways of FeO and Fe 2 O 3 in high-temperature toluene catalytic cracking and their effects on product selectivity and system energy, supporting the development of carbon build-up resistant iron-based catalysts for biomass tar cracking.