Fe2O3 nanoparticle mediated molecular growth and soot inception from the oxidative pyrolysis of 1-methylnaphthalene.

While it is well documented iron oxide can reduce soot through burnout in the oxidative regions of flames, it may also impact molecular growth and particle inception. The role of Fe2O3 nanoparticles in mass growth of soot from 1-methylnapthalene (1-MN) was studied in a dual-zone, high-temperature flow reactor. An iron substituted, dendrimer template was oxidized in the first zone to generate ~5 nm Fe2O3 nanoparticles, which were seeded into the second zone of the flow reactor containing 1-MN at 1100°C and ϕ = 1.4-5.0. Enhanced molecular growth in the presence of Fe2O3 nanoparticles resulted in increased yields of polycyclic aromatic hydrocarbons (PAH) and soot compared to purely gas-phase reactions of 1-MN at identical fuel-air equivalence ratios. This also resulted in an increase in soot-number concentration and a slight shift to smaller particles with increasing addition (from no addition to 3 mM) of Fe2O3. Introduction of Fe2O3 nanoparticles resulted in the formation of stabilization of environmentally persistent free radicals (EPFRs), including benzyl, phenoxyl, or semiquinone-type radicals as well as carbon-centered radicals, such as cyclopentadienyl or a delocalized electron in a carbon matrix. At the high concentrations in the flow reactor, these resonance-stabilized free radicals can undergo surface-mediated, radical-radical, molecular growth reactions which may contribute to molecular growth and soot particle inception.