The present work analyzes these particle evolution processes along the plane axis in an iron precursor (iron pentacarbonyl) loaded methane/air counterflow diffusion flame. The addition of iron pentacarbonyl into methane led to the formation of iron-based nanoparticles in the flame, together with the pre-existing soot particles. These two types of nanoparticles were found to be distinct in their shapes, chemical compositions, geometric mean particle diameters, total particle number concentrations, and particle size distributions. Nanoparticles produced in the flame were sampled from various axial and radial locations by means of a vacuum pump and their particle size distributions were characterized using a scanning mobility particle sizer (SMPS). The representative nanoparticle samples were also collected on the probe and examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDAX). SMPS, SEM and EDAX analysis revealed the nucleation, growth, agglomeration and interaction of these nanoparticles formed in the flame, evidenced by the changes of particle morphology, averaged particle size and elemental composition. Adding iron precursors was found to promote particle inception, leading to a greater total particle number concentration but a smaller mean particle diameter. Near the flame location, combustion of soot particles was accelerated due to the catalytic role of iron-based nanoparticles, which agrees the observation of primarily smaller iron-based nanoparticles dominating in the particle population. These findings shed light in studying the engine performance when the fuel borne catalysts are injected for abating particulate matters (PM) during regeneration of Diesel Particulate Filters (DPFs). (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.