Transformation of microcrystalline and graphitization of particulate matter during DPF regeneration driven by non-thermal plasma: Mechanisms and reaction pathways

The serious hazards of particulate matter (PM) to both ecological environments and human health necessitate the urgent development of green, sustainable technologies. This paper presents the application of non-thermal plasma (NTP) for low-temperature degradation of PM within a diesel particulate filter (DPF). The correlation between the evolution of primary particle crystallites and the degree of graphitization was elucidated, while key governing factors for PM decomposition were identified. The results indicate that the synergistic interplay of NTP active species concentration, reaction temperature, and duration governs PM microcrystalline evolution at position 2a. Moderate active species concentration coupled with an optimal temperature range (129.2 °C∼143.8 °C) drives maximum PM oxidation efficiency. The curvature of the “shell” crystallites increases, while the length, interlayer distance, width, and gap all decrease after the NTP reaction. It undergoes a dynamic process of “relaxation → rearrangement compression → repulsion equilibrium”. The disordered crystallites in the core are oxidized causing the curvature to increase and crystallites length and width to decrease. The overall crystallite length and layer width of primary particles are dominated by the “shell”, while the crystallite curvature is dominated by the “core”. The decrease in primary particle length and the increase in crystallite curvature lead to an increase in I_D1/I_G and a decrease in the degree of graphitization. The reaction parameters could be adjusted to optimize the PM oxidation and decomposition pathway, enhancing the efficiency of DPF regeneration by NTP. Non-thermal plasma provides a new technical path for the removal of environmental pollutants due to its significant hypothermia degradation ability.