In situ transmission electron microscopy displays the soot oxidation mechanism and structural evolution from nanoscale characterization to macroscopic reactions: A review

Soot originating from incomplete combustion of fossil fuels constitutes a critical threat to public health and ecological stability. With the implementation of stricter emission regulations, particularly regarding particle counts below 10 nm and cold start conditions of internal combustion engine, diesel/gasoline particulate filter (DPF/GPF) regeneration technology, which refers to the gas-solid oxidation of the soot particle at the micro-nano scale, faces considerable challenges as to the sub 10 nm particle emission limit. Insights into the oxidation of soot particles at this scale are indispensable for the precise control and optimize the DPF/GPF regeneration. While conventional macroscopic kinetic studies deliver integral reaction rate parameters, but are incapable of capturing the complex nano-structural evolution of soot particulates in catalytic oxidation process. Recent breakthroughs in in situ transmission electron microscopy (In situ TEM) technology now allow researchers to observe gas-solid reaction processes in real time at the nanoscale and even atomic level. Therefore, this work presents a systematic review of state-of-the-art investigations leveraging in situ TEM to reveal the mechanisms governing soot oxidation, supplemented by evidence from complementary experimental studies. It characterizes the intrinsic correlation between the structural maturity of soot nanostructures and corresponding oxidation pathways, provides a comprehensive analysis of catalyst dynamics at the microscale, and explores the feasibility of integrating quantitative interpretation of in situ imaging data to underpin the development of kinetic models. This review seeks to establish a unified theoretical paradigm linking microscopic physicochemical mechanisms to macroscopic exhaust aftertreatment engineering practices, thereby offering a scientific basis for developing advanced low-temperature, high-efficiency soot oxidation catalysts and rationalizing DPF/GPF regeneration strategy.