Revealing the dynamic formation mechanism of porous Mo₂C: an in-situ TEM study

In-situ transmission electron microscopy (TEM) enables direct observation of the micromorphology and microstructure evolution of catalysts in the chemical atmosphere. Studying the structural evolution during the formation of molybdenum carbide using in-situ TEM is helpful for the preparation of high-performance carbide catalysts. Herein, the formation mechanism of porous Mo2C from MoO2 nanoparticles (NPs) was studied by in-situ TEM. The formation of Mo2C was induced by the defects of MoO2, and the formed Mo2C facilitated the carbonization of neighboring MoO2 NPs. The growth rate of Mo2C between MoO2 NPs was slower compared to that within a single MoO2 NP. In addition, the formation and growth of pores in Mo2C were also studied; the pores grew radially during the early stages from the nucleation sites and later grew branched and curved. As Mo2C underwent competitive growth, the pores transitioned from straight to curved. Eventually, during prolonged carbonization at high temperatures, Mo2C underwent sintering.