Evaluating the Role\nof Metastable Surfaces in Mechanochemical\nReduction of Molybdenum Oxide

Mechanochemistry and mechanocatalysis are gaining increasing\nattention\nas environmentally friendly chemical processes because of their solvent-free\nnature and scalability. Significant effort has been devoted for studying\ncontinuum-scale phenomena in mechanochemistry, such as temperature\nand pressure gradients, but the atomic-scale mechanisms remain relatively\nunexplored. In this work, we focus on the mechanochemical reduction\nof MoO<sub>3</sub> as a case study. We use experimental techniques\nto determine the mechanochemical reduction conditions and density\nfunctional theory (DFT) simulations to establish an atomistic framework\nfor identifying the metastable surfaces that are most likely to enable\nthis process. Our results show that metastable surfaces can significantly\nlower or remove thermodynamic barriers for surface reduction and that\nkinetic energy from milling can facilitate the formation of metastable\nsurfaces that have high surface fracture energies and are not thermally\naccessible. These findings indicate that metastable surfaces are an\nimportant aspect of mechanochemistry along with hot spots and other\ncontinuum-scale phenomena.