A Milling Ball as Catalyst - The Concept of Direct Mechanocatalysis

Direct mechanocatalysis represents a novel catalytic approach that operates on mechanical energy, in contrast to conventional methods driven by light, heat, or electric potential. Mechanical energy is supplied through the collisions of milling balls inside a ball mill, where the milling ball itself acts as the catalyst. Unlike homogeneous or heterogeneous catalysis, this system requires neither dissolved catalysts, powders, nor packed beds. Through the continuous renewal of their active surfaces during collisions, milling balls enable solvent-free transformations across diverse reaction classes, including cross-coupling, oxidation, and hydrogenation. In situ characterization confirms that catalysis occurs directly at the ball surface and proceeds via mechanistic pathways distinct from those in solution-based chemistry.