Origins of the hydrogen spillover effect in d-block metals

Abstract The hydrogen spillover effect embodies a sophisticated and multifaceted phenomenon for H atom equivalents. Despite substantial efforts to identify potential candidates, including d -block metals like Ru and Pd, fundamental aspects of dynamic interplay of activation and spillover processes are still inadequately understood, hindering efficient hydrogenation reactions and high-capacity chemical hydrogen storage. Here, we quantify a comprehensive platform of thermodynamic‒kinetic descriptors to systematically elucidate the full scope of the hydrogen spillover pathway and transcend the limitations of conventional approaches that focus solely on the surface concentration of spilled-over hydrogen, shielding the signal heterogeneity inherent in zones of differential hydrogen availability. Taking a well-defined d -block M/TiO 2− x (M = Ru, Mn, Fe, Co, or Ni) as a representative case by combining spectroscopic quantification and computational investigation, the nonlinear spillover capability and rate of d -block metal originates from the synergistic overlap of its unoccupied d - s orbitals, and the σ and σ* orbitals of the H atom equivalents interact to form a weak antibonding state, reducing the dissociation of the H–H bond and M–H bond. This methodology provides a refined lens for dissecting spillover mechanisms, facilitating a profound mechanistic and spatial understanding of rational metal dilution.