Analogy in the Mechanism of Heterolytic H2 Dissociation

Hydrogenation is an essential type of reaction and dominates reduction reactions in the chemical industry, such as ammonia synthesis, Fischer–Tropsch synthesis, and the reduction of unsaturated chemical bonds. Metal nanoparticle-based homolytic H₂ dissociation enables hydrogenation reactions while being less selective for polar functional groups. Heterolytic H₂ dissociation creates polar reductive species of H^δ+ and H^δ− pairs, enabling regioselective hydrogenation and moderating the hydrogenation extent. Classical heterolytic H₂ dissociation on metal oxides occurs at elevated temperatures. Recent advances in heterolytic H₂ dissociation are identified at solid-frustrated Lewis pairs and supported metal catalysts including defective oxides, supported metal nanoparticles, single atoms, and ligand-decorated metal nanoparticles. Although exhibited in different forms, heterolytic H₂ dissociation necessitates polar pairs and can be simplified as acid–base pairs to polarize the H₂ molecule. In this Perspective, with an initial review of classic homolytic and heterolytic H₂ dissociation for comparison, we elucidate the unified mechanism of different forms of heterolytic H₂ dissociation on heterogeneous catalysts, aiming to inspire findings on heterolytic H₂ dissociation that operates with activity comparable to that of homolytic H₂ dissociation on metal nanoparticles.