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 Hδ+ and Hδ− 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.