Single Cu sites in synergy with Cu2O nanoparticles on rutile TiO2 for selective nitroarene hydrogenation

Catalytic hydrogenation of nitroarenes plays a crucial role in industrial production of arylamines which are main building blocks in a wide range of products. Supported noble metal catalysts and group VIII transition metals are generally encapsulated or anchored to heteroatoms to achieve high selectivity. In this work, we show that, among Cu based catalysts on various supports, copper on rutile TiO2 (TiO2-R) prepared simply by direct H2 reduction without the encapsulation or heteroatom modification is remarkably active, selective, and stable for hydrogenation of nitroarenes, producing arylamines in superhigh selectivity. Essential to the catalytic performance, a unique mechanism involving indispensable Cu2O nanoparticle sites and dispersed single CuI ion sites are identified. Specifically, Cu2O nanoparticles provide essential sites for H2 dissociation, and the colony of dispersed single CuI sites play two crucial roles: (1) as step-stones for H migration, as inferred by kinetic energy experiments, and (2) nitroarene adsorption/hydrogenation sites. This work provides new insights on the nature of the Cu/TiO2-R selective hydrogenation catalyst and also elucidates a method for the identification and distinction of spatially separated active sites on metal-oxide catalysts.