Fabrication of Ir-CoO_x@mesoporous SiO₂ Nanoreactors for Selective Hydrogenation of Substituted Nitroaromatics

Nanosized Ir catalysts suffer from serious side reactions and poor stability during hydrogenation of substituted nitroaromatics to produce aromatic amines. In this work, core–shell nanostructures with sub-4 nm Ir-CoOx hybrid cores and mesoporous SiO2 shells were designed and prepared to overcome these problems. The Ir-CoOx hybrid cores were converted from IrCo alloy nanoparticles (NPs) inside SiO2 through in situ calcination and reduction pretreatments. The SiO2 mesoporous shells in Ir-CoOx@SiO2 nanoreactors prevented the agglomeration/sintering of IrCo NPs, while allowing the free reactants and products (big molecules). The synergy between Ir and CoOx species improved H2 adsorption, thus affecting the reaction rate as well as the selectivity to aromatic amines. As a result, the obtained Ir-CoOx@SiO2 nanocatalyst showed tremendous improvement in catalytic activity, selectivity, and stability.