Fabrication of Ir-CoO<i>_x</i>@mesoporous SiO₂ Nanoreactors for Selective Hydrogenation of Substituted Nitroaromatics

Abstract

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-CoO<i>_x</i> hybrid cores and mesoporous SiO₂ shells were designed and prepared to overcome these problems. The Ir-CoO<i>_x</i> hybrid cores were converted from IrCo alloy nanoparticles (NPs) inside SiO₂ through in situ calcination and reduction pretreatments. The SiO₂ mesoporous shells in Ir-CoO<i>_x</i>@SiO₂ nanoreactors prevented the agglomeration/sintering of IrCo NPs, while allowing the free reactants and products (big molecules). The synergy between Ir and CoO<i>_x</i> species improved H₂ adsorption, thus affecting the reaction rate as well as the selectivity to aromatic amines. As a result, the obtained Ir-CoO<i>_x</i>@SiO₂ nanocatalyst showed tremendous improvement in catalytic activity, selectivity, and stability.