Selective\nReduction of Nitroarenes via Noncontact\nHydrogenation

In\ntraditional hydrogenation, where H<sub>2</sub> and substrates\nwith unsaturated bonds are activated on the same catalyst (contact\nmode), competitive hydrogenation of multiple reducible groups often\noccurs. We employ an unbiased H-cell for selective hydrogenation of\nthe nitro group when multiple reducible groups are present. The setup\nspatially separates H<sub>2</sub> and nitroarenes into two chambers\nconnected by a proton-exchange membrane, thus adding barriers for\na Langmuir–Hinshelwood-type mechanism that is common in thermocatalytic\nhydrogenation. Through a unique proton/electron transfer pathway that\nis specific to nitro functional group reduction to hydroxylamine,\nside reactions like CC, CO, and CC bond hydrogenation\nare fully avoided. Using Pd/C for H<sub>2</sub> activation, and CNT\nfor selective proton/electron transfer to −NO<sub>2</sub> groups\nwhile being inert to CC, CC, and CO hydrogenation,\nthe system effectively eliminates the competitive hydrogenation, achieving\n100% nitro-group reduction selectivity in the hydrogenation of various\nnitroarenes, in sharp contrast to negligible selectivity over the\nsame catalysts in a batch reactor under contact mode. This device\nenables selectivity control in hydrogenation reactions, moving beyond\nthe traditional focus on catalyst active site engineering.