Black gold-based "Antenna–reactor" to activate non-plasmonic nickel: photocatalytic Hydrodechlorination and hydrogenation reactions

Abstract

Activation of organic chlorides is a challenging reaction due to their chemical inertness, while hydrogenation of alkene and alkynes faces poor selectivity. In this work, we have demonstrated the use of nickel-loaded black gold (black Au–Ni) that absorbs broadband light from visible to near-infrared of the sunlight due to plasmonic coupling between Au NPs, for photocatalytic hydrodechlorination and propene and acetylene hydrogenation reactions. Hot carriers, the polarizing electric field, and the photothermal effect generated in these catalysts enabled photocatalytic bond activation of these two challenging reactions using visible light at lower temperatures and atmospheric pressure. The black Au–Ni catalyst showed a multifold increase in its activity as compared to black Au. The plasmon-assisted reaction mechanism of hydrodechlorination was supported by intensity-dependent catalysis, kinetic isotope effect (KIE), competitive C–Cl bond activation with one-electron ferricyanide reduction, finite-difference time-domain (FDTD) simulations, and quantum chemical studies. Cluster model-based density functional theory studies show that the reactions have substantial barriers, which were bypassed via an excited state accessed through plasmonic excitations. FDTD studies indicate substantial enhancement of the electric field at the hotspots, iron reduction competed for hot carriers when run in conjunction with C–Cl bond activation, KIE was marginally higher in light as compared to the dark, and the catalyst showed power-dependent activity. These observations indicated the hot carrier involvement in the hydrodechlorination reactions in addition to the photothermal effect.