Tuning chemical compositions of bimetallic AuPd catalysts for selective catalytic hydrogenation of halogenated quinolines

Abstract

Catalytic hydrogenation of halogenated quinolines is a longstanding challenge due to the harsh reaction conditions and disillusionary chemoselectivity owing to dehalogenation. Exploration of novel catalytic materials is still a big challenge. Herein, density functional theory calculations indicate that halogenated quinolines are selectively adsorbed on the Au surface via the nitrogen atom in the tilted orientation and on Pd via the quinoline ring in the flat orientation. In the tilted orientation, the C–Cl bond is away from the surface of catalysts, which can avoid the hydrogenation of the C–Cl bond by the surface activated hydrogen species. A series of Au_1−xPd_x bimetallic catalysts were deposited on CeO₂ nanorods by a facile electroless chemical deposition method. The Au_1−xPd_x catalysts with low Pd content delivered enhanced activity and improved chemoselectivity for the hydrogenation of halogenated quinolines. Highly dispersed Pd in the Au matrix of bimetallic catalysts with low Pd content triggers hydrogen activation on Pd sites and leads to the selective adsorption of halogenated quinolines on Au sites in the tilted orientation. The generated active hydrogen species can diffuse from Pd to Au sites for the hydrogenation of the tilted halogenated quinolines, resulting in suppressed dehalogenation and high chemoselectivity to the expected products.