Mesoporous Au–TiO2 nanoparticle assemblies as efficient catalysts for the chemoselective reduction of nitro compounds

In this article, we demonstrate novel mesoporous Au-loaded TiO2 nanoparticle assemblies (Au–MTA) as high-effective catalysts for the selective transformation of nitroaromatics into the corresponding aryl amine products. These materials feature a three-dimensional open porous structure consisting of interconnected uniform gold and TiO2 nanoparticles, large internal surface area (ca. 104–120 m2 g−1), and narrow mesopores (ca. 7.3–7.6 nm). Au–MTA displays outstanding performance for the selective reduction of nitro into amine groups using sodium borohydride as a reducing agent under ambient conditions. We show that both chemoselectivity and hydrogenation activity of the Au–MTA catalysts are highly related to the Au loading and particle size. As a result the 2% Au–MTA associated with 5 nm sized Au particles was found to be a prominent catalyst for hydrogenation reactions, providing exceptionally high selectivity (>96%) and conversion yield (>92%) to the corresponding amines. The implication of these results is that mesoporous ensembles of gold and TiO2 nanoparticles should be considered for the synthesis of fine amine chemicals.