Bimetallic PdM (M = Co, Ni) catalyzed hydrogenation of nitrobenzene at the water/oil interface in a Pickering emulsion

We successfully synthesized an interfacially active monometallic Pd/SM-CN and bimetallic PdM/SM-CN (M = Co, Ni) catalysts [SM-CN = silica microsphere (SM) modified with methyltrimethoxysilane = C and (3-aminopropyl) triethoxysilane = N] via wet impregnation method. The synthesized catalysts were used to stabilize a water/toluene emulsion system. The resulting stable droplets formed can serve as a microreactor to reduce nitroaromatic compounds at room temperature using NaBH₄ as the hydrogen source. Moreover, we discovered that through tuning the volume ratio of toluene/water, the mass concentration of the stabilizer and enhanced emulsion interface area could be well controlled, thereby facilitating the mass transfer significantly and resulting in higher catalytic efficiency in Pickering emulsion systems. Also, we report the first efficient application of bimetallic Pd based catalyst for the hydrogenation of aromatic compounds in the water Pickering emulsion system. The improved activity is ascribed to the electronic metal-metal interaction between the Pd and M nanoparticles. Furthermore, the catalysts retained their activity and selectivity after eight consecutive cycles.