Tetraalkylammonium Functionalized Hydrochars as Efficient Supports for Palladium Nanocatalysts

With the aim of preparing bio-sourced supports with enhanced properties in catalysis, we devised an original strategy allowing the immobilization of metal nanoparticles. Thus, size-controlled hydrochars with a high degree of hydroxyl functionalities, from both neat sucrose or modified with acrylic acid (10 wt.%), were derivatized with ether linkers containing ammonium groups. These non-porous carbon-based materials were used as suitable supports for the immobilization of palladium nanoparticles. The catalytic materials were synthesized by reduction of Pd(OAc)(2) to Pd(0) under H-2 atmosphere in the presence of the corresponding hydrochar, and fully characterized by standard methods. Among the different hydrochar-supported palladium materials, those functionalized with tetraalkylammonium groups afforded heterogeneous catalysts, exhibiting high activity in hydrogenations of different types of substrates (alkynes, alkenes, and carbonyl and nitro derivatives). The most efficient catalyst was recycled up to ten runs without loss of catalytic behavior, in agreement with the unchanged composite materials after catalysis (Transmission Electron Microscopy (TEM) analyses) and the lack of metal leaching in the extracted organic products (no palladium detected by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES)); these systems exhibited enhanced recyclability properties as compared to commercial Pd/C catalyst.