In situ immobilization of palladium nanoparticles in microfluidic reactors and assessment oftheir catalytic activity

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We report on the synthesis and characterization of catalytic palladium nanoparticles (Pd NPs)and their immobilization in microfluidic reactors fabricated from polydimethylsiloxane(PDMS). The Pd NPs were stabilized with D-biotin or 3-aminopropyltrimethoxysilane(APTMS) to promote immobilization inside the microfluidic reactors. The NPs werehomogeneous with narrow size distributions between 2 and 4 nm, and were characterizedby transmission electron microscopy (TEM), selected-area electron diffraction(SAED), and x-ray diffraction (XRD). Biotinylated Pd NPs were immobilized onAPTMS-modified PDMS and glass surfaces through the formation of covalentamide bonds between activated biotin and surface amino groups. By contrast,APTMS-stabilized Pd NPs were immobilized directly onto PDMS and glass surfaces richin hydroxyl groups. Fourier transform infrared spectroscopy (FT-IR) and x-rayphotoelectron spectroscopy (XPS) results showed successful attachment of bothtypes of Pd NPs on glass and PDMS surfaces. Both types of Pd NPs were thenimmobilized in situ in sealed PDMS microfluidic reactors after similar surfacemodification. The effectiveness of immobilization in the microfluidic reactors wasevaluated by hydrogenation of 6-bromo-1-hexene at room temperature and oneatmosphere of hydrogen pressure. An average first-run conversion of 85% andselectivity of 100% were achieved in approximately 18 min of reaction time. Controlexperiments showed that no hydrogenation occurred in the absence of the nanocatalysts.This system has the potential to provide a reliable tool for efficient and highthroughput evaluation of catalytic NPs, along with assessment of intrinsic kinetics.