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Size-controllable Ultrafine Palladium Nanoparticles Immobilized on Calcined Chitin Microspheres as Efficient and Recyclable Catalysts for Hydrogenation
X. Pei, Y. Deng, Y. Li, Y. Huang, K. Yuan, J.-F. Lee, T.-S. Chan, J. Zhou, A. Lei*, and L. Zhang*
In the present work, chitin microspheres were impregnated at different concentrations of palladium salt solution to generate the precursor-Pd2+/chitin, and then a series of size-controllable palladium nanocatalysts (Pd@chitin) were successfully constructed by calcining the composite microspheres. Transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) provided reliable evidence for well-dispersed and ultrafine palladium nanoparticles (Pd NPs) with mean diameters from about 1 to 3 nm. Chitin microspheres, as the supporting framework of these catalysts, played a significant role for stabilizing the highly dispersed Pd NPs based on their abundant functional groups and large surface areas. Moreover, the chitin matrix acted as a reductant for the precursor-Pd2+ during calcination, and the calcination process made Pd@chitin more stable. These Pd@chitin catalysts were further tested for the hydrogenations of styrene and benzaldehyde, and they displayed superior catalytic activities compared to commercial Pd/C and unsupported homogeneous Pd(OAc)2 catalysts. Notably, the most active catalyst of 1.2 wt% Pd@chitin had a highly competitive turnover frequency (TOF) of 50 000 h-1 in the hydrogenation of styrene, and the catalyst could be repeatedly used for more than 10 cycles with no decay of the catalytic activity, suggesting potential industrial applications.