Green One-Step Synthesis of Catalytically Active Palladium Nanoparticles Supported on Cellulose Nanocrystals

Palladium nanoparticles (PdNPs) supported on cellulose nanocrystals (CNXL) were synthesized in a single step from Pd(hexafluoroacetylacetonate) 2 (Pd(hfac) 2 ) in subcritical and supercritical carbon dioxide. CNXLs acted as both the reducing agent and support material for the obtained nanoparticles. Dry Pd nanoparticles supported on the cellulose nanocrystals (PdNP@CNXL) were obtained by simply venting the CO 2 and were characterized by FT-IR, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The results show that the Pd nanoparticle diameters varied between 6 and 13 nm with varying pressure (240–2200 psi), reaction time (2–17 h), and weight ratio of the precursor Pd(hfac) 2 to CNXL (1–4% w/w). Particles with diameters above 13 nm appeared not to remain attached to the CNXL surface. Reaction conditions also affected the Pd loading in the final PdNP@CNXL composite. Finally, the PdNP@CNXL composites were shown to be effective catalysts for carbon–carbon bond formation in the Mizoroki–Heck cross-coupling reaction, in line with other reports.