Mesoporous-silica-coated palladium-nanocubes as recyclable nanocatalyst in C-C-coupling reaction - a green approach

Local Hydrogen Concentration and Distribution in Pd Nanoparticles: An In Situ STEM-EELS Approach

Local detection of hydrogen concentration in metals is of central importance for many areas of hydrogen technology, such as hydrogen storage, detection, catalysis, and hydrogen embrittlement. A novel approach to measure the hydrogen concentration in a model system consisting of cubic palladium nanoparticles (Pd NPs), with a lateral resolution down to 4 nm is demonstrated. By measuring the shift of the Pd bulk plasmon peak with scanning transmission electron microscopy (STEM) combined with energy electron loss spectroscopy (EELS) during in situ hydrogen gas loading and unloading, local detection of the hydrogen concentration is achieved in TEM. With this method, concentration changes inside the NPs at various stages of hydrogenation/dehydrogenation are observed with nanometer resolution. The versatility of in situ TEM allows to link together microstructure, hydrogen concentration, and local strain, opening up a new chapter in hydrogen research.

Pd@l-asparagine-EDTA-chitosan: a highly effective and reusable bio-based and biodegradable catalyst for the Heck cross-coupling reaction under mild conditions

In this research, a novel supramolecular Pd(ii) catalyst supported on chitosan grafted by l-asparagine and an EDTA linker, named Pd@ASP-EDTA-CS, was prepared for the first time. The structure of the obtained multifunctional Pd@ASP-EDTA-CS nanocomposite was appropriately characterized by various spectroscopic, microscopic, and analytical techniques, including FTIR, EDX, XRD, FESEM, TGA, DRS, and BET. The Pd@ASP-EDTA-CS nanomaterial was successfully employed, as a heterogeneous catalytic system, in the Heck cross-coupling reaction (HCR) to afford various valuable biologically-active cinnamic acid derivatives in good to excellent yields. Different aryl halides containing I, Br and even Cl were used in HCR with various acrylates for the synthesis of corresponding cinnamic acid ester derivatives. The catalyst shows a variety of advantages including high catalytic activity, excellent thermal stability, easy recovery by simple filtration, more than five cycles of reusability with no significant decrease in its efficacy, biodegradability, and excellent results in the HCR using low-loaded Pd on the support. In addition, no leaching of Pd into the reaction medium and the final products was observed.