Water-soluble Pd and Pd-alloy nanoparticles as catalysts in biphasic solvent.

hydrogenation;isomerization;catalysis;suzuki;nanoparticles;homogeneous

Shekhar Bhama

University:University of Louisville

Department:Chemistry

关键词: hydrogenation;    isomerization;    catalysis;    suzuki;    nanoparticles;    homogeneous;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=3930&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

This dissertation shows the chemical synthesis of Pd and Pd-alloy nanoparticles (NPs) and their hydrogen and thermal stabilities for applications in the homogeneous and pseudo-homogeneous catalysis of organic reactions. Mainly, this dissertation describes 1) the chemical synthesis of Pd, PdPt, PdAu and Cu-Pd core-shell NPs coated with various organic ligands (thiols, amines and citrate), with different metal compositions in different synthetic environment, 2) the stability of solutions containing various NPs in the presence of hydrogen or varying temperatures, 3) the evaluation of the catalytic activity of Pd, PdPt, PdAu and CuPd NPs for hydrogenation/isomerization of allylic alcohols, and 4) the reactivity of Pd NPs towards the Suzuki-Miyaura reaction. We chemically synthesized water-soluble Pd and Pd-alloy (PdPt and PdAu) NPs stabilized with reduced-L-glutathione (Glu) ligands under both inert and aerobic atmosphere and measured their catalytic activity and selectivity towards the hydrogenation/isomerization of allyl alcohol in a biphasic organic solvent/water mixture. We observed that the oxygen synthesized NPs are catalytically more active than the inert ones; while those synthesized under nitrogen have higher recyclability. Interestingly, reactions were 80-90% selective to the isomer product for all NPs studied. The catalytic activity of various glutathione-coated NPs increased with increasing Au or Pt in the PdAu or PdPt alloy NPs, respectively. Glutathione-coated Pd:Au (50:50) alloy NPs showed best catalyst, exhibiting turnover frequencies of greater than 700 and 100% conversion for 9 cycles. We synthesized Pd NPs coated with weakly adsorbed citrate ligands under inert nitrogen atmosphere and showed their unique stability in an organic-aqueous biphasic solvent system in the presence of hydrogen gas, high catalytic activity with remarkably high turnover frequencies in the range of 4000 to 8000, and recyclability with 100% product conversion towards the hydrogenation/ isomerization of various chain-lengths of α, β–unsaturated alcohols for up to 5 cycles. We learned that substrate structure plays an important role in the catalytic activity of the NPs, resulting in 1-penten-3-ol being catalytically more active than allyl alcohol and 1-hepten-3-ol. The selectivity showed a similar ratio of 3:2 hydrogenation:isomerization product for all substrates. Interestingly, the synthesized Cu-Pd core-shell NPs showed a selectivity of 95:05 towards the hydrogenated:isomerized product, showing that selectivity can be controlled through metal composition. Finally, we also synthesized C16NH2 stabilized Pd NPs and showed their high thermal stability and catalytic activity towards Suzuki-Miyaura reaction. Overall, our research has lead to new fundamental insights about various topics including the different compositions of metals with Pd,