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Supported and unsupported palladium nanoparticles for heterogeneous catalysis

University of British Columbia

The development of new methods to prepare Pd-containing nanomaterials for catalysis are reported. Monodisperse, catalytically active Pd0 nanoparticles were prepared using a one-pot procedure, and new insights into the mechanism of the formation of these catalytically active Pd0 nanoparticles were obtained. A number of key intermediates and byproducts were determined using NMR and IR spectroscopies. Furthermore, addition of Lewis bases such as TOPO and DMSO to the reaction mixture greatly reduced the temperature at which highly monodisperse nanoparticles were formed. This effect was shown to be applicable to other Pd precursors in preparing Pd0 nanoparticles. Spherical Pd0@m-SiO2 core-shell nanoparticles were prepared and characterized by a number of techniques, including TEM, PXRD, TGA, and XPS. These nanoparticles consist of a Pd0 core enclosed by a mesoporous silica shell and are prepared using a simple, scalable one-pot procedure. The reaction conditions were crucial in controlling the morphology and pore diameter of the nanoparticles synthesized. Acid treatment of the Pd0@m-SiO2 nanoparticles was found to be the most suitable method in removing CTAB. The morphology, surface area, and pore diameter of the core-shell nanoparticles remained intact after removal of CTAB. A new ceria-containing core-shell material, PdO@m-CeO2, was prepared via templating from Pd0@m-SiO2 and PdO@m-SiO2 nanoparticles. The absence of Pd0 and presence of Pd2+ was explained by the possible formation of a solid solution composed of Ce1-xPdxO2-δ when Pd0 was the core. The catalytic activity of the nanoparticles was examined by performing the catalytic oxidation of methane. As well, the silica channels of the Pd0@m-SiO2 nanoparticles were used as selector to separate molecules based on their size. Size-selective hydrogenation was investigated using the porous silica shell of the Pd0@m-SiO2 nanoparticles as a selector, where the porous shell controlled the selectivity by the size of the substrates. Hydrogenation of a small molecule, 1-hexene, in CDCl3 using acid-treated Pd0@m-SiO2 nanoparticles occurred quickly, while the hydrogenation of a larger substrate, O-allyl cholesterol proceeded more slowly. However, similar results were observed using commercially available Pd/C as the catalyst. Narrowing the pore diameter of Pd0@m-SiO2 nanoparticles showed drastic difference in reaction rates between 1-hexene and O-allyl cholesterol.

Text

2015-10-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52934

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/