Browsing by Subject "Hydrogenation catalysis"
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Item Development of noble metal alloy nanoparticles and mesoporous metal oxides for applications in catalysis and charge storage(2017-06-12) Piburn, Graham William; Humphrey, Simon M.; Henkelman, Graham; Rose, Michael; Vanden Bout, David; Werth, CharlesThe creation of next-generation functional materials will require fine control of nanoscale surface characteristics. Two common approaches to this problem are the formation of nanoparticles and the synthesis of mesoporous materials. By incorporating nanoscale structural features, not only can a greater proportion of the material be devoted to active surface area, but properties can also emerge that are absent in the corresponding bulk material. For example, metals can be miscible on the nanoscale despite being immiscible in the bulk, and restrictive mesopores can lead to increased catalytic selectivity. Mesoporous LaMnO₃-SiO₂ composites were synthesized by several different nanocasting routes using SBA-15 silica as the hard template. The final composites were stable in refluxing NaOH solution, indicating encapsulation of the remaining SiO₂ in each case, although the exact structure of the composites depended on the solvent mixture in which they were prepared. All three composites displayed respectable pseudocapacitative capabilities, with normalized specific capacitances over 200 F g⁻¹. The next project revolved around the synthesis of RhPd alloy nanoparticles and the examination of their hydrogenation activity. RhPd alloy nanoparticles were synthesized using both microwave and conventional heating and a range of reaction times. Application of these particles to the hydrogenation of cyclohexene revealed that particles synthesized at very short reaction times showed comparable reactivity to particles that had been heated for hours longer. In addition, the empirical finding that RhPd alloys have a hydrogenation activity between those of the two pure metals was further supported by DFT calculations. Third, RhPdAu alloy nanoparticles were synthesized for use as hydrogenation catalysts. Tuning the exact composition of this alloy system is expected to influence the catalysts’ activity, and the inclusion of gold may promote selective hydrogenation of the carbonyl bond in unsaturated aldehydes. A series of alloy compositions has been successfully synthesized, but their catalytic properties remain untested. Finally, Rh nanoparticles supported on Co₃O₄ are also being studied for this selective hydrogenation of unsaturated aldehydes. Preliminary results suggest the mesoporosity of the support may play a crucial role in controlling the orientation of the substrate molecule, and therefore the selectivity toward the desired product.Item Synthesis and development of novel cost-effective nanocatalysts for hydrogenation purposes(2014-12) García, Stephany; Humphrey, Simon M.; Holliday, Bradley J; Crooks, Richard M; Stevenson, Keith J; Korgel, Brian AThis research has focused on the controlled synthesis of mono- and bimetallic noble metal nanoparticles (MNPs) for catalytic applications. MNPs such as Au, Rh, Pd, Pt and Ag have been synthesized with the aid of microwave heating (μwH) which provides a greener heating method. Furthermore, it provides kinetic control over the size, shape and composition of these NPs. Several bimetallic core-shell NPs have also been synthesized using this method, making it possible to overcome thermodynamic energy barriers that arise with this type of assembly when the metals used, greatly differ in surface energy and lattice constant. It has also been possible to tune the shell thickness of the NPs in order to have an impact in the kinetics of hydrogenation catalytic processes performed. ‘Non-equilibrium’ alloyed structures have been generated in the nanoscale as well, with the aid of μwH. These types of nanostructures are of particular interest because due to synergistic effects, the mixture of heteroatoms resulted in enhancement of catalytic activity and in chemical/physical stability in comparison to their monometallic components. These Rh[subscript x]M₁₀₀₋[subscript x] (M = Ag or Au) NPs displayed remarkable catalytic activities, as compared to pure Rh NPs. Furthermore, the composition was systematically varied in order to optimize the catalytic properties. These experimental observations were supported by theoretical modeling and calculations (DFT). Thus, very cost effective nanocatalysts have been prepared by diluting relatively inexpensive and catalytically inactive metals, such as Au and Ag, with active precious metals such as Rh. This research has also focused on the design and synthesis of novel capping agents for small metal NPs. The ultimate goal is to generate self-activating particles that when placed in a hydrogenation catalysis environment (reducing conditions), these will chemically rid themselves of the stabilizing agents in a clean and controlled fashion under mild conditions. Thus, naked NPs that are extremely active and still have defined facets that can potentially provide selectivity in certain catalytic processes will be left behind. These NPs are more cost-effective and have a lower impact on the environment due to the milder reaction conditions applied, yielding great candidates for hydrogenation catalysts in industrial processes.