Synthesis and development of novel cost-effective nanocatalysts for hydrogenation purposes
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This 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.