Engineering Multicomponent Nanomaterials for Plasmonic Catalysis

Heterogeneous Catalysis;Plasmonic;Nanotechnology;Photocatalysis;Chemical Engineering;Engineering;Chemical Engineering

Aslam, UmarSingh, Nirala ;

University of Michigan

关键词: Heterogeneous Catalysis;    Plasmonic;    Nanotechnology;    Photocatalysis;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/145860/uaslam_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Heterogenous catalysis is an important technology used to facilitate chemical transformations. As increasing demand for chemicals and materials stresses the availability of resources and the environment, it is becoming ever more important to design catalysts with near perfect selectivity in the conversion of reactant feedstock to desired products. In traditional heterogeneous catalysis, heat is used to drive the conversion of reactants to products. An unintended side effect of this approach is that energy is unselectively deposited into all possible reaction pathways resulting in the simultaneous activation of undesired reactions, waste of feedstock resources, and production of chemical waste. An alternative mechanism for activating chemical reactions employs visible light to deposit energy into reactants. This mechanism could in principle make it possible to achieve much higher product selectivities but has been considered impractical as it requires high intensity lasers to produce sufficiently high reaction rates. Recently, it has been shown that plasmonic metal nanoparticles (Cu, Ag, and Au) can perform light-driven chemical reactions under relatively low intensity light on the order of sunlight. These findings have reignited interest in light-driven chemical reactions in heterogeneous catalysis and led to the emergence of a new field known as plasmonic catalysis. A major limitation of plasmonic catalysis is that it is restricted to reactions that can be performed by the plasmonic metals, Cu, Ag, and Au. In this dissertation, we address this limitation through the design of multicomponent plasmonic catalysts which combine plasmonic metals with catalytically-active materials. In particular, we focus on combining plasmonic metals, such as Ag, with catalytically-active metals, such as Pt, through the fabrication of bimetallic nanoparticles. We consider two extremes for synthesizing nanoparticles composed of both metals: 1) alloy nanoparticles in which both metals are well-mixed and 2) core-shell structures in which a large Ag core is completely surrounded with a thin shell of Pt. We develop novel synthesis approaches for creating both structures and use a suite of characterization tools to shed light on the nanoscale structure and composition of the resulting materials. We then use the well-defined core-shell nanoparticles to perform a mechanistic investigation of the energy transfer mechanisms which allow for energy to be transferred from photoexcited plasmonic metals to catalytically-active sites. These studies demonstrate that coating a thin layer of a catalytic metal, such as Pt, on a plasmonic metal drastically biases the flow of energy in the nanoparticles towards absorption in the catalytic metal. We then design reactor studies showing that this re-routing of plasmonic energy enables plasmon-driven reactions to take place on non-plasmonic metal surfaces.Thesediscoveries not only introduce new methods for precision synthesis of multimetallic nanostructures but also present a clear understanding for the physical mechanisms which allow for energy transfer from plasmonic metals to catalytically active sites thereby paving the way for the design of new hybrid plasmonic-catalytic materials for performing light-driven chemical reactions.