Synthesis Characterization And Catalytic Properties Of Interfacial Sites On Supported Metal Catalysis PDF Download

The enhancement of catalytic activity is often attributed to special sites along a metal-oxide boundary, where an adsorbed species interacts with both the metal and the support. Indeed, such "dual" reaction sites often with emergent chemical properties have been implicated as the active sites for many chemical reactions, whether it be simpler molecular reactions such as CO oxidation and water-gas shift or far more complex reaction pathways such as de-oxygenation of multi-oxygenated reactants like furfuryl alcohol, m-cresol etc. Moreover, close connections of synthesis, characterization, kinetic testing, and computational modeling can enable researchers to tailor metal/metal-oxide catalytic systems towards such complex catalytic requirements. In this thesis, computational catalysis techniques are integrated with experimental efforts of collaborators to investigate two catalytic reactions: furfural hydrodeoxygenation (HDO) to methyl furan and CO oxidation. Experimental works motivate a series of research questions and hypotheses, towards connecting multi-component (oxide-metal) catalytic site properties to catalytic performance. In particular, Density Functional Theory (DFT) has been used in combination with experimental characterization and reactivity studies to underline the principles governing the potentials and design of multi-component catalytic systems. HDO of furfuryl alcohol was examined using a DFT model of a metal/TiO2 nanowire interface. Redox functionality of the metal oxide aids in breaking the C-O bond of the alcohol, while the metal facilitates C-H formation to the final product, 2-methylfuran. In addition to this "bifunctionality", electron transfer between the oxide and the metal alters reactivity, suggesting emergent chemical properties unique to the interface. Our DFT results were used to explain experimental observations of enhanced selectivity for TiO2-coated Pd nanoparticles. We have also successfully extended our TiO2/Pd interface model, altering the composition of this interface to develop a set of descriptors that predict optimal HDO activity at the metal oxide/metal interface. Low-temperature CO oxidation was examined over CeO2 supported single atoms, a probe for determining the synergetic roles of single metal atom catalysts (SACs) and redox active supports. The redox states involved in catalytic oxidation cycles on SACs are not well-determined and limit rational design of these catalytic systems. Experimental characterization observes only "resting states" of SACs, whereas DFT and microkinetic studies can be used to reconcile a full redox cycle. We addressed these challenges by developing a first principles microkinetic model and reconciling elementary step reaction kinetics with experimentally measured reaction orders and activation barriers. We calibrated the microkinetic model through Bayesian statistical inference approach to include the error in both DFT calculated energetics and experimental measurements in mechanism determination. This approach successfully elucidated reaction mechanisms and identified dominant reaction networks to directly match experimental reaction orders and barriers. Combining experiment and modeling, we demonstrated role of metal oxidation states with their reactivity for oxidation catalysis, indicating that the unique oxidation activity of these catalysts arises from the relatively close stability of the wide range of oxidation states achieved through synergistic interaction with metal oxides. In addition, to achieve proper active site environment over the oxide supports, a careful and controlled adsorption of ionic and/or hydrated metal precursors over the surface is essential during synthesis, therefore we also briefly examine synthesis rules for catalysts with precise control over size and uniformity in dispersion with specific potential to generate singly adsorbed metal catalysts over oxides. In short, these works combinedly demonstrate how metal/metal oxide catalytic systems can be used to improve heterogeneous catalytic activity and selectivity for important energy conversion processes, and further on, the broader perspective of active sites design along the metal and oxide boundaries for oxidation and reduction catalysis.