Authors: Fathima Sharfa Farzandh
Source: Scholar Commons (University of South Carolina) (article, 2020-01-01)
Field: Materials Science — Materials Chemistry

Fundamental Studies of Bimetallic Model Surfaces and Metal Organic Framework Thin Films This work is mainly focused on gaining a fundamental understanding of conventional bimetallic catalysts in order to correlate their macroscopic properties with the observed kinetic properties. This is achieved by synthesizing and studying fundamental model surface analogues of conventional catalysts that are difficult to study due to their complex, ill-defined nature. A wide array of surface science techniques that use ultra-high vacuum (UHV) conditions are readily available for detailed studies that can be conducted on model surfaces. This work focuses on the synthesis and investigation of two fundamental bimetallic catalysts formed via the addition of a second metal to an existing system in order to give rise to enhanced catalytic properties. The systems investigated are the bimetallic Pt-Sn catalysts and Cu-Rh metal organic frameworks consisting of benzene tricarboxylic acid (BTC) linkers. Monometallic Pt catalysts with excellent hydrogenation properties can preferably undergo C=C hydrogenation and decarbonylation while the addition of oxophillic Sn to Pt to form bimetallic catalysts is reported to improve the selectivity to unsaturated alcohol synthesis via preferential C=O bond hydrogenation for larger aldehydes with substituted groups. The greater selectivity to unsaturated alcohol formation with the bimetallic Pt-Sn catalyst is claimed to stem from the presence of oxophillic Sn addition to Pt, which helps anchor the oxygen from the C=O bond due to electronic and/or geometric effects while Pt dissociates H2 to synergistically hydrogenate the C=O bond. However, the exact source of the observed enhancement in selectivity is still unknown. Fundamental studies performed vi using model Pt-Sn ordered alloys with different surface metal ratios show that the selectivity to furfural alcohol formation and the resistance to catalyst deactivation increases with the surface Sn concentration while there was observed to be an optimum Pt:Sn surface ratio at which there was maximum activity with 50% conversion. DFT calculations predict the formation of a η1-(O)-intermediate that could be responsible for the observed selectivity to furfural alcohol formation. The synthesis of thin MOF films is a rising area of interest due to its increasing applications and ability to function as a model system to study powder MOFs that also have high end applications. Using sophisticated surface science techniques such as X-ray photoelectron spectroscopy, grazing incidence wide angle X-ray scattering and atomic force microscopy, this work demonstrates that crystalline, monometallic Cu based BTC MOF films can be synthesized via layer-by layer dip coating method. Node metal replacement of this monometallic CuBTC with a second metal such as Rh is also shown to produce bimetallic CuRhBTC MOF thin films that play an important role in heterogeneous catalysis. Bimetallic strip ; Materials science ; Metal ; Metallurgy Machine Learning in Materials Science ; Metal-Organic Frameworks: Synthesis and Applications ; Electron and X-Ray Spectroscopy Techniques