There is a growing need for selective alkane functionalization catalysts to convert small alkanes into value-added products and transportable chemicals. Programming the specific chemistry of single-site transition metal centers at surfaces by organic ligand design is a promising route to improve selectivity in surface catalysts. We work as a multi-disciplinary research team to design redox-active components for on-surface metal-organic complexation to achieve a high degree of uniformity in single-site transition metal centers on metal and oxide surfaces. We combine ultra-high vacuum surface chemistry studies on model systems with flow reactor and IR spectroscopy experiments in operando conditions on high surface area oxide powder supports to gain two perspectives on the structure and catalytic function of these systems. Our group has recently demonstrated the formation of structurally ordered and chemically uniform platinum, chromium, iron, and vanadium single-site centers with organic ligands on surfaces. The on-surface redox process on model surfaces in UHV relies on straightforward vapor deposition protocols and takes advantage of the catalytic role of the surface to show promise as an approach for the growth of inorganic complexes at surfaces. For the high powder supports, we use a wet-impregnation style synthesis. The ability to tune the reactivity and catalysis of these systems is a central question in this field. We report new results here that probe the extent of metal oxidation state control in these systems using tailored ligands and also probe the chemical activity of these transition metal single sites. The oxidizing power of the tetrazine species is tuned by peripheral functional groups to access two and three electron oxidation processes, as determined by X-ray photoelectron spectroscopy (XPS). Metal-ligand complexes take the form of nearly identical one-dimensional polymeric chains, resolved by molecular-resolution scanning tunneling microscopy (STM). These structures provide highly uniform quasi-square-planar coordination sites for the metal, which contributes to the well-defined chemical state of the metal. The chemical activity of the metal centers is characterized by adsorption studies on the model systems and by operando flow reactor and IR spectroscopy measurements.

Metal-organic coordination chains at surfaces: Chemical activity of single-site transition metal centers

253rd National Meeting (2017)

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