Paper SS-TuP11
Reactivity of CO₂ at Single-site Vanadium in Metal-Organic Coordination Networks at Surfaces

Tuesday, November 8, 2016, 6:30 pm, Room Hall D

Driven by growing concern of the effect of greenhouse gases on the environment, CO₂ chemistry has become an increasingly active area of research. The interaction of CO₂ with metal-organic complexes offers opportunities for CO₂ recycling, but those chemistries have not been developed in surface catalysts, which could offer much higher efficiency. We have developed a prototypical metal-organic network that shows chemical activity toward CO₂ by co-depositing bis-pyridinyltetrazine (DPTZ) and metallic vanadium on a Au(100) surface. These organize at room temperature into highly-ordered one-dimensional metal-organic chains. We characterized the assembly by high-resolution scanning tunneling microscopy. The chains align in specific orientations relative to the underlying gold surface due to their interaction with the gold. The assembly occurs by a redox-active self-assembly process, in which the vanadium oxidizes to the +2 state and there is corresponding reduction of the ligand, as observed by X-ray photoelectron spectroscopy. Exposure to CO₂ gas leads to a shift in the vanadium oxidation state to +4; the shift is gradual with increasing CO₂ exposure. The 1D chains generally remain intact during the CO₂ exposure, but become somewhat less ordered with increasing exposure time. Following gas exposure, the surface was annealed at various temperatures. At annealing temperatures of 250 °C and greater we observe desorption of the ligand and the shift of vanadium back to the +2 state, indicating a residual vanadium-oxo species on the surface. Developing single-site metal center surfaces systems with chemical activity toward CO₂ may lead to the development of new methods for CO₂ capture and recycling, as well as providing more general insight into the development of next-generation catalysts.