Vibrational Spectroscopy of Catalyst Systems for Electrified Chemical Processes

Abstract

Transitioning the chemical industry to electrified processes is an important part of the shift away from fossil fuels toward renewable energy. The synthesis of ammonia (NH3) is an important target for electrification given that it currently accounts for around 2% of global energy consumption. Additionally, electrified ammonia synthesis plants would be well suited to regularly responding to the fluctuations in the supply of renewable electricity because they operate under less severe conditions than do the Haber-Bosch plants currently used to produce ammonia. The reduction of CO2 to other valuable fuels and chemicals is also an area of interest for electrification as a supplement to or replacement for fossil fuels. Vibrational spectroscopy can be used to gain understanding about relevant catalyst materials, their interactions, and reaction environments which can inform the development of suitable catalysts for these electrified processes. The work presented herein has been aimed at improving the understanding of several catalyst systems relevant to electrified ammonia synthesis and CO2 reduction by studying specific catalyst systems and expanding the set of tools available to study them in situ. This dissertation presents one experimental design for in situ attenuated total reflectance (ATR) infrared spectroscopy of a semiconductor wafer surface and one reaction cell design for in situ ATR infrared spectroscopy of a catalyst film during dielectric barrier discharge (DBD) plasma exposure. ATR infrared spectroscopy was also used to observe in situ the reduction of CO2 to CO at the surface of a silver nano-island electrocatalyst film. Infrared reflection/absorption spectroscopy (IRRAS) was employed as one of several methods of characterization for ultrahigh vacuum (UHV) studies of methanol and water adsorption on a GaP(110) surface. These studies have shown that methanol and water can form ordered, partially dissociated adlayers on the GaP(110) surface. Finally, in situ Raman spectroscopy was used as part of the suite of characterization tools for two different metal-organic framework (MOF) electrocatalysts for CO2 reduction. The copper-based MOF (HKUST-1) was found to decompose under applied cathodic potentials to produce metallic copper nanostructures. The iron-porphyrin MOF appeared stable during electrolysis which allowed further characterization of its electrocatalytic performance.