Upgrading Carbon and Nitrogen to Fuels and Chemicals Using Heterogeneous and Plasma Catalysis

Fossil resources provide the raw materials for manufacturing a majority of commodity chemicals and fuels, but the release of this buried carbon accelerates environmental crises related to rising levels of atmospheric CO2. Engineering direct and energy-efficient pathways to synthesize chemicals and fuels from sustainable reagents and using CO2-free renewable energy could mitigate these challenges. Promising strategies for developing such reaction processes utilize non-precious metal catalysts to address kinetic challenges and non-thermal plasma activation to circumvent thermodynamic constraints. Non-precious bimetallic catalysts were employed to selectively convert CO2 with H2 to the building block chemical CO, and in situ X-ray and infrared techniques revealed the properties of the catalytic components. Significant oxygen exchange between the ceria catalyst support material and gas-phase CO2 was quantified under reaction conditions, and NiFe bimetallic catalysts tuned the reaction selectivity while maintaining high activity. In order to eliminate H2 as a reagent, ethane (an underutilized shale gas fraction) was reacted with CO2 to produce alcohols. This reaction is not thermodynamically feasible under mild conditions, so non-thermal/non-equilibrium plasma activation was implemented in order to achieve a one-step, H2-independent process to synthesize alcohols and other oxygenates under ambient temperature and pressure. The ability to use non-thermal plasma to activate N2 at mild conditions introduces the possibility of moving beyond the carbon-based paradigm for chemicals and fuels. Non-thermal plasma has been used to synthesize ammonia under mild conditions, but the dearth of fundamental understanding of plasma-catalyst interactions handicaps the development of plasma catalytic N2 conversion processes. Therefore, an in situ FTIR reactor was employed to identify the surface reaction intermediates during plasma catalytic ammonia synthesis. These results provide the first direct evidence of catalytic surface reactions under plasma activation and reveal the presence of reaction pathways that are distinct from analogous thermocatalytic reactions. Finally, an energy-based analysis evaluates the environmental and economic outlook for plasma-activated nitrogen fixation processes.