Semester

Fall

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Jianli Hu

Committee Member

Debangsu Bhattacharyya

Committee Member

Oishi Sanyal

Committee Member

Vyacheslav Akkerman

Committee Member

Cosmin Dumitrescu

Abstract

Ammonia synthesis is one of the greatest innovations of the 20th century with extensive applications from fertilizers to intermediates for nitrogen-containing chemicals and pharmaceuticals. Annually, more than 242 million tons of ammonia is produced globally, supporting approximately 27% of the world’s population. One of the fast-growing applications for ammonia is as H2 energy carrier due to its high energy storage capacity, considered to be a decarbonized energy source. The low volumetric energy density and incompressibility makes Hydrogen a non-preferable energy carrier; an alternative carrier becomes a requirement. Ammonia possesses unique property as an energy-dense carrier to store and transport renewable energy. The U.S. Department of Energy characterized ammonia as a carbon-neutral fuel that can be synthesized from stranded renewable energy. In recent years, ammonia has also emerged as a source of alternative renewable energy to fuel the shipping industry to transition away from traditional fossil fuels and mitigate GHG emissions.

Industrially, ammonia is produced by the Haber-Bosch (HB) process that operates under high temperatures (400–500 °C) and high pressures (150–300 bar) over an Iron-based catalyst from nitrogen and hydrogen. This process requires high energy and is capital intensive as it operates at high temperatures and pressures, consuming 2% of the world’s energy production and emitting 2.5% of the global CO2 emission. Microwave is a promising technology to produce ammonia at low temperatures and pressure with the use of an electromagnetic-sensitive catalyst. Microwave offers instantaneous and volumetric heating via interaction with electromagnetic radiation, which is fundamentally different from conventional thermal heat conductive or convective transfer through direct heating. Microwave technology and microwave susceptor catalysts can yield the desired ammonia product under mild conditions. Besides mild reaction conditions, microwave technology can also operate on intermittent renewable energy sources and is capable of accommodating small-medium scale plants, making microwave a potential candidate for renewable ammonia and H2 production.

A catalyst with high activity under microwave conditions is much desired to further improve energy efficiency and ammonia production. Cs-Ru/CeO2 is a promising catalyst for microwave-assisted ammonia synthesis and by further optimizing the catalyst, ammonia production can be enhanced. This dissertation utilizes microwave heating and Cs-Ru/CeO2 catalyst to enhance ammonia production at low temperatures and pressure that can operate on intermittent renewable energy to accommodate small-medium scale plants for renewable ammonia and H2 production. This work opens new avenues for improving microwave heating and heterogeneous catalysis to advance the transition into decarbonized ammonia production with the employment of microwave technology.

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