Zoom link: https://kaust.zoom.us/j/4022310687 

Abstract

Ammonia (NH?) plays a crucial role in modern industry, serving as a crucial building block for fertilizers, chemicals, and explosives. More recently, its potential as a hydrogen carrier has positioned it as a key player in the transition to a sustainable energy future. The widespread production of NH? relies on thermocatalytic processes, which have been fundamental in enabling large-scale synthesis and decomposition. The Haber-Bosch process, in particular, has been a technological triumph, providing the world with synthetic nitrogen fertilizers that sustain global food production. Similarly, NH? cracking has emerged as a viable method for on-demand hydrogen release. However, despite their effectiveness, these processes remain highly energy-intensive, requiring extreme temperatures and pressures that limit efficiency and sustainability. This dissertation explores an innovative photo-thermal catalytic approach to NH? synthesis and decomposition, leveraging the synergistic effects of light and heat to enhance catalytic efficiency and reduce energy demands.

The study systematically investigates three different catalyst systems: Ru-based catalysts supported on CeO? for low-temperature NH? synthesis, metal-organic framework-derived Co-based catalysts for NH? decomposition, and Fe@C catalysts obtained from pyrolyzed metal-organic frameworks for optimized NH? cracking. Advanced characterization techniques, including in-situ spectroscopy, transient photocurrent measurements, and computational modeling, provide mechanistic insights into the role of light-induced processes in accelerating reaction kinetics and enhancing catalyst stability.

Results demonstrate that K-promoted Ru/CeO? catalysts achieve a remarkable NH? production rate of 20 mmol g?¹ h?¹ under photo-thermal conditions, surpassing conventional thermocatalytic benchmarks. In NH? decomposition, MOF-derived Co-based catalysts exhibited different conversions depending on their respective topology and graphitic nitrogen content; while Fe@C catalysts enabled efficient hydrogen production at significantly lower temperatures compared to conventional thermo-catalysis. Light intensity experiments confirm that non-thermal effects, including charge carrier excitation and local heating, play a crucial role in accelerating reaction dynamics.

By closing the NH? chemistry loop through both synthesis and decomposition, this work establishes a framework for integrating photo-thermal catalysis into future ammonia-based energy cycles. The findings provide valuable insights into catalyst design principles and highlight the potential of light-assisted catalysis in advancing sustainable chemical processes. This dissertation contributes to the growing field of photo-thermal catalysis, intending to pave the way towards a greener, more energy-efficient NH? production and utilization.