Brandon Robinson

This work evaluates microwave-assisted calcination as a rapid, energy-efficient alternative to conventional resistive heating for complex oxide synthesis. Ce0.9Gd0.1O1.95 (GDC10) and La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF6428) were investigated using solid-state and co-precipitated precursors to assess the influence of precursor chemistry on microwave coupling, reaction kinetics, and powder characteristics. Experiments were conducted in a single-mode magnetic-field-extended reactor using a silicon carbide/alumina susceptor–insulation package to ensure uniform and reproducible heating. Microwave processing reduced calcination time to ~1 h, compared to >21 h in a conventional furnace, while yielding powders with 28% higher surface area. High-temperature dielectric measurements of LSCF (450–1000 oC) revealed strong temperature-dependent increases in dielectric constant and loss factor, governing self-heating behavior and distinct microwave-driven reaction pathways. Phase evolution and surface area were characterized by TGA, XRD, and BET. These results clarify microwave–material coupling mechanisms and demonstrate synergistic effects between precursor chemistry and microwave heating in complex oxide synthesis.

Enzyme-based complexes represent an emerging class of functional adsorbents combining specificity and environmentally friendly potential. We proposed the development of metal-enzyme-based complexes that leverage the unique properties of magnesium metal to increase enzyme-structure integration for the formation of hybrid porous matrices with the potential to modulate targeted gas adsorption under mild conditions. For this, ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO), a carboxyl-lyase responsible for carbon fixation in the Calvin–Benson–Bassham cycle, was used as a scaffold that supported stable coordination of its amino acids, water, and/or phosphate groups with magnesium ions. Time- and dose-dependent synthesis and characterization of the resulting metal–enzyme complexes, performed through electron microscopy, infrared spectroscopy, and X-ray diffraction, unraveled the high-resolution structure formation. Magnesium integration led to crystal lattice formation, resulting in complexes of defined porosity and size, as evaluated through particle diffraction studies helping connect metal–enzyme synthesis time and ratio with the observed physicochemical properties. Preliminary gas adsorption testing with N₂ and CO₂ conducted using both physisorption and static chemisorption methods demonstrated that the metal–enzyme complexes exhibit measurable gas uptake behavior, thus indicating potential for gas interaction and adsorption under controlled conditions. These findings lay the groundwork for further exploration of metal–enzyme hybrids as tunable, bio-inspired materials for gas adsorption, with future studies needed to optimize performance and assess such complexes potential in real-world applications.

This chapter introduces the applications of microwave energy combined with heterogeneous catalysis for the conversion of stable molecules, such as CH4, N2 and CO2, to value added chemicals. Experimental results show that methane and N2 can be simultaneously activated in a single-stage microwave-heated reactor to form ammonia, ethylene, and acetylene at atmospheric pressure. Microwave irradiation can also induce oxidative dehydrogenation of methane and ethane using CO2 as a mild oxidant. The chapter illustrates that microwave catalysis as a transformational technology has the potential to increase energy efficiency across various industries and decarbonize high GHG-emitting industrial subsectors including ammonia, ethylene and BTX.

A novel reactor methodology was developed for chemical looping ammonia synthesis processes using microwave plasma for pre-activation of the stable dinitrogen molecule before reaching the catalyst surface. Microwave plasma-enhanced reactions benefit from higher production of activated species, modularity, quick startup, and lower voltage input than competing plasma-catalysis technologies. Simple, economical, and environmentally benign metallic iron catalysts were used in a cyclical atmospheric pressure synthesis of ammonia. Rates of up to 420.9 μmol min^-1 g^-1 were observed under mild nitriding conditions. Reaction studies showed that both surface-mediated and bulk-mediated reaction domains were found to exist depending on the time under plasma treatment. The associated density functional theory (DFT) calculations indicated that a higher temperature promoted more nitrogen species in the bulk of iron catalysts but the equilibrium limited the nitrogen converion to ammonia, and vice versa. Generation of vibrationally active N₂ and, N₂⁺ ions is associated with lower bulk nitridation temperatures and increased nitrogen contents versus thermal-only systems. Additionally, the kinetics of other transition metal chemical looping ammonia synthesis catalysts (Mn and CoMo) were evaluated by high-resolution time-on-stream kinetic analysis and optical plasma characterization. This study sheds new light on phenomena arising in transient nitrogen storage, kinetics, effect of plasma treatment, apparent activation energies, and rate-limiting reaction steps.