Insight into Enhanced Microwave Heating for Ammonia Synthesis: Effects of CNT on the Cs-Ru/CeO₂ Catalyst

Ammonia is emerging as a potential decarbonized H₂ energy carrier when produced from renewable energy. The on-site production of liquid ammonia from stranded renewable energy can solve the current energy transportation challenges. The employment of microwave technology can produce the desired ammonia product at milder conditions with the supply of intermittent renewable energy sources. Our previous studies have indicated that the Cs-Ru/CeO₂ catalyst is a promising catalyst for microwave-driven ammonia synthesis. In this study, the Cs-Ru/CeO₂ catalyst mechanically mixed with carbon nanotubes (CNT) and chemically synthesized using coprecipitation and a hydrothermal method is investigated systematically at low temperatures and atmospheric pressure for microwave-assisted ammonia synthesis. Additionally, the combination of two Ru-based catalysts (Cs-Ru/CeO₂ and Cs-Ru/CNT) is studied as well. Mechanical mixing of Cs-Ru/CeO₂ with CNT exhibited superior activity as compared to the chemically synthesized Cs-Ru/CeO₂-CNT catalyst. Besides the enhancement in dielectric property, the probable synergistic effect leads to increased interfacial polarization at the interface of the mechanically mixed catalyst, improving the overall heating and ammonia production rate. Moreover, the combined Ru-based catalyst also exhibited higher activity as compared to their individual activity toward ammonia synthesis. Numerous characterization techniques were performed, including thermal imaging camera and dielectric measurements, to better understand microwave interaction with the composite catalysts.