Nonthermal-Plasma-Catalytic Ammonia Synthesis Using Fe2O3/CeO2 Mechanically Mixed with Al2O3: Insights into the Promoting Effect of Plasma Discharge Enhancement on the Role of Catalysts

Nonthermal plasma catalysis offers the potential to synthesize ammonia on a distributed scale under ambient pressure by consuming renewable electricity. Clarifying the relationship between plasma discharge and the role of catalysts is beneficial to the performance improvement of nonthermal-plasma-catalytic ammonia synthesis (NTPCAS). In this study, the plasma discharge was enhanced using CeO2 and Fe2O3/CeO2 (Fe/Ce) mechanically mixed with dielectric Al2O3, recorded as Ce@Al and Fe/Ce@Al, respectively, and the promoting effect of plasma discharge enhancement on the catalytic role of Fe/Ce and CeO2 in NTPCAS was investigated in a dielectric barrier discharge reactor under atmospheric pressure. The results indicate that the concentration of ammonia synthesized using Fe/Ce was only 2.7% higher than that synthesized using CeO2 and that synthesized using Fe/Ce@Al was 36.5% higher than that synthesized using Ce@Al and 102.6% higher than that synthesized using Fe/Ce at maximum. In addition, the ammonia production rate of Fe/Ce in Fe/Ce@Al with the optimum Al2O3 mixing ratio was 8.8 times that in pure Fe/Ce. U–I curves, U–Qc curves, and self-luminous optical imaging results of the discharge region packed with the catalysts indicated that Al2O3 mixing effectively strengthened the plasma discharge. Catalyst characterization showed that Fe/Ce had better catalytic properties than CeO2, explaining the better performance of Fe/Ce@Al than that of Ce@Al in the NTPCAS. In situ N2 and H2 adsorption, desorption, and reaction behaviors over catalysts revealed that significantly improved N2 adsorption and activation over Fe/Ce@Al under plasma conditions were the key to NTPCAS. The strategy of mixing highly active ammonia synthesis catalysts with discharge-enhanced materials can significantly improve the performance of NTPCAS catalysts, thus providing a novel approach to designing catalysts for NTPCAS.