Nonthermal-Plasma-Catalytic Ammonia Synthesis Using Fe<sub>2</sub>O<sub>3</sub>/CeO<sub>2</sub> Mechanically Mixed with Al<sub>2</sub>O<sub>3</sub>: Insights into the Promoting Effect of Plasma Discharge Enhancement on the Role of Catalysts
Guangzhao Zhou, Ziyu Wang, Xiaochao Wang, Yiran Zhang, Xuteng Zhao, Qi Chen, Ting Chen, Zhen Huang, He Lin
Abstract
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 CeO 2 and Fe 2 O 3 /CeO 2 (Fe/Ce) mechanically mixed with dielectric Al 2 O 3, 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 CeO 2 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 CeO 2 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 Al 2 O 3 mixing ratio was 8.8 times that in pure Fe/Ce. U – I curves, U – Q c curves, and self-luminous optical imaging results of the discharge region packed with the catalysts indicated that Al 2 O 3 mixing effectively strengthened the plasma discharge. Catalyst characterization showed that Fe/Ce had better catalytic properties than CeO 2, explaining the better performance of Fe/Ce@Al than that of Ce@Al in the NTPCAS. In situ N 2 and H 2 adsorption, desorption, and reaction behaviors over catalysts revealed that significantly improved N 2 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.