Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Abstract

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.