Fe/ZSM-5 catalysts for ammonia decomposition to COx-free hydrogen: Effect of SiO2/Al2O3 ratio

Abstract

HZSM-5 zeolites with different SiO2/Al2O3 ratios are employed as supports of Fe catalysts for NH3 decomposition. The structural and surface properties of the prepared Fe/ZSM-5 catalysts are characterized by solid-state NMR, XRD, N2 sorption, TEM, H2-TPR, NH3-TPD and XPS techniques, giving an insight into the active sites responsible for NH3 decomposition reaction. It is revealed that the catalytic activities of Fe/ZSM-5 catalysts are correlated with the SiO2/Al2O3 ratios of ZSM-5 support. And the SiO2/Al2O3 ratio of ZSM-5 zeolites could significantly affect the acidity, NH3 adsorption-desorption processes, metal-support interactions, and Fe particles size and distributions of Fe/ZSM-5 catalysts, and thus, affecting their catalytic performance. The Fe/ZSM-5 catalysts with low SiO2/Al2O3 ratio exhibit high catalytic performance. Almost 99% NH3 decomposition could be achieved over the 5%Fe/ZSM-5 catalyst with SiO2/Al2O3 ratio of 28 at 650 °C at a high space velocity of 30,000 cm3 h−1 gcat−1, suggesting a very promising catalyst in NH3 decomposition.