Effects of pore sizes and oxygen-containing functional groups on desulfurization activity of Fe/NAC prepared by ultrasonic-assisted impregnation

A series of Fe-loaded activated carbons treated by HNO3 (Fe/NAC) were prepared by incipient impregnation method with or without ultrasonic assistance and characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy disperse spectroscope (SEM-EDS), transmission electron microscopy (TEM) and N-2 adsorption/desorption. The desulfurization activities were evaluated at a fixed bed reactor under a mixed gas simulated from flue gas. The results showed that desulfurization activity from excellent to poor is as follows: Fe/NAC-60 > Fe/NAC-80 > Fe/NAC-30 > Fe/NAC-15 > Fe/NAC-0 > Fe/NAC-100 > NAC. Fe/NAC-60 exhibits the best desulfurization activity and has breakthrough sulfur capacity of 319 mg/g and breakthrough time of 540 min. The introduction of ultrasonic oscillation does not change the form of Fe oxides on activated carbon but can change the dispersion and relative contents of Fe3O4. The types of oxygen-containing functional groups have no obvious change for all samples but the texture properties show some differences when they are oscillated for different times. The fresh Fe/NAC-60 has a surface area of 1045 m(2)/g and total pore volume of 0.961 cm(3)/g with micropore volume of 0.437 cm(3)/g and is larger than Fe/NAC-0 (823 m(2)/g, 0.733 and 0.342 cm(3)/g). After desulfurization, surface area and pore volume of all samples decrease significantly, and those of the exhausted Fe/NAC-60 decrease to 233 m(2)/g and 0.481 cm(3)/g, indicating that some byproducts deposit on surface to cover pores. Pore size distribution influences SO2 adsorption, and fresh Fe/NAC-60 has more pore widths centralized at about 0.7 nm and 1.0-2.0 nm and corresponds to an excellent desulfurization activity, showing that micropore is conducive to the removal of SO2. (C) 2015 Elsevier B.V. All rights reserved.