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

Abstract

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 N2 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 319mg/g and breakthrough time of 540min. 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 1045m2/g and total pore volume of 0.961cm3/g with micropore volume of 0.437cm3/g and is larger than Fe/NAC-0 (823m2/g, 0.733 and 0.342cm3/g). After desulfurization, surface area and pore volume of all samples decrease significantly, and those of the exhausted Fe/NAC-60 decrease to 233m2/g and 0.481cm3/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 0.7nm and 1.0⿿2.0nm and corresponds to an excellent desulfurization activity, showing that micropore is conducive to the removal of SO2.