Role of Chlorine in β-FeOOH on Its Thermal Change and Reactivity to Sulfur Dioxide

Abstract

The state of Cl in β-ferric oxide hydroxide (β-FeOOH) was examined by X-ray diffraction, IR absorption, chemical analysis, DTA, and TGA. The adsorption of SO2 was determined as a measure of the surface activity. No influence of Cl contained in the crystal appeared in the X-ray diffraction patterns and surface area. The absorption bands at 640 and 840 cm−1 in IR spectra showing the deformation vibration of OH group diminished with the decrease of Cl content. It was shown that the path for β-FeOOH to transform into α-Fe2O3 by heating differentiates from the sample including more than 11.5% Cl/Fe to one including less than 11.5% Cl/Fe. This critical Cl content is equal to the amount of Cl when Cl fills up the characteristic tunnels existing in the β-FeOOH crystal. Cl in β-FeOOH interferes both its transformation into α-Fe2O3 and the recrystallization of resultant α-Fe2O3. These effects were explained by the stabilization of the β-FeOOH structure by Cl in tunnels and the bonding between Cl and Fe. The amount of chemisorbed SO2 was lowered by Cl which was adsorbed on outer surfaces.