Oxidation mechanisms of H2S by oxygen and oxygen-containing functional groups on activated carbon

Abstract

Activated carbon (AC) has the advantage of multi-pollutant control with a high removal efficiency for flue gas purification. It is necessary to determine the oxidation mechanism and oxidation products of hydrogen sulfide (H2S) on AC to simultaneously capture H2S and SO2. A fixed-bed reactor was coupled with a mass spectrometer (MS) to detect the gaseous components and X-ray photoelectron spectroscopy (XPS) was used to distinguish the sulfur-containing species in the oxidation products on AC and thermally treated AC to investigate the actions of the oxygen-containing functional groups. The results revealed that H2S was adsorbed on the AC surface and combined with oxygen-containing functional groups to form sulfate (SO42−) in the absence of O2. In the presence of O2, H2S and O2 in the atmosphere were adsorbed on the AC active sites, and the catalytic reaction produced elemental sulfur. Elemental sulfur further reacted with O2 to produce gaseous SO2. According to the detection results of XPS and the in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectra, an oxidation mechanism of H2S by O2 and oxygen-containing functional groups was described. The C=C and C=O bonds were broken by H2S, and then, C-S and S-O bonds of the intermediate products were generated. The C-S bond tended to form elemental sulfur, while the S-O bond likely formed a sulfate or gaseous SO2. Porosity analysis showed that the AC specific surface area decreased after H2S adsorption and that sulfate reduced the specific surface area much more than elemental sulfur.