Formation and role of Cu+ species on highly dispersed CuO/SBA-15 mesoporous materials for SOx removal: An XPS study

In the present work, copper species were incorporated in SBA-15 organized mesoporous silica (OMS) through wet impregnation of copper nitrate and the corresponding material was evaluated as SO2 adsorbent The calcination under a high flow of synthetic air leads to the formation of highly dispersed copper species in strong interaction with the support (Cu2+-O-Si). Indeed, the characterization of this material by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), do not indicate the presence of crystalline CuO. A comprehensive X-ray Photoelectron Spectroscopy (XPS) study allowed the identification of the active species in SO trapping and underlined the importance of a thermal pretreatment on the performances of the adsorbent in SO. trapping. It reveals that a pretreatment at 600 degrees C leads to the formation of active Cu+ species in higher amount ([Cu+) = 79.0%) than at 400 degrees C ([Cu+) = 37.6%), which strongly increases the adsorbent efficiency. These species were found to be stable in the presence of [O-2] = 10% (balance nitrogen) at 400 degrees C but unstable at ambient atmosphere at room temperature (presence of water). The treatment under SO2 at 400 degrees C leads to the reoxidation of the Cu+ species into Cu2+ ones, which are partially sulfated (formation of CuSO4). Additionally, the sulfation step causes the sintering of a part of the Cu2+-O-Si species into CuO. A reaction scheme was proposed according to which, in a first step Cu+ species catalyze the SO2 oxidation to SO3. In the second step, Cu(l) is reoxidized into Cu(It) as CuSO4. (C) 2016 Elsevier B.V. All rights reserved.