Abstract
SO2 storage by copper containing mixed oxides, such as CuTa2O6, CuNb2O6 and so on, was investigated. SO2 sorption occurred under the presence of oxygen and it was desorbed under the presence of H2. The sorption/desorption process can be regarded as not only the low concentration-SO2 removal from, e.g. flue gas but also the concentration process of SO2 to be a chemical feedstock. The crystals of CuTa2O6 and CuNb2O6 have perovskite- or columbite-type structure. These catalysts showed very high SO2 storage capacity by several cycles of oxidative sorption and reductive desorption. The amounts of the SO2 uptake per Cu atom were much more than those based on the assumption of surface adsorption and the specific surface area and also the amounts of SO2 uptake by CuO, Ta2O5 and Nb2O5. Hence, the storage occurs not only on the surface but also inside the bulk of the catalysts in probably in sulfates ion form and the storage is enhanced by the presence of Ta or Nb. In this study, this remarkably high sorption ability was named Synergetic Oxidative Sorption (SOS)of SO2. From XRD measurement, the crystal structures of the catalysts were gradually destroyed by the cycles and the XRD patterns showed that the catalysts finally became amorphous when SOS appeared. Another interesting finding was that just mechanical mixtures of CuO and Ta2O5 or Nb2O5 also showed the high SOS activity. Effect of partial replacement of Ta by Nb was also investigated.
