New Materials

SO2 oxidation catalysts: Solid phases in M'2S2O7-M''2S2O7 systems (M', M'' = Na, K, Rb, Cs) The most widely used catalyst for SO2 oxidation in sulphuric acid production and flue gas cleaning is under working condition a molten M2S2O7 - V2O5 mixture supported by a kieselguhr carrier. The M2S2O7 system acts as a solvent for the catalytically active vanadium complexes. In the "classical" catalyst M is a Na-K mixture, but also Rb and Cs have shown to be favourable additives. The project aims at determining the phase diagrams of these systems by means of theoretical, thermal and electrochemical methods as well as crystal structure determinations of the component phases. Recently the crystal structures of Na2S2O7, NaKS2O7 and two phases of Rb2S2O7 were solved from powder diffraction data. Cs2S2O7 was solved from single-crystal data and showed a remarkable structure. At 120 K it has 20 Cs, 20 S and 70 O in the asymmetric unit. The Cs arrangement is very similar to that of high-pressure Rb metal. Presently the K-Rb, K-Cs and MHSO4 systems are under study. The project is a collaboration with the Catalysis Group. 

The structure of Cs2S2O7 containing 20 Cs,

20 S and 70 O in the asymmetric unit