1. Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, P.O. Box 6100, FIN-02015 Espoo, Finland, Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland, and Institut de Recherches sur la Catalyse − UPR (CNRS) 5401, 2 Avenue A. Einstein, F-69626 Villeurbanne Cedex, France