1. Microchemistry Ltd., P.O. Box 45, FIN-02151 Espoo, Finland, Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FIN-02150 Espoo, Finland, Corporate Technology, Neste Oy, P.O. Box 310, FIN-06101 Porvoo, Finland, and Faculty of Physics and Schuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands