1. Laboratory of Industrial Chemistry, Ruhr-Universität Bochum, P.O. Box 10 21 48, D-44801 Bochum, Institute for Applied Chemistry Berlin-Adlershof e.V., Richard-Willstätter-Str. 12, D-12484 Berlin, Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle/Saale, and Department of Chemistry, Institute of Chemical Technology, Darmstadt University of Technology, Petersenstr. 20, D-64287 Darmstadt