1. Institute of Particle Technology, Friedrich-Alexander University, Erlangen-Nuremberg, Cauerstrasse 4, D-910 58 Erlangen, Germany
2. Department of Applied Physics and Competence Centre for Catalysis, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
3. USTEM, Vienna University of Technology, Wiedner Hauptstrasse 8-10/052 A-1040 Vienna, Austria