1. Process Technology,*Materials technology, Flemish Institute for Technological Research (VITO), Boeretang 200, B-2400 Mol, Belgium; Department of Chemical Engineering, Faculty of Applied Sciences, Katholieke Universiteit Leuven, de Croylaan 46, B-3001 Leuven, Belgium; Centre for Surface Chemistry and Catalysis, Faculty of Bio-engineering Sciences, Katholieke Universiteit Leuven, Kasteelpark Ar,enberg 23, B-3001 Leuven, Belgium.