1. R & D Division, Sasol Technology (Pty) Ltd., 1 Klasie Havenga Road, Sasolburg 1947, South Africa, Sasol Technology U.K. Ltd., Purdie Building, North Haugh, St. Andrews, KY16 9ST, U.K., School of Chemistry, University of St. Andrews, Purdie Building, St. Andrews, Fife, KY16 9ST, U.K., and Lehrstuhl fuer Chemische Reaktionstechnik der Universitaet Erlangen-Nuernberg, Egerlandstrasse 3, D-91058 Erlangen, Germany