1. Leibniz-Institut für Katalyse an der Universität Rostock e. V., Branch Berlin, P.O. Box 961156, D-12474 Berlin, Germany, Sasol Technology R&D, 1 Klasie Havenga Road, P.O. Box, 1947 Sasolburg, South Africa, and Sasol Technology UK Ltd, Purdie Building, North Haugh, St. Andrews, FIFE, KY16 9ST, U.K.