1. Department of Chemistry, University of the Free State, Nelson Mandela Drive, P.O. Box 339, Bloemfontein 9300, South Africa
2. Department of Physics, University of the Free State, Nelson Mandela Drive, P.O. Box 339, Bloemfontein 9300, South Africa
3. SynCat@DIFFER, Syngaschem BV, P.O. Box 6336, 5600 HH Eindhoven, The Netherlands