1. Department of MOL Hydrocarbon and Coal Processing, University of Pannonia, Egyetem utca. 10, H-8200 Veszprém, Hungary
2. Research Centre for Natural Sciences, Institute of Materials and Environmental Chemistry, Magyar Tudósok Körútja 2, H-1117 Budapest, Hungary
3. Clausthal University of Technology, Leibnizstraße 19, 38678 Clausthal-Zellerfeld, Germany