1. Bulgarian Academy of Sciences, Institute of Catalysis, Acad. G. Bonchev Str., bl 11, Sofia 1113, Bulgaria
2. University of Chemical Technology and Metallurgy, 8 Kliment Ohridski, 1756, Sofia, Bulgaria
3. Bulgarian Academy of Sciences, Institute of General and Inorganic Chemistry, Akad. G. Bontchev str. bl 11, 1113, Sofia, Bulgaria