1. G. Boreskov, V. Popovskii andV. Sazonov, in Proceedings of the IVth International Congress on Catalysis, Moscow, 1970, edited by T. Eidus, V. Vassenberg, S. Kipperman, A. Rubinstein, B. Polkovnikov and T. Vinikov (Nauka, Moscow, 1970) Vol. 1, p. 343.
2. D. G. Klissurski,Commun. Chem. Bulg. Acad. Sci. 8 (1961) 153.
3. Idem.,,Int. Chem. Engng 5 (1965) 19.
4. Idem.,,C.R. Acad. Bulg. Sci. 19 (1966) 297.
5. D. G. Klissurski, T. Popova, N. Abadjieva andD. Milanova,Chimia Industria 57 (1970) 293.