MECHANISM OF CARBON-NITROGEN BOND SCISSION ON UNSUPPORTED TRANSITION-METAL SULFIDES

The reactivity of a series of amines with various structures and diffe rent numbers of hydrogen atoms on the carbon atoms in the alpha and be ta position, with respect to the nitrogen atom;, was examined on four transition metal sulfides, i.e. NbS3, MoS2, RuS2, and Rh2S3, II is sho wn that the reaction mechanism proceeds via an elimination or a nucIeo philic substitution the relative importance of which depends on the st ructure of the substrate to be transformed and on the transition metal sulfides properties. NbS3 is the most active sulfide of the series fo r the elimination reaction due to its high acidity, but it is inactive for the nucleophilic substitution. On the other hand, the surface spe cies of Rh2S3;can be involved in a nucleophilic substitution but not i n an elimination reaction, The other sulfides of the series behave in between. These results clearly demonstrate that the catalysts interven e differently in the HDN mechanism. Moreover, for a given solid the st ructure of a nitrogen-containing; molecule strongly affects the elemen tary steps of its transformation, Accordingly, a precise mechanistic s tudy of the reactivity of a mode! molecule al the surface of a sulfide cannot be generalized to the overall HDN process which involves sever al types of molecules. (C) 1998 Academic Press.