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The catalytic decomposition of simple heterocyclic compounds. II 195 the sulphides of molybdenum, nickel and cobalt; they demonstrated the presence of tetrahydrothiophen among the reaction products. In the present series of experi ments at normal pressure, no tetrahydrothiophen could be detected under any conditions, whether the extent of thiophen decomposition was great or small. It seemed important, therefore, to compare the rate at which the hetero-atom was split off from the tetrahydro-compounds with that found for the unhydrogenated ring. As a result of these observations, the mechanism proposed by Moldavskii and Kumari proved untenable, and an alternative is now suggested.
196 R. H. Griffith, J. D. F. Marsh and W. B. S. Newling On MoS2 at 200° C the conversions were 69 % at 162 p.p.m., 31 % at 350p.p.m. and 19 % at 690 p.p.m. These results show that the reaction is of approximately zero order with respect to thiophen.
The catalytic decomposition of simple heterocyclic . II 197 The retardation of thiophen hydrogenation on JSTi3S2 by H2S On Ni3S2 at 400° C and at a concentration of 330 p.p.m. thiophen conversion was 40 %. Addition of 500 p.p.m. of H2S reduced it to 20 % or to half of the unretarded conversion. The catalyst was cooled in the H2-H2S mixture and its magnetic mass susceptibility found to be 7*5 x 10-6 showing that all large groups of Ni atoms had been resulphided.
198 R. H. Griffith, J. D. F. Marsh and W. B. S. Newling D iscussion of results (a) The mechanism on molybdenum disulphide catalysts The information provided by the adsorption measurements, given in part I, is most significant. On MoS2, hydrogen is very extensively adsorbed; at its maximum, about one molecule is held for each ten molecules of MoS2, which is equivalent to about four molecules of hydrogen for every surface atom indicated by the low temperature adsorption of nitrogen. The sharp increase at 150° C to a value which is nearly constant at higher temperatures suggests that little penetration of the lattice is occurring, but that the hydrogen atoms can penetrate between the plates of fhe MoS2 crystals where the nitrogen molecules are unable to do so.
The catalytic decomposition of simple heterocyclic compounds. II 199 on the molybdenum surface, but may only require single-point adsorption of the sulphur atom. Further attention is given to this suggestion in the discussion of the nickel sulphide catalysts.