Deuterium tracer study of the behaviour of chemisorbed hydrogen in some metal- and sulphide-catalysed hydrogenations and hydrodesulphurisations

The behaviour of chemisorbed hydrogen in metal- and sulphide-catalysed hydrogenations is reviewed by collation of information mostly from the author's previous publications. The use of molecular deuterium as an isotopic tracer, and the evaluation of the results by the numerical procedures originally proposed by BURWELL and by KEMBALL, permits the effective ratio of adsorbed-H to adsorbed-D in hydrogen addition steps to be calculated. This paper assembles evidence to show that, whereas some reactions behave as though adsorbed hydrocarbon species reacted with a single source or pool of adsorbed hydrogen, others behave as though two or more such sursources existed having different isotopic composition. Two examples of bi-phase systems are presented involving metal, and metal sulphide catalysts. This behaviour is demonstrated by reference to the hydrogenation of ethene, buta-1,3-diene, and but-2-yne, the geometrical isomerization of cis-penta-1,3-diene, and the hydrosulphurisation of thiophen and of tetrahydrothiophen. Recognition of such behaviour of chemisorbed hydrogen improves our understanding of catalyst activity and selectivity. (author)