Studies of molybdenum sulfide catalysts: Effects of pretreatment on olefin hydrogenation activity

Abstract

Various models have been proposed for the active sites in hydrogenation and hydrogenolysis reactions on molybdenum sulfide catalysts. The role played by edge and basal sites of the sulfide in both oxygen chemisorption and in hydrogenation is still moot, although the question has been often investigated. The authors have chosen to study the effect of catalyst preparation and pretreatment on the properties of unsupported molybdenum disulfide, to avoid some of the problems involved in characterizing supported catalysts. The unsupported sulfide was prepared in situ by the thermal decomposition of ammonium tetrathiomolybdate (ATTM) in flowing helium. In the present paper, unsupported molybdenum sulfide catalysts have been tested for catalytic activity in propene hydrogenation after various pretreatments. This was selected as a test reaction because it gives good conversions at temperatures below the TPR peaks; these mild conditions do not destroy the effects of catalyst pretreatment. Activity was measured with a pulse method, with determination of kinetic constants by a procedure recently described. 44 references.