Date of Award

Winter 1995

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

First Advisor

Palligarnai T Vasudevan

Abstract

Active sulfide catalysts are conventionally prepared by converting the respective oxides to sulfides. Reductive sulfiding of the oxides is usually difficult and does not proceed in a regular manner. In this dissertation, a supported molybdenum sulfide catalyst prepared by the decomposition of ammonium tetrathiomolybdate (ATTM) in hydrogen and helium was studied. The catalyst is unique in two respects, namely, the lower valence state of the supported molybdenum sulfide catalyst, and the presence of few oxygen atoms in the catalyst. The thiophene hydrodesulfurization (HDS) and propylene hydrogenation (HYD) activities of a catalyst prepared by this technique (and subjected to different pretreatments) are compared with the activities of both a conventional and a commercial catalyst. The pretreatments consisted of flash or temperature programmed decomposition of the supported ATTM in helium followed by removal of excess sulfur by temperature programmed reduction (TPR), or reduction in hydrogen. The results clearly indicate that the activity of the catalyst prepared by the decomposition of ATTM is much higher than the activities of both the conventionally prepared catalyst and the commercial catalyst, probably due to its lower valence state. In order to understand the nature of surface and catalytic sites, temperature programmed desorption (TPD) of hydrogen sulfide, low temperature oxygen chemisorption (LTOC), and BET area measurement have been conducted. Finally, the activity of a cobalt promoted molybdenum sulfide catalyst prepared by the decomposition of the thiosalt was investigated. For the same pretreatment, the Co-promoted catalyst has a higher HDS activity but a similar HYD activity compared to the unpromoted catalyst.

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