Sulfur exchange on Co---Mo/Al2O3 hydrodesulfurization catalyst using S radioisotope tracer

A commercial Co---Mo/Al₂O₃ catalyst was labeled with the radioisotope ³⁵S in hydrodesulfurization (HDS) of ³⁵S-labeled dibenzothiophene (³⁵S-DBT) in a high-pressure flow reactor at 50 kg/cm². Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H₂S were carried out on the labeled catalyst at 50 kg/cm² and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of ³⁵S---H₂S released from the ³⁵S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT> 4-MDBT> 4,6-DMDBT. In the sulfur exchange reaction with H₂S, the adsorption of H₂S on the catalyst reached saturation above a H₂S partial pressure of 0.36 kg/cm². It was suggested that the release of H₂S from the labile sulfur may be the rate determining step of the HDS reaction.