On the effects of calcination conditions on the surface and catalytic properties of γ-Al2O3-supported CoMo hydrodesulfurization catalysts

A series of alumina-supported cobalt-molybdenum catalysts were prepared by the incipient-wetness method. Different calcination temperatures (673-873 K) and durations (2-96 h) were used to obtain the catalysts. Samples of the catalysts were characterized by X-ray photoelectron spectroscopy (XPS). Depending on the calcination condition, two forms of molybdenum (Mo4+ and Mo6+) and sulfur (S1 and S2) were identified. The ratio of Mo4+/Mo6+ appeared to be affected more by the duration than by the calcination temperature. However, increase in the calcination temperature (673-873 K) led to an increase in the amount of cobalt interacting with the alumina support, with a corresponding decrease in Co-Mo-S ensembles. The catalysts were tested in hydrodesulfurization of dibenzothiophene (DBT). The catalyst with 24 h calcination time exhibited the highest DBT conversion. For the catalyst at a conversion of 38.8%, biphenyl (BP) and cyclohexylbenzene (CHB) were produced with selectivities of 82.8 and 17.2%, respectively. When either the calcination temperature or duration was increased, a smaller amount of CHB was observed. This has been associated with changes in the catalysts' surface properties.