On the effects of calcination conditions on the surface and catalytic properties of γ-Al 2O 3-supported CoMo hydrodesulfurization catalysts

Abstract

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 (Mo 4+ and Mo 6+) and sulfur (S 1 and S 2) were identified. The ratio of Mo 4+/Mo 6+ 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.