Active phase transformation in industrial CoMo/Al^sub 2^O^sub 3^ hydrotreating catalyst during its deactivation and rejuvenation with organic chemicals treatment

Reactivation of industrial CoMo/Al2O3 hydrotreating (HDT) catalysts was studied. A spent catalyst was used in the ULSD production for about 2.5 years. It was oxidatively regenerated and rejuvenated by organic acids (citric and thioglycolic), glycols (ethylene and triethylene), and dimethylsulfoxide solutions. All solids were characterized by the elemental analysis, N2 physisorption, X-ray powder diffraction, thermogravimetric analysis, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Changes in the active phase composition and morphology during the CoMo/Al2O3 HDT catalyst operation, regeneration and rejuvenation were shown. The rejuvenated catalysts were tested in hydrodesulfurization (HDS) of dibenzothiophene and hydrogenation (HYD) of naphthalene. It was found that oxidative regeneration allowed restoring about 70–85% rel. of initial activity. Rejuvenation with organic chemicals resulted in the complete restoration of HDS and HYD activities. Resulting catalytic activity of the reactivated catalysts depended on the properties of the formed active phase species. These correlations are discussed in the study.