Relation between hydrodesulfurization activity and the state of promoters in precursor calcined [formula omitted] catalysts

Abstract

Two series of NiCoMo Al 2O 3 hydrodesulfurization (HDS) catalysts prepared by different procedures were investigated. In each series the Mo loading and the total content of promoters (Co + Ni) were kept constant but the Co (Co + Ni) atomic ratio was varied from 0 to 1. The two series of catalysts were prepared by a sequential wet impregnation technique. In series I, the impregnations of both Mo and promoters were carried out at the pH of the impregnating aqueous solutions, employing an intermediate calcination; in series II, Mo was impregnated at pH 10, while the promoters were added in aqueous ethanol solutions without intermediate calcination. Catalysts in their calcined state were characterized by reduction in H 2 at 500 °C, O 2 chemisorption, and infrared spectroscopy of adsorbed NO. The HDS activity and the optimum Co (Co + Ni) atomic ratio were different for the two series, in agreement with our previous studies, HDS activity being generally higher for series II than for series I. Dispersion of Mo (as estimated from O 2 chemisorption) and NO adsorption on Mo in reduced catalysts (as judged from the intensity of the band at about 1705 cm −1) were not substantially different for the two series of catalysts and did not correlate with HDS activity. However, adsorbed NO on promoters in oxidized catalysts (bands at about 1880 and 1800 cm −1) followed roughly the same trend as HDS activity, suggesting that the active sites may be related to the Co and Ni atoms adsorbing NO. Possible reasons for the differences between HDS activity of the two series are considered.