DEACTIVATION OF HYDROTREATING MOLYBDATE CATALYSTS BY METAL-DEPOSITION

Nickel-molybdate and cobalt-molybdate catalysts were used for hydrotreating coal-derived oils and a petroleum vacuum gas oil. The metallic components deposited on the spent catalysts were characterized to reveal their inhibitory effects on hydrogenation and hydrocracking activities. Inhibition by typical metal components, such as Na, K, Mg, Ca, Fe, Ti, Ni and V, were also evaluated by doping such metals on the catalysts. Inhibitory effects of alkali and alkaline earth metals on hydrogenation and hydrocracking activities were significant, and their effects decreased in the following order for both catalytic activities; K > Na > Ca > Mg. Deposition of V, Fe and Ti resulted in an increase in hydrocracking, but a decrease in hydrogenation. The effect of these metals decreased in the following order: V > Fe > Ti. Data from X-ray photoelectron spectroscopy, X-ray diffraction and extended X-ray absorption fine structure showed that alkali and alkaline earth metals not only segregated on the catalyst surface to cover the active sites but also caused the lateral growth of MoS2-like structures, and that some of these metals formed double oxides with molybdenum after the oxidative regeneration. The neutralization of acidity was significant for these basic metals. On the other hand, V, Fe and Ti tended not only to disperse the MoS2-like species but also to increase the catalyst acidity through the formation of an acidic double oxide with molybdenum/alumina support.