REDUCIBILITY OF METALS ON FLUID CRACKING CATALYST

Temperature-programmed reduction (TPR) and high-temperature oxygen titration have been applied to characterize Ni and V in fluid cracking catalysts (FCC) as a function of catalyst composition and the method of metals impregnation and deactivation. The influence of the type of matrix, the level of nickel and vanadium, antimony and oxidation / reduction cycles have been examined. TPR spectra of nickel on cracking catalysts are characterized by a low-temperature peak at 680-degrees-C attributable to supported nickel oxide and a high-temperature peak in the range of 800 to 880-degrees-C attributable to highly dispersed nickel species such as Ni hydroxysilicate and Ni surface spinel. Increasing the alumina content of the catalyst generally leads to a decrease in the intensity of the low-temperature peak and an increase in the reduction temperature of the high-temperature peak. TPR spectra of vanadium on cracking catalysts are characterized by a single peak in the range of 550 to 650-degrees-C. Metals were introduced by pore volume impregnation followed by steaming in an inert or a cyclic oxidizing/reducing environment. Metals, especially vanadium, from pore volume impregnation are generally more easily reduced than metals in equilibrium catalyst. Steaming the metallated catalysts in a cyclic redox environment decreases the amount of reducible nickel and vanadium, increases the temperature required for the reduction of vandium, and decreases the dehydrogenation activity of the metals, especially vanadium. A survey of commercial equilibrium catalysts shows that the reducibility of metals, as measured by high-temperature oxygen titration can be correlated with the coke selectivity.