REDUCIBILITY OF METALS ON FLUID CRACKING CATALYST

Temperature-programmed reduction (TPR) and high-temperature oxygen tit ration have been applied to characterize Ni and V in fluid cracking ca talysts (FCC) as a function of catalyst composition and the method of metals impregnation and deactivation. The influence of the type of mat rix, the level of nickel and vanadium, antimony and oxidation / reduct ion cycles have been examined. TPR spectra of nickel on cracking catal ysts are characterized by a low-temperature peak at 680-degrees-C attr ibutable 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 t he alumina content of the catalyst generally leads to a decrease in th e intensity of the low-temperature peak and an increase in the reducti on temperature of the high-temperature peak. TPR spectra of vanadium o n cracking catalysts are characterized by a single peak in the range o f 550 to 650-degrees-C. Metals were introduced by pore volume impregna tion followed by steaming in an inert or a cyclic oxidizing/reducing e nvironment. 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 decr eases the amount of reducible nickel and vanadium, increases the tempe rature required for the reduction of vandium, and decreases the dehydr ogenation activity of the metals, especially vanadium. A survey of com mercial equilibrium catalysts shows that the reducibility of metals, a s measured by high-temperature oxygen titration can be correlated with the coke selectivity.