Investigation of the nature of V-species on alumina modified by alkali cations: Development of multi-functional DeSO_x catalysts

摘要

The location of vanadium species on 8-aluminas modified by lithium, sodium or potassium has been thoroughly investigated by means of several techniques. XRD, TPR and textural analyses showed that vanadium species are preferentially located on group 1 element or in its close vicinity when compared with the non-modified alumina. Vanadium species are localized nearby lithium and potassium cations, whilst vanadium species are partially distributed between sodium and alumina support in the sodium-modified alumina. A detailed XPS study was also carried out over potassium-promoted alumina catalysts and confirmed the vanadium distribution nearby potassium. Experiments of SO_x capture and sulfate reduction to H2S were performed under realistic Fluid Catalytic Cracking (FCC) conditions with respect to the temperature of the catalyst regeneration (at 725 °C) and during hydrocarbon reactions (around 575 =C). Among different alkali cation modifiers, alumina modified by potassium exhibited the best performance in the DeSO_x reaction (in terms of mole of absorbed sulfur per mole of group I cation) according to the following ratios: 0.74,0.34 and 0.24 observed for K, Li and Na, respectively. Finally, vanadium largely improved the rate of SO2 oxidation as well as the rate of sulfate reduction to H2S.