TIN PASSIVATION OF VANADIUM IN METAL-CONTAMINATED FLUID-CRACKING CATALYSTS - ELECTRON-PARAMAGNETIC RESONANCE STUDIES

Vanadium interactions with model fluid cracking catalysts and vanadium passivation with tin have been monitored by electron paramagnetic resonance (EPR). Model systems such as EuY, amorphous aluminosilicate gels, and EuY-gel mixtures have been investigated. Vanadium, introduced in the form of vanadyl naphthenate, is stabilized on the zeolite primarily as octahedrally coordinated VO2+ cations. In contrast, the gel preferentially sorbs vanadium where it is stabilized mainly in the form of V2O5. The presence of tin on the zeolite favors oxidation of VO2+ to V5+ and the generation of Sn4+OV5+ species during steaming. Formation of europium orthovanadate (EuVO4) is promoted by the presence of excess tin. Removal of Eu3+ ions from the zeolite lattice in the form of vanadates contributes to zeolite destabilization; thus excess tin is to be avoided. © 1990.