TIN PASSIVATION OF VANADIUM IN METAL-CONTAMINATED FLUID CRACKING CATALYSTS - SN-119 MOSSBAUER-SPECTROSCOPY

Tin Mössbauer spectroscopy has been used to probe the role of tin in the passivation of vanadium contaminants in model systems comprising EuY, aluminosilicate gels and EuY-gel mixtures. When tin is loaded on the catalysts in the form of tetraphenyl tin, Sn(Ph)4, it remains mostly intact on the zeolite, but on the gel forms oxygen ligands that replace one or two phenyl groups. On the zeolite, part of the tin remains on the surface while part migrates to internal sites. In zeolite-gel mixtures, tin is preferentially sorbed by the zeolite. At all stages of catalyst pretreatment, metallic tin, Sn(II) and tin-vanadium alloys are not formed. Calcination and steaming produced vanadium/tin oxide complexes (formed through oxygen bridges) in which tin is in the +4 oxidation state. Formation of Sn4+-O-V5+ linkages is probably responsible for the passivation of V by tetraphenyl tin deposition. © 1990.