INTERACTIONS IN ALUMINA-BASED IRON-OXIDE VANADIUM-OXIDE CATALYSTS UNDER HIGH-TEMPERATURE CALCINATION AND SO2 OXIDATION CONDITIONS

Depending on such variables as vanadium oxide content, calcination temperature and the content of sulfur dioxide in the oxidizing atmosphere, wide variations in surface area, phase composition. metal oxide-support interactions, and inter- and intraparticle metal oxide migration were observed in γ-alumina (PHF) catalysts containing iron oxide and vanadium oxide-two common contaminant metal oxides found in refinery catalysts-under conditions simulating FCC or resid hydrotreating catalyst regeneration. Samples were subjected to a wide range of calcination temperatures and were tested for the catalytic oxidation of sulfur dioxide by thermal gravimetric analysis (TGA). Catalysts were characterized by a number of techniques, including porosimetry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Mössbauer and 51V-NMR spectroscopy. IGA tests indicated that both iron and vanadium oxides catalyzed the formation of aluminum sulfate at lower temperatures compared with blank alumina, but that iron-vanadium mixed oxides were inactive. The results of this study suggest a possible need to incorproate sulfur dioxide in typical fluid catalytic cracking (FCC) laboratory steaming experiments, especially if contaminant metal oxides have been artificially introduced. Such incorporation may induce different metal oxide-metal oxide interactions and alumina phase transitions compared with steamings in the absence of sulfur dioxide and may better test the true passivating potential of commercially available SOx additives. © 1993 by Academic Press, Inc.