Vanadium contamination of FCC catalyst: Understanding the destruction and passivation mechanisms

Vanadium scavenging material comprising magnesium and yttrium oxides (Mg-Y-oxide) was prepared and evaluated for vanadium capture under simulated FCC regeneration conditions for typical FCC process. Vanadium trapping ability was measured using BET, XRD, FTIR, EDX coupled SEM and MAT. The results show that physiochemical properties, vanadium trapping and catalyst protection increase with amount of the trap material. SEM-EDX results confirm migration of vanadium as indicated by its presence in the passivator particle. Vanadium migrates within the catalyst particles by both inter and antra particles mechanisms. The XRD data further reveal high vanadium selectivity towards yttrium when passivator is incorporated after impregnation of vanadium, with the formation of crystalline yttrium vanadate (YVO4). Catalytic evaluation indicates improved activities of catalysts containing passivator which correlate with physiochemical parameters. In the passivation mechanism, mobile vanadic acid preferentially reacts more with Y2O3 in mixed metal oxide due to its higher activity (active sites), forming YVO4. These results therefore reveal that the passivator protects the catalyst by formation of immobile vanadate with mobile vanadic acid, thereby reducing hydrolysis of the catalyst framework and thus preserving important properties of the catalyst.