NICKEL CONTAMINATION OF FLUIDIZED CRACKING CATALYSTS - A MODEL STUDY

Metal poisoning of fluidised cracking catalysts is a major industrial problem. Focusing on nickel, the dispersion, chemical state and toxicity of this metal have been studied for various components of fluid catalytic cracking catalysts such as: silica, kaolin, magnesia, alumina, silica-aluminas and modified Y zeolites. Depending on the alumina content of the solid, nickel can be present in two main forms: nickel oxide-like particles and a nickel aluminate-like phase. The oxide form, reducible at low temperture, is favored on silica-rich supports. Conversely alumina-rich solids favor the formation of a nickel combined phase, reducible at higher temperature. Although both species exhibit dehydrogenation properties, micro activity test results would indicate that the most poisonous phase in fluidised catalytic cracking catalysts are nickel aluminate-like compounds.