Abstract
Metal poisoning of FCC catalysts is a major industrial problem. Focussing on nickel, the chemical state and the toxicity of this metal has been studied for Y zeolites with various physico-chemical characteristics. Depending on the extra-framework aluminium content, nickel can be present either as nickel oxyde particles or nickel combined with alumina and to a lesser extent with silica. The oxide form, which is reducible at low temperature (〈723K), is favored for zeolites nearly exempt from extraframework aluminium. Conversely the combined form, which is reducible at high temperature (〉1023K), is predominant for zeolites with significant amounts of extraframework aluminium. Both species show a significant dehydrogenation activity, however the MAT tests indicate that nickel combined with alumina is likely to be more poisonous than nickel oxyde.
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