Metallic area of supported iridium catalysts

Abstract

Iridium catalysts supported on alumina, magnesia, silica-alumina, cerium and niobium oxides were prepared by impregnation with iridium carbonyl. The metallic state was characterized by hydrogen and oxygen chemisorption as well as transmission electron microscopy (TEM). The activity in benzene hydrogenation was also measured. The direct reduction of the irridium precursor led to homogeneously dispersed iridium particles, as seen by TEM for alumina, magnesia and silica-alumina carriers. For these catalysts, hydrogen and oxygen chemisorption and TEM observations are in excellent agreement. The turn-over number for benzene hydrogenation was close to 70 h −1. For cerium and niobium oxide supported materials, neither oxygen nor TEM were able to give a good estimation of the metallic area. However, with the restriction of catalysts supported on ceria, for which the reproducibility of SMSI (strong metal support interaction) is doubtful, the hydrogen chemisorption and the benzene hydrogenation rate were shown to give coherent metallic areas in all cases.