CLUSTER CATALYSIS - PROPANE HYDROGENOLYSIS CATALYZED BY MGO-SUPPORTED TETRAIRIDIUM

A metal carbonyl cluster with a tetrahedral metal frame, [HIr4(CO)(11)](-), was prepared on the surface of partially hydroxylated MgO powder by adsorption of [Ir-4(CO)(12)]. A supported catalyst was prepared by decarbonylation of the supported [HIr4(CO)(11)](-) by treatment in He followed by Hz at 300 degrees C. The surface structures were characterized by infrared and X-ray absorption spectroscopies. The decarbonylated cluster had an average Ir-Ir coordination number of 3.4, consistent with the hypothesis that the tetrahedral metal frame was largely retained after decarbonylation. The sample incorporating the decarbonylated clusters was catalytically active for propane hydrogenolysis at 1 atm and 200 degrees C. The catalyst that had been used for 1 day in a flow reactor was characterized by an Ir-Ir coordination number of 3.3. The lack of any significant change in the average cluster size indicates the stability of the supported catalyst, which is modeled as tetrahedral Ir-4 clusters. The rate of the propane hydrogenolysis at 200 degrees C and atmospheric pressure with a H-2/propane molar ratio of 2.5 was 0.02 molecule of CH4 produced/(Ir-4 cluster s).