The support effect on the properties of iridium catalysts for C-C and C-O hydrogenolysis was investigated. Cyclohexane conversion and glycerol hydrogenolysis were used to compare the behavior of iridium catalysts in terms of C-C and C-O cleavage. The nature of the support influenced the catalyst performance in both cyclohexane conversion and glycerol hydrogenolysis. This effect was more evident on the product selectivity. Ir/SiO2 catalyst presented the highest cyclohexane hydrogenolysis activity and the highest selectivity to minor hydrocarbons formed from hexane re-adsorption. For glycerol hydrogenolysis, all catalysts displayed a higher selectivity to products formed by C-O cleavage, mainly 1,2-propanediol (1,2-PDO). Ir/ZrO2 catalyst presented the highest activity in all reaction conditions and the lowest selectivity to minor alcohols produced by C-C cleavage like methanol, ethanol and ethylene glycol. The results were explained in terms of the requirements and the structure of the catalytic sites.
Keywords:
iridium catalysts; hydrogenolysis; C-C cleavage; C-O cleavage; support effect
