Sulfur-resistant carbon-supported iridium catalysts: Cyclohexane dehydrogenation and benzene hydrogenation

Abstract

Carbon-supported iridium catalysts, with different metal loadings, were prepared by impregnation of a high-purity activated carbon. The dispersion of the metallic phase was studied by hydrogen and carbon monoxide chemisorption and transmission electron microscopy (TEM). The hydrogen chemisorption on the iridium crystallites supported on activated carbon was quite different from the chemisorption on an Ir/alumina catalyst. TEM observations of the catalysts show metal particles as spheres in the former case and as rafts in the latter. The cyclohexane dehydrogenation and the benzene hydrogenation were studied for both catalyst types. Both reactions are insensitive to the iridium dispersion and to the support. The thiotolerance level of the various catalysts was measured with feeds contaminated with 4 ppm of thiophene. In the case of the cyclohexane dehydrogenation, the thiotolerance level is affected neither by the support (activated carbon versus alumina) nor by the metallic dispersion of the Ir/carbon catalysts. However, in the benzene hydrogenation the carbon-supported iridium catalysts are more resistant toward the poisoning than the Ir/alumina counterpart. This behavior is interpreted as due to the different metallic microstructures produced on the two supports.