Surface features and catalytic performances of platinum/alumina and platinum-rhenium/alumina catalysts for n-heptane conversion prepared by metal carbonyl complexes

The catalytic performance of alumina supported platinum and platinum-rhenium metal cluster (mc) catalysts for the catalytic reforming of hydrocarbons was studied under conditions of reaction temperature and pressure (500°C and 1.2MPa) that approximated the conventional platinum-rhenium reforming process. The selectivity of a platinum (mc) catalyst for the aromatization of n-heptane was 6% higher than that of a conventional platinum catalyst prepared by impregnating the alumina with an aqueous solution of hexachloroplatinic acid, and the stability of the platinum (mc) catalyst was also found to be significantly improved in comparison with the conventional catalyst. Decarbonylation of the supported platinum carbonyl complex was studied by the temperature-programmed decomposition (TPDE) technique in an atmosphere of argon or hydrogen, and the results indicated that the carbon monoxide released during the decarbonylation process disproportionated to carbon and carbon dioxide. At the same time, the formation of highly dispersed active carbon species on the surface of the catalyst was confirmed by temperature-programmed oxidation (TPO) measurements on the catalyst. The higher selectivity and stability of the platinum (mc) catalyst for n-heptane aromatization might well be attributed to the occurrence of this type of surface carbon species. The stability of a platinum-rhenium (mc) catalyst was found to be better than that of the platinum (mc) catalyst, and markedly higher than that of the conventional platinum-rhenium catalyst.