Zirconia/carbon composites as monofunctional catalysts in C 6+ alkane aromatization

Abstract

High surface area materials composed of microcrystalline zirconia and amorphous carbon have been prepared by a sol–gel method, followed by a high temperature treatment of the resulting xerogel in inert gas. These composites have been characterized and tested in the dehydrocyclization of n-hexane and of n-octane at 550°C. They turned out to be highly selective aromatization catalysts. From n-octane, predominantly ethylbenzene and o-xylene are formed as products, demonstrating a C(1)–C(6) or C(2)–C(7) ring closure of the C 8 chain, respectively. The low rates of side reactions like isomerization or cracking of reactants and products correspond to the low acidity of the new catalysts and show that they are essentially monofunctional. One role of the carbon matrix could consist in the prevention of zirconia sintering, enabling the destruction of acid sites by high treatment temperatures. On the other hand, at present it cannot yet be excluded that the zirconia surface had been modified by carbidization or partial reduction or that the carbon surface of the composites exhibit special properties in contact with the zirconia surface.