Zirconia carbon composites as monofunctional catalysts in C6+ alkane aromatization

High surface area materials composed of microcrystalline zirconia and amorp hous carbon have been prepared by a sol-gel method, followed by a high temp erature treatment of the resulting xerogel in inert gas. These composites h ave been characterized and tested in the dehydrocyclization of n-hexane and of n-octane at 550 degrees C. They turned out to be highly selective aroma tization 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 isome rization or cracking of reactants and products correspond to the law acidit y of the new catalysts and show that they are essentially monofunctional. O ne role of the carbon matrix could consist in the prevention of zirconia si ntering, enabling the destruction of acid sites by high treatment temperatu res. On the other hand, at present it cannot yet be excluded that the zirco nia 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. (C) 1999 Elsevier Science B.V. All rights reser ved.