Transition metal oxide/carbon composite catalysts for n-alkane aromatization: structure and catalytic properties

Nanocrystalline panicles of high temperature pretreated titania, zirconia o r hafnium oxide, embedded in a carbon matrix, have been found to catalyze t he aromatization of n-octane into ethylbenzene (EB) and o-xylene (OX) with high selectivity The carbon matrix itself is catalytically not active, but seems to co-operate: with the transition metal oxides in such a way that th e various metal oxide/carbon composite materials exhibit equal selectivity patterns. In detail, the carbon component stabilizes a high dispersion of t he oxides during the high temperature pretreatment procedure. This thermal treatment results in a destruction of surface acidity of the oxides, which would otherwise be responsible for undesirable consecutive and parallel rea ctions. Moreover, the carbon component is involved in the deep dehydrogenat ion of alkanes to multiple unsaturated alkenes. This is explained by the ab ility of surface carbon atoms to interact with hydrogen. The bulk and surfa ce structure of the catalysts have been characterized by XRD, specific surf ace area measurements. XPS, UPS, Raman spectroscopy, in situ ESR and DRIFT spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.