KINETIC-STUDY OF THE OXIDATION OF N-BUTANE ON VANADIUM-OXIDE SUPPORTED ON AL MG MIXED-OXIDE/

The reaction kinetics of the oxidative dehydrogenation (ODH) of n-buta ne over vanadia supported on a heat-treated Mg/Al hydrotalcite (37.3 w t% of V2O5) was investigated by both linear and nonlinear regression t echniques. A reaction network including the formation of butenes (1-, 2-cis-, and 2-trans-butene), butadiene, and carbon oxides by parallel and consecutive reactions, at low and high n-butane conversions, has b een proposed. Langmuir-Hinshelwood (LH) models can be used as suitable models which allows reproduction of the global kinetic behavior, alth ough differences between oxydehydrogenation and deep oxidation reactio ns have been observed. Thus, the formation of oxydehydrogenation produ cts can be described by a LH equation considering a dissociative adsor ption of oxygen while the formation of carbon oxides is described by a LH equation with a nondissociative adsorption of oxygen. Two differen t mechanisms operate on the catalyst: (i) a redox mechanism responsibl e of the formation of olefins and diolefins and associated to vanadium species, which is initiated by a hydrogen abstraction; (ii) a radical mechanism responsible of the formation of carbon oxides from n-butane and butenes and associated to vanadium-free sites of the support. On the other hand, the selectivity to oxydehydrogenation products increas es with the reaction temperature. This catalytic performance can be ex plained taking into account the low reducibility of V5+-sites and the higher apparent activation energies of the oxydehydrogenation reaction s with respect to deep oxidation reactions.