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A new MoVTeO mixed oxide has been obtained during the calcination of the corresponding catalyst precursor mixture at 600 °C in N2. The crystal structure has been studied by means of X-ray diffraction, electron diffraction, high-resolution electron microscopy, and diffuse reflectance spectroscopy. Its XRD pattern, similar to those observed in hexagonal tungsten bronze (HTB) K0.13-0.33WO3, was indexed on the basis of a hexagonal cell of parameters a = 0.727 nm and c = 0.4012 nm. However, the electron microscopy study reveals the crystals as being formed by structural domains of an orthorhombically distorted unit cell derived from the HTB structure. Microstructural details are discussed in terms of tellurium location inside the hexagonal tunnels of the structure. The results obtained constitute the first step for elucidating the role of this new orthorhombic phase in the effectiveness of Mo−V−Te−Nb mixed oxide catalysts.

A fluidized-bed reactor with separate butane and oxygen feeds has been studied in the oxidative dehydrogenation of butane. Under suitable conditions, feed segregation allows the creation of separated oxidation and reduction zones in the same reaction vessel, between which a V/MgO catalyst is recirculated. The behavior of the reactor has been characterized, with the separation of oxidation and reduction zones as the focus of the study. The performance of the two-zone reactor has been compared to that of a conventional fluidized-bed reactor.

The reaction kinetics of the oxidative dehydrogenation (ODH) of n-butane over vanadia supported on a heat-treated Mg/Al hydrotalcite (37.3 wt % of V2O5) was investigated by both linear and nonlinear regression techniques. 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 been proposed. Langmuir−Hinshelwood (LH) models can be used as suitable models which allows reproduction of the global kinetic behavior, although differences between oxydehydrogenation and deep oxidation reactions have been observed. Thus, the formation of oxydehydrogenation products can be described by a LH equation considering a dissociative adsorption of oxygen while the formation of carbon oxides is described by a LH equation with a nondissociative adsorption of oxygen. Two different mechanisms operate on the catalyst:  (i) a redox mechanism responsible 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 increases with the reaction temperature. This catalytic performance can be explained taking into account the low reducibility of V⁵⁺-sites and the higher apparent activation energies of the oxydehydrogenation reactions with respect to deep oxidation reactions.