Abstract
Mesoporous MgO was synthesized by the nanoreplication method using CMK-3 carbon as a hard template and magnesium nitrate as a metal oxide precursor. The produced support was modified with different amounts of ammonium metavanadate solution. Various distributions of V-containing species on the MgO surface were found by XRD, low-temperature adsorption of N2, TEM, XPS and UV–vis-DR spectroscopy. At low V loadings isolated VO4 dominated. Increasing V content resulted in clustering of VO4 species and the formation of Mg3V2O8 crystallites. As found in temperature-programmed reduction (H2-TPR), the latter phase was clearly harder in reduction by H2 compared to highly dispersed VO4 forms. The developed materials appeared to be very active catalysts of oxidative dehydrogenation of ethylbenzene (ODH). The optimal catalytic performance was observed for the sample containing 10 wt% of vanadium. The initial ethylbenzene conversion of 63.6% at selectivity to styrene of 86.9% was achieved at temperature as low as 500 °C. A notable influence of carbonaceous deposit formed during the ODH reaction on the catalytic activity was discussed, including presentation of both coexisting superficial reaction mechanisms. A reasonable regeneration procedure to recover lost activity was developed.
Highlights
Styrene is a very important monomer in the global polymer industry, due to a common application of various forms of polystyrenecontaining homo- and copolymers
Bulk magnesium orthovanadate is significantly less active compared to supported systems, which are usually formed by an acid-base reaction of acidic vanadium oxide and basic MgO support [7,11]
A surface composition of samples was investigated with X-ray photoelectron spectroscopy (XPS) using a Prevac photoelectron spectrometer equipped with a hemispherical analyzer (VG SCIENTA R3000)
Summary
Styrene is a very important monomer in the global polymer industry, due to a common application of various forms of polystyrenecontaining homo- and copolymers. In recent years much research has focused on oxidative dehydrogenation of ethylbenzene (ODH), because this approach exhibits significant benefits in contrast to the common dehydrogenation, i.e. exothermic heat effect and operation out of thermodynamic limitations [2] Even though this technology was successfully implemented in the commercial butadiene manufacturing, no stable and selective enough system for the styrene production has been developed yet [3]. Hanuza et al [7] proposed a redox mechanism of ODH involving vanadium active sites and oxygen bridges located in a V2O5/ MgO system From this point of view, the kind of metal oxide phase is a key factor for achieving an acceptable catalytic performance. To the best of our knowledge, this is the first attempt on the investigation of catalytic activity of ordered mesoporous VOx-modified MgO replicas in the ODH reaction
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