V–Mg–Al catalyst from hydrotalcite for the oxidative dehydrogenation of propane
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Mixed oxides obtained by the calcination of hydrotalcite precursors intercalated with 30, 70 and 100 % of decavanadate (theoretical percentages) were used as catalysts for the oxidative dehydrogenation of propane. Propene selectivity values up to 80 % were reached under conditions of deficiency and excess of oxygen at 400 °C with the catalyst derived from the 70 % vanadium-intercalated precursor. The composition of precursors and catalysts was determined by thermogravimetry and X-ray fluorescence analyses; textural properties of the catalysts were evaluated by N2 adsorption. Characterization by X-ray diffraction and Raman spectroscopy confirmed the intercalation of polyoxometalate species into the interlayer space of the hydrotalcite phase. After calcination, the catalyst with the highest vanadium content exhibited mainly the magnesium pyrovanadate phase. EXAFS analyses at the vanadium K-edge confirmed the presence of decavanadate ion into the hydrotalcite precursor and formation of four-coordinated vanadate species in the calcined catalysts. Catalytic performances of the materials were interpreted on the basis of characterization results suggesting that the active and selective phase was magnesium pyrovanadate.
KeywordsMg–Al–V Hydrotalcite Mixed oxide catalyst Oxidative dehydrogenation of propane EXAFS Raman
This work was carried-out with a financial support of SENA and COLCIENCIAS. We acknowledge LNLS (Laboratório Nacional Luz Síncrotron – Campinas, Brazil) for XAS (Research project no. 1687) and XRD (Research project no. 6405) measurements, NUCAT and IQ (Universidade Federal do Rio de Janeiro, Brazil) for XRF and XRD analysis. J.-G. E. thanks CNPq (Conselho Nacional de Pesquisa e Desenvolvimento) of Brazil for support during this work.
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