Abstract
Co(x)MgAlO mixed oxide catalysts with cobalt content in the range from 1 to 20 at.%, were prepared by calcination of layered double hydroxide (LDH) precursors at 1023 K. Their characterization was performed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), N-2 adsorption, Raman and photoluminescence spectroscopies, TG-DTG and H-2-TPR techniques. The catalytic activities were evaluated in the oxidative dehydrogenation of propane in the temperature range from 723 to 873 K. For all the catalysts the conversion increased when the reaction temperature increased, while the propene selectivity decreased continuously to the benefit of COx for Co(20)MgAlO and Co(10)MgAlO catalysts and of cracking products for the other cobalt-containing catalysts. In all the temperature range studied, the catalytic activity increased with increasing the cobalt content in the catalyst in line with the increase of reducibility. The best yields in propene of about 10% were obtained with Co(5)MgAlO and Co(7)MgAlO catalysts for the reaction performed at 873 K. Besides, a comparison of the behavior of Co(3)MgAlO and Co(7)MgAlO catalysts at 823 K showed that, at isoconversion, the propene selectivity was higher for the sample with lower cobalt content. The well-dispersed cobalt species with tetrahedral coordination played a main role in the oxidative dehydrogenation reaction of propane into propene. When the propane-to-oxygen molar ratio was increased from 1 to 4, the conversion decreased while propene selectivity increased continuously and the best propene yields were obtained for a propane-to-oxygen molar ratio of 1.