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Preparation and evaluation of non supported and supported catalysts based on mixtures of vanadium and magnesium oxides for the ODH of n-butane

Abstract:

In this work the Oxidative Dehydrogenation (ODH) of n-butane has been studied over four supported and non-supported VMgO catalysts with an atomic Mg/V ratio of 4. One of them was supported over 30% by weight of SiO2 (S16) and another on 30% of á-Al2O3 (A16), both being calcined at 600°C. Two samples of the non-supported catalyst were prepared, one calcined at 600°C (B16) and the other at 700°C (B17). All catalysts were characterized by DRX, XPS, TPR, chemical analysis by atomic absorption, and by the specific surface (BET). With the exception of the sintering level and the lower specific surface area, the catalyst B17 gave results similar to those obtained with the B16. Experimental runs were done in a quartz tubular reactor with an inlet composition for reactants of C 4H10/O2/N2 = 8/12/80, the reaction temperature was varied from 480 to 550 °C and contact times of 6, 25 y 50 gcat min/moltot. were used. The change introduced in the catalysts preparation method has demonstrated to be effective in assuring the reproducibility in their synthesis. The reaction conditions for the catalyst B17 proved to be quite difficult to control and for this reason was not used. It was found that the addition of a third oxide, such as SiO2 or α-Al2O3, reduces the catalytic activity and selectivity of the active phase, but this variations are small: from 5 to 8 % in selectivity toward butadiene and from 3 to 5% for the activity. The experimental results showed a consistent improvement in the catalyst's behavior when it is compared with similar catalysts prepared by other researchers, which is explained by the improvement introduced in the preparation method. The catalyst A16 showed a higher activity (31% of conversion) and a higher overall selectivity (total) toward unsaturated hydrocarbons (80%) than the supported over SiO2 (S16), which showed a conversion of 29% with a total selectivity around 77 %.