Oxidative dehydrogenation of N-butane over VMgO catalysts supported and promoted with molybdenum or gallium

The present study investigates the n-butane oxidative dehydrogenation (ODH) using VMgO catalysts supported on SiO₂ or promoted with different amounts of Gallium or Molybdenum. The Mg/V atomic ratio used for all catalysts was four. Experiments were performed in a fixed bed reactor within the temperature range of 480 to 540°C and a residence time within the range of 6 to 50 (g_cat min mol_total^-1). The need for catalysts previously stabilized in order to avoid changes in behavior with time on run was demonstrated. The VMgO unsupported and unpromoted phase showed a good level of activity (conversions of ±30% at a contact time of 50 [g _cat min mol_total^-1] and a temperature of 540°C) with selectivities toward unsaturated hydrocarbons in the order of 90%. In order to increase the catalyst resistance to attrition, this active phase was supported on SiO₂ (30% by weight). The activity and selectivity of this catalyst was somewhat lower than the observed on the unsupported phase but still interesting. The additions of molybdenum or gallium oxides with an atomic ratio (Mo/V or Ga/V) in the range 0.1 to 1.0 show instead to have mixed effects. Molybdenum promotes the selectivity toward butylenes but with a reduction in activity. Instead, gallium introduces a rather small effect.