Oxidative conversion of light alkanes to olefins over alkali promoted oxide catalysts

Alkali promoted mixed oxides were studied as catalysts for the oxidative dehydrogenation (ODH) and cracking of butane and propane. Olefin yields as high as 50% were obtained with Li/MgO-based catalysts. Magnesia-based catalysts showed higher activity for olefin production than catalysts based on zirconia and niobia. Addition of Li to magnesia increases reaction rate normalized to the specific surface area about seven times and selectivity to olefins from 40 to 70%. Li is, therefore, an essential ingredient of the catalyst in order to create the active site. Cl-containing catalysts exhibit slightly higher olefin selectivity, but chloride-free catalysts show superior stability with time on stream. Alkanes show higher conversion rates than alkenes and this surprising result explains the high selectivity to olefins. It is suggested that Li+O- defect sites are the active site for activation of the alkane via hydrogen abstraction. Production of olefins via this oxidative dehydrogenation/cracking route may be an attractive alternative for steam-cracking. (C) 2002 Elsevier Science B.V. All rights reserved.