Promoted Oxide Catalysts Research Articles

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.

ZrO2 promoted with sulfate, iron and manganese: a solid superacid catalyst capable of low temperaturen-butane isomerization

A sulfated oxide of zirconium, iron and manganese is prepared and shown to isomerizen-butane to isobutane at 35°C with rates approximately 2–3 orders of magnitude greater than sulfated zirconia as claimed by workers at Sun Refining and Marketing Company. Temperature programmed desorption of benzene is used to investigate the acidity of this remarkable catalyst. Adsorbed benzene is oxidized to CO2 by the triply promoted oxide catalyst; CO2, SO2 and O2 are found to desorb at 525, 575 and 560°C, respectively. Sulfated zirconia does not adsorb benzene in a similar manner. The results from the temperature programmed desorption of benzene cannot be correlated with then-butane isomerization activity.

The importance of heterogeneous and homogeneous reactions in oxidative coupling of methane over chloride promoted oxide catalysts

The formation of ethene from ethane and methane in a silica reactor has been studied both in the presence and in the absence of chloride-containing catalysts. Some homogeneous conversion of ethane to ethene occurs in the gas phase through direct dehydrogenation, oxidative dehydrogenation, and, when HCl is present, chlorine radical induced reactions. Methyl chloride is detected in the gas phase but has no influence on the conversion of ethane to ethene. It is shown that under typical catalytic conditions, when a chloride-modified catalyst is used, ethane is mostly produced in the catalyst bed.