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Bromine mediated partial oxidation of ethane over nanostructured zirconia supported metal oxide/bromide

2005-04-01
Yılmaz, Ayşen
Zhou, XP
Lorkovic, IM
Ylmaz, GA
Laverman, L
Weiss, M
Sun, SL
Schaefer, D
Sherman, JH
McFarland, EW
Ford, PC
Stucky, GD
Partial oxidation of ethane to an array of products was achieved through use of bromine/supported metal bromide as redox mediator for oxygen activation. In a two stage flowing fixed bed reactor, ethane bromination (350-450 degrees C) to EtBr and HBr was followed by metathesis of these intermediates with supported cobalt or copper oxides (200-250 degrees C) to produce ethanol (up to 64% selectivity at 45% EtBr conversion), diethyl ether (64% selectivity at 44% conversion), and ethylene (26% selectivity at 68% conversion at 200 degrees C, but conversions and selectivities approaching 100% at temperatures > 300 degrees C) as major products, and butadiene, vinyl bromide, acetaldehyde, ethyl acetate, and acetone as minor products. The supported cobalt and copper bromides thus formed were reoxidized with flowing O-2 to liberate bromine and this cycle was repeated at least three (and as many as fifty) times to establish the reproducibility of both the metathesis product distribution and of the oxide delivery and bromide sequestration capacity of the metal oxide/metal bromide mediators. Different formulations of the supported and unsupported metal oxide/metal bromide were investigated; zirconia or titania-supported Cu and Co oxides prepared from oxalic acid gels showed higher and more reproducible oxide/bromide exchange activity and capacity. These materials' performance is discussed in terms of their morphology, crystallinity, and porosity at different states of bromination in the partial oxidation cycle. (c) 2004 Elsevier Inc. All rights reserved.