Electrocatalyticaly-Assisted Oxidative Dehydrogenation of Lower Alkanes to Olefins
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Type
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Conference
Paper
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Author
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Umit
Ozkan
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URL
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Date
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2016/06/02
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Conference
Name
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229th
ECS Meeting (May 29 - June 2, 2016)
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Abstract
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Conversion
of short-chain alkanes to olefins is a very important process for the
chemical industry. The large availability of lower alkanes from refineries as
well as their abundance in natural gas reserves and oil shale makes these
reactions economically very relevant. A major challenge in the
dehydrogenation of alkanes is that these reactions are highly endothermic. At
lower temperatures, thermodynamic equilibrium limits the conversion, making
use of high temperatures a necessity. When they are exposed to high
temperatures in an oxygen-free environment, however, cracking/decomposition
of alkanes becomes dominant, leading to coking, and hence deactivation of the
catalyst, as well as feedstock loss through coke formation. Oxidative
dehydrogenation (ODH) has been studied as an alternative to direct
dehydrogenation. In this reaction, hydrogen abstraction is achieved
oxidatively, hence removing the thermodynamic limitation. Also, ODH reactions
are exothermic and do not require additional energy input to the reaction. In
ODH, the major challenge is controlling the selectivity at high conversion
levels. The presence of gas phase oxygen at high temperatures leads to
complete oxidation products, mostly through further oxidation of the olefin
product, which is often more reactive than the alkane.
Electrocatalytic reactors using an oxide ion-conducting membrane offer a potential solution to control the selectivity to the desired olefins by regulating the availability of oxygen to the alkane. In this scheme, the hydrocarbons and gas-phase oxygen never come in contact, and the selectivity can be controlled by tuning the adsorption/desorption characteristics of the anode electro-catalyst and by controlling the oxide ion transfer rate. We have been working with Ti-based perovskites as anode electro-catalysts for this application. Lanthanum strontium titanates, LaxSr1-xTiO3-δ or LSTs, as well as chlorine-doped perovskites of the same form (LST-Cls) have been examined for potential anode catalysts in electrocatalytic ODH reactions. |
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