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Deactivation and regeneration of chromia and vanadia catalysts in alkane dehydrogenation

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Abstract

The deactivation and regeneration of a 6 % CrOx/alumina catalyst and a 3.5 % VOx/alumina catalyst has been studied after use in butane dehydrogenation at 873 K. Both catalysts deactivate due to carbonaceous deposits and with both catalysts the isomerisation reaction from 1-butene to cis and trans-2-butene is poisoned more effectively than the dehydrogenation reaction. The chromia catalyst deactivates three times faster than the vanadia system but the total amount of carbon deposited is similar indicating that the nature of the deposit on the chromia system is much more deleterious. The vanadia catalyst can be regenerated at room temperature in a flow of oxygen by removal of reaction intermediates, which desorb as butane, butene and butadiene. Over 75 % of the activity can be retrieved and by 1 hour on stream no difference can be discerned, whereas no significant desorption is detected from the chromia catalyst at room temperature and no regeneration is observed. TPO of both systems show different profiles with the deposit on the chromia catalyst more resistant to oxidation, which suggests a more dehydrogenated or more graphitic type material, which would be in keeping with the faster deactivation. After regeneration at 873 K the chromia catalyst recovers all its activity, whereas even after 873 K regeneration the vanadia catalyst does not recover all its activity. This is likely due to a change in structure and electronic properties of the polyvanadate species.

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