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Déshydrogénation oxydante du n-butane sur des catalyseurs à base de pyrophosphates métalliques

Abstract : Oxidative dehydrogenation of n-butane over Ti, Zr, Ce and Sn pyrophosphates based catalysts was studied. The catalysts were characterized by several physical techniques and the catalytic properties evaluated in the temperature range of 410-570°C. TiP2O7 led to the best yield with butenes and butadiene selectivities of 42% and 14%, respectively, for 25% conversion at 530°C. The addition of water to the gas feed has a negative effect on both the conversion and selectivity to butenes and butadiene. Except CeP2O7 which was totally decomposed after catalytic test leading to a mixture of Ce(III) phosphates, the catalysts remain unchanged and can be classified into two groups depending upon the reaction mechanism involved. The first one is composed of ZrP2O7, SnP2O7 and TiP2O7 at low temperature and the second of TiP2O7 at high temperature. The reaction mechanism was studied using electrical conductivity measurements, ESR, Raman spectroscopy and TAP experiments. On both types of catalysts the initial step of activation of alkane would correspond to the attack of the alkane by the O– species giving a radical. But whereas the radical formed rapidly undergo a second hydrogen abstraction according to a similar mechanism leading to butene on the first type, it would either be trapped into an anionic vacancy or on a Ti4+ Lewis acid site to be transformed into an alkoxide intermediate or directly into butene with the abstraction of a proton, on the second type. In the first mechanism the rate limiting step is the attack of the alkane by the O– species but in the second, the reoxidation of the catalytic site by diffusion of the lattice oxygen or directly by gas phase oxygen. For TiP2O7 between 400 et 450°C we observe a special behavior : the rate limiting step is still the attack of the alkane by the O– species but the formed intermediate may also be trapped on the catalyst.
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Contributor : Ioan-Cezar Marcu <>
Submitted on : Friday, June 28, 2002 - 3:59:40 PM
Last modification on : Wednesday, November 20, 2019 - 3:20:21 AM
Long-term archiving on: : Friday, April 2, 2010 - 6:11:14 PM

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Ioan-Cezar Marcu. Déshydrogénation oxydante du n-butane sur des catalyseurs à base de pyrophosphates métalliques. Catalyse. Université Claude Bernard - Lyon I, 2002. Français. ⟨tel-00001474⟩

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