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Effect of zeolite confinement on the conversion of 1-butanol to butene isomers: mechanistic insights from DFT based microkinetic modelling

Abstract

Ab initio based microkinetic modelling of 1-butanol dehydration to butene isomers is used to obtain mechanistic insights into the effect of zeolite framework. A detailed microkinetic model including double bond isomerization, skeletal isomerization and mechanisms for direct formation of 2t-butene from 1-butanol dimer and di-1-butyl ether (DBE) are considered for the dehydration in H-ZSM-5, H-ZSM-22 and H-FER. H-FER favors the production of 2t-butene and H-ZSM-22 achieves thermodynamic equilibrium composition for linear butenes even at low conversion levels, while H-ZSM-5 maximizes 1-butene selectivity. Significant differences are observed in the reaction mechanism leading to formation of 2t-butene. For H-ZSM-5 and H-ZSM-22, the formation of 2-butenes occurs via double bond isomerization of 1-butene produced from butanol dehydration. For the double bond isomerization of 1-butene to 2t-butene, both concerted and 2-butoxide mediated stepwise mechanisms contribute significantly in H-ZSM-5, while only the concerted mechanism is operative in H-ZSM-22. On the other hand for H-FER, 2t-butene is mainly produced from the butanol dimer via an E1 elimination accompanied by a 1,2-hydride shift. This in turn can be attributed to an increase in enthalpic stabilization of the E1 elimination transition state for the direct formation of 2t-butene from 1-butanol dimer when moving from H-ZSM-5 to H-FER. Isobutene formation is not observed in all three zeolites at the investigated temperature range of 450 – 500 K.

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Publication details

The article was received on 20 Mar 2017, accepted on 13 Jun 2017 and first published on 14 Jun 2017


Article type: Paper
DOI: 10.1039/C7CY00536A
Citation: Catal. Sci. Technol., 2017, Accepted Manuscript
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    Effect of zeolite confinement on the conversion of 1-butanol to butene isomers: mechanistic insights from DFT based microkinetic modelling

    M. John, K. Alexopoulos, M. Reyniers and G. B. Marin, Catal. Sci. Technol., 2017, Accepted Manuscript , DOI: 10.1039/C7CY00536A

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