Issue 14, 2017

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 a zeolite framework. A detailed microkinetic model including double bond isomerization, skeletal isomerization and mechanisms for the direct formation of 2t-butene from 1-butanol dimer and di-1-butyl ether (DBE) is 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.

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

Supplementary files

Article information

Article type
Paper
Submitted
20 mrt 2017
Accepted
13 jun 2017
First published
14 jun 2017

Catal. Sci. Technol., 2017,7, 2978-2997

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, 7, 2978 DOI: 10.1039/C7CY00536A

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