467716 Understanding the p-Xylene Formation Mechanism from Dimethylfuran and Ethanol

Wednesday, November 16, 2016: 1:35 PM
Franciscan D (Hilton San Francisco Union Square)
Pavlo Kostetskyy1, Giannis Mpourmpakis1, Michail Stamatakis2, Shik Chi Edman Tsang3 and Ivo Teixeira3, (1)Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA, (2)Chemical Engineering, University of Delaware, Newark, DE, (3)Department of Chemistry, University of Oxford, Oxford, United Kingdom

Understanding the p-Xylene Formation Mechanism from Dimethylfuran and Ethanol

Pavlo Kostetskyy1, Ivo Teixeira2, Michail Stamatakis3, Shik Chi Edman Tsang2 and Giannis Mpourmpakis1

1Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA 15621, USA

2Wolfson Catalysis Centre, Department of Chemistry, University of Oxford, Oxford, OX1 3QR, UK

3Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, UK

Abstract:

Renewable, biomass-based chemical feedstocks as alternatives to petrol-based commodities are of high industrial relevance1,2 and have attracted recent attention. A number of platform chemicals have been identified as industrially-important, including cyclic oxygenates such as 2,5-Dimethylfuran (DMF)2,3, which can be catalytically converted to p-xylene, an important precursor in the production of polymers. Acidic heterogeneous catalysts can catalyze the conversion of DMF to p-xylene by a Diels-Alder (DA) reaction with ethylene. The reaction can be divided into two stages: DA cycloaddition and cycloadduct water elimination (dehydration), with the DA being the rate-controlling step in the Bronsted acid-catalyzed (BA) reactions3. In this work we propose an alternative route for DMF conversion to p-xylene using BA zeolite catalyst and ethanol as the dienophile source. Using electronic structure calculations, we elucidate the detailed reaction pathways and associated energetics and demonstrate that the ethanol-based pathway is preferred to ethylene in terms of overall reaction rates. We demonstrate that the sequence of reactions in the ethanol route follows a proton affinity4 thermodynamic preference of the reacting species, initiated by ethanol dehydration to ethylene. Improved performance is rationalized by the generation of a water molecule in this first step of the mechanism. While absent in the ethylene route, the presence of additional water in the system reduces the entropy loss in key elementary steps and facilitates proton transfer reactions. As a result, activation free energy barriers for the catalytic cycle decrease relative to the ethylene pathway. The calculated activation free energy difference (using energetic span model) between the two routes is in excellent agreement with kinetic experiments.

References:

1.      Kunkes, E. L.; Simonetti, D. A.; West, R. M.; Serrano-Ruiz, J. C.; Gartner, C. A.; Dumesic, J. A., Science 2008, 322, 417-421.

2.      Williams, C.L.; Chang, C.C.; Do, P.T.; Nikbin, N.; Caratzoulas, S.; Vlachos, D.G.; Lobo, R.F.; Fan, W.; Dauenhaue, P.J.; ACS Catal. 2012, 2, 935-939.

3.      Nikbin, N.; Do, P.T.; Caratzoulas, S.; Lobo, R.F.; Dauenhauer, P.J.; Vlachos, D.G.; J. Catal. 2013, 35-43.

4.      Kostetskyy, P.; Maheswari, J. P.; Mpourmpakis, G., J. Phys. Chem. C 2015, 119, 16139-16147


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See more of this Session: Computational Catalysis III: Biomass Chemistry
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