(338d) Structure-Activity Relations on ?-Al2O3: From Alcohol Dehydration to Alkane Dehydrogenation

Authors: 
Kostetskyy, P., University of Pittsburgh
Mpourmpakis, G., University of Pittsburgh
Structure-Activity Relations on γ-Al2O3: From Alcohol Dehydration to Alkane Dehydrogenation

Pavlo Kostetskyy and Giannis Mpourmpakis

Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA

Abstract:

Nonoxidative dehydrogenation of alkanes is an important chemical reaction, as it can be used for production of alkenes – building blocks for a range of plastics and chemicals1-2. Several metal oxides, including gamma-alumina, have exhibited dehydrogenation activity, showing promise as candidates for the upgrade of alkanes. In this work we use computational chemistry methods to elucidate the surface mechanism of ethane, propane, n-butane and i-butane dehydrogenation pathways on gamma-alumina. Based on our calculations, it was shown that a concerted mechanism is energetically preferred for alkene formation, with a carbenium-ion-like transition state forming on surface acid-base pairs. A dehydrogenation model was developed as a screening tool for oxide catalysts, based on physicochemical properties of the oxide surface and stability of the reacting hydrocarbons. The dehydrogenation model was developed based on methodology previously applied in structure-activity relations (SAR) for alcohol dehydration on metal oxides3-4. The Carbenium Ion Stability (CIS), shown to be a descriptor in alcohol dehydration3-5, was used as a quantitative descriptor in alkane dehydrogenation and was found to correlate with the calculated activation energy barriers for the hydrocarbons in question. Increased hydrocarbon substitution (branching) was found to decrease the calculated reaction barriers, based on the CIS at the transition state. Finally, SARs developed for alcohol dehydration on various metal oxides were found to accurately capture the trends in alkane dehydrogenation, accounting for catalyst acid-base surface properties and CIS of intermediates at the transition state.

References:

1. Coperet, C., Chemical Reviews 2010, 110, 656-680.

2. Joubert, J.; Delbecq, F.; Sautet, P., Journal of Catalysis 2007, 251, 507-513.

3. Kostestkyy, P.; Yu, J.; Gorte, R. J.; Mpourmpakis, G., Catal. Sci. Technol. 2014, 4, 3861-3869.

4. Kostetskyy, P.; Mpourmpakis, G., Catal. Sci. Technol. 2015, 5, 4547-4555.

5. Roy, S.; Mpourmpakis, G.; Hong, D.-Y.; Vlachos, D. G.; Bhan, A.; Gorte, R. J., Acs Catalysis 2012, 2, 1846-1853.