(740a) On the Reaction Mechanism and Kinetics of Ethane Dehydrogenation to Ethylene on Ga-Modified Al2O3 Catalyst

Ethane dehydrogenation to ethylene over Ga-modified Al₂O₃ catalyst has attracted significant research attention.^1,2 Despite a number of studies, the role of Ga in activation of ethane is still unclear. Furthermore, the role of products on the reaction mechanism and kinetics remains elusive.

In order to elucidate the role of Ga, we investigate the mechanism of ethane dehydrogenation (EDH) over Ga-modified γ-Al₂O₃ (110) surfaces using density-functional theory calculations and microkinetic modelling. To validate our theoretical models, we perform extensive EDH kinetic experiments on both Al₂O₃ and Ga-modified γ-Al₂O₃ (110). We demonstrate that the synergy between neighboring Ga-Al sites and/or the synergy between neighboring Ga-Ga sites underlie the highest activity of Ga-modified Al₂O₃ compared to pristine Al₂O₃. We also observe in our models that even tiny fractions of water in the reaction environment, which are challenging to detect experimentally, can preferably hydroxylate specific surface sites, resulting in site blocking and a significant drop in the catalyst activity. This finding is consistent with our experimental observation of significant drop in reactivity when H₂O is added during ethane dehydrogenation. Considering the effect of water also brings the DFT-based microkinetic model predicted apparent activation energies and reaction orders close to the corresponding experimental values. These fundamental insights could guide the design and synthesis of high-performance Ga-modified Al₂O₃ surfaces by, for example, judicious choice of the Ga loading.

References:

1. B. Xu, B. Zheng, W. Hua, Y. Yue, and Z. Gao, J.Catal. 239, 470 (2006).
2. M. Chen, J. Xu, F.Z.Su, Y.M. Liu, Y. Cao, H.Y. He, and K.N. Fan, J. Catal. 256, 293 (2008).