Effect of Palladium Surface Structure on the Hydrodeoxygenation of Propanoic Acid: Identification of Active Sites

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• 作者：Sina Behtash ; Jianmin Lu ; Christopher T. Williams ; John R. Monnier ; Andreas Heyden
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：January 29, 2015
• 年：2015
• 卷：119
• 期：4
• 页码：1928-1942
• 全文大小：803K
• ISSN：1932-7455

文摘

The effect of palladium surface structure on the hydrodeoxygenation of propanoic acid has been investigated by studying the mechanism over Pd(111) and Pd(211) model surfaces. We developed a microkinetic model based on parameters obtained from density functional theory and harmonic transition state theory and studied the reaction mechanism at a characteristic experimental reaction temperature of 473 K. The activity of active sites on flat surface models was found to be 3鈥? times higher than the activity of stepped surface models, suggesting that the hydrodeoxygenation of propanoic acid over a palladium catalyst is not very sensitive to surface structure. Very good agreement between computations and experiments could be obtained for our Pd(111) model if we include dispersion interactions between the gas species and the metal surface approximately by using the PBE-D3 functional for adsorption/desorption processes. Our model calculations predict that on both stepped and flat surfaces, the dominant deoxygenation mechanism proceeds by a decarbonylation pathway; however, on stepped surface models, decarboxylation and decarbonylation are essentially competitive. A sensitivity analysis of our models suggests that C鈥揙H and C鈥揌 bond cleavages control the overall rate over both Pd(111) and (211) catalyst surface models. In addition, on Pd(211) the C鈥揅 bond dissociation of propionate to CH₃CH₂ and CO₂, a key step in the decarboxylation mechanism, is also partially rate controlling.