Ethanol Electro-oxidation on Palladium Revisited Using Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) and Density Functional Theory (DFT): Why Is It Difficult To Break the C–C Bond?

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• 作者：Evans A. Monyoncho ; Stephan N. Steinmann ; Carine Michel ; Elena A. Baranova ; Tom K. Woo ; Philippe Sautet
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：August 5, 2016
• 年：2016
• 卷：6
• 期：8
• 页码：4894-4906
• 全文大小：726K
• 年卷期：0
• ISSN：2155-5435

文摘

Insights into the ethanol electro-oxidation reaction mechanism on palladium in alkaline media are presented combining polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and density functional theory (DFT) calculations. The synergy between PM-IRRAS and DFT calculations helps to explain why the C–C bond is not broken during ethanol electro-oxidation, and the reaction stops at acetate. Coupling chronoamperometry (CA) with in situ PM-IRRAS enables us to simultaneously identify ethanol electro-oxidation products on the catalyst surface and in the bulk solution. We show that, at lower potential, it is possible to break the C–C bond on Pd/C in alkaline media to form CO₂. However, the selectivity is poor, because of competition with the formation of acetate and other side products, which gets worse at higher potentials. DFT computations complete the picture using the computational hydrogen electrode approach. The computations highlight the pivotal role of the CH₃CO intermediate that can either undergo a C–C bond scission yielding CO and then CO₂ or that can be oxidized toward CH₃COO^–. The latter is a dead end in the reaction scheme toward CO₂ production, since it cannot be easily oxidized nor broken into C₁ fragments. However, CH₃CO is not the most favored intermediate formed from ethanol electro-oxidation on Pd, hence limiting the production of CO₂.